Modelling Myc inhibition as a cancer therapy. Nature. 2008;455:679-683. [PMID: 18716624 DOI: 10.1038/nature07260]

Phylostratic Shift of Whole-Genome Duplications in Normal Mammalian Tissues towards Unicellularity Is Driven by Developmental Bivalent Genes and Reveals a Link to Cancer

Tumours were recently revealed to undergo a phylostratic and phenotypic shift to unicellularity. As well, aggressive tumours are characterized by an increased proportion of polyploid cells. In order to investigate a possible shared causation of these two features, we performed a comparative phylostratigraphic analysis of ploidy-related genes, obtained from transcriptomic data for polyploid and diploid human and mouse tissues using pairwise cross-species transcriptome comparison and principal component analysis. Our results indicate that polyploidy shifts the evolutionary age balance of the expressed genes from the late metazoan phylostrata towards the upregulation of unicellular and early metazoan phylostrata. The up-regulation of unicellular metabolic and drug-resistance pathways and the downregulation of pathways related to circadian clock were identified. This evolutionary shift was associated with the enrichment of ploidy with bivalent genes (p < 10⁻¹⁶). The protein interactome of activated bivalent genes revealed the increase of the connectivity of unicellulars and (early) multicellulars, while circadian regulators were depressed. The mutual polyploidy-c-MYC-bivalent genes-associated protein network was organized by gene-hubs engaged in both embryonic development and metastatic cancer including driver (proto)-oncogenes of viral origin. Our data suggest that, in cancer, the atavistic shift goes hand-in-hand with polyploidy and is driven by epigenetic mechanisms impinging on development-related bivalent genes.

Orally bioavailable CDK9/2 inhibitor shows mechanism-based therapeutic potential in MYCN-driven neuroblastoma

The undruggable nature of oncogenic Myc transcription factors poses a therapeutic challenge in neuroblastoma, a pediatric cancer in which MYCN amplification is strongly associated with unfavorable outcome. Here, we show that CYC065 (fadraciclib), a clinical inhibitor of CDK9 and CDK2, selectively targeted MYCN-amplified neuroblastoma via multiple mechanisms. CDK9 - a component of the transcription elongation complex P-TEFb - bound to the MYCN-amplicon superenhancer, and its inhibition resulted in selective loss of nascent MYCN transcription. MYCN loss led to growth arrest, sensitizing cells for apoptosis following CDK2 inhibition. In MYCN-amplified neuroblastoma, MYCN invaded active enhancers, driving a transcriptionally encoded adrenergic gene expression program that was selectively reversed by CYC065. MYCN overexpression in mesenchymal neuroblastoma was sufficient to induce adrenergic identity and sensitize cells to CYC065. CYC065, used together with temozolomide, a reference therapy for relapsed neuroblastoma, caused long-term suppression of neuroblastoma growth in vivo, highlighting the clinical potential of CDK9/2 inhibition in the treatment of MYCN-amplified neuroblastoma.

Turning Up the Heat on MYC: Progress in Small-Molecule Inhibitors

MYC is a highly validated oncogenic transcription factor and cancer target. However, the disordered nature of this protein has made it a challenging target, with no clinical stage, direct small-molecule MYC inhibitors available. Recent work leveraging a large in silico chemical library and a rapid in vivo screen has expanded the chemotypes of direct small-molecule inhibitors (MYCi). Novel MYCi represent a class of improved MYC chemical probes that bind directly to MYC to inhibit its function and to promote its degradation by enhancing GSK3β-mediated phosphorylation. One of these compounds, MYCi975, has shown remarkable tolerability and efficacy in vivo and is associated with a selective effect on MYC target gene expression. Additional effects of MYCi on the tumor immune microenvironment including immune cell infiltration and upregulation of PD-L1 expression provide a rationale for combining MYCi with anti-PD-1/PD-L1 therapy to enhance antitumor efficacy. Our strategy for developing MYCi demonstrates an efficient way to identify selective and well-tolerated MYC inhibitors. The new MYCi provide tools for probing MYC function and serve as starting points for the development of novel anti-MYC therapeutics.

Statins decrease the expression of c-Myc protein in cancer cell lines

Statins are potent inhibitors of the mevalonate/cholesterol biosynthetic pathway and are widely prescribed for the prevention of cardiovascular diseases. Here, we carried out a comprehensive analysis of the effects of three statins, simvastatin, atorvastatin, and lovastatin, on six different cancer cell lines that include a P-glycoprotein-expressing, multidrug resistant variant of an ovarian cancer cell line. Incubation of all cancer cell lines with statins resulted in suppression of cell proliferation without inducing apoptotic cell death. The cell proliferation arrest could be reversed upon transfer of cells to statin-free growth media as well as by the supplementation of the growth media with mevalonate. Further analysis suggested that statins induced cell cycle arrest at G0/G1 phase in four cancer cell lines and the loss of c-Myc protein in three cancer cell lines. The c-Myc expression and the progression of cell division cycle were restored upon the addition of mevalonate to the culture media containing statins. Finally, cells incubated with statins contained an increased level of phosphorylated histone H2AX, an observation previously correlated to cellular senescence. Together, these data demonstrate that statins inhibit the mevalonate pathway which is tightly coupled to oxidative branch of the pentose phosphate pathway, c-Myc expression, cell division cycle progression, and cellular senescence. Implications of these observations in the application of statins as cancer therapeutics are discussed.

Crosstalk Between MYC and lncRNAs in Hematological Malignancies

The human genome project revealed the existence of many thousands of long non-coding RNAs (lncRNAs). These transcripts that are over 200 nucleotides long were soon recognized for their importance in regulating gene expression. However, their poor conservation among species and their still controversial annotation has limited their study to some extent. Moreover, a generally lower expression of lncRNAs as compared to protein coding genes and their enigmatic biochemical mechanisms have impeded progress in the understanding of their biological roles. It is, however, known that lncRNAs engage in various kinds of interactions and can form complexes with other RNAs, with genomic DNA or proteins rendering their functional regulatory network quite complex. It has emerged from recent studies that lncRNAs exert important roles in gene expression that affect many cellular processes underlying development, cellular differentiation, but also the pathogenesis of blood cancers like leukemia and lymphoma. A number of lncRNAs have been found to be regulated by several well-known transcription factors including Myelocytomatosis viral oncogene homolog (MYC). The c-MYC gene is known to be one of the most frequently deregulated oncogenes and a driver for many human cancers. The c-MYC gene is very frequently activated by chromosomal translocations in hematopoietic cancers most prominently in B- or T-cell lymphoma or leukemia and much is already known about its role as a DNA binding transcriptional regulator. Although the understanding of MYC's regulatory role controlling lncRNA expression and how MYC itself is controlled by lncRNA in blood cancers is still at the beginning, an intriguing picture emerges indicating that c-MYC may execute part of its oncogenic function through lncRNAs. Several studies have identified lncRNAs regulating c-MYC expression and c-MYC regulated lncRNAs in different blood cancers and have unveiled new mechanisms how these RNA molecules act. In this review, we give an overview of lncRNAs that have been recognized as critical in the context of activated c-MYC in leukemia and lymphoma, describe their mechanism of action and their effect on transcriptional reprogramming in cancer cells. Finally, we discuss possible ways how an interference with their molecular function could be exploited for new cancer therapies.

