Shannon M. Matulis

Distribution of Bim determines Mcl-1 dependence or codependence with Bcl-xL/Bcl-2 in Mcl-1-expressing myeloma cells.

Dependence on Bcl-2 proteins is a common feature of cancer cells and provides a therapeutic opportunity. ABT-737 is an antagonist of antiapoptotic Bcl-2 proteins and therefore is a good predictor of Bcl-x(L)/Bcl-2 dependence. Surprisingly, analysis of Mcl-1-dependent multiple myeloma cell lines revealed codependence on Bcl-2/Bcl-x(L) in half the cells tested. Codependence is not predicted by the expression level of antiapoptotic proteins, rather through interactions with Bim. Consistent with these findings, acquired resistance to ABT-737 results in loss of codependence through redistribution of Bim to Mcl-1. Overall, these results suggest that complex interactions, and not simply expression patterns of Bcl-2 proteins, need to be investigated to understand Bcl-2 dependence and how to better use agents, such as ABT-737.

MLN4924, an NAE inhibitor, suppresses AKT and mTOR signaling via upregulation of REDD1 in human myeloma cells

The function and survival of normal and malignant plasma cells depends on the elaborately regulated ubiquitin proteasome system. Proteasome inhibitors such as bortezomib have proved to be highly effective in the treatment of multiple myeloma (MM), and their effects are related to normal protein homeostasis which is critical for plasma cell survival. Many ubiquitin ligases are regulated by conjugation with NEDD8. Therefore, neddylation may also impact survival and proliferation of malignant plasma cells. Here, we show that MLN4924, a potent NEDD8 activating enzyme (NAE) inhibitor, induced cytotoxicity in MM cell lines, and its antitumor effect is associated with suppression of the AKT and mammalian target of rapamycin (mTOR) signaling pathways through increased expression of REDD1. Combining MLN4924 with the proteasome inhibitor bortezomib induces synergistic apoptosis in MM cell lines which can overcome the prosurvival effects of growth factors such as interleukin-6 and insulin-like growth factor-1. Altogether, our findings demonstrate an important function for REDD1 in MLN4924-induced cytotoxicity in MM and also provide a promising therapeutic combination strategy for myeloma.

Darinaparsin Induces a Unique Cellular Response and is Active in an Arsenic Trioxide-Resistant Myeloma Cell Line

Here, we report on the organic arsenical darinaparsin (ZIO-101, S-dimethylarsino-glutathione) and its anti-myeloma activity compared with inorganic arsenic trioxide. Darinaparsin induced apoptosis in multiple myeloma cell lines in a dose-dependent manner, and the addition of N-acetylcysteine, which increases intracellular glutathione (GSH), blocked cytotoxicity of both darinaparsin and arsenic trioxide. In contrast to arsenic trioxide, intracellular GSH does not appear to be important for darinaparsin metabolism, as an inhibitor of GSH synthesis, buthionine sulfoximine, had little effect on drug activity. This discrepancy was resolved when we determined the effects of thiols on drug uptake. The addition of exogenous GSH, l-cysteine, or d-cysteine prevented darinaparsin cellular uptake and cell death but had no effect on the uptake or activity of arsenic trioxide, suggesting a difference in the transport mechanism of these two drugs. In addition, gene expression profiling revealed differences in the signaling of protective responses between darinaparsin and arsenic trioxide. Although both arsenicals induced a transient heat shock response, only arsenic trioxide treatment induced transcription of metal response genes and anti-oxidant genes related to the Nrf2-Keap1 pathway. In contrast to the protective responses, both arsenicals induced up-regulation of BH3-only proteins. Moreover, silencing of BH3-only proteins Noxa, Bim, and Bmf protected myeloma cells from darinaparsin-induced cell death. Finally, treatment of an arsenic trioxide-resistant myeloma cell line with darinaparsin resulted in dose-dependent apoptosis, indicating that cross-resistance does not necessarily develop between these two forms of arsenic in multiple myeloma cell lines. These results suggest darinaparsin may be useful as an alternative treatment in arsenic trioxide-resistant hematologic cancers.[Mol Cancer Ther 2009;8(5):OF1–10]

Dexamethasone treatment promotes Bcl-2 dependence in multiple myeloma resulting in sensitivity to venetoclax

Venetoclax (ABT-199), a specific inhibitor of the anti-apoptotic protein Bcl-2, is currently in phase I clinical trials for multiple myeloma. The results suggest that venetoclax is only active in a small cohort of patients therefore we wanted to determine its efficacy when used in combination. Combining venetoclax with melphalan or carfilzomib produced additive or better cell death in four of the five cell lines tested. The most striking results were seen with dexamethasone (Dex). Co-treatment of human myeloma cell lines and primary patient samples, with Dex and venetoclax, significantly increased cell death over venetoclax alone in four of the five cell lines, and in all patient samples tested. The mechanism by which this occurs is an increase in the expression of both Bcl-2 and Bim upon addition of Dex. This results in alterations in Bim binding to anti-apoptotic proteins. Dex shifts Bim binding towards Bcl-2 resulting in increased sensitivity to venetoclax. These data suggest that knowledge of drug-induced alterations of Bim-binding patterns may help inform better combination drug regimens. Furthermore, the data indicate combining this novel therapeutic with Dex could be an effective therapy for a broader range of patients than would be predicted by single-agent activity.

