Synergistic induction of apoptosis in high-risk DLBCL by BCL2 inhibition with ABT-199 combined with pharmacologic loss of MCL1

Venetoclax therapy and emerging resistance mechanisms in acute myeloid leukaemia

Acute myeloid leukaemia (AML) is a highly aggressive and devastating malignancy of the bone marrow and blood. For decades, intensive chemotherapy has been the frontline treatment for AML but has yielded only poor patient outcomes as exemplified by a 5-year survival rate of < 30%, even in younger adults. As knowledge of the molecular underpinnings of AML has advanced, so too has the development new strategies with potential to improve the treatment of AML patients. To date the most promising of these targeted agents is the BH3-mimetic venetoclax which in combination with standard of care therapies, has manageable non-haematological toxicity and exhibits impressive efficacy. However, approximately 30% of AML patients fail to respond to venetoclax-based regimens and almost all treatment responders eventually relapse. Here, we review the emerging mechanisms of intrinsic and acquired venetoclax resistance in AML and highlight recent efforts to identify novel strategies to overcome resistance to venetoclax.

Inhibition of glutaminase-1 in DLBCL potentiates venetoclax-induced antitumor activity by promoting oxidative stress

Diffuse large B-cell lymphoma (DLBCL) is the most common lymphoma in adults, but first-line immunochemotherapy fails to produce a durable response in about one-third of the patients. Because tumor cells often reprogram their metabolism, we investigated the importance of glutaminolysis, a pathway converting glutamine to generate energy and various metabolites, for the growth of DLBCL cells. Glutaminase-1 (GLS1) expression was robustly detected in DLBCL biopsy samples and cell lines. Both pharmacological inhibition and genetic knockdown of GLS1 induced cell death in DLBCL cells regardless of their subtype classification, whereas primary B cells remained unaffected. Interestingly, GLS1 inhibition resulted not only in reduced levels of intermediates of the tricarboxylic acid cycle but also in a strong mitochondrial accumulation of reactive oxygen species. Supplementation of DLBCL cells with α-ketoglutarate or with the antioxidant α-tocopherol mitigated oxidative stress and abrogated cell death upon GLS1 inhibition, indicating an essential role of glutaminolysis in the protection from oxidative stress. Furthermore, the combination of the GLS1 inhibitor CB-839 with the therapeutic BCL2 inhibitor ABT-199 not only induced massive reactive oxygen species (ROS) production but also exhibited highly synergistic cytotoxicity, suggesting that simultaneous targeting of GLS1 and BCL2 could represent a novel therapeutic strategy for patients with DLBCL.

Cyclin-dependent kinase-9 in B-cell malignancies: pathogenic role and therapeutic implications

Cyclin-dependent kinases (CDK) regulate cell cycle and transcriptional activity. Pan-CDK inhibitors demonstrated early efficacy in lymphoid malignancies, but also have been associated with narrow therapeutic index. Among transcriptional CDKs, CDK7 and CDK9 emerged as promising targets. CDK9 serves as a component of P-TEFb elongation complex and thus is indispensable in mRNA transcription. Selective CDK9 inhibitors demonstrated pre-clinical efficacy in in vitro and in vivo models of B-cell non-Hodgkin lymphoma. CDK9 inhibition results in transcriptional pausing with rapid downmodulation of short-lived oncogenic proteins, e.g. Myc and Mcl-1, followed by cell apoptosis. Early phase clinical trials established safety of CDK9 inhibitors, with manageable neutropenia, infections and gastrointestinal toxicities. In this review, we summarize the rationale of targeting CDK9 in lymphoid malignancies, as well as pre-clinical and early clinical data with pan-CDK and selective CDK9 inhibitors.

Patent landscape of inhibitors and PROTACs of the anti-apoptotic BCL-2 family proteins

INTRODUCTION

The anti-apoptotic BCL-2 family proteins, such as BCL-2, BCL-XL, and MCL-1, are excellent cancer therapeutic targets. The FDA approval of BCL-2 selective inhibitor venetoclax in 2016 validated the strategy of targeting these proteins with BH3 mimetic small molecule inhibitors.

AREAS COVERED

This review provides an overview of the patent literature between 2016 and 2021 covering inhibitors and PROTACs of the anti-apoptotic BCL-2 proteins.

EXPERT OPINION

Since the FDA approval of venetoclax, tremendous efforts have been made to develop its analogues with improved drug properties. These activities will likely result in new drugs in coming years. Significant progress on MCL-1 inhibitors has also been made, with multiple compounds entering clinical trials. However, MCL-1 inhibition could cause on-target toxicity to normal tissues especially the heart. Similar issue exists with BCL-XL inhibitors, which cause on-target platelet toxicity. To overcome this issue, several strategies have been applied, including prodrug, dendrimer-based drug delivery, antibody-drug conjugate (ADC), and proteolysis targeting chimera (PROTAC); and amazingly, each of these approaches has resulted in a drug candidate entering clinical trials. We envision technologies like ADC and PROTAC could also be utilized to increase the therapeutic index of MCL-1 inhibitors.

3,5,7-Substituted Pyrazolo[4,3-d]Pyrimidine Inhibitors of Cyclin-Dependent Kinases and Cyclin K Degraders

3,5,7-Trisubstituted pyrazolo[4,3-d]pyrimidines have been identified as potent inhibitors of cyclin-dependent kinases (CDKs), which are established drug targets. Herein, we describe their further structural modifications leading to novel nanomolar inhibitors with strong antiproliferative activity. We determined the crystal structure of fully active CDK2/A2 with 5-(2-amino-1-ethyl)thio-3-cyclobutyl-7-[4-(pyrazol-1-yl)benzyl]amino-1(2)H-pyrazolo[4,3-d]pyrimidine (24) at 1.7 Å resolution, confirming the competitive mode of inhibition. Biochemical and cellular assays in lymphoma cell lines confirmed the expected mechanism of action through dephosphorylation of retinoblastoma protein and RNA polymerase II, leading to induction of apoptosis. Importantly, we also revealed an interesting ability of compound 24 to induce proteasome-dependent degradation of cyclin K both in vitro and in a patient-derived xenograft in vivo. We propose that 24 has a dual mechanism of action, acting as a kinase inhibitor and as a molecular glue inducing an interaction between CDK12 and DDB1 that leads to polyubiquitination of cyclin K and its subsequent degradation.

Altered pathways and targeted therapy in double hit lymphoma

High-grade B-cell lymphoma with translocations involving MYC and BCL2 or BCL6, usually referred to as double hit lymphoma (DHL), is an aggressive hematological malignance with distinct genetic features and poor clinical prognosis. Current standard chemoimmunotherapy fails to confer satisfying outcomes and few targeted therapeutics are available for the treatment against DHL. Recently, the delineating of the genetic landscape in tumors has provided insight into both biology and targeted therapies. Therefore, it is essential to understand the altered signaling pathways of DHL to develop treatment strategies with better clinical benefits. Herein, we summarized the genetic alterations in the two DHL subtypes (DHL-BCL2 and DHL-BCL6). We further elucidate their implications on cellular processes, including anti-apoptosis, epigenetic regulations, B-cell receptor signaling, and immune escape. Ongoing and potential therapeutic strategies and targeted drugs steered by these alterations were reviewed accordingly. Based on these findings, we also discuss the therapeutic vulnerabilities that coincide with these genetic changes. We believe that the understanding of the DHL studies will provide insight into this disease and capacitate the finding of more effective treatment strategies.

