2',5'-OLIGOADENYLATE-ANTISENSE CHIMERAS CAUSE RNASE-L TO SELECTIVELY DEGRADE BCR ABL MESSENGER-RNA IN CHRONIC MYELOGENOUS LEUKEMIA-CELLS/

We report an RNA targeting strategy, which selectively degrades bcr/ab l mRNA in chronic myelogenous leukemia (CML) cells. A 2',5'-tetraadeny late activator (2-5A) of RNase L was chemically linked to oligonucleot ide antisense directed against either the fusion site or against the t ranslation start sequence in bcr/abl mRNA. Selective degradation of th e targeted RNA sequences was demonstrated in assays with purified RNas e L and decreases of p210(bcr/abt) kinase activity levels were obtaine d in the CML cell line, K562, Furthermore, the 2-5A-antisense chimeras suppressed growth of K562, while having substantially reduced effects on the promyelocytic leukemia cell line, HL60. Findings were extended to primary CML cells isolated from bone marrow of patients. The 2-5A- antisense treatments both suppressed proliferation of the leukemia cel ls and selectively depleted levels of bcr/abl mRNA without affecting l evels of beta-actin mRNA, determined by reverse transcriptase-polymera se chain reaction (RT-PCR). The specificity of this approach was furth er shown with control oligonucleotides, such as chimeras containing an inactive dimeric form of 2-5A, antisense lacking 2-5A, or chimeras wi th altered sequences including several mismatched nucleotides. The con trol oligonucleotides had either reduced or no effect on CML cell grow th and bcr/abl mRNA levels. These findings show that CML cell growth c an be selectively suppressed by targeting bcr/abl mRNA with 2-5A-antis ense for decay by RNase L and suggest that these compounds should be f urther explored for their potential as ex vivo purging agents of autol ogous hematopoietic stem cell transplants from CML patients. (C) 1998 by The American Society of Hematology.