Bleeding complications, some of them fatal, have been reported in clinical tests of an experimental Mersana Therapeutics ovarian cancer drug, prompting the FDA to pause enrollment in two studies. The setback comes three months after a fatality in a separate study for a different Mersana drug led the regulator to place that study under a clinical hold.
The FDA action announced Thursday covers the Mersana drug, upifitamab rilsodotin, typically shortened to UpRi. According to the Cambridge, Massachusetts-based company, a recent safety report covering bleeding events in all patients dosed with UpRi (about 560 patients total) found that the rate of bleeding appears to occur at a higher rate in those dosed with the experimental therapy compared to those receiving background therapies, which are medications currently taken as part of the standard of care.
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Most of the bleeding problems were classified as low-grade, Mersana said. But in five patients, the complication was classified as Grade 5, meaning they were fatal. Mersana said the cause of the bleeding events is under investigation.
The partial hold applies to UP-NEXT, a Phase 3 test of UpRi in platinum-sensitive cancer, disease that progresses six months following the last dose of platinum chemotherapy. It also applies to UPGRADE-A, a Phase 1 study evaluating the combination of UpRi and the chemotherapy carboplatin. UPLIFT, a single arm study intended to support an application seeking regulatory approval, had completed enrollment last October. The partial hold stops enrollment of new patients in the studies. Patients already enrolled may continue to receive the experimental therapy.
“Patient safety is always at the forefront for us, and work is now underway to compile further analyses that may inform FDA,” Mersana President and CEO Anna Protopapas said in a prepared statement. “Additionally, with UPLIFT top-line data on the near-term horizon, we will soon have a much more complete assessment of both the efficacy and safety profile for UpRi in platinum-resistant ovarian cancer.”
The Mersana ovarian cancer drug belongs to a class of therapies called antibody drug conjugates (ADCs). These therapies employ a targeting antibody to deliver a toxic drug payload to cancer cells. UpRi targets a protein called NaPi2b, which is expressed on ovarian cancer cells among other types of tumors. With several clinical trials underway simultaneously, Mersana has said it is looking to establish the safety and efficacy of UpRi across a wide range of ovarian cancer patients, from those who have become resistant to chemotherapy after receiving multiple treatments to those in earlier stages of disease.
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UpRi is Mersana’s most advanced drug candidate. The company has five more disclosed programs in the pipeline. Last summer, GSK began a research collaboration on one of them, XMT-2056. The pharmaceutical giant paid $100 million up front to share in the development of this ADC, which is designed to target the cancer protein HER2.
In March, Mersana said it was voluntarily suspending a Phase 1 test of XMT-2056 in HER2-expressing solid tumors following a fatality deemed to be related to the experimental therapy. Subsequently, the FDA placed the study under a clinical hold. In its report of first quarter 2023 financial results, Mersana said it is still investigating the cause of the fatality while also evaluating the next steps for XMT-2056.
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