Metabolomic Analysis of Intracellular Amino Acid Profile Differences Between Cisplatin-Resistant and Cisplatin- Sensitive CALU-1 Lung Cancer Cells.

Lung cancer remains one of the leading causes of cancer-related mortality worldwide, and resistance to cisplatin remains a major limitation in the treatment of non-small cell lung cancer (NSCLC). Accumulating evidence indicates that cancer cells reprogram amino acid metabolism to support proliferation, stress adaptation, redox balance, and therapeutic resistance. In this context, defining the amino acid-related metabolic alterations associated with cisplatin resistance may help identify potential metabolic vulnerabilities and biomarker candidates. In this study, intracellular free amino acid profiles were compared between cisplatin-sensitive parental human lung squamous cell carcinoma cells (CALU-1) and their cisplatin-resistant counterpart (cr-CALU-1) using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The analysis revealed marked differences in the intracellular amino acid profiles of cr-CALU-1 cells compared with parental CALU-1 cells. Several amino acids, including proline, glutamine, glutamate, arginine, and alanine, were detected at higher levels in parental CALU-1 cells, whereas their intracellular levels were significantly lower in cr-CALU-1 cells. In contrast, cystine and phosphoethanolamine were increased in resistant cells. Multivariate and pathway analyses indicated that arginine and proline metabolism, histidine metabolism, and glutathione metabolism were among the most prominently affected pathways. These findings suggest that cisplatin resistance in CALU-1 cells is associated with broad remodeling of intracellular amino acid homeostasis. However, because targeted LC-MS/MS provides static metabolite pool-size information, further isotope-tracing and functional validation studies are required to determine whether these alterations reflect changes in amino acid uptake, biosynthesis, catabolism, or downstream utilization.