Mersana Therapeutics enters option agreement with GSK

US clinical-stage biotech Mersana Therapeutics (Nasdaq: MRSN) saw its shares trading up 14.1% at $5.99 pre-market this morning, after it announced a global collaboration that provides UK pharma major GSK (LSE: GSK) with an exclusive option to co-develop and commercialize XMT-2056, an Immunosynthen ADC that targets a novel epitope of HER2. XMT-2056 is designed to activate the innate immune system through STING signaling in both tumor-resident immune cells and in tumor cells.

Under the terms of the accord, Mersana will receive an upfront option purchase fee of $100 million. Mersana 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.

Mersana has retained options to profit-share and to co-promote in the USA. If it exercises its profit-share option, Mersana will be eligible to receive tiered royalties on net sales outside of the USA. If Mersana does not elect to profit-share, it is eligible to receive double-digit tiered royalties on global net sales. If GSK opts into the license, the effectiveness of the license grant may be subject to customary closing conditions, including review under the Hart-Scott-Rodino Act.