Calistoga Pharmaceuticals’ delta isoform-selective PI3K (phosphoinositide 3-kinase) inhibitor programmes have caught the attention of Gilead Sciences, which has agreed to acquire the Seattle biotech for US$375 M upfront and up to US$225 M in potential milestone payments. The key driver of the deal is Calistoga’s lead product candidate CAL-101, which is in Phase II development for refractory indolent non-Hodgkin’s lymphoma and chronic lymphocytic leukaemia in treatment-naïve elderly patients. The acquisition continues Gilead’s strategy of diversifying its portfolio beyond antivirals ahead of the forthcoming patent expirations of some of its major HIV drugs.