GX15-070 (obatoclax) overcomes glucocorticoid resistance in acute lymphoblastic leukemia through induction of apoptosis and autophagy

Comprehensive review of Bcl-2 family proteins in cancer apoptosis: Therapeutic strategies and promising updates of natural bioactive compounds and small molecules

Cancer has a considerably higher fatality rate than other diseases globally and is one of the most lethal and profoundly disruptive ailments. The increasing incidence of cancer among humans is one of the greatest challenges in the field of healthcare. A significant factor in the initiation and progression of tumorigenesis is the dysregulation of physiological processes governing cell death, which results in the survival of cancerous cells. B-cell lymphoma 2 (Bcl-2) family members play important roles in several cancer-related processes. Drug research and development have identified various promising natural compounds that demonstrate potent anticancer effects by specifically targeting Bcl-2 family proteins and their associated signaling pathways. This comprehensive review highlights the substantial roles of Bcl-2 family proteins in regulating apoptosis, including the intricate signaling pathways governing the activity of these proteins, the impact of reactive oxygen species, and the crucial involvement of proteasome degradation and the stress response. Furthermore, this review discusses advances in the exploration and potential therapeutic applications of natural compounds and small molecules targeting Bcl-2 family proteins and thus provides substantial scientific information and therapeutic strategies for cancer management.

Unveiling autophagy complexity in leukemia: The molecular landscape and possible interactions with apoptosis and ferroptosis

Autophagy is a self-digestion multistep process in which causes the homeostasis through degradation of macromolecules and damaged organelles. The autophagy-mediated tumor progression regulation has been a critical point in recent years, revealing the function of this process in reduction or acceleration of carcinogenesis. Leukemia is a haematological malignancy in which abnormal expansion of hematopoietic cells occurs. The current and conventional therapies from chemotherapy to cell transplantation have failed to appropriately treat the leukemia patients. Among the mechanisms dysregulated in leukemia, autophagy is a prominent one in which can regulate the hallmarks of this tumor. The protective autophagy inhibits apoptosis and ferroptosis in leukemia, while toxic autophagy accelerates cell death. The proliferation and invasion of tumor cells are tightly regulated by the autophagy. The direction of regulation depends on the function of autophagy that is protective or lethal. The protective autophagy accelerates chemoresistance and radio-resistsance. The non-coding RNAs, histone transferases and other pathways such as PI3K/Akt/mTOR are among the regulators of autophagy in leukemia progression. The pharmacological intervention for the inhibition or induction of autophagy by the compounds including sesamine, tanshinone IIA and other synthetic compounds can chance progression of leukemia.

Filanesib plus bortezomib and dexamethasone in relapsed/refractory t(11;14) and 1q21 gain multiple myeloma

Filanesib is a first-in-class kinesin spindle protein inhibitor which demonstrated safety and encouraging activity in combination with bortezomib and dexamethasone in relapsed/refractory multiple myeloma in a preliminary analysis of dose-escalation phase results. This multicenter study included first a dose-escalation phase to determine maximum tolerated dose of two schedules of filanesib, bortezomib, and dexamethasone and a subsequent dose-expansion phase using the maximum tolerated doses. In the dose-expansion phase, 28 patients were evaluable for safety and efficacy. The most common grade ≥3 adverse events were neutropenia (21%) and anemia (18%), which were noncumulative and reversible, and hypertension (18%). The overall response rate was 43% with median duration of response not yet reached (range, 2.8-23.7+ months) with median follow-up of 6.3 months. A post hoc analysis incorporated 29 dose-escalation phase patients who received therapeutic filanesib doses, with an overall response rate of 39% and median duration of response of 18.0 months among the 57 total patients with median progression-free survival of 8.5 months. Notably, the PFS of high risk patients was comparable at 8.5 months, driven by the patients with 1q21 gain, characterized by increased MCL-1 expression, with a PFS of 9.1 months versus 3.5 months for the remainder of high risk patients. Patients with t(11;14) also had an encouraging PFS of 15.0 months. The combination of filanesib, bortezomib, and dexamethasone continues to show safety and encouraging activity in relapsed/refractory multiple myeloma, particularly in those patients with 1q21 gain and t(11;14).

Cell Survival and Cell Death at the Intersection of Autophagy and Apoptosis: Implications for Current and Future Cancer Therapeutics

Autophagy and apoptosis are functionally distinct mechanisms for cytoplasmic and cellular turnover. While these two pathways are distinct, they can also regulate each other, and central components of the apoptosis or autophagy pathway regulate both processes directly. Furthermore, several upstream stress-inducing signaling pathways can influence both autophagy and apoptosis. The crosstalk between autophagy and apoptosis has an integral role in pathological processes, including those related to cancer, homeostasis, and aging. Apoptosis is a form of programmed cell death, tightly regulated by various cellular and biochemical mechanisms, some of which have been the focus of drug discovery efforts targeting cancer therapeutics. Autophagy is a cellular degradation pathway whereby cells recycle macromolecules and organelles to generate energy when subjected to stress. Autophagy can act as either a prodeath or a prosurvival process and is both tissue and microenvironment specific. In this review we describe five groups of proteins that are integral to the apoptosis pathway and discuss their role in regulating autophagy. We highlight several apoptosis-inducing small molecules and biologics that have been developed and advanced into the clinic and discuss their effects on autophagy. For the most part, these apoptosis-inducing compounds appear to elevate autophagy activity. Under certain circumstances autophagy demonstrates cytoprotective functions and is overactivated in response to chemo- or radiotherapy which can lead to drug resistance, representing a clinical obstacle for successful cancer treatment. Thus, targeting the autophagy pathway in combination with apoptosis-inducing compounds may be a promising strategy for cancer therapy.

BH3-mimetics: recent developments in cancer therapy

The hopeful outcomes from 30 years of research in BH3-mimetics have indeed served a number of solid paradigms for targeting intermediates from the apoptosis pathway in a variety of diseased states. Not only have such rational approaches in drug design yielded several key therapeutics, such outputs have also offered insights into the integrated mechanistic aspects of basic and clinical research at the genetics level for the future. In no other area of medical research have the effects of such work been felt, than in cancer research, through targeting the BAX-Bcl-2 protein-protein interactions. With these promising outputs in mind, several mimetics, and their potential therapeutic applications, have also been developed for several other pathological conditions, such as cardiovascular disease and tissue fibrosis, thus highlighting the universal importance of the intrinsic arm of the apoptosis pathway and its input to general tissue homeostasis. Considering such recent developments, and in a field that has generated so much scientific interest, we take stock of how the broadening area of BH3-mimetics has developed and diversified, with a focus on their uses in single and combined cancer treatment regimens and recently explored therapeutic delivery methods that may aid the development of future therapeutics of this nature.

Autophagy and Metabolism in Normal and Malignant Hematopoiesis

The hematopoietic system relies on regulation of both metabolism and autophagy to maintain its homeostasis, ensuring the self-renewal and multipotent differentiation potential of hematopoietic stem cells (HSCs). HSCs display a distinct metabolic profile from that of their differentiated progeny, while metabolic rewiring from glycolysis to oxidative phosphorylation (OXPHOS) has been shown to be crucial for effective hematopoietic differentiation. Autophagy-mediated regulation of metabolism modulates the distinct characteristics of quiescent and differentiating hematopoietic cells. In particular, mitophagy determines the cellular mitochondrial content, thus modifying the level of OXPHOS at the different differentiation stages of hematopoietic cells, while, at the same time, it ensures the building blocks and energy for differentiation. Aberrations in both the metabolic status and regulation of the autophagic machinery are implicated in the development of hematologic malignancies, especially in leukemogenesis. In this review, we aim to investigate the role of metabolism and autophagy, as well as their interconnections, in normal and malignant hematopoiesis.

