Quercetin (Q), a flavonoid compound, which is obtained in variety of fruits, seeds, and vegetables, has been reported to possess many pharmacological properties including cancer-preventive and anticancer effects. However, studies on the anticancer effects and underlying mechanisms of Q in human hepatocellular carcinoma (HCC) are still limited. The present study is conducted to investigate the anticancer efficacy and adjuvant chemotherapy action of Q in HCC. HCC cell lines HepG2 and SMCC-7721 were treated with different concentrations of Q. The antiproliferative effects of Q were measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), and the apoptosis and cell cycle dynamics were assessed by flow cytometry; the expression of apoptosis-associated proteins were evaluated by Western blot and immunohistochemistry staining; the tumor growth in vivo was evaluated in a xenograft mouse model. Our results showed that Q effectively inhibited human HCC cell proliferation and induced apoptosis by upregulating the expression of Bad and Bax and downregulating the expression of Bcl-2 and Survivin in vitro. Furthermore, Q obviously inhibited the tumor growth and enhanced the 5-fluorouracil (5-FU) therapeutic efficacy in vitro and in vivo. Taken together, our findings highlight that Q effectively inhibited the growth of tumor and enhanced the sensitivity to thermotherapy, indicating Q is a potential treatment option for HCC.

We studied radioprotective and apoptotic properties of a combination ofα-tocopherol acetate and ascorbic acid. α-Tocopherol acetate (10 mg/kg body weight) or ascorbic acid (20 mg/kg) or combination of these agents in the same doses was orally administered to male rats at various terms before and after single whole-body exposure to γ-irradiation in the doses of 2 and8 Gy. Irradiation increased the frequency of chromosome aberrations in bone marrow cells and plasma level of low-molecular-weight DNA. Vitamin combination administered before or after irradiation significantly reduced the frequency of chromosome aberrations by 2-2.5 times. Administration of this combination 10 min before irradiation 1.5-fold increased the content of low-molecular-weight DNA in blood plasma in comparison with the control animals exposed to radiation. The combination of α-tocopherol acetate and ascorbic acid produced radioprotective effects and enhanced apoptosis in irradiatedcells.

Although epidemiologic studies have demonstrated that a high intake of vegetables containing beta-carotene lowers the risk of cancer, recent intervention studies have revealed that beta-carotene supplementation to smokers resulted in a high incidence of lung cancer. We hypothesized that beta-carotene may act as a pro- or anticancerogenic agent by modulating pathways involved in cell growth and that such a modulation may involve a redox mechanism. To test this hypothesis, cell proliferation, apoptosis and redox status were evaluated in undifferentiated and dimethylsulfoxide-differentiated HL-60 cells exposed to beta-carotene. The carotenoid modified cell cycle progression and induced apoptosis in a dose-dependent manner. These effects were more remarkable in undifferentiated cells than in differentiated cells. In accord with these findings, in undifferentiated cells, beta-carotene was more effective in decreasing cyclin A and Bcl-2 expression and in increasing p21 and p27 expression. Neither Bcl-xL nor Bax expression were significantly modified by the carotenoid. From a mechanistic point of view, the delay in cell growth by beta-carotene was highly coincident with the increased intracellular reactive oxygen species production and oxidized glutathione content induced by the carotenoid. Moreover, alpha-tocopherol minimized the effects of beta-carotene on cell growth. These data provide evidence that beta-carotene modulates molecular pathways involved in cell cycle progression and apoptosis and support the hypothesis that a redox mechanism may be implicated. They also suggest that differentiated cells may be less susceptible to the carotenoid than highly neoplastic undifferentiated cells.

