Retrovirally transduced antisense sequences stably suppress P210BCR-ABL expression and inhibit the proliferation of BCR/ABL-containing cell lines.

There is now strong evidence that the BCR-ABL gene product of the Philadelphia chromosome (P210) plays a crucial role in the pathogenesis of chronic myeloid leukemia (CML). We have previously shown that introduction of antisense oligonucleotides into K562 cells could transiently block the expression of P210 and specifically inhibit cellular growth in culture. In this report, we describe the use of a retroviral vector to introduce selected antisense and sense sequences, first into murine B10 cells, previously rendered interleukin-3 (IL-3) independent by transfection of BCR-ABL sequences, and second into K562 cells. The antisense transcripts generated under the control of MoMLV promoter specifically killed B10 cells in the absence of IL-3 and inhibited P210 expression almost completely. In K562 cells, the antisense sequences led to a dramatic reduction of P210 expression and increased their doubling time by more than twofold. This effect was not reversed by the addition of exogenous IL-3 to the culture medium. Control HeLa or HL60 cells infected with the same constructs did not show any change in proliferation rate, despite abrogation of the normal BCR gene products. Rather unexpectedly, P210 suppression was not lethal in K562 cells, showing that such a cell line does not rely entirely on the expression of P210 for surviving, but depends on it as far as growth properties are concerned. We conclude that this approach can successfully achieve stable suppression of the oncogenic protein P210 and may be used to study further the mechanisms by which P210 is transforming cells. The effect on fresh CML cells in bone marrow cultures remains to be assessed before we can tell whether this technique may be used for selective suppression of leukemic hematopoiesis in vitro.