Mersana halves workforce as shares plummet 75% in wake of lead cancer drug's failure

The failure of Mersana Therapeutics’ lead ovarian cancer drug in a phase 1/2 trial has sent the biotech into a tailspin, resulting in layoffs affecting half of the employees in an effort to conserve cash where possible.

The antibody-drug conjugate-focused company had been investigating upifitamab rilsodotin in the UPLIFT trial of 268 patients with platinum-resistant ovarian cancer, of which 141 were NaPi2b positive. But the overall response rate produced by the drug was a mere 13%, a negligible increase on the 12% rate offered by chemotherapy alone, the biotech reported.

“We are deeply disappointed that UPLIFT’s efficacy failed to replicate previous data from approximately 100 patients in the dose expansion portion of our phase 1b clinical trial,” Mersana’s Chief Medical Officer Arvin Yang, M.D., said in the release. “While the duration of response was longer than that from the dose expansion portion of UpRi’s phase 1b clinical trial, the lower bound of the confidence interval for the primary endpoint did not meet our goal of excluding a 12% rate seen with standard-of-care single-agent chemotherapy.”

There was already a cloud hanging over upifitamab rilsodotin, with the FDA placing a partial clinical hold on two trials of the drug last month in the wake of the company’s assessment that “serious bleeding events appear to occur at a higher rate than background.”

The biotech’s executives had hoped the UPLIFT results would shed more light on the ADC’s safety profile—instead the data have ended the program for good.

Mersana is dropping the drug and shifting focus to its dolasynthen and immunosynthen platforms. XMT-1660, an ADC produced from the former platform that is designed to target B7-H4, is currently in the dose escalation portion of a phase 1 trial in solid tumors, with a dose expansion portion to kick off next year, CEO Anna Protopapas noted in the release.

XMT-2056, an HER2 epitope produced by the same platform, has faced its own setbacks. The ADC—for which GSK paid $100 million for the license option last year—was slapped with a partial clinical hold by the FDA in March after a patient suffered a fatal serious adverse event that was deemed to be related to the therapy.

In the wake of the latest upset for the company’s pipeline prospects, Protopapas said Mersana is now “taking decisive action to extend our cash runway and ensure we have the resources to evaluate the clinical potential of our next-generation ADC product candidates.”

“Unfortunately, this necessitates reducing our workforce by approximately 50%,” the CEO said. “A very talented group of employees who helped to build Mersana will be departing as a result of this strategic reprioritization.”

Unsurprisingly, investors appeared keen to distance themselves from the company, sending Mersana’s stock plummeting 75% to just 92 cents per share in the opening hour of trading from a Wednesday close of $3.92.

The company does have some money in the bank to tide it over, with $286.6 million in cash and equivalents estimated to last through 2026.