Sanofi Genzyme will partner with Alnylam Pharmaceuticals to develop one of its drug candidates, while taking a pass on another, Alnylam said today.

The specialty care global business unit of Sanofi has opted to co-develop and co-commercialize the hemophilia and rare bleeding disorders candidate fitusiran in the U.S., Canada, and Western Europe.

The decision came, Alnylam said, based on promising interim results from a Phase I study of fitusiran presented at the World Federation of Hemophilia (WFH) in late July, as well as additional data to be presented next month at the 58th American Society of Hematology (ASH) Annual Meeting & Exposition, set for December 3–6 in San Diego.

Alnylam added that it was on track to initiate a Phase III program for fitusiran in early 2017. Sanofi Genzyme previously opted to develop fitusiran in the rest of the world, retaining exclusive rights.

“This decision allows us to broaden the global reach and accelerate the commercial development of fitusiran,” Alnylam CEO John Maraganore, Ph.D., said in a statement.

The companies launched their global alliance in 2014.

In the U.S., Canada, and Western Europe, the companies will share 50/50 development and sales and marketing costs related to fitusiran. Sanofi Genzyme agreed to pay Alnylam up to $75 million tied to achieving development and regulatory milestones for fitusiran, starting with $25 million upon the initiation of the first global Phase III clinical trial for fitusiran.

Sanofi Genzyme will also pay tiered double-digit royalties up to 20% on annual fitusiran net sales in the territories where the companies are co-developing the RNA interference (RNAi) candidate. In those areas, the companies agreed to share profits equally, with Alnylam expecting to book product sales.

Alnylam said it will go it alone on developing another drug candidate, the acute hepatic porphyrias candidate ALN-AS1, after Sanofi Genzyme elected not to opt in on developing the investigational RNAi therapeutic targeting aminolevulinic acid synthase 1 (ALAS1).

Alnylam did not disclose a reason for Sanofi Genzyme’s decision, which it said was based on Part A and Part B results from an ongoing Phase I study that were presented in September at the Society for the Study of Inborn Errors of Metabolism (SSIEM) meeting.

At the time, Alnylam said the results showed that ALN-AS1 administration resulted in rapid, dose-dependent, and durable silencing of liver ALAS1 messenger RNA (mRNA) in both the trial’s 20-patient Part A and the eight-patient Part B. In addition, the company, data showed rapid and dose-dependent lowering of ALA and PBG of up to 95%. Reductions in aminolevulinic acid (ALA) and porphobilinogen (PBG) were highly durable, with effects lasting for over 10 months following a single dose.

While there were three serious adverse events, all were all deemed unlikely to be related to study drug, according to Alnylam.