MCL-1 expression in B-cell non-Hodgkin’s lymphomas

The Mitochondrial Ubiquitin Ligase MARCHF5 Cooperates with MCL1 to Inhibit Apoptosis in KSHV-Transformed Primary Effusion Lymphoma Cell Lines

Kaposi's sarcoma-associated herpesvirus (KSHV) causes several malignancies in people with HIV including Kaposi's sarcoma and primary effusion lymphoma (PEL). We have previously shown that PEL cell lines require myeloid cell leukemia-1 (MCL1) to inhibit apoptosis. MCL1 is an oncogene that is amplified in cancers and causes resistance to chemotherapy regimens. MCL1 is thus an attractive target for drug development. The emerging clinical relevance and therapeutic potential of MCL1 motivated us to study the roles of this oncogene in PEL in depth. Using a systems biology approach, we uncovered an unexpected genetic interaction between MCL1 and MARCHF5 indicating that they function in the same pathway. MARCHF5 is an E3 ubiquitin ligase most known for regulating mitochondrial homeostasis and antiviral signaling, but not apoptosis. We thus investigated how MCL1 and MARCHF5 cooperate to promote PEL cell survival. CRISPR knockout (KO) of MARCHF5 in PEL cell lines resulted in a significant increase in apoptosis despite the presence of MCL1. The anti-apoptotic function of MARCHF5 was dependent on its E3 ligase and dimerization activities. Loss of MARCHF5 or inhibition of the 26S proteasome furthermore stabilized the MCL1 antagonist NOXA without affecting levels of MCL1. Interestingly, NOXA KO provides a fitness advantage to PEL cells suggesting that NOXA is the pro-apoptotic signal that necessitates the anti-apoptotic activities of MCL1 and MARCHF5. Finally, endogenous reciprocal co-immunoprecipitation experiments show that MARCHF5 and NOXA are found in the same protein complex. Our findings thus provide the mechanistic link that underlies the genetic interaction between MCL1 and MARCHF5. We propose that MARCHF5 induces the degradation of the MCL1 antagonist NOXA thus reinforcing the pro-survival role of MCL1 in these tumor cells. This newly appreciated interaction of the MCL1 and MARCHF5 oncogenes may be useful to improve the design of combination therapies for KSHV malignancies.

Evaluation of MCL-1 as a prognostic factor in canine mammary gland tumors

Myeloid cell leukemia-1 (MCL-1), which belongs to the anti-apoptotic B cell lymphoma-2 family protein, is overexpressed in various cancers and is associated with cell immortality, malignant transformation, chemoresistance, and poor prognosis in humans. However, the significance of MCL-1 in canine mammary gland tumors (MGTs) remains unknown. This study aimed to examine MCL-1 expression in normal canine mammary glands and tumors and to assess its correlation with clinical and histologic variables. In total, 111 samples were examined, including 12 normal mammary gland tissues, 51 benign MGTs, and 48 malignant MGTs. Immunohistochemistry revealed that 53% of benign tumors and 75% of malignant tumors exhibited high MCL-1 expression, whereas only 8% of normal mammary glands exhibited high MCL-1 expression. High MCL-1 expression correlated with tumor malignancy (p < 0.001), large tumor size (> 3 cm) (p = 0.005), high Ki-67 expression (p = 0.046), and metastasis (p = 0.027). Survival curve analysis of dogs with malignant MGTs demonstrated a significant association between high MCL-1 expression and shorter median overall survival (p = 0.027) and progression-free survival (p = 0.014). Our study identified MCL-1 as a prognostic factor and potential therapeutic target in canine MGTs.

In Vivo, In Vitro and In Silico Anticancer Activity of Ilama Leaves: An Edible and Medicinal Plant in Mexico

Ilama leaves are an important source of secondary metabolites with promising anticancer properties. Cancer is a disease that affects a great number of people worldwide. This work aimed to investigate the in vivo, in vitro and in silico anticancer properties of three acyclic terpenoids (geranylgeraniol, phytol and farnesyl acetate) isolated from petroleum ether extract of ilama leaves. Their cytotoxic activity against U-937 cells was assessed using flow cytometry to determine the type of cell death and production of reactive oxygen species (ROS). Also, a morphological analysis of the lymph nodes and a molecular docking study using three proteins related with cancer as targets, namely, Bcl-2, Mcl-1 and VEGFR-2, were performed. The flow cytometry and histomorphological analysis revealed that geranylgeraniol, phytol and farnesyl acetate induced the death of U-937 cells by late apoptosis and necrosis. Geranylgeraniol and phytol induced a significant increase in ROS production. The molecular docking studies showed that geranylgeraniol had more affinity for Bcl-2 and VEGFR-2. In the case of farnesyl acetate, it showed the best affinity for Mcl-1. This study provides information that supports the anticancer potential of geranylgeraniol, phytol and farnesyl acetate as compounds for the treatment of cancer, particularly with the potential to treat non-Hodgkin's lymphoma.

EBV and 1q Gains Affect Gene and miRNA Expression in Burkitt Lymphoma

Abnormalities of the long arm of chromosome 1 (1q) represent the most frequent secondary chromosomal aberrations in Burkitt lymphoma (BL) and are observed almost exclusively in EBV-negative BL cell lines (BL-CLs). To verify chromosomal abnormalities, we cytogenetically investigated EBV-negative BL patient material, and to elucidate the 1q gain impact on gene expression, we performed qPCR with six 1q-resident genes and analyzed miRNA expression in BL-CLs. We observed 1q aberrations in the form of duplications, inverted duplications, isodicentric chromosome idic(1)(q10), and the accumulation of 1q12 breakpoints, and we assigned 1q21.2-q32 as a commonly gained region in EBV-negative BL patients. We detected MCL1, ARNT, MLLT11, PDBXIP1, and FCRL5, and 64 miRNAs, showing EBV- and 1q-gain-dependent dysregulation in BL-CLs. We observed MCL1, MLLT11, PDBXIP1, and 1q-resident miRNAs, hsa-miR-9, hsa-miR-9*, hsa-miR-92b, hsa-miR-181a, and hsa-miR-181b, showing copy-number-dependent upregulation in BL-CLs with 1q gains. MLLT11, hsa-miR-181a, hsa-miR-181b, and hsa-miR-183 showed exclusive 1q-gains-dependent and FCRL5, hsa-miR-21, hsa-miR-155, hsa-miR-155*, hsa-miR-221, and hsa-miR-222 showed exclusive EBV-dependent upregulation. We confirmed previous data, e.g., regarding the EBV dependence of hsa-miR-17-92 cluster members, and obtained detailed information considering 1q gains in EBV-negative and EBV-positive BL-CLs. Altogether, our data provide evidence for a non-random involvement of 1q gains in BL and contribute to enlightening and understanding the EBV-negative and EBV-positive BL pathogenesis.

