Consistent with cancer stem cell theory, a small fraction of cancer cells, described as cancer stem cells (CSCs), may promote tumor recurrence and anti-cancer drug resistance. Therefore, much effort has been devoted to the development of CSC targeted therapy to vanquish drug resistance. In this study, we have investigated the effect of multiple light-emitting diode (LED) irradiation treatments with conventional anti-cancer drugs on CSC-like oral cancer cells that acquired stemness by ectopic over expression of CD133. To evaluate combined LED irradiation anti-cancer drug effects, we investigated the chemosensitizing effect of 635 nm irradiation on 5-fluorouracil (5FU)-treated KB(CD133+) and KB(Vec) cells, interrogating the underlying molecular mechanisms associated with stemness and apoptosis that are responsible for chemopreventive activity. In addition, combination therapy with LED irradiation and 5-FU treatment was carried out in KB(CD133+) and KB(Vec) cell-inoculated mouse models. LED irradiation of 635 nm inhibited CSC-like properties consistent with a decrease in OCT4 and NANOG protein expression, reducing colony-forming ability. In addition, LED irradiation enhanced 5-FU-induced cytotoxicity and improved 5-FUchemosensitivity in KB(CD133+) via enhancement of apoptosis. These findings were validated in vivo, wherein LED irradiation combined with 5-FU treatment inhibited tumor growth in KB(CD133+)-inoculated mice. Collectively, our results provide novel evidence for 635 nm irradiation-induced 5-FU chemosensitization of CSC in oral cancer. In addition, this research highlights that 635 nm LED irradiation may serve as an adjunct treatment to conventional chemotherapeutic drugs in patients with oral cancer.

Concurrent chemotherapy and radiotherapy (RT) is important for controlling oral squamous cell carcinoma (OSCC), which is often accompanied by significant acute and late toxicities. We investigated whether cordycepin, a small molecule extracted from Cordyceps sinensis, could enhance the radiosensitivity of oral cancer cells. Using colony formation assay, we demonstrated that cordycepin induces radiosensitizing effects on two OSCC cells. DNA histogram analysis showed that cordycepin combined with RT prolonged the RT-induced G2/M phase arrest. It protracted the duration of DNA double strand breaks, which was detected by immunofluorescent staining of phosphorylated histone H2AX (γ-H2AX). The underlying molecular mechanism might involve the downregulation of protein expression related to DNA damage repair, including phosphorylated ataxia-telangiectasia mutated (p-ATM) and phosphorylated checkpoint kinase 2. Reciprocal upregulation of phosphorylated checkpoint kinase 1 (Chk1) expression was noted, and the radiosensitizing effect of cordycepin could be further augmented by Chk1 mRNA knockdown, indicating a compensatory DNA repair machinery involving phosphorylation of Chk1. In vivo, the combination of cordycepin and RT exhibited greater growth inhibition on xenografts and stronger apoptosis induction than RT alone, without exacerbating major toxicities. In conclusion, cordycepin increased the radiosensitivity of OSCC cells, which is associated with the modulation of RT-induced DNA damage repair machinery.