Recent Advances in Liver Cancer Stem Cells: Non-coding RNAs, Oncogenes and Oncoproteins

Hepatocellular carcinoma (HCC) is one of the most prevalent malignancies worldwide, with high morbidity, relapse, metastasis and mortality rates. Although liver surgical resection, transplantation, chemotherapy, radiotherapy and some molecular targeted therapeutics may prolong the survival of HCC patients to a certain degree, the curative effect is still poor, primarily because of tumor recurrence and the drug resistance of HCC cells. Liver cancer stem cells (LCSCs), also known as liver tumor-initiating cells, represent one small subset of cancer cells that are responsible for disease recurrence, drug resistance and death. Therefore, understanding the regulatory mechanism of LCSCs in HCC is of vital importance. Thus, new studies that present gene regulation strategies to control LCSC differentiation and replication are under development. In this review, we provide an update on the latest advances in experimental studies on non-coding RNAs (ncRNAs), oncogenes and oncoproteins. All the articles addressed the crosstalk between different ncRNAs, oncogenes and oncoproteins, as well as their upstream and downstream products targeting LCSCs. In this review, we summarize three pathways, the Wnt/β-catenin signaling pathway, phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway, and interleukin 6/Janus kinase 2/signal transducer and activator of transcription 3 (IL6/JAK2/STAT3) signaling pathway, and their targeting gene, c-Myc. Furthermore, we conclude that octamer 4 (OCT4) and Nanog are two important functional genes that play a pivotal role in LCSC regulation and HCC prognosis.

Drugging "undruggable" genes for cancer treatment: Are we making progress?

RAS, TP53 (p53) and MYC are among the most frequently altered driver genes in cancer. Thus, RAS is the most frequently mutated oncogene, MYC the most frequently amplified gene and TP53 the most frequently mutated tumor suppressor gene and overall the most frequently mutated gene in cancer. Theoretically, therefore, these genes are highly attractive targets for cancer treatment. However, as the protein products of each of these genes lack an accessible hydrophobic pocket into which low molecular weight compounds might bind with high affinity, they have proved difficult to target and have traditionally been referred to as "undruggable." Despite this branding, several low molecular weight compounds targeting each of these proteins have recently been reported to have anticancer activity in preclinical models. Indeed, several drugs inhibiting mutant KRAS, MYC overexpression or reactivating mutant p53 have undergone or are currently undergoing clinical trials. For targeting mutant KRAS and reactivating mutant p53, trials have progressed to a Phase III stage, that is, the mutant-p53 reactivating drug, APR-246 is currently being investigated in patients with myelodysplastic syndrome (MDS) and the RAS inhibitor, rigosertib is also undergoing evaluation in patients with MDS. Although there appears to be no directly acting MYC inhibitor currently being tested in a clinical trial, an anti-MYC compound, known as OmoMYC has been extensively validated in multiple preclinical models and is being developed for clinical evaluation. Based on current evidence, the traditional perception of RAS, p53 and MYC as being "undruggable" would appear to be coming to an end.

Anti- c-myc cholesterol based lipoplexes as onco-nanotherapeutic agents in vitro

Background: Strategies aimed at inhibiting the expression of the c-myc oncogene could provide the basis for alternative cancer treatment. In this regard, silencing c-myc expression using small interfering RNA (siRNA) is an attractive option. However, the development of a clinically viable, siRNA-based, c-myc silencing system is largely dependent upon the design of an appropriate siRNA carrier that can be easily prepared. Nanostructures formed by the electrostatic association of siRNA and cationic lipid vesicles represent uncomplicated siRNA delivery systems. Methods: This study has focused on cationic liposomes prepared with equimolar quantities of the cytofectin, N,N-dimethylaminopropylamido-succinylcholesteryl-formylhydrazide (MS09), and cholesterol (Chol) for the development of a simple, but effective anti- c-myc onco-nanotherapeutic agent. Liposomes formulated with dioleoylphosphatidylethanolamine (DOPE) in place of Chol as the co-lipid were included for comparative purposes. Results: Liposomes successfully bound siRNA forming lipoplexes of less than 150 nm in size, which assumed bilamellar aggregrates. The liposome formulations were well tolerated in the human breast adenocarcinoma (MCF-7) and colon carcinoma (HT-29) cells, which overexpress c-myc. Lipoplexes directed against the c-myc transcript mediated a dramatic reduction in c-myc mRNA and protein levels. Moreover, oncogene knockdown and anti-cancer effects were superior to that of Lipofectamine™ 3000. Conclusion: This anti- c-myc MS09:Chol lipoplex exemplifies a simple anticancer agent with enhanced c-myc gene silencing potential in vitro.

MYC ASO Impedes Tumorigenesis and Elicits Oncogene Addiction in Autochthonous Transgenic Mouse Models of HCC and RCC

The MYC oncogene is dysregulated in most human cancers and hence is an attractive target for cancer therapy. We and others have shown experimentally in conditional transgenic mouse models that suppression of the MYC oncogene is sufficient to induce rapid and sustained tumor regression, a phenomenon known as oncogene addiction. However, it is unclear whether a therapy that targets the MYC oncogene could similarly elicit oncogene addiction. In this study, we report that using antisense oligonucleotides (ASOs) to target and reduce the expression of MYC impedes tumor progression and phenotypically elicits oncogene addiction in transgenic mouse models of MYC-driven primary hepatocellular carcinoma (HCC) and renal cell carcinoma (RCC). Quantitative image analysis of MRI was used to demonstrate the inhibition of HCC and RCC progression. After 4 weeks of drug treatment, tumors had regressed histologically. ASOs depleted MYC mRNA and protein expression in primary tumors in vivo, as demonstrated by real-time PCR and immunohistochemistry. Treatment with MYC ASO in vivo, but not with a control ASO, decreased proliferation, induced apoptosis, increased senescence, and remodeled the tumor microenvironment by recruitment of CD4⁺ T cells. Importantly, although MYC ASO reduced both mouse Myc and transgenic human MYC, the ASO was not associated with significant toxicity. Lastly, we demonstrate that MYC ASO inhibits the growth of human liver cancer xenografts in vivo. Our results illustrate that targeting MYC expression in vivo using ASO can suppress tumorigenesis by phenotypically eliciting both tumor-intrinsic and microenvironment hallmarks of oncogene addiction. Hence, MYC ASO therapy is a promising strategy to treat MYC-driven human cancers.

Regulation of cancer cell metabolism: oncogenic MYC in the driver's seat

Cancer cells must rewire cellular metabolism to satisfy the demands of unbridled growth and proliferation. As such, most human cancers differ from normal counterpart tissues by a plethora of energetic and metabolic reprogramming. Transcription factors of the MYC family are deregulated in up to 70% of all human cancers through a variety of mechanisms. Oncogenic levels of MYC regulates almost every aspect of cellular metabolism, a recently revisited hallmark of cancer development. Meanwhile, unrestrained growth in response to oncogenic MYC expression creates dependency on MYC-driven metabolic pathways, which in principle provides novel targets for development of effective cancer therapeutics. In the current review, we summarize the significant progress made toward understanding how MYC deregulation fuels metabolic rewiring in malignant transformation.