Synthetic lethality of cyclin-dependent kinase inhibitor Dinaciclib with VHL-deficiency allows for selective targeting of clear cell renal cell carcinoma

Clear cell renal cell carcinoma (CC-RCC) remains one of the most deadly forms of kidney cancer despite recent advancements in targeted therapeutics, including tyrosine kinase and immune checkpoint inhibitors. Unfortunately, these therapies have not been able to show better than a 16% complete response rate. In this study we evaluated a cyclin-dependent kinase inhibitor, Dinaciclib, as a potential new targeted therapeutic for CC-RCC. In vitro, Dinaciclib showed anti-proliferative and pro-apoptotic effects on CC-RCC cell lines in Cell Titer Glo, Crystal Violet, FACS-based cell cycle analysis, and TUNEL assays. Additionally, these responses were accompanied by a reduction in phospho-Rb and pro-survival MCL-1 cell signaling responses, as well as the induction of caspase 3 and PARP cleavage. In vivo, Dinaciclib efficiently inhibited primary tumor growth in an orthotopic, patient-derived xenograft-based CC-RCC mouse model. Importantly, Dinaciclib targeted both CD105⁺ cancer stem cells (CSCs) and CD105⁻ non-CSCs in vivo. Moreover, normal cell lines, as well as a CC-RCC cell line with re-expressed von-Hippel Lindau (VHL) tumor suppressor gene, were protected from Dinaciclib-induced cytotoxicity when not actively dividing, indicating an effective therapeutic window due to synthetic lethality of Dinaciclib treatment with VHL loss. Thus, Dinaciclib represents a novel potential therapeutic for CC-RCC.

Pembrolizumab plus dinaciclib in patients with hematologic malignancies: the phase 1b KEYNOTE-155 study

Preclinical data demonstrated that combining an anti-programmed cell death 1 (PD-1) inhibitor with a cyclin-dependent kinase 9 (CDK9) inhibitor provided enhanced antitumor activity with no significant toxicities, suggesting this combination may be a potential therapeutic option. The multicohort, phase 1 KEYNOTE-155 study evaluated the safety and antitumor activity of the PD-1 inhibitor pembrolizumab plus the CDK9 inhibitor dinaciclib in patients with relapsed or refractory (rr) chronic lymphocytic leukemia (CLL), diffuse large B-cell lymphoma (DLBCL) and multiple myeloma (MM). Patients enrolled were ≥18 years of age with a confirmed diagnosis of CLL, DLBCL, or MM. The study included 2 phases: a dose-evaluation phase to determine dose-limiting toxicities and a signal-detection phase. Patients received pembrolizumab 200 mg every 3 weeks plus dinaciclib 7 mg/m2 on day 1 and 10 mg/m2 on day 8 of cycle 1 and 14 mg/m2 on days 1 and 8 of cycles 2 and later. Primary endpoint was safety, and a key secondary endpoint was objective response rate (ORR). Seventy-two patients were enrolled and received ≥1 dose of study treatment (CLL, n = 17; DLBCL, n = 38; MM, n = 17). Pembrolizumab plus dinaciclib was generally well tolerated and produced no unexpected toxicities. The ORRs were 29.4% (5/17, rrCLL), 21.1% (8/38, rrDLBCL), and 0% (0/17, rrMM), respectively. At data cutoff, all 72 patients had discontinued treatment, 38 (52.8%) because of progressive disease. These findings demonstrate activity with combination pembrolizumab plus dinaciclib and suggest that a careful and comprehensive approach to explore anti-PD-1 and CDK9 inhibitor combinations is warranted. This trial was registered at www.clinicaltrials.gov as NCT02684617.

ABT199/venetoclax potentiates the cytotoxicity of alkylating agents and fludarabine in acute myeloid leukemia cells

The antineoplastic activity of pre-transplant regimens in hematopoietic stem cell transplantation (HSCT) is a critical factor for acute myeloid leukemia (AML) patients. There is an urgent need to identify novel approaches without jeopardizing patient safety. We hypothesized that combination of drugs with different mechanisms of action would provide better cytotoxicity. We, therefore, determined the synergistic cytotoxicity of various combinations of the alkylating agents busulfan (Bu) and 4-hydroperoxycyclophosphamide (4HC), the nucleoside analog fludarabine (Flu) and the BCL2 inhibitor ABT199/venetoclax in AML cells. [Bu+4HC] and [Bu+Flu] inhibited cell proliferation and activated apoptosis; addition of ABT199 to either combinations significantly increased these effects with combination indexes < 1. Apoptosis is suggested by cleavages of PARP1 and CASPASE 3, DNA fragmentation, increased reactive oxygen species, decreased mitochondrial membrane potential, and increased pro-apoptotic proteins in the cytoplasm. A similar enhancement of apoptosis was observed in patient-derived cell samples. ABT199/venetocalx upregulated anti-apoptotic MCL1 as a compensatory mechanism but addition of [Bu+4HC] or [Bu+Flu] negated this effect by CASPASE 3-mediated cleavage of MEK1/2 and its substrate MCL1. CASPASE 3 caused cleavage of pro-survival β-CATENIN, which likely contributed to the activation of stress signaling pathways involving SAPK/JNK and AMPK. The observed synergistic cytotoxicity was associated with an inhibition of pro-survival pathways involving STAT1, STAT5 and PI3K. These findings will be useful in designing clinical trials using these drug combinations as pre-transplant conditioning regimens for AML patients.

Anti-apoptotic MCL1 Protein Represents Critical Survival Molecule for Most Burkitt Lymphomas and BCL2-negative Diffuse Large B-cell Lymphomas

The pro-survival MCL1 protein is overexpressed in many cancers, including B-cell non-Hodgkin lymphomas (B-NHL). S63845 is a highly specific inhibitor of MCL1. We analyzed mechanisms of sensitivity/resistance to S63845 in preclinical models of diffuse large B-cell lymphoma (DLBCL) and Burkitt lymphoma. Annexin V-based cytotoxic assays, Western blot analysis, protein co-immunoprecipitation, and cell clones with manipulated expression of BCL2 family proteins were used to analyze mechanisms of sensitivity to S63845. Experimental in vivo therapy with S63845 and/or venetoclax was performed using patient-derived xenografts (PDX) of treatment-refractory B-NHL. A subset of DLBCL and majority of Burkitt lymphoma cell lines were sensitive to S63845. The level of BCL2 protein expression was the major determinant of resistance to S63845: BCL2 serves as a buffer for pro-apoptotic proteins released from MCL1 upon exposure to S63845. While BCL2-negative lymphomas were effectively eliminated by single-agent S63845, its combination with venetoclax was synthetically lethal in BCL2-positive PDX models. Concerning MCL1, both, the level of MCL1 protein expression, and its occupational status represent key factors mediating sensitivity to S63845. In contrast to MCL1-BIM/BAK1 complexes that prime lymphoma cells for S63845-mediated apoptosis, MCL1-NOXA complexes are associated with S63845 resistance. In conclusion, MCL1 represents a critical survival molecule for most Burkitt lymphomas and a subset of BCL2-negative DLBCLs. The level of BCL2 and MCL1 expression and occupational status of MCL1 belong to the key modulators of sensitivity/resistance to S63845. Co-treatment with venetoclax can overcome BCL2-mediated resistance to S63845, and enhance efficacy of MCL1 inhibitors in BCL2-positive aggressive B-NHL.

Inhibition of PIM Kinases in DLBCL Targets MYC Transcriptional Program and Augments the Efficacy of Anti-CD20 Antibodies

The family of PIM serine/threonine kinases includes three highly conserved oncogenes, PIM1, PIM2, and PIM3, which regulate multiple pro-survival pathways and cooperate with other oncogenes such as MYC. Recent genomic CRISPR-Cas9 screens further highlighted oncogenic functions of PIMs in diffuse large B cell lymphoma (DLBCL) cells, justifying development of small molecule PIM inhibitors and therapeutic targeting of PIM kinases in lymphomas. However, detailed consequences of PIM inhibition in DLBCL remain undefined. Using chemical and genetic PIM blockade, we comprehensively characterized PIM kinase-associated pro-survival functions in DLBCL and the mechanisms of PIM inhibition-induced toxicity. Treatment of DLBCL cells with SEL24/MEN1703, a pan PIM inhibitor in clinical development, decreased BAD phosphorylation and cap-dependent protein translation, reduced MCL1 expression, and induced apoptosis. PIM kinases were tightly coexpressed with MYC in diagnostic DLBCL biopsies, and PIM inhibition in cell lines and patient-derived primary lymphoma cells decreased MYC levels as well as expression of multiple MYC-dependent genes, including PLK1. Chemical and genetic PIM inhibition upregulated surface CD20 levels in a MYC-dependent fashion. Consistently, MEN1703 and other clinically available pan-PIM inhibitors synergized with the anti-CD20 monoclonal antibody rituximab in vitro, increasing complement-dependent cytotoxicity and antibody-mediated phagocytosis. Combined treatment with PIM inhibitor and rituximab suppressed tumor growth in lymphoma xenografts more efficiently than either drug alone. Taken together, these results show that targeting PIM in DLBCL exhibits pleiotropic effects that combine direct cytotoxicity with potentiated susceptibility to anti-CD20 antibodies, justifying further clinical development of such combinatorial strategies.

