Functional disparities among BCL-2 members in tonsillar and leukemic B-cell subsets assessed by BH3-mimetic profiling

Intracellular BAPTA directly inhibits PFKFB3, thereby impeding mTORC1-driven Mcl-1 translation and killing MCL-1-addicted cancer cells

Intracellular Ca2+ signals control several physiological and pathophysiological processes. The main tool to chelate intracellular Ca2+ is intracellular BAPTA (BAPTAi), usually introduced into cells as a membrane-permeant acetoxymethyl ester (BAPTA-AM). Previously, we demonstrated that BAPTAi enhanced apoptosis induced by venetoclax, a BCL-2 antagonist, in diffuse large B-cell lymphoma (DLBCL). This finding implied a novel interplay between intracellular Ca2+ signaling and anti-apoptotic BCL-2 function. Hence, we set out to identify the underlying mechanisms by which BAPTAi enhances cell death in B-cell cancers. In this study, we discovered that BAPTAi alone induced apoptosis in hematological cancer cell lines that were highly sensitive to S63845, an MCL-1 antagonist. BAPTAi provoked a rapid decline in MCL-1-protein levels by inhibiting mTORC1-driven Mcl-1 translation. These events were not a consequence of cell death, as BAX/BAK-deficient cancer cells exhibited similar downregulation of mTORC1 activity and MCL-1-protein levels. Next, we investigated how BAPTAi diminished mTORC1 activity and identified its ability to impair glycolysis by directly inhibiting 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) activity, a previously unknown effect of BAPTAi. Notably, these effects were also induced by a BAPTAi analog with low affinity for Ca2+. Consequently, our findings uncover PFKFB3 inhibition as an Ca2+-independent mechanism through which BAPTAi impairs cellular metabolism and ultimately compromises the survival of MCL-1-dependent cancer cells. These findings hold two important implications. Firstly, the direct inhibition of PFKFB3 emerges as a key regulator of mTORC1 activity and a promising target in MCL-1-dependent cancers. Secondly, cellular effects caused by BAPTAi are not necessarily related to Ca2+ signaling. Our data support the need for a reassessment of the role of Ca2+ in cellular processes when findings were based on the use of BAPTAi.

Emerging roles for heterogeneous ribonuclear proteins in normal and malignant B cells

Heterogeneous nuclear ribonucleoproteins (hnRNPs) are among the most abundantly expressed RNA binding proteins in the cell and play major roles in all facets of RNA metabolism. hnRNPs are increasingly appreciated as essential for mammalian B cell development by regulating the carefully ordered expression of specific genes. Due to this tight regulation of the hnRNP-RNA network, it is no surprise that a growing number of genes encoding hnRNPs have been causally associated with the onset or progression of many cancers, including B cell neoplasms. Here we discuss our current understanding of hnRNP-driven regulation in normal, perturbed, and malignant B cells, and the most recent and emerging therapeutic innovations aimed at targeting the hnRNP-RNA network in lymphoma.

BCL2 inhibitor ABT-199 and BCL2L1 inhibitor WEHI-539 coordinately promote NOXA-mediated degradation of MCL1 in human leukemia cells

Human leukemia U937 cells that were continuously treated with hydroquinone (HQ) were transformed into U937/HQ cells with increased MCL1 and BCL2L1 expression. Compared with their parental cells, U937/HQ cells were less sensitive to ABT-263 (BCL2/BCL2L1 inhibitor)/ABT-199 (BCL2 inhibitor) cytotoxicity. The combination of WEHI-539 (BCL2L1 inhibitor) with either ABT-199 or ABT-263 showed synergistic cytotoxicity to U937 and U937/HQ cells. Therefore, we further investigated the cytotoxic mechanism induced by the combination of WEHI-539 and ABT-199. The combined treatment of WEHI-539 and ABT-199 induced NOX4/ROS/p38 MAPK axis-mediated autophagy, which in turn accelerated β-TrCP mRNA turnover. Downregulation of β-TrCP increased Sp1 expression, thereby promoting Sp1-mediated NOXA transcription, which in turn induced NOXA-dependent MCL1 degradation. Enforced expression of MCL1 alleviated the cytotoxicity of WEHI-539 plus ABT-199 to induce the loss of mitochondrial membrane potential and cell viability. WEHI-539 alone induced Sp1/NOXA axis-mediated MCL1 downregulation, while ABT-199 significantly decreased the dose of WEHI-539 by approximately 350- and 50-fold to induce MCL1 suppression in parental and HQ-selected cells, respectively. Furthermore, WEHI-539 sensitized ABT-199-resistant U937 cells to ABT-199 cytotoxicity by inducing NOXA-mediated degradation of MCL1. Collectively, the data in this study indicate that ABT-199 and WEHI-539 cooperatively induce NOXA-dependent MCL1 degradation, and the inhibition of MCL1 mainly explains their combined cytotoxicity in parental, HQ-selected, and ABT-199-resistant U937 cells.

