Structure-Based Discovery of 4-(6-Methoxy-2-methyl-4-(quinolin-4-yl)-9H-pyrimido[4,5-b]indol-7-yl)-3,5-dimethylisoxazole (CD161) as a Potent and Orally Bioavailable BET Bromodomain Inhibitor

Targeting hematological malignancies with isoxazole derivatives

Compounds with a heterocyclic isoxazole ring are well known for their diverse biologic activities encompassing antimicrobial, antipsychotic, immunosuppressive, antidiabetic and anticancer effects. Recent studies on hematological malignancies have also shown that some of the isoxazole-derived compounds feature encouraging cancer selectivity, low toxicity to normal cells and ability to overcome cancer drug resistance of conventional treatments. These characteristics are particularly promising because patients with hematological malignancies face poor clinical outcomes caused by cancer drug resistance or relapse of the disease. This review summarizes the knowledge on isoxazole-derived compounds toward hematological malignancies and provides clues on their mechanism(s) of action (apoptosis, cell cycle arrest, ROS production) and putative pharmacological targets (c-Myc, BET, ATR, FLT3, HSP90, CARM1, tubulin, PD-1/PD-L1, HDACs) wherever known.

Discovery of (R)-4-(8-methoxy-2-methyl-1-(1-phenylethy)-1H-imidazo[4,5-c]quinnolin-7-yl)-3,5-dimethylisoxazole as a potent and selective BET inhibitor for treatment of acute myeloid leukemia (AML) guided by FEP calculation

The functions of the bromodomain and extra terminal (BET) family of proteins have been proved to be involved in various diseases, particularly the acute myeloid leukemia (AML). In this work, guided by free energy perturbation (FEP) calculation, a methyl group was selected to be attached to the 1H-imidazo[4,5-c]quinoline skeleton, and a series of congeneric compounds were synthesized. Among them, compound 10 demonstrated outstanding activity against BRD4 BD1 with an IC50 value of 1.9 nM and exhibited remarkable antiproliferative effects against MV4-11 cells. The X-ray cocrystal structure proved that 10 occupied the acetylated lysine (KAc) binding cavity and the WPF shelf of BRD4 BD1. Additionally, 10 displayed high selectivity towards BET family members, effectively inhibiting the growth of AML cells, promoting apoptosis, and arresting the cell cycle at the G0/G1 phase. Further mechanistic studies demonstrated that compound 10 could suppress the expression of c-Myc and CDK6 while enhancing the expression of P21, PARP, and cleaved PARP. Moreover, 10 exhibited remarkable pharmacokinetic properties and significant antitumor efficacy in vivo. Therefore, compound 10 may represent a new, potent and selective BET bromodomain inhibitor for the development of therapeutics to treat AML.

Cell-based Relay Delivery Strategy in Biomedical Applications

The relay delivery strategy is a two-step targeting approach based on two distinct modules in which the first step with an initiator is to artificially create a target/environment which can be targeted by the follow-up effector. This relay delivery concept creates opportunities to amplify existing or create new targeted signals through deploying initiators to enhance the accumulation efficiency of the following effector at the disease site. As the "live" medicines, cell-based therapeutics possess inherent tissue/cell homing abilities and favorable feasibility of biological and chemical modifications, endowing them the great potential in specifically interacting with diverse biological environments. All these unique capabilities make cellular products great candidates that can serve as either initiators or effectors for relay delivery strategies. In this review, we survey recent advances in relay delivery strategies with a specific focus on the roles of various cells in developing relay delivery systems.

Targeting bromodomain-containing proteins: research advances of drug discovery

Bromodomain (BD) is an evolutionarily conserved protein module found in 46 different BD-containing proteins (BCPs). BD acts as a specific reader for acetylated lysine residues (KAc) and serves an essential role in transcriptional regulation, chromatin remodeling, DNA damage repair, and cell proliferation. On the other hand, BCPs have been shown to be involved in the pathogenesis of a variety of diseases, including cancers, inflammation, cardiovascular diseases, and viral infections. Over the past decade, researchers have brought new therapeutic strategies to relevant diseases by inhibiting the activity or downregulating the expression of BCPs to interfere with the transcription of pathogenic genes. An increasing number of potent inhibitors and degraders of BCPs have been developed, some of which are already in clinical trials. In this paper, we provide a comprehensive review of recent advances in the study of drugs that inhibit or down-regulate BCPs, focusing on the development history, molecular structure, biological activity, interaction with BCPs and therapeutic potentials of these drugs. In addition, we discuss current challenges, issues to be addressed and future research directions for the development of BCPs inhibitors. Lessons learned from the successful or unsuccessful development experiences of these inhibitors or degraders will facilitate the further development of efficient, selective and less toxic inhibitors of BCPs and eventually achieve drug application in the clinic.

