The present invention relates to the field of glycoprotein hormone analogs and their uses as agonists, antagonists, targeting vectors, and immunogens. In particular, this invention describes a method for stabilizing a heterodimer that permits the preparation of functional glycoprotein hormone analogs.
Glycoprotein hormones control the functions of the gonads and the thyroid gland. These hormones are αβ heterodimers that are stabilized by a portion of the β-subunit known commonly as the “seatbelt.” The seatbelt contains a cysteine at its carboxyterminus that enables it to form a disulfide bond with another cysteine in the β-subunit. In most vertebrates the seatbelt is disulfide bridged to a cysteine in β-subunit loop 1. The seatbelt is bridged to a cysteine in the aminoterminal end of β-subunit loop 1 in several teleost fish follitropins. The present invention describes a method for stabilizing a heterodimer that permits the preparation of glycoprotein hormone analogs that lack portions of the seatbelt.
The Glycoprotein Hormone Family
The glycoprotein hormone family contains three members, namely lutropin (LH, which is also known a luteinizing hormone or interstitial cell stimulating hormone), follitropin (FSH, which is also known as follicle stimulating hormone), and thyrotropin (TSH, which is also known as thyroid stimulating hormone). Lutropins and follitropins of fish are also known as gonadotropin II (GTHII) and gonadotropin I (GTHI), respectively. These glycoprotein hormones are made in the anterior pituitary gland. The placentas of humans, other primates, and some mammals—e.g., horses—also make a glycoprotein hormone known as choriogonadotropin (CG) that has a similar or identical amino acid sequence as that of lutropin. CG interacts with lutropin receptors and, in some cases—e.g., equine CG—can interact with lutropin and follitropin receptors of many species (Murphy and Martinuk, 1991). CG has a role in the maintenance of pregnancy and that of humans (hCG) is essential for maintaining early pregnancy. Its presence in the urine of pregnant women is the basis of most pregnancy tests. hCG is also produced by many tumors and its presence in men and non-pregnant women is an indication of malignancy.
α and β Subunits
Glycoprotein hormones are composed of two subunits termed α and β (Pierce and Parsons, 1981). A single gene encodes the α-subunit in most vertebrate species and this subunit is common to lutropins, follitropins, thyrotropins, and choriogonadotropins. Post-translational modifications of the glycoprotein hormones can create differences in their α-subunits such as the finding that the α-subunit of LH usually contains a higher ratio of sulfate to sialic acid than that of FSH (Baenziger and Green, 1988). Some fish have two α-subunit genes that encode sequences that differ primarily in loops α1 and α3. The β-subunits of lutropins, follitropins, and thyrotropins are encoded by separate genes. Similarities in the locations of the cysteines and other residues in the β-subunits of all glycoprotein hormones suggest that genes encoding the β-subunits arose by gene duplication and then diverged during early vertebrate evolution (Li and Ford, 1998). The evolution of the primate CG genes occurred much later, most likely by read-through and duplication of the LH gene (Fiddes and Talmadge, 1984). Although the β-subunit controls the biological properties of each hormone (Pierce and Parsons, 1981), both hormone subunits are required for full activity in most assays.
Heterodimer Formation
Heterodimer formation and dissociation in vitro requires that the glycosylated end of α2 pass beneath the seatbelt through a hole in the β-subunit. The seatbelt presents a significant impediment to heterodimer dissociation and assembly at physiological temperature and pH (Xing et al., 2001b). This is due largely to the presence of the oligosaccharide on α2 as shown by the fact that its removal facilitates assembly (Xing and Moyle, 2003), a phenomenon that can be used as a method for preparing heterodimers lacking this oligosaccharide. Normally, the heterodimer is stable at pH 3-4 and above. Removal of the α−2 oligosaccharide decreases heterodimer stability significantly and, with the exception of heterodimers in which the seatbelt is latched to a cysteine in the aminoterminal end of the β-subunit, the absence of the α2 oligosaccharide renders the heterodimer unstable at pH 5. Heterodimers in which the seatbelt is latched to a cysteine in the aminoterminal end of the β-subunit are usually much more stable than those in which the seatbelt is latched to a cysteine in β-subunit loop 1.
Due to the role of the seatbelt in heterodimer stability, it was thought that the heterodimer was assembled before the seatbelt became latched. This notion was supported by studies using pulse chase analyses (Ruddon et al., 1996). Extensive studies of heterodimer formation in the endoplasmic reticulum (Xing et al., 2004a; Xing et al., 2004b; Xing et al., 2004c; Xing et al., 2004d), the major site of glycoprotein hormone assembly, revealed that it occurs by two mechanisms (
The heterodimer can also be assembled by a “threading pathway” in which the glycosylated end of α-subunit loop 2 passes beneath the seatbelt. This process is facilitated substantially by the presence of small concentrations of reducing agents (Xing et al., 2001b). Originally, it was thought that reduction disrupted the seatbelt latch disulfide, which enabled the heterodimer to form by the wraparound pathway. Reducing agents are now known to enhance assembly by disrupting the disulfide that stabilizes the small loop in the aminoterminal half of the seatbelt (Xing et al., 2001b). The redox potential of the endoplasmic reticulum promotes disruption of this disulfide in cells during the assembly of most choriogonadotropins, follitropins, and thyrotropins (Xing et al., 2004a). The ability of 1-3 mM (3-mercaptoethanol to promote assembly in vitro is due to the fact that the disulfide that stabilizes the small seatbelt loop is much more stable in the heterodimer than in the free β-subunit. Its stability in the heterodimer is due largely to interactions between the α- and β-subunits that stabilize the positions of β-subunit cysteines 10 and 11 near one another (
Receptor Binding Specificity
In addition to its role in stabilizing the heterodimer, the seatbelt has a substantial influence on receptor binding specificity. Indeed, the seatbelt is responsible for much of the influence of the hormone β-subunit on receptor binding specificity (Moyle et al., 1994; Han et al., 1996; Dias et al., 1994; Grossmann et al., 1997). Remarkably, the aminoterminal and carboxyterminal halves of the seatbelt appear to have separate influences on receptor binding specificity. The aminoterminal half has a much greater influence on binding to LH receptors than the carboxyterminal half. Conversely, the carboxyterminal half of the seatbelt has a much greater influence on binding to FSH receptors than the aminoterminal half. By changing the composition of the seatbelt, one can produce hormone analogs that interact with multiple receptors. Replacing hCG β-subunit residues between cysteines 11 and 12 with their FSH β-subunit counterparts led to a hormone analog that had the same high affinity for LH receptors as hCG and about half the affinity of FSH receptors for FSH (Moyle et al., 1994). By manipulating the composition of the seatbelt loop in this analog, one can alter the ratio of LH/FSH activity more than 100-fold (Han et al., 1996).
Glycoprotein Hormone Agonists and Antagonists
Efforts to design glycoprotein hormone agonists and antagonists would be facilitated by knowledge of the structures of their receptors and these membrane glycoproteins have been studied extensively. Receptors for all three hormone classes have similar components, namely a large extracellular domain, a rhodopsin-like (Palczewski et al., 2000) transmembrane domain (TMD), and a short cytoplasmic carboxyterminal domain. The cytoplasmic carboxyterminus is not needed for receptor expression or signaling (Sanchez-Yague et al., 1992; Zhu et al., 1993). The extracellular domain contains two subdomains. The largest of these contains approximately 250 residues and is composed of leucine-rich repeats (McFarland et al., 1989; Sprengel et al., 1990; Nagayama et al., 1989). The leucine-rich repeat domain (LRD) was modeled several years ago (Moyle et al., 1995; Kajava et al., 1995; Jiang et al., 1995) based on its similarity to ribonuclease inhibitor, the first leucine-rich repeat protein of known structure (Kobe and Deisenhofer, 1993). The LRD creates at least a part of the ligand binding site (Braun et al., 1991) and a crystal structure of hFSH bound to a fragment of the LRD has been determined (Fan and Hendrickson, 2005), although there is some doubt as to relevance of this structure to the manner in which the glycoprotein hormone ligands dock with their cell surface receptors (Moyle et al., 2005). Depending on the receptor, the remainder of the extracellular domain contains approximately 60-150 residues. This portion of the extracellular domain has been more difficult to model, however, since its amino acid sequence is not similar to proteins of known structure. It connects the LRD to the TMD and is often considered a hinge (Jiang et al., 1995; Ji et al., 2002; Rapoport et al., 1998; Dias, 2005; Fan and Hendrickson, 2005) and many diagrams suggest that it is disordered (
Models for Hormone-Receptor Interactions
Two models have been proposed to explain hormone receptor interactions. That favored by most investigators was devised several years ago (Jiang et al., 1995) and is supported by the crystal structure of hFSH bound to a fragment in the human FSH receptor (Fan and Hendrickson, 2005). In the crystal structure hFSH is oriented perpendicular to the concave surface of the LRD (
A contrasting view of the receptor (Moyle et al., 2004) maintains that ligands contact the glycosylated surfaces of the LRD and SSD, not the TMD or the concave surface of the LRD as is seen in the crystal structure (Fan and Hendrickson, 2005). Indeed, since the SSD would block access of the ligand to the concave surface of the LRD, both models of ligand binding are mutually exclusive. In the alternate view of the receptor (
Problems in Attempts to Design Agonists and Antagonists
The lack of structural knowledge has hampered development of glycoprotein hormone agonists and antagonists. Although methods for producing glycoprotein hormones were developed in 1985 (Reddy et al., 1985), these are not applicable to all ligands. For example, it has been particularly difficult to produce hormones and hormone analogs in which the seatbelt is latched to a cysteine in the N-terminal region of the β-subunit. This has limited the development of analogs that can be used to stimulate fertility in not only mammalian systems but also those of salmon, trout, and other fish that express follitropins (in which the seatbelt is latched to a cysteine in the aminoterminal region of the β-subunit).
In accordance with the present invention, it has now been shown for the first time a glycoprotein hormone analog capable of binding to a receptor selected from the group consisting of luteinizing hormone receptor, follicle stimulating hormone receptor, and thyroid stimulating hormone receptor, the analog comprising at least one α subunit polypeptide and at least one β subunit polypeptide. The β subunit comprises a seatbelt region comprising 1 to 20 consecutive amino acid residues. The α subunit comprises a first amino acid residue, and the seatbelt region comprises a second amino acid residue. The first second amino acid residues are covalently linked by a first covalent bond. The first amino acid residue corresponds to an amino acid residue selected from the group consisting of Glu 10, Thr 11, Leu12, Phe33, Arg35, Tyr37, Thr39, Thr40, Leu41, Thr54, Arg42, Ser43, Val53, Ser55, Glu56, Ser57, Thr58, His83, Ser85, Thr86, Tyr89, and Ser92 of a SEQ ID NO: 7. The second amino acid residue is selected from the group consisting of seatbelt residues 11 to 18.
