Loss of PTEN expression leading to high Akt activation in human multiple myelomas

PTEN, ERG, SPINK1, and TFF3 Status and Relationship in a Prostate Cancer Cohort from Jordanian Arab Population

Background and Objectives: Prognostic biomarkers in prostate cancer (PCa) include PTEN, ERG, SPINK1, and TFF3. Their relationships and patterns of expression in PCa in developing countries, including Jordan, have not yet been investigated. Materials and Methods: A tissue microarray (TMA) of PCa patients was taken from paraffin-embedded tissue blocks for 130 patients. PTEN, ERG, SPINK1, and TFF3 expression profiles were examined using immunohistochemistry (IHC) and correlated with each other and other clinicopathological factors. Results: PTEN loss of any degree was observed in 42.9% of PCa cases. ERG and TFF3 were expressed in 59.3% and 46.5% of PCa cases, respectively. SPINK1 expression was observed in 6 out of 104 PCa cases (5.4%). Among all PCa cases (n = 104), 3.8% (n = 4) showed SPINK1+/ERG+ phenotype, 1.9% (n = 2) showed SPINK1+/ERG- phenotype, 56.7% (n = 59) showed SPINK1-/ERG+ phenotype, and 37.5% showed SPINK1-/ERG- phenotype (n = 39). Among ERG positive cases (n = 63), 6.3% were SPINK1 positive. Among SPINK1 positive cases (n = 6), 66.7% were ERG positive. SPINK1 expression was predominantly observed in a subgroup of cancers that expressed TFF3 (6/6). Additionally, a statistically significant loss of PTEN expression was observed from Gleason Score 6 (GS6) (Grade Group 1 (GG1)) to GS9-10 (GG5); (p-value 0.019). Conclusions: This is the first study to look at the status of the PTEN, ERG, SPINK1, and TFF3 genes in a Jordanian Arab population. Loss of PTEN has been linked to more aggressive prostate cancer with high GSs/GGs. SPINK1 expression was predominantly observed in a subgroup of cancers that expressed TFF3. Our results call for screening these biomarkers for grading and molecular subtyping of the disease.

Inhibition of Sphingosine Kinase 2 Results in PARK2-Mediated Mitophagy and Induces Apoptosis in Multiple Myeloma

Mitophagy plays an important role in maintaining mitochondrial homeostasis by clearing damaged mitochondria. Sphingosine kinase 2 (SK2), a type of sphingosine kinase, is an important metabolic enzyme involved in generating sphingosine-1-phosphate. Its expression level is elevated in many cancers and is associated with poor clinical outcomes. However, the relationship between SK2 and mitochondrial dysfunction remains unclear. We found that the genetic downregulation of SK2 or treatment with ABC294640, a specific inhibitor of SK2, induced mitophagy and apoptosis in multiple myeloma cell lines. We showed that mitophagy correlates with apoptosis induction and likely occurs through the SET/PP2AC/PARK2 pathway, where inhibiting PP2AC activity may rescue this process. Furthermore, we found that PP2AC and PARK2 form a complex, suggesting that they might regulate mitophagy through protein-protein interactions. Our study demonstrates the important role of SK2 in regulating mitophagy and provides new insights into the mechanism of mitophagy in multiple myeloma.

Gou Qi Zi inhibits proliferation and induces apoptosis through the PI3K/AKT1 signaling pathway in non-small cell lung cancer

Background

Gou Qi Zi (Lycium barbarum) is a traditional herbal medicine with antioxidative effects. Although Gou Qi Zi has been used to prevent premature aging and in the treatment of non-small cell lung cancer (NSCLC), its mechanism of action in NSCLC remains unclear. The present study utilized network pharmacology to assess the potential mechanism of action of Gou Qi Zi in the treatment of NSCLC.

Methods

The TCMSP, TCMID, SwissTargetPrediction, DrugBank, DisGeNET, GeneCards, OMIM and TTD databases were searched for the active components of Gou Qi Zi and their potential therapeutic targets in NSCLC. Protein-protein interaction networks were identified and the interactions of target proteins were analyzed. Involved pathways were determined by GO enrichment and KEGG pathway analyses using the Metascape database, and molecular docking technology was used to study the interactions between active compounds and potential targets. These results were verified by cell counting kit-8 assays, BrdU labeling, flow cytometry, immunohistochemistry, western blotting, and qRT-PCR.

Results

Database searches identified 33 active components in Gou Qi Zi, 199 predicted biological targets and 113 NSCLC-related targets. A network of targets of traditional Chinese medicine compounds and potential targets of Gou Qi Zi in NSCLC was constructed. GO enrichment analysis showed that Gou Qi Zi targeting of NSCLC was mainly due to the effect of its associated lipopolysaccharide. KEGG pathway analysis showed that Gou Qi Zi acted mainly through the PI3K/AKT1 signaling pathway in the treatment of NSCLC. Molecular docking experiments showed that the bioactive compounds of Gou Qi Zi could bind to AKT1, C-MYC and TP53. These results were verified by experimental assays.

Conclusion

Gou Qi Zi induces apoptosis and inhibits proliferation of NSCLC in vitro and in vivo by inhibiting the PI3K/AKT1 signaling pathway.

TULP3 silencing suppresses cell proliferation, migration and invasion in gastric cancer via the PTEN/Akt/Snail pathway

BACKGROUND

Tubby-like protein 3 (TULP3) is a member of the tubby family, has been related to the development of nervous system by gene knockout researches. Nevertheless, the role of TULP3 in the gastric cancer is not clear.

METHODS

Western blotting and real-time polymerase chain reaction (PCR) were employed for the quantitative detection of TULP3 expression in the gastric cancer and consecutive non-cancerous tissues, and gastric cancer cells. The roles of TULP3 in invasion, migration as well as proliferation of the gastric cancer cell in vivo and in vitro through utilizing colony formation, MTT, wound-healing, transwell and mouse xenograft model. Western blotting assay was implemented in order to clarify the potential molecular mechanisms. Furthermore, electron microscopy and western blot were evaluated TULP3 expression in gastric cancer patient extracted serum exosomes.

RESULTS

TULP3 expression levels were remarkably upregulated in the gastric cancer tissues and cells. Subsequent functional assays demonstrated that TULP3 downregulation suppressed invasion, migration as well as the proliferation of the gastric cancer cell. Mechanism assays depicted that the PTEN/Akt/Snail signaling pathway can inhibit invasion, migration as well as the proliferation of the gastric cancer cell via TULP3 silencing. Finally, we found that the expression of TULP3 could be determined in the extracted serum exosomes. The expression of TULP3 in gastric cancer group was higher in comparison with normal group.

CONCLUSIONS

Our results reveal that TULP3 might serve as a potential prognostic biomarker and therapeutic target for the treatment of gastric cancer.

AKT signaling restrains tumor suppressive functions of FOXO transcription factors and GSK3 kinase in multiple myeloma

The phosphatidylinositide-3 kinases and the downstream mediator AKT drive survival and proliferation of multiple myeloma (MM) cells. AKT signaling is active in MM and has pleiotropic effects; however, the key molecular aspects of AKT dependency in MM are not fully clear. Among the various downstream AKT targets are the Forkhead box O (FOXO) transcription factors (TFs) and glycogen synthase kinase 3 (GSK3), which are negatively regulated by AKT signaling. Here we show that abrogation of AKT signaling in MM cells provokes cell death and cell cycle arrest, which crucially depends on both FOXO TFs and GSK3. Based on gene expression profiling, we defined a FOXO-repressed gene set that has prognostic significance in a large cohort of patients with MM, indicating that AKT-mediated gene activation is associated with inferior overall survival. We further show that AKT signaling stabilizes the antiapoptotic myeloid cell leukemia 1 (MCL1) protein by inhibiting FOXO- and GSK3-mediated MCL1 turnover. In concordance, abrogation of AKT signaling greatly sensitized MM cells for an MCL1-targeting BH3-mimetic, which is currently in clinical development. Taken together, our results indicate that AKT activity is required to restrain the tumor-suppressive functions of FOXO and GSK3, thereby stabilizing the antiapoptotic protein MCL1 in MM. These novel insights into the role of AKT in MM pathogenesis and MCL1 regulation provide opportunities to improve targeted therapy for patients with MM.