Targeting MCL-1 protein to treat cancer: opportunities and challenges

Evading apoptosis has been linked to tumor development and chemoresistance. One mechanism for this evasion is the overexpression of prosurvival B-cell lymphoma-2 (BCL-2) family proteins, which gives cancer cells a survival advantage. Mcl-1, a member of the BCL-2 family, is among the most frequently amplified genes in cancer. Targeting myeloid cell leukemia-1 (MCL-1) protein is a successful strategy to induce apoptosis and overcome tumor resistance to chemotherapy and targeted therapy. Various strategies to inhibit the antiapoptotic activity of MCL-1 protein, including transcription, translation, and the degradation of MCL-1 protein, have been tested. Neutralizing MCL-1's function by targeting its interactions with other proteins via BCL-2 interacting mediator (BIM)S2A has been shown to be an equally effective approach. Encouraged by the design of venetoclax and its efficacy in chronic lymphocytic leukemia, scientists have developed other BCL-2 homology (BH3) mimetics-particularly MCL-1 inhibitors (MCL-1i)-that are currently in clinical trials for various cancers. While extensive reviews of MCL-1i are available, critical analyses focusing on the challenges of MCL-1i and their optimization are lacking. In this review, we discuss the current knowledge regarding clinically relevant MCL-1i and focus on predictive biomarkers of response, mechanisms of resistance, major issues associated with use of MCL-1i, and the future use of and maximization of the benefits from these agents.

AMG176, an MCL-1 inhibitor, is active in pre-clinical models of aggressive B-cell lymphomas

Upregulation of the anti-apoptotic protein MCL-1 has been implicated in chemotherapy resistance and poor clinical outcomes in B-cell lymphoma (BCL). We report the activity of AMG176, a direct, selective MCL-1 inhibitor, in preclinical models of BCL. A panel of cell lines representing diffuse large B-cell lymphoma (DLBCL), double-hit lymphoma (DHL) and Burkitt's lymphoma (BL) was selected. AMG176 induced apoptotic cell death in a dose- and time-dependent manner in all BCL cell lines. Baseline MCL-1 expression was not predictive of response. AMG176 exhibited impressive synergy with venetoclax and chemotherapeutic agents, less so with proteasomal inhibitors, and antagonism with anti-CD20 monoclonal antibodies. The activity of AMG176 could not be confirmed in murine models of BCL. Combination therapy targeting MCL-1 and BCL-2 may provide an alternative therapeutic approach in BCL, however optimal patient selection will remain the key to obtaining high response rates and tolerability.

Current Status of Novel Agents for the Treatment of B Cell Malignancies: What's Coming Next?

Resistance to death is one of the hallmarks of human B cell malignancies and often contributes to the lack of a lasting response to today's commonly used treatments. Drug discovery approaches designed to activate the death machinery have generated a large number of inhibitors of anti-apoptotic proteins from the B-cell lymphoma/leukemia 2 family and the B-cell receptor (BCR) signaling pathway. Orally administered small-molecule inhibitors of Bcl-2 protein and BCR partners (e.g., Bruton's tyrosine kinase and phosphatidylinositol-3 kinase) have already been included (as monotherapies or combination therapies) in the standard of care for selected B cell malignancies. Agonistic monoclonal antibodies and their derivatives (antibody-drug conjugates, antibody-radioisotope conjugates, bispecific T cell engagers, and chimeric antigen receptor-modified T cells) targeting tumor-associated antigens (TAAs, such as CD19, CD20, CD22, and CD38) are indicated for treatment (as monotherapies or combination therapies) of patients with B cell tumors. However, given that some patients are either refractory to current therapies or relapse after treatment, novel therapeutic strategies are needed. Here, we review current strategies for managing B cell malignancies, with a focus on the ongoing clinical development of more effective, selective drugs targeting these molecules, as well as other TAAs and signaling proteins. The observed impact of metabolic reprogramming on B cell pathophysiology highlights the promise of targeting metabolic checkpoints in the treatment of these disorders.

The Pt(S-pr-thiosal)2 and BCL1 Leukemia Lymphoma: Antitumor Activity In Vitro and In Vivo

B cell malignancies are, despite the development of targeted therapy in a certain percentage of the patients still a chronic disease with relapses, requiring multiple lines of therapy. Regimens that include platinum-based drugs provide high response rates in different B cell lymphomas, high-risk chronic lymphocytic leukemia (CLL), and devastating complication of CLL, Richter’s syndrome. The aim of this study was to explore the potential antitumor activity of previously synthetized platinum(IV) complex with alkyl derivatives of thyosalicilc acid, PtCl2(S-pr-thiosal)2, toward murine BCL1 cells and to delineate possible mechanisms of action. The PtCl2(S-pr-thiosal)2 reduced the viability of BCL1 cells in vitro but also reduced the growth of metastases in the leukemia lymphoma model in BALB/c mice. PtCl2(S-pr-thiosal)2 induced apoptosis, inhibited proliferation of BCL1 cells, and induced cell cycle disturbance. Treatment of BCL1 cells with PtCl2(S-pr-thiosal)2 inhibited expression of cyclin D3 and cyclin E and enhanced expression of cyclin-dependent kinase inhibitors p16, p21, and p27 resulting in cell cycle arrest in the G1 phase, reduced the percentage of BCL1 cells in the S phase, and decreased expression of Ki-67. PtCl2(S-pr-thiosal)2 treatment reduced expression of phosphorylated STAT3 and downstream-regulated molecules associated with cancer stemness and proliferation, NANOG, cyclin D3, and c-Myc, and expression of phosphorylated NFκB in vitro and in vivo. In conclusion, PtCl2(S-pr-thiosal)2 reduces STAT3 and NFκB phosphorylation resulting in inhibition of BCL1 cell proliferation and the triggering of apoptotic cell death.

