Silence Therapeutics’ press release following the initiation of the Glover patent opposition hearings has to be counted as yet another example of the company’s series of misleading and factually flawed public statements.
Claiming that “the Glover patents was arguably Alnylam’s broadest patent” may be true in the sense that the patent claimed a lot, essentially double-stranded RNAs for gene silencing in mammals, but it is far from true, as Silence would want you to believe, that it represented Alnylam’s most important (RNAi trigger) patent. As Michael King from Rodman & Renshaw rightly noted in a report on the Xconomy blog, these are Tuschl II, followed by Crooke and Kreutzer-Limmer. Actually, when you would use the search function on my blog, yesterday may have been the first mention of the Glover patent. That’s how important I have considered this patent to be.
If I had been part in the early planning stages of Alnylam, a company that had been built around Tuschl II, Glover would have been a worry due to its early date and broad claims. But it is clear that Glover did not solve the non-specific interferon response issue that had critically impeded the broad application of RNAi in man, and claiming such based on studies in exceptional model systems such as oocytes and pre-implantation embryos may be overly ambitious. Still, a good patent to have control over and a weakening of Glover after the appeals have been heard, would only strengthen Tuschl II.
Another salient example of Silence’s overly zealous PR machine is the Quark issue. I’ve always found it amusing to come across Silence Therapeutics’ lengthy press releases that typically follow any pipeline and business development progress by their PR-wise much more conservative partner Quark Biotech, making it appear as if these achievements were almost entirely to the credit of Silence Therapeutics. Not surprisingly, according to a report in February this year by David P. Hamilton on the VentureBeat Blog, this appears to be a mis-representation and Quark is not very happy with this situation. I would not be surprised if Alnylam's COO Barry Greene, on his recent visit to Israel, had not visited Quark's operations there to see if the relationship between the two companies could be strengthened.
And finally, whether it’s liposomes or lipoplexes, hey, we are also working with some kind of a fat globule and if Merck says they are safe then we want to be part of it. And who really cares and understands the difference anyway?
I understand that PR is a very important element of the business strategy particularly of a developmental-stage biotech, but it has to be handled with care and, in a financial world where free and fair reporting is lacking, if careless may cost you the credibility in the eyes of one of your most important constituencies- your investor.
Friday, July 11, 2008
It’s Getting Lonely as Silence and Merck Attempt to Climb Alnylam’s Many RNAi Trigger Patent Walls
Today, Alnylam announced the completion of initial oral opposition proceedings concerning the Glover patent EP1230375 for the use of double-stranded RNA to inhibit gene expression in mammalian cells, one of the many RNAi trigger patents and patent applications Alnylam either owns or has (often exlusively) licensed access to and which are based on pioneering RNAi research in mammalian cells thus shoring up the company’s gate-keeper position in the therapeutic application of RNAi.
Such opposition proceedings are common in Europe, particularly for patents deemed valuable enough to have the potential to restrict the freedom-to-operate of other parties. One familiar example that has been the subject to similar proceedings in Europe is Kreutzer-Limmer, yet another of Alnylam’s RNAi trigger patents backing up its crown jewel Tuschl II which is currently successfully sailing through the global patent systems.
Most of you reading this blog will be well aware that while Fire and Mello’s seminal discovery shed light on double-stranded RNAs as the trigger of RNAi, subsequently found to be true throughout almost all eukaryotic life, its application to human cells was not immediately apparent as the long double-stranded RNAs used are well known to induce non-specific innate immune responses in most mammalian cell types, therefore making long double-stranded RNAs not useful for the vast majority of conceivable RNAi Therapeutics. It was therefore the breakthrough discovery by Tuschl and colleagues that opened up RNAi for widely applicable human use by showing that structurally defined short double-stranded RNAs, siRNAs, derived from the processing of long double-stranded RNAs can induce gene-specific gene silencing in essentially all mammalian cells without the induction of the non-specific responses.
One exception to the non-specific response to long double-stranded RNAs are oocytes and pre-implantation embryos, and indeed in the wake of Fire-Mello work underlying the Glover patent and published by Florence Wianny and Magdalena Zernicka-Goetz from Cambridge University (UK) in 2000 demonstrated that long double-stranded RNAs could be used for specific gene silencing in these cell types. While a highly exciting finding for reproductive biology, including potential uses for RNAi-enhanced ES cell therapeutics, it is clear that its impact for the wide development of RNAi Therapeutics is far more limited than Tuschl II. It is probably one of the patents that Alnylam would want to control to make sure that it was not construed to precede Tuschl II and forms part of a well thought-through patent strategy, but that it does not critically rely upon. Of course, because Glover, similar to Kreutzer-Limmer, also claims long double-stranded RNAs and would therefore also impinge on Dicer-substrates etc., it is particularly susceptible to attack by companies whose sole existence depends on having varied the size of the double-stranded RNA or having engineered a “proprietary” modification or pattern thereof into double-stranded RNAs.
From the title you might think that I am a blind Alnylam supporter (and, yes, I do own Alnylam shares, but, no, I am not paid by the company to write this), but note that I refer to RNAi trigger IP, that is the molecules themselves that induce RNAi silencing in mammalian cells by synthetic double-stranded RNAs. This does not mean that there is enough potential for big and small alike to create valuable enabling IP around these siRNAs (delivery, safety, and gene target-specific), also to gain some leverage with regards to Alnylam. It is interesting to speculate that the subject of another announcement today, namely the creation of Boston-based “Enlight Biosciences”, a technology incubator jointly sponsored by Pfizer, Merck, and Eli Lilly, of which one of the stated goals is the development of RNAi delivery methods all the while trying “…to find the next RNAi,” according to the Xconomist blog. A tall order, particularly the latter.
In the ideal world of free market capitalism, resources would flow to where problems need to be solved, in the case of RNAi delivery and safety, not into the coffers of lawyers- they get their share anyway in each and every deal sealed or not sealed even without patent litigation. It therefore certainly makes sense that rather than engaging in costly and futile battles with a strong company, more and more large biotech and pharma companies have opted to join a strong Alnylam in its quest to develop RNAi Therapeutics.
After Novartis, ISIS, Janssen/Johnson&Johnson, and Quark have withdrawn their opposition to Kreutzer-Limmer and Glover, it is now essentially Sirna Therapeutics/Merck and Silence Therapeutics with some of their partners that remain the only opposing parties. Meanwhile Alnylam, confident of their freedom-to-operate and overall strong IP position, continues to watch the early legal wranglings in the field, while focusing on the real issues at hand. As Nucleonics and Benitec would tell you, it’s probably wiser to handle patent violations by exacting appropriate royalties once products near the market, not now. Shares in Silence Therapeutics closed at 23.75p today on the London Stock Exchange, down almost another 10% and off more than 80% its high of last year.
