New Metabolic Pathway Unveiled: αKG-Carnitine Axis Drives DNA Repair and Influences Cancer Treatment Response

In the ongoing battle against cancer, DNA-damaging agents represent a cornerstone of many therapeutic regimens. These treatments are particularly effective against cancers with homologous recombination (HR) deficiency, a condition that makes cells more vulnerable to DNA damage. However, a significant challenge remains in treating HR-proficient cancers, where the metabolic pathways governing their response or resistance to these crucial agents have largely remained a mystery. Understanding these mechanisms is vital for developing more targeted and effective cancer therapies. A groundbreaking study published in Nature has now shed light on this enigma, identifying a novel metabolic pathway that dictates how HR-proficient cells respond to DNA-damaging agents. Researchers discovered that depleting α-ketoglutarate (αKG), a key metabolic intermediate, sensitizes these cells to such agents by metabolically regulating histone acetylation. While αKG is known for its role in activating αKG-dependent dioxygenases (αKGDDs), previous research predominantly focused on their demethylase functions, leaving other potential roles unexplored. Utilizing an advanced targeted CRISPR knockout library encompassing 64 αKGDDs, the team made a pivotal discovery: trimethyllysine hydroxylase epsilon (TMLHE). TMLHE, the initial and rate-limiting enzyme in the de novo synthesis of carnitine, was found to be indispensable for the survival of HR-proficient cells when exposed to DNA-damaging agents. Surprisingly, the study revealed that αKG-mediated, TMLHE-dependent carnitine synthesis is directly required for histone acetylation. This process was found to be unique and non-redundant, meaning other cellular pathways generating acetyl-CoA could not compensate for its absence. The research further elucidated that this increase in histone acetylation, facilitated by the newly identified αKG–carnitine axis, actively promotes homologous recombination-mediated DNA repair through site-specific histone acetylation. This intricate metabolic interplay ensures the cell's ability to repair damaged DNA, thereby influencing its resistance to therapeutic interventions. Moreover, the study established a significant clinical correlation: patient samples showed a positive link between TMLHE levels and histone acetylation. Crucially, high levels of TMLHE or acetylcarnitine were associated with worse progression-free survival in patients undergoing treatment with DNA-damaging agents. This landmark study marks the first time, to the researchers' knowledge, that αKG has been shown to influence site-specific histone acetylation, providing a clear metabolic mechanism for HR proficiency through carnitine synthesis. The findings not only deepen our understanding of fundamental cellular processes but also open up promising new avenues for cancer therapy. By identifying this metabolic pathway, scientists now have a potential target to induce HR deficiency in previously resistant cancers, thereby enhancing their sensitivity to existing DNA-damaging agents and potentially improving patient outcomes. This could pave the way for innovative metabolic interventions in cancer treatment.