A Driver Never Works Alone-Interplay Networks of Mutant p53, MYC, RAS, and Other Universal Oncogenic Drivers in Human Cancer

The knowledge accumulating on the occurrence and mechanisms of the activation of oncogenes in human neoplasia necessitates an increasingly detailed understanding of their systemic interactions. None of the known oncogenic drivers work in isolation from the other oncogenic pathways. The cooperation between these pathways is an indispensable element of a multistep carcinogenesis, which apart from inactivation of tumor suppressors, always includes the activation of two or more proto-oncogenes. In this review we focus on representative examples of the interaction of major oncogenic drivers with one another. The drivers are selected according to the following criteria: (1) the highest frequency of known activation in human neoplasia (by mutations or otherwise), (2) activation in a wide range of neoplasia types (universality) and (3) as a part of a distinguishable pathway, (4) being a known cause of phenotypic addiction of neoplastic cells and thus a promising therapeutic target. Each of these universal oncogenic factors—mutant p53, KRAS and CMYC proteins, telomerase ribonucleoprotein, proteasome machinery, HSP molecular chaperones, NF-κB and WNT pathways, AP-1 and YAP/TAZ transcription factors and non-coding RNAs—has a vast network of molecular interrelations and common partners. Understanding this network allows for the hunt for novel therapeutic targets and protocols to counteract drug resistance in a clinical neoplasia treatment.

The Role of Nuclear Receptor Subfamily 1 Group H Member 4 (NR1H4) in Colon Cancer Cell Survival through the Regulation of c-Myc Stability

Nuclear receptor subfamily group H member 4 (NR1H4), also known as farnesoid X receptor, has been implicated in several cellular processes in the liver and intestine. Preclinical and clinical studies have suggested a role of NR1H4 in colon cancer development; however, how NR1H4 regulates colon cancer cell growth and survival remains unclear. We generated NR1H4 knockout (KO) colon cancer cells using clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein-9 nuclease (CAS9) technology and explored the effects of NR1H4 KO in colon cancer cell proliferation, survival, and apoptosis. Interestingly, NR1H4 KO cells showed impaired cell proliferation, reduced colony formation, and increased apoptotic cell death compared to control colon cancer cells. We identified MYC as an important mediator of the signaling pathway alterations induced by NR1H4 KO. NR1H4 silencing in colon cancer cells resulted in reduced MYC protein levels, while NR1H4 activation using an NR1H4 ligand, chenodeoxycholic acid, resulted in time- and dose-dependent MYC induction. Moreover, NR1H4 KO enhanced the anti-cancer effects of doxorubicin and cisplatin, supporting the role of MYC in the enhanced apoptosis observed in NR1H4 KO cells. Taken together, our findings suggest that modulating NR1H4 activity in colon cancer cells might be a promising alternative approach to treat cancer using MYC-targeting agents.

Myc is a prognostic biomarker and potential therapeutic target in osteosarcoma

Background

Over the past four decades, outcomes for osteosarcoma patients have plateaued as there have been few emerging therapies showing clinical results. Thus, the identification of novel biomarkers and therapeutic strategies are urgently needed to address these primary obstacles in patient care. Although the Myc-oncogene has known roles in oncogenesis and cancer cell growth, its expression and function in osteosarcoma are largely unknown.

Methods

Expression of Myc was determined by Western blotting of osteosarcoma cell lines and patient tissues, and by immunohistochemistry of a unique osteosarcoma tissue microarray (TMA) constructed from 70 patient samples with extensive follow-up data. Myc specific siRNA and inhibitor 10058-F4 were applied to examine the effect of Myc inhibition on osteosarcoma cell proliferation. The clonogenicity and migration activity was determined by clonogenic and wound-healing assays. A mimic in vivo assay, three-dimensional (3D) cell culture model, was performed to further validate the effect of Myc inhibition on osteosarcoma cell tumorigenic markers.

Results

Myc was significantly overexpressed in human osteosarcoma cell lines compared with normal human osteoblasts, and also highly expressed in fresh osteosarcoma tissues. Higher Myc expression correlated significantly with metastasis and poor prognosis. Through the addition of Myc specific siRNA and inhibitor, we significantly reduced Myc protein expression, resulting in decreased osteosarcoma cell proliferation. Inhibition of Myc also suppressed the migration, clonogenicity, and spheroid growth of osteosarcoma cells.

Conclusion

Our results support Myc as an emerging prognostic biomarker and therapeutic target in osteosarcoma therapy.

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.

ADAM17 selectively activates the IL-6 trans-signaling/ERK MAPK axis in KRAS-addicted lung cancer

Oncogenic KRAS mutations are major drivers of lung adenocarcinoma (LAC), yet the direct therapeutic targeting of KRAS has been problematic. Here, we reveal an obligate requirement by oncogenic KRAS for the ADAM17 protease in LAC In genetically engineered and xenograft (human cell line and patient-derived) Kras ^G12D-driven LAC models, the specific blockade of ADAM17, including with a non-toxic prodomain inhibitor, suppressed tumor burden by reducing cellular proliferation. The pro-tumorigenic activity of ADAM17 was dependent upon its threonine phosphorylation by p38 MAPK, along with the preferential shedding of the ADAM17 substrate, IL-6R, to release soluble IL-6R that drives IL-6 trans-signaling via the ERK1/2 MAPK pathway. The requirement for ADAM17 in Kras ^G12D-driven LAC was independent of bone marrow-derived immune cells. Furthermore, in KRAS mutant human LAC, there was a significant positive correlation between augmented phospho-ADAM17 levels, observed primarily in epithelial rather than immune cells, and activation of ERK and p38 MAPK pathways. Collectively, these findings identify ADAM17 as a druggable target for oncogenic KRAS-driven LAC and provide the rationale to employ ADAM17-based therapeutic strategies for targeting KRAS mutant cancers.

Intrinsic cell-penetrating activity propels Omomyc from proof of concept to viable anti-MYC therapy

Inhibiting MYC has long been considered unfeasible, although its key role in human cancers makes it a desirable target for therapeutic intervention. One reason for its perceived undruggability was the fear of catastrophic side effects in normal tissues. However, we previously designed a dominant-negative form of MYC called Omomyc and used its conditional transgenic expression to inhibit MYC function both in vitro and in vivo. MYC inhibition by Omomyc exerted a potent therapeutic impact in various mouse models of cancer, causing only mild, well-tolerated, and reversible side effects. Nevertheless, Omomyc has been so far considered only a proof of principle. In contrast with that preconceived notion, here, we show that the purified Omomyc mini-protein itself spontaneously penetrates into cancer cells and effectively interferes with MYC transcriptional activity therein. Efficacy of the Omomyc mini-protein in various experimental models of non-small cell lung cancer harboring different oncogenic mutation profiles establishes its therapeutic potential after both direct tissue delivery and systemic administration, providing evidence that the Omomyc mini-protein is an effective MYC inhibitor worthy of clinical development.

