Sialic Acid-Targeted Ru(II)/Ir(III)/Re(I) Complexes for Ferroptosis Induction in Triple-Negative Breast Cancer

Ferroptosis has been recognized as an iron-based nonapoptotic-regulated cell death process. In the quest of resisting the unyielding vehemence of triple-negative breast cancer (TNBC), herein we have showcased the ferroptosis-inducing heteroleptic [LIr_cRu], [LIr_cIr_h], and [LIr_cRe] complexes, enabling them to selectively target "sialic acid", an overexpressed cancer cell-surface marker. The open-circuit potential (OCP) measurements in live cancer cells revealed the specific interaction between TNBC and the complexes, whereas control experiments with normal cells did not exhibit such interactions. GSH depletion, GPx4 inhibition, NADH/NADPH oxidation, lipid peroxidation, COX-2 activation, and Nrf2 inactivation were meticulously investigated upon treatment with these complexes to establish a strong basis for ferroptosis. Among all complexes, the complex [LIr_cIr_h] (IC₅₀ = 25 ± 2.17 μM) has been well-documented as a potent ferroptosis inducer, which unveils the sturdy interaction with sialic acid possessing the highest binding constant (K_b = 0.71 × 10⁵ M^-1, ΔG = -279345.8026 kcal/mol) along with the highest serum albumin binding affinity (K_HSA = 0.67 × 10⁶ M^-1) and significant DNA intercalation (K_b = 0.56 × 10⁵ M^-1, K_app = 1.06 × 10⁶ M^-1, and C₅₀ of intercalation is 76.56 μM), displaying the decreased current intensity in differential pulse voltammetry (DPV). Moreover, the complex [LIr_cIr_h] exhibited mitochondrial dysfunction and membrane damage (diminished MMP, ΔΨ_m) through the production of copious reactive oxygen species (ROS) in MDA-MB-231 cells upon considerable accumulation in mitochondria (Pearson's coefficient = 0.842). The analysis of the field emission scanning electron microscopy (FE-SEM) image has marked the vivid membrane damage induced by the complex [LIr_cIr_h], exhibiting ablaze evidence for the destruction of TNBC cells through ferroptosis.