Pan-mammalian target of rapamycin (mTOR) inhibitor AZD8055 primes rhabdomyosarcoma cells for ABT-737-induced apoptosis by down-regulating Mcl-1 protein

Unlocking the power of probiotics, postbiotics: targeting apoptosis for the treatment and prevention of digestive diseases

Digestive diseases are becoming an increasingly serious health burden, creating an urgent need to develop more effective treatment strategies. Probiotics and postbiotics have been extensively studied for their potential to prevent and treat digestive diseases. Growing evidence suggests that programmed cell death, especially apoptosis, is a critical mechanism influencing the molecular and biological aspects of digestive diseases, contributing to disease progression. Understanding the mechanisms and signaling pathways by which probiotics and postbiotics regulate apoptosis could reveal new therapeutic targets for treating digestive diseases. This review focuses on the beneficial effects of probiotics and postbiotics in regulating apoptosis across a range of liver diseases, including non-alcoholic fatty liver disease, liver injury, cirrhosis, and liver cancer. It also explores their effects on gastrointestinal diseases, such as colorectal cancer, colitis, gastrointestinal injury, and infectious diarrhea. Furthermore, some probiotics help balance the gut microbiota, enhance intestinal barrier function, and regulate the immune system, all of which are closely associated with apoptosis. Moreover, emerging technologies, such as encapsulation methods, have been developed to stabilize probiotics, primarily based on experimental findings from rodent and human studies.

The Emerging Role and Clinical Significance of PI3K-Akt-mTOR in Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is a common soft tissue sarcoma primarily affecting children and young adults. This disease is more prevalent in children under 15, with two main types: embryonal Rhabdomyosarcoma (eRMS), which has a better prognosis, and alveolar Rhabdomyosarcoma (aRMS), which is more aggressive and associated with specific genetic alterations. The PI3K-Akt-mTOR pathway is often hyperactivated in RMS, contributing to cell proliferation, survival, and resistance to therapies. The presence of phosphorylated components of this pathway correlates with poor survival outcomes. Here, we discuss various therapeutic approaches targeting the PI3K-Akt-mTOR pathway. These include the use of specific inhibitors (e.g., PI3K inhibitors, Akt inhibitors) and combination therapies that may enhance treatment efficacy. Dietary supplements like curcumin and repurposed drugs such as chloroquine are also mentioned for their potential to induce apoptosis in RMS cells. We also emphasize the need for innovative strategies to improve survival rates, which have remained stagnant over the years. Targeting super-enhancers and transcription factors associated with RMS may provide new therapeutic avenues. Overall, this review underscores the critical role of the PI3K-Akt-mTOR pathway in RMS and the potential for targeted therapies to improve patient outcomes.

Enhancement of the Sensitivity of the Acute Lymphoblastic Leukemia Cells to ABT-737 by Formononetin

Overexpression of (myeloid leukemia cell differentiation protein 1) Mcl-1 is associated with the reduction of ABT-737 toxicity and secondary resistance. In this study, the effect of formononetin (biochanin B) on Mcl-1 expression, cell growth, apoptosis, and ABT-737 sensitivity of the acute lymphoblastic leukemia (ALL) cells was investigated. In this experimental study, the cell proliferation and MTT assays were used to investigate the effect of formononetin on cell growth and survival. qRT-PCR was performed for the measurement of gene expression. Hoechst 33342 staining and caspase-3 activity assay were used for the determination of apoptosis. Our data showed that formononetin and ABT-737 both led to a significant reduction in the IC50 value and synergistically reduced the cell growth and survival relative to single treatment. Overexpression of Mcl-1 was found after the treatment with ABT-737. Formononetin decreased the expression of B-cell lymphoma 2 (Bcl-2) and Mcl-1 and increased the Bcl-2-associated protein x (Bax) and P21 expression. Moreover, formononetin enhanced the apoptotic effect of ABT-737 in ALL cells. In summary, formononetin showed anti-carcinogenic activities in human ALL cells via suppression of cell growth and survival. Formononetin enhanced the apoptotic effect of ABT-737, with contribution by inhibition of the Mcl-1 expression.

Dihydroartemisinin Enhances the Therapeutic Efficacy of BH3 Mimetic Inhibitor in Acute Lymphoblastic Leukemia Cells via Inhibition of Mcl-1

INTRODUCTION

Up-regulation of the anti-apoptotic proteins such as Mcl-1 is associated with the primary and secondary resistance of tumor cells to ABT-737 Bcl-2 inhibitor. The combined treatment of Bcl-2 inhibitors with Mcl-1 inhibitors has been proposed as an attractive therapeutic strategy to overcome this drug resistance. Here, we investigated the effect of dihydroartemisinin on Mcl-1 expression and sensitization of T-ALL cells to ABT-737.

METHODS

The cell growth and survival were tested by the cell proliferation and MTT assays, respectively. The mRNA levels of Bcl-2, Mcl-1, Bax and P21 were examined by qRT-PCR. Apoptosis were detected by Hoechst 33342 staining and caspase-3 activity assay.

RESULTS

Our data showed that combination treatment with dihydroartemisinin and ABT-737 caused a significant decrease in the IC50 value and synergistically reduced the cell survival compared with dihydroartemisinin or ABT-737 alone. ABT-737 enhanced the Mcl-1 mRNA expression. Dihydroartemisinin also down-regulated the expression of Bcl-2 and Mcl-1 and enhanced the P21 and Bax expression. Moreover, dihydroartemisinin enhanced the apoptosis induced by ABT-737 in MOLT-4 and MOLT-17 cell lines.

CONCLUSION

In conclusion, dihydroartemisinin demonstrates anti-tumor activities in human ALL cells via inhibition of cell survival and growth. Dihydroartemisinin augments the apoptotic effect of ABT-737 by inhibiting the expression of Mcl-1.

The Cytotoxic Effect of Curcumin in Rhabdomyosarcoma Is Associated with the Modulation of AMPK, AKT/mTOR, STAT, and p53 Signaling

Approximately 7% of cancers arising in children and 1% of those arising in adults are soft tissue sarcomas (STS). Of these malignancies, rhabdomyosarcoma (RMS) is the most common. RMS survival rates using current therapeutic protocols have remained largely unchanged in the past decade. Thus, it is imperative that the main molecular drivers in RMS tumorigenesis are defined so that more precise, effective, and less toxic therapies can be designed. Curcumin, a common herbal supplement derived from plants of the Curcuma longa species, has an exceptionally low dietary biotoxicity profile and has demonstrated anti-tumorigenic benefits in vitro. In this study, the anti-tumorigenic activity of curcumin was assessed in rhabdomyosarcoma cell lines and used to identify the major pathways responsible for curcumin's anti-tumorigenic effects. Curcumin treatment resulted in cell cycle arrest, inhibited cell migration and colony forming potential, and induced apoptotic cell death. Proteome profiler array analysis demonstrated that curcumin treatment primarily influenced flux through the AKT-mammalian target of rapamycin (mTOR), signal transducer and activator of transcription (STAT), AMP-dependent kinase (AMPK), and p53 associated pathways in a rhabdomyosarcoma subtype-specific manner. Thus, the strategic, combinational therapeutic targeting of these pathways may present the best option to treat this group of tumors.

Reciprocal effects of mTOR inhibitors on pro-survival proteins dictate therapeutic responses in tuberous sclerosis complex

mTORC1 is aberrantly activated in cancer and in the genetic tumor syndrome tuberous sclerosis complex (TSC), which is caused by loss-of-function mutations in the TSC complex, a negative regulator of mTORC1. Clinically approved mTORC1 inhibitors, such as rapamycin, elicit a cytostatic effect that fails to eliminate tumors and is rapidly reversible. We sought to determine the effects of mTORC1 on the core regulators of intrinsic apoptosis. In TSC2-deficient cells and tumors, we find that mTORC1 inhibitors shift cellular dependence from MCL-1 to BCL-2 and BCL-XL for survival, thereby altering susceptibility to BH3 mimetics that target specific pro-survival BCL-2 proteins. The BCL-2/BCL-XL inhibitor ABT-263 synergizes with rapamycin to induce apoptosis in TSC-deficient cells and in a mouse tumor model of TSC, resulting in a more complete and durable response. These data expose a therapeutic vulnerability in regulation of the apoptotic machinery downstream of mTORC1 that promotes a cytotoxic response to rapamycin.

