Patent Application
20150056133
The present invention relates to CX3CR1-binding polypeptides and their uses in in vivo imaging for the diagnosis and treatment of diseases including atherosclerosis.
Cardiovascular diseases are a major cause of death in the United States and other developed countries. Atherosclerosis is a progressive disease of the arterial wall where lipid deposition and chronic inflammation lead to the development of plaque. While most plaques will remain asymptomatic, some may become susceptible to thrombosis (vulnerable) and rupture resulting in myocardial infarctions or strokes. Various imaging modalities have been developed to view the vessel wall (Verjans, 2013; J. of Cardiovasc. Trans. Res. ePub June, 2013). Several technologies such as optical coherence tomography (OCT) and intravascular ultrasound (IVUS) can provide information on plaque composition and stability however they require invasive procedures. Another technology utilizes 18F-fluorodeoxyglucose, a substrate that is taken up by actively metabolizing cells such as plaque macrophages, and can be detected by positron emission tomography (PET). While 18F-FDG PET has shown clinical utility for monitoring plaque inflammation, it can also be taken up into many tissues nonselectively. New molecular imaging tools are needed to provide insight into the active cellular and molecular processes that drive the progression of atherosclerotic disease and the development of vulnerable plaques. Tools that support the detection of highly inflamed and/or rupture-prone lesions would provide a valuable mechanism for the identification of at-risk patients and for the assessment of the efficacy of novel therapies.
The present invention provides novel CX3CR1-targeted imaging agents. In another aspect, these imaging agents are useful for diagnosing atherosclerotic disease. In another aspect these imaging agents are useful in selecting or stratifying patients with atherosclerosis who would benefit by treatment with a CX3CR1 antagonist therapeutic or other known treatments for atherosclerotic disease. In a further aspect these imaging agents are useful in diagnosis of diseases characterized by increased tissue expression of CX3CR1.
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The present invention relates to imaging agents, also known as imaging tracers, based on immunoglobulin single variable domain polypeptides that specifically bind CX3CR1 and their use as diagnostic tools. The imaging agents are comprised of a CX3CR1-targeting single variable domain polypeptide linked to a detection label. The single variable domain polypeptides comprising the imaging agents of the present invention are preferably, but not limited to, VHH domains (or simply “VHHs”) from camelids, as defined hereinafter.
CX3CR1 is a G-protein coupled integral membrane protein, and a member of the chemokine receptor family. It has a unique ligand, fractalkine, which is produced as an integral membrane protein. It can also be released into the circulation by proteolytic cleavage. In humans, a CX3CR1 variant (V249I/T280M) with decreased activity has been shown to be associated with a lower risk of cardiovascular disease (coronary heart disease, cerebrovascular disease or peripheral vascular disease) (McDermott, 2001; Circ. Res. 89:401), coronary artery disease (angiographic evidence of stenosis) (McDermott, 2003; J. Clin. Invest. 111:1241), and carotid artery occlusive disease (Ghilardi, 2004; Stroke 35:1276). Several independent mouse genetic studies have shown a beneficial effect of CX3CR1 deficiency on atherosclerosis. A reduction in lesion area in the aortic arch and thoracic aorta as well as a decrease in monocyte/macrophage accumulation in in plaques were seen in two independently derived strains of CX3CR1−/− apoE−/− mice fed a high fat diet (Combadiëre, 2003; Circulation, 107:1009, Lesnik, 2003; J. Clin. Invest. 111:333).
CX3CR1 is predominantly expressed on cell types such as monocytes, dendritic cells and T cells that have been associated with the initiation and progression of atherosclerotic plaques. It is highly expressed on circulating human intermediate (CD14+CD16+) and non-classical (CD14dimCD16+) monocytes (Cros, 2010; Immunity 33:375). Increased numbers of circulating CD16+CX3CR1+ monocytes were observed in patients with unstable angina pectoris with evidence of ruptured plaques as determined by intravascular OCT (Ikejima, 2010; Circ. J. 74:337). Similarly, increased circulating CD16+ monocytes levels correlated with vulnerable plaque as measured by multidetector computed tomography in patients with stable angina pectoris (Kashiwagii, 2010; Atherosclerosis 212:71) and CD14+CD16+ monocyte levels independently predicted cardiovascular events in patients undergoing elective coronary angiography (Ragacev, 2012; J. Am. Coll. Cardiol. 60:1512). By immunohistochemistry, CX3CR1 has also been shown to be expressed in human carotid plaques with the number of CX3CR1+ cells increasing with lesion development (Stolla, 2012; PLOS One 7:e43572). CX3CR1 appears to be a marker for plaques with elevated levels of inflammation.
Immunoglobulin single variable (VHH) domains are well suited for use as imaging agents (De Vos, 2013; Expert Opin. Biol. Ther. 8:1149). One type of VHH is derived from the antigen binding domain of camelid single chain antibodies. Due to their small size (<15 kDa) which leads to rapid clearance from the blood and their high affinity which allows specific target binding, imaging with good signal to background can be carried out shortly after administration enabling the use of short-lived radioisotopes which minimizes patient exposure. VHH domains have also good physicochemical properties and are stable in blood and under conditions required for labeling for use in various imaging modalities. A VHH domain specific for CX3CR1 could provide a valuable non-invasive imaging tool identifying inflamed or unstable plaques and could be utilized for patient selection, stratification, diagnosis, prognosis or monitoring treatment success for new atherosclerosis therapies. It could also be used for in vivo imaging in other diseases characterized by elevated CX3CR1 tissue expression.
Unless indicated or defined otherwise, all terms used have their usual meaning in the art, which will be clear to the skilled person. Reference is for example made to the standard handbooks, such as Sambrook et al, “Molecular Cloning: A Laboratory Manual” (2nd Ed.), Vols. 1-3, Cold Spring Harbor Laboratory Press (1989); Lewin, “Genes IV”, Oxford University Press, New York, (1990), and Roitt et al., “Immunology” (2nd Ed.), Gower Medical Publishing, London, New York (1989), as well as to the general background art cited herein; Furthermore, unless indicated otherwise, all methods, steps, techniques and manipulations that are not specifically described in detail can be performed and have been performed in a manner known per se, as will be clear to the skilled person. Reference is for example again made to the standard handbooks, to the general background art referred to above and to the further references cited therein;
Unless indicated otherwise, the terms “immunoglobulin” and “immunoglobulin sequence”—whether used herein to refer to a heavy chain antibody or to a conventional 4-chain antibody—are used as general terms to include both the full-size antibody, the individual chains thereof, as well as all parts, domains or fragments thereof (including but not limited to antigen-binding domains or fragments such as VHH domains or VH/VL domains, respectively). In addition, the term “sequence” as used herein (for example in terms like “immunoglobulin sequence”, “antibody sequence”, “(single) variable domain sequence”, “VHH sequence” or “protein sequence”), should generally be understood to include both the relevant amino acid sequence as well as nucleic acid sequences or nucleotide sequences encoding the same, unless the context requires a more limited interpretation;
The term “domain” (of a polypeptide or protein) as used herein refers to a folded protein structure which has the ability to retain its tertiary structure independently of the rest of the protein. Generally, domains are responsible for discrete functional properties of proteins, and in many cases may be added, removed or transferred to other proteins without loss of function of the remainder of the protein and/or of the domain.
