Regulation of GLI Underlies a Role for BET Bromodomains in Pancreatic Cancer Growth and the Tumor Microenvironment

Epigenetic Regulation of Stromal and Immune Cells and Therapeutic Targets in the Tumor Microenvironment

The tumor microenvironment (TME) plays a pivotal role in neoplastic initiation and progression. Epigenetic machinery, governing the expression of core oncogenes and tumor suppressor genes in transformed cells, significantly contributes to tumor development at both primary and distant sites. Recent studies have illuminated how epigenetic mechanisms integrate external cues and downstream signals, altering the phenotype of stromal cells and immune cells. This remolds the area surrounding tumor cells, ultimately fostering an immunosuppressive microenvironment. Therefore, correcting the TME by targeting the epigenetic modifications holds substantial promise for cancer treatment. This review synthesizes recent research that elucidates the impact of specific epigenetic regulations-ranging from DNA methylation to histone modifications and chromatin remodeling-on stromal and immune cells within the TME. Notably, we highlight their functional roles in either promoting or restricting tumor progression. We also discuss the potential applications of epigenetic agents for cancer treatment, envisaging their ability to normalize the ecosystem. This review aims to assist researchers in understanding the dynamic interplay between epigenetics and the TME, paving the way for better epigenetic therapy.

Allysine-Targeted Molecular MRI Enables Early Prediction of Chemotherapy Response in Pancreatic Cancer

Neoadjuvant therapy is routinely used in pancreatic ductal adenocarcinoma (PDAC), but not all tumors respond to this treatment. Current clinical imaging techniques are not able to precisely evaluate and predict the response to neoadjuvant therapies over several weeks. A strong fibrotic reaction is a hallmark of a positive response, and during fibrogenesis, allysine residues are formed on collagen proteins by the action of lysyl oxidases. Here, we report the application of an allysine-targeted molecular MRI probe, MnL3, to provide an early, noninvasive assessment of treatment response in PDAC. Allysine increased 2- to 3-fold after one dose of neoadjuvant therapy with FOLFIRINOX in sensitive human PDAC xenografts in mice. Molecular MRI with MnL3 could specifically detect and quantify fibrogenesis in PDAC xenografts. Comparing the MnL3 signal before and 3 days after one dose of FOLFIRINOX predicted subsequent treatment response. The MnL3 tumor signal increased by 70% from day 0 to day 3 in mice that responded to subsequent doses of FOLFIRINOX, whereas no signal increase was observed in FOLFIRINOX-resistant tumors. This study indicates the promise of allysine-targeted molecular MRI as a noninvasive tool to predict chemotherapy outcomes. Significance: Allysine-targeted molecular MRI can quantify fibrogenesis in pancreatic tumors and predict response to chemotherapy, which could guide rapid clinical management decisions by differentiating responders from nonresponders after treatment initiation.

PRMT1 promotes epigenetic reprogramming associated with acquired chemoresistance in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) carries a dismal prognosis due to therapeutic resistance. We show that PDAC cells undergo global epigenetic reprogramming to acquire chemoresistance, a process that is driven at least in part by protein arginine methyltransferase 1 (PRMT1). Genetic or pharmacological PRMT1 inhibition impairs adaptive epigenetic reprogramming and delays acquired resistance to gemcitabine and other common chemo drugs. Mechanistically, gemcitabine treatment induces translocation of PRMT1 into the nucleus, where its enzymatic activity limits the assembly of chromatin-bound MAFF/BACH1 transcriptional complexes. Cut&Tag chromatin profiling of H3K27Ac, MAFF, and BACH1 suggests a pivotal role for MAFF/BACH1 in global epigenetic response to gemcitabine, which is confirmed by genetically silencing MAFF. PRMT1 and MAFF/BACH1 signature genes identified by Cut&Tag analysis distinguish gemcitabine-resistant from gemcitabine-sensitive patient-derived xenografts of PDAC, supporting the PRMT1-MAFF/BACH1 epigenetic regulatory axis as a potential therapeutic avenue for improving the efficacy and durability of chemotherapies in patients of PDAC.