Bioactive peptide isolated from sesame seeds inhibits cell proliferation and induces apoptosis and autophagy in leukemic cells

Leukemia is the most common type of hematological malignancies. Several natural products including bioactive peptides have been explored and studied for their anti-leukemic activities. In the present study, anti-leukemic peptide, IGTLILM (IM-7), was isolated and identified from the protein hydrolysate of sesame seeds by reverse phase-solid phase extraction, off-gel fractionation and nano LC-MS/MS. The cytotoxic effects of IM-7 were studied in MOLT-4 and NB4 acute leukemic cell lines using an MTT assay. The induction of apoptosis and autophagy was investigated by flow cytometry using Annexin V-FITC/PI staining and anti-LC3/FITC antibodies, respectively. The mRNA alterations of apoptotic and autophagic-related genes were determined by reverse transcription-quantitative PCR. The present study found that IM-7 inhibited the proliferation of MOLT-4 and NB4 cells in dose-dependent manner, but it showed a minimal effect on healthy mononuclear cells. IM-7 activated apoptosis and autophagy through the upregulation of CASP3, ULK1 and BECN1 and the downregulation of BCL2. In addition, IM-7 enhanced the cytotoxic effect of the anti-leukemic drug, daunorubicin. The findings suggested that IM-7 was potent to suppress the proliferation of MOLT-4 and NB4 leukemic cells and induce apoptosis and autophagy through the regulation of caspase 3-Bcl-2 and ULK1-Beclin1, respectively.

Overcoming Glucocorticoid Resistance in Acute Lymphoblastic Leukemia: Repurposed Drugs Can Improve the Protocol

Glucocorticoids (GCs) are a central component of multi-drug treatment protocols against T and B acute lymphoblastic leukemia (ALL), which are used intensively during the remission induction to rapidly eliminate the leukemic blasts. The primary response to GCs predicts the overall response to treatment and clinical outcome. In this review, we have critically analyzed the available data on the effects of GCs on sensitive and resistant leukemic cells, in order to reveal the mechanisms of GC resistance and how these mechanisms may determine a poor outcome in ALL. Apart of the GC resistance, associated with a decreased expression of receptors to GCs, there are several additional mechanisms, triggered by alterations of different signaling pathways, which cause the metabolic reprogramming, with an enhanced level of glycolysis and oxidative phosphorylation, apoptosis resistance, and multidrug resistance. Due to all this, the GC-resistant ALL show a poor sensitivity to conventional chemotherapeutic protocols. We propose pharmacological strategies that can trigger alternative intracellular pathways to revert or overcome GC resistance. Specifically, we focused our search on drugs, which are already approved for treatment of other diseases and demonstrated anti-ALL effects in experimental pre-clinical models. Among them are some “truly” re-purposed drugs, which have different targets in ALL as compared to other diseases: cannabidiol, which targets mitochondria and causes the mitochondrial permeability transition-driven necrosis, tamoxifen, which induces autophagy and cell death, and reverts GC resistance through the mechanisms independent of nuclear estrogen receptors (“off-target effects”), antibiotic tigecycline, which inhibits mitochondrial respiration, causing energy crisis and cell death, and some anthelmintic drugs. Additionally, we have listed compounds that show a classical mechanism of action in ALL but are not used still in treatment protocols: the BH3 mimetic venetoclax, which inhibits the anti-apoptotic protein Bcl-2, the hypomethylating agent 5-azacytidine, which restores the expression of the pro-apoptotic BIM, and compounds targeting the PI3K-Akt-mTOR axis. Accordingly, these drugs may be considered for the inclusion into chemotherapeutic protocols for GC-resistant ALL treatments.

Ligand-based discovery of small molecules suppressing cancer cell proliferation via autophagic flux inhibition

Autophagy is a conserved self-degradation system closely related to cancer progression. Small molecule inhibitors of autophagy have proven to be efficient tools in cancer therapy and are in high demand. Here we report the discovery of two compounds (LZ02/01) capable of suppressing cancer cell proliferation via inhibiting autophagy flux and promoting apoptosis. Potential autophagy inhibitors were selected based on the pharmacophore model derived from the structures of known autophagy inhibitors. LZ02/01-mediated autophagy flux disruption and apoptosis promotion in breast and hepatocellular carcinoma cells (MCF-7 and Hep3B) were examined using a combination of molecular methods in vitro and in vivo. The synergistic tumor-suppressing effects of LZ02 and chloroquine were validated by adopting a xenograft mice model of human breast cancer. Two potential inhibitors (LZ02/01) targeting an autophagy pathway were discovered from the Enamine database. In both MCF-7 and Hep3B cells, LZ02 and LZ01 had the effect of causing the co-occurrence of autophagic flux inhibition and apoptosis induction, robustly suppressing the growth, proliferation, and cell cycle progression. Further tests revealed that FoxO3a and its downstream target genes regulating autophagy, apoptosis, and cell cycle progression were activated and overexpressed, suggesting such effects of LZ02/01 on autophagy and apoptosis were associated with the activation and overexpression of FoxO3a. In addition, LZ02/01-mediated apoptosis is not independent; it was verified to be promoted by autophagic flux inhibition. Meanwhile, synergistic effects on tumor growth reduction were detected in the xenograft mice model of human breast cancer simultaneously treated with LZ02 and chloroquine. Our findings suggest that LZ01 and LZ02 are potent in suppressing cancer cell proliferation and tumor growth through autophagic flux inhibition and apoptosis promotion. The synergistic anti-cancer effects of LZ02 with chloroquine may provide a rational basis for prospective cancer therapy. KEY MESSAGES: A ligand-based pharmacophore model of high quality is constructed to query hits and two novel scaffold lead compounds LZ01/02 were identified by high-throughput virtual screening. LZ01/02 works to inhibit autophagic flux by attenuating lysosome function. LZ01/02 induces apoptosis through autophagic flux inhibition and apoptosis is the main mechanism to inhibit MCF-7 and Hep3B cancer cell proliferation. The synergistic antitumor growth effects of LZ02 and chloroquine are verified in human xenograft model.

Reversal of glucocorticoid resistance in paediatric acute lymphoblastic leukaemia is dependent on restoring BIM expression

BACKGROUND

Acute lymphoblastic leukaemia (ALL) is the most common paediatric malignancy. Glucocorticoids form a critical component of chemotherapy regimens and resistance to glucocorticoid therapy is predictive of poor outcome. We have previously shown that glucocorticoid resistance is associated with upregulation of the oncogene C-MYC and failure to induce the proapoptotic gene BIM.

METHODS

A high-throughput screening (HTS) campaign was carried out to identify glucocorticoid sensitisers against an ALL xenograft derived from a glucocorticoid-resistant paediatric patient. Gene expression analysis was carried out using Illumina microarrays. Efficacy, messenger RNA and protein analysis were carried out by Resazurin assay, reverse transcription-PCR and immunoblotting, respectively.

RESULTS

A novel glucocorticoid sensitiser, 2-((4,5-dihydro-1H-imidazol-2-yl)thio)-N-isopropyl-N-phenylacetamide (GCS-3), was identified from the HTS campaign. The sensitising effect was specific to glucocorticoids and synergy was observed in a range of dexamethasone-resistant and dexamethasone-sensitive xenografts representative of B-ALL, T-ALL and Philadelphia chromosome-positive ALL. GCS-3 in combination with dexamethasone downregulated C-MYC and significantly upregulated BIM expression in a glucocorticoid-resistant ALL xenograft. The GCS-3/dexamethasone combination significantly increased binding of the glucocorticoid receptor to a novel BIM enhancer, which is associated with glucocorticoid sensitivity.

CONCLUSIONS

This study describes the potential of the novel glucocorticoid sensitiser, GCS-3, as a biological tool to interrogate glucocorticoid action and resistance.

Autophagy regulation and its role in normal and malignant hematopoiesis

Autophagy, the molecular machinery of self-eating, plays a dual role of a tumor promoter and tumor suppressor. This mechanism affects different clinical responses in cancer cells. Autophagy is targeted for treating patients resistant to chemotherapy or radiation. Limited reports investigate the significance of autophagy in cancer therapy, the regulation of hematopoietic and leukemic stem cells and leukemia formation. In the current review, the role of autophagy is discussed in various stages of hematopoiesis including quiescence, self-renewal, and differentiation.

