As Ebola Spreads Fear in Western Africa, Pressure Mounts to Deploy RNAi Antiviral

A day or so following reassurances by the Guinean authorities that the Ebola virus outbreak had been contained and was under control, news is making the rounds of confirmed lethal cases in Conakry, the 2 million capital city of the country, and in neighboring countries in Western Africa.  With the death toll rising, the disease spreading internationally, and the virus paralyzing affected areas, pressure is mounting to call in an RNAi Therapeutic which has proven to be effective in the most stringent efficacy models possible.  66 are thought to have died from the disease by now, at least 4 of which are healthcare workers.

The therapeutic, developed by Tekmira Pharmaceuticals and funded by a $140M contract from the US Department of Defense, has shown 100% post-exposure survival in monkeys infected with the otherwise highly (90%) lethal Zaire strain of the virus.  This is the same virus ravaging through Western Africa right now.  Because of this, the Ebola therapeutic which targets two viral sequences simultaneously and which entered phase I in-man studies earlier this year, there is a very high likelihood that TKM-Ebola will be applicable in this situation.

Only days ago, TKM-Ebola was bestowed fast-track status by the FDA.

Under normal circumstances, licensure of TKM-Ebola would follow the Animal Rule.  According to the Animal Rule, treatments for diseases for which it is either impractical or unethical to conduct efficacy studies, can be approved by the US FDA if sufficient efficacy can be demonstrated in stringent animal models (monkeys here) and human safety at corresponding dose levels.  Ebola obviously is a candidate for the Animal Rule since experimental infections of humans cannot be done ethically and natural outbreaks are so rare and unpredictable.

Following the demonstrations of animal efficacy, the ongoing single- and multi-dose ascending phase I in-man study for which the single-dose phase appears to have already concluded is designed to confirm such safety.  To make sure that the findings are robust, this is typically followed by larger animal efficacy and human safety studies.  At this point (~2016/7), the FDA would make its decision regarding licensure which would lead to stockpiling orders from the US government for preparedness against bioterrorist attacks.

Arguments for deployment of TKM-Ebola in Western Africa

Although TKM-Ebola has not completed the formal requirements under the Animal Rule, it is fair to assume that TKM-Ebola, the most advanced Ebola anti-viral in development, will do more good than harm in a disease without alternatives besides supportive care.  With a lethality of 80-90%, I would certainly take my chances.

A deployment would serve at least two purposes.  Firstly, it would give us a chance to confirm the effectiveness of the RNAi Therapeutic in actual humans.  In addition to the scientific value, if I were the US government, I would be eager to take advantage of the unique opportunity at testing efficacy before spending billions on an agent for which there is only theoretical human efficacy.

Secondly, having TKM-Ebola as a standby in hospitals would help restore some calm and confidence, especially among the healthcare workers which need to contain the outbreak.  It is also most likely that from a logistics point-of-view, this is the population where TKM-Ebola would be most effective as it is here where the disease can be detected and drug administered early enough for the treatment to be effective (within 2 to 3 days following exposure).

In order for TKM-Ebola to have maximal impact, manufacturing would have to be scaled up (I estimate ~2 months for the production of large lots) and the logistics around diagnostics and treatment administration put in place.  Nobody knows whether the current outbreak will spread further, but it is better to be prepared in case it does.  As the suspected Canadian case this week illustrated, Ebola is now just a plane ride away from us. 

Watch out for the April 1 presentation by Dr. Ian MacLachlan from Tekmira on the latest data for TKM-Ebola which will be in front of a sell-out crowd at the FILO 2014 conference in Galveston, Texas.

Endocyte Success to Catalyze Interest in Folate-Targeted RNAi Therapeutics

One of the big stories on Wall Street this Friday was Endocyte and their folate-targeted drug vintafolide. All on the same day, Endocyte received a positive opinion by the CHMP in the EU, paving the way towards marketing authorizations of vintafolid in ovarian cancer in this important market.  Simultaneously, it announced encouraging phase II data in non-small cell lung cancer (NSCLC) in which the drug, in combination with chemotherapy agent docetaxel, met the primary endpoint in extending progression-free survival (PFS).