Selective degradation of cellular BRD3 and BRD4-L promoted by PROTAC molecules in six cancer cell lines

Targeted degradation of BET family proteins BRD2/3/4 or only BRD4 with PROTAC molecules has been a promising strategy for the treatment of human cancer. Meanwhile, selective degradation of cellular BRD3 and BRD4-L remains a challenging task. We report herein a novel PROTAC molecule 24 that promoted selective degradation of cellular BRD3 and BRD4-L, but not BRD2 or BRD4-S, in a panel of six cancer cell lines. The observed target selectivity was partially attributed to differences in protein degradation kinetics and in types of cell lines. In a MM.1S mouse xenograft model, an optimized lead compound 28 promoted selective degradation of BRD3 and BRD4-L in vivo and exhibited robust antitumor activity. In summary, we have demonstrated that selective degradation of BRD3 and BRD4-L over BRD2 and BRD4-S is a feasible and robust approach in multiple cancer cell lines and an animal model, which could be helpful for further investigations on BRD3 and BRD4-L that ultimately benefitting cancer research and therapeutics.

BET-HDAC Dual Inhibitors for Combinational Treatment of Breast Cancer and Concurrent Candidiasis

Breast cancer is susceptible to Candida infections, and candidiasis has an enhancing effect on the progression and metastasis of tumor. Breast cancer and concurrent candidiasis represent a significant challenge in clinical therapy. Herein, a series of novel small molecule inhibitors simultaneously targeting bromodomain and extra-terminal (BET) and histone deacetylase (HDAC) were designed for combinational treatment of breast cancer and resistant Candida albicans infections. Among them, compounds 13c and 17b exhibited excellent and balanced inhibitory activity against both BET family proteins BRD4 and HDAC1. As compared with BRD4 or HDAC1 inhibitors, dual inhibitors 13c and 17b displayed improved in vivo antitumor efficacy in MDA-MB-231 breast cancer xenograft models. Notably, they synergized with fluconazole (FLC) to effectively reduce the kidney fungal burden in a murine model of disseminated candidiasis. Thus, the BET-HDAC dual inhibitors represented a novel therapeutic strategy for combinational treatment of breast cancer and concurrent candidiasis.

Design, synthesis and pharmacological characterization of N-(3-ethylbenzo[d]isoxazol-5-yl) sulfonamide derivatives as BRD4 inhibitors against acute myeloid leukemia

BRD4 plays a key role in the regulation of gene transcription and has been identified as an attractive target for cancer treatment. In this study, we designed 26 new compounds by modifying 3-ethyl-benzo[d]isoxazole core with sulfonamides. Most compounds exhibited potent BRD4 binding activities with ΔTm values exceeding 6 °C. Two crystal structures of 11h and 11r in complex with BRD4(1) were obtained to characterize the binding patterns. Compounds 11h and 11r were effective for BRD4(1) binding and showed remarkable anti-proliferative activity against MV4-11 cells with IC50 values of 0.78 and 0.87 μM. Furthermore, 11r (0.5-10 μM) concentration-dependently inhibited the expression levels of oncogenes including c-Myc and CDK6 in MV4-11 cells. Moreover, 11r (0.5-10 μM) concentration-dependently blocked cell cycle in MV4-11 cells at G0/G1 phase and induced cell apoptosis. Compound 11r may serve as a new lead compound for further drug development.