Therapeutic Modulation of Autophagy in Leukaemia and Lymphoma

Haematopoiesis is a tightly orchestrated process where a pool of hematopoietic stem and progenitor cells (HSPCs) with high self-renewal potential can give rise to both lymphoid and myeloid lineages. The HSPCs pool is reduced with ageing resulting in few HSPC clones maintaining haematopoiesis thereby reducing blood cell diversity, a phenomenon called clonal haematopoiesis. Clonal expansion of HSPCs carrying specific genetic mutations leads to increased risk for haematological malignancies. Therefore, it comes as no surprise that hematopoietic tumours develop in higher frequency in elderly people. Unfortunately, elderly patients with leukaemia or lymphoma still have an unsatisfactory prognosis compared to younger ones highlighting the need to develop more efficient therapies for this group of patients. Growing evidence indicates that macroautophagy (hereafter referred to as autophagy) is essential for health and longevity. This review is focusing on the role of autophagy in normal haematopoiesis as well as in leukaemia and lymphoma development. Attenuated autophagy may support early hematopoietic neoplasia whereas activation of autophagy in later stages of tumour development and in response to a variety of therapies rather triggers a pro-tumoral response. Novel insights into the role of autophagy in haematopoiesis will be discussed in light of designing new autophagy modulating therapies in hematopoietic cancers.

miR-221/222-Mediated Inhibition of Autophagy Promotes Dexamethasone Resistance in Multiple Myeloma

Inherent or acquired resistance to chemotherapeutic drugs is still an obstacle for the treatment of multiple myeloma (MM). MicroRNA dysregulation is related to the development of chemoresistance in cancers. However, its role in chemoresistance of MM is largely unknown. Here we demonstrated that miR-221/222 were upregulated in plasma cells from patients with MM, especially those with relapsed or refractory disease. Moreover, expression levels of miR-221/222 were inversely correlated with dexamethasone (Dex) sensitivity of human MM cell lines. Importantly, we found that Dex induced pro-death autophagy in MM cells and the inhibition of autophagy significantly decreased Dex-induced cell death. Mechanistically, autophagy-related gene 12 (ATG12) was identified as a novel target gene of miR-221/222, and miR-221/222 overexpression inhibited autophagy by directly targeting ATG12 and the p27^kip (p27)-mammalian target of rapamycin (mTOR) pathway. Indeed, Dex treatment decreased the expression of miR-221/222, thereby activating the ATG12/p27-mTOR autophagy-regulatory axis and inducing cell death in Dex-sensitive MM cells. Furthermore, both in vitro and in vivo results showed that the inhibitions of miR-221/222 increased the expression of ATG12 and p27 and functionally induced extended autophagy and cell death of MM cells. In conclusion, our findings demonstrated the crucial role of the miR-221/222-ATG12/p27-mTOR autophagy-regulatory axis in Dex resistance of MM, and they suggest potential prediction and treatment strategies for glucocorticoid resistance.

Recent advancements in high-level synthesis of the promising clinical drug, prodigiosin

Prodigiosin, a red linear tripyrrole pigment and a member of the prodiginine family, is normally secreted by the human pathogen Serratia marcescens as a secondary metabolite. Studies on prodigiosin have received renewed attention as a result of reported immunosuppressive, antimicrobial and anticancer properties. High-level synthesis of prodigiosin and the bioengineering of strains to synthesise useful prodiginine derivatives have also been a subject of investigation. To exploit the potential use of prodigiosin as a clinical drug targeting bacteria or as a dye for textiles, high-level synthesis of prodigiosin is a prerequisite. This review presents an overview on the biosynthesis of prodigiosin from its natural host Serratia marcescens and through recombinant approaches as well as highlighting the beneficial properties of prodigiosin. We also discuss the prospect of adopting a synthetic biology approach for safe and cost-effective production of prodigiosin in a more industrially compliant surrogate host.

Plumbagin induces autophagy and apoptosis of SMMC-7721 cells in vitro and in vivo

Plumbagin (PL), an active naphthoquinone compound, has been demonstrated to be a potential anticancer agent. However, the underlying anticancer mechanism is not fully understood. In this study, the human hepatocellular carcinoma (HCC) SMMC-7721 cell line was studied in an in vitro model. The cell proliferation was inhibited by PL in a dose- and time-dependent manner. Electron microscopy, acridine orange staining, and immunofluorescence were used to evaluate autophagosome formation and LC3 protein expression in PL-treated SMMC-7721 cells. Real-time polymerase chain reaction and Western blot showed that PL treatment suppressed the expression of apoptosis and autophagy factors (LC3, Beclin1, Atg7, and Atg5), which are associated with tumor apoptosis and autophagy in SMMC-7721 cells. In the study of in vitro tumor nude mouse models, PL can inhibit tumor growth. Cell apoptosis and autophagy of the transplanted tumors were evaluated by hematoxylin and eosin staining, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling staining, and Western blot. In addition, in the in vivo studies of HCC cells, we found that pretreatment with the autophagy inhibitor 3-methyladenine blocked the formation of apoptosis induced by PL. In contrast, administration of the apoptosis inhibitor Z-VAD did not affect PL-induced autophagy. Taken together, our findings strongly suggest that PL is a promising drug with significant antitumor activity in HCC.

Obatoclax and Paclitaxel Synergistically Induce Apoptosis and Overcome Paclitaxel Resistance in Urothelial Cancer Cells

Paclitaxel is a treatment option for advanced or metastatic bladder cancer after the failure of first-line cisplatin and gemcitabine, although resistance limits its clinical benefits. Mcl-1 is an anti-apoptotic protein that promotes resistance to paclitaxel in different tumors. Obatoclax, a BH3 mimetic of the Bcl-2 family of proteins, antagonizes Mcl-1 and hence may reverse paclitaxel resistance in Mcl-1-overexpressing tumors. In this study, paclitaxel-sensitive 5637 and -resistant HT1197 bladder cancer cells were treated with paclitaxel, obatoclax, or combinations of both. Apoptosis, cell cycle, and autophagy were measured by Western blot, flow cytometry, and fluorescence microscopy. Moreover, Mcl-1 expression was analyzed by immunohistochemistry in bladder carcinoma tissues. Our results confirmed that paclitaxel alone induced Mcl-1 downregulation and apoptosis in 5637, but not in HT1197 cells; however, combinations of obatoclax and paclitaxel sensitized HT1197 cells to the treatment. In obatoclax-treated 5637 and obatoclax + paclitaxel-treated HT1197 cells, the blockade of the autophagic flux correlated with apoptosis and was associated with caspase-dependent cleavage of beclin-1. Obatoclax alone delayed the cell cycle in 5637, but not in HT1197 cells, whereas combinations of both retarded the cell cycle and reduced mitotic slippage. In conclusion, obatoclax sensitizes HT1197 cells to paclitaxel-induced apoptosis through the blockade of the autophagic flux and effects on the cell cycle. Furthermore, Mcl-1 is overexpressed in many invasive bladder carcinomas, and it is related to tumor progression, so Mcl-1 expression may be of predictive value in bladder cancer.

Ionophores: Potential Use as Anticancer Drugs and Chemosensitizers

Ion homeostasis is extremely important for the survival of both normal as well as neoplastic cells. The altered ion homeostasis found in cancer cells prompted the investigation of several ionophores as potential anticancer agents. Few ionophores, such as Salinomycin, Nigericin and Obatoclax, have demonstrated potent anticancer activities against cancer stem-like cells that are considered highly resistant to chemotherapy and responsible for tumor relapse. The preclinical success of these compounds in in vitro and in vivo models have not been translated into clinical trials. At present, phase I/II clinical trials demonstrated limited benefit of Obatoclax alone or in combination with other anticancer drugs. However, future development in targeted drug delivery may be useful to improve the efficacy of these compounds. Alternatively, these compounds may be used as leading molecules for the development of less toxic derivatives.

