Venetoclax-Related Neutropenia in Leukemic Patients: A Comprehensive Review of the Underlying Causes, Risk Factors, and Management

Venetoclax is a Bcl-2 homology domain 3 (BH3) mimetic currently approved for the treatment of chronic lymphocytic leukemia (CLL) and acute myeloid leukemia (AML) that has proven to be highly effective in reinstating apoptosis in leukemic cells through the highly selective inhibition of the anti-apoptotic protein B-cell lymphoma-2 (Bcl-2). Clinically, venetoclax has provided lasting remissions through the inhibition of CLL and AML blasts. However, this activity has often come at the cost of grade III/IV neutropenia due to hematopoietic cells' dependence on Bcl-2 for survival. As life-threatening infections are an important complication in these patients, an effective management of neutropenia is indispensable to maximize patient outcomes. While there is general consensus over dose reduction and scheduling modifications to minimize the risk of neutropenia, the impact of these modifications on survival is uncertain. Moreover, guidelines do not yet adequately account for patient-specific and disease-specific risk factors that may predict toxicity, or the role combination treatment plays in exacerbating neutropenia. The objective of this review is to discuss the venetoclax-induced mechanism of hematological toxicity, the potential predictive risk factors that affect patient vulnerability to neutropenia, and the current consensus on practices for management of neutropenia.

Co-operation of MCL-1 and BCL-XL anti-apoptotic proteins in stromal protection of MM cells from carfilzomib mediated cytotoxicity

Introduction

BCL-2 family proteins are important for tumour cell survival and drug resistance in multiple myeloma (MM). Although proteasome inhibitors are effective anti-myeloma drugs, some patients are resistant and almost all eventually relapse. We examined the function of BCL-2 family proteins in stromal-mediated resistance to carfilzomib-induced cytotoxicity in MM cells.

Methods

Co-cultures employing HS5 stromal cells were used to model the interaction with stroma. MM cells were exposed to CFZ in a 1-hour pulse method. The expression of BCL-2 family proteins was assessed by flow cytometry and WB. Pro-survival proteins: MCL-1, BCL-2 and BCL-XL were inhibited using S63845, ABT-199 and A-1331852 respectively. Changes in BIM binding partners were examined by immunoprecipitation and WB.

Results

CFZ induced dose-dependent cell death of MM cells, primarily mediated by apoptosis. Culture of MM cells on HS-5 stromal cells resulted in reduced cytotoxicity to CFZ in a cell contact-dependent manner, upregulated expression of MCL-1 and increased dependency on BCL-XL. Inhibiting BCL-XL or MCL-1 with BH-3 mimetics abrogated stromal-mediated protection only at high doses, which may not be achievable in vivo. However, combining BH-3 mimetics at sub-therapeutic doses, which alone were without effect, significantly enhanced CFZ-mediated cytotoxicity even in the presence of stroma. Furthermore, MCL-1 inhibition led to enhanced binding between BCL-XL and BIM, while blocking BCL-XL increased MCL-1/BIM complex formation, indicating the cooperative role of these proteins.

Conclusion

Stromal interactions alter the dependence on BCL-2 family members, providing a rationale for dual inhibition to abrogate the protective effect of stroma and restore sensitivity to CFZ.

The novel small molecule BH3 mimetic nobiletin synergizes with vorinostat to induce apoptosis and autophagy in small cell lung cancer

Small cell lung cancer (SCLC) is a highly lethal subtype of lung cancer with few therapeutic options; therefore, the identification of new targets and drugs with potent combination therapy is desirable. We previously screened BH3 mimetics from a natural product library, and in this study, we validated nobiletin as a BH3 mimetic. Specifically, we observed its combination potential and mechanism with vorinostat in SCLC in vitro and in vivo. The results showed that combination treatment with nobiletin and vorinostat reduced the proliferation of SCLC H82 cells and increased the levels of apoptotic proteins such as cleaved caspase-9 and cleaved PARP. The combination treatment increased LC3-II expression and induced autophagic cell death. In addition, this treatment significantly inhibited H82 cell xenograft SCLC tumor growth in nude mice. The combination treatment with nobiletin and vorinostat efficiently increased autophagy by inhibiting the PI3K-AKT-mTOR pathway and promoting dissociation of the BCL-2 and Beclin 1 complex, increasing the level of isolated Beclin 1 to stimulate autophagy. Molecular docking and surface plasmon resonance analysis showed that nobiletin stably bound to the BCL-2, BCL-XL and MCL-1 proteins with high affinity in a concentration-dependent manner. These results suggest that nobiletin is a BH3-only protein mimetic. Furthermore, the combination of nobiletin with vorinostat increased histone H3K9 and H3K27 acetylation levels in SCLC mouse tumor tissue and enhanced the expression of the BH3-only proteins BIM and BID. We conclude that nobiletin is a novel natural BH3 mimetic that can cooperate with vorinostat to induce apoptosis and autophagy in SCLC.

BCL2L1 inhibitor A-1331852 inhibits MCL1 transcription and triggers apoptosis in acute myeloid leukemia cells

BH3 mimetics exert anticancer activity by inhibiting anti-apoptotic BCL2 proteins. However, accumulating evidence indicates that the off-target effects of these drugs tightly modulates their anticancer activities. In this study, we investigated whether the BCL2L1 inhibitor A-1331852 induced the death of U937 acute myeloid leukemia (AML) cells through a non-BCL2L1-targeted effect. A-1331852-induced apoptosis in U937 cells was characterized by increased ROS production, downregulation of MCL1, and loss of mitochondrial membrane potential. Ectopic expression of MCL1 alleviated A-1331852-induced mitochondrial depolarization and cytotoxicity in U937 cells. A-1331852-induced ROS production increased p38 MAPK phosphorylation and inhibited MCL1 transcription. Inhibition of p38 MAPK activation restored MCL1 expression in A-1331852-treated cells. A-1331852 triggered p38 MAPK-mediated Cullin 3 downregulation, which in turn increased PP2Acα expression, thereby reducing CREB phosphorylation. A-1331852 reduced the binding of CREB to the MCL1 promoter, leading to the inhibition of CREB-mediated MCL1 transcription. Furthermore, A-1331852 acted synergistically with the BCL2 inhibitor ABT-199 to induce U937 and ABT-199-resistant U937 cell death by inhibiting MCL1 expression. A similar phenomenon caused A-1331852-induced MCL1 downregulation and cytotoxicity in AML HL-60 cells. Collectively, our data suggest that A-1331852 shows an off-target effect of inhibiting MCL1 transcription, ultimately leading to U937 and HL-60 cell death.

