Sunday, November 4, 2007

The Risk of Rushing RNAi Therapeutics into the Clinic

RNAi has always caught on very fast. It took only nine years for the Nobel Committee to recognize the importance of RNAi in medical biology and award The Prize for its discovery, and only 6 years following the discovery that siRNAs induce RNAi in mammalian cells by Tuschl to become an indispensable tool in the basic and applied studies of human gene function. Equally astounding is the fact that there are now close to 10 RNAi-based therapeutics that have entered the clinic since.

I have extensively described here before why I think RNAi has the potential to be the next great drug development engine, including the prospect of faster development timelines due to straight-forward mechanism of action and platform reproducibility. However, in the wake of Alnylam’s Q3 conference call announcing an insignificant delay in their RSV program, but a more open-ended delay in their liver programs, what I would like to do today is to point out the dangers of rushing RNAi Therapeutics into the clinic mainly borne out of the tension that exists between applying the best and safest science and satisfying investor demand for gushing clinical pipelines.

From the clinical perspective the ultimate danger is obvious: putting trial participants at risk, and disappointing patients’ expectations for a cure of their disease. From the perspective of running an early-stage biotech business that needs to raise money fairly regularly, the issues easily become more complicated. Although I admire the honesty and scientific intent that underlie statements like that by Nastech that one should not expect RNAi Therapeutics from your company until another 15 years, it certainly won’t capture the imagination of Wall Street. The easy way would be therefore to set your bar a little bit lower and signal to your potential investors that you deserve more money since you’ve been able to put so many drugs into the clinic in such a short period of time. A sophisticated biotech investor would know that these companies can be a good investment, although you do not necessarily want to stick it out until the Day of Reckoning comes.

The danger to the field of RNAi Therapeutics is therefore that as some of these rushed candidates come to a stage where they have to prove their safety and efficacy in large-scale clinical trials, a good number of them will fail, essentially because some of the Best Practices were not followed, including addressing cytokine induction issues, off-targeting profiles, RNAi delivery, and pre-clinical safety and efficacy studies that ideally include non-human primates.

Acuity Pharmaceuticals (now part of Opko Health) dazzled everybody when they came out of nowhere and can now claim to have been the first to put an RNAi candidate (for wet AMD) into the clinic. Unless they have changed the composition of their drug since study initiation, Cand5 appears to be an unmodified siRNA injected straight into the eye. This alone makes me wonder whether an optimized compound has been put into the clinic, and I have more confidence in a program run by Allergan and Sirna Therapeutics (Merck) targeting the same pathway for wet AMD, but with a modified siRNA formulation intended for slow release.

SiRNAs that induce cytokine responses may also have a number of additional biological properties, some of them even potentially beneficial for the disease at hand. Gunther Hartmann from Bonn, a scientist with a cytokine angle on oligonucleotide therapeutics, has even proposed at the recent OTS meeting to purposefully combine the immunostimulatory potential of RNAs (isRNA) with siRNA design. Cancer and infectious disease may be good areas to test this concept as isRNAs are thought to help the immune system in fighting related these diseases.

There has been similar discussion whether there would indeed be any harm if an RNAi therapeutic targeting the Hepatitis C Virus (HCV) had some concomitant interferon response. Isn’t interferon (and RNAi) nature’s first answer to viral infections and the mainstay of current HCV treatment regimens anyway? Similar arguments may also apply to RSV.

The fact that Alnylam is now focusing RSV-01 on adult populations makes me therefore wonder whether this was driven at least in part due to concern that the tender infant respiratory system may be more prone to overreact to a potentially immunogenic siRNA molecule than a lung hardened by years of air pollution. This siRNA is probably unmodified as it was this June that the first Alnylam compounds using ISIS modification patents moved into IND-enabling studies. Being unmodified from a pharmacokinetic perspective may not be that bad or even desirable in RSV, as RSV is an acute infection and long drug exposure may therefore have the potential to do more harm than good.

I should emphasise, however, that the early rodent RSV studies that form the basis of Alnylam’s RSV-01 and which have supposedly been replicated by the company, demonstrated sequence-specific antiviral activities. Furthermore, from Alnylam’s presentations one can assume that RSV-01 was carefully screened for cytokine induction in a number of human cell lines and animal models. I should add as well that the slight delay of the RSV experimental infection model studies is not the result of any of these considerations, but more simply reflects the fact that finding volunteers to be infected with a virus that gives you flu-like symptoms and requires you to be locked away from the outside world for a couple of weeks, is not that easy. However, 74 of the 88 subjects, I suppose mostly students, have already been recruited and we should hear top-line data early next year.

Alnylam’s conservative approach to drug development is further demonstrated by their delay of filing INDs for their liver programs, for hypercholesterolemia and liver cancer. While there is no doubt that with current systemic delivery capabilities it is possible to achieve potent gene knockdown in the liver, the safety and dose-response data so far would explain Alnylam’s caution into committing to a particular formulation by year-end as originally guided. Instead, I agree with their assessment that with new chemistries coming online, such as MIT’s lipidoids which formed the basis of the recent microRNA saturation data in Nature, it is wise to keep testing all of to find the formulations that offer the best therapeutic index. It would not be the first time that a drug for treating heart disease would fail in a large-scale trial because of unacceptable side-effects seen in a handful of participants. For what it’s worth and mindful of the business considerations about demonstrating human proof-of-concept of an RNAi Therapeutics with the hypercholesterolemia program, I wonder whether Alnylam should not go first with liver cancer anyway.

Needless to say, this cautious, data-driven approach not only benefits Alnylam the Science, but also Alnylam the Business. The importance of their scientific credibility through publications and conference presentations cannot be underestimated when it comes to their ability to execute on their business development goals, mainly in the form of lucrative license deals and access to enabling technologies. With a cash position of $468M, Alnylam is in a stronger position than ever to focus on the long-term success of the company and its shareholders.

Rosetta Genomics on Track to Bring the First Clinical RNAi-related Product to Market

Almost unnoticed in the microRNA diagnostics space, Rosetta Genomics reported this week that it had completed the pre-validation phase for its first microRNA diagnostic product scheduled to come into the clinic in the first half of next year. It would be exciting to see the first RNAi-related product have a direct clinical impact and, if successful, will fund Rosetta’s microRNA diagnostics and therapeutics programs with minimal shareholder dilution. The microRNA diagnostic is designed to differentiate between squamous and non-squamous lung cancer which is not always possible to tell under the microscope and an area of particular importance now that Genentech’s VEGF-targeting MAb Avastin showed life-threatening side-effects particularly in subjects with squamous cell cancer.

While RNAi Therapeutics has attracted most of the RNAi attention, microRNA-based diagnostics are set to become the first commercial success of RNAi-related products in the clinic. Their differential expression, scalability, and, equally important, potential relative stability advantages compared to protein and larger mRNA biomarkers means that microRNAs have the potential to become the biomarker platform of choice. The (near) future should tell.

1 comment:

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By Dirk Haussecker. All rights reserved.

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