Enhancing the Safety and Efficacy of PSMA-Based Small-Molecule Drug Conjugates by Linker Stabilization and Conjugation to Transthyretin Binding Ligand.

This work describes the enhancement of a novel antitumor therapeutic platform that combines advantages from small-molecule drug conjugates (SMDCs) and antibody drug conjugates (ADCs). Valine-citrulline (VCit) dipeptide linkers are commonly used cathepsin B cleavable linkers for ADCs. However, the instability of these linkers in mouse serum makes translating efficacy data from mouse to human more challenging. Replacing the VCit linker with glutamic acid-valine-citrulline (EVCit) has been reported to enhance the stability of ADCs in mouse serum. However, the effect of EVCit linker on the stability of SMDCs has not been reported. Here, we report that incorporating the EVCit linker in prostate-specific membrane antigen-targeting SMDCs, equipped with the transthyretin ligand AG10, resulted in conjugates with lower toxicity, an extended half-life, and superior therapeutic efficacy to docetaxel in a xenograft mouse model of prostate cancer. This should make SMDCs' preclinical toxicity and efficacy data from mice more reliable for predicting human results.

Enthalpy-Driven Stabilization of Transthyretin by AG10 Mimics a Naturally Occurring Genetic Variant That Protects from Transthyretin Amyloidosis.

Transthyretin (TTR) amyloid cardiomyopathy (ATTR-CM) is a fatal disease with no available disease-modifying therapies. While pathogenic TTR mutations (TTRm) destabilize TTR tetramers, the T119M variant stabilizes TTRm and prevents disease. A comparison of potency for leading TTR stabilizers in clinic and structural features important for effective TTR stabilization is lacking. Here, we found that molecular interactions reflected in better binding enthalpy may be critical for development of TTR stabilizers with improved potency and selectivity. Our studies provide mechanistic insights into the unique binding mode of the TTR stabilizer, AG10, which could be attributed to mimicking the stabilizing T119M variant. Because of the lack of animal models for ATTR-CM, we developed an in vivo system in dogs which proved appropriate for assessing the pharmacokinetics-pharmacodynamics profile of TTR stabilizers. In addition to stabilizing TTR, we hypothesize that optimizing the binding enthalpy could have implications for designing therapeutic agents for other amyloid diseases.