The apoptosis of grass carp (Ctenopharyngodon idella) muscle during postmortem condition regulated by the cytokines via TOR and NF-κB signaling pathways

Postmortem alteration by apoptosis has significant effects on flesh quality. Currently, the information necessary to understand the apoptotic behavior and the molecular mechanisms during postmortem alteration in fish muscle is still lacking. Activation of apoptosis and the cytokines involved in regulating apoptosis in fish muscle were evaluated during postmortem condition at 4 °C for 5 days in terms of apoptotic morphology changes, nucleus DNA fragmentation, caspases activation and related gene expressions. The triggering apoptotic mechanisms associated with multiple cytokines transcriptional levels showed that the up-regulated pro-apoptotic mediators [IFN-γ2, TNF-α, IL-6, IL-1β, IL-17D, IL-12p35 and IL-10 (except IL-15)] and the down-regulated anti-apoptotic mediators of [IL-8 and IL-11 (except TGF-β and IL-4)] both regulated apoptosis at early stage, which were regulated by NF-κB and TOR, respectively. Results suggested that transcriptional regulation of multiple cytokines produce a positive outcome on triggering apoptosis.

Molecular Targets for Novel Therapeutics in Pediatric Fusion-Positive Non-CNS Solid Tumors

Chromosomal fusions encoding novel molecular drivers have been identified in several solid tumors, and in recent years the identification of such pathogenetic events in tumor specimens has become clinically actionable. Pediatric sarcomas and other rare tumors that occur in children as well as adults are a group of heterogeneous tumors often with driver gene fusions for which some therapeutics have already been developed and approved, and others where there is opportunity for progress and innovation to impact on patient outcomes. We review the chromosomal rearrangements that represent oncogenic events in pediatric solid tumors outside of the central nervous system (CNS), such as Ewing Sarcoma, Rhabdomyosarcoma, Fibrolamellar Hepatocellular Carcinoma, and Renal Cell Carcinoma, among others. Various therapeutics such as CDK4/6, FGFR, ALK, VEGF, EGFR, PDGFR, NTRK, PARP, mTOR, BRAF, IGF1R, HDAC inhibitors are being explored among other novel therapeutic strategies such as ONC201/TIC10.

Pan-RAS inhibitors: Hitting multiple RAS isozymes with one stone

Mutations in the three RAS oncogenes are present in approximately 30% of all human cancers that drive tumor growth and metastasis by aberrant activation of RAS-mediated signaling. Despite the well-established role of RAS in tumorigenesis, past efforts to develop small molecule inhibitors have failed for various reasons leading many to consider RAS as "undruggable." Advances over the past decade with KRAS(G12C) mutation-specific inhibitors have culminated in the first FDA-approved RAS drug, sotorasib. However, the patient population that stands to benefit from KRAS(G12C) inhibitors is inherently limited to those patients harboring KRAS(G12C) mutations. Additionally, both intrinsic and acquired mechanisms of resistance have been reported that indicate allele-specificity may afford disadvantages. For example, the compensatory activation of uninhibited wild-type (WT) NRAS and HRAS isozymes can rescue cancer cells harboring KRAS(G12C) mutations from allele-specific inhibition or the occurrence of other mutations in KRAS. It is therefore prudent to consider alternative drug discovery strategies that may overcome these potential limitations. One such approach is pan-RAS inhibition, whereby all RAS isozymes co-expressed in the tumor cell population are targeted by a single inhibitor to block constitutively activated RAS regardless of the underlying mutation. This chapter provides a review of past and ongoing strategies to develop pan-RAS inhibitors in detail and seeks to outline the trajectory of this promising strategy of RAS inhibition.

A combinatorial drug screen in PDX-derived primary rhabdomyosarcoma cells identifies the NOXA - BCL-XL/MCL-1 balance as target for re-sensitization to first-line therapy in recurrent tumors

First-line therapy for most pediatric sarcoma is based on chemotherapy in combination with radiotherapy and surgery. A significant number of patients experience drug resistance and development of relapsed tumors. Drugs that have the potential to re-sensitize relapsed tumor cells toward chemotherapy treatment are therefore of great clinical interest. Here, we used a drug profiling platform with PDX-derived primary rhabdomyosarcoma cells to screen a large drug library for compounds re-sensitizing relapse tumor cells toward standard chemotherapeutics used in rhabdomyosarcoma therapy. We identified ABT-263 (navitoclax) as most potent compound enhancing general chemosensitivity and used different pharmacologic and genetic approaches in vitro and in vivo to detect the NOXA-BCL-XL/MCL-1 balance to be involved in modulating drug response. Our data therefore suggests that players of the intrinsic mitochondrial apoptotic cascade are major targets for stimulation of response toward first-line therapies in rhabdomyosarcoma.

mTORC1 stimulates cell growth through SAM synthesis and m6A mRNA-dependent control of protein synthesis

The mechanistic target of rapamycin complex 1 (mTORC1) regulates metabolism and cell growth in response to nutrient, growth, and oncogenic signals. We found that mTORC1 stimulates the synthesis of the major methyl donor, S-adenosylmethionine (SAM), through the control of methionine adenosyltransferase 2 alpha (MAT2A) expression. The transcription factor c-MYC, downstream of mTORC1, directly binds to intron 1 of MAT2A and promotes its expression. Furthermore, mTORC1 increases the protein abundance of Wilms' tumor 1-associating protein (WTAP), the positive regulatory subunit of the human N6-methyladenosine (m6A) RNA methyltransferase complex. Through the control of MAT2A and WTAP levels, mTORC1 signaling stimulates m6A RNA modification to promote protein synthesis and cell growth. A decline in intracellular SAM levels upon MAT2A inhibition decreases m6A RNA modification, protein synthesis rate, and tumor growth. Thus, mTORC1 adjusts m6A RNA modification through the control of SAM and WTAP levels to prime the translation machinery for anabolic cell growth.

mTOR as a senescence manipulation target: A forked road

Cellular senescence, cancer and aging are highly interconnected. Among many important molecular machines that lie at the intersection of this triad, the mechanistic (formerly mammalian) target of rapamycin (mTOR) is a central regulator of cell metabolism, proliferation, and survival. The mTOR signaling cascade is essential to maintain cellular homeostasis in normal biological processes or in response to stress, and its dysregulation is implicated in the progression of many disorders, including age-associated diseases. Accordingly, the pharmacological implications of mTOR inhibition using rapamycin or others rapalogs span the treatment of various human diseases from immune disorders to cancer. Importantly, rapamycin is one of the only known pan-species drugs that can extend lifespan. The molecular and cellular mechanisms explaining the phenotypic consequences of mTOR are vast and heavily studied. In this review, we will focus on the potential role of mTOR in the context of cellular senescence, a tumor suppressor mechanism and a pillar of aging. We will explore the link between senescence, autophagy and mTOR and discuss the opportunities to exploit senescence-associated mTOR functions to manipulate senescence phenotypes in age-associated diseases and cancer treatment.

