Targeting monocarboxylate transporter 1 with a copper-chelating coumarin-based bioconjugate: Synthesis and characterization

Monocarboxylate Transporters (MCTs), particularly MCT1, are increasingly recognized as key regulators of cancer metabolism, facilitating lactate exchange and contributing to tumor aggressiveness. Their overexpression in various malignancies makes them attractive targets for both therapeutic and diagnostic strategies. In this study, we report the design, synthesis, and comprehensive characterization of a novel chimeric bioconjugate, L^CPn, integrating a coumarin-based MCT1-targeting moiety with a TACN(1,4,7-triazacyclononane)-containing chelator, optimized for copper radioisotope binding. The synthetic route was refined through strategic modifications, including mono-Boc (tert-butyloxycarbonyl) protecting group protection of the macrocycle and efficient SN₂-type coupling via thionyl chloride activation. Structural confirmation was achieved through nuclear magnetic resonance and mass spectrometry. Five protonation constants were determined for L^CPn, reflecting contributions from both the chelator and targeting domains. Complexation studies with Cu²⁺ and Zn²⁺ confirmed the formation of stable 1:1 metal-to-ligand complexes, while cyclic voltammetry studies indicated a quasi-reversible redox behaviour upon Cu²⁺ to Cu⁺ reduction. Docking simulations and cell-based assays demonstrated that the coumarin-based targeting moiety exhibits high affinity for MCT1 and effectively inhibits lactate uptake in prostate cancer models. These findings underscore the dual functionality of L^CPn as a selective MCT1-targeting agent and a robust copper-chelating platform, paving the way for future theranostics applications in oncology exploiting inorganic bioconjugates.