Amgen and Cytokinetics have expanded their strategic collaboration to provide the biotech giant rights in Japan to Cytokinetics’ experimental heart failure drug for a $15 million license fee. In addition, Amgen is purchasing $10 million of Cytokinetics common stock.

The two companies first entered their collaboration in 2006 to develop and commercialize small molecule drugs that activate cardiac muscle contractility to treat heart failure. The original license agreement for the lead compound in the collaboration excluded rights in Japan. The amended agreement now grants those rights for the experimental drug omecamtiv mecarbil, as well as related compounds.

In addition, Cytokinetics is eligible to receive additional pre-commercialization milestone payments for the development of omecamtiv mecarbil in Japan of up to $50 million as well as royalties on sales of the drug in Japan.

Cytokinetics plans to conduct an early-stage pharmacokinetic study to support the inclusion of Japanese patients in a potential late-stage trial for omecamtiv mecarbil. Under the terms of the expanded agreement, Amgen will reimburse Cytokinetics for the cost of that study.

The terms of the stock purchase agreement calls for Amgen to purchase shares at a price per share equal to the 10-day trailing average of the closing price of Cytokinetics’ stock on the last trading day prior to execution of the stock purchase agreement

When the companies began their collaboration, Amgen paid Cytokinetics a $42 million upfront license fee. It also purchased nearly 3.5 million shares of Cytokinetics common stock for $9.47 a share or about $33 million in total.

In May 2009, following completion of mid-stage studies, Amgen exercised an option to participate in future development of omecamtiv mecarbil.