Myeloid cell leukemia-1: a formidable barrier to anticancer therapeutics and the quest of targeting it

The antiapoptotic B cell lymphoma-2 (Bcl-2) family members are apical regulators of the intrinsic pathway of apoptosis that orchestrate mitochondrial outer membrane permeabilization (MOMP) through interactions with their proapoptotic counterparts. Overexpression of antiapoptotic Bcl-2 family proteins has been linked to therapy resistance and poor prognosis in diverse cancers. Among the antiapoptotic Bcl-2 family members, predominant overexpression of the prosurvival myeloid cell leukemia-1 (Mcl-1) has been reported in a myriad of hematological malignancies and solid tumors, contributing to therapy resistance and poor outcomes, thus making it a potential druggable target. The unique structure of Mcl-1 and its complex regulatory mechanism makes it an adaptive prosurvival switch that ensures tumor cell survival despite therapeutic intervention. This review focusses on diverse mechanisms adopted by tumor cells to maintain sustained elevated levels of Mcl-1 and how high Mcl-1 levels contribute to resistance in conventional as well as targeted therapies. Moreover, recent developments in the Mcl-1-targeted therapeutics and the underlying challenges and considerations in designing novel Mcl-1 inhibitors are also discussed.

Targeted Agents in the Treatment of Indolent B-Cell Non-Hodgkin Lymphomas

Targeted therapies continue to change the landscape of lymphoma treatment, resulting in improved therapy options and patient outcomes. Numerous agents are now approved for use in the indolent lymphomas and many others under development demonstrate significant promise. In this article, we review the landscape of targeted agents that apply to the indolent lymphomas, predominantly follicular lymphoma, lymphoplasmacytic lymphoma/Waldenstrom macroglobulinaemia and marginal zone lymphoma. The review covers small molecule inhibitors, immunomodulators and targeted immunotherapies, as well as presenting emerging and promising combination therapies.

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.

Expression of BCL2 alternative proteins and association with outcome in CLL patients treated with venetoclax

Venetoclax, a BCL-2 inhibitor, is highly effective for the treatment of patients with chronic lymphocytic leukemia (CLL) and dependence on alternative proteins may result in resistance to BCL-2 inhibition. Patients with CLL treated with venetoclax as monotherapy at MD Anderson Cancer Center between 05/2012 and 01/2016 were included and pretreatment bone marrow was analyzed by immunohistochemistry (IHC) for BCL-W, BCL-XL, BCL2-A1 and MCL-1. Twenty-seven patients were included. BCL-W + and BCL-2A1+ was found in 15% and 7% of the patients, respectively. Both BCL-XL and MCL-1 were negative in all samples. A higher CR and longer PFS rates were observed in patients with BCL-W+ (p = .60, p = .46), BCL-2A1+ (p = .60, p = .29), and either BCL-W + or BCL-2A1+ (p = .33, p = .20), though not statistically significant. Pretreatment IHC expression of BCL-2 alternative proteins does not predict response to venetoclax in CLL, but may be a surrogate for an indolent biology. Sensitive techniques are needed to explore anti-apoptotic pathways.

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.

Co-Operativity between MYC and BCL-2 Pro-Survival Proteins in Cancer

B-Cell Lymphoma 2 (BCL-2), c-MYC and related proteins are arguably amongst the most widely studied in all of biology. Every year there are thousands of papers reporting on different aspects of their biochemistry, cellular and physiological mechanisms and functions. This plethora of literature can be attributed to both proteins playing essential roles in the normal functioning of a cell, and by extension a whole organism, but also due to their central role in disease, most notably, cancer. Many cancers arise due to genetic lesions resulting in deregulation of both proteins, and indeed the development and survival of tumours is often dependent on co-operativity between these protein families. In this review we will discuss the individual roles of both proteins in cancer, describe cancers where co-operativity between them has been well-characterised and finally, some strategies to target these proteins therapeutically.

Targeting MCL-1 in hematologic malignancies: Rationale and progress

Myeloid cell leukemia sequence 1 (MCL-1) is an antiapoptotic protein that plays a key role in promoting cell survival in multiple myeloma (MM), acute myeloid leukemia (AML), and non-Hodgkin lymphoma (NHL). Overexpression of MCL-1 is associated with treatment resistance and poor prognosis; thus, MCL-1 inhibitors are rational therapeutic options for malignancies depending on MCL-1. Several MCL-1 inhibitors have entered clinical trials, including AZD5991, S64315, AMG 176, and AMG 397. A key area of investigation is whether MCL-1 inhibitors will complement the activity of BCL-2 inhibitors, such as venetoclax, and synergistically enhance anti-tumor efficacy when given in combination with other anti-cancer drugs. Another important question is whether a safe therapeutic window can be found for this new class of inhibitors. In summary, inhibition of MCL-1 shows potential as a treatment for hematologic malignancies and clinical evaluation of MCL-1 inhibitors is currently underway.

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.

Efficacy of the novel CDK7 inhibitor QS1189 in mantle cell lymphoma

Mantle cell lymphoma (MCL) is typically an aggressive and rare form of non-Hodgkin lymphoma (NHL) with a poor prognosis despite recent advances in immunochemotherapy and targeted therapeutics against NHL. New therapeutic agents are needed for MCL. In this study, we generated a potent inhibitor of cyclin-dependent kinase 7 (CDK7), designated QS1189, and confirmed its anti-cancer effects towards MCL and other lymphomas. QS1189 was highly selective for CDK7 and showed potent anticancer effects in MCL compared to other targeted therapeutic agents, such as ibrutinib and venetoclax. Consistent with a conventional CDK7 inhibitor, QS1189 treatment significantly decreased phosphorylation of the carboxyl-terminal domain of RNA polymerase II and transcription-associated genes. QS1189 induced cell cycle arrest at the G2/M phase and apoptosis. Interestingly, QS1189 overcame the acquired resistance to venetoclax, which is mediated by Bcl-xL. Similarly, QS1189 showed potent tumour cell growth inhibition of various lymphomas. Thus, CDK7 might be a suitable therapeutic target for inhibiting lymphoma, and QS1189 is a promising therapeutic option for various lymphomas and cells with acquired resistance to targeted therapy.

Regulation of Mcl-1 alternative splicing by hnRNP F, H1 and K in breast cancer cells

Myeloid cell leukemia-1 (Mcl -1) is one of the most frequently amplified genes in cancer, and its overexpression is associated with poor prognosis and drug resistance. As a member of the Bcl-2 family it is involved in the control of the mitochondrial (intrinsic) cell death pathway. Alternative splicing of the (Mcl-1) gene results in the expression of two functionally distinct proteins, the anti-apoptotic Mcl-1L (exon 2 included) and the pro-apoptotic Mcl-1S (exon 2 skipped). Our data shows that transfecting siRNAs that target hnRNP K and the hnRNP F/H family result in a switch in splicing towards the pro-apoptotic Mcl-1S. Specific binding sites for these and other Mcl-1 splicing factors were investigated and identified by RNA immunoprecipitation and through construction of a Mcl-1 minigene construct. Moreover, this study shows up to a 30 fold change in the levels of Mcl-1S can be achieved through double and triple knockdowns of the most significant RNA binding proteins involved in Mcl-1 splicing, as well as activation of the mitochondrial cell death pathway. Targeting the splicing process of Mcl-1 along with other apoptotic regulators provides an exciting new therapeutic target in cancer cells, and may provide a way to overcome therapy resistance.

