Patent Application
20110035819
This invention is related to the area of Cystic Fibrosis. In particular, it relates to the area of gene therapy vectors for Cystic Fibrosis and other diseases.
Cystic fibrosis is caused by various mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, a membrane-bound chloride channel. Mutations in CF results in thick, inspisated pulmonary mucus, which results in recurrent lung infections, subsequent structural lung damage, and eventual respiratory failure. Patients with CF also develop other manifestations due to blockage of ducts by thick secretions, including insufficient release of pancreatic digestive enzymes and insulin, resulting in malnutrition and diabetes. Most CF patients require ingestion of pancreatic enzyme supplements. The average survival of CF patients is in the mid 30s.
To address the pulmonary manifestations of CF, it is generally believed that one needs to obtain expression of hCFTR (human CFTR) in the proximal lung epithelium, and possibly in the proximal ductal epithelium, as well. An expression level of an exogenous CFTR gene at 10% of the endogenous CFTR mRNA level may be therapeutic. See Davis, P. B., Centennial Review, Am. J. Respir. Crit. Care Med., 173: 475-482, 2006. This assessment is based on the level of CFTR mRNA in various sub-populations of CF carriers who have low levels of CFTR mRNA but are asymptomatic. Other supportive data for this estimate include measurements in tissue culture models and evidence of electrical correction of the Cl− channel defect if normal CFTR mRNA is on the order of 6-10%.
In most patients, the CF airways are covered with thick mucus, which may impede effective gene transfer to the underlying epithelial cells of the lung. Thus prospective gene transfer systems that address such physiologic barriers may be important for effective CF gene therapy. Previous studies have demonstrated that nanoparticle vectors effectively transfect respiratory epithelial cells in the nares of CF subjects [Konstan M W, Davis P B, Wagener J S, Hilliard K A, Stern R C, Milgram L J, Kowalczyk T H, Hyatt S L, Fink T L, Gedeon C R, Oette S M, Payne J M, Muhammad O, Ziady A G, Moen R C, Cooper M J. “Compacted DNA nanoparticles administered to the nasal mucosa of cystic fibrosis subjects are safe and demonstrate partial to complete cystic fibrosis transmembrane regulator reconstitution.” Hum Gene Ther. 2004 December; 15 (12):1255-69.]
Initial phase I intranasal clinical trials have been concluded and provided encouraging results: no adverse events were attributed to the DNA nanoparticles and 8/12 subjects demonstrated improved CFTR chloride channel function as assessed by nasal potential difference measurements. In addition, 4/12 subjects had nasal potential difference (NPD) values within the normal range [Konstan et al, supra].
There is a continuing need in the art to improve existing vectors so that meaningful levels of CFTR expression can be achieved to provide clinically measurable improvements.
According to one embodiment of the invention a composition is provided that comprises a nucleic acid molecule comprising a sequence as shown in SEQ ID NO: 1 or 2 (DNA) or SEQ ID NO: 3 or 4 (RNA).
According to another embodiment a method is provided for producing hCFTR-encoding mRNA and hCFTR protein. A composition comprising a nucleic acid molecule comprising a sequence as shown in SEQ ID NO: 1 or 2 (DNA) or SEQ ID NO: 3 or 4 (RNA) is introduced into mammalian cells. The sequence can be operably linked to expression control sequences. The cells express hCFTR-encoding mRNA and hCFTR protein as a result of the introduction.
According to yet another embodiment of the invention a method is provided for producing hCFTR-encoding mRNA and hCFTR protein. A composition comprising a nucleic acid molecule comprising a sequence as shown in SEQ ID NO: 1 or 2 (DNA) or SEQ ID NO: 3 or 4 (RNA) is introduced into human lung cells in a human Cystic Fibrosis patient via an aerosol. The sequence can be operably linked to expression control sequences. The nucleic acid molecule is compacted in particles with a polycation; the particles are unimolecular with respect to nucleic acid. As a result of the introduction, the cells express hCFTR-encoding mRNA and hCFTR protein.