Mechanistic Analysis of Chemically Diverse Bromodomain-4 Inhibitors Using Balanced QSAR Analysis and Supported by X-ray Resolved Crystal Structures

Bromodomain-4 (BRD-4) is a key enzyme in post-translational modifications, transcriptional activation, and many other cellular processes. Its inhibitors find their therapeutic usage in cancer, acute heart failure, and inflammation to name a few. In the present study, a dataset of 980 molecules with a significant diversity of structural scaffolds and composition was selected to develop a balanced QSAR model possessing high predictive capability and mechanistic interpretation. The model was built as per the OECD (Organisation for Economic Co-operation and Development) guidelines and fulfills the endorsed threshold values for different validation parameters (R²_tr = 0.76, Q²_LMO = 0.76, and R²_ex = 0.76). The present QSAR analysis identified that anti-BRD-4 activity is associated with structural characters such as the presence of saturated carbocyclic rings, the occurrence of carbon atoms near the center of mass of a molecule, and a specific combination of planer or aromatic nitrogen with ring carbon, donor, and acceptor atoms. The outcomes of the present analysis are also supported by X-ray-resolved crystal structures of compounds with BRD-4. Thus, the QSAR model effectively captured salient as well as unreported hidden pharmacophoric features. Therefore, the present study successfully identified valuable novel pharmacophoric features, which could be beneficial for the future optimization of lead/hit compounds for anti-BRD-4 activity.

Probing GPCR Dimerization Using Peptides

G protein-coupled receptors (GPCRs) are the largest class of membrane proteins and the most common and extensively studied pharmacological target. Numerous studies over the last decade have confirmed that GPCRs do not only exist and function in their monomeric form but in fact, have the ability to form dimers or higher order oligomers with other GPCRs, as well as other classes of receptors. GPCR oligomers have become increasingly attractive to investigate as they have the ability to modulate the pharmacological responses of the receptors which in turn, could have important functional roles in diseases, such as cancer and several neurological & neuropsychiatric disorders. Despite the growing evidence in the field of GPCR oligomerisation, the lack of structural information, as well as targeting the 'undruggable' protein-protein interactions (PPIs) involved in these complexes, has presented difficulties. Outside the field of GPCRs, targeting PPIs has been widely studied, with a variety of techniques being investigated; from small-molecule inhibitors to disrupting peptides. In this review, we will demonstrate several physiologically relevant GPCR dimers and discuss an array of strategies and techniques that can be employed when targeting these complexes, as well as provide ideas for future development.

Bioactivation of Isoxazole-Containing Bromodomain and Extra-Terminal Domain (BET) Inhibitors

The 3,5-dimethylisoxazole motif has become a useful and popular acetyl-lysine mimic employed in isoxazole-containing bromodomain and extra-terminal (BET) inhibitors but may introduce the potential for bioactivations into toxic reactive metabolites. As a test, we coupled deep neural models for quinone formation, metabolite structures, and biomolecule reactivity to predict bioactivation pathways for 32 BET inhibitors and validate the bioactivation of select inhibitors experimentally. Based on model predictions, inhibitors were more likely to undergo bioactivation than reported non-bioactivated molecules containing isoxazoles. The model outputs varied with substituents indicating the ability to scale their impact on bioactivation. We selected OXFBD02, OXFBD04, and I-BET151 for more in-depth analysis. OXFBD’s bioactivations were evenly split between traditional quinones and novel extended quinone-methides involving the isoxazole yet strongly favored the latter quinones. Subsequent experimental studies confirmed the formation of both types of quinones for OXFBD molecules, yet traditional quinones were the dominant reactive metabolites. Modeled I-BET151 bioactivations led to extended quinone-methides, which were not verified experimentally. The differences in observed and predicted bioactivations reflected the need to improve overall bioactivation scaling. Nevertheless, our coupled modeling approach predicted BET inhibitor bioactivations including novel extended quinone methides, and we experimentally verified those pathways highlighting potential concerns for toxicity in the development of these new drug leads.

Design, synthesis and biological evaluation of imidazolopyridone derivatives as novel BRD4 inhibitors

Bromodomain containing protein 4 (BRD4) has been demonstrated to play critical roles in cellular proliferation and cell cycle progression. In this study, using the BRD4 inhibitor Fragment 9 as a lead compound, a series of imidazolopyridone derivatives were designed and tested for their inhibitory activity against BRD4 protein in vitro. Among them, HB100-A7 showed excellent BRD4(1) inhibitory activities with an IC₅₀ value of 0.035 μM in amplified luminescent proximity homogeneous assay (Alphascreen). The result of MTT assay showed that HB100-A7 could suppress the proliferation of pancreatic cancer cells. In addition, flow cytometry further illustrated that HB100-A7 treatment resulted in G0/G1 phase arrest and promoted apoptosis of BxPc3 cells. Furthermore, the in vivo study found that HB100-A7 displayed significant tumor growth inhibition in a pancreatic mouse tumor model (Panc-02). Moreover, IHC staining suggested that HB100-A7 induce cell apoptosis in pancreatic cancer tumor tissue. Together, this study revealed, for the first time, HB100-A7 is a promising lead compound for further development as a new generation of small molecule inhibitors targeting the BRD4 protein.