According to one aspect of the present invention provides a glycoprotein hormone analog capable of binding to a receptor selected from the group consisting of luteinizing hormone receptor, follicle stimulating hormone receptor, and thyroid stimulating hormone receptor, comprising at least one α subunit polypeptide and at least one β subunit polypeptide, wherein the α subunit comprises a first amino acid residue, the seatbelt region comprises a second amino acid residue, and wherein the first and second amino acid residues are covalently linked by a first covalent bond and wherein the C-terminal amino acid of the β subunit polypeptide is from seatbelt residue 10 to seatbelt residue 20.
Other aspects of the present invention include targeting compounds comprising the analogs of the present invention, nucleic acids encoding the analogs of the present invention, and methods of treating a disease or condition in a subject comprising administering the analogs of the present invention.
AMP accumulation in assays employing CHO cells that over express the rat LH receptor. The oligosaccharide at the N-terminal end of the β-subunit in this analog was not removed prior to assay.
In one aspect, the present invention relates to a glycoprotein hormone analog capable of binding to a receptor selected from the group consisting of luteinizing hormone receptor, follicle stimulating hormone receptor, and thyroid stimulating hormone receptor, the analog comprising at least one α subunit polypeptide and at least one β subunit polypeptide. The β subunit comprises a seatbelt region comprising 1 to 20 consecutive amino acid residues. The α subunit comprises a first amino acid residue, and the seatbelt region comprises a second amino acid residue. The first second amino acid residues are covalently linked by a first covalent bond. The first amino acid residue corresponds to an amino acid residue selected from the group consisting of Glu9, Thr11, Leu12, Phe33, Arg35, Tyr37, Thr39, Pro40, Leu41, Arg42, Ser43, Val53, Thr54, Ser55, Glu56, Ser57, Thr58, His83, Ser85, Thr86, Tyr89, and Ser92 of SEQ ID NO: 7. The second amino acid residue is selected from the group consisting of seatbelt residues 11 to 18. In an especially preferred embodiment the first amino acid residue corresponds to Thr86 of SEQ ID NO: 7 and the second amino acid residue is seatbelt residue 12. In other preferred embodiments the α subunit polypeptide has an amino acid sequence comprising a sequence selected from the group consisting of SEQ ID NO: 1, 2, 9, 10, 11, 12, 17, 23, 24, 26, 27, 28, 29, 39, 40, 41, 54, 56, 61, 64, and 66 and the β subunit polypeptide has an amino acid comprising a sequence selected from the group consisting of SEQ ID NO: 3, 4, 6, 13, 14, 15, 16, 18, 19, 20, 21, 22, 25, 30, 31, 32, 33, 35, 36, 37 46, 47, 48, 51, 53, 55, 57, and 60.
As used herein, the term “glycoprotein hormone analog” refers to a molecule that possesses a similar structural configuration as a native or wildtype glycoprotein hormone. The analog does not necessarily have a similar activity or function as the native glycoprotein hormone. In some instances the analog comprises a similar amino acid sequence the native glycoprotein hormone. In one embodiment the analog is an agonist, or activator, of a glycoprotein hormone receptor. In other embodiments, the analog is an antagonist, or inhibitor, of a glycoprotein hormone receptor.
Structures in Detail—The “Seatbelt” Region
The seatbelt region of the analog is located on the β subunit. The seatbelt region is generally 20 consecutive amino acids in length (see
The structures of hCG and human follitropin (hFSH) have been determined by crystallography (Lapthorn et al., 1994; Wu et al., 1994; Fox et al., 2001). Each subunit of all glycoprotein hormones contains a cystine knot that is responsible for the formation of the three large loops—i.e., α1, α2, α3 and β1, β2, β3—that are seen in their structures (
The seatbelt is a critical portion of all glycoprotein hormones and is essential for their biological activities. It originates at the end of the β-subunit cystine knot and its carboxyterminal end is latched to a cysteine in the β subunit. A key feature of all seatbelts is that they are wrapped around the α-subunit loop 2. Indeed, the observation that the hCG seatbelt begins at the end of the β-subunit cystine knot, that it is wrapped around α-subunit loop 2, and that it forms a disulfide bond with a cysteine in the remainder of the β-subunit was responsible for the origin of the name “seatbelt” (Lapthorn et al., 1994). This arrangement of the seatbelt is observed in all the vertebrate glycoprotein hormones. The third and tenth residues of the seatbelts of all vertebrate glycoprotein hormones except that in Zebrafish FSH are cysteines. These cysteines form a disulfide stabilized small loop that is important for the activities of mammalian lutropins (Campbell et al., 1991; Moyle et al., 1994) and for formation of the natural heterodimer (Xing et al., 2004d). It is not known why the Zebrafish FSH β-subunit lacks these two cysteines, but it is presumed that the hydrophobic residues that replace them enable the small loop to form in a manner that is sufficient to stabilize the heterodimer. The cysteine that constitutes the twentieth residue of most vertebrate glycoprotein hormone β-subunits and the twenty-first or twenty-second residues of some piscine thyrotropins forms a disulfide with a cysteine in the β-subunit that latches the carboxyterminal end of the seatbelt to the β-subunit. In most vertebrate glycoprotein hormones, the cysteine that forms the seatbelt latch site is found in β-subunit loop 1 and is the third cysteine in the mature β-subunit. In some piscine follitropins, the seatbelt latch site is found in the aminoterminal end of the β-subunit and is the first cysteine in the mature β-subunit. Changes in the composition of the seatbelt alter hormone activity (Campbell et al., 1991; Moyle et al., 1994; Dias et al., 1994; Grossmann et al., 1997). Seatbelt residues 1-10 are more important for mammalian lutropin activity. Seatbelt residues 10-20 contain a determinant that is more important for mammalian follitropin activity (Moyle et al., 1994).
The seatbelt must be kept latched for the heterodimer to remain intact; disruption of the seatbelt latch disulfide prevents its stable heterodimer formation. It is not essential for the seatbelt to be latched to the β-subunit for the heterodimer to be stabilized, however, and some glycoprotein hormone analogs can be stabilized by forcing the seatbelt to be latched to the α-subunit (Xing et al., 2001a). Some glycoprotein hormone analogs that lack the disulfide bond that latches the end of the seatbelt to the β-subunit can be stabilized by expressing them as a single chain βα fusion protein in which the α-subunit is fused to the end of the β-subunit. In this format, contacts between the α- and β-subunits stabilize the end of the seatbelt near its natural latch site even when the cysteines that form the normal seatbelt latch—i.e., β-subunit Cys26 and Cys110 are both replaced by alanine. B111 is an antibody that recognizes an epitope that contains residues in the vicinity of the natural hCG seatbelt disulfide latch site—i.e., β-subunit Cys26 and Cys110. B111 fails to recognize the (3-subunit of human LH, a molecule that is very similar to hCG. Furthermore, B111 also fails to recognize hCG analogs in which the seatbelt is latched to the α-subunit or to a cysteine present in any part of the β-subunit other than to Cys26 (Xing et al., 2001a; Xing et al., 2004a; Xing et al., 2004b; Xing et al., 2004c; Xing et al., 2004d). B111 also fails to recognize the free hCG β-subunit in which Cys26 and Cys110 are both replaced by alanine, which enables the seatbelt to move in a much less restricted fashion than the β-subunit in βα fusion proteins. The fact that B111 recognizes hCG βα fusion proteins in which β-subunit Cys26 and Cys110 are both replaced by alanine (Xing et al., 2001a) shows that the seatbelt of this hormone analog has formed, even though it is not stabilized by a disulfide.
Subunits can be covalently linked by any type of chemical bond. Such bonds include but are not limited to disulfide and peptide bonds. In a preferred embodiment the bond is a disulfide bond.
SEQ ID NO: 7 (
In another embodiment the analog comprises at least one α subunit polypeptide and at least one β subunit polypeptide, wherein the α subunit comprises a first amino acid residue, the seatbelt region comprises a second amino acid residue, wherein the first and the second amino acid residues are covalently linked by a first covalent bond, and wherein the C-terminal amino acid of the β subunit polypeptide is from seatbelt residue 10 to seatbelt residue 20. The C-terminal amino acid of a polypeptide according to the present invention is the last amino acid of the polypeptide. Accordingly, a β subunit wherein the C-terminal amino acid of the β subunit polypeptide is from seatbelt residue 10 to seatbelt residue 20 has as its last amino acid seatbelt residue 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20. In certain embodiments the first amino acid residue corresponds to an amino acid residue selected from the group consisting of Glu9, Thr11, Leu12, Phe33, Arg35, Tyr37, Thr39, Pro40, Leu41, Arg42, Ser43, Val53, Thr54, Ser55, Glu56, Ser57, Thr58, His83, Ser85, Thr86, Tyr89, and Ser92 of SEQ ID NO: 7; and the second amino acid residue is selected from the group consisting of seatbelt residues 11 to 18. In an especially preferred embodiment the first amino acid residue corresponds to Thr86 of SEQ ID NO: 7 and the second amino acid residue is seatbelt residue 12.
In a preferred embodiment, the first amino acid residue and the second amino acid residue are both mutated. The first and second amino acid residues can be mutated to any amino acid, including any of the so-called rare or modified amino acids may also be incorporated into a peptide of the invention, including but not limited to the following: 2-Aminoadipic acid, 3-Aminoadipic acid, beta-Alanine (beta-Aminopropionic acid), 2-Aminobutyric acid, 4-Aminobutyric acid (piperidinic acid), 6-Aminocaproic acid, 2-Aminoheptanoic acid, 2-Aminoisobutyric acid, 3-Aminoisobutyric acid, 2-Aminopimelic acid, 2,4-Diaminobutyric acid, Desmosine, 2,2′-Diaminopimelic acid, 2,3-Diaminopropionic acid, N-Ethylglycine, N-Ethylasparagine, Hydroxylysine, allo-Hydroxylysine, 3-Hydroxyproline, 4-Hydroxyproline, Isodesmosine, allo-Isoleucine, N-Methylglycine (sarcosine), N-Methylisoleucine, N-Methylvaline, Norvaline, Norleucine, Ornithine, 2-Napthylalanine, Threoninol, Tetrahydroisoquinoline 3-carboxlic acid, 4-Indoyl alanine, beta-Tryptophan, cyclo-Leucine. Methods of mutating amino acids are well known. In a preferred embodiment the mutations are generated using PCR-based site-directed mutagenesis.
