Homare Eda

Preclinical activity, pharmacodynamic, and pharmacokinetic properties of a selective HDAC6 inhibitor, ACY-1215, in combination with bortezomib in multiple myeloma

Histone deacetylase (HDAC) enzymatic activity has been linked to the transcription of DNA in cancers including multiple myeloma (MM). Therefore, HDAC inhibitors used alone and in combination are being actively studied as novel therapies in MM. In the present study, we investigated the preclinical activity of ACY-1215, an HDAC6-selective inhibitor, alone and in combination with bortezomib in MM. Low doses of ACY-1215 combined with bortezomib triggered synergistic anti-MM activity, resulting in protracted endoplasmic reticulum stress and apoptosis via activation of caspase-3, caspase-8, and caspase-9 and poly (ADP) ribosome polymerase. In vivo, the anti-MM activity of ACY-1215 in combination with bortezomib was confirmed using 2 different xenograft SCID mouse models: human MM injected subcutaneously (the plasmacytoma model) and luciferase-expressing human MM injected intravenously (the disseminated MM model). Tumor growth was significantly delayed and overall survival was significantly prolonged in animals treated with the combination therapy. Pharmacokinetic data showed peak plasma levels of ACY-1215 at 4 hours after treatment coincident with an increase in acetylated α-tubulin, a marker of HDAC6 inhibition, by immunohistochemistry and Western blot analysis. These studies provide preclinical rationale for acetylated α-tubulin use as a pharmacodynamic biomarker in future clinical trials.

In vivo and in vitro effects of a novel anti-Dkk1 neutralizing antibody in multiple myeloma

Over-expression of the protein Dickkopf-1 (Dkk1) has been associated with multiple myeloma bone disease. Previous reports with the use of anti-Dkk1 neutralizing Ab directed strategies have demonstrated a pro-anabolic effect with associated anti-myeloma activity in 2 in vivo mouse models. However new insights on the role of the wnt pathway in osteoclasts (OC) are emerging and the potential effect of a neutralizing Ab to Dkk1 in osteoclastogenesis remains to be elucidated. In order to better define the effect of an anti-Dkk1 neutralizing Ab on osteoclastogenesis and myeloma, we studied a novel anti-Dkk1 monoclonal Ab in our preclinical models. In vivo data confirmed the pro-anabolic and anti-MM effect. In vitro data in part confirmed the in vivo observation, suggesting an indirect anti-MM effect secondary to inhibition of osteoclastogenesis and thus the interaction between MM and bone microenvironment. However, when studies on osteoclastogenesis were extended to samples derived from MM patients, we observed a variable response to anti-Dkk1 treatment without correlation to expression of surface receptors for Dkk1 in OCs suggesting potential heterogeneity in the efficacy of such a strategy. In conclusion, Dkk1 is a promising target for the treatment of both MM and bone disease, and ongoing clinical studies will help elucidate its efficacy.

Ricolinostat (ACY-1215) induced inhibition of aggresome formation accelerates carfilzomib-induced multiple myeloma cell death.

Proteasome inhibition induces the accumulation of aggregated misfolded/ubiquitinated proteins in the aggresome; conversely, histone deacetylase 6 (HDAC6) inhibition blocks aggresome formation. Although this rationale has been the basis of proteasome inhibitor (PI) and HDAC6 inhibitor combination studies, the role of disruption of aggresome formation by HDAC6 inhibition has not yet been studied in multiple myeloma (MM). The present study aimed to evaluate the impact of carfilzomib (CFZ) in combination with a selective HDAC6 inhibitor (ricolinostat) in MM cells with respect to the aggresome‐proteolysis pathway. We observed that combination treatment of CFZ with ricolinostat triggered synergistic anti‐MM effects, even in bortezomib‐resistant cells. Immunofluorescent staining showed that CFZ increased the accumulation of ubiquitinated proteins and protein aggregates in the cytoplasm, as well as the engulfment of aggregated ubiquitinated proteins by autophagosomes, which was blocked by ricolinostat. Electron microscopy imaging showed increased autophagy triggered by CFZ, which was inhibited by the addition of ACY‐1215. Finally, an in vivo mouse xenograft study confirmed a decrease in tumour volume, associated with apoptosis, following treatment with CFZ in combination with ricolinostat. Our results suggest that ricolinostat inhibits aggresome formation, caused by CFZ‐induced inhibition of the proteasome pathway, resulting in enhanced apoptosis in MM cells.

