Astellas Pharma Inc. exercised its option to buy Potenza Therapeutics Inc. for $164.6 million up front under a collaboration deal between the companies.

Astellas and privately held Potenza entered a deal in 2015 to develop immuno-oncology therapies — drugs which modify the immune system to fight cancer — including an exclusive option for the Japanese drugmaker to acquire the Cambridge, Mass.-based company.

The collaboration yielded three cancer therapies — ASP8374/PTZ-201 and ASP1948/PTZ-329, which are in phase 1 studies; and ASP1951/PTZ-522.

U.S.-based Potenza will become a wholly owned unit of Astellas following the deal. Potenza's shareholders will also be eligible for additional payments of up to $240.1 million depending on the success of certain clinical development programs.