A credit-card library approach for disrupting protein-protein interactions

MYC the oncogene from hell: Novel opportunities for cancer therapy

Cancer comprises a heterogeneous disease, characterized by diverse features such as constitutive expression of oncogenes and/or downregulation of tumor suppressor genes. MYC constitutes a master transcriptional regulator, involved in many cellular functions and is aberrantly expressed in more than 70 % of human cancers. The Myc protein belongs to a family of transcription factors whose structural pattern is referred to as basic helix-loop-helix-leucine zipper. Myc binds to its partner, a smaller protein called Max, forming an Myc:Max heterodimeric complex that interacts with specific DNA recognition sequences (E-boxes) and regulates the expression of downstream target genes. Myc protein plays a fundamental role for the life of a cell, as it is involved in many physiological functions such as proliferation, growth and development since it controls the expression of a very large percentage of genes (∼15 %). However, despite the strict control of MYC expression in normal cells, MYC is often deregulated in cancer, exhibiting a key role in stimulating oncogenic process affecting features such as aberrant proliferation, differentiation, angiogenesis, genomic instability and oncogenic transformation. In this review we aim to meticulously describe the fundamental role of MYC in tumorigenesis and highlight its importance as an anticancer drug target. We focus mainly on the different categories of novel small molecules that act as inhibitors of Myc function in diverse ways hence offering great opportunities for an efficient cancer therapy. This knowledge will provide significant information for the development of novel Myc inhibitors and assist to the design of treatments that would effectively act against Myc-dependent cancers.

Identification of hub genes and their correlation with infiltration of immune cells in MYCN positive neuroblastoma based on WGCNA and LASSO algorithm

Background

The prognosis of MYCN positive NB is poor, and there is no targeted drug for N-myc at present. This study aims to screen out hub genes closely related to MYCN, analyze the relationship between hub genes and NB microenvironment, and provide basis for molecular targeted therapy of MYCN positive NB.

Methods

We combined the microarray data of GSE45547 (n=649) and GSE49710 (n=498), screened the DEGs between MYCN positive (n=185) and MYCN negative NB (n=951), performed WGCNA, Lasso regression and Roc analyses on the merged matrix, and obtained the hub genes related to MYCN in the training group. We performed ssGSEA on the experimental group to calculate the infiltration level of 28 kinds of immune cells in each sample, compared the differences of immune cell infiltration between MYCN positive and MYCN negative group. The influences of hub genes on the distribution of each immune cell were also analyzed by ssGSEA. The expression differences of the three hub genes were verified in the E-MTAB-8248 cohort (n=223), and the correlation between hub genes and prognosis of NB was calculated by Kaplan-Meier method in GSE62564 (n=498) and the validation group. We also verified the expression differences of hub genes by qRT-PCR in SK-N-BE(2), SKNDZ, Kelly and SH-SY5Y cell lines.

Results

Here were 880 DEGs including 420 upregulated and 460 downregulated genes in MYCN positive NB in the training group. Overlap of the DEGs and WGCNA networks identified four shared genes, namely, ZNF695, CHEK1, C15ORF42 and EXO1, as candidate hub genes in MYCN positive NB. Three core genes, ZNF695, CHEK1 and C15ORF42, were finally identified by Lasso regression and Roc analyses. ZNF695, CHEK1 and C15ORF42 were highly expressed in MYCN positive NB tissues and cell lines. These three genes were closely related to the prognosis of children with NB. Except that Activated CD4 T cell and Type2 T helper cell increased, the infiltration levels of the other 26 cells decreased significantly in MYCN positive NB tissues. The infiltration levels of Type2 T helper cell and Activated CD4 T cell were also significantly positively correlated with the expression levels of the three hub genes.

Conclusion

ZNF695, CHEK1 and C15ORF42 are highly expressed in MYCN positive NB, and their expression levels are negatively correlated with the prognosis of children with NB. The infiltration levels of Activated CD4 T cell and Type2 T helper cell increased in the microenvironment of MYCN positive NB and were significantly positively correlated with the expression levels of the three hub genes. The results of this study provide that ZNF695, CHEK1 and C15ORF42 may be potential prognostic markers and immunotherapy targets for MYCN positive NB.

A Small Molecule Stabilizes the Disordered Native State of the Alzheimer's Aβ Peptide

The stabilization of native states of proteins is a powerful drug discovery strategy. It is still unclear, however, whether this approach can be applied to intrinsically disordered proteins. Here, we report a small molecule that stabilizes the native state of the Aβ42 peptide, an intrinsically disordered protein fragment associated with Alzheimer's disease. We show that this stabilization takes place by a disordered binding mechanism, in which both the small molecule and the Aβ42 peptide remain disordered. This disordered binding mechanism involves enthalpically favorable local π-stacking interactions coupled with entropically advantageous global effects. These results indicate that small molecules can stabilize disordered proteins in their native states through transient non-specific interactions that provide enthalpic gain while simultaneously increasing the conformational entropy of the proteins.

Selective targeting of MYC mRNA by stabilized antisense oligonucleotides

MYC is a prolific proto-oncogene driving the malignant behaviors of numerous common cancers, yet potent and selective cell-permeable inhibitors of MYC remain elusive. In order to ultimately realize the goal of therapeutic MYC inhibition in cancer, we have initiated discovery chemistry efforts aimed at inhibiting MYC translation. Here we describe a series of conformationally stabilized synthetic antisense oligonucleotides designed to target MYC mRNA (MYCASOs). To support bioactivity, we designed and synthesized this focused library of MYCASOs incorporating locked nucleic acid (LNA) bases at the 5'- and 3'-ends, a phosphorothioate backbone, and internal DNA bases. Treatment of MYC-expressing cancer cells with MYCASOs leads to a potent decrease in MYC mRNA and protein levels. Cleaved MYC mRNA in MYCASO-treated cells is detected with a sensitive 5' Rapid Amplification of cDNA Ends (RACE) assay. MYCASO treatment of cancer cell lines leads to significant inhibition of cellular proliferation while specifically perturbing MYC-driven gene expression signatures. In a MYC-induced model of hepatocellular carcinoma, MYCASO treatment decreases MYC protein levels within tumors, decreases tumor burden, and improves overall survival. MYCASOs represent a new chemical tool for in vitro and in vivo modulation of MYC activity, and promising therapeutic agents for MYC-addicted tumors.

