Molecular Partners AG will present preliminary data from its ongoing Phase 1/2a trial of MP0533, a novel tetra-specific T cell engager at the 65thAmerican Society of Hematology (ASH) Annual Meeting and Exposition being held from December 9-12 in San Diego, California. MP0533 is in development for the treatment of patients with relapsed/refractory acute myeloid leukemia (r/r AML) and myelodysplastic syndrome (AML/MDS). As of data cut-off (20 July 2023) of the abstract published today, five patients across three dosing regimens had been treated.

The preliminary data reported indicate an acceptable safety profile, with no dose-limiting toxicity or Grade =3 adverse reactions. Grade 1/2 events considered related to MP0533 included infusion-related reactions and cytokine release syndromes. One of the two patients evaluable for MP0533 antitumor activity in the third treatment cohort achieved a response.

The study is currently enrolling its fifth cohort with up to seven dose-escalating cohorts planned and a total enrollment of up to 45 patients. The Company anticipates to present data including from the fourth dose cohort at the ASH Annual Meeting and Exposition in December this year. The clonal heterogeneity and lack of single AML-specific target antigens represent major challenges for the development of targeted immune therapies for AML.

To overcome these hurdles, Molecular Partners designed MP0533, a novel tetra-specific T cell-engaging, half-life extended DARPin, which simultaneously targets CD33, CD123 and CD70, as well as CD3 on T cells. This unique mode of action is designed to enable avidity-driven, T cell-mediated killing of leukemic stem cells and malignant blast cells, which commonly co-express at least two of the three target antigens, while preserving a therapeutic window that minimizes damage to healthy cells. The ongoing single-arm, open-label, multicenter Phase 1/2a study of MP0533 is designed to evaluate the safety, tolerability, pharmacokinetics, and pharmacodynamics, as well as assess preliminary antileukemic activity of MP0533 as a monotherapy for patients with r/r AML and AML/MDS.