Inhibitor of apoptosis proteins as therapeutic targets in multiple myeloma

The novel drug candidate S2/IAPinh improves survival in models of pancreatic and ovarian cancer

Cancer selective apoptosis remains a therapeutic challenge and off-target toxicity has limited enthusiasm for this target clinically. Sigma-2 ligands (S2) have been shown to enhance the cancer selectivity of small molecule drug candidates by improving internalization. Here, we report the synthesis of a novel drug conjugate, which was created by linking a clinically underperforming SMAC mimetic (second mitochondria-derived activator of caspases; LCL161), an inhibitor (antagonist) of inhibitor of apoptosis proteins (IAPinh) with the sigma-2 ligand SW43, resulting in the new chemical entity S2/IAPinh. Drug potency was assessed via cell viability assays across several pancreatic and ovarian cancer cell lines in comparison with the individual components (S2 and IAPinh) as well as their equimolar mixtures (S2 + IAPinh) both in vitro and in preclinical models of pancreatic and ovarian cancer. Mechanistic studies of S2/IAPinh-mediated cell death were investigated in vitro and in vivo using syngeneic and xenograft mouse models of murine pancreatic and human ovarian cancer, respectively. S2/IAPinh demonstrated markedly improved pharmacological activity in cancer cell lines and primary organoid cultures when compared to the controls. In vivo testing demonstrated a marked reduction in tumor growth rates and increased survival rates when compared to the respective control groups. The predicted mechanism of action of S2/IAPinh was confirmed through assessment of apoptosis pathways and demonstrated strong target degradation (cellular inhibitor of apoptosis proteins-1 [cIAP-1]) and activation of caspases 3 and 8. Taken together, S2/IAPinh demonstrated efficacy in models of pancreatic and ovarian cancer, two challenging malignancies in need of novel treatment concepts. Our data support an in-depth investigation into utilizing S2/IAPinh for the treatment of cancer.

Simultaneous XIAP and cIAP1/2 inhibition by a dimeric SMAC mimetic AZD5582 induces apoptosis in multiple myeloma

Overexpression of inhibitor of apoptosis (IAP) proteins is associated with poor prognosis. In multiple myeloma (MM), the IAP inhibitors (IAPi), LCL161, have been evaluated in preclinical and clinical settings but are not fully effective. Among IAPs, XIAP has the strongest anti-apoptotic function with direct binding activity to caspases and cIAP1 and cIAP2 are positive regulator of NF-κB signaling. Prior IAPi such as LCL161 has high affinity to cIAP1 and cIAP2 resulting in inferior inhibiting activity against XIAP. A novel dimeric IAPi, AZD5582 (C58H78N8O8), have high binding potency to XIAP with EC50 dose of 15 nM, enabling to simultaneous inhibit XIAP and cIAP1/2. AZD5582 monotherapy showed cell growth inhibition for all MM cell lines, MM1S, RPMI8226, U266 and KMS-5 and induced apoptosis. AZD5582 further showed anti-proliferation effect under the IL-6 additional condition and inhibited JAK-STAT signaling triggered by IL-6. AZD5582 combined with carfilzomib therapy showed a synergistic effect. Enhanced apoptosis was also observed in combination therapy. Synergistic effect was further observed with other conventional therapeutics. Simultaneous XIAP and cIAP1/2 inhibition by the dimeric IAPi AZD5582 is promising. This study provides a rationale of AZD5582 as a new treatment strategy in monotherapy and in combination therapy.

Quaternary Benzophenanthridine Alkaloids Act as Smac Mimetics and Overcome Resistance to Apoptosis

Defects in cell death signaling pathways are one of the hallmarks of cancer and can lead to resistance to conventional therapy. Natural products are promising compounds that can overcome this resistance. In the present study we studied the effect of six quaternary benzophenanthridine alkaloids (QBAs), sanguinarine, chelerythrine, sanguirubine, chelirubine, sanguilutine, and chelilutine, on Jurkat leukemia cells, WT, and cell death deficient lines derived from them, CASP3/7/6-/- and FADD-/-, and on solid tumor, human malignant melanoma, A375 cells. We demonstrated the ability of QBAs to overcome the resistance of these deficient cells and identified a novel mechanism for their action. Sanguinarine and sanguirubine completely and chelerythrine, sanguilutine, and chelilutine partially overcame the resistance of CASP3/7/6-/- and FADD-/- cells. By detection of cPARP, a marker of apoptosis, and pMLKL, a marker of necroptosis, we proved the ability of QBAs to induce both these cell deaths (bimodal cell death) with apoptosis preceding necroptosis. We identified the new mechanism of the cell death induction by QBAs, the downregulation of the apoptosis inhibitors cIAP1 and cIAP2, i.e., an effect similar to that of Smac mimetics.

LCL161 enhances expansion and survival of engineered anti-tumor T cells but is restricted by death signaling

Background

The genesis of SMAC mimetic drugs is founded on the observation that many cancers amplify IAP proteins to facilitate their survival, and therefore removal of these pathways would re-sensitize the cells towards apoptosis. It has become increasingly clear that SMAC mimetics also interface with the immune system in a modulatory manner. Suppression of IAP function by SMAC mimetics activates the non-canonical NF-κB pathway which can augment T cell function, opening the possibility of using SMAC mimetics to enhance immunotherapeutics.

Methods

We have investigated the SMAC mimetic LCL161, which promotes degradation of cIAP-1 and cIAP-2, as an agent for delivering transient costimulation to engineered BMCA-specific human TAC T cells. In doing so we also sought to understand the cellular and molecular effects of LCL161 on T cell biology.

Results

LCL161 activated the non-canonical NF-κB pathway and enhanced antigen-driven TAC T cell proliferation and survival. Transcriptional profiling from TAC T cells treated with LCL161 revealed differential expression of costimulatory and apoptosis-related proteins, namely CD30 and FAIM3. We hypothesized that regulation of these genes by LCL161 may influence the drug's effects on T cells. We reversed the differential expression through genetic engineering and observed impaired costimulation by LCL161, particularly when CD30 was deleted. While LCL161 can provide a costimulatory signal to TAC T cells following exposure to isolated antigen, we did not observe a similar pattern when TAC T cells were stimulated with myeloma cells expressing the target antigen. We questioned whether FasL expression by myeloma cells may antagonize the costimulatory effects of LCL161. Fas-KO TAC T cells displayed superior expansion following antigen stimulation in the presence of LCL161, suggesting a role for Fas-related T cell death in limiting the magnitude of the T cell response to antigen in the presence of LCL161.

Conclusions

Our results demonstrate that LCL161 provides costimulation to TAC T cells exposed to antigen alone, however LCL161 did not enhance TAC T cell anti-tumor function when challenged with myeloma cells and may be limited due to sensitization of T cells towards Fas-mediated apoptosis.