Pyrido-Fused Deazapurine Bases: Synthesis and Glycosylation of 4-Substituted 9H-Pyrido[2',3':4,5]- and Pyrido[4',3':4,5]pyrrolo[2,3-d]pyrimidines

Two isomeric sets of 4-substituted pyridopyrrolopyrimidine nucleobases were prepared through nucleophilic substitutions or cross-coupling reactions of 4-chloropyridopyrrolopyrimidines. The corresponding 4-amino-pyridopyrrolopyrimidines were glycosylated with 5-O-tritylribose using the modified Mitsunobu protocol. Several examples of the title heterocycles showed blue or green fluorescence. Testing of the pyridopyrrolopyrimidine nucleobases for the cytotoxic effect revealed micromolar activity of 4-benzofuryl derivatives in both series, preferentially in multidrug-resistant cancers.

Current advances on the development of BET inhibitors: insights from computational methods

Epigenetics was coined almost 70 years ago for the description of heritable phenotype without altering DNA sequences. Research on the field has uncovered significant roles of such mechanisms, that account for the biogenesis of several diseases. Further studies have led the way for drug development which targets epi-enzymes, mainly for cancer treatment. Of the numerous epi-targets involved with histone acetylation, bromodomains have captured the spotlight of drug discovery focused on novel therapies. However, due to high sequence identity, the development of potent and selective inhibitors poses a significant challenge. Herein, we discuss recent computational developments on BET inhibitors and other methods that may be applied for drug discovery in general. As a proof-of-concept, we discuss a virtual screening to identify novel BET inhibitors based on coumarin derivatives. From public data, we identified putative structure-activity relationships of coumarin scaffold and propose R-group modifications for BET selectivity. Results showed that the optimization and design of novel coumarins could be further explored.

Rational Design and Evaluation of 6-(Pyrimidin-2-ylamino)-3,4-dihydroquinoxalin-2(1H)-ones as Polypharmacological Inhibitors of BET and Kinases

Cancer exhibits diverse heterogeneity with a complicated molecular basis that usually harbors genetic and epigenetic abnormality, which poses a big challenge for single-target agents. In the current work, we proposed a hybrid strategy by incorporating pharmacophores that bind to the acetylated lysine binding pocket of BET proteins with a typical kinase hinge binder to generate novel polypharmacological inhibitors of BET and kinases. Through elaborating the core structure of 6-(pyrimidin-2-ylamino)-3,4-dihydroquinoxalin-2(1H)-one, we demonstrated that this rational design can produce high potent inhibitors of CDK9 and BET proteins. In this series, compound 40 was identified as the potential lead compound with balanced activities of BRD4 (IC₅₀ = 12.7 nM) and CDK9 (IC₅₀ = 22.4 nM), as well as good antiproliferative activities on a small cancer cell panel. Together, the current study provided a new method for the discovery of bromodomain and kinase dual inhibitors rather than only being discovered by serendipity.

Design, Synthesis and Biological Evaluation of 7-Chloro-9H-pyrimido[4,5-b]indole-based Glycogen Synthase Kinase-3β Inhibitors

Glycogen synthase kinase-3β (GSK-3β) represents a relevant drug target for the treatment of neurodegenerative pathologies including Alzheimer's disease. We herein report on the optimization of a novel class of GSK-3β inhibitors based on the tofacitinib-derived screen hit 3-((3R,4R)-3-((7-chloro-9H-pyrimido[4,5-b]indol-4-yl)(methyl)amino)-4-methylpiperidin-1-yl)-3-oxopropanenitrile (1). We synthesized a series of 19 novel 7-chloro-9H-pyrimido[4,5-b]indole-based derivatives and studied their structure-activity relationships with focus on the cyanoacetyl piperidine moiety. We unveiled the crucial role of the nitrile group and its importance for the activity of this compound series. A successful rigidization approach afforded 3-(3aRS,7aSR)-(1-(7-chloro-9H-pyrimido[4,5-b]indol-4-yl)octahydro-6H-pyrrolo[2,3-c]pyridin-6-yl)-propanenitrile (24), which displayed an IC₅₀ value of 130 nM on GSK-3β and was further characterized by its metabolic stability. Finally, we disclosed the putative binding modes of the most potent inhibitors within the ATP binding site of GSK-3β by 1 µs molecular dynamics simulations.