MYC: a multipurpose oncogene with prognostic and therapeutic implications in blood malignancies

MYC oncogene is a transcription factor with a wide array of functions affecting cellular activities such as cell cycle, apoptosis, DNA damage response, and hematopoiesis. Due to the multi-functionality of MYC, its expression is regulated at multiple levels. Deregulation of this oncogene can give rise to a variety of cancers. In this review, MYC regulation and the mechanisms by which MYC adjusts cellular functions and its implication in hematologic malignancies are summarized. Further, we also discuss potential inhibitors of MYC that could be beneficial for treating hematologic malignancies.

Inhibition of the ALDH18A1-MYCN positive feedback loop attenuates MYCN-amplified neuroblastoma growth

MYCN-amplified neuroblastoma (NB) is characterized by poor prognosis, and directly targeting MYCN has proven challenging. Here, we showed that aldehyde dehydrogenase family 18 member A1 (ALDH18A1) exerts profound impacts on the proliferation, self-renewal, and tumorigenicity of NB cells and is a potential risk factor in patients with NB, especially those with MYCN amplification. Mechanistic studies revealed that ALDH18A1 could both transcriptionally and posttranscriptionally regulate MYCN expression, with MYCN reciprocally transactivating ALDH18A1 and thus forming a positive feedback loop. Using molecular docking and screening, we identified an ALDH18A1-specific inhibitor, YG1702, and demonstrated that pharmacological inhibition of ALDH18A1 was sufficient to induce a less proliferative phenotype and confer tumor regression and prolonged survival in NB xenograft models, providing therapeutic insights into the disruption of this reciprocal regulatory loop in MYCN-amplified NB.

Gene Transactivation and Transrepression in MYC-Driven Cancers

MYC is a proto-oncogene regulating a large number of genes involved in a plethora of cellular functions. Its deregulation results in activation of MYC gene expression and/or an increase in MYC protein stability. MYC overexpression is a hallmark of malignant growth, inducing self-renewal of stem cells and blocking senescence and cell differentiation. This review summarizes the latest advances in our understanding of MYC-mediated molecular mechanisms responsible for its oncogenic activity. Several recent findings indicate that MYC is a regulator of cancer genome and epigenome: MYC modulates expression of target genes in a site-specific manner, by recruiting chromatin remodeling co-factors at promoter regions, and at genome-wide level, by regulating the expression of several epigenetic modifiers that alter the entire chromatin structure. We also discuss novel emerging therapeutic strategies based on both direct modulation of MYC and its epigenetic cofactors.

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.

Taking the Myc out of cancer: toward therapeutic strategies to directly inhibit c-Myc

c-Myc is a transcription factor that is constitutively and aberrantly expressed in over 70% of human cancers. Its direct inhibition has been shown to trigger rapid tumor regression in mice with only mild and fully reversible side effects, suggesting this to be a viable therapeutic strategy. Here we reassess the challenges of directly targeting c-Myc, evaluate lessons learned from current inhibitors, and explore how future strategies such as miniaturisation of Omomyc and targeting E-box binding could facilitate translation of c-Myc inhibitors into the clinic.

Two decades of recent advances of Ugi reactions: synthetic and pharmaceutical applications

Multicomponent reactions (MCRs) are powerful synthetic tools in which more than two starting materials couple with each other to form multi-functionalized compounds in a one-pot process, the so-called "tandem", "domino" or "cascade" reaction, or utilizing an additional step without changing the solvent, the so-called a sequential-addition procedure, to limit the number of synthetic steps, while increasing the complexity and the molecular diversity, which are highly step-economical reactions. The Ugi reaction, one of the most common multicomponent reactions, has recently fascinated chemists with the high diversity brought by its four- or three-component-based isonitrile. The Ugi reaction has been introduced in organic synthesis as a novel, efficient and useful tool for the preparation of libraries of multifunctional peptides, natural products, and heterocyclic compounds with stereochemistry control. In this review, we highlight the recent advances of the Ugi reaction in the last two decades from 2000-2019, mainly in the synthesis of linear or cyclic peptides, heterocyclic compounds with versatile ring sizes, and natural products, as well as the enantioselective Ugi reactions. Meanwhile, the applications of these compounds in pharmaceutical trials are also discussed.

Selective antagonism of cJun for cancer therapy

The activator protein-1 (AP-1) family of transcription factors modulate a diverse range of cellular signalling pathways into outputs which can be oncogenic or anti-oncogenic. The transcription of relevant genes is controlled by the cellular context, and in particular by the dimeric composition of AP-1. Here, we describe the evidence linking cJun in particular to a range of cancers. This includes correlative studies of protein levels in patient tumour samples and mechanistic understanding of the role of cJun in cancer cell models. This develops an understanding of cJun as a focal point of cancer-altered signalling which has the potential for therapeutic antagonism. Significant work has produced a range of small molecules and peptides which have been summarised here and categorised according to the binding surface they target within the cJun-DNA complex. We highlight the importance of selectively targeting a single AP-1 family member to antagonise known oncogenic function and avoid antagonism of anti-oncogenic function.