I hope I got all of that right.  What is more important in the context of RNAi Therapeutics and this blog is that folates have been considered by the field as a promising targeting agent in the past and the successes by Endocyte and progress in RNAi delivery could lead to a new push in that direction.

The idea behind vintafolide is simple.  Since non-targeted small molecule chemotherapeutics inhibiting basic cell division processes cause widespread toxicity in normally proliferating tissues (e.g. GI tract, bone marrow), often times preventing their use at therapeutic dosages, targeting such agents specifically to cancer cells should greatly increase their therapeutic window and utility.  In the case of vintafolide, the chemotherapeutic agent (DAVLBH) is targeted towards the folate receptor that is overexpressed in many tumors as tumors have an increased demand for folates to support their growth.

Following binding of the folate drug-conjugate to the folate receptor, the conjugate is taken up by the cancer cell through endocytosis.  Once in the endosome, the folate falls off the drug which in turn is then free to diffuse into the cytoplasm to inhibit cell division by binding to tubulin. Meanwhile, the folate receptor recycles back to the cell surface.  All analogous to ASGPR and galactose in the liver.

One challenge with folate-targeted RNAi Therapeutics that I have heard a number of times, is the concern that folate receptor expression is not sufficiently uniform to get at all/most the cancer cells.  This assumes that in order to be successful, a cancer RNAi Therapeutics would have to reach the majority of cancer cells.

Interestingly, vintafolide is used in combination with a companion diagnostic comprising folate with a molecule that can be imaged.  By first running the imaging test, Endocyte has been able to focus their studies on those patients which express folate receptor on all their tumor masses.  Importantly, apparent anti-tumor activity correlated with folate receptor expression.  Such enrichment strategies could obviously also be applied to folate-targeted RNAi Therapeutics.

Imaging tests, however, would not be able to address folate receptor expression heterogeneity within a tumor mass.  It would be interesting to know to what degree vintafolide activity was restricted to the cell that has taken it up or whether it could also act on by-stander cells.

RNAi Therapeutics companies that could take an interest

I can remember Alnylam-related OTS presentations before 2009 that looked at simple folate-siRNA conjugate delivery with promising localization data.  Knockdown efficacy, however, seemed limited. 

This is not surprising given the absence of endosomal release chemistries in those molecules.  Endosomal release of receptor-targeted RNAi Therapeutics could obviously be addressed by Arrowhead’s DPC technology.  A folate-targeted single molecule DPC would be my front-runner in realizing the potential of folate receptor-targeting for RNAi Therapeutics. 

Curiously, Merck has partnered with Endocyte on vintafolide and as we know had been busy copying delivery technologies by Arrowhead and Tekmira.   It would therefore greatly surprise me if Merck had not looked at folate-targeted RNAi Therapeutics, which might strengthen Alnylam’s effort in developing folate-targeted DPCs following their acquisition of Merck's RNAi assets in January.

In addition to the conjugate companies, liposomal players such as Tekmira and Dicerna could get in on the folate action as well.  This is because receptor-mediated endocytosis is believed to play an important role in the cellular uptake of liposomes that are not constitutively positively charged (àApoE-LDL receptor).  By adding folate to the mix, one could a) extend the utility of a liposomal cancer RNAi Therapeutic to cancers overexpressing either receptor, and/or b) enhance cellular uptake by interacting with 2 receptors simultaneously on cancer cells that express both receptors.

Further Possibilities for Arrowhead Phase I Dose Extension

Last night’s speculations on the reason for the phase I dose extension of the HBV RNAi phase I trial by Arrowhead Research was actually positive: they are tackling the potency issue presented by the 2mg/kg dose. 

In addition to further increase dose, it could also involve prolonging drug infusion times which we know, based on Alnylam’s GalNAc data, could optimize hepatocyte uptake by the GalNAc-targeted DPCs.

Regardless, you have got to question why extending beyond 2mg/kg had not been part of the original plan and why the study extension has not been publicly discussed, e.g. in the latest conference call.   

Extending the study to further potency is the most rose-colored scenario that one can draw.  The other scenario would have to do with safety concerns, possibly raised by regulators.  As I had discussed before, for DPC, especially the 2 molecule version, the tox-limiting element is the melittin-like peptide.  Melittin is derived from bee venom and although the MLP is not the identical sequence as melittin, there are theoretical concerns around allergic reactions.  In general, having peptides involved raises a new set of immune issues, especially when you require 2mg/kg of them.