The comprehensive landscape of prognosis, immunity, and function of the GLI family by pan-cancer and single-cell analysis

The Hedgehog (Hh) signaling pathway has been implicated in the pathogenesis of various cancers. However, the roles of the downstream GLI family (GLI1, GLI2, and GLI3) in tumorigenesis remain elusive. This study aimed to unravel the genetic alterations of GLI1/2/3 in cancer and their association with the immune microenvironment and related signaling pathways. Firstly, we evaluated the expression profiles of GLI1/2/3 in different cancer types, analyzed their prognostic and predictive values, and assessed their correlation with tumor-infiltrating immune cells. Secondly, we explored the relationships between GLI1/2/3 and genetic mutations, epigenetic modifications, and clinically relevant drugs. Finally, we performed enrichment analysis to decipher the underlying mechanisms of GLI1/2/3 in cancer initiation and progression. Our results revealed that the expression levels of GLI1/2/3 were positively correlated in most cancer tissues, suggesting a cooperative role of these factors in tumorigenesis. We also identified tissue-specific expression patterns of GLI1/2/3, which may reflect the distinct functions of these factors in different cell types. Furthermore, GLI1/2/3 expression displayed significant associations with poor prognosis in several cancers, indicating their potential as prognostic biomarkers and therapeutic targets. Importantly, we found that GLI1/2/3 modulated the immune microenvironment by regulating the recruitment, activation, and polarization of cancer-associated fibroblasts, endothelial cells, and macrophages. Additionally, functional enrichment analyses indicated that GLI1/2/3 are involved in the regulation of epithelial-mesenchymal transition (EMT). Together, our findings shed new light on the roles of GLI1/2/3 in tumorigenesis and provide a potential basis for the development of novel therapeutic strategies targeting GLI-mediated signaling pathways in cancer.

Epigenetic small-molecule screen for inhibition and reversal of acinar ductal metaplasia in mouse pancreatic organoids

Background: Acinar ductal metaplasia (ADM) is among the earliest initiating events in pancreatic ductal adenocarcinoma (PDAC) development. Methods: We developed a novel morphology-based screen using organoids from wildtype and p48Cre/+ (Cre) mice to discover epigenetic modulators that inhibit or reverse pancreatic ADM more effectively than the broad-spectrum HDAC inhibitor trichostatin A (TSA). Results: Of the 144 compounds screened, nine hits and two additional natural product HDAC inhibitors were validated by dose-response analysis. The class I HDAC inhibitors apicidin and FK228, and the histone methyltransferase inhibitor chaetocin demonstrated pronounced ADM inhibition and reversal without inducing significant cytotoxicity at 1 µM. Thioester prodrug class I HDAC inhibitor largazole attenuated ADM while its disulfide homodimer was effective in both ADM inhibition and reversal. Prioritized compounds were validated for ADM reversal in p48Cre/+; LSL-KrasG12D/+ (KC) mouse organoids using both morphological and molecular endpoints. Molecular index analysis of ADM reversal in KC mouse organoids demonstrated improved activity compared to TSA. Improved prodrug stability translated into a stronger phenotypic and molecular response. RNA-sequencing indicated that angiotensinogen was the top inhibited pathway during ADM reversal. Conclusion: Our findings demonstrate a unique epigenetic mechanism and suggest that the phenotypic screen developed here may be applied to discover potential treatments for PDAC.

Small-molecule agents for cancer immunotherapy

Cancer immunotherapy, exemplified by the remarkable clinical benefits of the immune checkpoint blockade and chimeric antigen receptor T-cell therapy, is revolutionizing cancer therapy. They induce long-term tumor regression and overall survival benefit in many types of cancer. With the advances in our knowledge about the tumor immune microenvironment, remarkable progress has been made in the development of small-molecule drugs for immunotherapy. Small molecules targeting PRR-associated pathways, immune checkpoints, oncogenic signaling, metabolic pathways, cytokine/chemokine signaling, and immune-related kinases have been extensively investigated. Monotherapy of small-molecule immunotherapeutic drugs and their combinations with other antitumor modalities are under active clinical investigations to overcome immune tolerance and circumvent immune checkpoint inhibitor resistance. Here, we review the latest development of small-molecule agents for cancer immunotherapy by targeting defined pathways and highlighting their progress in recent clinical investigations.

Epigenetic Small-Molecule Screen for Inhibition and Reversal of Acinar Ductal Metaplasia in Mouse Pancreatic Organoids

Background

Acinar ductal metaplasia (ADM) is among the earliest initiating events in pancreatic ductal adenocarcinoma (PDAC) development.

Methods

We developed a novel morphology-based screen using organoids from wildtype and p48 Cre/+ (Cre) mice to discover epigenetic modulators that inhibit or reverse pancreatic ADM more effectively than the broad-spectrum HDAC inhibitor trichostatin A (TSA).

