Discovery of an orally bioavailable small molecule inhibitor of prosurvival B-cell lymphoma 2 proteins

Bcl-XL: A multifunctional anti-apoptotic protein

B-cell lymphoma-extra large (Bcl-X_L) is one of the anti-apoptotic proteins of the Bcl-2 family that is localized in the mitochondria. Bcl-X_L is one of the key regulators of apoptosis that can also regulate other important cellular functions. Bcl-X_L is overexpressed in many cancers, and its inhibitors have shown good therapeutic effects. Bcl-X_L interacts with Beclin 1, a key factor regulating autophagy. Bcl-X_L is essential for the survival of neurons and plays protective roles in neuronal injuries. It can promote the growth of neurons and the correct formation of neural networks, enhance synaptic plasticity, and control neurotoxicity. Bcl-X_L can also promote the transport of Ca²⁺ to mitochondria, increase the production of ATP, and improve metabolic efficiency. In addition, targeting Bcl-X_L has shown potential value in autoimmune diseases and aging. In this review, we summarize the functions of Bcl-X_L in cancer, autophagy, Ca²⁺ signaling, neuroprotection, neuronal growth and synaptic plasticity, energy metabolism, immunity, and senescence as revealed by investigations conducted in the past 10 years. Moreover, we list some inhibitors that have been developed based on the functions of Bcl-X_L.

Formal α-trifluoromethylthiolation of carboxylic acid derivatives via N-acyl pyrazoles

A direct and general one-pot approach to α-trifluoromethylthiolated amides, esters and carboxylic acids has been successfully developed under mild, catalytic and metal-free conditions.

Side-by-side comparison of BH3-mimetics identifies MCL-1 as a key therapeutic target in AML

Despite advances in the treatment of acute myeloid leukemia (AML), prognosis of AML patients is still dismal and better treatment options are required. B-cell Lymphoma 2 (BCL-2) homology domain 3 (BH3)-mimetics are emerging as a novel class of apoptosis-inducing agents that are currently being tested for the treatment of different hematological malignancies including AML. Particularly, the selective BCL-2 inhibitor ABT-199/Venetoclax is demonstrating clinical responses and has recently been approved in combination for the treatment of AML. Compounds targeting the related protein MCL-1 have recently entered clinical trials, highlighting the urgency to compare the different BH3-mimetics and identify the most promising antiapoptotic target in AML. We performed a side-by-side comparison of different highly selective and potent BH3-mimetics targeting BCL-2 (ABT-199), MCL-1 (S63845) or BCL-x_L (A1331852) in a panel of AML cell lines and primary patient cells. Gene knockdown using siRNAs was utilized to investigate the functional relevance of BCL-2 proteins. Western blotting and immunoprecipitations were used to explore the influence of BH3-mimetics on interactions between pro- and antiapoptotic BCL-2 proteins. A1331852 induced apoptosis only in selected cases, indicating that BCL-x_L is not a very promising therapeutic target in AML. However, S63845 displayed higher potency than ABT-199, with more cell lines and primary cells responding to S63845 than to ABT-199. MCL-1 dependency in AML cells was confirmed by siRNA-mediated knockdown of MCL-1, which was sufficient to induce apoptosis. S63845-induced cell death was accompanied by a displacement of the BH3-only protein BIM as well as BAK, resulting in BAK-dependent apoptosis. In contrast, ABT-199-induced cell death was mediated by BAX rather than BAK, indicating distinct non-redundant molecular functions of BCL-2 and MCL-1 in AML. Our study reveals that MCL-1 may be a more prevalent therapeutic target than BCL-2 in AML and identifies BIM and BAK as important mediators of S63845-induced apoptosis in AML.

Mimicking Strategy for Protein-Protein Interaction Inhibitor Discovery by Virtual Screening

As protein–protein interactions (PPIs) are highly involved in most cellular processes, the discovery of PPI inhibitors that mimic the structure of the natural protein partners is a promising strategy toward the discovery of PPI inhibitors. In this review, we discuss recent advances in the application of virtual screening for identifying mimics of protein partners. The classification and function of the mimicking protein partner inhibitor discovery by virtual screening are described. We anticipate that this review would be of interest to medicinal chemists and chemical biologists working in the field of protein–protein interaction inhibitors or probes.

