Pyrazole-Infused Metal Complexes: Anticancer Activity, DNA Cleavage, and Biophysical Insights into DNA/BSA Interactions

A pyrazole-based ligand bearing dimethyl substituents
was used
in the synthesis of Co(II), Cu(II), and Zn(II) complexes, specifically
[CoCl2(dmp)2] (1), [CuCl2(dmp)2]2 (2), and [ZnCl2(dmp)2] (3), where dmp = 3,5-dimethylpyrazole.
The ligand dmp and complexes 1–3 were
precisely characterized through various spectroscopic and analytical
techniques, i.e., FTIR, UV–vis, and ESI-HRMS. The molecular
structures of all complexes were confirmed by single-crystal X-ray
diffraction, except for the ligand dmp, which was additionally characterized
by 1H NMR spectroscopy. UV–vis and fluorescence
studies revealed that these complexes strongly bind with bovine serum
albumin and calf thymus DNA. The DNA cleavage activity of complexes 1–3 and ligand dmp was assessed using
gel electrophoresis. Concentration-dependent studies revealed that
the compounds act as self-activating chemical nucleases, inducing
hydrolytic DNA cleavage at varying concentrations, with complex 2 exhibiting a particularly promising DNA cleavage activity.
It was observed that complex 2 significantly enhances
DNA cleavage at a very low concentration of 15 μM in the presence
of activators, namely ascorbate and H2O2. However,
the contribution of the GSH activator toward the DNA cleavage was
found to be extremely negligible. Further, the use of reactive oxygen
species (ROS) scavengers, such as hydroxyl radical scavenger, singlet
oxygen scavenger, and superoxide scavenger, resulted in a significant
decrease in the DNA cleavage efficiency. These suggest that the diffusible
species, including hydroxyl radical (HO•), singlet
oxygen (1O2), and superoxide (O2•–), play a major role in the oxidative cleavage
of DNA. The cytotoxicities of dmp and its complexes were investigated
using the MTT assay, with the evaluation of their IC50 values
for the MCF-7 and MDA-MB-231 breast cancer cell lines, as well as
a normal epithelial HEK-293 cell line. Furthermore, flow cytometry
analysis using Annexin V-FITC/PI double staining revealed that the
apoptotic effects of these potent compounds on MDA-MB-231 cells are
primarily mediated through the late apoptotic pathway.