It's time to die: BH3 mimetics in solid tumors

The removal of cells by apoptosis is an essential process regulating tissue homeostasis. Cancer cells acquire the ability to circumvent apoptosis and survive in an unphysiological tissue context. Thereby, the Bcl-2 protein family plays a key role in the initiation of apoptosis, and overexpression of the anti-apoptotic Bcl-2 proteins is one of the molecular mechanisms protecting cancer cells from apoptosis. Recently, small molecules targeting the anti-apoptotic Bcl-2 family proteins have been identified, and with venetoclax the first of these BH3 mimetics has been approved for the treatment of leukemia. In solid tumors the anti-apoptotic Bcl-2 family proteins Mcl-1 and Bcl-xL are frequently overexpressed or genetically amplified. In this review, we summarize the role of Mcl-1 and Bcl-xL in solid tumors and compare the different BH3 mimetics targeting Mcl-1 or Bcl-xL.

miRNA Modulation and Antitumor Activity by the Extra-Virgin Olive Oil Polyphenol Oleacein in Human Melanoma Cells

Extra-virgin olive oil (EVOO) polyphenols contribute to Mediterranean diet health-promoting properties. One of the most abundant secoiridoid present in EVOO, Oleacein (OA), demonstrated anticancer activity against several tumors. Nevertheless, its role against melanoma has not still investigated. This study aimed at determining in vitro the antimelanoma activity of OA and the relative mechanism of action. OA induced cell growth inhibition in 501Mel melanoma cells with an IC50 in the low micromolar range of concentrations. Moreover, an OA concentration approximating the IC50 induced G1/S phase arrest, DNA fragmentation, and downregulation of genes encoding antiapoptotic (BCL2 and MCL1) and proproliferative (c-KIT, K-RAS, PIK3R3, mTOR) proteins, while increased transcription levels of the proapoptotic protein BAX. Concordantly, OA increased the levels of miR-193a-3p (targeting MCL1, c-KIT and K-RAS), miR-193a-5p (targeting PIK3R3 and mTOR), miR-34a-5p (targeting BCL2 and c-KIT) and miR-16-5p (miR-16-5p targeting BCL2, K-RAS and mTOR), while decreased miR-214-3p (targeting BAX). These modulatory effects might contribute to the inhibition of 501Mel melanoma cell growth observed after treatment with an olive leaves-derived formulation rich in OA, with potential application against in situ cutaneous melanoma. Altogether, these results demonstrate the ability of OA to contrast the proliferation of cutaneous melanoma cells through the transcriptional modulation of relevant genes and microRNAs, confirming the anticancer potential of EVOO and suggesting OA as a chemopreventive agent for cancer disease therapy.

Sequential combinations of chemotherapeutic agents with BH3 mimetics to treat rhabdomyosarcoma and avoid resistance

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in childhood and adolescence. Refractory/relapsed RMS patients present a bad prognosis that combined with the lack of specific biomarkers impairs the development of new therapies. Here, we utilize dynamic BH3 profiling (DBP), a functional predictive biomarker that measures net changes in mitochondrial apoptotic signaling, to identify anti-apoptotic adaptations upon treatment. We employ this information to guide the use of BH3 mimetics to specifically inhibit BCL-2 pro-survival proteins, defeat resistance and avoid relapse. Indeed, we found that BH3 mimetics that selectively target anti-apoptotic BCL-xL and MCL-1, synergistically enhance the effect of clinically used chemotherapeutic agents vincristine and doxorubicin in RMS cells. We validated this strategy in vivo using a RMS patient-derived xenograft model and observed a reduction in tumor growth with a tendency to stabilization with the sequential combination of vincristine and the MCL-1 inhibitor S63845. We identified the molecular mechanism by which RMS cells acquire resistance to vincristine: an enhanced binding of BID and BAK to MCL-1 after drug exposure, which is suppressed by subsequently adding S63845. Our findings validate the use of DBP as a functional assay to predict treatment effectiveness in RMS and provide a rationale for combining BH3 mimetics with chemotherapeutic agents to avoid tumor resistance, improve treatment efficiency, and decrease undesired secondary effects.

HDAC inhibitors elicit metabolic reprogramming by targeting super-enhancers in glioblastoma models

The Warburg effect is a tumor-related phenomenon that could potentially be targeted therapeutically. Here, we showed that glioblastoma (GBM) cultures and patients' tumors harbored super-enhancers in several genes related to the Warburg effect. By conducting a transcriptome analysis followed by ChIP-Seq coupled with a comprehensive metabolite analysis in GBM models, we found that FDA-approved global (panobinostat, vorinostat) and selective (romidepsin) histone deacetylase (HDAC) inhibitors elicited metabolic reprogramming in concert with disruption of several Warburg effect-related super-enhancers. Extracellular flux and carbon-tracing analyses revealed that HDAC inhibitors blunted glycolysis in a c-Myc-dependent manner and lowered ATP levels. This resulted in the engagement of oxidative phosphorylation (OXPHOS) driven by elevated fatty acid oxidation (FAO), rendering GBM cells dependent on these pathways. Mechanistically, interference with HDAC1/-2 elicited a suppression of c-Myc protein levels and a concomitant increase in 2 transcriptional drivers of oxidative metabolism, PGC1α and PPARD, suggesting an inverse relationship. Rescue and ChIP experiments indicated that c-Myc bound to the promoter regions of PGC1α and PPARD to counteract their upregulation driven by HDAC1/-2 inhibition. Finally, we demonstrated that combination treatment with HDAC and FAO inhibitors extended animal survival in patient-derived xenograft model systems in vivo more potently than single treatments in the absence of toxicity.

Current and Future Treatment Strategies for Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children, and can be subcategorized histologically and/or based on PAX-FOXO1 fusion gene status. Over the last four decades, there have been no significant improvements in clinical outcomes for advanced and metastatic RMS patients, underscoring a need for new treatment options for these groups. Despite significant advancements in our understanding of the genomic landscape and underlying biological mechanisms governing RMS that have informed the identification of novel therapeutic targets, development of these therapies in clinical trials has lagged far behind. In this review, we summarize the current frontline multi-modality therapy for RMS according to pediatric protocols, highlight emerging targeted therapies and immunotherapies identified by preclinical studies, and discuss early clinical trial data and the implications they hold for future clinical development.

Destined to Die: Apoptosis and Pediatric Cancers

Apoptosis (programmed cell death) is a systematic and coordinated cellular process that occurs in physiological and pathophysiological conditions. Sidestepping or resisting apoptosis is a distinct characteristic of human cancers including childhood malignancies. This review dissects the apoptosis pathways implicated in pediatric tumors. Understanding these pathways not only unraveled key molecules that may serve as potential targets for drug discovery, but also molecular nodes that integrate with other signaling networks involved in processes such as development. This review presents current knowledge of the complex regulatory system that governs apoptosis with respect to other processes in pediatric cancers, so that fresh insights may be derived regarding treatment resistance or for more effective treatment options.

Therapeutic inhibition of Mcl-1 blocks cell survival in estrogen receptor-positive breast cancers

Cancers often overexpress anti-apoptotic Bcl-2 proteins for cell death evasion, a recognized hallmark of cancer progression. While estrogen receptor (ER)-α+ breast cancers express high levels of three anti-apoptotic Bcl-2 family members (Bcl-2, Bcl-xL, and Mcl-1), pharmacological inhibition of Bcl-2 and/or Bcl-xL fails to induce cell death in ERα+ breast cancer cell lines, due to rapid and robust Mcl-1 upregulation. The mechanisms of acute Mcl-1 upregulation in response to Bcl-2/Bcl-xL inhibition remain undefined in in ERα+ breast cancers. We report here that blockade of Bcl-2 or Bcl-xL, alone or together, rapidly induced mTOR signaling in ERα+ breast cancer cells, rapidly increasing cap-dependent Mcl-1 translation. Cells treated with a pharmacological inhibitor of cap-dependent translation, or with the mTORC1 inhibitor RAD001/everolimus, displayed reduced protein levels of Mcl-1 under basal conditions, and failed to upregulate Mcl-1 protein expression following treatment with ABT-263, a pharmacological inhibitor of Bcl-2 and Bcl-xL. Although treatment with ABT-263 alone did not sustain apoptosis in tumor cells in culture or in vivo, ABT-263 plus RAD001 increased apoptosis to a greater extent than either agent used alone. Similarly, combined use of the selective Mcl-1 inhibitor VU661013 with ABT-263 resulted in tumor cell apoptosis and diminished tumor growth in vivo. These findings suggest that rapid Mcl-1 translation drives ABT-263 resistance, but can be combated directly using emerging Mcl-1 inhibitors, or indirectly through existing and approved mTOR inhibitors.