Aging and stress induced β cell senescence and its implication in diabetes development

Cellular senescence is a well-established defensive mechanism for tumor suppression, and is also proposed to play a crucial role in embryonic development, wound repair, aging and age-related diseases. Senescent cell is characterized by the marked morphological changes and active metabolism along with a distinctive senescence associated secretion phenotype (SASP). Cellular senescence is triggered by multiple endogenous and exogenous stressors, which collectively induce three types of senescence. It is believed that senescence represents a programmed phenomenon to facilitate β cell functional maturation and, therefore, senescence has been suggested to be involved in β cell regeneration, insulin secretion and diabetes development. Nevertheless, despite past extensive studies, the exact impact of senescence on β cell viability, regeneration and functionality, and its relevance to the development of diabetes are yet to be fully addressed. In this review, we will summarize the recent progress in β cell senescence, through which we intend to spark more instructive discussion and perspective with regard to the mechanisms underlying β cell senescence and their links to the pathogenesis of diabetes and the development of therapeutic strategies.

Emerging approaches to target mitochondrial apoptosis in cancer cells

Apoptosis is a highly conserved programme for removing damaged and unwanted cells. Apoptosis in most cells is coordinated on mitochondria by the Bcl-2 family of proteins. The balance between pro- and anti-apoptotic Bcl-2 family proteins sets a threshold for mitochondrial apoptosis, a balance that is altered during cancer progression. Consequently, avoidance of cell death is an established cancer hallmark. Although there is a general perception that tumour cells are more resistant to apoptosis than their normal counterparts, the realities of cell death regulation in cancer are more nuanced. In this review we discuss how a profound understanding of this control has led to new therapeutic approaches, including the new class of BH3-mimetics, which directly target apoptosis as a vulnerability in cancer. We discuss recent findings that highlight the current limitations in our understanding of apoptosis and how these novel therapeutics work.

Drugs and Clinical Approaches Targeting the Antiapoptotic Protein: A Review

B-cell lymphoma 2 (Bcl-2) is a regulator protein involved in apoptosis. In the past few decades, this protein has been demonstrated to have high efficacy in cancer therapy, and several approaches targeting Bcl-2 have been tested clinically (e.g., oblimersen, ABT-737, ABT-263, obatoclax mesylate, and AT-101). This review reports potential Bcl-2 inhibitors according to current information on their underlying mechanism and the results of clinical trials. In addition, the function and mechanisms of other potentially valuable Bcl-2 inhibitors that did not show efficacy in clinical studies are also discussed. This summary of the development of Bcl-2 inhibitors provides worthwhile viewpoints on the use of biomedical approaches in future cancer therapy.

Camel Whey Protein Disrupts the Cross-Talk Between PI3K and BCL-2 Signals and Mediates Apoptosis in Primary Acute Myeloid Leukemia Cells

In the present study, we investigated the impact of camel whey protein (CWP) on the survival of primary acute myeloid leukemia (AML) cells that were isolated from 20 patients diagnosed with AML. We found that CWP induced apoptosis in the primary AML cells without affecting the normal PBMCs that were isolated from healthy individuals, as determined by PI/annexin V double staining followed by flow-cytometry analysis. Furthermore, we demonstrated that these primary AML cells exhibited aberrant phosphorylation of AKT, mTOR and STAT3. Treatment of AML cells with CWP mediated significant reduction in the phosphorylation of AKT, mTOR and STAT3. Additionally, we demonstrated that blockade of PI3K/AKT signaling pathway by wortmannin (WM) impaired the expression of Bcl-2 and Bcl_XL in the primary AML cells, suggesting an essential cross-talk between PI3K and Bcl-2 that maintains the survival of AML cells. In this context, treatment of AML cells with CWP disrupted the PI3K/Bcl-2 cross-talk; significantly downregulated the expression of anti-apoptotic Bcl-2 family members Bcl-2 and Bcl_XL; markedly upregulated the expression of the pro-apoptotic Bcl-2 family members Bak and Bax; and subsequently sensitized tumor cells to growth arrest. Our data revealed the therapeutic potential of CWP and the underlying mechanisms against leukemia.