A novel heteropolysaccharide from Grifola frondosa mycelia was extracted and purified using DEAE Sephadex A-50 and Sephadex G-200 chromatography. Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance ((1)H NMR and (13)C NMR) spectroscopy were used to decipher the structure of the purified G. frondosa polysaccharide (GFP1). Chemical and spectral analysis revealed that GFP1, with an average molecular weight of 40.5kDa, possessed a 1,6-β-d-glucan backbone with a single 1,3-α-d-fucopyranosyl side-branching unit. Enterovirus 71 (EV71) is the causative pathogen of hand-foot-and-mouth disease. GFP1 was tested for its anti-EV71 activity in cultured cells, which showed that EV71 viral replication was blocked and viral VP1 protein expression and genomic RNA synthesis were suppressed. Moreover, GFP1 exhibited apoptotic and other activities by suppressing the EV71-induced caspase-3 cleavage and IκBα down regulation. Our results demonstrate that the novel G. frondosa polysaccharide has antiviral activity, which could be valuable as a potentially new anti-EV71 therapeutic compound.

Ganoderma triterpenes (GTs) are the major secondary metabolites of Ganoderma lucidum, which is a popularly used traditional Chinese medicine for complementary cancer therapy. In the present study, systematic isolation, and in silico pharmacological prediction are implemented to discover potential anti-cancer active GTs from G. lucidum. Nineteen GTs, three steroids, one cerebroside, and one thymidine were isolated from G. lucidum. Six GTs were first isolated from the fruiting bodies of G. lucidum, including 3β,7β,15β-trihydroxy-11,23-dioxo-lanost-8,16-dien-26-oic acid methyl ester (1), 3β,7β,15β-trihydroxy-11,23-dioxo-lanost-8,16-dien-26-oic acid (2), 3β,7β,15α,28-tetrahydroxy-11,23-dioxo-lanost-8,16-dien-26-oic acid (3), ganotropic acid (4), 26-nor-11,23-dioxo-5α-lanost-8-en-3β,7β,15α,25-tetrol (5) and (3β,7α)-dihydroxy-lanosta-8,24-dien- 11-one (6). (4E,8E)-N-d-2'-hydroxypalmitoyl-l-O-β-d-glucopyranosyl-9-methyl-4,8-spingodienine (7), and stigmasta-7,22-dien-3β,5α,6α-triol (8) were first reported from the genus Ganodema. By using reverse pharmacophoric profiling of the six GTs, thirty potential anti-cancer therapeutic targets were identified and utilized to construct their ingredient-target interaction network. Then nineteen high frequency targets of GTs were selected from thirty potential targets to construct a protein interaction network (PIN). In order to cluster thepharmacological activity of GTs, twelve function modules were identified by molecular complex detection (MCODE) and gene ontology (GO) enrichment analysis. The results indicated that anti-cancer effect of GTs might be related to histone acetylation and interphase of mitotic cell cycle by regulatinggeneral control non-derepressible 5 (GCN5) and cyclin-dependent kinase-2 (CDK2), respectively. This research mode of extraction, isolation, pharmacological prediction, and PIN analysis might be beneficial to rapidly predict and discover pharmacological activities of novel compounds.

The aim of this study was to investigate the inhibition of daidzein or/and regular exercise on breast cancer and to reveal the potential biological mechanisms. BALB/c mice pretreated with regular exercise training for 20 days (15 m/min, 60 min/d) were orthotopically transplanted with mouse breast cancer cells (4T1), and then treated with daidzein (145 mg/kg) by gavage for another 22 days. Results showed that exercise or daidzein inhibited tumor growth in mice to a different degree. Particularly, co-treatment with exercise and daidzein showed an obviously synergistic inhibition on the tumor growth (P < 0.01), compared with the tumor control. Further researches indicated that the combination of exercise and daidzein synergistically mobilized and redistributed natural killer cells through upregulating the level of epinephrine and interleukin-6. Moreover, exercise combined with daidzein induces apoptosis in cancer cells via Fas/FasL-initiated mitochondrial apoptosis signaling pathway. These results suggested that regular exercise combined with daidzein may explore a candidate way to prevent and treat the breast cancer.

