Preclinical Data Do Not Instill Confidence in iCo Therapeutics Trial Outcome

Oligonucleotide Therapeutics investors keen on playing binary events such as clinical trial read-outs should have the phase II iDEAL study of RNaseH antisense compound iCo-007 in diabetic macular edema (DME) on their radars.  This 2^nd generation compound targeting c-Raf had been discovered by ISIS Pharmaceuticals and was then licensed to iCo Therapeutics.

The outcome of that trial will also serve as a proxy for the utility of RNaseH antisense for ocular indications, although higher-affinity chemistries might be expected to achieve superior results. In January, Roche gave their nod of approval to this approach in signing a partnership with Danish LNA company Santaris.

In trying to predict the outcome of the iDEAL study, I focused on the dose regimen in the trial in light of the preclinical data.  Once again, given that Oligonucleotide Therapeutics enjoy virtually unlimited target space, I typically give the target the benefit of the doubt.  To be successful, however, you need both a good target and sufficient targeting.

Preclinical studies

Similar to OGX-011 discussed recently, the history of iCo-007 goes back to the time when ISIS transitioned to second-generation 2’MOE gapmer chemistry.  Following failure in clinical studies for cancer indications with first-generation chemistry, the antisense compound was converted into 2^nd generation chemistry with the same sequence and re-positioned for ocular indications.

In a seminal study by Danis et al. from 2003, a pig-specific anti-c-Raf sequence (ISIS 107189) was tested in pigs for c-Raf knockdown and a retinal vein occlusion model of neovascularization (c-Raf is thought to play a role in the neovascularization aspect of DME, e.g. downstream of VEGF signaling).

Disappointingly, regardless of whether 34ug or 180ug of antisense were injected into the pig eyes, there mere 40% target gene knockdowns were observed.

Of course, it would have been more insightful if the human sequence, i.e. iCo-007, had been evaluated in an animal efficacy model. Although I looked in vain for such data, a 2009 analyst note by Versant noted that in a mouse model this had indeed been done.  Unfortunately, the knockdown, again, was merely 40%:

iCo-007 preclinical data was encouraging and was generated by partner Isis prior

to out-licensing the drug to iCo. In mice experiencing new ocular blood vessel

growth, Isis administered iCo-007 (then called ISIS 13650) to one eye and saline

to the other in two separate injections, one administered seven days before

blood vessel growth commenced, and then at onset of growth. Three days after

antisense dosing, c-raf kinase mRNA levels in the eye were reduced by 40% but

were unaffected in the saline-treated eye, and after seven days, c-raf kinase

mRNA levels were still reduced from baseline by 30%.

Question marks over phase II study design

The phase II DME study is testing 350ug and 700ug iCo-007 either as monotherapy or in combination with anti-VEGF antibody Lucentis or laser photocoagulation.   

Although 350ug and 700ug in humans appear to be higher relative doses than 34ug and 180ug in pigs, given that there was no dose response in pigs I am not sure why we should expect much increased c-Raf knockdown potencies in the phase II study.

Another cause for concern is the fact that the 208 subject study appears to lack a control group according to the clinicaltrials.gov entry.  So be prepared for positive headlines and fanciful comparisons to historical controls, similar to the ‘positive’ results from the uncontrolled phase I study.  

Altogether, given the weak preclinical data and the questionable phase II trial design, I remain highly skeptical that truly medically positive results, barring non-specific anti-angiogenic effects due to immunostimulation of the antisense molecule, will be forthcoming.   

RNAi and Antisense Targeting the Same Gene: Not a Zero-Sum Game

Transthyretin-mediated amyloidosis has become the single-most important factor for the 3-5 year valuation of certainly Alnylam, and possibly ISIS Pharmaceuticals as well. After TTR, Z-alpha-1-antitrypsin (Z-AAT) is gearing up as the next Alnylam(RNAi)-ISIS(antisense) battleground. Expect to hear competitive language from the two camps why their approach will prove superior over the other.  It is, however, worth keeping in mind that having two candidates race towards approval can also have significant pie-enlarging benefits.