Effective tumor cell abrogation via Venetoclax-mediated BCL-2 inhibition in KMT2A-rearranged acute B-lymphoblastic leukemia

Dysregulation of the intrinsic BCL-2 pathway-mediated apoptosis cascade is a common feature of hematological malignancies including acute B-lymphoblastic leukemia (B-ALL). The KMT2A-rearranged high-risk cytogenetic subtype is characterized by high expression of antiapoptotic protein BCL-2, likely due to the direct activating binding of KMT2A fusion proteins to the BCL2 gene. The BCL-2 inhibitor venetoclax (VEN) has proven great clinical value in other blood cancers, however, data on B-ALL is sparse and past studies have not so far described the effects of VEN on gene and protein expression profiles. Using cell lines and patient-derived in vivo xenograft models, we show BCL-2 pathway-mediated apoptosis induction and decelerated tumor cell counts in KMT2A-rearranged B-ALL but not in other cytogenetic subtypes. VEN treatment of cell line- and patient-derived xenografts reduced blast frequencies in blood, bone marrow, and spleen, and tumor cell doubling times were increased. Growth rates are further correlated with VEN concentrations in blood. In vitro incubation with VEN resulted in BCL-2 dephosphorylation and targeted panel RNA sequencing revealed reduced gene expression of antiapoptotic pathway members BCL2, MCL1, and BCL2L1 (BCL-XL). Reinforced translocation of BAX proteins towards mitochondria induced caspase activation and cell death commitment. Prolonged VEN application led to upregulation of antiapoptotic proteins BCL-2, MCL-1, and BCL-XL. Interestingly, the extrinsic apoptosis pathway was strongly modulated in SEM cells in response to VEN. Gene expression of members of the tumor necrosis factor signaling cascade was increased, resulting in canonical NF-kB signaling. This possibly suggests a previously undescribed mechanism of BCL-2-independent and NF-kB-mediated upregulation of MCL-1 and BCL-XL. In summary, we herein prove that VEN is a potent option to suppress tumor cells in KMT2A-rearranged B-ALL in vitro and in vivo. Possible evasion mechanisms, however, must be considered in subsequent studies.

Dynamic Intracellular Metabolic Cell Signaling Profiles During Ag-Dependent B-Cell Differentiation

Human B-cell differentiation has been extensively investigated on genomic and transcriptomic grounds; however, no studies have accomplished so far detailed analysis of antigen-dependent maturation-associated human B-cell populations from a proteomic perspective. Here, we investigate for the first time the quantitative proteomic profiles of B-cells undergoing antigen-dependent maturation using a label-free LC-MS/MS approach applied on 5 purified B-cell subpopulations (naive, centroblasts, centrocytes, memory and plasma B-cells) from human tonsils (data are available via ProteomeXchange with identifier PXD006191). Our results revealed that the actual differences among these B-cell subpopulations are a combination of expression of a few maturation stage-specific proteins within each B-cell subset and maturation-associated changes in relative protein expression levels, which are related with metabolic regulation. The considerable overlap of the proteome of the 5 studied B-cell subsets strengthens the key role of the regulation of the stoichiometry of molecules associated with metabolic regulation and programming, among other signaling cascades (such as antigen recognition and presentation and cell survival) crucial for the transition between each B-cell maturation stage.