Activation of LXRβ inhibits tumor respiration and is synthetically lethal with Bcl-xL inhibition

Liver-X-receptor (LXR) agonists are known to bear anti-tumor activity. However, their efficacy is limited and additional insights regarding the underlying mechanism are necessary. By performing transcriptome analysis coupled with global polar metabolite screening, we show that LXR agonists, LXR623 and GW3965, enhance synergistically the anti-proliferative effect of BH3 mimetics in solid tumor malignancies, which is predominantly mediated by cell death with features of apoptosis and is rescued by exogenous cholesterol. Extracellular flux analysis and carbon tracing experiments (U-13 C-glucose and U-13 C-glutamine) reveal that within 5 h, activation of LXRβ results in reprogramming of tumor cell metabolism, leading to suppression of mitochondrial respiration, a phenomenon not observed in normal human astrocytes. LXR activation elicits a suppression of respiratory complexes at the protein level by reducing their stability. In turn, energy starvation drives an integrated stress response (ISR) that up-regulates pro-apoptotic Noxa in an ATF4-dependent manner. Cholesterol and nucleotides rescue from the ISR elicited by LXR agonists and from cell death induced by LXR agonists and BH3 mimetics. In conventional and patient-derived xenograft models of colon carcinoma, melanoma, and glioblastoma, the combination treatment of ABT263 and LXR agonists reduces tumor sizes significantly stronger than single treatments. Therefore, the combination treatment of LXR agonists and BH3 mimetics might be a viable efficacious treatment approach for solid malignancies.

Concomitant targeting of Hedgehog signaling and MCL-1 synergistically induces cell death in Hedgehog-driven cancer cells

In the present study, we show that concomitant inhibition of Hedgehog (HH) signaling by the glioma-associated oncogene homolog1 (GLI1)-targeting agent GANT61 and the antiapoptotic BCL-2 protein family member MCL-1 by A-1210477 synergistically induces cell death in HH-driven cancers, i.e. rhabdomyosarcoma (RMS) and medulloblastoma (MB) cells. Combined genetic and pharmacological inhibition emphasized that co-treatment of GANT61 and A-1210477 indeed relies on inhibition of GLI1 (by GANT61) and MCL-1 (by A-1210477). Mechanistic studies revealed that A-1210477 triggers the release of BIM from MCL-1 and its shuttling to BCL-x_L and BCL-2. Indeed, BIM proved to be required for GANT61/A-1210477-induced cell death, as genetic silencing of BIM using siRNA significantly rescues cell death upon GANT61/A-1210477 co-treatment. Similarly, genetic silencing of NOXA results in a significant reduction of GANT61/A-1210477-mediated cell death. Also, overexpression of MCL-1 or BCL-2 significantly protects RMS cells from GANT61/A-1210477-triggered cell death. Addition of the pan-caspase inhibitor zVAD.fmk significantly decreases GANT61/A-1210477-stimulated cell demise, indicating apoptotic cell death. In conclusion, GANT61 and A-1210477 synergize to engage mitochondrial apoptosis. These findings provide the rationale for further evaluation of dual inhibition of HH signaling and MCL-1 in HH-driven cancers.

Targeted Therapy-based Combination Treatment in Rhabdomyosarcoma

Targeted therapies have revolutionized cancer treatment; however, progress lags behind in alveolar (ARMS) and embryonal rhabdomyosarcoma (ERMS), a soft-tissue sarcoma mainly occurring at pediatric and young adult age. Insulin-like growth factor 1 receptor (IGF1R)-directed targeted therapy is one of the few single-agent treatments with clinical activity in these diseases. However, clinical effects only occur in a small subset of patients and are often of short duration due to treatment resistance. Rational selection of combination treatments of either multiple targeted therapies or targeted therapies with chemotherapy could hypothetically circumvent treatment resistance mechanisms and enhance clinical efficacy. Simultaneous targeting of distinct mechanisms might be of particular interest in this regard, as this affects multiple hallmarks of cancer at once. To determine the most promising and clinically relevant targeted therapy-based combination treatments for ARMS and ERMS, we provide an extensive overview of preclinical and (early) clinical data concerning a variety of targeted therapy-based combination treatments. We concentrated on the most common classes of targeted therapies investigated in rhabdomyosarcoma to date, including those directed against receptor tyrosine kinases and associated downstream signaling pathways, the Hedgehog signaling pathway, apoptosis pathway, DNA damage response, cell-cycle regulators, oncogenic fusion proteins, and epigenetic modifiers. Mol Cancer Ther; 17(7); 1365-80. ©2018 AACR.

Genetics, epigenetics and redox homeostasis in rhabdomyosarcoma: Emerging targets and therapeutics

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma accounting for 5-8% of malignant tumours in children and adolescents. Children with high risk disease have poor prognosis. Anti-RMS therapies include surgery, radiation and combination chemotherapy. While these strategies improved survival rates, they have plateaued since 1990s as drugs that target differentiation and self-renewal of tumours cells have not been identified. Moreover, prevailing treatments are aggressive with drug resistance and metastasis causing failure of several treatment regimes. Significant advances have been made recently in understanding the genetic and epigenetic landscape in RMS. These studies have identified novel diagnostic and prognostic markers and opened new avenues for treatment. An important target identified in high throughput drug screening studies is reactive oxygen species (ROS). Indeed, many drugs in clinical trials for RMS impact tumour progression through ROS. In light of such emerging evidence, we discuss recent findings highlighting key pathways, epigenetic alterations and their impacts on ROS that form the basis of developing novel molecularly targeted therapies in RMS. Such targeted therapies in combination with conventional therapy could reduce adverse side effects in young survivors and lead to a decline in long-term morbidity.

ETV7 is an essential component of a rapamycin-insensitive mTOR complex in cancer

The mechanistic target of rapamycin (mTOR) serine/threonine kinase, a critical regulator of cell proliferation, is frequently deregulated in human cancer. Although rapamycin inhibits the two canonical mTOR complexes, mTORC1 and mTORC2, it often shows minimal benefit as an anticancer drug. This is caused by rapamycin resistance of many different tumors, and we show that a third mTOR complex, mTORC3, contributes to this resistance. The ETS (E26 transformation-specific) transcription factor ETV7 interacts with mTOR in the cytoplasm and assembles mTORC3, which is independent of ETV7's transcriptional activity. This complex exhibits bimodal mTORC1/2 activity but is devoid of crucial mTORC1/2 components. Many human cancers activate mTORC3 at considerable frequency, and tumor cell lines that lose mTORC3 expression become rapamycin-sensitive. We show mTORC3's tumorigenicity in a rhabdomyosarcoma mouse model in which transgenic ETV7 expression accelerates tumor onset and promotes tumor penetrance. Discovery of mTORC3 represents an mTOR paradigm shift and identifies a novel target for anticancer drug development.

Inhibition of Bcl-2/Bcl-xL and c-MET causes synthetic lethality in model systems of glioblastoma

Recent data suggest that glioblastomas (GBM) activate the c-MET signaling pathway and display increased levels in anti-apoptotic Bcl-2 family members. Therefore, targeting these two deregulated pathways for therapy might yield synergistic treatment responses. We applied extracellular flux analysis to assess tumor metabolism. We found that combined treatment with ABT263 and Crizotinib synergistically reduces the proliferation of glioblastoma cells, which was dependent on dual inhibition of Bcl-2 and Bcl-xL. The combination treatment led to enhanced apoptosis with loss of mitochondrial membrane potential and activation of caspases. On the molecular level, c-MET-inhibition results in significant energy deprivation with a reduction in oxidative phosphorylation, respiratory capacity and a suppression of intracellular energy production (ATP). In turn, loss of energy levels suppresses protein synthesis, causing a decline in anti-apoptotic Mcl-1 levels. Silencing of Mcl-1 enhanced ABT263 and MET-inhibitor mediated apoptosis, but marginally the combination treatment, indicating that Mcl-1 is the central factor for the induction of cell death induced by the combination treatment. Finally, combined treatment with BH3-mimetics and c-MET inhibitors results in significantly smaller tumors than each treatment alone in a PDX model system of glioblastoma. These results suggest that c-MET inhibition causes a selective vulnerability of GBM cells to Bcl-2/Bcl-xL inhibition.

Targeting BCL-2 regulated apoptosis in cancer

The ability of a cell to undergo mitochondrial apoptosis is governed by pro- and anti-apoptotic members of the BCL-2 protein family. The equilibrium of pro- versus anti-apoptotic BCL-2 proteins ensures appropriate regulation of programmed cell death during development and maintains organismal health. When unbalanced, the BCL-2 family can act as a barrier to apoptosis and facilitate tumour development and resistance to cancer therapy. Here we discuss the BCL-2 family, their deregulation in cancer and recent pharmaceutical developments to target specific members of this family as cancer therapy.

