Heidelberg Pharma’s Lead ATAC Candidate HDP-101 Shows Progress in Phase I/IIa Trial in Multiple Myeloma

EQS-News: Heidelberg Pharma AG / Key word(s): Study results Heidelberg Pharma’s Lead ATAC Candidate HDP-101 Shows Progress in Phase I/IIa Trial in Multiple Myeloma 06.11.2025 / 07:09 CET/CEST The issuer is solely responsible for the content of this announcement. PRESS RELEASE

Heidelberg Pharma’s Lead ATAC Candidate HDP-101 Shows Progress in Phase I/IIa Trial in Multiple Myeloma

• Evidence of clinical activity observed in Cohort 8, including stringent complete remission in two patients from Cohort 8
• HDP-101 continues to demonstrate a favorable safety profile with no dose-limiting toxicities observed in Cohort 8

• R&D Webinar to be hosted on 11 November 2025 at 05:00 pm CET (08:00 am PST)

Ladenburg, Germany, 6 November 2025 – Heidelberg Pharma AG (FSE: HPHA), a clinical-stage biotech company developing innovative Antibody Drug Conjugates (ADCs), today announced that HDP-101 (INN: pamlectabart tismanitin), the Company’s lead ATAC candidate for the treatment of relapsed or refractory multiple myeloma, shows further clinical activity in Cohort 8 at a dose level of 140 µg/kg. These findings are highlighted by observed stringent complete remissions in two patients from Cohort 8.

Seven patients were evaluated in Cohort 8, and all patients demonstrated a favorable safety and tolerability profile throughout. Encouraging signs of clinical activity have also emerged. Four patients showed biological activity of HDP-101 (INN: pamlectabart tismanitin), with one partial response, one very good partial response and two stringent complete remissions (sCR). For sCR, no tumor cells are detectable in blood and bone marrow.

Dr András Strassz, Chief Medical Officer at Heidelberg Pharma, said: “We are very delighted by the data seen so far. Several patients across different cohorts have shown objective responses and promising anti-tumor activity. Observing two stringent complete remissions is an encouraging validation of our therapeutic approach. We have previously seen complete remission in one patient from Cohort 5, but in Cohort 8 onset of the response was more rapid. These findings further strengthen our confidence in the therapeutic potential of HDP-101 in heavily pretreated patients with relapsed or refractory multiple myeloma, and we are now progressing with Cohort 9 with an escalated dose of 175 µg/kg to continue its clinical evaluation.”