Cancer Biology and Signal Transduction Inhibition of Glucosylceramide Synthase Sensitizes Head and Neck Cancer to Cisplatin

Glucosylceramide synthase (GCS) overexpression is associated with multidrug resistance in several human cancers. GCS blockade, which overcomes multidrug resistance by downregulating P-glycoprotein (P-gp), has not been tested inhead andneck cancer (HNC). This study investigates whether GCS is targetable in HNC by assessing whether GCS inhibition sensitizes HNC to cisplatin. The effect of genetic or pharmacologic GCS inhibition (usingGCS siRNA/shRNA or D,L-threo-PPMP, respectively) on cisplatin sensitivity was assessed in several human HNC cells and acquired cisplatin-resistant HNC cells bymeasuring cell viability, cell cycle, death, mRNA and protein expression, ceramide production, and in preclinical tumor xenograft mouse models. GCS and P-gp expression were significantly associated with cisplatin resistance in several HNC cell lines (P 1⁄4 0.007). Both were significantly increased in HN9-cisR cells, which display acquired cisplatin resistance (P < 0.001). Genetic or pharmacologic inhibition of GCS induced accumulation of increased ceramide levels. GCS inhibition increased cisplatin-induced cell death in HNC cells via P-gp downregulation and proapoptotic protein activation, which were abrogated by siPUMA transfection. Genetic and pharmacologic GCS inhibition sensitized resistant HNC cells to cisplatin in vitro and in vivo. GCS and P-gp overexpression is associatedwith acquired cisplatin resistance, suggesting a role for thesemolecules as therapeutic targets for HNC. Genetic or pharmacologic GCS blockademay have therapeutic benefit in cisplatin-resistantHNC. Mol Cancer Ther; 14(8); 1–9. 2015 AACR.