Results

Of the 144 compounds screened, nine hits and two additional natural product HDAC inhibitors were validated by dose-response analysis. The class I HDAC inhibitors apicidin and FK228, and the histone methyltransferase inhibitor chaetocin demonstrated pronounced ADM inhibition and reversal without inducing significant cytotoxicity at 1 µM. Thioester prodrug class I HDAC inhibitor largazole attenuated ADM while its disulfide homodimer was effective in both ADM inhibition and reversal. Prioritized compounds were validated for ADM reversal in p48 Cre/+ ;LSL-Kras G12D/+ (KC) mouse organoids using both morphological and molecular endpoints. Molecular index analysis of ADM reversal in KC mouse organoids demonstrated improved activity compared to TSA. Improved prodrug stability translated into a stronger phenotypic and molecular response. RNA-sequencing indicated that angiotensinogen was the top inhibited pathway during ADM reversal.

Conclusion

Our findings demonstrate a unique epigenetic mechanism and suggest that the phenotypic screen developed here may be applied to discover potential treatments for PDAC.

Hedgehog signaling and the glioma-associated oncogene in cancer radioresistance

Tumor radioresistance remains a key clinical challenge. The Hedgehog (HH) signaling pathway and glioma-associated oncogene (GLI) are aberrantly activated in several cancers and are thought to contribute to cancer radioresistance by influencing DNA repair, reactive oxygen species production, apoptosis, autophagy, cancer stem cells, the cell cycle, and the tumor microenvironment. GLI is reported to activate the main DNA repair pathways, to interact with cell cycle regulators like Cyclin D and Cyclin E, to inhibit apoptosis via the activation of B-cell lymphoma-2, Forkhead Box M1, and the MYC proto-oncogene, to upregulate cell stemness related genes (Nanog, POU class 5 homeobox 1, SRY-box transcription factor 2, and the BMI1 proto-oncogene), and to promote cancer stem cell transformation. The inactivation of Patched, the receptor of HH, prevents caspase-mediated apoptosis. This causes some cancer cells to survive while others become cancer stem cells, resulting in cancer recurrence. Combination treatment using HH inhibitors (including GLI inhibitors) and conventional therapies may enhance treatment efficacy. However, the clinical use of HH signaling inhibitors is associated with toxic side effects and drug resistance. Nevertheless, selective HH agonists, which may relieve the adverse effects of inhibitors, have been developed in mouse models. Combination therapy with other pathway inhibitors or immunotherapy may effectively overcome resistance to HH inhibitors. A comprehensive cancer radiotherapy with HH or GLI inhibitor is more likely to enhance cancer treatment efficacy while further studies are still needed to overcome its adverse effects and drug resistance.

Deoxyribonucleic acid methylation driven aberrations in pancreatic cancer-related pathways

Pancreatic cancer (PanCa) presents a catastrophic disease with poor overall survival at advanced stages, with immediate requirement of new and effective treatment options. Besides genetic mutations, epigenetic dysregulation of signaling pathway-associated enriched genes are considered as novel therapeutic target. Mechanisms beneath the deoxyribonucleic acid methylation and its utility in developing of epi-drugs in PanCa are under trails. Combinations of epigenetic medicines with conventional cytotoxic treatments or targeted therapy are promising options to improving the dismal response and survival rate of PanCa patients. Recent studies have identified potentially valid pathways that support the prediction that future PanCa clinical trials will include vigorous testing of epigenomic therapies. Epigenetics thus promises to generate a significant amount of new knowledge of biological and medical importance. Our review could identify various components of epigenetic mechanisms known to be involved in the initiation and development of pancreatic ductal adenocarcinoma and related precancerous lesions, and novel pharmacological strategies that target these components could potentially lead to breakthroughs. We aim to highlight the possibilities that exist and the potential therapeutic interventions.

Molecular profiling and specific targeting of gemcitabine-resistant subclones in heterogeneous pancreatic cancer cell populations

Purpose

Chemotherapy is pivotal in the multimodal treatment of pancreatic ductal adenocarcinoma (PDAC). Technical advances unveiled a high degree of inter- and intratumoral heterogeneity. We hypothesized that intratumoral heterogeneity (ITH) impacts response to gemcitabine treatment and demands specific targeting of resistant subclones.

Methods

Using single cell-derived cell lines (SCDCLs) from the classical cell line BxPC3 and the basal-like cell line Panc-1, we addressed the effect of ITH on response to gemcitabine treatment.