Blocking Myc to Treat Cancer: Reflecting on Two Decades of Omomyc

First designed and published in 1998 as a laboratory tool to study Myc perturbation, Omomyc has come a long way in the past 22 years. This dominant negative has contributed to our understanding of Myc biology when expressed, first, in normal and cancer cells, and later in genetically-engineered mice, and has shown remarkable anti-cancer properties in a wide range of tumor types. The recently described therapeutic effect of purified Omomyc mini-protein—following the surprising discovery of its cell-penetrating capacity—constitutes a paradigm shift. Now, much more than a proof of concept, the most characterized Myc inhibitor to date is advancing in its drug development pipeline, pushing Myc inhibition into the clinic.

Synthetic lethality on drug discovery: an update on cancer therapy

INTRODUCTION

A novel anticancer therapy is the need of the hour due to growing incidences of resistance to first line cancer chemotherapy. Synthetic lethality (SL) is one of the new age treatment methods being explored for combating the resistance to anticancer agents. In this method, cell mutations are exploited for the development of new therapeutic agents, where, if there is loss of function of one gene, the cell mutations can still be fixed by alternative machinery but if two genes involved in DNA repair undergo loss of function, it causes lethality to the cell.

AREAS COVERED

The authors condense findings of SL-based novel anticancer regimen. The review emphasizes some of the SL based clinical and preclinical studies of novel targets and therapy.

EXPERT OPINION

SL conceptualizes a resolution against treatment resistance to anticancer regimen by recognition of therapeutic vulnerabilities in particular cancer cells. A multitude of clinical trials associated with SL and DNA repair are being conducted that will be useful in obtaining a clearer picture pertaining to the use of cancer biomarkers and effectiveness of drugs acting via target-based molecular changes. Furthermore, new anticancer regimen focused on personalized medicines will emerge basing their development upon SL.

MYC Instructs and Maintains Pancreatic Adenocarcinoma Phenotype

The signature features of pancreatic ductal adenocarcinoma (PDAC) are its fibroinflammatory stroma, poor immune activity, and dismal prognosis. We show that acute activation of Myc in indolent pancreatic intraepithelial neoplasm (PanIN) epithelial cells in vivo is, alone, sufficient to trigger immediate release of instructive signals that together coordinate changes in multiple stromal and immune-cell types and drive transition to pancreatic adenocarcinomas that share all the characteristic stromal features of their spontaneous human counterpart. We also demonstrate that this Myc-driven PDAC switch is completely and immediately reversible: Myc deactivation/inhibition triggers meticulous disassembly of advanced PDAC tumor and stroma and concomitant death of tumor cells. Hence, both the formation and deconstruction of the complex PDAC phenotype are continuously dependent on a single, reversible Myc switch. SIGNIFICANCE: We show that Myc activation in indolent Kras G12D-induced PanIN epithelium acts as an immediate pleiotropic switch, triggering tissue-specific signals that instruct all the diverse signature stromal features of spontaneous human PDAC. Subsequent Myc deactivation or inhibition immediately triggers a program that coordinately disassembles PDAC back to PanIN.See related commentary by English and Sears, p. 495.

MicroRNAs Targeting MYC Expression: Trace of Hope for Pancreatic Cancer Therapy. A Systematic Review

Background

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest malignancies and a major health problem worldwide. There were no major advances in conventional treatments in inhibiting tumor progression and increasing patient survival time. In order to suppress mechanisms responsible for tumor cell development such as those with oncogenic roles, more advanced therapeutic strategies should be sought. One of the most important oncogenes of pancreatic cancer is the MYC gene. The overexpression of MYC can activate many tumorigenic processes such as cell proliferation and pancreatic cancer cell invasion. MiRNAs are important molecules that are confirmed by targeting mRNA transcripts to regulate the expression of the MYC gene. Therefore, restoring MYC-repressing miRNAs expression tends to be an effective method of treating MYC-driven cancers.

Objective

The purpose of this study was to identify all validated microRNAs targeting C-MYC expression to inhibit PDAC progression by conducting a systematic review.

Methods

In this systematic review study, the papers published between 2000 and 2020 in major online scientific databases including PubMed, Scopus, and Web of Science were screened, following inclusion and exclusion criteria. We extracted all the experimental studies that showed miRNAs could target the expression of the MYC gene in PDAC.

Results

Eight papers were selected from a total of 89 papers. We found that six miRNAs (Let-7a, miR-145, miR-34a, miR-375, miR-494, and miR-148a) among the selected studies were validated for targeting MYC gene and three of them confirmed Let-7a as a direct MYC expression regulator in PC cells. Finally, we summarized the latest shreds of evidence of experimentally validated miRNAs targeting the MYC gene with respect to PDAC’s therapeutic potential.

Conclusion

Restoring the expression of MYC-repressing miRNAs tends to be an effective way to treat MYC-driven cancers such as PDAC. Several miRNAs have been proposed to target this oncogene via bioinformatics tools, but only a few have been experimentally validated for pancreatic cancer cells and models. Further studies should be conducted to find the interaction network of miRNA-MYC to develop more successful therapeutic strategies for PC, using the synergistic effects of these miRNAs.

Targeting MYC Proteins for Tumor Therapy

Targeting the function of MYC oncoproteins holds the promise of achieving conceptually new and effective anticancer therapies that can be applied to a broad range of tumors. The nature of the target however—a broadly, possibly universally acting transcription factor that has no enzymatic activity and is largely unstructured unless complexed with partner proteins—has so far defied the development of clinically applicable MYC-directed therapies. At the same time, lingering questions about exactly which functions of MYC proteins account for their pervasive oncogenic role in human tumors and need to be targeted have prevented the development of effective therapies using surrogate targets that act in critical MYC-dependent pathways. In this review, we therefore argue that rigorous testing of critical oncogenic functions and protein/protein interactions and new chemical approaches to target them are necessary to successfully eradicate MYC-driven tumors.

Target gene-independent functions of MYC oncoproteins

Oncoproteins of the MYC family are major drivers of human tumorigenesis. Since a large body of evidence indicates that MYC proteins are transcription factors, studying their function has focused on the biology of their target genes. Detailed studies of MYC-dependent changes in RNA levels have provided contrasting models of the oncogenic activity of MYC proteins through either enhancing or repressing the expression of specific target genes, or as global amplifiers of transcription. In this Review, we first summarize the biochemistry of MYC proteins and what is known (or is unclear) about the MYC target genes. We then discuss recent progress in defining the interactomes of MYC and MYCN and how this information affects central concepts of MYC biology, focusing on mechanisms by which MYC proteins modulate transcription. MYC proteins promote transcription termination upon stalling of RNA polymerase II, and we propose that this mechanism enhances the stress resilience of basal transcription. Furthermore, MYC proteins coordinate transcription elongation with DNA replication and cell cycle progression. Finally, we argue that the mechanism by which MYC proteins regulate the transcription machinery is likely to promote tumorigenesis independently of global or relative changes in the expression of their target genes.

