AstraZeneca has entered into a definitive agreement to acquire a majority stake in Acerta Pharma, a Redwood City, Calif.-based clinical-stage biopharmaceutical company.

The transaction provides AstraZeneca with Acerta’s potential best-in-class irreversible oral Bruton’s tyrosine kinase (Btk) inhibitor, acalabrutinib (ACP-196), currently in phase III development for B-cell blood cancers and in phase I/II clinical trials in multiple solid tumors.

David Johnson, chief executive officer of Acerta, said, “AstraZeneca brings tremendous expertise and resources that will help us maximize the potential of acalabrutinib as we continue down multiple development paths in both hematologic malignancies and solid tumors. Together with AstraZeneca and their global footprint, we believe we will further accelerate our global clinical development program and maximize the future commercial potential of acalabrutinib. We look forward to working closely with the AstraZeneca team to realize our mutual goal of transforming cancer care.”

AstraZeneca will acquire 55% of the entire issued share capital of Acerta for total consideration of $4 billion, comprised of upfront consideration of $2.5 billion and further unconditional consideration of $1.5 billion to be paid either on receipt of the first regulatory approval for acalabrutinib for any indication in the U.S., or the end of 2018, depending on which is first. The agreement also includes options which, if exercised, provide the opportunity for Acerta shareholders to sell, and AstraZeneca to buy, the remaining 45% of shares in Acerta.

The options can be exercised at various points in time, conditional on the first approval of acalabrutinib in both the U.S. and Europe and when the extent of the commercial opportunity has been fully established, at a price of $3 billion net of certain costs and payments incurred by AstraZeneca and net of agreed future adjusting items, using a pre-agreed pricing mechanism.