In an especially preferred embodiment the first amino acid residue and the second amino acid residue are both mutated to cysteine residues and the first covalent bond is a disulfide bond.
In another preferred embodiment, residue 20 of the seatbelt region is not covalently linked to a distal portion of the β subunit. In native glycoprotein hormone β subunits, seatbelt residue 20 is a cysteine residue that forms a disulfide bond with another cysteine of the 3 subunit. In this embodiment seatbelt residue 20 is either absent, or it is only bound to the β subunit via its peptide bond with seatbelt residue 19 on its N-terminal side and possibly an another adjacent amino on its C-terminal side. Accordingly, a “distal portion” refers to binding to any amino acid except the two adjacent amino acids of seatbelt residue 20. In an especially preferred embodiment, seatbelt residue 20 is mutated from a cysteine residue to another amino acid residue, which can be any amino acid except cysteine.
In another embodiment the second amino acid residue of the β subunit polypeptide is the C-terminal residue of the β subunit polypeptide. In this embodiment the β subunit amino acid which is linked to the α subunit is also the last amino acid of the β subunit polypeptide.
In another embodiment the β subunit polypeptide and the α subunit polypeptide are covalently linked via a second covalent bond. In one embodiment the analogs of the present invention comprise a fusion protein of α and β subunits. The α subunit polypeptide and β subunit polypeptide are linked by a peptide bond. In a preferred embodiment the peptide bond is between the C-terminus of the α subunit polypeptide and the N-terminus of the β subunit polypeptide. In an especially preferred embodiment the wherein the analog comprises a cleavage site in between the α subunit and the β subunit. Possible cleavage sites include, but are not limited to a furin cleavage site, a thrombin cleavage site, a Factor Xa cleavage site, and an enterokinase cleavage site.
In another embodiment the α subunit comprises a third amino acid residue, the β subunit polypeptide comprises a fourth amino acid residue, and the third and the fourth amino acid residue are covalently linked via a the second covalent bond. In a preferred embodiment the third amino acid residue and the fourth amino acid residue are both mutated. In an especially preferred embodiment the third amino acid residue and the fourth amino acid residue are both mutated to cysteine residues and the second covalent bond is a disulfide bond.
In a preferred embodiment the third residue of the α subunit polypeptide is selected from the group consisting of Gln5, Arg35, and Tyr37. In a preferred embodiment the fourth residue of the β subunit polypeptide is selected from the group consisting of Leu5, Arg6, Arg8, Ile33, and Ala35.
Role of Glycosylation
The oligosaccharides have a substantial influence on hormone efficacy, but the reason for this remains unexplained (Moyle et al., 1975; Sairam and Bhargavi, 1985; Matzuk et al., 1989; Valove et al., 1994; Fares et al., 1996; Trout et al., 1999; Flack et al., 1994; Min et al., 1996). The oligosaccharides of hCG were found to be essential for its full efficacy; enzymatic deglycosylation reduced its efficacy by 90% in cyclic AMP accumulation assays (Moyle et al., 1975). Subsequent studies using chemical deglycosylation revealed that the oligosaccharides on the α-subunit were more important than those on the β-subunit (Sairam and Bhargavi, 1985). The use of genetic engineering methods to remove the oligosaccharides showed that the α2 oligosaccharide was the most important of all (Matzuk et al., 1989). Removal of this oligosaccharide by itself reduced the efficacy of hCG by half or more. Removal of all the oligosaccharides reduced the efficacy of hCG considerably more (Matzuk et al., 1989), but this also made the heterodimers harder to produce (Matzuk and Boime, 1988).
The contributions of the oligosaccharides to heterodimer production (Matzuk and Boime, 1989), hormone clearance (Baenziger et al., 1992; Cassels et al., 1989; Rosa et al., 1984), and efficacy (Matzuk et al., 1989) confound efforts to use deglycosylated hormone analogs as therapeutics and it is likely that the most useful antagonist analogs will retain most of their oligosaccharides. The presence of sialic acid at the terminal end of the oligosaccharides will also increase the half-life in circulation. This is due to the fact that sulfated and desialylated hormones have long been known to be cleared rapidly (Baenziger et al., 1992; Morell et al., 1971). Thus, it would be best to prepare antagonist analogs that have as much sialylated oligosaccharides as possible.
In another embodiment, the α subunit polypeptide has reduced glycosylation relative to a native α subunit polypeptide. In a one embodiment, the α subunit polypeptide comprises an α2 loop which has reduced glycosylation relative to an α2 loop of a native α subunit polypeptide. In a preferred embodiment the α subunit polypeptide comprises a mutation of at least one asparagine residue relative to a native α subunit polypeptide. In another embodiment the serine/threonine residue of the Asn-Xaa-(Ser/Thr) glycosylation consensus sequence (wherein Xaa is any amino acid exept proline) is mutated. In an especially preferred embodiment the asparagine corresponds to Asn52 of SEQ ID NO: 7
Nucleic Acids
Another aspect of the invention provides a nucleic acid comprising a nucleic acid encoding α and β subunits of the analogs. It is within the scope of the invention that such nucleic acid sequences can be RNA, DNA, or a hybrid of either.
It is well recognized that the genetic code is degenerate, i.e., an amino acid may be coded for by more than one codon. Degenerate codons encode the same amino acid residue, but contain different triplets of nucleotides. Accordingly, for a given nucleic acid sequence encoding an amino acid sequence of the present invention, there will be many degenerate nucleic acid sequences encoding that modulator. These degenerate nucleic acid sequences are considered within the scope of this invention.
In addition, it will also be appreciated by one of skill in the art that different organisms, cells, and cellular compartments may utilize different genetic codes. Thus, a single nucleic acid sequence may encode different polypeptides depending on its cellular context. Accordingly, in addition to the standard genetic code, polypeptides encoded by non-standard genetic codes are also considered within the scope of this invention. These non-standard genetic codes include, but are not limited to, the vertebrate mitochondrial code, the yeast mitochondrial code, the mold, protozoan, and coelenterate mitochondrial code, the mycoplasma/spiroplasma code, the invertebrate mitochondrial code, the ciliate, dasycladacean and hexamita nuclear code, the echinoderm mitochondrial code, the euplotid nuclear code, the bacterial and plant plastid code, the alternative yeast nuclear code, the ascidian mitochondrial code, the flatworm mitochondrial code, blepharisma nuclear code, chlorophycean mitochondrial code, trematode mitochondrial code, scenedesmus obliquus mitochondrial code, and the thraustochytrium mitochondrial code.
The nucleic acid is preferably included within a vector. The nucleic acid is operably linked to signals enabling expression of the nucleic acid sequence and is introduced into a cell utilizing, preferably, recombinant vector constructs, which will express the nucleic acid once the vector is introduced into the cell. A variety of viral-based systems are available, including adenoviral, retroviral, adeno-associated viral, lentiviral, herpes simplex viral or a sendaviral vector systems, and all may be used to introduce and express nucleic acid sequence encoding the analogs of the present invention.
Preferably, the viral vectors used in the methods of the present invention are replication defective. Such replication defective vectors will usually pack at least one region that is necessary for the replication of the virus in the infected cell. These regions can either be eliminated (in whole or in part), or be rendered non-functional by any technique known to a person skilled in the art. These techniques include the total removal, substitution, partial deletion or addition of one or more bases to an essential (for replication) region. Such techniques may be performed in vitro (on the isolated DNA) or in situ, using the techniques of genetic manipulation or by treatment with mutagenic agents. Preferably, the replication defective virus retains the sequences of its genome, which are necessary for encapsidating, the viral particles.
In the vector construction, the nucleic acid agents of the present invention may be linked to one or more regulatory regions. Selection of the appropriate regulatory region or regions is a routine matter, within the level of ordinary skill in the art. Regulatory regions include promoters, and may include enhancers, suppressors, etc.
Promoters that may be used in the expression vectors of the present invention include both constitutive promoters and regulated (inducible) promoters. Among the promoters useful for practice of this invention are ubiquitous promoters (e.g. HPRT, vimentin, actin, tubulin), intermediate filament promoters (e.g. desmin, neurofilaments, keratin, GFAP), therapeutic gene promoters (e.g. MDR type, CFTR, factor VIII), tissue-specific promoters (e.g. actin promoter in smooth muscle cells, or Flt and Flk promoters active in endothelial cells), including animal transcriptional control regions, which exhibit tissue specificity and have been utilized in transgenic animals.
Other promoters which may be used in the practice of the invention include promoters which are preferentially activated in dividing cells, promoters which respond to a stimulus (e.g. steroid hormone receptor, retinoic acid receptor), tetracycline-regulated transcriptional modulators, cytomegalovirus immediate-early, retroviral LTR, metallothionein, SV-40, E1a, and MLP promoters.
Additional vector systems include the non-viral systems that facilitate introduction of nucleic acid agents into a patient. For example, a DNA vector encoding a desired sequence can be introduced in vivo by lipofection. Synthetic cationic lipids designed to limit the difficulties encountered with liposome-mediated transfection can be used to prepare liposomes for in vivo transfection of a gene encoding a marker. The use of cationic lipids may promote encapsulation of negatively charged nucleic acids, and also promote fusion with negatively charged cell membranes. The use of lipofection to introduce exogenous genes into the specific organs in vivo has certain practical advantages and directing transfection to particular cell types would be particularly advantageous in a tissue with cellular heterogeneity, for example, pancreas, liver, kidney, and the brain. Lipids may be chemically coupled to other molecules for the purpose of targeting. Targeted peptides, e.g., hormones or neurotransmitters, and proteins for example, antibodies, or non-peptide molecules could be coupled to liposomes chemically. Other molecules are also useful for facilitating transfection of a nucleic acid in vivo, for example, a cationic oligopeptide, peptides derived from DNA binding proteins, or a cationic polymer.
It is also possible to introduce a DNA vector in vivo as a naked DNA plasmid. Naked DNA vectors for therapeutic purposes can be introduced into the desired host cells by methods known in the art, e.g., transfection, electroporation, microinjection, transduction, cell fusion, DEAE dextran, calcium phosphate precipitation, use of a gene gun, or use of a DNA vector transporter.
