Prostate cancer remains a major global health burden with limited therapeutic options and poor prognosis in advanced disease. To extend survival and improve quality of life, targeted therapies have emerged as an important treatment modality. The reported study presents a novel targeted approach intended to overcome limitations of existing conjugate formats for prostate cancer.
Antibody-drug conjugates (ADC) have achieved notable clinical success across several tumor types, but their large molecular size can limit tumor penetration and thereby reduce therapeutic effect in prostate cancer. Small molecule-drug conjugates (SMDC) use a small targeting moiety linked to a cytotoxic payload and can penetrate tumors more effectively due to their smaller size. However, SMDCs have been hampered by short plasma half-lives and limited efficacy in clinical development.
To combine the advantages of both approaches, fragment crystallizable–grafted SMDCs (Fc-SMDC) attach an Fc fragment to a SMDC to extend systemic half-life. Historically, Fc attachment has been performed with designs that rely on enzymatically cleavable linkers to release the cytotoxic payload, making linker cleavage a prerequisite for activity and contributing potential opportunities for premature release and systemic toxicity.
The authors describe a first-in-class Fc-SMDC that targets prostate-specific membrane antigen (PSMA) and carries the RNA polymerase inhibitor α-amanitin as payload. Crucially, the construct uses a noncleavable linker between payload and Fc to minimize premature drug release and improve plasma stability. This represents a departure from conventional Fc-SMDCs that require cleavable linkers for payload liberation.
Rather than attaching the Fc to the targeting moiety directly, the investigators conjugated the payload to the Fc region via an engineered cysteine residue. This spatial separation places the cytotoxic α-amanitin payload on the Fc and leaves the small-molecule targeting ligand free to engage PSMA. The design enables the use of a noncleavable linker because payload release does not depend on an enzymatic cleavage event at the linker between the targeting ligand and the Fc.
The noncleavable-linker Fc-SMDC showed increased plasma stability and an extended systemic half-life compared with expectations for unconjugated SMDCs. Enhanced half-life contributes to prolonged tumor exposure by maintaining circulating concentrations over time, a key aim of Fc grafting. The noncleavable linker strategy was presented as a mechanism to reduce premature systemic release of the cytotoxic payload.
In xenograft models, the Fc-SMDC achieved prolonged tumor exposure and demonstrated excellent antitumor efficacy. The extended half-life and improved tumor pharmacokinetics correlated with strong activity in these preclinical tumor models, supporting the hypothesis that combining PSMA-targeting SMDCs with an Fc fragment and a noncleavable linker can enhance therapeutic effect.
The construct displayed high tolerability in the reported preclinical studies. Use of the noncleavable linker was associated with low systemic toxicity attributed to minimal premature payload release. The authors also report favorable tolerability in non-human primates, findings that the authors highlight as supportive evidence for potential clinical translation.
This Fc-SMDC architecture aims to bridge the gap between ADC and SMDC approaches by combining the tumor penetration benefits of small targeting ligands with Fc-mediated half-life extension, while addressing safety and stability concerns via a noncleavable linker strategy. The reported preclinical efficacy, extended half-life, and tolerability in both rodent xenograft models and non-human primates position this design as a potential next-generation targeted therapeutic for prostate cancer.
This work was published in Molecular Cancer Therapeutics: Mol Cancer Ther. 2026 Sep 2;25(9):1433-1446. DOI 10.1158/1535-7163.MCT-25-1274. PubMed ID (PMID) 41841414. Authors and affiliations are reported from Heidelberg Pharma Research GmbH and Heidelberg Pharma AG, Ladenburg, Germany.
Note: The source abstract summarizes the approach, pharmacokinetic and preclinical efficacy outcomes, and tolerability in non-human primates. Detailed experimental methods, quantitative results, and statistical analyses were not provided in the abstract and are not reported here.