Apoptosis activities of nickel and copper complexes from thymoquinone and dithiocarbamate on oral cancer cell lines in vitro

Abstract

Oral squamous cell carcinoma (OSCC) has been associated with high morbidity and mortality rate. Metal-based anticancer drugs such as platinum-based agents have been widely used to treat various cancer cells including OSCC. However, their efficiency is limited by the side effects and frequent development of chemoresistant cancer cells. To date, research on metal-based compounds has been extensively continued to develop more promising chemotherapeutic compounds capable to overcome these limitations. Thymoquinone (TQ) has been reported to have numerous biological activities, including anticancer in vitro and in vivo. Similarly, dithiocarbamate (PEDTC) is also known to have in vitro antineoplastic potential against several types of cell lines. Nickel and copper complexes from TQ (NiTQPy, CuTQPy) and PEDTC (NiPEDTC, CuPEDTC) were successfully synthesized and characterized. These metal complexes provide new approach to broaden the spectrum of biological activities their parent ligands. The study is aimed to investigate and determine anticancer potential of the metal complexes derived from TQ and PEDTC. Human OSCC HSC-3 and HSC-4 cell lines were chosen as in vitro model. The cells were exposed to various concentrations of the compound substances and examined by MTT assay for cytotoxicity analysis. Normal human oral fibroblast and human keratinocyte (HACAT) cells were also included in the assay. Zebrafish was used as a model for in vivo toxicity study. The number of apoptotic cells was quantified by flow cytometry and confirmed by Caspase 3/7 assay. Quantitative RT PCR was performed to analyze the mRNA expression of apoptotic-regulator genes. The protein expression was observed by western blot. The MTT assay demonstrated that the metal complexes induced cytotoxicity on HSC-3 and HSC-4 cells. Exposure of the metal complexes at the concentration similar to cancer cells relatively did not affect the normal cells and zebrafish embryo development, except for those treated with copper complexes. Flow cytometry showed the metal complexes increased the number of sub-G1 population, which represent apoptotic cells. The apoptotic activities were supported by Caspase 3/7 analysis. The various degree of apoptosis induction by metal complexes from TQ and PEDTC are associated with the elevation of BAX/BCL-2 ratio in both transcriptional (mRNA) and translational (protein) levels. NiPEDTC and NiTQPy was shown to be the most effective to induce apoptosis in HSC-3 and HSC-4 cells among the metal complexes. To conclude, these models of study are useful to demonstrate apoptosis activities in OSCC. The metal complexes from TQ and PEDTC are suggested to merit further investigation for its potentiation as anticancer agents.