Evaluation of DNA/BSA interaction and in vitro cell cytotoxicity of μ2-oxido bridged divanadium(V) complexes containing ONO donor ligands

Abstract

Two new μ₂-oxido bridged divanadium (V) complexes, [V^V₂O₃(L^1,2)₂] (1 and 2) have been synthesized using bi-negative tridentate ONO-donor ligands, H₂L^1,2 (H₂L¹ = 4-tert-butyl-2-[[[3,5-di-tert-butyl-2-hydroxyphenyl]methylene]amino]phenol and H₂L² = 5-bromo-2-[[[4-(diethylamino)-2-hydroxyphenyl]methylene]amino]phenol). The synthesized ligands and complexes have been characterized through FT-IR, UV-vis, NMR, and HR-ESI-MS techniques. Single crystal X-ray crystallography data confirmed distorted square pyramidal geometry for both the complexes. The aqueous phase stability of these complexes has been evaluated through HR-ESI-MS in CH₃CN:H₂O (80:20) mixture. Thereafter their interaction with calf thymus DNA (CT-DNA) have been studied using electronic absorption and fluorescence spectroscopy, revealing an intercalation mode of binding, with binding constant in the order of 10⁴ M^-1. Moreover, bovine serum albumin (BSA) interaction of 1 and 2 has been evaluated via fluorescence quenching experiment, which suggests that the quenching mechanism is static (~10¹³ M^-1) in nature. Additionally, the in vitro cytotoxicity of the complexes has been evaluated in human cervical cancer cells (HeLa) (IC₅₀ = 13.57-16.62 μM) and normal mouse embryonic fibroblasts cells (NIH-3T3). The mechanism of cell death brought about by these complexes was studied by nuclear staining, cell cycle and Annexin V/PI double staining apoptotic assay. These studies indicate that 1 and 2 exert inhibitory effects on the S and G2M phase of cell cycle, which is an indication of apoptotic cell death. Also, a clonogenic assay was performed, which showed that the complexes could effectively inhibit colony formation.

Keywords: Apoptotic activity; Biomolecular interaction; Cytotoxicity; ONO donor ligand; μ(2)-oxido bridged divanadium (V).