Targeting Triple Negative Breast Cancer with a Dinuclear Copper(II) Thiocarbohydrazone Complex: Efficacy Evaluation and Cellular Response

The importance of copper complexes in bioinorganic chemistry and medicinal chemistry has been thoroughly documented in the literature. In recent years, extensive studies have focused on copper complexes of Schiff bases that can bind to DNA and proteins, exhibiting significant cytotoxic activity against various cancer cell lines, paving the way for the development of novel copper-based anticancer therapeutics. In this regard, we have synthesized a new dinuclear Cu-(II) complex <b>1</b> (<b>K38</b>) with a thiocarbohydrazone Schiff base ligand in order to study its anticancer potential. This complex was characterized by HRMS, IR, UV-vis, and EPR spectroscopic studies. The methanol frozen glass of the compound at liquid nitrogen temperature (LNT) exhibited an axial EPR spectrum which was found to contain two sets of parallel lines suggesting the presence of two very weakly interacting Cu-(II) centers with average <i>g</i> _∥ = 2.258 and <i>g</i> _⊥ = 2.057 values (approximately) suggesting a pseudo-octahedral or distorted square pyramidal structure of each Cu-(II) center with axial (<i>Z</i>) elongation and the unpaired electron being in the d _<i>x</i> ²- _<i>y</i> ² orbital of each of the Cu-(II) ions. Biological studies revealed strong DNA binding affinity of complex <b>1</b>, exhibiting an intrinsic binding constant <i>K</i> _b of 1.14 × 10⁵ M^-1. Further, <b>1</b> was also capable of DNA cleavage and DNA fragmentation as observed by TUNEL positive cells. Cytotoxicity assays indicated potent effects against tested breast cancer (BC) cell lines like MDA-MB-231 and MCF-7 where the IC₅₀ values were found to be 0.41 ± 0.03 and 0.89 ± 0.08 μM, respectively. On the other hand, compound <b>1</b> was found to be remarkably nontoxic in the nonmalignant breast epithelial MCF-10A cells even at very high concentrations of <b>1</b> (75 μM) showing its selectivity toward TNBC (MDA-MB-231) cells. Complex <b>1</b> generated substantial ROS as evident from the DCFDA assay. Mechanistic studies using western blot showed a caspase cascade triggered by complex <b>1</b> through an intrinsic mitochondrial pathway. Complex <b>1</b> led to a decrease in mitochondrial mass, increased mROS, and significant mitochondrial membrane depolarization as evident from MitoTracker, MitoSOX, and TMRM assays, confirming mitochondrial dysfunction leading to cell death.