Phosphatase PP2A enhances MCL-1 protein half-life in multiple myeloma cells

Multiple myeloma (MM), a treatable but incurable malignancy, is characterized by the growth of clonal plasma cells in protective niches in the bone marrow. MM cells depend on expression of BCL-2 family proteins, in particular MCL-1, for survival. The regulation of MCL-1 is complex and cell type-dependent. Unraveling the exact mechanism by which MCL-1 is overexpressed in MM may provide new therapeutic strategies for inhibition in malignant cells, preferably limiting side effects in healthy cells. In this study, we reveal that one cause of overexpression could be stabilization of the MCL-1 protein. We demonstrate this in a subset of MM and diffuse large B cell lymphoma (DLBCL) cell lines and MM patient samples. We applied a phosphatase siRNA screen to identify phosphatases responsible for MCL-1 stabilization in MM, and revealed PP2A as the MCL-1 stabilizing phosphatase. Using the PP2A inhibitor okadaic acid, we validated that PP2A dephosphorylates MCL-1 at Ser159 and/or Thr163, and thereby stabilizes MCL-1 in MM cells with long MCL-1 half-life, but not in DLBCL cells. Combined kinase and phosphatase inhibition experiments suggest that the MCL-1 half-life in MM is regulated by the counteracting functions of JNK and PP2A. These findings increase the understanding of the mechanisms by which MCL-1 is post-translationally regulated, which may provide novel strategies to inhibit MCL-1 in MM cells.

Changes in Bcl-2 members after ibrutinib or venetoclax uncover functional hierarchy in determining resistance to venetoclax in CLL

Chronic lymphocytic leukemia (CLL) cells cycle between lymph node (LN) and peripheral blood (PB) and display major shifts in Bcl-2 family members between those compartments. Specifically, Bcl-XL and Mcl-1, which are not targeted by the Bcl-2 inhibitor venetoclax, are increased in the LN. Because ibrutinib forces CLL cells out of the LN, we hypothesized that ibrutinib may thereby affect expression of Bcl-XL and Mcl-1 and sensitize CLL cells to venetoclax. We investigated expression of Bcl-2 family members in patients under ibrutinib or venetoclax treatment, combined with dissecting functional interactions of Bcl-2 family members, in an in vitro model of venetoclax resistance. In the PB, recent LN emigrants had higher Bcl-XL and Mcl-1 expression than did cells immigrating back to the LN. Under ibrutinib treatment, this distinction collapsed; significantly, the pretreatment profile reappeared in patients who relapsed on ibrutinib. However, in response to venetoclax, Bcl-2 members displayed an early increase, underlining the different modes of action of these 2 drugs. Profiling by BH3 mimetics was performed in CLL cells fully resistant to venetoclax due to CD40-mediated induction of Bcl-XL, Mcl-1, and Bfl-1. Several dual or triple combinations of BH3 mimetics were highly synergistic in restoring killing of CLL cells. Lastly, we demonstrated that proapoptotic Bim interacts with antiapoptotic Bcl-2 members in a sequential manner: Bcl-2 > Bcl-XL > Mcl-1 > Bfl-1. Combined, the data indicate that Bcl-XL is more important in venetoclax resistance than is Mcl-1 and provide biological rationale for potential synergy between ibrutinib and venetoclax.

Targeting the B-cell lymphoma 2 anti-apoptotic proteins for cervical cancer treatment

The B-cell lymphoma 2 (BCL-2) anti-apoptotic proteins have become attractive therapeutic targets especially with the development of BH3-mimetics which selectively target these proteins. However, it is important to note that expression levels of the anti-apoptotic proteins and their relevance in inhibiting apoptosis varies between different cell lineages. This addiction to certain anti-apoptotic proteins for survival, can be determined with various techniques and targeted effectively with selective BH3-mimetics. Studies have highlighted that anti-apoptotic proteins BCL-XL and MCL-1 are crucial for cervical cancer cell survival. Co-targeting BCL-XL and MCL-1 with selective BH3-mimetics yielded promising results in cervical cancer cell lines. In this review, we focus on the expression levels of the anti-apoptotic proteins in cervical cancer tissues and how to possibly target them with BH3-mimetics.

