Developing Aerosolized TKM-EBOLA as Airborne Transmission of Ebola Likely

Knowing how a virus is spread, also from a cell biology point-of-view, is critical to curtailing its spread and devising effective treatment strategies.   

According to the World Health Organization (WHO), the first symptoms of an Ebola infection are ‘the sudden onset of fever fatigue, muscle pain, headache and sore throat’ (emphasis mine). Then also consider the following:

1)      Ebola once killed a number of monkeys are apparently spreading through the ventilation system in Reston, VA; 

2)      A nurse became infected in a reference hospital for infectious diseases in Spain despite the protective clothing she was wearing and her limited contacts with the infected patients she was looking after (taking temperatures twice);

3)      A single pregnant woman in Liberia infected atleast 10 people helping her as she came down with Ebola;

4)      Ebola virus can infect numerous cell types in the body (frequently cited are the liver, endothelial cells, and phagocytic cells) and is found in high amounts inthe respiratory tract in infected pigs with the virus spreading readily to cohabiting pigs in the colony;

If you still believe in the narrative, even propagated byotherwise fairly reliable sources such as the CDC, that Ebola is only transmitted by direct contact with body fluids, then you should start considering airborne transmission as a main route the infection is spread.

After all, since when are cough droplets not a bodily fluid?

If airborne is indeed an important route of transmission, this would not only raise concerns that just like in avian flu, a few mutations in the virus adapting it to better latch on to the human respiratory tract could further catalyze the spread of the virus, but would also mean that treating it at the respiratory stage could both prevent the virus from fully entering the body as well as limit its spread from person-to-person.

Enter TKM-EBOLA

An RNAi viral knockdown approach in the respiratory epithelium should obviously be able to achieve that goal.  All that would be required is to take the same RNAi triggers now part of the intravenous TKM-EBOLA formulation and incorporate it in something amenable for respiratory delivery.

Back in 2011, Tekmira revealed that it was developing aerosolized liposomal nanoparticles (LNPs) to deliver RNAi triggers to the respiratory epithelium.  A key challenge was to find formulations that not only could successfully transfect respiratory epithelial cells, but also withstand the shear forces involved in nebulizing them.  Initial structural and tissue culture RNAi knockdown results showed that this can be achieved.

The development was seemingly halted at the rodent preclinical stage as the company had to save financial resources as it was fighting off Alnylam in a trade secret case.  After coming out on top of the litigation in November 2012, the company was then able to once again expand the development of its LNP-based nucleic acid delivery technology, in addition to churning out clinical development candidates (e.g. the important HBV candidate to be revealed next week).

 

Given that the company established a separate biodefense unit headed by the ‘LNP-brain’ of the company, now Chief-Technology-Officer Ian MacLachlan, I would not be surprised if LNP nebulization was part of that effort with the next goal of showing efficacy in monkeys.

Such reformulation of TKM-EBOLA is just another example of the versatility of RNA Therapeutics, just as is the ability to rapidly adjust and optimize the medicine as the virus evolves (note: this is e.g. not possible with antibodies).  It also adds to the importance of scaling up the supply of the RNAi trigger now should airborne be recognized as a major route of transmission.  

Long-term, such developments would obviously benefit the development of LNP-delivered RNA Therapeutics for the lung epithelium in general, including mRNA delivery (e.g. for Cystic Fibrosis) and a universal RNAi agent against flu.   

A Defining Month for Tekmira

As if Ebola has not showered Tekmira with enough attention, Tekmira will be front and center in the RNA Therapeutics industry in October.  It will be clinical results from two other drug candidates utilizing Tekmira’s RNAi delivery technology (TKM-PLK1 and ALN-TTR02) and pre-clinical data for TKM-HBV that will define Tekmira's trajectory as a 'normal' biotech company.  'Normal' as I have little idea how Ebola will change all this.

Accordingly, depending on the dataflow, Tekmira could finally be transformed into an established biotech company.  If there are serious disappointments, Tekmira risks being delegated to being 'the Ebola company'.

Event 1 (October 10-11): Do GI-NET patients respond to TKM-PLK1?

The first upcoming data event is the phase IIa update for TKM-PLK1 in gastrointestinal neuroendocrine tumor (GI-NET) and adrenocortical carcinoma (ACC) patients.  This one can be considered a bonus event for Tekmira as barely anybody has been paying attention to the potential of this first-generation SNALP-based product candidate.

 

Results from a  multi-dose escalating phase I study suggested a dose-dependent benefit with patients receiving 0.6mg/kg or more having an increased likelihood of showing ‘clinical benefit’ (stable disease or partial response) than those receiving less of the drug.  In particular, almost all (5/6) GI-NET and ACC patients in that trial with otherwise enrolled across a wide range of cancer types exhibited at least stable disease, with a partial response by RECIST and a 19.3% reduction in tumor size.

One aspect that I found particularly encouraging in these results was that TKM-PLK1 which involves a long-circulating form of SNALP achieved ‘several fold’ increased target tumor concentrations compared to an earlier, short-circulating SNALP product (ALN-VSP02 from Alnylam).   Unfortunately, the precise differences were not disclosed.

The factor that makes me most optimistic about a positive update (--> multiple tumor responses) at the upcoming 7^th Annual NET Conference in Nashville is that there is evidence that SNALP LNP delivery should work particularly well in the GI-NET and ACC settings.  Not only did GI-NET and ACC patients seem to perform well in the phase I study, there have historically been apparent biological effects of other nanoparticulate cancer RNAi Therapeutics in neuroendocrine tumor patients, including cases of extended stable disease with Atu027 by Silence Therapeutics.  

Moreover, the adrenal cortex, and possibly other endocrine structures, seems to be a preferred target organ (next to liver) for SNALP LNP delivery.

What makes me less excited about this program is that TKM-PLK1 is based on fairly old SNALP LNP delivery technology, and wouldn’t it be nice to see the potent PLK1 RNAi trigger being utilized in the latest delivery formulation.

Event 2 (October 13): Does ALN-TTR02 show a therapeutic benefit in TTR amyloidosis?

