PRESS RELEASE

Heidelberg Pharma to Present New Clinical Data on Lead ATAC Candidate Pamlectabart Tismanitin at International Myeloma Society Annual Meeting 2026

Ladenburg, Germany, 7 September 2026 – Heidelberg Pharma AG (FSE: HPHA), a clinical stage company developing innovative Antibody Drug Conjugates (ADCs), will present new data from its Phase I/IIa clinical study with lead Amanitin-based ADC candidate, pamlectabart tismanitin (HDP-101), at the 23rd International Myeloma Society (IMS) Annual Meeting, being held in Glasgow, Scotland, on 23 to 26 September 2026.

Pamlectabart tismanitin is an Anti-BCMA antibody-Amanitin drug conjugate for the treatment of relapsed or refractory multiple myeloma (RRMM), a bone marrow cancer with a high unmet medical need. Phase I of the trial was a dose escalation study to determine an optimal and safe dose level of the candidate for the Phase IIa part of the study.

Details of the presentation are as follows:

Poster title: HDP-101, a BCMA-Targeting Antibody-Drug Conjugate with a Novel Amanitin Payload, Establishes the Recommended Phase 2 Dose (RP2D) in a clinical Phase 1 trial on Relapsed/Refractory Multiple Myeloma

The Phase I part of the study including ten patient cohorts was completed in April 2026 and the recommended dose for the Phase IIa part (Recommended Phase 2 Dose; RP2D) was determined. The Phase IIa part is progressing as planned.

Pamlectabart tismanitin demonstrated consistent clinical activity with a favorable safety profile in heavily pretreated RRMM patients supporting the potential of the candidate as a novel payload BCMA-targeted ADC therapy.

About Heidelberg Pharma

Heidelberg Pharma is the first company to develop cancer therapies using Amanitin, a compound derived from the green death cap mushroom. The biological mechanism of action of the toxin represents a new therapeutic modality and is used as a compound in the Amanitin-based ADC technology, the so-called ATAC technology.

Lead candidate HDP-101 (INN: pamlectabart tismanitin) is a BCMA ATAC in clinical development for multiple myeloma. The candidate has been granted Orphan Drug Designation and Fast Track Designation from the FDA. A second ATAC candidate, HDP-102 is in clinical development stage in Non-Hodgkin Lymphoma. HDP-103 against metastatic castration-resistant prostate cancer and HDP-104 targeting gastrointestinal tumors such as colorectal cancer have completed preclinical development. These programs are available for partnering.

The company is based in Ladenburg, Germany, and is listed on the Frankfurt Stock Exchange: ISIN DE000A11QVV0 / WKN A11QVV / Symbol HPHA. More information is available at http://www.heidelberg-pharma.com/.

ATAC^® is a registered trademark of Heidelberg Pharma Research GmbH.

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