T-Cell Prolymphocytic Leukemia: Diagnosis, Pathogenesis, and Treatment

T-cell prolymphocytic leukemia (T-PLL) is a rare and aggressive neoplasm of mature T-cells. Most patients with T-PLL present with lymphocytosis, anemia, thrombocytopenia, and hepatosplenomegaly. Correct identification of T-PLL is essential because treatment for this disease is distinct from that of other T-cell neoplasms. In 2019, the T-PLL International Study Group (TPLL-ISG) established criteria for the diagnosis, staging, and assessment of response to treatment of T-PLL with the goal of harmonizing research efforts and supporting clinical decision-making. T-PLL pathogenesis is commonly driven by T-cell leukemia 1 (TCL1) overexpression and ATM loss, genetic alterations that are incorporated into the TPLL-ISG diagnostic criteria. The cooperativity between TCL1 family members and ATM is seemingly unique to T-PLL across the spectrum of T-cell neoplasms. The role of the T-cell receptor, its downstream kinases, and JAK/STAT signaling are also emerging themes in disease pathogenesis and have obvious therapeutic implications. Despite improved understanding of disease pathogenesis, alemtuzumab remains the frontline therapy in the treatment of naïve patients with indications for treatment given its high response rate. Unfortunately, the responses achieved are rarely durable, and the majority of patients are not candidates for consolidation with hematopoietic stem cell transplantation. Improved understanding of T-PLL pathogenesis has unveiled novel therapeutic vulnerabilities that may change the natural history of this lymphoproliferative neoplasm and will be the focus of this concise review.

An updated patent review of Mcl-1 inhibitors (2020-2022)

INTRODUCTION

Myeloid leukemia 1 (Mcl-1), an antiapoptotic protein of the Bcl-2 family, is an attractive target for cancer therapy. In recent years, significant progress has been made with regard to Mcl-1 inhibitors, leading to the generation of highly potent Mcl-1 inhibitors that have entered clinical trials.

AREAS COVERED

This review provides an overview of the patent literature between 2020 and 2022covering inhibitors, antibody-drug conjugate (ADC), and proteolysis targeting chimera (PROTAC) of Mcl-1.

EXPERT OPINION

Despite the great success of Mcl-1 inhibitor development, the on-target toxicity to heart indicated that the BH3 mimetic Mcl-1 inhibitors could have a limited therapeutic window.Drug combinations of Mcl-1 inhibitors with targeted therapies or chemotherapies may improve safety as they may reduce the dose of Mcl-1 inhibitors. Alternatively, some technologies like ADC and PROTACS could also be utilized to improve the therapeutic window. We envision a precision medicine platform like BH3 profiling or single-molecule pull-down and co-immunoprecipitation platform will enable the tailored use of Mcl-1 inhibitors utilizing the unique molecular information of individual patients.

Subcutaneous delivery of a dendrimer-BH3 mimetic improves lymphatic uptake and survival in lymphoma

As a malignant tumour of lymphatic origin, B-cell lymphoma represents a significant challenge for drug delivery, where effective therapies must access malignant cells in the blood, organs and lymphatics while avoiding off-target toxicity. Subcutaneous (SC) administration of nanomedicines allows preferential access to both the lymphatic and blood systems and may therefore provide a route to enhanced drug exposure to lymphomas. Here we examine the impact of SC dosing on lymphatic exposure, pharmacokinetics (PK), and efficacy of AZD0466, a small molecule dual Bcl-2/Bcl-xL inhibitor conjugated to a 'DEP®' G5 poly-l-lysine dendrimer. PK studies reveal that the plasma half-life of the dendrimer-drug conjugate is 8-times longer than that of drug alone, providing evidence of slow release from the circulating dendrimer nanocarrier. The SC dosed construct also shows preferential lymphatic transport, with over 50% of the bioavailable dose recovered in thoracic lymph. Increases in dose (up to 400 mg/kg) are well tolerated after SC administration and studies in a model of disseminated lymphoma in mice show that high dose SC treatment outperforms IV administration using doses that lead to similar total plasma exposure (lower peak concentrations but extended exposure after SC). These data show that the DEP® dendrimer can act as a circulating drug depot accessing both the lymphatic and blood circulatory systems. SC administration improves lymphatic exposure and facilitates higher dose administration due to improved tolerability. Higher dose SC administration also results in improved efficacy, suggesting that drug delivery systems that access both plasma and lymph hold significant potential for the treatment of haematological cancers where lymphatic and extranodal dissemination are poor prognostic factors.

PALVEN: phase Ib trial of palbociclib, letrozole and venetoclax in estrogen receptor- and BCL2-positive advanced breast cancer

The addition of a CDK4/6 inhibitor to endocrine therapy improves progression-free and overall survival in women with metastatic estrogen receptor-positive breast cancer. In that setting, CDK4/6 inhibitors induce a potent cell-cycle arrest (which may be accompanied by tumor senescence) but fail to induce apoptotic cell death. Venetoclax is a potent inhibitor of BCL2, a pro-survival protein overexpressed in the majority of estrogen receptor-positive cancers. Pre-clinical findings indicate that venetoclax augments tumor response to the CDK4/6 inhibitor palbociclib by triggering apoptosis, including in senescent cells. The PALVEN phase Ib trial will further examine this finding. The primary objective is to identify the maximum tolerated dose and determine the recommended phase II dose for palbociclib, letrozole and venetoclax combination therapy. Clinical Trial Registration: NCT03900884 (ClinicalTrials.gov).

A Novel Regimen for Treating Melanoma: MCL1 Inhibitors and Azacitidine

Although treatment options for melanoma patients have expanded in recent years with the approval of immunotherapy and targeted therapy, there is still an unmet need for new treatment options for patients that are ineligible for, or resistant to these therapies. BH3 mimetics, drugs that mimic the activity of pro-apoptotic BCL2 family proteins, have recently achieved remarkable success in the clinical setting. The combination of BH3 mimetic ABT-199 (venetoclax) plus azacitidine has shown substantial benefit in treating acute myelogenous leukemia. We evaluated the efficacy of various combinations of BH3 mimetic + azacitidine in fourteen human melanoma cell lines from cutaneous, mucosal, acral and uveal subtypes. Using a combination of cell viability assay, BCL2 family knockdown cell lines, live cell imaging, and sphere formation assay, we found that combining inhibition of MCL1, an anti-apoptotic BCL2 protein, with azacitidine had substantial pro-apoptotic effects in multiple melanoma cell lines. Specifically, this combination reduced cell viability, proliferation, sphere formation, and induced apoptosis. In addition, this combination is highly effective at reducing cell viability in rare mucosal and uveal subtypes. Overall, our data suggest this combination as a promising therapeutic option for some patients with melanoma and should be further explored in clinical trials.

Pimozide and Imipramine Blue Exploit Mitochondrial Vulnerabilities and Reactive Oxygen Species to Cooperatively Target High Risk Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a heterogeneous disease with a high relapse rate. Cytokine receptor targeted therapies are therapeutically attractive but are subject to resistance-conferring mutations. Likewise, targeting downstream signaling pathways has been difficult. Recent success in the development of synergistic combinations has provided new hope for refractory AML patients. While generally not efficacious as monotherapy, BH3 mimetics are very effective in combination with chemotherapy agents. With this in mind, we further explored novel BH3 mimetic drug combinations and showed that pimozide cooperates with mTOR inhibitors and BH3 mimetics in AML cells. The three-drug combination was able to reach cells that were not as responsive to single or double drug combinations. In Flt3-internal tandem duplication (ITD)-positive cells, we previously showed pimozide to be highly effective when combined with imipramine blue (IB). Here, we show that Flt3-ITD⁺ cells are sensitive to an IB-induced dynamin 1-like (Drp1)-p38-ROS pathway. Pimozide contributes important calcium channel blocker activity converging with IB on mitochondrial oxidative metabolism. Overall, these data support the concept that antioxidants are a double-edged sword. Rationally designed combination therapies have significant promise for further pre-clinical development and may ultimately lead to improved responses.