Another aspect of the present invention provides a cell transformed with a nucleic acid of the present invention. Also included in the scope of the present invention is a transgenic organism comprising a recombinant nucleic acid of the present invention. A transgenic animal is an animal into which has been introduced, by human manipulation, one or more genes not native to the animal.
Also included in the scope of the present invention, is a method for producing an analog of the present invention, the method comprising:
a) transforming a cell with a recombinant nucleic acid, and the recombinant nucleic acid comprises a promoter sequence operably linked to a nucleic acid encoding a analog of the present invention, and
b) culturing the cell under conditions suitable for expression of the analog, and
c) recovering the analog so expressed.
The analogs of the present invention may be prepared by recombinant technology methods, isolated from natural sources, or prepared synthetically, and may be, of prokaryotic or eukaryotic origin. The analogs of the present invention may be unglycosylated or modified subsequent to translation. Such modifications include glycosylation, phosphorylation, acetylation, myristoylation, methylation, isoprenylation, and palmitoylation. Glycosylated analogs are produced in mammalian cells. Using recombinant DNA technology, the nucleic acid encoding the analog is inserted into a suitable vector, which is inserted into a suitable host cell. The analog produced by the resulting host cell is recovered and purified. The analogs are characterized by amino acid composition and sequence, and biological activity.
Use of Glycoprotein Hormone Analogs to Deliver Toxins and Other Agents
Glycoprotein hormone analogs can be used to deliver toxins or other agents to LH receptor bearing cells. Sairam et al. attached the potent toxin gelonin to hCG (Marcil et al., 1993; Singh and Sairam, 1989; Singh et al., 1989). Hansel et al. (Hansel et al., 2001) attached toxic peptides to synthetic hLH analogs during efforts to target receptors in ovarian and prostate carcinomas. While it would be possible to attach these toxins to the antagonists, this approach per se is not likely to be desirable for targeting the cystic follicles in polycystic ovary syndrome (PCOS) patients. Toxins such as gelonin are likely to be antigenic, which would reduce the attractiveness of the approach for repeated use. Furthermore, since gelonin works inside the cell, it must enter the cell to function. Since hCG antagonists have reduced cellular entry (Hoelscher et al., 1991), use of proteins similar to gelonin might reduce their activities. Toxins delivered in liposomes may have significant “bystander” effects, i.e., the abilities to kill cells that are nearby those that are being targeted. Thus, they would have the potential to reduce the ovarian reserve. They may also have serious side effects on the kidney and liver, tissues that participate in hormone clearance (Ascoli et al., 1976; Wehmann et al., 1984). Fusion proteins containing clinically approved drugs—i.e., interferon γ—would be more useful. Fusion proteins containing sphingomyelinase linked to the antagonists might also be useful since they would be likely to produce ceramide only in sufficient quantity to kill cells to which the proteins are bound, i.e., only those cells that have LH receptors. Also, since androgens have been shown to promote the early events in follicle formation, but retard full follicle development (Vendola et al., 1998), the use of gonadotropin antagonists to deliver high local concentrations of drugs that inhibit steroidogenesis—e.g., in liposomal vesicles—would also be very attractive. Only those granulosa cells that require LH and/or steroids for survival would be expected to undergo apoptosis. Turnover of these cells would reverse the symptoms of PCOS.
Another aspect of the invention provides for a targeting compound comprising an analog of the present invention. The targeting compound utilizes the ability of an analog of the present invention to direct an active agent to the specific target cell population in a subject, for example, cystic follicles of an ovary. In one embodiment the targeting compound is complexed with an active agent. An “active agent”, as used herein, includes any diagnostic, prophylactic or therapeutic agent that can be used in an animal, including a human. An “active particle”, as used herein is a particle into which one or more active agents have been loaded. “Complexed to”, as used herein, includes adsorption, noncovalent coupling and covalent coupling of a targeting compound to an active agent or to an active particle.
The active agent used depends on the pathological condition to be diagnosed, prevented or treated, the individual to whom it is to be administered, and the route of administration. Active agents include, but are not limited to, imaging agents, antigens, antibodies, oligonucleotides, antisense oligonucleotides, genes, gene correcting hybrid oligonucleotides, aptameric oligonucleotides, triple-helix forming oligonucleotides, ribozymes, signal transduction pathway inhibitors, tyrosine kinase inhibitors, DNA-modifying agents, therapeutic genes, and systems for therapeutic gene delivery. Also included are drugs; hormones; analgesics; anti-migraine agents; anti-coagulant agents; cardiovascular, anti-hypertensive and vasodilator agents; sedatives; narcotic antagonists; chelating agents; anti-diuretic agents; chemotherapeutic agents; apoptosis-inducing agents; and other agents including, but not limited to, those listed in the United States Pharmacopeia and in other known pharmacopeias.
Drugs include, but are not limited to, peptides, proteins, hormones and analgesics, cardiovascular, narcotic, antagonist, chelating, chemotherapeutic, sedative, anti-hypertensive, anti-anginal, anti-migraine, anti-coagulant, anti-emetic anti-neoplastic and anti-diuretic agents. Hormones include, but are not limited to, insulin, calcitonin, calcitonin gene regulating protein, atrial natriuretic protein, colony stimulating factor, erythropoietin (EPO), interferons, somatotropin, somatostatin, somatomedin, luteinizing hormone releasing hormone (LHRH), tissue plasminogen activator (TPA), growth hormone releasing hormone (GHRH), oxytocin, estradiol, growth hormones, leuprolide acetate, factor VIII, testosterone and analogs thereof. Analgesics include, but are not limited to, fentanyl, sufentanil, butorphanol, buprenorphine, levorphanol, morphine, hydromorphone, hydrocodeine, oxymorphone, methadone, lidocaine, bupivacaine, diclofenac, naproxen, paverin, and analogs thereof. Anti-migraine agents include, but are not limited to heparin, hirudin, and analogs thereof. Anti-coagulant agents include, but are not limited to, scopolamine, ondansetron, domperidone, etoclopramide, and analogs thereof. Cardiovascular, anti-hypertensive and vasodilator agents include, but are not limited to, diltiazem, clonidine, nifedipine, verapamil, isosorbide-5-mononitrate, organic nitrates, nitroglycerine and analogs thereof. Sedatives include, but are not limited to, benzodiazeines, phenothiozines and analogs thereof. Narcotic antagonists include, but are not limited to, naltrexone, naloxone and analogs thereof. Chelating agents include, but are not limited to deferoxamine and analogs thereof. Anti-diuretic agents include, but are not limited to, desmopressin, vasopressin and analogs thereof. Chemotherapeutic agents include any chemical compound useful in the treatment of cancer, including but not limited to alkylating agents such as thiotepa and cyclosphosphamide; alkyl sulfonates such as busulfan, improsulfan and piposulfan; aziridines such as benzodopa, carboquone, meturedopa, and uredopa; ethylenimines and methylamelamines including altretamine, triethylenemelamine, trietylenephosphoramide, triethylenethiophosphaoramide and trimethylolomelamine; nitrogen mustards such as chlorambucil, chlomaphazine, cholophosphamide, estramustine, ifosfamide, mechlorethamine, mechlorethamine oxide hydrochloride, melphalan, novembichin, phenesterine, prednimustine, trofosfamide, uracil mustard; nitrosureas such as carmustine, chlorozotocin, fotemustine, lomustine, nimustine, ranimustine; antibiotics such as aclacinomysins, actinomycin, authramycin, azaserine, bleomycins, cactinomycin, calicheamicin, carabicin, carnomycin, carzinophilin, chromomycins, dactinomycin, daunorubicin, detorubicin, 6-diazo-5-oxo-L-norleucine, doxorubicin, epirubicin, esorubicin, idarubicin, marcellomycin, mitomycins, mycophenolic acid, nogalamycin, olivomycins, peplomycin, potfiromycin, puromycin, quelamycin, rodorubicin, streptonigrin, streptozocin, tubercidin, ubenimex, zinostatin, zorubicin; anti-metabolites such as methotrexate and 5-fluorouracil (5-FU); folic acid analogues such as denopterin, methotrexate, pteropterin, trimetrexate; purine analogs such as fludarabine, 6-mercaptopurine, thiamiprine, thioguanine; pyrimidine analogs such as ancitabine, azacitidine, 6-azauridine, carmofur, cytarabine, dideoxyuridine, doxifluridine, enocitabine, floxuridine, 5-FU; androgens such as calusterone, dromostanolone propionate, epitiostanol, mepitiostane, testolactone; anti-adrenals such as aminoglutethimide, mitotane, trilostane; folic acid replenisher such as frolinic acid; aceglatone; aldophosphamide glycoside; aminolevulinic acid; amsacrine; bestrabucil; bisantrene; edatraxate; defofamine; demecolcine; diaziquone; elformithine; elliptinium acetate; etoglucid; gallium nitrate; hydroxyurea; lentinan; lonidamine; mitoguazone; mitoxantrone; mopidamol; nitracrine; pentostatin; phenamet; pirarubicin; podophyllinic acid; 2-ethylhydrazide; procarbazine; razoxane; sizofiran; spirogermanium; tenuazonic acid; triaziquone; 2,2′,2″-trichlorotriethylamine; urethan; vindesine; dacarbazine; mannomustine; mitobronitol; mitolactol; pipobroman; gacytosine; arabinoside (“Ara-C”); cyclophosphamide; thiotepa; taxanes, e.g. paclitaxel and docetaxel; chlorambucil; gemcitabine; 6-thioguanine; mercaptopurine; methotrexate; platinum analogs such as cisplatin and carboplatin; vinblastine; platinum; etoposide (VP-16); ifosfamide; mitomycin C; mitoxantrone; vincristine; vinorelbine; navelbine; novantrone; teniposide; daunomycin; aminopterin; xeloda; ibandronate; CPT-11; topoisomerase inhibitor RFS 2000; difluoromethylomithine (DMFO); retinoic acid; esperamicins; capecitabine; and pharmaceutically acceptable salts, acids or derivatives of any of the above. Also included in this definition are anti-hormonal agents that act to regulate or inhibit hormone action on tumors such as anti-estrogens including for example tamoxifen, raloxifene, aromatase inhibiting 4(5)-imidazoles, 4-hydroxytamoxifen, trioxifene, keoxifene, LY117018, onapristone, and toremifene (Fareston); and anti-androgens such as flutamide, nilutamide, bicalutamide, leuprolide, and goserelin; and pharmaceutically acceptable salts, acids or derivatives of any of the above. Apoptosis-inducing agents include but are not limited to the TNFα family of ligands
An active agent can be formulated in neutral or salt form. Pharmaceutically acceptable salts include, but are not limited to, those formed with free amino groups; those formed with free carboxyl groups; and, those derived from sodium, potassium, ammonium, calcium, ferric hydroxide, isopropylamine, triethylamine, 2-ethylaminoethanol, histidine and procaine. An active agent can be loaded into a particle prepared from pharmaceutically acceptable ingredients including, but not limited to, soluble, insoluble, permeable, impermeable, biodegradable or gastroretentive polymers or liposomes. Such particles include, but are not limited to, nanoparticles, biodegradable nanoparticles, microparticles, biodegradable microparticles, nanospheres, biodegradable nanospheres, microspheres, biodegradable microspheres, capsules, emulsions, liposomes, micelles and viral vector systems.
