Heidelberg Pharma AG, a clinical-stage biotech company developing Antibody Drug Conjugates (ADCs), announced it will present promising preclinical data for its amanitin-based ADC HDP-103 at the upcoming American Association for Cancer Research (AACR) Annual Meeting 2026. The data highlight the potential of HDP-103 in treating metastatic castration-resistant prostate cancer (mCRPC), particularly in patients with heterogeneous PSMA expression and those harboring a del(17p) genetic alteration, who have high unmet medical needs.
The poster presentation, scheduled for April 21, 2026, at the AACR meeting in San Diego, details the efficacy of HDP-103 in patient-derived xenograft (PDX) models representative of mCRPC. According to the company, HDP-103 demonstrated target-specific binding in human tissues and robust and durable antitumor activity, including in models with heterogeneous PSMA expression and del(17p). Importantly, the amanitin-based ADC was superior to an anti-PSMA Exatecan ADC in these models. The full abstract is available online at the AACR abstract site.
Amanitin, the toxin derived from the green death cap mushroom, is the basis of Heidelberg Pharma's ATAC technology. Unlike conventional ADC payloads, amanitin inhibits RNA polymerase II, offering a unique mode of action. In non-human primate studies, adverse events with HDP-103 were restricted to known off-target effects of amanitin-based ADCs, primarily in the liver and kidney, which were transient and readily monitored. The ADC showed favorable pharmacokinetics, including stability in circulation, no evidence of drug accumulation, no sex differences, and dose-linearity.
The potent anti-tumor efficacy combined with a manageable safety profile results in a comfortable therapeutic index (TI) for HDP-103, well within the range of other approved or developing ADCs for solid tumors. Heidelberg Pharma believes these data support further clinical development of HDP-103 as a novel treatment option for mCRPC. The company's lead candidate, HDP-101, is already in clinical development for multiple myeloma and has received FDA Orphan Drug and Fast Track Designations. HDP-103 is among several programs available for partnering, as noted on the company's website at www.heidelberg-pharma.com.
The AACR presentation underscores Heidelberg Pharma's commitment to advancing its ATAC technology platform and addressing significant unmet needs in oncology. With HDP-103 showing advantages over other modalities in mCRPC, including in patients with del(17p), the company is poised to enter clinical trials and potentially offer a new therapeutic option for this challenging disease.