Mitochondrial matrix chaperone and c-myc inhibition causes enhanced lethality in glioblastoma

Malignant gliomas display high levels of the transcription factor c-myc and organize a tumor specific chaperone network within mitochondria. Here, we show that c-myc along with mitochondrial chaperone inhibition displays massive tumor cell death. Inhibition of mitochondrial matrix chaperones and c-myc was established by utilizing genetic as well as pharmacological approaches. Bromodomain and extraterminal (BET) family protein inhibitors, JQ1 and OTX015, were used for c-myc inhibition. Gamitrinib was applied to interfere with mitochondrial matrix chaperones. A xenograft model was used to determine the in vivo efficacy. Combined inhibition of c-myc and mitochondrial matrix chaperones led to a synergistic reduction of cellular proliferation (CI values less than 1) in established glioblastoma, patient-derived xenograft and stem cell-like glioma cultures. The combinatorial treatment of BET inhibitors and Gamitrinib elicited massive apoptosis induction with dissipation of mitochondrial membrane potential and activation of caspases. Mechanistically, BET-inhibitors and Gamitrinib mediated a pronounced integrated stress response with a PERK-dependent up regulation of ATF4 and subsequent modulation of Bcl-2 family of proteins with down-regulation of Mcl-1 and its interacting partner, Usp9X, and an increase in pro-apoptotic Noxa. Blocking ATF4 by siRNA attenuated Gamitrinib/BET inhibitor mediated increase of Noxa. Knockdown of Noxa and Bak protected from the combinatorial treatment. Finally, the combination treatment of Gamitrinib and OTX015 led to a significantly stronger reduction of tumor growth as compared to single treatments in a xenograft model of human glioma without induction of toxicity. Thus, Gamitrinib in combination with BET-inhibitors should be considered for the development for clinical application.

BH3-mimetics and BET-inhibitors elicit enhanced lethality in malignant glioma

Drug combination therapies remain pivotal for the treatment of heterogeneous malignancies, such as glioblastomas. Here, we show a novel lethal interaction between Bcl-xL and c-myc inhibition accomplished by bromodomain protein inhibitors. Established, patient-derived xenograft and stem cell-like glioma cells were treated with the novel bromodomain protein inhibitors, JQ1 and OTX015, along with BH3-mimetics, ABT263 or Obatoclax. Synergy was assessed by calculation of CI values. Small interfering RNAs (siRNAs) were used for gene silencing and mechanistic studies. In vivo experiments were performed in a glioblastoma xenograft model. Single treatments with JQ1 and OTX015 had only moderate effects on the reduction of cellular viability. However, the combination treatment of BH3-mimetics along with JQ1 or OTX015 resulted in a highly synergistic reduction of cellular viability in a broad range of different model systems of malignant glioma. Similarly, knockdown of c-myc sensitized glioma cells for ABT263 mediated cell death. The enhanced loss of cellular viability in the combination treatment was mediated by activation of apoptosis with dissipation of mitochondrial membrane potential and caspase cleavage. The combination treatment led to a modulation of anti- and pro-apoptotic Bcl-2 family members with an increase in pro-apoptotic Noxa mediated by ATF4. Small interfering RNA mediated knockdown of Bak and Noxa protected glioma cells from ABT263/JQ1 mediated apoptosis. Finally, the combination treatment of ABT263 and OTX015 resulted in a regression of tumors and a significantly smaller tumor size as compared to single or vehicle treated tumors. Thus, these results warrant clinical testing for the drug combination of BH3-mimetics along with bromodain protein inhibitors.

Inhibition of deubiquitinases primes glioblastoma cells to apoptosis in vitro and in vivo

It remains a challenge in oncology to identify novel drug regimens to efficiently tackle glioblastoma, the most common primary brain tumor in adults. Here, we target deubiquitinases for glioblastoma therapy by utilizing the small-molecule inhibitor WP1130 which has been characterized as a deubiquitinase inhibitor that interferes with the function of Usp9X. Expression analysis data confirm that Usp9X expression is increased in glioblastoma compared to normal brain tissue indicating its potential as a therapeutic. Consistently, increasing concentrations of WP1130 decrease the cellular viability of established, patient-derived xenograft (PDX) and stem cell-like glioblastoma cells. Specific down-regulation of Usp9X reduces viability in glioblastoma cells mimicking the effects of WP1130. Mechanistically, WP1130 elicits apoptosis and increases activation of caspases. Moreover, WP1130 and siRNAs targeting Usp9X reduce the expression of anti-apoptotic Bcl-2 family members and Inhibitor of Apoptosis Proteins, XIAP and Survivin. Pharmacological and genetic interference with Usp9X efficiently sensitized glioblastoma cells to intrinsic and extrinsic apoptotic stimuli. In addition, single treatment with WP1130 elicited anti-glioma activity in an orthotopic proneural murine model of glioblastoma. Finally, the combination treatment of WP1130 and ABT263 inhibited tumor growth more efficiently than each reagent by its own in vivo without detectable side effects or organ toxicity. Taken together, these results suggest that targeting deubiquitinases for glioma therapy is feasible and effective.

Inhibition of Mitochondrial Matrix Chaperones and Antiapoptotic Bcl-2 Family Proteins Empower Antitumor Therapeutic Responses

Rational therapeutic approaches based on synthetic lethality may improve cancer management. On the basis of a high-throughput drug screen, we provide preclinical proof of concept that targeting the mitochondrial Hsp90 chaperone network (mtHsp90) and inhibition of Bcl-2, Bcl-xL, and Mcl-1 is sufficient to elicit synthetic lethality in tumors recalcitrant to therapy. Our analyses focused on BH3 mimetics that are broad acting (ABT263 and obatoclax) or selective (ABT199, WEHI-539, and A1210477), along with the established mitochondrial matrix chaperone inhibitor gamitrinib-TPP. Drug combinations were tested in various therapy-resistant tumors in vitro and in vivo in murine model systems of melanoma, triple-negative breast cancer, and patient-derived orthotopic xenografts (PDX) of human glioblastoma. We found that combining BH3 mimetics and gamitrinib-TPP blunted cellular proliferation in a synergistic manner by massive activation of intrinsic apoptosis. In like manner, suppressing either Bcl-2, Bcl-xL, or Mcl-1 recapitulated the effects of BH3 mimetics and enhanced the effects of gamitrinib-TPP. Mechanistic investigations revealed that gamitrinib-TPP activated a PERK-dependent integrated stress response, which activated the proapoptotic BH3 protein Noxa and its downstream targets Usp9X and Mcl-1. Notably, in the PDX glioblastoma and BRAFi-resistant melanoma models, this drug combination safely and significantly extended host survival. Our results show how combining mitochondrial chaperone and Bcl-2 family inhibitors can synergize to safely degrade the growth of tumors recalcitrant to other treatments. Cancer Res; 77(13); 3513-26. ©2017 AACR.

YM155 enhances ABT-737-mediated apoptosis through Mcl-1 downregulation in Mcl-1-overexpressed cancer cells

ABT-737 is a BH3 mimetic inhibitor of Bcl-xL, Bcl-2, and Bcl-w, and it has been reported for anti-cancer effects in various types of cancer cells. However, ABT-737 fails to induce apoptosis in cancer cell with high levels of Mcl-1 expression. The pharmacological survivin inhibitor YM155 has been reported to induce downregulation of Mcl-1 expression. Therefore, we investigated the effect of YM155 to sensitize resistance against ABT-737 in Mcl-1-overexpressed human renal carcinoma Caki cells. We found that ABT-737 alone and YM155 alone did not induce apoptosis, but YM155 markedly sensitized ABT-737-mediated apoptosis in Mcl-1-overexpressed Caki cells, human glioma cells (U251MG), and human lung carcinoma cells (A549). In contrast, combined treatment with ABT-737 and YM155 did not increase apoptosis in normal mouse kidney cells (TCMK-1) and human mesangial cells (MC). YM155 induced lysosome-dependent downregulation of Mcl-1 expression in Mcl-1-overexpressed Caki cells. In addition, combined treatment with ABT-737 and YM155 induced loss of mitochondrial membrane potential and inhibited interaction of Bcl-xL and Bax. Taken together, our results suggested that YM155 effectively improves sensitivity to ABT-737 through downregulation of Mcl-1 expression.