Results

Individual SCDCLs of both parental tumor cell populations showed considerable heterogeneity in response to gemcitabine. Unsupervised PCA including the 1,000 most variably expressed genes showed a clustering of the SCDCLs according to their respective sensitivity to gemcitabine treatment for BxPC3, while this was less clear for Panc-1. In BxPC3 SCDCLs, enriched signaling pathways EMT, TNF signaling via NfKB, and IL2STAT5 signaling correlated with more resistant behavior to gemcitabine. In Panc-1 SCDCLs MYC targets V1 and V2 as well as E2F targets were associated with stronger resistance. We used recursive feature elimination for Feature Selection in order to compute sets of proteins that showed strong association with the response to gemcitabine. The optimal protein set calculated for Panc-1 comprised fewer proteins in comparison to the protein set determined for BxPC3. Based on molecular profiles, we could show that the gemcitabine-resistant SCDCLs of both BxPC3 and Panc-1 are more sensitive to the BET inhibitor JQ1 compared to the respective gemcitabine-sensitive SCDCLs.

Conclusion

Our model system of SCDCLs identified gemcitabine-resistant subclones and provides evidence for the critical role of ITH for treatment response in PDAC. We exploited molecular differences as the basis for differential response and used these for more targeted therapy of resistant subclones.

Multiprotein GLI Transcriptional Complexes as Therapeutic Targets in Cancer

The Hedgehog signaling pathway functions in both embryonic development and adult tissue homeostasis. Importantly, its aberrant activation is also implicated in the progression of multiple types of cancer, including basal cell carcinoma and medulloblastoma. GLI transcription factors function as the ultimate effectors of the Hedgehog signaling pathway. Their activity is regulated by this signaling cascade via their mRNA expression, protein stability, subcellular localization, and ultimately their transcriptional activity. Further, GLI proteins are also regulated by a variety of non-canonical mechanisms in addition to the canonical Hedgehog pathway. Recently, with an increased understanding of epigenetic gene regulation, novel transcriptional regulators have been identified that interact with GLI proteins in multi-protein complexes to regulate GLI transcriptional activity. Such complexes have added another layer of complexity to the regulation of GLI proteins. Here, we summarize recent work on the regulation of GLI transcriptional activity by these novel protein complexes and describe their relevance to cancer, as such GLI regulators represent alternative and innovative druggable targets in GLI-dependent cancers.

Epigenetic regulation of pancreatic adenocarcinoma in the era of cancer immunotherapy

Pancreatic adenocarcinoma is a lethal cancer with poor response to chemotherapy and immune checkpoint inhibitors. Recent studies suggest that epigenetic alterations contribute to its aggressive biology and the tumor microenvironment which render it unresponsive to immune checkpoint blockade. Here, we review our current understandings of epigenetic dysregulation in pancreatic adenocarcinoma, its effect on the tumor immune microenvironment, and the potential for epigenetic therapy to be combined with immune checkpoint inhibitors.

Ecoevolutionary biology of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC), the most common histological subtype of pancreatic cancer, is an aggressive disease predicted to be the 2nd cause of cancer mortality in the US by 2040. While first-line therapy has improved, 5-year overall survival has only increased from 5 to ∼10%, and surgical resection is only available for ∼20% of patients as most present with advanced disease, which is invariably lethal. PDAC has well-established highly recurrent mutations in four driver genes including KRAS, TP53, CDKN2A, and SMAD4. Unfortunately, these genetic drivers are not currently therapeutically actionable. Despite extensive sequencing efforts, few additional significantly recurrent and druggable drivers have been identified. In the absence of targetable mutations, chemotherapy remains the mainstay of treatment for most patients. Further, the role of the above driver mutations on PDAC initiation and early development is well-established. However, these mutations alone cannot account for PDAC heterogeneity nor discern early from advanced disease. Taken together, management of PDAC is an example highlighting the shortcomings of the current precision medicine paradigm. PDAC, like other malignancies, represents an ecoevolutionary process. Better understanding the disease through this lens can facilitate the development of novel therapeutic strategies to better control and cure PDAC. This review aims to integrate the current understanding of PDAC pathobiology into an ecoevolutionary framework.