At the upcoming American Neurological Association’s 2014 Annual Meeting, Alnylam will present first data from its high-profile ALN-TTR02 product candidate that will look not just at target gene knockdown (expected to be in the 80% range), but also whether this translates into an apparent therapeutic benefit.

ALN-TTR02 is an RNAi Therapeutic for the treatment of the FAP form of TTR amyloidosis and uses Tekmira’s delivery technology.  As a result, Tekmira stands to financially benefit from it in the form of development milestone payments and royalties (in the low to mid single-digit percent of revenues) which may reach ~$50-100M annually for this $500M market cap company if analyst projections as to the FAP market prove correct.

The data to be presented comes from the open-label extension (OLE) of the relatively short phase II study.  In this OLE study, Alnylam will look every 6 months how patients are doing according to the mNIS+7 functional score which will then be compared to data gathered from a Natural History study of the disease. 

It is expected that 20 patients that had been rolled over from the phase II study will now have reached the first 6 month time-point.  The phase II study was too short (2 doses spaced apart 3-4 weeks) to reasonably expect an obvious therapeutic benefit from the knockdown of the disease-causing transthyretin gene.

It is important to remember that a failure to see a therapeutic improvement after 6 months with ALN-TTR02 does not necessarily reflect badly on SNALP LNP delivery technology as long as the knockdown remains in the 80% range and is well tolerated.  In that scenario, target risk and an insufficient period of knockdown may be responsible instead and this is where each RNAi Therapeutic has its unique development risk.

My prognosis is that first divergences from the Natural History will be seen if the preclinical experiences and those from other amyloidotic diseases such as AA amyoloidosis are any guide (~50% knockdown and beyond should lead to a benefit).  From a Tekmira technology point-of-view, I will pay close attention as to the safety and tolerability of longer-term dosing, which so far looks quite good.

  

                Event 3 (October 15): Coming out for TKM-HBV

Possibly the dataset with the most impact on Tekmira is the revelation of the company’s RNAi candidate for HBV infection.  Based on data revealed earlier this year by Alnylam which showed a SNALP LNP-based RNAi compound to have multi-log viral knockdown and 2 log HBsAg knockdown in the challenging chimpanzee model with moderate amounts of drug, TKM-HBV is set to become most-potent and therefore hopefully best-in-class among the knockdown approaches by Arrowhead Research (ARC520, first-mover), ISIS/GSK, and Alnylam.

To facilitate cross-comparisons, Tekmira may wish to directly compare its candidate with Arrowhead’s ARC520 for which the structural identity is known.

One aspect that I will be paying particular attention to is whether the data support dosing without transient immune suppression.  This is because I am concerned that such a regimen, especially if it involved steroid use, would not be acceptable in the HBV setting. As you may remember, the company attempted to get away without immune suppression with TKM-EBOLA in a trial in healthy volunteers, but at moderate-to-high dose levels immune stimulations were seen prompting the FDA to put that program on Clinical Hold for the volunteer population. 

Having said that, TKM-Ebola is now being used in much more fragile patients actually infected with Ebola, and anecdotally even the most stringent dosing regimens such as 7x daily appear to be tolerated here, presumably without pre-medication.

As per the last quarterly conference call, Tekmira management seemed confident that TKM-HBV would not require pre-medication.  Since such immune stimulation is thought to be highly sequence-dependent, I do not fully understand their confidence, but maybe a little bit of immune stimulation is not that bad in the Ebola setting after all.

An IND for TKM-HBV is planned by the end of the year with first dosing starting in early 2015.

Buckle up for an exciting month with Tekmira, and if all that weren’t enough, it unfortunately looks like we are still in the early innings with Ebola as being ahead of the curve is a concept foreign to the governing authorities.

Disclosure: long Tekmira.

TKM-EBOLA Making RNAi History

Today, Tekmira disclosed that an acceptable regulatory pathway has been found with US and Canadian regulators to use its RNAi Therapeutic against Ebola infection, TKM-EBOLA, in the current outbreak.  In fact, the company added that 'TKM-Ebola, has been administered to patients on an emergency basis and the repeat infusions have been well-tolerated'.

While not going into specifics, it is more or less a confirmation that Dr Sacra who was said to have received multiple courses of a treatment was indeed treated with TKM-EBOLA (he seems to have pulled through).  Further substantiating that suspicion was a comment by a relative that subsequent administrations of the experimental drug were better tolerated:

'He also tolerated the research drug well – better than he had the previous doses he was given.”'

This is consistent with infusion reactions of many intravenously administered drugs being a particular problem during the first administration only.

Then there was another report that a number of suspected, early cases had been evacuated from Western Africa to the US with the intention of giving them experimental treatments.  This, in fact, would be the ideal setting for using TKM-EBOLA, or for that matter most other experimental treatments against Ebola.  It should be remembered that while in the preclinical monkey studies, the efficacy of TKM-EBOLA started to wane if treatment was delayed for more than 3 days following infection of the animal, this experimental setting is more akin to a needle stick accident in the lab given the large amount of virus involved in the innoculum.

By contrast, in the current outbreak in Western Africa, not every contact obviously leads to a successful transmission of the virus, a reflection of the fact that the starting viral population will be much less compared to the experimental setting.  This means that it would take the virus more than 3 days to overwhelm the capacity of TKM-EBOLA and the immune system to stall the infection in its tracks.  Hopefully, Tekmira is conducting analogous innoculum-window-of-opportunity studies in monkeys to get a better sense of how much treatment can be delayed when infectious doses are quite low.

With this in mind, I am more or less convinced that RNAi Therapeutics is saving patient lives for the first time.  I personally would risk an anaphylactic shock in a closely supervised clinical setting any day over the prospect of not getting specific treatment when infected with Ebola. #RNAiHistory

FDA Greenlights Use of TKM-EBOLA in Current Outbreak

Canadian drug developer Tekmira just disclosed that the FDA verbally notified them that it would partially lift the clinical hold it had placed on TKM-EBOLA a month ago.  The clinical hold had been instituted as the result of cytokine elevations that had been observed in a healthy volunteer study of the drug.

