Shingen Nakamura

TGF-β Inhibition Restores Terminal Osteoblast Differentiation to Suppress Myeloma Growth

Background Multiple myeloma (MM) expands almost exclusively in the bone marrow and generates devastating bone lesions, in which bone formation is impaired and osteoclastic bone resorption is enhanced. TGF-β, a potent inhibitor of terminal osteoblast (OB) differentiation, is abundantly deposited in the bone matrix, and released and activated by the enhanced bone resorption in MM. The present study was therefore undertaken to clarify the role of TGF-β and its inhibition in bone formation and tumor growth in MM. Methodology/Principal Findings TGF-β suppressed OB differentiation from bone marrow stromal cells and MC3T3-E1 preosteoblastic cells, and also inhibited adipogenesis from C3H10T1/2 immature mesenchymal cells, suggesting differentiation arrest by TGF-β. Inhibitors for a TGF-β type I receptor kinase, SB431542 and Ki26894, potently enhanced OB differentiation from bone marrow stromal cells as well as MC3T3-E1 cells. The TGF-β inhibition was able to restore OB differentiation suppressed by MM cell conditioned medium as well as bone marrow plasma from MM patients. Interestingly, TGF-β inhibition expedited OB differentiation in parallel with suppression of MM cell growth. The anti-MM activity was elaborated exclusively by terminally differentiated OBs, which potentiated the cytotoxic effects of melphalan and dexamethasone on MM cells. Furthermore, TGF-β inhibition was able to suppress MM cell growth within the bone marrow while preventing bone destruction in MM-bearing animal models. Conclusions/Significance The present study demonstrates that TGF-β inhibition releases stromal cells from their differentiation arrest by MM and facilitates the formation of terminally differentiated OBs, and that terminally differentiated OBs inhibit MM cell growth and survival and enhance the susceptibility of MM cells to anti-MM agents to overcome the drug resistance mediated by stromal cells. Therefore, TGF-β appears to be an important therapeutic target in MM bone lesions.

The serine/threonine kinase Pim-2 is a novel anti-apoptotic mediator in myeloma cells

Bone marrow stromal cells (BMSCs) and osteoclasts (OCs) confer multiple myeloma (MM) cell survival through elaborating factors. We demonstrate herein that IL-6 and TNF family cytokines, TNFα, BAFF and APRIL, but not IGF-1 cooperatively enhance the expression of the serine/threonine kinase Pim-2 in MM cells. BMSCs and OCs upregulate Pim-2 expression in MM cells largely via the IL-6/STAT3 and NF-κB pathway, respectively. Pim-2 short interfering RNA reduces MM cell viability in cocultures with BMSCs or OCs. Thus, upregulation of Pim-2 appears to be a novel anti-apoptotic mechanism for MM cell survival. Interestingly, the mammalian target of rapamycin inhibitor rapamycin further suppresses the MM cell viability in combination with the Pim-2 silencing. The Pim inhibitor (Z)-5-(4-propoxybenzylidene) thiazolidine-2, 4-dione and the PI3K inhibitor LY294002 cooperatively enhance MM cell death. The Pim inhibitor suppresses 4E-BP1 phosphorylation along with the reduction of Mcl-1 and c-Myc. Pim-2 may therefore become a new target for MM treatment.

Glycolysis Inhibition Inactivates ABC Transporters to Restore Drug Sensitivity in Malignant Cells

Cancer cells eventually acquire drug resistance largely via the aberrant expression of ATP-binding cassette (ABC) transporters, ATP-dependent efflux pumps. Because cancer cells produce ATP mostly through glycolysis, in the present study we explored the effects of inhibiting glycolysis on the ABC transporter function and drug sensitivity of malignant cells. Inhibition of glycolysis by 3-bromopyruvate (3BrPA) suppressed ATP production in malignant cells, and restored the retention of daunorubicin or mitoxantrone in ABC transporter-expressing, RPMI8226 (ABCG2), KG-1 (ABCB1) and HepG2 cells (ABCB1 and ABCG2). Interestingly, although side population (SP) cells isolated from RPMI8226 cells exhibited higher levels of glycolysis with an increased expression of genes involved in the glycolytic pathway, 3BrPA abolished Hoechst 33342 exclusion in SP cells. 3BrPA also disrupted clonogenic capacity in malignant cell lines including RPMI8226, KG-1, and HepG2. Furthermore, 3BrPA restored cytotoxic effects of daunorubicin and doxorubicin on KG-1 and RPMI8226 cells, and markedly suppressed subcutaneous tumor growth in combination with doxorubicin in RPMI8226-implanted mice. These results collectively suggest that the inhibition of glycolysis is able to overcome drug resistance in ABC transporter-expressing malignant cells through the inactivation of ABC transporters and impairment of SP cells with enhanced glycolysis as well as clonogenic cells.

