Mersana stings GSK for $100m to option novel Her2-conjugate

Though clinical disappointment has dented interest in the Sting pathway a couple of big names have pushed on, including GSK, which is running a broad phase 1 trial with the agonist GSK3745417. To this it yesterday added Mersana’s XMT-2056, an antibody conjugate that delivers a Sting agonist rather than a cytotoxic payload. The idea is that targeted activation of the innate immune system could be useful in checkpoint-refractory or relapsed tumours, with the ADC approach opening up the potential of the Sting pathway. Mersana only has preclinical data to support this theory so far: ‘2056 is due to enter the clinic in the second half of this year. Even so GSK was apparently convinced, paying $100m for an option and agreeing to a further $90m if that option is exercised, which must occur during phase 1 after completion of dose-escalation, according to SVB analysts. Another $1.3bn in milestones then comes into play. These terms seem surprisingly generous considering that ‘2056 targets Her2, a crowded space that is currently being wowed by the Daiichi/Astrazeneca ADC Enhertu. Combining ‘2056 with other Her2 agents looks to be the premise – what that means for toxicity is presumably the first question that needs answering.