Heidelberg Pharma’s Amanitin-Based ADC Shows Promise Against Aggressive Prostate Cancer

Heidelberg Pharma AG will present promising preclinical data for its investigational antibody-drug conjugate HDP-103 at the American Association of Cancer Research Annual Meeting 2026. The data focuses on the compound’s efficacy against metastatic castration-resistant prostate cancer, a challenging and often fatal form of the disease. The 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,’ is scheduled for April 21 during the Antibody-Drug Conjugates and Linker Engineering session.

According to the company’s abstract, available at https://www.abstractsonline.com/pp8/#!/21436/presentation/5438, HDP-103 demonstrated target-specific binding in human tissues and robust, durable antitumor activity in patient-derived xenograft models. These models represent mCRPC, including tumors with heterogeneous PSMA expression and those harboring a specific genetic deletion known as del(17p). In these preclinical tests, the Amanitin-based HDP-103 showed superior efficacy compared to an anti-PSMA Exatecan ADC, another type of antibody-drug conjugate.

The data indicates HDP-103 possesses a favorable pharmacokinetic profile. Serum level analysis showed stability of the ADC in circulation, no evidence of drug accumulation, no differences between sexes, and dose-linearity. Adverse events observed in non-human primate studies were restricted to known off-target effects of Amanitin-based ADCs, primarily affecting the liver and kidney. The company notes these effects are transient and can be readily monitored.

The combination of potent anti-tumor efficacy, a favorable half-life, and a manageable safety profile results in a therapeutic index for HDP-103 that falls within the range of other ADCs approved or in development for solid tumors. Heidelberg Pharma states this data warrants further clinical development of HDP-103 as a novel treatment option for mCRPC. The company highlights HDP-103’s unique mode of action, derived from the toxin Amanitin, as providing advantages over other treatment modalities, particularly for patients with the del(17p) genetic alteration who represent a population with high unmet medical need.

The AACR Annual Meeting serves as a key platform for presenting early-stage cancer research. The presentation of these preclinical findings marks a significant step for HDP-103, positioning it as a candidate for clinical trials. The company’s broader ATAC technology platform, which utilizes Amanitin, is also being applied to other cancer types, including multiple myeloma and non-Hodgkin lymphoma.

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