The term “immunoglobulin domain” as used herein refers to a globular region of an antibody chain (such as e.g. a chain of a conventional 4-chain antibody or of a heavy chain antibody), or to a polypeptide that essentially consists of such a globular region. Immunoglobulin domains are characterized in that they retain the immunoglobulin fold characteristic of antibody molecules, which consists of a 2-layer sandwich of about 7 antiparallel beta-strands arranged in two beta-sheets, optionally stabilized by a conserved disulphide bond.
The term “immunoglobulin variable domain” as used herein means an immunoglobulin domain essentially consisting of four “framework regions” which are referred to in the art and herein below as “framework region 1” or “FR1”; as “framework region 2” or“FR2”; as “framework region 3” or “FR3”; and as “framework region 4” or “FR4”, respectively; which framework regions are interrupted by three “complementarity determining regions” or “CDRs”, which are referred to in the art and herein below as “complementarity determining region 1” or “CDR1”; as “complementarity determining region 2” or “CDR2”; and as “complementarity determining region 3” or “CDR3”, respectively. Thus, the general structure or sequence of an immunoglobulin variable domain can be indicated as follows: FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4. It is the immunoglobulin variable domain(s) that confer specificity to an antibody for the antigen by carrying the antigen-binding site.
The terms “immunoglobulin single variable domain” and “single variable domain” as used herein mean an immunoglobulin variable domain which is capable of specifically binding to an epitope of the antigen without pairing with an additional variable immunoglobulin domain. One example of immunoglobulin single variable domains in the meaning of the present invention are “domain antibodies”, such as the immunoglobulin single variable domains VH and VL (VH domains and VL domains). Another example of immunoglobulin single variable domains are “VHH domains” (or simply “VHHs”) from camelids, as defined hereinafter.
In view of the above definition, the antigen-binding domain of a conventional 4-chain antibody (such as an IgG, IgM, IgA, IgD or IgE molecule; known in the art) or of a Fab fragment, a F(ab′)2 fragment, an Fv fragment such as a disulphide linked Fv or a scFv fragment, or a diabody (all known in the art) derived from such conventional 4-chain antibody, would normally not be regarded as an immunoglobulin single variable domain, as, in these cases, binding to the respective epitope of an antigen would normally not occur by one (single) immunoglobulin domain but by a pair of (associating) immunoglobulin domains such as light and heavy chain variable domains, i.e. by a VH-VL pair of immunoglobulin domains, which jointly bind to an epitope of the respective antigen.
“VHH domains”, also known as VHHs, VHH domains, VHH antibody fragments, and VHH antibodies, have originally been described as the antigen binding immunoglobulin (variable) domain of “heavy chain antibodies” (i.e. of “antibodies devoid of light chains”; C. Hamers-Casterman et al., 1993; Nature 363: 446). The term “VHH domain” has been chosen in order to distinguish these variable domains from the heavy chain variable domains that are present in conventional 4-chain antibodies (which are referred to herein as “VH domains” or “VH domains”) and from the light chain variable domains that are present in conventional 4-chain antibodies (which are referred to herein as “VL domains” or “VL domains”). VHH domains can specifically bind to an epitope without an additional antigen binding domain (as opposed to VH or VL domains in a conventional 4-chain antibody, in which case the epitope is recognized by a VL domain together with a VH domain). VHH domains are small, robust and efficient antigen recognition units formed by a single immunoglobulin domain.
In the context of the present invention, the terms VHH domain, VHH, VHH domain, VHH antibody fragment, VHH antibody, as well as “Nanobody®” and “Nanobody® domain” (“Nanobody” being a trademark of the company Ablynx N.V.; Ghent; Belgium) are used interchangeably and are representatives of immunoglobulin single variable domains (having the structure: FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4 and specifically binding to an epitope without requiring the presence of a second immunoglobulin variable domain), and which are distinguished from VH domains by the so-called “hallmark residues”, as defined in e.g. WO2009/109635, FIG. 1.
The amino acid residues of a VHH domain are numbered according to the general numbering for VH domains given by Kabat et al. (“Sequence of proteins of immunological interest”, US Public Health Services, NIH Bethesda, Md., Publication No. 91), as applied to VHH domains from Camelids, as shown e.g. in FIG. 2 of Riechmann and Muyldermans, 1999; J. Immunol. Methods, 231: 25. According to this numbering,
However, it should be noted that—as is well known in the art for VH domains and for VHH domains—the total number of amino acid residues in each of the CDRs may vary and may not correspond to the total number of amino acid residues indicated by the Kabat numbering (that is, one or more positions according to the Kabat numbering may not be occupied in the actual sequence, or the actual sequence may contain more amino acid residues than the number allowed for by the Kabat numbering). This means that, generally, the numbering according to Kabat may or may not correspond to the actual numbering of the amino acid residues in the actual sequence.
Alternative methods for numbering the amino acid residues of VH domains, which methods can also be applied in an analogous manner to VHH domains, are known in the art. However, in the present description, claims and figures, the numbering according to Kabat and applied to VHH domains as described above will be followed, unless indicated otherwise.
The total number of amino acid residues in a VHH domain will usually be in the range of from 110 to 120, often between 112 and 115. It should however be noted that smaller and longer sequences may also be suitable for the purposes described herein.
Determination of CDR regions may also be done according to different methods. In the CDR determination according to Kabat, FR1 of a VHH comprises the amino acid residues at positions 1-30, CDR1 of a VHH comprises the amino acid residues at positions 31-35, FR2 of a VHH comprises the amino acids at positions 36-49, CDR2 of a VHH comprises the amino acid residues at positions 50-65, FR3 of a VHH comprises the amino acid residues at positions 66-94, CDR3 of a VHH comprises the amino acid residues at positions 95-102, and FR4 of a VHH comprises the amino acid residues at positions 103-113.
In the present application, however, CDR sequences were determined according to Kontermann and Dübel (Eds., Antibody Engineering, vol 2, Springer Verlag Heidelberg Berlin, Martin, Chapter 3, pp. 33-51, 2010). According to this method, FR1 comprises the amino acid residues at positions 1-25, CDR1 comprises the amino acid residues at positions 26-35, FR2 comprises the amino acids at positions 36-49, CDR2 comprises the amino acid residues at positions 50-58, FR3 comprises the amino acid residues at positions 59-94, CDR3 comprises the amino acid residues at positions 95-102, and FR4 comprises the amino acid residues at positions 103-113.
Further structural characteristics and functional properties of VHH domains and polypeptides containing the same can be summarized as follows:
VHH domains (which have been “designed” by nature to functionally bind to an antigen without the presence of, and without any interaction with, a light chain variable domain) can function as a single, relatively small, functional antigen-binding structural unit, domain or polypeptide. This distinguishes the VHH domains from the VH and VL domains of conventional 4-chain antibodies, which by themselves are generally not suited for practical application as single antigen-binding proteins or immunoglobulin single variable domains, but need to be combined in some form or another to provide a functional antigen-binding unit (as in for example conventional antibody fragments such as Fab fragments; in scFv's, which consist of a VH domain covalently linked to a VL domain).