By partially lifting the clinical hold, the FDA ‘blesses’ the use of TKM-EBOLA in actually infected patients whose odds otherwise would be to die from the infection.  Since the FDA only has authority over health matters in the US, this is strictly only of relevance for the use in people infected with Ebola either brought back from Africa for treatment just as the two US aid workers, or in case the virus started to crop up in the US. 

I am, however, inclined to interpret the news that the FDA is encouraging Tekmira to consider the use of TKM-EBOLA in Western Africa at the epicenter of the epidemic.   You could imagine that if anything went wrong with the use of TKM-EBOLA, it might have had adverse consequences for the future clinical development of the drug candidate in the US.

Overall, I am pleased with this development as the clinical hold in light of the current health emergency was just unbearable. How to handle the practicalities of using TKM-EBOLA in the field, including who will bear the costs, we will have to see.  Remember, financially, it is Tekmira's HBV candidate that has priority over TKM-EBOLA and so I expect TKM-EBOLA to be part of a broader effort funded by the public health bodies.

What TKM-Ebola Could Achieve in the Current Outbreak

(please read financial conflict at the end)

We are in the midst of the largest recorded outbreak of Ebola hemorrhagic fever virus ever and there is little evidence that its spread is being contained.   Here, I will make the case how TKM-Ebola, the most advanced Ebola therapeutic in clinical development, could help in avoiding ever more damage from the deadly virus.

How TKM-Ebola could help

1.       Give suspected cases an incentive to go to the treatment centers.

2.       Provide medical personnel with a stand-by and therefore help in their recruitment.

The continued spread of Ebola can be partly attributed to a breakdown in confidence in the authorities and fear by medical personnel. 

I have been viciously attacking the World Health Organization (WHO) that by downplaying the significance of the outbreak it has been a key factor in re-igniting viral spread.  It is the WHO who have tried to minimize the true numbers of infected, possibly in cahoots with local authorities, and laughed off the suggestion that the virus could get on a plane in arguing against any kind of travel restrictions.  Of course, it recently did and I am still waiting to see top WHO officials send their families on a vacation to Western Africa.  But probably the most outrageous insult was in suggesting that the spread of the virus is explained by ‘funny’ cultural practices in these countries such as kissing the dead during burials.

The WHO, probably in the comfort of their headquarters in Geneva, even attacked on-the-ground Medecins Sans Frontieres as alarmist for calling the outbreak ‘unprecedented’ in late March.

This notion that the virus is very bad in spreading from person-to-person and can only do so with the help of obscure practices is obviously wrong given that more than 100 medical personnel have become infected. While I am still waiting for an explanation by the WHO of how this could happen, I refuse to believe that they kissed the dead in the treatment centers or licked any other of their body fluids for that matter.  Has the WHO (and others) maybe considered the unthinkable, namely that the reason why this is the biggest ever spread of the virus is because the virus has mutated and new routes of infections are possible, such as by aerosol?  The US military will have its reason to believe that this could happen, otherwise why would they be so concerned about it being weaponized and spending hundreds of million dollars on the development and stockpile of an Ebola therapeutic such as TKM-Ebola?

And if people that protect themselves with space-suits get infected, how would you feel as a suspected case of Ebola? 

I know I would do anything NOT to go to these treatment centers, because what is obviously for the good of the overall population would only exponentially increase my risk of contracting the infection in case I was one of those wrongly suspected to have Ebola.

In my opinion, providing individual isolation wards with the best medical equipment possible, a dignified environment, and a drug as an option for the patient could make the difference in whether suspected cases will turn themselves in or not.  The argument that ‘this is Africa’ and you cannot expect good medical care there should not count in this day and age when equipment can easily be shipped between continents.  It’s probably far cheaper to do it now than further risking for the virus to go global (obviously, the WHO thinks this is impossible).

And for medical personnel, the benefit of making TKM-Ebola available is obvious and most tangible: since the onset of flu-like symptoms in this population is highly likely to be due to Ebola and because they have ready access to the necessary equipment such as infusion apparatus, they could be treated immediately with the agent.  Treating as soon as possible is thought to be critical for TKM-Ebola to be efficacious.

What is TKM-Ebola?

TKM-Ebola is an intravenously infused RNAi Therapeutic that has been demonstrated to save the lives of monkeys infected with an otherwise fatal dose of Ebola.  It is being developed under the ‘Animal Rule’ in efforts funded by the US government which is afraid that this virus could be weaponized and used as a bioterror agent.  The ‘Animal Rule’ is a development pathway instituted by the US FDA for diseases such as Ebola for which it would either be impractical or unethical to conduct efficacy studies in humans. 

Because natural outbreaks are unpredictable and experimentally infecting volunteers with the virus out of the question, these monkey studies are as good as it gets regarding drug efficacy (so much for the mantra that there are ‘no drugs for Ebola’).

An important second element of the Animal Rule is that human volunteer studies demonstrate acceptable safety at the doses corresponding to the efficacious dose in monkeys.  For this reason, pivotal phase I safety studies have begun this year in healthy volunteers (so much for the notion that licensed Ebola drugs are far off- ‘phase I’ is misleading).

Clinical Hold

Unfortunately, in the midst of the outbreak, the FDA instituted a Clinical Hold on the TKM-Ebola safety study because a case of dangerously high cytokine elevations was observed at the highest dose planned in this dose-escalating/dose-finding study (0.5mg/kg).  I agree that this is to be considered a serious adverse event in a volunteer that is not infected with the virus.

The reason for the cytokine stimulation is likely due to TLR-mediated, lipid-amplified innate immune stimulation, a known risk of liposomal RNAi delivery, especially at doses of 0.5mg/kg and higher.  It is also the reason why all other active development candidates by Tekmira and their licensee Alnylam are conducted in the presence of transient immune suppression with steroids and the like which in many cases is acceptable given the severe diseases these treatments go after.

As indicated, the adverse event at 0.5mg/kg should by no means spell the end of TKM-Ebola.  Firstly, the company argues that the pharmacologic corresponding dose to those curing the monkeys is lower than 0.5mg/kg.  Secondly, a side effect that is not tolerable in healthy volunteers (usually ~20-year old male students) could be well tolerated in subjects with a 70-90% likelihood of dying from a disease in a matter of days.  It is ethically more troubling to involve healthy volunteers in such drug development just as aggressive experimental cancer drugs are hardly ever tested in healthy volunteers.  Lastly, there may be ways to avoid the side effect altogether, such as by using transient immune suppression.  However, I do not know whether transient immune suppression is possible for Ebola, but I expect Tekmira will have the answer for this from their large-scale animal experience.