A MCP1 fusokine with CCR2-specific tumoricidal activity.

BackgroundThe CCL2 chemokine is involved in promoting cancer angiogenesis, proliferation and metastasis by malignancies that express CCR2 receptor. Thus the CCL2/CCR2 axis is an attractive molecular target for anticancer drug development.MethodsWe have generated a novel fusion protein using GMCSF and an N-terminal truncated version of MCP1/CCL2 (6-76) [hereafter GMME1] and investigated its utility as a CCR2-specific tumoricidal agent.ResultsWe found that distinct to full length CCL2 or its N-truncated derivative (CCL2 5-76), GMME1 bound to CCR2 on mouse lymphoma EG7, human multiple myeloma cell line U266, or murine and human medulloblastoma cell lines, and led to their death by apoptosis. We demonstrated that GMME1 specifically blocked CCR2-associated STAT3 phosphorylation and up-regulated pro-apoptotic BAX. Furthermore, GMME1 significantly inhibited EG7 tumor growth in C57BL/6 mice, and induced apoptosis of primary myeloma cells from patients.ConclusionOur data demonstrate that GMME1 is a fusokine with a potent, CCR2 receptor-mediated pro-apoptotic effect on tumor cells and could be exploited as a novel biological therapy for CCR2+ malignancies including lymphoid and central nervous system malignancies.

Determination of multiple human arsenic metabolites employing high performance liquid chromatography inductively coupled plasma mass spectrometry.

During the metabolism of different arsenic-containing compounds in human, a variety of metabolites are produced with significantly varying toxicities. Currently available analytical methods can only detect a limited number of human metabolites in biological samples during one run due to their diverse characteristics. In addition, co-elution of species is often unnoticeable with most detection techniques leading to inaccurate metabolic profiles and assessment of toxicity. A high performance liquid chromatography inductively coupled mass spectrometry (HPLC-ICP-MS) method was developed that can identify thirteen common arsenic metabolites possibly present in human with special attention dedicated to thiolated or thiol conjugated arsenicals. The thirteen species included in this study are arsenite (As(III)), arsino-glutathione (As(GS)3), arsenate (As(V)), monomethylarsonous acid (MMA(III)), monomethylarsino-glutathione (MMA(III)(GS) 2), monomethylarsonic acid (MMA(V)), dimethylarsinous acid (DMA(III) (from DMA(III)I)), S-(dimethylarsinic)cysteine (DMA(III) (Cys)), dimethylarsino-glutathione (DMA(III)(GS)), dimethylarsinic acid (DMA(V)), dimethylmonothioarsinic acid (DMMTA(V)), dimethyldithioarsinic acid (DMDTA(V)), dimethylarsinothioyl glutathione (DMMTA(V)(GS)). The developed method was applied for the analysis of cancer cells that were incubated with darinaparsin (DMA(III)(GS)), a novel chemotherapeutic agent for refractory malignancies, and the arsenic metabolic profile obtained was compared to results using a previously developed method. This method provides a useful analytical tool which is much needed in unequivocally identifying the arsenicals formed during the metabolism of environmental arsenic exposure or therapeutic arsenic administration.

In Silico Modeling-based Identification of Glucose Transporter 4 (GLUT4)-selective Inhibitors for Cancer Therapy.

Background: GLUT4 is a promising target for multiple myeloma therapy. Results: In silico modeling of GLUT4, followed by virtual screening and validation, led to the identification of GLUT4-selective inhibitors. Conclusion: Despite significant homology between GLUT1 and GLUT4, we have identified GLUT4-selective inhibitors exhibiting cytotoxicity in myeloma. Significance: Potent selective GLUT4 inhibitors are promising cancer therapeutics with both cytostatic and chemosensitizing properties warranting further development. Tumor cells rely on elevated glucose consumption and metabolism for survival and proliferation. Glucose transporters mediating glucose entry are key proximal rate-limiting checkpoints. Unlike GLUT1 that is highly expressed in cancer and more ubiquitously expressed in normal tissues, GLUT4 exhibits more limited normal expression profiles. We have previously determined that insulin-responsive GLUT4 is constitutively localized on the plasma membrane of myeloma cells. Consequently, suppression of GLUT4 or inhibition of glucose transport with the HIV protease inhibitor ritonavir elicited growth arrest and/or apoptosis in multiple myeloma. GLUT4 inhibition also caused sensitization to metformin in multiple myeloma and chronic lymphocytic leukemia and a number of solid tumors suggesting the broader therapeutic utility of targeting GLUT4. This study sought to identify selective inhibitors of GLUT4 to develop a more potent cancer chemotherapeutic with fewer potential off-target effects. Recently, the crystal structure of GLUT1 in an inward open conformation was reported. Although this is an important achievement, a full understanding of the structural biology of facilitative glucose transport remains elusive. To date, there is no three-dimensional structure for GLUT4. We have generated a homology model for GLUT4 that we utilized to screen for drug-like compounds from a library of 18 million compounds. Despite 68% homology between GLUT1 and GLUT4, our virtual screen identified two potent compounds that were shown to target GLUT4 preferentially over GLUT1 and block glucose transport. Our results strongly bolster the utility of developing GLUT4-selective inhibitors as anti-cancer therapeutics.