Signaling Pathway Mediating Myeloma Cell Growth and Survival

Simple Summary

The bone marrow (BM) microenvironment plays a crucial role in pathogenesis of multiple myeloma (MM), and delineation of the intracellular signaling pathways activated in the BM microenvironment in MM cells is essential to develop novel therapeutic strategies to improve patient outcome.

Abstract

The multiple myeloma (MM) bone marrow (BM) microenvironment consists of different types of accessory cells. Both soluble factors (i.e., cytokines) secreted from these cells and adhesion of MM cells to these cells play crucial roles in activation of intracellular signaling pathways mediating MM cell growth, survival, migration, and drug resistance. Importantly, there is crosstalk between the signaling pathways, increasing the complexity of signal transduction networks in MM cells in the BM microenvironment, highlighting the requirement for combination treatment strategies to blocking multiple signaling pathways.

Nuclear Heparanase Regulates Chromatin Remodeling, Gene Expression and PTEN Tumor Suppressor Function

Heparanase (HPSE) is an endoglycosidase that cleaves heparan sulfate and has been shown in various cancers to promote metastasis, angiogenesis, osteolysis, and chemoresistance. Although heparanase is thought to act predominantly extracellularly or within the cytoplasm, it is also present in the nucleus, where it may function in regulating gene transcription. Using myeloma cell lines, we report here that heparanase enhances chromatin accessibility and confirm a previous report that it also upregulates the acetylation of histones. Employing the Multiple Myeloma Research Foundation CoMMpass database, we demonstrate that patients expressing high levels of heparanase display elevated expression of proteins involved in chromatin remodeling and several oncogenic factors compared to patients expressing low levels of heparanase. These signatures were consistent with the known function of heparanase in driving tumor progression. Chromatin opening and downstream target genes were abrogated by inhibition of heparanase. Enhanced levels of heparanase in myeloma cells led to a dramatic increase in phosphorylation of PTEN, an event known to stabilize PTEN, leading to its inactivity and loss of tumor suppressor function. Collectively, this study demonstrates that heparanase promotes chromatin opening and transcriptional activity, some of which likely is through its impact on diminishing PTEN tumor suppressor activity.

Enhancing venetoclax activity in hematological malignancies

INTRODUCTION

Targeting anti-apoptotic pathways involving the BCL2 family proteins represents a novel treatment strategy in hematologic malignancies. Venetoclax, a selective BCL2 inhibitor, represents the first approved agent of this class, and is currently used in CLL and AML. However, monotherapy is rarely sufficient for sustained responses due to the development of drug resistance and loss of dependence upon the targeted protein. Numerous pre-clinical studies have shown that combining venetoclax with other agents may represent a more effective therapeutic strategy by circumventing resistance mechanisms. In this review, we summarize pre-clinical data providing a foundation for rational combination strategies involving venetoclax.

AREAS COVERED

Novel combination strategies in hematologic malignancies involving venetoclax, primarily at the pre-clinical level, will be reviewed. We emphasize novel agents that interrupt complementary or compensatory pro-survival pathways, and particularly mechanistic insights underlying synergism. PubMed, Cochrane, EMBASE, and Google scholar were searched from 2000.

EXPERT OPINION

Although venetoclax has proven to be an effective therapeutic in hematologic malignancies, monotherapy may be insufficient for maximal effectiveness due to the development of resistance and/or loss of BCL2 addiction. Further pre-clinical and clinical development of combination therapies may be necessary for optimal outcomes in patients with diverse blood cancers.

Molecular characterization of prostate cancer in Middle Eastern population highlights differences with Western populations with prognostic implication

BACKGROUND

To investigate the incidence and prognostication of ERG, PTEN and SPINK1 protein expressions in prostate cancer cohort of Middle Eastern descent in comparison to published data from Western population.

METHODS

Immunohistochemistry for ERG, PTEN and SPINK1 was performed in a cohort of localized PCA (n = 340). The data were correlated to pathological and clinical outcomes and compared to Western populations.

RESULTS

ERG expression and PTEN loss were noted in 123/288 (42.7%) and 91/297 (30.6%) of patients, respectively. SPINK1 expression was assessed in a subset of cases, noted in 6/150 (4%) of patients. Only ERG expression was associated with grade groups, being more common in the lower grade groups (1-3 vs 4-5; p = 0.04). In contrast to the Western population, PTEN loss foci were more likely to be ERG negative, observed in 81% of tumor foci and patients with PTEN neg/ERG pos were more likely to exhibit biochemical recurrence (OR 2.831; 95% CI 1.10-726, p = 0.03). This association remained significant in multivariate analysis (OR 2.68; 95% CI 0.98-7.33, p = 0.05), after adjusting for GG, path stage and surgical margin.

CONCLUSION

This study documents significant differences in key molecular events in PCA in Middle Eastern population compared to Western populations that could explain differences in PCA incidence, progression and prognostication. ERG, PTEN and SPINK1 genomic alteration occur less frequently and the enrichment of ERG for PTEN loss is not observed. Additionally, patients with combined PTEN loss/ERG positive are at highest risk for BCR vs North American Caucasian population where PTEN loss alone seems to be associated with the worst clinical outcome. The data presented here further support differences in clonal evolution between Middle Eastern and Western population in relation to PCA and add further insight to understanding PCA molecular pathways.

Exon-4 Mutations in KRAS Affect MEK/ERK and PI3K/AKT Signaling in Human Multiple Myeloma Cell Lines

Approximately 20% of multiple myeloma (MM) cases harbor a point mutation in KRAS. However, there is still no final consent on whether KRAS-mutations are associated with disease outcome. Specifically, no data exist on whether KRAS-mutations have an impact on survival of MM patients at diagnosis in the era of novel agents. Direct blockade of KRAS for therapeutic purposes is mostly impossible, but recently a mutation-specific covalent inhibitor targeting KRAS^p.G12C entered into clinical trials. However, other KRAS hotspot-mutations exist in MM patients, including the less common exon-4 mutations. For the current study, the coding regions of KRAS were deep-sequenced in 80 newly diagnosed MM patients, uniformely treated with three cycles of bortezomib plus dexamethasone and cyclophosphamide (VCD)-induction, followed by high-dose chemotherapy and autologous stem cell transplantation. Moreover, the functional impact of KRAS^p.G12A and the exon-4 mutations p.A146T and p.A146V on different survival pathways was investigated. Specifically, KRAS^WT, KRAS^p.G12A, KRAS^p.A146T, and KRAS^p.A146V were overexpressed in HEK293 cells and the KRAS^WT MM cell lines JJN3 and OPM2 using lentiviral transduction and the Sleeping Beauty vector system. Even though KRAS-mutations were not correlated with survival, all KRAS-mutants were found capable of potentially activating MEK/ERK- and sustaining PI3K/AKT-signaling in MM cells.

Bone marrow fibroblasts overexpress miR-27b and miR-214 in step with multiple myeloma progression, dependent on tumour cell-derived exosomes

Aberrant microRNA (miR) expression has an important role in tumour progression, but its involvement in bone marrow fibroblasts of multiple myeloma patients remains undefined. We demonstrate that a specific miR profile in bone marrow fibroblasts parallels the transition from monoclonal gammopathy of undetermined significance (MGUS) to myeloma. Overexpression of miR-27b-3p and miR-214-3p triggers proliferation and apoptosis resistance in myeloma fibroblasts via the FBXW7 and PTEN/AKT/GSK3 pathways, respectively. Transient transfection of miR-27b-3p and miR-214-3p inhibitors demonstrates a cooperation between these two miRNAs in the expression of the anti-apoptotic factor MCL1, suggesting that miR-27b-3p and miR-214-3p negatively regulate myeloma fibroblast apoptosis. Furthermore, myeloma cells modulate miR-27b-3p and miR-214-3p expression in fibroblasts through the release of exosomes. Indeed, tumour cell-derived exosomes induce an overexpression of both miRNAs in MGUS fibroblasts not through a simple transfer mechanism but by de novo synthesis triggered by the transfer of exosomal WWC2 protein that regulates the Hippo pathway. Increased levels of miR-27b-3p and miR-214-3p in MGUS fibroblasts co-cultured with myeloma cell-derived exosomes enhance the expression of fibroblast activation markers αSMA and FAP. These data show that the MGUS-to-myeloma transition entails an aberrant miRNA profile in marrow fibroblasts and highlight a key role of myeloma cells in modifying the bone marrow microenvironment by reprogramming the marrow fibroblasts' behaviour. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Natural products targeting the PI3K-Akt-mTOR signaling pathway in cancer: A novel therapeutic strategy

The phosphatidylinositol 3-kinase (PI3K)-Akt and the mammalian target of rapamycin (mTOR) represent two vital intracellular signaling pathways, which are associated with various aspects of cellular functions. These functions play vital roles in quiescence, survival, and growth in normal physiological circumstances as well as in various pathological disorders, including cancer. These two pathways are so intimately connected to each other that in some instances these are considered as one unique pathway crucial for cell cycle regulation. The purpose of this review is to emphasize the role of PI3K-Akt-mTOR signaling pathway in different cancer conditions and the importance of natural products targeting the PI3K-Akt-mTOR signaling pathway. This review also aims to draw the attention of scientists and researchers to the assorted beneficial effects of the numerous classes of natural products for the development of new and safe drugs for possible cancer therapy. We also summarize and critically analyze various preclinical and clinical studies on bioactive compounds and constituents, which are derived from natural products, to target the PI3K-Akt-mTOR signaling pathway for cancer prevention and intervention.

