Drug developer Cytokinetics and Astellas Pharma Inc. are teaming up on the research, development and commercialization of skeletal muscle activators.

The companies said Tuesday that the main goal is to advance some therapies for diseases and medical conditions related to muscle weakness.

Japan’s Astellas will have exclusive rights to develop and commercialize drug candidates that may come about from these activities, subject to certain Cytokinetics’ development and commercialization rights. Astellas also has an exclusive license from South San Francisco, Calif.-based Cytokinetics Inc. for the rights to co-develop and commercialize one of its drug candidates, CK-2127107 in certain indications. The drug candidate is currently in early-stage testing.

The companies expect to collaborate over two years, and Cytokinetics is eligible to receive about $40 million as an upfront payment and reimbursement of research and development during that time. In addition, Cytokinetics is eligible to receive more than $450 million in pre-commercialization and commercialization milestones plus royalties.

Cytokinetics’ stock fell 40 cents, or 3.2 percent, to $11.90 in afternoon trading. The stock has more than doubled in the year to date.