Co-targeting of Bcl-2 and mTOR pathway triggers synergistic apoptosis in BH3 mimetics resistant acute lymphoblastic leukemia

Several chemo-resistance mechanisms including the Bcl-2 protein family overexpression and constitutive activation of the PI3K/Akt/mTOR signaling have been documented in acute lymphoblastic leukemia (ALL), encouraging targeted approaches to circumvent this clinical problem. Here we analyzed the activity of the BH3 mimetic ABT-737 in ALL, exploring the synergistic effects with the mTOR inhibitor CCI-779 on ABT-737 resistant cells. We showed that a low Mcl-1/Bcl-2 plus Bcl-xL protein ratio determined ABT-737 responsiveness. ABT-737 exposure further decreased Mcl-1, inducing apoptosis on sensitive models and primary samples, while not affecting resistant cells. Co-inhibition of Bcl-2 and the mTOR pathway resulted cytotoxic on ABT-737 resistant models, by downregulating mTORC1 activity and Mcl-1 in a proteasome-independent manner. Although Mcl-1 seemed to be critical, ectopic modulation did not correlate with apoptosis changes. Importantly, dual targeting proved effective on ABT-737 resistant samples, showing additive/synergistic effects. Together, our results show the efficacy of BH3 mimetics as single agent in the majority of the ALL samples and demonstrate that resistance to ABT-737 mostly correlated with Mcl-1 overexpression. Co-targeting of the Bcl-2 protein family and mTOR pathway enhanced drug-induced cytotoxicity by suppressing Mcl-1, providing a novel therapeutic approach to overcome BH3 mimetics resistance in ALL.

Arsenic trioxide induces Noxa-dependent apoptosis in rhabdomyosarcoma cells and synergizes with antimicrotubule drugs

The prognosis of metastatic or relapsed rhabdomyosarcoma (RMS) is poor, highlighting the need of new treatment options. In the present study, we evaluated the in vitro efficacy of arsenic trioxide (ATO) in RMS, a FDA-approved drug used in pediatric leukemia. Here, we report that ATO exerts antitumor activity against RMS cells both as single agent and in combination with microtubule-targeting drugs. Monotherapy with ATO reduces cell viability, triggers apoptosis and suppresses clonogenic survival of RMS cells, at least in part, by transcriptional induction of the proapoptotic BH3-only protein Noxa. siRNA-mediated knockdown of Noxa significantly rescues ATO-mediated cell death, demonstrating that Noxa is required for cell death. Also, ATO suppresses endogenous Hedgehog (Hh) signaling, as it significantly reduces Gli1 transcriptional activity and expression levels of several Hh target genes. Furthermore, we identify synergistic induction of apoptosis by ATO together with several antimicrotubule agents including vincristine (VCR), vinblastine and eribulin. The addition of the broad-range caspase inhibitor zVAD.fmk or overexpression of the antiapoptotic protein Bcl-2 significantly reduce ATO/VCR-induced cell death, indicating that the ATO/VCR combination triggers caspase-dependent apoptosis via the mitochondrial pathway. In summary, ATO exerts antitumor activity against RMS, especially in combination with antimicrotubule drugs. These findings have important implications for the development of novel therapeutic strategies for RMS.

Pro-survival responses to the dual inhibition of anti-apoptotic Bcl-2 family proteins and mTOR-mediated signaling in hypoxic colorectal carcinoma cells

Background

The use of targeted agents to impel dual inhibition of anti-apoptotic mechanisms and mTOR-mediated pro-survival signaling in colorectal carcinoma (CRC) cell lines with KRAS or BRAF mutation has been shown to induce apoptosis, a timely result given CRC entities harboring such mutations are in need of new therapies. Since CRC comprises heterogeneous tumors with predominant hypoxic components, we investigated effects of an inhibitor of anti-apoptotic Bcl-2 family proteins (ABT-737) in combination with an mTOR inhibitor (AZD8055)—collectively referred to as combo-Rx, in hypoxic CRC cell lines.

Methods

Cell viability measures, expression of proteins implicated in apoptosis and MAPK/PI3K-AKT/mTOR pathway signaling, and profiling of composite kinase activities were undertaken in a panel of 14 cell lines.

Results

In hypoxic conditions, combo-Rx suppressed viability of 13 of the cell lines, albeit ABT-737 did not significantly potentiate the inhibitory effect of single-agent AZD8055 in six of the models. Hypoxic KRAS/PIK3CA-mutant HCT-116 and HCT-15 cell lines (both with low endogenous expression of the anti-apoptotic Mcl-1 protein and showing augmented inhibition of viability following the addition of ABT-737 to AZD8055) responded to combo-Rx by induction of apoptosis but with the simultaneous strong Mcl-1 up-regulation and activation of MAPK/PI3K-conducted signaling. In contrast, in hypoxic KRAS-mutant LoVo (devoid of PIK3CA mutation), BRAF/PIK3CA-mutant RKO, and wild-type Colo320DM cell lines (all with high endogenous Mcl-1 expression and being resistant to the additional effect of ABT-737 to AZD8055), combo-Rx did not elicit apoptotic or pro-survival responses.

Conclusions

The concurrent inhibition of anti-apoptotic proteins and mTOR-mediated signaling in hypoxic KRAS/PIK3CA-mutant CRC cell lines resulted in pro-survival responses in parallel with the intended anti-proliferative effects, a finding that should be of note if considering combinatory targeting of multiple pathways in this CRC entity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2600-y) contains supplementary material, which is available to authorized users.

Nuclear receptor 4A1 (NR4A1) as a drug target for treating rhabdomyosarcoma (RMS)

The orphan nuclear receptor NR4A1 is expressed in tumors from rhabdomyosarcoma (RMS) patients and Rh30 and RD RMS cell lines, and we used RNA interference (RNAi) to investigate the role of this receptor in RMS cells. Knockdown of NR4A1 in Rh30 cells decreased cell proliferation, induced Annexin V staining and induced polyADPribose polymerase (PARP) cleavage and these results were similar to those observed in other solid tumors. Previous studies show that NR4A1 regulates expression of growth promoting/pro-survival genes with GC-rich promoters, activates mTOR through suppression of p53, and maintains low oxidative stress by regulating expression of isocitrate dehydrogenase 1 (IDH1) and thioredoxin domain containing 5 (TXNDC5). Results of RNAi studies demonstrated that NR4A1 also regulates these pathways and associated genes in RMS cells and thereby exhibits pro-oncogenic activity. 1,1-Bis(3-indolyl)-1-(p-substituted phenyl)methane (C-DIM) analogs containing p-hydroxyl (DIM-C-pPhOH) and p-carboxymethyl (DIM-C-pPhCO2Me) substituents are NR4A1 ligands that decreased NR4A1-dependent transactivation in RMS cells and inhibited RMS cell and tumor growth and induced apoptosis. Moreover, the effects of NR4A1 knockdown and the C-DIM/NR4A1 antagonists were comparable as inhibitors of NR4A1-dependent genes/pathways. Both NR4A1 knockdown and treatment with DIM-C-pPhOH and DIM-C-pPhCO2Me also induced ROS which activated stress genes and induced sestrin 2 which activated AMPK and inhibited mTOR in the mutant p53 RMS cells. Since NR4A1 regulates several growth-promoting/pro-survival pathways in RMS, the C-DIM/NR4A1 antagonists represent a novel mechanism-based approach for treating this disease alone or in combination and thereby reducing the adverse effects of current cytotoxic therapies.

Combined inhibition of Bcl-2/Bcl-xL and Usp9X/Bag3 overcomes apoptotic resistance in glioblastoma in vitro and in vivo

Despite great efforts taken to advance therapeutic measures for patients with glioblastoma, the clinical prognosis remains grim. The antiapoptotic Bcl-2 family protein Mcl-1 is overexpressed in glioblastoma and represents an important resistance factor to the BH-3 mimetic ABT263.

In this study, we show that combined treatment with ABT263 and GX15-070 overcomes apoptotic resistance in established glioblastoma cell lines, glioma stem-like cells and primary cultures. Moreover, this treatment regimen also proves to be advantageous in vivo. On the molecular level, GX15-070 enhanced apoptosis by posttranslational down-regulation of the deubiquitinase, Usp9X, and the chaperone Bag3, leading to a sustained depletion of Mcl-1 protein levels. Moreover, knock-down of Usp9X or Bag3 depleted endogenous Mcl-1 protein levels and in turn enhanced apoptosis induced through Bcl-2/Bcl-xL inhibition.