The Role of Inhibition of Apoptosis in Acute Leukemias and Myelodysplastic Syndrome

Avoidance of apoptosis is a key mechanism that malignancies, including acute leukemias and MDS, utilize in order to proliferate and resist chemotherapy. Recently, venetoclax, an inhibitor of the anti-apoptotic protein BCL-2, has been approved for the treatment of upfront AML in an unfit, elderly population. This paper reviews the pre-clinical and clinical data for apoptosis inhibitors currently in development for the treatment of AML, ALL, and MDS.

Combined MEK and BCL-2/XL Inhibition Is Effective in High-Grade Serous Ovarian Cancer Patient-Derived Xenograft Models and BIM Levels Are Predictive of Responsiveness

Most patients with late-stage high-grade serous ovarian cancer (HGSOC) initially respond to chemotherapy but inevitably relapse and develop resistance, highlighting the need for novel therapies to improve patient outcomes. The MEK/ERK pathway is activated in a large subset of HGSOC, making it an attractive therapeutic target. Here, we systematically evaluated the extent of MEK/ERK pathway activation and efficacy of pathway inhibition in a large panel of well-annotated HGSOC patient-derived xenograft models. The vast majority of models were nonresponsive to the MEK inhibitor cobimetinib (GDC-0973) despite effective pathway inhibition. Proteomic analyses of adaptive responses to GDC-0973 revealed that GDC-0973 upregulated the proapoptotic protein BIM, thus priming the cells for apoptosis regulated by BCL2-family proteins. Indeed, combination of both MEK inhibitor and dual BCL-2/XL inhibitor (ABT-263) significantly reduced cell number, increased cell death, and displayed synergy in vitro in most models. In vivo, GDC-0973 and ABT-263 combination was well tolerated and resulted in greater tumor growth inhibition than single agents. Detailed proteomic and correlation analyses identified two subsets of responsive models-those with high BIM at baseline that was increased with MEK inhibition and those with low basal BIM and high pERK levels. Models with low BIM and low pERK were nonresponsive. Our findings demonstrate that combined MEK and BCL-2/XL inhibition has therapeutic activity in HGSOC models and provide a mechanistic rationale for the clinical evaluation of this drug combination as well as the assessment of the extent to which BIM and/or pERK levels predict drug combination effectiveness in chemoresistant HGSOC.

Apoptosis and apoptotic body: disease message and therapeutic target potentials

Apoptosis is widely known as programmed cell death eliciting no inflammatory responses. The intricacy of apoptosis has been a focus of an array of researches, accumulating a wealth of knowledge which led to not only a better understanding of the fundamental process, but also potent therapies of diseases. The classic intrinsic and extrinsic signaling pathways of apoptosis, along with regulatory factors have been well delineated. Drugs and therapeutic measures designed based on current understanding of apoptosis have long been employed. Small-molecule apoptosis inducers have been clinically used for eliminating morbid cells and therefore treating diseases, such as cancer. Biologics with improved apoptotic efficacy and selectivity, such as recombinant proteins and antibodies, are being extensively researched and some have been approved by the FDA. Apoptosis also produces membrane-bound vesicles derived from disassembly of apoptotic cells, now known as apoptotic bodies (ApoBDs). These little sealed sacs containing information as well as substances from dying cells were previously regarded as garbage bags until they were discovered to be capable of delivering useful materials to healthy recipient cells (e.g., autoantigens). In this review, current understandings and knowledge of apoptosis were summarized and discussed with a focus on apoptosis-related therapeutic applications and ApoBDs.

Targeting the Bcl-2 Family in B Cell Lymphoma

Although lymphoma is a very heterogeneous group of biologically complex malignancies, tumor cells across all B cell lymphoma subtypes share a set of underlying traits that promote the development and sustain malignant B cells. One of these traits, the ability to evade apoptosis, is essential for lymphoma development. Alterations in the Bcl-2 family of proteins, the key regulators of apoptosis, is a hallmark of B cell lymphoma. Significant efforts have been made over the last 30 years to advance knowledge of the biology, molecular mechanisms, and therapeutic potential of targeting Bcl-2 family members. In this review, we will highlight the complexities of the Bcl-2 family, including our recent discovery of overexpression of the anti-apoptotic Bcl-2 family member Bcl-w in lymphomas, and describe recent advances in the field that include the development of inhibitors of anti-apoptotic Bcl-2 family members for the treatment of B cell lymphomas and their performance in clinical trials.