Chemistries of bifunctional PROTAC degraders

Proteolysis targeting chimeras (PROTACs) technology is a novel and promising therapeutic strategy using small molecules to induce ubiquitin-dependent degradation of proteins. It has received extensive attention from both academia and industry as it can potentially access previously inaccessible targets. However, the design and optimization of PROTACs present big challenges for researchers, and the general strategy for its development and optimization is a lot of trial and error based on experience. This review highlights the important advances in this rapidly growing field and critical limitations of the traditional trial-and-error approach to developing PROTACs by analyzing numerous representative examples of PROTACs development. We summarize and analyze the general principles and strategies for PROTACs design and optimization from the perspective of chemical structure design, and propose potential future pathways to facilitate the development of PROTACs.

BRCA mutations lead to XIAP overexpression and sensitise ovarian cancer to inhibitor of apoptosis (IAP) family inhibitors

Background

We tested the hypothesis that inhibitor of apoptosis family (IAP) proteins may be altered in BRCA1-mutated ovarian cancers and that could affect the sensitivity to IAP inhibitors.

Methods

The levels of IAP proteins were evaluated in human cancers and cell lines. Cell lines were used to determine the effects of IAP inhibitors. The in vivo effects of treatments were evaluated in PDX mouse models.

Results

Expression of X-linked inhibitor of apoptosis (XIAP) is increased in BRCA1-mutated cancers and high levels are associated with improved patient outcomes after platinum chemotherapy. XIAP overexpression is mediated by NF-kB activation and is associated with an optimisation of PARP. BRCA1-mutated cell lines are particularly sensitive to IAP inhibitors due to an inhibitory effect on PARP. Both a BRCA1-mutated cell line with acquired resistance to PARP inhibitors and one with restored BRCA1 remain sensitive to IAP inhibitors. Treatment with IAP inhibitors restores the efficacy of PARP inhibition in these cell lines. The IAP inhibitor LCL161 alone and in combination with a PARP inhibitor, exhibited antitumour effects in PDX mouse models of resistant BRCA2 and 1-mutated ovarian cancer, respectively.

Conclusion

A clinical trial may be justified to further investigate the utility of IAP inhibitors.

1H, 13C and 15N resonance assignments of the first BIR domain of cellular inhibitor of apoptosis protein 1

Cellular inhibitor of apoptosis protein-1 (cIAP-1) is member of inhibitor of apoptosis proteins (IAPs) which can affect apoptosis through interactions with caspases. cIAP-1 is a multi-domain protein and able to regulate apoptosis through interactions with proteins such as caspases and possesses E3 ligase activity. Human cIAP-1 contains three baculovirus IAP repeat (BIR) domains which are critical for protein-protein interactions. Here, we report NMR resonance assignments of the first BIR domain of human cIAP. Its secondary structures in solution were determined based on the assigned resonances. The dynamics of this domain was obtained, and our hydrogen-deuterium exchange experiment reveals that the first helix in BIR1 is exposed to the solvent. The availability of assignments of backbone and side chain resonances will be useful for probing protein-protein interactions.

The combination of TRAIL and the Smac mimetic LCL-161 induces an irreversible phenotypic change of MCF-7 breast cancer cells

BACKGROUND

Breast cancer is the most common malignancy affecting women. Although the prognosis generally is good, a substantial number of patients still suffer from relapse, emphasizing the need for novel treatments. Smac mimetics were developed to facilitate cell death by blocking inhibitor of apoptosis proteins (IAPs). It has been suggested that TNF-related apoptosis inducing ligand (TRAIL) can be used together with Smac mimetics to induce cancer cell death.

METHODS

Cell viability was studied with Trypan blue staining and Annexin V assay, siRNA was used to downregulate specific proteins, protein levels were estimated with Western blot, and mRNA levels were analyzed with qPCR, microarray and RNA-seq. For global expression, groups were compared with principal component analysis and the limma package in R. Gene enrichment was analyzed with Fisher's test. For other experiments, significance of difference was tested by one-way ANOVA, followed by Tukey's HSD test.

RESULTS

The combination of Smac mimetic LCL-161 and TRAIL induces an irreversible change in phenotype, but not cell death, of luminal MCF-7 breast cancer cells. The cells become small and circular and dissociate from each other and the effect could not be reversed by returning the cells to regular growth medium. The morphology change could be prevented by caspase inhibition using z-VAD-FMK and downregulation of caspase-8. Caspase-7 is also indicated to be of importance since downregulation of this caspase resulted in fewer morphologically changed cells. Enrichment analyses of changes in global gene expression demonstrated that genes associated with estrogen receptor (ER) signaling are downregulated, whereas nuclear factor kappa B- (NF-κB) and interferon- (IFN) driven genes are upregulated in altered cells. However, inhibition of these pathways did not influence the change in morphology. Induction of IFN-induced genes were potentiated but NF-ĸB-driven genes were slightly suppressed by caspase inhibition.

CONCLUSIONS

The results demonstrate that LCL-161 and TRAIL can irreversibly alter the MCF-7 breast cancer cell phenotype. However, the changes in morphology and global gene expression are mediated via separate pathways.

IAP and HDAC inhibitors interact synergistically in myeloma cells through noncanonical NF-κB- and caspase-8-dependent mechanisms

Interactions between the inhibitor of apoptosis protein antagonist LCL161 and the histone deacetylase inhibitor panobinostat (LBH589) were examined in human multiple myeloma (MM) cells. LCL161 and panobinostat interacted synergistically to induce apoptosis in diverse MM cell lines, including those resistant to bortezomib (PS-R). Similar interactions were observed with other histone deacetylase inhibitors (MS-275) or inhibitors of apoptosis protein antagonists (birinapant). These events were associated with downregulation of the noncanonical (but not the canonical) NF-κB pathway and activation of the extrinsic, caspase-8-related apoptotic cascade. Coexposure of MM cells to LCL161/LBH589 induced TRAF3 upregulation and led to TRAF2 and NIK downregulation, diminished expression of BCL-XL, and induction of γH2A.X. Ectopic expression of TRAF2, NIK, or BCL-XL, or short hairpin RNA TRAF3 knock-down, significantly reduced LCL161/LBH589 lethality, as did ectopic expression of dominant-negative FADD. Stromal/microenvironmental factors failed to diminish LCL161/LBH589-induced cell death. The LCL161/LBH589 regimen significantly increased cell killing in primary CD138+ cells (N = 31) and was particularly effective in diminishing the primitive progenitor cell-enriched CD138-/19+/20+/27+ population (N = 23) but was nontoxic to normal CD34+ cells. Finally, combined LCL161/LBH589 treatment significantly increased survival compared with single-agent treatment in an immunocompetent 5TGM1 murine MM model. Together, these findings argue that LCL161 interacts synergistically with LBH589 in MM cells through a process involving inactivation of the noncanonical NF-κB pathway and activation of the extrinsic apoptotic pathway, upregulation of TRAF3, and downregulation of TRAF2/BCL-XL. Notably, this regimen overcomes various forms of resistance, is active against primary MM cells, and displays significant in vivo activity. This strategy warrants further consideration in MM.

