The next big thing in drug development might be very small.

MicroRNAs (miRNAs) are the focus of Regulus Therapeutics, a seven-month-old partnership between Alnylam Pharmaceuticals (Nasdaq: ALNY) and Isis Pharmaceuticals (Nasdaq: ISIS). These molecular mini-messengers hit the big time this week when Regulus signed a development deal with GlaxoSmithKline (NYSE: GSK).

MiRNAs are naturally occurring molecules that only recently were discovered to individually regulate different genes. A drug developed to target one miRNA would affect several proteins at once. Glaxo and Regulus are working to apply this discovery to treat widespread diseases such as rheumatoid arthritis.

The miRNA method is different from the industry's more standard "one drug, one protein" method. For example, Abbott Labs' (NYSE: ABT) Humira or Johnson & Johnson's (NYSE: JNJ) Remicade both target a single protein, TNF alpha.

The development deal is a big one, but like Glaxo's other deals with development-stage drugmakers, such as Exelixis (Nasdaq: EXEL), most payments won't happen until a new drug proves its effectiveness. Regulus gets only $20 million upfront -- $5 million of which is a loan that can turn into Regulus stock for Glaxo.

The prize for Regulus lies in the roughly $600 million it could receive in milestone payments. The company gets that sum if all four compounds discovered so far meet their development, regulatory, and sales goals. Regulus will also get tiered royalties as high as double digits on sales of drugs developed by the partnership. Sounds enticing.

Glaxo is shrewd to hedge its bets, and I expect that any other deals Regulus signs with it will have similar structures. The study of miRNAs is in its infancy -- Regulus doesn't expect to have clinical candidates from this Glaxo deal for three years at least, and the first miRNA might be a decade away from the market.

Still, I like Glaxo's move to get in on the ground floor. Even if miRNAs turn out to be horrible drug targets, the pharma is in for such a relatively low initial cost that the gamble is worth it.

Other Foolishness on RNA:

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. Glaxo and J&J are selections of the Income Investor newsletter. The Motley Fool owns shares of Exelixis. The Fool has a disclosure policy.