Because of these unique properties, the use of VHH domains—either alone or as part of a larger polypeptide—offers a number of significant advantages over the use of conventional VH and VL domains, scFv's or conventional antibody fragments (such as Fab- or F(ab′)2-fragments):
Methods of obtaining VHH domains binding to a specific antigen or epitope have been described earlier, e.g. in WO2006/040153 and WO2006/122786. As also described therein in detail, VHH domains derived from camelids can be “humanized” by replacing one or more amino acid residues in the amino acid sequence of the original VHH sequence by one or more of the amino acid residues that occur at the corresponding position(s) in a VH domain from a conventional 4-chain antibody from a human being. A humanized VHH domain can contain one or more partially or fully human framework region sequences, and, in an even more specific embodiment, can contain human framework region sequences derived from DP-29, DP-47, DP-51, or parts thereof, optionally combined with JH sequences, such as JHS.
The terms “epitope” and “antigenic determinant”, which can be used interchangeably, refer to the part of a macromolecule, such as a polypeptide, that is recognized by antigen-binding molecules, such as conventional antibodies or the polypeptides of the invention, and more particularly by the antigen-binding site of said molecules. Epitopes define the minimum binding site for an immunoglobulin, and thus represent the target of specificity of an immunoglobulin.
A polypeptide (such as an immunoglobulin, an antibody, an immunoglobulin single variable domain, a polypeptide of the invention, or generally an antigen binding molecule or a fragment thereof) that can “bind to” or “specifically bind to”, that “targets” or “is targeting for” that “has affinity for” and/or that “has specificity for” a certain epitope, antigen or protein (or for at least one part, fragment or epitope thereof) is said to be “against” or “directed against” said epitope, antigen or protein or is a “binding” molecule with respect to such epitope, antigen or protein, or is said to be “anti”-epitope, “anti”-antigen or “anti”-protein (e.g anti-CX3CR1).
Generally, the term “specificity” refers to the number of different types of antigens or epitopes to which a particular antigen-binding molecule or antigen-binding protein (such as an immunoglobulin, an antibody, an immunoglobulin single variable domain, or a polypeptide of the invention) can bind. The specificity of an antigen-binding protein can be determined based on its affinity and/or avidity. The affinity, represented by the equilibrium constant for the dissociation of an antigen with an antigen-binding protein (KD), is a measure for the binding strength between an epitope and an antigen-binding site on the antigen-binding protein: the lesser the value of the KD, the stronger the binding strength between an epitope and the antigen-binding molecule (alternatively, the affinity can also be expressed as the affinity constant (KA), which is 1/KD). As will be clear to the skilled person (for example on the basis of the further disclosure herein), affinity can be determined in a manner known per se, depending on the specific antigen of interest. Avidity is the measure of the strength of binding between an antigen-binding molecule (such as an immunoglobulin, an antibody, an immunoglobulin single variable domain, or a polypeptide of the invention) and the pertinent antigen. Avidity is related to both the affinity between an epitope and its antigen binding site on the antigen-binding molecule and the number of pertinent binding sites present on the antigen-binding molecule.
Amino acid residues will be indicated according to the standard three-letter or one-letter amino acid code, as generally known and agreed upon in the art. When comparing two amino acid sequences, the term “amino acid difference” refers to insertions, deletions or substitutions of the indicated number of amino acid residues at a position of the reference sequence, compared to a second sequence. In case of substitution(s), such substitution(s) will preferably be conservative amino acid substitution(s), which means that an amino acid residue is replaced with another amino acid residue of similar chemical structure and which has little or essentially no influence on the function, activity or other biological properties of the polypeptide. Such conservative amino acid substitutions are well known in the art, for example from WO 98/49185, wherein conservative amino acid substitutions preferably are substitutions in which one amino acid within the following groups (i)-(v) is substituted by another amino acid residue within the same group: (i) small aliphatic, nonpolar or slightly polar residues: Ala, Ser, Thr, Pro and GIy; (ii) polar, negatively charged residues and their (uncharged) amides: Asp, Asn, Glu and GIn; (iii) polar, positively charged residues: His, Arg and Lys; (iv) large aliphatic, nonpolar residues: Met, Leu, Ile, VaI and Cys; and (v) aromatic residues: Phe, Tyr and Trp. Particularly preferred conservative amino acid substitutions are as follows:
Ala into GIy or into Ser;
Arg into Lys;
Asn into GIn or into His;
Asp into GIu;
Cys into Ser;
GIn into Asn;
GIu into Asp;
GIy into Ala or into Pro;
His into Asn or into GIn;
Ile into Leu or into VaI;
Leu into Ile or into VaI;
Lys into Arg, into GIn or into GIu;
Met into Leu, into Tyr or into Be;
Phe into Met, into Leu or into Tyr;
Ser into Thr;
Thr into Ser;
Trp into Tyr;
Tyr into Trp or into Phe;
VaI into Ile or into Leu.
“Sequence identity” between e.g. two immunoglobulin single variable domain sequences indicates the percentage of amino acids that are identical between these two sequences. It may be calculated or determined as described in paragraph f) on pages 49 and 50 of WO08/020079. “Sequence similarity” indicates the percentage of amino acids that either are identical or that represent conservative amino acid substitutions.
Target Specificity The CX3CR1-targeting polypeptides of the invention have specificity for human CX3CR1. Thus, the imaging agents of the invention comprising CX3CR1-targeting polypeptides and a detection label preferably bind to human CX3CR1 (SEQ ID NO:230).
The CX3CR1-targeting polypeptide portion of the imaging agents described herein is comprised of VHH domains. Representative VHH domains have CDR sequences shown in Tables 1, 2, 3 (representative polypeptides of families 101, 9 and 13, respectively) and 4 (representative polypeptides of optimized variants of family 101. An optimized variant is humanized and/or optimized for stability, potency, manufacturability and/or similarity to human framework regions.
Representative sequences of VHH domains that may comprise the CX3CR1-targeting polypeptide portion of the imaging agents described herein are shown in Tables 5 and 6 below:
Representative sequences of CX3CR1-binding bivalent VHH domains that may comprise the CX3CR1-targeting polypeptide portion of the imaging agents described herein are shown in Tables 7 below. As seen in the sequences, the two VHH domains are joined by a Gly/Ser linker:
The VHH domain or bivalent VHH domains that comprise the CX3CR1-targeting portion of the imaging agent may be further modified by methods known in the art in order to enable linking to the detection label as described herein, below. For example, in order enable linking to a 99mTc detection label by the tricarbonyl method (described below), a hexahistidine or myc-hexahistidine tag may be added to the C-terminal of the desired VHH domain or bivalent VHH domains. Representative examples of such modified VHH domains, monovalent or bivalent, are shown below in Table 8.
