Dive Brief:
- Mersana Therapeutics announced Monday the Food and Drug Administration has lifted a partial hold on clinical testing for its solid tumor antibody-drug conjugate XMT-1522.
- The agency and company "reached alignment" on changes to the protocol, Mersana said in a statement. As a result, Mersana will increase monitoring, exclude patients with advanced hepatic impairment, and change dosing regimens for both XMT-1522 and another ADC it has in development, XMT-1536.
- The company expects all trial sites to be back up to speed within around four weeks. However, the markets weren't as upbeat; after a brief flick up by 8%, shares closed more than 22% down Monday. The stock did partially rebound on market open Tuesday, up roughly 8%.
Dive Insight:
In June, Mersana Therapeutics announced that the FDA slapped a partial clinical hold on the Phase 1 trial of its antibody-drug conjugate (ADC) XMT-1522, under assessment in solid tumors.
This stopped the recruitment of further patients, while those already enrolled could continue. The hold was a result of a patient death at dose level 7, classified by the investigator as "possibly drug-related". The patient had metastatic disease since 2014, and also had advanced hepatic cirrhosis.
Mersana is developing two Phase 1 Dolaflexin ADCs in parallel — XMT-1522, which targets HER2, and XMT-1536, which targets NaPi2b. While the latter was not subject to the clinical hold, the company decided to change both protocols.
The reasons for the stock drop aren't exactly clear, given the positive news, but highlights the roller-coaster market ride many biotechs in early clinical stages go through.
"Clinical proof-of-concept is still outstanding and the ADC space is competitive. We await further clinical data given the competitive landscape and the notorious tolerability challenges many ADCs have faced historically," said Jonathan Chang of Leerink in a note to investors.
Data on XMT-1536, which has already implemented the alternative dosing regimen, is expected in the first half of 2019.