Heidelberg Pharma to Present Data from its ADC Technology Platform at AACR Annual Meeting 2026

PRESS RELEASE

Heidelberg Pharma to Present Data from its ADC Technology Platform at AACR Annual Meeting 2026 

Ladenburg, Germany, 4 April 2026 – Heidelberg Pharma AG (FSE: HPHA), a clinical-stage biotech company developing innovative Antibody Drug Conjugates (ADCs), will present promising preclinical data from its Amanitin-based ADC HDP-103 targeting metastatic castration‑resistant prostate cancer (mCRPC) at the American Association of Cancer Research (AACR) Annual Meeting 2026 in San Diego, California, USA, from 17 to 22 April.

AACR Annual Meeting 2026

Details of the conference and poster presentation are as follow:

Poster: HDP-103, a PSMA targeting amanitin-based ADC, is efficacious even in difficult to treat patient derived xenograft models with heterogenous PSMA expression

Poster number:	5639
Session:	Antibody-Drug Conjugates and Linker Engineering 4
Presentation time:	21 April, 2:00 pm – 5:00 pm PDT
Link to abstract:	https://www.abstractsonline.com/pp8/#!/21436/presentation/5438

HDP-103 demonstrates target specific binding in human tissues and robust and durable antitumor activity in patient-derived xenograft (PDX) models representative of mCRPC, including tumors with heterogeneous PSMA expression and those harboring a del(17p). In these models, Amanitin-based HDP-103 was superior to an anti-PSMA Exatecan ADC. Adverse events with HDP-103 in non-human primates were restricted to known off-target effects of Amanitin-based ADCs, primarily in the liver and kidney. These effects can be readily monitored and are transient. HDP-103 serum levels demonstrate stability of the ADC in circulation, no evidence of drug accumulation, no differences between sexes, and dose-linearity.

The potent anti-tumor efficacy of HDP-103 combined with a favorable half-life and a manageable safety profile, leads to a comfortable therapeutic index (TI) of HDP-103 that is well in the range of other ADCs that are approved or in development for solid tumor indications. Taken together, these data warrant further clinical development of HDP-103 as a novel treatment option for mCRPC. HDP-103´s unique mode of action gives it advantages over other treatment modalities in use or development for mCRPC including in patients with del(17p) who have a high unmet medical need.

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 www.heidelberg-pharma.com

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

Contact Heidelberg Pharma AG Sylvia Wimmer Senior Director Corporate Communications Tel.: +49 6203 1009 1004 E-mail: investors@hdpharma.com Gregor-Mendel-Str. 22, 68526 Ladenburg

IR/PR-Support MC Services AG Katja Arnold (CIRO) Managing Director & Partner Tel.: +49 89 210 228-40 E-mail: katja.arnold@mc-services.eu

This communication contains certain forward-looking statements relating to the Company's business, which can be identified by the use of forward-looking terminology such as "estimates", "believes", "expects", "may", "will”, "should”, "future", "potential" or similar expressions or by a general discussion of the Company's strategy, plans or intentions. Such forward-looking statements involve known and unknown risks, uncertainties and other factors, which may cause our actual results of operations, financial condition, performance, achievements, or industry results, to be materially different from any future results, performance or achievements expressed or implied by such forward-looking statements. Given these uncertainties, prospective investors and partners are cautioned not to place undue reliance on such forward-looking statements. We disclaim any obligation to update any such forward-looking statements to reflect future events or developments.