The CX3CR1-targeting polypeptide components of the imaging agents described herein may be prepared by methods known in the art, for example, see U.S. application Ser. No. 13/775,307, incorporated herein by reference. Such methods generally comprise the steps of:
In one aspect of the invention these imaging agents may be used in non-invasive imaging of atherosclerosis, for example to diagnose atherosclerotic disease. In another aspect the imaging agents of the invention would be useful as a companion diagnostic for a CX3CR1-antagonist therapeutic. That is, they may be used for patient stratification, i.e. to pre-select patients with atherosclerosis that may respond favorably to a CX3CR1-antagonist therapeutic. The imaging agents may also be used to monitor the effects of treatment with any therapeutic by evaluating the progression or regression of the atherosclerotic lesion.
In another aspect of the invention, the imaging agents may be used in non-invasive imaging to diagnose other diseases characterized by increased expression of CX3CR1. Increased CX3CR1 expression is also known to be associated with multiple inflammatory disease states or conditions including cardio- and cerebrovascular atherosclerotic disorders, peripheral artery disease, restenosis, diabetic nephropathy, glomerulonephritis, human crescentic glomerulonephritis, IgA nephropathy, membranous nephropathy, lupus nephritis, pancreatitis, vasculitis including Henoch-Schonlein purpura and Wegener's granulomatosis, rheumatoid arthritis, osteoarthritis, allograft rejection, systemic sclerosis, neurodegenerative disorders and demyelinating disease, multiple sclerosis (MS), Alzheimer's disease, pulmonary diseases such as COPD, asthma, neuropathic pain, inflammatory pain, and cancer.
Single variable domain polypeptides, such as VHH domains have favorable properties for use in imaging agents. They have high affinity and specificity for their target as well as good physicochemical properties such as serum stability. They have molecular weights below the renal cutoff for glomerular filtration and therefore are rapidly cleared, allowing in vivo imaging of the tissues where specific binding occurs. In one embodiment the CX3CR1-binding single variable domain comprising the imaging agent is a monovalent VHH domain. In another embodiment it is bivalent, comprising two VHH domains, which may be identical or different, covalently linked by a linker peptide. The linker peptide may be a naturally occurring sequence or a non-naturally occurring sequence, preferably non-immunogenic. Non-limiting examples of linker sequences are Gly/Ser linkers of different length such as (glyxsery)z linkers, including (gly4ser)3, (gly4ser)4, (gly4ser), (gly3ser), gly3, and (gly3ser2)3.
For use as an imaging agent the single variable domain polypeptide is linked to a detection label. Various detection labels and linking methods are known in the art. For example, non-limiting examples of detection labels may include fluorescent, chemiluminescent, bioluminescent, phosphorescent labels, paramagnetic labels, radioisotope or radiotracer labels, microbubbles or imaging dyes. The detection label may be selected according to the desired use and imaging application.
Various imaging technologies are well known and currently in use in the art. Non-limiting examples of imaging applications or technologies that may be used include:
Single photon emission computed tomography (SPECT). Non-limiting examples of radio-isotopes that may be used in detection labels for SPECT imaging include 99mTc, 111In, 123I, 201Tl and 133Xe.
Positron emission tomography (PET). Non-limiting examples of radio-isotopes that may be used in detection labels for PET imaging include 11C, 64Cu, 18F, 68Ga, 13N, 15O, 82Rb, 124I and 89Zr.
Near infrared fluorescence imaging (NIR or NIRF). Non-limiting examples of imaging dyes that may be used in detection labels for NIRF include Cy5.5, Alexa680, Dylight680, Dylight800 and IRDye800CW.
Ultrasound imaging. A non-limiting example of a detection label suitable for ultrasound imaging is microbubbles.
Magnetic resonance imaging (MRI). Non-limiting examples of paramagnetic materials suitable for MRI imaging include iron oxide or carbon-coated iron-cobalt nanoparticles and gadolinium chelates.
Methods for linking detection labels to a targeting antibody fragment, for example a CX3CR1-targeting single domain polypeptide, are well known in the art. Detection labels may be linked directly or indirectly, via another linking molecule, to the targeting polypeptide. The detection label may be joined covalently, for example by formation of an amide bond with an amino acid, or non-covalently, for example by an ionic interaction with a linking, chelating molecule.
Non-limiting examples of a covalent linking method include:
99mTc linking by a tricarbonyl method. 99mTc-tricarbonyl is reacted with the hexahistidine tagged-targeting polypeptide followed by purification (for example, see V. Cortez-Retamozo, 2008; Curr Radiopharm 1:37).
IRDye800CW linking by NHS-ester method. IRDye800CW N-hydroxysuccinimide (NHS) ester is reacted with the targeting polypeptide followed by purification (for example, see S. Oliveira, 2012; Mol. Imaging, 7:254-264).
Microbubble linking by biotin-streptavidin bridge. Targeting polypeptide is biotinylated. The biotinylated targeting polypeptide is coupled to biotinylated microbubble by biotin-streptavidin bridge (for example, see S. Hernot, 2012; J. Control. Release 158:346-353).
A non-limiting example of a chelating linking method includes:
The targeting polypeptide is reacted with Df-Bz-NCS to form the chelating linker. The modified targeting polypeptide is then radiolabeled with 68Ga. (for example, see M.J.W.D. Vosjan, 2011; Eur J. Nucl. Med. Mol. Imaging, 38:753-763).
The targeting polypeptide is conjugated with S-2-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (pSCN-Bn-NOTA) and then radiolabelled with 68Ga. (for example, see C. Xavier, 2013; J. Nucl. Med., 54: 776-784).
For use in in vivo imaging, the imaging agents of the invention may be formulated as a pharmaceutical preparation comprising (i) at least one imaging agent of the invention and (ii) at least one pharmaceutically acceptable carrier, diluent, excipient, adjuvant, and/or stabilizer. By “pharmaceutically acceptable” is meant that the respective material does not show any biological or otherwise undesirable effects when administered to an individual and does not interact in a deleterious manner with any of the other components of the pharmaceutical composition (such as e.g. the imaging agent) in which it is contained. Specific examples can be found in standard handbooks, such as e.g. Remington's Pharmaceutical Sciences, 18th Ed., Mack Publishing Company, USA (1990). For example, the imaging agents of the invention may be formulated and administered in any manner known per se for conventional antibodies and antibody fragments and other pharmaceutically active proteins. Thus, according to a further embodiment, the invention relates to a pharmaceutical composition or preparation that contains at least one imaging agent of the invention and at least one pharmaceutically acceptable carrier, diluent, excipient, adjuvant and/or stabilizer.
Such a formulation may be in a form suitable for parenteral administration (such as by intravenous, intramuscular, subcutaneous, intrathecal, intracavernosal or intraperitoneal injection or intravenous infusion). Such suitable administration forms—which may be solid, semi-solid or liquid, depending on the manner of administration—as well as methods and carriers for use in the preparation thereof, will be clear to the skilled person. The preferred formulation and route of administration would be known by one skilled in the art and would depend in part on the imaging method being used and tissue being examined.
Preparations for parenteral administration may for example be sterile solutions, suspensions, dispersions, emulsions, or powders which comprise the active ingredient and which are suitable, optionally after a further dissolution or dilution step, for infusion or injection. Suitable carriers or diluents for such preparations for example include, without limitation, sterile water and pharmaceutically acceptable aqueous buffers and solutions such as physiological phosphate-buffered saline, Ringer's solutions, dextrose solution, and Hank's solution; water oils; glycerol; ethanol; glycols such as propylene glycol, as well as mineral oils, animal oils and vegetable oils, for example peanut oil, soybean oil, as well as suitable mixtures thereof.