Co-inhibition of BCL-XL and MCL-1 with selective BCL-2 family inhibitors enhances cytotoxicity of cervical cancer cell lines

Development of resistance to chemo- and radiotherapy in patients suffering from advanced cervical cancer narrows the therapeutic window for conventional therapies. Previously we reported that a combination of the selective BCL-2 family inhibitors ABT-263 and A-1210477 decreased cell proliferation in C33A, SiHa and CaSki human cervical cancer cell lines. As ABT-263 binds to both BCL-2 and BCL-XL with high affinity, it was unclear whether the synergism of the drug combination was driven either by singly inhibiting BCL-2 or BCL-XL, or inhibition of both. In this present study, we used the BCL-2 selective inhibitor ABT-199 and the BCL-XL selective inhibitor A1331852 to resolve the individual antitumor activities of ABT-263 into BCL-2 and BCL-XL dependent mechanisms. A-1210477 was substituted for the orally bioavailable S63845. Four cervical cancer cell lines were treated with the selective BCL-2 family inhibitors ABT-199, A1331852 and S63845 alone and in combination using 2-dimensional (2D) and 3-dimensional (3D) cell culture models. The SiHa, C33A and CaSki cell lines were resistant to single agent treatment of all three drugs, suggesting that none of the BCL-2 family of proteins mediate survival of the cells in isolation. HeLa cells were resistant to single agent treatment of ABT-199 and A1331852 but were sensitive to S63845 indicating that they depend on MCL-1 for survival. Co-inhibition of BCL-2 and MCL-1 with ABT-199 and S63845, inhibited cell proliferation of all cancer cell lines, except SiHa. However, the effect of the combination was not as pronounced as combination of A1331852 and S63845. Co-inhibition of BCL-XL and MCL-1 with A1331852 and S63845 significantly inhibited cell proliferation of all four cell lines. Similar data were obtained with 3-dimensional spheroid cell culture models generated from two cervical cancer cell lines in vitro. Treatment with a combination of A1331852 and S63845 resulted in inhibition of growth and invasion of the 3D spheroids. Collectively, our data demonstrate that the combination of MCL-1-selective inhibitors with either selective inhibitors of either BCL-XL or BCL-2 may be potentially useful as treatment strategies for the management of cervical cancer.

•

Co-inhibition of BCL-XL and MCL-1 inhibited cervical cancer cell proliferation.

•

Co-inhibition of BCL-XL and MCL-1 inhibited growth and invasion of 3D spheroids.

•

MCL-1-BCL-XL selective inhibitors are potential treatment strategies.

Mesothelioma Cells Depend on the Antiapoptotic Protein Bcl-xL for Survival and Are Sensitized to Ionizing Radiation by BH3-Mimetics

PURPOSE

The incidence of mesothelioma continues to rise and prognosis remains dismal owing to resistance to conventional therapies and few novel treatment options. Failure to activate apoptotic cell death is a resistance mechanism that may be overcome by inhibition of antiapoptotic Bcl-2 proteins using BH3-mimetic drugs. We investigated the role of antiapoptotic proteins in the radioresistance of mesothelioma, identifying clinically relevant targets for radiosensitization and evaluating the activity of BH3-mimetics alone and in combination with radiation therapy in preclinical models.

METHODS, MATERIALS AND RESULTS

Mesothelioma cell lines 211H, H2052, and H226 exposed to BH3-mimetics demonstrated Bcl-xL dependence that correlated with protein expression and was confirmed by genetic knockdown. The Bcl-xL inhibitor A1331852 exhibited cytotoxic (EC50, 0.13-1.42 μmol/L) and radiosensitizing activities (sensitizer enhancement ratios, 1.3-1.8). Cytotoxicity was associated with induction of mitochondrial outer membrane permeabilization and caspase-3/7 activation. Efficacy was maintained in a 3-dimensional model in which combination therapy completely eradicated mesothelioma spheroids. Clinical applicability was confirmed by immunohistochemical analysis of Bcl-2 proteins in patient samples and radiosensitizing activity of A1331852 in primary patient-derived mesothelioma cells.

CONCLUSIONS

Mesothelioma cells exhibit addiction to the antiapoptotic protein Bcl-xL, and their intrinsic radioresistance can be overcome by small molecule inhibition of this novel therapeutic target.