BET inhibitors: an updated patent review (2018-2021)

INTRODUCTION

Bromodomain and extraterminal (BET) proteins are epigenetic readers that regulate gene transcription and cell growth by binding to acetylated lysine resides on histones. They are involved in many physiological processes and pathological conditions such as cancer, inflammation, and metabolic diseases. Blockade of BET proteins has become an encouraging approach for the treatment of these human diseases, especially cancer. To date, a number of potent and specific BET inhibitors have been discovered and many of them have entered clinical trials.

AREAS COVERED

This review aims at providing an overview of molecular mechanisms of BET inhibitors and highlighting the research advancements published in recent patent literatures between 2018 and 2021. Web of Science, PubMed, SciFinder, WIPO, EPO, USPTO and CNIPA databases were used for searching the literature and patents for BET inhibitors.

EXPERT OPINION

In recent years, an increasing number of structurally diverse BET inhibitors have been identified, including pan BET inhibitors, BD1 or BD2 selective BET inhibitors, bivalent BET inhibitors, kinase and BET dual inhibitors and BET-PROTACs. Despite of many challenges, BET inhibitors have high potential in the treatment of cancer and other diseases and the development of next-generation BET inhibitors could be promising.

Advances in glioma-associated oncogene (GLI) inhibitors for cancer therapy

The Hedgehog/Glioma-associated oncogene homolog (HH/GLI) signaling pathway regulates self-renewal of rare and highly malignant cancer stem cells, which have been shown to account for the initiation and maintenance of tumor growth as well as for drug resistance, metastatic spread and relapse. As an important component of the Hh signaling pathway, glioma-associated oncogene (GLI) acts as a key signal transmission hub for various signaling pathways in many tumors. Here, we review direct and indirect inhibitors of GLI; summarize the abundant active structurally diverse natural GLI inhibitors; and discuss how to better develop and utilize GLI inhibitors to solve the problem of drug resistance in tumors of interest. In summary, GLI inhibitors will be promising candidates for various cancer treatments.

Potent pro-apoptotic combination therapy is highly effective in a broad range of cancers

Primary or acquired therapy resistance is a major obstacle to the effective treatment of cancer. Resistance to apoptosis has long been thought to contribute to therapy resistance. We show here that recombinant TRAIL and CDK9 inhibition cooperate in killing cells derived from a broad range of cancers, importantly without inducing detectable adverse events. Remarkably, the combination of TRAIL with CDK9 inhibition was also highly effective on cancers resistant to both, standard-of-care chemotherapy and various targeted therapeutic approaches. Dynamic BH3 profiling revealed that, mechanistically, combining TRAIL with CDK9 inhibition induced a drastic increase in the mitochondrial priming of cancer cells. Intriguingly, this increase occurred irrespective of whether the cancer cells were sensitive or resistant to chemo- or targeted therapy. We conclude that this pro-apoptotic combination therapy has the potential to serve as a highly effective new treatment option for a variety of different cancers. Notably, this includes cancers that are resistant to currently available treatment modalities.

Mutant GNAS limits tumor aggressiveness in established pancreatic cancer via antagonizing the KRAS-pathway

BACKGROUND

Mutations in GNAS drive pancreatic tumorigenesis and frequently occur in intraductal papillary mucinous neoplasm (IPMN); however, their value as a therapeutic target is yet to be determined. This study aimed at evaluating the involvement of mutant GNAS in tumor aggressiveness in established pancreatic cancer.

METHODS

CRISPR/Cas9-mediated GNAS R201H silencing was performed using human primary IPMN-associated pancreatic cancer cells. The role of oncogenic GNAS in tumor maintenance was evaluated by conducting cell culture and xenograft experiments, and western blotting and transcriptome analyses were performed to uncover GNAS-driven signatures.

RESULTS

Xenografts of GNAS wild-type cells were characterized by a higher Ki-67 labeling index relative to GNAS-mutant cells. Phenotypic alterations in the GNAS wild-type tumors resulted in a significant reduction in mucin production accompanied by solid with massive stromal components. Transcriptional profiling suggested an apparent conflict of mutant GNAS with KRAS signaling. A significantly higher Notch intercellular domain (NICD) was observed in the nuclear fraction of GNAS wild-type cells. Meanwhile, inhibition of protein kinase A (PKA) induced NICD in GNAS-mutant IPMN cells, suggesting that NOTCH signaling is negatively regulated by the GNAS-PKA pathway. GNAS wild-type cells were characterized by a significant invasive property relative to GNAS-mutant cells, which was mediated through the NOTCH regulatory pathway.

