Proceedings of Oncobiology Symposiums
Proceedings of XIV Oncobiology Symposium

INTRODUCTION AND OBJECTIVES: The oral squamous cell carcinoma (OSCC) stands out as a public health problem due to its high incidence and low survival rate, despite advances in diagnosis and treatment. Therefore, the development of new drugs is urgent. Naphthoquinones are an important class of natural products or synthetic compounds with cytotoxic effect demonstrated on different cancer types. In the present study, thirty-five 1,4-naphthoquinones tethered to 1,2,3-1H-triazoles were synthesized and the antitumor activity and molecular mechanisms were evaluated. MATERIAL AND METHODS: Cell viability, compound stability, clonogenic and selective index (SI) determination assays were performed by MTT. The IC50 was calculated by a non-linear regression curve in the GraphPad Prism 5 program. Hemolytic assay was performed to discard any effects of surfactant activity of the compounds. For the acute toxicological testing, the compounds were administered intraperitoneally in C56BL/6 mice at different concentrations and their effect was observed along 14 days. The release of reactive oxygen species (ROS) was investigated by DHR123 labeling. DNA biding of the compounds was assessed using isothermal titration calorimetry. Microtubule instability was analyzed by the staining of α–tubulin. Pyknotic nuclei and caspase-3 analysis were performed to evaluate the type of cell death. A possible molecular mechanism for compounds action was investigated using binding in silico technique. RESULTS AND CONCLUSION: Compounds 16a, 16b and 16g were able to induce cytotoxicity in three different tumor cell lines of human OSCC (SCC4, SCC9 and SCC25) and were more toxic and selective to tumor cells (SI > 2) than classical and chemically similar controls (Carboplatin and Lapachol). Compound 16g showed the higher SI value. Besides, these compounds significantly reduced colony formation of SCC9 cells. Hemolytic assay using compounds at high concentrations showed none exhibited hemolysis higher than 5%, similar to controls. In vivo acute toxicity study showed that 16g was the only compound with no apparent limiting toxic effects on mice. Thus, the investigation of cell death mechanisms was conducted with this compound. 16g does not trigger ROS production nor binds to DNA. On the other hand, compound 16g induced microtubule disorganization, and molecular modeling studies suggest a potential mechanism of action related to inhibition of topoisomerases and/or hPKM2 activities. Cell morphology, pyknotic nuclei presence, cleaved caspase-3 staining and viability assays using caspase-3 inhibitors demonstrate compound 16g induced cell death through apoptosis. Among the 35 synthesized triazole naphthoquinones, compound 16g was the most effective compound against OSCC cells, presenting high cytotoxicity (~ 35 µM), selectivity (SI ~ 6) and low acute toxicity on animals, and therefore might be considered for future cancer therapy.