Discrepancy in Claimed Injection Site Reaction Frequency with ISIS-ApoCIII

My fundamental believe as to why RNAi is fundamentally preferable over phosphorothioate (PS) antisense for therapeutic gene knockdown, is that PS antisense involves the saturation of various tissues in the body with a sticky chemistry that is associated with inflammation.  By contrast, with RNAi Therapeutics, you only need to transiently achieve relatively high tissue levels so that enough of the RNAi silencing machinery can be fed with the RNAi triggers.  Unincorporated oligonucleotides can, and usually are, then washed out without much or any loss of efficacy.

Especially in chronic settings and systemic administration, this persistent inflammatory herd raises the specter of multi-organ fibroses and other adverse immune effects, including vasculitis.  The mipomersen briefing docs showed that such concern is warranted, especially with the findings of vasculitis in non-human primates and frequent injection site reactions which, in contrast to ISIS management which routinely characterizes them as ‘cosmetic’ and ‘nuisance’ side effects, should be interpreted as indicators of what might be happening more systemically.

As you also know, I am equally wary of the reliability of ISIS’ forward and backward looking statements.

Obviously, when ISIS reported phase II data from theISIS-ApoCIII study showing a deep 88% knockdown of the target gene and impressive >70% reductions in serum triglycerides, the question of whether this is a real drug or another KYNAMRO/mipo-like dud hinges on its safety profile.  Unfortunately, no hard numbers were provided on this front in the initial press release.  Instead, there was much beating around the bush characterizing them as being very infrequent and mild in nature. 

However, in the conference call, one analyst apparently wasn’t satisfied with this and asked for a straightforward quantification of the injection site reactions (the following is an adaptation of the telcotranscript on Seeking Alpha):

Jim Birchenough – BMO Capital Markets

Yeah. Hi, guys. Congratulations on the data. A few questions…And then just final [third] question, if you could quantify injection site reaction profile and contrast it with KYNAMRO, I think that would be helpful…

Richard S Geary (ISIS Pharmaceuticals)

Good. This is Richard, and thank you for those questions...The third question, I don’t think I got.

Stanley T Crooke

Reactions compare and contrast to KYNAMRO.

Richard S Geary

So you will remember that in our Phase 1 experience we actually compared directly with three weeks study in normals and we saw almost a 90% reduction in the frequency of ISRs.

Stanley T Crooke

Compared to KYNAMRO.

Richard S Geary

Compared to KYNAMRO, and I would say that looking at these Phase 2 studies, this is being replicated very low frequency and much less severity. These are very mild and it’s almost all erythema that resolves very quickly.

Stanley T Crooke

So we’re seeing much more mild and much less frequent injection site reactions in this study as we saw in earlier work. Is that a fair way to say it, Richard?

Richard S Geary

Yes.

A 5-fold exaggeration of the reduction in injection site reactions

So while ISIS did not add much regarding the frequency of injection site reactions in the phase II study, at least a relative number was provided for ISIS-ApoCIIIRx.  Going back to the phase I trial for which the results were recently published (Graham et al. 2013), the following was said about the frequency of injection site reactions:

‘The most common adverse event was mild injection site reaction, a typical response to subcutaneously administered drugs.52 No subject dosed with placebo complained of injection site reactions, al- though 13 of 25 (52%) subjects dosed with ISIS 304801 experienced at least one. Approximately 1 of 6 injections (median, 17%) led to an injection site reaction, the majority of which resolved within an hour.’

To test the veracity of ISIS’ comments, you would then have to dig up the numbers for mipomersen.  In the FDA briefing docs, the following can be found about the frequency of injection site reactions:

‘ISRs were the most commonly reported AE in the clinical development program. In the pooled Phase 3 trials, 84.3% (220/261) of mipomersen-treated individuals experienced 3,683 ISR events and 33.3% (43/129) of individuals in the placebo group experienced 139 ISR events.’

Assuming for simplicity that the 261 subjects in the phase III studies received 52 injections minus X due to drop outs (note: this fudge factor actually favors ISIS’ numbers as it increases the injection site rate for mipo) we arrive at around 3683 injection site reactions from 10,000 injections, i.e. a rate of around 37%.  If ISIS’ comments on the 90% drop in injection site reaction frequency were then true, the rate for ApoCIII should be 3-4% and not 17% (according to ISIS the mipo injection site reaction rate would have to be 170% for the numbers to match up).  In a 13-week trial, a 17% injection site reaction rate also means that the majority of subjects will experience such reactions, some more often and severe than others.

Of course, I am just a molecular biologist and know little math. I therefore look forward to the ISIS bulls or even the company itself to point out where I went wrong in my calculations.

First Antisense Oligo Approved for Gene Knockdown in Liver

In a milestone for antisense oligonucleotide technology, Kynamro (aka mipomersen) yesterday received US regulatory approval for the treatment of homozygous familial hypercholesterolemia (hoFH).  It is the first regulatory approval for a systemically delivered oligonucleotide-based drug addressing a target in the liver, following two locally applied oligonucleotide drugs (aptamer Macugen and antisense oligo Vitravene) that have been approved for ocular diseases.  Considering that next month a TLR oligo-enhanced HepB vaccine by Dynavax could join the ranks of oligonucleotides licensed for medical use, oligo drug technology is rapidly shedding its image as an oddball technology and going mainstream.

Commercial Prospects

The hope, of course, is that Kynamro will also be the first commercially meaningful oligonucleotide considering lackluster sales histories by Macugen and Vitravene.  Favoring such success is the strong pricing power with drugs for orphan indications such as hoFH which is estimated to affect 3000 patients in the US and Europe each.  Small molecule drug Juxtapid by Aegerion for example received approval for the same indication last month and will price at $250.000 per annum.  With 1000 patients on the drug, this would mean sales of $250M already. And with the fudgible definition of symptomatic, instead of strictly genetically defined homoFH and the aggressive ‘friending’ of orphan drug salesforces with disease groups, I expect quite a bit of ‘label creep’ (Aegerion's CEO has indicated that he expects hoFH patients to somewhat respond to PCSK9 inhibitors which I can only explain if the patient population he considers homoFH includes quite a few non-hoFH when defined genetically).

With an expected price for Kynamro of $100k per annum, I optimistically project around $100M in annual sales assuming marketing partner Genzyme can get 1000 patients on drug in the US. With a ~35% profit share, a 50% profit margin and 50% attrition, ISIS Pharmaceuticals would pocket around $10M in annual profit share from this approval in a few years.

Update 30Jan13: It appears that according to a WSJ article (to which I cannot get access), Kynamro will be priced at $176k per year.  This, of course, would significantly improve ISIS profit share assuming same patient numbers treated (possibly 70% profit margin, slightly higher royalty rate in addition to higher sales --> $20-25M p.a.).