CONCLUSIONS

Oncogenic GNAS induces mucin production, not only via MUC2 but also via MUC5AC/B, which may enlarge cystic lesions in the pancreas. The mutation may also limit tumor aggressiveness by attenuating NOTCH signaling; therefore, such tumor-suppressing effects must be considered when therapeutically inhibiting the GNAS pathway.

Emerging Role of Epigenetic Alterations as Biomarkers and Novel Targets for Treatments in Pancreatic Ductal Adenocarcinoma

Simple Summary

Epigenetic alterations cause changes in gene expression without affecting the DNA sequence and are found to affect several molecular pathways in pancreatic tumors. Such changes are reversible, making them potential drug targets. Furthermore, epigenetic alterations occur early in the disease course and may thus be explored for early detection. Hence, a deeper understanding of epigenetics in pancreatic cancer may lead to improved diagnostics, treatments, and prognostication.

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease with limited treatment options. Emerging evidence shows that epigenetic alterations are present in PDAC. The changes are potentially reversible and therefore promising therapeutic targets. Epigenetic aberrations also influence the tumor microenvironment with the potential to modulate and possibly enhance immune-based treatments. Epigenetic marks can also serve as diagnostic screening tools, as epigenetic changes occur at early stages of the disease. Further, epigenetics can be used in prognostication. The field is evolving, and this review seeks to provide an updated overview of the emerging role of epigenetics in the diagnosis, treatment, and prognostication of PDAC.

Bromodomain and extra-terminal inhibitors emerge as potential therapeutic avenues for gastrointestinal cancers

Gastrointestinal (GI) cancers, including colorectal cancer, pancreatic cancer, liver cancer and gastric cancer, are severe social burdens due to high incidence and mortality rates. Bromodomain and extra-terminal (BET) proteins are epigenetic readers consisting of four conserved members (BRD2, BRD3, BRD4 and BRDT). BET family perform pivotal roles in tumorigenesis through transcriptional regulation, thereby emerging as potential therapeutic targets. BET inhibitors, disrupting the interaction between BET proteins and acetylated lysines, have been reported to suppress tumor initiation and progression in most of GI cancers. In this review, we will demonstrate how BET proteins participate in the GI cancers progression and highlight the therapeutic potential of targeting BET proteins for GI cancers treatment.

Hedgehog Pathway Inhibitors against Tumor Microenvironment

Targeting the hedgehog (HH) pathway to treat aggressive cancers of the brain, breast, pancreas, and prostate has been ongoing for decades. Gli gene amplifications have been long discovered within malignant glioma patients, and since then, inhibitors against HH pathway-associated molecules have successfully reached the clinical stage where several of them have been approved by the FDA. Albeit this success rate implies suitable progress, clinically used HH pathway inhibitors fail to treat patients with metastatic or recurrent disease. This is mainly due to heterogeneous tumor cells that have acquired resistance to the inhibitors along with the obstacle of effectively targeting the tumor microenvironment (TME). Severe side effects such as hyponatremia, diarrhea, fatigue, amenorrhea, nausea, hair loss, abnormal taste, and weight loss have also been reported. Furthermore, HH signaling is known to be involved in the regulation of immune cell maturation, angiogenesis, inflammation, and polarization of macrophages and myeloid-derived suppressor cells. It is critical to determine key mechanisms that can be targeted at different levels of tumor development and progression to address various clinical issues. Hence current research focus encompasses understanding how HH controls TME to develop TME altering and combinatorial targeting strategies. In this review, we aim to discuss the pros and cons of targeting HH signaling molecules, understand the mechanism involved in treatment resistance, reveal the role of the HH pathway in anti-tumor immune response, and explore the development of potential combination treatment of immune checkpoint inhibitors with HH pathway inhibitors to target HH-driven cancers.

Targeting non-canonical activation of GLI1 by the SOX2-BRD4 transcriptional complex improves the efficacy of HEDGEHOG pathway inhibition in melanoma