Emerging protein kinase inhibitors for the treatment of multiple myeloma

Introduction: Significant advances have been made during the last two decades in terms of new therapeutic options but also of innovative approaches to diagnosis and management of multiple myeloma (MM). While patient survival has been significantly prolonged, most patients relapse. Including the milestone approval of the first kinase inhibitor imatinib mesylate for CML in 2001, 48 small molecule protein kinase (PK) inhibitors have entered clinical practice until now. However, no PK inhibitor has been approved for MM therapy yet. Areas covered: This review article summarizes up-to-date knowledge on the pathophysiologic role of PKs in MM. Derived small molecules targeting receptor tyrosine kinases (RTKs), the Ras/Raf/MEK/MAPK- pathway, the PI3K/Akt/mTOR- pathway as well as Bruton tyrosine kinase (BTK), Aurora kinases (AURK), and cyclin-dependent kinases (CDKs) are most promising. Preclinical as well as early clinical data focusing on these molecules will be presented and critically reviewed. Expert opinion: Current MM therapy is directed against general vulnerabilities. Novel therapeutic strategies, inhibition of PKs in particular, are directed to target tumor-specific driver aberrations such as genetic abnormalities and microenvironment-driven deregulations. Results of ongoing Precision Medicine trials with PK inhibitors alone or in combination with other agents are eagerly awaited and hold the promise of once more improving MM patient outcome.

High-throughput Exploration of the Network Dependent on AKT1 in Mouse Ovarian Granulosa Cells

The PI3K/AKT signaling pathway is known to regulate a broad range of cellular processes, and it is often altered in several types of cancers. Recently, somatic AKT1 mutations leading to a strong activation of this kinase have been reported in juvenile granulosa cell tumors. However, the molecular role of AKT1 in the supporting cell lineage of the ovary is still poorly understood. To get insights into its function in such cells, we depleted Akt1 in murine primary granulosa cells and assessed the molecular consequences at both the transcript and protein levels. We were able to corroborate the involvement of AKT1 in the regulation of metabolism, apoptosis, cell cycle, or cytoskeleton dynamics in this ovarian cell type. Consistently, we showed in established granulosa cells that depletion of Akt1 provoked altered directional persistent migration and increased its velocity. This study also allowed us to put forward new direct and indirect targets of the kinase. Indeed, a series of proteins involved in intracellular transport and mitochondrial physiology were significantly affected by Akt1 depletion. Using in silico analyses, we also propose a set of kinases and transcription factors that can mediate the action of AKT1 on the deregulated transcripts and proteins. Taken altogether, our results provide a resource of direct and indirect AKT1 targets in granulosa cells and may help understand its roles in this ovarian cell type.

High-throughput Exploration of the Network Dependent on AKT1 in Mouse Ovarian Granulosa Cells

The PI3K/AKT signaling pathway is known to regulate a broad range of cellular processes, and it is often altered in several types of cancers. Recently, somatic AKT1 mutations leading to a strong activation of this kinase have been reported in juvenile granulosa cell tumors. However, the molecular role of AKT1 in the supporting cell lineage of the ovary is still poorly understood. To get insights into its function in such cells, we depleted Akt1 in murine primary granulosa cells and assessed the molecular consequences at both the transcript and protein levels. We were able to corroborate the involvement of AKT1 in the regulation of metabolism, apoptosis, cell cycle, or cytoskeleton dynamics in this ovarian cell type. Consistently, we showed in established granulosa cells that depletion of Akt1 provoked altered directional persistent migration and increased its velocity. This study also allowed us to put forward new direct and indirect targets of the kinase. Indeed, a series of proteins involved in intracellular transport and mitochondrial physiology were significantly affected by Akt1 depletion. Using in silico analyses, we also propose a set of kinases and transcription factors that can mediate the action of AKT1 on the deregulated transcripts and proteins. Taken altogether, our results provide a resource of direct and indirect AKT1 targets in granulosa cells and may help understand its roles in this ovarian cell type.

Clinical utility of assessing PTEN and ERG protein expression in prostate cancer patients: a proposed method for risk stratification

OBJECTIVES

To assess the prognostic value of ERG and PTEN protein expression as two of the most common genetic aberration in men with prostate cancer managed non-surgically by androgen deprivation therapy (ADT).

MATERIALS AND METHODS

463 tumor samples were assessed by double immunohistochemistry stains for ERG and PTEN and data correlated with clinical pathological features including, Gleason score, patients' outcome and ADT.

RESULTS

ERG expression and PTEN protein loss were present in 28.2% and 38% of total patients respectively. There was a significant interplay between ERG and PTEN expression with 21.8% PTEN negative tumors being ERG positive (p < 0.001). Both ERG and PTEN showed significant association with lethal disease in all patients and those treated with prior ADT representing castrate-resistant disease. However, only PTEN remained significant in multivariable proportional hazards regression analysis, when including Gleason score and patients' age. Depending on patient's subgroup, intact positive PTEN intensity showed better cancer-specific survival with HR ranging from 0.25 to 0.4 compared to tumors with loss of PTEN expression. Assessing combined marker status, patients with decreased PTEN intensity without ERG positivity showed the worst clinical outcome compared to those with no PTEN loss and no ERG expression, where they had best clinical outcome. Patients with ERG expression with or without PTEN loss showed intermediate risk in relation to lethal disease.

CONCLUSION

This study confirms a significant prognostic role for assessing ERG and PTEN in men with prostate cancer. It supports a role for utilizing combined ERG/PTEN status clinically and prospectively for stratifying PCa patients into different prognostic groups.

MAFb protein confers intrinsic resistance to proteasome inhibitors in multiple myeloma

Background

Multiple myeloma (MM) patients with t(14;20) have a poor prognosis and their outcome has not improved following the introduction of bortezomib (Bzb). The mechanism underlying the resistance to proteasome inhibitors (PIs) for this subset of patients is unknown.

Methods

IC50 of Bzb and carfilzomib (CFZ) in human myeloma cell lines (HMCLs) were established by MTT assay. Gene Expression profile (GEP) analysis was used to determine gene expression in primary myeloma cells. Immunoblotting analysis was performed for MAFb and caspase family proteins. Immunofluorescence staining was used to detect the location of MAFb protein in MM cells. Lentiviral infections were used to knock-down MAFb expression in two lines. Apoptosis detection by flow cytometry and western blot analysis was performed to determine the molecular mechanism MAFb confers resistance to proteasome inhibitors.

Results

We found high levels of MAFb protein in cell lines with t(14;20), in one line with t(6;20), in one with Igλ insertion into MAFb locus, and in primary plasma cells from MM patients with t(14;20). High MAFb protein levels correlated with higher IC50s of PIs in MM cells. Inhibition of GSK3β activity or treatment with Bzb or CFZ prevented MAFb protein degradation without affecting the corresponding mRNA level indicating a role for GSK3 and proteasome inhibitors in regulation of MAFb stability. Silencing MAFb restored sensitivity to Bzb and CFZ, and enhanced PIs-induced apoptosis and activation of caspase-3, − 8, − 9, PARP and lamin A/C suggesting that high expression of MAFb protein leads to insensitivity to proteasome inhibitors.

