We also detected a significant increase in PKCb activity, both by MIB/MS and by immunoblotting. PKCb has been shown to regulate anti-apoptotic Ibrutinib msds responses in myeloid leukemias, however inhibition of PKCb with bryostatin did not affect the viability of MYL-R cells. Interestingly, a recent proteomics study profiling kinase expression in drugrefractory head and neck squamous cell carcinoma identified a number of the same kinases as we did in MYL-R cells, suggesting that these may represent a drug resistance kinome profile. Considerable insight may also be obtained from the MIB/MS analysis of the kinases decreased in MYL-R cells. Approximately twice as many kinases were decreased as increased in the MYL-R cells and this was confirmed by both iTRAQ and SILAC quantification methods. Reduced levels of some of these kinases may be expected given that they are direct targets for inhibition by imatinib and MYL-R cells were generated by continuous exposure of MYL cells to imatinib. Interestingly, the decreased binding of JNK and kinase regulators of JNK, indicate a decrease in this pro-apoptotic regulatory pathway in MYL-R cells. Down-regulation of these kinases could potentially contribute to the anti-apoptotic properties of MYL-R cells. Decreased NDKM or dCK may also contribute to the reduced sensitivity of MYL-R cells to nucleoside analogs that we observed previously. The marked reduction of ATM may result from the reduced BCR-Abl protein in MYL-R cells as ATM has been shown to directly interact with Abl kinase, however the effect of this on cell survival is unclear. NF-kB plays a key role in regulating anti-apoptotic reactions and responses to chemotherapy. Because we detected increased IKKa and NF-kB signaling in MYL-R cells we examined the specific effects of targeting this pathway. BAY 65- 1942 is a selective inhibitor of IKK and an inhibitor of NF-kB responses. While BAY 65-1942 effectively blocked IkBa expression as expected, it stimulated a surprising increase in IL-6 expression in MYL-R cells that correlated with increased ERK phosphorylation. MIBs analysis of MYL-R cells treated with BAY 65-1942 confirmed the activation of the MEK/ERK pathway and an increase in B-Raf, ERK and RSK binding was detected. Since our CYT 11387 results suggested that BAY 65-1942 triggered a compensatory activation of the MEK/ERK pathway, we examined the effects of co-targeting these pathways. The MIB/MS analysis of the response to BAY 65-1942 and the MEK inhibitor AZD6244 was complex, with many kinases significantly lowered, including B-Raf, MEK, and RSK1 after combination treatment. Importantly, the combination of these inhibitors not only prevented the BAY 65-1942- stimulated increase in IL-6 and phospho-ERK, but substantially reduced cell viability and increased apoptosis as determined by PARP cleavage and caspase 3/7 activation. Thus these studies demonstrate that MIB/MS profiling provided an experimental rationale for co-targeting the IKK and MEK/ERK pathways and provided insight into why combined inhibition was synergistic compared to inhibition of MEK or IKK alone.