Of note, one of the exclusion criteria for the phase IIa HongKong trial is excluding those with a history of allergy to bee venom, indicating that this has been an issue with regulators:

·         Has a history of allergy to bee venom or history of hypersensitivity reaction requiring an emergency visit to a physician or hospital and/or requirement for treatment with steroids and/or epinephrine.

So how about adding transient immune suppressant to the mix- e.g. an anti-histamine?  Nothing spectacular, a safety precaution, but once again highlighting the benefit of Arrowhead Research making advances with the single-molecule version, also for applications outside the liver (see today’s positive news around Endocyte and folate targeting for cancer as just one example of where such research could be directed at).

Potency matters, and wouldn’t it be ironic that as Tekmira is weaning itself off immune suppression (à dose-intensive TKM-EBOLA trial), on the back of developing more potent formulations, Arrowhead Research, not known as a public supporter of liposomal RNAi delivery, is adopting such?  

Potency Concerns and Tekmira Could Be Spurring Extension of Arrowhead HBV Study

As

As picked up by sooner_or_later55 on the InvestorVillage mssage board on Arrowhead Research, there have been changes to the clinicaltrials.gov entry for the phase I study of ARC520.  These indicate that the study has not been concluded as I and probably most others had assumed following the release of top-line data in October 2013 and the more detailed results presented at HepDART 2013 last December.

At that point, 36 subjects had been treated in the single-dose dose-escalating study up to 2mg/kg.  In this healthy volunteer dose-finding safety study, the most significant event possibly related to ARC520 was a case of urticarial rash of moderate intensity.  In general, the safety profile was quite encouraging for the first test of DPC delivery technology in humans.

According to the clinicaltrials.gov entry, the target enrollment was upped to 48 subjects in February 2014.  The company has more or less confirmed the renewed activity in this email to an investor ('Linda').

So why is there still activity in a trial we thought had been wrapped up?  

After all, the 2mg/kg upper dose informed the dose selection for the single-dose study in HBV-infected patients in Hong Kong which is about to commence dosing any day.

My favorite hypothesis is that it has to do with concerns around efficacy.

 

As I had discussed in my companion HBV blog before, 2mg/kg may not be enough for the type of 1log+ knockdown activity that may be necessary for the Hepatitis B surface antigen (HBsAg) knockdown-immune reactivation hypothesis to really kick in.   3, 4, and especially 6mg/kg could make a big difference according to the preclinical studies by Arrowhead Research in achieving much greater HBsAg knockdowns (it is important to focus on the dose of the melittin-like peptide when reading these papers). 

And for this indication, the deeper and the more rapid the knockdown, the more patients to benefit from such a treatment.  Say with an 80% HBsAg knockdown (my prediction for the outcome of the single-dose Hong Kong study for 2mg/kg which is the approved top dose in the study), an HBV RNAi therapeutic can achieve a cure rate of 10%.  Similar to the interferons, the best we have right now for curing HBV, but with presumably much improved tolerability.  However, with 90% knockdown (half the HBsAg left to immune suppress compared to 80%), this could jump to 30% cure rates, with 95% knockdowns to 50% etc etc.

I already hear you cringe that all this is speculation.  To this, I respond that not only all of life and particularly drug development and the stock markets are a speculation, but that it is informed by biological intuition.  You either sufficiently lift your foot off the (immune) brake or not (--> threshold).  Throw in the fact that the set point where the brakes have been released will vary due to the variability in how much individuals’ immune systems have been repressed and damaged by HBsAg, you probably end up with a sigmoidal knockdown-response curve. 

Tekmira competition

As we consider the importance of knockdown efficacy in absolute terms, it will also not have been lost on Arrowhead Research that other companies, most notably Tekmira, has been gearing up with their own HBV RNAi and antisense knockdown drug candidates.

 

I call out Tekmira because I not only own the stock, but because of the value of knockdown potency in this indication and the fact that SNALP LNP delivery is and will remain the most potent gene knockdown technology for the foreseeable future.  SNALP LNP potency has been validated in humans with over 90% target gene knockdowns in the ALN-TTR02 study using 2^nd generation technology and it is reasonable to expect that Tekmira’s most recent 3^rd generation formulations will exceed that.