AIM:In this study, we evaluated the carcinostatic effects of combined ascorbic acid (AsA) and a capacitive-resistive electric transfer (CRet) hyperthermic apparatus-induced hyperthermic treatment on Ehrlich ascites tumor (EAT) cells.

MATERIALS AND METHODS:EAT cells were exposed to various AsA (0-10 mM) concentrations for 1 h; they subsequently underwent CRet treatment for 15 min at 42 °C. Cell viability was assessed by the WST-8 assay 24 h after the combined treatment. Reactive oxygen species involvement was evaluated using catalase and tempol; caspase-3/7 activation was determined by their fluorescent substrates; cell proliferation were estimated by time-lapse observation. The effect on the cell cycle was analyzed by flow cytometry.

RESULTS:Combined AsA and CRet treatment synergistically suppressed cell viability compared with either treatment alone, and these synergistically carcinostatic effects were evident even at noncytotoxic concentrations of AsA alone (≤ 2 mM). The carcinostatic effects of combined AsA and CRet treatment were attenuated in a dose-dependent manner by catalase addition, but not by the superoxide anion radical scavenger tempol. Time-lapse observation revealed that combined AsA and CRet treatment activated caspase-3/7 at 10-24 h after treatment, accompanied by significant cell growth suppression. Cell cycle analysis revealed that the rate of sub-G1-phase (apoptotic) cells was drastically increased at 12 h and 24 h, and that the G2/M-phase cells gradually increased at 6-24 h after treatment.

CONCLUSION:These results indicate that combined AsA and CRet treatment synergistically inhibits EAT cell growth through G2/M arrest and apoptosis induction via H2O2 generation at lower AsA concentrations; this carcinostatic effect cannot be exer-ted by AsA alone.

We have shown previously that pure polyphenol curcumin I (CUR-I) shows antifungal activity against Candida species. By employing the chequerboard method, filter disc and time-kill assays, in the present study we demonstrate that CUR-I at non-antifungal concentration interacts synergistically with azoles and polyenes. For this, pure polyphenol CUR-I was tested for synergy with five azole and two polyene drugs - fluconazole (FLC), miconazole, ketoconazole (KTC), itraconazole (ITR), voriconazole (VRC), nystatin (NYS) and amphotericin B (AMB) - against 21 clinical isolates of Candida albicans with reduced antifungal sensitivity, as well as a drug-sensitive laboratory strain. Notably, there was a 10-35-fold drop in the MIC(80) values of the drugs when CUR-I was used in combination with azoles and polyenes, with fractional inhibitory concentration index (FICI) values ranging between 0.09 and 0.5. Interestingly, the synergistic effect of CUR-I with FLC and AMB was associated with the accumulation of reactive oxygen species, which could be reversed by the addition of an antioxidant such as ascorbic acid. Furthermore, the combination of CUR-I and FLC/AMB triggered apoptosis that could also be reversed by ascorbic acid. We provide the first evidence that pure CUR-I in combination with azoles and polyenes represents a novel therapeutic strategy to improve the activity of common antifungals.

The aim of this study was to investigate the anticancer effect of a combination of D-fraction polysaccharide from Grifola frondosa (DFP) and vitamin C (VC) on hepatocellular carcinoma in vitro. DFP is a bioactive extract from the maitake mushroom. Anticancer activity was demonstrated using various concentrations of DFP alone or in combination with VC against the human hepatocarcinoma SMMC-7721 cell line. To investigate the anticancer mechanism, studies designed to detect cell apoptosis were conducted. Results from the MTT assay indicated that a combination of DFP (0.2 mg/mL) and VC (0.3 mmol/L) led to a 70% reduction in cell viability. Flow cytometry results indicated that DFP/VC treatment induced apoptosis in approximately 65% SMMC-7721 cells. Cell cycle analysis identified cell cycle arrest at the G2/M phase following DFP/VC treatment for 48 hours. In addition, cellular morphological changes were observed using transmission electron microscopy. Western blot analysis revealed that the upregulation of BAX, downregulation of Bcl-2, activation of poly-(ADP-ribose)-polymerase (PARP), and the release of cytochrome c were observed in cells treated with the combination of DFP/VC, which showed that the mechanism of anticancer activity in the SMMC-7721 hepatocarcinoma cells involved induction of apoptosis.

