Astex Pharmaceuticals Inc. is getting $35 million up front and up to $500 million per program as it extends its drug discovery collaboration with Merck & Co. Inc. to include small-molecule activators of the p53 tumor suppressor protein. The number of programs was not disclosed, but they will target forms of p53 that have lost their function as a result of cancer-induced mutations in the TP53 gene. The aim will be to override the mutation and restore the ability of the wild-type protein to bind DNA and perform its functions as a transcription factor.