Cross Talk Between Cellular Redox State and the Antiapoptotic Protein Bcl-2

SIGNIFICANCE

B cell lymphoma-2 (Bcl-2) was discovered over three decades ago and is the prototype antiapoptotic member of the Bcl-2 family that comprises proteins with contrasting effects on cell fate. First identified as a consequence of chromosomal translocation (t 14:18) in human lymphoma, subsequent studies have revealed mutations and/or gene copy number alterations as well as post-translational modifications of Bcl-2 in a variety of human cancers. The canonical function of Bcl-2 is linked to its ability to inhibit mitochondrial membrane permeabilization, thereby regulating apoptosome assembly and activation by blocking the cytosolic translocation of death amplification factors. Of note, the identification of specific domains within the Bcl-2 family of proteins (Bcl-2 homology domains; BH domains) has not only provided a mechanistic insight into the various interactions between the member proteins but has also been the impetus behind the design and development of small molecule inhibitors and BH3 mimetics for clinical use. Recent Advances: Aside from its role in maintaining mitochondrial integrity, recent evidence provides testimony to a novel facet in the biology of Bcl-2 that involves an intricate cross talk with cellular redox state. Bcl-2 overexpression modulates mitochondrial redox metabolism to create a "pro-oxidant" milieu, conducive for cell survival. However, under states of oxidative stress, overexpression of Bcl-2 functions as a redox sink to prevent excessive buildup of reactive oxygen species, thereby inhibiting execution signals. Emerging evidence indicates various redox-dependent transcriptional changes and post-translational modifications with different functional outcomes.

CRITICAL ISSUES

Understanding the complex interplay between Bcl-2 and the cellular redox milieu from the standpoint of cell fate signaling remains vital for a better understanding of pathological states associated with altered redox metabolism and/or aberrant Bcl-2 expression.

FUTURE DIRECTIONS

Based on its canonical functions, Bcl-2 has emerged as a potential druggable target. Small molecule inhibitors of Bcl-2 and/or other family members with similar function, as well as BH3 mimetics, are showing promise in the clinic. The emerging evidence for the noncanonical activity linked to cellular redox metabolism provides a novel avenue for the design and development of diagnostic and therapeutic strategies against cancers refractory to conventional chemotherapy by the overexpression of this prosurvival protein.

Fragment-Based Drug Discovery: Advancing Fragments in the Absence of Crystal Structures

Fragment-based drug discovery typically requires an interplay between screening methods, structural methods, and medicinal chemistry. X-ray crystallography is generally the method of choice to obtain three-dimensional structures of the bound ligand/protein complex, but this can sometimes be difficult, particularly for early, low-affinity fragment hits. In this Perspective, we discuss strategies to advance and evolve fragments in the absence of crystal structures of protein-fragment complexes, although the structure of the unliganded protein may be available. The strategies can involve other structural techniques, such as NMR spectroscopy, molecular modeling, or a variety of chemical approaches. Often, these strategies are aimed at guiding evolution of initial fragment hits to a stage where crystal structures can be obtained for further structure-based optimization.

Development of high potent and selective Bcl-2 inhibitors bearing the structural elements of natural product artemisinin

By taking advantage of the apoptosis-inducing capacity of artemisinin derivatives, we developed several series of compounds by merging the basic structural elements of the natural product artemisinin into the P2 interaction pocket of the clinically prescribed Bcl-2 inhibitor venetoclax. Most of the new compounds displayed improved biochemical potency against Bcl-2 and high selectivity over Bcl-xL. Specifically, compounds 27c and 34c were found to be the most potent with IC₅₀ values less than 2.0 nM. Unfortunately, these compounds only showed moderate antiproliferative effects against Bcl-2 dependent cells. Though further structural optimization is needed to improve the cellular absorptive permeability, the current approach represents an alternative strategy to develop novel Bcl-2 inhibitors with greater selectivity over Bcl-xL, which is related to the off-target adverse effects of venetoclax.

