Glutaminase I and glutamine transaminase-ω-amidase pathways in colorectal cancer: Metabolic reprogramming and emerging therapeutic strategies.

Colorectal cancer (CRC) cells exhibit a pronounced dependence on l-glutamine to support anabolic growth, redox balance, and mitochondrial metabolism, a phenomenon known as "glutamine addiction." The canonical glutaminase I pathway is mediated by a liver type glutaminase isozyme (LGA; GLS1), a kidney type glutaminase isozyme (KGA; GLS2), and a shortened form (glutaminase C, GAC). GLS1 and GLS2 convert glutamine to glutamate and subsequently to α-ketoglutarate (α-KG) by glutamate dehydrogenase, fueling the TCA cycle. GLS1 inhibitors, such as CB-839 (Telaglenastat), are under clinical evaluation and shows promise in treatment of CRC, particularly in combination therapies. In addition to the canonical pathway, the glutamine transaminase-ω-amidase (GTωA) pathway, a noncanonical route involving transamination of glutamine to α-ketoglutaramate (KGM) by KYAT1/2 and subsequent hydrolysis by ω-amidase (NIT2), offers metabolic flexibility under hypoxic or nutrient-limited conditions. Preclinical studies suggest that GTωA may compensate for GLS1 inhibition, contributing to therapeutic resistance. This review explores the dual roles of glutamine metabolism in CRC, emphasizing the GTωA pathway as a potentially targetable metabolic route that may contribute to therapeutic resistance. While GLS1 inhibitors are under clinical evaluation, emerging evidence suggests that dual targeting of both pathways may enhance treatment efficacy by overcoming metabolic compensation. Understanding the regulatory mechanisms driving the "glutamine shift" between these pathways is critical for developing effective metabolic interventions in CRC.