UPDATE 1-Sanofi signs up to $750 mln drug deal with Regulus

* Initial focus of alliance is fibrosis

* Regulus gets $25 mln upfront plus $10 equity investment * Regulus is jointly owned by Alnylam and Isis

(Adds details on deal value, background)

PARIS, June 22 (Reuters) - French drugmaker Sanofi-Aventis (SASY.PA) has struck a strategic alliance potentially worth up to $750 million with Regulus Therapeutics, taking it into the emerging field of microRNA.

The alliance will initially focus on developing new treatments for fibrosis, an excessive growth of fibrous tissue that can cause various disorders, Sanofi said on Tuesday.

MicroRNAs are small scraps of genetic material which are being explored as a new class of therapies for a range of diseases, given their ability to regulate gene expression.

Sanofi and Regulus will collaborate on microRNA drug discovery and preclinical development for an initial four targets, including the lead fibrosis programme. Sanofi also has an option to develop and commercialise other compounds, beyond the first four targets.

Regulus, which is jointly owned by Alnylam Pharmaceuticals (ALNY.O) and Isis Pharmaceuticals (ISIS.O), will receive a $25 million upfront fee and a future $10 million equity investment.

In total, the alliance could be valued at over $750 million when taking into account upfront payments, equity investment, research funding, and potential preclinical, clinical and commercial milestone payments for multiple products. (Reporting by Ben Hirschler; Editing by Hans Peters)