CAMBRIDGE, MA, USA I August 16, 2022 I 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, today announced the initiation of patient dosing in the company’s Phase 1 trial of XMT-1660, the company’s Dolasynthen ADC targeting B7-H4.

“The initiation of this Phase 1 trial represents an important milestone for Mersana as we continue to build our pipeline across three ADC platforms and seek to further demonstrate the potential of our Dolalock payload and Dolasynthen platform,” said Anna Protopapas, President and Chief Executive Officer of Mersana Therapeutics. “Based on our promising preclinical data, we believe XMT-1660 has the potential to serve as a highly impactful cancer treatment. We are excited to begin investigating how it may benefit patients in a range of cancers with high unmet needs.”

XMT-1660 is a B7-H4-directed Dolasynthen antibody drug conjugate with a precise, target-optimized drug-to-antibody ratio (DAR 6) and Mersana’s clinically validated DolaLock microtubule inhibitor payload with controlled bystander effect. B7-H4 is overexpressed in a range of cancers, including breast, endometrial and ovarian tumors. In pre-clinical studies, XMT-1660 demonstrated robust anti-tumor activity across models representing each of these three cancers, as well as in multiple patient-derived xenograft models.

The multicenter Phase 1 trial is investigating the safety, tolerability and anti-tumor activity of XMT-1660 in patients with solid tumors, including in breast, endometrial and ovarian cancers. The initial dose escalation portion of this trial will evaluate the safety and tolerability of XMT-1660 as a single agent. The dose expansion portion of the trial will evaluate the tolerability and efficacy of XMT-1660 with primary endpoints of investigator-assessed objective response rate and duration of response.

About Mersana Therapeutics
Mersana Therapeutics is a clinical-stage biopharmaceutical company using its differentiated and proprietary ADC platforms to rapidly develop novel ADCs with optimal efficacy, safety and tolerability to meaningfully improve the lives of people fighting cancer. Mersana’s lead product candidate, upifitamab rilsodotin (UpRi), is a Dolaflexin ADC targeting NaPi2b that is being studied in UPLIFT, a single-arm registrational trial in patients with platinum-resistant ovarian cancer; UPGRADE, a Phase 1/2 umbrella trial evaluating UpRi in combination with other ovarian cancer therapies; and UP-NEXT, a Phase 3 clinical trial of UpRi as monotherapy maintenance following treatment with platinum doublets in recurrent platinum-sensitive ovarian cancer. Mersana is also advancing XMT-1660, a Dolasynthen ADC targeting B7-H4, and XMT-2056, an Immunosynthen ADC targeting a novel epitope of human epidermal growth factor receptor 2 (HER2), in addition to other earlier-stage assets. In addition, multiple partners are using Mersana’s platforms to advance their ADC pipelines. Mersana Therapeutics was named among the 2021 Top Places to Work in Massachusetts by The Boston Globe. Mersana routinely posts information that may be useful to investors on the “Investors and Media” section of its website at

SOURCE: Mersana Therapeutics