| Objective To investigate the anti-tumor effect and explore its possible mechanisms of melatonin(MT)combined with gemcitabine(GEM)on the treatment of human pancreatic carcinoma(SW1990)in BALB/C nude mice subcutaneous xenograft model .Methods The cell line SW1990 in log phase of human pancreatic carcinoma was implanted subcutaneously in BALB/C nude mice to develop implant-tumor. The 25 nude mice were randomly allocated into five groups: 1.Control group: inject saline IH around the tumor and inject saline IP; 2.Low dose of MT group: inject MT 10mg/kg·d IH around the tumor and inject saline IP ;3.High dose of MT group:inject MT 20mg/kg·d IH around the tumor and inject saline IP; 4.GEM group: inject saline IH around the tumor and inject GEM 50mg/kg·d IP; 5.Combination group:inject high dose of MT IH around the tumor and inject GEM 50mg/kg·d IP. The tumor growth in mice were observed.The volume and weight of implant-tumor were measured and the rates of cancer inhibition were evaluated. The activity of NK cells were measured by MTT, and the expression of VEGF,TGF-β1mRNA were detected by RT-PCR.Simultaneously the method of immunohistochemistry were used to estimate the expression of caspase-3 and caspase-9.Results None of the nude mice died and all of them formed implant-tumor. 1.Compared with the control group(1.476±0.075)cm3,tumor volumes in low dose of MT group(0.998±0.112)cm3,high dose of MT group (0.756±0.128) cm3,GEM group (0.746±0.115)cm3, combination group (0.305±0.111) cm3 were significantly shrunk (P<0.01) ,tumor volumes in high dose of MT group was significantly smaller than low dose of MT group(P<0.05).Besides, tumor volumes in combination group is the smallest. 2.The respective rates of the tumor inhibition of in low dose of MT group, high dose of MT group ,GEM group and combination group were 41.57%,58.62%,59.27%and 77.55%. 3.Compared with control group(3.0868±0.1317)nmol/ml ,the concentration of serum MDA in low dose of MT group (2.5567±0.1600)nmol/ml, high dose of MT group (2.0874±0.1159)nmol/ml,combination group(2.1007±0.0973)nmol/ml were significantly decreased(P<0.01). Besides, the concentration of MDA in high dose of MT group was significantly lower than low dose of MT group(P<0.05). 4.The significant difference was found the killing activity of NK cell in low dose of MT group (44.27±3.19)% ,high dose of MT group (45.16±3.20)% and combination group (30.29±2.91)% significantly increased than that of the controls (18.07±1.23)% (P<0.01). Meanwhile,the activity of NK cells in combination group was markedly enhanced when compared with GEM alone (14.24±2.70)% (P<0.01). 5.The expression of TGF-β1,VEGFmRNA decreased in treated groups(P<0.01) .The expression of VEGFmRNA in high dose of MT group was significantly lower than low dose of MT group(P<0.05).Besides, combination group is the lowest. The statistical differences of the expression of TGF-β1 mRNA among the treated groups were also significant(P<0.05). 6.The means of immunohistochemistry display that the expression of caspase-3 and caspase-9 of treated groups increased obviously compared with the control group(P<0.01).Meanwhile the statistical differences of the expression of caspase-3 and caspase-9 among the treated groups were also significant(P<0.05).Conclusions MT have effect to inhibit the growth of tumor. High dose of MT may perform better antitumor effect than low dose of MT,and MT combining with GEM significantly inhibited the growth of human pancreatic cancer in nude mice subcutaneous xenograft. MT can induce apoptosis, inhibit angiogenesis,enhance host immune fuction and antioxidant ability,which might be related to its anti-tumor effect .
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