Blocking cytokine signaling along with intense Bcr-Abl kinase inhibition induces apoptosis in primary CML progenitors

Abstract

In chronic myeloid leukemia (CML) cell lines, brief exposure to pharmacologically relevant dasatinib concentrations results in apoptosis. In this study, we assess the impact of intensity and duration of Bcr-Abl kinase inhibition on primary CD34(+) progenitors of chronic phase CML patients. As CML cells exposed to dasatinib in vivo are in a cytokine-rich environment, we also assessed the effect of cytokines (six growth factors cocktail or granulocyte-macrophage colony-stimulating factor (CSF) or granulocyte-CSF) in combination with dasatinib. In the presence of cytokines, short-term intense Bcr-Abl kinase inhibition (>or=90% p-Crkl inhibition) with 100 nM dasatinib did not reduce CD34(+) colony-forming cells (CFCs). In contrast, without cytokines, short-term exposure to dasatinib reduced CML-CD34(+) CFCs by 70-80%. When cytokines were added immediately after short-term exposure to dasatinib, CML-CD34(+) cells remained viable, suggesting that oncogene dependence of these cells can be overcome by concomitant or subsequent exposure to cytokines. Additional inhibition of Janus tyrosine kinase (Jak) activity re-established the sensitivity of CML progenitors to intense Bcr-Abl kinase inhibition despite the presence of cytokines. These findings support the contention that therapeutic strategies combining intense Bcr-Abl kinase inhibition and blockade of cytokine signaling pathways can be effective for eradication of CML progenitors.

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

“…Interestingly, the effects of RUX as a single agent were modest, but became more dramatic when combined with NL, suggesting that the role of JAK2 is particularly prominent during TKI therapy and that CML CD34 1 cells become more reliant on JAK2 kinase when BCR-ABL is fully inhibited. These findings are consistent with those published recently by other research groups, mainly using nonclinically developed JAK2 inhibitors, [40][41][42][43] but are contrary to those reported by Hantschel et al, showing that BCR-ABL is still able to transform murine BM cells in which JAK2 has been deleted, both in vitro and in vivo. 27 Moreover, a recent report suggested that JAK2 deletion might accelerate CML development in mouse models by preferentially causing elimination of normal HSC which are more dependent on JAK2 signaling compared with CML LSC where BCR-ABL is active.…”

“…We also noted that when RUX and NL were combined in CML cells grown in the absence of GFs, the additional effects of the JAK2 inhibitor were abolished, suggesting that one of the main roles of JAK2, independent of BCR-ABL kinase and in the presence of NL, is to relay survival signals from exogenous GFs which can be effectively inhibited by RUX, as also previously reported. [40][41][42][43] This further helps to resolve the discrepancy between our findings and those of Hantschel et al Our data therefore, suggested that in the absence of GFs, JAK2 signals were either absent or under the direct control of BCR-ABL, hence completely abrogated by the high doses of NL used in our experiments. Based on our data, one of the putative mechanisms of action of the NL and RUX combination in the presence of exogenous GFs was a more profound inhibition of JAK2/ STAT5 activity, as shown by the correlative changes in both p-JAK2 and p-STAT5 levels, with combined treatment, associated with correlative changes in STAT5 target genes.…”

Minimal Residual Disease and Discontinuation of Therapy in Chronic Myeloid Leukemia: Can We Aim at a Cure?

“…The addition of hematopoietic growth factors to the culture medium of primary CML cells exposed to dasatinib in vitro increases the survival of these cells. 49 Because many cytokines signal through the JAK-STAT pathway, the combination of a TKI with a JAK2 inhibitor might be beneficial to target MRD. Stromal interactions have also been proposed to protect stem cells in vivo, providing a rationale for disrupting marrow homing through the CXCR4 with the mobilizing agent plerixafor.…”

Monoclonal antibody targeting of IL-3 receptor α with CSL362 effectively depletes CML progenitor and stem cells

“…[12][13][14] Also, CML CD34 1 and CD34 1 /CD38 -cells are thought to produce interleukin (IL) 3 and granulocyte colony-stimulating factor (G-CSF) providing an autocrine activation loop that contributes to their innate resistance. [15][16][17] Accordingly, the concept of targeting CML leukemic stem and progenitor cells (LSPCs) at the cytokine receptor level might be a promising approach, especially because some cytokine receptors are overexpressed in stem cells of certain leukemias.…”