The RON receptor tyrosine kinase is a therapeutic target for cancer treatment. Here, we report therapeutic effect and phenotypic change of breast cancer cells in response to BMS-777607, a RON tyrosine kinase inhibitor. Treatment of breast cancer cells with BMS-777607 at therapeutic doses inhibited cancerous clonogenic growth but had only minimal effect on cell apoptosis. Significantly, BMS-777607 induced extensive polyploidy with multiple sets of chromosomes in cancer cells. This effect is independent of RON expression. Knockdown of RON in T-47D and ZR-75-1 cells by specific siRNA did not prevent polyploid formation. Immunofluorescent analysis of a-tubulin and g-tubulin expression in polyploid cells revealed that BMS-777607 disrupts bipolar spindle formation and causes multipolar-like microtubule assembly. Also, both metaphase equatorial alignment and chromosomal segregation were absent in polyploid cells. These results suggest that cellular mitosis arrests at prophase/pro-metaphase and fails to undergo cytokinesis. By analyzing kinase-inhibitory profiles, aurora kinase B was identified as the target molecule inhibited by BMS-777607. In BMS-777607-treated cells, aurora kinase B was inhibited followed by protein degradation. Moreover, BMS-777607 inhibited Ser10 phosphorylation of histone H3, a substrate of aurora kinase B. Chemosensitivity analysis indicated the resistance of polyploid cells toward chemotherapeutics. Treatment with doxorubicin, bleomycin, methotrexate, and paclitaxel significantly increased cellular IC 50 values. These findings highlight the theory that BMS-777607 acts as a multikinase inhibitor at therapeutic doses and is capable of inducing polyploidy by inhibiting aurora kinase B. Increased resistance of polyploid cells to cytotoxic chemotherapeutics could have a negative impact on targeted cancer therapy using BMS-777607. Mol Cancer Ther; 12(5); 725-36. Ó2013 AACR.

Abl interactor 1 (Abi1) is a key regulator of actin polymerization/depolymerization. The involvement of Abi1 in the development of abnormal cytoskeletal functions of cancer cells has recently been reported. It remains unclear, however, how Abi1 exerts its effects in tumor cells and whether it contributes to tumor progression in vivo. We report here a novel function for Abi1 in the regulation of invadopodia formation and Src-inhibitor of differentiation protein 1 (Id1)-matrix metalloproteinase (MMP)-9 pathway in MDA-MB-231 human breast cancer cells. Abi1 is found in the invadopodia of MDA-MB-231 cells. Epigenetic silencing of the Abi1 gene by short hairpin RNA in MDA-MB-231 cells impaired the formation of invadopodia and resulted in downregulation of the Src activation and Id1/MMP-9 expression. The decreased invadopodia formation and MMP-9 expression correlate with a reduction in the ability of these cells to degrade extracellular matrix. Remarkably, the knockdown of Abi1 expression inhibited tumor cell proliferation and migration in vitro and slowed tumor growth in vivo. Taken together, these results indicate that the Abi1 signaling plays a critical role in breast cancer progression and suggest that this pathway may serve as a therapeutic target for the treatment of human breast cancer.