Final results of a phase 2 clinical trial of LCL161, an oral SMAC mimetic for patients with myelofibrosis

Outcomes in patients with high-risk and treatment-resistant myelofibrosis (MF) post-JAK inhibitor therapy remain poor, with no approved drug therapies beyond the JAK inhibitor class. In certain clinical situations, such as severe thrombocytopenia, administration of most JAK inhibitors are contraindicated. Thus, there is an unmet medical need for the development of novel agents for patients with MF. SMAC mimetics [or inhibitor of apoptosis (IAP) antagonists] induce apoptosis in cancer cells. Because these agents are hypothesized to have increased activity in a tumor necrosis factor-α cytokine-rich microenvironment, as is the case with MF, we conducted a single-center, investigator-initiated phase 2 clinical trial, with a monovalent SMAC mimetic LCL161 (oral, starting dose, 1500 mg per week) in patients with intermediate to high-risk MF. In an older group, 66% with ≥2 prior therapies and a median baseline platelet count of 52 × 103/μL and 28% with ASXL1 mutations, we observed a 30% objective response by Revised International Working Group-Myeloproliferative Neoplasms Research and Treatment (IWG-MRT) 2013 criteria. Notably, 6 responding patients achieved clinical improvement of anemia: 4, hemoglobin response; 2, transfusion independence. Median OS was 34 months (range, 2.2-60.1+). Reductions of cIAPs were observed in all responders. The most common toxicity was nausea/vomiting (N/V) in 64% (mostly grade 1/2); fatigue in 46%; and dizziness/vertigo in 30%. There were 4 grade 3/4 adverse events (2, syncope; 1, N/V; 1, skin eruption/pruritis). There were 2 deaths during the study period, both unrelated to the study drug. SMAC mimetics may represent an option for older patients with thrombocytopenia or for those in whom prior JAK inhibitors has failed. This trial was registered at www.clinicaltrials.gov as #NCT02098161.

Proteomic Level Changes on Treatment in MCF-7/DDP Breast Cancer Drug- Resistant Cells

Background

LCL161, a SMAC’S small molecule mimetic, can bind to a variety of IAPs and activate Caspases. We found that on its own, LCL161induces apoptosis of drug-resistant breast cancer cells by binding to a variety of IAPs and activating Caspases. However, when LCL161 is used in combination with Caspase Inhibitors (CI), its capacity to induce apoptosis of breast cancer cells is enhanced.

Objective

To carry out proteomic and bioinformatics analysis of LCL161 in combination with CI. We aim to identify the key proteins and mechanisms of breast cancer drug-resistant apoptosis, thereby aiding in the breast cancer drug resistance treatment and identification of drug targeting markers.

Methods

Cell culture experiments were carried out to explore the effect of LCL161 combined with CI on the proliferation of breast cancer drug-resistant cells. Proteomic analysis was carried out to determine the protein expression differences between breast cancer drug-resistant cells and LCL161 combined with CI treated cells. Bioinformatics analysis was carried out to determine its mechanism of action. Validation of proteomics results was done using Parallel Reaction Monitoring (PRM).

Results

Cell culture experiments showed that LCL161 in combination with CI can significantly promote the apoptosis of breast cancer drug-resistant cells. Up-regulation of 92 proteins and down-regulation of 114 proteins protein were noted, of which 4 were selected for further validation.

Conclusion

Our results show that LCL161 combined with CI can promote the apoptosis of drug-resistant breast cancer cells by down-regulation of RRM2, CDK4, and ITGB1 expression through Cancer pathways, p53 or PI3K-AKT signaling pathway. In addition, the expression of CDK4, RRM2, and CDC20 can be down-regulated by the nuclear receptor pathway to affect DNA transcription and replication, thereby promoting apoptosis of breast cancer drug-resistant cells.

An Updated Review of Smac Mimetics, LCL161, Birinapant, and GDC-0152 in Cancer Treatment

Inhibitor of apoptosis proteins (IAPs) are suggested as therapeutic targets for cancer treatment. Smac/DIABLO is a natural IAP antagonist in cells; therefore, Smac mimetics have been developed for cancer treatment in the past decade. In this article, we review the anti-cancer potency and novel molecular targets of LCL161, birinapant, and GDC-0152. Preclinical studies demonstrated that Smac mimetics not only induce apoptosis but also arrest cell cycle, induce necroptosis, and induce immune storm in vitro and in vivo. The safety and tolerance of Smac mimetics are evaluated in phase 1 and phase 2 clinical trials. In addition, the combination of Smac mimetics and chemotherapeutic compounds was reported to improve anti-cancer effects. Interestingly, the novel anti-cancer molecular mechanism of action of Smac mimetics was reported in recent studies, suggesting that many unknown functions of Smac mimetics still need to be revealed. Exploring these currently unknown signaling pathways is important to provide hints for the modification and combination therapy of further compounds.

Potency and Selectivity of SMAC/DIABLO Mimetics in Solid Tumor Therapy

Aiming to promote cancer cell apoptosis is a mainstream strategy of cancer therapy. The second mitochondria-derived activator of caspase (SMAC)/direct inhibitor of apoptosis protein (IAP)-binding protein with low pI (DIABLO) protein is an essential and endogenous antagonist of inhibitor of apoptosis proteins (IAPs). SMAC mimetics (SMs) are a series of synthetically chemical compounds. Via database analysis and literature searching, we summarize the potential mechanisms of endogenous SMAC inefficiency, degradation, mutation, releasing blockage, and depression. We review the development of SMs, as well as preclinical and clinical outcomes of SMs in solid tumor treatment, and we analyze their strengths, weaknesses, opportunities, and threats from our point of view. We also highlight several questions in need of further investigation.

Future Therapeutic Directions for Smac-Mimetics

It is well accepted that the ability of cancer cells to circumvent the cell death program that untransformed cells are subject to helps promote tumor growth. Strategies designed to reinstate the cell death program in cancer cells have therefore been investigated for decades. Overexpression of members of the Inhibitor of APoptosis (IAP) protein family is one possible mechanism hindering the death of cancer cells. To promote cell death, drugs that mimic natural IAP antagonists, such as second mitochondria-derived activator of caspases (Smac/DIABLO) were developed. Smac-Mimetics (SMs) have entered clinical trials for hematological and solid cancers, unfortunately with variable and limited results so far. This review explores the use of SMs for the treatment of cancer, their potential to synergize with up-coming treatments and, finally, discusses the challenges and optimism facing this strategy.

