Additive effects of C₂-ceramide on paclitaxel-induced premature senescence of human lung cancer cells

Aims: The aims of the study are to investigate the additive effect of exogenous short-carbon chain phospholipids, C₂-ceramide, on an anti-cancer drug paclitaxel (PTX)-induced senescence of human non-small cell lung cancer (NSCLC) cells deficient in functional p53 and p16, and to examine whether mitogen-activated protein kinase (MAPK) plays a role in ceramide-sensitized senescence of NSCLC cells. Main methods: To determine whether exogenous C₂-ceramide renders lung cancer cells more sensitive to PTX treatment, techniques employing a flow cytometry-based cell cycle analysis and acidic β-galactosidase staining for senescent cells were used. Furthermore, to elucidate the role of MAPK proteins in modulating senescence, assays for protein levels of selective MAPKs and Bcl-2 family members, and detection of transcriptional levels senescence-associated genes were used in the study. Key findings: A sub-lethal dose of C₂-ceramide sensitized the NSCLC H1299 cells to PTX treatment. The additive effects of C₂-ceramide and PTX resulted in proliferative inhibition, G₂-phase arrest of cell cycle, activation of p38 and eventually premature senescence. Importantly, neither p53, p21^waf1/cip1 nor p16^ink4 was shown to be involved in C₂-ceramide-sensitized proliferative inhibition and senescence of H1299 cells by PTX in our study. Significance: Our study demonstrates that the short-carbon chain C₂-ceramide can effectively sensitize PTX-induced senescence of H1299 cells via both p21^waf1/cip1- and p16^ink4-independent pathways.