Cytotoxicity of Topoisomerease I/II inhibitors against OSCC Cell Lines

Objective: Relatively limited sets of chemotherapeutic agents have been administered to oral cancer patients. To get more specific compounds for the treatment of OSCC patients, five topoisomerase inhibitors (with one active metabolite) were tested for their activity to induce tumor-selective cytotoxicity. Methods: OSCC cell lines (HSC-2, HSC-3, HSC-4, NA, Ca9-22), human glioblastoma (T98G, U87MG), human myelogenous leukemia (HL-60, ML-1, KG-1) and normal oral cells (gingival fibroblast, pulp cell, periodontal ligament fibroblast) were cultured in RPMI1640 (for only leukemia) or DMEM supplemented with 10% FBS. Near confluent cells were treated for 48 hours with various concentrations of topoisomerase I inhibitor (camptothecin, irinotecan, SN-38 (a active metabolite of irinotecan), topotecan) or topoisomerase II inhibitor (etoposide, teniposide). The dose-response curve was used to determine the 50% cytotoxic concentration (CC₅₀). Tumor-specificity index was calculated by the ratio of mean CC₅₀ for normal cells to that for tumor cell lines. Apoptosis markers used were internucleosomal DNA fragmentation and caspase-3,-8, -9 activation. Autophagy markers used were autophagosome and secondary lysosome detected by acridine orange staining and transmission electron microscopy. Results: Camptotechin showed the highest cytotoxicity, followed by SN-38 (I) >topotecan (I) > teniposide (II) > etoposide (II)> irinotecan (pro-drug of SN-38) (I). Leukemic celll lines showed the highest sensitivity, followed by OSCC, human glioblastoma and then normal cells. Five OSCC cell lines showed considerable variation in the sensitivity. Conclusion: Generally, topoisomerase I inhibitors showed higher cytotoxicity against OSCC cell lines than topoisomerase II inhibitors. The type of cell death induced is underway.