Raising Awareness and Pressuring Regulators

A good competition will attract attention, from patient groups, physicians, regulators, and the investor community.  Patient groups and physicians will be primed that after years of lacking treatment options, the time for change has come.  We have seen this with the trifecta ofweight-loss drug candidates, two of which have recently been virtually willed into approval.  Given the enormous problem of obesity, it became politically untenable to further withhold treatment options.  Eventually, the regulators were forced to give in to the pressure despite their original objections over safety.

Closer to home, similar awareness and pressure is being brought to bear on getting exon-skipping oligonucleotides approved for the treatment of Duchenne Muscular Dystrophy, stoked by the competition between Prosensa/GSK and Sarepta .  If you caution about hurried, aka accelerated approval, then you are readily labeled as a heartless misanthrope.  Similarly, the homozygous familial hypercholesterolemia population has already been educated, targeted, and friended by both patient-access specialist Genzyme and competitor Aegerion and probably strongly expect the new drug approvals.  

Understand that these comments are not meant to be judgments on the respective drug candidates, but just the way I view current dynamics.  In fact, I agree that developing drugs for many of the rare and severe (orphan) diseases requires more risk-taking, usually biomarker-based approaches, and that not too long ago patient needs were not sufficiently considered in a highly risk-averse regulatory climate.

The TTR Amyloidosis Race

Given that Pfizer’s drug candidate tafamidis does not appear about to revolutionize the treatment of TTR amyloidosis, I see similar pressure building for the approvals of gene knockdown approaches ALN-TTR02 and ISIS-TTRRx in 2015-6.  The intense competition between ISIS and Alnylam will provide good fodder for the press (just as it does for this blog), engage the minds and pad the pockets of key opinion leaders and consequently raise the expectations of the public and hopes of those suffering from the disease.

While I have 2015-6 approvals baked into my projections of the RNAi Therapeutics story, I wouldn’t mind a year’s delay if the competitive dynamics would allow for it.  In fact, I expect the FDA to manipulate the process in a way that both drug candidates will come before an AdCom panel together, making the obsession with speed over good science even more so nonsensical.

My problem with ISIS and GSK speeding straight into a phase III study after a single phase I study is that they do not seem to have identified a suitable dosing regimen: 400mg/week good efficacy (-81% knockdown), but probably too high a dose from what we know about the safety of phosphorothioate oligonucleotides; 200mg/week could fare better in terms of safety, but has shown only modest knockdown efficacy (-44% knockdown).  In my opinion, another dose-finding study would be in order under normal circumstances.

[Update 29Nov2012: The Clinicaltrials.gov entry for the upcoming phaseII/III ISIS-TTRRx trial shows that the companies have chosen the stab-in-the-dark 300mg/week dose.  Although the January 2012 phase I results press release made no mention of such a cohort, the June 2012 Annual Shareholder Meeting TTR poster shows data from a 300mg cohort (~70% knockdown).  Unlike all the other cohorts were 90+ day data, the 300mg cohort data was less than 50 days.  It thus looks like a 300mg cohort was included post-hoc. Unfortunately, ISIS has chosen not to list the phase I trial on clinicaltrials.gov.]

This concern over uncertain dosing schedules also applies to Alnylam's ALN-TTR02 (-87% peak knockdown, -67% knockdown after 28 days following single dose) where the current ‘multi-dose’ phase II study only seems to cover two doses.  You would hope that Alnylam presses hard to amend the study to include further doses to gain more experience with the repeat-dosing pharmacology of ALN-TTR02 before betting their house on a single pivotal phase III trial.

Once approvals are obtained, however, the beneficial aspects of competition should disappear quickly especially when small orphan disease populations are involved.  But until then, the race towards approval should free energies allowing TTR amyloidosis to become the first real commercial success story of either RNAi Therapeutics or RNaseH antisense.

Who do you think will win the TTR race? Take part in the survey (upper right hand corner).