Mission Possible: Advances in MYC Therapeutic Targeting in Cancer

MYC is a master transcriptional regulator that controls almost all cellular processes. Over the last several decades, researchers have strived to define the context-dependent transcriptional gene programs that are controlled by MYC, as well as the mechanisms that regulate MYC function, in an effort to better understand the contribution of this oncoprotein to cancer progression. There are a wealth of data indicating that deregulation of MYC activity occurs in a large number of cancers and significantly contributes to disease progression, metastatic potential, and therapeutic resistance. Although the therapeutic targeting of MYC in cancer is highly desirable, there remain substantial structural and functional challenges that have impeded direct MYC-targeted drug development and efficacy. While efforts to drug the ‘undruggable’ may seem futile given these challenges and considering the broad reach of MYC, significant strides have been made to identify points of regulation that can be exploited for therapeutic purposes. These include targeting the deregulation of MYC transcription in cancer through small-molecule inhibitors that induce epigenetic silencing or that regulate the G-quadruplex structures within the MYC promoter. Alternatively, compounds that disrupt the DNA-binding activities of MYC have been the long-standing focus of many research groups, since this method would prevent downstream MYC oncogenic activities regardless of upstream alterations. Finally, proteins involved in the post-translational regulation of MYC have been identified as important surrogate targets to reduce MYC activity downstream of aberrant cell stimulatory signals. Given the complex regulation of the MYC signaling pathway, a combination of these approaches may provide the most durable response, but this has yet to be shown. Here, we provide a comprehensive overview of the different therapeutic strategies being employed to target oncogenic MYC function, with a focus on post-translational mechanisms.

Downregulation of SNRPG induces cell cycle arrest and sensitizes human glioblastoma cells to temozolomide by targeting Myc through a p53-dependent signaling pathway

Objective: Temozolomide (TMZ) is commonly used for glioblastoma multiforme (GBM) chemotherapy. However, drug resistance limits its therapeutic effect in GBM treatment. RNA-binding proteins (RBPs) have vital roles in posttranscriptional events. While disturbance of RBP-RNA network activity is potentially associated with cancer development, the precise mechanisms are not fully known. The SNRPG gene, encoding small nuclear ribonucleoprotein polypeptide G, was recently found to be related to cancer incidence, but its exact function has yet to be elucidated. Methods:SNRPG knockdown was achieved via short hairpin RNAs. Gene expression profiling and Western blot analyses were used to identify potential glioma cell growth signaling pathways affected by SNRPG. Xenograft tumors were examined to determine the carcinogenic effects of SNRPG on glioma tissues. Results: The SNRPG-mediated inhibitory effect on glioma cells might be due to the targeted prevention of Myc and p53. In addition, the effects of SNRPG loss on p53 levels and cell cycle progression were found to be Myc-dependent. Furthermore, SNRPG was increased in TMZ-resistant GBM cells, and downregulation of SNRPG potentially sensitized resistant cells to TMZ, suggesting that SNRPG deficiency decreases the chemoresistance of GBM cells to TMZ via the p53 signaling pathway. Our data confirmed that SNRPG suppression sensitizes GBM cells to TMZ by targeting Myc via the p53 signaling cascade. Conclusions: These results indicated that SNRPG is a probable molecular target of GBM and suggested that suppressing SNRPG in resistant GBM cells might be a substantially beneficial method for overcoming essential drug resistance.

Transcription Factor Inhibition: Lessons Learned and Emerging Targets

Transcription factors have roles at focal points in signaling pathways, controlling many normal cellular processes, such as cell growth and proliferation, metabolism, apoptosis, immune responses, and differentiation. Their activity is frequently deregulated in disease and targeting this class of proteins is a major focus of interest. However, the structural disorder and lack of binding pockets have made design of small molecules for transcription factors challenging. Here, we review some of the most recent developments for small molecule inhibitors of transcription factors emphasized in James Darnell's vision 17 years ago. We also discuss the progress so far on transcription factors recently nominated by genome-scale loss-of-function screens from the cancer dependency map project.

MYC, MYCL, and MYCN as therapeutic targets in lung cancer

Introduction: Lung cancer is the leading cause of cancer-related mortality globally. Despite recent advances with personalized therapies and immunotherapy, the prognosis remains dire and recurrence is frequent. Myc is an oncogene deregulated in human cancers, including lung cancer, where it supports tumorigenic processes and progression. Elevated Myc levels have also been associated with resistance to therapy.Areas covered: This article summarizes the genomic and transcriptomic studies that compile evidence for (i) MYC, MYCN, and MYCL amplification and overexpression in lung cancer patients, and (ii) their prognostic significance. We collected the most recent literature regarding the development of Myc inhibitors where the emphasis is on those inhibitors tested in lung cancer experimental models and their potential for future clinical application.Expert opinion: The targeting of Myc in lung cancer is potentially an unprecedented opportunity for inhibiting a key player in tumor progression and maintenance and therapeutic resistance. Myc inhibitory strategies are on the path to their clinical application but further work is necessary for the assessment of their use in combination with standard treatment approaches. Given the role of Myc in immune suppression, a significant opportunity may exist in the combination of Myc inhibitors with immunotherapies.

The Antipsychotic Agent Sertindole Exhibited Antiproliferative Activities by Inhibiting the STAT3 Signaling Pathway in Human Gastric Cancer Cells

Gastric cancer (GC) is the third leading cause of cancer-related death. Although the therapeutic approaches have improved, the 5-year survival rate of GC patients after surgical resection remains low due to the high rates of metastasis and recurrence. Patients with schizophrenia have significantly lower incidences of cancer after long-term drug treatment, suggesting the potential or partially ameliorate the risk of cancer development of antipsychotic drugs. The goal of this study was to explore antipsychotic drugs with an optional effective therapy against gastric cellular carcinoma. We found that sertindole, an atypical antipsychotic, exhibited anti-tumor efficacy on human GC cells in vitro and in vivo. Moreover, sertindole in combination with cisplatin dramatically enhanced apoptosis-induction in GC cells. In addition, the pro-apoptotic effect of sertindole on GC might in part, involved in inhibition of STAT3 activation and downstream signals, including Mcl1, surviving, c-Myc, cyclin D1. Collectively, these results suggested that sertindole could be a potential anticancer reagent and be an attractive therapeutic adjuvant for the treatment of human GC.

MYC in Germinal Center-derived lymphomas: Mechanisms and therapeutic opportunities

The rearrangement of immunoglobulin loci during the germinal center reaction is associated with an increased risk of chromosomal translocations that activate oncogenes such as MYC, BCL2 or BCL6, thus contributing to the development of B-cell lymphomas. MYC and BCL2 activation are initiating events in Burkitt's (BL) and Follicular Lymphoma (FL), respectively, but can occur at later stages in other subtypes such as Diffuse Large-B Cell Lymphoma (DLBCL). MYC can also be activated during the progression of FL to the transformed stage. Thus, either DLBCL or FL can give rise to aggressive double-hit lymphomas (DHL) with concurrent activation of MYC and BCL2. Research over the last three decades has improved our understanding of the functions of these oncogenes and the basis for their cooperative action in lymphomagenesis. MYC, in particular, is a transcription factor that contributes to cell activation, growth and proliferation, while concomitantly sensitizing cells to apoptosis, the latter being blocked by BCL2. Here, we review our current knowledge about the role of MYC in germinal center B-cells and lymphomas, discuss MYC-induced dependencies that can sensitize cancer cells to select pharmacological inhibitors, and illustrate their therapeutic potential in aggressive lymphomas-and in particular in DHL, in combination with BCL2 inhibitors.