Methods of making a targeting compound-active agent complex include, but are not limited to, covalent coupling of a targeting compound and an active agent and noncovalent coupling of a targeting compound and an active agent.
Methods of making a targeting compound-active particle complex include, but are not limited to, incorporating an active agent into a particle including, but not limited to, a nanoparticle, a microparticle, a capsule, a liposome, a non-viral vector system and a viral vector system. The targeting compound can be complexed to the active particle by methods including, but not limited to, adsorption to the active particle, noncovalent coupling to the active particle and covalent coupling, either directly or via a linker, to the active particle, to the polymer or polymers used to synthesize the active particle, to the monomer or monomers used to synthesize the polymer, and to other components comprising the active particle.
Another aspect of the invention provides a pharmaceutical composition comprising an analog of the present invention in admixture with a pharmaceutically acceptable carrier. The term “carrier” means a non-toxic material used in the formulation of pharmaceutical compositions to provide a medium, bulk and/or useable form to a pharmaceutical composition. A carrier may comprise one or more of such materials such as an excipient, stabilizer, or an aqueous pH buffered solution. Examples of physiologically acceptable carriers include aqueous or solid buffer ingredients including phosphate, citrate, and other organic acids; antioxidants including ascorbic acid; low molecular weight (less than about 10 residues) polypeptide; proteins, such as serum albumin, gelatin, or immunoglobulins; hydrophilic polymers such as polyvinylpyrrolidone; amino acids such as glycine, glutamine, asparagine, arginine or lysine; monosaccharides, disaccharides, and other carbohydrates including glucose, mannose, or dextrins; chelating agents such as EDTA; sugar alcohols such as mannitol or sorbitol; salt-forming counter ions such as sodium; and/or nonionic surfactants such as TWEEN™, polyethylene glycol (PEG), and PLURONICS™.
Pharmaceutical compositions for oral administration can be formulated using pharmaceutically acceptable carriers well known in the art in dosages suitable for oral administration. Such carriers enable the pharmaceutical compositions to be formulated as tablets, pills, dragees, capsules, liquids, gels, syrups, slurries, suspensions, and the like, for ingestion by the patient. Pharmaceutical compositions for oral use can be prepared by combining analogs with solid excipient, optionally grinding a resulting mixture, and processing the mixture of granules, after adding suitable auxiliaries, if desired, to obtain tablets or dragee cores. Suitable excipients are carbohydrate or protein fillers, such as sugars, including lactose, sucrose, mannitol, or sorbitol; starch from corn, wheat, rice, potato, or other plants; cellulose, such as methyl cellulose, hydroxypropylmethyl-cellulose, or sodium carboxymethyl-cellulose; gums including arabic and tragacanth; and proteins such as gelatin and collagen. If desired, disintegrating or solubilizing agents may be added, such as the cross-linked polyvinyl pyrrolidone, agar, alginic acid, or a salt thereof, such as sodium alginate. Dragee cores may be used in conjunction with suitable coatings, such as concentrated sugar solutions, which may also contain gum arabic, talc, polyvinyl-pyrrolidone, carbopol gel, polyethylene glycol, and/or titanium dioxide, lacquer solutions, and suitable organic solvents or solvent mixtures. Dyestuffs or pigments may be added to the tablets or dragee coatings for product identification or to characterize the quantity of analog, i.e., dosage.
Pharmaceutical preparations that can be used orally include push-fit capsules made of gelatin, as well as soft, sealed capsules made of gelatin and a coating, such as glycerol or sorbitol. Push-fit capsules can contain active ingredients mixed with filler or binders, such as lactose or starches, lubricants, such as talc or magnesium stearate, and, optionally, stabilizers. In soft capsules, the analogs may be dissolved or suspended in suitable liquids, such as fatty oils, liquid, or liquid polyethylene glycol with or without stabilizers.
Preferred sterile injectable preparations can be a solution or suspension in a non-toxic parenterally acceptable solvent or diluent. Examples of pharmaceutically acceptable carriers are saline, buffered saline, isotonic saline (e.g. monosodium or disodium phosphate, sodium, potassium; calcium or magnesium chloride, or mixtures of such salts), Ringer's solution, dextrose, water, sterile water, glycerol, ethanol, and combinations thereof 1,3-butanediol and sterile fixed oils are conveniently employed as solvents or suspending media. Any bland fixed oil can be employed including synthetic mono- or di-glycerides. Fatty acids such as oleic acid also find use in the preparation of injectables.
The composition medium can also be a hydrogel, which is prepared from any biocompatible or non-cytotoxic homo- or hetero-polymer, such as a hydrophilic polyacrylic acid polymer that can act as a drug absorbing sponge. Certain of them, such as, in particular, those obtained from ethylene and/or propylene oxide are commercially available. A hydrogel can be deposited directly onto the surface of the tissue to be treated, for example during surgical intervention.
The analogs may also be entrapped in microcapsules prepared, for example, by interfacial polymerization, for example, hydroxymethylcellulose or gelatin-microcapsules and poly-(methylmethacylate) microcapsules, respectively, in colloidal drug delivery systems (for example, liposomes, albumin microspheres, microemulsions, nano-particles and nanocapsules) or in macroemulsions.
Sustained-release preparations may be prepared. Suitable examples of sustained-release preparations include semi-permeable matrices of solid hydrophobic polymers containing the antibody, which matrices are in the form of shaped articles, e.g. films, or microcapsules. Examples of sustained-release matrices include polyesters, hydrogels (for example, poly(2-hydroxyethyl-methacrylate), or poly(vinylalcohol)), polylactides (U.S. Pat. No. 3,773,919), copolymers of L-glutamic acid and gamma-ethyl-L-glutamate, non-degradable ethylene-vinyl acetate, degradable lactic acid-glycolic acid copolymers such as the LUPRON DEPOT™ (injectable microspheres composed of lactic acid-glycolic acid copolymer and leuprolide acetate), and poly-D-(−)-3-hydroxybutyric acid. While polymers such as ethylene-vinyl acetate and lactic acid-glycolic acid enable release of molecules for over 100 days, certain hydrogels release proteins for shorter time periods.
The pharmaceutical compositions according to this invention may be administered to a subject by a variety of methods. They may be added directly to target tissues, complexed with cationic lipids, packaged within liposomes, or delivered to target cells by other methods known in the art. Localized administration to the desired tissues may be done by catheter, infusion pump or stent. The DNA, DNA/vehicle complexes, or the recombinant virus particles are locally administered to the site of treatment. Alternative routes of delivery include, but are not limited to, intravenous injection, intramuscular injection, subcutaneous injection, aerosol inhalation, oral (tablet or pill form), topical, systemic, ocular, intraperitoneal and/or intrathecal delivery.
Therapeutic Uses of Analogs
Another aspect of the invention provides a method of treating a disease or condition in a subject comprising administering an effective dose of a formulation comprising an analog of the present invention to the subject. In a preferred embodiment the disease or condition infertility and in particular infertility caused by polycystic ovary syndrome (PCOS).
Gonadotropin antagonists would have substantial uses for the treatment of PCOS. This syndrome is seen in approximately 5% of women of reproductive age and accounts for roughly a third or more of human infertility. PCOS patients have oligomenorrhea and fail to ovulate or ovulate less frequently than women who have regular menstrual cycles. Although the etiology of PCOS is poorly understood, the cystic follicles that are present in the ovaries of these patients are almost certainly responsible for their infertility; surgical removal of these follicles usually results in reduction of androgen levels and the resumption of ovulatory menstrual cycles (Stein and Leventhal, 1935; Greenblatt and Casper, 1987; Liguori et al., 1996). Removal of the cystic follicles does not “cure” PCOS, however, and these patients become infertile when the cystic follicles re-accumulate. The association between cystic follicles and infertility in PCOS patients implies that development of a non-surgical method for removing the cysts would restore fertility to these women, at least until new cystic follicles accumulate in the ovary. Furthermore, since elimination of the cystic follicles promotes ovulation with little risk of ovarian hyperstimulation or multiple pregnancy (Shanti and Murphy, 1997), a non-surgical procedure that had the same effect as wedge resection would have significant advantages relative to gonadotropin therapy. In principle, it could be attained with only a single injection of an agent that is targeted to LHR or LHR/FSHR expressing cells that has the ability to promote apoptosis of these cells. Furthermore, it could be explored without the danger of creating adhesions and other unwanted side effects of surgery. Adhesions themselves are thought to interfere with fertility if they restrict access of the ovulated egg to the fallopian tube or restrict movements of its fimbriated end.
PCOS is universally associated with hyper secretion of ovarian androgens (Balen et al., 1995), a phenomenon that may have several etiologies and that becomes self sustaining once established. Factors that contribute to PCOS include hyperinsulinemia, which is particularly noticeable in obese patients, but often observed in lean patients (Dunaif, 1997; Dunaif et al., 1996), and aberrant gonadotropin secretion, which is manifested as an increased ratio of LH to FSH (Hall et al., 1998). The latter may be a response to the increased production of ovarian or adrenal androgens. These can become converted to estradiol, a potent inhibitor of FSH secretion. Since LH can enhance androgen production and since this can be augmented by insulin (Franks et al., 1999), elevated ratios of LH/FSH or increased insulin secretion would tend to produce more ovarian androgens and thereby contribute to the self-sustaining nature of PCOS. PCOS may also be exacerbated by the manner in which androgens are made in the adrenal and ovary (Rosenfield, 1999). The gene for CYP17 encodes a protein that has two activities, i.e., 17 hydroxylase and 17,20 lyase (Zhang et al., 1995). This enables the enzyme to hydroxylate pregnenolone and progesterone and then cleave the products to C19 steroids, i.e., androgens and androgen precursors. While only the hydroxylase is needed for the production of adrenal steroids, both activities are required for production of androgens and estrogens. The activities of the lyase appear to be controlled differently than those of the hydroxylase, probably by serine phosphorylation or cytochrome b5 expression (Zhang et al., 1995; Lee-Robichaud et al., 2004). Excessive lyase activity has been proposed to be responsible for the unwanted androgens associated with PCOS.