For use in in vivo imaging a detectable amount of the composition containing the imaging agent is administered to a subject. The detectable amount may vary depending on a number of factors including the imaging agent, the route of administration, the imaging method and the subject and tissue being examined and can be determined by one skilled in the art.
The invention provides a method for detecting CX3CR1-containing atherosclerotic plaques in vivo comprising:
Vasculature that may be examined by in vivo imaging for detecting atherosclerotic plaque includes, for example, the carotid artery, coronary artery, femoral artery, abdominal artery and thoracic artery.
The invention also provides a method for ex vivo detection of atherosclerotic disease comprising:
In a further aspect, the invention provides the following:
An imaging agent comprising a CX3CR1-targeting polypeptide linked to a detection label.
An imaging agent according to embodiment 1, wherein the CX3CR1-targeting polypeptide is an immunoglobulin single variable domain.
An imaging agent according to embodiment 1 or 2, wherein the CX3CR1-targeting polypeptide is a VHH domain.
An imaging agent according to any one of embodiments 1 to 3, wherein the CX3CR1-targeting polypeptide includes CDR1, CDR2 and CDR3 sequences selected from:
An imaging agent according to any one of embodiments 1 to 4, wherein the CX3CR1-targeting polypeptide includes CDR1, CDR2 and CDR3 sequences selected from:
An imaging agent according to any one of embodiments 1-3, wherein the CX3CR1-targeting polypeptide is a VHH domain having a sequence selected from:
An imaging agent according to embodiment 6, wherein the CX3CR1-targeting polypeptide is a VHH domain having a sequence selected from:
An imaging agent according to embodiment 1 or 2, wherein the CX3CR1-targeting polypeptide is bivalent comprising two VHH domains, which may be identical or different, covalently linked by a linker peptide, wherein the sequence of the VHH domains are selected from:
An imaging agent according to any one of embodiments 1, 2 or 8, wherein the sequence of the bivalent CX3CR1-targeting polypeptide is selected from:
An imaging agent according to any one of embodiments 1-9, wherein the detection label is selected from a radio-isotope, an imaging dye, a paramagnetic material or a microbubble.
An imaging agent according to any one of embodiments 1-10, wherein the detection label is a radio-isotope.
An imaging agent according to any one of embodiments 1-11, wherein the detection label is selected from 99mTc, 111In, 123I, 201Tl, 133Xe, 11C, 64Cu, 18F, 68Ga, 13N, 15O, 82Rb, 124I and 89Zr.
An imaging agent according to any one of embodiments 1-12, wherein the detection label is selected from 99mTc and 68Ga.
An imaging agent according to embodiment 1, wherein the CX3CR1-targeting polypeptide is an immunoglobulin that competes for binding to CX3CR1 with a VHH domain selected from:
An in vivo method for diagnosing a disease characterized by increased expression of CX3CR1 in a subject, comprising:
An in vivo method for diagnosing a disease characterized by increased expression of CX3CR1 in a subject, the method comprising:
A method according to embodiment 15 or 16, wherein the disease is selected from cardio- and cerebrovascular atherosclerotic disorders, peripheral artery disease, restenosis, diabetic nephropathy, glomerulonephritis, human crescentic glomerulonephritis, IgA nephropathy, membranous nephropathy, lupus nephritis, pancreatitis, vasculitis including Henoch-Schonlein purpura and Wegener's granulomatosis, rheumatoid arthritis, osteoarthritis, allograft rejection, systemic sclerosis, neurodegenerative disorders and demyelinating disease, multiple sclerosis (MS), Alzheimer's disease, pulmonary diseases such as COPD, asthma, neuropathic pain, inflammatory pain, and cancer.
A method according to any one of embodiments 15-17, wherein the disease is atherosclerosis.
A method according to any one of embodiments 15-18 wherein the method for detecting the binding of the imaging agent is selected from:
A method according to any one of embodiments 15-19 wherein the method for detecting the binding of the imaging agent is positron emission tomography.
A method according to any one of embodiments 15-20, wherein the subject is a human.
An ex vivo method for diagnosing a disease characterized by increased expression of CX3CR1 in a subject, comprising:
An ex vivo method for diagnosing a disease characterized by increased expression of CX3CR1 in a subject, comprising:
A method for identifying and treating patients suffering from a disease characterized by increased expression of CX3CR1 comprising:
A method for treating a patient having a disease characterized by increased expression of CX3CR1 comprising:
The method according to embodiment 24 or 25, wherein the disease is selected from cardio- and cerebrovascular atherosclerotic disorders, peripheral artery disease, restenosis, diabetic nephropathy, glomerulonephritis, human crescentic glomerulonephritis, IgA nephropathy, membranous nephropathy, lupus nephritis, pancreatitis, vasculitis including Henoch-Schonlein purpura and Wegener's granulomatosis, rheumatoid arthritis, osteoarthritis, allograft rejection, systemic sclerosis, neurodegenerative disorders and demyelinating disease, multiple sclerosis (MS), Alzheimer's disease, pulmonary diseases such as COPD, asthma, neuropathic pain, inflammatory pain, and cancer.
The method according to embodiment 25 or 26, wherein the disease is atherosclerosis.
The method according to any of embodiments 24 to 27, wherein the effective therapeutic agent is a CX3CR1 antagonist.
A method for the manufacturing of an imaging agent according to any of embodiments 1 to 14 comprising the steps of
Use of a detection label selected from a radio-isotope, an imaging dye, a paramagnetic material or a microbubble for the manufacturing of an imaging agent according to any of embodiments 1 to 14.
Use of an imaging agent according to any of embodiments 1 to 14 for the preparation of a composition for the diagnosis of a disease characterized by increased expression of CX3CR1 in a subject.
A composition comprising an imaging agent according to any of embodiments 1 to 14 for use in a method for the diagnosis of a disease characterized by increased expression of CX3CR1 in a subject.
A kit for use in a method for the diagnosis of a disease characterized by increased expression of CX3CR1 in a subject comprising an imaging agent according to any of embodiments 1 to 14.
A polypeptide comprising an anti-CX3CR1 immunoglobulin single variable domain, wherein said polypeptide is capable of blocking the binding of human fractalkine to human CX3CR1, wherein said anti-CX3CR1 immunoglobulin single variable domain is a VHH domain comprising the sequence set forth in any one of SEQ ID NO: 200-202.
A nucleic acid molecule encoding a polypeptide according to embodiment 35.
A pharmaceutical composition comprising (i) a polypeptide according to embodiment 35, and (ii) a pharmaceutically acceptable carrier, and optionally (iii) a diluent, excipient, adjuvant and/or stabilizer.
A method for the treatment of a CX3CR1-associated disease, disorder or condition, comprising administering a therapeutic amount of a compound according to embodiment 35 to a patient in need thereof.