Next steps

For TKM-Ebola to have the best impact on the current epidemic, the first step would be to start manufacturing it at scales sufficient to treat at least ~1000-5000 patients.  This takes time and given the uncertainty around the future course of the epidemic, the investment needs to be made now instead of waiting until it is too late for a treatment center-focused approached involving an intravenously infused agent.

The next step depends on the feasibility of steroid pre-treatment during an Ebola infection.

In case that it is known that steroid pre-treatment was of little concern (e.g. based on infected monkey studies), start treating rather aggressively (e.g. start at doses of 0.25mg/kg).  In case it was not, go about more slowly by starting at sub-therapeutic doses as low as 0.025mg/kg and treat the initial experience like a dose-escalation study in actually infected patients.  Of course, everybody would need to provide informed consent.  In general, any semblance that the use of TKM-Ebola was imposed by the Western world and the local population used as guinea pigs is to be avoided which is probably a key reason why Tekmira to my mind has been almost in hiding during this whole episode almost to the point that they (and the FDA) are glad about the Clinical Hold.  

To support the accelerated development of Ebola therapeutics and vaccines, including TKM-EBOLA you can add your signature to the following change.org initiative: http://www.change.org/en-GB/petitions/food-and-drug-adminstration-fast-track-drug-and-vaccine-research-for-ebola-hemorrhagic-fever

Disclosure: Tekmira constitutes a meaningful part of my investment portfolio and I have to credit the WHO for greatly increasing its value.

Implications of Ebola data for Tekmira HBV Program

Like it or not, it is the HBV program that is driving the interest in Tekmira, at least in the near-term.  Therefore, the 15% sell-off in the stock yesterday following the Clinical Hold imposed by the FDA can be interpreted to be due to the uncertainty of what it means for the HBV program.

It is my working hypothesis that for the treatment of HBV via the immune reactivation pathway, the use of even transient immune suppression is to be avoided.  On the other hand, the recent Ebola clinical results by Tekmira suggest that transient immune suppression may also be desirable for 3^rd gen SNALP delivery.  As TKM-HBV is expected to utilize '3^rd gen' SNALP delivery, too, the Ebola results with immune activation seem like a bad omen.

While this cannot be ignored, there are a few reasons to believe that this might be too simplistic.

1.       Difference in dose

Although there was an apparent tendency for immune stimulation throughout the dose escalation with TKM-EBOLA, it was only at the high dose of 0.5mg/kg where a dose-limiting toxicity was observed. And according the yesterday's press release on the Clinical Hold, it is in particular cytokine elevations that were observed at 'higher doses' that are the issue.  

 Since unlike Ebola, HBV only replicates in hepatocytes, and because SNALP potency is highest in hepatocytes, the efficacious dose for HBV may be well below 0.5mg/kg with 3^rd gen formulations.  Of note, even 2nd gen SNALPs are highly effective at 0.3mg/kg based on the Tekmira-enabled ALN-TTR02 candidate now in phase III.

2.       Different sequence, different immune stimulation

It is known (e.g. Judge et al. 2005: Sequence-dependent immune stimulation of the mammalian innate immune response by synthetic siRNAs) that immune stimulation by RNAi, especially when liposomally formulated, is highly dependent on the actual sequence and modification pattern of the RNAi trigger.  Since TKM-EBOLA and TKM-HBV are different in that regard, it is well possible that while one 3^rd gen formulation is immunostimulatory, the other is not.

3.       Immunostimulatory by design/by screen

Scientifically, I was most disappointed by the Ebola immune stimulations as Tekmira made a big deal in the wake of similar observation in 2010 with TKM-ApoB that with improved, more predictive immune stimulation assays, they would now be able to screen out the immunostimulatory formulations.  In a black-and-white world you would conclude ‘obviously not!’.

In a world of shades of grey, I can imagine that TKM-EBOLA might have happened to slip through this part of the screening process.  The reason is that since Ebola infects a number of cell types besides hepatocytes (endothelial cells, phagocytes etc), the impressive efficacy of TKM-EBOLA always stood out as something quite unusual.  So while containing the spread of the virus by hitting it particularly hard in the liver might be part of the mechanism, I am quite receptive to the notion that the scientists did not mind all that much some immune stimulation when the RNAi formulation had so much efficacy.

With HBV, however, the company might be much more careful in screening out immunostimulatory potential.

I can now hear Sarepta investors yell ‘it’s an artefact’, but I would caution them that Sarepta and the morpholino field at large is proposing morpholinos with cationic appendices for infectious diseases while these are not really considered for genetic diseases.  What I don’t understand is that why a modification that is supposed to be helpful in e.g. suppressing viral gene expression should not likewise be useful for suppressing human gene expression.  So maybe the value of these modifications is in tickling the immune system?

4.       Not all 3^rd gen are created equal

In response to a questioner in the Q1 financial conference call, the CEO of Tekmira said that the definitions of the various SNALP generations is not as clean as you would like from a chemical point-of-view.  Instead, the definition largely is a reflection of the potency improvements of the formulations.  Therefore, since TKM-EBOLA has a different set of target cells than TKM-HBV, it is well possible, even expected, that the formulations will also differ in their lipid compositions.  Since lipids are an amplifier of the liposomal-RNAi immune response, differences therein could have big implications as to the immune stimulation of the various formulations.

Disclosure: I am long Tekmira and only partially heeded my own advice of stepping out of the TKM-Ebola ‘Haertetest’ (trial provided not much upside to investors).  On the other hand, Tekmira has upside potential from a number of non-Ebola programs especially HBV and mRNA delivery.  As the worst case scenario, an outright termination of TKM-EBOLA, is a real risk, it becomes more and more difficult to get the timing right ahead of the upcoming TKM-HBV data.  If, however, you don’t mind volatility and are a long-term investor, it’s another matter.  However, at least for me, Tekmira is not the stock any more to maintain a 100% position in.