Reactive Oxygen Species and Oncoprotein Signaling-A Dangerous Liaison

SIGNIFICANCE

There is evidence to implicate reactive oxygen species (ROS) in tumorigenesis and its progression. This has been associated with the interplay between ROS and oncoproteins, resulting in enhanced cellular proliferation and survival. Recent Advances: To date, studies have investigated specific contributions of the crosstalk between ROS and signaling networks in cancer initiation and progression. These investigations have challenged the established dogma of ROS as agents of cell death by demonstrating a secondary function that fuels cell proliferation and survival. Studies have thus identified (onco)proteins (Bcl-2, STAT3/5, RAS, Rac1, and Myc) in manipulating ROS level as well as exploiting an altered redox environment to create a milieu conducive for cancer formation and progression.

CRITICAL ISSUES

Despite these advances, drug resistance and its association with an altered redox metabolism continue to pose a challenge at the mechanistic and clinical levels. Therefore, identifying specific signatures, altered protein expressions, and modifications as well as protein-protein interplay/function could not only enhance our understanding of the redox networks during cancer initiation and progression but will also provide novel targets for designing specific therapeutic strategies.

FUTURE DIRECTIONS

Not only a heightened realization is required to unravel various gene/protein networks associated with cancer formation and progression, particularly from the redox standpoint, but there is also a need for developing more sensitive tools for assessing cancer redox metabolism in clinical settings. This review attempts to summarize our current knowledge of the crosstalk between oncoproteins and ROS in promoting cancer cell survival and proliferation and treatment strategies employed against these oncoproteins. Antioxid. Redox Signal.

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.

Angelica gigas Nakai and Decursin Downregulate Myc Expression to Promote Cell Death in B-cell Lymphoma

Angelica gigas Nakai (AGN) is an oriental traditional medicine to treat anemia, dysmenorrhea, and migraine. However, its anti-lymphoma effect is yet to be tested. Here, we demonstrated that AGN and its major component decursin target Myc to suppress lymphomagenesis in vitro and in vivo. AGN inhibited cell viability in multiple B lymphoma cells, while sparing normal splenocytes and bone marrow cells. Increased cleaved PARP level and caspase 3/7 activity and the repression of survival-promoting AKT/mTOR and MAPK pathways downstream of BCR, were responsible for the pro-apoptotic effects of AGN. We found that Myc, a prominent downstream target of these signaling pathways, contributes to AGN-induced cell death. Moreover, co-treatment with AGN and a Myc inhibitor, JQ1 or 10058-F4 yielded synergistic cytotoxic activities against cancer cells with markedly reduced Myc expression. AGN downregulated Myc expression and suppressed tumorigenesis in Eμ-myc transgenic mice. The proapoptotic activities of AGN were recapitulated by decursin, indicating that the anti-tumor effect of AGN was mainly caused by decursin. These findings suggest that AGN and decursin possess potent anti-lymphoma activity, and combination therapies with AGN/decursin and a Myc inhibitor to target Myc more efficiently could be a valuable avenue to explore in the treatment of B-cell lymphoma.

Regulation of the Tumor-Suppressor BECLIN 1 by Distinct Ubiquitination Cascades

Autophagy contributes to cellular homeostasis through the degradation of various intracellular targets such as proteins, organelles and microbes. This relates autophagy to various diseases such as infections, neurodegenerative diseases and cancer. A central component of the autophagy machinery is the class III phosphatidylinositol 3-kinase (PI3K-III) complex, which generates the signaling lipid phosphatidylinositol 3-phosphate (PtdIns3P). The catalytic subunit of this complex is the lipid-kinase VPS34, which associates with the membrane-targeting factor VPS15 as well as the multivalent adaptor protein BECLIN 1. A growing list of regulatory proteins binds to BECLIN 1 and modulates the activity of the PI3K-III complex. Here we discuss the regulation of BECLIN 1 by several different types of ubiquitination, resulting in distinct polyubiquitin chain linkages catalyzed by a set of E3 ligases. This contribution is part of the Special Issue “Ubiquitin System”.

Early stages in the ontogeny of small B-cell lymphomas: genetics and microenvironment

In this review, we focus on the mechanisms underlying lymphomagenesis in chronic lymphocytic leukaemia, follicular lymphoma, mantle cell lymphoma and splenic marginal zone lymphoma. The cells of origin of these small B-cell lymphomas are distinct, as are the characteristic chromosomal lesions and clinical courses. One shared feature is retention of expression of surface immunoglobulin. Analysis of this critical receptor reveals the point of differentiation reached by the cell of origin. Additionally, the sequence patterns of the immunoglobulin-variable domains can indicate a role for stimulants of the B-cell receptor before, during and after malignant transformation. The pathways driven via the B-cell receptor are now being targeted by specific kinase inhibitors with exciting clinical effects. To consider routes to pathogenesis, potentially offering earlier intervention, or to identify causative factors, genetic tools are being used to track pretransformation events and the early phases in lymphomagenesis. These methods are revealing that chromosomal changes are only one of the many steps involved, and that the influence of surrounding cells, probably multiple and variable according to tissue location, is required, both to establish tumours and to maintain growth and survival. Similarly, the influence of the tumour microenvironment may protect malignant cells from eradication by treatment, and the resulting minimal residual disease will eventually give rise to relapse. The common and different features of the four lymphomas will be summarized to show how normal B lymphocytes can be subverted to generate tumours, how these tumours evolve and how their weaknesses can be attacked by targeted therapies.

Intersection of mitochondrial fission and fusion machinery with apoptotic pathways: Role of Mcl-1

Mitochondria actively contribute to apoptotic cell death through mechanisms including the loss of integrity of the outer mitochondrial membrane, the release of intermembrane space proteins, such as cytochrome c, in the cytosol and the caspase cascade activation. This process is the result of careful cooperation not only among members of the Bcl-2 family but also dynamin-related proteins. These events are often accompanied by fission of the organelle, thus linking mitochondrial dynamics to apoptosis. Emerging evidences are suggesting a fine regulation of mitochondrial morphology by Bcl-2 family members and active participation of fission-fusion proteins in apoptosis. The debate whether in mitochondrial morphogenesis the role of Bcl-2 family members is functionally distinct from their role in apoptosis is still open and, above all, which morphological changes are associated with cell death sensitisation. This review will cover the findings on how the mitochondrial fission and fusion machinery may intersect apoptotic pathways focusing on recent advances on the key role played by Mcl-1.