Most ovarian androgens are produced by cells that have LH receptors. Ovarian androgens are thought to promote the survival of small follicles in the primate ovary and to prevent them from developing fully (Vendola et al., 1998). Thus, once initiated, the production of ovarian androgens would be expected to sustain PCOS. This notion is supported by the observation that treatments of monkeys with testosterone or dihydrotestosterone, an androgen that cannot be converted to estradiol, develop “cystic follicles” (Vendola et al., 1998). Thus antagonists that reduce the abilities of LH to promote androgen production by these cells would be expected to mitigate PCOS.
The influence of dihydrotestosterone on cystic follicle production suggests that conversion of androgens to estradiol is not required for the development of PCOS. Nonetheless, the abilities of anti-estrogens to induce ovulation in a majority of PCOS patients suggest that inappropriate aromatization of estradiol, one of the most potent inhibitors of FSH secretion, may also have a role in this process (Homburg, 2003). Indeed, the effectiveness of clomiphene citrate, the most commonly used therapeutic for ovulation induction (Yildiz et al., 2003), rests on its ability to block the feedback inhibition of FSH secretion by estradiol. The enhanced pituitary gland FSH secretion then stimulates follicular growth in PCOS patients. The advantage of clomiphene therapy for ovulation induction is that it can be used without extensive patient monitoring and has a relatively low incidence of multiple pregnancies (Homburg, 2004). The downside of this therapy is that clomiphene can inhibit endometrial development, which may explain why many clomiphene treated PCOS patients fail to become pregnant, even after multiple treatment cycles. Combination of clomiphene or other anti-estrogen treatment with an LH receptor antagonist would be expected to facilitate the activity of the anti-estrogen and thereby reduce the amount of drug needed to promote ovulation. This would also reduce the likelihood that anti-estrogen therapy would have unwanted effects on the endometrium and fallopian tubes that could interfere with their abilities to enhance fertility.
Patients who fail to become pregnant after repeated clomiphene therapy are usually treated with FSH and/or mixtures of FSH and LH or hCG (Homburg, 2004), gonadotropins that stimulate follicle growth and ovulation. Unfortunately, this therapy can cause ovarian hyperstimulation and often results in multiple pregnancies. Considerable attention has been focused on procedures that might reduce the potential for multiple pregnancies, including the way the hormone is given (Buvat et al., 1989). Gonadotropin therapy may also be combined with GnRH antagonists and agonists (Cardone, 2003). Treatments that promote the turnover of ovarian PCOS tissues would also be expected to enhance the efficacy of gonadotropin therapy and may reduce the incidence of multiple pregnancy.
The role of insulin sensitivity in PCOS has also been studied extensively. Many PCOS patients become pregnant after they lose weight (Homburg, 2004) or after they are treated with insulin potentiating agents such as metformin (Homburg, 2004). The notion that insulin may have a role in the development of PCOS is supported by a case report showing that the PCOS in a patient with an insulinoma disappeared after the tumor was removed (Murray et al., 2000). The use of metformin for ovulation induction remains controversial (Ehrmann et al., 1997; De et al., 1999) although long term treatment may have some benefit for non obese patients (Maciel et al., 2004). Combination of metformin with other therapy may also be beneficial (Homburg, 2004). This would include combination with an inhibitor of LH activity that promotes the turnover of PCOS tissues or that suppresses the production of ovarian androgens.
The earliest method of treating infertility in PCOS patients involved removing their cystic follicles by wedge resection surgery (Stein and Leventhal, 1935). Several other modifications of this procedure have been introduced during the ensuing years (Campo, 1998), but these have largely been replaced by anti-estrogen and gonadotropin therapies, which do not have risks associated with surgery. Most PCOS patients resume menstrual cycles shortly after their cystic follicles have been removed. Since follicle development is then controlled by the intrinsic feedback regulation inherent in the hypothalamic/pituitary/ovarian axis, this procedure does not cause ovarian hyperstimulation or multiple pregnancies (Campo, 1998). Wedge resection and related surgeries do not eliminate the underlying factors that cause the development of cystic follicles, however, and the condition usually returns. Whereas it is not practical to do multiple wedge resection surgeries to remove the follicles, repeat treatments would not be a problem for a non-surgical method such as that involving the use of an antagonist that blocked androgen secretion or an antagonist coupled to an apoptosis inducing agent. The apoptosis inducing agent in the latter therapeutic would facilitate turnover and removal of the unwanted ovarian cells.
The incidence of PCOS usually falls with age (Elting et al., 2000), a decline that appears to parallel the reduction in ovarian reserve. This supports the notion that the self-sustaining aspect of PCOS requires a continued input of follicular tissue and that the accumulation of cystic follicles depends on a balance between follicle production and atresia. Since ovarian androgen production may exert a positive feedback effect on cystic follicle development, even a small reduction in ovarian androgen production would be expected to facilitate the turnover of cystic follicles. Therefore, brief treatments with agents capable of blocking gonadotropin induced steroidogenesis and/or initiating apoptosis would be expected to increase the removal of cystic follicles from the ovaries of PCOS patients in a synergistic fashion.
Another aspect of the invention provides a method of inducing follicle development in fish comprising administering an effective dose of a formulation comprising an analog of the present invention to said fish. Species of fish that can be treated using this method include, but are not limited to, those species listed in
An effective dose means that amount of active agent which ameliorates the symptoms or condition. Therapeutic efficacy and toxicity of such active agents can be determined by standard pharmaceutical procedures in cell cultures or experimental animals, e.g., ED50 (the dose therapeutically effective in 50% of the population) and LD50 (the dose lethal to 50% of the population). The dose ratio of toxic to therapeutic effects is the therapeutic index, and it can be expressed as the ratio, LD50/ED50. Pharmaceutical compositions that exhibit large therapeutic indices are preferred. The data obtained from cell culture assays and animal studies is used in formulating a range of dosage for human use. The dosage of such active agents lies preferably within a range of circulating concentrations that include the ED50 with little or no toxicity. The dosage varies within this range depending upon the dosage form employed, sensitivity of the patient, and the route of administration.
For any compound, the therapeutically effective dose can be estimated initially either in cell culture assays or in animal models, usually mice, rabbits, dogs, or pigs. The animal model is also used to achieve a desirable concentration range and route of administration. Such information can then be used to determine useful doses and routes for administration in humans. The exact dosage is chosen by the individual physician in view of the patient to be treated. Dosage and administration are adjusted to provide sufficient levels of the active moiety or to maintain the desired effect. Additional factors which may be taken into account include the severity of the disease state, age, weight and gender of the patient; diet, desired duration of treatment, method of administration, time and frequency of administration, drug combination(s), reaction sensitivities, and tolerance/response to therapy. Long acting pharmaceutical compositions might be administered every 3 to 4 days, every week, or once every two weeks depending on half-life and clearance rate of the particular formulation.
All patents and publications cited above are herein incorporated by reference. The various aspects of the present invention are further described in the following non-limiting examples.
The wraparound pathway can be used to prepare hCG analogs in which the seatbelt is latched to the α-subunit rather than to the β-subunit (Xing et al., 2001a). The efficiency of this process depends on the location of the seatbelt latch site. Seatbelt latch sites that are located on α-subunit loop 2 are usually the most efficient and, when the seatbelt is latched to some of these, the heterodimer retains its biological activity. The hCG seatbelt can be forced to latch to a cysteine added to the α-subunit when the normal seatbelt latch site—i.e., Cys26 in β-subunit loop 1—is disrupted. Using this approach (Xing et al., 2001a) prepared heterodimers in which the seatbelt became latched to cysteines that had been substituted for several α-subunit residues. With the exception of hCG analogs in which the seatbelt was latched to cysteines nearby the normal seatbelt latch site—e.g., α-subunit residues Leu41 and Ser43—this approach to crosslinking the heterodimer led to a loss in LH receptor recognition. Although it was possible to latch the seatbelt to α-subunit residue 86 by replacing the threonine normally found at this site with cysteine, the resulting analog was nearly unable to bind to LH receptors (Xing et al., 2001a). Furthermore, it was not possible to obtain active FSH analogs using this approach, most likely because the carboxyterminal half of the seatbelt has a much more important role in the activities of follitropins than lutropins (Campbell et al., 1991; Moyle et al., 1994; Campbell et al., 1997).
Studies of the interaction of hCG, bovine LH, and glycoprotein hormone analogs with rat lutropin receptors and receptor analogs suggested that parts of the seatbelt near its carboxyterminal end are important for hormone efficacy. This portion of the hormone contains the primary epitope for monoclonal antibody B111 (Moyle et al., 1990; Xing et al., 2004a; Moyle et al., 2004). Binding of B111 and to a lesser degree B110, an antibody to an overlapping epitope, restored the efficacy of an hCG analog that lacked an oligosaccharide on α2 (Moyle et al., 2004). Monoclonal antibodies to other sites of the hormone did not restore efficacy to this hCG analog, indicating that they recognized sites that that are distant from those that have an influence on efficacy (Moyle et al., 2004).
The region of the SSD encoded by exon 10 also appears to be important for efficacy. human LHR residues derived from the region of the SSD encoded by exon 10 are needed for full LH responsiveness; their absence leads to infertility (Gromoll et al., 2000). Exon 10 is missing in the marmoset LHR (Zhang et al., 1997; Gromoll et al., 2003) and its ability to respond much better to CG than LH will explain why the marmoset pituitary produces a CG-like hormone rather than LH (Muller et al., 2004b). SSD residues derived from rat LHR exon 10 are not essential for hCG binding, but contribute to the binding of bovine LH and several hCG analogs (Moyle et al., 2004). Analyses of these observations suggest that residues from exon 10 are likely to contact the β-subunit near its seatbelt latch site (Muller et al., 2004a; Moyle et al., 2004). Furthermore, removal of the residues encoded by exon 10 from the rat LH receptor created a receptor that is much less able to respond to hCG analogs that lack the α2 oligosaccharide (Moyle et al., 2004). Removal of the β-subunit carboxyterminus reduced the efficacy of hCG by roughly half (Moyle et al., 2004), indicating that this portion of the hormone is likely to interact with residues derived from exon 10 or nearby sites of the receptor. This also revealed that these contacts may have a role in signal transduction.