Targeting intrinsically disordered proteins involved in cancer

Intrinsically disordered proteins (IDPs) do not have a well-defined structure under physiological conditions, but they have key roles in cell signaling and regulation, and they are frequently related to the development of diseases, such as cancer and other malignancies. This has converted IDPs in attractive therapeutic targets; however, targeting IDPs is challenging because of their dynamic nature. In the last years, different experimental and computational approaches, as well as the combination of both, have been explored to identify molecules to target either the hot-spots or the allosteric sites of IDPs. In this review, we summarize recent developments in successful targeting of IDPs, all of which are involved in different cancer types. The strategies used to develop and design (or in one particular example, to repurpose) small molecules targeting IDPs are, in a global sense, similar to those used in well-folded proteins: (1) screening of chemically diverse or target-oriented compound libraries; or (2) study of the interfaces involved in recognition of their natural partners, and design of molecular candidates capable of binding to such binding interface. We describe the outcomes of using these approaches in targeting IDPs involved in cancer, in the view to providing insight, to target IDPs in general. In a broad sense, the designed small molecules seem to target the most hydrophobic regions of the IDPs, hampering macromolecule (DNA or protein)-IDP interactions; furthermore, in most of the molecule-IDP complexes described so far, the protein remains disordered.

Structural and Biophysical Insights into the Function of the Intrinsically Disordered Myc Oncoprotein

Myc is a transcription factor driving growth and proliferation of cells and involved in the majority of human tumors. Despite a huge body of literature on this critical oncogene, our understanding of the exact molecular determinants and mechanisms that underlie its function is still surprisingly limited. Indubitably though, its crucial and non-redundant role in cancer biology makes it an attractive target. However, achieving successful clinical Myc inhibition has proven challenging so far, as this nuclear protein is an intrinsically disordered polypeptide devoid of any classical ligand binding pockets. Indeed, Myc only adopts a (partially) folded structure in some contexts and upon interacting with some protein partners, for instance when dimerizing with MAX to bind DNA. Here, we review the cumulative knowledge on Myc structure and biophysics and discuss the implications for its biological function and the development of improved Myc inhibitors. We focus this biophysical walkthrough mainly on the basic region helix-loop-helix leucine zipper motif (bHLHLZ), as it has been the principal target for inhibitory approaches so far.

Small-Molecule MYC Inhibitors Suppress Tumor Growth and Enhance Immunotherapy

Small molecules that directly target MYC and are also well tolerated in vivo will provide invaluable chemical probes and potential anti-cancer therapeutic agents. We developed a series of small-molecule MYC inhibitors that engage MYC inside cells, disrupt MYC/MAX dimers, and impair MYC-driven gene expression. The compounds enhance MYC phosphorylation on threonine-58, consequently increasing proteasome-mediated MYC degradation. The initial lead, MYC inhibitor 361 (MYCi361), suppressed in vivo tumor growth in mice, increased tumor immune cell infiltration, upregulated PD-L1 on tumors, and sensitized tumors to anti-PD1 immunotherapy. However, 361 demonstrated a narrow therapeutic index. An improved analog, MYCi975 showed better tolerability. These findings suggest the potential of small-molecule MYC inhibitors as chemical probes and possible anti-cancer therapeutic agents.

Mining a Kröhnke Pyridine Library for Anti-Arenavirus Activity

Several arenaviruses cause hemorrhagic fever (HF) disease in humans and represent important public health problems in their endemic regions. In addition, evidence indicates that the worldwide-distributed prototypic arenavirus lymphocytic choriomeningitis virus is a neglected human pathogen of clinical significance. There are no licensed arenavirus vaccines, and current antiarenavirus therapy is limited to an off-label use of ribavirin that is only partially effective. Therefore, there is an unmet need for novel therapeutics to combat human pathogenic arenaviruses, a task that will be facilitated by the identification of compounds with antiarenaviral activity that could serve as probes to identify arenavirus-host interactions suitable for targeting, as well as lead compounds to develop future antiarenaviral drugs. Screening of a combinatorial library of Krönhke pyridines identified compound KP-146 [(5-(5-(2,3-dihydrobenzo[ b][1,4] dioxin-6-yl)-4'-methoxy-[1,1'-biphenyl]-3-yl)thiophene-2-carboxamide] as having strong anti-lymphocytic choriomeningitis virus (LCMV) activity in cultured cells. KP-146 did not inhibit LCMV cell entry but rather interfered with the activity of the LCMV ribonucleoprotein (vRNP) responsible for directing virus RNA replication and gene transcription, as well as with the budding process mediated by the LCMV matrix Z protein. LCMV variants with increased resistance to KP-146 did not emerge after serial passages in the presence of KP-146. Our findings support the consideration of Kröhnke pyridine scaffold as a valuable source to identify compounds that could serve as tools to dissect arenavirus-host interactions, as well as lead candidate structures to develop antiarenaviral drugs.

Multiple spatially related pharmacophores define small molecule inhibitors of OLIG2 in glioblastoma

Transcription factors (TFs) are a major class of protein signaling molecules that play key cellular roles in cancers such as the highly lethal brain cancer—glioblastoma (GBM). However, the development of specific TF inhibitors has proved difficult owing to expansive protein-protein interfaces and the absence of hydrophobic pockets. We uniquely defined the dimerization surface as an expansive parental pharmacophore comprised of several regional daughter pharmacophores. We targeted the OLIG2 TF which is essential for GBM survival and growth, we hypothesized that small molecules able to fit each subpharmacophore would inhibit OLIG2 activation. The most active compound was OLIG2 selective, it entered the brain, and it exhibited potent anti-GBM activity in cell-based assays and in pre-clinical mouse orthotopic models. These data suggest that (1) our multiple pharmacophore approach warrants further investigation, and (2) our most potent compounds merit detailed pharmacodynamic, biophysical, and mechanistic characterization for potential preclinical development as GBM therapeutics.

