European drugmaker Sanofi-Aventis ( SNY) is paying up to $500 million to acquire privately held BiPar Sciences to bolster its cancer drug research pipeline, the company said Wednesday. BiPar, based in Brisbane, Calif., which is just south of San Francisco, is working on a new class of targeted drug called PARP inhibitors that work by preventing cancer cells from repairing their own DNA, thereby causing the cancer cells to die. In recent months, Sanofi-Aventis CEO Christopher Viehbacher has stated publicly that the company was interested in making small to mid-sized acquisitions in order to cushion the financial blow coming when top-selling drugs like the blood thinner Plavix go generic. Last week, market rumors had Sanofi-Aventis considering a bid for Biogen Idec ( BIIB). Sanofi-Aventis sells Taxotere and Eloxatin, two of the most commonly used cancer chemotherapies, but the company's cancer drug pipeline lags behind other large drugmakers, especially when it comes to developing new targeted therapies. "The acquisition of BiPar, one of the pioneer for novel tumor-selective therapies, is a further step in our company's goal to focus on new approaches to strengthen our oncology R&D portfolio,'' said Viehbacher, in a statement. BiPar's lead drug, BS-201, is currently in phase II studies for triple-negative breast cancer, an aggressive form of the disease that doesn't typically respond to currently approved treatments. Abbott Labs ( ABT), Pfizer ( PFE) and AztraZeneca ( AZN) also have PARP inhibitor drugs in various stages of human testing, according to research firm BioMedTracker.