Synthesis and Biological Evaluation of NH2-Sulfonyl Oseltamivir Analogues as Influenza Neuraminidase Inhibitors

A series of NH₂-sulfonyl oseltamivir analogues were designed, synthesized, and their inhibitory activities against neuraminidase from H5N1 subtype evaluated. The results indicated that the IC₅₀ value of compound 4a, an oseltamivir analogue via methyl sulfonylation of C5-NH₂, was 3.50 μM. Molecular docking simulations suggested that 4a retained most of the interactions formed by oseltamivir carboxylate moieties and formed an additional hydrogen bond with the methylsulfonyl group. Meanwhile, 4a showed high stability towards human liver microsomes. More importantly, 4a without basic moieties is not a zwitterion as reported on the general structure of neuraminidase inhibitors. This research will provide valuable reference for the research of new types of neuraminidase inhibitors.

Small-molecule PROTAC degraders of the Bromodomain and Extra Terminal (BET) proteins - A review

The PROteolysis TArgeting Chimeric (PROTAC) concept has provided an opportunity for the discovery and development of a completely new type of therapy involving induction of protein degradation. The BET proteins, comprised of BRD2, BRD3, BRD4 and the testis-specific BRDT protein, are epigenetic readers and master transcription coactivators. Extremely potent and efficacious small-molecule PROTAC degraders of the BET proteins, based on available, potent and selective BET inhibitors, have been reported. BET degraders differ from BET inhibitors in their cellular potency, phenotypic effects, pharmacokinetic properties and toxicity profiles. Herein, we provide a review of BET degraders and the differential outcome observed in the cellular and animal models for BET degraders in comparison to BET inhibitors.

Lead optimization and efficacy evaluation of quinazoline-based BET family inhibitors for potential treatment of cancer and inflammatory diseases

Extensive optimization of quinazoline-based lead 8 is described. The structure-activity relationship studies indicate the S-configuration is preferred for the phenylmorpholine substitution. Together with incorporation of a (2-hydroxyl-2-methylpropyl)pyrazole moiety at the 2-position leads to analogs with comparable potency and marked improvement in the pharmacokinetic profile over our previously reported lead compounds. Further in vivo efficacy studies in Kasumi-1 xenograft mouse model demonstrates that the selected inhibitors are well tolerated and highly efficacious in the inhibition of tumor growth. Additionally, the representative analog 19 also demonstrated significant improvement of arthritis severity in a collagen-induced arthritis (CIA) mouse model. These results indicate potential use of these quinazoline-based BET inhibitors for treatment of cancer and inflammatory diseases. A brief discussion of the co-crystallized structure of 19 with BRD4 (BD1) is also highlighted.

Discovery of QCA570 as an Exceptionally Potent and Efficacious Proteolysis Targeting Chimera (PROTAC) Degrader of the Bromodomain and Extra-Terminal (BET) Proteins Capable of Inducing Complete and Durable Tumor Regression

Proteins of the bromodomain and extra-terminal (BET) family are epigenetics "readers" and promising therapeutic targets for cancer and other human diseases. We describe herein a structure-guided design of [1,4]oxazepines as a new class of BET inhibitors and our subsequent design, synthesis, and evaluation of proteolysis-targeting chimeric (PROTAC) small-molecule BET degraders. Our efforts have led to the discovery of extremely potent BET degraders, exemplified by QCA570, which effectively induces degradation of BET proteins and inhibits cell growth in human acute leukemia cell lines even at low picomolar concentrations. QCA570 achieves complete and durable tumor regression in leukemia xenograft models in mice at well-tolerated dose-schedules. QCA570 is the most potent and efficacious BET degrader reported to date.

