An Experimental Study Of Radiotherapy Sensitivity And Influence The Expression Of Cycling Of Different Degrees Of Differentiation Of Human Colorectal Cancer By Idoine-125Seeds Brachytherapy

Objective:Our work aims to explore the effect of continuous irradiation with125I seeds on different differentiation degrees of human colorectal cancer cell, in order to restrain growth, and mechanisms related to apoptosis and expression of cycling protein. Methods:Part1:The well-differentiated (THC-8307), moderately differentiated (SW480) and undifferentiated (HCT-116) colorectal cancer xenograft nude mice model were constructed. The72mice with THC-8307、SW480、 HCT-116colorectal cancer xenografts were randomly separated into3groups:sham seeds (OmCi) were implanted into the control group (n=8);125I seeds (0.8mCi) for the treatment group (n=8).; No treatment for Control Group (n=8). After implantation, tumor volumes were calculated every three days and the tumor growth were curved. Nude mice were killed28days later, and their tumor tissues were dissected to weigh and produce tumor tissue samples for pathological examination. The mitotic index and apoptotic index were evaluated by quantitative morph metric analysis of the expression of proliferating cell nuclear antigen and in situ terminal transferase-mediated fluoresce in deoxy-UTP nick end labelling (TUNEL), respectively. Part2:The effect of irradiation on tumor cell was studied in vitro. The irradiator consists of three125I (Model6711) seed groups of different average apparent activity at29.97MB q(0.8mCi), and each group has nine125I seeds at the same dose. Eight seeds were equally laid around the circumference of diameter3cm and the ninth seed was confined to the center for each group. THC-8307、SW480、HCT-116colorectal cancer were placed6mm above the seed plane to accept continuous irradiation for72hours respectively. The total delivered dose was226cGy, meanwhile the control group did not receice any125I seed irradiation. The expressions of Cycling proteins were detected by RT-PCR and the cell growth condition was analyzed by cytometry. The rates of apoptosis were determined by flow cytometry. Results:Part1:The tumor growth of THC-8307、SW480、HCT-116colorectal cancer-bearing nude mice in the experiment group slowed down, and shown a tendency of shrink; while the tumor of control group grew rapidly. The average inhibition rate of THC-8307, SW480and HCT-116colorectal cancer cell was30.07%,33.65%and42.33%by measuring tumor weight. The apoptosis indexs were23.2%and8.1%in the experiment group and control group respectively by the examination of TUNELImmunohistochemical staining method, the expression of PCNA was found to be significantly lower in the experiment group than that in the control group (p<0.05). Part2:After being irradiated for72hours, the growth rate of the THC-8307, SW480and HCT-116cell lines stepped down dramatically comparing to the control group (P <0.05), meanwhile, flow cytometry showed that the apoptosis rates were greatly increased compared with the control group (P<0.05). The expressions of CDK2、 CDK4、CDK6、CyclinD1、CyclinE reduced in the experiment group. Conclusions: This study revealed that both inhibition of cell proliferation and induction of apoptosis contribute to the125I-induced tumor suppression in nude mouse model. Furthermore,125I seed irradiation could significantly induce the up-regulation of apoptosis-and cell cycle-related genes in human colorectal cancer xenografts. The ratio of apoptosis of well-differentiated (THC-8307) was significantly lower than that in low-differentiated (HCT-116) and moderately differentiated (SW480) colorectal cancer (P<0.05). The expression of PCNA and Cycling in low-differentiated (HCT-116) human colorectal cancer was lower than those in well-differentiated group.