On May 27, 2025 Phanes Therapeutics, Inc. (Phanes), a clinical stage biotech company focused on innovative drug discovery and development in oncology, reported that the first patient has been dosed in the clinical study of mavrostobart (PT199) in combination with chemotherapy (Press release, Phanes Therapeutics, MAY 27, 2025, View Source [SID1234653416]).

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Mavrostobart is an anti-CD73 monoclonal antibody with a differentiated mechanism of action and is designed to counter the adenosine-mediated immunosuppressive tumor microenvironment (TME). Mavrostobart fully inhibits the enzyme activities of both soluble and membrane-bound CD73, unlike several other anti-CD73 antibodies which exhibit incomplete inhibition. Moreover, at higher concentrations, no loss of inhibition or "hook effect" is observed with mavrostobart. Hence, mavrostobart addresses the limitations of current CD73 inhibitors and is expected to increase antitumor immune activation, and potentially offer a new treatment option for cancer patients.

The multi-center Phase I/II clinical trial of mavrostobart (NCT05431270), known as the MORNINGSTAR study, is currently evaluating the safety, tolerability, pharmacokinetics and preliminary efficacy of mavrostobart alone and in combination with a PD-1 Inhibitor or chemotherapy. A Phase I clinical trial of mavrostobart is also ongoing in China (CTR20242381).