Tekmira Ebola Candidate Halted as Disease Spreads in Western Africa

There could not have been a worse timing for the Clinical Halt imposed on Tekmira’s RNAi candidate for the treatment of Ebola viral infection, TKM-EBOLA.  Just as the disease is reaching epidemic proportions in Western Africa (>500 dead), the world’s leading drug candidate for this infection with validation in the most stringent monkey models got stopped in its tracks following concerns by the US FDA regarding its immunostimulatory potential that was evidenced in the single-ascending dose part of the study (discussed here).

Efficacy in monkeys is the best you can hope for in the absence of an actual outbreak such as the current one, so I was hopeful that TKM-EBOLA could become part of the solution, especially by providing an incentive for patients to identify themselves and come to the treatment centers.  It is the prospect of dying surrounded by people in space suits instead of loved ones, and even worse the prospect of being infected by Ebola in the first place from fellow ‘inmates’ if you have been misdiagnosed that keeps people away from the hospitals.  This appears to have been key to the continued spread in addition to cultural practices such as kissing the dead as the WHO likes to emphasize (in my opinion, the condescending attitude by the behind-the-curve, out-of-touch WHO has been the 3rd key factor).

I suggest to mobilize the financial resources to fly in the latest medical equipment and offer patients to be treated with something that might help them survive.

Instead, immune-related side effects such as flu-like symptoms in healthy volunteers made the FDA ask Tekmira to provide additional data and explanations to justify proceeding to the multi-dose ascending part of the study conducted under the Animal Rule regulatory pathway.

In a way, this development might be considered support for those that have said that it is too early to treat patients with TKM-EBOLA, or any other experimental treatment for that matter.  On the other hand, you could also argue that this only shows that it is unethical to test it in human volunteers where the tolerance for side effects is much less than in somebody with a ~70% risk of dying from an infection otherwise.  Just look at the cancer drug development field, and at least in RNAi Therapeutics, I have never seen them tested in healthy volunteers even in phase I, but straight in cancer patients that have little to lose.

In fact, the immune stimulation could be the price to pay for a cure as it might be part of the mechanism of action of TKM-EBOLA either by shutting down viral protein translation and/or by interfering with the virally-induced cytokine storm itself.  These scientific issues, also as it relates to Tekmira’s platform in general, will be discussed in a follow-up post.

Test of Tekmira's credibility

I would like to close with some remarks on the credibility of Tekmira’s management.  

Management did in fact disclose the risk that there might be delays with the phase I study following results from the single-dose part of the study when it said there would be FDA review ahead of the multi-dose part of the study: 'Interim safety data submitted to the FDA for review May 7, 2014.'

Although this could be read as part of the normal regulatory process, the fact that they disclosed it made me believe that this was a real possibility.  The positive spin on the data obviously falls under the Safe Harbor of ‘forward-looking statements’ and no foul play here.  In fact, many biotechs would not even have disclosed the FDA review. 

On the other hand, many investors went along with the positive sentiments by management and will feel disappointed now.  In order to redeem themselves to this constituency, management will now have to prove that they were already prepared for this event and that they can speedily answer the questions and provide the requested data so that the trial may resume asap and that TKM-EBOLA may be offered to those in Western Africa now that it can be considered that the drug has been fully vetted for safety.

Ebola Update Questions Whether SNALP Ready to Wean Off Transient Immune Suppression

At the annual gathering of the gene therapy community today, Tekmira presented  an update on their ongoing phase I trial with TKM-Ebola, the company’s biodefense candidate for the treatment of Ebola infection developed with funding by the US government (press release here, presentation here).  I have long considered this to be a 'thankless' trial, a real ‘Haertetest’ of SNALP delivery because a) Tekmira took the risk of not employing transient immune suppression as it otherwise does, and b) the multi-ascending dose schedule (5x daily) would be as intense as in no other setting.  While taking on all these safety risks, the company would not be able to balance any safety findings with efficacy/knockdown data in this safety trial.

Indeed, what we got today was an update from the single-ascending dose part of the study which showed a dose-limiting toxicity (DLT) in the form of immune stimulation resulting in the potentially serious condition of hypotension at the top, 0.5mg/kg dose level.   

From the many emails I have received and message board postings that I have read on InvestorVillage, it seems that a common misinterpretation of the data was that they reflected poorly on the safety of 3^rd gen SNALP delivery, the most recent and most potent version of SNALP. 

It is important to emphasize that the reason why we saw this DLT in this study, but not in the various, preceding SNALP-enabled studies such as TKM-PLK1 (1^st gen), ALN-TTR01 (1^st gen), ALN-TTR02 (2^nd gen), or ALN-PCS02 (2^nd gen), is because Tekmira did not employ the transient immune suppression around the time of dosing that has become routine for SNALP technology following a similar finding of immune stimulation in the first-ever trial with SNALP-RNAi, TKM-ApoB (2009/2010).

What it means for the pipeline

This means that if the company re-adopted transient immune suppression for their other pipeline candidates, there would not be all that much to worry about with regard to encountering this type of immune stimulation again.  Transient immune suppression will not matter much for most of the diseases of high unmet need and severity pursued by Tekmira and partners (e.g. cancer, TTR amyloidosis). 

The reason why Tekmira likely did not employ transient immune suppression for TKM-Ebola is because the help by the immune system is thought to be an important adjunct mechanism to achieving cures with an RNAi approach to this highly severe, acute infection.  Moreover, suppressing the immune system might actually make the Ebola infection worse than it already is.

For other viral infections, especially HBV, the issues become more complex.  For example, it is known that with immune suppression such as steroids or certain monoclonal antibody therapies, HBV may dangerously reactivate.  However, if the immune suppression was only transient (~1 day versus an RNAi duration of activity of weeks), I am not aware that the same risks exist.  Moreover, doing something to get the virus out of its hiding place and then coming in to knock it down may actually result in the highest cure rates just as the likelihood of e-antigen seroconversion increases in immune active versus immune silent patients.   