High MYC mRNA Expression Is More Clinically Relevant than MYC DNA Amplification in Triple-Negative Breast Cancer

DNA abnormalities are used in inclusion criteria of clinical trials for treatments with specific targeted molecules. MYC is one of the most powerful oncogenes and is known to be associated with triple-negative breast cancer (TNBC). Its DNA amplification is often part of the targeted DNA-sequencing panels under the assumption of reflecting upregulated signaling. However, it remains unclear if MYC DNA amplification is a surrogate of its upregulated signaling. Thus, we investigated the difference between MYC DNA amplification and mRNA high expression in TNBCs utilizing publicly available cohorts. MYC DNA amplified tumors were found to have various mRNA expression levels, suggesting that MYC DNA amplification does not always result in elevated MYC mRNA expression. Compared to other subtypes, both MYC DNA amplification and mRNA high expression were more frequent in the TNBCs. MYC mRNA high expression, but not DNA amplification, was significantly associated with worse overall survival in the TNBCs. The TNBCs with MYC mRNA high expression enriched MYC target genes, cell cycle related genes, and WNT/β-catenin gene sets, whereas none of them were enriched in MYC DNA amplified TNBCs. In conclusion, MYC mRNA high expression, but not DNA amplification, reflects not only its upregulated signaling pathway, but also clinical significance in TNBCs.

HOXC-AS1-MYC regulatory loop contributes to the growth and metastasis in gastric cancer

BACKGROUND

Gastric cancer (GC) is one of the most prevalent and deadly malignancies worldwide. Accumulating reports have indicated the participation of long non-coding RNAs (lncRNAs) in the onset and progression of GC.

METHODS

GSE109476 data was utilized to screen out lncRNAs dysregulated in GC. Gene expressions were determined by qRT-PCR and western blot. Both in vitro and in vivo experiments were carried out to assess the function of HOXC-AS1 in GC. The association between genes was verified via RIP, ChIP, CoIP, RNA pull down and luciferase reporter assays, as appropriate.

RESULTS

HOXC-AS1 was discovered to be upregulated in GC and located both in cytoplasm and in nucleus in GC cells. Functionally, inhibition of HOXC-AS1 restrained GC cell growth and metastasis both in vitro and in vivo. Moreover, HOXC-AS1 was proved to be trans-activated by c-MYC in GC. In return, HOXC-AS1 positively regulated MYC expression in GC through targeting miR-590-3p/MYC axis in cytoplasm and modulating BRG1/β-catenin complex-activated MYC transcription in nucleus. Furthermore, the rescue assays verified that MYC mediated HOXC-AS1-affected GC progression.

CONCLUSION

Our research illustrated a feedback loop of HOXC-AS1-MYC in aggravating GC cell growth and metastasis, highlighting HOXC-AS1 as a promising target for GC diagnosis and treatment.

A Self-Assembled Platform Based on Branched DNA for sgRNA/Cas9/Antisense Delivery

Precisely assembled DNA nanostructures are promising candidates for the delivery of biomolecule-based therapeutics. Herein, we introduce a facile strategy for the construction of a branched DNA-based nanoplatform for codelivery of gene editing (sgRNA/Cas9, targeting DNA in the nucleus) and gene silencing (antisense, targeting mRNA in the cytoplasm) components for synergistic tumor therapy in vitro and in vivo. In our design, the branched DNA structure can efficiently load a sgRNA/Cas9/antisense complex targeting a tumor-associated gene, PLK1, through DNA self-assembly. With the incorporation of an active targeting aptamer and an endosomal escape peptide by host-guest interaction, the biocompatible DNA nanoplatform demonstrates efficient inhibition of tumor growth without apparent systemic toxicity. This multifunctional DNA nanocarrier provides a new strategy for the development of gene therapeutics.

Targeting bromodomain-containing protein 4 (BRD4) inhibits MYC expression in colorectal cancer cells

The transcriptional regulator BRD4 has been shown to be important for the expression of several oncogenes including MYC. Inhibiting of BRD4 has broad antiproliferative activity in different cancer cell types. The small molecule JQ1 blocks the interaction of BRD4 with acetylated histones leading to transcriptional modulation. Depleting BRD4 via engineered bifunctional small molecules named PROTACs (proteolysis targeting chimeras) represents the next-generation approach to JQ1-mediated BRD4 inhibition. PROTACs trigger BRD4 for proteasomale degradation by recruiting E3 ligases. The aim of this study was therefore to validate the importance of BRD4 as a relevant target in colorectal cancer (CRC) cells and to compare the efficacy of BRD4 inhibition with BRD4 degradation on downregulating MYC expression. JQ1 induced a downregulation of both MYC mRNA and MYC protein associated with an antiproliferative phenotype in CRC cells. dBET1 and MZ1 induced degradation of BRD4 followed by a reduction in MYC expression and CRC cell proliferation. In SW480 cells, where dBET1 failed, we found significantly lower levels of the E3 ligase cereblon, which is essential for dBET1-induced BRD4 degradation. To gain mechanistic insight into the unresponsiveness to dBET1, we generated dBET1-resistant LS174t cells and found a strong downregulation of cereblon protein. These findings suggest that inhibition of BRD4 by JQ1 and degradation of BRD4 by dBET1 and MZ1 are powerful tools for reducing MYC expression and CRC cell proliferation. In addition, downregulation of cereblon may be an important mechanism for developing dBET1 resistance, which can be evaded by incubating dBET1-resistant cells with JQ1 or MZ1.

A view on drug resistance in cancer

The problem of resistance to therapy in cancer is multifaceted. Here we take a reductionist approach to define and separate the key determinants of drug resistance, which include tumour burden and growth kinetics; tumour heterogeneity; physical barriers; the immune system and the microenvironment; undruggable cancer drivers; and the many consequences of applying therapeutic pressures. We propose four general solutions to drug resistance that are based on earlier detection of tumours permitting cancer interception; adaptive monitoring during therapy; the addition of novel drugs and improved pharmacological principles that result in deeper responses; and the identification of cancer cell dependencies by high-throughput synthetic lethality screens, integration of clinico-genomic data and computational modelling. These different approaches could eventually be synthesized for each tumour at any decision point and used to inform the choice of therapy.

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.

Long non-coding RNA PVT1 interacts with MYC and its downstream molecules to synergistically promote tumorigenesis

Numerous studies have shown that non-coding RNAs play crucial roles in the development and progression of various tumor cells. Plasmacytoma variant translocation 1 (PVT1) mainly encodes a long non-coding RNA (lncRNA) and is located on chromosome 8q24.21, which constitutes a fragile site for genetic aberrations. PVT1 is well-known for its interaction with its neighbor MYC, which is a qualified oncogene that plays a vital role in tumorigenesis. In the past several decades, increasing attention has been paid to the interaction mechanism between PVT1 and MYC, which will benefit the clinical treatment and prognosis of patients. In this review, we summarize the coamplification of PVT1 and MYC in cancer, the positive feedback mechanism, and the latest promoter competition mechanism of PVT1 and MYC, as well as how PVT1 participates in the downstream signaling pathway of c-Myc by regulating key molecules. We also briefly describe the treatment prospects and research directions of PVT1 and MYC.