My strong opinion is founded on having looked at the totality of the high quality science underlying Alnylam’s fundamental patent estate, and I would consider it a travesty of the patent system if as a result of a gap in the understanding of the science of RNAi by judges or patent attorneys, the commercial value of the IP would be eroded, with serious consequences for the therapeutic exploitation of RNAi. Such a weakening of the patent system would not only hurt Alnylam, but the entire drug industry which will only survive if truly deserving innovation can be protected. So far, this has not happened to RNAi, and I believe the outcome of these proceedings and future Alnylam deal flow will substantiate this.
Big Pharma would therefore do well not to attempt to kill the goose that lays the golden RNAi eggs for them.
Such opposition proceedings are common in Europe, particularly for patents deemed valuable enough to have the potential to restrict the freedom-to-operate of other parties. One familiar example that has been the subject to similar proceedings in Europe is Kreutzer-Limmer, yet another of Alnylam’s RNAi trigger patents backing up its crown jewel Tuschl II which is currently successfully sailing through the global patent systems.
Most of you reading this blog will be well aware that while Fire and Mello’s seminal discovery shed light on double-stranded RNAs as the trigger of RNAi, subsequently found to be true throughout almost all eukaryotic life, its application to human cells was not immediately apparent as the long double-stranded RNAs used are well known to induce non-specific innate immune responses in most mammalian cell types, therefore making long double-stranded RNAs not useful for the vast majority of conceivable RNAi Therapeutics. It was therefore the breakthrough discovery by Tuschl and colleagues that opened up RNAi for widely applicable human use by showing that structurally defined short double-stranded RNAs, siRNAs, derived from the processing of long double-stranded RNAs can induce gene-specific gene silencing in essentially all mammalian cells without the induction of the non-specific responses.
One exception to the non-specific response to long double-stranded RNAs are oocytes and pre-implantation embryos, and indeed in the wake of Fire-Mello work underlying the Glover patent and published by Florence Wianny and Magdalena Zernicka-Goetz from Cambridge University (UK) in 2000 demonstrated that long double-stranded RNAs could be used for specific gene silencing in these cell types. While a highly exciting finding for reproductive biology, including potential uses for RNAi-enhanced ES cell therapeutics, it is clear that its impact for the wide development of RNAi Therapeutics is far more limited than Tuschl II. It is probably one of the patents that Alnylam would want to control to make sure that it was not construed to precede Tuschl II and forms part of a well thought-through patent strategy, but that it does not critically rely upon. Of course, because Glover, similar to Kreutzer-Limmer, also claims long double-stranded RNAs and would therefore also impinge on Dicer-substrates etc., it is particularly susceptible to attack by companies whose sole existence depends on having varied the size of the double-stranded RNA or having engineered a “proprietary” modification or pattern thereof into double-stranded RNAs.
From the title you might think that I am a blind Alnylam supporter (and, yes, I do own Alnylam shares, but, no, I am not paid by the company to write this), but note that I refer to RNAi trigger IP, that is the molecules themselves that induce RNAi silencing in mammalian cells by synthetic double-stranded RNAs. This does not mean that there is enough potential for big and small alike to create valuable enabling IP around these siRNAs (delivery, safety, and gene target-specific), also to gain some leverage with regards to Alnylam. It is interesting to speculate that the subject of another announcement today, namely the creation of Boston-based “Enlight Biosciences”, a technology incubator jointly sponsored by Pfizer, Merck, and Eli Lilly, of which one of the stated goals is the development of RNAi delivery methods all the while trying “…to find the next RNAi,” according to the Xconomist blog. A tall order, particularly the latter.
In the ideal world of free market capitalism, resources would flow to where problems need to be solved, in the case of RNAi delivery and safety, not into the coffers of lawyers- they get their share anyway in each and every deal sealed or not sealed even without patent litigation. It therefore certainly makes sense that rather than engaging in costly and futile battles with a strong company, more and more large biotech and pharma companies have opted to join a strong Alnylam in its quest to develop RNAi Therapeutics.
After Novartis, ISIS, Janssen/Johnson&Johnson, and Quark have withdrawn their opposition to Kreutzer-Limmer and Glover, it is now essentially Sirna Therapeutics/Merck and Silence Therapeutics with some of their partners that remain the only opposing parties. Meanwhile Alnylam, confident of their freedom-to-operate and overall strong IP position, continues to watch the early legal wranglings in the field, while focusing on the real issues at hand. As Nucleonics and Benitec would tell you, it’s probably wiser to handle patent violations by exacting appropriate royalties once products near the market, not now. Shares in Silence Therapeutics closed at 23.75p today on the London Stock Exchange, down almost another 10% and off more than 80% its high of last year.
My strong opinion is founded on having looked at the totality of the high quality science underlying Alnylam’s fundamental patent estate, and I would consider it a travesty of the patent system if as a result of a gap in the understanding of the science of RNAi by judges or patent attorneys, the commercial value of the IP would be eroded, with serious consequences for the therapeutic exploitation of RNAi. Such a weakening of the patent system would not only hurt Alnylam, but the entire drug industry which will only survive if truly deserving innovation can be protected. So far, this has not happened to RNAi, and I believe the outcome of these proceedings and future Alnylam deal flow will substantiate this.
Big Pharma would therefore do well not to attempt to kill the goose that lays the golden RNAi eggs for them.
Sunday, July 6, 2008
The Potential for AAV-mediated RNAi Therapeutics
There is good reason to believe that synthetic siRNA-mediated RNAi Therapeutics should emerge as the most commonly used form of RNAi Therapeutics. Nevertheless, DNA-directed RNAi Therapeutics also has a number of potential uses where it should not only be competitive with, but even superior to synthetic RNAi. Unfortunately, the commercial development of DNA-directed RNAi Therapeutics has been somewhat hampered due to litigation and other management issues as well as funding problems that all things “gene therapies” face. In an effort to dispel some of the myths surrounding DNA-directed RNAi Therapeutics and since I’m somewhat familiar with particularly AAV-mediated DNA-directed RNAi, I would like to take the opportunity here to briefly highlight some of the potential applications for this particular technology.
DNA-directed RNAi can either by delivered by non-viral or viral means. For the most part, current systemic non-viral delivery technologies for DNA vectors that need to get into the nucleus for functional activity may not be adequate as a result of their inability to transfect sufficient cell numbers as well as support long-term expression. By contrast, viral vectors, particularly AAV and lentivirus, are capable of very efficiently and stably transducing many cell types. In fact, in vivo potencies are often greater than with most current synthetic RNAi methods with essentially knock-out phenotypes in the liver and eye observed for months and years using self-complementary AAV8 vectors in work reported by the laboratory I work in and collaborators to name just one example.