Although genes vary by the ease of knocking them down, I expect HBV to be an easier target than TTR given that its genes are expressed from an episomal template, i.e. not from copies integrated into the genome.   

Add to this potency advantage the decade-long experience of Tekmira working on HBV and other viral applications (e.g. HCV, Ebola, Marburg) of SNALP RNAi (see Nature Biotech publication from 2005 using 1st generation technology), which includes the design of escape-resistant and pan-genotypic RNAi triggers and should also manifest in a more thoughtful/thorough trial design, it is not a stretch to imagine that it was partly the Tekmira competition that is spurring Arrowhead Research to presumably be testing the feasibility of higher doses now.  

Moreover, the first-mover advantage of Arrowhead may not be as big as widely assumed since Tekmira could be moving directly into single-/multi-dose ascending studies in HBV infected patients in early 2015, just months behind, if at all, the Arrowhead multi-dose phase IIb study.  

The prospect of higher cure rates will not only inform the RNAi drugs a patient will be taking in the future, it may also divert investments today in an area that is rapidly gaining in investor and pharmaceutical interest.  After all, even just 10 million of the ~300 million HBV patients that would require treatment for medical reasons and could afford it would make for a ~10 million*$20k = $200B market, and that could well be an underestimate...  

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.   

Imetelstat Off-Target Mechanism Might Be Its Therapeutic Mechanism of Action

This morning’s biotech news featured a clinical hold on Geron’s imetelstat, a 13-mer lipid-conjugated N3’-P5’ thio-phosphoroamidate oligonucleotide telomerase inhibitor.  Since maintaining chromosome ends by telomerase is important for repeated cell replication, it is not surprising that the company is aiming this compound at proliferative disorders such as cancers and essential thrombocythemia (ET).  The latter is a condition in which there are too many platelets.

The clinical hold imposed by the FDA relates to apparent liver toxicity.  Liver toxicity as evidenced by elevated liver enzymes has been a known side effect of imetelstat with 90% of subjects in the phase II trial of imetelstat exhibiting low-grade elevated liver enzymes.  What is more, about 30% of the subjects had concurrent increases in bilirubin.  Taken together this strongly smells like cases of Hy’s Law, the nuclear liver tox bomb of drug development.

No wonder the alarm bells at the FDA are ringing.  According to the press release by Geron this morning, the agency is concerned about the reversibility of these elevations.  If not reversible, chronic liver disease, if not failure might ensue.  

I am not too surprised by these developments.  What surprises me is that the stock market apparently has not picked up on the concurrent liver enzyme/bilirubin increases since these had already been known.

The reason why I am not surprised is that phosphorothioate oligonucleotides can be expected to result in liver injury at the ~10mg/kg very high dosages given in the ET trial (dosage similar to the 640mg phase III prostate cancer trial of OncoGeneX discussed yesterday).  Note that ISIS Pharmaceuticals generally settles with 200mg, at most 300mg of systemically administered phosphorothioates and Santaris had to terminate two candidates targeting genes expressed in the liver due to liver tox.

It should be added here that the Geron, ISIS, and Santaris chemistries are slightly different, but share the phosphorothioate modification which in my opinion is what is causing these toxicities.

Given that the half-lives of phosphorothioate oligonucleotides in the liver are about 1 month, one would expect the low-grade liver enzyme elevations to go away with time and they might not be a show-stopper for non-chronic applications of imetelstat.   

That’s the somewhat good news.

The bad news: applying a phosphorothioate oligonucleotide-based telomerase inhibitor for the treatment of cancer and increases in platelet counts sounds like a bad joke.  Thrombocytopenia (decreases in platelet counts) and anti-proliferative immunostimulation are well known side effects of large doses of phosphorothioate oligonucleotides.  In light of that, claiming that imetelstat works via telomerase inhibition seems a bit optimistic to put it kindly.