Identifying the druggable interactome of EWS-FLI1 reveals MCL-1 dependent differential sensitivities of Ewing sarcoma cells to apoptosis inducers

Ewing sarcoma (EwS) is an aggressive pediatric bone cancer in need of more effective therapies than currently available. Most research into novel targeted therapeutic approaches is focused on the fusion oncogene EWSR1-FLI1, which is the genetic hallmark of this disease. In this study, a broad range of 3,325 experimental compounds, among them FDA approved drugs and natural products, were screened for their effect on EwS cell viability depending on EWS-FLI1 expression. In a network-based approach we integrated the results from drug perturbation screens and RNA sequencing, comparing EWS-FLI1-high (normal expression) with EWS-FLI1-low (knockdown) conditions, revealing novel interactions between compounds and EWS-FLI1 associated biological processes. The top candidate list of druggable EWS-FLI1 targets included genes involved in translation, histone modification, microtubule structure, topoisomerase activity as well as apoptosis regulation. We confirmed our in silico results using viability and apoptosis assays, underlining the applicability of our integrative and systemic approach. We identified differential sensitivities of Ewing sarcoma cells to BCL-2 family inhibitors dependent on the EWS-FLI1 regulome including altered MCL-1 expression and subcellular localization. This study facilitates the selection of effective targeted approaches for future combinatorial therapies of patients suffering from Ewing sarcoma.

Targeting autophagy for the treatment of cancer

Macroautophagy (herein termed autophagy) is evolutionarily highly conserved across eukaryotic cells and represents an intracellular catabolic process that targets damaged macromolecules and organelles for degradation. Autophagy is dysregulated in various human diseases including cancer. In addition, many drugs currently used for the treatment of cancer can engage autophagy, which typically promotes cancer cell survival by mitigating cellular stress. However, under certain circumstances activation of autophagy upon anticancer drug treatment can also trigger a lethal type of autophagy termed autophagic cell death (ACD). This may pave new avenues for exploiting the autophagic circuitry in oncology. This review presents the concept and some examples of anticancer drug-induced ACD.

Combing oncolytic adenovirus expressing Beclin-1 with chemotherapy agent doxorubicin synergistically enhances cytotoxicity in human CML cells in vitro

Cancer virotherapy provides a new strategy to treat cancer that can directly kill cancer cells by oncolysis. Insertion of therapeutic genes into the genome of a modified adenovirus, thereby creating a so-called gene-virotherapy that shares the advantages of gene therapy and virotherapy. In this study we investigated whether a strategy that combines the oncolytic effects of an adenoviral vector with the simultaneous expression of the autophagy gene Beclin-1 offered a therapeutic advantage for chronic myeloid leukemia (CML) cells with resistance to chemotherapy and evaluated the synergistic effects of SG511-BECN and doxorubicin (Dox) in human CML cells in vitro. Oncolytic virus SG511-BECN was constructed through introducing the Beclin-1 gene into the oncolytic adenoviral backbone. SG511-BECN displayed significantly improved antileukemia activity on multidrug-resistant CML cell line K562/A02, which was mediated via induction of autophagic cell death. Furthermore, Dox could synergize with SG511-BECN to kill the CML cells by improving the infectious efficiency of the oncolytic adenovirus without causing significant damage to normal human mononuclear cells. The results demonstrate that targeting the autophagic cell death pathway and combination of a chemotherapy agent with oncolytic adenovirus may be a novel strategy for the treatment of leukemia with chemotherapy resistance.

Obatoclax impairs lysosomal function to block autophagy in cisplatin-sensitive and -resistant esophageal cancer cells

Obatoclax, a pan-inhibitor of anti-apoptotic Bcl-2 proteins, exhibits cytotoxic effect on cancer cells through both apoptosis-dependent and -independent pathways. Here we show that obatoclax caused cytotoxicity in both cisplatin-sensitive and -resistant esophageal cancer cells. Although obatoclax showed differential apoptogenic effects in these cells, it consistently blocked autophagic flux, which was evidenced by concomitant accumulation of LC3-II and p62. Obatoclax was trapped in lysosomes and induced lysosome clustering. Obatoclax also substantially reduced the expression of lysosomal cathepsins B, D and L. Moreover, cathepsin knockdown was sufficient to induce cytotoxicity, connecting lysosomal function to cell viability. Consistent with the known function of autophagy, obatoclax caused the accumulation of polyubiquitinated proteins and showed synergy with proteasome inhibition. Taken together, our studies unveiled impaired lysosomal function as a novel mechanism whereby obatoclax mediates its cytotoxic effect in esophageal cancer cells.

Therapeutic Implications of Autophagy Inducers in Immunological Disorders, Infection, and Cancer

Autophagy is an essential catabolic program that forms part of the stress response and enables cells to break down their own intracellular components within lysosomes for recycling. Accumulating evidence suggests that autophagy plays vital roles in determining pathological outcomes of immune responses and tumorigenesis. Autophagy regulates innate and adaptive immunity affecting the pathologies of infectious, inflammatory, and autoimmune diseases. In cancer, autophagy appears to play distinct roles depending on the context of the malignancy by either promoting or suppressing key determinants of cancer cell survival. This review covers recent developments in the understanding of autophagy and discusses potential therapeutic interventions that may alter the outcomes of certain diseases.

The pan-BCL-2-blocker obatoclax (GX15-070) and the PI3-kinase/mTOR-inhibitor BEZ235 produce cooperative growth-inhibitory effects in ALL cells

Acute lymphoblastic leukemia (ALL) is characterized by leukemic expansion of lymphoid blasts in hematopoietic tissues. Despite improved therapy only a subset of patients can be cured. Therefore, current research is focusing on new drug-targets. Members of the BCL-2 family and components of the PI3-kinase/mTOR pathway are critically involved in the regulation of growth and survival of ALL cells. We examined the effects of the pan-BCL-2 blocker obatoclax and the PI3-kinase/mTOR-inhibitor BEZ235 on growth and survival of ALL cells. In ³H-thymidine uptake experiments, both drugs suppressed the in vitro proliferation of leukemic cells in all patients with Philadelphia chromosome-positive (Ph⁺) ALL and Ph⁻ ALL (obatoclax IC₅₀: 0.01-5 μM; BEZ235, IC₅₀: 0.01-1 μM). Both drugs were also found to produce growth-inhibitory effects in all Ph⁺ and all Ph⁻ cell lines tested. Moreover, obatoclax and BEZ235 induced apoptosis in ALL cells. In drug-combination experiments, obatoclax and BEZ235 exerted synergistic growth-inhibitory effects on ALL cells. Finally, we confirmed that ALL cells, including CD34⁺/CD38⁻ stem cells and all cell lines express transcripts for PI3-kinase, mTOR, BCL-2, MCL-1, and BCL-xL. Taken together, this data shows that combined targeting of the PI3-kinase/mTOR-pathway and BCL-2 family-members is a potent approach to counteract growth and survival of ALL cells.

Autophagy in Cancer Therapy

Autophagy represents a catabolic program involved in the degradation of cellular components via lysosomes. It serves to mitigate cellular stress and to provide metabolic precursors especially upon starvation. Thereby, autophagy can support the survival of cancer cells. In addition, there is now convincing evidence showing that under certain conditions autophagy can also foster cell death. This dual function of autophagy is also relevant upon anticancer treatment, as many chemotherapeutic agents engage autophagy. A better understanding of the molecular mechanisms that are critical for mediating autophagic cell death in cancer cells will be instrumental to selectively interfere with this cellular program in order to increase the cancer cell’s response to cytotoxic drugs. This review illustrates how anticancer drug-induced autophagy is involved in mediating cell death.