Before focusing more on AAV with which I am most familiar with (learning by osmosis), lentivirally delivered RNAi has much potential for disease of the CNS, largely for the same reasons as outlined for AAV below, and in combination with cell therapeutics. The latter would involve the ex vivo transduction of lentiviral RNAi constructs for example into stem cells similar to the ongoing phase I HIV-RNAi trial by the City of Hope and sponsored by Benitec, or also to enhance dendritic cell cancer vaccine strategies. Many of these applications take advantage the stable integration of lentiviral vectors into the host genome such that the vector and its expression/knock down will be maintained even in dividing tissues.
By contrast, due to its largely episomal nature, AAV gets rapidly during cell division thus limiting their applicability for cancer therapy or in other situations that involve cell division (regenerating liver, stem cell differentiation etc). Moreover, in certain settings humoral and T-cell mediated immune responses against AAV viral proteins present another challenge for achieving persistent gene silencing (the transduced cell may be recognized by the immune system and be eliminated) and where repeat-administration is desirable (due to neutralizing antibodies generated following the first administration).
For these reasons, AAV RNAi appears most promising for diseases of the eye and CNS as immuno-privileged sites. Although infusion pumps may address some of the challenges of allowing for long-term intracranial gene silencing by synthetic means, due to the ability to mediated sustained gene silencing for 6-12 months if not several years as suggested by canine AAV studies for hemophilia, the prospect of maybe having to subject a patient only once or very few times to an invasive operation makes AAV and lentivirus attractive alternatives for diseases such as Huntington’s Disease and other neurodegenerative disorders.
Not coincidentally, Targeted Genetics and the University of Iowa are currently pursuing an AAV RNAi program (pre-clinical stage) for Huntingon’s Disease that has shown promise. A critical factor for the success of this program should be the design of the shRNA expression cassette, and I personally would feel more comfortable with an H1 promoter-driven instead of a U6 promoter-driven construct that has been the front-runner so far. Another interesting application may be for the treatment of PML viral infection. Biogen Idec and Alnylam have been working on an siRNA-mediated approach, but due to serious nature of JC virus reactivation during PML, rapid onset of gene silencing by self-complementary AAV RNAi and the efficient vector delivery achieved for a number of neuronal cell types, AAV-mediated RNAi warrants consideration for this devastating disease.
Suitable non-CNS applications for AAV ddRNAi candidate may be instances where a single administration may already be therapeutic without the need for sustained gene silencing and repeat administration. HCV infection of the liver may be one such case as it is now possible to essentially transduce every liver cell, at least in mice, and effect long-term silencing after a single administration. AAV-medicated RNAi could therefore be an important component of combination therapies for patients that do not respond to current therapies and could also quite easily be tailored to the different HCV genotypes. Pfizer just recently acquired co-development rights for the pre-clinical stage AAV RNAi program for HCV from the Benitec spin-off Tacere.
AAV gene therapy is relatively new, but it is making rapid progress. Two independent phase I/II AAV gene therapy trial for Leber’s Congenital Amaurosis caused by RPE65 deficiency, a condition that leads to blindness later in life, demonstrated clear improvement in vision and treating children early on promises to even cure the disease. One of the studies was conducted by an academic group in London and was sponsored by Targeted Genetics, the other by a group from the University of Pennsylvania.
It is not clear whether an immune reaction that eliminated transduced liver cells in a hemophilia trial was specific for the AAV 2 serotype used, as most of us will have been exposed to this type of AAV during childhood and may therefore harbor some immune memory for it. A number of strategies have been proposed to minimize the risk of immune recognition in future trials, for example transient immune suppression or the use of alternative serotypes. The search for and development of alternative AAV serotypes is truly exploding and is rapidly yielding new AAV vectors with various tissue tropisms and immune properties.
The less AAV that needs to be administered the better also from an immune point of view. Very promising in that regard is the finding that the self-complementary AAVs which by-pass the rate-limiting second-strand synthesis step during the establishment of gene expression much more efficiently and functionally transduce target cells than conventional single-stranded AAV vectors. While this halves the vector capacity to less than 2kb, a size that is not very practical for expressing many protein-encoding genes, this does not matter at all in the context of small hairpin expression cassettes and appears to be just made for AAV RNAi. Actually, it was this property of self-complementary AAV vectors that was one of the main reasons for me to come to Stanford to conduct post-doctoral research. A patent for this possibly critically enabling technology has been issued to Targeted Genetics.
RNAi Therapeutics Portfolio Review: Increasing Position of Targeted Genetics
The technology is certainly there to be harnessed for therapy, but the development of AAV RNAi Therapeutics is not trivial and is a collaborative effort that requires careful gene target selection, safe and potent hairpin vectors, thoughtful clinical trial designs, and the manufacture of large amounts of high-quality AAV particles. Nevertheless, with the right team and some luck, it should possible to do.
It has both amazed and scared me to learn in a vivid report by RNAiNews that DNA-directed RNAi company Nucleonics whose lead program was a very long-shot (to put it mildly) RNAi program for HBV, was close to raising $25M in a series C round that would have included a venture capital arm from Johnson & Johnson. How that was even a remote possibility given the odds for that particular HBV RNAi program and the uncertain IP of that company is a mystery to me and makes the ~$13M market cap of Targeted Genetics’ look very cheap by comparison.
For this reason and given the promise of AAV-mediated RNAi Therapeutics in general, Targeted Genetics’ AAV gene therapy know-how and IP, including IP directly related to RNAi -especially the one for the double-stranded AAV and apparently another one for the expression of non-coding RNAs- I will add $680 worth of TGEN to the RNAi Therapeutics model portfolio and will pay for this with the sale of some stock in ISIS Pharmaceutcals (-$280), Oxford Biomedica (-$200), Silence Therapeutics (-$100) and Rosetta Genomics (-$100).
Remember, an investment in Targeted Genetics is highly speculative, its balance sheet somewhat ugly which is made worse by current market conditions which make it almost impossible to raise small biotech capital on reasonable terms. This investment thesis therefore is that Targeted Genetics will be able to win the race against the clock by being an attractive partner for other drug companies interested in RNAi Therapeutics with the resulting license fees and development milestones helping the company through the hard times. Maybe Genzyme with its considerable AAV gene therapy efforts and orphan disease management expertise or Biogen Idec with its long-standing ties to Targeted and interest in PML will bite.
Disclosure: The lab that I work in has an interest in AAV-mediated RNAi Therapeutics. The author has also been accumulating shares in Targeted Genetics between $0.58 and $0.72. The stock is not suitable for most due to adverse market conditions and the precarious balance sheet of the company. The thin trading volume of the stock causes volatilities in share price, usually to the downside, and there is a real chance that the stock will be de-listed from the Nasdaq exchange which will make this little company even more opaque to investors. On the other hand, conditions will improve at some point and in an environment where venture capital exits have become increasingly difficult and considering the attractive relative valuation and maturity of the company and technology, Targeted Genetics may represent an interesting, somewhat more liquid piece of RNAi Therapeutics real estate for investors otherwise specializing in private start-up companies.