AT101 [(-)-Gossypol] Selectively Inhibits MCL1 and Sensitizes Carcinoma to BH3 Mimetics by Inducing and Stabilizing NOXA

Anti-apoptotic BCL2 proteins are important targets for cancer therapy as cancers depend on their activity for survival. Direct inhibitors of MCL1 have entered clinical trials, although their efficacy may be limited by toxicity. An alternative approach may be to induce the pro-apoptotic protein NOXA which selectively inhibits MCL1 in cells. Many compounds originally proposed as inhibitors of the BCL2 family were subsequently found to induce the pro-apoptotic protein NOXA through the unfolded protein response. In the present study, we compared various putative BH3 mimetics across a panel of carcinoma cell lines and measured expression of NOXA protein and mRNA, as well as the kinetics of NOXA induction. We found that AT101 [(-)-gossypol] induces high levels of NOXA in carcinoma cell lines yet cells survive. When combined with an appropriate BCL2 or BCL-XL inhibitor, NOXA-dependent sensitization occurs. NOXA protein continues to accumulate for many hours after AT101 is removed, providing a window for administering these combinations. As MCL1 promotes drug resistance and overall survival, we propose that NOXA induction is an alternative therapeutic strategy to target MCL1 and either kill cancer cells that are dependent on MCL1 or sensitize cancer cells to other BCL2 inhibitors.

Comparison of putative BH3 mimetics AT-101, HA14-1, sabutoclax and TW-37 with ABT-737 in platelets

Platelet lifespan is regulated by intrinsic apoptosis. Platelet apoptosis can be triggered by BH3 mimetics that inhibit the pro-survival Bcl-2 family protein, Bcl-xL. Here, we investigated several small molecules that are reported to act as BH3 mimetics and compared their effects to the well-established BH3 mimetic, ABT-737. Platelet phosphatidylserine (PS) exposure was determined by flow cytometry. Changes in cytosolic Ca²⁺ signaling were detected using Cal-520. Plasma membrane integrity was determined by calcein leakage. The roles of caspases and calpain in these processes were determined using Q-VD-OPh and calpeptin, respectively. As previously reported, ABT-737 triggered PS exposure in a caspase-dependent manner and calcein loss in a caspase and calpain-dependent manner. In contrast, AT-101 and sabutoclax triggered PS exposure independently of caspases. HA14-1 also triggered PS exposure in a caspase-independent but calpain-dependent manner. There were also significant differences in the pattern and protease-dependency of cytosolic Ca²⁺ signaling in response to these drugs compared to ABT-737. Since there are clear differences between the action of ABT-737 and the other putative BH3 mimetics investigated here, AT-101, HA14-1 and sabutoclax cannot be considered as acting as BH3 mimetics in platelets. Furthermore, the platelet death caused by these drugs is likely to be distinct from apoptosis.

Targeting Apoptotic Pathways in Acute Myeloid Leukaemia

Acute Myeloid Leukaemia is a devastating disease that continues to have a poor outcome for the majority of patients. In recent years, however, a number of drugs have received FDA approval, following on from successful clinical trial results. This parallels the characterization of the molecular landscape of Acute Myeloid Leukaemia (AML) over the last decade, which has led to the development of drugs targeting newly identified recurring mutations. In addition, basic biological research into the pathobiology of AML has identified aberrant programmed cell death pathways in AML. Following on from successful outcomes in lymphoid malignancies, drugs targeting the B Cell Lymphoma 2 (BCL-2) family of anti-apoptotic proteins have been explored in AML. In this review, we will outline the preclinical and clinical work to date supporting the role of drugs targeting BCL-2, with Venetoclax being the most advanced to date. We will also highlight rationale combinations using Venetoclax, ongoing clinical trials and biomarkers of response identified from the early phase clinical trials performed.

Preferential targeting of MCL-1 by a hydrocarbon-stapled BIM BH3 peptide

BCL-2 family proteins are central regulators of apoptosis and represent prime therapeutic targets for overcoming cell death resistance in malignancies. However, plasticity of anti-apoptotic members, such as MCL-1, often allows for a switch in cell death dependency patterns that lie outside the binding profile of targeted BH3-mimetics. Therefore discovery of therapeutics that effectively inactivate all anti-apoptotic members is a high priority. To address this we tested the potency of a hydrocarbon stapled BIM BH3 peptide (BIM SAHB_A) to overcome both BCL-2 and MCL-1 apoptotic resistance given BIM’s naturally wide ranging affinity for all BCL-2 family multidomain members. BIM SAHB_A effectively killed diffuse large B-cell lymphoma (DLBCL) cell lines regardless of their anti-apoptotic dependence. Despite BIM BH3’s ability to bind all BCL-2 anti-apoptotic proteins, BIM SAHB_A’s dominant intracellular target was MCL-1 and this specificity was exploited in sequenced combination BH3-mimetic treatments targeting BCL-2, BCL-X_L, and BCL-W. Extending this MCL-1 functional dependence, mouse embryonic fibroblasts (MEFs) deficient in MCL-1 were resistant to mitochondrial changes induced by BIM SAHB_A. This study demonstrates the importance of understanding BH3 mimetic functional intracellular affinities for optimized use and highlights the diagnostic and therapeutic promise of a BIM BH3 peptide mimetic as a potential MCL-1 inhibitor.

Hypertonicity primes malignant melanoma cells for apoptosis

The tumor environment critically influences responsiveness of cancer cells to chemotherapies, most of which activate the mitochondria-regulated (intrinsic) apoptotic cascade to kill malignant cells. Especially skin tumors encounter an environment with remarkable biophysical properties. Cutaneous accumulation of Na⁺ locally establishes osmotic pressure gradients in vivo (hypertonicity or hyperosmotic stress), but whether cutaneous hypertonicity is a factor that modulates the responsiveness of skin cancers to therapeutic apoptosis-induction has thus far not been investigated. Here, we show that hyperosmotic stress lowers the threshold for apoptosis induction in malignant melanoma, the deadliest form of skin cancer. Hypertonic conditions enforce addiction to BCL-2-like proteins to prevent initiation of the mitochondria-regulated (intrinsic) apoptotic pathway. Essentially, hyperosmotic stress primes mitochondria for death. Our work identifies osmotic pressure in the tumor microenvironment as a cell extrinsic factor that modulates responsiveness of malignant melanoma cells to therapy.

MIM1 induces COLO829 melanoma cell death through mitochondrial membrane breakdown, GSH depletion, and DNA damage

Malignant melanoma is a high aggressive malignancy in humans and causes 60-80% of deaths from skin cancer. Defect in an intrinsic pathway of apoptosis via overexpression of Mcl-1 is responsible for malignant melanoma development and progression, and also for resistance to chemotherapeutic agents. MIM1 is a specific low molecular Mcl-1 protein inhibitor that is able to induce Mcl-1-dependent cancer cells death. Here, we examined the effect of MIM1 as well as MIM1 and dacarbazine (DTIC) mixture on cell viability, apoptosis, and cell cycle progression in COLO829 melanoma cells. Cell viability was performed by the WST-1 assay. Analysis of apoptosis as well as cell cycle progression was determined by fluorescence image cytometer NucleoCounter NC-3000. The obtained results demonstrated that the MIM1 exhibited high cytotoxicity against melanotic melanoma cells and induced mitochondrial membrane breakdown, GSH depletion, and DNA fragmentation. Additionally, MIM1 enhanced the proapoptotic effect of DTIC toward melanoma cells; furthermore, a mixture of these drugs caused cell cycle arrest at G2/M phase in COLO829 cells. Taken together, these data provide, for the first time, evidence that a low molecular weight Mcl-1 inhibitor-MIM1 may be a promising agent with antitumor and proapoptotic properties toward melanoma cells.

