It is therefore important to test whether the combined treatment of bortezomib and paclitaxel is also active on cells expressing Oxaceprol Bcr-Abl with the T315I mutation. While 7nM bortezomib and 7nM paclitaxel alone did not significantly affect the total levels and phosphorylation of Bcr-Abl T315I in the Baf3 Bcr-Abl T315I cells, the combined treatment was highly effective in decreasing the total levels and phosphorylation of Bcr-Abl T315I. Our results show that bortezomib and paclitaxel combined treatment is able to target the TKIsresistant cell lines with the T315I mutation in Bcr-Abl. To determine if bortezomib in combination with other known mitotic inhibitors can result in similar inhibition of Bcr-Abl activity and downstream signaling, we analyzed the combined effect of bortezomib with the known PLK1 inhibitor BI2536. PLK1 is a well conserved kinase, critical in all phases of the mitosis. A previous report suggested that BI2536 has a growth inhibitory effect on Bcr-Abl-positive cells, which is not amplified by bortezomib after 16h of co-treatment. Here we show that while each treatment alone at 9nM or 10nM bortezomib and 8nM or 10nM BI 2536 does not significantly induce cell death in K562 as measured by the Trypan Blue exclusion method, the combined treatment resulted in a significant decrease in cell number and in the percentage of the viable cells. In addition, the prolonged co-treatment with 9nM bortezomib and 8nM BI 2536 is effective in cleaving initiator caspases 8, 9, effector caspase 3 and caspase-substrate PARP, in both K562 and K562-R cells. Moreover, the combined treatment also resulted in an efficient decrease of the total levels of Bcr-Abl, which correlates with a decrease in the phosphorylation of the downstream STAT5 DprE1-IN-1 protein, in both K562 and K562-R cells. The combined effects of bortezomib with the mitotic inhibitors docetaxel and vincristine were also tested. Similar to paclitaxel, docetaxel induces m
