Mersana Therapeutics Announces Initiation of Phase 1 Trial of XMT-2056 in HER2-Expressing Tumors

On January 25, 2023 Mersana Therapeutics, Inc. (NASDAQ: MRSN), a clinical-stage biopharmaceutical company focused on discovering and developing a pipeline of antibody-drug conjugates (ADCs) targeting cancers in areas of high unmet medical need, reported the initiation of patient dosing in its Phase 1 clinical trial of XMT-2056, the company’s lead Immunosynthen product candidate (Press release, Mersana Therapeutics, JAN 25, 2023, View Source [SID1234626544]).

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XMT-2056 is a systemically administered Immunosynthen STING agonist ADC that is designed to target a novel HER2 epitope and locally activate STING signaling in both tumor-resident immune cells and in tumor cells to provide the potential to treat patients with HER2-high or -low tumors as monotherapy or in combination with standard-of-care agents. The U.S. Food and Drug Administration (FDA) has granted orphan drug designation to XMT-2056 for the treatment of gastric cancer.

"We believe this trial will give us important insights into XMT-2056’s tolerability and clinical activity profile across a range of solid tumors while also helping to demonstrate the differentiated nature of our Immunosynthen platform, which is designed to take ADCs beyond the cytotoxic realm by enabling innate immune activation," said Anna Protopapas, President and Chief Executive Officer of Mersana Therapeutics. "Given the preclinical activity XMT-2056 has demonstrated as a monotherapy and in combination with multiple agents, including standard-of-care HER2 therapies, we believe XMT-2056 may offer a differentiated and highly complementary therapeutic approach. We are excited to have candidates derived from all three of our ADC platforms in active clinical trials, demonstrating our continued innovation and leadership within the ADC space."

The multicenter Phase 1 open-label trial will investigate XMT-2056 in previously treated patients with advanced/recurrent solid tumors expressing HER2, including breast, gastric, colorectal and non-small-cell lung cancers. The dose escalation and dose expansion portions of the trial will evaluate and characterize the relationship of safety, tolerability and exposure of XMT-2056 and the ADC’s effect on patient responses by overall response rate, duration of response and disease control rate.

Mersana recently entered into an agreement with GSK that provides GSK with an exclusive option for a global license to co-develop and commercialize XMT-2056. Under the terms of the agreement, Mersana received an upfront option purchase fee of $100 million and 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 United States. If it exercises its profit-share option, Mersana will be eligible to receive tiered royalties on net sales of licensed products outside of the United States. 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.