Multifaceted anticancer activity of BH3 mimetics: Current evidence and future prospects

BH3 mimetics are a novel class of anticancer agents designed to specifically target pro-survival proteins of the Bcl-2 family. Like endogenous BH3-only proteins, BH3 mimetics competitively bind to surface hydrophobic grooves of pro-survival Bcl-2 family members, counteracting their protective effects and thus facilitating apoptosis in cancer cells. Among the small-molecule BH3 mimetics identified, ABT-737 and its analogs, obatoclax as well as gossypol derivatives are the best characterized. The anticancer potential of these compounds applied as a single agent or in combination with chemotherapeutic drugs is currently being evaluated in preclinical studies and in clinical trials. In spite of promising results, the actual mechanisms of their anticancer action remain to be identified. Findings from preclinical studies point to additional activities of BH3 mimetics in cancer cells that are not connected with apoptosis induction. These off-target effects involve induction of autophagy and necrotic cell death as well as modulation of the cell cycle and multiple cell signaling pathways. For the optimization and clinical implementation of BH3 mimetics, a detailed understanding of their role as inhibitors of the pro-survival Bcl-2 proteins, but also of their possible additional effects is required. This review summarizes the most representative BH3 mimetic compounds with emphasis on their off-target effects. Based on the present knowledge on the multifaceted effects of BH3 mimetics on cancer cells, the commentary outlines the potential pitfalls and highlights the considerable promise for cancer treatment with BH3 mimetics.

Obatoclax and LY3009120 Efficiently Overcome Vemurafenib Resistance in Differentiated Thyroid Cancer

Although the prognosis of differentiated thyroid cancer (DTC) is relatively good, 30-40% of patients with distant metastases develop resistance to radioactive iodine therapy due to tumor dedifferentiation. For DTC patients harboring BRAF^V600E mutation, Vemurafenib, a BRAF kinase inhibitor, has dramatically changed the therapeutic landscape, but side effects and drug resistance often lead to termination of the single agent treatment. In the present study, we showed that either LY3009120 or Obatoclax (GX15-070) efficiently inhibited cell cycle progression and induced massive death of DTC cells. We established that BRAF/CRAF dimerization was an underlying mechanism for Vemurafenib resistance. LY3009120, the newly discovered pan-RAF inhibitor, successfully overcame Vemurafenib resistance and suppressed the growth of DTC cells in vitro and in vivo. We also observed that expression of anti-apoptotic Bcl-2 increased substantially following BRAF inhibitor treatment in Vemurafenib-resistant K1 cells, and both Obatoclax and LY3009120 efficiently induced apoptosis of these resistant cells. Specifically, Obatoclax exerted its anti-cancer activity by inducing loss of mitochondrial membrane potential (ΔΨm), dysfunction of mitochondrial respiration, reduction of cellular glycolysis, autophagy, neutralization of lysosomes, and caspase-related apoptosis. Furthermore, the cancer killing effects of LY3009120 and Obatoclax extended to two more Vemurafenib-resistant DTC cell lines, KTC-1 and BCPAP. Taken together, our results highlighted the potential value of LY3009120 for both Vemurafenib-sensitive and -resistant DTC and provided evidence for the combination therapy using Vemurafenib and Obatoclax for radioiodine-refractory DTC.

The roles of reactive oxygen species (ROS) and autophagy in the survival and death of leukemia cells

As a clonal disease of hematopoietic stem cells (HSCs), the etiology and pathogenesis of leukemia is not fully understood. Recent studies suggest that cellular homeostasis plays an essential role in maintaining the function of HSCs because dysregulation of cellular homeostasis is one of the major factors underlying the malignant transformation of HSCs. Reactive oxygen species (ROS) and autophagy, key factors regulating cellular homeostasis, are commonly observed in the human body. Autophagy can be induced by ROS through a variety of signaling pathways, and conversely inhibits ROS-induced damage to cells and tissues. ROS and autophagy coordinate to maintain cellular homeostasis. Previous studies have demonstrated that both of ROS and autophagy play important roles in the development of leukemia and are closely involved in drug resistance in leukemia. Interference with cellular homeostasis by promoting programmed leukemia cell death via ROS and autophagy has been verified to be an efficient technique in the treatment of leukemia. However, the critical roles of ROS and autophagy in the development of leukemia are largely unknown. In this review, we summarize the roles of ROS and autophagy in the pathogenesis of leukemia, which may allow the identification of novel targets and drugs for the treatment of leukemia based on the regulation of HSCs homeostasis through ROS and autophagy.

Comparison of in vitro antileukemic activity of obatoclax and ABT-737

Obatoclax and ABT-737 belong to a new class of anticancer agents known as BH3-mimetics. These agents antagonize the anti-apoptotic members of Bcl-2 family. The Bcl-2 proteins modulate sensitivity of many types of cancer cells to chemotherapy. Therefore, the objective of the present study was to examine and compare the antileukemic activity of obatoclax and ABT-737 applied alone, and in combination with anticancer agent, mafosfamide and daunorubicin. The in vitro cytotoxic effects of the tested agents on human leukemia cells were determined using the spectrophotometric MTT test, Coulter electrical impedance method, flow cytometry annexin V-fluorescein/propidium iodide assay, and light microscopy technique. The combination index analysis was used to quantify the extent of agent interactions. BH3 mimetics significantly decreased the leukemia cell viability and synergistically enhanced the cytotoxic effects induced by mafosfamide and daunorubicin. Obatoclax affected the cell viability to a greater degree than did ABT-737. In addition, various patterns of temporary changes in the cell volume and count, and in the frequency of leukemia cells undergoing apoptosis, were found 24 and 48 h after the tested agent application. ABT-737 combined with anticancer agents induced apoptosis more effectively than obatoclax when given in the same combination regimen. The results of the present study point to the different antileukemic activities of obatoclax and ABT-737, when applied alone, and in combination with anticancer agents. A better understanding of the exact mechanisms of BH3 mimetic action is of key importance for their optional use in cancer therapy.

A phase 1 dose-escalation study of filanesib plus bortezomib and dexamethasone in patients with recurrent/refractory multiple myeloma

BACKGROUND

Filanesib is a kinesin spindle protein inhibitor that has demonstrated encouraging activity in patients with recurrent/refractory multiple myeloma. Preclinical synergy with bortezomib was the rationale for the current phase 1 study.

METHODS

The current study was a multicenter study with an initial dose-escalation phase to determine the maximum tolerated dose of 2 schedules of filanesib plus bortezomib with and without dexamethasone, followed by a dose-expansion phase.

RESULTS

With the addition of prophylactic filgastrim, the maximum planned dose was attained: 1.3 mg/m² /day of bortezomib plus 40 mg of dexamethasone on days 1, 8, and 15 of a 28-day cycle, with filanesib given intravenously either at a dose of 1.5 mg/m² /day (schedule 1: days 1, 2, 15, and 16) or 3 mg/m² /day (schedule 2: days 1 and 15). The most common adverse events (assessed for severity using version 4.0 of the National Cancer Institute Common Terminology Criteria for Adverse Events) were transient, noncumulative neutropenia and thrombocytopenia with grade 3/4 events reported in 44% (16% in cycle 1 with filgastrim) and 29% of patients, respectively. A low (≤11%) overall rate of nonhematological grade 3/4 toxicity was observed. With a median of 3 prior lines of therapy and 56% of patients with disease that was refractory to proteasome inhibitors, the overall response rate was 20% (55 patients), and was 29% in 14 patients with proteasome inhibitors-refractory disease receiving filanesib at a dose of ≥1.25 mg/m² (duration of response, 5.2 to ≥21.2 months).

CONCLUSIONS

The current phase 1 study established a dosing schedule for the combination of these agents that demonstrated a favorable safety profile with a low incidence of nonhematologic toxicity and manageable hematologic toxicity. The combination of filanesib, bortezomib, and dexamethasone appears to have durable activity in patients with recurrent/refractory multiple myeloma. Cancer 2016;122:3327-3335. © 2016 American Cancer Society.