DNA-directed RNAi can either by delivered by non-viral or viral means. For the most part, current systemic non-viral delivery technologies for DNA vectors that need to get into the nucleus for functional activity may not be adequate as a result of their inability to transfect sufficient cell numbers as well as support long-term expression. By contrast, viral vectors, particularly AAV and lentivirus, are capable of very efficiently and stably transducing many cell types. In fact, in vivo potencies are often greater than with most current synthetic RNAi methods with essentially knock-out phenotypes in the liver and eye observed for months and years using self-complementary AAV8 vectors in work reported by the laboratory I work in and collaborators to name just one example.
Before focusing more on AAV with which I am most familiar with (learning by osmosis), lentivirally delivered RNAi has much potential for disease of the CNS, largely for the same reasons as outlined for AAV below, and in combination with cell therapeutics. The latter would involve the ex vivo transduction of lentiviral RNAi constructs for example into stem cells similar to the ongoing phase I HIV-RNAi trial by the City of Hope and sponsored by Benitec, or also to enhance dendritic cell cancer vaccine strategies. Many of these applications take advantage the stable integration of lentiviral vectors into the host genome such that the vector and its expression/knock down will be maintained even in dividing tissues.
By contrast, due to its largely episomal nature, AAV gets rapidly during cell division thus limiting their applicability for cancer therapy or in other situations that involve cell division (regenerating liver, stem cell differentiation etc). Moreover, in certain settings humoral and T-cell mediated immune responses against AAV viral proteins present another challenge for achieving persistent gene silencing (the transduced cell may be recognized by the immune system and be eliminated) and where repeat-administration is desirable (due to neutralizing antibodies generated following the first administration).
For these reasons, AAV RNAi appears most promising for diseases of the eye and CNS as immuno-privileged sites. Although infusion pumps may address some of the challenges of allowing for long-term intracranial gene silencing by synthetic means, due to the ability to mediated sustained gene silencing for 6-12 months if not several years as suggested by canine AAV studies for hemophilia, the prospect of maybe having to subject a patient only once or very few times to an invasive operation makes AAV and lentivirus attractive alternatives for diseases such as Huntington’s Disease and other neurodegenerative disorders.
Not coincidentally, Targeted Genetics and the University of Iowa are currently pursuing an AAV RNAi program (pre-clinical stage) for Huntingon’s Disease that has shown promise. A critical factor for the success of this program should be the design of the shRNA expression cassette, and I personally would feel more comfortable with an H1 promoter-driven instead of a U6 promoter-driven construct that has been the front-runner so far. Another interesting application may be for the treatment of PML viral infection. Biogen Idec and Alnylam have been working on an siRNA-mediated approach, but due to serious nature of JC virus reactivation during PML, rapid onset of gene silencing by self-complementary AAV RNAi and the efficient vector delivery achieved for a number of neuronal cell types, AAV-mediated RNAi warrants consideration for this devastating disease.
Suitable non-CNS applications for AAV ddRNAi candidate may be instances where a single administration may already be therapeutic without the need for sustained gene silencing and repeat administration. HCV infection of the liver may be one such case as it is now possible to essentially transduce every liver cell, at least in mice, and effect long-term silencing after a single administration. AAV-medicated RNAi could therefore be an important component of combination therapies for patients that do not respond to current therapies and could also quite easily be tailored to the different HCV genotypes. Pfizer just recently acquired co-development rights for the pre-clinical stage AAV RNAi program for HCV from the Benitec spin-off Tacere.
AAV gene therapy is relatively new, but it is making rapid progress. Two independent phase I/II AAV gene therapy trial for Leber’s Congenital Amaurosis caused by RPE65 deficiency, a condition that leads to blindness later in life, demonstrated clear improvement in vision and treating children early on promises to even cure the disease. One of the studies was conducted by an academic group in London and was sponsored by Targeted Genetics, the other by a group from the University of Pennsylvania.
It is not clear whether an immune reaction that eliminated transduced liver cells in a hemophilia trial was specific for the AAV 2 serotype used, as most of us will have been exposed to this type of AAV during childhood and may therefore harbor some immune memory for it. A number of strategies have been proposed to minimize the risk of immune recognition in future trials, for example transient immune suppression or the use of alternative serotypes. The search for and development of alternative AAV serotypes is truly exploding and is rapidly yielding new AAV vectors with various tissue tropisms and immune properties.
The less AAV that needs to be administered the better also from an immune point of view. Very promising in that regard is the finding that the self-complementary AAVs which by-pass the rate-limiting second-strand synthesis step during the establishment of gene expression much more efficiently and functionally transduce target cells than conventional single-stranded AAV vectors. While this halves the vector capacity to less than 2kb, a size that is not very practical for expressing many protein-encoding genes, this does not matter at all in the context of small hairpin expression cassettes and appears to be just made for AAV RNAi. Actually, it was this property of self-complementary AAV vectors that was one of the main reasons for me to come to Stanford to conduct post-doctoral research. A patent for this possibly critically enabling technology has been issued to Targeted Genetics.
RNAi Therapeutics Portfolio Review: Increasing Position of Targeted Genetics
The technology is certainly there to be harnessed for therapy, but the development of AAV RNAi Therapeutics is not trivial and is a collaborative effort that requires careful gene target selection, safe and potent hairpin vectors, thoughtful clinical trial designs, and the manufacture of large amounts of high-quality AAV particles. Nevertheless, with the right team and some luck, it should possible to do.
It has both amazed and scared me to learn in a vivid report by RNAiNews that DNA-directed RNAi company Nucleonics whose lead program was a very long-shot (to put it mildly) RNAi program for HBV, was close to raising $25M in a series C round that would have included a venture capital arm from Johnson & Johnson. How that was even a remote possibility given the odds for that particular HBV RNAi program and the uncertain IP of that company is a mystery to me and makes the ~$13M market cap of Targeted Genetics’ look very cheap by comparison.
For this reason and given the promise of AAV-mediated RNAi Therapeutics in general, Targeted Genetics’ AAV gene therapy know-how and IP, including IP directly related to RNAi -especially the one for the double-stranded AAV and apparently another one for the expression of non-coding RNAs- I will add $680 worth of TGEN to the RNAi Therapeutics model portfolio and will pay for this with the sale of some stock in ISIS Pharmaceutcals (-$280), Oxford Biomedica (-$200), Silence Therapeutics (-$100) and Rosetta Genomics (-$100).
Remember, an investment in Targeted Genetics is highly speculative, its balance sheet somewhat ugly which is made worse by current market conditions which make it almost impossible to raise small biotech capital on reasonable terms. This investment thesis therefore is that Targeted Genetics will be able to win the race against the clock by being an attractive partner for other drug companies interested in RNAi Therapeutics with the resulting license fees and development milestones helping the company through the hard times. Maybe Genzyme with its considerable AAV gene therapy efforts and orphan disease management expertise or Biogen Idec with its long-standing ties to Targeted and interest in PML will bite.
