2.2 Phytochemicals used as adjuvants for Radiotherapy
Additive effect of curcumin with radiation was observed as a result of inhibition of phosphorylation of EGFR and decrease in COX-2 levels in SCC-1 cells. A significant decrease in tumor weight was also observed inin-vivo in mice treated with combination treatment as compared to non-treated mice (Khafif et al. , 2009).
In combination with radiotherapy, Honokiol downregulated survivin expression which significantly enhanced cytotoxicity and increased DNA damage in HNC cells (Tu 212, Tu 686, PCI-15A, JHU-022) andin-vivo xenograft tumors (Wang et al. , 2018).
Sulforaphane (SFN) is an important phytochemical found mostly in cruciferous vegetables and is well kown for its chemopreventive effects in many cancers (Liang et al. , 2019). It shows synergistic effect with radiation in inhibiting the proliferation and survival of HNC. Radiosensitizing effect of SFN was reported in many HNC cell lines (FaDu, CAL27, SCC9 and SCC25) (Kotowski et al. , 2011).
Resveratrol also acts as a radiosensitizer in nasopharyngeal cancer (NPC) both in-vitro & in-vivo . 50 μM of resveratrol radiosensitized the CNE-1 cells & inhibited the colony formation. Resveratrol and 2Gy of radiation synergistically increased apoptosis & downregulated E2F1 & phospho- AKT [p-AKT] in time and dose-dependent manner. 50 mg/kg/day resveratrol along with 4 Gy irradiation reduced tumor weight & volume as compared to either of the agents alone in-vivo also (Tan et al. , 2017). Radiosensitizing effects of resveratrol in in-vivo nude mice xenograft bearing FaDu hypopharyngeal carcinoma cell line was also reported. It significantly decreases the microvessel density (MVD) and inhibited the tumor growth. (Quan et al. , 2014)
Thymoquinone (TQ) also showed additive effect with radiation and significantly reduced the clonogenic survival of HNC. TQ was found to be an effective phytochemical with antiproliferative and radiosensitizing properties in HNC. Due to its low toxicity TQ could be used as an adjuvant to radiotherapy (Kotowski et al. , 2017).