Abstract 2176: Thymoquinone synergizes the anticancer properties of cisplatin against head and neck squamous cell carcinoma and protects normal oral epithelial cells

Cisplatin (CDDP) is potent anticancer agent different tumors such as head and neck cancers. Thymoquinone is natural compound drawing attention as chemotherapeutic and chemomodulator. Herein, we studied the chemomodulatory effect of thymoquinone to CDDP against squamous cell carcinoma cells. CDDP killed head and neck squamous cell carcinoma cells (UMSCC-14C) with IC₅₀’s of 5.2±0.2, 2.6±0.2 and 1.6±0.1 µM after treatment for 24h, 48 h and 72 h, respectively. On the other hand, IC₅₀’s of CDDP against normal oral epithelial cells were 36.4±1.1, 16.3±0.6 and 6.7±1.1 µM after exposure for 24h, 48 h and 72 h, respectively. Thymoquinone alone exerted considerable cytotoxicity against UMSCC-14C cells with IC₅₀’s of 9.0±0.2, 6.9±0.1 and 5.0±0.2 µM after treatment for 24h, 48 h and 72 h, respectively. While significantly weaker killing effect was noticed for thymoquinone against normal oral epithelial cells (OEC) with IC₅₀’s of 41.1±0.5, 36.6±1.1and 26.3±1.2µM after exposure for 24h, 48 h and 72 h, respectively. Equitoxic combination of thymoquinone and CDDP showed synergistic interaction against UMSCC-14C cells (Combination index of 0.58) and antagonistic interaction against OEC cells (Combination index of 1.12). Using annexin-V/PI staining, it was found that thymoquinone alone (5 µM) increased apoptotic cell fraction in UMSCC-14C cells, as early as after only 6 hours, from 1.7±0.1% to 24.4±0.6% compared to 2.7±0.04 apoptosis induced by CDDP (5 µM). Combination of CDDP with thymoquinone further increased total apoptosis in UMSCC-14C to 32.9±1.5% after 6 h. prolonged exposure of UMSCC-14C to thymoquinone (5 µM) alone for 24 h resulted in 96.7±1.6% total apoptosis which was increased after combination with CDDP to 99.3±1.2% in UMSCC-14C cells. In contrast to UMSCC-14C cells, thymoquinone did not induce any significant apoptosis in OEC and even decreased apoptosis induced by CDDP alone from 4.5±0.3% to 3.4±0.2% after combination for 24 h. Using western blot analysis, neither thymoquinone nor CDDP managed to increase the expression level of p53 apoptotic protein; while combination of CDDP with thymoquinone significantly increased p53 expression by 4.5 folds. On the other hand, both CDDP and thymoquinone decreased the expression level of the anti-apoptotic protein Bcl-2 to be 60% and 20% of control level, respectively. Combination of both agents further abolished the level of Bcl-2 to be 10% of control level. Caspase-9 expression was similarly induced by 2 folds and 4.5 folds after treatment with CDDP and thymoquinone, respectively. Combination of CDDP and thymoquinone further induced the level of caspase-9 to be 6 folds original basal expression level. None of these finding could be detected in normal OEC cell line. In conclusion, thymoquinone synergize the anticancer properties of CDDP against squamous cell carcinoma cells and protects from its damaging effect against normal epithelial cells

Citation Format: Abdulwahab Noorwali, Omar Aloafi, Safia Al-Attas, Fatheya Zahran, Ahmed M. Al-Abd. Thymoquinone synergizes the anticancer properties of cisplatin against head and neck squamous cell carcinoma and protects normal oral epithelial cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2176. doi:10.1158/1538-7445.AM2017-2176