Disclosure: The lab that I work in has an interest in AAV-mediated RNAi Therapeutics. The author has also been accumulating shares in Targeted Genetics between $0.58 and $0.72. The stock is not suitable for most due to adverse market conditions and the precarious balance sheet of the company. The thin trading volume of the stock causes volatilities in share price, usually to the downside, and there is a real chance that the stock will be de-listed from the Nasdaq exchange which will make this little company even more opaque to investors. On the other hand, conditions will improve at some point and in an environment where venture capital exits have become increasingly difficult and considering the attractive relative valuation and maturity of the company and technology, Targeted Genetics may represent an interesting, somewhat more liquid piece of RNAi Therapeutics real estate for investors otherwise specializing in private start-up companies.
Friday, July 4, 2008
Metabolic Disease Drug Development Anxieties Highlight Benefit of Diversified RNAi Therapeutics Pipeline
Like the commodity bubble, it seems that the regulatory hurdles to drug development are mounting just when we thought we had reached the top. This is the impression one gets from the vote taken by an FDA advisory panel this week that can be essentially boiled down to the presumption that lowering blood sugar increases the risk of heart attack. The prospect of longer and more expensive clinical trials has certainly caused a few mini heart attacks to a number of drug companies developing medicines for diabetes and other metabolic diseases thinking that the obesity epidemic in the prosperous half of the world was bad enough such that regulatory agencies, politicians, and certain clinicians involved in drug development would have a keen interest in new treatment options. Don’t get me wrong here, I see very well the problem of millions of real patients and maybe not-so-needy folks taking drugs from which they do not derive any benefit, but there certainly are other ways of ensuring drug safety and efficacy without rendering drug development, and eventually the cost of drugs just unaffordable to anybody, and often without good reason.
Now that I got this off my chest, what does the broad attack on metabolic disease drug development mean for RNAi Therapeutics?
Metabolic disease, because of the ability of current systemic delivery methods to effectively knock down genes in the liver which is critically involved in regulating blood sugar and lipid levels, is one of the main therapeutic focus areas of current RNAi Therapeutics development. It shares this position with cancer, followed by respiratory, ocular and CNS-related disease. It may therefore be tempting, if you have the ability to target a range of hot metabolic disease targets, to create a development pipeline based on metabolic disease and little else. ISIS Pharmaceuticals from the related field of antisense therapeutics is probably the best example here as it has very much limited their internal drug development activities on metabolic disease, while handing off some of the more challenging targets such as for cancer to one of their many satellite companies.
Of course, if you don’t have the capability to diversify, concentrating on building a franchise around a single, but potentially very lucrative market may be the most efficient way of maximizing shareholder value given the many synergies derived from largely having only to exchange the siRNA inside and comparatively few other changes. However, if you can afford it and you are interested in establishing RNAi Therapeutics as a broadly applicable drug development platform, you probably would want to spread your risk more widely even if all the programs added up individually would yield a higher valuation. The fact that the regulatory environment may change overnight while drug development is a 12-15 year effort being one reason.
Next to insuring from regulatory risk, diversification also means that failure of one drug candidate such as for a given organ does not necessarily have to impact the perceived probability of success for candidates aimed at other organs. In the same vein, it may also be wise not to be too dogmatic about delivery technologies, siRNA modification or DNA-directed RNAi methods and structures. For example, if your entire IP claim depends on just one siRNA modification pattern even without so much as functional validation in a non-human primate, you may have ended up totally reliant on clinically non-viable chemistries. Related technologies have shown that developing chemistries in generations rather than multiple chemistries in parallel may mean that if your chosen chemistry generation turns out to be either inefficient or unsafe, it may take another 7 years to get a shot with the next generation.
Meanwhile, all bets are off what steps the FDA will take next.
Now that I got this off my chest, what does the broad attack on metabolic disease drug development mean for RNAi Therapeutics?
Metabolic disease, because of the ability of current systemic delivery methods to effectively knock down genes in the liver which is critically involved in regulating blood sugar and lipid levels, is one of the main therapeutic focus areas of current RNAi Therapeutics development. It shares this position with cancer, followed by respiratory, ocular and CNS-related disease. It may therefore be tempting, if you have the ability to target a range of hot metabolic disease targets, to create a development pipeline based on metabolic disease and little else. ISIS Pharmaceuticals from the related field of antisense therapeutics is probably the best example here as it has very much limited their internal drug development activities on metabolic disease, while handing off some of the more challenging targets such as for cancer to one of their many satellite companies.
Of course, if you don’t have the capability to diversify, concentrating on building a franchise around a single, but potentially very lucrative market may be the most efficient way of maximizing shareholder value given the many synergies derived from largely having only to exchange the siRNA inside and comparatively few other changes. However, if you can afford it and you are interested in establishing RNAi Therapeutics as a broadly applicable drug development platform, you probably would want to spread your risk more widely even if all the programs added up individually would yield a higher valuation. The fact that the regulatory environment may change overnight while drug development is a 12-15 year effort being one reason.
Next to insuring from regulatory risk, diversification also means that failure of one drug candidate such as for a given organ does not necessarily have to impact the perceived probability of success for candidates aimed at other organs. In the same vein, it may also be wise not to be too dogmatic about delivery technologies, siRNA modification or DNA-directed RNAi methods and structures. For example, if your entire IP claim depends on just one siRNA modification pattern even without so much as functional validation in a non-human primate, you may have ended up totally reliant on clinically non-viable chemistries. Related technologies have shown that developing chemistries in generations rather than multiple chemistries in parallel may mean that if your chosen chemistry generation turns out to be either inefficient or unsafe, it may take another 7 years to get a shot with the next generation.
Meanwhile, all bets are off what steps the FDA will take next.
Sunday, June 29, 2008
Alnylam’s RSV Program Causes Excitement Among Lung Transplant Surgeons- An Example for a Shrewd RNAi Therapeutics Development Strategy?
“Yes, it’s interesting how what we think about most often begins to surround us” replied Chris, a friend from down the hall with whom I share an addiction of going to Stanford biomedical seminars, to an email of mine where I noted that RNAi Therapeutics is honestly popping up almost everywhere now. It happened this week Monday in a chemical engineering seminar on the delivery of crystal-like drug particles (think small 20-30nm, stable needle-like siRNA particles) or during a lung transplant talk on Friday.
Despite close to half a century of lung transplantation, with more than 2000 procedures performed annually world-wide, there has been very little progress in the 2-5 year morbidity and mortality, meaning that less than half of transplant recipients survive beyond 5 years. Community-acquired viral infections in the immuno-suppressed patients are responsible for roughly a third of such chronic rejection and declining lung function cases, with the respiratory syncytial virus (RSV) clearly topping the list.