Conclusion

These results highlight the role of post-translational modification of MAFb in maintaining its protein level, and identify a mechanism by which proteasome inhibitors induced stabilization of MAFb confers resistance to proteasome inhibitors, and provide a rationale for the development of targeted therapeutic strategies for this subset of patients.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4602-4) contains supplementary material, which is available to authorized users.

PDK1 inhibitor GSK2334470 exerts antitumor activity in multiple myeloma and forms a novel multitargeted combination with dual mTORC1/C2 inhibitor PP242

A deeper understanding of the complex pathogenesis of multiple myeloma (MM) continues to lead to novel therapeutic approaches. Prior studies suggest that 3-phosphoinositide-dependent kinase 1 (PDK1) is expressed and active, acting as a crucial regulator of molecules that are essential for myelomagenesis. In the present study, we show that GSK2334470 (GSK-470), a novel and highly specific inhibitor of PDK1, induces potent cytotoxicity in MM cell lines including Dexamethasone-resistant cell line, but not in human normal cells. Insulin-like growth factor-1 could not rescue GSK-470-induced cell death. Moreover, GSK-470 down-modulates phosphor-PDK1, thereby inhibiting downstream phosphor-AKT at Thr308 and mTOR complex 1 (mTORC1) activity. However, GSK-470 could not affect mTORC2 activity and phosphor-AKT at Ser473. RPMI 8226 and OPM-2 cells with low expression of PTEN show relative resistant to GSK-470. Knockout of PTEN by shRNA resulted in a partial reversion of GSK-470-mediated growth inhibition, whereas overexpression of PTEN enhanced myeloma cell sensitivity to GSK-470, suggesting that the sensitivity to GSK-470 is correlated with PTEN expression statue in MM cells. Combining PP242, a dual mTORC1/C2 inhibitor, with GSK-470, had greater antimyeloma activity than either one alone in vitro and in MM xenograft model established in immunodeficient mice. In particular, this combination was able to result in a complete inhibition of mTORC1/C2 and full activity of AKT. Together, these findings raise the possibility that combining PDK1 antagonist GSK-470 with mTORC1/C2 inhibitors may represent a novel strategy against MM including drug-resistant myeloma, regardless of PTEN expression status.

Young female patients with multiple myeloma have low occurrence of osteolytic lesion

OBJECTIVE

Osteolytic lesion (OL) and bone damage are common complications in multiple myeloma (MM). This study aimed to analyze the occurrence of OL in MM patient groups of different ages and genders.

PATIENTS AND METHODS

We performed a retrospective study of 762 MM patients admitted to West China Hospital from 2009 to 2014 to investigate the association between OL occurrence with patients' ages and genders. The presence or absence of OL was confirmed by X-ray, computed tomography (CT) or magnetic resonance imaging (MRI) examination. We also downloaded MM patients' published gene expression profiles and performed microarray-based analyses to identify differentially regulated genes and signaling pathways. Finally, we examined target gene expressions in MM bone marrow (BM) biopsies through immunohistochemistry (IHC).

RESULTS

We calculated the frequency of OL in female and male MM patients with different age cut-offs. From West China Hospital data, we found that in young female MM patients aged under 55, the frequency of OL was 16.67%, significantly lower than the frequencies in other groups of patients (young males: 34.38%; old males: 31.04%; old females: 29.24%; p < .05). The same was true in another independent MM cohort. Microarray-based analyses showed that Microtubule Associated Serine/Threonine Kinase Family Member 4 (MAST4), an estrogen-responsive gene, expression was up-regulated in MM patients without OL and in young female MM patients (p < .05). The expression of MAST4 in MM BM was confirmed by IHC. The perspective of cell signaling network suggested that MAST4 might interact with phosphatase and tensin homolog (PTEN) and control the expression of a panel of osteoclast-regulatory cytokines, such as TNFSF11 and CCL2.

CONCLUSIONS

Young female (<55 years) MM patients have significantly lower OL frequency than other groups. MAST4 gene expression is thought to be associated with this phenomenon.

Type I insulin-like growth factor receptor signaling in hematological malignancies

The insulin-like growth factor (IGF) signaling system plays key roles in the establishment and progression of different types of cancer. In agreement with this idea, substantial evidence has shown that the type I IGF receptor (IGF-IR) and its primary ligand IGF-I are important for maintaining the survival of malignant cells of hematopoietic origin. In this review, we discuss current understanding of the role of IGF-IR signaling in cancer with a focus on the hematological neoplasms. We also address the emergence of IGF-IR as a potential therapeutic target for the treatment of different types of cancer including plasma cell myeloma, leukemia, and lymphoma.

UCHL1 is a biomarker of aggressive multiple myeloma required for disease progression

The success of proteasome inhibition in multiple myeloma highlights the critical role for the ubiquitin-proteasome system (UPS) in this disease. However, there has been little progress in finding more specific targets within the UPS involved in myeloma pathogenesis. We previously found the ubiquitin hydrolase UCH-L1 to be frequently over-expressed in B-cell malignancies, including myeloma, and showed it to be a potent oncogene in mice. Here we show that UCH-L1 is a poor prognostic factor that is essential for the progression of myeloma. We found high levels of UCHL1 to predict early progression in newly diagnosed patients; a finding reversed by the inclusion of bortezomib. We also found high UCHL1 levels to be a critical factor in the superiority of bortezomib over high-dose dexamethasone in relapsed patients. High UCHL1 partially overlaps with, but is distinct from, known genetic risks including 4p16 rearrangement and 1q21 amplification. Using an orthotopic mouse model, we found UCH-L1 depletion delays myeloma dissemination and causes regression of established disease. We conclude that UCH-L1 is a biomarker of aggressive myeloma that may be an important marker of bortezomib response, and may itself be an effective target in disseminated disease.

B Cell Receptor Activation Predominantly Regulates AKT-mTORC1/2 Substrates Functionally Related to RNA Processing

Protein kinase B (AKT) phosphorylates numerous substrates on the consensus motif RXRXXpS/T, a docking site for 14-3-3 interactions. To identify novel AKT-induced phosphorylation events following B cell receptor (BCR) activation, we performed proteomics, biochemical and bioinformatics analyses. Phosphorylated consensus motif-specific antibody enrichment, followed by tandem mass spectrometry, identified 446 proteins, containing 186 novel phosphorylation events. Moreover, we found 85 proteins with up regulated phosphorylation, while in 277 it was down regulated following stimulation. Up regulation was mainly in proteins involved in ribosomal and translational regulation, DNA binding and transcription regulation. Conversely, down regulation was preferentially in RNA binding, mRNA splicing and mRNP export proteins. Immunoblotting of two identified RNA regulatory proteins, RBM25 and MEF-2D, confirmed the proteomics data. Consistent with these findings, the AKT-inhibitor (MK-2206) dramatically reduced, while the mTORC-inhibitor PP242 totally blocked phosphorylation on the RXRXXpS/T motif. This demonstrates that this motif, previously suggested as an AKT target sequence, also is a substrate for mTORC1/2. Proteins with PDZ, PH and/or SH3 domains contained the consensus motif, whereas in those with an HMG-box, H15 domains and/or NF-X1-zinc-fingers, the motif was absent. Proteins carrying the consensus motif were found in all eukaryotic clades indicating that they regulate a phylogenetically conserved set of proteins.

mTOR pathway activation in multiple myeloma cell lines and primary tumour cells: pomalidomide enhances cytoplasmic-nuclear shuttling of mTOR protein

mTOR is a protein kinase that plays a central role in regulating critical cellular processes. We evaluated the activation and cellular localization of the mTOR pathway in multiple myeloma (MM) and analyzed the role of pomalidomide in regulating mTOR. By immunohistochemistry cytoplasmic p-mTOR stained positive in 57 out 101 (57.6%) cases with a nuclear p-mTOR localization in 14 out 101 samples (13.8%). In the 70 MM samples analyzed for the entire pathway, p-mTOR expression significantly correlated with p-AKT, p-P70S6K, and p-4E-BP1 suggesting that the AKT/mTOR pathway is activated in a subset of MM patients. Immunofluorescence assays demonstrated that mTOR protein is distributed throughout the cytoplasm and the nucleus at baseline in MM cell lines and in plasma cells of 13 MM patients and that pomalidomide facilitated the shift of the mTOR protein in the nucleus. By western blotting, treatment with pomalidomide increased nuclear mTOR and p-mTOR expression levels in the nucleus with a concomitant decrease of the cytoplasmic fractions while does not seem to affect significantly AKT phosphorylation status. In MM cells the anti-myeloma activity of pomalidomide may be mediated by the regulation of the mTOR pathway.

