A Cytotoxic Indazole-based Gold(III) Carboxamide Pincer Complex Targeting DNA Through Dual Binding Modes of Groove Binding and Alkylation

Abstract

Gold(III) complexes have garnered increasing attention in drug delivery due to their structural and mechanistic similarities to cisplatin. This study investigates an indazole-based gold(III) carboxamide pincer complex, [N²·N⁶-bis(1-methyl-¹H-indazol-3-yl)pyridine-2·6-dicarboxamide]gold(III) chloride (AuL), for its potential as an anticancer agent. Speciation analysis at physiological pH revealed that AuL predominantly exists as a neutral chlorinated species. The complex exhibited strong cytotoxicity against the MCF-7 breast cancer cell line, with an impressive IC₅₀ value of 9 µM, while showing no significant activity against the HT-29 colon cancer cell line. Comprehensive analysis using electrophoresis, viscometry, ultraviolet-visible spectroscopy (UV-Vis), circular dichroism (CD), linear dichroism (LD) spectroscopy, and biomolecular simulations demonstrated that AuL binds to DNA via a dual mechanism, specifically minor groove binding and alkylation, with binding constants K_a1 = 1.48 × 10⁹ M⁻¹ and K_a2 = 6.59 × 10⁵ M⁻¹, respectively. Our data indicate that AuL initially binds to the minor groove of DNA, at which point a nucleobase substitutes the Cl ion, resulting in AuL binding directly to the DNA bases. In conclusion, the dual binding mode of AuL with DNA underscores its potential as a promising anticancer agent, opening new avenues for drug discovery and the development of metal-based therapeutics.