Despite the development of new targeted and immune therapies, the prognosis of metastatic melanoma remains bleak. Therefore, it is critical to better understand the mechanisms controlling advanced melanoma to develop more effective treatment regimens. Hedgehog/GLI (HH/GLI) signaling inhibitors targeting the central pathway transducer Smoothened (SMO) have shown to be clinical efficacious in skin cancer; however, several mechanisms of non-canonical HH/GLI pathway activation limit their efficacy. Here, we identify a novel SOX2-BRD4 transcriptional complex driving the expression of GLI1, the final effector of the HH/GLI pathway, providing a novel mechanism of non-canonical SMO-independent activation of HH/GLI signaling in melanoma. Consistently, we find a positive correlation between the expression of GLI1 and SOX2 in human melanoma samples and cell lines. Further, we show that combined targeting of canonical HH/GLI pathway with the SMO inhibitor MRT-92 and of the SOX2-BRD4 complex using a potent Proteolysis Targeted Chimeras (PROTACs)-derived BRD4 degrader (MZ1), yields a synergistic anti-proliferative effect in melanoma cells independently of their BRAF, NRAS, and NF1 mutational status, with complete abrogation of GLI1 expression. Combination of MRT-92 and MZ1 strongly potentiates the antitumor effect of either drug as single agents in an orthotopic melanoma model. Together, our data provide evidence of a novel mechanism of non-canonical activation of GLI1 by the SOX2-BRD4 transcriptional complex, and describe the efficacy of a new combinatorial treatment for a subset of melanomas with an active SOX2-BRD4-GLI1 axis.

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

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

Targeting the GLI family of transcription factors for the development of anti-cancer drugs

INTRODUCTION

GLI1 is a transcription factor that has been identified as a downstream effector for multiple tumorigenic signaling pathways. These include the Hedgehog, RAS-RAF-MEK-ERK, and PI3K-AKT-mTOR pathways, which have all been separately validated as individual anti-cancer drug targets. The identification of GLI1 as a key transcriptional regulator for each of these pathways highlights its promise as a therapeutic target. Small molecule GLI1 inhibitors are potentially efficacious against human malignancies arising from multiple oncogenic mechanisms.

AREAS COVERED

This review provides an overview of the key oncogenic cellular pathways that regulate GLI1 transcriptional activity. It also provides a detailed account of small molecule GLI1 inhibitors that are currently under development as potential anti-cancer chemotherapeutics.

EXPERT OPINION

Interest in developing inhibitors of GLI1-mediated transcription has significantly increased as its role in multiple oncogenic signaling pathways has been elucidated. To date, it has proven difficult to directly target GLI1 with small molecules, and the majority of compounds that inhibit GLI1 activity function through indirect mechanisms. To date, no direct-acting GLI1 inhibitor has entered clinical trials. The identification and development of new scaffolds that can bind and directly inhibit GLI1 are essential to further advance this class of chemotherapeutics.

Neoplastic-Stromal Cell Cross-talk Regulates Matrisome Expression in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a highly desmoplastic reaction, warranting intense cancer-stroma communication. In this study, we interrogated the contribution of the BET family of chromatin adaptors to the cross-talk between PDAC cells and the tumor stroma. Short-term treatment of orthotopic xenograft tumors with CPI203, a small-molecule inhibitor of BET proteins, resulted in broad changes in the expression of genes encoding components of the extracellular matrix (matrisome) in both cancer and stromal cells. Remarkably, more than half of matrisome genes were expressed by cancer cells. In vitro cocultures of PDAC cells and cancer-associated fibroblasts (CAF) demonstrated that matrisome expression was regulated by BET-dependent cancer-CAF cross-talk. Disrupting this cross-talk in vivo resulted in diminished growth of orthotopic patient-derived xenograft tumors, reduced proliferation of cancer cells, and changes in collagen structure consistent with that of patients who experienced better survival. Examination of matrisome gene expression in publicly available data sets of 573 PDAC tumors identified a 65-gene signature that was able to distinguish long- and short-term PDAC survivors. Importantly, the expression of genes predictive of short-term survival was diminished in the cancer cells of orthotopic xenograft tumors of mice treated with CPI203. Taken together, these results demonstrate that inhibiting the activity BET proteins results in transcriptional and structural differences in the matrisome are associated with better patient survival. IMPLICATIONS: These studies highlight the biological relevance of the matrisome program in PDAC and suggest targeting of epigenetically driven tumor-stroma cross-talk as a potential therapeutic avenue.