How to unleash mitochondrial apoptotic blockades to kill cancers?

Apoptosis, especially the intrinsic mitochondrial cell death pathway, is regulated by the BCL-2 family of proteins. Defects in apoptotic machinery are one of the main mechanisms that cells employ to evade cell death and become cancerous. Targeting the apoptotic defects, either by direct inhibition of BCL-2 family proteins or through modulation of regulatory pathways, can restore cell sensitivity to cell death. This review will focus on the aspects of BCL-2 family proteins, their interactions with kinase pathways, and how novel targeted agents can help overcome the apoptotic blockades. Furthermore, functional assays, such as BH3 profiling, may help in predicting responses to chemotherapies and aid in the selection of combination therapies by determining the mitochondrial threshold for initiating cell death.

Targeting BCL2 With BH3 Mimetics: Basic Science and Clinical Application of Venetoclax in Chronic Lymphocytic Leukemia and Related B Cell Malignancies

The intracellular protein B‐cell‐lymphoma‐2 (BCL2) has been considered an attractive target for cancer therapy since the discovery of its function as a major promoter of cell survival (an anti‐apoptotic) in the late 1980s. However, the challenges of targeting a protein‐protein interaction delayed the discovery of fit‐for‐purpose molecules until the mid‐2000s. Since then, a series of high affinity small organic molecules that inhibits the interaction of BCL2 with the apoptotic machinery, the so‐called BH3‐mimetics, have been developed. Venetoclax (formerly ABT‐199) is the first to achieve US Food and Drug Administration approval, with an indication for treatment of patients with previously treated chronic lymphocytic leukemia (CLL) bearing deletion of the long arm of chromosome 17. Here, we review key aspects of the science underpinning the clinical application of BCL2 inhibitors and explore both our current knowledge and unresolved questions about its clinical utility, both in CLL and in other B‐cell malignancies that highly express BCL2.

Mcl-1 inhibitors: a patent review

INTRODUCTION

The myeloid cell leukemia-1 (MCL-1) protein is one of the key anti-apoptotic members of the B-cell lymphoma-2 (BCL-2) protein family. Over-expression of MCL-1 has been closely related to tumor progression as well as to resistance, not only to traditional chemotherapies but also to targeted therapeutics including BCL-2 inhibitors such as ABT-263. Therefore, there has been extensive research and development in the last decade in both academic and industrial settings to address this unmet medical need. Areas covered: This review covers the research and patent literature of the past 10 years in the field of discovery and development of small-molecule inhibitors of the MCL-1 anti-apoptotic protein. Expert opinion: Small-molecule strategies to disrupt the protein-protein interactions between MCL-1 and its pro-apoptotic counterparts, such as BAK and BIM, have recently emerged. Several small-molecules based on different scaffolds describe promising in vitro data as MCL-1 selective inhibitors. While many lead compounds remain at the in vitro preclinical development stage, the two most recent patent applications describe promising in vivo data, and one small molecule inhibitor has recently entered into clinical development. It is such an exciting moment that the long awaited clinical studies will generate some insight into the therapeutic potential of this anti-cancer approach, and possibly facilitate the further development of other early stage inhibitors.

Survival control of malignant lymphocytes by anti-apoptotic MCL-1

Programmed apoptotic cell death is critical to maintain tissue homeostasis and cellular integrity in the lymphatic system. Accordingly, the evasion of apoptosis is a critical milestone for the transformation of lymphocytes on their way to becoming overt lymphomas. The anti-apoptotic BCL-2 family proteins are pivotal regulators of the mitochondrial apoptotic pathway and genetic aberrations in these genes are associated with lymphomagenesis and chemotherapeutic resistance. Pharmacological targeting of BCL-2 is highly effective in certain indolent B-cell lymphomas; however, recent evidence highlights a critical role for the BCL-2 family member MCL-1 in several lymphoma subtypes. MCL-1 is recurrently highly expressed in various kinds of cancer including non-Hodgkin's lymphoma of B- and T-cell origin. Moreover, both indolent and aggressive forms of lymphoma require MCL-1 for lymphomagenesis and for their continued survival. This review summarizes the role of MCL-1 in B- and T-cell lymphoma and discusses its potential as a therapeutic target.

The BCL2 Family: Key Mediators of the Apoptotic Response to Targeted Anticancer Therapeutics

The ability of cancer cells to suppress apoptosis is critical for carcinogenesis. The BCL2 family proteins comprise the sentinel network that regulates the mitochondrial or intrinsic apoptotic response. Recent advances in our understanding of apoptotic signaling pathways have enabled methods to identify cancers that are "primed" to undergo apoptosis, and have revealed potential biomarkers that may predict which cancers will undergo apoptosis in response to specific therapies. Complementary efforts have focused on developing novel drugs that directly target antiapoptotic BCL2 family proteins. In this review, we summarize the current knowledge of the role of BCL2 family members in cancer development and response to therapy, focusing on targeted therapeutics, recent progress in the development of apoptotic biomarkers, and therapeutic strategies designed to overcome deficiencies in apoptosis.

SIGNIFICANCE

Apoptosis, long known to be important for response to conventional cytotoxic chemotherapy, has more recently been shown to be essential for the efficacy of targeted therapies. Approaches that increase the likelihood of a cancer to undergo apoptosis following therapy may help improve targeted treatment strategies. Cancer Discov; 5(5); 475-87. ©2015 AACR.

Phase II study of perifosine and sorafenib dual-targeted therapy in patients with relapsed or refractory lymphoproliferative diseases

PURPOSE

To evaluate safety and activity of perifosine and sorafenib combination therapy in patients with lymphoproliferative diseases.

EXPERIMENTAL DESIGN

Patients with relapsed and refractory lymphoproliferative diseases received perifosine (50 mg twice daily) for 1 month. Patients achieving less than partial response (PR) after perifosine alone were administered the combination therapy [perifosine plus sorafenib (400 mg twice daily)] until progressive disease (PD) or unacceptable toxicity occurred. The pERK and pAKT in peripheral blood lymphocytes as well as serum cytokine levels were investigated as predictive biomarkers of response.