A Deep Insight Into CAR-T Cell Therapy in Non-Hodgkin Lymphoma: Application, Opportunities, and Future Directions

Non-Hodgkin's lymphoma (NHL) is a cancer that starts in the lymphatic system. In NHL, the important part of the immune system, a type of white blood cells called lymphocytes become cancerous. NHL subtypes include marginal zone lymphoma, small lymphocytic lymphoma, follicular lymphoma (FL), and lymphoplasmacytic lymphoma. The disease can emerge in either aggressive or indolent form. 5-year survival duration after diagnosis is poor among patients with aggressive/relapsing form of NHL. Therefore, it is necessary to understand the molecular mechanisms of pathogenesis involved in NHL establishment and progression. In the next step, we can develop innovative therapies for NHL based on our knowledge in signaling pathways, surface antigens, and tumor milieu of NHL. In the recent few decades, several treatment solutions of NHL mainly based on targeted/directed therapies have been evaluated. These approaches include B-cell receptor (BCR) signaling inhibitors, immunomodulatory agents, monoclonal antibodies (mAbs), epigenetic modulators, Bcl-2 inhibitors, checkpoint inhibitors, and T-cell therapy. In recent years, methods based on T cell immunotherapy have been considered as a novel promising anti-cancer strategy in the treatment of various types of cancers, and particularly in blood cancers. These methods could significantly increase the capacity of the immune system to induce durable anti-cancer responses in patients with chemotherapy-resistant lymphoma. One of the promising therapy methods involved in the triumph of immunotherapy is the chimeric antigen receptor (CAR) T cells with dramatically improved killing activity against tumor cells. The CAR-T cell-based anti-cancer therapy targeting a pan-B-cell marker, CD19 is recently approved by the US Food and Drug Administration (FDA) for the treatment of chemotherapy-resistant B-cell NHL. In this review, we will discuss the structure, molecular mechanisms, results of clinical trials, and the toxicity of CAR-T cell-based therapies. Also, we will criticize the clinical aspects, the treatment considerations, and the challenges and possible drawbacks of the application of CAR-T cells in the treatment of NHL.

Venetoclax response is enhanced by selective inhibitor of nuclear export compounds in hematologic malignancies

The selective inhibitor of nuclear export (SINE) compounds selinexor (KPT-330) and eltanexor (KPT-8602) are from a novel class of small molecules that target exportin-1 (XPO1 [CRM1]), an essential nucleo-cytoplasmic transport protein responsible for the nuclear export of major tumor suppressor proteins and growth regulators such as p53, p21, and p27. XPO1 also affects the translation of messenger RNAs for critical oncogenes, including MYC, BCL2, MCL1, and BCL6, by blocking the export of the translation initiation factor eIF4E. Early trials with venetoclax (ABT-199), a potent, selective inhibitor of BCL2, have revealed responses across a variety of hematologic malignancies. However, many tumors are not responsive to venetoclax. We used models of acute myeloid leukemia (AML) and diffuse large B-cell lymphoma (DLBCL) to determine in vitro and in vivo responses to treatment with venetoclax and SINE compounds combined. Cotreatment with venetoclax and SINE compounds demonstrated loss of viability in multiple cell lines. Further in vitro analyses showed that this enhanced cell death was the result of an increase in apoptosis that led to a loss of clonogenicity in methylcellulose assays, coinciding with activation of p53 and loss of MCL1. Treatment with SINE compounds and venetoclax combined led to a reduction in tumor growth in both AML and DLBCL xenografts. Immunohistochemical analysis of tissue sections revealed that the reduction in tumor cells was partly the result of an induction of apoptosis. The enhanced effects of this combination were validated in primary AML and DLBCL patient cells. Our studies reveal synergy with SINE compounds and venetoclax in aggressive hematologic malignancies and provide a rationale for pursuing this approach in a clinical trial.

Genetic Events Inhibiting Apoptosis in Diffuse Large B Cell Lymphoma

Simple Summary

Diffuse large B cell lymphoma (DLBCL) is the most common type of non-Hodgkin lymphoma (NHL). Despite the genetic heterogeneity of the disease, most patients are initially treated with a combination of rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP), but relapse occurs in ~50% of patients. One of the hallmarks of DLBCL is the occurrence of genetic events that inhibit apoptosis, which contributes to disease development and resistance to therapy. These events can affect the intrinsic or extrinsic apoptotic pathways, or their modulators. Understanding the factors that contribute to inhibition of apoptosis in DLBCL is crucial in order to be able to develop targeted therapies and improve outcomes, particularly in relapsed and refractory DLBCL (rrDLBCL). This review provides a description of the genetic events inhibiting apoptosis in DLBCL, their contribution to lymphomagenesis and chemoresistance, and their implication for the future of DLBCL therapy.

Abstract

Diffuse large B cell lymphoma (DLBCL) is curable with chemoimmunotherapy in ~65% of patients. One of the hallmarks of the pathogenesis and resistance to therapy in DLBCL is inhibition of apoptosis, which allows malignant cells to survive and acquire further alterations. Inhibition of apoptosis can be the result of genetic events inhibiting the intrinsic or extrinsic apoptotic pathways, as well as their modulators, such as the inhibitor of apoptosis proteins, P53, and components of the NF-kB pathway. Mechanisms of dysregulation include upregulation of anti-apoptotic proteins and downregulation of pro-apoptotic proteins via point mutations, amplifications, deletions, translocations, and influences of other proteins. Understanding the factors contributing to resistance to apoptosis in DLBCL is crucial in order to be able to develop targeted therapies that could improve outcomes by restoring apoptosis in malignant cells. This review describes the genetic events inhibiting apoptosis in DLBCL, provides a perspective of their interactions in lymphomagenesis, and discusses their implication for the future of DLBCL therapy.

Overexpression of KDM4D promotes acute myeloid leukemia cell development by activating MCL-1

Acute myeloid leukemia (AML) is regarded as a fatal cancer in the world. The overall survival in adult patients with AML is still poor. As lysine demethylases, the KDM4 family is found highly expressed in many kinds of tumors. In this study, we demonstrate that KDM4D is overexpressed in AML and knockdown of KDM4D not only inhibits the proliferation of AML cells, but also induces cell cycle arrest and apoptosis. Furthermore, our research shows that KDM4D can regulate the expression of MCL-1 by demethylating H3K9me3 at the promoter region in AML cells. Besides, we find that high expression of KDM4D is correlated with poor overall survival in AML patients. Taken together, our study demonstrated that KDM4D can promote MCL-1 expression in AML and may serve as a novel target for the treatment of AML.

High-Throughput Screening Identifies Idasanutlin as a Resensitizing Drug for Venetoclax-Resistant Neuroblastoma Cells

Neuroblastoma tumors frequently overexpress the anti-apoptotic protein B-cell lymphoma/leukemia 2 (BCL-2). We previously showed that treating BCL-2-dependent neuroblastoma cells with the BCL-2 inhibitor venetoclax results in apoptosis, but unfortunately partial therapy resistance is observed. The current study describes the identification of drugs capable of resensitizing venetoclax-resistant neuroblastoma cells to venetoclax. To examine these effects, venetoclax resistance was induced in BCL-2-dependent neuroblastoma cell lines KCNR and SJNB12 by continuous exposure to high venetoclax concentrations. Non-resistant and venetoclax-resistant neuroblastoma cell lines were exposed to a 209-compound library in the absence and presence of venetoclax to identify compounds that were more effective in the venetoclax-resistant cell lines under venetoclax pressure. Top hits were further validated in combination with venetoclax using BCL-2-dependent neuroblastoma model systems. Overall, high-throughput drug screening identified the MDM2 inhibitor idasanutlin as a promising resensitizing agent for venetoclax-resistant neuroblastoma cell lines. Idasanutlin treatment induced BAX-mediated apoptosis in venetoclax-resistant neuroblastoma cells in the presence of venetoclax, whereas it caused p21-mediated growth arrest in control cells. In vivo combination treatment showed tumor regression and superior efficacy over single-agent therapies in a BCL-2-dependent neuroblastoma cell line xenograft and a patient-derived xenograft. However, xenografts less dependent on BCL-2 were not sensitive to venetoclax-idasanutlin combination therapy. This study demonstrates that idasanutlin can overcome resistance to the BCL-2 inhibitor venetoclax in preclinical neuroblastoma model systems, which supports clinical development of a treatment strategy combining the two therapies.

