Cytotoxicity and Type of Cell Death Induced by Local Anesthetics in Human Oral Normal and Tumor cells

Background: Local anesthetics are often administered to tumors and surrounding tissues during the surgery of the head and neck area, however their effects on oral tissues is not well understood. In the present study, the cytotoxicity of a total of seven local anesthetics towards oral tumor and normal cells was compared. Materials and Methods: Tumor-specificity index was determined by the ratio of the mean 50% cytotoxic concentration against normal cells to that for tumor cells. Apoptosis induction was monitored by internucleosomal DNA fragmentation and caspase-3, -8, and -9 activation. Fine cell structure was observed under transmission electron microscopy. Results: All local anesthetics showed slightly higher cytotoxicity towards oral squamous cell carcinoma (OSCC) cell lines than towards normal oral cells. Dibucaine, with a log p-value of approximately 3, was the most cytotoxic, followed by tetracaine, bupivacaine or ethylaminobenzoate, whereas lidocaine, procaine and mepivacain were much less cytotoxic. When the tumor-specificity was evaluated between OSCC and human skin keratinocytes, the index was 6.6. Dibucaine did not induce apoptosis of OSCC cells. On the other hand, dibucaine did induce mitochondrial injury and swelling, formation of secondary lysosomes, and at high concentrations, rupture of the cell membrane. Autophagy inhibitors did not reduce the cytotoxicity of dibucaine. Conclusion: Necrosis may be involved in the induction of antitumor activity by dibucaine.