Comprehensive Safety Analysis of Venetoclax Monotherapy for Patients with Relapsed/Refractory Chronic Lymphocytic Leukemia

Purpose: The oral BCL-2 inhibitor venetoclax is an effective therapy for patients with relapsed/refractory (R/R) chronic lymphocytic leukemia (CLL), including disease with high-risk genomic features such as chromosome 17p deletion [del(17p)] or progressive disease following B-cell receptor pathway inhibitors.Patients and Methods: We conducted a comprehensive analysis of the safety of 400 mg daily venetoclax monotherapy in 350 patients with CLL using an integrated dataset from three phase I/II studies.Results: Median age was 66 years and 60% had del(17p). Patients had received a median of three prior therapies (range: 0-15); 42% previously received ibrutinib or idelalisib. Median duration of exposure to venetoclax was 16 months (0-56). In the pooled analysis, the most common adverse events (AE) of any grade were diarrhea (41%), neutropenia (40%), nausea (39%), anemia (31%), fatigue (28%), and upper respiratory tract infection (25%). The most common grade 3/4 AEs were neutropenia (37%), anemia (17%), and thrombocytopenia (14%). With the current 5-week ramp-up dosing, the incidence of laboratory TLS was 1.4% (2/166), none had clinical sequelae, and all of these patients were able to ramp-up to a daily dose of 400 mg. Grade 3/4 neutropenia was manageable with growth factor support and dose adjustments; the incidence of serious infections in these patients was 15%. Ten percent of patients discontinued venetoclax due to AEs and 8% died while on study, with the majority of deaths in the setting of disease progression.Conclusions: Venetoclax as a long-term continuous therapy is generally well tolerated in patients with R/R CLL when initiated with the current treatment algorithm. Clin Cancer Res; 24(18); 4371-9. ©2018 AACR.

Restoring the switch for cancer cell death: Targeting the apoptosis signaling pathway

PURPOSE

The relevance of apoptosis to cancer development and pharmacologic agents that target this pathway in selected malignancies are described.

SUMMARY

Apoptosis is a tightly regulated biological process mediated by both proapoptotic (i.e., prodeath) and antiapoptotic (i.e., prosurvival) proteins. While apoptosis represents a well-established effector mechanism induced by conventional chemotherapy in many malignancies, the development of apoptosis-based targeted therapy is relatively new. The pharmacologic restoration of apoptotic functions, either by blocking the action of antiapoptotic proteins/regulators (e.g., through investigational therapies such as inhibitors of apoptosis proteins, SMAC [second mitochondria-derived activator of caspases] mimetics, MDM2 [murine double minute 2] antagonists) or by inducing apoptosis (e.g., through investigational agonistic monoclonal antibodies or fusion proteins), holds robust potential for cancer pharmacotherapy. Notably, BH domain 3 (BH3) mimetics, a new class of small molecules that block the action antiapoptotic proteins, are touted a success for apoptosis-based targeted therapy. Venetoclax, a synthetic peptide that belongs to this class of BH3 mimetics, is currently approved by the Food and Drug Administration for the treatment of relapsed/refractory chronic lymphocytic leukemia in patients with 17p deletion as a single agent. This agent has been increasingly used either alone or as part of combination therapy for diverse hematologic malignancies in clinical trials.

CONCLUSION

Advances in the understanding of molecular mechanisms of apoptosis have given rise to more-refined targeted therapies for diverse malignancies, with the goal to improve survival outcome while sparing treatment-related toxicities.

Cotargeting BCL-2 and PI3K Induces BAX-Dependent Mitochondrial Apoptosis in AML Cells