Methods of probing the interactions between small molecules and disordered proteins

It is generally recognized that a large fraction of the human proteome is made up of proteins that remain disordered in their native states. Despite the fact that such proteins play key biological roles and are involved in many major human diseases, they still represent challenging targets for drug discovery. A major bottleneck for the identification of compounds capable of interacting with these proteins and modulating their disease-promoting behaviour is the development of effective techniques to probe such interactions. The difficulties in carrying out binding measurements have resulted in a poor understanding of the mechanisms underlying these interactions. In order to facilitate further methodological advances, here we review the most commonly used techniques to probe three types of interactions involving small molecules: (1) those that disrupt functional interactions between disordered proteins; (2) those that inhibit the aberrant aggregation of disordered proteins, and (3) those that lead to binding disordered proteins in their monomeric states. In discussing these techniques, we also point out directions for future developments.

Strategies to Inhibit Myc and Their Clinical Applicability

Myc is an oncogene deregulated in most-perhaps all-human cancers. Each Myc family member, c-, L-, and N-Myc, has been connected to tumor progression and maintenance. Myc is recognized as a "most wanted" target for cancer therapy, but has for many years been considered undruggable, mainly due to its nuclear localization, lack of a defined ligand binding site, and physiological function essential to the maintenance of normal tissues. The challenge of identifying a pharmacophore capable of overcoming these hurdles is reflected in the current absence of a clinically-viable Myc inhibitor. The first attempts to inhibit Myc used antisense technology some three decades ago, followed by small molecule inhibitors discovered through "classical" compound library screens. Notable breakthroughs proving the feasibility of systemic Myc inhibition were made with the Myc dominant negative mutant Omomyc, showing both the great promise in targeting this infamous oncogene for cancer treatment as well as allaying fears about the deleterious side effects that Myc inhibition might have on normal proliferating tissues. During this time many other strategies have appeared in an attempt to drug the undruggable, including direct and indirect targeting, knockdown, protein/protein and DNA interaction inhibitors, and translation and expression regulation. The inhibitors range from traditional small molecules to natural chemicals, to RNA and antisense, to peptides and miniproteins. Here, we briefly describe the many approaches taken so far, with a particular focus on their potential clinical applicability.

Perturbation of the c-Myc-Max protein-protein interaction via synthetic α-helix mimetics

The rational design of inhibitors of the bHLH-ZIP oncoprotein c-Myc is hampered by a lack of structure in its monomeric state. We describe herein the design of novel, low-molecular-weight, synthetic α-helix mimetics that recognize helical c-Myc in its transcriptionally active coiled-coil structure in association with its obligate bHLH-ZIP partner Max. These compounds perturb the heterodimer's binding to its canonical E-box DNA sequence without causing protein-protein dissociation, heralding a new mechanistic class of "direct" c-Myc inhibitors. In addition to electrophoretic mobility shift assays, this model was corroborated by further biophysical methods, including NMR spectroscopy and surface plasmon resonance. Several compounds demonstrated a 2-fold or greater selectivity for c-Myc-Max heterodimers over Max-Max homodimers with IC50 values as low as 5.6 μM. Finally, these compounds inhibited the proliferation of c-Myc-expressing cell lines in a concentration-dependent manner that correlated with the loss of expression of a c-Myc-dependent reporter plasmid despite the fact that c-Myc-Max heterodimers remained intact.

Identification of inhibitors of biological interactions involving intrinsically disordered proteins

Protein-protein interactions involving disordered partners have unique features and represent prominent targets in drug discovery processes. Intrinsically Disordered Proteins (IDPs) are involved in cellular regulation, signaling and control: they bind to multiple partners and these high-specificity/low-affinity interactions play crucial roles in many human diseases. Disordered regions, terminal tails and flexible linkers are particularly abundant in DNA-binding proteins and play crucial roles in the affinity and specificity of DNA recognizing processes. Protein complexes involving IDPs are short-lived and typically involve short amino acid stretches bearing few "hot spots", thus the identification of molecules able to modulate them can produce important lead compounds: in this scenario peptides and/or peptidomimetics, deriving from structure-based, combinatorial or protein dissection approaches, can play a key role as hit compounds. Here, we propose a panoramic review of the structural features of IDPs and how they regulate molecular recognition mechanisms focusing attention on recently reported drug-design strategies in the field of IDPs.

Therapeutic strategies to inhibit MYC

MYC is a master regulator of stem cell state, embryogenesis, tissue homeostasis, and aging. As in health, in disease MYC figures prominently. Decades of biological research have identified a central role for MYC in the pathophysiology of cancer, inflammation, and heart disease. The centrality of MYC to such a vast breadth of disease biology has attracted significant attention to the historic challenge of developing inhibitors of MYC. This review will discuss therapeutic strategies toward the development of inhibitors of MYC-dependent transcriptional signaling, efforts to modulate MYC stability, and the elusive goal of developing potent, direct-acting inhibitors of MYC.