Targeting transcription of MCL-1 sensitizes HER2-amplified breast cancers to HER2 inhibitors

Human epidermal growth factor receptor 2 gene (HER2) is focally amplified in approximately 20% of breast cancers. HER2 inhibitors alone are not effective, and sensitizing agents will be necessary to move away from a reliance on heavily toxic chemotherapeutics. We recently demonstrated that the efficacy of HER2 inhibitors is mitigated by uniformly low levels of the myeloid cell leukemia 1 (MCL-1) endogenous inhibitor, NOXA. Emerging clinical data have demonstrated that clinically advanced cyclin-dependent kinase (CDK) inhibitors are effective MCL-1 inhibitors in patients, and, importantly, well tolerated. We, therefore, tested whether the CDK inhibitor, dinaciclib, could block MCL-1 in preclinical HER2-amplified breast cancer models and therefore sensitize these cancers to dual HER2/EGFR inhibitors neratinib and lapatinib, as well as to the novel selective HER2 inhibitor tucatinib. Indeed, we found dinaciclib suppresses MCL-1 RNA and is highly effective at sensitizing HER2 inhibitors both in vitro and in vivo. This combination was tolerable in vivo. Mechanistically, liberating the effector BCL-2 protein, BAK, from MCL-1 results in robust apoptosis. Thus, clinically advanced CDK inhibitors may effectively combine with HER2 inhibitors and present a chemotherapy-free therapeutic strategy in HER2-amplified breast cancer, which can be tested immediately in the clinic.

Prognostic value of lymphocyte-to-monocyte ratio and histone methyltransferase G9a histone methyltransferase in patients with double expression lymphoma: A retrospective observational study

ABSTRACT

In patients with diffuse large B-cell lymphoma, MYC combined with Bcl2 and/or Bcl6-based protein expression is called double expression lymphoma (DEL). R-DA-EPOCH program chemotherapy is typically recommended because these patients often have a poor prognosis. Although numerous factors affect survival of patients with DEL, the roles of the tumor biomarker histone methyltransferase G9a (G9a) and the lymphocyte-to-monocyte ratio (LMR) are unknown.We performed a retrospective analysis of data from 51 patients. These patients were newly diagnosed with DEL and treated with R-DA-EPOCH at Taizhou People' s Hospital and Northern Jiangsu People's Hospital between June 2014 and December 2019. Receiver operator characteristic curve results were used to calculate the LMR cutoff value. We used an immunohistochemical analysis to examine G9a expression in DEL tissues. The Kaplan-Meier method was used to determine progression-free survival (PFS) and overall survival (OS) characteristics. Cox proportional-hazards models were constructed for univariate and multivariate analyses to examine the prognostic values of LMRs and G9a in patients with DEL.The cutoff value for LMR was 2.18. The 5-year PFS rate was 35.3%, and the 5-year OS rate was 39.2%. Patients with DEL with lower LMRs and who were G9a-positive predicted inferior PFS and OS. Univariate analysis revealed that patients with elevated LDH levels, high National Comprehensive Cancer Network International Prognostic Index (NCCN-IPI) scores, LMRs ≤2.18, and G9a-positive results had relatively poorer PFS and OS. The multivariate analysis revealed that LMRs ≤2.18 and a G9a-positive result were independent prognostic factors for PFS and OS in patients with DEL treated with R-DA-EPOCH.The study results suggested that peripheral blood LMRs were an important marker for evaluation of prognosis in patients with DEL. High expression of G9a was associated with worse outcomes, indicating that G9a may serve as a prognostic biomarker for patients with DEL who undergo R-DA-EPOCH program chemotherapy.

Molecular Genetics of Relapsed Diffuse Large B-Cell Lymphoma: Insight into Mechanisms of Therapy Resistance

The majority of patients with diffuse large B-cell lymphoma (DLBCL) can be treated successfully with a combination of chemotherapy and the monoclonal anti-CD20 antibody rituximab. Nonetheless, approximately one-third of the patients with DLBCL still experience relapse or refractory (R/R) disease after first-line immunochemotherapy. Whole-exome sequencing on large cohorts of primary DLBCL has revealed the mutational landscape of DLBCL, which has provided a framework to define novel prognostic subtypes in DLBCL. Several studies have investigated the genetic alterations specifically associated with R/R DLBCL, thereby uncovering molecular pathways linked to therapy resistance. Here, we summarize the current state of knowledge regarding the genetic alterations that are enriched in R/R DLBCL, and the corresponding pathways affected by these gene mutations. Furthermore, we elaborate on their potential role in mediating therapy resistance, also in connection with findings in other B-cell malignancies, and discuss alternative treatment options. Hence, this review provides a comprehensive overview on the gene lesions and molecular mechanisms underlying R/R DLBCL, which are considered valuable parameters to guide treatment.

Targeting BCL-2 in B-cell malignancies and overcoming therapeutic resistance

Defects in apoptosis can promote tumorigenesis and impair responses of malignant B cells to chemotherapeutics. Members of the B-cell leukemia/lymphoma-2 (BCL-2) family of proteins are key regulators of the intrinsic, mitochondrial apoptotic pathway. Overexpression of antiapoptotic BCL-2 family proteins is associated with treatment resistance and poor prognosis. Thus, inhibition of BCL-2 family proteins is a rational therapeutic option for malignancies that are dependent on antiapoptotic BCL-2 family proteins. Venetoclax (ABT-199, GDC-0199) is a highly selective BCL-2 inhibitor that represents the first approved agent of this class and is currently widely used in the treatment of chronic lymphocytic leukemia (CLL) as well as acute myeloid leukemia (AML). Despite impressive clinical activity, venetoclax monotherapy for a prolonged duration can lead to drug resistance or loss of dependence on the targeted protein. In this review, we provide an overview of the mechanism of action of BCL-2 inhibition and the role of this approach in the current treatment paradigm of B-cell malignancies. We summarize the drivers of de novo and acquired resistance to venetoclax that are closely associated with complex clonal shifts, interplay of expression and interactions of BCL-2 family members, transcriptional regulators, and metabolic modulators. We also examine how tumors initially resistant to venetoclax become responsive to it following prior therapies. Here, we summarize preclinical data providing a rationale for efficacious combination strategies of venetoclax to overcome therapeutic resistance by a targeted approach directed against alternative antiapoptotic BCL-2 family proteins (MCL-1, BCL-xL), compensatory prosurvival pathways, epigenetic modifiers, and dysregulated cellular metabolism/energetics for durable clinical remissions.

Combination strategies to overcome resistance to the BCL2 inhibitor venetoclax in hematologic malignancies

Venetoclax has been approved by the United States Food and Drug Administration since 2016 as a monotherapy for treating patients with relapsed/refractory chronic lymphocytic leukemia having 17p deletion. It has led to a breakthrough in the treatment of hematologic malignancies in recent years. However, unfortunately, resistance to venetoclax is inevitable. Multiple studies confirmed that the upregulation of the anti-apoptotic proteins of the B-cell lymphoma 2 (BCL2) family mediated by various mechanisms, such as tumor microenvironment, and the activation of intracellular signaling pathways were the major factors leading to resistance to venetoclax. Therefore, only targeting BCL2 often fails to achieve the expected therapeutic effect. Based on the mechanism of resistance in specific hematologic malignancies, the combination of specific drugs with venetoclax was a clinically optional treatment strategy for overcoming resistance to venetoclax. This study aimed to summarize the possible resistance mechanisms of various hematologic tumors to venetoclax and the corresponding clinical strategies to overcome resistance to venetoclax in hematologic malignancies.