Lenalidomide in combination with an activin A-neutralizing antibody: preclinical rationale for a novel anti-myeloma strategy

Given the prevalence of osteolytic bone disease in multiple myeloma (MM), novel therapies targeting bone microenvironment are essential. Previous studies have identified activin A to be of critical importance in MM-induced osteolysis. Lenalidomide is a known and approved treatment strategy for relapsed MM. Our findings demonstrate that lenalidomide acts directly on bone marrow stromal cells via an Akt-mediated increase in Jun N-terminal kinase-dependent signaling resulting in activin A secretion, with consequent inhibition of osteoblastogenesis. Here, we attempted to augment the antitumor benefits of lenalidomide while overcoming its effects on osteoblastogenesis by combining it with a neutralizing antibody to activin A. Increased activin A secretion induced by lenalidomide was abrogated by the addition of activin A-neutralizing antibody, which effectively restored osteoblast function and inhibited MM-induced osteolysis without negating the cytotoxic effects of lenalidomide on malignant cells. This provides the rationale for an ongoing clinical trial (NCT01562405) combining lenalidomide with an anti-activin A strategy.

Small Molecule Multi-Targeted Kinase Inhibitor RGB-286638 Triggers P53-Dependent and -Independent Anti-Multiple Myeloma Activity through Inhibition of Transcriptional CDKs

Small-molecule multi-targeted cyclin-dependent kinase (CDK) inhibitors (CDKIs) are of particular interest due to their potent antitumor activity independent of p53 gene alterations. P53 deletion is associated with a very poor prognosis in multiple myeloma (MM). In this regard, we tested the anti-MM activity of RGB-286638, an indenopyrazole-derived CDKI with Ki-nanomolar activity against transcriptional CDKs. We examined RGB-286638’s mode-of-action in MM cell lines with wild-type (wt)-p53 and those expressing mutant p53. RGB-286638 treatment resulted in MM cytotoxicity in vitro associated with inhibition of MM tumor growth and prolonged survival in vivo. RGB-286638 displayed caspase-dependent apoptosis in both wt-p53 and mutant-p53 cells that was closely associated with the downregulation of RNA polymerase II phosphorylation and inhibition of transcription. RGB-286638 triggered p53 accumulation via nucleolar stress and loss of Mdm2, accompanied by induction of p53 DNA-binding activity. In addition, RGB-286638 mediated p53-independent activity, which was confirmed by cytotoxicity in p53-knockdown and p53-mutant cells. We also demonstrated downregulation of oncogenic miR-19, miR-92a-1 and miR-21. Our data provide the rationale for the development of transcriptional CDKIs as therapeutic agents, which activate p53 in competent cells, while circumventing p53 deficiency through alternative p53-independent cell death mechanisms in p53-mutant/deleted cells.

Regulation of Sclerostin Expression in Multiple Myeloma by Dkk‐1; A Potential Therapeutic Strategy for Myeloma Bone Disease

Sclerostin is a potent inhibitor of osteoblastogenesis. Interestingly, newly diagnosed multiple myeloma (MM) patients have high levels of circulating sclerostin that correlate with disease stage and fractures. However, the source and impact of sclerostin in MM remains to be defined. Our goal was to determine the role of sclerostin in the biology of MM and its bone microenvironment as well as investigate the effect of targeting sclerostin with a neutralizing antibody (scl‐Ab) in MM bone disease. Here we confirm increased sclerostin levels in MM compared with precursor disease states like monoclonal gammopathy of undetermined significance (MGUS) and smoldering MM. Furthermore, we found that a humanized MM xenograft mouse model bearing human MM cells (NOD‐SCID.CB17 male mice injected intravenously with 2.5 million of MM1.S‐Luc‐GFP cells) demonstrated significantly higher concentrations of mouse‐derived sclerostin, suggesting a microenvironmental source of sclerostin. Associated with the increased sclerostin levels, activated β‐catenin expression levels were lower than normal in MM mouse bone marrow. Importantly, a high‐affinity grade scl‐Ab reversed osteolytic bone disease in this animal model. Because scl‐Ab did not demonstrate significant in vitro anti‐MM activity, we combined it with the proteasome inhibitor carfilzomib. Our data demonstrated that this combination therapy significantly inhibited tumor burden and improved bone disease in our in vivo MM mouse model. In agreement with our in vivo data, sclerostin expression was noted in marrow stromal cells and osteoblasts of MM patient bone marrow samples. Moreover, MM cells stimulated sclerostin expression in immature osteoblasts while inhibiting osteoblast differentiation in vitro. This was in part regulated by Dkk‐1 secreted by MM cells and is a potential mechanism contributing to the osteoblast dysfunction noted in MM. Our data confirm the role of sclerostin as a potential therapeutic target in MM bone disease and provides the rationale for studying scl‐Ab combined with proteasome inhibitors in MM.

