Astellas shares were off nearly 1% to $17.01.
Tokyo-based Astellas said it would pay $60 for each share of the San Francisco-based Audentes. The boards of both companies approved the transaction, which is expected to be completed in the first quarter of 2020.
Astellas will acquire Audentes through Asilomar Acquisition Corp., a wholly-owned subsidiary of Astellas US Holding. Astellas said it was still reviewing the impact of the completion of the transaction on its financial results for the fiscal year ending March 31.
Audentes will operate as an independent subsidiary, the companies said, "with access to the global scientific and development resources of Astellas to accelerate product development and manufacturing expansion for the combined entity."
Kenji Yasukawa, Astellas' president and CEO, said in a statement that "Audentes has developed a robust pipeline of promising product candidates which are complementary to our existing pipeline, including its lead program AT132 for the treatment of X-Linked Myotubular Myopathy (XLMTM)."
Matthew Patterson, Audentes' chairman and CEO, said that "with its focus on innovative science and a global network of research, development and commercialization resources, we believe that operating as part of the Astellas organization optimally positions us to advance our pipeline programs and serve our patients."
Last month, Audentes reported a third-quarter net loss of $45.7 million, or $1 a share, compared with a loss of $36.3 million, or 97 cents a share, a year ago.
Research and development expense for the period totaled $37.6 million, up from $29.9 million a year. The increase was primarily attributable to higher program expenses for AT845, new programs AT466 and AT702 initiated in 2019, and additional R&D headcount to advance clinical and pre-clinical programs, the company said.