RESULTS

Forty patients enrolled in this study. After 1 month of perifosine alone, 36 who achieved less than PR went on to combination therapy, whereas four patients with chronic lymphocytic leukemia (CLL) who achieved PR continued with perifosine alone for a median of 10 months (range, 4-21). The most common drug-related toxicities were grade 1-2 anemia (17%), thrombocytopenia (9%), diarrhea (25%), joint pain (22%), and hand-foot skin reaction (25%). Three patients experienced grade 3 pneumonitis. Eight patients (22%) achieved PR, 15 (42%) achieved stable disease, and 13 (36%) experienced PD. A 28% PR rate was recorded for 25 patients with Hodgkin lymphoma. Among all patients, median overall survival and progression-free survival were 16 and 5 months, respectively. Early reductions in pERK and pAKT significantly correlated with the probability of clinical response.

CONCLUSIONS

Perifosine and sorafenib combination therapy is feasible with manageable toxicity and demonstrates promising activity in patients with Hodgkin lymphoma. The predictive value of pERK and pAKT should be confirmed in a larger patient cohort.

SNS01-T modulation of eIF5A inhibits B-cell cancer progression and synergizes with bortezomib and lenalidomide

The high rates of recurrence and low median survival in many B-cell cancers highlight a need for new targeted therapeutic modalities. In dividing cells, eukaryotic translation initiation factor 5A (eIF5A) is hypusinated and involved in regulation of protein synthesis and proliferation, whereas the non-hypusinated form of eIF5A is a potent inducer of cell death in malignant cells. Here, we demonstrate the potential of modulating eIF5A expression as a novel approach to treating B-cell cancers. SNS01-T is a nonviral polyethylenimine-based nanoparticle, designed to induce apoptosis selectively in B-cell cancers by small interfering RNA-mediated suppression of hypusinated eIF5A and plasmid-based overexpression of a non-hypusinable eIF5A mutant. In this study, we show that SNS01-T is preferentially taken up by malignant B cells, inhibits tumor growth in multiple animal models of B-cell cancers without damaging normal tissues, and synergizes with the current therapies bortezomib and lenalidomide to inhibit tumor progression. The results collectively demonstrate the potential of SNS01-T as a novel therapeutic for treatment of a diverse range of B-cell malignancies.

Restoration of miR-193b sensitizes Hepatitis B virus-associated hepatocellular carcinoma to sorafenib

BACKGROUND

Chronic infection with Hepatitis B virus (HBV) is the major risk factor of Hepatocellular Carcinoma (HCC). This study is to explore the mechanism of sorafenib resistance and find an effective strategy to sensitize HBV-associated HCC to sorafenib.

METHODS

Cytotoxicity to sorafenib was evaluated in HBV-positive/negative HCC cell lines. Expression of miR-193b and myeloid cell leukemia-1 (Mcl-1) protein were assessed by Q-PCR, in situ hybridization and western blot, immunohistochemistry, respectively. A luciferase reporter of Mcl-1 3'-UTR was used for validation as a target of miR-193b. Cell apoptosis was measured by flow cytometry, caspase-3 activity assay and DAPI staining.

RESULT

The IC50 to sorafenib was significantly higher in HBV-positive HCC cells than those without HBV infection. Significant downregulation of miR-193b and a higher level of Mcl-1 were observed in HBV-positive HCC cells and tissues. The activity of Mcl-1 3'-UTR reporter was inhibited by co-transfection with miR-193b mimic. Restoring the expression of miR-193b sensitized HBV-associated HCC cells to sorafenib treatment and facilitated sorafenib-induced apoptosis.

CONCLUSIONS

Modulation of miRNAs expression might be a potential way to enhance response to sorafenib in HBV-associated HCC.

3-Substituted-N-(4-hydroxynaphthalen-1-yl)arylsulfonamides as a novel class of selective Mcl-1 inhibitors: structure-based design, synthesis, SAR, and biological evaluation

Mcl-1, an antiapoptotic member of the Bcl-2 family of proteins, is a validated and attractive target for cancer therapy. Overexpression of Mcl-1 in many cancers results in disease progression and resistance to current chemotherapeutics. Utilizing high-throughput screening, compound 1 was identified as a selective Mcl-1 inhibitor and its binding to the BH3 binding groove of Mcl-1 was confirmed by several different, but complementary, biochemical and biophysical assays. Guided by structure-based drug design and supported by NMR experiments, comprehensive SAR studies were undertaken and a potent and selective inhibitor, compound 21, was designed which binds to Mcl-1 with a Ki of 180 nM. Biological characterization of 21 showed that it disrupts the interaction of endogenous Mcl-1 and biotinylated Noxa-BH3 peptide, causes cell death through a Bak/Bax-dependent mechanism, and selectively sensitizes Eμ-myc lymphomas overexpressing Mcl-1, but not Eμ-myc lymphoma cells overexpressing Bcl-2. Treatment of human leukemic cell lines with compound 21 resulted in cell death through activation of caspase-3 and induction of apoptosis.

The copper chelator ATN-224 induces caspase-independent cell death in diffuse large B cell lymphoma

Bcl-2 and other anti-apoptotic proteins are associated with defective caspase-dependent apoptotic pathways, resulting in chemoresistance. We have previously shown that ATN-224, a copper chelator drug, induces cell death in murine thymic lymphoma cells transfected with Bcl-2. In the current study, we tested whether ATN-224 was effective in diffuse large B cell lymphoma (DLBCL) cells, which have increased anti-apoptotic proteins through translocation or amplification. We found that nanomolar concentrations of ATN-224 induced cell death in DLBCL cells independent of Bcl-2, Bcl-xL or Mcl-1 status. ATN-224 treatment resulted in mitochondrial dysfunction, release of apoptosis-inducing factor (AIF) and induction of caspase-independent cell death. In addition, ATN-224 degraded Mcl-1 and enhanced the effect of the BH3 mimetic ABT-263. These findings indicate that ATN-224 has potential as a therapeutic for the treatment of DLBCL. Induction of caspase-independent cell death in apoptosis-resistant DLBCL would provide a therapeutic alternative for the treatment of refractory disease.

Hydroxyquinoline-derived compounds and analoguing of selective Mcl-1 inhibitors using a functional biomarker

Anti-apoptotic Bcl-2 family proteins are important oncology therapeutic targets. To date, BH3 mimetics that abrogate anti-apoptotic activity have largely been directed at Bcl-2 and/or Bcl-xL. One observed mechanism of resistance to these inhibitors is increased Mcl-1 levels in cells exposed to such therapeutics. For this reason, and because Mcl-1 is important in the onset of lymphoid, myeloid, and other cancers, it has become a target of great interest. However, small molecule inhibitors displaying potency and selectivity for Mcl-1 are lacking. Identifying such compounds has been challenging due to difficulties in translating the target selectivity observed at the biochemical level to the cellular level. Herein we report the results of an HTS strategy coupled with directed hit optimization. Compounds identified have selective Mcl-1 inhibitory activity with greater than 100-fold reduced affinity for Bcl-xL. The selectivity of these compounds at the cellular level was validated using BH3 profiling, a novel personalized diagnostic approach. This assay provides an important functional biomarker that allows for the characterization of cells based upon their dependencies on various anti-apoptotic Bcl-2 proteins. We demonstrate that cells dependent on Mcl-1 or Bcl-2/Bcl-xL for survival are commensurately responsive to compounds that genuinely target those proteins. The identification of compound 9 with uniquely validated and selective Mcl-1 inhibitory activity provides a valuable tool to those studying the intrinsic apoptosis pathway and highlights an important approach in the development of a first-in-class cancer therapeutic.

