Tekmira Reports Important Advances in Widening Applications of SNALP RNAi Therapeutics Delivery

‘We Make RNAi Work.’

Tekmira’s slogan may sound a bit cheesy as they all do, but when you consider that it is the only company that has managed to translate the theoretically very powerful unilamellar liposome technology into the clinic and ready for commercialization while essentially everybody else is being frustrated from following up on promising early-stage results with liposomal delivery, it is a very appropriate one.

This leadership position was underlined in a recent presentation by Tekmira Pharmaceuticals at the CC-CRS meeting on May 25 (see related press release here). There, the company presented the advances it has made in widening the applications of SNALP delivery for use in major additional medical and commercial opportunities. Some of these advances were made in collaboration with large pharmaceutical/biotech companies, illustrating that Tekmira views these collaborations not only as a way to simply monetize their assets, but also as a way to grow the potential of SNALP delivery to areas such as respiratory disease (after cancer arguably the highest priority area in drug development) and targeted RNAi delivery by leveraging the partners' capabilities.

However, before reporting on the company’s advances in nebulizing and tagging SNALPs with monoclonal antibodies, the presenter made the point that more potent lipids is not what is holding it, or the field back from applying SNALP technology. Using ApoB as a target in rodents (mouse and rats), the data show that many of Tekmira’s lipids developed without Alnylam, including Alnylam’s Canadian subsidiary Al-Cana, have equal or superior potency to the MC lipids that have become one point of contention in the Tekmira-Alnylam litigation as such lipids, in addition to manufacturing, have been one of the pillars of Tekmira's gate-keeping position in SNALP delivery. For example, in the case of ApoB and the 2111 lipid 10 microgram/kg SNALP-formulated siRNA triggered more than 50% target gene suppression.

The presentation then moved on to demonstrating the progress Tekmira has made in formulating SNALP for respiratory and actively targeted delivery applications. Actually, it is formulating SNALP at commercially relevant scales that is Tekmira’s most valuable competitive asset, and this is why the unbelievable disclosures in the Amended Complaint that Alnylam abused its insights into Tekmira’s technology to misappropriate and represent formulation technology as its own are so grave (I will give it a couple of more days rest before I comment on Tekmira's Amended Complaint).

Data on the Ebola biodefense program show that the US government contract has been successfully commenced and is working just as the program was intended to work: not only is the company on track to developing a treatment for Ebola infection with the goal of filing an IND in the second half of this year, but the process has proven very valuable in maturing and bringing SNALP delivery to the next level, especially in terms of one of the most critical steps in SNALP delivery: high-quality manufacturing at commercial scale. Being able to formulate 1 kilo-gram siRNA instead of just 10 grams at a time without changing critical SNALP parameters such as size, encapsulation efficiency and poly-dispersity is enormous and means that SNALP can not only be used for running clinical trials, but can also be readily commercialized.

Data on targeted SNALP delivery showed that it is possible to decorate SNALPs with antibodies using Genentech’s defined THIOMAB antibody conjugation technology, again without compromising on critical SNALP parameters. Tissue culture data show that highly specific, targeted uptake and gene silencing can be achieved using these antibody-decorated particles. Such liposomes will have particular utility for applications outside the liver where delivery does not rely on ApoE (apparently initially an insight of Tekmira, not Alnylam as that company claims- more on this in that other blog post). I look forward to learning more about the performance of these particles in animal models, especially for cancer applications.

Another area where antibody-targeting could have utility is in the delivery of siRNA to the respiratory epithelium following nebulization. As we know, Alnylam’s ALN-RSV01 has been overshadowed by concerns that some, or even most of the antiviral activity of the nebulized naked and unmodified siRNAs may be due to innate immune stimulation. More generally, while I am convinced by now that high concentrations of naked siRNAs on the epithelial lining of the respiratory tract can achieve some target gene knockdown, to my knowledge, there has been no convincing report of RNAi knockdown through inhaled siRNA delivery robust enough to warrant clinical development.

Tekmira’s success in nebulizing SNALP particles therefore is the first critical step in opening up the respiratory space for inhaled RNAi Therapeutics (there are some strategies such as cationic lipoplexes or PEIs that can deliver to parts of the lung following systemic administration). Again, the key to success will likely come from proper formulation/manufacturing.

Using traditional LNPs, nebulization leads to gross changes in morphology, uniformity, size, and dramatic loss of encapsulation efficiency (from mid 90%s to 10%s). However, with undisclosed changes to Tekmira’s SNALP formulation, it is now possible to nebulize SNALP without changing these parameters. Tissue culture data confirm that these particles retain unchanged knockdown activity.