   

RNAi versus Antisense for gene knockdown in the liver

To maintain such sales numbers, however, the salesforce will have to fight hard to keep patients on the drug.  During the extension of the phase III study in homoFH, over half of patients  discontinued due to safety and tolerability issues, injection site reactions and liver safety (prompting a Black Box warning) being the main culprits. Having said that, the label for Juxtapid does not look any better, in fact a bit worse with all the intestinal side effects and drug-drug interactions, offset, however, by the increased potency in LDL-c lowering.

As some of the side effects are not target-specific (e.g. the injection site reactions and flu-like symptoms and also some of the liver enzyme elevations which are not fully accounted for by the liver fat elevations), the modest tolerability of and safety concerns with Kynamro (including vasculitis as well as liver and skin cancers especially when considering the preclinical data) raises the question whether systemically delivered phosphorothioate-based antisense technology has much of a future for gene knockdown in the liver also in light of increasing competition from RNAi delivery technologies.  You will not be surprised that I subscribe to the view that among Tekmira’s SNALP and the subcutaneous alternatives by Arrowhead (DPC) and Alnylam (GalNAc), RNAi will become the preferred technology for gene knockdown in the liver.

Whether RNAi or antisense, oligonucleotide therapeutics are here to stay. 

Bullish on RNAi Therapeutics

Attending the Oligonucleotide Therapeutics Society meeting last week in Boston, I could sense a new bullishness around RNAi Therapeutics like I haven’t in a long time.   

Big Pharma: Tipping the Scales in Favor of RNAi Therapeutics

Over the last year, we have been witness to the clinical successes of Tekmira’s SNALP delivery that literally saved the sector.  After nightmarish years, these results had investors enjoy the doubling and tripling of the share prices of companies like Alnylam, Tekmira, and even non-SNALP players such as Silence Therapeutics.

For the next leg of expanding investments in RNAi Therapeutics, a renewed, publicly visible commitment by Big Pharma would be important.  With Genzyme taking a license to Alnylam’s transthyretin amyloidosis program, a first step in that direction has been just made.  On the platform side, it is worth noting that the two most significant Big Pharma players in RNAi Therapeutics, Merck and Novartis, were also represented at the conference.  One can only hope that the current RNAi Therapeutics clinical and scientific tailwind will give their internal champions the ammunition to push the technology into the clinic in the next 2-3 years and therefore escape the Sword of Damocles that surely must have been felt dangling above them.

Unfortunately, if these two companies, like so many others it seems, big and small, insist on using ‘their’ own delivery technologies, chances for that will be much reduced.  With all due respect, but the presentation on RNAi delivery by Merck was just a review of the most advanced systemic delivery technologies, SNALP (Tekmira), DPCs (Arrowhead Research), and GalNAcs (Alnylam) exemplified by Merck’s homebrew versions.  Somebody needs to show me the math behind it- I just don’t get it.  The only explanation for me is pride and the resistance against collaborating after having invested internally so much.

A re-commitment towards RNAi Therapeutics should also be at the expense of ‘naked’ RNaseH antisense.  Although in his keynote speech, Alnylam’s CEO made a point of congratulating ISIS CEO Stan Crooke (sitting in the first row) on the recent mipomersen Advisory Panel, there was considerable talk during the conference about antisense-related toxicity, also as regards the high-affinity versions.   And even Stan Crooke could not help but admit that the RNAi Therapeutics results have ‘exceeded [his] expectations’.  However, since ISIS claims ownership over RNAi Therapeutics, as it does indeed over most of oligonucleotide therapeutics anyway, his pain should be limited if indeed he believes what he is saying [note: Dr. Crooke in discussing the safety of mipomersen went as far as saying that there has been no imbalance in its safety profile compared to placebo, and when there was an imbalance, it was in favor of mipomersen...for a starkly different view, see here].

A Breath of Fresh Air in Delivery

A conference highlight were the new results from Arrowhead Research on their new DPC delivery, a conjugate approach.  Potent gene knockdowns in the liver with an apparently reassuring safety profile in non-human primates using subcutaneous delivery is certainly deserving of some serious attention.  Having had systemic delivery of synthetic RNAi triggers almost for themselves for the last few years, Tekmira seems to be finally getting some company- although in terms of validation, SNALP is still years ahead and more de-risked.  Such increased diversity of approaches should also be good for attracting general interest to the sector as it would be viewed as more vibrant and with more disease opportunities.

5 Reasons to be Bullish on RNAi Therapeutics

1)      Clinical results show that RNAi Therapeutics in Man can be made to work (Tekmira’s SNALP delivery);

2)      RNAi Therapeutics ideally suited to address orphan disease, the hottest category in drug development;

3)      RNAi Therapeutics has taken the lead over RNaseH antisense for gene knockdown;

4)      Big Pharma coming back to RNAi Therapeutics;

      5)      Vibrancy of sector increasing (e.g. recent results on Arrowhead’s DPC technology). 

A Side Note on the Conference

To some degree reflecting the increasing maturity of Oligonucleotide Therapeutics, the 4-day program did not include important programs in the field.  Not only was Tekmira notably missing, but also efforts such as Dynavax’ important HepB vaccine candidate that could soon allow oligonucleotide ‘therapeutics’ to touch many lives.  Moreover, the industry-academia balance was tilted in favor of industry like I have not seen before.   

The Mipomersen Briefing Docs: Gymnotic Delivery Revealed

After Alnylam’s CEO John Maraganore famously failed to deliver on his Big Pharma platform partnership promise in 2009 (aka ‘SRTL’), and ISIS Pharmaceuticals announced a preferred partnership with GSK in March 2010, it seemed that Dr. Maraganore salesmanship was outdone by one of the best biotech salesmen ever: Dr. Stanley Crooke. 

In addition to likely having deprived Alnylam of a deal, what is this salesmanship claim based on?  It is the fact that not all that long ago, antisense technology had fallen out of favor in Big Pharma.  This was because it required large amounts of oligonucleotides and, partly as a result of that, was associated with non-specific immunostimulatory effects.  And this is where the more elegant RNAi Therapeutics was supposed to take over. Despite this poor track record, the technology managed a comeback, ironically partly on the back of RNAi Therapeutics which was seen stumbling at the ‘delivery’ stage.  In some cases out of the frustration of making RNAi delivery work, the 'naked' delivery approach of antisense would be embraced by the likes of GSK, BiogenIdec, Pfizer, Genzyme, and VCs making the application of Santaris' LNA technology the basis of start-up biotechs targeting emerging classes of non-coding RNAs such as microRNAs or long non-coding RNAs.

The reason, however, why I had always favored RNAi as the more ‘natural’ gene silencing modality over antisense is that antisense, to this day, relies on achieving extremely high steady-state tissue concentrations (>100-300mg/kg of liver and kidney tissue e.g., see ISIS TTR patent application US2011/0294868) either by using reactive/sticky chemistries such as the phosphorotioate backbone or more gentle backbones such as the morpholino chemistry that, however, require even larger amounts of oligonucleotides.  