Sorafenib inhibits lymphoma xenografts by targeting MAPK/ERK and AKT pathways in tumor and vascular cells

The anti-lymphoma activity and mechanism(s) of action of the multikinase inhibitor sorafenib were investigated using a panel of lymphoma cell lines, including SU-DHL-4V, Granta-519, HD-MyZ, and KMS-11 cell lines. In vitro, sorafenib significantly decreased cell proliferation and phosphorylation levels of MAPK and PI3K/Akt pathways while increased apoptotic cell death. In vivo, sorafenib treatment resulted in a cytostatic rather than cytotoxic effect on tumor cell growth associated with a limited inhibition of tumor volumes. However, sorafenib induced an average 50% reduction of tumor vessel density and a 2-fold increase of necrotic areas. Upon sorafenib treatment, endothelial and tumor cells from SU-DHL-4V, Granta-519, and KMS-11 nodules showed a potent inhibition of either phospho-ERK or phospho-AKT, whereas a concomitant inhibition of phospho-ERK and phospho-AKT was only observed in HD-MyZ nodules. In conclusion, sorafenib affects the growth of lymphoid cell lines by triggering antiangiogenic mechanism(s) and directly targeting tumor cells.

Death of multiple myeloma cells induced by cAMP-signaling involves downregulation of Mcl-1 via the JAK/STAT pathway

There is a continuous search for new therapeutic targets for treatment of multiple myeloma (MM). Here we investigated the mechanisms involved in cAMP-induced apoptosis of human MM cells. cAMP-increasing agents rapidly inhibited activation of JAK1 and its substrate STAT3. In line with STAT3 being a regulator of Mcl-1 transcription, the expression of this pro-survival factor was rapidly and selectively reduced. Notably, exogenous interleukin-6 neither prevented the inhibition of JAK1/STAT3 nor the death of MM cells induced by cAMP. Our results suggest that cAMP-mediated killing of MM cells involves inhibition of the JAK/STAT pathway, making the cAMP-pathway a promising target for treatment of MM.

The stress protein BAG3 stabilizes Mcl-1 protein and promotes survival of cancer cells and resistance to antagonist ABT-737

Members of the Bcl-2 family of proteins are important inhibitors of apoptosis in human cancer and are targets for novel anticancer agents such as the Bcl-2 antagonists, ABT-263 (Navitoclax), and its analog ABT-737. Unlike Bcl-2, Mcl-1 is not antagonized by ABT-263 or ABT-737 and is considered to be a major factor in resistance. Also, Mcl-1 exhibits differential regulation when compared with other Bcl-2 family members and is a target for anticancer drug discovery. Here, we demonstrate that BAG3, an Hsp70 co-chaperone, protects Mcl-1 from proteasomal degradation, thereby promoting its antiapoptotic activity. Using neuroblastoma cell lines, with a defined Bcl-2 family dependence, we found that BAG3 expression correlated with Mcl-1 dependence and ABT-737 resistance. RNA silencing of BAG3 led to a marked reduction in Mcl-1 protein levels and overcame ABT-737 resistance in Mcl-1-dependent cells. In ABT-737-resistant cells, Mcl-1 co-immunoprecipitated with BAG3, and loss of Mcl-1 after BAG3 silencing was prevented by proteasome inhibition. BAG3 and Mcl-1 were co-expressed in a panel of diverse cancer cell lines resistant to ABT-737. Silencing BAG3 reduced Mcl-1 protein levels and overcame ABT-737 resistance in several of the cell lines, including triple-negative breast cancer (MDA-MB231) and androgen receptor-negative prostate cancer (PC3) cells. These studies identify BAG3-mediated Mcl-1 stabilization as a potential target for cancer drug discovery.

Altered Ca(2+) signaling in cancer cells: proto-oncogenes and tumor suppressors targeting IP3 receptors

Proto-oncogenes and tumor suppressors critically control cell-fate decisions like cell survival, adaptation and death. These processes are regulated by Ca(2+) signals arising from the endoplasmic reticulum, which at distinct sites is in close proximity to the mitochondria. These organelles are linked by different mechanisms, including Ca(2+)-transport mechanisms involving the inositol 1,4,5-trisphosphate receptor (IP3R) and the voltage-dependent anion channel (VDAC). The amount of Ca(2+) transfer from the endoplasmic reticulum to mitochondria determines the susceptibility of cells to apoptotic stimuli. Suppressing the transfer of Ca(2+) from the endoplasmic reticulum to the mitochondria increases the apoptotic resistance of cells and may decrease the cellular responsiveness to apoptotic signaling in response to cellular damage or alterations. This can result in the survival, growth and proliferation of cells with oncogenic features. Clearly, proper maintenance of endoplasmic reticulum Ca(2+) homeostasis and dynamics including its links with the mitochondrial network is essential to detect and eliminate altered cells with oncogenic features through the apoptotic pathway. Proto-oncogenes and tumor suppressors exploit the central role of Ca(2+) signaling by targeting the IP3R. There are an increasing number of reports showing that activation of proto-oncogenes or inactivation of tumor suppressors directly affects IP3R function and endoplasmic reticulum Ca(2+) homeostasis, thereby decreasing mitochondrial Ca(2+) uptake and mitochondrial outer membrane permeabilization. In this review, we provide an overview of the current knowledge on the proto-oncogenes and tumor suppressors identified as IP3R-regulatory proteins and how they affect endoplasmic reticulum Ca(2+) homeostasis and dynamics.

Combined administration of rituximab and on 013105 induces apoptosis in mantle cell lymphoma cells and reduces tumor burden in a mouse model of mantle cell lymphoma

PURPOSE

Mantle cell lymphoma (MCL) is an incurable B-cell lymphoma, and new therapeutic strategies are urgently needed.