In conclusion, combined treatment with ABT263 and GX15-070 results in a significantly enhanced anti-cancer activity in vitro as well as in vivo in the setting of glioblastoma. Both drugs, ABT263 and GX15-070 have been evaluated in clinical studies which facilitates the translational aspect of taking this combinatorial approach to the clinical setting. Furthermore we present a novel mechanism by which GX15-070 counteracts Mcl-1 expression which may lay a foundation for a novel target in cancer therapy.

A Synthetic Cell-Penetrating Dominant-Negative ATF5 Peptide Exerts Anticancer Activity against a Broad Spectrum of Treatment-Resistant Cancers

PURPOSE

Despite significant progress in cancer research, many tumor entities still have an unfavorable prognosis. Activating transcription factor 5 (ATF5) is upregulated in various malignancies and promotes apoptotic resistance. We evaluated the efficacy and mechanisms of the first described synthetic cell-penetrating inhibitor of ATF5 function, CP-d/n-ATF5-S1.

EXPERIMENTAL DESIGN

Preclinical drug testing was performed in various treatment-resistant cancer cells and in vivo xenograft models.

RESULTS

CP-d/n-ATF5-S1 reduced the transcript levels of several known direct ATF5 targets. It depleted endogenous ATF5 and induced apoptosis across a broad panel of treatment-refractory cancer cell lines, sparing non-neoplastic cells. CP-d/n-ATF5-S1 promoted tumor cell apoptotic susceptibility in part by reducing expression of the deubiquitinase Usp9X and led to diminished levels of antiapoptotic Bcl-2 family members Mcl-1 and Bcl-2. In line with this, CP-d/n-ATF5-S1 synergistically enhanced tumor cell apoptosis induced by the BH3-mimetic ABT263 and the death ligand TRAIL. In vivo, CP-d/n-ATF5-S1 attenuated tumor growth as a single compound in glioblastoma, melanoma, prostate cancer, and triple receptor-negative breast cancer xenograft models. Finally, the combination treatment of CP-d/n-ATF5-S1 and ABT263 significantly reduced tumor growth in vivo more efficiently than each reagent on its own.

CONCLUSIONS

Our data support the idea that CP-d/n-ATF5-S1, administered as a single reagent or in combination with other drugs, holds promise as an innovative, safe, and efficient antineoplastic agent against treatment-resistant cancers. Clin Cancer Res; 22(18); 4698-711. ©2016 AACR.

PI3K/AKT/mTOR inhibition in combination with doxorubicin is an effective therapy for leiomyosarcoma

BACKGROUND

Leiomyosarcoma (LMS) is a common type of soft tissue sarcoma that responds poorly to standard chemotherapy. Thus the goal of this study was to identify novel selective therapies that may be effective in leiomyosarcoma by screening cell lines with a small molecule library comprised of 480 kinase inhibitors to functionally determine which signalling pathways may be critical for LMS growth.

METHODS

LMS cell lines were screened with the OICR kinase library and a cell viability assay was used to identify potentially effective compounds. The top 10 % of hits underwent secondary validation to determine their EC50 and immunoblots were performed to confirm selective drug action. The efficacy of combination drug therapy with doxorubicin (Dox) in vitro was analyzed using the Calcusyn program after treatment with one of three dosing schedules: concurrent treatment, initial treatment with a selective compound followed by Dox, or initial treatment with Dox followed by the selective compound. Single and combination drug therapy were then validated in vivo using LMS xenografts.

RESULTS

Compounds that targeted PI3K/AKT/mTOR pathways (52 %) were most effective. EC50s were determined to validate these initial hits, and of the 11 confirmed hits, 10 targeted PI3K and/or mTOR pathways with EC50 values <1 μM. We therefore examined if BEZ235 and BKM120, two selective compounds in these pathways, would inhibit leiomyosarcoma growth in vitro. Immunoblots confirmed on-target effects of these compounds in the PI3K and/or mTOR pathways. We next investigated if there was synergy with these agents and first line chemotherapy doxorubicin (Dox), which would allow for earlier introduction into patient care. Only combined treatment of BEZ235 and Dox was synergistic in vitro. To validate these findings in pre-clinical models, leiomyosarcoma xenografts were treated with single agent and combination therapy. BEZ235 treated xenografts (n = 8) demonstrated a decrease in tumor volume of 42 % whereas combining BEZ235 with Dox (n = 8) decreased tumor volume 68 % compared to vehicle alone.

CONCLUSIONS

In summary, this study supports further investigation into the use of PI3K and mTOR inhibitors alone and in combination with standard treatment in leiomyosarcoma patients.

Inhibition of mTOR complex 2 induces GSK3/FBXW7-dependent degradation of sterol regulatory element-binding protein 1 (SREBP1) and suppresses lipogenesis in cancer cells

Cancer cells feature increased de novo lipogenesis. Sterol regulatory element-binding protein 1 (SREBP1), when presented in its mature form (mSREBP1), enhances lipogenesis by increasing transcription of several of its target genes. Mammalian target of rapamycin (mTOR) complexes, mTORC1 and mTORC2, are master regulators of cellular survival, growth and metabolism. A role for mTORC1 in the regulation of SREBP1 activity has been suggested; however, the connection between mTORC2 and SREBP1 has not been clearly established and hence is the focus of this study. mTOR kinase inhibitors (for example, INK128), which inhibit both mTORC1 and mTORC2, decreased mSREBP1 levels in various cancer cell lines. Knockdown of rictor, but not raptor, also decreased mSREBP1. Consistently, reduced mSREBP1 levels were detected in cells deficient in rictor or Sin1 compared with parent or rictor-deficient cells with re-expression of ectopic rictor. Hence it is mTORC2 inhibition that causes mSREBP1 reduction. As a result, expression of the mSREBP1 target genes acetyl-CoA carboxylase and fatty-acid synthase was suppressed, along with suppressed lipogenesis in cells exposed to INK128. Moreover, mSREBP1 stability was reduced in cells treated with INK128 or rictor knockdown. Inhibition of proteasome, GSK3 or the E3 ubiquitin ligase, FBXW7, prevented mSREBP1 reduction induced by mTORC2 inhibition. Thus mTORC2 inhibition clearly facilitates GSK3-dependent, FBXW7-mediated mSREBP1 degradation, leading to mSREBP1 reduction. Accordingly, we conclude that mTORC2 positively regulates mSREBP1 stability and lipogenesis. Our findings reveal a novel biological function of mTORC2 in the regulation of lipogenesis and warrant further study in this direction.

Identification of synthetic lethality of PLK1 inhibition and microtubule-destabilizing drugs

Polo-like kinase 1 (PLK1) is frequently overexpressed in cancer, which correlates with poor prognosis. Therefore, we investigated PLK1 as therapeutic target using rhabdomyosarcoma (RMS) as a model. Here, we identify a novel synthetic lethal interaction of PLK1 inhibitors and microtubule-destabilizing drugs in preclinical RMS models and elucidate the underlying molecular mechanisms of this synergism. PLK1 inhibitors (i.e., BI 2536 and BI 6727) synergistically induce apoptosis together with microtubule-destabilizing drugs (i.e., vincristine (VCR), vinblastine (VBL) and vinorelbine (VNR)) in several RMS cell lines (combination index <0.9) including a patient-derived primary RMS culture. Importantly, PLK1 inhibitors and VCR cooperate to significantly suppress RMS growth in two in vivo models, including a mouse xenograft model, without causing additive toxicity. In addition, no toxicity was observed in non-malignant fibroblast or myoblast cultures. Mechanistically, BI 2536/VCR co-treatment triggers mitotic arrest, which initiates mitochondrial apoptosis by inactivation of antiapoptotic BCL-2 family proteins, followed by BAX/BAK activation, production of reactive oxygen species (ROS) and activation of caspase-dependent or caspase-independent effector pathways. This conclusion is supported by data showing that BI 2536/VCR-induced apoptosis is significantly inhibited by preventing cells to enter mitosis, by overexpression of BCL-2 or a non-degradable MCL-1 mutant, by BAK knockdown, ROS scavengers, caspase inhibition or endonuclease G silencing. This identification of a novel synthetic lethality of PLK1 inhibitors and microtubule-destabilizing drugs has important implications for developing PLK1 inhibitor-based combination treatments.