Mipomersen Briefing Docs Surprises

Unfortunately, the publication last week of the FDA Briefing Document related to the new drug application (NDA) for Mipomersen (tradename: KYNAMRO) by ISIS and partner Genzyme, should serve as a reminder that giving an old technology new names such as ‘gymnotic’ or saying that the algorithms now allow for the discovery of much more potent antisense sequences without any new chemistry (despite the fact that narrow tiling had always been practiced) are telltale signs that the biggest change that has occurred was in the marketing department.

The selective disclosure strategy by ISIS Pharmaceuticals on mipomersen has certainly contributed to the impression that antisense technology had indeed made important progress.  Dr. Crooke claimed in a recent interview on Mad Money with Jim Cramer that ISIS had been very transparent with mipomersen.  I could agree that there has been a lot of scientific data released on mipomersen by ISIS and their clinical investigators, but in hindsight this was arguably not for the claimed sake of transparency, but for providing the impression that mipomersen was a safer drug than it probably is. 

Here are a few examples of the ‘surprises’ that were revealed in the Briefing Docs:  

1) Liver Fat: More and Persistent

While the significance of the non-alcohol-related accumulation of fats in the liver in predisposing towards liver fibrosis is still hotly debated among experts, ISIS tried to dispel the still understandable fears about ApoB-knockdown-related fat accumulation in the liver by claiming a) that it was only modest, and b) that feedback mechanisms allowed the liver to adjust and that liver fat would decrease over time.  Supporting the impression that ISIS was concerned about transparency was the publication (Visser et al. 2010) of liver fat data from a 13-week study in a small, 21-patient study population which only showed a trend of such accumulation (median control-adjusted increase from baseline to day 99 of < 1%).  

Compare that to the actual results (as revealed in the Briefing Docs): In study ISIS301012-CS7 and CS12, 61.8% (63/102) in the mipomersen group had a > 5% increase in hepatic fat content.  This already shows that the median increase is definitely higher than 5%, not < 1%. Moreover, in study CS6, 16% had average liver fat of > 20% measured at least once.  30-40% liver fat contents also were not uncommon.  Such values were practically not observed at baseline or in control subjects despite ISIS’ repeated claims that such values are of no concern since NAFLD is so common anyway.

Furthermore, the data such as capture in Figure 10 of the Briefing Document show that there is no basis for claiming that the liver adapts and liver fat contents come down over time.  They only come down after you discontinue treatment.

Suggesting that the fat accumulations could be of clinical significance, a fibrosis-related biomarker score (ELF) was elevated in the mipomersen population.

To be clear, at least the liver fat accumulations (not sure about  the ELF score) is very likely a target-related side effect and cannot be attributed to the phosphorothioate antisense platform per se, but it is an important issue for mipomersen and raises suspicions about the way ISIS Pharmaceuticals has dealt publicly with platform-related safety issues.

2) Partial Clinical Hold: Vasculitis

Were you surprised by the fact that, according to the Briefing Doc, the FDA issued a Partial Clinical Hold for the non-severe LDL patient population in January 2008?  I certainly was taken by surprise and would also think that this should have been disclosed in an SEC filing as a Partial Clinical Hold for your lead program should be considered a material event.  Not only can shareholders be pitied, but also Genzyme which less than a month before invested more than $300M in mipomersen! I cannot imagine that they would have closed such a deal had it known that there was data that would trigger such a Hold (I do not exclude that the data was there under their nose, but in that case it was probably either buried under a pile of paper, or Genzyme just did not do their job well).

Apparently (à Briefing Doc), the ‘final interim report’ from the 52-week monkey tox study that was submitted in June 2007 showed vasculitis (inflammation of the vasculature which can impair blood supply and therefore organ function, possibly leading to organ failure) at clinically relevant doses of 3mg/kg and up, mainly, but not exclusively, in the gastrointestinal tract. Although the Hold was lifted after the actual clinical safety data did not indicate vasculitis to be an issue, subsequent skin biopsies around the injection sites showed an accumulation of inflammatory cells around the vasculature.

Although similar to the liver fat issue, the clinical significance and degree of systemic vasculitis due to phosphorothioate oligonucleotides remains unknown in Man, the potential for sustained inflammatory processes in the entire vasculature is a serious safety concern that needs to be studied in more detail before the technology can be applied to less than the most severe, 'orphan' patient populations- if at all.

3) Liver Enzyme Increases

That mipomersen increased liver enzymes in the serum, a measure of liver tox, has been widely known.  But ISIS used to claim that in a given individual these were one-off findings that could just as well have come after a night of heavy drinking.  By contrast, it seemed to me new news that there were cases where elevated (>3x ULN) liver enzymes were found on at least two subsequent investigations.  In fact, the FDA feels that the liver enzyme increases warrant them be tightly monitored as part of a REMS program should mipomersen be approved in the homoFH population.

4) Injection-Site Reactions and Discontinuations

One of the major marketing tools, and in fact actual draws, of ‘gymnotic delivery’ has been that it can be subcutaneously administered, while the leading RNAi Therapeutics delivery technologies, foremost Tekmira’s SNALP, still rely on intravenous infusion (for most applications at least).  Turns out that injection site reactions ranging from pain, redness, swelling, to skin discolorations and haematomas were a major factor for study drug discontinuations, especially in the open-label phases of the studies which should be indicative of what will happen in a real-world setting.  Overall, 61% of HoFH patients (23 of 38) discontinued study drug during the open-label phase, and 77 of 141 discontinued in the pooled Phase 3 population (including non-hoFH subjects).  Other adverse events attributable to the inflammatory potential of the technology, such as flu-like symptoms, contributed to the high discontinuation rate.

A curious, hitherto undisclosed finding, were injection site recall reactions with mipomersen (but not control).  This refers to an inflammatory reaction at an old injection site when the drug was administered at a new site.  The molecular basis and importance for such recall reactions seem unknown.  In fact, my literature searches suggest that they have almost exclusively been described for the TNF-alpha blocking antibody Enbrel.  However, to me, they once again indicate the systemic inflammatory potential of phosphorothioate antisense chemistry, likely involving adaptive immunity.  Accordingly, 30/50 patients (60%) in the CS5 and 6 studies exhibited mipomersen antibodies compared to none in the control population- another ‘surprise’ that should be applicable to the phosphorothioate platform in general.

5) Carcinogenicity

While there were ~2-3x more cases of tumors in the mipomersen-treated population compared to control, I agree with the reviewers that they are not the basis for concluding that mipomersen increases the risk of developing cancer.  This is because of the nature of the reported cases and the relatively short treatment duration after which many of them occurred.