An additional embodiment of the invention provides a method to increase the expression of an mRNA or protein from a cDNA molecule. The cDNA molecule is inspected to ascertain the presence of a premature transcription termination signal. The premature transcription termination signal of the cDNA molecule is eliminated without altering its encoded amino acid sequence, thereby forming a cDNA molecule with an altered sequence. The cDNA molecule with the altered sequence is introduced into a cell where it is expressed.
These and other embodiments which will be apparent to those of skill in the art upon reading the specification provide the art with improved methods and reagents for gene therapy and protein expression.
The present inventors have developed a synthetic CFTR DNA segment (‘CO-CFTR’; SEQ ID NO: 1 and 2) that produces improves mRNA and protein levels in the mouse lung (mRNA) and cells (protein) compared to “natural” hCFTR cDNA (i.e., cDNA made from native mRNA; SEQ ID NO: 5). This synthetic CFTR segment is codon optimized (hence the ‘CO’ label), CpG depleted, removes endogenous 5′ and 3′ UTRs, and has an optimized Kozak sequence. One version has one C-terminal CpG island (SEQ ID NO: 2), and another version has no CpG islands (SEQ ID NO: 1). Quantitative RT-PCR data demonstrate 35-fold increase in CFTR mRNA compared to “natural” cDNA in the mouse lung. Immunoprecipitation Western blots show 9-fold improvement in CFTR protein compared to “natural” cDNA. Human CFTR ELISA (enzyme-linked immunoadsorbent assay) in transfected HEK293 (human kidney) cells show an ˜19-fold increase in hCFTR protein compared to an analogous plasmid encoding “natural” hCFTR cDNA.
Because of the many differences between natural and synthetic hCFTR cDNA it is not known whether one or more of the changes contribute to or are responsible for the improved expression. Although applicants do not intend to be bound by any theory or mechanism, it is possible that the improvement is due, in part, to the obliteration of a premature transcriptional terminator in the “natural” cDNA. This terminator is not present in genomic DNA, hence it is not relevant in whole animals that are not transgenic. We have identified such a transcriptional terminator in the “natural” cDNA which is not present in the codon-optimized hCFTR DNA.
Nucleic acid compositions according to the present invention may be solid (e.g., lyophilized or precipitated) or liquid or aerosolized. They may be RNA (e.g., SEQ ID NO: 3 and 4) or DNA (SEQ ID NO: 1 and 2). Such compositions may be linear nucleic acid fragments or included in plasmid or viral vectors, whether linear or circular. Many viral vectors are known in the art and they can be selected by the skilled artisan for their known properties. Exemplary vectors are employed in the working examples below, but others can be used as well. Nonviral vectors for cystic fibrosis therapy are discussed in Alton, E.W.F.W., Proceedings of the American Thoracic Society, 1, 296-301, 2004.
Expression control sequences are known in the art and will be typically employed in the invention. These may be used to initiate, promote, or terminate transcription, for example, or to enhance translation. These are operably linked to the coding sequence, i.e., they are within the requisite proximity on a nucleic acid molecule to affect the function. Proper placement for these elements is well known in the art.
Mammalian cells are the typical targets of the human nucleic acid molecules of the invention. These can be in culture, in tissues, in perfused organs, in whole animal models, or in patients or control individuals. In the case of Cystic Fibrosis, typical target cells are lung cells or pancreatic cells. Epithelial and ductal cells of the lung and pancreatic may be particularly targeted. Targeting can be effected by local delivery or installation of the nucleic acids. Other delivery means include intravenous and endoscopic delivery. Other targeted cells may include those of the gastrointestinal tract, of the endocrine system, and any other affected organ or organ system. Delivery can also be performed in utero to a fetus.
The nucleic acid vectors may be delivered by any means known in the art. One way to package and deliver nucleic acids is via compacted nanoparticles. These are typically formed with a polycation, such as polylysine. Nanoparticles can be formed which have a single molecule of nucleic acid.