The Immuno-Modulatory Effects of Inhibitor of Apoptosis Protein Antagonists in Cancer Immunotherapy

One of the hallmarks of cancer cells is their ability to evade cell death via apoptosis. The inhibitor of apoptosis proteins (IAPs) are a family of proteins that act to promote cell survival. For this reason, upregulation of IAPs is associated with a number of cancer types as a mechanism of resistance to cell death and chemotherapy. As such, IAPs are considered a promising therapeutic target for cancer treatment, based on the role of IAPs in resistance to apoptosis, tumour progression and poor patient prognosis. The mitochondrial protein smac (second mitochondrial activator of caspases), is an endogenous inhibitor of IAPs, and several small molecule mimetics of smac (smac-mimetics) have been developed in order to antagonise IAPs in cancer cells and restore sensitivity to apoptotic stimuli. However, recent studies have revealed that smac-mimetics have broader effects than was first attributed. It is now understood that they are key regulators of innate immune signalling and have wide reaching immuno-modulatory properties. As such, they are ideal candidates for immunotherapy combinations. Pre-clinically, successful combination therapies incorporating smac-mimetics and oncolytic viruses, as with chimeric antigen receptor (CAR) T cell therapy, have been reported, and clinical trials incorporating smac-mimetics and immune checkpoint blockade are ongoing. Here, the potential of IAP antagonism to enhance immunotherapy strategies for the treatment of cancer will be discussed.

Modulation of Respiration and Mitochondrial Dynamics by SMAC-Mimetics for Combination Therapy in Chemoresistant Cancer

Inhibitor of apoptosis proteins (IAP) are cell death regulators that bind caspases and interfere with apoptotic signalling via death receptors or intrinsic cell death pathways. BIRC4/XIAP is the most potent anti-apoptotic IAP-member and it physically interacts with caspases via its BIR2 and its BIR3 domain. These domains are also critical for the interaction with mitochondria-derived SMAC/Diablo and with the IAP protein survivin. Survivin is frequently overexpressed in neuroblastoma due to a gain of 17q and we have demonstrated that survivin confers resistance to chemotherapeutic agents and reprograms metabolism of neuroblastoma cells towards glycolysis. As regulator of mitochondrial fission and autophagy survivin acts at the crossroads of mitochondrial architecture, autophagy and cellular energy metabolism.

Methods: We tested the effect of SMAC-mimetics on the XIAP/survivin axis as modulator of cellular metabolism analysing mitochondrial morphology, metabolic intermediates and cellular survival. Finally, the impact of the combined treatment was evaluated in a xenograft neuroblastoma mouse model assessing the therapy effect on tumour size and volume.

Results: Here we demonstrated that XIAP sequesters significant amounts of survivin within the cell that can be mobilized by so called SMAC-mimetics. SMAC-mimetics are drugs that are designed to bind with high affinity to XIAP-BIR2 / BIR3 domains to release caspases and re-sensitize XIAP-overexpressing tumors for chemotherapy. However, SMAC-mimetic treatment releases also survivin from XIAP and thereby induces mitochondrial fragmentation, prevents ROS accumulation and leads to the Warburg effect, an unwanted side effect of this therapy. Importantly, cells that drift into a highly glycolytic state due to SMAC-mimetic treatment become also highly sensitive to non-genotoxic treatment with glycolysis inhibitors such as 2-Deoxy-D-glucose (2DG) in vitro and in vivo.

Conclusion: A combinational therapy of non-genotoxic SMAC-mimetics and glycolysis-inhibitors overcomes IAP-mediated cell survival in cancer and provides therefore an attractive usage of SMAC-mimetics.

STAT3: A Promising Therapeutic Target in Multiple Myeloma

Multiple myeloma (MM) is an incurable plasma cell malignancy for which novel treatment options are required. Signal Transducer and Activator of Transcription 3 (STAT3) overexpression in MM appears to be mediated by a variety of factors including interleukin-6 signaling and downregulation of Src homology phosphatase-1 (SHP-1). STAT3 overexpression in MM is associated with an adverse prognosis and may play a role in microenvironment-dependent treatment resistance. In addition to its pro-proliferative role, STAT3 upregulates anti-apoptotic proteins and leads to microRNA dysregulation in MM. Phosphatase of regenerating liver 3 (PRL-3) is an oncogenic phosphatase which is upregulated by STAT3. PRL-3 itself promotes STAT-3 phosphorylation resulting in a positive feedback loop. PRL-3 is overexpressed in a subset of MM patients and may cooperate with STAT3 to promote survival of MM cells. Indirectly targeting STAT3 via JAK (janus associated kinase) inhibition has shown promise in early clinical trials. Specific inhibitors of STAT3 showed in vitro efficacy but have failed in clinical trials while several STAT3 inhibitors derived from herbs have been shown to induce apoptosis of MM cells in vitro. Optimising the pharmacokinetic profiles of novel STAT3 inhibitors and identifying how best to combine these agents with existing anti-myeloma therapy are key questions to be addressed in future clinical trials.

SM‑164 enhances the antitumor activity of adriamycin in human U2‑OS cells via downregulation of X‑linked inhibitor of apoptosis protein

The antitumor effects of SM‑164 and adriamycin (ADM) on human osteosarcoma U2‑OS cells, the underlying mechanism are yet to be investigated. In the present study, U2‑OS cells were divided into control, ADM, SM‑164, and ADM + SM‑164 groups. In addition, cells treated with both SM‑164 and ADM were further divided into three subgroups: SM‑164 + ADM, SM‑164 + ADM + vector and SM‑164 + ADM + X‑linked inhibitor of apoptosis protein (XIAP) silencing groups. XIAP expression was achieved via transfection with shRNA lentiviral vectors. Reverse transcription‑quantitative polymerase chain reaction and western blotting were used to detect the expression of caspases‑7, ‑9, and ‑3, poly ADP‑ribose polymerase (PARP), XIAP, cellular inhibitor of apoptosis protein‑1 (cIAP‑1) and survivin. Cell viability and apoptosis were evaluated using MTT and flow cytometry assays, respectively. Compared with the control group, cell viability decreased, while apoptosis was increased in the ADM and SM‑164‑treatment group. ADM and SM‑164 treatment promoted the expression of caspases‑7, ‑9 and ‑3, and PARP, but reduced the expression of XIAP, survivin and cIAP‑1. Compared with ADM + SM‑164 group, XIAP silencing with ADM + SM‑164 treatment further reduced cell viability, promoted apoptosis, increased caspase‑7, ‑9 and ‑3, and PARP expression; however the expression of survivin and cIAP‑1 were reduced. Combined ADM and SM‑164 treatment may be considered as potential therapeutic agent in the treatment of osteosarcoma, possibly via reductions XIAP expression.