However, what would worry me more is that in the preclinical carcinogenicity studies in rodents (mice and rats), mipomersen clearly increased cancer risk- despite ISIS’ claim that they have been ‘clean’.  Among the findings were hepatocellular adenoma and subcutaneous tumors.  Having a report by your CRO stating the findings are likely species-specific issues and not applicable to humans, does not mean that the findings are not material in a regulatory sense, especially as they were made during a period at the FDA when the agency was much more risk-averse.  I expect the clinical and preclinical findings to cause carcinogenicity to be included in a REMS program.    

6) Kidney Damage

The liver, spleen, and kidneys are the major sites of phosphorothioate accumulations.  Consequently, it is not surprising that kidney damage has been an important safety concern of such antisense technology.  Although the clinical safety findings did not demonstrate that mipomersen impaired kidney function, the study drug did increase the amount of protein found in the urine (proteinuria).  This finding supports that kidney function remains a safety concern and such monitoring should be included in a REMS.

In summary, the safety findings were not all that surprising given what we know about phosphorothioate safety in animals and study discontinuations by competitor Santaris, very likely due to safety.  However, if you indeed have taken the reassurances by ISIS CEO Dr. Crooke literally, you may be justified in feeling misled.  Even on that count, however, I am not all that surprised, and his salesmanship may indeed be one of ISIS' great assets.  

Disclosure: The author is 'long' the stock ($ISIS).

Clarification: The term 'gymnotic delivery' in the linked paper refers to a specific protocol for optimizing gene knockdown in tissue culture in the absence of assisted delivery.  However, the term has been more broadly used by Santaris to refer to unassisted delivery in general (including clinical applications), obviously in an effort to express that in contrast to phosphorothioate oligonucleotides, RNAi needed assisted delivery.  I found it suspect, however, that they used a new term to refer to an over decade-old industry practice.  In a further clarification, I have not seen ISIS Pharmaceuticals adopt the term either. But clearly, not using (in most cases) assisted delivery has been a greatly exploited marketing tool of the antisense industry built on the back of RNAi Therapeutics.

Obesity Drug Approval to Unlock Low-Hanging RNAi Therapeutics Opportunities

The FDA approval of weight-loss drug Lorcaserin (to be sold as BELVIQ) a week ago symbolizes a recent shift in the regulatory climate from an extremely conservative, risk-averse one (remember Vioxx and Avandia) to one that tries to better balance the safety concern with providing patients and physicians with new treatment options.  This is also good news for the field of RNAi Therapeutics as the technically lowest-hanging fruits happen to be for targeting genes in the liver, an organ rich in well-validated gene targets related to the metabolic and cardiovascular disease, the two therapeutic fields that arguably suffered the most from the risk-averseness as they had grown heavily reliant on biomarkers in favor of outcomes.  Of course, Tekmira’s SNALP delivery technology, already clinically validated for target gene knockdown in the liver (SNALP Works!), is first in line to benefit from the change, although companies like Merck, Arrowhead Research, and Silence Therapeutics are trying hard to replicate Tekmira’s success with similar and also differentiated approaches.

Lorcaserin Symbolic

The approval path of Lorcaserin has been symbolic for the shift in the regulatory climate.  Despite meeting- in large clinical trials- the FDA’s very own guidelines for weight loss efficacy with what was one of the most benign safety profiles that I have seen, the agency, in briefing documents and Advisory Committee meetings alike seemed about to change the goal-post in the middle of the game by demanding greater degrees of weight loss which it was clear Lorcaserin, as a single agent, could never achieve.  To further justify the negative stance on Lorcaserin, theoretical safety concerns, particularly stemming from clinically irrelevant cases of breast cancer in rats were suddenly picked up on.  If you are a scientist, this scenario might sound familiar to you: if a reviewer of a scientific paper does not like your study or even you personally [on a personal note, the term ‘blogger’ is often used here in a derogative way], he/she will always come up with a reason to reject your study.  In other words, as in publishing, also in drug regulation, no matter how good, anything can be made to look bad if that's the motivation.  

To add insult to injury, Lorcaserin’s two main competitors, Qnexa from Vivus and Contrave from Orexigen, came up ahead of Lorcaserin at least from the AdCom meetings 1-2 years ago, despite these formulations being nothing more than the combination of two established ingredients, the type of life-cycle re-formulation strategy that has pushed the pharmaceutical industry and the healthcare system to the brink of financial viability.  

Thankfully, these events prompted a wide public outcry, including vocal, often ridiculed ‘retail’ shareholders which together with the recognition of the enormous unmet medical need (obesity) caused a remarkable turnaround in the regulatory fortunes of the drug climaxing in a broad label with the main restrictions being that Arena Pharmaceuticals and partner Eisai conduct a number of post-marketing cardiovascular outcome and safety studies- reasonable.  Such a preliminary approval process (witness also the Avastin-breast cancer controversy) that post-pones these studies to a post-marketing setting was also in recognition of the fact that demanding them pre-approval would be financially prohibitive for most small and medium-sized pharmaceutical companies. Moreover, the fact that the only new, single agent among the three weight loss contenders happens to be the first one approved, should be further encouragement for innovative drug developers.

What it means for RNAi Therapeutics

The acceptance of biomarkers such as weight loss, LDL-cholesterol, and glycated hemoglobin, together with postponing hard outcomes studies to the post-marketing setting are the two key ingredients that should greatly increase the attractiveness of harnessing the liver-targeting potential of RNAi Therapeutics to go after metabolic and cardiovascular disease opportunities.  What is more, what in the end may have tilted the agency’s opinion in favor of Lorcaserin (in addition to bowing to political pressure) was the fact that the drug not only promoted weight loss, but also provided clear benefits in terms of other biomarkers such as lowering blood sugar levels in diabetic patients. 

RNAi Therapeutics candidates should be particularly well positioned to take advantage of the regulators valuing the totality of the efficacy data rather than myopically focusing on single end-points that may have been met just marginally.  This is because RNAi Therapeutics have the unique potential to simultaneously go after multiple targets (multi-targeting).  At the risk of repeating myself, an RNAi Therapeutic that could reduce not only atherogenic lipids, but also hepatic fat and increase insulin sensitivity should be very welcome in such an environment.   

The experience with ISIS Pharmaceutical’s mipomersen for which an NDA has been submitted recently, however, also shows that while the emerging approach can speed up drug approval, it can also limit the initial market potential (here, the rare homozygous FH population) and costly outcomes trials may be necessary to address wider patient populations.  It can be argued that ISIS and partner Genzyme simply got unlucky as, unlike the European counterpart, the FDA will only accept LDL-cholesterol lowering as a sufficient end-point for the hoFH population; there should be other cases, however, where the first population in such a staged approval process will justify the investment in the drug development program already.    

