Monday, July 28, 2008
RNAi Therapeutics delivery: not a zero-sum game
To my surprise, however, it then transpired that the Roche acquisition had been interpreted by some as a vote for DPC and against SNALP RNAi delivery, leading some to sell in a panic. This blog will briefly outline why, unlike is the case in the battle for core RNAi trigger IP, RNAi Therapeutics delivery is not a zero-sum game with room for more than just a handful of technology platforms.
As is becoming more evident by the day, RNAi Therapeutics offers the opportunity to address a very wide range of diseases. As all disease has a genetic element, regulating gene expression should always be able to modify or even correct a disease. To do this, however, one has to be able to knock down the desired genes in various different organs, tissues, and cell types. If there was a universal RNAi delivery technology, it would have to be able to physically contact every cell in the body, yet only knock down genes in the disease-related subset of cells.
Based on the limited publicly avaibable data, Mirus’ DPC technology actually promises to come close to that dream. It is very small in size (~20nm) and therefore satisfies at least one of the pre-requisites of achieving a broad biodistribution. Moreover, it has been shown to be capable of differentiating between the different cell types within an organ, in this case the liver, depending on which sugar had been added- all in the absence of apparent toxicity! It will clearly be exciting to learn more about the delivery profile of DPCs. Nevertheless, I doubt that DPC will necessarily be the delivery system of choice for every indication.
This is because the choice of a delivery system is not only determined by the ability to knock down a gene in a given cell, but also by factors such as overall maturity of the technology, safety as determined by the dose required to achieve such gene knockdown, the biodistribution and cell type-specific gene knockdown on a systemic level, as well as by cost, route of administration, and stability of the formulation.
Consider for example an RNAi Therapeutics against the kinesin spindle protein (KSP) that is being developed by Alnylam as a treatment for liver cancer. Although directly interfering with cell division by down-regulating KSP is seen as a very promising anti-cancer strategy, anti-KSP small molecule programs have indicated considerable dose-limiting toxicities that appear to be target specific. This, however, should not come as that much of a surprise since interfering with spindle function would be predicted to affect normally proliferating cells as well, particularly those of the hematopoietic system. Well, this dilemma is not new at all to the cancer field, and often the benefits outweigh the side-effects, but this example illustrates the value of a delivery technology such as SNALP-RNAi that can be tuned to deliver around 95% of the injected dose to the liver, including hepatic tumor tissue.
Certainly, Roche may elect DPC delivery over SNALP delivery (note: Roche has access to both) for some liver indications, but that type of competition has actually only decreased with Mirus Bio out of play. This is because all the other two dozen or so pharmaceutical companies equally interested in RNAi Therapeutics, will now have access to one less viable delivery technology. The incentive to gain access to the still fairly accessible RNAi delivery platforms with clinical potential has therefore never been greater. Roche, of course, enjoys the luxury of being able to choose between two technologies that, maybe in an effort to avoid the appearance of favoritism, it has valued essentially identically based on their $5M equity investment in Tekmira at $2.4 per share(Tekmira now has 51.6M shares outstanding).
Bottom line, due to the ever growing attraction of RNAi Therapeutics, any company, and that goes beyond Tekmira-SNALP, with clinically relevant RNAi delivery technology and a good IP package to protect it can rest assured that they own a very hot commodity.
RNAi Therapeutics portfolio update: With Roche’s validation of the value attributed to clinically relevant RNAi delivery technologies and with increased clinical visibility, I have slightly increased my position in Tekmira while paring back on the overweight ALNY position. In another attempt to capitalize on the idiosyncracies of the stock market, I have converted the RXi Pharmaceutical holdings back into CytRx shares (CytRx owns about 50% of RXi, but none of that is reflected in CytRx’s market cap) and added some more at the cost of largely cashing out of RNAi trigger competitor Silence Therapeutics (a token $1 investment is maintained to monitor stock performance).
Disclosure: Long Tekmira, Alnylam, Targeted Genetics, Oxford Biomedica.
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