Targeting Ferroptosis to Overcome Radioresistance and Enhance Immunotherapy in Colorectal Cancer.

Locally advanced rectal cancer is commonly treated using total neoadjuvant therapy (TNT), which integrates radiotherapy with systemic chemotherapy to improve tumor downstaging, local control, and long-term oncologic outcomes. Despite its central role in treatment, responses to radiotherapy remain highly heterogeneous. While some tumors undergo complete regression, others exhibit intrinsic or acquired treatment resistance, resulting in incomplete tumor control while experiencing treatment-related toxicity. Understanding the biological determinants that govern radiation sensitivity in rectal cancer, therefore, represents a major clinical challenge.

Ionizing radiation induces tumor cell death primarily through the generation of reactive oxygen species (ROS) and DNA damage, particularly DNA double-strand breaks. In addition to nuclear DNA injury, radiation-induced oxidative stress can initiate lipid peroxidation within cellular membranes. When lipid peroxide accumulation exceeds the capacity of cellular antioxidant systems, this process can trigger ferroptosis, an iron-dependent form of regulated cell death driven by phospholipid oxidation. Ferroptotic susceptibility is regulated by interconnected metabolic pathways, including cystine transport through system Xc- (SLC7A11/SLC3A2), glutathione synthesis, glutathione peroxidase-4 (GPX4) activity, iron metabolism, and membrane lipid remodeling.

Recent evidence further indicates that ferroptosis intersects with antitumor immunity. Ferroptotic tumor cells release oxidized lipid mediators and damage-associated molecular signals that can influence immune activation, while interferon-γ produced by activated CD8+ T cells during immune checkpoint blockade suppresses SLC7A11 expression, limiting cystine uptake and promoting ferroptotic tumor cell death.

These findings suggest that ferroptosis represents a mechanistic interface between tumor metabolic vulnerability and immune-mediated cytotoxicity. This interaction is particularly relevant in colorectal cancer biology, where immune checkpoint inhibitors demonstrate clinical benefit primarily in tumors with deficient mismatch repair or microsatellite instability-high (MSI-H) status. The vast majority of rectal cancers are microsatellite stable (MSS) and exhibit limited responsiveness to immunotherapy due to reduced immunogenicity and immune exclusion within the tumor microenvironment. Strategies capable of increasing tumor immunogenicity in this setting are therefore of considerable interest.

In this review, we examine the molecular mechanisms linking radiation-induced oxidative stress to ferroptosis and tumor immunity in colorectal cancer, while focusing on the clinical context of radiotherapy in rectal cancer. We discuss how lipid metabolism, iron homeostasis, cysteine-dependent antioxidant systems, and immune signaling pathways converge to regulate ferroptotic vulnerability and radiation response. We further explore the therapeutic potential of integrating radiotherapy, ferroptosis-targeting strategies, and immunotherapy to overcome radioresistance and improve treatment outcomes in colorectal cancer.