In this environment, I look forward to TKM-ApoB and ALN-PCS02 being followed by more metabolic/cardiovascular RNAi Therapeutics candidates, particularly of the multi-targeting type, SNALP-delivered, multi-cassette ddRNAi or otherwise.  With the biomarker-based and staged approval approach, it should be possible again for even small companies like Tekmira to bring such programs into later-stage development on their own.

Merck Double-Knockdown Strategy to Ameliorate Toxicity from Mtp and ApoB Inhibition

The signs are that the next RNAi Therapeutics metabolic/cardiovascular disease candidate will be a dual-targeting one.  While the initial attempts in this area were directed at specifically reducing the well-known cardiovascular risk factor LDL-cholesterol (preferred targets: ApoB and PCSK9), it has become quite tempting to exploit the rare opportunity offered by RNAi Therapeutics to target multiple gene targets with just one formulation to both broaden the therapeutic benefits in patients that typically suffer from a plethora of metabolic dysfunctions (obesity, insulin resistance, and hypercholesterolemia to name a few) and to balance the adverse effects that may result from inhibiting certain targets.

Most notable among the latter is the liver fat accumulation following ApoB knockdown.  Clinical studies with ISIS Pharmaceuticals’ antisense compound mipomersen/KYNAMRO have clearly evidenced such liver fat accumulations which were often accompanied by increases in liver enzymes, general indicators of liver toxicity.  These results further are corroborated by similar clinical observations with the small molecule lomitapide by Aegerion targeting microsomal triglyceride transfer protein (Mtp) which acts essentially at the same stage as ApoB in packaging triglycerides and cholesterol for transport out of liver cells into the circulation.  Aegerion obtained this drug candidate from BMS via UPenn as BMS did not want to further develop this compound due to these safety risks.

Both mipomersen and lomipatide have completed phase III studies and new drug applications for approval in the rare genetic disease homozygous familial hypercholesterolemia (hoFH), and in the case of mipo also for severe heterozygous FH have been submitted to the FDA and EMA.   In terms of therapeutic profile, mipomersen seems to have the edge as, being a phosphorothioate antisense compound, it preferentially accumulates in the liver.  Consequently, it does not cause the side effects resulting from the intestinal inhibition of this pathway that  have been observed with small molecule lomatipe (note: SNALP-delivered RNAi Therapeutics should have similar benefits over small molecules).  Moreover, mipomersen not only lowers LDLc, but also moderately reduces the independent cardiovascular risk factor Lp(a).   Although not a prospective primary goal of mipomersen clinical development, incidental positive findings like this one can go a long way in having regulators take a benevolent look at drug candidates.  This can be seen in the related obesity space where one of the attractive benefits of Arena Pharmaceutical's lorcaserin is that it lowers blood glucose levels.

Obviously, there should be plenty of potential gene targets involved in triglyceride synthesis and utilization/oxidation that could be exploited to concomitantly lower triglyceride content in ApoB/Mtp-inhibited livers while maintaining LDLc-lowering.

Merck Tests ApoB and Mtp Knockdown, Finds Mtp-DGAT Co-Knockdown Promising

Tep and colleagues from Merck published a paper on a study that tested whether an RNAi co-knockdown strategy could be implemented to alleviate the liver fat accumulations due to Mtp and ApoB inhibition.  To be clear, Merck did not state that they have firm intentions of developing such a co-knockdown strategy, but nevertheless noted that such a strategy would have the advantage of  not having to ‘add[ ] a novel compound on top of an approved drug’ and that dual-targeting RNAi Therapeutics candidates are already in clinical development, therefore paving the regulatory path (see ALN-VSP02, and TKM-EBOLA).

In a first step the scientists confirmed the liver fat accumulation following Mtp and ApoB siRNA knockdown.  Not only were they of similar magnitude, the effects of the two knockdowns where essentially the same in almost every other investigated regard.  Notably, there was no reduction in liver fat accumulation following prolonged siRNA treatment as one might have expected based on claims by ISIS Pharmaceuticals of liver fat normalizations with time, but widespread changes in the expression of lipid-related genes were nevertheless observed- this time consistent with claims by ISIS Pharmaceuticals.

Among the genes that were downregulated following Mtp siRNA treatment, presumably as a result of negative feedback, was DGAT2, a key enzyme in triglyceride synthesis that is also thought to represent an important regulatory node in lipid metabolism (e.g. by promoting fatty acid oxidation).  Reasoning that further reducing DGAT2 with liposomally formulated siRNAs may lead to a measurable reduction in liver fat, they then co-formulated the Mtp siRNA with a DGAT2 siRNA and injected them into mice.  Indeed, this resulted in not only the expected LDL-cholesterol reduction, but liver triglyceride increases were mitigated.  According to data not shown, it was claimed that the same beneficial effect could not be observed with an ApoB-DGAT2 siRNA combination, suggesting that Mtp may be the better target for co-knockdown strategies.

It should be added, however, that the day 14 time-point data these conclusions were based on were somewhat of an outlier as at this time the co-formulation with DGAT2 siRNA reduced the LDLc-lowering potency of Mtp knockdown.  On the other hand, the scientists report (also in data not shown) that they tested the co-inhibition strategy using DNA-directed RNAi and thus validated this conclusion.    Moreover, given the multitude of genes involved in lipid metabolism, the Merck scientists stated that the Mtp-DGAT2 co-knockdown is a proof-of-concept and that other targets besides DGAT2 are also being considered (especially Gpat1).

Given Tekmira’s interest in ApoB as a target and recent LNP work by Alnylam and their PCSK9 collaborators from UT Southwestern (Horton, Goldstein) on SCAP knockdown to alleviate hepatic steatosis and Alnylam's general interest in co-knockdown for metabolic applications, Merck will not be alone in their endeavor of finding an RNAi Therapeutic candidate that can do it all, LDLc lowering, triglyceride lowering, and more.  Given that SNALP technology would likely be used in such a clinical program, this could particularly benefit Tekmira.  

New Antibody Data Indicate Tough Battle for RNAi Therapeutic PCSK9 Approach

The past week has been a busy one for the hypercholesterolemia field. New clinical data for PCSK9-targeting monoclonal antibodies from Amgen and Regeneron/Sanofi-Aventis were presented at the 2012 American College of Cardiology meeting, while ISIS/Sanofi-Aventis separately presented long-term efficacy, and especially safety data on the ApoB antisense compound mipomersen (aka KYNAMRO) for which marketing applications have now been submitted in Europe and the US. As hypercholesterolemia also represents a significant medical and commercial opportunity for RNAi Therapeutics due to the advances in knocking down genes in the liver, I will briefly summarize the new data and discuss some of the implications for RNAi approaches, including the phase I candidate ALN-PCS02 by Alnylam.