Inhibitors targeting BCL-2 apoptotic proteins have significant potential for the treatment of acute myeloid leukemia (AML); however, complete responses are observed in only 20% of patients, suggesting that targeting BCL-2 alone is insufficient to yield durable responses. Here, we assessed the efficacy of coadministration of the PI3K/mTOR inhibitor GDC-0980 or the p110β-sparing PI3K inhibitor taselisib with the selective BCL-2 antagonist venetoclax in AML cells. Tetracycline-inducible downregulation of BCL-2 significantly sensitized MV4-11 and MOLM-13 AML cells to PI3K inhibition. Venetoclax/GDC-0980 coadministration induced rapid and pronounced BAX mitochondrial translocation, cytochrome c release, and apoptosis in various AML cell lines in association with AKT/mTOR inactivation and MCL-1 downregulation; ectopic expression of MCL-1 significantly protected cells from this regimen. Combined treatment was also effective against primary AML blasts from 17 patients, including those bearing various genetic abnormalities. Venetoclax/GDC-0980 markedly induced apoptosis in primitive CD34⁺/38^-/123⁺ AML cell populations but not in normal hematopoietic progenitor CD34⁺ cells. The regimen was also active against AML cells displaying intrinsic or acquired venetoclax resistance or tumor microenvironment-associated resistance. Either combinatorial treatment markedly reduced AML growth and prolonged survival in a systemic AML xenograft mouse model and diminished AML growth in two patient-derived xenograft models. Venetoclax/GDC-0980 activity was partially diminished in BAK^-/- cells and failed to induce apoptosis in BAX^-/- and BAX^-/-BAK^-/- cells, whereas BIM^-/- cells were fully sensitive. Similar results were observed with venetoclax alone in in vitro and in vivo systemic xenograft models. Collectively, these studies demonstrate that venetoclax/GDC-0980 exhibits potent anti-AML activity primarily through BAX and, to a lesser extent, BAK. These findings argue that dual BCL-2 and PI3K inhibition warrants further evaluation in AML.Significance: Combined treatment with clinically relevant PI3K and BCL-2 inhibitors may prove effective in the treatment of acute myeloid leukemia. Cancer Res; 78(11); 3075-86. ©2018 AACR.

Synthesis of Aryl Triflones through the Trifluoromethanesulfonylation of Benzynes

The direct synthesis of aryl triflones, that is, trifluoromethanesulfonyl arenes, was achieved through the trifluoromethanesulfonylation of benzynes. The trifluoromethanesulfonyl group, one of the fluorinated functional groups, is a highly electron-negative and mild lipophilic substituent. Aryl triflones have high potential in the synthesis of bioactive compounds and specialty materials. The treatment of 2-(trimethylsilyl)aryl trifluoromethanesulfonates with cesium fluoride in the presence of 15-crown-5 generated benzynes, which reacted with sodium trifluoromethanesulfinate followed by protonation with tBuOH under heating conditions, provided aryl triflones in moderated to good yields. Both symmetrical and unsymmetrical triflones were nicely accessed under the same reaction conditions. Interestingly, the trifluoromethanesulfonylation of unsymmetrical benzyne precursors proceeded smoothly to furnish corresponding aryl triflones in good yields with good to high regioselectivities. The balance of polarization of electric charge as well as steric hindrance of the benzyne intermediates are central factors to control the outcome of regioselectivity.

Total synthesis of conosilane A via a site-selective C–H functionalization strategy

The strategy developed for the first total synthesis of highly oxygenated natural product conosilane A involving double manipulation of allylic C(sp³)–H functionalization renders the power of C–H functionalization in organic syntheses.

Identification of insulin-sensitizing molecules acting by disrupting the interaction between the Insulin Receptor and Grb14

Metabolic diseases are characterized by a decreased action of insulin. During the course of the disease, usual treatments frequently fail and patients are finally submitted to insulinotherapy. There is thus a need for innovative therapeutic strategies to improve insulin action. Growth factor receptor-bound protein 14 (Grb14) is a molecular adapter that specifically binds to the activated insulin receptor (IR) and inhibits its tyrosine kinase activity. Molecules disrupting Grb14-IR binding are therefore potential insulin-sensitizing agents. We used Structure-Based Virtual Ligand Screening to generate a list of 1000 molecules predicted to hinder Grb14-IR binding. Using an acellular bioluminescence resonance energy transfer (BRET) assay, we identified, out of these 1000 molecules, 3 compounds that inhibited Grb14-IR interaction. Their inhibitory effect on insulin-induced Grb14-IR interaction was confirmed in co-immunoprecipitation experiments. The more efficient molecule (C8) was further characterized. C8 increased downstream Ras-Raf and PI3-kinase insulin signaling, as shown by BRET experiments in living cells. Moreover, C8 regulated the expression of insulin target genes in mouse primary hepatocytes. These results indicate that C8, by reducing Grb14-IR interaction, increases insulin signalling. The use of C8 as a lead compound should allow for the development of new molecules of potential therapeutic interest for the treatment of diabetes.