Restoring Apoptosis with BH3 Mimetics in Mature B-Cell Malignancies

Apoptosis is a highly conserved mechanism enabling the removal of unwanted cells. Mitochondrial apoptosis is governed by the B-cell lymphoma (BCL-2) family, including anti-apoptotic and pro-apoptotic proteins. Apoptosis evasion by dysregulation of anti-apoptotic BCL-2 members (BCL-2, MCL-1, BCL-XL) is a common hallmark in cancers. To divert this dysregulation into vulnerability, researchers have developed BH3 mimetics, which are small molecules that restore effective apoptosis in neoplastic cells by interfering with anti-apoptotic proteins. Among them, venetoclax is a potent and selective BCL-2 inhibitor, which has demonstrated the strongest clinical activity in mature B-cell malignancies, including chronic lymphoid leukemia, mantle-cell lymphoma, and multiple myeloma. Nevertheless, mechanisms of primary and acquired resistance have been recently described and several features such as cytogenetic abnormalities, BCL-2 family expression, and ex vivo drug testing have to be considered for predicting sensitivity to BH3 mimetics and helping in the identification of patients able to respond. The medical need to overcome resistance to BH3 mimetics supports the evaluation of innovative combination strategies. Novel agents including MCL-1 targeting BH3 mimetics are currently evaluated and may represent new therapeutic options in the field. The present review summarizes the current knowledge regarding venetoclax and other BH3 mimetics for the treatment of mature B-cell malignancies.

Therapeutic Inducers of Apoptosis in Ovarian Cancer

Ovarian cancers remain one of the most common causes of gynecologic cancer-related death in women worldwide. The standard treatment comprises platinum-based chemotherapy, and most tumors develop resistance to therapeutic drugs. One mechanism of developing drug resistance is alterations of molecules involved in apoptosis, ultimately assisting in the cells’ capability to evade death. Thus, there is a need to focus on identifying potential drugs that restore apoptosis in cancer cells. Here, we discuss the major inducers of apoptosis mediated through various mechanisms and their usefulness as potential future treatment options for ovarian cancer. Broadly, they can target the apoptotic pathways directly or affect apoptosis indirectly through major cancer-pathways in cells. The direct apoptotic targets include the Bcl-2 family of proteins and the inhibitor of apoptotic proteins (IAPs). However, indirect targets include processes related to homologous recombination DNA repair, micro-RNA, and p53 mutation. Besides, apoptosis inducers may also disturb major pathways converging into apoptotic signals including janus kinase (JAK)/signal transducer and activator of transcription 3 (STAT3), wingless-related integration site (Wnt)/β-Catenin, mesenchymal-epithelial transition factor (MET)/hepatocyte growth factor (HGF), mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK), and phosphatidylinositol 3-kinase (PI3K)/v-AKT murine thymoma viral oncogene homologue (AKT)/mammalian target of rapamycin (mTOR) pathways. Several drugs in our review are undergoing clinical trials, for example, birinapant, DEBIO-1143, Alisertib, and other small molecules are in preclinical investigations showing promising results in combination with chemotherapy. Molecules that exhibit better efficacy in the treatment of chemo-resistant cancer cells are of interest but require more extensive preclinical and clinical evaluation.

Suppression of BCL6 function by HDAC inhibitor mediated acetylation and chromatin modification enhances BET inhibitor effects in B-cell lymphoma cells

Multiple genetic aberrations in the regulation of BCL6, including in acetyltransferase genes, occur in clinically aggressive B-cell lymphomas and lead to higher expression levels and activity of this transcriptional repressor. BCL6 is, therefore, an attractive target for therapy in aggressive lymphomas. In this study romidepsin, a potent histone deacetylase inhibitor (HDACi), induced apoptosis and cell cycle arrest in Burkitt and diffuse large B-cell lymphoma cell lines, which are model cells for studying the mechanism of action of BCL6. Romidepsin caused BCL6 acetylation at early timepoints inhibiting its function, while at later timepoints BCL6 expression was reduced and target gene expression increased due to chromatin modification. MYC contributes to poor prognosis in aggressive lymphoma. MYC function is reduced by inhibition of chromatin readers of the bromodomain and extra-terminal repeat (BET) family, which includes BRD4. The novel combination of romidepsin and JQ1, a BRD4 inhibitor was investigated and showed synergy. Collectively we suggest that the combination of HDACi and BRD4i should be pursued in further pre-clinical testing.