Combination of the dual PIM/PI3-kinase inhibitor IBL-202 and venetoclax is effective in diffuse large B-cell lymphoma

Current chemoimmunotherapy is unable to cure up to 40% of patients diagnosed with diffuse large B-cell lymphoma (DLBCL). Targeting the mechanisms by which DLBCL evades apoptosis is crucial to overcoming treatment failure in this heterogeneous disease as both current and novel treatments depend on the apoptosis of malignant cells. Despite the common overexpression of BCL-2, venetoclax is ineffective in DLBCL due to MCL-1 co-expression. This is driven by pro-growth PI3-kinase signaling, which is promoted in turn by PIM kinases. In this study, the novel dual-kinase inhibitor, IBL-202, was combined with venetoclax against a panel of DLBCL cell lines that have variable expression of pro-survival proteins. The results support the efficacy of simultaneously targeting inter-related molecules to overcome apoptotic escape in this biologically heterogeneous disease. As venetoclax, pan-PIM-kinase and pan-PI3-kinase inhibitors have, or are currently being studied in clinical trials, it may be rational to consider these drugs in combination for the treatment of DLBCL.

Enhancing venetoclax activity in hematological malignancies

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Inhibition of cyclin-dependent kinase 9 synergistically enhances venetoclax activity in mantle cell lymphoma

Mantle cell lymphoma (MCL) is an aggressive and largely incurable subtype of non-Hodgkin's lymphoma. Venetoclax has demonstrated efficacy in MCL patients with relapsed or refractory disease, however response is variable and less durable than CLL. This may be the result of co-expression of other anti-apoptotic proteins such as MCL-1, which is associated with both intrinsic and acquired resistance to venetoclax in B-cell malignancies. One strategy for neutralizing MCL-1 and other short-lived survival factors is to inhibit CDK9, which plays a key role in transcription. Here, we report the response of MCL cell lines and primary patient samples to the combination of venetoclax and novel CDK9 inhibitors. Primary samples represented de novo patients and relapsed disease, including relapse after ibrutinib failure. Despite the diverse responses to each single agent, possibly due to variable expression of the BCL-2 family members, venetoclax plus CDK9 inhibitors synergistically induced apoptosis in MCL cells. The synergistic effect was also confirmed via venetoclax plus a direct MCL-1 inhibitor. Murine xenograft studies demonstrated potent in vivo efficacy of venetoclax plus CDK9 inhibitor that was superior to each agent alone. Together, this study supports clinical investigation of this combination in MCL, including in patients who have progressed on ibrutinib.

Nationwide study of pediatric B-cell precursor acute lymphoblastic leukemia with chromosome 8q24/MYC rearrangement in Japan

BACKGROUND

Rearrangements of chromosome 8q24/MYC (8q24/MYC-r), resulting from t(8;14)(q24;q32), t(2;8)(p11;q24), or t(8;22)(q24;q11), are mainly associated with Burkitt lymphoma/leukemia (BL) and rarely observed in patients with B-cell precursor acute lymphoblastic leukemia (BCP-ALL). The characteristics of BCP-ALL with 8q24/MYC-r are poorly understood.

PROCEDURE

A retrospective nationwide study of data from patients with pediatric BCP-ALL with 8q24/MYC-r in Japan was conducted to clarify the clinical and biological characteristics associated with 8q24/MYC-r BCP-ALL.

RESULTS

Ten patients with BCP-ALL with 8q24/MYC-r, including three with double-hit leukemia (DHL) (two with t(8;14)(q24;q32) and t(14;18)(q32;q21) and one with t(8;14) and t(3;22)(q27;q11)), were identified. Patients with BCP-ALL with 8q24/MYC-r had higher median age and uric acid and lactate dehydrogenase levels, than those without 8q24/MYC-r. All patients were initially treated with ALL-type chemotherapy; however, four, including one with DHL, were switched to BL-type chemotherapy, based on cytogenetic findings. One patient relapsed after standard-risk ALL-type chemotherapy, and two patients with DHL did not attain complete remission with chemotherapy; all three died within 11 months. The other seven patients treated with BL-type or high-risk ALL-type chemotherapy are alive without disease.

CONCLUSIONS

The clinical and laboratory features of BL with IG-MYC rearrangement, displaying a BCP immunophenotype (Wagener et al. and Herbrueggen et al. termed it as pre-BLL), are similar to those of BCP-ALL with 8q24/MYC-r. Low-risk ALL-type chemotherapy may not be appropriate for them, and further studies are required to establish an adequate therapeutic strategy. Further studies of DHL to identify new treatment strategies are also needed.

A novel CDK9 inhibitor increases the efficacy of venetoclax (ABT-199) in multiple models of hematologic malignancies

MCL-1 is one of the most frequently amplified genes in cancer, facilitating tumor initiation and maintenance and enabling resistance to anti-tumorigenic agents including the BCL-2 selective inhibitor venetoclax. The expression of MCL-1 is maintained via P-TEFb-mediated transcription, where the kinase CDK9 is a critical component. Consequently, we developed a series of potent small-molecule inhibitors of CDK9, exemplified by the orally active A-1592668, with CDK selectivity profiles that are distinct from related molecules that have been extensively studied clinically. Short-term treatment with A-1592668 rapidly downregulates RNA pol-II (Ser 2) phosphorylation resulting in the loss of MCL-1 protein and apoptosis in MCL-1-dependent hematologic tumor cell lines. This cell death could be attenuated by either inhibiting caspases or overexpressing BCL-2 protein. Synergistic cell killing was also observed between A-1592668 or the related analog A-1467729, and venetoclax in a number of hematologic cell lines and primary NHL patient samples. Importantly, the CDK9 inhibitor plus venetoclax combination was well tolerated in vivo and demonstrated efficacy superior to either agent alone in mouse models of lymphoma and AML. These data indicate that CDK9 inhibitors could be highly efficacious in tumors that depend on MCL-1 for survival or when used in combination with venetoclax in malignancies dependent on MCL-1 and BCL-2.

BCL-2 Proteins in Pathogenesis and Therapy of B-Cell Non-Hodgkin Lymphomas

The ability to inhibit mitochondrial apoptosis is a hallmark of B-cell non-Hodgkin lymphomas (B-NHL). Activation of mitochondrial apoptosis is tightly controlled by members of B-cell leukemia/lymphoma-2 (BCL-2) family proteins via protein-protein interactions. Altering the balance between anti-apoptotic and pro-apoptotic BCL-2 proteins leads to apoptosis evasion and extended survival of malignant cells. The pro-survival BCL-2 proteins: B-cell leukemia/lymphoma-2 (BCL-2/BCL2), myeloid cell leukemia-1 (MCL-1/MCL1) and B-cell lymphoma-extra large (BCL-XL/BCL2L1) are frequently (over)expressed in B-NHL, which plays a crucial role in lymphoma pathogenesis, disease progression, and drug resistance. The efforts to develop inhibitors of anti-apoptotic BCL-2 proteins have been underway for several decades and molecules targeting anti-apoptotic BCL-2 proteins are in various stages of clinical testing. Venetoclax is a highly specific BCL-2 inhibitor, which has been approved by the US Food and Drug Agency (FDA) for the treatment of patients with chronic lymphocytic leukemia (CLL) and is in advanced clinical testing in other types of B-NHL. In this review, we summarize the biology of BCL-2 proteins and the mechanisms of how these proteins are deregulated in distinct B-NHL subtypes. We describe the mechanism of action of BH3-mimetics and the status of their clinical development in B-NHL. Finally, we summarize the mechanisms of sensitivity/resistance to venetoclax.