Don’t Bank on OncoGeneX Phase III Data

As much as RNAi Therapeutics is contributing to and benefiting from the fact that RNA Therapeutics as a whole is rapidly materializing as the 3^rd major drug discovery platform, this relationship could also backfire to some extent.  I am particularly thinking here about the upcoming OncoGeneX 2nd gen RNaseH-antisense (ASO) phase III results in prostate cancer (partnered with TEVA).

Obviously, a successful outcome of the SYNERGY trial which is analyzing the ASO compound custirsen (aka OGX-011) in combination with chemotherapy would be a big win for the field and represent the first more significant commercial success.  In February, the company announced that the pre-specified number of ‘events’ (i.e. deaths) had been reached in this ~1000-patient study, and depending on the robustness of the results (good or bad) we could be hearing any day now of the top-line results.

Reasons to be skeptical

In evaluating the prospects of an Oligonucleotide Therapeutics compound, I first ask whether the delivery has been firmly established and how good the target is. 

Usually, since Oligonucleotide Therapeutics enjoy the benefit of being able to pursue virtually any target, target risk should be minimal.

Unfortunately, in this case, there are considerable risks in both the delivery and the target.

Custirsen targets clusterin expression.  Clusterin has chaperone activity and is thought to protect cancer cells from stress, including stress arising from cancer therapies such as radiation and chemo.  Accordingly, limiting clusterin activity by knocking it down would be predicted to improve the effectiveness of conventional cancer therapies.

The most important validating preclinical study in that regard comes from a publication by Zellweger and colleagues…from the year 2001 (which got me wondering about the patent clock).  While some of the predicted effects were seen such as increased sensitivity to chemotherapy agents, the effect sizes were rather modest and their correlation with ASO potencies poor. 

In general, in reviewing even more recent ASO chemistries such as cET2.5 for cancer (e.g. STAT3 by ISIS/AstraZeneca), I was struck by the poor correlation often seen between knockdown potency and therapeutic effect (e.g. much more potent anti-cancer effects with an ASO that had 20% knockdown activity compared to one that had 60% knockdown activity) and sometimes also between mRNA and protein levels (mRNA e.g. reduced by 50%, protein essentially disappearing; patent application WO2012/135736).

This raises the prospect that some of the apparent anti-cancer activities were not due to on-target efficacy, but due to some unintended side effects such as immune stimulation.

Promising phase I PK-PD data at very high dose of 640mg

Consistent with the concern of unintended/undesirable immune stimulation, the apparent increase in overall survival observed in the phase II prostate cancer study of custirsen was seen at the dose of 640mg, a dose at the very upper limit of phosphorothioate chemistry (Chi et al. 2010).  This study in ~80 prostate cancer patients provided the rationale for investing in the ongoing phase III trial.

Unsurprisingly, immunostimulatory side effects in the form of chills and fevers were seen in the majority of subjects taking custirsen in combination with chemo, but not those on chemo alone (plus the liver and kidney tox you’d expect from such a high PS-ASO dose).  Moreover, the apparent clusterin knockdown, as assessed on the basis of the protein found in serum (not in cancer tissue directly), was a very modest ~30%.

This unsatisfactory degree of knockdown stands in stark contrast to a promising phase I PK-PD study which showed >90% knockdowns in prostate/tumor biopsies (Chi et al. 2005).  This was accompanied by mid- to high single-digit microgram of oligonucleotide concentrations per gram tumor tissue.  Such concentrations do not necessarily predict (normal) mRNA knockdown efficacy, but do not exclude such activity either. 

One explanation for the apparent discrepancy could be that the phosphorothioate oligo preferentially localizes to solid tumors and that solid tumors are not a significant source of serum clusterin. Possible, but...  

Under the radar for a reason

A sub $200M market cap for a company with imminent pivotal phase III data in prostate cancer and low trading volumes indicate that the market has not been paying all that much attention to Oncogenex. 

In this case, I would like to think for a good reason, and while I do not exclude ‘positive’ results (at the cost of considerable side effects and an uncertain mechanism of action), I hope that the public won’t read too much into them regarding the ongoing RNA Therapeutics revolution.  Every mechanism and chemistry has its place. PS-ASOs knockdown of (cytoplasmic) mRNA for cancer is not it. 

For cancer, RNAi and microRNA Therapeutics have the edge.