Confounding off-target effects of BH3 mimetics at commonly used concentrations: MIM1, UMI-77, and A-1210477

Targeting anti-apoptotic BCL2 family proteins has become an attractive therapeutic strategy for many cancers, and the BCL2-selective inhibitor ABT-199 (venetoclax) has obtained clinical success. However, MCL1 can promote drug resistance and overall cancer cell survival. Thus, there is a critical need to develop an effective drug that antagonizes MCL1. However, most putative MCL1 inhibitors have been misclassified as they fail to directly inhibit MCL1 in cells, but rather induce the pro-apoptotic protein NOXA. We have investigated three putative MCL1 inhibitors: MIM1, UMI-77, and A-1210477. All three compounds were developed in cell-free assays and then found to be cytotoxic, and hence assumed to directly target MCL1 in cells. Here, we investigated whether these compounds directly inhibit MCL1 or inhibit MCL1 indirectly through the induction of NOXA. Both MIM1- and UMI-77-induced NOXA through the unfolded protein response pathway, and sensitized leukemia cells to ABT-199; this cytotoxicity was dependent on NOXA suggesting that these compounds do not directly target MCL1. A-1210477 was the only compound that did not induce NOXA, but it still sensitized cells to ABT-199. A-1210477 induced accumulation of MCL1 protein consistent with it binding and preventing MCL1 degradation. However, at concentrations used in several prior studies, A-1210477 also induced cytochrome c release, caspase activation, and apoptosis in a BAX/BAK-independent manner. Furthermore, the release of cytochrome c occurred without loss of mitochondrial membrane potential. This apoptosis was extremely rapid, sometimes occurring within 0.5-1 h. Hence, we have identified a novel mechanism of apoptosis that circumvents the known mechanisms of cytochrome c release. It remains to be determined whether these unexpected mechanisms of action of putative BH3 mimetics will have therapeutic potential.

Cell death pathologies: targeting death pathways and the immune system for cancer therapy

Alterations in the molecular mechanisms of cell death are a common feature of cancer. These alterations enable malignant cells to survive intrinsic death signalling leading to accumulation of genetic aberrations and helping them to cope with adverse conditions. Regulated cell death has historically been exclusively associated with classical apoptosis; however, increasing evidence indicates that several alternative mechanisms orchestrate multiple death pathways, such as ferroptosis, entosis, necroptosis and immunogenic cell death, each with distinct underlying molecular mechanisms. Although pharmacological targeting of cell death pathways has been the subject of intensive efforts in recent decades with a dominant focus on targeting apoptosis, the identification of these novel death pathways has opened additional venues for intervention in cancer cells and the immune system. In this mini-review, we cover some recent progress on major recently emerged cell death modalities, emphasizing their potential clinical and therapeutic implications. We also discuss the interplay between cell death and immune response, highlighting the potential of the combination of traditional anticancer therapy and immunocheckpoint blockade. While attempting to stimulate discussion and draw attention to the possible clinical impact of these more recently emerged cell death modalities, we also cover the major progress achieved in translating strategies for manipulation of apoptotic pathways into the clinic, focusing on the attempts to target the anti-apoptotic protein BCL-2 and the tumour suppressor p53.

Role and Regulation of Pro-survival BCL-2 Proteins in Multiple Myeloma

Apoptosis plays a key role in protection against genomic instability and maintaining tissue homeostasis, and also shapes humoral immune responses. During generation of an antibody response, multiple rounds of B-cell expansion and selection take place in germinal centers (GC) before high antigen affinity memory B-cells and long-lived plasma cells (PC) are produced. These processes are tightly regulated by the intrinsic apoptosis pathway, and malignant transformation throughout and following the GC reaction is often characterized by apoptosis resistance. Expression of pro-survival BCL-2 family protein MCL-1 is essential for survival of malignant PC in multiple myeloma (MM). In addition, BCL-2 and BCL-XL contribute to apoptosis resistance. MCL-1, BCL-2, and BCL-XL expression is induced and maintained by signals from the bone marrow microenvironment, but overexpression can also result from genetic lesions. Since MM PC depend on these proteins for survival, inhibiting pro-survival BCL-2 proteins using novel and highly specific BH3-mimetic inhibitors is a promising strategy for treatment. This review addresses the role and regulation of pro-survival BCL-2 family proteins during healthy PC differentiation and in MM, as well as their potential as therapeutic targets.