Stanford is a fairly large lung transplant center, and the situation is not much different here. The seminar I attended concerned a review of the history of 25 lung transplant patients that had acquired either RSV or paraflu viral infections (23 of which with RSV) and were treated with the broad-spectrum antiviral ribavirin either alone or in addition to pavlizumab, a neutralizing antibody that is normally used for and really only effective in the prophylaxis of RSV.
Without going into the details, at the end of the presentation it was clear that, in the absence of any effective treatment, ribavirin and pavlizumab are given as a last resort and desperate effort (yes, despite of what you read in the press these days, these people really seem to care about improving the health of their patients) to make a dent against RSV, but that nobody was really convinced that this would more good than harm. Actually, inhaled ribavirin is even considered a safety hazard to attending nurses and docs.
Then suddenly, there was a commotion in the room as somebody mentioned the word “s-i-r-n-a”. Wasn’t there something in clinical trials right now that would attack the virus directly, a treatment that would even work in immuno-compromised patients? And yes, hadn’t it shown already some kind of antiviral activity in the clinic? Wow, maybe we should give it a try- anything that had been shown anywhere to inhibit RSV in man… There was a lot of excitement and confusion, for example about the mechanism of action, and "some commercial company” was mentioned. Probably worth revisiting.
This experience told me that, no, I am not living in an RNAi Therapeutics bubble, but that RNAi Therapeutics slowly, but surely is making its way into mainstream medicine. Given that there was confusion about what exactly RNAi was even among Stanford lung transplant surgeons, maybe some education would help. A better understanding should also help in recruiting the best centers for clinical trials and consequently facilitate drug development, and maybe if Alnylam reads this, they may want to approach them and spend a couple of minutes educating them what ALN-RSV01 is about. I'm confident they would find receptive ears.
It also changed my view about the prospect for ALN-RSV01 and the development path Alnylam has taken. It is clear that the experimental infection model studies were not, as sometimes criticized, an advertisement ploy irrelevant to the development path and future use of ALN-RSV01. With no alternatives, it appears that having shown some type of antiviral activity, ALN-RSV01, similar to ribavirin, could be widely applied for the treatment of RSV infection even if only approved for a small sub-population of RSV patients.
Testing ALN-RSV01 in the lung transplant setting therefore makes a lot of sense, as this may turn out to be the setting where ALN-RSV01 could be approved first. Lung transplant patients have the highest medical need for such a treatment, even more so than other immuno-suppressed transplant patients as the infection affects the graft itself and may lead to graft failure. Moreover, any type of therapy that depends on the immune system is unlikely to work in this setting due to the immuno-suppression therefore increasing the competitiveness of an RNAi Therapeutics. As the early detection of RSV should be critical for the success of ALN-RSV01, the fact that lung transplant patients are regularly monitored for and highly sensitized to the possibility of RSV infections is highly advantageous. And finally, as I learned this Friday, the viral shedding of RSV is prolonged in immuno-suppressed patients, meaning that instead of the typical 5 day RSV infection window, ALN-RSV01 gets more time to attack RSV. An interesting aside to the immuno-suppression theme here is that any efficacy of ALN-RSV01 would be much less likely due to non-specific immune responses elicited by the unmodified siRNA.
When the RNAi Therapeutics story has have been written and taught in business schools, one of the main lessons for which ALN-RSV01 could be a prime example should be that by applying innovation to areas of large medical unmet need, a sweet spot can easily develop into a large market opportunity. Due to its unique mechanism of action, RNAi Therapeutics is ideally positioned to repeatedly take advantage of that strategy.
Despite close to half a century of lung transplantation, with more than 2000 procedures performed annually world-wide, there has been very little progress in the 2-5 year morbidity and mortality, meaning that less than half of transplant recipients survive beyond 5 years. Community-acquired viral infections in the immuno-suppressed patients are responsible for roughly a third of such chronic rejection and declining lung function cases, with the respiratory syncytial virus (RSV) clearly topping the list.
Stanford is a fairly large lung transplant center, and the situation is not much different here. The seminar I attended concerned a review of the history of 25 lung transplant patients that had acquired either RSV or paraflu viral infections (23 of which with RSV) and were treated with the broad-spectrum antiviral ribavirin either alone or in addition to pavlizumab, a neutralizing antibody that is normally used for and really only effective in the prophylaxis of RSV.
Without going into the details, at the end of the presentation it was clear that, in the absence of any effective treatment, ribavirin and pavlizumab are given as a last resort and desperate effort (yes, despite of what you read in the press these days, these people really seem to care about improving the health of their patients) to make a dent against RSV, but that nobody was really convinced that this would more good than harm. Actually, inhaled ribavirin is even considered a safety hazard to attending nurses and docs.
Then suddenly, there was a commotion in the room as somebody mentioned the word “s-i-r-n-a”. Wasn’t there something in clinical trials right now that would attack the virus directly, a treatment that would even work in immuno-compromised patients? And yes, hadn’t it shown already some kind of antiviral activity in the clinic? Wow, maybe we should give it a try- anything that had been shown anywhere to inhibit RSV in man… There was a lot of excitement and confusion, for example about the mechanism of action, and "some commercial company” was mentioned. Probably worth revisiting.
This experience told me that, no, I am not living in an RNAi Therapeutics bubble, but that RNAi Therapeutics slowly, but surely is making its way into mainstream medicine. Given that there was confusion about what exactly RNAi was even among Stanford lung transplant surgeons, maybe some education would help. A better understanding should also help in recruiting the best centers for clinical trials and consequently facilitate drug development, and maybe if Alnylam reads this, they may want to approach them and spend a couple of minutes educating them what ALN-RSV01 is about. I'm confident they would find receptive ears.
It also changed my view about the prospect for ALN-RSV01 and the development path Alnylam has taken. It is clear that the experimental infection model studies were not, as sometimes criticized, an advertisement ploy irrelevant to the development path and future use of ALN-RSV01. With no alternatives, it appears that having shown some type of antiviral activity, ALN-RSV01, similar to ribavirin, could be widely applied for the treatment of RSV infection even if only approved for a small sub-population of RSV patients.
Testing ALN-RSV01 in the lung transplant setting therefore makes a lot of sense, as this may turn out to be the setting where ALN-RSV01 could be approved first. Lung transplant patients have the highest medical need for such a treatment, even more so than other immuno-suppressed transplant patients as the infection affects the graft itself and may lead to graft failure. Moreover, any type of therapy that depends on the immune system is unlikely to work in this setting due to the immuno-suppression therefore increasing the competitiveness of an RNAi Therapeutics. As the early detection of RSV should be critical for the success of ALN-RSV01, the fact that lung transplant patients are regularly monitored for and highly sensitized to the possibility of RSV infections is highly advantageous. And finally, as I learned this Friday, the viral shedding of RSV is prolonged in immuno-suppressed patients, meaning that instead of the typical 5 day RSV infection window, ALN-RSV01 gets more time to attack RSV. An interesting aside to the immuno-suppression theme here is that any efficacy of ALN-RSV01 would be much less likely due to non-specific immune responses elicited by the unmodified siRNA.
