EX-VIVO EFFECTS ASSOCIATED WITH THE EXPRESSION OF A BCR-ABL-SPECIFIC RIBOZYME IN A CML CELL-LINE

The bcr-abl chimeric gene is found in 95% of chronic myeloid leukemia (CML) patients and is thought to be seminal to the etiology of the dis ease. The possibility of using ribozymes to suppress bcr-abl gene expr ession and subsequently alter the malignant phenotype of hematopoietic cells may provide an alternative therapeutic approach to current regi mens. A series of hammerhead ribozymes targeted to a b3a2 bcr-abl tran script has been developed and previously shown to be capable of cleavi ng the desired sequence with varying degrees of specificity. This stud y investigated the ex vivo effects of endogenous expression of these r ibozymes in a CML cell line, K562. We demonstrated a 53% decrease in b cr-abl mRNA levels in a clone induced to express Rz8, compared with it s uninduced control. Phenotypic analysis of this clone also revealed a 63% decrease in colony-forming ability and a 43% inhibition of cell p roliferation following ribozyme expression. Morphologic analysis of ce lls showed there was a slight increase (2.5% to 15%) in the number of cells undergoing apoptosis. These results suggest that Rz8 was effecti ve in suppressing bcr-abl gene expression within a cellular environmen t and altering the leukemic nature of a CML cell line.