Sanguinarine Induces Apoptosis Pathway in Multiple Myeloma Cell Lines via Inhibition of the JaK2/STAT3 Signaling

Sanguinarine (SNG), a benzophenanthridine alkaloid, has displayed various anticancer abilities in several vivo and in vitro studies. However, the anticancer potential of SNG is yet to be established in multiple myeloma (MM), a mostly incurable malignancy of plasma cells. In this study, we aimed to investigate the potential anti-proliferative and pro-apoptotic activities of SNG in a panel of MM cell lines (U266, IM9, MM1S, and RPMI-8226). SNG treatment of MM cells resulted in a dose-dependent decrease in cell viability through mitochondrial membrane potential loss and activation of caspase 3, 9, and cleavage of PARP. Pre-treatment of MM cells with a universal caspase inhibitor, Z-VAD-FMK, prevented SNG mediated loss of cell viability, apoptosis, and caspase activation, confirming that SNG-mediated apoptosis is caspase-dependent. The SNG-mediated apoptosis appears to be resulted from suppression of the constitutively active STAT3 with a concomitant increase in expression of protein tyrosine phosphatase (SHP-1). SNG treatment of MM cells leads to down-regulation of the anti-apoptotic proteins including cyclin D, Bcl-2, Bclxl, and XIAP. In addition, it also upregulates pro-apoptotic protein, Bax. SNG mediated cellular DNA damage in MM cell lines by induction of oxidative stress through the generation of reactive oxygen species and depletion of glutathione. Finally, the subtoxic concentration of SNG enhanced the cytotoxic effects of anticancer drugs bortezomib (BTZ) by suppressing the viability of MM cells via induction of caspase-mediated apoptosis. Altogether our findings demonstrate that SNG induces mitochondrial and caspase-dependent apoptosis, generates oxidative stress, and suppresses MM cell lines proliferation. In addition, co-treatment of MM cell lines with sub-toxic doses of SNG and BTZ potentiated the cytotoxic activity. These results would suggest that SNG could be developed into therapeutic agent either alone or in combination with other anticancer drugs in MM.

Aurora kinase and FGFR3 inhibition results in significant apoptosis in molecular subgroups of multiple myeloma

Aberrant expression of proteins involved in cell division is a constant feature in multiple myeloma (MM), especially in high-risk disease. Increasingly, therapy of myeloma is moving towards individualization based on underlying genetic abnormalities. Aurora kinases are important mediators of cell cycle and are up regulated in MM. Functional loss of Aurora kinases results in genetic instability and dysregulated division leading to cellular aneuploidy and growth arrest. We investigated the role of Aurora kinase inhibition in MM, using a small molecule inhibitor A1014907. Low nanomolar A1014907 concentrations induced aneuploidy in MM cell lines independent of underlying cytogenetic abnormalities by inhibiting Aurora Kinases. However, A1014907 induced more pronounced and dose dependent apoptosis in cell lines with t(4;14) translocation. Translocation t(4;14) is observed in about 15% of patients with MM leading to constitutive activation of FGFR3 in two-thirds of these patients. Further investigation of the mechanism of action of A1014907 revealed potent FGFR3 pathway inhibition only in the sensitive cell lines. Thus, our results show that aurora kinase inhibition causes cell cycle arrest and aneuploidy with minimal apoptosis whereas inhibiting both aurora kinase and FGFR3 activity induced potent apoptosis in MM cells. These results support clinical evaluation of A1014907 in MM patients with t(4;14) translocation and/or FGFR3 expression.

Inhibitors of apoptosis: clinical implications in cancer

Inhibitor of apoptosis (IAP) family comprises a group of endogenous proteins that function as main regulators of caspase activity and cell death. They are considered the main culprits in evasion of apoptosis, which is a fundamental hallmark of carcinogenesis. Overexpression of IAP proteins has been documented in various solid and hematological malignancies, rendering them resistant to standard chemotherapeutics and radiation therapy and conferring poor prognosis. This observation has urged their exploitation as therapeutic targets in cancer with promising pre-clinical outcomes. This review describes the structural and functional features of IAP proteins to elucidate the mechanism of their anti-apoptotic activity. We also provide an update on patterns of IAP expression in different tumors, their impact on treatment response and prognosis, as well as the emerging investigational drugs targeting them. This aims at shedding the light on the advances in IAP targeting achieved to date, and encourage further development of clinically applicable therapeutic approaches.

Design of Potent pan-IAP and Lys-Covalent XIAP Selective Inhibitors Using a Thermodynamics Driven Approach

Recently we reported that rapid determination of enthalpy of binding can be achieved for a large number of congeneric agents or in combinatorial libraries fairly efficiently. We show that using a thermodynamic Craig plot can be very useful in dissecting the enthalpy and entropy contribution of different substituents on a common scaffold, in order to design potent, selective, or pan-active compounds. In our implementation, the approach identified a critical Lys residue in the BIR3 domain of XIAP. We report for the first time that it is possible to target such residue covalently to attain potent and selective agents. Preliminary cellular studies in various models of leukemia, multiple myeloma, and pancreatic cancers suggest that the derived agents possess a potentially intriguing pattern of activity, especially for cell lines that are resistant to the pan-IAP antagonist and clinical candidate LCL161.

Single agent and synergistic combinatorial efficacy of first-in-class small molecule imipridone ONC201 in hematological malignancies

ONC201, founding member of the imipridone class of small molecules, is currently being evaluated in advancer cancer clinical trials. We explored single agent and combinatorial efficacy of ONC201 in preclinical models of hematological malignancies. ONC201 demonstrated (GI50 1-8 µM) dose- and time-dependent efficacy in acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), chronic myelogenous leukemia (CML), chronic lymphocytic leukemia (CLL), diffuse large B-cell lymphoma (DLBCL), mantle cell lymphoma (MCL), Burkitt's lymphoma, anaplastic large cell lymphoma (ALCL), cutaneous T-cell lymphoma (CTCL), Hodgkin's lymphoma (nodular sclerosis) and multiple myeloma (MM) cell lines including cells resistant to standard of care (dexamethasone in MM) and primary samples. ONC201 induced caspase-dependent apoptosis that involved activation of the integrated stress response (ATF4/CHOP) pathway, inhibition of Akt phosphorylation, Foxo3a activation, downregulation of cyclin D1, IAP and Bcl-2 family members. ONC201 synergistically reduced cell viability in combination with cytarabine and 5-azacytidine in AML cells. ONC201 combined with cytarabine in a Burkitt's lymphoma xenograft model induced tumor growth inhibition that was superior to either agent alone. ONC201 synergistically combined with bortezomib in MM, MCL and ALCL cells and with ixazomib or dexamethasone in MM cells. ONC201 combined with bortezomib in a Burkitt's lymphoma xenograft model reduced tumor cell density and improved CHOP induction compared to either agent alone. These results serve as a rationale for ONC201 single-agent trials in relapsed/refractory acute leukemia, non-Hodgkin's lymphoma, MM and combination trial with dexamethasone in MM, provide pharmacodynamic biomarkers and identify further synergistic combinatorial regimens that can be explored in the clinic.