Heightening Energetic Stress Selectively Targets LKB1-Deficient Non-Small Cell Lung Cancers

Inactivation of the LKB1 tumor suppressor is a frequent event in non-small cell lung carcinoma (NSCLC) leading to the activation of mTOR complex 1 (mTORC1) and sensitivity to the metabolic stress inducer phenformin. In this study, we explored the combinatorial use of phenformin with the mTOR catalytic kinase inhibitor MLN0128 as a treatment strategy for NSCLC bearing comutations in the LKB1 and KRAS genes. NSCLC is a genetically and pathologically heterogeneous disease, giving rise to lung tumors of varying histologies that include adenocarcinomas and squamous cell carcinomas (SCC). We demonstrate that phenformin in combination with MLN0128 induced a significant therapeutic response in KRAS/LKB1-mutant human cell lines and genetically engineered mouse models of NSCLC that develop both adenocarcinomas and SCCs. Specifically, we found that KRAS/LKB1-mutant lung adenocarcinomas responded strongly to phenformin + MLN0128 treatment, but the response of SCCs to single or combined treatment with MLN0128 was more attenuated due to acquired resistance to mTOR inhibition through modulation of the AKT-GSK signaling axis. Combinatorial use of the mTOR inhibitor and AKT inhibitor MK2206 robustly inhibited the growth and viability of squamous lung tumors, thus providing an effective strategy to overcome resistance. Taken together, our findings define new personalized therapeutic strategies that may be rapidly translated into clinical use for the treatment of KRAS/LKB1-mutant adenocarcinomas and squamous cell tumors.

Co-administration of the mTORC1/TORC2 inhibitor INK128 and the Bcl-2/Bcl-xL antagonist ABT-737 kills human myeloid leukemia cells through Mcl-1 down-regulation and AKT inactivation

Effects of concurrent inhibition of mTORC1/2 and Bcl-2/Bcl-xL in human acute myeloid leukemia cells were examined. Tetracycline-inducible Bcl-2/Bcl-xL dual knockdown markedly sensitized acute myeloid leukemia cells to the dual TORC1/2 inhibitor INK128 in vitro as well as in vivo. Moreover, INK128 co-administered with the Bcl-2/xL antagonist ABT-737 sharply induced cell death in multiple acute myeloid leukemia cell lines, including TKI-resistant FLT3-ITD mutants and primary acute myeloid leukemia blasts carrying various genetic aberrations e.g., FLT3, IDH2, NPM1, and Kras, while exerting minimal toxicity toward normal hematopoietic CD34(+) cells. Combined treatment was particularly active against CD34(+)/CD38(-)/CD123(+) primitive leukemic progenitor cells. The INK128/ABT-737 regimen was also effective in the presence of a protective stromal microenvironment. Notably, INK128 was more potent than the TORC1 inhibitor rapamycin in down-regulating Mcl-1, diminishing AKT and 4EBP1 phosphorylation, and potentiating ABT-737 activity. Mcl-1 ectopic expression dramatically attenuated INK128/ABT-737 lethality, indicating an important functional role for Mcl-1 down-regulation in INK128/ABT-737 actions. Immunoprecipitation analysis revealed that combined treatment markedly diminished Bax, Bak, and Bim binding to all major anti-apoptotic Bcl-2 members (Bcl-2/Bcl-xL/Mcl-1), while Bax/Bak knockdown reduced cell death. Finally, INK128/ABT-737 co-administration sharply attenuated leukemia growth and significantly prolonged survival in a systemic acute myeloid leukemia xenograft model. Analysis of subcutaneous acute myeloid leukemia-derived tumors revealed significant decrease in 4EBP1 phosphorylation and Mcl-1 protein level, consistent with results obtained in vitro. These findings demonstrate that co-administration of dual mTORC1/mTORC2 inhibitors and BH3-mimetics exhibits potent anti-leukemic activity in vitro and in vivo, arguing that this strategy warrants attention in acute myeloid leukemia.

Attacking cancer's Achilles heel: antagonism of anti-apoptotic BCL-2 family members

Malignant cells routinely violate cellular checkpoints that should initiate cell death in normal cells by triggering pro-apoptotic members of the BCL-2 family of proteins. To escape such death inducing signals, cancer cells often select for upregulation of anti-apoptotic BCL-2 family members including BCL-2, BCL-XL , BFL-1, BCL-W and MCL-1. These family members prevent death by sequestering pro-apoptotic molecules. To counter this resistance mechanism, small molecule inhibitors of anti-apoptotic BCL-2 family members have been under development. These molecules have shown promise in pre-clinical and clinical testing to overcome apoptotic resistance, prompting cancer cells to undergo apoptosis. Alternatively, other strategies have taken advantage of the normal regulatory machinery controlling anti-apoptotic molecules and have used inhibitors of signaling pathways to down-modulate the expression of anti-apoptotic molecules, thus tilting the balance in cancer cells to cell death. This review explores recent developments and strategies aimed at antagonizing anti-apoptotic BCL-2 family member action to promote the induction of cell death in cancer therapy.

Eribulin synergizes with Polo-like kinase 1 inhibitors to induce apoptosis in rhabdomyosarcoma

Eribulin, a novel microtubule-interfering drug, was recently shown to exhibit high antitumor activity in vivo against various pediatric cancers. Here, we identify a novel synthetic lethal interaction of Eribulin together with Polo-like kinase 1 (PLK1) inhibitors against rhabdomyosarcoma (RMS) in vitro and in vivo. Eribulin and the PLK1 inhibitor BI 2536 at subtoxic concentrations synergize to induce apoptosis in RMS cells as confirmed by calculation of combination index (CI). Also, Eribulin/BI 2536 co-treatment is significantly more effective than monotherapy to reduce cell viability and inhibit colony formation of RMS cells. Similarly, Eribulin and BI 2536 act in concert to trigger apoptosis in a primary, patient-derived ARMS culture, underscoring the clinical relevance of this combination. Importantly, Eribulin and BI 2536 cooperate to suppress tumor growth in an in vivo model of RMS. On molecular grounds, Eribulin/BI 2536 co-treatment causes profound mitotic arrest, which is critically required for synergism, since inhibition of mitotic arrest by CDK1 inhibitor RO-3306 abolishes Eribulin/BI 2536-mediated apoptosis. Eribulin and BI 2536 cooperate to activate caspase-9, -3 and -8, which is necessary for apoptosis induction, since the broad-range caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (zVAD.fmk) reduces Eribulin/BI 2536-induced apoptosis significantly, yet partially. Intriguingly, knockdown of endonuclease G (ENDOG) also significantly inhibits Eribulin/BI 2536-triggered apoptosis, demonstrating the involvement of both caspase-dependent and -independent effector pathways. Synergistic induction of apoptosis is similarly found for Eribulin/BI 2536 co-treatment in neuroblastoma cells and for the combination of vincristine (another antimicrotubule chemotherapeutic) with Poloxin (another PLK1 inhibitor), thus pointing to a broader significance of this concomitant microtubule- and PLK1-targeting strategy for pediatric oncology. In conclusion, the identification of a novel synthetic lethality by dual targeting of mitosis using microtubule-interfering and PLK1-targeted drugs, i.e. Eribulin and BI 2536, has important implications for the development of more effective treatment strategies for RMS.

A Pan-GTPase Inhibitor as a Molecular Probe

Overactive GTPases have often been linked to human diseases. The available inhibitors are limited and have not progressed far in clinical trials. We report here a first-in-class small molecule pan-GTPase inhibitor discovered from a high throughput screening campaign. The compound CID1067700 inhibits multiple GTPases in biochemical, cellular protein and protein interaction, as well as cellular functional assays. In the biochemical and protein interaction assays, representative GTPases from Rho, Ras, and Rab, the three most generic subfamilies of the GTPases, were probed, while in the functional assays, physiological processes regulated by each of the three subfamilies of the GTPases were examined. The chemical functionalities essential for the activity of the compound were identified through structural derivatization. The compound is validated as a useful molecular probe upon which GTPase-targeting inhibitors with drug potentials might be developed.