| The incidence of colorectal cancer, third of carcinoma in gastrointestinal tract, trend to elevate in recent years in our country. In some of the patients, the opportunity of surgical operation were missed because of their received medical treatment too late. Much of the patiens would sustain liver metastasis and postoperative reoccurrence. Treating advanced colorectal carcinoma systemly is urgent in clinical affairs.Cytosine deaminase/5-fluorocytosine is one of the promising gene therapy approach. Cytosine deaminase exists in some bacteria and fungi but not in mammal, which can convert a nontoxic prodrug 5-fluorocytosine to a toxic metabolite 5-fluorouracil by catalysis of the deamino procedure of cytosine to uridine and has the potential antimetabolism of pyrimidine. In this study, the colorectal carcinoma cells were modified to express CD by transfection of GlCEACDNa, a retro virus vector, by liposomes methods. The expression of CD gene were examined by RT-PCR. The SW480 cell groupswhich were transferred with CD gene followed by prodrug 5-fluorocytosine administration were observed on morphology and detected by FCM. The bystander effects in vitro were observed and its mechanisms were investigated. Following results were obtained:1. An approximate 1.5kb band was showed when the amplified products of RT-PCR were electrophoresed on agarose gels.2. Data from cell growth curve indicated that doubling time of the CD positive SW480 cell groups were 34h.3. When the CD gene transduced SW480 cells were exposured in 5-fluorocytosine, the morphologic change were observed at 72h, both apoptosis and necrosis evidences were obtained by transmission electron microscope, the rates of apoptosis and necrosis at 72h, 96h were 20.2%, 30.7% and 19.6%,21.1% respectively by means of flow cytometry.4. The bystander effects were observed apparently. When 10% and 30% cells of the group were expressed cytosine deaminase, 60% and 70% of the total were killed respectively on eighth day after exposuring in 5-fluorocytosine.5. The apparent cytotoxicity were observed hi the medium of the CD gene transduced colorectal carcinoma cells when exposuring in 5-fluorocytosine, and it caused the change on cell cycle that were the percentage of Gl phase decreased and that of S, G2 phase increased.Recently, some evidence demonstrated that progastrin and glycine-extended gastrin can stimulate the proliferation of colorectal carcinoma cells by many mechanisms, including triggering some kind of apoptosis. The inhibition effects of some kinds of gastrin-receptor antagonist10were confirmed on colorectal carcinoma cell lines. In this study, we observed the killing effects of prodrug 5-fluorocytosine and gastrin antagonist CI-988 on CD gene transduced colorectal LoVo cell lines. Following results were obtained:1. The inhibition rates of cell growth were 40% and 97% respectively on 3d and 6d when combined CD/5-FC (IMmol.L-1) and gastrin-receptor antagonist CI-988(1 X 10"8Mmol 昄-1), which were higher than that of using one of the two methods singularly.2. The nude mice were inoculated with CD gene transduced LoVo cells (1 X 107cell in 0.2mL PBS) and were grouped randomly at 14d followed by different treatment. The treatment of group 1 and group 2 were respectively 5-fluorocytosine(500mg/kg i.p. )and CI-988(10mg/kg,orally) singularly. That of group 3 was administrating the both agents simultaneously. The weight of carcinomar tissue of group 1,2,3, and the control at 14d after inoculation were 261.62 + 126.36mg?281.94?136.22mg? 244.21 + 111.91mg? 266.15 ?140.75mg, no significant difference among the groups. Correspondingly, that weight of group 1,2,3 and the central were 0.69 + 0. llg, 1. 22?. 22g, 0. 42 + 0.12g, 2.26+0.23g when administration once a day for 20 consecutive days(group 1,2,3 vs control, P<0. 01). The inhibition rates in group 1,2,3 were 69.4%, 45.9%, 81.5% respectively. Signs of necrosis and inflammatory cell...
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