Clonal diversity of MYC amplification evaluated by fluorescent in situ hybridisation and digital droplet polymerase chain reaction in oesophagogastric cancer: Results from a prospective clinical trial screening programme

INTRODUCTION

The MYC proto-oncogene is among the most commonly dysregulated genes in human cancers. We report screening data from the iMYC trial, an ongoing phase II study assessing ibrutinib monotherapy in advanced pretreated MYC- and/or HER2-amplified oesophagogastric cancer, representing the first attempt to prospectively identify MYC amplifications in this tumour type for the purposes of therapeutic targeting.

METHODS

Screening utilising a fluorescent in situ hybridisation (FISH) assay for assessment of tumour MYC amplification has been instituted. An experimental digital droplet polymerase chain reaction (ddPCR) assay to assess MYC amplification in both tumour and circulating-tumour (ct)DNA has been developed and investigated.

RESULTS

One hundred thirty-five archival tumour specimens have undergone successful FISH analysis with 23% displaying evidence of MYC amplification. Intertumour heterogeneity was observed, with the percentage of cancer cells harbouring MYC amplification ranging widely between samples (median 51%, range 11-94%). Intratumoural clonal diversity of MYC amplification was also observed, with a significant degree of variance in amplification ratios (Bartlett's test for equal variance p < 0.001), and an association between greater variance in MYC amplification and improved outcome with prior first-line chemotherapy. ddPCR was most accurate in quantifying MYC amplification in tumour-derived DNA from cases with a high proportion (>70%) of amplified cells within the tumour specimen but was not reliable in samples containing a low proportion of amplified cells or in ctDNA.

CONCLUSIONS

Our results illustrate the utility of FISH to assess MYC amplification prospectively for a biomarker-selected trial by providing reliable and reproducible results in real time, with a high degree of heterogeneity of MYC amplification observed. We show that ddPCR can potentially detect high-level MYC amplifications in tumour tissue.

Regulation of senescence and the SASP by the transcription factor C/EBPβ

Oncogene-induced senescence (OIS) serves as an important barrier to tumor progression in cells that have acquired activating mutations in RAS and other oncogenes. Senescent cells also produce a secretome known as the senescence-associated secretory phenotype (SASP) that includes pro-inflammatory cytokines and chemokines. SASP factors reinforce and propagate the senescence program and identify senescent cells to the immune system for clearance. The OIS program is executed by several transcriptional effectors that include p53, RB, NF-κB and C/EBPβ. In this review, we summarize the critical role of C/EBPβ in regulating OIS and the SASP. Post-translational modifications induced by oncogenic RAS signaling control C/EBPβ activity and dimerization, and these alterations switch C/EBPβ to a pro-senescence form during OIS. In addition, C/EBPβ is regulated by a unique 3'UTR-mediated mechanism that restrains its activity in tumor cells to facilitate senescence bypass and suppression of the SASP.

Precision medicine by designer interference peptides: applications in oncology and molecular therapeutics

In molecular cancer therapeutics only 10% of known cancer gene products are targetable with current pharmacological agents. Major oncogenic drivers, such as MYC and KRAS proteins are frequently highly overexpressed or mutated in multiple human malignancies. However, despite their key role in oncogenesis, these proteins are hard to target with traditional small molecule drugs due to their large, featureless protein interfaces and lack of deep pockets. In addition, they are inaccessible to large biologicals, which are unable to cross cell membranes. Designer interference peptides (iPeps) represent emerging pharmacological agents created to block selective interactions between protein partners that are difficult to target with conventional small molecule chemicals or with large biologicals. iPeps have demonstrated successful inhibition of multiple oncogenic drivers with some now entering clinical settings. However, the clinical translation of iPeps has been hampered by certain intrinsic limitations including intracellular localization, targeting tissue specificity and pharmacological potency. Herein, we outline recent advances for the selective inhibition of major cancer oncoproteins via iPep approaches and discuss the development of multimodal peptides to overcome limitations of the first generations of iPeps. Since many protein–protein interfaces are cell-type specific, this approach opens the door to novel programmable, precision medicine tools in cancer research and treatment for selective manipulation and reprogramming of the cancer cell oncoproteome.

Glucose Metabolism in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive and lethal cancers, with a five-year survival rate of around 5% to 8%. To date, very few available drugs have been successfully used to treat PDAC due to the poor understanding of the tumor-specific features. One of the hallmarks of pancreatic cancer cells is the deregulated cellular energetics characterized by the “Warburg effect”. It has been known for decades that cancer cells have a dramatically increased glycolytic flux even in the presence of oxygen and normal mitochondrial function. Glycolytic flux is the central carbon metabolism process in all cells, which not only produces adenosine triphosphate (ATP) but also provides biomass for anabolic processes that support cell proliferation. Expression levels of glucose transporters and rate-limiting enzymes regulate the rate of glycolytic flux. Intermediates that branch out from glycolysis are responsible for redox homeostasis, glycosylation, and biosynthesis. Beyond enhanced glycolytic flux, pancreatic cancer cells activate nutrient salvage pathways, which includes autophagy and micropinocytosis, from which the generated sugars, amino acids, and fatty acids are used to buffer the stresses induced by nutrient deprivation. Further, PDAC is characterized by extensive metabolic crosstalk between tumor cells and cells in the tumor microenvironment (TME). In this review, we will give an overview on recent progresses made in understanding glucose metabolism-related deregulations in PDAC.

Targeting Antitumoral Proteins to Breast Cancer by Local Administration of Functional Inclusion Bodies

Two structurally and functionally unrelated proteins, namely Omomyc and p31, are engineered as CD44-targeted inclusion bodies produced in recombinant bacteria. In this unusual particulate form, both types of protein materials selectively penetrate and kill CD44+ tumor cells in culture, and upon local administration, promote destruction of tumoral tissue in orthotropic mouse models of human breast cancer. These findings support the concept of bacterial inclusion bodies as versatile protein materials suitable for application in chronic diseases that, like cancer, can benefit from a local slow release of therapeutic proteins.

A Yap-Myc-Sox2-p53 Regulatory Network Dictates Metabolic Homeostasis and Differentiation in Kras-Driven Pancreatic Ductal Adenocarcinomas

Employing inducible genetically engineered and orthotopic mouse models, we demonstrate a key role for transcriptional regulator Yap in maintenance of Kras-mutant pancreatic tumors. Integrated transcriptional and metabolomics analysis reveals that Yap transcribes Myc and cooperates with Myc to maintain global transcription of metabolic genes. Yap loss triggers acute metabolic stress, which causes tumor regression while inducing epigenetic reprogramming and Sox2 upregulation in a subset of pancreatic neoplastic cells. Sox2 restores Myc expression and metabolic homeostasis in Yap-deficient neoplastic ductal cells, which gradually re-differentiate into acinar-like cells, partially restoring pancreatic parenchyma in vivo. Both the short-term and long-term effects of Yap loss in inducing cell death and re-differentiation, respectively, are blunted in advanced, poorly differentiated p53-mutant pancreatic tumors. Collectively, these findings reveal a highly dynamic and interdependent metabolic, transcriptional, and epigenetic regulatory network governed by Yap, Myc, Sox2, and p53 that dictates pancreatic tumor metabolism, growth, survival, and differentiation.