Aloperine executes antitumor effects against multiple myeloma through dual apoptotic mechanisms

BACKGROUND

Aloperine, a natural alkaloid constituent isolated from the herb Sophora alopecuroides displays anti-inflammatory properties in vitro and in vivo. Our group previously demonstrated that aloperine significantly induced apoptosis in colon cancer SW480 and HCT116 cells. However, its specific target(s) remain to be discovered in multiple myeloma (MM) and have not been investigated.

METHODS

Human myeloma cell lines (n = 8), primary myeloma cells (n = 12), drug-resistant myeloma cell lines (n = 2), and animal models were tested for their sensitivity to aloperine in terms of proliferation and apoptosis both in vitro and in vivo, respectively. We also examined the functional mechanisms underlying the apoptotic pathways triggered by aloperine.

RESULTS

Aloperine induced MM cell death in a dose- and time-dependent manner, even in the presence of the proliferative cytokines interleukin-6 and insulin-like growth factor I. Mechanistic studies revealed that aloperine not only activated caspase-8 and reduced the expression of FADD-like interleukin-1β-converting enzyme (FLICE)-like inhibitory protein long (FLIPL) and FLICE-inhibitory proteins (FLIPS) but also activated caspase-9 and decreased the expression of phosphorylated (p)-PTEN. Moreover, co-activation of the caspase-8/cellular FLICE-inhibitory protein (cFLIP)- and caspase-9/p-PTEN/p-AKT-dependent apoptotic pathways by aloperine caused irreversible inhibition of clonogenic survival. Aloperine induce more MM apoptosis with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) or borterzomib. A U266 xenograft tumor model and 5T33 MM cells recapitulated the antitumor efficacy of aloperine, and the animals displayed excellent tolerance of the drug and few adverse effects.

CONCLUSIONS

Aloperine has multifaceted antitumor effects on MM cells. Our data support the clinical development of aloperine for MM therapy.

AKT as a therapeutic target in multiple myeloma

INTRODUCTION

Multiple myeloma remains an incurable malignancy with poor survival. Novel therapeutic approaches capable of improving outcomes in patients with multiple myeloma are urgently required. AKT is a central node in the phosphatidylinositol-3-kinase/AKT/mammalian target of rapamycin signaling pathway with high expression in advanced and resistant multiple myeloma. AKT contributes to multiple oncogenic functions in multiple myeloma which may be exploited therapeutically. Promising preclinical data has lent support for pursuing further development of AKT inhibitors in multiple myeloma. Lead drugs are now entering the clinic.

AREAS COVERED

The rationale for AKT inhibition in multiple myeloma, pharmacological subtypes of AKT inhibitors in development, available results of clinical studies of AKT inhibitors and suitable drug partners for further development in combination with AKT inhibition in multiple myeloma are discussed.

EXPERT OPINION

AKT inhibitors are a welcome addition to the armamentarium against multiple myeloma and promising clinical activity is being reported from ongoing trials in combination with established and/or novel treatment approaches. AKT inhibitors may be set to improve patient outcomes when used in combination with synergistic drug partners.

miR-21 promotes human nucleus pulposus cell proliferation through PTEN/AKT signaling

The precise role of nucleus pulposus cell proliferation in the pathogenesis of intervertebral disc degeneration remains to be elucidated. Recent findings have revealed that microRNAs, a class of small noncoding RNAs, may regulate cell proliferation in many pathological conditions. Here, we showed that miR-21 was significantly upregulated in degenerative nucleus pulposus tissues when compared with nucleus pulposus tissues that were isolated from patients with idiopathic scoliosis and that miR-10b levels were associated with disc degeneration grade. Moreover, bioinformatics target prediction identified PTEN as a putative target of miR-21. miR-21 inhibited PTEN expression by directly targeting the 3′UTR, and this inhibition was abolished through miR-21 binding site mutations. miR-21 overexpression stimulated cell proliferation and AKT signaling pathway activation, which led to cyclin D1 translation. Additionally, the increase in proliferation and cyclin D1 expression induced by miR-21 overexpression was almost completely blocked by Ly294002, an AKT inhibitor. Taken together, aberrant miR-21 upregulation in intervertebral disc degeneration could target PTEN, which would contribute to abnormal nucleus pulposus cell proliferation through derepressing the Akt pathway. Our study also underscores the potential of miR-21 and the PTEN/Akt pathway as novel therapeutic targets in intervertebral disc degeneration.

Anticarcinogenic effect of quercetin by inhibition of insulin-like growth factor (IGF)-1 signaling in mouse skin cancer

It has been shown that dysregulation of IGF-1 signaling is associated with tumor incidence and progression, whereas blockade of the signaling can effectively inhibit carcinogenesis. Although several mechanisms of anticancer activity of quercetin were proposed, molecular targets of quercetin have not been identified yet. Hence, we assessed the effect of quercetin on IGF-1 signaling inhibition in BK5.IGF-1 transgenic (Tg) mice, which over-expresses IGF-1 in the skin epidermis. A quercetin diet (0.02% wt/wt) for 20 weeks remarkably delayed the incidence of skin tumor by 2 weeks and reduced tumor multiplicity by 35% in a 7,12-dimethylbenz(a)anthracene (DMBA)-tetradecanoyl phorbol-13-acetate (TPA) two stage mouse skin carcinogenesis protocol. Moreover, skin hyperplasia in Tg mice was significantly inhibited by a quercetin supplementation. Further analysis of the MT1/2 skin papilloma cell line showed that a quercetin treatment dose dependently suppressed IGF-1 induced phosphorylation of the IGF-1 receptor (IGF-1R), insulin receptor substrate (IRS)-1, Akt and S6K; however, had no effect on the phosphorylation of PTEN. Additionally, the quercetin treatment inhibited IGF-1 stimulated cell proliferation in a dose dependent manner. Taken together, these data suggest that quercetin has a potent anticancer activity through the inhibition of IGF-1 signaling.

Blockade of reactive oxygen species and Akt activation is critical for anti-inflammation and growth inhibition of metformin in phosphatase and tensin homolog-deficient RAW264.7 cells

CONTEXT

Metformin is widely used for treatment of type 2 diabetes and has a potential application on the treatment of inflammation and cancer. Phosphatase and tensin homolog (PTEN) plays a critical role in cancer cell growth and inflammation; however, precise mechanisms remain unclear.

OBJECTIVE

We aimed to investigate the possible mechanisms of how PTEN regulates metformin against cell growth and inflammation.

MATERIALS AND METHODS

We established PTEN knockdown in RAW264.7 murine macrophages (shPTEN cells) to detect inflammatory mediators using commercial kits, production of reactive oxygen species (ROS) by flow cytometry, cell growth by MTT assay and phosphorylated levels of signal molecules by western blot.

RESULTS

The shPTEN cells had a significant large amount of inflammatory mediators, such as inducible nitric oxide synthase (iNOS)/nitric oxide (NO) and cyclooxygenase-2 (COX-2)/prostaglandin E(2) (PGE(2)); and also elevated the production of ROS and increased cell proliferation. These effects were accompanied with the activation of Akt and p38 mitogen-activated protein kinase (MAPK), and the inactivation of an AMP-activated protein kinase (AMPK) activator and extracellular signal-regulated kinase 1/2. Pretreatment with metformin not only blocked these inflammatory mediators, but also caused growth inhibition induced by significant apoptosis. Furthermore, inactivation of Akt, blockade of ROS generation and independence of activations of AMPK and MAPK by metformin were also observed.

CONCLUSION

Macrophages with PTEN deficiency developed a continuous inflammatory microenvironment, which further aggravated tumor cell growth. Moreover, metformin affected PTEN-deficient cells dependent of inhibition of ROS production and Akt activation against enlarged inflammatory mediators and/or cell growth in shPTEN cells.