Allosteric modulation of sigma receptors by BH3 mimetics ABT-737, ABT-263 (Navitoclax) and ABT-199 (Venetoclax)

ABT-737, ABT-263 (Navitoclax) and ABT-199 (Venetoclax) are under intensive preclinical and clinical investigation as treatments for hematologic and other malignancies. These small molecules mimic pro-death B-cell lymphoma-2 (Bcl-2) Homology 3 (BH3) domain-only proteins. They also bear a structural resemblance to certain sigma (σ) receptor ligands. Moreover, the Bcl-2 and σ receptor protein families are both located primarily at the endoplasmic reticulum, mediate cell death and survival through protein-protein interactions, and physically associate. Accordingly, we examined the ability of the ABT series of BH3 mimetics to interact with σ receptors using radioligand-binding techniques. Negative allosteric modulation of [3H](+)-pentazocine, an agonist, binding to σ1 receptors in guinea pig brain membranes was observed for ABT-737, ABT-263 and ABT-199. Findings included reduction of specific binding to distinct plateaus in concentration-dependent fashion, significant slowing of radioligand dissociation kinetics, and decreases in radioligand affinity with no or modest changes in maximal receptor densities. Using a ternary complex model, dissociation constants (KX) for modulator binding to the σ1 receptor ranged from 1 to 2.5 μM, while negative cooperativity factors (α), representing the changes in affinity of ligand and modulator when bound as a ternary complex with the receptor, ranged from 0.15 to 0.42. These observations were extended and reinforced by studies using intact small cell (NCI-H69) and non-small cell (NCI-H23) lung cancer cells, and by using an antagonist σ1 receptor radioligand, E-N-1-(3'-[125I]iodoallyl)-N'-4-(3″,4″-dimethoxyphenethyl)piperazine, in mouse brain membranes. By contrast, exploratory studies indicate marked enhancement of the σ2 receptor binding of [3H]1,3-di-(o-tolyl)guanidine/(+)-pentazocine in NCI-H23 cells and guinea pig brain membranes. These findings raise intriguing questions regarding mechanism and potential functional outcomes.

Rapid Imaging of BCL-2 Family Interactions in Live Cells Using FLIM-FRET

The Bcl-2 proteins control cell death via interchanging interactions within the Bcl-2 family. Fluorescence lifetime imaging microscopy (FLIM) is used to detect Förster resonance energy transfer (FRET) between two fluorescent-fusion proteins in live cells. FLIM-FRET has been used to detect specific interactions and their disruption, for Bcl-2 family proteins. To date, this has been possible only in low throughput, due to the time required for serial data acquisition. We developed an automated optical system with eight parallel detectors for rapid and efficient data collection. Here we describe how to use this system for FLIM-FRET imaging of Bcl-2 family protein interactions in a 384-well plate format.

Effect of the BH3 Mimetic Polyphenol (-)-Gossypol (AT-101) on the in vitro and in vivo Growth of Malignant Mesothelioma

Malignant mesothelioma (MM) is a primary tumor arising from mesothelial cells. The survival of MM patients following traditional chemotherapy is poor, thus innovative treatments for MM are needed. (-)-gossypol (AT-101) is a BH3 mimetic compound which possesses anti-tumoral activity by targeting multiple signaling transduction pathways. Several clinical trials employing AT-101 have been performed and some of them are still ongoing. Accordingly, we investigated the in vitro effects of AT-101 on cell proliferation, cell cycle regulation, pro-survival signaling pathways, apoptosis and autophagy of human (MM-B1, H-Meso-1, and MM-F1) and mouse (#40a) MM cell lines. In addition, we explored the in vivo anti-tumor activities of AT-101 in a mouse model, in which the transplantation of MM cells induces ascites in the peritoneal space. AT-101 inhibited in vitro MM cells survival in a dose- and time-dependent manner and triggered autophagy, but the process was then blocked and was coincident with apoptosis activation. To confirm the effect of AT-101 in inducing the apoptosis of MM cells, MM cells were simultaneously treated with AT-101 and with the caspase inhibitor, Z-VAD-FMK. Z-VAD-FMK was able to significantly reduce the number of cells in the subG1 phase compared to the treatment with AT-101 alone. This result corroborates the induction of cell death by apoptosis following treatment with AT-101. Indeed, Western blotting results showed that AT-101 increases Bax/Bcl-2 ratio, modulates p53 expression, activates caspase 9 and the cleavage of PARP-1. In addition, the treatment with AT-101 was able to: (a) decrease the ErbB2 protein expression; (b) increase the EGFR protein expression; (c) affect the phosphorylation of ERK1/2, p38 and AKT; (d) stimulate JNK1/2 and c-jun phosphorylation. Our in vivo results showed that the intraperitoneal administration of AT-101 increased the median survival of C57BL/6 mice intraperitoneally transplanted with #40a cells and reduced the risk of developing tumors. Our findings may have important implications for the design of MM therapies by employing AT-101 as an anticancer agent in combination with standard therapies.

MIM1, the Mcl-1 - specific BH3 mimetic induces apoptosis in human U87MG glioblastoma cells

Glioblastoma multiforme (GBM) is the most common and high aggressive malignant brain tumor. Despite evolving oncology treatment and novel chemotherapeutic agents the median survival of patients diagnosed with GBM is only 12-15 months. This grim fact highlights necessity to identify new drugs that could improve the effectiveness of GBM patients treatment. MIM1 is a specific low molecular Mcl-1 protein inhibitor able to induce Mcl-1-dependent cancer cells death. The aim of this study was to examine the effect of MIM1 as well as MIM1 and temozolomide (TMZ) mixture on cell viability, apoptosis and cell cycle progression in human U87MG glioblastoma cells. Cell viability was performed by the WST-1 assay. Mitochondrial membrane potential, Annexin V assay, DNA fragmentation and cell cycle distribution were determined by fluorescence image cytometer NucleoCounter NC-3000. The obtained results show that MIM1 and MIM1/TMZ mixture decrease glioblastoma cells viability in a dose- and time- dependent manner. Moreover, the exposure of U87MG cells to MIM1 and MIM1/TMZ mixture causes mitochondrial dysfunction as well as DNA fragmentation and cell cycle arrest at G₂/M phase. This study provides for the first time convincing evidence that BH3 mimetic MIM1, which inhibits Mcl-1 antiapoptotic protein may be an efficacious molecule able to induction of apoptosis and sensitize GBM cells to alkylating agents.