Cell death in cancer in the era of precision medicine

Tumors constitute a large class of diseases that affect different organs and cell lineages. The molecular characterization of cancers of a given type has revealed an extraordinary heterogeneity in terms of genetic alterations and DNA mutations; heterogeneity that is further highlighted by single-cell DNA sequencing of individual patients. To address these issues, drugs that specifically target genes or altered pathways in cancer cells are continuously developed. Indeed, the genetic fingerprint of individual tumors can direct the modern therapeutic approaches to selectively hit the tumor cells while sparing the healthy ones. In this context, the concept of precision medicine finds a vast field of application. In this review, we will briefly list some classes of target drugs (Bcl-2 family modulators, Tyrosine Kinase modulators, PARP inhibitors, and growth factors inhibitors) and discuss the application of immunotherapy in tumors (T cell-mediated immunotherapy and CAR-T cells) that in recent years has drastically changed the prognostic outlook of aggressive cancers. We will also consider how apoptosis could represent a primary end point in modern cancer therapy and how "classic" chemotherapeutic drugs that induce apoptosis are still utilized in therapeutic schedules that involve the use of target drugs or immunotherapy to optimize the antitumor response.

Immunotherapy and Targeted Therapy for Small Cell Lung Cancer: There Is Hope

Small cell lung cancer (SCLC) is a devastating and aggressive neuroendocrine carcinoma of the lung. It accounts for ~15% of lung cancer mortality and has had no improvement in standard treatment options for nearly 30 years. However, there is now hope for change with new therapies and modalities of therapy. Immunotherapies and checkpoint inhibitors are entering clinical practice, selected targeted therapies show promise, and "smart bomb"-based drug/radioconjugates have led to good response in early clinical trials. Additionally, new research insights into the genetics and tumor heterogeneity of SCLC alongside the availability of new tools such as patient-derived or circulating tumor cell xenografts offer the potential to shine light on this beshadowed cancer.

Epstein-Barr virus nuclear antigen EBNA-LP is essential for transforming naïve B cells, and facilitates recruitment of transcription factors to the viral genome

The Epstein-Barr virus (EBV) nuclear antigen leader protein (EBNA-LP) is the first viral latency-associated protein produced after EBV infection of resting B cells. Its role in B cell transformation is poorly defined, but it has been reported to enhance gene activation by the EBV protein EBNA2 in vitro. We generated EBNA-LP knockout (LPKO) EBVs containing a STOP codon within each repeat unit of internal repeat 1 (IR1). EBNA-LP-mutant EBVs established lymphoblastoid cell lines (LCLs) from adult B cells at reduced efficiency, but not from umbilical cord B cells, which died approximately two weeks after infection. Adult B cells only established EBNA-LP-null LCLs with a memory (CD27+) phenotype. Quantitative PCR analysis of virus gene expression after infection identified both an altered ratio of the EBNA genes, and a dramatic reduction in transcript levels of both EBNA2-regulated virus genes (LMP1 and LMP2) and the EBNA2-independent EBER genes in the first 2 weeks. By 30 days post infection, LPKO transcription was the same as wild-type EBV. In contrast, EBNA2-regulated cellular genes were induced efficiently by LPKO viruses. Chromatin immunoprecipitation revealed that EBNA2 and the host transcription factors EBF1 and RBPJ were delayed in their recruitment to all viral latency promoters tested, whereas these same factors were recruited efficiently to several host genes, which exhibited increased EBNA2 recruitment. We conclude that EBNA-LP does not simply co-operate with EBNA2 in activating gene transcription, but rather facilitates the recruitment of several transcription factors to the viral genome, to enable transcription of virus latency genes. Additionally, our findings suggest that EBNA-LP is essential for the survival of EBV-infected naïve B cells.