An RNAi Therapeutic Could Be Last Man Standing in PCSK9

PCSK9 has arguably become biotech’s hottest drug target as it promises to unlock much of the remaining unmet need in lowering ‘bad’ LDL cholesterol.  While monoclonal antibodies have been the predominant and most advanced modality to address PCSK9 (e.g  alirocumab Regeneron/Sanofi-Aventis and AMG145 by Amgen), RNAi Therapeutics have made tremendous, yet widely underappreciated progress in this area with predicted potencies equivalent to if not superior to monoclonal antibodies.

Alnylam’s ALN-PCS leads in this effort (preclinical 67% LDLc lowering without statins) and should have entered clinical development by the beginning of 2015.  It is partnered with The Medicines Company.

The news today that the FDA has become concerned about neurocognitive adverse events in the ‘PCSK9 class’ could mean that RNAi Therapeutics, despite their development delays, will carve out a nice junk of the PCSK9 market which is widely estimated to be a multi-billion dollar market in terms of annual sales.

But if it’s a ‘PCSK9 class’ issue, so how could this be positive for RNAi Therapeutics?  Wouldn’t this concern also apply to ALN-PCS?

Not necessarily.  Since by far the most clinical experience with PCSK9 has been obtained with monoclonal antibodies, the FDA may be inappropriately lumping all PCSK9 inhibitor agents in one bucket confusing a short-coming of a therapeutic target with a short-coming of monoclonal antibodies.

The reason why I have a good feeling that this turn of events could be very positive for RNAi Therapeutics is that RNAi is a genetic tool that reduces PCSK9 expression before any protein is made.  The approach therefore resembles populations that under-express PCSK9 for genetic reasons and which enjoy improved cardiovascular health compared to the general population without any apparent negative consequences of their PCSK9 deficiencies.  It is for this very observation that PCSK9 has become such a sought-after target and RNAi, a gene knockdown approach, best mimics human genetics.

Monoclonal antibodies don’t.  One mechanism by which antibody-specific toxicity might arise from is the fact that they form complexes with their target.  Such complexes could elicit adverse immune reactions in organs where they form and accumulate.  While I am not familiar with the binding sites of the particular Regeneron and Amgen antibodies to PCSK9, it might also be possible that the immune complexes form directly on neuronal cells expressing LDL-receptor-like proteins (note: PCSK9 binds the LDL-receptor).

Beyond PCSK9, today’s events emphasize yet another hitherto under-appreciated value proposition of RNAi Therapeutics, namely providing differentiation value when going head-to-head with the small molecules and monoclonal drug establishments.

With Success, Pure-Play RNAi Therapeutics No More

As RNAi Therapeutics are charging forward towards first marketing approvals, it is time to consider how this will change the face of some of the pure-play companies involved.  Alnylam is set to become the dominant player in TTR amyloidosis, Arrowhead Research and Tekmira are vying to become just that in Hepatitis B, and Tekmira is increasingly isolating their biodefense division involving the formation of a filovirus alliance with non-RNAi modalities (prophylactic and therapeutic vaccines) as revealed yesterday.

Under normal circumstances, getting drugs approved that revolutionize the treatment of particular diseases provides great incentives to protect the resultant franchises.  Witness BiogenIdec .  BiogenIdec started out as a molecular biology pioneer and serendipitously established itself as the major player in multiple sclerosis, and is now considering all therapeutic modalities, including RNA Therapeutics, to build on that strength and further expand into neurology.  

Although it breaks my scientific heart, I do not expect that to be any different for RNAi Therapeutics companies.  HBV is a great example since an immune de-repressing RNAi Therapeutic alone is unlikely to facilitate the 100% cure rates now seen with combinatorial HCV treatments.  Instead, the addition of a direct immune-activating agent such as a TLR agonist should enhance cure rates and shorten treatment durations.  For an acute fatal infection such as Ebola, you also do not want to limit yourself to one treatment, but recruit multiple mechanisms to save an infected person, or start vaccinating populations around areas of viral outbreaks.

To extract maximal value from such disease indications, it is often best to combine the various options under one roof.  It may be partly this fear of moving away from your roots that is responsible for ISIS Pharmaceuticals giving up marketing rights early on for a few cents on the dollar worth (SMN, myotonic dystrophy, TTR).

