Sunday, July 22, 2007
Looking Ahead: Alnylam-Medtronic Alliance Stop-Go Decision Expected Soon
According to regulatory filings, the original decision making due date was April 2007, but was then postponed to July 2007. It is interesting to speculate that this delay may have been either caused by scientific uncertainties or is the consequence of drafting a comprehensive and therefore complicated co-operation agreement. Certainly, in development time-frames, 3 months do not seem to be sufficient to reasonably expect major new breakthroughs had there been fundamental scientific problems.
Medtronic realised early on the potential of RNAi as a new class of drugs that could be used with their drug delivery devices. Only shortly before the 2005 agreement, in August 2004, Medtronic published a patent on the treatment of neurodegenerative diseases such as Parkinson’s, Alzheimer’s, and Huntington’s, through intracranially delivered siRNAs using Medtronic’s implantable catheters (United States Patent 20040162255). Two years later, a similar patent was published for the treatment of neuropathic pain.
While pertinent in vivo data are lacking in these patents, it is clear that Alnylam already has amply tested Medtronic’s devices. Josephine Lai from the University of Arizona Health Sciences Center in Tucson, a Alnylam collaborator, for example has published strong in vivo data on intrathecally delivered siRNAs [Luo et al. Mol. Pain 1: 29 (2005)]. It is also of note that in this study, siRNAs were most efficient when formulated in the liposomal i-Fect transfection reagent from Neuromics. The same reagent was also successfully applied in rescuing mice from lethal flavivirus infection of the CNS [Kumar et al. Plos Med. 3: e96 (2006)].
One potential limitation with the local delivery of siRNAs and shRNA vectors such as AAV, however, is to achieve sufficient diffusion of the RNAi inducing agent to its target cells. That diffusion of macromolecules in the dense matrix of the CNS may also be an issue with a device from Medtronic similar to the one Alnylam is evaluating, is suggested by the failure of a phase II clinical experience of the neurotrophic factor GDNF for Parkinson’s [Salvatore et al. Exp. Neurol. 202:497 (2006)]. This particular experience, however, has to be taken with a grain of salt, as there appears to be some controversy about the interpretation of the trial results [Slevin et al. Annals Neurol. 59:989 (2006)]. A positive announcement on the Medtronic-Alnylam alliance may therefore indicate that it is possible to achieve sufficient siRNA diffusion.
Nevertheless, local delivery may not be sufficient for diseases where the whole brain has to be targeted, such as in viral infections and brain tumours. Here, systemic delivery solutions are needed. While the blood-brain barrier has historically been regarded as a major obstacle to achieving that goal, targeted approaches such as the rabies-peptide conjugation approach that I have highlighted in my June 19 Blog (“New Breakthrough in the Systemic Delivery of RNAi for the Brain”) and similar efforts make me hopeful that a range of both local and systemic delivery strategies will eventually prove successful in addressing a number of diseases of unmet medical need. These issues also highlight once more, that it will be critical to carefully tailor the delivery of an RNAi Therapeutic to its disease application.
Blog Watch: The ‘Old Vic’ blog talks about a possible takeover or significant RNAi Therapeutics alliance involving Silence Therapeutics: http://www.sharescity.com/2007/07/silence-therapeutics-takeover-rumours.html
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