Targeting cannabinoid receptors has recently been shown to trigger apoptosis and offers a novel treatment modality against malignancies of the immune system. However, the precise mechanism of apoptosis in such cancers has not been previously addressed. In this study, we used human Jurkat leukemia cell lines with defects in intrinsic and extrinsic signaling pathways to elucidate the mechanism of apoptosis induced by Delta9-tetrahydrocannabinol (THC). We observed that Jurkat cells deficient in FADD or caspase-8 were partially resistant to apoptosis, while dominant-negative caspase-9 mutant cells were completely resistant to apoptosis. Use of caspase inhibitors confirmed these results. Furthermore, overexpression of Bcl-2 rendered the cells resistant to THC at early time points but not upon prolonged exposure. THC treatment led to loss of Deltapsi(m), in both wild-type and FADD-deficient Jurkat cells thereby suggesting that THC-induced intrinsic pathway was independent of FADD. THC treatment of wild-type Jurkat cells caused cytochrome c release, and cleavage of caspase-8, -9, -2, -10, and Bid. Caspase-2 inhibitor blocked THC-induced caspase-3 in wild-type Jurkat cells but not loss of Deltapsi(m). Together, these data suggest that the intrinsic pathway plays a more critical role in THC-induced apoptosis while the extrinsic pathway may facilitate apoptosis via cross-talk with the intrinsic pathway.

Delta9-tetrahydrocannabinol and other cannabinoids exert pro-apoptotic actions in tumor cells via the CB2 cannabinoid receptor. However, the molecular mechanism involved in this effect has remained elusive. Here we used the human leukemia cell line Jurkat-that expresses CB2 as the unique CB receptor-to investigate this mechanism. Our results show that incubation with the selective CB2 antagonist SR144528 abrogated the pro-apoptotic effect of Delta9-tetrahydrocannabinol. Cannabinoid treatment led to a CB2 receptor-dependent stimulation of ceramide biosynthesis and inhibition of this pathway prevented Delta9-tetrahydrocannabinol-induced mitochondrial hypopolarization and cytochrome c release, indicating that ceramide acts at a pre-mitochondrial level. Inhibition of ceramide synthesis de novo also prevented caspase activation and apoptosis. Caspase 8 activation-an event typically related with the extrinsic apoptotic pathway-was also evident in this model. However, activation of this protease was post-mitochondrial since (i) a pan-caspase inhibitor as well as a selective caspase 8 inhibitor were unable to prevent Delta9-tetrahydrocannabinol-induced loss of mitochondrial-membrane transmembrane potential, and (ii) cannabinoid-induced caspase 8 activation was not observed in Bcl-xL over-expressing cells. In summary, results presented here show that CB2 receptor activation signals apoptosis via a ceramide-dependent stimulation of the mitochondrial intrinsic pathway.

BACKGROUND:Cannabinoids represent unique compounds for treating tumors, including astrocytomas. Whether CB(1) and CB(2) receptors mediate this therapeutic effect is unclear.

PRINCIPAL FINDINGS:We generated astrocytoma subclones that express set levels of CB(1) and CB(2), and found that cannabinoids induce apoptosis only in cells expressing low levels of receptors that couple to ERK1/2. In contrast, cannabinoids do not induce apoptosis in cells expressing high levels of receptors because these now also couple to the prosurvival signal AKT. Remarkably, cannabinoids applied at high concentration induce apoptosis in all subclones independently of CB(1), CB(2) and AKT, but still through a mechanism involving ERK1/2.