The method according to embodiment 38, wherein the disease, disorder or condition is selected from cardio- and cerebrovascular atherosclerotic disorders, peripheral artery disease, restenosis, diabetic nephropathy, glomerulonephritis, human crescentic glomerulonephritis, IgA nephropathy, membranous nephropathy, lupus nephritis, vasculitis including Henoch-Schonlein purpura and Wegener's granulomatosis, rheumatoid arthritis, osteoarthritis, allograft rejection, systemic sclerosis, neurodegenerative disorders and demyelinating disease, multiple sclerosis (MS), Alzheimer's disease, pulmonary diseases such as COPD, asthma,neuropathic pain, inflammatory pain, or cancer.
The method according to embodiment 39, wherein the disease, disorder or condition is atherosclerosis.
Llamas were immunized according to standard protocols with pVAX1-hCX3CR1 plasmid vector (Invitrogen, Carlsbad, Calif., USA), Camel Kidney (Caki) cells overexpressing human CX3CR1 and/or recombinant peptides derived from the N-terminus and the third extracellular loop of CX3CR1 coupled to BSA. Peptides were ordered at Neo MPS (Polypeptidegroup, Strasbourg, France) and coupled to BSA according to standard protocols. At various times during the immunizations and following the final immunogen injection, blood samples and lymph node biopsies which served as the source of B-cells that produce the heavy-chain antibodies were collected from the llamas. From the blood samples, peripheral blood lymphocytes (PBLs) were prepared using Ficoll-Hypaque according to the manufacturer's instructions (Amersham Biosciences, Piscataway, N.J., USA). From the PBLs and the lymph node biopsies (LN), total RNA was extracted, which was used as starting material for RT-PCR to amplify the VHH encoding DNA segments.
From each immunized llama, libraries were constructed by pooling the total RNA isolated from samples originating from a certain subset of the immunization schedule i.e. after one type of immunization antigen, and for some llamas samples from the different animals were pooled into one library. In short, the PCR-amplified VHH repertoire was cloned via specific restriction sites into a vector designed to facilitate phage display of the VHH library. The vector was derived from pUC119 and contains the LacZ promoter, a M13 phage gIII protein coding sequence, a resistance gene for ampicillin or carbenicillin, a multiple cloning site and a hybrid gIII-pelB leader sequence (pAX050). In frame with the VHH coding sequence, the vector encodes a C-terminal c-myc tag and a hexahistidine tag. Phages were prepared according to standard protocols and stored after filter sterilization at 4° C. or at −80° C. in 20% glycerol for further use.
VHH repertoires obtained from all llamas and cloned as phage libraries were used in different selection strategies, applying a multiplicity of selection conditions. All solid coated phase selections were done in Maxisorp 96-well plates (Nunc, Wiesbaden, Germany). Selections were performed as follows: CX3CR1 antigen preparations for solid (CX3CR1 expressed on liposomes/VLPs, Integral Molecular, Philadelphia, Pa., USA) and solution (cells recombinantly expressing CX3CR1) phase selection formats were presented at multiple concentrations. After 2 hours incubation with the phage libraries followed by extensive washing, bound phages were eluted with trypsin (1 mg/mL) for 15 minutes. When trypsin was used for phage elution, the protease activity was immediately neutralized by applying 0.8 mM protease inhibitor ABSF. As a control, selections without antigen were performed in parallel.
Phage outputs were used to infect E. coli which were then in turn used to prepare phage for the next selection round (phage rescue) After the second round selection the phage outputs were used to infect E. coli which were then plated on agar plates (LB+carb+glucose2%) for analysis of individual VHH clones. In order to screen a selection output for specific binders, single colonies were picked from the agar plates and grown in 1 mL 96-deep-well plates. LacZ-controlled VHH expression was induced by adding IPTG (1 mM final) in the absence of glucose. Periplasmic extracts (in a volume of ˜80 uL) were prepared according to standard protocols.
Periplasmic extracts were screened in a human CX3CR1/human fractalkine FACS competition assay to assess the ability of the expressed VHHs to block the binding of the unique CX3CR1 ligand to the receptor. Human CX3CR1 was presented on CHO cells. As a detection reagent fractalkine (R&D Systems, Minneapolis, Minn., USA) labeled with Alexa Fluor 647 (A647-Fractalkine) at a degree of labeling of 1 was used. In brief, 50 μl of periplasmic extract was added to 6 nM labeled fractalkine (50 μl) and 2E5 CHO-hCX3CR1 cells. After one hour incubation at 4° C., cells were washed three times before analysis on a FACS Array (Becton Dickinson). First a gate was set on the intact cells as determined from the scatter profile. Next, dead cells were gated out by their fluorescence profile from the PI stain (Sigma, St Louis, US). The fluorescence profile from the Alexa Fluor 647 label was determined for each sample and used for the calculation of blocking capacity. As controls, conditions were taken along where there was no VHH present in the periplasmic extract or a known irrelevant VHH and samples were included with excess cold fractalkine. For each sample the percentage block was determined using the control samples to determine the assay window.
From this screening, VHHs were selected and sequence analysis revealed unique VHHs belonging to 3 different B-cell lineages designated families 9, 13 and 101. In order to determine whether formatting monovalent VHHs as bivalent molecules would increase potency and/or efficacy, bivalent molecules were constructed by genetic engineering. Two VHHs were genetically linked together with a 35GS linker in between the two building blocks.
Anti-CX3CR1 VHHs were expressed and purified for further characterization. Monovalent and bivalent VHHs were expressed in E. coli TG1 as c-myc, His6-tagged proteins. Expression was induced by addition of 1 mM IPTG and allowed to continue for 4 hours at 37° C. After spinning the cell cultures, periplasmic extracts were prepared by freeze-thawing the pellets. These extracts were used as starting material and VHHs were purified via IMAC and size exclusion chromatography (SEC) resulting in 95% purity as assessed via SDS-PAGE.
Representative epitope tagged monovalent and bivalent VHH domains from different families and with diverse predicted charge and pI were selected for evaluation as imaging reagents. All of these VHH domains were shown to block fractalkine binding to the receptor in the competition FACS assay outlined above. Either BA/F3-hCX3CR1 cells, CHO-hCX3CR1 cells or transiently transfected HEK293T cells were used. The amount of labeled ligand used in the different competition setups was also varied. The IC50 values for VHHs blocking the interaction of human fractalkine to human CX3CR1 are depicted Table 9.
Specificity for the hCX3CR1 receptor was evaluated by performing a FACS binding experiment on CHO-K1 parental cells or CHO cells expressing human CCR2, human CCR5 or mouse CX3CR1. The VHHs were incubated with the respective cell lines for 30 minutes at 4° C. followed by three wash steps and subsequently incubated with the detection reagents. As detection, a mouse anti-cmyc antibody (Serotec, MCA2200) followed by a goat anti-mouse antibody coupled to PE (Jackson 115-116-071) was used, each incubation was for 30 minutes at 4° C. and was followed by three wash steps. For each cell line a quality control with receptor-specific antibody was included. In addition, the highest concentration of each VHH was also incubated with CHO cells expressing hCX3CR1 as a positive control. No binding to mouse CX3CR1, human CCR2 or human CCR5 could be observed.
