| The specific structure at the end of the chromosome named "telomere" is essential for chromosome stability. The gene involves no functional structures, but is crucial to protect chromosome against end to end fusion, degeneration and rearrangment. All these changes influence the replication of chromosome and cell life. Telomerase is a special reverse transcriptase enzyme, which uses its own RNA component as a template to elongate the 3'-single-strand DNA extension of the chromosome terminus by the sythesis of telomeric repeats. And a protein subunit(human telomerase reverse transcriptase hTERT) catalyze the sytheses reaction. Thus, the telomerase complex comprises of telomerase RNA (hTR), catalytic subunit and hTERT-associated proteins such as Hsp90 and p23. hTERTexpression is the essential factor of the telomerase activity.It has been noted that normal somatic cells would progressingly lose some part of telomere during replication. When telomere was shortened to a critical length, the chromosome will lose its stability and cells would be induced into replication senescence. So the length of telomere determinates lives of cells. But when telomerase is activated, and can synthesis telomere added to the end of the chromosome, the telomere woule not reach the critical point and cells would achieveimmortalization. At present, it is thought to be the molecular mechenism of cell oncogenesis. Telomerse activity has been found in about 85 percent of human cancer. A lot of studies have confirmed the association between telomerase and cancer. In choriocarcinoma tissues and cell lines, the telomerase activity was also found highly positive.The relationship between telomerase and cancer makes it possible that telomerase became a target for anti-cancer therapy. The inhibition of telomerase activity would cause progressingly shortening of telomere and would inhibit growth of tumor by inducing differentiation or apotosis of cells.The technique of antisense nucleotide is to design special antisense nucleotide, which can inhibit expression of the gene by hybridism with certain sequence. This technique includes antisense RNA, antisense DNA, and Ribozyme. A lot of research which telomerase was used as a target is about antisense nuleotide.Gestational trophoblastic tumor(GTT) is caused by high proliferation of trophoblasts. Because of its sensitivity to chemotherapy, it is a kind of eusemia gynecologic tumor. The total remission rate is more than 90 percent. But, high-risk and drug resistant cases are difficult in therapy. Sometimes side effects of chemical drugs influence the effect of treatment. So, we need to investigate new treatment protocols or to find new therapeutic target.In this study, we established choriocarcinoma xenografts in nude mice. And we demonstrated that by treating xenografts with antisense oligonucleotides against telomerase RNA, the growth of tumors would be inhibited.JAR cells were injected subcutaneous into female nude mice. And characterstics of xenografts were studied. Treatment began when tumor volumns reached to 15-75mm3. All nude mice were divided into five groups randomly. Each group werecomprised of six mice. Group one were injected anti-hTR 2nmol/200ul. Group two were anti-hTR 5nmol/200μl. Group three were random sequence 5nmol/200μl. Group four were drug ACTD, Bμg/day. Group five were NS 200μl. Drugs were used for fourteen days continually.Tumor volumes were calculated by V=L(Length) X W(Width)2/2 every other day. In fifteenth day, nude mice were killed by spine dislocation. One part of tissues were preserved in 70 under zero degree, one part were fixed in 10 percent of formalin to do routine hematoxylin-eosin staining, others were fixed to do ultrastructure examination. TRAP-PCR ELISA was used to detect telomerase activity. And hTERT protein expression was assayed by Western blotting.Our results showed that characteristics of xenografts established by JAR cells were similiar with human choriocarcinoma. The difference between them was the tissue's angiogenesis.A... |
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