Small molecules targeting c-Myc oncogene: promising anti-cancer therapeutics

The nuclear transcription factor c-Myc is a member of the Myc gene family with multiple functions and located on band q24.1 of chromosome 8. The c-Myc gene is activated by chromosomal translocation, rearrangement, and amplification. Its encoded protein transduces intracellular signals to the nucleus, resulting in the regulation of cell proliferation, differentiation, and apoptosis, and has the ability to transform cells and bind chromosomal DNA. c-Myc also plays a critical role in malignant transformation. The abnormal over-expression of c-Myc is frequently observed in some tumors, including carcinomas of the breast, colon, and cervix, as well as small-cell lung cancer, osteosarcomas, glioblastomas, and myeloid leukemias, therefore making it a possible target for anticancer therapy. In this minireview, we summarize unique characteristics of c-Myc and therapeutic strategies against cancer using small molecules targeting the oncogene, and discuss the prospects in the development of agents targeting c-Myc, in particular G-quadruplexes formed in c-Myc promoter and c-Myc/Max dimerization. Such information will be of importance for the research and development of c-Myc-targeted drugs.

Discovery of methyl 4'-methyl-5-(7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)-[1,1'-biphenyl]-3-carboxylate, an improved small-molecule inhibitor of c-Myc-max dimerization

c-Myc is a basic helix-loop-helix-leucine zipper (bHLH-ZIP) transcription factor that is responsible for the transcription of a wide range of target genes involved in many cancer-related cellular processes. Over-expression of c-Myc has been observed in, and directly contributes to, a variety of human cancers including those of the hematopoietic system, lung, prostate and colon. To become transcriptionally active, c-Myc must first dimerize with Myc-associated factor X (Max) via its own bHLH-ZIP domain. A proven strategy towards the inhibition of c-Myc oncogenic activity is to interfere with the structural integrity of the c-Myc-Max heterodimer. The small molecule 10074-G5 is an inhibitor of c-Myc-Max dimerization (IC50 =146 μM) that operates by binding and stabilizing c-Myc in its monomeric form. We have identified a congener of 10074-G5, termed 3jc48-3 (methyl 4'-methyl-5-(7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)-[1,1'-biphenyl]-3-carboxylate), that is about five times as potent (IC50 =34 μM) at inhibiting c-Myc-Max dimerization as the parent compound. 3jc48-3 exhibited an approximate twofold selectivity for c-Myc-Max heterodimers over Max-Max homodimers, suggesting that its mode of action is through binding c-Myc. 3jc48-3 inhibited the proliferation of c-Myc-over-expressing HL60 and Daudi cells with single-digit micromolar IC50 values by causing growth arrest at the G0 /G1 phase. Co-immunoprecipitation studies indicated that 3jc48-3 inhibits c-Myc-Max dimerization in cells, which was further substantiated by the specific silencing of a c-Myc-driven luciferase reporter gene. Finally, 3jc48-3's intracellular half-life was >17 h. Collectively, these data demonstrate 3jc48-3 to be one of the most potent, cellularly active and stable c-Myc inhibitors reported to date.

Small-molecule inhibitors of the Myc oncoprotein

The c-Myc (Myc) oncoprotein is among the most attractive of cancer targets given that it is de-regulated in the majority of tumors and that its inhibition profoundly affects their growth and/or survival. However, its role as a seldom-mutated transcription factor, its lack of enzymatic activity for which suitable pharmaceutical inhibitors could be crafted and its expression by normal cells have largely been responsible for its being viewed as "undruggable". Work over the past several years, however, has begun to reverse this idea by allowing us to view Myc within the larger context of global gene regulatory control. Thus, Myc and its obligate heterodimeric partner, Max, are integral to the coordinated recruitment and post-translational modification of components of the core transcriptional machinery. Moreover, Myc over-expression re-programs numerous critical cellular functions and alters the cell's susceptibility to their inhibition. This new knowledge has therefore served as a framework upon which to develop new pharmaceutical approaches. These include the continuing development of small molecules which act directly to inhibit the critical Myc-Max interaction, those which act indirectly to prevent Myc-directed post-translational modifications necessary to initiate productive transcription and those which inhibit vital pathways upon which the Myc-transformed cell is particularly reliant. This article is part of a Special Issue entitled: Myc proteins in cell biology and pathology.

Development of a high-throughput screen and its use in the discovery of Streptococcus pneumoniae immunoglobulin A1 protease inhibitors

Streptococcus pneumoniae relies on a number of virulence factors, including immunoglobulin A1 protease (IgA1P), a Zn(2+) metalloprotease produced on the extracellular surface of the bacteria, to promote pathogenic colonization. IgA1P exhibits a unique function, in that it catalyzes the proteolysis of human IgA1 at its hinge region to leave the bacterial cell surface masked by IgA1 Fab, enabling the bacteria to evade the host's immune system and adhere to host epithelial cells to promote colonization. Thus, S. pneumoniae IgA1P has emerged as a promising antibacterial target; however, the lack of an appropriate screening assay has limited the investigation of this metalloprotease virulence factor. Relying on electrostatics-mediated AuNP aggregation, we have designed a promising high-throughput colorimetric assay for IgA1P. By using this assay, we have uncovered inhibitors of the enzyme that should be useful in deciphering its role in pneumococcal colonization and virulence.

Association of a novel preribosomal complex in Trypanosoma brucei determined by fluorescence resonance energy transfer

We have previously reported that the trypanosome-specific proteins P34 and P37 form a unique preribosomal complex with ribosomal protein L5 and 5S rRNA in the nucleoplasm. We hypothesize that this novel trimolecular complex is necessary for stabilizing 5S rRNA in Trypanosoma brucei and is essential for the survival of the parasite. In vitro quantitative analysis of the association between the proteins L5 and P34 is fundamental to our understanding of this novel complex and thus our ability to exploit its unique characteristics. Here we used in vitro fluorescence resonance energy transfer (FRET) to analyze the association between L5 and P34. First, we demonstrated that FRET can be used to confirm the association between L5 and P34. We then determined that the binding constant for L5 and P34 is 0.60 ± 0.03 μM, which is in the range of protein-protein binding constants for RNA binding proteins. In addition, we used FRET to identify the critical regions of L5 and P34 involved in the protein-protein association. We found that the N-terminal APK-rich domain and RNA recognition motif (RRM) of P34 and the L18 domain of L5 are important for the association of the two proteins with each other. These results provide us with the framework for the discovery of ways to disrupt this essential complex.