SIGNIFICANCE:The high expression level of CB(1) and CB(2) receptors commonly found in malignant astrocytomas precludes the use of cannabinoids as therapeutics, unless AKT is concomitantly inhibited, or cannabinoids are applied at concentrations that bypass CB(1) and CB(2) receptors, yet still activate ERK1/2.

Polysaccharides extracted from the mushroom Grifola frondosa (GFP) are a potential anticancer agent. The objective of this study was to investigate the effect of GFP and vitamin C (VC) alone and in combination on the viability of human hepatocarcinoma SMMC-7721 and HepG2 cells. Studies designed to detect cell apoptosis and autophagy were also conducted to investigate the mechanism. Results from the cell viability assay indicated that a combination of GFP (0.2 or 0.25 mg/mL) and VC (0.3 mmol/L) (GFP/VC) led to 52.73 and 53.93% reduction in cell viability of SMMC-7721 and HepG2 cells separately after 24 h. Flow cytometric analysis indicated that GFP/VC treatment induced cell cycle arrest at the G2/M phase, and apoptosis occurred in approximately 43.62 and 42.46% of the SMMC-7721 and HepG2 cells separately. Moreover, results of Hoechst33258 and monodansylcadaverine staining, and transmission electron microscopy, showed that GFP/VC induced apoptosis and autophagy in SMMC-7721 and HepG2 cells. Western blot analysis showed changes in the expression of apoptosis-related proteins [upregulation of BAX and caspase-3, downregulation of Bcl-2, and activation of poly-(ADP-ribose)-polymerase] and autophagy protein markers (upregulation of beclin-1 and microtubule-associated protein 1A/1B light chain-3). We also demonstrated that the expression of both Akt andp-Akt was enhanced, suggesting the PI3K/Akt/mTOR pathway might not be involved in this process. Our study shows that the combined application of GFP and VC induced cell apoptosis and autophagy in vitro, and might have antitumor activity in vivo.

BACKGROUND:Decitabine is widely used in the treatment of acute myeloid leukemia (AML) in elderly patients. Low-dose Vitamin C has also been indicated to induce DNA demethylation at the cellular level. However, little is known whether low-dose Vitamin C has a synergistic effect with decitabine in clinic.

METHODS:The effect of combined low-dose Vitamin C and decitabine on cell proliferation, the cell cycle, apoptosis and the expression level and activity of TET2 was investigated in HL60 and NB4 human leukemic cells. Additionally, we analyzed the clinical outcomes of 73 elderly AML patients who received A-DCAG (intravenous Vitamin C [IVC] plus DCAG [n = 39]) or DCAG (n = 34) treatment.

RESULTS:We found that low-dose Vitamin C and decitabine has a synergistic efficacy on proliferation, apoptosis, TET2 expression and activity, compared to drug-alone treatment in HL60 and NB4 cell lines in vitro. In clinic, feasibility and safety evaluations revealed that patients who received A-DCAG regimen have a higher complete remission (CR) rate than those who received the DCAG regimen (79.92% vs. 44.11%; P = 0.004) after one cycle of chemotherapy. The median overall survival (OS) was better in the A-DCAG group compared with the DCAG group (15.3 months vs. 9.3 months, P = 0.039). Patients with adverse cytogenetics did benefit from CR. There was no clinically significant additional toxicity observed with the addition of IVC.

CONCLUSION:On the basis of these results, the addition of IVC at low doses to DCAG appeared to improve CR and prolong OS, compared with DCAG, in elderly patients with AML.