Consideration of these observations suggested that it might be possible to prepare hCG analogs that had greatly reduced efficacy for the full-length receptor by removing portions of the seatbelt near the normal seatbelt latch site. Unfortunately, efforts to remove the seatbelt latch site per se destabilize the heterodimer, making it impossible to simply truncate all or part of the seatbelt. There are two ways to produce heterodimers lacking the disulfide that stabilizes the seatbelt, but neither of these would be expected to create a useful antagonist. One of these methods involves production of hCG analogs in a single chain format in which the codons for the α-subunit are fused to codons for the β-subunit or vice versa, codons for the β-subunit are fused to codons for the α-subunit. This type of analog has been prepared and found to have full (Sugahara et al., 1996a; Sugahara et al., 1996b; Sugahara et al., 1995) or significant (Heikoop et al., 1997a) efficacy. Apparently, the single chain format can stabilize the carboxyterminal end of the seatbelt close enough to its natural site that it retains its ability to interact with the receptor to initiate signal transduction, even when the sequences of this region of the seatbelt are altered (Heikoop et al., 1997a). Therefore, it seemed less likely that single chain fusion proteins in which the α-subunit is coupled to the carboxyterminus of the β-subunit can be used to create a useful antagonist, even if the seatbelt latch disulfide is removed. The second method for producing an analog that lacks the seatbelt latch disulfide involves the use of an aminoterminal stabilization domain. This type of domain can be either a disulfide crosslink at the aminoterminal end of the hormone, such as one between α-subunit residue 5 and β-subunit residue 8 (Heikoop et al., 1997b) or other nearby β-subunit residue such as β-subunit residues 6 or 7. Other α-subunit residues in this region can also be crosslinked to the β-subunit including residues 6 and 7. Use of the latter for crosslinking is facilitated by replacing α-subunit residue cysteine 31 with alanine. Heterodimers lacking the seatbelt latch disulfide can also be stabilized by addition of a Fos-Jun dimerization domain (Lin et al., 1999). Unfortunately, analogs lacking the seatbelt latch site that are stabilized in this fashion have very little ability to bind to the receptor, most likely because the carboxyterminal end of the seatbelt is free to move and may destabilize the hormone-receptor complex.
To assemble heterodimers that lack parts of the carboxyterminal region of the seatbelt that are likely to contribute to efficacy and act as LH receptor antagonists, it was necessary to devise methods that would 1) prevent dissociation of the heterodimer after the seatbelt latch disulfide was removed, 2) restrain the region of the small seatbelt loop in a position similar to that seen in the heterodimer, and 3) minimize the amount of seatbelt and other nearby parts of the β-subunit. Since the small seatbelt loop is required for lutropin activity, retention of this part of the β-subunit in a conformation that approximates that seen in hCG or hLH was considered to be important.
Molecular modeling suggested that introduction of a disulfide crosslink between α-subunit residue 86 and seatbelt residue 102 had the potential to stabilize the small seatbelt loop in a position needed for LH receptor interaction. Since the resulting disulfide would crosslink the heterodimer, it would also stabilize heterodimers that lack the seatbelt. Starting with constructs that encode the native human α-subunit sequence (pMB574,
This analog contained all the N-linked glycosylation signals normally found on hCG, including that at α-subunit residue Asn52 required for full hormone efficacy reduce efficacy (Matzuk et al., 1989). Removal of this oligosaccharide by replacing the codon for α-subunit residue Asn52 with one for aspartic acid created a construct that encoded the α-subunit sequence pMB2472 (
Some procedures for preparing lutropin antagonists yield compounds that cross react with follitropin receptors as well as lutropin receptors (Bernard et al., 2005). In contrast, the analog containing sequences pMB2472 and pMB2419 did not interact with FSH receptors and was unable to inhibit the binding of 1251-hFSH to cells that over express human FSH receptor. Neither it, nor its precursor (pMB1010+pMB2419), which has a much greater efficacy, were able to initiate signaling in CHO cells that overexpress the FSH receptor (
The analogs illustrated in Example 1 are assembled by the wraparound pathway. This is because the seatbelt cannot be latched before the subunits dock, a phenomenon that will prevent premature latching of the seatbelt. Premature latching of the seatbelt can disrupt the formation of some heterodimers (Xing et al., 2004c), notably those between salmon FSH α and β subunits as well as those of related species of fish. Thus, the approach to produce the heterodimers described in this example is expected to create analogs of salmon FSH that are formed efficiently because they lack the ability to latch their seatbelts before the subunits dock—i.e., prematurely.
Crosslinks between α86-β103 that were produced by co-expressing pMB2472 and pMB2674, (
Crosslinked heterodimers were formed that had the potential to contain two intersubunit disulfides. Co-expression of pRM917 with pMB2545 (
The aminoterminal end of the α-subunit was also not required for LH receptor binding and did not appear to contribute to heterodimer efficacy in rat LH receptor assays. Heterodimers containing pMB2538+pMB2545 or pMB2538+pMB2546 were highly potent inhibitors of hCG signal transduction in signal transduction assays employing CHO cells that overexpress the rat LHR (
Crosslinks that disrupt the small seatbelt loop—i.e., that involve hCG β-subunit residues Cys93 or Cys100—reduced the affinity of the analog for LH receptors substantially (Xing et al., 2004a; Xing et al., 2004b). Thus, crosslinks to these cysteines would not be nearly as useful as those just described for producing antagonists or targeting vehicles. Crosslinks between α-subunit residue 86 and β-subunit residue cysteine 110, the natural end of the seatbelt, have been described (Xing et al., 2001a) and have low affinity for LH receptors. Thus, they would also not be as useful as antagonists or targeting vehicles.
These observations suggested that the most useful crosslinks involved cysteines that were located in regions of the heterodimer that would be capable of stabilizing the position of the small seatbelt more or less in the position it occupies in the heterodimer. Thus, it would also be expected that a crosslink between α86-β101 would also stabilize the seatbelt in a position in which it could form an antagonist. It would also be expected that crosslinks that involved α-subunit residue 85 rather than α-subunit residue 86 would also work.
Since heterodimers containing β-subunit analogs pMB2674, pMB2672, and pMB2673 contain a free cysteine at residue 26, it can be seen that removal of this cysteine is not essential for preparing this type of analog. In addition, it is possible to form a disulfide between hCG β-subunit Cys26 and a cysteine substituted for either hCG β-subunit residue Ala17 or hCG β-subunit residue Glu19. One of the first steps that takes place during the folding of the hCG β-subunit is the formation of loop 1. This causes Ala17 and Glu19 to become located near Cys26. A cysteine that is substituted for either Ala17 and Glu19 has been found to form a disulfide with Cys26, which makes this cysteine unavailable for other interactions. Examples of these sequences are pMB2567 and pMB2567, respectively (
The addition of other cysteines to the amino terminal regions α- or β-subunits of the analogs of the types described in Example 1 did not interfere with heterodimer production or analog activity. Heterodimers containing a disulfide crosslink between α-subunit residue 5 (pRM917,
Single chain analogs of hCG and other glycoprotein hormones are often expressed better than the individual subunits. This is most likely because in the single chain format their subunit components are present at extremely high concentrations relative to one another. This phenomenon would be expected to facilitate heterodimer assembly in the endoplasmic reticulum, its normal site. Most hCG single chain constructs have a format in which the α-subunit component is linked to the carboxyterminal end of the β-subunit component. This is done to take advantage of the long disordered “tail” of the β-subunit, which facilitates assembly. It is also done because addition of residues to the α-subunit terminus can reduce receptor interactions (Furuhashi et al., 1995b). The antagonist analog described in Example 1 lacks much of the seatbelt and all of the β-subunit carboxyterminus. Therefore, it would not be expected that a single chain construct created by fusing the codons for the α-subunit directly to those of the β-subunit would be able to fold into a molecule that has many of the same structural properties as a glycoprotein hormone heterodimer. Furthermore, introduction of an artificial linker resulted in the production of an analog that retained significant efficacy (Heikoop et al., 1997a).
Proteins can be fused to the α-subunit C-terminus of hCG without reducing ligand-receptor interactions (Bernard et al., 2004) in spite of the notion that this region of the protein has long been thought to be required for receptor binding (Pierce and Parsons, 1981) and reports that fusions to this site reduce receptor binding (Furuhashi et al., 1995a). The key to making these types of analogs is to employ residues near the junction of α-subunit and the linker that are sufficiently hydrophilic to keep the C-terminal extension from folding back under the receptor binding surface of the heterodimer.
The orientation of the ligand in the putative LH receptor complex (Moyle et al., 2004) suggests that fusion of proteins to the carboxyterminal end of the α-subunit would be the most useful site for targeting cells that express LH receptor. This is because the additional residues that are downstream of this portion of the molecule would be least likely to enhance signal transduction. Efforts to express heterodimers containing pRM902 (
The difficulty of attaching proteins to the C-terminus of the α-subunit was eliminated by fabricating the molecule in a single-chain format wherein the C-terminal end of the α-subunit was connected to the N-terminal end of the β-subunit. Thus, the protein encoded by sequence pRM903 (
Other useful fusion proteins can be made in a “cleavable” single chain format. These contain a furin (Trout et al., 1999) or other enzymatic cleavage sequence at the end of the linker that will enable them to be cleaved after they have folded and passed through the secretory machinery of the cell. One such protein having the sequence DDPRFQDSSSSKAPPPSLPSPSRLPGPSDSGRRFKRRPR [SEQ ID NO: 68; underlined sequence is an optimized furin cleavage site (Matthews et al., 1994)] between the α- and β-subunits was also expressed well (81 ng/ml). This is shown as pMB2553 (
Fusion proteins were also useful for preparing hormone analogs that contained deletions in parts of the molecule that were not expressed efficiently. An example of this is the fusion construct pMB2619 (
The use of a fusion protein for expression did not appear to alter the receptor binding specificity. Thus, a fusion protein that contained a small seatbelt loop that was derived from the hFSH βsubunit (pMB2616,
It is expected that the ability of the antagonist analogs described in examples 1-4 to reverse the symptoms of PCOS will be potentiated by the addition of proteins that can help to promote apoptosis of unwanted ovarian tissues that contain lutropin receptors. These include nearly any apoptosis inducing protein, but a preferred protein is Interferonγ, a molecule that is already approved for clinical use. To facilitate production of the fusion proteins, they should be expressed as single chains having a cleavage site—i.e., furin—that permits cleavage of the linker between the components of the heterodimer.