Small molecule antibody targeting HLA class I inhibits myeloma cancer stem cells by repressing pluripotency-associated transcription factors

Cancer stem cells have been proposed to be responsible for tumorigenesis and recurrence in various neoplastic diseases, including multiple myeloma (MM). We have previously reported that MM cells specifically express HLA class I at high levels and that single-chain Fv diabody against this molecule markedly induces MM cell death. Here we investigated the effect of a new diabody (C3B3) on cancer stem cell-like side population (SP) cells. SP fraction of MM cells highly expressed ABCG2 and exhibited resistance to chemotherapeutic agents; however, C3B3 induced cytotoxicity in both SP cells and main population (MP) cells to a similar extent. Moreover, C3B3 suppressed colony formation and tumorigenesis of SP cells in vitro and in vivo. Crosslinking of HLA class I by C3B3 mediated disruption of lipid rafts and actin aggregation, which led to inhibition of gene expression of β-catenin and pluripotency-associated transcription factors such as Sox2, Oct3/4 and Nanog. Conversely, knockdown of Sox2 and Oct3/4 mRNA reduced the proportion of SP cells, suggesting that these factors are essential in maintenance of SP fraction in MM cells. Thus, our findings reveal that immunotherapeutic approach by engineered antibodies can overcome drug resistance, and provide a new basis for development of cancer stem cell-targeted therapy.

Up-regulation of hexokinaseII in myeloma cells: targeting myeloma cells with 3-bromopyruvate.

AbstractsHexokinase II (HKII), a key enzyme of glycolysis, is widely over-expressed in cancer cells. However, HKII levels and its roles in ATP production and ATP-dependent cellular process have not been well studied in hematopoietic malignant cells including multiple myeloma (MM) cells. We demonstrate herein that HKII is constitutively over-expressed in MM cells. 3-bromopyruvate (3BrPA), an inhibitor of HKII, promptly and substantially suppresses ATP production and induces cell death in MM cells. Interestingly, cocultures with osteoclasts (OCs) but not bone marrow stromal cells (BMSCs) enhanced the phosphorylation of Akt along with an increase in HKII levels and lactate production in MM cells. The enhancement of HKII levels and lactate production in MM cells by OCs were mostly abrogated by the PI3K inhibitor LY294002, suggesting activation of glycolysis in MM cells by OCs via the PI3K-Akt-HKII pathway. Although BMSCs and OCs stimulate MM cell growth and survival, 3BrPA induces cell death in MM cells even in cocultures with OCs as well as BMSCs. Furthermore, 3BrPA was able to diminish ATP-dependent ABC transporter activity to restore drug retention in MM cells in the presence of OCs. These results may underpin possible clinical application of 3BrPA in patients with MM.

Delayed treatment with vitamin C and N-acetyl-l-cysteine protects Schwann cells without compromising the anti-myeloma activity of bortezomib

Bortezomib-induced peripheral neuropathy (BIPN) emerges as a disabling adverse effect. As rat models for BIPN have demonstrated damage in nerve Schwann cells, we screened for cytoprotective agents to devise a method of rescuing Schwann cells from the cytotoxic effects of bortezomib without compromising its anti-myeloma effects. Schwann cells underwent macroautophagy along with cytoplasmic inclusion body and vacuole formation, and appeared much less susceptible to bortezomib-induced cytotoxicity than did myeloma cells. Vitamin C or N-acetyl-l-cysteine (NAC) achieved near-complete rescue of Schwann cells treated with bortezomib at 30 nM or less, and these agents in combination are able to cooperatively inhibit the morphological changes and the cytotoxicity in Schwann cells with higher doses of bortezomib. The delayed addition of vitamin C and/or NAC after the exposure to bortezomib alleviated the cytotoxicity in Schwann cells but not myeloma cells. These results suggest that delayed treatment with these agents may be instrumental in prophylaxis of BIPN.

Pim-2 kinase is an important target of treatment for tumor progression and bone loss in myeloma.