When the RNAi Therapeutics story has have been written and taught in business schools, one of the main lessons for which ALN-RSV01 could be a prime example should be that by applying innovation to areas of large medical unmet need, a sweet spot can easily develop into a large market opportunity. Due to its unique mechanism of action, RNAi Therapeutics is ideally positioned to repeatedly take advantage of that strategy.
Friday, June 27, 2008
Quark Biotech Dazzles RNAi Therapeutics World with Expanding Pipeline, Adds to Evidence that Delivery Walls to Kidney Crumbling
Yesterday, the US-Israeli company Quark Biotech announced the filing of their now third RNAi Therapeutics IND. The latest IND candidate, DGFi, is the siRNA knockdown of p53 in the kidney for the treatment of kidney transplantation-associated ischemia-reperfusion injury. This program follows a similar systemic kidney-p53 oxidative stress RNAi program, Akli-5, for acute kidney injury, and a local RNAi program (RTP-801i) for age-related macular degeneration targeting the apoptosis-related gene RTP801/REDD1 that came out of Quark’s own gene discovery program.
This likely makes Quark Biotech, which specializes in the discovery of disease-associated genes that it then targets by in-licensed RNAi technology, the company with the most RNAi candidates in the clinic, unless, of course, Merck has early clinical programs that we haven’t heard about. This is quite remarkable given that very little is known about Quark’s RNAi science as judged by the literature and presence at leading RNAi conferences. My own patent search for Quark-related RNAi delivery technologies failed, although their IPO documents stated that they had been building an IP estate around RNAi Therapeutics, including proprietary delivery technologies [Note: the planned ~$80M IPO failed last year due to a difficult market; instead the company earlier this year raised around $27M from private Japanese investors].
So I can only speculate as to the systemic delivery technology employed. Given that unformulated and unmodified oligonucleotides have the propensity to end up being rapidly excreted by the kidney, it is well possible that some of these siRNAs get functionally taken up for gene silencing. In fact, the ground-breaking systemic siRNA delivery paper by Soutschek and colleagues from Alnylam employing cholesterol-conjugated siRNAs showed that the lipophilic siRNA conjugate was taken up reasonably well not only in the liver, but also jejunum, heart, adipose tissue, the lung, and kidney, albeit at quite high 50mg/kg dosages. Similarly, a recent publication by the Natarajan group from the City of Hope, CA, showed that subcutaneous administration of ~20mg/kg cholesterol-siRNA reduced gene expression in the kidney by about 50-80% with promising therapeutic effects in a mouse model for diabetic nephropathy. It is, however, possible that the apparently intravenous formulation is composed of a nanoparticle as suggested by the second name of the Akli-5 progam, I5NP (NP=nanoparticle?). In any case, the evidence is growing that the fact that siRNAs like to go to the kidney could be exploited for treating kidney-related disease by RNAi, slowly clearing yet another organ for RNAi.
Although I feel more comfortable judging an RNAi Therapeutics company with some scientific data at hand, Quark Biotech’s speed of entering the clinic while others are humbly optimizing their own candidates, particularly with regards to delivery, warrants some attention. In addition to the AMD program, the company has licensed a second RNAi program to the emerging RNAi superpower Pfizer, a program for COPD likely to be administered by inhalation. Overall, the Pfizer relationship has brought in over $25M of realized funding as of the filing of the IPO documents in March 2007. Another important relationship exists with Silence Therapeutics, although a report earlier this year suggested that there might be some frictions in that relationship. This would be consistent with Quark having subsequently licensed IP from Alnylam as well as Quark’s ambitions of developing proprietary RNAi trigger IP, whatever that is supposed to mean. I guess by providing a little more transparency, Quark Biotech might be able to attract more investor interest for a second IPO attempt. With so many clinical candidates and more coming up, such a cash infusion could be necessary soon.
In other news: The Pharmalot Blog posted yesterday that the approval rate of innovative medicines continues to be anemic. Only 5 new molecular entities were approved by the almighty FDA in the year through May. It’s time for RNAi to contribute to the development of more innovative drugs addressing unmet medical needs, and the regulatory agencies and society as a whole to understand that overdone conservatism and by killing the profitability of drug development aren’t helping in that regard.
This likely makes Quark Biotech, which specializes in the discovery of disease-associated genes that it then targets by in-licensed RNAi technology, the company with the most RNAi candidates in the clinic, unless, of course, Merck has early clinical programs that we haven’t heard about. This is quite remarkable given that very little is known about Quark’s RNAi science as judged by the literature and presence at leading RNAi conferences. My own patent search for Quark-related RNAi delivery technologies failed, although their IPO documents stated that they had been building an IP estate around RNAi Therapeutics, including proprietary delivery technologies [Note: the planned ~$80M IPO failed last year due to a difficult market; instead the company earlier this year raised around $27M from private Japanese investors].
So I can only speculate as to the systemic delivery technology employed. Given that unformulated and unmodified oligonucleotides have the propensity to end up being rapidly excreted by the kidney, it is well possible that some of these siRNAs get functionally taken up for gene silencing. In fact, the ground-breaking systemic siRNA delivery paper by Soutschek and colleagues from Alnylam employing cholesterol-conjugated siRNAs showed that the lipophilic siRNA conjugate was taken up reasonably well not only in the liver, but also jejunum, heart, adipose tissue, the lung, and kidney, albeit at quite high 50mg/kg dosages. Similarly, a recent publication by the Natarajan group from the City of Hope, CA, showed that subcutaneous administration of ~20mg/kg cholesterol-siRNA reduced gene expression in the kidney by about 50-80% with promising therapeutic effects in a mouse model for diabetic nephropathy. It is, however, possible that the apparently intravenous formulation is composed of a nanoparticle as suggested by the second name of the Akli-5 progam, I5NP (NP=nanoparticle?). In any case, the evidence is growing that the fact that siRNAs like to go to the kidney could be exploited for treating kidney-related disease by RNAi, slowly clearing yet another organ for RNAi.
Although I feel more comfortable judging an RNAi Therapeutics company with some scientific data at hand, Quark Biotech’s speed of entering the clinic while others are humbly optimizing their own candidates, particularly with regards to delivery, warrants some attention. In addition to the AMD program, the company has licensed a second RNAi program to the emerging RNAi superpower Pfizer, a program for COPD likely to be administered by inhalation. Overall, the Pfizer relationship has brought in over $25M of realized funding as of the filing of the IPO documents in March 2007. Another important relationship exists with Silence Therapeutics, although a report earlier this year suggested that there might be some frictions in that relationship. This would be consistent with Quark having subsequently licensed IP from Alnylam as well as Quark’s ambitions of developing proprietary RNAi trigger IP, whatever that is supposed to mean. I guess by providing a little more transparency, Quark Biotech might be able to attract more investor interest for a second IPO attempt. With so many clinical candidates and more coming up, such a cash infusion could be necessary soon.
