Investigation of proapoptotic and cytotoxic effects of 2-aminobenzothiazole on human laryngeal carcinoma cells.

OBJECTIVE: In the present study, we investigated the effects of 2-aminobenzothiazole application on human laryngeal carcinoma cells.

MATERIALS AND METHODS: Human larynx epidermoid carcinoma (HEp-2) (ATCC® CCL-23™) cells were purchased from American Type Culture Collection (ATCC, USA). Human larynx epidermoid carcinoma HEp-2 cells were cultured in complete Dulbecco's Modified Eagle's Medium (DMEM) supplemented with fetal bovine serum (FBS) (10%) and penicillin/streptomycin (1%) in a CO2 (5%) incubator under standard cell culture conditions. 2-aminobenzothiazole was prepared, and further dilutions ranging from 3.13 to 100 μM were prepared in fresh culture DMEM. HEp-2 cells on 96 well plates were incubated with the prepared dilutions of 2-aminobenzothiazole for 24, 48, and 72 hours. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) test performed cytotoxicity evaluation and viability percentages. The annexin-V staining technique detected 2-aminobenzothiazole-triggered apoptosis of HEp-2 cells. The activated caspases 3/7 on HEp-2 cells after 2-aminobenzothiazole exposure were evaluated with flow cytometric analysis. The membrane potential changing of HEp-2 cells was measured following the Muse™ MitoPotential kit manufacturer instructions.

RESULTS: MTT cytotoxicity test results showed that the viability of human laryngeal carcinoma cells decreased with an increase in the application of 2-aminobenzothiazole for 24 hours. The highest growth inhibition by 2-aminobenzothiazole for short-term application of 24 hours was detected at the highest concentration of 2-aminobenzothiazole (100 µM). The results underline that the cytotoxic effect of 2-aminobenzothiazole is dose-dependent. Cytotoxicity test results for an application time of 48 hours showed that the cytotoxicity of 2-aminobenzothiazole is dose-dependent on HEp-2 cells. The required dose of 2-aminobenzothiazole to decrease the cell viability to 50 percent has been 9-fold augmented. Annexin-V findings showed that after exposure to IC50 concentration of 2-aminobenzothiazole for 24 hours, HEp-2 cells underwent the early apoptotic stage (25.99%) and late apoptotic (16.69%), whereas 56.93% of the treated cells were alive. Only 0.39% of 2-aminobenzothiazole treated cells were necrotic. All study results showed that 2-aminobenzothiazole triggered apoptosis on HEp-2 cells with a percentage of total apoptotic cells 42.62 compared to untreated HEp-2 cells. Caspase 3/7 activation results showed that only 0.65% of control HEp-2 cells were with activated caspase 3/7, and 99.35% live cells. The analysis data from the Muse cell analyzer revealed that the percentage of cells with intact mitochondrial membranes was 21.30 after 2-aminobenzothiazole application, and 79.9% were cells with depolarized mitochondrial membranes. It has been understood that the depolarization of the inner mitochondrial membrane has been considered a dysfunction in mitochondria as a sign of apoptosis and drug toxicity.

CONCLUSIONS: Based on all study findings, 2-aminobenzothiazole has cytotoxicity on human laryngeal carcinoma cells in a dose and time-dependent manner. That means that it decreased viability via inducing caspase-dependent apoptosis. Consequently, it was concluded that 2-aminobenzothiazole has good potential to lead to cytotoxicity and apoptosis on human laryngeal carcinoma cells and, after deeper in vitro and in vivo investigations, can be a good candidate for designing anticancer drugs with high efficiency.