Mersana Therapeutics has begun a Phase Ib extension study to evaluate its lead cancer product, XMT-1001, as a treatment for second-line gastric cancer and second-line and third-line non-small cell lung cancer.

The study will be conducted at ten clinical centres in the US.

The Phase Ib study follows the successful completion of a 74-patient Phase I clinical trial, which showed high and prolonged plasma levels of XMT-1001 active release products.

The study showed a safety profile free of the toxicities normally associated with topoisomerase I inhibitors, such as haemorrhagic cystitis and diarrhoea.

In addition, XMT-1001 demonstrated clinical activity, including tumour shrinkage and prolonged stable disease, in a heavily pre-treated patient population.

XMT-1001 is a novel DNA topoisomerase I inhibitor based on Mersana’s Fleximer polymer conjugate platform.