Combined inhibition of p97 and the proteasome causes lethal disruption of the secretory apparatus in multiple myeloma cells

Inhibition of the proteasome is a widely used strategy for treating multiple myeloma that takes advantage of the heavy secretory load that multiple myeloma cells (MMCs) have to deal with. Resistance of MMCs to proteasome inhibition has been linked to incomplete disruption of proteasomal endoplasmic-reticulum (ER)-associated degradation (ERAD) and activation of non-proteasomal protein degradation pathways. The ATPase p97 (VCP/Cdc48) has key roles in mediating both ERAD and non-proteasomal protein degradation and can be targeted pharmacologically by small molecule inhibition. In this study, we compared the effects of p97 inhibition with Eeyarestatin 1 and DBeQ on the secretory apparatus of MMCs with the effects induced by the proteasome inhibitor bortezomib, and the effects caused by combined inhibition of p97 and the proteasome. We found that p97 inhibition elicits cellular responses that are different from those induced by proteasome inhibition, and that the responses differ considerably between MMC lines. Moreover, we found that dual inhibition of both p97 and the proteasome terminally disrupts ER configuration and intracellular protein metabolism in MMCs. Dual inhibition of p97 and the proteasome induced high levels of apoptosis in all of the MMC lines that we analysed, including bortezomib-adapted AMO-1 cells, and was also effective in killing primary MMCs. Only minor toxicity was observed in untransformed and non-secretory cells. Our observations highlight non-redundant roles of p97 and the proteasome in maintaining secretory homeostasis in MMCs and provide a preclinical conceptual framework for dual targeting of p97 and the proteasome as a potential new therapeutic strategy in multiple myeloma.

Characterization of arsenic trioxide resistant clones derived from Jurkat leukemia T cell line: focus on PI3K/Akt signaling pathway

In this study the role of PI3K/Akt signaling pathway in arsenic trioxide (ATO)-treated parental Jurkat cells and also in derived ATO-resistant clones grown in the presence of given ATO concentration was investigated. ATO-resistant clones (cultured for 8-12weeks in the presence of 1, 2.5 and 5μM ATO) were characterized by high viability in the presence of ATO but slower growth rate compared to the parental cells. Morphological and functional characterization of derived ATO-resistant clones revealed that they did not differ fundamentally from parental Jurkat cells in terms of cell size, level of GSH, the lysosomal fluorescence or CD95/Fas surface antigen expression. However, a slight increase in the mitochondrial potential (JC-1 staining) was detected in the clones compared to parental Jurkat cells. Side population analysis (Vybrant DyeCycle Violet™ staining) in ATO resistant clones did not indicate any enrichment withcancer stem cells. Akt1/2, AktV or wortmannin inhibitors decreased viability of ATO-resistant clones grown in the presence of ATO, with no effect on ATO-treated parental cells. Flow cytometry analysis showed that ATO decreased the level of p-Akt in ATO-treated parental cells, while the resistant clones exhibited higher levels of p-Akt immunostaining than parental Jurkat cells. Expression analysis of 84 genes involved in the PI3K/Akt pathway revealed that this pathway was predominantly active in ATO-resistant clones. c-JUN seems to play a key role in the induction of cell death in ATO-treated parental Jurkat cells, as dose-dependent strong up-regulation of JUN was specific for the ATO-treated parental Jurkat cells. On the other hand, changes in expression of cyclin D1 (CCND1), insulin receptor substrate 1 (IRS1) and protein kinase C isoforms (PRKCZ,PRKCB and PRKCA) may be responsible for the induction of resistance to ATO. The changes in expression of growth factor receptor-bound protein 10 (GRB10) observed in ATO-resistant clones suggest a possibility of induction of different mechanisms in development of resistance to ATO depending on the drug concentration and thus involvement of different signaling mediators.

Combined targeting of MEK/MAPK and PI3K/Akt signalling in multiple myeloma

So-called RAS-dependent pathways, such as those signalling via mitogen-activated protein kinase kinase (MEK)/mitogen-activated protein kinase (MAPK) and phosphoinositide-3 kinase (PI3K)/Akt, are implicated in proliferation and survival of multiple myeloma (MM) cells. However, the effects of their combined blockade and its potential therapeutic utility for the treatment of RAS-mutated MM have not systematically been analysed. Here, we tested the functional consequences of single versus combined inhibition of the MEK/MAPK and PI3K/Akt pathways in a large series of primary MM samples (n = 55) and MM cell lines (n = 11). Additionally, the anti-myeloma activity of different treatments was analysed with respect to the RAS mutation status. PI3K/Akt blockade was generally more pro-apoptotic than blockade of MEK/MAPK both in cell lines and in primary MM samples. Simultaneous blockade of both pathways led to significantly enhanced anti-myeloma activity in 75% of primary MM samples, whereas the remainder was largely resistant. Resistance to combination blockade was exclusively observed in RAS wildtype cases, whereas sensitivity was noted in RAS wildtype and in RAS mutated MM. These results suggest that oncogenic RAS is a predictor of sensitivity to combination treatment with PI3K/Akt and MEK/MAPK inhibitors and that such an approach might therefore be beneficial for this genetically well-defined subgroup of MM patients.

Optimal induction of myeloma cell death requires dual blockade of phosphoinositide 3-kinase and mTOR signalling and is determined by translocation subtype

Novel inhibitors of PI3K, Akt and mTOR have been developed recently, some of which have entered clinical trials. Although such compounds inhibit cell proliferation, their effects on cell survival, an important determinant of clinical response, are less distinct. Using a broad panel of myeloma cell lines and primary patient samples, we show that dual PI3K and mTOR inhibition can induce cell death. The effects are most marked in cells expressing the t(4;14) translocation, whereas t(11;14) cells are largely resistant. Using specific inhibitors of individual pathway components, we show that optimal induction of cell death requires inhibition of both PI3K and mTOR. This is due to a PI3K-independent component of mTOR activation downstream of the MAP kinase pathway. Novel mTOR kinase inhibitors, which block both TORC1 and TORC2 complexes thereby also reducing Akt activity, are less effective than dual PI3K/mTOR inhibitors because of feedback activation of PI3K signalling. Dual PI3K/mTOR inhibitors sensitise t(4;14) and t(14;16), but not t(11;14), expressing cells to the cytotoxic effects of dexamethasone. We have identified a robust cytogenetic biomarker for response to PI3K/mTOR inhibition--these results will inform the design and prioritisation of clinical studies with novel inhibitors in genetic subgroups of myeloma.

Phosphatase and tensin homolog on chromosome 10 is phosphorylated in primary effusion lymphoma and Kaposi's sarcoma

Primary effusion lymphoma (PEL) is a non-Hodgkin's B-cell lymphoma driven by Kaposi's sarcoma-associated herpesvirus. It is uniquely sensitive to mTOR, PI3K, and Akt inhibitors; however, the basis of this requirement for the mTOR pathway remains to be elucidated. The phosphatase and tensin homolog gene (PTEN) on chromosome 10 controls the first step in the phosphatidylinositol 3 kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR) pathway and is genetically inactivated in many solid tumors. We find an absence of PTEN deletions, mutations, or protein mislocalization in PEL. However, we find consistent hyperphosphorylation at serine 380 of PTEN, which is an inactivating modification, in PEL cell lines and in tumor xenografts. We also evaluated a large tissue microarray of Kaposi's sarcoma biopsies and observed concordant high levels of phospho-PTEN, phospho-Akt, and phospho-S6 ribosomal protein. Reintroduction of PTEN into PEL inhibited colony formation in soft agar, verifying the functional dependence of PEL on PI3K signaling. This was also true for PEL cell lines that carried mutant p53 and for KS-like cell lines. Activating PTEN in these cancers may yield a new treatment strategy for PEL, KS, and similar PTEN wild-type lymphomas.

The mammalian target of rapamycin pathway as a therapeutic target in multiple myeloma

The mammalian target of rapamycin (mTOR) is centrally located, linking proximal oncogenic cascades to critical downstream pathways that drive tumor growth. mTOR regulates such diverse functions as protein translation, proliferation, viability, autophagy, metabolism homeostasis, monitoring of energy reserves, and induction of angiogenesis. Given its fundamental role in tumorigenesis, it is not surprising that a huge effort is being made to develop mTOR inhibitors. The existence of feedback pathways that become activated subsequent to mTOR inhibition has complicated these efforts. However, the fact that mTOR exists in two separate complexes, TORC1 and TORC2, and rapalogs primarily inhibit only TORC1 and TORC2 is actually a key activator of AKT, has injected new energy into the quest to find inhibitors that can inhibit both complexes. In myeloma models, preclinical studies confirm the activity of rapalogs as well as newer TORC1/TORC2 inhibitors, and early phase clinical trials have begun. In addition, the recent finding of up-regulated myeloma cell expression of DEPTOR, an mTOR binding protein that restricts mTOR activity, suggests an additional future therapeutic target specific to the myeloma tumor model.

