| Cancer is regarded as a major public health problem worldwide and remains as a threat to health despite advances in modern medical diagnosis and treatment.The morbidity and mortality is continually increasing because of the aging of the population,environment pollution,as well as changes in lifestyle.The options for cancer treatment are currently limited to surgery,chemotherapy,and radiation.Chemotherapy is commonly used in the treatment of cancer.According to the mechanism,chemotherapeutic drugs can be divided into the following categories:alkylation agent,antimetabolite,anti-tumor antibiotic,topoisomerase inhibitor and mitotic inhibitor.But their usage is limited by toxic side effects,the development of resistance,and other defects.Hence,it is necessary to develop less toxic and more efficient anticancer drugs which could relieve the pain,improve the quality of life and prolong the survival in the meantime.Natural dietary agents are considered as the most interesting agents for cancer prevention and therapy,due to their anticipated multimodal actions and limited toxicity.Garlic(Allium sativum),a widely used herbal vegetable and natural dietary factor,has drawn much attention because garlic and its derivatives have been shown to possess chemopreventive and therapeutic potential against a variety of cancers based mainly on epidemiological studies of digestive tract tumor as well as carcinogenic processes from several experimental animal models.Garlic contains high levels of organosulfur compounds(OSCs)including lipid soluble compounds DAS,DADS and DATS and water-soluble compounds SAC and SAMC,which are the main anti-cancer constituents.Since DAS,DADA,DATS and other sulfur compounds can be transformed to SAMC in the intestinal tract,studies of SAMC are of interest because of the likely high local concentration of this compound in the intestinal mucosa and the potential effects of this compound on digestive tract cancer prevention.To date the evidence for possible therapeutic effects of SAMC are mostly derived from in vitro studies on a variety of cancer cell lines including colon cancer,prostate cancer,liver cancer and so on.These preclinical studies have provided strong evidence to indicate that SAMC is much effective in suppressing proliferation of cancer cells in culture by inducing apoptosis or arresting cell cycle progression.However,the in vivo studies related to therapeutic effects of SAMC are rare and its anticancer mechanisms haven’t been comprehensively elucidated to date.Therefore,its potential effects should be further confirmed by in vivo situations and further studies are required to fully elucidate its mechanisms of action.A previous study has shown that aged garlic extract(AGE)can reduce the toxicity of cisplatin,a widely used chemotherapy drug,in rats.Since SAMC is the main water-soluble sulftur compound present in AGE,it is particularly meaningful to investigate if SAMC can exert synergistic effects with other chemotherapy drugs in suppressing cancer growth and attenuating the toxicity that the chemical drugs caused in animal models.Metabonomics is a non-targeted global analysis of tissues or biofluids for organic metabolites of low molecular mass.It can be used to clarify the metabolic characteristics of disease and the action mechanisms of drug in an integrated manner,and to reveal in the patterns of metabolic markers associated with toxic responses to drug therapies,pathological changes,disease diagnosis and ecology.So the metabonomics approach was used in our study to investigate the potential antitumor activity of SAMC in combination with cisplatin in human gastric cancer xenografts and to explore its possible mechanism.Based on above background,our research was divided into the following three parts.(1)The antitumor effect and mechanism of SAMC.Firstly,the antitumor effect of SAMC was studied in nine cancer cells and four cancer xenografts.Based on the results,the effect of SAMC on SGC7901 gastric cancer an HCT116 colon cancer and the underlying mechanism were further measured.Then,we examined the effect of SAMC on human gastric carcinoma growth and explored the underlying molecular mechanisms.SAMC significantly inhibited human gastric cancer cell growth in vitro,showing arrest of the cell cycle in S phase and induction of apoptosis in SGC7901 cells.Statistical analysis indicated that the IC50 value,based on the inhibition rates of 48 h exposure,was 231.2 μM.We also observed that SAMC administration in mice effectively delayed the growth of SGC7901 xenografts without signs of toxicity.The T/C of SAMC administration(40,60,80 mg/kg)is 44.5%(p<0.01),39.8%(p<0.01)and 38.9%(p<0.01).Mechanistic studies suggested that this activity may arise from its multiple effects on the activation of apoptotic proteins and modulation of MAPK and PI3K/Akt signaling pathways.Collectively,SAMC could prevent the growth of gastric cancer through modulation of multiple signaling pathways,and it might be a promising agent for gastric cancer therapy.Besides,we explored the effects of SAMC on colon