Data from Cucurbitacin I Suppressed Stem-Like Property and Enhanced Radiation-Induced Apoptosis in Head and Neck Squamous Carcinoma–Derived CD44<sup>+</sup>ALDH1<sup>+</sup> Cells

Head and neck squamous cell carcinoma (HNSCC) is a prevalent cancer worldwide. Signal transducers and activators of transcription 3 (STAT3) signaling is reported to promote tumor malignancy and recurrence in HNSCC. Cucurbitacins, triterpenoid derivatives, are strong STAT3 inhibitors with anticancer properties. Recent studies have shown aldehyde dehydrogenase 1 (ALDH1) to be a marker of cancer stem cells (CSC) in HNSCC. The aim of this study was to investigate the therapeutic effect of cucurbitacin I in HNSCC-derived CSCs. Using immunohistochemical analysis, we firstly showed that CD44, ALDH1, and phosphorylated STAT3 (p-STAT3) were higher in high-grade HNSCCs, and that triple positivity for CD44/ALDH1/p-STAT3 indicated a worse prognosis for HNSCC patients. Secondly, CD44⁺ALDH1⁺ cells isolated from seven HNSCC patients showed greater tumorigenicity, radioresistance, and high expression of stemness (Bmi-1/Oct-4/Nanog) and epithelial-mesenchymal-transitional (Snail/Twist) genes as p-STAT3 level increased. Furthermore, we found that cucurbitacin I (JSI-124) can effectively inhibit the expression of p-STAT3 and capacities for tumorigenicity, sphere formation, and radioresistance in HNSCC-CD44⁺ALDH1⁺. Notably, 150 nmol/L cucurbitacin I effectively blocked STAT3 signaling and downstream survivin and Bcl-2 expression, and it induced apoptosis in HNSCC-CD44⁺ALDH1⁺. Moreover, microarray data indicated that 100 nmol/L cucurbitacin I facilitated CD44⁺ALDH1⁺ cells to differentiate into CD44⁻ALDH1⁻ and enhanced the radiosensitivity of HNSCC-CD44⁺ALDH1⁺. Xenotransplant experiments revealed that cucurbitacin I combined with radiotherapy significantly suppressed tumorigenesis and lung metastasis and further improved the survival rate in HNSCC-CD44⁺ALDH1⁺-transplanted immunocompromised mice. Taken together, our data show that cucurbitacin I, STAT3 inhibitor, reduces radioresistant, distant-metastatic, and CSC-like properties of HNSCC-CD44⁺ALDH1⁺ cells. The potential of cucurbitacin I as a radiosensitizer should be verified in future anti-CSC therapy. Mol Cancer Ther; 9(11); 2879–92. ©2010 AACR.