L-Arginine in Cancer Immunity and Therapy.

L-Arginine (L-Arg), a conditionally essential and versatile amino acid, exhibits important research values in cancer biology and therapy. L-Arg exerts antitumor effects through multiple mechanisms, of which immune regulation represents a pivotal mechanism. As a potential adjuvant for cancer therapy, L-Arg contributes to the inhibition of malignant cell growth and enhancement of therapeutic efficacy, and it has shown potential as a predictive biomarker for immunotherapy response. Moreover, microbiota-mediated regulation of L-Arg and its metabolic pathways can influence tumor progression and immune response, offering new insights into cancer treatment. However, intrinsic heterogeneity across tumor types has yielded seemingly contradictory findings-elimination of L-Arg shows remarkable efficacy in arginine-auxotrophic tumors, whereas L-Arg supplementation improves therapeutic outcomes in non-auxotrophic cancers. These complexities pose challenges for the clinical application of L-Arg and highlight the need for context-dependent and biomarker-guided strategies rather than uniform supplementation. Current strategies targeting L-Arg and its metabolic pathways are under active investigation, and integrating L-Arg modulation with other therapeutic modalities may enhance efficacy, offering novel perspectives and opportunities for exploring innovative approaches in the field of cancer therapy.