RNAi relies on the use of short nucleic acid sequences that bind to and inactivate the machinery in the cell that leads to protein transcription - a process known as gene silencing - in a manner that is similar to that achieved using antisense oligonucleotides.
It has emerged as a valuable tool for drug discovery and research but, as with antisense before it, difficulties in getting the compounds to where they are needed in the body has held back its development as a therapy.
The new alliance between Merck and Alnylam is focussing on using RNAi to treat macular degeneration of the eye, a leading cause of blindness, as well as other ocular diseases caused by abnormal growth or leakage of small blood vessels in the eye.
Delivering drugs into the eye is relatively simple - this is why the first and only antisense treatment approved to date is for an eye disease - and with Merck's drug development expertise behind the alliance, the prospects of an RNAi-based drug reaching the market have got brighter.
Under the terms of the agreement, Alnylam will receive an initial cash payment from Merck and could receive additional payments on the achievement of specified progress milestones, up to a total of $19.5 million (€16m).
Merck and Alnylam will jointly fund the development and share the profits from any resulting RNAi therapeutics in the US. Meanwhile, Alnylam will also have the option to co-promote these RNAi therapeutics in the US. Marketing and sales outside of this territory will be conducted by Merck, with Alnylam receiving royalties.
More than 1.6 million adults over the age of 50 in the US currently suffer from advanced AMD, a condition that causes severe deterioration of vision and may ultimately cause blindness.
Last September, Merck and Alnylam entered into a broad-ranging collaboration to develop RNAi-based therapeutics and technologies.