Using Informatics Tools to Identify Opportunities for Precision Medicine in Diffuse Large B-cell Lymphoma

INTRODUCTION

Diffuse large B-cell lymphoma (DLBCL) is genetically and clinically heterogeneous. Despite advances in genomic subtyping, standard frontline chemoimmunotherapy has remained unchanged for years. As high-throughput analysis becomes more accessible, characterizing drug-gene interactions in DLBCL could support patient-specific treatment strategies.

MATERIALS AND METHODS

From our systematic literature review, we compiled a comprehensive list of somatic mutations implicated in DLBCL. We extracted reported and primary sequencing data for these mutations and assessed their association with signaling pathways, cell-of-origin subtypes, and clinical outcomes.

RESULTS

Twenty-two targetable mutations present in ≥ 5% of patients with DLBCL were associated with unfavorable outcomes, yielding a predicted population of 31.7% of DLBCL cases with poor-risk disease and candidacy for targeted therapy. A second review identified 256 studies that had characterized the drug-gene interactions for these mutations via in vitro studies, mouse models, and/or clinical trials.

CONCLUSIONS

Our novel approach linking the data from our systematic reviews with informatics tools identified high-risk DLBCL subgroups, DLBCL-specific drug-gene interactions, and potential populations for precision medicine trials.

Mcl-1 as a "barrier" in cancer treatment: Can we target it now?

During the last two decades, the study of Mcl-1, an anti-apoptotic member of the Bcl-2 family, attracted researchers due to its important role in cancer cell survival and tumor development. The significance of Mcl-1 protein in resistance to chemotherapeutics makes it an attractive target in cancer therapy. Here, we discuss the diverse possibilities for indirect Mcl-1 inhibition through its downregulation, for example, via targeting for proteasomal degradation or blockage of translation and transcription. We also provide an overview of the direct blocking of protein-protein interactions with pro-apoptotic Bcl-2 family proteins, including examples of the most promising regulators of Mcl-1 and selective BH3-mimetics, which at present are under clinical evaluation. Moreover, several approaches for the co-targeting of Mcl-1 and other proteins (e.g., CDKs) are also presented. In addition, we highlight the broad spectrum of problems that accompanied the discovery and development of effective Mcl-1 inhibitors.

Targeting chronic NFAT activation with calcineurin inhibitors in diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) represents the most common adult lymphoma and can be divided into 2 major molecular subtypes: the germinal center B-cell-like and the aggressive activated B-cell-like (ABC) DLBCL. Previous studies suggested that chronic B-cell receptor signaling and increased NF-κB activation contribute to ABC DLBCL survival. Here we show that the activity of the transcription factor NFAT is chronically elevated in both DLBCL subtypes. Surprisingly, NFAT activation is independent of B-cell receptor signaling, but mediated by an increased calcium flux and calcineurin-mediated dephosphorylation of NFAT. Intriguingly, although NFAT is activated in both DLBCL subtypes, long-term calcineurin inhibition with cyclosporin A or FK506, both clinically approved drugs, triggers potent cytotoxicity specifically in ABC DLBCL cells. The antitumor effects of calcineurin inhibitors are associated with the reduced expression of c-Jun, interleukin-6, and interleukin-10, which were identified as NFAT target genes that are particularly important for the survival of ABC DLBCL. Furthermore, calcineurin blockade synergized with BCL-2 and MCL-1 inhibitors in killing ABC DLBCL cells. Collectively, these findings identify constitutive NFAT signaling as a crucial functional driver of ABC DLBCL and highlight calcineurin inhibition as a novel strategy for the treatment of this aggressive lymphoma subtype.

The Dual Cell Cycle Kinase Inhibitor JNJ-7706621 Reverses Resistance to CD37-Targeted Radioimmunotherapy in Activated B Cell Like Diffuse Large B Cell Lymphoma Cell Lines

The CD37 targeting radioimmunoconjugate ¹⁷⁷Lu-lilotomab satetraxetan (Betalutin) is currently being evaluated in a clinical phase 2b trial for patients with follicular lymphoma (FL) and in a phase 1 trial for patients with diffuse large B-cell lymphoma (DLBCL). Herein we have investigated the effect of ¹⁷⁷Lu-lilotomab satetraxetan in seven activated B-cell like (ABC) DLBCL cell lines. Although the radioimmunoconjugate showed anti-tumor activity, primary resistance was observed in a subset of cell lines. Thus, we set out to identify drugs able to overcome the resistance to ¹⁷⁷Lu-lilotomab satetraxetan in two resistant ABC-DLBCL cell lines. We performed a viability-based screen combining ¹⁷⁷Lu-lilotomab satetraxetan with the 384-compound Cambridge Cancer Compound Library. Drug combinations were scored using Bliss and Chou-Talalay algorithms. We identified and characterized the dual-specific CDK1/2 and AURA/B kinase inhibitor JNJ-7706621 as compound able to revert the resistance to RIT, alongside topoisomerase and histone deacetylases (HDAC) inhibitors.

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.

Cyclin-dependent kinase (CDK) 9 and 4/6 inhibitors in acute myeloid leukemia (AML): a promising therapeutic approach

Introduction: Despite advancements over the last 2 years, outcomes for acute myeloid leukemia (AML) are poor; however, a greater comprehension of disease mechanisms has driven the investigation of new targeted treatments. Cyclin-dependent kinases (CDKs) regulate cell cycle progression, transcription and DNA repair, and are aberrantly expressed in AML. Targeting the CDK pathway is an emerging promising therapeutic strategy in AML.Areas covered: We describe the rationale for targeting CDK9 and CDK4/6, the ongoing preclinical and clinical trials and the potential of these inhibitors in AML. Our analysis included an extensive literature search via the Pubmed database and clinicaltrials.gov (March to August, 2019).Expert opinion: While CDK4/6 inhibitors are early in development for AML, CDK9 inhibition with alvocidib has encouraging clinical activity in newly diagnosed and relapsed/refractory AML. Preclinical data suggests that leukemic MCL-1 dependence may predict response to alvocidib. Moreover, MCL-1 plays a key role in resistance to BCL-2 inhibition with venetoclax. Investigational strategies of concomitant BCL-2 and CDK9 inhibition represent a promising therapeutic platform for AML. Furthermore, preclinical data suggests that CDK4/6 inhibition has selective activity in patients with KMT2A-rearrangements and FLT3 mutations. Incorporation of CDK9 and 4/6 inhibitors into the existing therapeutic armamentarium may improve outcomes in AML.

Statins enhance efficacy of venetoclax in blood cancers

Statins have shown promise as anticancer agents in experimental and epidemiologic research. However, any benefit that they provide is likely context-dependent, for example, applicable only to certain cancers or in combination with specific anticancer drugs. We report that inhibition of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) using statins enhances the proapoptotic activity of the B cell lymphoma-2 (BCL2) inhibitor venetoclax (ABT-199) in primary leukemia and lymphoma cells but not in normal human peripheral blood mononuclear cells. By blocking mevalonate production, HMGCR inhibition suppressed protein geranylgeranylation, resulting in up-regulation of proapoptotic protein p53 up-regulated modulator of apoptosis (PUMA). In support of these findings, dynamic BH3 profiling confirmed that statins primed cells for apoptosis. Furthermore, in retrospective analyses of three clinical studies of chronic lymphocytic leukemia, background statin use was associated with enhanced response to venetoclax, as demonstrated by more frequent complete responses. Together, this work provides mechanistic justification and clinical evidence to warrant prospective clinical investigation of this combination in hematologic malignancies.