The results of the experiments below indicate that unsuspected premature termination of transcription from a terminator formed by making a cDNA can hamper expression. Noting such fortuitous terminators and removing them can increase expression. This may be a generally useful method for increasing expression in the class of cDNA molecules that contain such a fortuitous terminator. To ascertain if a terminator is present, the sequence of the cDNA molecule in question is inspected. This may be by eye/hand/human brain, or by machine/computer. The features of transcription termination signals are well known in the art. Following ‘AAUAAA’ there typically is a uridine rich element (URE). The cleavage site typically occurs 11 to 24 bases downstream of ‘AAUAAA’, and the URE sequence occurs 10 to 30 bp after the cleavage site. Eliminating the signal involves changing the sequence sufficiently so that it no longer functions as a transcription termination signal. The “eliminated” cDNA is then introduced into cells so that it can drive expression of mRNA and/or protein.
The above disclosure generally describes the present invention. All references disclosed herein are expressly incorporated by reference. A more complete understanding can be obtained by reference to the following specific examples which are provided herein for purposes of illustration only, and are not intended to limit the scope of the invention.
Since codon-optimization of the hCFTR sequence might improve translation efficiency in transfected lung cells, the following hCFTR DNA was synthesized. Presented below is an analysis of the natural hCFTR cDNA and a codon-optimized hCFTR sequence. The latter also was CpG-island depleted except for a single CpG island in the 3-prime region. In other versions, this single CpG island was removed (no CpG islands)
Note that the preferred codon-usage has increased from 33.3% to 83.9%. Note that the pattern of preferred codon usage in humans and mice is very similar (identical in 18 amino acids, with very slight second codon preference for proline and arginine).
We first evaluated hCFTR mRNA levels in mice dosed with our prior CMVCFTR clinical trial plasmid, with lung harvests at days 2 and 14 (
It is appreciated that multiple factors may be involved in hCFTR mRNA expression levels, including CpG motifs in CFTR cDNA and their potential influence on expression extinction; promoter transcriptional efficiency; appropriate post-transcriptional CFTR mRNA splicing and its linkage to cytoplasmic transport, post-transcriptional CFTR mRNA stability as linked to secondary structure (which likely would be altered in the process of codon-optimization); and post-transcriptional CFTR mRNA stability as controlled by interactive domains in the 3′ UTR (as recently described by Baudouin-Legros et. al (1)). Regarding protein expression levels, both codon-optimization and presence of a full Kozak consensus sequence are likely important. In an effort to modulate and hopefully improve the influence of some of these factors, we designed a codon-optimized CFTR (CO-CFTR) DNA that has a single CpG in the 3′ terminus and completely lacks the natural 5′ and 3′ UTRs. Table 3 summarizes important properties of pCMVCFTR, pUCF, and pUCF2 (a derivative of pUCF containing CO-CFTR). CO-CFTR has a different mRNA sequence than natural CFTR and this may influence mRNA stability relative to its secondary structure. Of note, both pCMVCFTR and pUCF contain identical CFTR sequences, including 2 potential alternative splice acceptor sites in the first 300 bp of coding sequences, whereas there are no alternative splice acceptor sites in CO-CFTR within this region—a finding that might be important in optimizing appropriate splicing. Also note that there are only minor differences in the size of 5′ and 3′ UTRs in these constructs and the natural CFTR 3′ UTR in our vectors does not include the poly U or G regulatory regions described by Baudouin-Legros et al.—so differences in post-transcriptional stability mediated by the 3′UTR appear moot. Lastly, the natural CFTR cDNA has a partial Kozak sequence (agACCatg) whereas a full Kozak sequence (CCACCatg) was included in the design of CO-CFTR.
