Seiichi Okabe

The oral iron chelator deferasirox represses signaling through the mTOR in myeloid leukemia cells by enhancing expression of REDD1.

To evaluate the effect of deferasirox in human myeloid leukemia cells, and to identify the moleclular pathways responsible for antiproliferative effects on leukemia cells during chelation therapy, we performed gene expression profiling to focus on the pathway involved in the anticancer effect of deferasirox. The inhibitory concentration (IC50) of deferasirox was 17–50 µM in three human myeloid cell lines (K562, U937, and HL60), while those in fresh leukemia cells obtained from four patients it varied from 88 to 172 µM. Gene expression profiling using Affymerix GeneChips (U133 Plus 2.0) revealed up‐regulation of cyclin‐dependent kinase inhibitor 1A (CDKN1A) encoding p21CIP, genes regulating interferon (i.e. IFIT1). Pathways related to iron metabolism and hypoxia such as growth differentiation factor 15 (GDF‐15) and Regulated in development and DNA damage response (REDD1) were also prominent. Based on the results obtained from gene expression profiling, we particularly focused on the REDD1/mTOR (mammalian target of rapamycin) pathway in deferasirox‐treated K562 cells, and found an enhanced expression of REDD1 and its down‐stream protein, tuberin (TSC2). Notably, S6 ribosomal protein as well as phosphorylated S6, which is known to be a target of mTOR, was significantly repressed in deferasirox‐treated K562 cells, and REDD1 small interfering RNA restored phosphorylation of S6. Although iron chelation may affect multiple signaling pathways related to cell survival, our data support the conclusion that REDD1 functions up‐stream of tuberin to down‐regulate the mTOR pathway in response to deferasirox. Deferasirox might not only have benefit for iron chelation but also may be an antiproliferative agent in some myeloid leukemias, especially patients who need both iron chelation and reduction of leukemia cells. (Cancer Sci 2009; 100: 970–977)

Thrombopoietin induces an SH2-containing protein, CIS1, which binds to Mpl: Involvement of the ubiquitin proteosome pathway

The interaction of thrombopoietin (TPO) with its receptor, Mpl, triggers growth and differentiation of megakaryocytes and their progenitors. The Mpl cytoplasmic domain controls this process through src homology 2 (SH2)-containing target molecules and their receptor docking sites. A novel cytokine inducible SH2-containing protein, CIS1, has been isolated. CIS1 is induced by interleukin-2 (IL-2), IL-3, GM-CSF, and erythropoietin (EPO), but not by IL-6, granulocyte colony-stimulating factor (G-CSF), or stem cell factor. To investigate the functional domains of Mpl for induction of CIS1, we examined FDCP-2 cell lines expressing seven carboxyl truncations of the human Mpl cytoplasmic domain. We found that the box1 and box2 regions of Mpl were necessary for induction of CIS1 after TPO stimulation. CIS1 was degraded very quickly and was found to be involved in the ubiquitin-proteosome pathway. A 4-hour depletion of TPO almost completely eliminated CIS1 protein; within 1 hour after TPO stimulation, CIS1 protein reappeared as 37- and 32-kDa proteins in the wild type Mpl-expressing FDCP-2 cells. Further, CIS1 was stably associated with tyrosine-phosphorylated Mpl. The SH2 domains of CIS1, constructed as glutathione S-transferase fusion protein, bound to activated Mpl in vitro. These results suggest that CIS1 may be an important signaling component downstream of Mpl and may regulate the proliferation and differentiation of hematopoietic cells.

Human herpesvirus 6 reactivation on the 30th day after allogeneic hematopoietic stem cell transplantation can predict grade 2–4 acute graft‐versus‐host disease

Viral infections and their occult reactivation occasionally cause not only organ damage, but also exacerbation of acute graft‐versus‐host disease (aGVHD), which may increase transplantation‐related mortality synergistically. To determine correlations between viral reactivation and transplantation‐related complications, we performed various viral screening tests on the 30th day after allogeneic hematopoietic stem cell transplantation (HSCT), and assessed the clinical implications.

Efficacy of the dual PI3K and mTOR inhibitor NVP-BEZ235 in combination with nilotinib against BCR-ABL-positive leukemia cells involves the ABL kinase domain mutation

Imatinib, an ABL tyrosine kinase inhibitor (TKI), has shown clinical efficacy against chronic myeloid leukemia (CML). However, a substantial number of patients develop resistance to imatinib treatment due to the emergence of clones carrying mutations in the protein BCR-ABL. The phosphoinositide 3 kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway regulates various processes, including cell proliferation, cell survival, and antiapoptosis activity. In this study, we investigated the efficacy of NVP-BEZ235, a dual PI3K and mTOR inhibitor, using BCR-ABL-positive cell lines. Treatment with NVP-BEZ235 for 48 h inhibited cell growth and induced apoptosis. The phosphorylation of the AKT kinase, eukaryotic initiation factor 4-binding protein 1 (4E-BP1), and p70 S6 kinase were decreased after NVP-BEZ235 treatment. The combination of NVP-BEZ235 with a BCR-ABL kinase inhibitor, imatinib, or nilotinib, induced a more pronounced colony growth inhibition, whereas the combination of NVP-BEZ235 and nilotinib was more effective in inducing apoptosis and reducing the phosphorylation of AKT, 4E-BP1, and S6 kinase. NVP-BEZ235 in combination with nilotinib also inhibited tumor growth in a xenograft model and inhibited the growth of primary T315I mutant cells and ponatinib-resistant cells. Taken together, these results suggest that administration of the dual PI3K and mTOR inhibitor NVP-BEZ235 may be an effective strategy against BCR-ABL mutant cells and may enhance the cytotoxic effects of nilotinib in ABL TKI-resistant BCR-ABL mutant cells.