Kaempferol mitigates Endoplasmic Reticulum Stress Induced Cell Death by targeting caspase 3/7

The Endoplasmic Reticulum (ER) plays a fundamental role in executing multiple cellular processes required for normal cellular function. Accumulation of misfolded/unfolded proteins in the ER triggers ER stress which contributes to progression of multiple diseases including neurodegenerative disorders. Recent reports have shown that ER stress inhibition could provide positive response against neuronal injury, ischemia and obesity in in vivo models. Our search towards finding an ER stress inhibitor has led to the functional discovery of kaempferol, a phytoestrogen possessing ER stress inhibitory activity in cultured mammalian cells. We have shown that kaempferol pre-incubation significantly inhibits the expression of GRP78 (a chaperone) and CHOP (ER stress associated pro-apoptotic transcription factor) under stressed condition. Also, our investigation in the inhibitory specificity of kaempferol has revealed that it inhibits cell death induced by diverse stimuli. Further study on exploring the molecular mechanism implied that kaempferol renders protection by targeting caspases. Both the in silico docking and in vitro assay using recombinant caspase-3 enzyme confirmed the binding of kaempferol to caspases, through an allosteric mode of competitive inhibition. Altogether, we have demonstrated the ability of kaempferol to alleviate ER stress in in vitro model.

Smac mimetic LCL161 overcomes protective ER stress induced by obatoclax, synergistically causing cell death in multiple myeloma

Bcl2 and IAP families are anti-apoptotic proteins deregulated in multiple myeloma (MM) cells. Pharmacological inhibition of each of these families has shown significant activity only in subgroups of MM patients. Here, we have examined a broad-spectrum Bcl2 family inhibitor Obatoclax (OBX) in combination with a Smac mimetic LCL161 in MM cell lines and patient cells. LCL161/OBX combination induced synergistic cytotoxicity and anti-proliferative effects on a broad range of human MM cell lines. The cytotoxicity was mediated through inhibition of the IAPs, activation of caspases and up regulation of the pro-apoptotic proteins Bid, Bim, Puma and Noxa by the drug combination. In addition, we observed that OBX caused ER stress and activated the Unfolded Protein Response (UPR) leading to drug resistance. LCL161, however inhibited spliced Xbp-1, a pro-survival factor. In addition, we observed that OBX increased GRP78 localization to the cell surface, which then induced PI3K dependent Akt activation and resistance to cell death. LCL161 was able to block OBX induced Akt activation contributing to synergistic cell death. Our results support clinical evaluation of this combination strategy in relapsed refractory MM patients.

Signaling Pathways and Emerging Therapies in Multiple Myeloma

Multiple myeloma (MM) is a devastating malignancy of antibody-producing plasma cells. In the absence of a single unifying genetic event contributing to disease manifestation, efforts have focused on understanding signaling events deregulated in myeloma plasma cells. MM cells are dependent on both cellular and non-cellular components of the tumor microenvironment such as bone marrow stromal cells, endothelial cells, and cytokines such as interleukin 6 (IL6), vascular endothelial growth factor (VEGF), and insulin-like growth factor (IGF) for their growth and survival. The cumulative effect of such interactions is the aberrant activation of numerous signal transduction pathways within the MM plasma cells leading to uncontrolled growth and prevention of apoptosis. Here, we will review our current understanding of some of the key signal transduction pathways dysregulated in MM and emerging therapies targeting these pathways in MM.

Overexpression of RKIP and its cross-talk with several regulatory gene products in multiple myeloma

Multiple myeloma (MM) is a clonal plasma-cell neoplastic disorder arising from an indolent premalignant disease known as monoclonal gammopathy of undetermined significance (MGUS). MM is a biologically complex heterogeneous disease reflected by its variable clinical responses of patients receiving the same treatment. Therefore, a molecular identification of stage-specific biomarkers will support a more individualized precise diagnostic/prognostic approach, an effective therapeutic regime, and will assist in the identification of novel therapeutic molecular targets. The metastatic suppressor/anti-resistance factor Raf-1 kinase inhibitor protein (RKIP) is poorly expressed in the majority of cancers and is often almost absent in metastatic tumors. RKIP inhibits the Raf/MEK/ERK1/2 and the NF-κB pathways. Whereby all tumors examined exhibited low levels of RKIP, in contrast, our recent findings demonstrated that RKIP is overexpressed primarily in its inactive phosphorylated form in MM cell lines and patient-derived tumor tissues. The underlying mechanism of RKIP overexpression in MM, in contrast to other tumors, is not known. We examined transcriptomic datasets on Oncomine platform (Life Technologies) for the co-expression of RKIP and other gene products in both pre-MM and MM. The transcription of several gene products was found to be either commonly overexpressed (i.e., RKIP, Bcl-2, and DR5) or underexpressed (i.e., Bcl-6 and TNFR2) in both pre-MM and MM. Noteworthy, a significant inverse correlation of differentially expressed pro-apoptotic genes was observed in pre-MM: overexpression of Fas and TNF-α and underexpression of YY1 versus expression of anti-apoptotic genes in MM: overexpression of YY1 and underexpression of Fas and TNF-α. Based on the analysis on mRNA levels and reported studies on protein levels of the above various genes, we have constructed various schemes that illustrate the possible cross-talks between RKIP (active/inactive) and the identified gene products that underlie the mechanism of RKIP overexpression in MM. Clearly, such cross-talks would need to be experimentally validated in both MM cell lines and patient-derived tumor tissues. If validated, the differential molecular signatures between pre-MM and MM might lead to a more precise diagnosis/prognosis of the disease and disease stages and will also identify novel molecular therapeutic targets for pre-MM and MM.

IAP antagonists induce anti-tumor immunity in multiple myeloma

The cellular inhibitors of apoptosis (cIAP) 1 and 2 are amplified in about 3% of cancers and have been identified in multiple malignancies as being potential therapeutic targets as a result of their role in the evasion of apoptosis. Consequently, small-molecule IAP antagonists, such as LCL161, have entered clinical trials for their ability to induce tumor necrosis factor (TNF)-mediated apoptosis of cancer cells. However, cIAP1 and cIAP2 are recurrently homozygously deleted in multiple myeloma (MM), resulting in constitutive activation of the noncanonical nuclear factor (NF)-κB pathway. To our surprise, we observed robust in vivo anti-myeloma activity of LCL161 in a transgenic myeloma mouse model and in patients with relapsed-refractory MM, where the addition of cyclophosphamide resulted in a median progression-free-survival of 10 months. This effect was not a result of direct induction of tumor cell death, but rather of upregulation of tumor-cell-autonomous type I interferon (IFN) signaling and a strong inflammatory response that resulted in the activation of macrophages and dendritic cells, leading to phagocytosis of tumor cells. Treatment of a MM mouse model with LCL161 established long-term anti-tumor protection and induced regression in a fraction of the mice. Notably, combination of LCL161 with the immune-checkpoint inhibitor anti-PD1 was curative in all of the treated mice.