Altogether the presentation emphasizes that not only has Tekmira/Protiva been leading SNALP technology in the past but is continuing to do so…by a distance. It seems that in order for it and shareholders to capitalize on this leadership, more than getting the technology right, it is preventing Alnylam from using partnership status, money and PR from misappropriating the technology and representing it as its own.

Comment on referring to Tekmira’s delivery technology as SNALP versus LNP

Stable nucleic acid lipid particles (SNALPs) are a form of liposomal nanoparticle (LNP). The reason why I prefer to keep using the narrower term ‘SNALP’ when referring to Tekmira’s liposomal delivery technology instead of adopting the broader term ‘LNP’ as both Tekmira and Alnylam have done, is that the liposomes in clinical development by Tekmira and Alnylam currently and in the foreseeable future are still based on the original formulation (cationic/ionizable lipid+neutral helper lipid+PEG-lipid+siRNA), whether the cationic/ionizable lipid is a different one or whether a ligand is added or not. The term ‘SNALP’ is therefore a reminder of the innovator behind the technology, Protiva (now part of Tekmira), as they coined the term.

In a way, you would think that such terms that lack precise scientific definition anyway should not matter that much. However, in Alnylam’s efforts to marginalize Tekmira’s role in liposomal delivery, first changing from ‘SNALP’ to ‘LNP’, and then calling the newer formulations ‘second-gen LNPs’ has been an effective way of hiding ownership of the technology with the goal of eventually not only denying Tekmira contractually owed milestones and royalties, but by-passing Tekmira altogether (incl. manufacturing) also to appease partners such as Novartis and Takeda. ALN-PCS01 looks set to be the first battleground.

Breaking News: Alnylam Reports on the Safety of Inhaled ALN-RSV01

The eyes of the RNAi Therapeutics world are on Alnylam as they are approaching critical clinical milestones for their lead development program ALN-RSV01 for the treatment of respiratory syncytial virus infection.

Before initiating phase II studies in naturally infected adults, the company seeks to gather more information first on the pharmacodynamics of RSV-01 in an experimental infection model where the siRNA is administered by nasal administration (top-line data expected early 2008; company reported patient enrollement complete now), and second from the safety of an inhaled version of RSV-01, the eventual route of administration, in healthy adult volunteers. Results from the latter phase I trial were just reported at the 18th Annual Drug Delivery to the Lungs meeting in Edinburgh, Scotland.

This study included 109 subjects, 71 of whom received siRNA either in a single dose (0.1mg/kg to 3mg/kg) or multiple doses (0.01mg/kg to 0.6mg/kg once daily for 3 days). The safety data were encouraging as there were no serious adverse events reported. Nevertheless, the press release mentioned a “mild to moderate flu-like adverse event” at the higher dose group in the single-dose arm. While this is pure speculation, this reminds me of the fact that RSV-01 is an unmodified siRNA and should therefore be more prone to elicit cytokine responses, an area Alnylam by the way is taking quite seriously as they actively seek to recruit scientists working in the field of immunostimulatory nucleic acids, which by the way may be accelerated by the recent acquisition of Coley by Pfizer. Indeed, I would not be surprised if part of the remarkable antiviral efficacy of RSV-01 is based on the siRNA acting as an isiRNA, the term with which Gunther Hartmann from Bonn describes small interfering RNAs with immunostimulatory properties.

In order to find the best therapeutic window, Alnylam has also been working on comparing the pre-clinical efficacy of single-dose versus multiple dose RSV-01. Gratifyingly, for the same amount of total siRNA administered, multiple dose administration was significantly more potent. This means that a good strategy of increasing antiviral efficacy while at the same time decreasing the risk of eliciting flu-like effects may be to choose multiple dose administration for the phase II studies of naturally infected patients.

Another interesting point mentioned in the press release is that siRNA delivery as evidenced by siRNA plasma levels was remarkably efficient compared to some pre-clinical data. Well, I guess had they not observed siRNA in the plasma, then the press release would have stated that avoiding systemic exposure was an additional safety feature of RSV01. This is how the phase I nasal data were interpreted. In any case, this is reminiscent of recent data for systemic siRNA administration to the liver where the efficacy and duration of RNA silencing in non-human primates was above expectation based on small animal experience and may have in fact contributed to the side-effects observed at the higher doses. But before actual plasma levels are reported, it is premature to speculate whether systemic siRNA administration by inhalation should be considered for other indications.

Overall, while the results indicate that the development of RSV-01 is not without risk, Alnylam continues to demonstrate that by conducting a wide-ranging scientific program supporting the compound, it will allow them to choose the most promising development path. The apparently efficient delivery efficacy via nebulizer makes me quite bullish about the antiviral efficacy of ALN-RSV01 so that safety should be the focus of future studies.