Pharmacophore identification of c-Myc inhibitor 10074-G5

A structure-activity relationship (SAR) study of the c-Myc (Myc) inhibitor 10074-G5 (N-([1,1'-biphenyl]-2-yl)-7-nitrobenzo[c][1,2,5]oxadiazol-4-amine, 1) - which targets a hydrophobic domain of the Myc oncoprotein that is flanked by arginine residues - was executed in order to determine its pharmacophore. Whilst the 7-nitrobenzofurazan was found to be critical for inhibitory activity, the ortho-biphenyl could be replaced with a para-carboxyphenyl group to furnish the new inhibitor JY-3-094 (3q). Around five times as potent as the lead with an IC(50) of 33 μM for disruption of the Myc-Max heterodimer, JY-3-094 demonstrated excellent selectivity over Max-Max homodimers, with no apparent effect at 100 μM. Importantly, the carboxylic acid of JY-3-094 improves the physicochemical properties of the lead compound, which will facilitate the incorporation of additional hydrophobicity that might enhance Myc inhibitory activity further still.

Features of protein-protein interactions that translate into potent inhibitors: topology, surface area and affinity

Protein-protein interactions (PPIs) control the assembly of multi-protein complexes and, thus, these contacts have enormous potential as drug targets. However, the field has produced a mix of both exciting success stories and frustrating challenges. Here, we review known examples and explore how the physical features of a PPI, such as its affinity, hotspots, off-rates, buried surface area and topology, might influence the chances of success in finding inhibitors. This analysis suggests that concise, tight binding PPIs are most amenable to inhibition. However, it is also clear that emerging technical methods are expanding the repertoire of 'druggable' protein contacts and increasing the odds against difficult targets. In particular, natural product-like compound libraries, high throughput screens specifically designed for PPIs and approaches that favour discovery of allosteric inhibitors appear to be attractive routes. The first group of PPI inhibitors has entered clinical trials, further motivating the need to understand the challenges and opportunities in pursuing these types of targets.

The use of small molecule probes to study spatially separated stimulus-induced signaling pathways

Simultaneous activation of signaling pathways requires dynamic assembly of higher-order protein complexes at the cytoplasmic domains of membrane-associated receptors in a stimulus-specific manner. Here, using the paradigm of cellular activation through cytokine and innate immune receptors, we demonstrate the proof-of-principle application of small molecule probes for the dissection of receptor-proximal signaling processes, such as activation of the transcription factor NF-κB and the protein kinase p38.

Targeting the Wolbachia cell division protein FtsZ as a new approach for antifilarial therapy

The use of antibiotics targeting the obligate bacterial endosymbiont Wolbachia of filarial parasites has been validated as an approach for controlling filarial infection in animals and humans. Availability of genomic sequences for the Wolbachia (wBm) present in the human filarial parasite Brugia malayi has enabled genome-wide searching for new potential drug targets. In the present study, we investigated the cell division machinery of wBm and determined that it possesses the essential cell division gene ftsZ which was expressed in all developmental stages of B. malayi examined. FtsZ is a GTPase thereby making the protein an attractive Wolbachia drug target. We described the molecular characterization and catalytic properties of Wolbachia FtsZ. We also demonstrated that the GTPase activity was inhibited by the natural product, berberine, and small molecule inhibitors identified from a high-throughput screen. Furthermore, berberine was also effective in reducing motility and reproduction in B. malayi parasites in vitro. Our results should facilitate the discovery of selective inhibitors of FtsZ as a novel anti-symbiotic approach for controlling filarial infection. NOTE: The nucleotide sequences reported in this paper are available in GenBank™ Data Bank under the accession number wAlB-FtsZ (JN616286).

Proteomic approaches in understanding action mechanisms of metal-based anticancer drugs

Medicinal inorganic chemistry has been stimulating largely by the success of the anticancer drug, cisplatin. Various metal complexes are currently used as therapeutic agents (e.g., Pt, Au, and Ru) in the treatment of malignant diseases, including several types of cancers. Understanding the mechanism of action of these metal-based drugs is for the design of more effective drugs. Proteomic approaches combined with other biochemical methods can provide comprehensive understanding of responses that are involved in metal-based anticancer drugs-induced cell death, including insights into cytotoxic effects of metal-based anticancer drugs, correlation of protein alterations to drug targets, and prediction of drug resistance and toxicity. This information, when coupled with clinical data, can provide rational basses for the future design and modification of present used metal-based anticancer drugs.

A small molecule antagonist of ghrelin O-acyltransferase (GOAT)

Using our recently disclosed fluorescence-based assay to monitor acyltransferase activity, the first non-peptidic, small molecule antagonists of ghrelin O-acyltransferase (GOAT), a potential anti-obesity and anti-diabetes target, have been discovered. Each exhibits micromolar inhibition of the enzyme, and may be useful probes for future study of the ghrelin-GOAT system.

Targeting intrinsically disordered proteins in neurodegenerative and protein dysfunction diseases: another illustration of the D(2) concept

Many biologically active proteins, which are usually called intrinsically disordered or natively unfolded proteins, lack stable tertiary and/or secondary structure under physiological conditions in vitro. Their functions complement the functional repertoire of ordered proteins, with intrinsically disordered proteins (IDPs) often being involved in regulation, signaling and control. Their amino acid sequences and compositions are very different from those of ordered proteins, making reliable identification of IDPs possible at the proteome level. IDPs are highly abundant in various human diseases, including neurodegeneration and other protein dysfunction maladies and, therefore, represent attractive novel drug targets. Some of the aspects of IDPs, as well as their roles in neurodegeneration and protein dysfunction diseases, are discussed in this article, together with the peculiarities of IDPs as potential drug targets.