Mechanisms for mTORC1 activation and synergistic induction of apoptosis by ruxolitinib and BH3 mimetics or autophagy inhibitors in JAK2-V617F-expressing leukemic cells including newly established PVTL-2

The activated JAK2-V617F mutant is very frequently found in myeloproliferative neoplasms (MPNs), and its inhibitor ruxolitinib has been in clinical use, albeit with limited efficacies. Here, we examine the signaling mechanisms from JAK2-V617F and responses to ruxolitinib in JAK2-V617F-positive leukemic cell lines, including PVTL-2, newly established from a patient with post-MPN secondary acute myeloid leukemia, and the widely used model cell line HEL. We have found that ruxolitinib downregulated the mTORC1/S6K/4EBP1 pathway at least partly through inhibition of the STAT5/Pim-2 pathway with concomitant downregulation of c-Myc, MCL-1, and BCL-xL as well as induction of autophagy in these cells. Ruxolitinib very efficiently inhibited proliferation but only modestly induced apoptosis. However, inhibition of BCL-xL/BCL-2 by the BH3 mimetics ABT-737 and navitoclax or BCL-xL by A-1331852 induced caspase-dependent apoptosis involving activation of Bak and Bax synergistically with ruxolitinib in HEL cells. On the other hand, the putative pan-BH3 mimetic obatoclax as well as chloroquine and bafilomycin A1 inhibited autophagy at its late stage and induced apoptosis in PVTL-2 cells synergistically with ruxolitinib. The present study suggests that autophagy as well as the anti-apoptotic BCL-2 family members, regulated at least partly by the mTORC1 pathway downstream of STAT5/Pim-2, protects JAK2-V617F-positive leukemic cells from ruxolitinib-induced apoptosis depending on cell types and may contribute to development of new strategies against JAK2-V617F-positive neoplasms.

BH3 mimetics suppress CXCL12 expression in human malignant peripheral nerve sheath tumor cells

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive, Schwann cell-derived neoplasms of the peripheral nervous system that have recently been shown to possess an autocrine CXCL12/CXCR4 signaling loop that promotes tumor cell proliferation and survival. Importantly, the CXCL12/CXCR4 signaling axis is driven by availability of the CXCL12 ligand rather than CXCR4 receptor levels alone. Therefore, pharmacological reduction of CXCL12 expression could be a potential chemotherapeutic target for patients with MPNSTs or other pathologies wherein the CXCL12/CXCR4 signaling axis is active. AT101 is a well-established BCL-2 homology domain 3 (BH3) mimetic that we recently demonstrated functions as an iron chelator and thus acts as a hypoxia mimetic. In this study, we found that AT101 significantly reduces CXCL12 mRNA and secreted protein in established human MPNST cell lines in vitro. This effect was recapitulated by other BH3 mimetics [ABT-737 (ABT), obatoclax (OBX) and sabutoclax (SBX)] but not by desferrioxamine (DFO), an iron chelator and known hypoxia mimetic. These data suggest that CXCL12 reduction is a function of AT101's BH3 mimetic property rather than its iron chelation ability. Additionally, this study investigates a potential mechanism of BH3 mimetic-mediated CXCL12 suppression: liberation of a negative CXCL12 transcriptional regulator, poly (ADP-Ribose) polymerase I (PARP1) from its physical interaction with BCL-2. These data suggest that clinically available BH3 mimetics might prove therapeutically useful at least in part by virtue of their ability to suppress CXCL12 expression.

BH3 mimetics as anti-fibrotic therapy: Unleashing the mitochondrial pathway of apoptosis in myofibroblasts

Organs and tissues in mammals can undergo self-repair following injury. However, chronic or severe tissue injury leads to the development of dense scar tissue or fibrosis at the expense of regeneration. The identification of novel therapeutic strategies aiming at reversing fibrosis is therefore a major clinical unmet need in regenerative medicine. Persistent activation of scar-forming myofibroblasts distinguishes non-resolving pathological fibrosis from self-limited physiological wound healing. Thus, therapeutic strategies selectively inducing myofibroblast apoptosis could prevent progression and potentially reverse established fibrosis in fibrotic diseases. In this Review, we discuss recent findings that have demonstrated that activated myofibroblasts, traditionally viewed as apoptosis-resistant cells, are actually "primed for death". In this state, mitochondria of activated myofibroblasts are loaded with proapoptotic BH3 proteins, which creates a cellular "addiction" to individual antiapoptotic proteins to block prodeath signaling and ensure survival. This creates a novel therapeutic opportunity to treat organ fibrosis by inducing myofibroblast apoptosis with the so-called BH3 mimetic drugs, which have recently shown potent antifibrotic activities in experimental models. Finally, we discuss the potential use of BH3 profiling as a functional tool to diagnose myofibroblast addiction to individual antiapoptotic proteins, which may serve to guide and assign the most effective BH3 mimetic drug for patients with fibrotic disease.

Iterative optimization yields Mcl-1-targeting stapled peptides with selective cytotoxicity to Mcl-1-dependent cancer cells

Bcl-2 family proteins regulate apoptosis, and aberrant interactions of overexpressed antiapoptotic family members such as Mcl-1 promote cell transformation, cancer survival, and resistance to chemotherapy. Discovering potent and selective Mcl-1 inhibitors that can relieve apoptotic blockades is thus a high priority for cancer research. An attractive strategy for disabling Mcl-1 involves using designer peptides to competitively engage its binding groove, mimicking the structural mechanism of action of native sensitizer BH3-only proteins. We transformed Mcl-1-binding peptides into α-helical, cell-penetrating constructs that are selectively cytotoxic to Mcl-1-dependent cancer cells. Critical to the design of effective inhibitors was our introduction of an all-hydrocarbon cross-link or "staple" that stabilizes α-helical structure, increases target binding affinity, and independently confers binding specificity for Mcl-1 over related Bcl-2 family paralogs. Two crystal structures of complexes at 1.4 Å and 1.9 Å resolution demonstrate how the hydrophobic staple induces an unanticipated structural rearrangement in Mcl-1 upon binding. Systematic sampling of staple location and iterative optimization of peptide sequence in accordance with established design principles provided peptides that target intracellular Mcl-1. This work provides proof of concept for the development of potent, selective, and cell-permeable stapled peptides for therapeutic targeting of Mcl-1 in cancer, applying a design and validation workflow applicable to a host of challenging biomedical targets.

The selective Bcl-2 inhibitor venetoclax, a BH3 mimetic, does not dysregulate intracellular Ca2+ signaling

Anti-apoptotic B cell-lymphoma-2 (Bcl-2) proteins are emerging as therapeutic targets in a variety of cancers for precision medicines, like the BH3-mimetic drug venetoclax (ABT-199), which antagonizes the hydrophobic cleft of Bcl-2. However, the impact of venetoclax on intracellular Ca²⁺ homeostasis and dynamics in cell systems has not been characterized in detail. Here, we show that venetoclax did not affect Ca²⁺-transport systems from the endoplasmic reticulum (ER) in permeabilized cell systems. Venetoclax (1μM) did neither trigger Ca²⁺ release by itself nor affect agonist-induced Ca²⁺ release in a variety of intact cell models. Among the different cell types, we also studied two Bcl-2-dependent cancer cell models with a varying sensitivity towards venetoclax, namely SU-DHL-4 and OCI-LY-1, both diffuse large B-cell lymphoma cell lines. Acute application of venetoclax did also not dysregulate Ca²⁺ signaling in these Bcl-2-dependent cancer cells. Moreover, venetoclax-induced cell death was independent of intracellular Ca²⁺ overload, since Ca²⁺ buffering using BAPTA-AM did not suppress venetoclax-induced cell death. This study therefore shows that venetoclax does not dysregulate the intracellular Ca²⁺ homeostasis in a variety of cell types, which may underlie its limited toxicity in human patients. Furthermore, venetoclax-induced cell death in Bcl-2-dependent cancer cells is not mediated by intracellular Ca²⁺ overload. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.