pUCF2 was dosed intranasally (IN) into Balb/C mice and lungs were harvested at days 2 and 14 for evaluation of CFTR mRNA. As shown in
It is appreciated that CFTR protein production mediated by pUCF and pUCF2 likely involve differences in both transcriptional and translational efficiency. To directly compare these constructs, CFTR-negative HEK293 cells were transfected with lipofectamine and either pUCF or pUCF2. To minimize differences in transfection efficiency between plates, each liposome/DNA transfection mixture contained an equal total amount of plasmid DNA but differing amounts of test plasmid, an equal amount of luciferase plasmid (10 ng, to assess transfection efficiency), and appropriate amounts of ‘filler’ plasmid (Bluescript). Two days after transfection, lysates were prepared, luciferase activity assessed, and an IP/Western for CFTR performed (
We have established an ELISA assay for hCFTR that incorporates anti-hCFTR Mab 1660 (R&D Systems) as capture and rabbit anti-hCFTR antibody (Santa Cruz, #10747) for detection. Mab 1660 detects a hCFTR epitope between codons 590-830 and rabbit polyclonal #10747 detects the N-terminus, amino acids 1-182, of human, rat, and mouse CFTR. The assay was optimized using lysates from HEK293 cells transfected with pUCF2 and a typical standard curve is shown in
qRT-PCR data for hCFTR indicated that CO-CFTR (codon-optimized, CpG depleted except for one 3′ site, natural UTRs depleted, optimized Kozak sequence) generated 35-fold higher levels of hCFTR/mCFTR mRNA in murine lung at day 2 compared to natural CFTR cDNA in the identical plasmid (pUCF2 vs. pUCF, see
Removal of the 3′ CpG in CO-CFTR did not improve persistence. The 5-fold improvement of hCFTR expression on day 2 for pUCF22 compared to pUCF2 can be explained by the difference in route of administration. As we have previously published, a 3-fold improvement in lung expression is expected comparing intratracheal and intranasal administration (Mol Therapy 8:936-947, 2003). In an intratracheal dose response study, there was little difference between 100 and 300 μg DNA doses (Mol Therapy 8:936-947, 2003).
As summarized in Table 4, it is apparent that the identical plasmid design encoding luciferase (e.g. pUL, pUL8) produces high level and maintained activity at day 14 whereas CFTR mRNA expression is extinguished, which could be due to:
The mechanism(s) accounting for these results is currently undefined. It is possible that autoregulatory pathways exist that control CFTR mRNA expression. Although each CFTR plasmid had significantly reduced mRNA expression by day 14, both plasmids encoding codon-optimized and CpG-depleted CFTR had hCFTR/mCFTR levels about 35-fold higher than natural CFTR cDNA, suggesting that removal of CpGs, and/or the altered DNA and/or mRNA sequence, influenced the extinction process.
One possible mechanism that may influence CFTR mRNA expression is intron-mediated 5′ splicing. A detailed analysis of alternative splice acceptor sites in natural and CO-CFTR shows several 5′ sites present in natural but not CO-CFTR that result in out-of-frame transcripts. To assess intron splicing, hCFTR cDNA was evaluated by qRT-PCR analysis using primer sets bridging the desired donor-acceptor sequence as well as a 3′ primer set used previously in our hCFTR mRNA analysis (
This transcript splicing analysis demonstrates some interesting and unexpected findings. Table 5 summarizes key results from this qRT-PCR analysis and the full data set are included in the Table 7 to permit detailed review of findings in this summary table.
The data for CO-CFTR (pUCF2) indicate that ˜23% of transcripts are appropriately spliced, whereas findings for natural CFTR expressed by either pUCF or pCMVCFTR transfectants generate non-logical results (bolded in table), with the 5′ signal (spliced) being more abundant than the 3′ signal (total). This can occur only if the 3′ primers and probes are NOT detecting the total population of transcripts. This phenomenon could occur if there is an alternative, ‘stealth’ pA site within the natural hCFTR cDNA. Interestingly, a sequence analysis of natural hCFTR cDNA for the ‘AATAAA’ transcription termination consensus sequence did turn up 1 match, at position 1100 of the open reading frame. Because of the codon-optimization of hCFTR in pUCF2, there are NO ‘AATAAA’ sequences in CO-CFTR.
The data are consistent with the following working hypothesis (
As noted in
Based on our data, it appears that a significant percentage of hCFTR transcripts generated by pUCF and pCMVCFTR are truncated, with quantification pending the ‘Z’ probe analysis. This finding may account, in part, for multiple findings, including: i) the significant increase in the 3′-based qRT-PCR hCFTR signal for pUCF2 compared to pUCF (35-fold increase at day 2 in mouse lung, 16-39-fold increase in HEK293 cells); and most importantly, ii) the difficulty in measuring hCFTR mRNA in various CF clinical trials, which often have employed 3′ primer sets.