Electrophilic Triflyl-arylation and Triflyl-pyridylation by Unsymmetrical Aryl/Pyridyl-λ3-iodonium Salts: Synthesis of Aryl and Pyridyl Triflones

Unsymmetrical diaryl-λ³-iodonium salts containing aryl triflone (Ar-SO₂CF₃) were designed and synthesized. X-ray crystal structure analysis of the salt indicated a T-shaped geometry at the iodine atom. The salts were found to be powerful electrophilic reagents for triflyl-arylation of C-, N-, and O-centered nucleophiles under mild conditions. Electrophilic transfer of pyridine triflone (Py-SO₂CF₃) to nucleophiles was also realized by the use of corresponding triflylpyridyl-aryl-λ³-iodonium salts. Selection of auxiliaries (dummy ligands) of unsymmetrical diaryl-λ³-iodonium salts is crucial for this transformation.

Identification of an in vivo orally active dual-binding protein-protein interaction inhibitor targeting TNFα through combined in silico/in vitro/in vivo screening

TNFα is a homotrimeric pro-inflammatory cytokine, whose direct targeting by protein biotherapies has been an undeniable success for the treatment of chronic inflammatory diseases. Despite many efforts, no orally active drug targeting TNFα has been identified so far. In the present work, we identified through combined in silico/in vitro/in vivo approaches a TNFα direct inhibitor, compound 1, displaying nanomolar and micromolar range bindings to TNFα. Compound 1 inhibits the binding of TNFα with both its receptors TNFRI and TNFRII. Compound 1 inhibits the TNFα induced apoptosis on L929 cells and the TNFα induced NF-κB activation in HEK cells. In vivo, oral administration of compound 1 displays a significant protection in a murine TNFα-dependent hepatic shock model. This work illustrates the ability of low-cost combined in silico/in vitro/in vivo screening approaches to identify orally available small-molecules targeting challenging protein-protein interactions such as homotrimeric TNFα.

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

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

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.

Rule of five in 2015 and beyond: Target and ligand structural limitations, ligand chemistry structure and drug discovery project decisions

The rule of five (Ro5), based on physicochemical profiles of phase II drugs, is consistent with structural limitations in protein targets and the drug target ligands. Three of four parameters in Ro5 are fundamental to the structure of both target and drug binding sites. The chemical structure of the drug ligand depends on the ligand chemistry and design philosophy. Two extremes of chemical structure and design philosophy exist; ligands constructed in the medicinal chemistry synthesis laboratory without input from natural selection and natural product (NP) metabolites biosynthesized based on evolutionary selection. Exceptions to Ro5 are found mostly among NPs. Chemistry chameleon-like behavior of some NPs due to intra-molecular hydrogen bonding as exemplified by cyclosporine A is a strong contributor to NP Ro5 outliers. The fragment derived, drug Navitoclax is an example of the extensive expertise, resources, time and key decisions required for the rare discovery of a non-NP Ro5 outlier.

Modulation of Protein-Protein Interactions for the Development of Novel Therapeutics

Protein-protein interactions (PPIs) underlie most biological processes. An increasing interest to investigate the unexplored potential of PPIs in drug discovery is driven by the need to find novel therapeutic targets for a whole range of diseases with a high unmet medical need. To date, PPI inhibition with small molecules is the mechanism that has most often been explored, resulting in significant progress towards drug development. However, also PPI stabilization is gradually gaining ground. In this review, we provide a focused overview of a number of PPIs that control critical regulatory pathways and constitute targets for the design of novel therapeutics. We discuss PPI-modulating small molecules that are already pursued in clinical trials. In addition, we review a number of PPIs that are still under preclinical investigation but for which preliminary data support their use as therapeutic targets.

Select Bcl-2 antagonism restores chemotherapy sensitivity in high-risk neuroblastoma

Background

Pediatric patients with high-risk neuroblastoma (HR NB) often fail to respond to upfront intensive multimodal therapy. Tumor-acquired suppression of apoptosis contributes to therapy resistance. Many HR NB tumors depend on the anti-apoptotic protein Bcl-2 for survival, through Bcl-2 sequestration and inhibition of the pro-apoptotic protein, Bim. Bcl-2 dependent xenografts derived from aggressive human NB tumors are cured with a combination of cyclophosphamide and ABT-737, a Bcl-2/Bcl-X_L/Bcl-w small molecule antagonist. The oral analogue to ABT-737, Navitoclax (ABT-263), clinically causes an immediate drop in peripheral platelet counts as mature platelets depend on Bcl-x_L for survival. This led to the creation of a Bcl-2 selective inhibitor, ABT-199 (Venetoclax). A Phase I trial of ABT-199 in CLL showed remarkable antitumor activity and stable patient platelet counts. Given Bcl-X_L does not play a role in HR NB survival, we hypothesized that ABT-199 would be equally potent against HR NB.