If there ever were doubts as to the commercial attractiveness of PCSK9 as a target for treating high cholesterol, last week dispelled them all. When it seems that all the thought leaders in the field, including famed cardiologist Steven Nissen, otherwise known for his ultra-critical views of certain medicines, and Wall Street (expected annual sales as a class of up to $20B thrown out) hail the data as proof that PCSK9 will be the final nail in the hypercholesterolemia coffin and thus throw their support behind the class, the commercial success of PCSK9-targeting therapeutics seems a foregone conclusion.

Although pretty much every large pharmaceutical company sports a PCSK9-targeting antibody, the excitement this time centered around the phase II data of Regeneron’s/Sanofi-Aventis’ REGN727 and phase I data of Amgen’s AMG145.

The REGN727 phase II 8-12 week multi-dose studies were conducted in close to 300 patients with elevated ‘bad’ LDL-cholesterol (LDLc) on statins. Depending on the amount and schedule of antibody administered, mean LDLc reductions (note: it is not entirely clear to me whether this refers to the LDLc reduction over time, or the peak LDLc reductions) of 40-73% were achieved. Interestingly, one press report said that ‘727 suffered from relatively short-lived activity such that subcutaneous administrations every 2 weeks would be required.

The phase I studies with ‘727, just published in NEJM (Stein et al.) indicated that the apparent rebound effect after 2 weeks may be due to the concomitant use of statins and that without statins, 50-55% persistent LDLc reductions can be achieved with close to 4-week dosing intervals. This is relevant for example for the statin-intolerant population. With statins, that type of persistent knockdown (more on the higher end of that range) would probably require every 2 week dosing.

AMG145 seemed to attract even more excitement than '727. In the 6 to 8-week phase I studies in around 100 patients taking statins, mean LDLc reductions of 63-75% were observed. These numbers indicate more potent, and likely more persistent LDLc lowering compared to REGN727, although without having seen the LDLc response curves over time, it is difficult to conclude that for sure.

Route of administration and dosing frequency are often cited as important competitive criteria for this class of drugs. In the case of ALN-PCS02 which is enabled by Tekmira’s SNALP technology, the current data indicate that a range of 40-55% persistent LDLc reductions with intravenous dosing every 4 weeks are conceivable. This, however, would require further improvements in potency over the 0.25mg/kg dose level which was the highest dose for which data was presented by Alnylam at their early January update. For this indication, it will also be important to wean the SNALP formulation off the transient immune suppression currently used. This would not only address criticisms that such immune suppressions carry risks, but it also would likely get rid of the observed PCSK9 rebound effect that was apparently linked to it and would thus contribute to prolonging the efficacy.

Of course, an important wildcard in the competition between MAbs and RNAi pertains to the safety of each drug candidate, especially when they are used long-term. The monoclonal antibodies seem to perform quite well in this regard in the short-term, albeit multi-dose studies. RNAi, however, has the theoretical advantage in that it does not involve the formation of antibody-PCSK9 complexes which could eventually have an impact on both long-term safety and efficacy/dosing frequency.

In retrospect, RNAi has picked a tough battle here. As a target that acts extracellularly, readily accessible from the blood, it seems an ideal target for monoclonal antibodies and thus falls outside the undruggable target space that currently still drives the interest of large pharmaceutical companies in RNAi Therapeutic development. On the other hand, the PCSK9 field is populated with antibody approaches, and should there be antibody-specific class adverse effects, RNAi could be the last one standing (note: the antisense candidates by ISIS and Santaris have already dropped out of the race, at least for now), something that one of the few Big Pharma/Biotech that has not yet invested in a PCSK9 candidate may value from a strategic point of view alone (RE partnering).

Meanwhile, the mipomersen extension study data presented this week suggest that the high drop-out rates and liver fat accumulations* (both possibly linked to some extent) at modest ~30% LDLc reductions make it a niche drug for the very small indication of homozygous familial hypercholesterolemia in the US and Europe, and possibly severe hypercholesterolemia in Europe. Although ISIS continues to claim that the liver fat accumulations normalize after reaching maximum median increases of +13% over baseline at week 52 (note: according to the mipo-related Visser et al. 2009 study, 5.6% absolute intrahepatic triglyceride contents are considered the upper-limit of normal), the absolute values would call for caution, especially when there are outliers in whom almost half the liver consists of fat. In the related conference call, ISIS further claimed that the apparent normalizations were not the result of the patients that discontinued mipomersen (possibly due to high liver fat contents). However, since ISIS has a history of erring on the side of optimism when it comes to mipomersen safety and tolerability, I’d like to see the liver fat-related sub-group analyses that take into account the discontinuations, dose reductions and interruptions.

The liver fat data may also mean that ApoB is unlikely to be a suitable stand-alone target for an RNAi Therapeutic, especially if even more pronounced ApoB knockdowns can be achieved than with mipomersen. Consequently, in order to exploit the therapeutic utility of ApoB as the critical protein of atherogenic lipoproteins, an ApoB-targeting RNAi Therapeutic should involve at least one other target gene which will also reduce liver fat content. It remains to be seen whether ApoC-III can be that target.

* Note: Despite the caution expressed in this article, I should add that there is general controversy about the relevance of simply elevated liver fat (NAFLD) in the absence of inflammation.

Merck Seeks to Optimize Value of ApoB as Target for Hypercholesterolemia with Combinatorial RNAi Therapeutics

A series of recent papers (e.g. Ason et al. 1; Tadin-Strapps et al.; Ason et al. 2) shows that Merck wishes to use RNAi Therapeutics for the treatment of hypercholesterolemia, a precursor of cardiovascular disease. Despite the success that widely prescribed drugs such as statins have had in lowering bad cholesterol, there are still many patients in need of additional treatment options, patients that either have very high cholesterol levels to start off with or those that do not respond to or tolerate these drugs. As a result, interest in the pharmaceutical industry remains high in developing new approaches to treat these underserved patient populations.

The Pros and Cons of ApoB as a Target

ApoB has emerged as a very attractive, hitherto undruggable target in this endeavor, and indeed ISIS in partnership with Sanofi-Aventis are currently knocking on regulators’ doors to get their ApoB-targeting RNaseH-antisense drug mipomersen (commercial name: Kynamro) approved for familial hypercholesterolemia. Meanwhile, Tekmira and apparently Merck are in the early stages of developing ApoB-based RNAi Therapeutics for hypercholesterolemia.

What makes ApoB such an attractive target is that it is the critical protein component of bad LDL cholesterol (LDLc) and knocking it down therefore very potently reduces LDLc levels in the blood. Not only that, it seems that through the wonders of sophisticated feedback control mechanisms of lipid metabolism, essentially all other atherogenic lipids are reduced, too, following ApoB knockdown (e.g. Tadin-Strapps). There remain, however, two concerns with ApoB as a target.

