Molecular Partners presents positive data from ongoing Phase 1/2a trial of MP0533 in AML at EHA 2025

• Three of eight evaluable patients with R/R AML responded after cycle 1 in ongoing cohort 8, including 1 patient with ongoing response beyond 6 months
• Acceptable safety profile across all cohorts, including in cohort 8 with steeper step-up dosing
  
• Data support further dose optimization to maximize therapeutic benefit of MP0533, with dosing in cohort 9 now ongoing
  

ZURICH-SCHLIEREN, Switzerland and CONCORD, Mass., June 11, 2025 (GLOBE NEWSWIRE) -- Ad hoc announcement pursuant to Art. 53 LRMolecular PartnersAG (SIX: MOLN; NASDAQ: MOLN), a clinical-stage biotech company developing a new class of custom-built protein drugs known as DARPin therapeutics ("Molecular Partners" or the "Company"), today announced a poster presentation with positive, updated data from a Phase 1/2a trial of the tetraspecific T-cell engager MP0533 in relapsed/refractory acute myeloid leukemia (AML), at the 30^th EHA (European Hematology Association) Congress, taking place in Milan on June 12-15, 2025.

The poster, Updated Results from the Ongoing Phase 1/2a Study of MP0533, a Tetra-Specific Designed Ankyrin Repeat Protein (DARPin; CD33 x CD123 x CD70 x CD3), in Patients with Relapsed/Refractory AML or MDS/AML, outlines the impact of accelerated step-up dosing regimen (steeper and faster) of MP0533 on exposure and clinical responses in cohort 8, providing the rationale for further optimization to the dosing regimen implemented in the ongoing cohort 9.

Data from cohort 8 show that 3 of 8 evaluable patients (> 30%) achieved a clinical response after the first cycle, with one patient achieving a complete response and two patients a complete response with partial hematologic recovery as best overall response. Two patients maintained a response for more than 3 months and one patient remains on treatment, maintaining a response beyond 6 months at the time of data cutoff (14 April 2025). Cohort 8 implemented a higher starting dose than cohorts 1-7, and the inclusion of an additional day of dosing, reaching the target dose by day 12, as opposed to day 15 previously.

Cohort 8 data indicate that patients maintained exposure to MP0533 for a longer period of time within the predicted therapeutic range through the accelerated step-up dosing scheme, within the first cycle. Data show that patients reached over 4 days of relevant exposure, with 5 out of 8 patients displaying > 50% blast reduction. MP0533 shows an acceptable safety profile after adjustment of the target dose in cohort 8.

"I am encouraged by the number and level of responses observed in the most recent cohort and have started to include patients with the new 'dense administration' schedule aiming to establish the full potential of this product for our R/R AML patients," said Pierre Bories, MD, PhD, Principal Investigator at Institut Universitaire du Cancer Toulouse - Oncopole, France.

In cohorts 1-7, where step-up dosing reached target dose by day 15, exposure to predicted therapeutic doses was limited to roughly 2 days in the first cycle, most likely due to target-mediated-drug deposition. This prior treatment protocol, despite demonstrating initial blast reductions in ~30% of patients, resulted in limited responses.

Based on the encouraging antitumor activity observed in cohort 8, the amended protocol for cohort 9 and beyond includes further acceleration of the step-up dosing to reach therapeutically-relevant doses faster, increased frequency of dosing for higher cumulative MP0533 exposure, and the introduction of anti-CD20 premedication to mitigate loss of exposure, with the objective to further increase the depth and duration of responses in patients.

Cohort 9 is currently dosing patients and initial data from the amended dosing scheme are expected in H2 2025. Additionally, future study cohorts will evaluate the combination of azacitidine/venetoclax with MP0533.

Details of the presentation:

Updated Results from the Ongoing Phase 1/2a Study of MP0533, a Tetra-Specific
Designed Ankyrin Repeat Protein (DARPin; CD33 x CD123 x CD70 x CD3), in Patients with
Relapsed/Refractory AML or MDS/AML
Time: June 13, 18:30 - 19:30 CEST (Poster Session 1)

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For further details, please contact:
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Concord, Massachusetts, U.S.
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Laura Jeanbart, PhD, Head of Portfolio Management & Communications
Zurich-Schlieren, Switzerland
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