Cucurbitacin B inhibits growth, arrests the cell cycle, and potentiates antiproliferative efficacy of cisplatin in cutaneous squamous cell carcinoma cell lines.

Cutaneous squamous cell carcinoma (CSCC) is the second most common skin cancer with a substantial risk of metastasis which causes clinical treatment failure. This study investigated the anti-CSCC effects of a triterpenoid compound, Cucurbitacin B (CuB). Dose-response studies showed that CuB inhibited 50% growth (ED50) of the CSCC cell lines (SRB1, SRB12, SCC13, COLO16) in liquid culture at 4 x 10(-7)-10(-5) M. Soft-agar assays demonstrated that nearly all of the CSCC clonogenic cells were inhibited at 10(-7) M CuB. FACS analysis found that the compound (10(-7) M, 48 h) caused G2/M arrest. The CSCC cells underwent profound morphologic changes within 60 min after exposure to CuB (10(-7) M), rounding up and losing their pseudopodia. CuB (10(-7) M) caused prominent multinucleation of the cells after they were pulse-exposed (24 h) to the drug, washed and cultured in normal medium for an additional 24 h. The drug (10(-8)-10(-6) M, 3-24 h) decreased levels of CDC2 and cyclin B1 in SRB1 and SRB12 cell lines as seen by Western blot analysis. Migration of SRB1 and SRB12 cells was inhibited by 10(-7) M CuB. Interestingly, CuB synergistically potentiated the anti-proliferative effect of cisplatin in CSCC. In summary, CuB has a prominent anti-proliferative activity on CSCC cells. In vivo studies and clinical trials of this drug should be pursued in CSCC.