Targeting Primitive Chronic Myeloid Leukemia Cells by Effective Inhibition of a New AHI-1–BCR-ABL–JAK2 Complex

Abstract

BackgroundImatinib mesylate (IM) induces clinical remission of chronic myeloid leukemia (CML). The Abelson helper integration site 1 (AHI-1) oncoprotein interacts with BCR-ABL and Janus kinase 2 (JAK2) to mediate IM response of primitive CML cells, but the effect of the interaction complex on the response to ABL and JAK2 inhibitors is unknown.MethodsThe AHI-1–BCR-ABL–JAK2 interaction complex was analyzed by mutational analysis and coimmunoprecipitation. Roles of the complex in regulation of response or resistance to ABL and JAK2 inhibitors were investigated in BCR-ABL + cells and primary CML stem/progenitor cells and in immunodeficient NSG mice. All statistical tests were two-sided.ResultsThe WD40-repeat domain of AHI-1 interacts with BCR-ABL, whereas the N-terminal region interacts with JAK2; loss of these interactions statistically significantly increased the IM sensitivity of CML cells. Disrupting this complex with a combination of IM and an orally bioavailable selective JAK2 inhibitor (TG101209 [TG]) statistically significantly induced death of AHI-1–overexpressing and IM-resistant cells in vitro and enhanced survival of leukemic mice, compared with single agents (combination vs TG alone: 63 vs 53 days, ratio = 0.84, 95% confidence interval [CI] = 0.6 to 1.1, P = .004; vs IM: 57 days, ratio = 0.9, 95% CI = 0.61 to 1.2, P = .003). Combination treatment also statistically significantly enhanced apoptosis of CD34+ leukemic stem/progenitor cells and eliminated their long-term leukemia-initiating activity in NSG mice. Importantly, this approach was effective against treatment-naive CML stem cells from patients who subsequently proved to be resistant to IM therapy.ConclusionsSimultaneously targeting BCR-ABL and JAK2 activities in CML stem/progenitor cells may improve outcomes in patients destined to develop IM resistance.

CML cells actively evade host immune surveillance through cytokine-mediated downregulation of MHC-II expression

“…Because of the BCR-ABL-independent nature of MHC-II downregulation, combination therapies of JAK inhibitors with TKI could target the disease bulk and the LSCs. 39,48 Indeed, recent studies demonstrate synergy between RUX and NIL, inducing apoptosis in CML LSCs. 49 Our studies could suggest that LSCs remaining after dual RUX/TKI treatment may have a reduced ability to evade host immunity because of re-expression of MHC-II.…”

Current pre-clinical and clinical advances in the BCR-ABL1-positive and -negative chronic myeloproliferative neoplasms

“…In contrast, Perez et al demonstrated the DNA methylation pattern to be similar in chronic phase PV, ET and PMF, and differentially methylated genes were mostly enriched in the NF-κB pathway. 17 They also noted that in MPN patients who transform to AML, the number of differentially methylated regions increased significantly and the aberrant genes were involved in the 'interferon pathway' or were represented by genes already reported in de novo AML. Collectively, these efforts suggest underlying epigenome differences between the MPN subtypes with potential clinical impact, and provide motivation for the use of hypomethylating and other novel agents targeting the epigenome in the MPNs.…”

JAK2/STAT5 inhibition by nilotinib with ruxolitinib contributes to the elimination of CML CD34+ cells in vitro and in vivo

“…18,19 25 Pharmacologic interference with the JAK2/STAT5 pathway, therefore, represents an attractive therapeutic strategy in CML; however, STAT5 is a difficult drug target as it lacks an enzymatic domain and a simpler approach to interfere with STAT5 function is to inhibit its predominant activating kinase, JAK2.…”