| Prostate cancer is one of the most common malignant tumor of genitourinary system in male. In the western country, the incidence of the death caused by prostate cancer is the second in the male whose age is older than 40. In recent years, the incidence of the prostate cancer is increasing year by year in our country, and the majority of patients were advanced prostate cancer when they were diagnosed. Endocrine therapy is the most important way in the therapy of the prostate cancer recently, but after few years major of prostate cancer relapse to the status of hormone-independent prostate cancer which will induce the failure of the therapy. Therefore, investigation of novel therapies for hormonal-independent prostate cancer is urgently needed.The occurrence and development of prostate cancer have an intensive relation with androgen, Endocrine therapy can inhibit the growth of hormone-dependent prostate cancer cells by intercepting the combination between androgen and androgen receptor (AR). The abnormal expression of AR is play a role in the formation of hormone-independent prostate cancer. The researches show that about 1 13 of the hormone-independent prostate cancer lost of AR expression. The mechanism of AR gene expression silencing is probably associated with the CpG island's methylation in the core promoter of AR gene.DNA methylation is the process that the organisms with the help of the DNA methyltransferase (DNMT) added an activated methyl group which come from the s-adenosyl methionine (SAM) methyl donor to the cell pyrimidine C-5 position. In mammals,50%～60% genes have the CpG Island. The CpG island (CpG island) which is usually about lkb～2kb, covered gene promoter and the first exon is not methylated modified normally. If CpG islands are methylated, the promoter was also methylated, that is the promoter hypermethylation (aberrantmethylation). DNA methylation's process is short, which is mainly through DNMT to Complete. DNA methyltransferase (DNMT) is the key enzyme in the process of DNA methylation, mammalian cells presently have three kinds of activity of DNA methyltransferase: Dnmtl, Dnmt2, Dnmt3. Gene promoter region methylation in many tumors are relatively common.The CpG island's methylation is reversible. CpG island related gene's methylation can be restored to its expression, through human intervention or other factors. Thus, the demethylation of AR gene becomes a new therapeutic strategy for AR-negative prostate cancer.Arsenic is a high degree of affinity with the thiol of protoplasmic poison, has long been considered to be highly toxic substances, with a cancer-causing teratogenic effects.As2O3 can inhibit the growth of the variety of tumor cells. China had reported in the literature that As2O3 can be used as a new demethylation agent, which indicates a good prospect for clinical application.As2O3 demethylation mechanism may include the following:Firstly, the competitively deplete DNA methyl donor S-adenosyl methionine. As2O3 come into being a methyl arsenate and dimethyl arsenate in the effect of arsenic methyltransferase, with S-adenosyl methionine as methyl donor. In this process S-adenosylmethionine was consumed. The methyltransferase (DNMT) catalyzed DNA methylation process which also need S-adenosyl methionine as methyl donor, as a result S-adenosyl methionine will be relatively or absolutely shortage in the process of DNA methylation. Secondly, As2O3 can inhibition the methyltransferase (DNMT), at the same time inhibition DNA methylation process. As2O3 two metabolic pathways can produce S-adenosyl homocysteine, and S-adenosyl homocysteine is the inhibitor of methyltransferase (DNMT). Thirdly, As2O3 may also directly inhibit the activity of Dnmt3a and Dnmt3b. Arsenic is recognized as the thiol enzyme inhibitors, Dnmt3a and 3b carboxy-terminal catalytic domain are rich in cysteine thiol. Methyltransferase was interferenced in duce to the cellular barriers of DNA methylation and genomic hypomethylation, the gene silenced by hypermethylation may be re-expression with the gene demethylation.This study investigated two different concentrations of As2O3 to reverse AR expression of PC-3 androgen-independent prostate cancer in nude mice, and speculated that the possible mechanism of inhibiting the tumor's growth which provides experimental basis for further study.Materials and methods1. The model of xenograft tumor in nude mice were established by inoculating androgen-independent prostate cancer cell line PC-3 into the back of nude mice subcutaneously, and 36 tumor-bearing nude mice were established. They were then divided into 6 groups by tumor volume randomly:A:control group; B: bicalutamide; C:1.5mg/kg.d As2O3; D:1.5mg/kg.d As2O3+Bicalutamide; E: 3mg/kg.d As2O3; F:3mg/kg.d As2O3+Bicalutamide. They were administered once a day by intraperitoneal injection of As2O3 and Bicalutamide gavage, tumor volume was measured every 3 days.The mice were sacrificed after 21 days treatment. Tumor tissues were stripped completely, then weighed and removed the vital organs such as liver and kidney, fixed tumor tissues in the 4% paraformaldehyde solution. Calculated tumor volume inhibition rate and tumor weight inhibition rate.2. Using immunohistochemical methods to detect the experimental group's AR protein expression of PC-3 cells, HE stained important organs to observe the toxicity of drugs.3. Experimental datas are disposed by SPSS 17.0 statistics soft ware, deploying one-way analysis of variance, significance of difference standard (a=0.05).Resuls:1. As2O3can be able to reverse the AR re-expression of androgen-independent prostate cancer PC-3 xenografts in nude mice, the greater the dose of As2O3be used, the more AR be re-expressed. AR mainly located in the nucleus, immunohistochemistry showed that brown-yellow particles is in the nucleus expression of AR is negative in the group of negative control and bicalutamide. AR expression in a very small amount were also negative in the 1.5mg/kg.d arsenic trioxide group,1.5mg/kg.d arsenic trioxide+bicalutamide group; it is positive in the 3mg/kg.d arsenic trioxide group and 3mg/kg.d arsenic trioxide +bicalutamide group.2. AR of re-expression have a certain amount of activity and the sensitivity of endocrine therapy. Tumor volume inhibition rate of 3mg/kg.d arsenic trioxide+ bicalutamide group is 35.61%, tumor weight inhibition rate is 60.71% which were greater than 3mg/kg.d arsenic trioxide group of 27.27%,44.65%, Difference between the two groups were statistically significant (P<0.05).3. Arsenic trioxide is not only the demethylation which has a role in re-expressing AR, but also has a role in tumor suppression. Dose was positively correlated: tumor volume inhibition rates of 1.5mg/kg.d arsenic trioxide group,1.5mg/kg.d arsenic trioxide+bicalutamide group,3mg/kg.d arsenic trioxide group and 3mg/kg.d arsenic trioxide+bicalutamide group were 12.57%,16.40%,27.27%, 35.61%, tumor weight inhibition rates were 23.87%,27.00%,44.65%,60.71%, which were statistically significant (P<0.05) compared with blank control group, and Bicalutamide group, high-dose group was higher than low-dose group, there are statistically significant (P<0.05).Conclusions:1. A certain dose of As2O3 can induce AR receptor re-expression of hormone-independent prostate cancer PC-3 xenografts in nude mice in a dose-dependent.2. A certain dose of As2O3 induced re-expression of AR while inhibiting the tumor's growth, in a dose-dependent.3. Androgen receptor of re-expression has a certain activity.
|
PDF Full Text Request