The first one relates to the observation that in most rodent models, not only all the atherogenic lipids are reduced, but also the ‘good’ HDL-cholesterol which is responsible for reverse cholesterol transport from the plaques (where they are dangerous) back to the liver for excretion in bile (which is where they belong to). Research by Merck, of course using LNP technology, shows that when ApoB is knocked down by ~95%, both HDLc and LDLc where reduced by more than 2/3 (Tadin-Strapps et al. 2011; 79-90% non-HDLc lowering and 67-78% HDLc lowering in Ason et al). This was highly unlikely due to an off-target effect as various ApoB-targeting siRNAs exhibited this phenotype while non-targeting LNP formulations did not.

Nevertheless, it is unclear whether these rodent and similar non-human primate findings translate into humans, and what ApoB knockdown levels would need to be achieved to start seeing an effect on HDL. Mipomersen e.g. reduces LDLc by about a third and does not seem to affect HDLc in humans. The Merck scientists also speculate that the HDLc reduction simply reflects that in the absence of LDLc, ApoE redistributes to HDLc leading to their more rapid uptake in the liver. Therefore, despite the mantra that it is all about the HDL:LDL ratio, HDLc reductions via this route would actually be positive.

The second, probably more pressing concern is that ApoB inhibition leads to a failure to export lipids from and their accumulation in the liver, a condition known as hepatosteatosis or ‘fatty liver’. This has not only been observed in pre-clinical studies of ApoB knockdown, but was also observed in the mipomersen clinical studies (Visser et al. 2010). ISIS Pharmaceuticals, the discoverers behind mipomersen, argue that this accumulation is likely to be temporary only as compensatory genetic circuits get switched on to reverse the phenotype, a mechanism that is supported by Merck's own gene expression analysis. Moreover, it has yet to be shown that ApoB-related fatty liver predisposes to the development of liver fibrosis and ultimately liver failure or cancer which is really why we care about fatty liver in the first place.

Enhancing the Therapeutic Profile of ApoB-targeting Drugs

Giving up on ApoB in hypercholesterolemia because of the fatty liver concerns would mean forfeiting the potential of one of the most if not the most potent target in the hypercholesterolemia space. I therefore fully agree with the strategy by Merck to exploit the combinatorial potential of RNAi Therapeutics to optimize the profile of an ApoB-targeting RNAi Therapeutic, a strategy that I would fully expect of Tekmira to be evaluating as well.

The combinatorial potential of RNAi Therapeutics is one of the major attractions of this technology. Because of the almost identical pharmacological behaviors of siRNAs, it is relatively simple to employ multiple instead of just a single siRNA payload in an RNAi Therapeutic. This is particularly useful for complex diseases such as metabolic syndromes and diseases that involve resistance/escape such as cancer and viral infections. ALN-VSP02 is a dual-targeting example in oncology that is already in the clinic, and Tekmira’s Ebola RNAi Therapeutic candidate slated to enter the clinic in early 2012 will also involve at least two different RNAi triggers.

You can thus imagine that knocking down a gene along ApoB that leads to increased lipid excretion via the bile, increased fat oxidation in the liver, or redu­ced hepatic fat synthesis or reduced uptake of dietary fats in the liver, would greatly enhance the therapeutic profile of an ApoB-based drug by countering the development of fatty liver. It is the latter approach that Ason and colleagues from Merck took in their recent paper by targeting fatty acid transport protein 5 (Fatp5) alongside ApoB as Fatp5 had been described, also through the elegant application of ddRNAi, to reverse diet-induced hepatosteatosis.­

To study the effect of Fatp5 co-knockdown on ApoB-induced fatty liver, the researchers formulated both siRNAs into LNPs and infused them into mice. Both genes were knocked down efficiently (89-95%) and as you can imagine, at these ApoB knockdown levels, the fatty liver phenotype was quite robust. Predicted Fatp5-dependent phenotypes, such as an almost 1000-fold increase in the ratio of unconjugated to conjugated bile acids in the bile, were also observed (Fatp5 plays a role in bile acid conjugation) confirming the functional knockdown of both ApoB and Fatp5.

Unfortunately, despite the potent knockdown of Fatp5, the ApoB-dependent fatty liver phenotype was not reversed in the mice which were fed a ‘Western low-fat diet’. It therefore appears that Fatp5 intervention is only useful for diet-induced fatty liver, and that approaches specific to fat excretion or fatty acid oxidation in the liver will be more promising. Nevertheless, the scientists seem to be on the right track, and with SNALP siRNA delivery, it should be relatively easy to characterize other candidate genes. Indeed, due to competition, the Mercks, Tekmiras, and Alnylams may not necessarily want to disclose their magic siRNA cocktail.

So as we are on the eve of seeing mipomersen being approved as the first ApoB-targeting compound for the treatment of hypercholesterolemia, a second generation of ApoB-targeting RNAi Therapeutics are being readied that not only aim at incremental improvements in potency and dosing frequency, but completely rehaul the therapeutic profile of ApoB-based therapeutics.

Mipomersen Efficacy Surprises to the Upside, on Track to Become First Commercially Meaningful Antisense Therapeutic

ISIS Pharmaceuticals and co-development partner Genzyme reported today top-line data from the final 2 out of 4 phase III studies with the ApoB-targeting antisense compound mipomersen for the treatment of hypercholesterolemia. The efficacy results came in above my lowered expectations and support mipomersen to be an attractive treatment option for the many patients with severe hypercholesterolemia for which current care is still inadequate and who are therefore at a high risk of suffering cardiovascular events. Further studies, however, will be needed to better understand the clinical relevance of the observed liver enzyme and fat elevations.

As I wrote earlier this year, the first 2 phase III studies in patients with homozygous (25% LDL-cholesterol reductions) and heterozygous (28% LDLc reductions) familial hypercholesterolemia raised concerns that the efficacy of mipomersen could be less than one might have expected based on the initial phase I/II trial results. Couple this with a number of safety and tolerability issues such as elevated liver enzymes, fat accumulation, plus wide-spread injection site and flu-like reactions, the overall profile may not have looked that attractive. The 36-37% reductions in LDLc reported today for the severe hypercholesterolemic and high-risk/high-cholesterol patient populations, however, put efficacy concerns to rest, and it is possible that intact LDL-receptor function contributes to LDLc lowering, somewhat similar to statins.

Actually, due to the high drop-out rates in the latest studies (31-41% for those on drug), the LDLc reductions are likely to be quite a bit higher, at least on par or superior to LDL-apheresis which many of these patients are eligible for, but not widely used due to cost and safety/tolerability/patient convenience reasons. Moreover, the on-target efficacy, and not 2^nd gen antisense as a class, may indeed be responsible for some of the safety issues as the companies strongly suggest that the liver enzyme and fat elevations were in fact correlated with the speed and degree of the LDLc reductions. In some cases apparently more than 80% reductions in LDLc were achieved!