VHH domains were radiolabeled site-specifically on their hexahistidine tags with 99mTc using the 99mTc-tricarbonyl-method. [99mTc(H2O)3(CO)3]+ (99mTc-tricarbonyl) was synthesized by adding 99mTcO4− solution (99Mo/99mTc generator eluate; 0.74-3.7 GBq; Drytec; GE Healthcare, Piscataway, N.J.) to an Isolink kit (Covidien, St Louis, Mo.). The vial was incubated at 100° C. for 20 minutes. After cooling, the 99mTc-tricarbonyl solution was neutralized to pH 7.4 with 1 M HCl. 500 μl 99mTc-tricarbonyl was then added to 50 μl of VHH domain (1 mg/ml for monovalent VHH domains, 2 mg/ml for bivalent VHH domains) and incubated for 90 minutes at 50° C. Separation of labeled molecules from free label and buffer exchange into phosphate buffered saline (PBS) was carried out by gel filtration using Sephadex G25 disposable columns (NAP-5; GE Healthcare, Piscataway, N.J.). The labeled VHH domains were then passed through a 0.22 μm filter (Millipore, Bedford, Mass.) to remove aggregates.
All VHH domains were successfully labeled with 99mTc. Radiochemical purity was shown to be >95% by Instant Thin Layer Chromatography using acetone as the mobile phase. The radiochemical purity was also assessed by RP-HPLC analysis and shown to be >89% using an analytical C4 column 214TP53 (Grace Vydac, Deerfield, Ill.) with 0.1% trifluoracetic acid in H2O (solvent A)/0.1% trifluoracetic acid in acetonitrile (solvent B) gradient as the mobile phase.
To confirm that the labeled VHH domain molecules retained their binding to CX3CR1, binding studies were carried out utilizing CHO-hCX3CR1 cells. Untransfected CHO cells (CHO-WT) were included as controls. CHO-hCX3CR1 or CHO-WT cells were plated at 2 E5 cells/well in 24-well plates containing F12 medium supplemented with 10% FBS, 500 μg/ml G418 and 100 μg/ml Zeocin (CHO-hCX3CR1) or RPMI medium supplemented with 10% FBS, 100 U/ml Penicillin, 100 μg/ml Streptavidin and 2 mM L-glutamine (CHO-WT) and incubated overnight at 37° C. After blocking of non-specific binding with 0.5% HSA in F12 medium, 1 nM of 99mTc-VHH domain in 0.5 ml F12 medium+0.5% HSA was added to the wells in triplicate and the plates were incubated for 1 hour at 37° C. Unbound 99mTc-VHH domain was removed by washing the cells three times with ice-cold PBS+0.5% HSA. The cells were solubilized with 1 M NaOH and 99mTc- was quantitated in a gamma-well counter (Cobra II Inspector 5003, Canberra-Packard). The results are shown in
Binding to CX3CR1-positive CHO cells was significantly higher than to untransfected cells for all six 99mTc-labeled VHH domains (*p≦0.001) demonstrating that specific binding to CX3CR1 was preserved with the 99mTc-labeling of the VHH domains. While strong binding and a large window was observed with 5 of the 6 VHH domains, weaker binding was seen with CX3CR1BII315.
Experiments were carried out to examine the biodistribution of the labeled VHH domains in healthy (nondiseased) mice. Since the VHH domains identified did not cross react with mouse CX3CR1, a human CX3CR1 knock-in mouse line (hCX3CR1 KI) was generated at TaconicArtemis (Koeln, Germany) to enable testing of these molecules in mouse disease models. A strategy was employed that allowed the expression of the human chemokine receptor under the control of the corresponding mouse promoter while disrupting the expression of the endogenous mouse protein. Briefly, a targeting vector was constructed where the mouse CX3CR1 coding region in exon 2 was replaced with the complete human CX3CR1 open reading frame and flanked by selection markers and loxP sites. The targeting vector was introduced into mouse ES cells and clones that had successfully undergone homologous recombination were used to generate chimeric mice. These mice were bred to highly efficient Flp-deleter mice to achieve removal of the selection marker and germline transmission. C57BL/6 mice were utilized as controls to evaluate non-specific target independent binding.
17 week old female C57BL/6 (n=35) and hCXCR3 KI mice (n=35) were fed a normal chow diet. Each VHH domain was evaluated in six C57BL/6 and six hCX3CR1 KI mice, except 99mTc-CX3CR1BII315 (2×n=5). 100 μl of the 99mTc-VHH domain solution (53±10 MBq) was injected intravenously via the tail vein. Three hours post-injection, anesthetized animals were placed in prone position in an animal bed along with six 57Co landmarks and sequentially subjected to pinhole-SPECT and microCT. The pinhole-SPECT acquisitions were performed using a dual-headed gamma camera (e.cam180 Siemens Medical Solutions, Wheaton, Ill., USA) equipped with a triple 1.5 mm pinhole collimator. Sixty-four projections, 10 seconds each, were acquired over 360° of rotation into a 128×128 matrix with a zoom factor of 1. The microCT imaging was performed on a Skyscan 1178 (Skyscan, Kontich, Belgium) using the following acquisition parameters: 50 kV, 615 μA and 83 μm resolution. After reconstruction, both data sets were automatically fused on the basis of the six 57Co landmarks. Images were analyzed with the software Amide (http://amide.sourceforge.net) and Osirix (Pixmeo SARL, Bernex, Switzerland). The color scale of SPECT images was normalized to % IA/cm3 to allow direct visual comparison between the animals (
After the imaging, animals were euthanized by an overdose of sodium pentobarbital (CEVA, Libourne, France). All major organs and tissues were harvested, weighed and their radioactivity was quantitated in the gamma-well counter. Counts were corrected for background and decay, and expressed as percentage of injected activity per gram tissue (% IA/g). Statistical analysis was performed using both a parametric test (ANOVA) and a non-parametric test (Mann-Whitney U) (SPSS Statistics 20). P-values<0.05 were considered significant.
The biodistribution data of the 99mTc-VHH domains in C57BL/6 and hCX3CR1 KI mice are summarized in Table 10.
In C57BL/6 mice all VHH domains showed the typical biodistribution of molecules with a molecular weight lower than 60 kDa: fast blood clearance with high renal excretion (Table 10,
Although significant, these differences were minor for the following organs: heart, lungs, liver, pancreas, kidneys, brain, aorta and muscles. The difference was more remarkable for spleen, stomach, intestines, bone and lymph nodes, presumably reflecting binding to tissue-resident immune cells in these organs such as macrophages and dendritic cells. The highest specific targeting was observed for the monovalent 99mTc-CX3CR1BII66B02 and bivalent 99mTc-CX3CR1BII318.
In Vivo Competition Experiments in Mice with Atherosclerotic Disease
To show specific targeting of the anti-CX3CR1 VHH domains to atherosclerotic plaques, the hCX3CR1 KI mice were crossed to Apo E−/− mice (The Jackson Laboratory, Bar Harbor, Me., USA) to generate hCX3CR1 KI Apo E−/− mice. The Apo E−/− mouse model provides a robust method to elicit extensive atherosclerotic plaque formation that is grossly similar to the human disease with respect to the site-specific localization of plaque formation, histological composition, and the known risk factors (cholesterol, inflammation, hypertension, etc).
