WP1130 Inhibits Signaling through BCR-ABL Ubiquitination and Cytoplasmic to Aggresome Trafficking to Induce Apoptosis of CML Cells.

Abstract 3303

Poster Board III-191

BCR-ABL remains the primary target for chronic myelogenous leukemia (CML) therapy but longstanding control and complete suppression of the disease may require additional strategies beyond kinase inhibition. We previously described a small molecule, WP1130, that mediated down-regulation of BCR-ABL, induced apoptosis of CML cells with limited toxicity against normal myeloid progenitors and decreased CML tumor growth in mice (Blood. 2007;109(8):3470-8). In this report we further investigated the BCR-ABL targeting activity and mechanism of action of WP1130 in CML cells. WP1130 rapidly (within 30 to 60 min) reduced cytoplasmic levels of BCR-ABL protein and suppressed Stat5 tyrosine phosphorylation without affecting Jak2, c-Abl, BCR, Erk, Akt, Lyn, Hck or gp130. Down-regulation of BCR-ABL by WP1130 was not affected by point mutations that alter imatinib or dasatinib binding or BCR-ABL kinase inhibitory activity. Examination of the cellular distribution of BCR-ABL in treated cells revealed that BCR-ABL was sequestered into compact, cytoskeletal-enriched aggresomal structures that were recovered in the detergent-insoluble fraction of the cell. WP1130-mediated translocation of BCR-ABL was associated with increased cellular poly-ubiquitination without 20S proteosome inhibition, disruption of Hsp90/BCR-ABL complexes or increased reactive oxygen species. WP1130 induced BCR-ABL trafficking into aggresomes correlated with its poly-ubiquitination (primarily K63) and lysates from WP1130 treated cells demonstrated reduced capacity to hydrolyze ubiquitinated substrate. Together, these results suggest that WP1130 induces poly-ubiquitination and trafficking of BCR-ABL into signaling incompetent aggresomes in CML cells through a unique mechanism that may involve inhibition of deubiquitinase activity and define a unique pathway to suppress BCR-ABL signaling and induce CML cell destruction.