Synergistic effects of proteasome inhibitor carfilzomib in combination with tyrosine kinase inhibitors in imatinib-sensitive and -resistant chronic myeloid leukemia models.

The tyrosine kinase inhibitor (TKI) imatinib has transformed the treatment and outlook of chronic myeloid leukemia (CML); however, the development of drug resistance and the persistence of TKI-resistant stem cells remain obstacles to eradicating the disease. Inhibition of proteasome activity with bortezomib has been shown to effectively induce apoptosis in TKI-resistant cells. In this study, we show that exposure to the next generation proteasome inhibitor carfilzomib is associated with a decrease in ERK signaling and increased expression of Abelson interactor proteins 1 and 2 (ABI-1/2). We also investigate the effect of carfilzomib in models of imatinib-sensitive and -resistant CML and demonstrate a potent reduction in proliferation and induction of apoptosis in a variety of models of imatinib-resistant CML, including primitive CML stem cells. Carfilzomib acts synergistically with the TKIs imatinib and nilotinib, even in imatinib-resistant cell lines. In addition, we found that the presence of immunoproteasome subunits is associated with an increased sensitivity to carfilzomib. The present findings provide a rational basis to examine the potential of carfilzomib in combination with TKIs as a potential therapy for CML, particularly in imatinib-resistant disease.

Methods for measuring proteasome activity: current limitations and future developments.

The proteasome has been validated as a therapeutic target, with proteasome inhibitors showing particular efficacy in the treatment of Multiple Myeloma. A wide range of methods have been developed to profile proteasome activity. These include the current method of choice fluorogenic peptide substrates, as well as bioluminescent imaging, immunological methods, and more recently, site-specific fluorescent probes. The aim of this review is to evaluate the currently available methods for profiling proteasome activity and their suitability for use in translational studies. Ongoing development of techniques for profiling proteasome activity will facilitate future research into proteasome-related pathologies, thus accelerating the development of more specific drug regimes.