Rhaponitin Reverses Cisplatin Resistance and Impairs Cancer Stemness Through HIF-1α/MCT4/Wnt Pathway in Tongue Squamous Cell Carcinoma.

Rhaponitin (Rha) possesses anti-tumor activity and mediates the transcriptional activity of hypoxia-inducible factor (HIF)-1α that affects cisplatin (Cis) resistance. However, whether Rha can lessen Cis resistance in tongue squamous cell carcinoma (TSCC) by mediating HIF-1α activity is unclear. Cis-resistant SCC9 (SCC9-CisR) cells were treated with Cis, Rha, or Cis plus Rha to explore the effect of Rha on Cis resistance using a cell counting kit-8, flow cytometry, and tumor sphere formation assays. Stemness markers CD44 and SOX2 and HIF-1α mRNA levels were detected by quantitative PCR. The GSE115119 database and plugin iRegulon were employed to select target genes mediated by HIF-1α. Protein levels of HIF-1α, monocarboxylate transporter 4 (MCT4), and the Wnt/β-catenin pathway were measured by western blot. Subcutaneous xenograft models were constructed to explore the efficacy of Rha in combating Cis resistance. Rha repressed the growth and stemness of SCC9-CisR cells in vitro and in vivo. HIF-1α protein levels were markedly elevated in SCC9-CisR cells, yet Rha treatment attenuated the transcriptional activity of HIF-1α but not HIF-1α mRNA levels. Rha plus Cis repressed the viability and stemness of SCC9-CisR cells, but not HIF-1α-knockdown SCC9-CisR cells, compared with Cis alone. Rha-induced stemness inhibition and apoptosis in SCC9-CisR cells were overridden after HIF-1α overexpression. Rha inhibited the Wnt/β-catenin signaling by regulating the HIF-1α/MCT4 axis. In conclusion, Rha reduced cell stemness and enhanced Cis sensitivity in TSCC, which was achieved possibly via suppressing the Wnt/β-catenin signaling through mediation of the HIF-1α/MCT4 axis.