Reactivity-Guided Selective Covalent Targeting of mtDNA over nDNA by an NHC–Rhenium Complex Triggers Bioenergetic Collapse in Cancer Cells

Mitochondrial DNA (mtDNA) has emerged as a promising target for the development of next-generation chemotherapeutics, as its damage can disrupt key processes that drive cancer progression and resistance to nuclear DNA (nDNA)-targeting drugs. However, achieving selective and direct targeting of mtDNA remains a significant challenge due to its nucleobase similarity to nDNA and necessitates mitochondria-directed delivery strategies. This study reports the identification of a novel N-heterocyclic carbene (NHC) rhenium (Re) complex 4 that selectively targets and damages mtDNA in cancer cells without the need for mitochondria-directed delivery, while sparing nDNA. This remarkable selectivity arises from the inherent reactivity preference of this complex toward mtDNA, rather than from distribution-driven effects. The in vitro potency of complex 4 outperformed that of nDNA-targeting cisplatin. In-depth mechanistic studies revealed that complex 4 forms covalent adducts with mtDNA, leading to disruption of mitochondrial gene replication and transcription. This triggers various downstream effects, including mitochondrial superoxide generation, dissipation of membrane potential, downregulation of nucleoid-associated proteins and polymerase γ expression, and depletion of OXPHOS proteins and ATP, leading to induction of mitophagy and endoplasmic reticulum stress. It induced necroptosis-mediated cell death and has the ability to overcome cisplatin resistance across multiple cancer cell lines. Furthermore, it significantly reduces the volume of 3D tumor spheroids, demonstrating efficacy in a physiologically relevant tumor model. Overall, this study identifies for the first time the unique mtDNA-targeting capability of [Re(I)(bisNHC)(CO)3Cl] complexes without the need for mitochondria-targeting vectors.