Sal-B inhibits Cisplatin-resistant HNSCC Growth by Targeting Ceramide-mediated Signaling Pathways

Objective: Cisplatin is widely used to treat different types of cancers, but resistance to cisplatin hampers ongoing treatment. Abnormal ceramide metabolism can lead to cisplatin-resistance by increasing ceramide-glycosylation and reducing ceramide-mediated apoptosis.  Salvianolic acid B (Sal-B) is a compound extracted from Salvia miltiorrhiza Bge, which is widely used in China for treatment of chronic inflammatory diseases. In this study, we investigated the anticancer properties of Sal-B in inhibition of cisplatin-resistant HNSCC growth by regulating ceramide-mediated signaling pathways.

Method: Two pairs of isogeneic, cisplatin-sensitive, and cisplatin-resistant cell lines derived from two parental cell lines (KB-3-1 and SCC25) were used to test the hypothesis. The cell lines were treated with 0-100μg/ml Sal-B or 0-10μg/ml cisplatin.  Cell viability and cell cycle were analyzed by colony assay and flow cytometry.  Tumor xenograft growth was also evaluated with treatment of 80mg/kg Sal-B or 5mg/kg cisplatin in NU/NU mice inoculated with cisplatin-sensitive or resistant HNSCC cells. Key apoptotic proteins were examined by Western blot assay.

Result: Cell cycle was arrested in S-phase and there was no cell colony formation when the resistant cells (KBCP) where treated with100μg/ml Sal-B. In contract, with sensitive cells (KB-3-1 cells), 10μg/ml cisplatin was a sufficient concentration to inhibit colony formation.  In vivo mass of tumor xenografts decreased significantly in mice treated with Sal-B compared to cisplatin treated or untreated groups.  Sal-B enables the decrease of glucosylceramide synthase expression to enhance ceramide-mediated apoptosis. Expectedly, pro-apoptotic proteins Bax and Bad were elevated and anti-apoptotic proteins survivin and Bcl-xL were decreased markedly in cells treated with Sal-B.

Conclusion: Our results demonstrate that Sal-B is effective in inhibiting tumor growth and inducing apoptosis of cisplatin-resistant HNSCC, in part by suppressing ceramide glycosylation to enhance ceramide-mediated signaling pathways. A greater understanding of how ceramide glycosylation is regulated by Sal-B may lead to prevention of drug resistance.