Design, synthesis, and evaluation of an alpha-helix mimetic library targeting protein-protein interactions

The design and solution-phase synthesis of an alpha-helix mimetic library as an integral component of a small-molecule library targeting protein-protein interactions are described. The iterative design, synthesis, and evaluation of the candidate alpha-helix mimetic was initiated from a precedented triaryl template and refined by screening the designs for inhibition of MDM2/p53 binding. Upon identifying a chemically and biologically satisfactory design and consistent with the screening capabilities of academic collaborators, the corresponding complete library was assembled as 400 mixtures of 20 compounds (20 x 20 x 20-mix), where the added subunits are designed to mimic all possible permutations of the naturally occurring i, i + 4, i + 7 amino acid side chains of an alpha-helix. The library (8000 compounds) was prepared using a solution-phase synthetic protocol enlisting acid/base liquid-liquid extractions for purification on a scale that insures its long-term availability for screening campaigns. Screening of the library for inhibition of MDM2/p53 binding not only identified the lead alpha-helix mimetic upon which the library was based, but also suggests that a digestion of the initial screening results that accompany the use of such a comprehensive library can provide insights into the nature of the interaction (e.g., an alpha-helix mediated protein-protein interaction) and define the key residues and their characteristics responsible for recognition.

In vitro cytotoxicity and in vivo efficacy, pharmacokinetics, and metabolism of 10074-G5, a novel small-molecule inhibitor of c-Myc/Max dimerization

The c-Myc oncoprotein is overexpressed in many tumors and is essential for maintaining the proliferation of transformed cells. To function as a transcription factor, c-Myc must dimerize with Max via the basic helix-loop-helix leucine zipper protein (bHLH-ZIP) domains in each protein. The small molecule 7-nitro-N-(2-phenylphenyl)-2,1,3-benzoxadiazol-4-amine (10074-G5) binds to and distorts the bHLH-ZIP domain of c-Myc, thereby inhibiting c-Myc/Max heterodimer formation and inhibiting its transcriptional activity. We report in vitro cytotoxicity and in vivo efficacy, pharmacodynamics, pharmacokinetics, and metabolism of 10074-G5 in human xenograft-bearing mice. In vitro, 10074-G5 inhibited the growth of Daudi Burkitt's lymphoma cells and disrupted c-Myc/Max dimerization. 10074-G5 had no effect on the growth of Daudi xenografts in C.B-17 SCID mice that were treated with 20 mg/kg 10074-G5 intravenously for 5 consecutive days. Inhibition of c-Myc/Max dimerization in Daudi xenografts was not seen 2 or 24 h after treatment. Concentrations of 10074-G5 in various matrices were determined by high-performance liquid chromatography-UV, and metabolites of 10074-G5 were identified by liquid chromatography/tandem mass spectrometry. The plasma half-life of 10074-G5 in mice treated with 20 mg/kg i.v. was 37 min, and peak plasma concentration was 58 μM, which was 10-fold higher than peak tumor concentration. The lack of antitumor activity probably was caused by the rapid metabolism of 10074-G5 to inactive metabolites, resulting in tumor concentrations of 10074-G5 insufficient to inhibit c-Myc/Max dimerization. Our identification of 10074-G5 metabolites in mice will help design new, more metabolically stable small-molecule inhibitors of c-Myc.

Therapeutic Targeting of Myc

Protein-protein interactions between members of the Myc transcription factor network are potential targets of small molecule inhibitors and stabilizers. Diverse screening strategies, including fluorescence resonance energy transfer, fluorescence polarization, two hybrid and protein complementation assays have identified several lead compounds that inhibit Myc-Max dimerization and one compound that stabilizes the Max homodimer. Representative compounds interfere with Myc-induced transcriptional activation, Myc-mediated oncogenic transformation, Myc-driven cellular replication and DNA binding of Myc. For the best characterized compounds, specific binding sites have been determined, and molecular mechanisms of action have been documented. This knowledge of small molecule - protein interaction is currently applied to highly targeted approaches that seek to identify novel compounds with improved potency.

Intrinsically disordered proteins are potential drug targets

Intrinsically disordered (ID) proteins that lack stable secondary and tertiary structure in substantial regions (or throughout) are prevalent in eukaryotes. They exist as ensembles of rapidly fluctuating structures and many undergo coupled folding and binding reactions. Because ID proteins are overrepresented in major disease pathways they are desirable targets for inhibition; however, the feasibility of targeting proteins without defined structures was unclear. Recently, small molecules have been found that bind to the disordered regions of c-Myc, Abeta, EWS-Fli1, and various peptides. As with structured targets, initial hits were further optimized to increase specificity and affinity. Given the number and biological importance of ID proteins, the ability to inhibit their interactions opens tremendous potential in chemical biology and drug discovery.

