Gilead Sciences has signed a definitive agreement to buy Canada's YM BioSciences and its investigational JAK inhibitor for myelofibrosis.

The all-cash deal will see Gilead pay $2.95 per share, which values YM at $510 million. This represents an 81% premium over the Canadian group's closing price on December 12.

The principal attraction is YM's CYT387, an oral once-daily, selective inhibitor of the Janus kinase (JAK) family, specifically JAK1 and JAK2. The firm reported positive results from a Phase I/II trial of the drug as a treatment for MF at the just-ended American Society of Hematology meeting in Atlanta and Gilead says that pending completion of the acquisition, it intends to initiate a Phase III trial in the second half of 2013.

Norbert Bischofberger, Gilead’s chief scientific officer, said the acquisition “represents an opportunity to add a complementary clinical program in the area of haematologic cancers to our growing oncology portfolio". Best-known for its AIDS drugs, Gilead has sought to expand in cancer and its lead compound in that area, idelalisib, is in five Phase III studies in chronic lymphocytic leukaemia and indolent non-Hodgkin’s lymphoma.

Gilead is also conducting Phase II studies of simtuzumab, an investigational monoclonal antibody targeting the human lysyl oxidase-like 2 (LOXL2) protein, in MF, colorectal and pancreatic cancers and certain fibrotic diseases.