Another part of the equation would be whether doses anywhere near 0.5mg/kg would be required for 3^rd generation SNALP-based TKM-HBV.  If say 0.15mg/kg or less would be enough, transient immune suppression may not need to be considered.

What it means for TKM-EBOLA

Today’s data raises most uncertainty with regard to TKM-EBOLA and the timeline of potential stockpiling.  In the non-human primate studies, it was the 0.5mg/kg dose that resulted in 100% protection in a post-exposure treatment setting.  If the 0.5mg/kg dose level would have been clean in the current trial, I would have been very optimistic about the prospect of accelerated stockpiling, even before full FDA approval.  At 0.2mg/kg in the NHP studies, protection was incomplete with 2/3 of the animal surviving.

In their presentation, Tekmira points to pharmacokinetic data, especially the maximal drug concentration in serum that was higher in humans than the monkeys at the same mg/kg dose levels.  In other words, Tekmira makes the case that a 0.24mg/kg dose in humans would be therapeutically equivalent to the therapeutic 0.5mg/kg dose in the monkeys.

It is true that under the Animal Rule, you have to demonstrate sufficient safety in humans at doses that are pharmacologically equivalent to those found to be therapeutic in the animal models, and these do not have to be numerically the same on a mg/kg basis.

However, based on the limited monkey-human PK-PD bridging data provided, I am yet to be fully convinced by this argument.  Ideally, there would be knockdown efficacy data for 3^rd gen SNALP available already, data showing that on a mg/kg basis, 3^rd gen knocks down genes slightly more efficiently in humans than in non-human primates. 

The best sign that Tekmira is getting crucial buy-in from the FDA and DoD would be if these agencies were in support of the dose levels chosen by Tekmira for the multi-ascending dose part of the study that is planned to start next month (0.06mg/kg, 0.12mg/kg, 0.24mg/kg).  The presentation indicated that the single-ascending dose data is under review by the FDA, and the MAD going ahead could be a positive sign with regard to agency support.

Long-term  research challenge: new modifications

Long-term, it is still desirable for SNALP to fully wean itself off from any transient immune suppression at any dose and in any indication to maximize the therapeutic opportunities.  One avenue which I have not seen Tekmira adequately explore is the use of chemical RNAi trigger modifications beyond 2’-O-methyl.  Although Tekmira scientists have nicely shown that 2-O-methylation can be very effective in dampening the innate immunostimulatory potential of an RNAi trigger sequence, comparative chemistry studies by ISIS and the clinical experience by Prosensa indicate that larger modifications on the 2’ position are even more effective in circumventing recognition by innate immune sensors such as toll-like receptors.  

With the healthy cash balance, I would expect Tekmira to reinvigorate their efforts in identifying even better immune-reducing RNAi trigger chemistries.  It could also be a worthwhile endeavor to be funded under the EBOLA contract as it has been a very successful program so far in furthering the platform while at the same time developing a biodefense agent.

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.

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.    

Viruses, Beware! This time, RNAi Therapeutics Mean Business

Viral infections have long been thought of as an attractive therapeutic area for RNAi Therapeutics.  Unfortunately, with the exception of Tekmira’s Ebola biodefense effort funded by the US Department of Defense, this area has had trouble taking off: Nucleonic’s ddRNAi-based HBV program should never have gone into the clinic (and as expected was soon terminated thereafter), and there is considerable concern that the main mechanism of action of Alnylam’s ALN-RSV01 for respiratory viral infection is due to innate immune stimulation of the unmodified RNAi trigger, not RNAi-mediated gene knockdown.

As RNAi Therapeutics as a whole has turned the corner in 2012, so has antiviral RNAi Therapeutics. 

This assessment is based on two quality programs that have either made it into the clinic recently, Calimmune’s ddRNAi candidate for HIV (LVsh5/C46), or is close to it (Arrowhead’s DPC-delivered anti-HBV candidate ARC520 for which an IND is planned in Q2 2013).  In addition, there is expectation that Tekmira’s Ebola program will be able to take advantage of the significant improvements in SNALP delivery technology, thereby considerably increasing the odds for an FDA approval under the Animal Rule (note the recentapproval of a second drug under this rule).

Suppressing Immune Suppression

Antiviral RNAi Therapeutics have to overcome the important theoretical limitation that even a potent, e.g. 99% knockdown of a viral transcript or particles may not be sufficient as in theory a single infected cell may fuel viral rebound.  It turns out that rather than blindly aiming at knockdown potency, RNAi Therapeutics are likely to be more successful when targeting an important mechanism employed by virtually all viruses: avoiding detection or removal by the immune system.

In the case of HBV, a disease affecting North of 200 million patients worldwide, the virus produces large amounts of the Hepatitis B Surface antigen (HBsAg).  This is thought to suppress, by acting as a decoy, the development of a productive anti-HBsAg immune reponse.   It is thus widely believed in the industry that reducing HBsAg is required to finally generate a drug that can achieve a functional cure, essentially paralleling the recent developments in HCV.  Interferon-based treatment regimens may actually partially work via this mechanism, but cure rates are rather low and come with considerable side effects in the form of severe flu-like symptoms.  Moreover, protein-targeting anti-HBV agents such as small molecule-based polymerase inhibitors do not seem to reduce HBsAg.  This leaves RNAi Therapeutics as the most promising mechanism of action.

A recent article in PLOS Pathogen suggests that the Ebola virus similarly churns out decoy viral proteins so as to subvert the immune system into making antibody duds that do not effectively remove the real viral particles.  It is therefore intriguing that an Ebola drug candidate by Tekmira should not only aim at providing the immune system with more time, but also that it would facilitate it mount a more effective antibody response.

No Escape

Another attraction of the RNAi Therapeutics approach for viral diseases is the fact that such agents may be more successful in prohibiting the virus to mutate around the drug and thereby escape its actions (viral escape).  Consequently, all antiviral RNAi trigger selection strategies focus on sites that are conserved in the various genotypes and quasispecies.  Even if the virus is successful at mutating around conserved sites, it is then relatively simple to include a second (such as in Tekmira’s Ebola program) or third RNAi trigger targeting a conserved site such that the virus would have to mutate around two sites at the same time- a highly unlikely event.