Pim-2 kinase is overexpressed in multiple myeloma (MM) cells to enhance their growth and survival, and regarded as a novel therapeutic target in MM. However, the impact of Pim-2 inhibition on bone disease in MM remains unknown. We demonstrated here that Pim-2 expression was also upregulated in bone marrow stromal cells and MC3T3-E1 preosteoblastic cells in the presence of cytokines known as the inhibitors of osteoblastogenesis in MM, including interleukin-3 (IL-3), IL-7, tumor necrosis factor-α, transforming growth factor-β (TGF-β) and activin A, as well as MM cell conditioned media. The enforced expression of Pim-2 abrogated in vitro osteoblastogenesis by BMP-2, which suggested Pim-2 as a negative regulator for osteoblastogenesis. Treatment with Pim-2 short-interference RNA as well as the Pim inhibitor SMI-16a successfully restored osteoblastogenesis suppressed by all the above inhibitory factors and MM cells. The SMI-16a treatment potentiated BMP-2-mediated anabolic signaling while suppressing TGF-β signaling. Furthermore, treatment with the newly synthesized thiazolidine-2,4-dione congener, 12a-OH, as well as its prototypic SMI-16a effectively prevented bone destruction while suppressing MM tumor growth in MM animal models. Thus, Pim-2 may have a pivotal role in tumor progression and bone loss in MM, and Pim-2 inhibition may become an important therapeutic strategy to target the MM cell–bone marrow interaction.

Combination with a Defucosylated Anti-HM1.24 Monoclonal Antibody plus Lenalidomide Induces Marked ADCC against Myeloma Cells and Their Progenitors

The immunomodulatory drug lenalidomide (Len) has drawn attention to potentiate antibody-dependent cellular cytotoxicity (ADCC)-mediated immunotherapies. We developed the defucosylated version (YB-AHM) of humanized monoclonal antibody against HM1.24 (CD317) overexpressed in multiple myeloma (MM) cells. In this study, we evaluated ADCC by YB-AHM and Len in combination against MM cells and their progenitors. YB-AHM was able to selectively kill via ADCC MM cells in bone marrow samples from patients with MM with low effector/target ratios, which was further enhanced by treatment with Len. Interestingly, Len also up-regulated HM1.24 expression on MM cells in an effector-dependent manner. HM1.24 was found to be highly expressed in a drug-resistant clonogenic “side population” in MM cells; and this combinatory treatment successfully reduced SP fractions in RPMI 8226 and KMS-11 cells in the presence of effector cells, and suppressed a clonogenic potential of MM cells in colony-forming assays. Collectively, the present study suggests that YB-AHM and Len in combination may become an effective therapeutic strategy in MM, warranting further study to target drug-resistant MM clonogenic cells.

Association of Th1 and Th2 cytokines with transient inflammatory reaction during lenalidomide plus dexamethasone therapy in multiple myeloma

Transient inflammatory reactions have been reported in a subpopulation of patients with multiple myeloma (MM) during lenalidomide (Len) plus dexamethasone (DEX) therapy. Here, we examined serum levels of Th1 (IL-2 and IFN-γ) and Th2 cytokines (IL-6 and TNF-α) in nine refractory or relapsed MM patients treated with Len plus low-dose DEX. Six patients showed elevation of C-reactive protein (CRP) after the initiation of therapy. In these patients, IFN-γ and IL-6 were also elevated in two and three patients, respectively. The remaining three patients showed no appreciable changes in CRP or these cytokines. Furthermore, Len enhanced the production of both Th1 and Th2 cytokines in normal peripheral blood mononuclear cells and in patient bone marrow mononuclear cells containing primary myeloma cells and lymphocytes. These results suggest that the modulation of the Th1 and Th2 cytokine production by Len may contribute to transient inflammatory reaction in MM patients.

Effective impairment of myeloma cells and their progenitors by blockade of monocarboxylate transportation.

Cancer cells robustly expel lactate produced through enhanced glycolysis via monocarboxylate transporters (MCTs) and maintain alkaline intracellular pH. To develop a novel therapeutic strategy against multiple myeloma (MM), which still remains incurable, we explored the impact of perturbing a metabolism via inhibiting MCTs. All MM cells tested constitutively expressed MCT1 and MCT4, and most expressed MCT2. Lactate export was substantially suppressed to induce death along with lowering intracellular pH in MM cells by blockade of all three MCT molecules with α-cyano-4-hydroxy cinnamate (CHC) or the MCT1 and MCT2 inhibitor AR-C155858 in combination with MCT4 knockdown, although only partially by knockdown of each MCT. CHC lowered intracellular pH and severely curtailed lactate secretion even when combined with metformin, which further lowered intracellular pH and enhanced cytotoxicity. Interestingly, an ambient acidic pH markedly enhanced CHC-mediated cytotoxicity, suggesting preferential targeting of MM cells in acidic MM bone lesions. Furthermore, treatment with CHC suppressed hexokinase II expression and ATP production to reduce side populations and colony formation. Finally, CHC caused downregulation of homing receptor CXCR4 and abrogated SDF-1-induced migration. Targeting tumor metabolism by MCT blockade therefore may become an effective therapeutic option for drug-resistant MM cells with elevated glycolysis.