Understanding protein non-folding

This review describes the family of intrinsically disordered proteins, members of which fail to form rigid 3-D structures under physiological conditions, either along their entire lengths or only in localized regions. Instead, these intriguing proteins/regions exist as dynamic ensembles within which atom positions and backbone Ramachandran angles exhibit extreme temporal fluctuations without specific equilibrium values. Many of these intrinsically disordered proteins are known to carry out important biological functions which, in fact, depend on the absence of a specific 3-D structure. The existence of such proteins does not fit the prevailing structure-function paradigm, which states that a unique 3-D structure is a prerequisite to function. Thus, the protein structure-function paradigm has to be expanded to include intrinsically disordered proteins and alternative relationships among protein sequence, structure, and function. This shift in the paradigm represents a major breakthrough for biochemistry, biophysics and molecular biology, as it opens new levels of understanding with regard to the complex life of proteins. This review will try to answer the following questions: how were intrinsically disordered proteins discovered? Why don't these proteins fold? What is so special about intrinsic disorder? What are the functional advantages of disordered proteins/regions? What is the functional repertoire of these proteins? What are the relationships between intrinsically disordered proteins and human diseases?

A complex task? Direct modulation of transcription factors with small molecules

Transcription factors with aberrant activity in disease are promising yet untested targets for therapeutic development, particularly in oncology. Directly inhibiting or activating the function of a transcription factor requires specific disruption or recruitment of protein-protein or protein-DNA interactions. The discovery or design of small molecules that specifically modulate these interactions has thus far proven to be a significant challenge and the protein class is often perceived to be 'undruggable.' This review will summarize recent progress in the development of small-molecule probes of transcription factors and provide evidence to challenge the notion that this important protein class is chemically intractable.

MYC in oncogenesis and as a target for cancer therapies

MYC proteins (c-MYC, MYCN, and MYCL) regulate processes involved in many if not all aspects of cell fate. Therefore, it is not surprising that the MYC genes are deregulated in several human neoplasias as a result from genetic and epigenetic alterations. The near "omnipotency" together with the many levels of regulation makes MYC an attractive target for tumor intervention therapy. Here, we summarize some of the current understanding of MYC function and provide an overview of different cancer forms with MYC deregulation. We also describe available treatments and highlight novel approaches in the pursuit for MYC-targeting therapies. These efforts, at different stages of development, constitute a promising platform for novel, more specific treatments with fewer side effects. If successful a MYC-targeting therapy has the potential for tailored treatment of a large number of different tumors.

12 Arylstibonic acids that inhibit the DNA binding of five B-ZIP dimers

Previously, we identified an arylstibonic acid, NSC13778 that specifically binds to the basic region of the C/EBPalpha B-ZIP domain and disrupts DNA binding. We now examine a panel of 14 additional arylstibonic acid derivatives of NSC13778 for their ability to inhibit the DNA binding of five B-ZIP dimers (c-Fos|JunD, VBP, C/EBPalpha, C/EBPbeta, and CREB). They show various specificities at inhibiting the DNA binding of five B-ZIP domains. NSC13746 inhibits the DNA binding of C/EBPbeta and CREB at 100nM and promiscuously inhibiting the DNA binding of all five proteins in the 1muM range. Dialysis experiments indicate that NSC 13746 binding to the B-ZIP domain is reversible. Thermal denaturation studies indicate that NSC13746 binds the B-ZIP domain. Some compounds specifically inhibit DNA binding, with VBP and c-Fos|JunD being most easily disrupted. These compounds inhibit, with similar specificities to the pure B-ZIP domains, the DNA binding of nuclear extract to the AP1 DNA sequence but no inhibition is observed to SP1 containing oligonucleotide. Transient transfection assays indicate that NSC13746 can inhibit the TPA induced activation of two B-ZIP dependent reporters. These experiments suggest that arylstibonic acids are promising leads for inhibiting the DNA binding of a group of B-ZIP proteins in cells.

Small-molecule modulators of c-Myc/Max and Max/Max interactions

The transcription factor c-Myc is overexpressed in many tumors in human beings and has been identified as a highly promising target for cancer therapy. Most biological functions of c-Myc require heterodimerization with its activation partner Max. Inhibition of the protein-protein interactions between c-Myc and Max by small molecules has been shown to be a feasible and powerful approach toward the inhibition of c-Myc functions. More recently, stabilization of Max homodimers to reduce the amount of Max available for activating c-Myc has also been demonstrated to counteract Myc activity. This review summarizes our current knowledge on small organic molecules that inhibit c-Myc by modulating protein-protein interactions relevant for the biological function of this important oncoprotein.

Small molecule inhibitors of Myc/Max dimerization and Myc-induced cell transformation

The preparation and evaluation of a series of inhibitors of Myc/Max dimerization and Myc-induced cell transformation are described providing mycmycin-1 (3) and mycmycin-2 (4).

Posttranslational regulation of Myc by promyelocytic leukemia zinc finger protein

The promyelocytic leukemia zinc finger (PLZF) protein, a transcriptional repressor, induces cellular resistance to oncogenic transformation by diverse oncoproteins. Two point mutants of PLZF that have lost the antioncogenic activity of the wild-type protein are oncogenic in chicken embryo fibroblasts; this activity is correlated with differential effects on Myc. Wild-type PLZF represses Myc transcription without affecting total Myc protein levels and reduces the levels of phosphorylated Myc. The PLZF mutants do not alter Myc transcription or protein expression but increase the levels of phosphorylated Myc. These modifications of Myc are correlated with PLZF-induced changes in Akt and the mitogen-activated protein kinase (MAPK) pathway. Wild-type PLZF downregulates the MAPK pathway and activates Akt, resulting in reduced phosphorylation on serine 62 of Myc by Erk and on threonine 58 by glycogen synthase kinase 3beta. The mutants fail to activate Akt and only slightly downregulate phospho-Erk. We postulate that the 2 PLZF mutants are oncogenic, because they function as dominant negatives of wild-type PLZF, enhancing Myc phosphorylation and increasing Myc transcriptional and oncogenic activity. In support of this suggestion, a specific inhibitor of Myc is able to revert the transformed phenotype of PLZF mutant-expressing cells.