Liquid-Liquid Phase Separation in Disease

We have made rapid progress in recent years in identifying the genetic causes of many human diseases. However, despite this recent progress, our mechanistic understanding of these diseases is often incomplete. This is a problem because it limits our ability to develop effective disease treatments. To overcome this limitation, we need new concepts to describe and comprehend the complex mechanisms underlying human diseases. Condensate formation by phase separation emerges as a new principle to explain the organization of living cells. In this review, we present emerging evidence that aberrant forms of condensates are associated with many human diseases, including cancer, neurodegeneration, and infectious diseases. We examine disease mechanisms driven by aberrant condensates, and we point out opportunities for therapeutic interventions. We conclude that phase separation provides a useful new framework to understand and fight some of the most severe human diseases.

Site-specific amino acid substitution in dodecameric peptides determines the stability and unfolding of c-MYC quadruplex promoting apoptosis in cancer cells

c-MYC proto-oncogene harbours a transcription-inhibitory quadruplex-forming scaffold (Pu27) upstream P₁ promoter providing anti-neoplastic therapeutic target. Previous reports showed the binding profile of human Cathelicidin peptide (LL37) and telomeric G-quadruplex. Here, we truncated the quadruplex-binding domain of LL37 to prepare a small library of peptides through site-specific amino acid substitution. We investigated the intracellular selectivity of peptides for Pu27 over other oncogenic quadruplexes and their role in c-MYC promoter repression by dual-luciferase assays. We analysed their thermodynamics of binding reactions with c-MYC quadruplex isomers (Pu27, Myc22, Pu19) by Isothermal Titration Calorimetry. We discussed how amino acid substitutions and peptide helicity enhanced/weakened their affinities for c-MYC quadruplexes and characterized specific non-covalent inter-residual interactions determining their selectivity. Solution NMR structure indicated that KR12C, the best peptide candidate, selectively stabilized the 5′-propeller loop of c-MYC quadruplex by arginine-driven electrostatic-interactions at the sugar-phosphate backbone while KR12A peptide destabilized the quadruplex inducing a single-stranded hairpin-like conformation. Chromatin immunoprecipitations envisaged that KR12C and KR12A depleted and enriched Sp1 and NM23-H2 (Nucleoside diphosphate kinase) occupancy at Pu27 respectively supporting their regulation in stabilizing and unfolding c-MYC quadruplex in MCF-7 cells. We deciphered that selective arresting of c-MYC transcription by KR12C triggered apoptotic-signalling pathway via VEGF-A-BCL-2 axis.

Application of a MYC degradation screen identifies sensitivity to CDK9 inhibitors in KRAS-mutant pancreatic cancer

Stabilization of the MYC oncoprotein by KRAS signaling critically promotes the growth of pancreatic ductal adenocarcinoma (PDAC). Thus, understanding how MYC protein stability is regulated may lead to effective therapies. Here, we used a previously developed, flow cytometry-based assay that screened a library of >800 protein kinase inhibitors and identified compounds that promoted either the stability or degradation of MYC in a KRAS-mutant PDAC cell line. We validated compounds that stabilized or destabilized MYC and then focused on one compound, UNC10112785, that induced the substantial loss of MYC protein in both two-dimensional (2D) and 3D cell cultures. We determined that this compound is a potent CDK9 inhibitor with a previously uncharacterized scaffold, caused MYC loss through both transcriptional and posttranslational mechanisms, and suppresses PDAC anchorage-dependent and anchorage-independent growth. We discovered that CDK9 enhanced MYC protein stability through a previously unknown, KRAS-independent mechanism involving direct phosphorylation of MYC at Ser⁶² Our study thus not only identifies a potential therapeutic target for patients with KRAS-mutant PDAC but also presents the application of a screening strategy that can be more broadly adapted to identify regulators of protein stability.

Crystal Structures and Nuclear Magnetic Resonance Studies of the Apo Form of the c-MYC:MAX bHLHZip Complex Reveal a Helical Basic Region in the Absence of DNA

The c-MYC transcription factor is a master regulator of cell growth and proliferation and is an established target for cancer therapy. This basic helix–loop–helix Zip protein forms a heterodimer with its obligatory partner MAX, which binds to DNA via the basic region. Considerable research efforts are focused on targeting the heterodimerization interface and the interaction of the complex with DNA. The only available crystal structure is that of a c-MYC:MAX complex artificially tethered by an engineered disulfide linker and prebound to DNA. We have carried out a detailed structural analysis of the apo form of the c-MYC:MAX complex, with no artificial linker, both in solution using nuclear magnetic resonance (NMR) spectroscopy and by X-ray crystallography. We have obtained crystal structures in three different crystal forms, with resolutions between 1.35 and 2.2 Å, that show extensive helical structure in the basic region. Determination of the α-helical propensity using NMR chemical shift analysis shows that the basic region of c-MYC and, to a lesser extent, that of MAX populate helical conformations. We have also assigned the NMR spectra of the c-MYC basic helix–loop–helix Zip motif in the absence of MAX and showed that the basic region has an intrinsic helical propensity even in the absence of its dimerization partner. The presence of helical structure in the basic regions in the absence of DNA suggests that the molecular recognition occurs via a conformational selection rather than an induced fit. Our work provides both insight into the mechanism of DNA binding and structural information to aid in the development of MYC inhibitors.

MYC deregulates TET1 and TET2 expression to control global DNA (hydroxy)methylation and gene expression to maintain a neoplastic phenotype in T-ALL

BACKGROUND

While aberrant DNA methylation is a characteristic feature of tumor cells, our knowledge of how these DNA methylation patterns are established and maintained is limited. DNA methyltransferases and ten-eleven translocation methylcytosine dioxygenases (TETs) function has been found altered in a variety of cancer types.

RESULTS

Here, we report that in T cell acute lymphoblastic leukemia (T-ALL) the MYC oncogene controls the expression of TET1 and TET2 to maintain 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) patterns, which is associated with tumor cell-specific gene expression. We found that cellular senescence and tumor regression upon MYC inactivation in T-ALL was associated with genome-wide changes in 5mC and 5hmC patterns. Correlating with the changes in DNA (hydroxy)methylation, we found that T-ALL overexpress TET1, while suppressing TET2 in a MYC-dependent fashion. Consequently, MYC inactivation led to an inverse expression pattern, decreasing TET1, while increasing TET2 levels. Knockdown of TET1 or ectopic expression of TET2 in T-ALL was associated with genome-wide changes in 5mC and 5hmC enrichment and decreased cell proliferation, suggesting a tumor promoting function of TET1, and a tumor suppressing role for TET2. Among the genes and pathways controlled by TET1, we found ribosomal biogenesis and translational control of protein synthesis highly enriched.

CONCLUSIONS

Our finding that MYC directly deregulates the expression of TET1 and TET2 in T-ALL provides novel evidence that MYC controls DNA (hydroxy)methylation in a genome-wide fashion. It reveals a coordinated interplay between the components of the DNA (de)methylating machinery that contribute to MYC-driven tumor maintenance, highlighting the potential of specific TET enzymes for therapeutic strategies.