In other news: The Pharmalot Blog posted yesterday that the approval rate of innovative medicines continues to be anemic. Only 5 new molecular entities were approved by the almighty FDA in the year through May. It’s time for RNAi to contribute to the development of more innovative drugs addressing unmet medical needs, and the regulatory agencies and society as a whole to understand that overdone conservatism and by killing the profitability of drug development aren’t helping in that regard.
Tuesday, June 24, 2008
Developing Multi-Functional RNAi Therapeutics
The great attraction of developing therapeutics based on RNAi is its inherent specificity and applicability to virtually any gene for the rational design of drugs. The specificity of gene silencing is not just a theory, but very powerfully attested by the many successes of applying RNAi even to genome-wide screens to uncover gene function (and also more targets for RNAi). Delivery of the RNAi inducer to the cells of interest would further add to such specificity and consequently safety.
However, as has long been known, certain nucleic acids elicit immune responses, and siRNAs are no exception to this. Although this does not apply to appropriately designed and vetted siRNAs, when it does, it may well interfere with the interpretation and predictability of the knockdown phenotype. However, instead of describing once again methods whereby such responses can be avoided and phenotypes more consistently obtained (siRNA length, structure, and modifications; bioinformatics etc), I would like to take the opportunity here to point out the potential for RNAi Therapeutics that include a immune-regulatory element. Moreover, as this is typically related to the uptake of the RNAi formulation in cells other than the primary target cells, I would also like to make us consider the potential for RNAi Therapeutics exploiting the entire biodistribution of a particular RNAi drug delivery system.
When we think about indications such as cancer and viral infections, the importance of the immune system in eliminating the disease cannot be underestimated. Cytokine therapies e.g. are well known to these areas of medicine and it is no coincidence that there have been long-standing efforts in harnessing the ability of nucleic acids to induce TLR and other immune signaling pathways to improve both cellular and humoral immune responses.
It is therefore conceivable that an immuno-stimulatory siRNA is not necessarily screened out during the siRNA selection process, but is deliberately packaged into a nanoparticle which in addition to the primary target cells (cancer cell, virus infected cell, etc.) would also be taken up by phagocytic cells where the cytokine stimulation would lead to enhanced antigen presentation or the augmentation of monoclonal antibody therapies. To further take full advantage of the biodistribution of the RNAi formulation, the RNAi drug could also contain two or more different siRNAs, each one designed to knock down a suitable gene in the various cell types that the nanoparticle is taken up in (e.g. in the case of a liver delivery system that enters both Kupffer cells and hepatocytes, an siRNA against a immuno-regulatory gene expressed in the Kupffer cells and maybe other phagocytes and one siRNA for a hepatocyte-specific gene).
In addition to immune-stimulation, certain siRNA formulations could be used for concomitant gene knockdown and immune suppression. As work by Protiva (now Tekmira) has shown, siRNA modifications may not only be used to avoid unwanted TLR signaling through siRNAs, but to inhibit these TLR responses in trans. A single modified siRNA could thus be employed in a two-pronged gene knockdown/TLR signaling inhibition strategy for treating autoimmune disorders.
Based on the acquisition of prior TLR company Coley by Pfizer, Alnylam’s vaccine spin-off intentions, and Tekmira’s IP and know-how on the immunological properties of nucleic acids, I would not be surprised if we should be hearing relatively soon more about such multi-functional RNAi Therapeutics.
Rather than considering innate immune responses and imperfect biodistribution as nuisances, it may well turn out that a number of RNAi Therapeutics may get the extra bit of efficacy out of simultaneously modulating immune responses and knocking down genes in multiple cell types. In my opinion, the medical and commercial opportunities for that are currently underappreciated.
However, as has long been known, certain nucleic acids elicit immune responses, and siRNAs are no exception to this. Although this does not apply to appropriately designed and vetted siRNAs, when it does, it may well interfere with the interpretation and predictability of the knockdown phenotype. However, instead of describing once again methods whereby such responses can be avoided and phenotypes more consistently obtained (siRNA length, structure, and modifications; bioinformatics etc), I would like to take the opportunity here to point out the potential for RNAi Therapeutics that include a immune-regulatory element. Moreover, as this is typically related to the uptake of the RNAi formulation in cells other than the primary target cells, I would also like to make us consider the potential for RNAi Therapeutics exploiting the entire biodistribution of a particular RNAi drug delivery system.
When we think about indications such as cancer and viral infections, the importance of the immune system in eliminating the disease cannot be underestimated. Cytokine therapies e.g. are well known to these areas of medicine and it is no coincidence that there have been long-standing efforts in harnessing the ability of nucleic acids to induce TLR and other immune signaling pathways to improve both cellular and humoral immune responses.
It is therefore conceivable that an immuno-stimulatory siRNA is not necessarily screened out during the siRNA selection process, but is deliberately packaged into a nanoparticle which in addition to the primary target cells (cancer cell, virus infected cell, etc.) would also be taken up by phagocytic cells where the cytokine stimulation would lead to enhanced antigen presentation or the augmentation of monoclonal antibody therapies. To further take full advantage of the biodistribution of the RNAi formulation, the RNAi drug could also contain two or more different siRNAs, each one designed to knock down a suitable gene in the various cell types that the nanoparticle is taken up in (e.g. in the case of a liver delivery system that enters both Kupffer cells and hepatocytes, an siRNA against a immuno-regulatory gene expressed in the Kupffer cells and maybe other phagocytes and one siRNA for a hepatocyte-specific gene).
In addition to immune-stimulation, certain siRNA formulations could be used for concomitant gene knockdown and immune suppression. As work by Protiva (now Tekmira) has shown, siRNA modifications may not only be used to avoid unwanted TLR signaling through siRNAs, but to inhibit these TLR responses in trans. A single modified siRNA could thus be employed in a two-pronged gene knockdown/TLR signaling inhibition strategy for treating autoimmune disorders.
Based on the acquisition of prior TLR company Coley by Pfizer, Alnylam’s vaccine spin-off intentions, and Tekmira’s IP and know-how on the immunological properties of nucleic acids, I would not be surprised if we should be hearing relatively soon more about such multi-functional RNAi Therapeutics.
Rather than considering innate immune responses and imperfect biodistribution as nuisances, it may well turn out that a number of RNAi Therapeutics may get the extra bit of efficacy out of simultaneously modulating immune responses and knocking down genes in multiple cell types. In my opinion, the medical and commercial opportunities for that are currently underappreciated.
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