Expression of a truncated first exon BCR sequence in chronic myelogenous leukemia cells blocks cell growth and induces cell death

We have shown that a deletion mutant form of Bcr [Bcr(61-413)] is a strong inhibitor of the tyrosine kinase of Bcr-Abl in vitro and also inhibits its oncogenic growth effects (Liu et al., Cancer Res., 56: 5120-5124, 1996). To determine the effects of this Bcr-Abl kinase inhibitor on chronic myelogen ous leukemia (CML) cells, we cloned BCR(64-413) into a recombinant, replica tion-defective adenovirus to express useful quantities of Bcr(64-413) in a wide variety of cells in culture. Infection of Cos1 cells with plaque-purif ied virus at a multiplicity of infection of 20-40 induced high expression o f Bcr(64-413) as detected by Western blotting. Infection of hematopoietic c ells at modest multiplicities of infection (20-40) required special conditi ons involving shifting cycling cells to a nongrowing condition involving se rum starvation and cell crowding. Under these conditions, both Bcr-Abl-posi tive and -negative hematopoietic cells can be efficiently infected by adeno virus, as demonstrated by 5-bromo-4-chloro-3-indolyl-beta -D-galactopyranos ide staining of cells infected by beta -galactosidase (beta -GAL) adenoviru s. We found that expression of Bcr(64-413) in Bcr-Abl-positive K562 and BV- 173 cells, but not Bcr-Abl-negative SMS-SB cells, increased cell-cell clump ing and inhibited cell growth. In contrast to the effects of the Bcr(64-413 ) adenovirus, the beta -GAL adenovirus, despite infecting both types of cel ls, did not block growth or increase cell-cell clumping of Bcr-Abl-positive and -negative hematopoietic cells. Expression of Bcr(64-413) protein in pr imary cultures of cells from CML patients with active disease interfered,wi th cell growth, induced apoptosis (as measured by annexin staining), and in creased cell-cell clumping, whereas the beta -GAL adenovirus and mock-infec ted cells lacked these effects. In contrast, normal marrow cells did not ex hibit these effects on infection with Bcr(61-413) adenovirus. We conclude f rom these findings that Bcr(64-413) interferes with the oncogenic effects o f Bcr-Abl and therefore has the potential for use in therapy of CML.