PR: Heidelberg Pharma Announces New Clinical Data on Lead ATAC Candidate HDP-101 to be Presented at International Myeloma Society Annual Meeting 2025

Ladenburg, Germany, 4 September 2025 – Heidelberg Pharma AG (FSE: HPHA), a clinical stage company developing innovative Antibody Drug Conjugates (ADCs), today announces that new data from its Phase I/IIa clinical study with lead Amanitin-based ADC candidate, HDP-101, will be presented at the 22^st International Myeloma Society (IMS) Annual Meeting, being held in Toronto, Canada, on 17 to 20 September 2025.

HDP-101 is an Anti-BCMA antibody-Amanitin drug conjugate for the treatment of relapsed or refractory multiple myeloma, a bone marrow cancer with a high unmet medical need. Phase I of the trial is a dose escalation study to determine an optimal and safe dose level of HDP-101 in patients in preparation for Phase II clinical studies.

Professor Jonathan L. Kaufman, MD, David Bankes Glass Professor, Department of Hematology and Medical Oncology, Emory University, Atlanta, USA and clinical investigator of the study will present new findings from eight patient cohorts of the ongoing open-label, multicenter Phase I/IIa trial evaluating HDP-101 in multiple myeloma.

Details of the presentation are as follows:

Presentation title: The Anti-BCMA Antibody-Drug Conjugate HDP-101 with a Novel Amanitin Payload Shows Promising Data in Relapsed/Refractory Multiple Myeloma in a Phase 1/2a clinical trial as it advances into Cohort 7

The first seven patient cohorts and dose levels have been completed. Treatment with HDP-101 was well tolerated and the study has shown very encouraging results, including one patient from the fifth cohort in whom no tumor cells are detectable on a permanent basis. She had been treated with multiple other therapies and is since then being treated continuously with HDP-101 alone. In addition, several patients from different cohorts showed promising anti-tumor activity and objective improvements.