4 week old female ApoE−/− and hCX3CR1 KI ApoE−/− mice were fed a high fat/high cholesterol diet containing 1.5% cholesterol for 16 weeks. Each 99mTc-VHH domain was evaluated in six ApoE−/− and six hCX3CR1KI ApoE−/− mice (The monovalent 99mTc-VHH domain CX3CR1BII315 was excluded, based on the loss of functionality after 99mTc-labeling observed by in vitro cell binding and biodistribution studies in non-diseased mice). A control 99mTc-VHH domain cAbBCII10 generated against a bacterial enzyme (Conrath, 2001; Antimicrob. Agents Chemother. 45: 2807) was evaluated in six hCX3CR1 KI ApoE−/− mice. 100 μl of a 99mTc-VHH domain solution (61±16 MBq) was injected intravenously via the tail vein. A group of mice were also co-injected with a 100-fold excess of the equivalent unlabeled VHH molecule (referred to as “blocking”). Three hours post-injection, anesthetized animals were placed in prone position in an animal bed along with six 57Co landmarks and sequentially subjected to pinhole-SPECT and microCT as described in Example 4. After the imaging, animals were euthanized by an overdose of sodium pentobarbital, and tissue and organs were harvested for further ex vivo analysis.
Representative images of the biodistribution of 99mTc-CX3CR1BII66B02 and 99mTc-CX3CR1BII318 in ApoE−/− and hCX3CR1KI ApoE−/− mice with and without blocking are shown in
The ex vivo biodistribution of each VHH domain was evaluated in ApoE−/− and hCX3CR1 KI ApoE−/− mice, as well as in hCX3CR1 KI ApoE−/− mice in the presence of an excess of unlabeled VHH domain. Uptake of hCX3CR1-specific VHH domains related with the SPECT/CT images presented above and was higher in the hCX3CR1KI ApoE−/− mice than in ApoE−/− mice consistent with target expression of CX3CR1 (Table 11). Uptake of VHH domain was blocked by competition with the unlabeled VHH domain. Since the control 99mTc-VHH domain cAbBcII10 does not recognize any target in mammalian cells, clearance through the kidneys was observed as with all VHH domains, but 99mTc-cAbBCII10 was not taken up by any other organ. The results largely correspond to the biodistribution data obtained in hCX3CR1 KI mice, demonstrating the lack of large differences in biodistribution of anti-hCX3CR1-targeting VHH domains between healthy mice and mice with atherosclerotic disease.
Lesion-to-heart ratios were calculated as a read-out to quantitate atherosclerotic lesions in coronary arteries close to heart muscle. It is clear from the dissection analyses and autoradiography that the major sites of plaque formation in the atherosclerotic mice were the aortic root and arch, and that these sites are associated with the highest accumulation of 99mTc-CX3CR1B1166B02. As discussed above and shown in
As compared to the targeting group (99mTc-CX3CR1B1166B02 in hCX3CR1KI ApoE−/− mice), the arch signals were 6- to 8-fold lower when tracer binding was blocked by injection of unlabeled 66B02 and 2- to 3-fold lower in the absence of molecular target (ApoE−/− mice). The arch signals of control VHH domain 99mTc-cAbBcII10 in hCX3CR1KI ApoE−/− mice were about 4-fold lower than the targeting group. Using CT images, equally-sized regions of interest (ROIs) were drawn over the aortic arch/root and the heart left ventricle (as a measure of blood pool activity). SPECT signals in these ROIs were calculated and expressed as percentage of injected activity per volume (% IA/cm3). These values were used to calculate arch-to-blood ratios. Statistical analysis was performed using a parametric test (ANOVA). P-values<0.05 were considered significant.
Arch-to-blood ratios were calculated by drawing a ROI in the heart left ventricle (LV), as a measurement of blood pool (Table 12). The arch-to-blood ratios in atherosclerotic mice were 2-to 3-fold lower when uptake of 99mTc-CX3CR1BII66B02 was blocked by injection of excess unlabeled 66B02 or in the absence of hCX3CR1 expression. A similar significant difference was observed for 99mTc-cAbBcII10 or for 99mTc-CX3CR1BII66B02 in mice without atherosclerotic disease. The specific uptake of 99mTc-CX3CR1BII66B02 and 99mTc-CX3CR1BII318 in the atherosclerotic aortic arch and root was clearly visible on SPECT/CT images and demonstrates the utility of CX3CR1 VHH domains as radiotracers for noninvasive imaging of atherosclerotic lesions in live animals.
The aorta from each of the mice in the study was carefully excised, cleaned free from adherent tissues and cut in 10 segments. Upon visual examination, each segment was given a score between 0 and 3 (0: 0%, 1: 1-50%, 2: 51-75%, 3: 76-100% of area covered with atherosclerotic lesions). All segments, along with other organs and tissues, were collected, weighed and their radioactivity quantitated. Counts were corrected for background and decay and expressed as percentage of injected activity per gram tissue (% IA/g). Statistical analysis was performed using a parametric test (ANOVA). P-values<0.05 were considered significant. For each animal, autoradiographic images were obtained after overnight exposure of all aorta segments to a dedicated phosphorscreen (Typhoon FLA 7000, GE Healthcare). Images were analysed with ImageQuant (GE Healthcare Biosciences, Pittsburgh, Pa.).
Based on visual inspection of the whole aorta, atherosclerotic lesions were seen to be most prevalent at the root and in the arch of the aorta. These segments generally had a lesion score of 3 or 2. In the abdominal section of the aorta, segments with small individual lesions were alternated with segments without lesions. These segments were scored as 1 and 0, respectively. The scores of the thoracic segments varied between 0 and 2. In all mice and for all conditions, the uptake of a 99mTc-VHH domain in a segment was significantly increased for hCX3CR1-specific 99mTc-VHH domains in hCX3CR1KI ApoE−/− mice (Table 13).
The highest values in segments with score 3 were obtained for the monovalent VHH domain 99mTc-CX3CR1BII66B02 and the bivalent VHH domain 99mTc-CX3CR1BII318, with average values of 2.68 and 2.37% IA/g respectively (Table 14). Addition of excess unlabeled VHH domains reduced the uptake of the anti-hCX3CR1 99mTc-VHH domains to the level of uptake in the control conditions (anti-hCX3CR1 99mTc-VHH domain in ApoE−/− mice or 99mTc-cAbBCII10 in hCX3CR1 KI ApoE−/− mice,
Besides evaluating tracer uptake in individual aortic segments by quantification of lesion weight and radioactive counts, these segments were also exposed to radiosensitive phosphorscreens in order to visualize the spatial distribution of radioactive signals. Elevated uptake of 99mTc-CX3CR1B1166B02 was observed in segments with increasing lesion burden in hCX3CR1KI ApoE−/− mice as compared to segments from ApoE−/− mice, or with 99mTc-cAbBcII10 in hCX3CR1 KI ApoE−/− mice. 99mTc-CX3CR1B1166B02 was shown to bind focally to small plaques in segments with a low lesion score (white arrows in
| Number | Date | Country | |
|---|---|---|---|
| 61868144 | Aug 2013 | US |