In addition to these general antiviral mechanisms, RNAi Therapeutics may also work through more virus-specific mechanisms.  Calimmune’s ddRNAi-based HIV candidate LVsh5/C46 for example down-regulates the cellular receptor for viral entry, CCR5, such that HIV particles cannot enter cells and integrate into their genomes in the first place.  As an ddRNAi gene therapy approach, LVsh5/C46 further takes advantage of the fact that you can express a therapeutic protein along with the RNAi trigger, thus uniquely combining mechanisms of actions in a single drug.    

Smooth Sailing Ahead

Of course, it is impossible to tell whether an RNAi Therapeutic will actually overcome a virus in each case and receive regulatory approval.  Nevertheless, I believe that the above candidates for Ebola, HBV, and HIV stand a real chance. 

The Ebola program by Tekmira is arguably the most advanced, and it is difficult for me to see how based on the non-human primate data and the lower dosages required for SNALP delivery, which should widen the therapeutic window, approval can be denied under the Animal Rule.

For the HBV and HIV candidates that are being developed along more conventional regulatory pathways, I  am similarly optimistic that they will generate some excitement in the near-term.  This is because viral load is a powerful biomarker, often also an approvable endpoint, and even early clinical studies should be able to generate such outcome data (if Arrowhead could help it, they should go straight into patients with ARC520). 

After orphan diseases involving the liver and oncology, antiviral applications are therefore poised to become the third major support of the RNAi Therapeutics platform.

SNALP Delivery Keeps On Giving: Tekmira Receives OK for Ebola Clinical Studies

On Monday, Tekmira announced that it has received the Green Light from the FDA to go ahead with clinical studies of its SNALP-enabled biodefense candidate for the treatment of Ebola infection. Tekmira is developing TKM-EBOLA under a $140M contract from the US Department of Defense following spectacular results in non-human primates reported last year in The Lancet. Depending on whether you want to count in the stalled TKM-ApoB program or not, this marks the 5^th or 6^th SNALP-enabled candidate in clinical development, illustrating the strength of this systemic RNAi trigger delivery platform: TKM-ApoB, ALN-VSP02, TKM-PLK1, ALN-TTR01, ALN-PCS02, and TKM-EBOLA.

In other words, 6 of the last 7 systemic RNAi INDs or IND equivalents were for SNALP-enabled product candidates (period: 2008-2011). This plus the unparalleled, strong pre-clinical track record of this platform demonstrating efficient knockdown in the liver, solid tumors, and viral infections not only in rodents, but also a number of non-human primate models supports the notion that Tekmira’s SNALP is the industry’s most advanced and valuable RNAi delivery platform. There are thankfully other promising RNAi delivery technologies lining up behind SNALP, but this is not Lake Wobegon where everybody can be above average

Next Steps for TKM-EBOLA

Since TKM-EBOLA, as a treatment for a disease in which controlled human studies are ethically or practically impossible, is being developed under the Animal Rule, this phase I study will not only have to demonstrate adequate safety, but more importantly yield pharmacokinetic and potentially biomarker data that replicates what is seen in the successful treatment of the pre-clinical animal models of the infection. At the same time, it may be worth trying to test the limits of how long treatment can be delayed after symptom onset in the animal models as a common criticism of these studies is that in the real world it may take some time before Ebola victims are identified and treated. In The Lancet studies, rhesus monkeys received first treatments already 30 minutes after exposure to the virus which may model a needle stick scenario in an Ebola research laboratory, but not exposure of the civilian population e.g. in a subway system. Similarly, achieving similar pre-clinical efficacies with 1mg/kg as with the tested 2mg/kg dose in The Lancet studies may bring it more in line with the clinical SNALP safety experience so far. On the manufacturing front, it would be helpful if Tekmira succeeded in providing SNALP in lyophilized form which would increase its utility in the field.

On the other hand, the fact that the rhesus model seems to closely replicate, if not represent a particularly severe form of the human disease, and the absence of a (experimental) therapy for Ebola that has shown comparable promise, should position TKM-EBOLA well for stockpiling despite any lingering real-world concerns. From an Army point-of-view, as long as it has been shown to be safe and well tolerated in humans, having the most promising treatment as a stand-by for a virus as deadly as Ebola is better than nothing at all, a consideration that may result in stockpiling even before, or in the absence of FDA licensure.

In that regard, TKM-EBOLA will be mainly competing with AVI Biopharma’s morpholino antisense candidate AVI-6002 which is being developed under an essentially identical contract with the DoD. A Nature Medicine paper published last year reported that this candidate was successful in rescuing ~60% of infected rhesus macaques, although this represents a roughly 3-fold increase in risk of dying compared to the highly comparable SNALP studies in The Lancet. Nevertheless, AVI Biopharma still enjoys a slight time advantage as it has already begun phase I safety studies earlier this year. A late-October 2011 update by AVI stated that treatment in the first 5 of 6 dose-escalating cohorts was well tolerated and that the Data Safety Monitoring Board recommended further escalation to the last 9mg/kg cohort. Nevertheless, once years behind the AVI program, Tekmira has done well catching up with the competition.

Importance beyond TKM-EBOLA

Besides representing an invaluable strategic asset for Tekmira (it is earning the company significant hard cash now and revenues from stockpiling may come well ahead of the customary 5-10 years it usually takes a normal drug to navigate the FDA approval maze), the approval of the IND further demonstrates that SNALP is indeed the productive delivery platform that also I have long had hopes for it to be, with applications not only for knockdown in the liver and solid cancers, but also phagocytic cells (an important target cell population for the Ebola indication). It is also a stamp of approval by various regulatory agencies around the world that SNALP (including reliable manufacturing) is fit for clinical development. An IND for ALN-TTR02 and phase I results for ALN-PCS02 are next.

Comment on Roche Partnership with PTC

Roche disclosed today that it has signed a collaboration with PTC Therapeutics for the treatment of Spinal Muscular Atrophy, including a $30M upfront fee for pre-clinical assets. This follows a similar deal by AstraZeneca and PTC in oncology earlier this year. PTC develops a platform for the modulation of post-transcriptional processes using orally available small molecules.