Mammalian target of rapamycin as a target in hematological malignancies

The mammalian target of rapamycin (mTOR) regulates protein synthesis in addition to cell growth and cell proliferation. Elucidation of the roles of the phosphatidylinositol 3-kinase (PI3K)/Akt/mTOR pathway in the regulation of the pathogenesis of hematological neoplasms has led to the development and clinical evaluation of agents targeting this pathway for the treatment of leukemia and lymphomas. Clinical trials conducted to date have shown modest responses to mTOR inhibition in patients with various hematological malignancies. Novel agents that simultaneously target mTOR complex 2 (mTORC2) or AKT in addition to mTOR complex 1 (mTORC1) may offer an opportunity to improve therapeutic efficacy.

Phosphoinositide 3-kinase regulates plasma membrane targeting of the Ras-specific exchange factor RasGRP1

Receptor-induced targeting of exchange factors to specific cellular membranes is the predominant mechanism for initiating and compartmentalizing signal transduction by Ras GTPases. The exchange factor RasGRP1 has a C1 domain that binds the lipid diacylglycerol and thus can potentially mediate membrane localization in response to receptors that are coupled to diacylglycerol-generating phospholipase Cs. However, the C1 domain is insufficient for targeting RasGRP1 to the plasma membrane. We found that a basic/hydrophobic cluster of amino acids within the plasma membrane-targeting domain of RasGRP1 is instead responsible for plasma membrane targeting. This basic/hydrophobic cluster binds directly to phospholipid vesicles containing phosphoinositides via electrostatic interactions with polyanionic phosphoinositide headgroups and insertion of a tryptophan into the lipid bilayer. B cell antigen receptor ligation and other stimuli induce plasma membrane targeting of RasGRP1 by activating the phosphoinositide 3-kinase signaling pathway, which generates phosphoinositides within the plasma membrane. Direct detection of phosphoinositides by the basic/hydrophobic cluster of RasGRP1 provides a novel mechanism for coupling and co-compartmentalizing phosphoinositide 3-kinase and Ras signaling and, in coordination with diacylglycerol detection by the C1 domain, gives RasGRP1 the potential to serve as an integrator of converging signals from the phosphoinositide 3-kinase and phospholipase C pathways.

Cyclin-dependent kinase inhibitor, P276-00 induces apoptosis in multiple myeloma cells by inhibition of Cdk9-T1 and RNA polymerase II-dependent transcription

P276-00 is a novel cyclin-dependent kinase inhibitor especially potent for Cdk9-T1, Cdk4-D1 and Cdk1-B. Multiple myeloma (MM) is a B-cell malignancy characterized by the accumulation of malignant plasma cells. Treatment of MM cell lines with P276-00 resulted in apoptosis that correlated with transcription inhibition and a significant decline in Mcl-1 protein levels with the appearance of cleaved PARP in these cells. In vivo studies of P276-00 confirmed antitumor activity in RPMI-8226 xenograft. These results suggest that P276-00 causes multiple myeloma cell death by disrupting the balance between cell survival and apoptosis through inhibition of transcription and downregulation of Mcl-1.

Insulin is a potent myeloma cell growth factor through insulin/IGF-1 hybrid receptor activation

Insulin and insulin growth factor type 1 (IGF-1) and their receptors are closely related molecules, but both factors bind to the receptor of the other one with a weak affinity. No study has presently documented a role of insulin as a myeloma growth factor (MGF) for human multiple myeloma cells (MMCs), whereas many studies have concluded that IGF-1 is a major MGF. IGF-1 receptor (IGF-1R) is aberrantly expressed by MMCs in association with a poor prognosis. In this study we show that insulin receptor (INSR) is increased throughout normal plasma cell differentiation. INSR gene is also expressed by MMCs of 203/206 newly diagnosed patients. Insulin is an MGF as potent as IGF-1 at physiological concentrations and requires the presence of insulin/IGF-1 hybrid receptors, stimulating INSR(+)IGF-1R(+) MMCs, unlike INSR(+)IGF-1R(-) or INSR(-)IGF-1R(-) MMCs. Immunoprecipitation experiments indicate that INSR is linked with IGF-1R in MMCs and that insulin induces both IGF-1R and INSR phosphorylations and vice versa. In conclusion, we demonstrate for the first time that insulin is an MGF as potent as IGF-1 at physiological concentrations and its activity necessitates insulin/IGF-1 hybrid receptor activation. Further therapeutic strategies targeting the IGF/IGF-1R pathway have to take into account neutralizing the IGF-1R-mediated insulin MGF activity.

GCS-100, a novel galectin-3 antagonist, modulates MCL-1, NOXA, and cell cycle to induce myeloma cell death

GCS-100 is a galectin-3 antagonist with an acceptable human safety profile that has been demonstrated to have an antimyeloma effect in the context of bortezomib resistance. In the present study, the mechanisms of action of GCS-100 are elucidated in myeloma cell lines and primary tumor cells. GCS-100 induced inhibition of proliferation, accumulation of cells in sub-G(1) and G(1) phases, and apoptosis with activation of both caspase-8 and -9 pathways. Dose- and time-dependent decreases in MCL-1 and BCL-X(L) levels also occurred, accompanied by a rapid induction of NOXA protein, whereas BCL-2, BAX, BAK, BIM, BAD, BID, and PUMA remained unchanged. The cell-cycle inhibitor p21(Cip1) was up-regulated by GCS-100, whereas the procycling proteins CYCLIN E2, CYCLIN D2, and CDK6 were all reduced. Reduction in signal transduction was associated with lower levels of activated IkappaBalpha, IkappaB kinase, and AKT as well as lack of IkappaBalpha and AKT activation after appropriate cytokine stimulation (insulin-like growth factor-1, tumor necrosis factor-alpha). Primary myeloma cells showed a direct reduction in proliferation and viability. These data demonstrate that the novel therapeutic molecule, GCS-100, is a potent modifier of myeloma cell biology targeting apoptosis, cell cycle, and intracellular signaling and has potential for myeloma therapy.

Kinome-wide RNAi studies in human multiple myeloma identify vulnerable kinase targets, including a lymphoid-restricted kinase, GRK6

A paucity of validated kinase targets in human multiple myeloma has delayed clinical deployment of kinase inhibitors in treatment strategies. We therefore conducted a kinome-wide small interfering RNA (siRNA) lethality study in myeloma tumor lines bearing common t(4;14), t(14;16), and t(11;14) translocations to identify critically vulnerable kinases in myeloma tumor cells without regard to preconceived mechanistic notions. Fifteen kinases were repeatedly vulnerable in myeloma cells, including AKT1, AK3L1, AURKA, AURKB, CDC2L1, CDK5R2, FES, FLT4, GAK, GRK6, HK1, PKN1, PLK1, SMG1, and TNK2. Whereas several kinases (PLK1, HK1) were equally vulnerable in epithelial cells, others and particularly G protein-coupled receptor kinase, GRK6, appeared selectively vulnerable in myeloma. GRK6 inhibition was lethal to 6 of 7 myeloma tumor lines but was tolerated in 7 of 7 human cell lines. GRK6 exhibits lymphoid-restricted expression, and from coimmunoprecipitation studies we demonstrate that expression in myeloma cells is regulated via direct association with the heat shock protein 90 (HSP90) chaperone. GRK6 silencing causes suppression of signal transducer and activator of transcription 3 (STAT3) phosphorylation associated with reduction in MCL1 levels and phosphorylation, illustrating a potent mechanism for the cytotoxicity of GRK6 inhibition in multiple myeloma (MM) tumor cells. As mice that lack GRK6 are healthy, inhibition of GRK6 represents a uniquely targeted novel therapeutic strategy in human multiple myeloma.