EXPERIMENTAL DESIGN

The effects of ON 013105, a novel benzylstyryl sulfone kinase inhibitor, alone or with doxorubicin or rituximab, were examined in Granta 519 and Z138C cells. For in vivo studies, CB17/SCID mice were implanted subcutaneously with Z138C cells and treated with various combinations of ON 013105, doxorubicin, and rituximab. Tumor burden and body weight were monitored for 28 days.

RESULTS

ON 013105 induced mitochondria-mediated apoptosis in MCL cells. Death was preceded by translocation of tBid to the mitochondria and cytochrome c release. In addition, ON 013105-treated cells exhibited reduced levels of cyclin D1, c-Myc, Mcl-1, and Bcl-xL. Using nuclear magnetic resonance (NMR) spectroscopy, we showed specific binding of ON 013105 to eIF4E, a critical factor for the initiation of protein translation. We proffer that this drug-protein interaction preferentially prevents the translation of the aforementioned proteins and may be the mechanism by which ON 013105 induces apoptosis in MCL cells. Efficacy studies in a mouse xenograft model showed that ON 013105 inhibited MCL tumor growth and that combining ON 013105 with rituximab reduced tumor burden further with negligible unwanted effects.

CONCLUSIONS

Our findings suggest that ON 013105, alone or in combination with rituximab, may be a potent therapeutic agent to treat MCLs.

Association of anti-apoptotic Mcl-1L isoform expression with radioresistance of oral squamous carcinoma cells

Background

Oral cancer is a common cancer and a major health problem in the Indian subcontinent. At our laboratory Mcl-1, an anti-apoptotic member of the Bcl-2 family has been demonstrated to be overexpressed in oral cancers and to predict outcome in oral cancer patients treated with definitive radiotherapy. To study the role of Mcl-1 isoforms in radiation response of oral squamous carcinoma cells (OSCC), we investigated in the present study, the association of Mcl-1 isoform expression with radiosensitivity of OSCC, using siRNA strategy.

Methods

The time course expression of Mcl-1 splice variants (Mcl-1L, Mcl-1S & Mcl-1ES) was studied by RT-PCR, western blotting & immunofluorescence, post-irradiation in oral cell lines [immortalized FBM (radiosensitive) and tongue cancer AW8507 & AW13516 (radioresistant)]of relatively differing radiosensitivities. The effect of Mcl-1L knockdown alone or in combination with ionizing radiation (IR) on cell proliferation, apoptosis & clonogenic survival, was investigated in AW8507 & AW13516 cells. Further the expression of Mcl-1L protein was assessed in radioresistant sublines generated by fractionated ionizing radiation (FIR).

Results

Three to six fold higher expression of anti-apoptotic Mcl-1L versus pro-apoptotic Mcl-1S was observed at mRNA & protein levels in all cell lines, post-irradiation. Sustained high levels of Mcl-1L, downregulation of pro-apoptotic Bax & Bak and a significant (P < 0.05) reduction in apoptosis was observed in the more radioresistant AW8507, AW13516 versus FBM cells, post-IR. The ratios of anti to pro-apoptotic proteins were high in AW8507 as compared to FBM. Treatment with Mcl-1L siRNA alone or in combination with IR significantly (P < 0.01) increased apoptosis viz. 17.3% (IR), 25.3% (siRNA) and 46.3% (IR plus siRNA) and upregulated pro-apoptotic Bax levels in AW8507 cells. Combination of siRNA & IR treatment significantly (P < 0.05) reduced cell proliferation and clonogenic survival of radioresistant AW8507 & AW13516 cells, suggesting a synergistic effect of the Mcl-1L siRNA with IR on radiosensitivity. Interestingly, during the development of radioresistant sublines using FIR, high expression of Mcl-1L was observed.

Conclusion

Our studies suggest that Mcl-1L isoform has an important role in the survival and radioresistance of OSCC and may be a promising therapeutic target in oral cancers.

Phase II study of sorafenib in patients with relapsed or refractory lymphoma

The safety and activity of the multikinase inhibitor sorafenib were investigated in patients with relapsed or refractory lymphoproliferative disorders who received sorafenib (400 mg) twice daily until disease progression or appearance of significant clinical toxicity. The primary endpoint was overall response rate (ORR). Biomarkers of sorafenib activity were analysed at baseline and during treatment. Thirty patients (median age, 61 years; range, 18-74) received a median of 4 months of therapy. Grade 3-4 toxicities included hand/foot skin reactions (20%), infections (12%), neutropenia (20%) and thrombocytopenia (14%). Two patients achieved complete remission (CR), and two achieved partial remission (PR) for an ORR of 13%. Stable disease (SD) and progressive disease (PD) was observed in 15 (50%) and 11 patients (37%), respectively. The median overall survival (OS) for all patients was 16 months. For patients who achieved CR, PR and SD, the median time to progression and OS was 5 and 24 months, respectively. Compared with patients with PD, responsive patients had significantly higher baseline levels of extracellular signal-regulated kinase phosphorylation and autophagy and presented a significant reduction of these parameters after 1 month of therapy. Sorafenib was well tolerated and had a clinical activity that warrants development of combination regimens.

Retinoic acid/alpha-interferon combination inhibits growth and promotes apoptosis in mantle cell lymphoma through Akt-dependent modulation of critical targets

Mantle cell lymphoma (MCL) is characterized by a profound deregulation of the mechanisms controlling cell-cycle progression and survival. We herein show that the combination of 9-cis-retinoic acid (RA) and IFN-α induces marked antiproliferative and proapoptotic effects in MCL cells through the modulation of critical targets. Particularly, IFN-α enhances RA-mediated G(0)-G(1) cell accumulation by downregulating cyclin D1 and increasing p27(Kip1) and p21(WAF1/Cip1) protein levels. Furthermore, RA/IFN-α combination also induces apoptosis by triggering both caspases-8 and -9 resulting in Bax and Bak activation. In particular, RA/IFN-α treatment downregulates the antiapoptotic Bcl-xL and Bfl-1 proteins and upregulates the proapoptotic BH3-only Noxa protein. Sequestration of Mcl-1 and Bfl-1 by upregulated Noxa results in the activation of Bid, and the consequent induction of apoptosis is inhibited by Noxa silencing. Noxa upregulation is associated with nuclear translocation of the FOXO3a transcription factor as consequence of RA/IFN-α-induced Akt inhibition. Pharmacologic suppression of Akt, but not of TORC1, increases Noxa protein levels and downregulates Bfl-1 protein supporting the conclusion that the inhibition of the Akt pathway, the resulting FOXO3a activation and Noxa upregulation are critical molecular mechanisms underlying RA/IFN-α-dependent MCL cell apoptosis. These results support the potential therapeutic value of RA/IFN-α combination in MCL management.