What is disappointing to me is that these are examples of Big Pharma companies with an interest in RNA Therapeutics (note that AstraZeneca has a relationship with Silence Therapeutics for which a go/no-go is imminent), but which feel more comfortable risking their money on a technology based on phenotypic tissue culture screens with considerable uncertainty as to clinical relevance and the safety risks inherent in modulating very general gene regulatory mechanisms, instead of using the much more straight-forward oligonucleotide approaches. The reason? Oral bioavailability and coziness with small molecule chemistry. The fate of these collaborations will be an important test case of whether putting patient convenience and other marketing considerations ahead of what is the scientifically best approach will bring Big Pharma the desired outcome. Of note, only a few months ago, Genzyme handed back PTC a candidate for the treatment of Duchenne Muscular Dystrophy and Cystic Fibrosis after spending more than $100M on it.

My view: Technical success trumps patient convenience when it comes to diseases as severe as SMA, DMD, or cancer.

Interested in the Chinese market for RNAi Therapeutics, but language barriers exist? Get expert help from somebody that understands RNAi.

A comparison of Tekmira’s and AVI Biopharma’s Candidates for the Treatment of Ebola Virus

I was quite amused today, while driving a car on Borneo, the local radio report the headline ‘US scientists said that they are ready to start clinical trials for Ebola’. It was yet another reminder that oligonucleotide therapeutics, including RNAi is firmly emerging from the research stage, entering the medical arena and gaining more widespread attention.

As you may also have heard by now, 3 months after the impressive publication in The Lancet by Tekmira and collaborators that liposomal siRNA essentially cured non-human primates from otherwise lethal infections of Ebola virus, morpholino antisense company AVI Biopharmaceuticals followed up with results from their own Ebola non-human primate treatment studies in the equally prestigious journal Nature Medicine (Warren et al.: Advanced antisense therapies for postexposure protection against filovirus infections). Since both companies were recently awarded highly lucrative government contracts from the US Department of Defense to further develop these two oligonucleotide therapeutic candidates for the treatment of Ebola and therefore have to be considered competitors for further contracts, I will briefly compare and contrast the results from the two studies.

One remarkable benefit of having both lines of research enjoy funding from the DoD is that they have been highly standardized which makes them very comparable to the extent that even the animal laboratory was shared, I believe. So no excuses with 'in our hands' or the likes. In each case the goal was to evaluate the RNAi or antisense in a post-infection model whereby the oligo Rx was first given once 30-60min following intramuscular injection of rhesus macaques with 1,000 plaque forming units of the Zaire strain of Ebola, an amount many orders of magnitudes higher than needed to kill such an animal if left untreated.

Just as a reminder, in this treatment regimen, Tekmira’s intravenously administered SNALP-RNAi when given 3 times every other day or daily for 6 days following viral exposure rescued 2 of 3 and 4 of 4 animals, respectively.

In the AVI study, morpholino antisense molecules which have been slightly altered compared to previous studies to be positively charged to facilitate enhanced cellular uptake and improved target RNA binding, were also given daily, although in this case the follow-up administration period lasted for 10-14 days and the dosage was 40mg/kg compared to 2mg/kg siRNA. In addition to intravenous administration which the investigators refer to as the preferred route of administration for needle stick scenarios and the like, some studies involved simultaneous intraperitoneal and subcutaneous administrations.

Route of administration, however, did not seem to make much of a difference since in both cases around 60% of the monkeys were rescued from near-certain death: 5 of 8 in the subQ+i.p. regimen, and 3 of 5 in the intravenous regimen.

Put differently, the risk of dying from Ebola infection was 14% in the Tekmira study (1 out of 7 animals; 0 of 4 with the optimized protocol) compared to 39% in the AVI studies. Although the numbers are still small, this indicates an almost 3-fold risk reduction with SNALP-RNAi compared to morpholino antisense.

So while Tekmira’s SNALP-RNAi may in fact now lead the race towards a drug that can treat Ebola virus infection, it is far from over. AVI is apparently ready to move into safety studies with human (healthy) volunteers. In addition to such clinical studies, both companies and their collaborators will have to test in further non-human primate studies how long they can delay treatment after the initial infection, as ‘in the field’, as opposed to laboratory accidents and first responder situations, treatment will only begin after first symptoms emerge.

However, with the current efficacy of TKM-Ebola and what appears to be an already extensive pre-clinical safety database, if the initial human studies are uneventful, the case could be made that a first-generation Ebola standby for needle pricks and first responders in local outbreaks may be quite close indeed. In fact, researchers exposed to these viruses should be pushing for it, and the fact that the current SNALP-RNAi has to be administered intravenously should not be a problem for such purposes.

AVI’s antisense morpholino though may have some advantages over the SNALP-RNAi for wider outbreaks in that it may be administered subQ, although a pure subQ protocol has not been tested yet in the post-infection model and I am not clear about the practicalities of administering 40mg/kg x70kg= 2.8 grams (!) of oligonucleotides subQ. With the more potent, second generation SNALP-RNAi formulations ('LNP' is the official designation now), subQ administration of liposomal siRNAs should become more practical and I would not be surprised if some of the future Ebola contract funds were to be spent on further developing subcutaneous LNP administration.

While it was not obvious from the paper in The Lancet, reading the latest paper, it is quite clear that the 2 companies and probably even different groups within the Army that work on Ebola Rx are strongly competing with each other. It reminds me of the strategy of principal investigators of some ‘post-doc labs’ where at least 2 different post-docs are being competitively put on the same project. This way, the principal investigator increases his chances of timely success. Not being a military man myself, it would also make sense from a military point of view to even have 2 alternative Ebola Rx stockpiles, just in case one turns out to be more desirable than the other in a real emergency.

In the end, while the value of biodefense agents is often difficult to determine, the DoD Ebola program brings two significant benefits. One is that the program allows the involved companies plenty of room to develop their underlying platform technologies such as facilitating the scale-up of their manufacturing processes. The other is the images evoked by viruses such as Ebola and the attention it directs towards this rapidly growing area of oligonucleotide therapeutics. Even a remote island like Borneo is an escape from it no more.