A phase II trial of the BCL-2 homolog domain 3 mimetic AT-101 in combination with docetaxel for recurrent, locally advanced, or metastatic head and neck cancer

BACKGROUND

AT-101 is a BCL-2 Homolog domain 3 mimetic previously demonstrated to have tumoricidal effects in advanced solid organ malignancies. Given the evidence of activity in xenograft models, treatment with AT-101 in combination with docetaxel is a therapeutic doublet of interest in metastatic head and neck squamous cell carcinoma.

PATIENTS AND METHODS

Patients included in this trial had unresectable, recurrent, or distantly metastatic head and neck squamous cell carcinoma (R/M HNSCC) not amenable to curative radiation or surgery. This was an open label randomized, phase II trial in which patients were administered AT-101 in addition to docetaxel. The three treatment arms were docetaxel, docetaxel plus pulse dose AT-101, and docetaxel plus metronomic dose AT-101. The primary endpoint of this trial was overall response rate.

RESULTS

Thirty-five patients were registered and 32 were evaluable for treatment response. Doublet therapy with AT-101 and docetaxel was well tolerated with only 2 patients discontinuing therapy due to treatment related toxicities. The overall response rate was 11 % (4 partial responses) with a clinical benefit rate of 74 %. Median progression free survival was 4.3 months (range: 0.7-13.7) and overall survival was 5.5 months (range: 0.4-24). No significant differences were noted between dosing strategies.

CONCLUSION

Although met with a favorable toxicity profile, the addition of AT-101 to docetaxel in R/M HNSCC does not appear to demonstrate evidence of efficacy.

Therapy of prostate cancer using a novel cancer terminator virus and a small molecule BH-3 mimetic

Despite recent advances, treatment options for advanced prostate cancer (CaP) remain limited. We are pioneering approaches to treat advanced CaP that employ conditionally replication-competent oncolytic adenoviruses that simultaneously produce a systemically active cancer-specific therapeutic cytokine, mda-7/IL-24, Cancer Terminator Viruses (CTV). A truncated version of the CCN1/CYR61 gene promoter, tCCN1-Prom, was more active than progression elevated gene-3 promoter (PEG-Prom) in regulating transformation-selective transgene expression in CaP and oncogene-transformed rat embryo cells. Accordingly, we developed a new CTV, Ad.tCCN1-CTV-m7, which displayed dose-dependent killing of CaP without harming normal prostate epithelial cells in vitro with significant anti-cancer activity in vivo in both nude mouse CaP xenograft and transgenic Hi-Myc mice (using ultrasound-targeted microbubble (MB)-destruction, UTMD, with decorated MBs). Resistance to mda-7/IL-24-induced cell deathcorrelated with overexpression of Bcl-2 family proteins. Inhibiting Mcl-1 using an enhanced BH3 mimetic, BI-97D6, sensitized CaP cell lines to mda-7/IL-24-induced apoptosis. Combining BI-97D6 with Ads expressing mda-7/IL-24promoted ER stress, decreased anti-apoptotic Mcl-1 expression and enhanced mda-7/IL-24expression through mRNA stabilization selectively in CaP cells. In Hi-myc mice, the combination induced enhanced apoptosis and tumor growth suppression. These studies highlight therapeutic efficacy of combining a BH3 mimetic with a novel CTV, supporting potential clinical applications for treating advanced CaP.

Constitutive BAK activation as a determinant of drug sensitivity in malignant lymphohematopoietic cells

Mitochondrial outer membrane permeabilization (MOMP), a key step in the intrinsic apoptotic pathway, is incompletely understood. Current models emphasize the role of BH3-only BCL2 family members in BAX and BAK activation. Here we demonstrate concentration-dependent BAK autoactivation under cell-free conditions and provide evidence that this autoactivation plays a key role in regulating the intrinsic apoptotic pathway in intact cells. In particular, we show that up to 80% of BAK (but not BAX) in lymphohematopoietic cell lines is oligomerized and bound to anti-apoptotic BCL2 family members in the absence of exogenous death stimuli. The extent of this constitutive BAK oligomerization is diminished by BAK knockdown and unaffected by BIM or PUMA down-regulation. Further analysis indicates that sensitivity of cells to BH3 mimetics reflects the identity of the anti-apoptotic proteins to which BAK is constitutively bound, with extensive BCLXL•BAK complexes predicting navitoclax sensitivity, and extensive MCL1•BAK complexes predicting A1210477 sensitivity. Moreover, high BAK expression correlates with sensitivity of clinical acute myelogenous leukemia to chemotherapy, whereas low BAK levels correlate with resistance and relapse. Collectively, these results inform current understanding of MOMP and provide new insight into the ability of BH3 mimetics to induce apoptosis without directly activating BAX or BAK.

The BIM deletion polymorphism: A paradigm of a permissive interaction between germline and acquired TKI resistance factors in chronic myeloid leukemia

Both germline polymorphisms and tumor-specific genetic alterations can determine the response of a cancer to a given therapy. We previously reported a germline deletion polymorphism in the BIM gene that was sufficient to mediate intrinsic resistance to tyrosine kinase inhibitors (TKI) in chronic myeloid leukemia (CML), as well as other cancers [1]. The deletion polymorphism favored the generation of BIM splice forms lacking the pro-apoptotic BH3 domain, conferring a relative resistance to the TKI imatinib (IM). However, CML patients with the BIM deletion polymorphism developed both partial and complete IM resistance. To understand the mechanisms underlying the latter, we grew CML cells either with or without the BIM deletion polymorphism in increasing IM concentrations. Under these conditions, the BIM deletion polymorphism enhanced the emergence of populations with complete IM resistance, mimicking the situation in patients. Importantly, the combined use of TKIs with the BH3 mimetic ABT-737 overcame the BCR-ABL1-dependent and -independent resistance mechanisms found in these cells. Our results illustrate the interplay between germline and acquired genetic factors in confering TKI resistance, and suggest a therapeutic strategy for patients with complete TKI resistance associated with the BIM deletion polymorphism.