Identification of early growth response protein 1 (EGR-1) as a novel target for JUN-induced apoptosis in multiple myeloma

Tumor-bone marrow microenvironment interactions in multiple myeloma (MM) are documented to play crucial roles in plasma-cell growth/survival. In vitro coculture of MM cells with osteoclasts supported cell survival and significantly down-regulated JUN expression. JUN expression in myeloma cells from late-stage and high-risk MM was significantly lower than in plasma cells from healthy donors, monoclonal gammopathy of undetermined significance, smoldering MM, and low-risk MM; patients with low-JUN-expressing MM cells had earlier disease-related deaths. JUN overexpression in MM cells induced cell death and growth inhibition and up-regulated expression of early growth response protein 1 (EGR-1), whose low expression also carried unfavorable clinical implications. EGR-1 knockdown in MM cells abrogated JUN overexpression-induced MM cell death and growth inhibition, indicating that EGR-1 acts directly downstream of JUN. JUN modulates myeloma cell apoptosis through interacting with EGR-1, which down-regulates Survivin and triggers caspase signaling. Importantly, high JUN or EGR-1 expression was associated with improved outcome in Total Therapy 3, in which bortezomib is given throughout therapy, versus Total Therapy 2, in which bortezomib is given only at relapse. Consistently, JUN or EGR-1 knockdown in cultured MM cells enhanced their resistance to bortezomib, demonstrating the crucial role of low JUN/EGR-1 expression in MM resistance to bortezomib.

N-Benzoylstaurosporine (PKC412) inhibits Akt kinase inducing apoptosis in multiple myeloma cells

Multiple myeloma is a clonal malignancy of plasma cells that invariably progresses to a chemoresistant state. The PI3K/Akt pathway mediates signals downstream of several growth factors involved in myeloma pathogenesis, and constitutive activation of Akt was observed in myeloma cells. We now report that a staurosporine derivative, N-benzoylated staurosporine or PKC412, induces cell death in myeloma cell lines (RPMI8226S, U266, MM1S and MM1R) with loss of mitochondrial membrane potential Delta psi m, caspase 3 and PARP cleavage. ZVAD.fmk, but not interleukin-6, rescued these cells from PKC412 effects. Upstream of the mitochondria, PKC412 inhibited Bad phosphorylation and attenuated Akt kinase activity by suppressing its phosphorylation on serine residue in its activation loop. Reduced phosphorylation of downstream Akt substrates GSK3 alpha/beta and FKHR was also noted. Stable transfection of 8226S cells with constitutively active Akt (8226S-myAkt) partially protected against PKC412 cytotoxicity. Primary myeloma cells isolated from refractory myeloma patients (n=4), were equally sensitive to PKC412 treatment. More importantly, PKC412 did not affect CFU-GM or BFU-E colony formation. In summary, our results demonstrate that PKC412 suppresses Akt kinase activation and induces apoptosis in myeloma cell lines, as well as primary resistant cells. PKC412 is an appropriate candidate for novel treatment protocols for multiple myeloma.

Emerging role of insulin-like growth factor receptor inhibitors in oncology: early clinical trial results and future directions

Preclinical evidence that targeting the insulin-like growth factor receptor (IGF-IR) is effective in cancer treatment has been accumulating for almost two decades. Efforts to develop drugs began in the late 1990s, and initial data from clinical trials were reported in 2006. The biological rationale for IGF-IR targeting has potential relevance to many tumor types, and early results have justified expanded programs to evaluate IGF-IR-targeting agents in many areas of clinical need. More than two dozen drug candidates have been developed and clinical trials are underway for at least 12 of these. Early clinical trials reveal an acceptable safety profile together with pharmacodynamic evidence that the receptor can be successfully targeted. It is premature to draw conclusions regarding efficacy, but well-documented instances of single-agent activity were noted during phase I evaluations, and recent evidence from a phase II study suggests that co-administration of an anti-IGF-IR antibody with chemotherapy for non-small-cell lung cancer improves objective response rate and progression-free survival. With more than 70 trials involving a variety of drug candidates underway, the IGF-IR is becoming one of the most intensively investigated molecular targets in oncology. Early results justify the continuation of ongoing research across a broad range of cancer indications.

Geldanamycin, an inhibitor of Hsp90, sensitizes human tumour cells to radiation

PURPOSE

The effects of the heat shock protein 90 (Hsp90) inhibitor geldanamycin (GA) were examined on the radiosensitivity and signal transduction pathways in human tumour cell lines.

MATERIALS AND METHODS

Two human cell lines, SQ-5 and DLD-1, derived from lung carcinoma and colon adenocarcinoma, respectively, were incubated for 16 h at 37 degrees C in medium containing 0.2 microM GA. The cells were then irradiated with X-rays and incubated with GA for a further 8 h. Radiation sensitivity was determined by clonogenic assays and protein levels were examined by Western blotting.

RESULTS

GA radiosensitized both cell lines, but potentiated X-ray sensitivity more in SQ-5 than in DLD-1 cells. It was found that GA depleted EGFR and ErbB-2 in DLD-1 cells and depleted only ErbB-2 in SQ-5 cells. GA also reduced the expression of Akt and phosphorylated Akt (pAkt) expression in SQ-5 cells. In addition, the ratio (%) of apoptotic cells and poly [ADP-ribose] polymerase cleavage increased in SQ-5 but not in DLD-1 cells after exposure to GA and X-ray irradiation. The findings suggest that GA enhances the radiation sensitivity of human tumour cells by inhibiting the EGFR signal transduction system and the Akt signalling pathway.

CONCLUSION

Targeting Hsp90 with GA provides a promising experimental strategy for radiosensitization of carcinoma.

A novel interaction between fibroblast growth factor receptor 3 and the p85 subunit of phosphoinositide 3-kinase: activation-dependent regulation of ERK by p85 in multiple myeloma cells

Ectopic activation of fibroblast growth factor receptor 3 (FGFR3) is associated with several cancers, including multiple myeloma (MM). FGFR3 inhibition in these cells inhibits proliferation and induces apoptosis, validating FGFR3 signaling as a therapeutic target in t(4;14) MM cases. We have identified the PI3K regulatory subunit, p85alpha, as a novel interactor of FGFR3 by yeast two-hybrid, and confirmed an interaction with both p85alpha and p85beta in mammalian cells. The interaction of FGFR3 with p85 is dependent upon receptor activation. In contrast to the Gab1-mediated association of FGFRs with p85, the FGFR3-p85 interaction we observed requires FGFR3 Y760, previously identified as a PLCgamma binding site. The interaction of p85 with FGFR3 does not require PLCgamma, suggesting the p85 interaction is direct and independent of PLCgamma binding. FGFR3 and p85 proteins also interact in MM cell lines which consistently express p85alpha and p85beta, but not p50 or p55 subunits. siRNA knockdown of p85beta in MM cells caused an increased ERK response to FGF2. These data suggest that an endogenous negative regulatory role for the p85-FGFR3 interaction on the Ras/ERK/MAPK pathway may exist in response to FGFR3 activity and identifies a novel therapeutic target for MM.

Genetic aberrations and survival in plasma cell leukemia

Plasma cell leukemia (PCL) is an aggressive and rare hematological malignancy that originates either as primary disease (pPCL) or as a secondary leukemic transformation (sPCL) of multiple myeloma (MM). We report here the genetic aberrations and survival of 80 patients with pPCL or sPCL and make comparisons with 439 cases of MM. pPCL presents a decade earlier than sPCL (54.7 vs 65.3 years) and is associated with longer median overall survival (11.1 vs 1.3 months; P<0.001). 14q32 (IgH) translocations are highly prevalent in both sPCL and pPCL (82-87%); in pPCL IgH translocations almost exclusively involve 11q13 (CCND1), supporting a central etiological role, while in sPCL multiple partner oncogenes are involved, including 11q13, 4p16 (FGFR3/MMSET) and 16q23 (MAF), recapitulating MM. Both show ubiquitous inactivation of TP53 (pPCL 56%; sPCL 83%) by coding mutation or 17p13 deletion; complemented by p14ARF epigenetic silencing in sPCL (29%). Both show frequent N-RAS or K-RAS mutation. Poor survival in pPCL was predicted by MYC translocation (P=0.006). Survival in sPCL was consistently short. Overall pPCL and sPCL are different disorders with distinct natural histories, genetics and survival.