Dimethylarsinothioyl glutathione as a metabolite in human multiple myeloma cell lines upon exposure to Darinaparsin.

Here, we report the identification of dimethylarsinothioyl glutathione (DMMTAV(GS)) as a metabolite in cellular extracts of dimethyarsinous glutathione (Darinaparsin, DMAIII(GS)) treated human multiple myeloma (MM) cell lines. Co-elution of sulfur and arsenic on the inductively coupled plasma mass spectrometer (ICP-MS) indicated the presence of sulfur along with arsenic in the newly observed unidentified molecule on the speciation chromatograms of cell lines treated with DMAIII(GS). Liquid chromatography–electrospray ionization–mass spectrometry of the unknown peak in the MS and tandem MS modes revealed molecular ion peaks at m/z = 443.9 and 466.0, corresponding to [DMMTAV(GS) + H]+ and [DMMTAV(GS) + Na]+, as well as peaks at 314.8 for the loss of glutamic acid and 231.1 for the loss of glycine. In addition, peaks were observed at 176.9 corresponding to cysteine and glycine adducts and at 137.1 for the [C2H6AsS]+ ion. An increase in the peak area of the unidentified peak was observed upon spiking the cell extracts with a standard of DMMTAV(GS). Heat deactivation of MM cells prevented the formation of DMMTAV(GS) raising the possibility of its formation via an enzymatic reaction. Formation studies in DMAIII(GS) treated MM cells revealed the dependence of DMMTAV(GS) formation on the depletion of DMAIII(GS). The presence of 5 mM glutathione prevented its formation, indicating that DMAIII, a dissociation product of DMAIII(GS), is likely a precursor for the formation of DMMTAV(GS). DMMTAV(GS) was observed to form under acidic and neutral pH conditions (pH 3.0–7.4). In addition, DMMTAV(GS) was found to be stable in cell extracts at both acidic and neutral pH conditions. When assessing the toxicity by exposing multiple myeloma cells to arsenicals externally, DMMTAV(GS) was found to be much less toxic than DMAIII(GS) and DMMTAV, potentially due to its limited uptake in the cells (10 and 16% of the uptakes of DMAIII(GS) and DMMTAV, respectively).

Targeting glutamine metabolism in multiple myeloma enhances BIM binding to BCL-2 eliciting synthetic lethality to venetoclax

Multiple myeloma (MM) is a plasma cell malignancy that is largely incurable due to development of resistance to therapy-elicited cell death. Nutrients are intricately connected to maintenance of cellular viability in part by inhibition of apoptosis. We were interested to determine if examination of metabolic regulation of BCL-2 proteins may provide insight on alternative routes to engage apoptosis. MM cells are reliant on glucose and glutamine and withdrawal of either nutrient is associated with varying levels of apoptosis. We and others have demonstrated that glucose maintains levels of key resistance-promoting BCL-2 family member, myeloid cell leukemic factor 1 (MCL-1). Cells continuing to survive in the absence of glucose or glutamine were found to maintain expression of MCL-1 but importantly induce pro-apoptotic BIM expression. One potential mechanism for continued survival despite induction of BIM could be due to binding and sequestration of BIM to alternate pro-survival BCL-2 members. Our investigation revealed that cells surviving glutamine withdrawal in particular, enhance expression and binding of BIM to BCL-2, consequently sensitizing these cells to the BH3 mimetic venetoclax. Glutamine deprivation-driven sensitization to venetoclax can be reversed by metabolic supplementation with TCA cycle intermediate α-ketoglutarate. Inhibition of glucose metabolism with the GLUT4 inhibitor ritonavir elicits variable cytotoxicity in MM that is marginally enhanced with venetoclax treatment, however, targeting glutamine metabolism with 6-diazo-5-oxo-l-norleucine uniformly sensitized MM cell lines and relapse/refractory patient samples to venetoclax. Our studies reveal a potent therapeutic strategy of metabolically driven synthetic lethality involving targeting glutamine metabolism for sensitization to venetoclax in MM.

Discovery and biological characterization of potent myeloid cell leukemia‐1 inhibitors

Myeloid cell leukemia 1 (Mcl‐1) is an antiapoptotic member of the Bcl‐2 family of proteins that when overexpressed is associated with high tumor grade, poor survival, and resistance to chemotherapy. Mcl‐1 is amplified in many human cancers, and knockdown of Mcl‐1 using RNAi can lead to apoptosis. Thus, Mcl‐1 is a promising cancer target. Here, we describe the discovery of picomolar Mcl‐1 inhibitors that cause caspase activation, mitochondrial depolarization, and selective growth inhibition. These compounds represent valuable tools to study the role of Mcl‐1 in cancer and serve as useful starting points for the discovery of clinically useful Mcl‐1 inhibitors.