Heidelberg Pharma AG (FSE: HPHA), a clinical-stage biotech company developing innovative Antibody Drug Conjugates (ADCs), announced that it 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, taking place in San Diego, California, USA, from 17 to 22 April.
The poster presentation, titled "HDP-103, a PSMA targeting amanitin-based ADC, is efficacious even in difficult to treat patient derived xenograft models with heterogenous PSMA expression," will be held on 21 April from 2:00 pm to 5:00 pm PDT (Poster number 5639, Session: Antibody-Drug Conjugates and Linker Engineering 4). The abstract is available online at https://www.abstractsonline.com/pp8/#!/21436/presentation/5438.
HDP-103 demonstrated 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) genetic alteration. 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) well within 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.
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 and has been granted Orphan Drug Designation and Fast Track Designation from the FDA. A second ATAC candidate, HDP-102, is in clinical development for Non-Hodgkin Lymphoma. HDP-103 against mCRPC and HDP-104 targeting gastrointestinal tumors such as colorectal cancer have completed preclinical development and 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.