Structure-Based Discovery of CF53 as a Potent and Orally Bioavailable Bromodomain and Extra-Terminal (BET) Bromodomain Inhibitor

We report the structure-based discovery of CF53 (28) as a highly potent and orally active inhibitor of bromodomain and extra-terminal (BET) proteins. By the incorporation of a NH-pyrazole group into the 9H-pyrimido[4,5- b]indole core, we identified a series of compounds that bind to BRD4 BD1 protein with K_i values of <1 nM and achieve low nanomolar potencies in the cell growth inhibition of leukemia and breast cancer cells. The most-promising compound, CF53, possesses excellent oral pharmacokinetic properties and achieves significant antitumor activity in both triple-negative breast cancer and acute leukemia xenograft models in mice. Determination of the co-crystal structure of CF53 with the BRD4 BD1 protein provides a structural basis for its high binding affinity to BET proteins. CF53 is very selective over non-BET bromodomain-containing proteins. These data establish CF53 as a potent, selective, and orally active BET inhibitor, which warrants further evaluation for advanced preclinical development.

BET bromodomain ligands: Probing the WPF shelf to improve BRD4 bromodomain affinity and metabolic stability

Ligands for the bromodomain and extra-terminal domain (BET) family of bromodomains have shown promise as useful therapeutic agents for treating a range of cancers and inflammation. Here we report that our previously developed 3,5-dimethylisoxazole-based BET bromodomain ligand (OXFBD02) inhibits interactions of BRD4(1) with the RelA subunit of NF-κB, in addition to histone H4. This ligand shows a promising profile in a screen of the NCI-60 panel but was rapidly metabolised (t½ = 39.8 min). Structure-guided optimisation of compound properties led to the development of the 3-pyridyl-derived OXFBD04. Molecular dynamics simulations assisted our understanding of the role played by an internal hydrogen bond in altering the affinity of this series of molecules for BRD4(1). OXFBD04 shows improved BRD4(1) affinity (IC50 = 166 nM), optimised physicochemical properties (LE = 0.43; LLE = 5.74; SFI = 5.96), and greater metabolic stability (t½ = 388 min).

Inhibitors of protein-protein interactions (PPIs): an analysis of scaffold choices and buried surface area

Protein-protein interactions (PPI) were once considered 'undruggable', but clinical successes, driven by advanced methods in drug discovery, have challenged that notion. Here, we review the last three years of literature on PPI inhibitors to understand what is working and why. From the 66 recently reported PPI inhibitors, we found that the average molecular weight was significantly greater than 500Da, but that this trend was driven, in large part, by the contribution of peptide-based compounds. Despite differences in average molecular weight, we found that compounds based on small molecules or peptides were almost equally likely to be potent inhibitors (K_D<1μM). Finally, we found PPIs with buried surface area (BSA) less than 2000Ų were more likely to be inhibited by small molecules, while PPIs with larger BSA values were typically inhibited by peptides. PPIs with BSA values over 4000Ų seemed to create a particular challenge, especially for orthosteric small molecules. Thus, it seems important to choose the inhibitor scaffold based on the properties of the target interaction. Moreover, this survey suggests a (more nuanced) conclusion to the question of whether PPIs are good drug targets; namely, that some PPIs are readily 'druggable' given the right choice of scaffold, while others still seem to deserve the 'undruggable' moniker.

Chemoprevention of Preclinical Breast and Lung Cancer with the Bromodomain Inhibitor I-BET 762

Breast cancer and lung cancer remain the top two leading causes of cancer-related deaths in women. Because of limited success in reducing the high mortality of these diseases, new drugs and approaches are desperately needed. Cancer prevention is one such promising strategy that is effective in both preclinical and clinical studies. I-BET 762 is a new bromodomain inhibitor that reversibly targets BET (bromodomain and extraterminal) proteins and impairs their ability to bind to acetylated lysines on histones, thus interrupting downstream transcription. This inhibitor has anti-inflammatory effects and induces growth arrest in many cancers and is currently under clinical trials for treatment of cancer. However, few studies have investigated the chemopreventive effects of bromodomain inhibitors. Here, we found that I-BET 762 significantly delayed tumor development in preclinical breast and lung cancer mouse models. This drug not only induced growth arrest and downregulated c-Myc, pSTAT3, and pERK protein expression in tumor cells in vitro and in vivo but also altered immune populations in different organs. These results demonstrate the promising potential of using I-BET 762 for cancer prevention and suggest the striking effects of I-BET 762 are the result of targeting both tumor cells and the tumor microenvironment. Cancer Prev Res; 11(3); 143-56. ©2017 AACR.