Investigation In Gene Therapy Of Chronic Myelocytic Leukemia

Chronic myelocytic leukemia ( CML ) is a malignant disorder in hematopoietic stem cell. It is generally believed that the Philadelphia (Ph) chromosome plays a key role in the origination of CML, which confers on its progeny a proliferative advantage over normal hematopoietic elements and thus allows the Ph+positive clone gradually to displace residual normal hematopoiesis. The discovery of the Ph chromosome as the first consistent chromosomal abnormality associated with a specific type of leukemia was a breakthrough in cancer biology. And the Ph chromosome is the result of a t ( 9;22 ) (q34;q11) reciprocal chromosomal translocation, which in fact creats a chimeric bcr-abl gene , encoding a p210bcr-ab1 chimeric protein. p210bcr-ab1 has deregulated ABL tyrosine kinase activity. As a result, this abnormal activation therefore lead to an expanded clonal hematopoiesis , altered adhesion properties and inhibition of apoptosis of myeloid cells.During the past twenty years hematopoietic stem cell transplantation ( HSCT ) and a- interferon ( a-IFN ) have greatly improved the prognosis of CML. However, the insight into the molecular pathology of CML gave rise to a new mothod which aimed at the chimeric bcr-abl gene and the p210BCR-ABL chimeric protein. Imatinib (Gleevec, Glivec, formerly STI571) , which selectively inhibited the proliferation of cells expressing p210BCR-ABL in vitro and in vivo is an specific inhibitor of the p210BCR-ABL tyrosine kinase . In preclinical studies , the remarkable results of STI 571 in clinical trials have led to a revolution in CML therapy. However, neither antisense oligonucleotides nor nucleus enzyme, nor even STI 571 can get a complete remission . At the same time, the efficacy of the antisense oligonucleotides and nucleus enzyme and the nonspecific toxic effect of the antisense oligonucleotides are still questionable. The long - term efficacy of STI 571 is to be verified by clinical trials in the future as well.RNA interference ( RNAi) ranked one of the top-ten breakthrough in science in 2001 by Science . Introduction of double - stranded RNA into cells can induce specific mRNA degradation . This process is called RNA interference . It is a kind of post-transcriptional gene silencing ( PTGS). RNAi has proved to be an efficient tool in biology and medicine . In the past several years , people have tried to take advantage of RNAi to treat diseases such as virus infectious diseases , malignant diseases and some genetic diseases . Therefore , we believe that it will probably be an opportunity for the therapy of CML tospecifically inhibit the expression of the chimeric bcr-abl gene byRNAi.Besides, many clinical trials shows us that none of the single agent can obtain a complete remission from CML. The cooperation of multiple therapy methods and the exploitation of new gene target are of importance for the treatment of CML . Recently, Scientists began to notice some signaling molecular lower reaches of the BCR-ABL chimeric protein, such as MYC CRKL Grb2 KIT VAV and MYB.As one of the most important adaptors of p210BCR-ABL chimeric protein, CRKL includes one SH2 and two SH3 domains. It can be phophorylated by p210BCR-ABL and its SH3 domain can bind the ABL onco-protein through the sequence rich in proline protein in ABL. Many experiments have proved that CRKL takes part in the p210 bcr-abl signaling pathway and as a signaling switch. We have researched the role of CRKL as an adaptor in the pathogenesis of CML and found that it plays a role in the overproduction of CML cells. Therefore, we conceived that the inhibition of crkl gene and bcr-abl chimeric gene simultaneously will be advantageous over inhibiting either of the two genes.According to the unique cytogenetical Characteristic owned by CML and the great breakthrough in its gene therapy, we are going to use the new biologic technique - RNAi to interfere with the expression of the bcr-abl chimeric gene and observe its effect on the CML cells ; besides, we hope to find a synergistic effect in crkl gene in combination with bcr-abl...