FDA slaps clinical hold on XMT-2056 Phase I trial

The Phase I trial of XMT-2056 has been placed on clinical hold by the US Food and Drug Administration (FDA), said the drug’s developer, US clinical-stage biotech Mersana Therapeutics (Nasdaq: MRSN), whose shares fell over 2% to $4.6 in pre-market trading today.

The FDA move follows Mersana’s communication to FDA that the company was voluntarily suspending the trial due to a recent Grade 5 (fatal) serious adverse event (SAE) that was deemed to be related to XMT-2056. The SAE and its cause remain under investigation, the company noted.

The news comes only six months after UK pharma major GSK LSE: GSK paid $100 million for the license option on XMT-2056. Mersana was also is eligible to receive up to $1.36 billion in the form of an option exercise payment and development, regulatory and commercial milestone payments if GSK exercises its option.