Having said that, just like BiogenIdec with recombinant proteins and monoclonal antibodies, most of these RNAi Therapeutics companies will continue to focus their internal R&D efforts on RNAi Therapeutics.  In special cases such as Ebola and other biodefense opportunities, a spin-out may create most shareholder value without damaging the platform technology value of the parent company.

Nothing of what I just said is revolutionary.  It is, however, worth keeping in mind as the first major RNA(i) Therapeutics wave will make landfall in 2-3 years. 

The Ebola Clinical Trial a Real ‘Haertetest’ for SNALP LNP Delivery

In German, a Haertetest is a test that challenges the performance of something under the most exacting conditions.  

It is therefore an apt description for the Ebola clinical trial now underway which is testing the safety and tolerability of SNALP LNP delivery following multiple consecutive daily administrations.  This compares to once-weekly and once-a-monthly regimens tested so far.  If SNALP LNP comes out positive from this, it would provide great comfort around the safety and tolerability of the industry’s most potent delivery technology for gene knockdown in the liver, in addition to paving the way towards more biodefense applications.

Teething problems with 1^st gen SNALP LNP

In January 2010, Tekmira reported clinical results from the phase I study of TKM-ApoB, the first clinical candidate employing SNALP LNP technology.  This trial was terminated prematurely due to immune stimulations observed at 0.6mg/kg, a dose at which only minimal target knockdown was observed at that.

This event triggered a healthy amount of soul searching and meant that subsequent SNALP LNP trials had to employ transient immune suppression.  A number of important practical lessons were learned from this.  

Firstly, it showed that the preclinical immune stimulation tests had been inadequate and this prompted the development and adoption of a more predictive test to better screen out candidates that are immunostimulatory before they enter humans.  Secondly, the phase I results were consistent with the notion that the DLinDMA lipid itself (and not just the RNAi trigger), the basis for the 1^st gen SNALP formulations, was immunostimulatory and that new lipids were needed.  And lastly, it highlighted the need to develop more potent SNALP formulations, including new lipids.

Research rises to the challenge

Three years following these events, all three challenges have been successfully addressed.  Today, the potency of SNALP LNP has increased ~30 fold from 1^st gen to 3^rd gen formulations (based on measuring gene knockdown in the liver), with the 2^nd gen MC3-based SNALP generation already with a confirmed 10-fold improvement in clinical potency based on phase I and II results of ALN-TTR02.

Tekmira not shy to ask the tough questions

Despite the progress, detractors of the technology like to point out that (transient) immune suppressions has still been employed in subsequent clinical trials.  With the recent initiation of the phase I study of TKM-Ebola by Tekmira, this has changed however.  Not only that, transient immune suppression has been dropped even as administration intensity is ratcheted up to 5-7 daily administrations. This compares to once-a-month and once-a-week dosing schedules anticipated for SNALP LNP applications involving gene knockdown in the liver and solid cancers, respectively.

The reason why TKM-Ebola necessitates daily administrations is due to the rapid progression of the otherwise fatal Ebola virus.  Therefore, in order to get it approved under the Animal Rule, Tekmira needs to demonstrate the safety and tolerability of SNALP LNP in human volunteers under conditions where they are able to rescue monkeys from succumbing to otherwise fatal infections.  

Moreover, while 0.2mg/kg already provided good protection in the monkey studies (2/3 survival), it was the 0.5mg/kg dose that complete protections were achieved.  0.5mg/kg also happens to be the ‘magic’ dose for SNALP LNPs following which idiosyncratic immune stimulations and other side effects may be expected.

The reason why I am pretty sure that TKM-EBOLA, despite the daily administrations and up to 0.5mg/kg dose, should not involve immune suppression is because it would be incompatible in a viral infection.  There is also no evidence that such pre-treatments are planned in the clinicaltrials.gov entry nor when Tekmira reported the monkey results.  The same considerations apply to the HBV candidate by Tekmira for which an IND is expected by year-end.

Should Tekmira come out of this trial unscathed, it would further de-risk the entire SNALP LNP platform and solidify its position as the most potent oligonucleotide therapeutics technology for gene knockdown in the liver, for hemorrhagic fever applications, and possibly oncology.

Where some see risk, others see opportunity.