Emerging evidence suggests that increased nicotinamide phosphoribosyltransferase (NAMPT) expression is associated with the development and prognosis of many cancers, but it remains unknown regarding its role in oral squamous cell carcinoma (OSCC). In the present study, the results from tissue microarray showed that NAMPT was overexpressed in OSCC patients and its expression level was directly correlated with differential grades of cancer. Interestingly, treatment of OSCC cells with chemotherapy agent arsenic trioxide (ATO) decreased the levels of NAMPT protein and increased cellular death in an ATO dose- and time-dependent manner. Most importantly, combination of low concentration ATO with FK866 (a NAMPT inhibitor) exerted enhanced inhibitive effect on NAMPT protein and mRNA expressions, leading to synergistic cytotoxicity on cancer cells through increasing cell apoptosis and depleting intracellular nicotinamide adenine dinucleotide levels. These findings demonstrate the crucial role of NAMPT in the prognosis of OSCC and reveal inhibition of NAMPT as a novel mechanism of ATO in suppressing cancer cell growth. Our results suggest that ATO can significantly enhance therapeutic efficacy of NAMPT inhibitor, and combined treatment may be a novel and effective therapeutic strategy for OSCC patients.

Purpose: Nicotinamide phosphoribosyltransferase (NAMPT) is a key enzyme for a rate-limiting step in the nicotinamide adenine dinucleotide (NAD) salvage pathway. Tumor cells are reliant on the NAMPT salvage pathway for NAD regeneration, thus making this enzyme an attractive therapeutic target for cancer treatment. Overexpression of NAMPT has been observed across a broad range of solid tumors including ovarian, breast, and prostate cancers. However, it is unknown regarding the expression and function of NAMPT in oral cancer. Arsenic trioxide (ATO) has been approved for the treatment of acute promyelocytic leukemia, and accumulating evidence indicate that it is a promising therapeutic drug for certain solid malignant tumors. Up to now, the effect of ATO on NAMPT in oral cancer remains unclear. In the present study, we investigated the expression of NAMPT in different differentiated degree oral cancer and examined the effects of ATO on NAMPT in oral cancer cell line. Materials and methods: Tissue microarray (TMA) was performed by immunohistochemistry to examine the NAMPT expression in well differentiated (n = 39), moderately differentiated (n = 6), and poorly differentiated (n = 5) tissue samples collected from surgical specimens of the oral cancer patients. Human oral squamous cell carcinoma Tca-8113 cells were treated with ATO for 48 hrs. PrestoBlue activity assay was used to detect cell activity and NAMPT mRNA expression was measured by RT-PCR. Results: In paracancer tissue, NAMPT was mainly distributed in cytoplasma and lightly located in nuclear. Intensely increased staining of NAMPT was found in all differentiated grade oral cancer by immunohistochemistry. Moreover, while increased NAMPT are mainly located in cytoplasma in well-differentiated cancer, the marked increase of NAMPT occurred both in cytoplasma and nuclear in moderate- and poor-differentiated cancer. TMA results showed that comparing with normal oral tissue, the protein expression of NAMPT increased by 2.20, 2.66, and 3.03 fold in well-, moderate-, and poor- differentiated oral cancer, respectively. ATO (1, 2.5, 5, and 10 μmol/L) pretreatment of Tca8113 cells significantly reduced the cell activity in an ATO concentration-dependent manner. More importantly, NAMPT mRNA expression was markedly decreased 8.60%, 26.92%, 71.01%, and 78.26%, respectively, compared with control cells. Conclusion: Our novel findings suggest that increased NAMPT expression were highly associated with cellular differentiation in oral cancer, indicating that NAMPT may participate in the development of oral cancer. ATO can inhibit cell activity by depressing NAMPT transcription in oral cancer. These findings may have implications for exploring the NAMPT pathway for oral cancer treatment. Citation Format: Jin Zhi Wang, Yan Liu, Xin Yue Wang, Li Chi Han, Fu Yin Zhang, Ke Liu, Bin Xiang. Arsenic trioxide inhibits overexpression of NAMPT in oral cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3006.