Combined expression of miR-34a and Smac mediated by oncolytic vaccinia virus synergistically promote anti-tumor effects in Multiple Myeloma

Despite great progress made in the treatment of multiple myeloma (MM), it is still incurable. Promising phase II clinical results have been reported recently for oncolytic vaccinia virus (OVV) clinic therapeutics. One reason for this has focused on the critical therapeutic importance of the immune response raised by these viruses. However, few studies have performed their applications as an optimal delivery system for therapeutic gene, especially miRNA in MM. In this study, we constructed two novel OVVs (TK deletion) that express anti-tumor genes, miR-34a and Smac, respectively, in MM cell lines and xenograft model. The results demonstrated that the novel OVV can effectively infect MM cell lines, and forcefully enhance the exogenous gene (miR-34a or Smac) expression. Furthermore, utilization of VV-miR-34a combined with VV-Smac synergistically inhibited tumor growth and induced apoptosis in vitro and in vivo. The underlying mechanism is proposed that blocking of Bcl-2 by VV-miR-34a increases the release of cytochrome c from mitochondria and then synergistically amplifies the antitumor effects of Smac-induced cell apoptosis. Our study is the first to utilize OVV as the vector for miR-34a or Smac expression to treat MM, and lays the groundwork for future clinical therapy for MM.

The SMAC mimetic BV6 induces cell death and sensitizes different cell lines to TNF-α and TRAIL-induced apoptosis

The inhibitors of apoptosis proteins are implicated in promoting cancer cells survival and resistance toward immune surveillance and chemotherapy. Second mitochondria-derived activator of caspases (SMAC) mimetics are novel compounds developed to mimic the inhibitory effect of the endogenous SMAC/DIABLO on these IAPs. Here, we examined the potential effects of the novel SMAC mimetic BV6 on different human cancer cell lines. Our results indicated that BV6 was able to induce cell death in different human cancer cell lines. Mechanistically, BV6 dose dependently induced degradation of IAPs, including cIAP1 and cIAP2. This was coincided with activating the non-canonical NF -kappa B (NF-κB) pathway, as indicated by stabilizing NF-κB-inducing kinase (NIK) for p100 processing to p52. More interestingly, BV6 was able to sensitize some of the resistant cancer cell lines to apoptosis induced by the death ligands tumor necrosis factor-α (TNF-α) and TNF-related apoptosis-inducing ligand (TRAIL) that are produced by different cells of the immune system. Such cell death enhancement was mediated by inducing an additional cleavage of caspase-9 to augment that of caspase-8 induced by death ligands. This eventually led to more processing of the executioner caspase-3 and poly (ADP-ribose) polymerase (PARP). In conclusion, therapeutic targeting of IAPs by BV6 might be an effective approach to enhance cancer regression induced by immune system. Our data also open up the future possibility of using BV6 in combination with other antitumor therapies to overcome cancer drug resistance.

Increased resistance to proteasome inhibitors in multiple myeloma mediated by cIAP2--implications for a combinatorial treatment

Despite the introduction of new treatment options for multiple myeloma (MM), a majority of patients relapse due to the development of resistance. Unraveling new mechanisms underlying resistance could lead to identification of possible targets for combinatorial treatment. Using TRAF3 deleted/mutated MM cell lines, we evaluated the role of the cellular inhibitor of apoptosis 2 (cIAP2) in drug resistance and uncovered the plausible mechanisms underlying this resistance and possible strategies to overcome this by combinatorial treatment. In MM, cIAP2 is part of the gene signature of aberrant NF-κB signaling and is heterogeneously expressed amongst MM patients. In cIAP2 overexpressing cells a decreased sensitivity to the proteasome inhibitors bortezomib, MG132 and carfilzomib was observed. Gene expression analysis revealed that 440 genes were differentially expressed due to cIAP2 overexpression. Importantly, the data imply that cIAPs are rational targets for combinatorial treatment in the population of MM with deleted/mutated TRAF3. Indeed, we found that treatment with the IAP inhibitor AT-406 enhanced the anti-MM effect of bortezomib in the investigated cell lines. Taken together, our results show that cIAP2 is an important factor mediating bortezomib resistance in MM cells harboring TRAF3 deletion/mutation and therefore should be considered as a target for combinatorial treatment.

A dominant-negative F-box deleted mutant of E3 ubiquitin ligase, β-TrCP1/FWD1, markedly reduces myeloma cell growth and survival in mice

Treatment of multiple myeloma with bortezomib can result in severe adverse effects, necessitating the development of targeted inhibitors of the proteasome. We show that stable expression of a dominant-negative F-box deleted (ΔF) mutant of the E3 ubiquitin ligase, SCF^β-TrCP/FWD1, in murine 5TGM1 myeloma cells dramatically attenuated their skeletal engraftment and survival when inoculated into immunocompetent C57BL/KaLwRij mice. Similar results were obtained in immunodeficient bg-nu-xid mice, suggesting that the observed effects were independent of host recipient immune status. Bone marrow stroma offered no protection for 5TGM1-ΔF cells in cocultures treated with tumor necrosis factor (TNF), indicating a cell-autonomous anti-myeloma effect. Levels of p100, IκBα, Mcl-1, ATF4, total and cleaved caspase-3, and phospho-β-catenin were elevated in 5TGM1-ΔF cells whereas cIAP was down-regulated. TNF also activated caspase-3 and downregulated Bcl-2, correlating with the enhanced susceptibility of 5TGM1-ΔF cells to apoptosis. Treatment of 5TGM1 tumor-bearing mice with a β-TrCP1/FWD1 inhibitor, pyrrolidine dithiocarbamate (PDTC), significantly reduced tumor burden in bone. PDTC also increased levels of cleaved Mcl-1 and caspase-3 in U266 human myeloma cells, correlating with our murine data and validating the development of specific β-TrCP inhibitors as an alternative therapy to nonspecific proteasome inhibitors for myeloma patients.