If this were the case, one can easily imagine that in real life, patients could be simply monitored for liver enzymes and fat content as they go on drug, similar to what is already routine for other widely used drugs such as warfarin. Although clearly something that regulatory agencies will want to see studied further (e.g. the ~200 persons that have received full 26-week course of drug may alone not be sufficient to argue against liver tox based on Hy’s Law), at this point it is actually not clear to what degree ApoB knockdown-related enzyme and fat elevations would be clinically relevant. The strategy of the companies to pursue a step-wise filing strategy starting with the highest risk patient populations (planned for early 2011) before seeking to expand the label is therefore very reasonable. For commercial success, the severe hypercholesterolemia population should be key and could already be part of the first filing cohort.

SNALP-ApoB in light of mipomersen data

Now a few words on how the mipomersen results may impact Tekmira’s RNAi Therapeutics candidate SNALP-ApoB which targets the same gene as mipomersen for the treatment of hypercholesterolemia. Assuming that liver enzyme and particularly fat elevations are indeed a function of ApoB knockdown, then some of the same strategies such as gradual dose adjustments may be applicable. In general, as the runner-up, Tekmira has a lot of valuable lessons to learn from mipomersen especially with regard to its regulatory path.

At the same time, to differentiate itself in the market, Tekmira may also want to take advantage of some of the challenges that mipomersen is encountering when it comes to drug tolerability, particularly the injection site reactions and flu-like symptoms that appear to be responsible for quite a few of the study drop-outs and where I believe that SNALP-ApoB could do better. Although I had never thought that being intravenously administered as opposed to the subcutaneous administration of mipomersen would be a major issue, competitive or otherwise, for the high-risk patient populations we are talking about, the fact that ISIS and Genzyme are now considering daily injections as an option to address the injection site reactions even makes intravenous infusion every 2-4 weeks look like a competitive advantage now.

Meanwhile, due to the satisfactory efficacy of mipomersen and the fact that you probably don’t want to overdo it with lowering ApoB as long as it is in the 32-40% range, efficacy should not be too much of a differentiating factor.

All of this is in no way to suggest that the current value of SNALP-ApoB is comparable to ISIS’ mipomersen. Tekmira has yet to enter the clinic with its improved SNALP-ApoB candidate and we all know that clinical development is fraught with surprises. In any case, it is quite satisfying to see oligonucleotide therapeutics progress in the clinic on so many fronts and I wish ISIS and Genzyme well for the commercialization of mipomersen as it would also reflect well on the commercial value of the entire space in general.

Recent Mipomersen Publication Questions Company Credibility

As you may remember, I had become quite bullish about ISIS the stock for the potential of its lead drug candidate, the ApoB-antisense inhibitor mipomersen for the treatment of hypercholesterolemia, to surprise to the upside. Based on the combined phase I and II data, the recent phase III data in the homozygous and heterozygous familial hypercholesterolemia populations appeared to have been on the lower end (~25-30% LDL-c reductions) of what I thought might be the true efficacy of mipomersen and maybe influenced by the genetic background of those patients. More importantly, the rate with which patients from these earlier studies were supposed to have entered the open-label extension studies and the apparent absence of increased safety liabilities with consequent prolonged dosing made the extent of the analyst scrutiny of the liver enzyme elevations appear overly alarmist.

Well, so I thought and was waiting for the release of the data from the phase III trial in the patients with severe hypercholesterolemia, the patient population with arguably the largest commercial potential for mipomersen, when, without much, or should I say any fanfare, a paper (Akdim et al, 2010) on a phase II study for which top-line data had been announced in a press release in November 2007 came out. I have followed biotech long enough now to know that companies like to put their topline data in the best possible light which is usually followed by the subsequent revelation of a few warts here and there. In light of the published data, however, I found in this case the take-home message of the press release to have been sufficiently misleading to warrant this blog entry and take back some of my optimism with regard to mipomersen…both efficacy-wise and, more significantly, with respect to safety.

The November 2007 press release which can be found here reported on the efficacy of ApoB and LDL-cholesterol lowering following 13 weeks of treatment at the important 200mg/week dosage which forms the basis for the current registration trials to be 42% and 48% reductions, respectively. What struck me a little bit as odd at the time, but interpreted as rather a sign of strength of mipo’s safety, was that no trial-specific safety data were offered. Instead, the safety data in that press release was an ‘integrated safety analysis’ comprising all the mipomersen studies until that date which were largely short-term studies.

This analysis claimed that, while on treatment, only 3% of the more than 250 patients exposed to mipomersen had experienced ALT elevations of 3-5x upper-limit of normal (ULN), the same percentage as in the combined placebo group, and none experienced more than 5x ULN. Taking into account also the follow-up periods (‘entire study period), the numbers would increase to 5% (placebo) and 7% (mipomersen), a slight, but not worrisome increase it would seem. Only by studying the tables, one would have noticed that there was one case of >5x ULN that apparently occurred during the follow-up of dosing part of the study (‘entire study period’). Injection site reactions that, as we now know, poses a number of development challenges for ISIS/Genzyme (soon daily injections?), were mentioned as a side-effect but characterized as ‘cosmetic inconveniences’ of no medical concern.

The fact that there were 2 more patients in the Akdim et al. paper than in the press release for the 200mg cohort could be due to many things (including drop-outs), but it is quite unfortunate that with the enlarged patient group LDL-cholesterol lowering suddenly would drop from the 48% in the PR to 36% in the paper. Well, 36% should be a degree of knockdown that the company should be able to live with, but sets off alarm bells that maybe some of the other data could have been presented in an overly positive light as well.

And indeed this is my conclusion after seeing the safety data: 5 out of the 10 patients (granted a small population, but this is 50%, nothing like the 3-7% mentioned in the press release!) in the 13-week 200mg cohort had an ALT increase of >3X ULN, 4 of which on 2 consecutive occasions! One patient even experienced an increase of >5x ULN and subsequently dropped out before all planned doses had been administered (which was then included in the ‘entire study period’ group, but not on-treatment group). Also not mentioned in the original press release was the fact that the ‘cosmetic’ injection site reactions applied to almost all patients receiving mipomersen (much, much less in placebo obviously) and that these accounted for 2 drop-outs in the 10-patient 200mg cohort.

Everybody, of course, has to form his/her own opinion about how much to rely on press releases reporting top-line clinical trial data. The way these phase II data were handled, however, rocks my confidence in how much to trust management’s contention that the wide-spread mipomersen concerns are ill-founded. The company does not have to be surprised that its credibility in the investment world is what it is and will be difficult to repair without structural changes. This is unfortunate, because I believe ISIS has otherwise made an admirable contribution to the development of oligonucleotide-based therapeutics.

PS: The purpose of this blog entry is not beat up on ISIS for the sake of it. Unfortunately, attempts to resolve my concerns first with the company directly failed as an email to ISIS investors relations (info@isisph.com) two days ago remained unreplied to.