Combination of Ponatinib with Hedgehog Antagonist Vismodegib for Therapy-Resistant BCR-ABL1–Positive Leukemia

Purpose: The Hedgehog signaling pathway is a key regulator of cell growth and differentiation during development. Whereas the Hedgehog pathway is inactive in most normal adult tissues, Hedgehog pathway reactivation has been implicated in the pathogenesis of several neoplasms including BCR-ABL1–positive leukemia. The clear link between the Hedgehog pathway and BCR-ABL1–positive leukemia led to an effort to identify small molecules to block the pathway. Experimental Design: We investigated the combined effects of vismodegib and ponatinib, a pan-ABL1 kinase inhibitor, in nonobese diabetic/severe-combined immunodeficiency (NOD/SCID) repopulating T315I BCR-ABL1–positive cells in vitro and in vivo. Results: We observed that combination with vismodegib and ponatinib helps to eliminate therapy-resistant NOD/SCID repopulating T315I BCR-ABL1–positive cells. The percentage of CD19-positive leukemia cells in peripheral blood was significantly lower in vismodegib + ponatinib–treated mice than that of the vehicle or ponatinib alone (P < 0.001). Spleen weights were also lower in vismodegib + ponatinib–treated mice than in ponatinib alone (P < 0.05). Overall tumor burden, as assessed by BCR-ABL mRNA from bone marrow cells, was significantly lower in vismodegib + ponatinib–treated mice than in ponatinib alone (P < 0.005). We also found that vismodegib significantly reduced BCR-ABL1–positive leukemia cell self-renewal in vitro as well as during serial transplantation in vivo. Conclusions: The combination with a Smo inhibitor and ABL1 tyrosine kinase inhibitors may help eliminate therapy-resistant T315I BCR-ABL1–positive leukemia cells. Our preclinical results indicate that vismodegib has potential as an important option for controlling minimal residual cells in BCR-ABL1–positive leukemia. Clin Cancer Res; 19(6); 1422–32. ©2012 AACR.

Characteristics of Dasatinib- and Imatinib-Resistant Chronic Myelogenous Leukemia Cells

Purpose: Although dual src-family kinase/BCR/ABL inhibitor, dasatinib (BMS-354825), provides therapeutic advantages to imatinib-resistant cells, the mechanism of dasatinib resistance was not fully known. Experimental Design: We used TF-1 BCR/ABL cells, by introducing the BCR/ABL gene into a leukemia cell line, TF-1 and K562, and established dasatinib- (BMS-R) and imatinib-resistant (IM-R) cells. We characterized chronic myelogenous leukemia drug-resistant cells and examined intracellular signaling. Results: The IC50 of dasatinib was 0.75 nmol/L (TF-1 BCR/ABL), 1 nmol/L (K562), 7.5 nmol/L (TF-1 BCR/ABL IM-R), 10 nmol/L (K562 IM-R), 15 μmol/L (TF-1 BCR/ABL BMS-R), and 25 μmol/L (K562 BMS-R). The number of BCR/ABL copies in resistant cell lines was the same as the parental cell line by fluorescence in situ hybridization analysis. There was no mutation in Abl kinase. We found that protein levels of BCR/ABL were reduced in dasatinib-resistant cell lines. BCR/ABL protein was increased by treatment of an ubiquitin inhibitor. The Src kinase, Lck, as well as mitogen-activated protein kinase and Akt were activated, but p21WAF, phosphatase and tensin homologue was reduced in K562 BMS-R cells. Removal of dasatinib from the culture medium of K562 BMS-R cells led to apoptosis, and activated caspase 3 and poly (ADP-ribose) polymerase. Conclusion: These results suggest that the expression and protein activation signatures identified in this study provide insight into the mechanism of resistance to dasatinib and imatinib and may be of therapeutic chronic myelogenous leukemia value clinically.

Membranous glomerulonephritis with nephrotic syndrome associated with chronic lymphocytic leukemia.

A 66-year-old woman was admitted to our hospital for evaluation of edema of the extremities. Laboratory findings suggested that she had nephrotic syndrome and chronic lymphocytic leukemia (CLL). Renal biopsy (with PAM staining) showed a spike formation in the capillary wall. Immunofluorescent staining revealed deposition of immunoglobulin G (IgG) and the third component of complement in the glomerular basement membrane. Electron microscopy showed fibrillary deposits in the subepithelium. These findings indicated membranous glomerulonephritis (MGN). In addition, focal segmental sclerosis and interstitial lymphocytic infiltration were observed in the renal biopsy specimen. In CLL patients nephrotic syndrome occurs rarely. Even if the complication occurs, MGN is not frequent. Both diseases are suspected to occur in association with each other, and immunologic abnormality contributes to their coexistence. Although administration of prednisolone and endoxan improved leukocytosis, proteinuria was not sufficiently improved with combination therapy.