Methods

Cytotoxicity and apoptosis were measured in human derived NB cell lines exposed to ABT-199 combinations. Co-Immunoprecipitation evaluated Bim displacement from Bcl-2, following ABT-199. Murine xenografts of NB cell lines were grown and then exposed to a 14-day course of ABT-199 alone and with cyclophosphamide.

Results

Bcl-2 dependent NB cell lines are exquisitely sensitive to ABT-199 (IC₅₀ 1.5–5 nM) in vitro, where Mcl-1 dependent NBs are completely resistant. Treatment with ABT-199 displaces Bim from Bcl-2 in NB to activate caspase 3, confirming the restoration of mitochondrial apoptosis. Murine xenografts of Mcl-1 and Bcl-2 dependent NBs were treated with a two-week course of ABT-199, cyclophosphamide, or ABT-199/cyclophosphamide combination. Mcl-1 dependent tumors did not respond to ABT-199 alone and showed no significant difference in time to tumor progression between chemotherapy alone or ABT-199/cyclophosphamide combination. In contrast, Bcl-2 dependent xenografts responded to ABT-199 alone and had sustained complete remission (CR) to the ABT-199/cyclophosphamide combination, with one recurrent tumor maintaining Bcl-2 dependence and obtaining a second CR after a second course of therapy.

Conclusion

HR NB patients are often thrombocytopenic at relapse, raising concerns for therapies like ABT-263 despite its HR NB tumor targeting potential. Our data confirms that Bcl-2 selective inhibitors like ABT-199 are equally potent in HR NB in vitro and in vivo and given their lack of platelet toxicity, should be translated into the clinic for HR NB.

Targeting BCL2 with Venetoclax in Relapsed Chronic Lymphocytic Leukemia

BACKGROUND

New treatments have improved outcomes for patients with relapsed chronic lymphocytic leukemia (CLL), but complete remissions remain uncommon. Venetoclax has a distinct mechanism of action; it targets BCL2, a protein central to the survival of CLL cells.

METHODS

We conducted a phase 1 dose-escalation study of daily oral venetoclax in patients with relapsed or refractory CLL or small lymphocytic lymphoma (SLL) to assess safety, pharmacokinetic profile, and efficacy. In the dose-escalation phase, 56 patients received active treatment in one of eight dose groups that ranged from 150 to 1200 mg per day. In an expansion cohort, 60 additional patients were treated with a weekly stepwise ramp-up in doses as high as 400 mg per day.

RESULTS

The majority of the study patients had received multiple previous treatments, and 89% had poor prognostic clinical or genetic features. Venetoclax was active at all dose levels. Clinical tumor lysis syndrome occurred in 3 of 56 patients in the dose-escalation cohort, with one death. After adjustments to the dose-escalation schedule, clinical tumor lysis syndrome did not occur in any of the 60 patients in the expansion cohort. Other toxic effects included mild diarrhea (in 52% of the patients), upper respiratory tract infection (in 48%), nausea (in 47%), and grade 3 or 4 neutropenia (in 41%). A maximum tolerated dose was not identified. Among the 116 patients who received venetoclax, 92 (79%) had a response. Response rates ranged from 71 to 79% among patients in subgroups with an adverse prognosis, including those with resistance to fludarabine, those with chromosome 17p deletions (deletion 17p CLL), and those with unmutated IGHV. Complete remissions occurred in 20% of the patients, including 5% who had no minimal residual disease on flow cytometry. The 15-month progression-free survival estimate for the 400-mg dose groups was 69%.

CONCLUSIONS

Selective targeting of BCL2 with venetoclax had a manageable safety profile and induced substantial responses in patients with relapsed CLL or SLL, including those with poor prognostic features. (Funded by AbbVie and Genentech; ClinicalTrials.gov number, NCT01328626.).