Killing Two Cells with One Stone: Pharmacologic BCL-2 Family Targeting for Cancer Cell Death and Immune Modulation

A crucial component of regulating organismal homeostasis is maintaining proper cell number and eliminating damaged or potentially malignant cells. Apoptosis, or programed cell death, is the mechanism responsible for this equilibrium. The intrinsic apoptotic pathway is also especially important in the development and maintenance of the immune system. Apoptosis is essential for proper positive and negative selection during B- and T-cell development and for efficient contraction of expanded lymphocytes following an immune response. Tight regulation of the apoptotic pathway is critical, as excessive cell death can lead to immunodeficiency while apoptotic resistance can lead to aberrant lymphoproliferation and autoimmune disease. Dysregulation of cell death is implicated in a wide range of hematological malignancies, and targeting various components of the apoptotic machinery in these cases is an attractive chemotherapeutic strategy. A wide array of compounds has been developed with the purpose of reactivating the intrinsic apoptotic pathway. These compounds, termed BH3 mimetics are garnering considerable attention as they gain greater clinical oncologic significance. As their use expands, it will be imperative to understand the effects these compounds have on immune homeostasis. Uncovering their potential immunomodulatory activity may allow for administration of BH3 mimetics for direct tumor cell killing as well as novel therapies for a wide range of immune-based directives. This review will summarize the major proteins involved in the intrinsic apoptotic pathway and define their roles in normal immune development and disease. Clinical and preclinical BH3 mimetics are described within the context of what is currently known about their ability to affect immune function. Prospects for future antitumor immune amplification and immune modulation are then proposed.

AT-101 simultaneously triggers apoptosis and a cytoprotective type of autophagy irrespective of expression levels and the subcellular localization of Bcl-xL and Bcl-2 in MCF7 cells

The effects of autophagy on cell death are highly contextual and either beneficial or deleterious. One prime example for this dual function of autophagy is evidenced by the cell responses to the BH3 mimetic AT-101 that is known to induce either apoptotic or autophagy-dependent cell death in different settings. Based on previous reports, we hypothesized that the expression levels of pro-survival Bcl-2 family members may be key determinants for the respective death mode induced by AT-101. Here we investigated the role of autophagy in the response of MCF7 breast cancer cells to AT-101. AT-101 treatment induced a prominent conversion of LC3-I to LC3-II and apoptotic cell death characterized by the appearance of Annexin-positive/PI-negative early apoptotic cells and PARP cleavage. Inhibition of the autophagy pathway, either through application of 3-MA or by lentiviral knockdown of ATG5, strongly potentiated cell death, indicating a pro-survival function of autophagy. Overexpression of wild type Bcl-xL significantly diminished the net amount of AT-101-induced cell death, but failed to alter the death-enhancing effects of the ATG5 knockdown. This was also observed with the organelle-specific variants Bcl-xL-ActA and Bcl-2-ActA (mitochondrial) as well as Bcl-xL-cb5 and Bcl-2-cb5 (ER) which all reduced AT-101-induced cell death, but did not affect the death-enhancing effects of 3-MA. Collectively, our data indicate that in apoptosis-proficient MCF7 cells, AT-101 triggers Bcl-2- and Bcl-xL-dependent apoptosis and a cytoprotective autophagy response that is independent of the expression and subcellular localization of Bcl-xL and Bcl-2.

The Mutant KRAS Gene Up-regulates BCL-XL Protein via STAT3 to Confer Apoptosis Resistance That Is Reversed by BIM Protein Induction and BCL-XL Antagonism

In colorectal cancers with oncogenic GTPase Kras (KRAS) mutations, inhibition of downstream MEK/ERK signaling has shown limited efficacy, in part because of failure to induce a robust apoptotic response. We studied the mechanism of apoptosis resistance in mutant KRAS cells and sought to enhance the efficacy of a KRAS-specific MEK/ERK inhibitor, GDC-0623. GDC-0623 was shown to potently up-regulate BIM expression to a greater extent versus other MEK inhibitors in isogenic KRAS HCT116 and mutant KRAS SW620 colon cancer cells. ERK silencing enhanced BIM up-regulation by GDC-0623 that was due to its loss of phosphorylation at Ser(69), confirmed by a BIM-EL phosphorylation-defective mutant (S69G) that increased protein stability and blocked BIM induction. Despite BIM and BIK induction, the isogenic KRAS mutant versus wild-type cells remained resistant to GDC-0623-induced apoptosis, in part because of up-regulation of BCL-XL. KRAS knockdown by a doxycycline-inducible shRNA attenuated BCL-XL expression. BCL-XL knockdown sensitized KRAS mutant cells to GDC-0623-mediated apoptosis, as did the BH3 mimetic ABT-263. GDC-0623 plus ABT-263 induced a synergistic apoptosis by a mechanism that includes release of BIM from its sequestration by BCL-XL. Furthermore, mutant KRAS activated p-STAT3 (Tyr(705)) in the absence of IL-6 secretion, and STAT3 knockdown reduced BCL-XL mRNA and protein expression. These data suggest that BCL-XL up-regulation by STAT3 contributes to mutant KRAS-mediated apoptosis resistance. Such resistance can be overcome by potent BIM induction and concurrent BCL-XL antagonism to enable a synergistic apoptotic response.

Emerging understanding of Bcl-2 biology: Implications for neoplastic progression and treatment

Bcl-2, the founding member of a family of apoptotic regulators, was initially identified as the protein product of a gene that is translocated and overexpressed in greater than 85% of follicular lymphomas (FLs). Thirty years later we now understand that anti-apoptotic Bcl-2 family members modulate the intrinsic apoptotic pathway by binding and neutralizing the mitochondrial permeabilizers Bax and Bak as well as a variety of pro-apoptotic proteins, including the cellular stress sensors Bim, Bid, Puma, Bad, Bmf and Noxa. Despite extensive investigation of all of these proteins, important questions remain. For example, how Bax and Bak breach the outer mitochondrial membrane remains poorly understood. Likewise, how the functions of anti-apoptotic Bcl-2 family members such as eponymous Bcl-2 are affected by phosphorylation or cancer-associated mutations has been incompletely defined. Finally, whether Bcl-2 family members can be successfully targeted for therapeutic advantage is only now being investigated in the clinic. Here we review recent advances in understanding Bcl-2 family biology and biochemistry that begin to address these questions.

A phase II, multicenter, open-label study of obatoclax mesylate in patients with previously untreated myelodysplastic syndromes with anemia or thrombocytopenia

BACKGROUND

Obatoclax mesylate is a small-molecule Bcl-2 homology domain-3 mimetic that neutralizes antiapoptotic Bcl-2-related proteins. We evaluated obatoclax in untreated MDS patients with anemia/thrombocytopenia.

PATIENTS AND METHODS

Twenty-four patients with a bone marrow blast count of ≤ 10% and anemia (hemoglobin level < 10 g/dL) or thrombocytopenia (platelet count < 50 × 10(9)/L) were eligible to receive intravenous obatoclax 60 mg over 24 hours every 2 weeks.

RESULTS

Response rate was 8% (2 patients; hematologic improvement). Disease stabilization/response was maintained ≥ 12 weeks in 50% (12 patients). Because the response rate was below a predetermined threshold, the study was terminated. Adverse events (any grade) included euphoric mood (63%; 15 patients), nausea (38%; 9 patients), and diarrhea (25%; 6 patients); Grade 3/4 adverse events included anemia (21%; 5 patients), thrombocytopenia (13%; 3 patients), and pneumonia (13%; 3 patients).

CONCLUSIONS

Obatoclax 60 mg every 2 weeks was feasible, but had limited first-line activity in MDS.

IL-10/Janus kinase/signal transducer and activator of transcription 3 signaling dysregulates Bim expression in autoimmune lymphoproliferative syndrome

BACKGROUND

Autoimmune lymphoproliferative syndrome (ALPS) is a human disorder of T cell homeostasis caused by mutations that impair FAS-mediated apoptosis. A defining characteristic of ALPS is the expansion of double negative T cells (DNTC). Relatively little is known about how defective FAS-driven cell death and the Bcl-2 apoptotic pathway intersect in ALPS patients.

