Abstract
BackgroundAs the selective inhibitor of BRAF kinase, vemurafenib exhibits effective antitumor activities in patients with V600 BRAF mutant melanomas. However, acquired drug resistance invariably develops after its initial treatment.MethodsImmunohistochemical staining was performed to detect the expression of iNOS and hTERT, p-p65, Epcam, CD44, PCNA in mice with melanoma xenografts. The proliferation and migration of melanoma cells were detected by MTT, tumorsphere culture, cell cycle, cell apoptosis, AO/EB assay and colony formation, transwell assay and scratch assay in vitro, and tumor growth differences were observed in xenograft nude mice. Changes in the expression of key molecules in the iNOS/hTERT signaling pathways were detected by western blot. Nucleus-cytoplasm separation, and immunofluorescence analyses were conducted to explore the location of p50/p65 in melanoma cell lines. Flow cytometry assay were performed to determine the expression of CD44. Pull down assay and ChIP assay were performed to detect the binding ability of p65 at iNOS and hTERT promoters. Additionally, hTERT promoter-driven luciferase plasmids were transfected in to melanoma cells with indicated treatment to determine luciferase activity of hTERT.ResultsMelatonin significantly and synergistically enhanced vemurafenib-mediated inhibitions of proliferation, colony formation, migration and invasion and promoted vemurafenib-induced apoptosis, cell cycle arresting and stemness weakening in melanoma cells. Further mechanism study revealed that melatonin enhanced the antitumor effect of vemurafenib by abrogating nucleus translocation of NF-κB p50/p65 and their binding at iNOS and hTERT promoters, thereby suppressing the expression of iNOS and hTERT. The elevated anti-tumor capacity of vemurafenib upon co-treatment with melatonin was also evaluated and confirmed in mice with melanoma xenografts.ConclusionsCollectively, our results demonstrate melatonin synergizes the antitumor effect of vemurafenib in human melanoma by inhibiting cell proliferation and cancer-stem cell traits via targeting NF-κB/iNOS/hTERT signaling pathway, and suggest the potential of melatonin in antagonizing the toxicity of vemurafenib and augmenting its sensitivities in melanoma treatment.
Highlights
Melanoma is one of the most threatening malignancies and has high metastatic potential
Inflammation is an important feature of the tumor microenvironment in melanoma, and previous studies showed that inducible nitric oxide synthase (INOS), one of the most common inflammation factors, is an important inducer of melanoma tumorigenesis, tumor growth, invasion and metastasis [9, 10], and INOS abrogation has been proved to contribute to melanoma treatment
Vemurafenib significantly decreased the cell viability compared with the untreated control in melanoma cell lines with a protein called B-raf (BRAF) V600E mutant, and combined treatment with melatonin significantly enhanced the suppression of cell viability in a dose-dependent manner compared with the treatment with vemurafenib alone (Fig. 1a)
Summary
Melanoma is one of the most threatening malignancies and has high metastatic potential. In the recent years, significant progresses have been made in melanoma treatment with the appearance and widespread application of the combinational immunotherapy [1,2,3,4], it is still necessary to explore other treatment options to get better clinical output because the response rates to immunotherapy are not 100%. This might be mainly due to that the antigens selected for these approaches do not cover the full spectrum of melanoma cells present in a tumor [5, 6]. Acquired drug resistance invariably develops after its initial treatment
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