Individual Amino Acid Supplementation Does Not Enhance Short-Term Proliferation of Selected Cancer Cell Lines In Vitro: Potential Implications for Nutritional Support in Cancer Cachexia

Background: Cancer-related cachexia is primarily characterized by systemic inflammation and progressive muscle wasting, which is why a high-protein diet (from 1.2 to 1.5 g/kg/day) is commonly recommended. However, concerns remain that an excessive supply of amino acids could promote tumor growth due to the metabolic flexibility of cancer cells, thereby favoring proliferation and survival. Systematic evidence addressing these concerns under controlled conditions for various types of cancer cells remains limited and inconclusive. Methods: We investigated the short-term effects of all 20 amino acids at both moderate (2×) and high (10×) concentrations to evaluate three key oncological endpoints in four human cancer cell lines: MDA-MB-231 (breast), HT29 (colorectal), PC3 (prostate), and PANC-1 (pancreatic). Cell proliferation was assessed by BrdU incorporation, metabolic activity by WST-1 assay, and apoptosis signaling by caspase-3/7 activity measurement. Results: Amino acid supplementation was not associated with a significant change in proliferation at either concentration across all four cell lines studied. Metabolic activity showed only minor variations throughout, with PC3 cells exhibiting slightly greater variability, although this did not reach statistical significance. Caspase-3/7 activity remained largely unchanged under all conditions; however, high-concentration lysine induced an approximately 2.5-fold increase in PANC1 cells, which was not statistically significant. Conclusions: These findings suggest that short-term exposure to individual amino acids, even at supraphysiological conditions, does not acutely enhance proliferative activity in the cancer cell lines studied, supporting the rationale for adequate protein and amino acid intake in patients with cancer cachexia.