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GSK, Mersana Therapeutics Ink $100M Option Agreement for Antibody-Drug Conjugate

NEW YORK – GlaxoSmithKline has purchased a global license option for Mersana Therapeutics' HER2-targeting antibody-drug conjugate XMT-2056, the companies announced Monday.

Mersana expects to begin a Phase I trial of XMT-2056 in HER2-expressing tumors including breast, gastric, and non-small cell lung cancers. The drug has orphan drug designation from the US Food and Drug Administration as a gastric cancer therapy.

In the deal, GSK will pay Mersana $100 million upfront for the option to exclusively license XMT-2056 for development and commercialization. If GSK exercises the option, Mersana will also receive up to $1.36 billion in option exercise and potential milestone payments.

Mersana also has the option to profit share and co-promote the drug in the US. If it exercises that option, the firm would receive tiered royalty payments in ex-US markets. If it passes on profit sharing, Mersana will be eligible to receive double-digit royalties on global net sales. 

Cambridge, Massachusetts-based Mersana designed the antibody-drug conjugate (ADC) to target a novel epitope of HER2, which activates the innate immune system through STING signaling. XMT-2056 has so far demonstrated anti-tumor activity in cancer models with high and low HER2 expression.

In preclinical studies, therapeutic activity has been enhanced when the drug is combined with Genentech's HER2-targeted therapies Herceptin (trastuzumab) and Perjeta (pertuzumab), AstraZeneca/Daiichi Sankyo's HER2-directed ADC Enhertu (trastuzumab deruxtecan), or anti-PD-1 agents. The preclinical data further suggest that XMT-2056 may allow for longer anti-tumor activity by enabling immunological memory, the firm said.

"We believe this agreement [with GSK] … serves as validation for our Immunosynthen platform, which takes ADCs beyond the cytotoxic realm by enabling a targeted stimulation of the innate immune system," Mersana President and CEO Anna Protopapas said in a statement.