A novel Bruton’s tyrosine kinase inhibitor CC-292 in combination with the proteasome inhibitor carfilzomib impacts the bone microenvironment in a multiple myeloma model with resultant antimyeloma activity

Bruton’s tyrosine kinase (Btk) modulates B-cell development and activation and has an important role in antibody production. Interestingly, Btk may also affect human osteoclast (OC) function; however, the mechanism was unknown. Here we studied a potent and specific Btk inhibitor, CC-292, in multiple myeloma (MM). In this report, we demonstrate that, although CC-292 increased OC differentiation, it inhibited OC function via inhibition of c-Src, Pyk2 and cortactin, all involved in OC-sealing zone formation. As CC-292 did not show potent in vitro anti-MM activity, we next evaluated it in combination with the proteasome inhibitor, carfilzomib. We first studied the effect of carfilzomib on OC. Carfilzomib did not have an impact on OC-sealing zone formation but significantly inhibited OC differentiation. CC-292 combined with carfilzomib inhibited both sealing zone formation and OC differentiation, resulting in more profound inhibition of OC function than carfilzomib alone. Moreover, the combination treatment in an in vivo MM mouse model inhibited tumor burden compared with CC-292 alone; it also increased bone volume compared with carfilzomib alone. These results suggest that CC-292 combined with carfilzomib augments the inhibitory effects against OC within the bone microenvironment and has promising therapeutic potential for the treatment of MM and related bone disease.

Delineating the mTOR Kinase Pathway Using a Dual TORC1/2 Inhibitor, AZD8055, in Multiple Myeloma

Despite promising preclinical results with mTOR kinase inhibitors in multiple myeloma, resistance to these drugs may arise via feedback activation loops. This concern is especially true for insulin-like growth factor 1 receptor (IGF1R), because IGF1R signaling is downregulated by multiple AKT and mTOR feedback mechanisms. We have tested this hypothesis in multiple myeloma using the novel selective mTOR kinase inhibitor AZD8055. We evaluated p-mTOR S2481 as the readout for mTORC2/Akt activity in multiple myeloma cells in the context of mTOR inhibition via AZD8055 or rapamycin. We next validated AZD8055 inhibition of mTORC1 and mTORC2 functions in multiple myeloma cells alone or in culture with bone marrow stroma cells and growth factors. Unlike rapamycin, AZD8055 resulted in apoptosis of multiple myeloma cells. AZD8055 treatment, however, induced upregulation of IGF1R phosphorylation in p-Akt S473–expressing multiple myeloma cell lines. Furthermore, exposure of AZD8055-treated cells to IGF1 induced p-Akt S473 and rescued multiple myeloma cells from apoptosis despite mTOR kinase inhibition and TORC2/Akt blockage. The addition of blocking IGF1R antibody resulted in reversing this effect and increased AZD8055-induced apoptosis. Our study suggests that combination treatment with AZD8055 and IGF1R-blocking agents is a promising strategy in multiple myeloma with potential IGF1R/Akt signaling–mediated survival. Mol Cancer Ther; 13(11); 2489–500. ©2014 AACR.

Role of Decorin in Multiple Myeloma (MM) Bone Marrow Microenvironment

Decorin is a small, leucine‐rich proteoglycan found in the extracellular matrix of various connective tissues with potential effective tumor suppressive properties. Recent data suggest low levels of decorin in multiple myeloma (MM) patients compared to healthy volunteers, as well as in patients with osteolytic bone lesions compared to non‐osteolytic lesions. In the present report, we investigated the role of decorin in the MM microenvironment or niche. Our data suggests that decorin is produced by osteoblasts (OBs) but not by MM cells. Furthermore, MM cells decrease OB‐induced decorin secretion and this effect is mediated by CCL3. Importantly, neutralizing CCL3 from MM cells restores decorin levels in OBs as does proteasome inhibitors such as carfilzomib. These findings indicate that decorin may indirectly act as an antagonist to MM cell survival and that the interplay between MM and decorin may be an important target to explore in manipulating the tumor niche to inhibit tumorigenesis.

Preclinical activity of CPI-0610, a novel small-molecule bromodomain and extra-terminal protein inhibitor in the therapy of multiple myeloma

Inhibition of the bromodomain and extra-terminal (BET) proteins is a promising therapeutic strategy for various hematologic cancers. Previous studies suggest that BET inhibitors constrain tumor cell proliferation and survival mainly through the suppression of MYC transcription and activity. However, suppression of the transcription of additional genes also contributes to the antitumor activity of BET inhibitors but is less well understood. Here we examined the therapeutic potential of CPI-0610, a potent BET inhibitor currently undergoing phase I clinical testing, in multiple myeloma (MM). CPI-0610 displays potent cytotoxicity against MM cell lines and patient-derived MM cells through G1 cell cycle arrest and caspase-dependent apoptosis. CPI-0610-mediated BET inhibition overcomes the protective effects conferred by cytokines and bone marrow stromal cells. We also confirmed the in vivo efficacy of CPI-0610 in a MM xenograft mouse model. Our study found IKZF1 and IRF4 to be among the primary targets of CPI-0610, along with MYC. Given that immunomodulatory drugs (IMiDs) stabilize cereblon and facilitate Ikaros degradation in MM cells, we combined it with CPI-0610. Combination studies of CPI-0610 with IMiDs show in vitro synergism, in part due to concomitant suppression of IKZF1, IRF4 and MYC, providing a rationale for clinical testing of this drug combination in MM patients.