It is important to note that a DNA sequence analysis suggests that this putative transcriptional terminator is active in natural hCFTR cDNA but NOT in genomic DNA (
If our pending ‘Z’ and ‘Q’ probe studies generate data as predicted, then there are several important implications of this splice analysis:
HEK293 cells were transfected with either 0.75 or 3 μg of each plasmid (along with ‘blank’ irrelevant plasmid so that the total DNA/lipofectamine ratios were the same) and harvested 2 days later. qRT-PCR was performed using TaqMan chemistry and FAM-TAMRA labeled probes. Each reaction was performed as quadruplicate replica. In some cases, outrangers were removed and analysis was performed on three point average values. The Cts for 5′ hCFTR and 3′ hCFTR were estimated using a 0.4 threshold value. The Cts for hGAPDH were estimated using a 0.2 threshold value. Vector contamination was insignificant. R.E., relative expression.
HEK293 cells were transfected with either 0.75 or 3 μg of either pCMVCFTR or pUCF. Cells were harvested 2 days later for RNA preparation and qRT-PCR analysis using validated primer sets J and Z6. Shown in Table 8 is a summary of these findings. Approximately 27-38% of these vector-derived natural hCFTR transcripts appear to demonstrate premature truncation. Primer-probe validation experiments show that qPCR Δ Ct accuracy is in the +/−7% range. So, the observed differences in Z6 and J amplification cannot be explained by different amplification efficiencies. Otherwise, note that HEK293 cells do not transcribe detectable endogenous hCFTR mRNA (saline controls were negative), so all signals are derived from the vector. These results are consistent with the known ability of natural hCFTR cDNA to produce functional hCFTR protein, but underscore the potential inefficiency of this cDNA. Of note, the CO-CFTR and the CO*-CFTR constructs do not have this transcriptional termination sequence.
The next step was to determine if natural hCFTR cDNA prematurely truncates in transfected mouse lungs (Table 9). To conduct this analysis, four lung samples with the highest level of hCFTR mRNA expression (based on 3′ J primers) were selected; all of these samples were from the day 2 pCMVCFTR group, which had a ˜30-fold higher level of hCFTR/mCFTR expression than pUCF transfectants. Based on mGAPDH primers, the M5 sample had ˜2-4-fold less cDNA than the other samples, which otherwise were comparable. All samples demonstrated evidence of premature truncation, ranging from 14% to 62%. The reason for the lower value for sample M5 is unclear, although its lower mGAPDH signal raises a question about sample integrity (versus smaller sample). In summary, studies from HEK293 cells and mouse lungs dosed with pCMVCFTR both demonstrate evidence of premature transcriptional truncation for natural hCFTR cDNA. Similar data in both cells and animals strongly support this conclusion.
A truncation analysis of hCFTR mRNA transcribed from the pCMVCFTR vector (natural hCFTR cDNA) in both HEK293 cells and the mouse lung demonstrates evidence of premature truncation. The percentage of transcripts that are truncated range from 27-38% in HEK293 cells and 14-62% in the mouse lung.
Premature transcriptional termination may only partially account for the 35-fold difference in hCFTR/mCFTR mRNA expression in the mouse lung on day 2 when comparing pUCF2 (CO*-hCFTR) to pUCF (natural hCFTR cDNA). Other factors may be important, including potential differences in nucleosome formation within the plasmid, CpG depletion of the transgene, and potential improvement in mRNA half-life due to changes in the primary ribonucleotide sequence. The 9- to 19-fold improvement in hCFTR protein in HEK293 cells transfected with pUCF2 compared to pUCF may be accounted for by improved hCFTR mRNA abundance, although codon-optimization also may be important.
The disclosure of each reference cited is expressly incorporated herein.
This application claims the benefit of provisional application Ser. No. 60/851,055 filed Oct. 12, 2006, Ser. No. 60/885,827 filed Jan. 19, 2007, and Ser. No. 60/907,852 filed Apr. 19, 2007. The disclosures of each are expressly incorporated herein.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US07/21862 | 10/12/2007 | WO | 00 | 8/18/2009 |
| Number | Date | Country | |
|---|---|---|---|
| 60851055 | Oct 2006 | US | |
| 60885827 | Jan 2007 | US | |
| 60907852 | Apr 2007 | US |