Obatoclax kills anaplastic thyroid cancer cells by inducing lysosome neutralization and necrosis

Poorly differentiated and anaplastic thyroid carcinomas are very aggressive, almost invariably lethal neoplasms for which no effective treatment exists. These tumors are intrinsically resistant to cell death, even when their driver oncogenic signaling pathways are inhibited.We have undertaken a detailed analysis, in mouse and human thyroid cancer cells, of the mechanism through which Obatoclax, a pan-inhibitor of the anti-apoptotic proteins of the BCL2 family, effectively reduces tumor growth in vitro and in vivo.We demonstrate that Obatoclax does not induce apoptosis, but rather necrosis of thyroid cancer cells, and that non-transformed thyroid cells are significantly less affected by this compound. Surprisingly, we show that Obatoclax rapidly localizes to the lysosomes and induces loss of acidification, block of lysosomal fusion with autophagic vacuoles, and subsequent lysosomal permeabilization. Notably, prior lysosome neutralization using different V-ATPase inhibitors partially protects cancer cells from the toxic effects of Obatoclax. Although inhibition of autophagy does not affect Obatoclax-induced cell death, selective down-regulation of ATG7, but not of ATG5, partially impairs Obatoclax effects, suggesting the existence of autophagy-independent functions for ATG7. Strikingly, Obatoclax killing activity depends only on its accumulation in the lysosomes, and not on its interaction with BCL2 family members.Finally, we show that also other lysosome-targeting compounds, Mefloquine and LLOMe, readily induce necrosis in thyroid cancer cells, and that Mefloquine significantly impairs tumor growth in vivo, highlighting a clear vulnerability of these aggressive, apoptosis-resistant tumors that can be therapeutically exploited.

MEK Inhibition Sensitizes Precursor B-Cell Acute Lymphoblastic Leukemia (B-ALL) Cells to Dexamethasone through Modulation of mTOR Activity and Stimulation of Autophagy

Resistance to glucocorticosteroids (GCs) is a major adverse prognostic factor in B-ALL, but the molecular mechanisms leading to GC resistance are not completely understood. Herein, we sought to elucidate the molecular background of GC resistance in B-ALL and characterize the therapeutic potential of targeted intervention in these mechanisms. Using exploratory bioinformatic approaches, we found that resistant cells exhibited significantly higher expression of MEK/ERK (MAPK) pathway components. We found that GC-resistant ALL cell lines had markedly higher baseline activity of MEK and small-molecule MEK1/2 inhibitor selumetinib increased GCs-induced cell death. MEK inhibitor similarly increased in vitro dexamethasone activity in primary ALL blasts from 19 of 22 tested patients. To further confirm these observations, we overexpressed a constitutively active MEK mutant in GC-sensitive cells and found that forced MEK activity induced resistance to dexamethasone. Since recent studies highlight the role GC-induced autophagy upstream of apoptotic cell death, we assessed LC3 processing, MDC staining and GFP-LC3 relocalization in cells incubated with either DEX, SEL or combination of drugs. Unlike either drug alone, only their combination markedly increased these markers of autophagy. These changes were associated with decreased mTOR activity and blocked 4E-BP1 phosphorylation. In cells with silenced beclin-1 (BCN1), required for autophagosome formation, the synergy of DEX and SEL was markedly reduced. Taken together, we show that MEK inhibitor selumetinib enhances dexamethasone toxicity in GC-resistant B-ALL cells. The underlying mechanism of this interaction involves inhibition of mTOR signaling pathway and modulation of autophagy markers, likely reflecting induction of this process and required for cell death. Thus, our data demonstrate that modulation of MEK/ERK pathway is an attractive therapeutic strategy overcoming GC resistance in B-ALL patients.

The BH3 Mimetic Obatoclax Accumulates in Lysosomes and Causes Their Alkalinization

Obatoclax belongs to a class of compounds known as BH3 mimetics which function as antagonists of Bcl-2 family apoptosis regulators. It has undergone extensive preclinical and clinical evaluation as a cancer therapeutic. Despite this, it is clear that obatoclax has additional pharmacological effects that contribute to its cytotoxic activity. It has been claimed that obatoclax, either alone or in combination with other molecularly targeted therapeutics, induces an autophagic form of cell death. In addition, obatoclax has been shown to inhibit lysosomal function, but the mechanism of this has not been elucidated. We have evaluated the mechanism of action of obatoclax in eight ovarian cancer cell lines. Consistent with its function as a BH3 mimetic, obatoclax induced apoptosis in three cell lines. However, in the remaining cell lines another form of cell death was evident because caspase activation and PARP cleavage were not observed. Obatoclax also failed to show synergy with carboplatin and paclitaxel, chemotherapeutic agents which we have previously shown to be synergistic with authentic Bcl-2 family antagonists. Obatoclax induced a profound accumulation of LC-3 but knockdown of Atg-5 or beclin had only minor effects on the activity of obatoclax in cell growth assays suggesting that the inhibition of lysosomal function rather than stimulation of autophagy may play a more prominent role in these cells. To evaluate how obatoclax inhibits lysosomal function, confocal microscopy studies were conducted which demonstrated that obatoclax, which contains two basic pyrrole groups, accumulates in lysosomes. Studies using pH sensitive dyes demonstrated that obatoclax induced lysosomal alkalinization. Furthermore, obatoclax was synergistic in cell growth/survival assays with bafilomycin and chloroquine, two other drugs which cause lysosomal alkalinization. These studies explain, for the first time, how obatoclax inhibits lysosomal function and suggest that lysosomal alkalinization contributes to the cytotoxic activity of obatoclax.

Clinical relevance of autophagic therapy in cancer: Investigating the current trends, challenges, and future prospects

Oncophagy (cancer-related autophagy) has a complex dual character at different stages of tumor progression. It remains an important clinical problem to unravel the reasons that propel the shift in the role of oncophagy from tumor inhibition to a protective mechanism that shields full-blown malignancy. Most treatment strategies emphasize curbing protective oncophagy while triggering the oncophagy that is lethal to tumor cells. In this review, we focus on the trends in current therapeutics as well as various challenges in clinical trials to address the oncophagic dilemma and evaluate the potential of these developing therapies. A detailed analysis of the clinical and pre-clinical scenario of the anticancer medicines highlights the various inducers and inhibitors of autophagy. The ways in which tumor stage, the microenvironment and combination drug treatment continue to play an important tactical role are discussed. Moreover, autophagy targets also play a crucial role in developing the best possible solution to this oncophagy paradox. In this review, we provide a comprehensive update on the current clinical impact of autophagy-based cancer therapeutic drugs and try to lessen the gap between translational medicine and clinical science.

The Retinoblastoma Tumor Suppressor Protein (pRb)/E2 Promoter Binding Factor 1 (E2F1) Pathway as a Novel Mediator of TGFβ-induced Autophagy

TGFβ is a multifunctional cytokine that regulates cell proliferation, cell immortalization, and cell death, acting as a key homeostatic mediator in various cell types and tissues. Autophagy is a programmed mechanism that plays a pivotal role in controlling cell fate and, consequently, many physiological and pathological processes, including carcinogenesis. Although autophagy is often considered a pro-survival mechanism that renders cells viable in stressful conditions and thus might promote tumor growth, emerging evidence suggests that autophagy is also a tumor suppressor pathway. The relationship between TGFβ signaling and autophagy is context-dependent and remains unclear. TGFβ-mediated activation of autophagy has recently been suggested to contribute to the growth inhibitory effect of TGFβ in hepatocarcinoma cells. In the present study, we define a novel process of TGFβ-mediated autophagy in cancer cell lines of various origins. We found that autophagosome initiation and maturation by TGFβ is dependent on the retinoblastoma tumor suppressor protein/E2 promoter binding factor (pRb/E2F1) pathway, which we have previously established as a critical signaling axis leading to various TGFβ tumor suppressive effects. We further determined that TGFβ induces pRb/E2F1-dependent transcriptional activation of several autophagy-related genes. Together, our findings reveal that TGFβ induces autophagy through the pRb/E2F1 pathway and transcriptional activation of autophagy-related genes and further highlight the central relevance of the pRb/E2F1 pathway downstream of TGFβ signaling in tumor suppression.