cancer both in vitro and in vivo and further elucidated the underlying molecular mechanisms.In this part,we found that SAMC potently suppressed cell viability and induced G2/M phase arrest and apoptosis in colon cancer HCT116 cells.Statistical analysis indicated that the IC50 value,based on the inhibition rates of 24 h exposure,was 314.7 μM.Further studies showed that reactive oxygen species(ROS)attributed to SAMC-induced cell cycle arrest and apoptosis,which was attenuated by N-acetyl cysteine(NAC),an ROS scavenger.Moreover,we found that SAMC activated p38 and c-Jun N-terminal kinase(JNK)signal pathway,which was also blocked by NAC.Finally,SAMC administration in mice effectively delayed the growth of HCT116 xenografts without signs of toxicity.The T/C of SAMC administration(40,60,80 mg/kg)is 48.3%(p<0.01),40.1%(p<0.01)and 34.6%(p<0.01).In conclusion,SAMC induced cell cycle G2/M phase arrest and apoptosis via ROS-mediated p38 and JNK signaling pathway in colon cancer HCT116 cells.In light of these results,SAMC may be a promising agent for anticancer therapy against colon cancer.(2)The antitumor effect of SAMC in combination with cisplatin and serum metabolism in SGC7901 tumor-bearing mice.Firstly,we inoculated BALB/c nude mice with a subcutaneous injection of human gastric SGC7901 cells to generate the animal model.Mice were randomly divided into 4 groups and treated with vehicle control,SAMC(40 mg/kg/day),DDP(5 mg/kg/5 days),and a combination of DDP and SAMC.Tumor growth and body weight of the mice were monitored.Serum creatinine(Cr),blood urea nitrogen(BUN),alanine transaminase(ALT),aspartate transaminase(AST),and histopathological examination of liver and kidney tissues after DDP and/or SAMC therapy were also investigated.We found that SAMC could not markedly enhance the efficacy of DDP,but SAMC could ameliorate DDP-induced toxicity in the xenograft mouse model.The serum metabonomics method based on GC-MS and UPLC-MS had been established to investigate the antitumor and protective effects of SAMC and to explore its possible metabolism mechanism.The results of our study clearly showed that there were different phenotypes of metabolites between normal mice and tumor-bearing mice.The abnormal changes of these metabolites might be associated with metabolic disturbance and these metabolites were considered as potential biomarkers.The related metabolic pathways may be energy metabolism and amino acid metabolism.In addition,the results also showed that SAMC could restore the metabolite network that disturbed by tumor bearing and DDP administration,which would be a proof of therapeutic efficacy of SAMC to attenuate DDP-induced toxicity by metabonomics study.(3)The protective effect of SAMC on cisplatin-induced nephrotoxicity.This part aims to examine the protective effects of SAMC on cisplatin nephrotoxicity and to explore the mechanism of its renoprotection.Rats were treated with cisplatin with or without pre-treatment with SAMC.Renal function,histological change,oxidative stress markers and antioxidant enzyme activities were investigated.Apoptotic marker,nuclear factor(NF)-κB activity,expression of Nrf2,NQO1 and inflammatory cytokines were also examined.The effect of SAMC on cell viability and apoptosis was examined in cultured human kidney(HK-2)cells.SAMC was confirmed to significantly attenuate cisplatin-induced renal damage,by using histological pathology and molecular biological method.Pre-treatment with SAMC reduced NF-κB activity,up-regulated Nrf2 and NQO1 expression and down-regulated inflammatory cytokines levels after cisplatin administration.Cisplatin-induced apoptosis in HK-2 cells was significantly attenuated by SAMC.Thus our results suggest that SAMC could be a potential therapeutic agent in cisplatin-induced nephrotoxicity through inhibition of apoptosis as well as its antioxidant and anti-inflammatory effect.In summary,the present studies indicate that SAMC can effectively suppress the growth of gastric cancer and colon cancer under in vitro and in vivo conditions without toxicity.The underlying mechanisms of SAMC in SGC7901 gastric cancer are attributed to its effect on anti-proliferation,apoptosis induction and the regulation of MAPK and PI3K/Akt pathways.Besides,we found that SAMC significantly induced G2/M cell cycle arrest and cell apoptosis regulated via ROS-mediated JNK and p38 signaling pathway in HCT116 colon cancer cells.When SAMC was used in combination with cisplatin in SGC7901-bearing mice,SAMC was demonstrated to ameliorate the toxicity induced by cisplatin.This ability might be linked to synergistic changes in energy metabolism and amino acid metabolism.Furthermore,the present study demonstrated the protective effect of SAMC against cisplatin-induced nephrotoxicity in rats and cisplatin-induced cytotoxicity in HK-2 proximal tubular cells.The renoprotective effect of SAMC could be due to the suppression of apoptosis,oxidative stress and inflammation.Therefore,our results suggest that SAMC might be a promising candidate in cancer therapeutics and combination therapy. |