P53/PUMA are potential targets that mediate the protection of brain-derived neurotrophic factor (BDNF)/TrkB from etoposide-induced cell death in neuroblastoma (NB)

The over-expressions of brain-derived neurotrophic factor (BDNF) and its tyrosine kinase receptor TrkB have been reported to induce chemo-resistance in neuroblastoma (NB) cells. In this study, we investigated the roles of P53 and BCL2 family members in the protection of BDNF/TrkB from etoposide-induced NB cell death. TB3 and TB8, two tetracycline (TET)-regulated TrkB-expressing NB cell lines, were utilized. The expressions of P53 and BCL2 family members were detected by Western blot or RT-PCR. Transfection of siRNAs was used to knockdown P53 or PUMA. Activated lentiviral was used to over-express PUMA. Cell survival was performed by MTS assay, and the percentage of cell confluence was measured by IncuCyte ZOOM. Our results showed that etoposide treatment induced significant and time-dependent increase of P53, which could be blocked by pre-treatment with BDNF, and knockdown P53 by transfecting siRNA attenuated etoposide-induced TrkB-expressing NB cell death. PUMA was the most significantly changed BCL2 family member after treatment with etoposide, and pre-treatment with BDNF blocked the increased expression of PUMA. Transfection with siRNA inhibited etoposide-induced increased expression of PUMA, and attenuated etoposide-induced NB cell death. We also found that over-expression of PUMA by infection of activated lentiviral induced TrkB-expressing NB cell death in the absence of etoposide, and treatment of BDNF protected NB cells from PUMA-induced cell death. Our results suggested that P53 and PUMA may be potential targets that mediated the protection of BDNF/TrkB from etoposide-induced NB cell death.

Current perspectives on the treatment of double hit lymphoma

Introduction: Double hit lymphoma (DHL) represents a new diagnostic category with genetic, immunohistochemical and clinical characteristics intermediate between diffuse large B-cell lymphoma and Burkitt lymphoma. Patients with DHL usually experience poor survival after frontline R-CHOP treatment and require alternative therapies. However, the ideal therapeutic options remain undefined. Areas covered: Traditional therapies for the treatment of DHL are discussed, including intensive induction, hematopoietic stem cell transplantation (HSCT), methotrexate CNS-directed prophylaxis, and radiation therapy. The authors further introduce small-molecule inhibitors targeting myc or bcl-2 signaling pathways, chimeric antigen receptor T-cell therapy, programmed death-1 monoclonal antibody and immunomodulatory drugs as novel approaches. Expert opinion: No standard treatment exists for DHL. At present, DA-EPOCH-R exhibits an upfront induction option. Central nervous system prophylaxis with methotrexate is recommended as part of the induction therapy. For those who do not obtain complete remission, HSCT or clinical trials should be considered. Targeted approaches, especially chimeric antigen receptor T-cell therapies and small-molecule inhibitors targeting myc or bcl-2, exhibit the potential of improving outcomes for patients with DHL. High-throughput sequencing is a promising technique both at diagnosis and relapse, in order to predict outcomes and potential novel therapies.

Inhibition of SYK or BTK augments venetoclax sensitivity in SHP1-negative/BCL-2-positive diffuse large B-cell lymphoma

The BCL-2 inhibitor venetoclax has only limited activity in DLBCL despite frequent BCL-2 overexpression. Since constitutive activation of the B cell receptor (BCR) pathway has been reported in both ABC and GCB DLBCL, we investigated whether targeting SYK or BTK will increase sensitivity of DLBCL cells to venetoclax. We report that pharmacological inhibition of SYK or BTK synergistically enhances venetoclax sensitivity in BCL-2-positive DLBCL cell lines with an activated BCR pathway in vitro and in a xenograft model in vivo, despite the only modest direct cytotoxic effect. We further show that these sensitizing effects are associated with inhibition of the downstream PI3K/AKT pathway and changes in the expression of MCL-1, BIM, and HRK. In addition, we show that BCR-dependent GCB DLBCL cells are characterized by deficiency of the phosphatase SHP1, a key negative regulator of the BCR pathway. Re-expression of SHP1 in GCB DBLCL cells reduces SYK, BLNK, and GSK3 phosphorylation and induces corresponding changes in MCL1, BIM, and HRK expression. Together, these findings suggest that SHP1 deficiency is responsible for the constitutive activation of the BCR pathway in GCB DLBCL and identify SHP1 and BCL-2 as potential predictive markers for response to treatment with a venetoclax/BCR inhibitor combination.

Dysregulation of Cell Survival in Diffuse Large B Cell Lymphoma: Mechanisms and Therapeutic Targets

Diffuse large B cell lymphoma (DLBCL) is the most common type of lymphoma worldwide, representing 30-40% of non-Hodgkin lymphomas, and is clinically aggressive. Although more than half of patients with DLBCL are cured by using standard first-line immunochemotherapy, the remaining patients are refractory to the first-line therapy or relapse after complete remission and these patients require novel therapeutic approaches. Understanding the pathogenesis of DLBCL is essential for identifying therapeutic targets to tackle this disease. Cell survival dysregulation, a hallmark of cancer, is a characteristic feature of DLBCL. Intrinsic signaling aberrations, tumor microenvironment dysfunction, and viral factors can all contribute to the cell survival dysregulation in DLBCL. In recent years, several novel drugs that target abnormal cell survival pathways, have been developed and tested in clinical trials of patients with DLBCL. In this review, we discuss cell survival dysregulation, the underlying mechanisms, and how to target abnormal cell survival therapeutically in DLBCL patients.

Recent advances in the development of Mcl-1 inhibitors for cancer therapy

Dysregulation of the mitochondrial apoptotic pathway controlled by members of the Bcl-2 protein family plays a central role in cancer development and resistance to conventional cytotoxic as well as targeted therapies. Hence, selective inhibition of pro-survival Bcl-2 family of proteins to activate apoptosis in malignant cells represents an exciting anti-cancer strategy. The remarkable clinical performance of the selective Bcl-2 antagonist venetoclax has highlighted the potential for selective inhibitors of the other pro-survival members of the Bcl-2 family, particularly Mcl-1. Here we review the latest progress on the discovery and development of selective inhibitors of Mcl-1 that are undergoing clinical evaluation for cancer therapy.

Flavonoids in Cancer and Apoptosis

Cancer is the second leading cause of death globally. Although, there are many different approaches to cancer treatment, they are often painful due to adverse side effects and are sometimes ineffective due to increasing resistance to classical anti-cancer drugs or radiation therapy. Targeting delayed/inhibited apoptosis is a major approach in cancer treatment and a highly active area of research. Plant derived natural compounds are of major interest due to their high bioavailability, safety, minimal side effects and, most importantly, cost effectiveness. Flavonoids have gained importance as anti-cancer agents and have shown great potential as cytotoxic anti-cancer agents promoting apoptosis in cancer cells. In this review, a summary of flavonoids and their effectiveness in cancer treatment targeting apoptosis has been discussed.

Discovery of Mcl-1-specific inhibitor AZD5991 and preclinical activity in multiple myeloma and acute myeloid leukemia

Mcl-1 is a member of the Bcl-2 family of proteins that promotes cell survival by preventing induction of apoptosis in many cancers. High expression of Mcl-1 causes tumorigenesis and resistance to anticancer therapies highlighting the potential of Mcl-1 inhibitors as anticancer drugs. Here, we describe AZD5991, a rationally designed macrocyclic molecule with high selectivity and affinity for Mcl-1 currently in clinical development. Our studies demonstrate that AZD5991 binds directly to Mcl-1 and induces rapid apoptosis in cancer cells, most notably myeloma and acute myeloid leukemia, by activating the Bak-dependent mitochondrial apoptotic pathway. AZD5991 shows potent antitumor activity in vivo with complete tumor regression in several models of multiple myeloma and acute myeloid leukemia after a single tolerated dose as monotherapy or in combination with bortezomib or venetoclax. Based on these promising data, a Phase I clinical trial has been launched for evaluation of AZD5991 in patients with hematological malignancies (NCT03218683).

hnRNP L-dependent protection of normal mRNAs from NMD subverts quality control in B cell lymphoma

The human nonsense-mediated mRNA decay pathway (NMD) performs quality control and regulatory functions within complex post-transcriptional regulatory networks. In addition to degradation-promoting factors, efficient and accurate detection of NMD substrates involves proteins that safeguard normal mRNAs. Here, we identify hnRNP L as a factor that protects mRNAs with NMD-inducing features including long 3'UTRs. Using biochemical and transcriptome-wide approaches, we provide evidence that the susceptibility of a given transcript to NMD can be modulated by its 3'UTR length and ability to recruit hnRNP L. Integrating these findings with the previously defined role of polypyrimidine tract binding protein 1 in NMD evasion enables enhanced prediction of transcript susceptibility to NMD. Unexpectedly, this system is subverted in B cell lymphomas harboring translocations that produce BCL2:IGH fusion mRNAs. CRISPR/Cas9 deletion of hnRNP L binding sites near the BCL2 stop codon reduces expression of the fusion mRNAs and induces apoptosis. Together, our data indicate that protection by hnRNP L overrides the presence of multiple 3'UTR introns, allowing these aberrant mRNAs to evade NMD and promoting BCL2 overexpression and neoplasia.