Thioimidazoline based compounds reverse glucocorticoid resistance in human acute lymphoblastic leukemia xenografts

Glucocorticoids form a critical component of chemotherapy regimens for pediatric acute lymphoblastic leukemia (ALL) and the initial response to glucocorticoid therapy is a major prognostic factor, where resistance is predictive of poor outcome. A high-throughput screen identified four thioimidazoline-containing compounds that reversed dexamethasone resistance in an ALL xenograft derived from a chemoresistant pediatric ALL. The lead compound (1) was synergistic when used in combination with the glucocorticoids, dexamethasone or prednisolone. Synergy was observed in a range of dexamethasone-resistant xenografts representative of B-cell precursor ALL (BCP-ALL) and T-cell ALL. We describe here the synthesis of twenty compounds and biological evaluation of thirty two molecules that explore the structure-activity relationships (SAR) of this novel class of glucocorticoid sensitizing compounds. SAR analysis has identified that the most effective dexamethasone sensitizers contain a thioimidazoline acetamide substructure with a large hydrophobic moiety on the acetamide.

Cell death induction by the BH3 mimetic GX15-070 in thyroid carcinoma cells

Background

The evasion of cell death is one of the hallmarks of cancer, contributing to both tumor progression and resistance to therapy. Dedifferentiated and anaplastic thyroid carcinomas that do not take up radioiodine are resistant to conventional anticancer treatments and patients with these tumors are difficult to treat. BH3 mimetics are a new class of drugs that target anti-apoptotic proteins of the BCL-2 family and promote cell death. The purpose of this study was to analyze the molecular effects of the BH3 mimetic GX15-070 on thyroid carcinoma cell lines and to characterize cell death induced by GX15-070.

Methods

A total of 17 cell lines derived from follicular, papillary, and anaplastic thyroid carcinomas were treated with GX15-070. Cell viability was measured with MTT assay while cell cycle phase distribution and subG1 peaks were determined after propidium iodide staining. We assessed cell death via the caspase 3/7 activity, caspase cleavage products, lactate dehydrogenase (LDH) liberation assays, and a LC3 analysis by western blot. Ultrastructural changes were analysed by electron microscopy of GX15-070-treated cells.

Results

After GX15-070 treatment, the number of viable cells was decreased in all cell lines examined, with IC50 values ranging from 48nM to 3.25 μM. We observed biochemical markers of autophagic cell death and necrosis like LC3 conversion and LDH release after the GX15-070 treatment. Electron microscopy revealed several common characteristic ultrastructural changes like swelling of mitochondria, dilatation of rough endoplasmic reticulum, membrane blebbing and formation of vacuoles. GX15-070 treatment induced DNA fragmentation detected by subG1-peak induction and an arrest in G1 phase of the cell cycle. Caspase activation after GX15-070 incubation was detected but had no effect on viability of cells.

Conclusions

With these experiments we demonstrated the efficacy of the BH3 mimetic drug GX15-070 acting against dedifferentiated thyroid carcinoma cells of various histological origins by the induction of cell death. GX15-070-treated cells underwent non-classical cell death with signs of apoptosis, autophagy and necrosis in parallel. GX15-07 and related compounds thus may be a new therapeutic option for dedifferentiated thyroid carcinoma of various histological subtypes.

Bcl-2 family of proteins as drug targets for cancer chemotherapy: the long way of BH3 mimetics from bench to bedside

Bcl-2 proteins are key determinants in the life-death balance. In recent years, proteins in this family have been identified as drug targets in the design of new anti-tumor therapies. Advances in the knowledge of the mechanism of action of anti-apoptotic and pro-apoptotic members of the Bcl-2 family have enabled the development of the so-called 'BH3 mimetics'. These compounds act by inhibiting anti-apoptotic proteins of the family, imitating the function of the BH3-only subset of pro-apoptotic members. Combinations of BH3-mimetics with anti-tumor drugs are being evaluated in both preclinical models and clinical trials. Recent advances in these approaches will be reviewed.

Cell death by autophagy: emerging molecular mechanisms and implications for cancer therapy

Autophagy is a tightly-regulated catabolic process of cellular self-digestion by which cellular components are targeted to lysosomes for their degradation. Key functions of autophagy are to provide energy and metabolic precursors under conditions of starvation and to alleviate stress by removal of damaged proteins and organelles, which are deleterious for cell survival. Therefore, autophagy appears to serve as a pro-survival stress response in most settings. However, the role of autophagy in modulating cell death is highly dependent on the cellular context and its extent. There is an increasing evidence for cell death by autophagy, in particular in developmental cell death in lower organisms and in autophagic cancer cell death induced by novel cancer drugs. The death-promoting and -executing mechanisms involved in the different paradigms of autophagic cell death (ACD) are very diverse and complex, but a draft scenario of the key molecular targets involved in ACD is beginning to emerge. This review provides an up-to-date and comprehensive report on the molecular mechanisms of drug-induced autophagy-dependent cell death and highlights recent key findings in this exciting field of research.

Autophagy in acute leukemias: a double-edged sword with important therapeutic implications

Macroautophagy, usually referred to as autophagy, is a degradative pathway wherein cytoplasmatic components such as aggregated/misfolded proteins and organelles are engulfed within double-membrane vesicles (autophagosomes) and then delivered to lysosomes for degradation. Autophagy plays an important role in the regulation of numerous physiological functions, including hematopoiesis, through elimination of aggregated/misfolded proteins, and damaged/superfluous organelles. The catabolic products of autophagy (amino acids, fatty acids, nucleotides) are released into the cytosol from autophagolysosomes and recycled into bio-energetic pathways. Therefore, autophagy allows cells to survive starvation and other unfavorable conditions, including hypoxia, heat shock, and microbial pathogens. Nevertheless, depending upon the cell context and functional status, autophagy can also serve as a death mechanism. The cohort of proteins that constitute the autophagy machinery function in a complex, multistep biochemical pathway which has been partially identified over the past decade. Dysregulation of autophagy may contribute to the development of several disorders, including acute leukemias. In this kind of hematologic malignancies, autophagy can either act as a chemo-resistance mechanism or have tumor suppressive functions, depending on the context. Therefore, strategies exploiting autophagy, either for activating or inhibiting it, could find a broad application for innovative treatment of acute leukemias and could significantly contribute to improved clinical outcomes. These aspects are discussed here after a brief introduction to the autophagic molecular machinery and its roles in hematopoiesis.

Obatoclax overcomes resistance to cell death in aggressive thyroid carcinomas by countering Bcl2a1 and Mcl1 overexpression

Poorly differentiated tumors of the thyroid gland (PDTC) are generally characterized by a poor prognosis due to their resistance to available therapeutic approaches. The relative rarity of these tumors is a major obstacle to our understanding of the molecular mechanisms leading to tumor aggressiveness and drug resistance, and consequently to the development of novel therapies. By simultaneously activating Kras and deleting p53 (Trp53) in thyroid follicular cells, we have generated a novel mouse model that develops papillary thyroid cancer invariably progressing to PDTC. In several cases, tumors further progress to anaplastic carcinomas. The poorly differentiated tumors are morphologically and functionally similar to their human counterparts and depend on MEK/ERK signaling for proliferation. Using primary carcinomas as well as carcinoma-derived cell lines, we also demonstrate that these tumors are intrinsically resistant to apoptosis due to high levels of expression of the Bcl2 family members, Bcl2a1 (Bcl2a1a) and Mcl1, and can be effectively targeted by Obatoclax, a small-molecule pan-inhibitor of the Bcl2 family. Furthermore, we show that Bcl2 family inhibition synergizes with MEK inhibition as well as with doxorubicin in inducing cell death. Thus, our studies in a novel, relevant mouse model have uncovered a promising druggable feature of aggressive thyroid cancers.