The importance of the oligosaccharides has long been known for the actions of the glycoprotein hormones (Moyle et al., 1975; Matzuk et al., 1989) and it is clear that efficacy is directly proportional to the extent of hormone glycosylation (Moyle et al., 1975; Matzuk et al., 1989). Although the efficacy of the antagonists is already lower than that of other hCG analogs of this type when tested in assays employing cells that overexpress LH receptors, studies were initiated to learn if the residual efficacy could be reduced further by removing some or all of the oligosaccharides on the β-subunit. The hCG β-subunit contains two N-linked oligosaccharides and that at Asn13 is nearest the portion carboxyterminal portion of the seatbelt. Therefore, it seemed possible that disrupting this glycosylation signal would have the greatest influence on the efficacies of analogs that lack this region of the seatbelt and that lack the glycosylation signal at loop α2. All N-linked glycosylation signals have the sequence Asn-Xaa-Ser/Thr where Asn is the amino acid that is glycosylated, Xaa is any residue other than proline, and Ser/Thr are the residues serine or threonine. To disrupt the glycosylation signal one can change Asn to any other residue, Xaa to a proline, or Ser/Thr to a residue other than serine or threonine Heterodimers made by co-expressing pMB2472 and pMB2437 in COS-7 cells were monitored in sandwich immunoassays using antibody A113 for capture and 125I-B110 for detection. These interacted well with rat LH receptors and had similar efficacies as heterodimers prepared by co-expressing pMB2472 and pMB2419. This suggested that the dramatic reduction in efficacy caused by truncating the seatbelt, removing the α2 oligosaccharide, and introducing the α86-β02 disulfide may have obscured the potential role of the oligosaccharide at residue Asn13.
Conceivably, the presence of the oligosaccharide at β-subunit residue Asn30 was sufficient to overcome the influence of removing the oligosaccharide at β-subunit residue Asn13. This possibility was tested by removing both the Asn13 and Asn30 glycosylation signals, a phenomenon that would have removed all the oligosaccharides from the (3-subunit. The β-subunit oligosaccharides appear to have a role in its β-subunit folding, possibly by enabling the unfolded β-subunit to be a substrate for an endoplasmic reticulum oligosaccharide binding chaperone. This was overcome by creating a glycosylation site in the aminoterminal end of the β-subunit that would permit it to be glycosylated and thereby facilitate folding. This would create an oligosaccharide in a highly exposed portion of the β-subunit that might permit it to be removed after the protein had folded by the enzyme N-glycanase. COS-7 cell expression of pMB2472 with pMB2484 (
The cysteines that latch the seatbelt do not interfere with the formation of a disulfide between α-subunit residue 86 and β-subunit residue 102 and can lead to altered hormone activity. The seatbelt controls receptor binding specificity and seatbelt residues 11-20 have a greater influence on interactions with FSH receptors than LH receptors (Campbell et al., 1991; Moyle et al., 1994). Co-expression of pMB2472 (
Follitropin activity is needed to stimulate the production of female gametes from all vertebrate species, including fish. Piscine follitropins would be useful for stimulating the reproduction of endangered species as well as to facilitate the reproduction of captive animals such as those used in aquaculture. Many piscine follitropins, including those of salmon, trout, bass, bonito, sea bream, Conger eel, gourami, halibut, tilapia and tuna, among others have a structure in which their seatbelts are latched to a cysteine in the aminoterminal end of the β-subunit. Preparation of these analogs is often difficult, due largely to the location of the seatbelt latch site (Xing et al., 2004c). Initial efforts to prepare salmon FSH analogs involved obtaining vectors that encode the salmon αII subunit (PS1,
Co-expression of pMB575 and pRM783 (
Several methods have been developed to promote heterodimer assembly, one of which involves the use of an aminoterminal dimerization domain (Lin et al., 1999). This procedure works well for promoting the formation of most glycoprotein hormone heterodimers, including those that have altered tensor loops and/or that lack a seatbelt latch disulfide (Lin et al., 1999). Efforts to produce salmon FSH analogs by attaching the Fos dimerization domain to the human α-subunit to create the sequence that encoded pMB1197 (
Another method for producing “heterodimers” involves expressing glycoprotein hormone analogs as fusion proteins in which the α-subunit is fused to the end of the (3-subunit or in which the β-subunit is fused to the end of the α-subunit. This procedure has been shown to enable the formation and secretion of heterodimers having altered disulfides (Ben-Menahem et al., 1997) and was expected to be useful for producing the salmon hormones efficiently. Expression of single chain constructs pRM784 or pRM787 separately in COS-7 cells led to the accumulation of somewhat more material in the culture medium, but this was deemed too small to be useful. These constructs encoded the salmon FSHβ-subunit upstream of an hCGβ-subunit tail and either lacking the α2 oligosaccharide or a human α-subunit having the α2 oligosaccharide, respectively. The reason for the low production of “heterodimer” was not clear, but might have been due to the possibility that the seatbelt became latched before the subunits had reached their normal position in the heterodimer in which the seatbelt is wrapped around α2. Expression of heterodimer from COS-7 cells that had been transfected with pRM798 (
The use of the human α-subunit in these constructs might have also been responsible for the low production of heterodimer. This possibility was tested using expression vectors that encode the Flag-tagged salmon α-subunit (pRM796,
Together these data suggested that several factors might suppress the secretion of the salmon FSH heterodimer. Unlike the seatbelts of most vertebrate follitropins, those of salmon and several related species are latched to a cysteine in the aminoterminal end of the β-subunit. This places the carboxyterminal portion of these piscine follitropin seatbelts in a very different position than those of most vertebrate follitropins. If the salmon seatbelt reduces assembly, it seemed possible that production of this type of follitropin heterodimer would be enhanced by eliminating the piscine seatbelt latch site and replacing it with a disulfide comparable to that described in Example 1. The role of the salmon FSH seatbelt in hormone activity is unknown. In mammalian follitropins, the carboxyterminal portion of the follitropin seatbelt is known to be essential for its activity (Moyle et al., 1994; Campbell et al., 1991; Dias et al., 1994) and it is not possible to relocate the seatbelt latch site to a site in α-subunit loop 2 without disrupting follitropin activity. The fact that the salmon FSH seatbelt is located at a very different site than the mammalian FSH seatbelt suggested that the carboxyterminal portion of the salmon FSH seatbelt as well as those of other piscine species may not be required for follitropin activity in the same fashion as the mammalian FSH seatbelt. Therefore, salmon follitropin analogs having a folding pattern similar to those in Example 1 might activate the salmon FSH receptor.
To test this possibility, it was necessary to prepare a cell line that expressed the salmon FSH receptor. A vector that encoded the salmon FSH receptor was obtained from Dr. Penny Swanson (PS3,
Following transfection of Chinese hamster ovary cells (CHO cells) with 6 μg of plasmid encoding pMB2811 and selection in the presence of 1 mg G418/ml of culture medium (DMEM), several G418 resistant cell lines were selected and tested for their abilities to express neo' in Western Blots using a polyclonal antibody prepared against neo that was purchased from Upstate USA, Inc. Charlottesville, Va. The presence of reactive material was determined by chemiluminescence using the BM Chemiluminescence Western Blotting Kit, Roche Diagnostics, Indianapolis, Ind. Several G418 resistant cell lines expressed the salmon follitropin receptor—rat lutropin receptor chimera—neo fusion protein—i.e., pMB2811 (
To determine if it was the LH or the FSH in the partially purified preparation of salmon gonadotropins, the sample was treated at pH 2, 37° C., for 30 minutes as described (Xing et al., 2004a). This procedure is known to disrupt heterodimers in which the seatbelt is latched to a cysteine in β-subunit loop 1 but not to a cysteine in the aminoterminal end of the β-subunit (Xing et al., 2004c). This treatment did not reduce the activity of the preparation. This showed that it was the FSH and not the LH in the preparation that interacted with the receptor to initiate signal transduction.
Preparations of heterodimer made by expressing pRM917 and pMB2827 in COS-7 cells stimulated cyclic AMP accumulation in CHO cells that expressed the salmon FSH receptor—rat LH receptor—neo' fusion protein. This analog would be expected to contain two disulfide crosslinks. One of these is between the cysteine found at the substitution of cysteine for Gln5 in pRM917 and the normal salmon FSH β-subunit seatbelt latch site found in pMB2827. The other is between the cysteine substituted for human α-subunit residue Thr86 and that substituted for Arg98 in the portion of salmon FSH β-subunit that constitutes pMB2827. The amount of pRM917-pMB2827 produced by COS-7 cells was estimated in an A113-125I-M1 sandwich immunoassay. The precise amount of heterodimer produced could not be quantified accurately in sandwich immunoassays due to the lack of an appropriate standard but was as high or higher than materials produced by expressing the human α-subunit with the Flag-tagged salmon FSHβ-subunit. The fact that it elicited a response in cells that expressed pMB2811 receptors (
The fact that the heterodimer prepared by expressing pMB2472 and pMB2827 is active in COS-7 cells shows that several related analogs of this heterodimer will also be active salmon follitropins. These include those that have the α-subunit loop 2 oligosaccharide. It would be expected that analogs of pMB2472 that contain salmon α-subunit residues derived from α-subunit loop 2—i.e., FSRAYPTPLRSKQTMLVPKNITSEAT (SEQ ID NO: 69)—rather than their human counterparts found in loop 2 of pMB2472—i.e., FSRAYPTPLRSKKTMLVQKNVTSEST (SEQ ID NO: 70)—would enhance the activity of the analog. This α-subunit analog (pEX1,
This application is a Continuation Application claiming priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 11/911,571, filed Oct. 15, 2007, which is a National Stage filing under 35 U.S.C. §371 of International Application No. PCT/US2006/014103, filed Apr. 13, 2006. The International Application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 60/671,117, filed Apr. 13, 2005. The disclosures of all three applications are incorporated herein by reference.
This research has been funded by NIH Grant HD14907. The U.S. government has certain rights to the invention.
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Related U.S. Appl. No. 11/911,571, filed Oct. 15, 2007. |
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