Massachusetts-based Mersana Therapeutics announced the initiation of a phase 1b extension study with its lead cancer product, XMT-1001, a novel DNA topoisomerase I inhibitor based on the company's Fleximer polymer conjugate platform, in second-line gastric cancer and second-/third-line non-small cell lung cancer.  The study will be carried out in 10 clinical centers in the U.S. 

The phase Ib follows the successful completion of a 74-patient phase I clinical trial, which demonstrated high and prolonged plasma levels of XMT-1001 active release products and a safety profile free of the toxicities normally associated with topoisomerase 1 inhibitors, such as hemorrhagic cystitis and diarrhea.  Additionally, XMT-1001 showed promising evidence of clinical activity, including tumor shrinkage and prolonged stable disease, in a heavily pre-treated patient population.

"Our clinical experience with XMT-1001 to date suggests that it can be safely given up to doses limited by its mechanism, and thus may be useful in maximizing the therapeutic potential of its class.  The potential benefit of this agent in second-line gastric cancer and in second-/third-line non-small cell lung cancer, areas of great medical need, is well worth investigating," said Edward A. Sausville, M.D., Ph.D, professor of medicine and associate director for clinical research, University of Maryland Greenebaum Cancer Center and a principal investigator in the phase Ib study.