Pan-Bcl-2 inhibitor obatoclax delays cell cycle progression and blocks migration of colorectal cancer cells

Despite the fact that new treatment regimes have improved overall survival of patients challenged by colorectal cancer (CRC), prognosis in the metastatic situation is still restricted. The Bcl-2 family of proteins has been identified as promising anti cancer drug target. Even though small molecules targeting Bcl-2 proteins are in clinical trials, little is known regarding their effects on CRC. The aim of this study was to preclinically investigate the value of ABT-737 and Obatoclax as anticancer drugs for CRC treatment. The effects of the BH3-mimetics ABT-737 and Obatoclax on CRC cells were assessed using viability and apoptosis assays. Wound healing migration and boyden chamber invasion assays were applied. 3-dimensional cell cultures were used for long term assessment of invasion and proliferation. Clinically relevant concentrations of pan-Bcl-2 inhibitor Obatoclax did not induce cell death. In contrast, the BH3-mimetic ABT-737 induced apoptosis in a dose dependent manner. Obatoclax caused a cell line specific slowdown of CRC cell growth. Furthermore, Obatoclax, but not ABT-737, recovered E-Cadherin expression and led to impaired migration and invasion of CRC cells. The proliferative capacity and invasiveness of CRC cells was strikingly inhibited by low dose Obatoclax in long term 3-dimensional cell cultures. Obatoclax, but not ABT-737, caused a G1-phase arrest accompanied by a downregulation of Cyclin D1 and upregulation of p27 and p21. Overexpression of Mcl-1, Bcl-xL or Bcl-2 reversed the inhibitory effect of Obatoclax on migration but failed to restore the proliferative capacity of Obatoclax-treated CRC cells. The data presented indicate broad and multifaceted antitumor effects of the pan-Bcl-2 inhibitor Obatoclax on CRC cells. In contrast to ABT-737, Obatoclax inhibited migration, invasion and proliferation in sublethal doses. In summary, this study recommends pan-Bcl-2 inhibition as a promising approach for clinical trials in CRC.

High-throughput screening of human leukemia xenografts to identify dexamethasone sensitizers

Acute lymphoblastic leukemia (ALL) is the most common pediatric malignancy. Glucocorticoids (e.g., dexamethasone) form a critical component of chemotherapy regimens for pediatric ALL, and the initial response to glucocorticoid therapy is a major prognostic factor, where resistance is predictive of poor outcome. We have previously established a clinically relevant ALL xenograft model, consisting of primary pediatric ALL biopsies engrafted into immune-deficient mice, in which in vitro and in vivo dexamethasone sensitivity significantly correlated with patient outcome. In this study, we used high-throughput screening (HTS) to identify novel compounds that reverse dexamethasone resistance in a xenograft (ALL-19) derived from a chemoresistant pediatric ALL patient that is representative of the most common pediatric ALL subtype (B-cell precursor [BCP-ALL]). The compound 2-(4-chlorophenoxy)-2-methyl-N-(2-(piperidin-1-yl)phenyl)propanamide showed little cytotoxic activity alone (IC50 = 31 µM), but when combined with dexamethasone, it caused a marked decrease in cell viability. Fixed-ratio combination assays were performed against a broad panel of dexamethasone-resistant and -sensitive xenografts representative of BCP-ALL, T-cell ALL, and Mixed Lineage Leukemia-rearranged ALL, and synergy was observed in six of seven xenografts. We describe here the development of a novel 384-well cell-based high-throughput screening assay for identifying potential dexamethasone sensitizers using a clinically relevant ALL xenograft model.

Potent antitumor activity of oncolytic adenovirus expressing Beclin-1 via induction of autophagic cell death in leukemia

An attractive strategy among adenovirus-based oncolytic systems is to design adenoviral vectors to express pro-apoptotic genes, in which this gene-virotherapy approach significantly enhances tumor cell death by activating apoptotic pathways. However, the existence of cancer cells with apoptotic defects is one of the major obstacles in gene-virotherapy. Here, we investigated whether a strategy that combines the oncolytic effects of an adenoviral vector with simultaneous expression of Beclin-1, an autophagy gene, offers a therapeutic advantage for leukemia. A Beclin-1 cDNA was cloned in an oncolytic adenovirus with chimeric Ad5/11 fiber (SG511-BECN). SG511-BECN treatment induced significant autophagic cell death, and resulted in enhanced cell killing in a variety of leukemic cell lines and primary leukemic blasts. SG511-BECN effects were seen in chronic myeloid leukemia and acute myeloid leukemia with resistance to imatinib or chemotherapy, but exhibited much less cytotoxicity on normal cells. The SG511-BECN-induced autophagic cell death could be partially reversed by RNA interference knockdown of UVRAG, ATG5, and ATG7. We also showed that SG511-BECN strongly inhibited the growth of leukemic progenitors in vitro. In murine leukemia models, SG511-BECN prolonged the survival and decreased the xenograft tumor size by inducing autophagic cell death. Our results suggest that infection of leukemia cells with an oncolytic adenovirus overexpressing Beclin-1 can induce significant autophagic cell death and provide a new strategy for the elimination of leukemic cells via a unique mechanism of action distinct from apoptosis.

Glucocorticoid sensitisation in Mixed Lineage Leukaemia-rearranged acute lymphoblastic leukaemia by the pan-BCL-2 family inhibitors gossypol and AT-101

AIM OF THE STUDY

Resistance to glucocorticoids (GCs) remains a major problem in the treatment of infants with acute lymphoblastic leukaemia (ALL) carrying Mixed Lineage Leukaemia (MLL) translocations. Despite intensive research, the mechanism(s) underlying GC resistance remain poorly understood. Recent studies suggested an important role for the pro-survival BCL-2 family member MCL1 in GC resistance in MLL-rearranged ALL.

METHODS

We exposed GC-resistant MLL-rearranged SEMK2 cells to potent MCL1-inhibiting agents, including gossypol, AT-101, rapamycin, SU9516 and obatoclax (GX15-070) and determined GC sensitisation using 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) assays. Using Western blotting we analysed the protein expression of most BCL-2 family members in MLL-rearranged SEMK2 cells after treatment with potent MCL-1 inhibiting agents.

RESULTS

Only gossypol and its synthetic analogue AT-101 induced GC sensitivity in MLL-rearranged ALL cells. Remarkably, the GC-sensitising effects of gossypol and AT-101 appeared not to be mediated by down-regulation MCL1 or other anti-apoptotic BCL-2 family members, but rather involved up-regulation of multiple pro-apoptotic BCL-2 family members, in particular that of BIM and BID.

CONCLUDING REMARKS

In conclusion, gossypol and AT-101 induce GC sensitivity in MLL-rearranged ALL cells, most likely mediated by the activation of BID and BIM without the necessity to down-regulate anti-apoptotic BCL-2 family members like MCL1. Hence, co-administration of either gossypol or AT-101 during GC treatment of GC-resistant MLL-rearranged ALL patients may overcome GC resistance and improve prognosis in this high-risk childhood leukaemia.

Adenosine monophosphate-activated protein kinase is required for pulmonary artery smooth muscle cell survival and the development of hypoxic pulmonary hypertension

Human pulmonary artery smooth muscle cells (HPASMCs) express both adenosine monophosphate-activated protein kinase (AMPK) α1 and α2. We investigated the distinct roles of AMPK α1 and α2 in the survival of HPASMCs during hypoxia and hypoxia-induced pulmonary hypertension (PH). The exposure of HPASMCs to hypoxia (3% O2) increased AMPK activation and phosphorylation, and the inhibition of AMPK with Compound C during hypoxia decreased their viability and increased lactate dehydrogenase activity and apoptosis. Although the suppression of either AMPK α1 or α2 expression led to increased cell death, the suppression of AMPK α2 alone increased caspase-3 activity and apoptosis in HPASMCs exposed to hypoxia. It also resulted in the decreased expression of myeloid cell leukemia sequence 1 (MCL-1). The knockdown of MCL-1 or MCL-1 inhibitors increased caspase-3 activity and apoptosis in HPASMCs exposed to hypoxia. On the other hand, the suppression of AMPK α1 expression alone prevented hypoxia-mediated autophagy. The inhibition of autophagy induced cell death in HPASMCs. Our results suggest that AMPK α1 and AMPK α2 play differential roles in the survival of HPASMCs during hypoxia. The activation of AMPK α2 maintains the expression of MCL-1 and prevents apoptosis, whereas the activation of AMPK α1 stimulates autophagy, promoting HPASMC survival. Moreover, treatment with Compound C, which inhibits both isoforms of AMPK, prevented and partly reversed hypoxia-induced PH in mice. Taking these results together, our study suggests that AMPK plays a key role in the pathogenesis of pulmonary arterial hypertension, and AMPK may represent a novel therapeutic target for the treatment of pulmonary arterial hypertension.