NOXA genetic amplification or pharmacologic induction primes lymphoma cells to BCL2 inhibitor-induced cell death

Although diffuse large B cell lymphoma (DLBCL) cells widely express the BCL2 protein, they rarely respond to treatment with BCL2-selective inhibitors. Here we show that DLBCL cells harboring PMAIP1/NOXA gene amplification were highly sensitive to BCL2 small-molecule inhibitors. In these cells, BCL2 inhibition induced cell death by activating caspase 9, which was further amplified by caspase-dependent cleavage and depletion of MCL1. In DLBCL cells lacking NOXA amplification, BCL2 inhibition was associated with an increase in MCL1 protein abundance in a BIM-dependent manner, causing a decreased antilymphoma efficacy. In these cells, dual inhibition of MCL1 and BCL2 was required for enhanced killing. Pharmacologic induction of NOXA, using the histone deacetylase inhibitor panobinostat, decreased MCL1 protein abundance and increased lymphoma cell vulnerability to BCL2 inhibitors in vitro and in vivo. Our data provide a mechanistic rationale for combination strategies to disrupt lymphoma cell codependency on BCL2 and MCL1 proteins in DLBCL.

Hematologic Tumor Cell Resistance to the BCL-2 Inhibitor Venetoclax: A Product of Its Microenvironment?

BCL-2 family proteins regulate the intrinsic pathway of programmed cell death (apoptosis) and play a key role in the development and health of multicellular organisms. The dynamics of these proteins' expression and interactions determine the survival of all cells in an organism, whether the healthy cells of a fully competent immune system or the diseased cells of an individual with cancer. Anti-apoptotic proteins like BCL-2, BCL-XL, and MCL-1 are well-known for maintaining tumor cell survival and are therefore attractive drug targets. The BCL-2-selective inhibitor venetoclax has been approved for use in chronic lymphocytic leukemia and is now being studied in a number of other hematologic malignancies. As clinical data mature, hypotheses have begun to emerge regarding potential mechanisms of venetoclax resistance. Here, we review accumulating evidence that lymphoid microenvironments play a key role in determining hematologic tumor cell sensitivity to venetoclax.

Targeted inhibition of PI3Kα/δ is synergistic with BCL-2 blockade in genetically defined subtypes of DLBCL

Inhibition of the B-cell receptor (BCR) signaling pathway is a promising treatment strategy in multiple B-cell malignancies. However, the role of BCR blockade in diffuse large B-cell lymphoma (DLBCL) remains undefined. We recently characterized primary DLBCL subsets with distinct genetic bases for perturbed BCR/phosphoinositide 3-kinase (PI3K) signaling and dysregulated B-cell lymphoma 2 (BCL-2) expression. Herein, we explore the activity of PI3K inhibitors and BCL-2 blockade in a panel of functionally and genetically characterized DLBCL cell line models. A PI3K inhibitor with predominant α/δ activity, copanlisib, exhibited the highest cytotoxicity in all BCR-dependent DLBCLs. The proapoptotic effect of copanlisib was associated with DLBCL subtype-specific dysregulated expression of BCL-2 family members including harakiri (HRK) and its antiapoptotic partner BCL extra large (BCL-xL), BCL2 related protein A1, myeloid cell leukemia 1 (MCL-1), and BCL2 interacting mediator of cell death. Using functional BH3 profiling, we found that the cytotoxic activity of copanlisib was primarily mediated through BCL-xL and MCL-1-dependent mechanisms that might complement BCL-2 blockade. For these reasons, we evaluated single-agent activity of venetoclax in the DLBCLs and identified a subset with limited sensitivity to BCL-2 blockade despite having genetic bases of BCL-2 dysregulation. As these were largely BCR-dependent DLBCLs, we hypothesized that combined inhibition of PI3Kα/δ and BCL-2 would perturb BCR-dependent and BCL-2-mediated survival pathways. Indeed, we observed synergistic activity of copanlisib/venetoclax in BCR-dependent DLBCLs with genetic bases for BCL-2 dysregulation in vitro and confirmed these findings in a xenograft model. These results provide preclinical evidence for the rational combination of PI3Kα/δ and BCL-2 blockade in genetically defined DLBCLs.

Variable Responses of MYC Translocation Positive Lymphoma Cell Lines To Different Combinations of Novel Agents: Impact of BCL2 Family Protein Expression

Several newly developed drugs including JQ1 (BET inhibitor), ABT199 (BCL2 inhibitor), and bortezomib (proteasome inhibitor) may offer novel therapeutic strategies for aggressive diffuse large B-cell lymphoma (DLBCL). We tested these drugs together with doxorubicin in a series of combinations in 16 DLBCL cell lines including 4 ABC-DLBCL (OCI-Ly3, OCI-Ly10, SUDHL2, RIVA) and 12 GCB-DLBCL lines (OCI-Ly4, OCI-Ly18, BJAB, SUDHL4, SUDHL6, SUDHL10, DB, PR1, VAL, SC1, Karpas-231, Karpas-422). Among these cell lines, ABT199 and doxorubicin, and to a lesser extent JQ1 and bortezomib, showed high variations in their ED50 values. Of the six cell lines showing high ABT199 ED50 values, four (SUDHL10, OCI-Ly4, SUDHL2, and BJAB) had no or little BCL2 expression, and SUDHL6 also displayed a low BCL2 expression. There was no association between the ED50 value of doxorubicin, JQ1 and bortezomib, and TP53/MYC/BCL2 genetic abnormalities or cell of origin subtype. A synergistic effect in all or the majority of drug combinations was seen in 11 cell lines, while an antagonistic effect in a high proportion of drug combinations was observed in the remaining 5 cell lines including the 3 (SUDHL10, OCI-Ly4, and SUDHL2) with little BCL2 expression, and additionally OCI-Ly18 and RIVA. Extensive Western blot analyses revealed high MCL1 expression in SUDHL10 and OCI-Ly4 but no apparent alterations in other cell lines. The molecular mechanism underlying the antagonistic effect of drug combinations in DLBCL is heterogeneous with the altered BCL2 family protein expression (absent BCL2, but high MCL1) in some cell lines.

The rise of apoptosis: targeting apoptosis in hematologic malignancies

Dysregulation of the B-cell leukemia/lymphoma-2 (BCL-2) family of proteins of the intrinsic apoptotic pathway is fundamental to the pathophysiology of many hematologic malignancies. The BCL-2 family consists of regulatory proteins that either induce apoptosis (proapoptotic) or inhibit it (prosurvival). BCL-2, myeloid cell leukemia-1, and B-cell lymphoma–extra large are prosurvival proteins that are prime targets for anticancer therapy, and molecules targeting each are in various stages of preclinical and clinical development. The US Food and Drug Administration (FDA)-approved BCL-2 inhibitor venetoclax was first proven to be highly effective in chronic lymphocytic leukemia and some B-cell non-Hodgkin lymphoma subtypes. Subsequently, venetoclax was found to be active clinically against a diverse array of hematologic malignancies including multiple myeloma, acute myeloid leukemia, myelodysplastic syndrome, acute lymphoblastic leukemia, and others. Here, we give a brief introduction to BCL-2 family biology and the mechanism of action of BCL-2 Homology 3 (BH3) mimetics, and provide an overview of the clinical data for therapeutically targeting prosurvival proteins in hematologic malignancies, with a focus on BCL-2 inhibition. To prioritize novel agent combinations and predict responders, we discuss the utility of functional assays such as BH3 profiling. Finally, we provide a perspective on how therapies targeting BCL-2 family proteins may be optimally implemented into future therapeutic regimens for hematologic malignancies.