OBJECTIVE

We studied changes in Bcl-2 family member expression in ALPS to determine whether the Bcl-2 pathway might provide a therapeutic target.

METHODS

We used flow cytometry to analyze the expression of pro- and anti-apoptotic Bcl-2 family members in T cells from 12 ALPS patients and determined the in vitro sensitivity of ALPS DNTC to the pro-apoptotic BH3 mimetic, ABT-737.

RESULTS

The pro-apoptotic molecule, Bim, was significantly elevated in DNTC. Although no general pattern of individual anti-apoptotic Bcl-2 family members emerged, increased expression of Bim was always accompanied by increased expression of at least 1 anti-apoptotic Bcl-2 family member. Strikingly, Bim levels in DNTC correlated significantly with serum IL-10 in ALPS patients, and IL-10 was sufficient to mildly induce Bim in normal and ALPS T cells via a Janus kinase/signal transducer and activator of transcription 3-dependent mechanism. Finally, ABT-737 preferentially killed ALPS DNTC in vitro.

CONCLUSION

Combined, these data show that an IL-10/Janus kinase/signal transducer and activator of transcription 3 pathway drives Bim expression in ALPS DNTC, which renders them sensitive to BH3 mimetics, uncovering a potentially novel therapeutic approach to ALPS.

Prosurvival Bcl-2 family members affect autophagy only indirectly, by inhibiting Bax and Bak. Proc Natl Acad Sci U S A. 2014;111:8512-8517. [PMID: 24912196 DOI: 10.1073/pnas.1406425111]

Antiapoptotic B-cell lymphoma 2 (Bcl-2) family members such as Bcl-2, myeloid cell leukemia 1 (Mcl-1), and B-cell lymphoma-X large (Bcl-xL) are proposed to inhibit autophagy by directly binding to the BH3 domain of Beclin 1/Atg6. However, these Bcl-2 family proteins also block the proapoptotic activity of Bcl-2-associated X (Bax) and Bcl-2 homologous antagonist/killer (Bak), and many inducers of autophagy also cause cell death. Therefore, when the mitochondrial-mediated apoptosis pathway is functional, interpretation of such experiments is complicated. To directly test the impact of the endogenous antiapoptotic Bcl-2 family members on autophagy in the absence of apoptosis, we inhibited their activity in cells lacking the essential cell death mediators Bax and Bak. We also used inducible lentiviral vectors to overexpress Bcl-2, Bcl-xL, or Mcl-1 in cells and subjected them to treatments that promote autophagy. In the absence of Bax and Bak, Bcl-2, Bcl-xL, and Mcl-1 had no detectable effect on autophagy or cell death in myeloid or fibroblast cell lines. On the other hand, when Bax and Bak were present, inhibiting the prosurvival Bcl-2 family members stimulated autophagy, but this correlated with increased cell death. In addition, inhibition of autophagy induced by amino acid starvation, etoposide, or interleukin-3 withdrawal did not affect cell death in the absence of Bax and Bak. These results demonstrate that the antiapoptotic Bcl-2 family members do not directly inhibit components of the autophagic pathway but instead affect autophagy indirectly, owing to their inhibition of Bax and Bak.

The role of apoptosis in megakaryocytes and platelets

The role of apoptotic pathways in the development and function of the megakaryocyte lineage has generated renewed interest in recent years. This has been driven by the advent of BH3 mimetic drugs that target BCL2 family proteins to induce apoptosis in tumour cells: agents such as ABT-263 (navitoclax, which targets BCL2, BCL-XL [BCL2L1] and BCL2L2) and ABT-199 (a BCL2-specific agent) are showing great promise in early stage clinical trials. However, the major dose-limiting toxicity of navitoclax has proven to be thrombocytopenia, an on-target effect of inhibiting BCL-XL . It transpires that the anucleate platelet contains a classical intrinsic apoptosis pathway, which at steady state regulates its life span in the circulation. BCL-XL is the critical pro-survival protein that restrains apoptosis and maintains platelet viability. These findings have paved the way to a deeper understanding of apoptotic pathways and processes in platelets, and their precursor cell, the megakaryocyte.

S1 kills MCF-7/ADR cells more than MCF-7 cells: A protective mechanism of endoplasmic reticulum stress

Drug resistance in chemotherapy for breast cancer is associated with high levels of P-glycoprotein (P-gp) as well as endoplasmic reticulum (ER) stress. In this paper, we aimed to evaluate the efficacy of a pan-BH3 mimetic S1 on drug-resistant MCF-7/ADR cells, and the roles of S1-induced ER stress in cell death. S1 exhibited greater and faster mitochondrial apoptosis in MCF-7/ADR cells than in MCF-7 cells. We demonstrated by Bax/Bak activation and cyrochrome c release that the p-glycprotein had little influence on S1 entering cells and hitting its targets in MCF-7/ADR cells. An IRE1-mediated ER stress response followed by c-Jun N-terminal kinase (JNK) and extracellular signal-regulated protein kinase (ERK) activation was specifically induced by S1 in MCF-7 cells, but not in MCF-7/ADR cells. Coimmunoprecipitation and western blotting analysis determined that ER stress played a protective role in S1-induced apoptosis by triggering Bcl-2 phosphorylation, which grabbed more pro-apoptotic proteins. The synergism effect of ERK inhibitor PD98059 with S1 confirmed the protective role of ER stress. Defective ER stress in MCF-7/ADR cells confers the more sensitivity toward S1.

An evidence-based review of obatoclax mesylate in the treatment of hematological malignancies

Obatoclax mesylate is an intravenously-administered drug under investigation in Phase I and II clinical trials as a novel anticancer therapeutic for hematological malignancies and solid tumors. Obatoclax was developed as a pan-inhibitor of antiapoptotic members of the B cell chronic lymphocytic leukemia/lymphoma 2 (BCL-2) family of proteins, which control the intrinsic or mitochondrial pathway of apoptosis. Resistance to apoptosis through dysregulation of BCL-2 family members is commonly observed in hematological malignancies, and can be linked to therapeutic resistance and poor clinical outcomes. By inhibiting pro-survival BCL-2 family proteins, including MCL-1, obatoclax is proposed to (1) trigger cell death as a single agent, and (2) potentiate the anticancer effects of other therapeutics. Preclinical investigations have supported these proposals and have provided evidence suggestive of a promising therapeutic index for this drug. Phase I trials of obatoclax mesylate in leukemia and lymphoma have defined well-tolerated regimens and have identified transient neurotoxicity as the most common adverse effect of this drug. In these studies, a limited number of objective responses were observed, along with hematological improvement in a larger proportion of treated patients. Published Phase II evaluations in lymphoma and myelofibrosis, however, have not reported robust single-agent activity. Emerging evidence from ongoing preclinical and clinical investigations suggests that the full potential of obatoclax mesylate as a novel anticancer agent may be realized (1) in rational combination treatments, and (2) when guided by molecular predictors of therapeutic response. By understanding the molecular underpinnings of obatoclax response, along with optimal therapeutic regimens and indications, the potential of obatoclax mesylate for the treatment of hematological malignancies may be further clarified.