Cannabis is the most commonly used illegal drug of abuse in Western society. Delta(9)-tetrahydrocannabinol, the psychoactive ingredient of marijuana, regulates a variety of neuronal processes including neurotransmitter release and synaptic transmission. An increasing body of evidence suggests that cannabinoids play a key role in the regulation of neuronal viability. In cortical neurons tetrahydrocannabinol has a neurodegenerative effect, the mechanisms of which are poorly understood, but involve the cannabinoid receptor subtype, CB(1). In this study we report that tetrahydrocannabinol (5 muM) evokes a rapid phosphorylation, and thus activation, of the tumour suppressor protein, p53, in a manner involving the cannabinoid CB(1) receptor, and the stress-activated protein kinase, c-jun N-terminal kinase, in cultured cortical neurons. Tetrahydrocannabinol increased expression of the p53-transcriptional target, Bax and promoted Bcl phosphorylation. These events were abolished by the p53 inhibitor, pifithrin-alpha (100 nM). The tetrahydrocannabinol-induced activation of the pro-apoptotic cysteine protease, caspase-3, and DNA fragmentation was also blocked by pifithrin-alpha. A siRNA knockdown of p53 further verified the role of p53 in tetrahydrocannabinol-induced apoptosis. This study demonstrates a novel cannabinoid signalling pathway involving p53 that culminates in neuronal apoptosis.

OBJECTIVES:Curcumin, a natural pigment from the traditional Chinese herb, has shown promise as an efficient enhancer of ultrasound. The present study aims to investigate ultrasound-induced cellular destruction of nasopharyngeal carcinoma cells in the presence of curcumin in vitro.

METHODS:Nasopharyngeal carcinoma cell line CNE2 cells were incubated by 10μm curcumin and then were treated by ultrasound for 8s at the intensity of 0.46W/cm(2). Cytotoxicity was evaluated using MTT assay and light microscopy. Mitochondrial damage was analyzed using a confocal laser scanning microcopy with Rhodamine 123 and ultrastructural changes were observed using a transmission electron microscopy (TEM).

RESULTS:MTT assay showed that cytotoxicity induced by ultrasound treatment alone and curcumin treatment alone was 18.16±2.37% and 24.93±8.30%, respectively. The cytotoxicity induced by the combined treatment of ultrasound and curcumin significantly increased up to 86.67±7.78%. TEM showed that microvillin disappearance, membrane blebbing, chromatin condensation, swollen mitochondria, and mitochondrial myelin-likebody were observed in the cells treated by ultrasound and curcumin together. The significant collapse of mitochondrial membrane potential (MMP) was markedly observed in the CNE2 cells after the combined treatment of curcumin and ultrasound.

CONCLUSIONS:Our findings demonstrated that ultrasound sonication in the presence of curcumin significantly killed the CNE2 cells and induced ultrastructural damage and the dysfunction of mitochondria, suggesting that ultrasound treatment remarkably induced cellular destruction of nasopharyngeal carcinoma cells in the presence of curcumin.

Objectives. Curcumin, a natural pigment from a traditional Chinese herb, has been attracting extensive attention. The present study aims to investigate cell death of nasopharyngeal carcinoma (NPC) cells induced by ultrasound sonication in the presence of curcumin in vitro. METHODS: The NPC cell line CNE2 was chosen as a tumor model, and curcumin concentration was kept constant at 10 muM while the cells were subjected to ultrasound exposure for 8 s at an intensity of 0.46 W/cm(2). Cell death was evaluated using flow cytometry with annexinV-FITC and propidium iodine staining, and nuclear staining with Hoechst 33258. Mitochondrial membrane potential and intracellular reactive oxygen species (ROS) were analyzed using flow cytometry with rhodamine 123 and dichlorodihydrofluorecein diacetate staining. RESULTS: Flow cytometry showed that the combination of ultrasound and curcumin significantly increased the necrotic or late apoptotic rate by up to 31.37% compared with the controls. Nuclear condensation was observed in the nuclear staining, and collapse of DeltaPsim and ROS increase were found in the CNE2 cells after the treatment with curcumin and ultrasound. CONCLUSIONS: The findings demonstrate that the presence of curcumin significantly enhances the ultrasound-induced cell death and ROS level, and induces the collapse of DeltaPsim, suggesting that ultrasound sonication can increase the cell death of NPC cells in the presence of curcumin and that the treatment using curcumin and ultrasound together is a potential therapeutic modality in the management of malignant tumors.

