Raman spectroscopy for detecting gastric and liver cancer cells that entered a tolerant persistence state to survive cisplatin chemotherapy.

The persistence of minimal residual disease (MRD), a small population of tumor cells that survive therapy but remain below the limit of conventional detection methods, often leads to relapse. The residual disease is attributed to drug-tolerant persister (DTP) cells at the cellular level. In the present study, the differences in drug-tolerant persister cells, which represent a transient, reversible survival state, and drug-resistant cells, which reflect a stable, fixed phenotype of gastric and liver cancer cell lines, were investigated. The ultramicroscopic and confocal studies revealed a phenotypic shift in DTP cells induced upon drug treatment, characterized by cytoplasmic expansion, enhanced mitochondrial biogenesis, and active intercellular communication, potentially contributing to the survival of the drug-tolerant cells. The observed morphological alterations in a cell's physical characteristics are associated with underlying biochemical changes. Further, Raman spectroscopy provides a non-invasive method for studying biochemical alterations; Raman spectral analysis demonstrated precision in distinguishing with significant accuracy between DTP cells compared to resistant and parental cells. Multivariate Curve Resolution-alternating least squares (MCR-ALS) analysis showed alteration of lipid, nucleic acid, and protein-related features. The accumulation of lipid vacuoles inside the cytoplasm of DTP cells, and gene set enrichment analysis (GSEA) showed significant downregulation of metabolic pathways purine and pyrimidine, highlighting the potential metabolic shift in imparting a survival advantage to DTP cells. Thus, Raman analysis has confirmed the biochemical changes and provides proof of concept for identifying cisplatin-induced DTP and resistant tumor cells for a better therapeutic approach in resistant and relapse management.