Heterogeneity of anticancer drug sensitivity in squamous cell carcinoma of the tongue.

Heterogeneity is known to be present to varying degrees in cancer cell groups. There have been no reports, however, of studies in which a single cell clone was prepared from a cancer cell group to examine heterogeneity with respect to anticancer drug sensitivity. Thus, the authors herein report an investigation into the heterogeneity of cancer cells within the same tumor with respect to anticancer drug sensitivity. Anticancer drug sensitivity was investigated in primary tumors, metastatic lymph node tumors, recurrent tumors and established cell lines obtained from four cases of tongue cancer using an oxygen electrode apparatus. As differences were observed in anticancer drug sensitivity from one case to another, even though all four were of the same pathological tissue type, the individual differences were apparently significant. Moreover, primary tumors and recurrent tumors demonstrated different sensitivities to the anticancer drugs even in the same patient. When single cell clones were prepared from primary tumors and anticancer drug sensitivity testing was carried out, sensitivity to anticancer drugs that was not seen in the primary tumors was observed. We performed RT-PCR on cell groups derived from this single cell using MDR1, MRP1, MRP2 and ERCC1, which are primary genes that are resistant to anticancer drugs. Expression of MDR and ERCC1 was not observed in single cell clones nos. 1-10. MRP1 and MRP2, on the other hand, were expressed in all of these single cell clones. Because cells with different sensitivity levels were initially present in the cancer cell groups, even when large numbers of cancer cells died in response to anticancer drug therapy, the results suggest the possibility that recurrence and metastasis occur based on cells with differing sensitivities. After examining anticancer drug sensitivity at the single cell level, we believe that anticancer drug-resistant genes may be involved in the heterogeneity of anticancer drug sensitivity with respect to cancer cell groups.