Ultraviolet (UV) radiation is considered to be a potent cell-damaging agent in various cell lineages; however, the effect of UV light‑emitting diode (LED) irradiation on human cells remains unclear. The aim of the present study was to examine the effect of UV LED irradiation emitting at 280 nm on cultured HL‑60 human leukemia cells, and to explore the underlying mechanisms. HL‑60 cells were irradiated with UV LED (8, 15,30 and 60 J/m2) and incubated for 2 h after irradiation. The rates of cell proliferation and apoptosis, the cell cycle profiles and the mRNA expression of B‑cell lymphoma 2 (Bcl‑2) were detected using cell counting kit‑8, multicaspase assays, propidium iodide staining and reverse transcription‑quantitative polymerase chain reaction, respectively. The results showed that UV LED irradiation (8‑60 J/m2) inhibited the proliferation of HL‑60 cells in a dose‑dependent manner. UV LED at 8‑30 J/m2 induced dose‑dependent apoptosis and G0/G1 cell cycle arrest, and inhibited theexpression of Bcl‑2 mRNA, while UV LED at 60 J/m2 induced necrosis. In conclusion, 280 nm UV LED irradiation inhibits proliferation and induces apoptosis and necrosis in cultured HL‑60 cells. In addition, the cell cycle arrest at the G0/G1 phase and the downregulation of Bcl‑2 mRNA expression were shown to be involved in UV LED-induced apoptosis.

Vitamin C is an essential dietary nutrient that has a variety of biological functions. Recent studies have provided promising evidence for its additional health benefits including anti-cancer activity. Vitamin B2, another essential dietary nutrient, is often coexisted with vitamin C in some fruits, vegetables or dietary supplements. The objective of the present study is to determine whether combination of vitamin C and B2 can achieve a synergistic anti-cancer activity. MDA-MB-231, MCF-7 and A549 cells were employed to evaluate the combinatory effects of vitamin C and B2. We found that combination of vitamin C and vitamin B2 resulted in a synergistic cell death induction in all cell lines tested. Further mechanistic investigations revealed that vitamin B2 sensitized cancer cells to vitamin C through inhibition of Akt and Bad phosphorylation. Our findings identified vitamin B2 as a promising sensitizer for improving the efficacy of vitamin C-based cancer chemoprevention and chemotherapy.

Vitamin C has been used in complementary and alternative medicine for cancers regardless of its ineffectiveness in clinical trials and the paradoxical effects antioxidants have on cancer. Vitamin C was found to induce cytotoxicity against cancers. However, the mechanisms of action have not been fully elucidated, and the effects of vitamin C on human malignant melanoma have not been examined. This study revealed that vitamin C at millimolar concentrations significantly reduced the cell viability as well as invasiveness, and induced apoptosis in human malignant melanoma cells. Vitamin C displayed stronger cytotoxicity against the Vemurafenib-resistance cell line A2058 compared with SK-MEL-28. In contrast, vitamin C at micromolar concentrations promoted cell growth, migration and cell cycle progression, and protected against mitochondrial stress. Vemurafenib paradoxically activated the RAS-RAF-MEK-ERK signaling pathway in the Vemurafenib-resistant A2058, however, vitamin C abolished the activations. Vitamin C displayed synergistic cytotoxicity with Vemurafenib against the Vemurafenib-resistant A2058. In vivo assay suggested that lower dosage (equivalent to 0.5g/70kg) of vitamin C administered orally increased the melanoma growth. Therefore, vitamin C may exert pro- or anti-melanoma effect depending on concentration. The combination of vitamin C at high dosage and Vemurafenib is promising in overcoming the action of drug resistance. This article is protected by copyright. All rights reserved.