Post-translational modification profiling - A novel tool for mapping the protein modification landscape in cancer

The ubiquitin system plays an important role in essentially every cellular process, regulating numerous pathways ranging from development, transcription, DNA damage response, cell cycle, and signal transduction. Its best studied role involves removal of faulty proteins or those that are not necessary anymore. Aberrations in the ubiquitin system have been implicated in various pathologies including cancer, where specific mutations in E3 ligases such as Mdm2, pVHL, and BRCA1 have been linked to disease progression, prognosis, and resistance to drugs. Yet, there are hundreds of E3 ligases in the human genome and our knowledge of their target proteins and their dynamic regulation in the cellular environment is largely limited. In addition, fundamental questions related to recognition and specificity in ubiquitin conjugation remain unanswered. It is thus of major importance to characterize the ubiquitin landscape under various cellular conditions, and study how the regulatory network is altered in health and disease. To do so, analytical tools that allow identification of ubiquitin substrates, the conjugation and removal of ubiquitin, and the nature of specific ubiquitin linkages that are formed are needed. In this mini-review, we discuss common proteomic methodologies applied to studying the ubiquitome, and specifically focus on our recently developed post-translational modification (PTM) profiling approach. PTM profiling is a functional assay, amenable to biochemical manipulation, which allows the detection of protein modifications in a high-throughput manner. We discuss in detail the advantages and limitations of this system, focusing primarily on examples for analyzing the ubiquitin system in cancer. Uncovering the intricate signaling dynamics governed by and regulating ubiquitin modifications should clearly evolve into a new paradigm in understanding the molecular basis of malignant transformation and the development of novel therapeutic modalities.

The SMAC mimetic, LCL-161, reduces survival in aggressive MYC-driven lymphoma while promoting susceptibility to endotoxic shock

Inhibitor of apoptosis proteins (IAPs) antagonize caspase activation and regulate death receptor signaling cascades. LCL-161 is a small molecule second mitochondrial activator of caspase (SMAC) mimetic, which both disengages IAPs from caspases and induces proteasomal degradation of cIAP-1 and -2, resulting in altered signaling through the NFκB pathway, enhanced TNF production and sensitization to apoptosis mediated by the extrinsic pathway. SMAC mimetics are undergoing clinical evaluation in a range of hematological malignancies. Burkitt-like lymphomas are hallmarked by a low apoptotic threshold, conveying sensitivity to a range of apoptosis-inducing stimuli. While evaluating LCL-161 in the Eμ-Myc model of aggressive Burkitt-like lymphoma, we noted unexpected resistance to apoptosis induction despite ‘on-target' IAP degradation and NFκB activation. Moreover, LCL-161 treatment of lymphoma-bearing mice resulted in apparent disease acceleration concurrent to augmented inflammatory cytokine-release in the same animals. Indiscriminate exposure of lymphoma patients to SMAC mimetics may therefore be detrimental due to both unanticipated prolymphoma effects and increased susceptibility to endotoxic shock.

Icaritin suppresses multiple myeloma, by inhibiting IL-6/JAK2/STAT3

Icaritin is an active prenylflavonoid derived from Epimedium genus, a traditional Chinese medicine. Icaritin has a wide range of pharmacological and biological activities, including cardiovascular function improvement, hormone regulation and antitumor activity. Here, we investigated the effect of icaritin on multiple myeloma (MM) in vitro and in vivo. Icaritin inhibited cell growth of MM cell line and primary MM cells. In contrast, icaritin had low or no cytotoxic effect on normal hematopoiesis. We also demonstrated that in MM xenograft mouse models, icaritin suppressed tumor growth and decreased serum IL-6 and IgE levels, but did not show adverse reactions such as body weight loss. The anti-MM activity of icaritin was mainly mediated by inhibiting IL-6/JAK2/STAT3 signaling. We suggest that icaritin can be further tested in clinical trials in MM.

Novel strategies to target the ubiquitin proteasome system in multiple myeloma

Multiple myeloma (MM) is a hematological malignancy characterized by the accumulation of plasma cells in the bone marrow (BM). The success of the proteasome inhibitor bortezomib in the treatment of MM highlights the importance of the ubiquitin proteasome system (UPS) in this particular cancer. Despite the prolonged survival of MM patients, a significant amount of patients relapse or become resistant to therapy. This underlines the importance of the development and investigation of novel targets to improve MM therapy. The UPS plays an important role in different cellular processes by targeted destruction of proteins. The ubiquitination process consists of enzymes that transfer ubiquitin to proteins targeting them for proteasomal degradation. An emerging and promising approach is to target more disease specific components of the UPS to reduce side effects and overcome resistance. In this review, we will focus on different components of the UPS such as the ubiquitin activating enzyme E1, the ubiquitin conjugating enzyme E2, the E3 ubiquitin ligases, the deubiquitinating enzymes (DUBs) and the proteasome. We will discuss their role in MM and the implications in drug discovery for the treatment of MM.

Myxoma Virus Induces Ligand Independent Extrinsic Apoptosis in Human Myeloma Cells

INTRODUCTION

Multiple myeloma is a clonal malignancy of plasma B cells. Although recent advances have improved overall prognosis, virtually all myeloma patients still succumb to relapsing disease. Therefore, novel therapies to treat this disease remain urgently needed. We have recently shown that treatment of human multiple myeloma cells with an oncolytic virus known as myxoma results in rapid cell death even in the absence of viral replication; however, the specific mechanisms and pathways involved remain unknown.

MATERIALS AND METHODS

To determine how myxoma virus eliminates human multiple myeloma cells, we queried the apoptotic pathways that were activated after viral infection using immunoblot analysis and other cell biology approaches.

RESULTS

Our results indicate that myxoma virus infection initiates apoptosis in multiple myeloma cells through activation of the extrinsic initiator caspase-8. Caspase-8 activation subsequently results in cleavage of BH3 interacting-domain death agonist and loss of mitochondrial membrane potential causing secondary activation of caspase-9. Activation of caspase-8 appears to be independent of extrinsic death ligands and instead correlates with depletion of cellular inhibitors of apoptosis. We hypothesize that this depletion results from virally mediated host-protein shutoff because a myxoma construct that overexpresses the viral decapping enzymes displays improved oncolytic potential.

CONCLUSION

Taken together, these results suggest that myxoma virus eliminates human multiple myeloma cells through a pathway unique to oncolytic poxviruses, making it an excellent therapeutic option for the treatment of relapsed or refractory patients.

Multiple mechanisms contribute to the synergistic anti-myeloma activity of the pan-histone deacetylase inhibitor LBH589 and the rapalog RAD001

We examined the pre-clinical activity of pan-histone deacetylase inhibitor LBH589 in combination with mTORC1 inhibitor RAD001 and observed that the drug combination strongly synergized in inducing cytotoxicity in multiple myeloma (MM) cells. LBH589 caused an increase in acetylated histones and RAD001 inhibited mTORC1 activity. RAD001 caused potent G0/G1 arrest while LBH589 induced pronounced apoptosis, both of which were enhanced when the drugs were used in combination. LBH589/RAD001 combination led to down regulation of pStat3, cyclins, CDKs and XIAP and up regulation of pro-apoptotic Bcl-2 family proteins. A clinical trial is underway using LBH589/RAD001 combination in relapsed MM patients.