Efficacy of MK-0457 and in combination with vorinostat against Philadelphia chromosome positive acute lymphoblastic leukemia cells

Aurora kinases play a pivotal role in the regulator of mitotic processes during cell division and Aurora kinases are overexpressed in a number of human cancers. In this study, we examined the intracellular signaling of Aurora kinases inhibitor, MK-0457 (VX-680), in BCR-ABL positive cell lines and in primary samples. MK-0457 induced apoptosis. Caspase 3 and poly (ADP-ribose) polymerase (PARP) were activated and heat shock proteins were reduced. A combination of MK-0457 and histone deacetylase inhibitor, vorinostat, increased apoptosis. Caspase 3 and PARP were activated and phosphorylation of BCR-ABL, Lyn, and Crk-L were reduced. BCR-ABL and Aurora A and B were reduced after vorinostat treatment. Moreover, combination of vorinostat and MK-0457 synergistically increased the extent of apoptosis in primary acute lymphoblastic leukemia cells with T315I mutation. Our study increases insight into how MK-0457 may mediate its effects on BCR-ABL positive leukemia cells with T315I mutation, and information of potential therapeutic relevance.

Activity of a novel Aurora kinase inhibitor against the T315I mutant form of BCR-ABL: In vitro and in vivo studies

Despite promising results from clinical studies of ABL kinase inhibitors, a challenging problem that remains is the T315I mutation against which neither nilotinib nor dasatinib show significant activity. In the present study, we investigated the activity of a novel Aurora kinase inhibitor, VE‐465, against leukemia cells expressing wild‐type BCR‐ABL or the T315I mutant form of BCR‐ABL. We observed a dose‐dependent reduction in the level of BCR‐ABL autophosphorylation in VE‐465‐treated cells. Exposure to the combination of VE‐465 and imatinib exerted an enhanced apoptotic effect in K562 cells. Combined treatment with VE‐465 and imatinib caused more attenuation of the levels of phospho‐AKT and c‐Myc in K562 cells. Further, the isobologram indicated the synergistic effect of simultaneous exposure to VE‐465 and imatinib in K562 cells. To assess the in vivo efficacy of VE‐465, athymic nude mice were injected intravenously with BaF3 cells expressing wild‐type BCR‐ABL or the T315I mutant form. The vehicle‐treated mice died of a condition resembling acute leukemia by 28 days; however, nearly all mice treated with VE‐465 (75 mg/kg, twice daily; intraperitoneally for 14 days) survived for more than 56 days. Histopathological analysis of vehicle‐treated mice revealed infiltration of the spleen. In contrast, histopathological analysis of organs from VE‐465‐treated mice demonstrated normal tissue architecture. Taken together, the present study shows that VE‐465 exhibits a desirable therapeutic index that can reduce the in vivo growth of T315I mutant form and wild‐type BCR‐ABL‐expressing cells in an efficacious manner. (Cancer Sci 2008; 99: 1251–1257)

Activity of histone deacetylase inhibitors and an Aurora kinase inhibitor in BCR-ABL-expressing leukemia cells: Combination of HDAC and Aurora inhibitors in BCR-ABL-expressing cells

BackgroundThe use of imatinib, an ABL tyrosine kinase inhibitor, has led to a dramatic change in the management of BCR-ABL-positive leukemia patients. However, resistance to imatinib mediated by mutations in the BCR-ABL domain has become a major problem in the treatment of these patients.MethodsIn the present study, we examined the activity of histone deacetylase (HDAC) inhibitors in combination with an Aurora kinase inhibitor in BCR-ABL-expressing cells.ResultsWe found the HDAC inhibitors vorinostat and/or pracinostat (SB939) induced apoptosis in BCR-ABL-expressing cells. Additionally, HDAC inhibitors reduced levels of Aurora A and B protein. An Aurora kinase inhibitor, tozasertib (VX-680), inhibited growth, promoted pro-apoptotic activity, reduced the phosphorylation of BCR-ABL and Crk-L, and activated caspase-3 and poly (ADP-ribose) polymerase (PARP) in BCR-ABL-positive cells. Moreover, after treatment with tozasertib, HDAC protein expression was decreased. Combination of vorinostat or pracinostat with tozasertib had a synergistic inhibitory effect on the proliferation of T315I cells. Phosphorylation of Crk-L decreased, and PARP activation increased after treatment with vorinostat or pracinostat and tozasertib. Moreover, combination of vorinostat or pracinostat and tozasertib significantly increased the extent of apoptosis in primary chronic myeloid leukemia cells.ConclusionsThis study demonstrated that combination of HDAC and Aurora inhibitors was highly effective against BCR-ABL-expressing cells.