Metformin and Mitochondrial Apoptosis in Breast Cancer: Mechanistic Insights and Therapeutic Implications

Abstract

Metformin, a first-line treatment for type 2 diabetes, has gained potential for its anti-cancer properties. Evidence suggests that metformin suppresses tumour growth and induces apoptosis, particularly through its effects on mitochondrial pathways. This review explores three interconnected mechanisms by which metformin promotes mitochondrial-induced apoptosis and inhibits tumorigenesis in breast cancer: AMPK activation, reduced Bcl-2 protein activity, and ROS accumulation. These processes contribute to apoptotic reactivation mechanisms such as mitochondrial outer membrane permeabilization (MOMP), cytochrome c release, and cell death, offering insight into how metformin may help overcome treatment resistance in hormone receptor-positive and triple-negative breast cancers. Breast cancer was selected for this study due to its high global incidence and marked variability in treatment response, making it an ideal framework to evaluate metformin’s effects across different breast cancer subtypes. A systematic review was conducted to review metformin’s role in inducing apoptosis, focusing on its effects on mitochondrial processes related to AMPK activation, reduced Bcl-2 protein activity, and ROS production. The review draws research from databases such as PubMed, ScienceDirect, and the National Institutes of Health, using keywords such as metformin, mitochondrial apoptosis, tumorigenesis, and anticancer pathways. Studies were selected based on relevance to AMPK signaling, Bcl-2 modulation, and ROS involvement, with emphasis on apoptosis markers, breast cancer subtypes, and metformin dosage-response outcomes. Metformin’s role to activate AMPK, reduce Bcl-2 protein activity , and increase ROS collectively promote BAX/BAK oligomerization, mitochondrial outer membrane permeabilization (MOMP, and both caspase-dependent and caspase-independent apoptosis). These effects are expected to vary across breast cancer subtypes based on p53 status, ER expression, and metabolic profile. This review highlights metformin's potential as an anti-cancer agent by targeting various mitochondrial mechanisms, each contributing to apoptosis and inhibiting tumorigenesis. The findings can guide clinicians in integrating metformin into targeted cancer treatments to overcome cancer resistance. This research can support the development of metformin-based therapies that selectively target cancer cell vulnerabilities and guide future efforts in personalizing treatment based on tumour metabolism and genetic context.