Epstein-Barr virus (EBV) infects almost everyone. Once infected, people harbor the virus for life, shedding it in saliva. Infection of children is asymptomatic, but a first infection during adolescence or adulthood can cause glandular fever (infectious mononucleosis). EBV is also implicated in several different cancers. EBV infection of B cells (antibody-producing immune cells) can drive them to replicate almost indefinitely (‘transformation’), generating cell lines. We have investigated the role of an EBV protein (EBNA-LP) which is thought to support gene activation by the essential virus protein EBNA2. We have made an EBV in which the EBNA-LP gene has been disrupted. This virus (LPKO) shows several properties. 1. It is reduced in its ability to transform B cells; 2. ‘Naïve’ B cells (those whose antibodies have not adapted to fight infections) die two weeks after LPKO infection; 3. Some virus genes fail to turn on immediately after LPKO infection. 4. Binding of EBNA2 and various cellular factors to these genes is delayed. 5. EBNA-LP does not affect EBNA2-targeted cellular genes in the same way. This shows that EBNA-LP is more important in naïve B cells, and that it helps to turn on virus genes, but not cell genes.

Intracellular BH3 Profiling Reveals Shifts in Antiapoptotic Dependency in Human B Cell Maturation and Mitogen-Stimulated Proliferation

Apoptosis is critical to B cell maturation, but studies of apoptotic regulation in primary human B cells is lacking. In this study, we sought to better understand the mechanisms of apoptotic regulation in normal and activated B cells. Using intracellular BH3 profiling, we defined the Bcl2 dependency of B cell subsets from human peripheral blood and tonsillar lymphoid tissue as well as mitogen-activated B cells. We found that naive and memory B cells were BCL-2-dependent, whereas germinal center B cells were MCL-1-dependent and plasma cells were BCL-X_L-dependent. B cells stimulated to proliferate ex vivo by CpG or CD40L/IL-4 became more dependent on MCL-1 and BCL-X_L As B cell lymphomas often rely on survival mechanisms derived from normal and activated B cells, these findings offer new insight into potential therapeutic strategies for lymphomas.

Dynein light chain 1 induces assembly of large Bim complexes on mitochondria that stabilize Mcl-1 and regulate apoptosis

In this study, Singh et al. investigated Bim structure and activity and show that Bim is regulated by the formation of large protein complexes containing dynein light chain 1 (DLC1). Their findings demonstrate that control of apoptosis at mitochondria extends beyond the interaction of monomers of proapoptotic and anti-apoptotic Bcl-2 family members and involves more complex structures of proteins at the mitochondrial outer membrane.

The Bcl-2 family protein Bim triggers mitochondrial apoptosis. Bim is expressed in nonapoptotic cells at the mitochondrial outer membrane, where it is activated by largely unknown mechanisms. We found that Bim is regulated by formation of large protein complexes containing dynein light chain 1 (DLC1). Bim rapidly inserted into cardiolipin-containing membranes in vitro and recruited DLC1 to the membrane. Bim binding to DLC1 induced the formation of large Bim complexes on lipid vesicles, on isolated mitochondria, and in intact cells. Native gel electrophoresis and gel filtration showed Bim-containing mitochondrial complexes of several hundred kilodaltons in all cells tested. Bim unable to form complexes was consistently more active than complexed Bim, which correlated with its substantially reduced binding to anti-apoptotic Bcl-2 proteins. At endogenous levels, Bim surprisingly bound only anti-apoptotic Mcl-1 but not Bcl-2 or Bcl-X_L, recruiting only Mcl-1 into large complexes. Targeting of DLC1 by RNAi in human cell lines induced disassembly of Bim–Mcl-1 complexes and the proteasomal degradation of Mcl-1 and sensitized the cells to the Bcl-2/Bcl-X_L inhibitor ABT-737. Regulation of apoptosis at mitochondria thus extends beyond the interaction of monomers of proapoptotic and anti-apoptotic Bcl-2 family members but involves more complex structures of proteins at the mitochondrial outer membrane, and targeting complexes may be a novel therapeutic strategy.