The Impact of obesity and diabetes mellitus on pancreatic cancer: Molecular mechanisms and clinical perspectives

The incidence of obesity and type 2 diabetes (T2DM) in the Western world has increased dramatically during the recent decades. According to the American Cancer Society, pancreatic cancer (PC) is the fourth leading cause of cancer‐related death in the United States. The relationship among obesity, T2DM and PC is complex. Due to increase in obesity, diabetes, alcohol consumption and sedentary lifestyle, the mortality due to PC is expected to rise significantly by year 2040. The underlying mechanisms by which diabetes and obesity contribute to pancreatic tumorigenesis are not well understood. Furthermore, metabolism and microenvironment within the pancreas can also modulate pancreatic carcinogenesis. The risk of PC on a population level may be reduced by modifiable lifestyle risk factors. In this review, the interactions of diabetes and obesity to PC development were summarized, and novel strategies for the prevention and treatment of diabetes and PC were discussed.

Breast Tumor Microenvironment: Emerging target of therapeutic phytochemicals

Triple negative breast cancer (TNBC) is the most aggressive and challenging form of breast cancers. Tumor microenvironment (TME) of TNBC is associated with induction of metastasis, immune system suppression, escaping immune detection and drug resistance. TME is highly complex and heterogeneous, consists of tumor cells, stromal cells and immune cells. The rapid expansion of tumors induce hypoxia, which concerns the reprogramming of TME components. The reciprocal communication of tumor cells and TME cells predisposes cancer cells to metastasis by modulation of developmental pathways, Wnt, notch, hedgehog and their related mechanisms in TME. Dietary phytochemicals are non-toxic and associated with various human health benefits and remarkable spectrum of biological activities. The phytochemicals serve as vital resources for drug discovery and also as a source for breast cancer therapy. The novel properties of dietary phytochemicals propose platform for modulation of tumor signaling, overcoming drug resistance, and targeting TME. Therefore, TME could serve as promising target for the treatment of TNBC. This review presents current status and implications of experimentally evaluated therapeutic phytochemicals as potential targeting agents of TME, potential nanosystems for targeted delivery of phytochemicals and their current challenges and future implications in TNBC treatment. The dietary phytochemicals especially curcumin with significant delivery system could prevent TNBC development as it is considered safe and well tolerated in phase II clinical trials.

Non-canonical Hedgehog Signaling Pathway in Cancer: Activation of GLI Transcription Factors Beyond Smoothened

The Hedgehog-GLI (HH-GLI) pathway is a highly conserved signaling that plays a critical role in controlling cell specification, cell–cell interaction and tissue patterning during embryonic development. Canonical activation of HH-GLI signaling occurs through binding of HH ligands to the twelve-pass transmembrane receptor Patched 1 (PTCH1), which derepresses the seven-pass transmembrane G protein-coupled receptor Smoothened (SMO). Thus, active SMO initiates a complex intracellular cascade that leads to the activation of the three GLI transcription factors, the final effectors of the HH-GLI pathway. Aberrant activation of this signaling has been implicated in a wide variety of tumors, such as those of the brain, skin, breast, gastrointestinal, lung, pancreas, prostate and ovary. In several of these cases, activation of HH-GLI signaling is mediated by overproduction of HH ligands (e.g., prostate cancer), loss-of-function mutations in PTCH1 or gain-of-function mutations in SMO, which occur in the majority of basal cell carcinoma (BCC), SHH-subtype medulloblastoma and rhabdomyosarcoma. Besides the classical canonical ligand-PTCH1-SMO route, mounting evidence points toward additional, non-canonical ways of GLI activation in cancer. By non-canonical we refer to all those mechanisms of activation of the GLI transcription factors occurring independently of SMO. Often, in a given cancer type canonical and non-canonical activation of HH-GLI signaling co-exist, and in some cancer types, more than one mechanism of non-canonical activation may occur. Tumors harboring non-canonical HH-GLI signaling are less sensitive to SMO inhibition, posing a threat for therapeutic efficacy of these antagonists. Here we will review the most recent findings on the involvement of alternative signaling pathways in inducing GLI activity in cancer and stem cells. We will also discuss the rationale of targeting these oncogenic pathways in combination with HH-GLI inhibitors as a promising anti-cancer therapies.

The BET inhibitor JQ1 attenuates double-strand break repair and sensitizes models of pancreatic ductal adenocarcinoma to PARP inhibitors

BACKGROUND

DNA repair deficiency accumulates DNA damage and sensitizes tumor cells to PARP inhibitors (PARPi). Based on our observation that the BET inhibitor JQ1 increases levels of DNA damage, we evaluated the efficacy of JQ1 + the PARPi olaparib in preclinical models of pancreatic ductal adenocarcinoma (PDAC). We also addressed the mechanism by which JQ1 increased DNA damage.

METHODS

The effect of JQ1 + olaparib on in vivo tumor growth was assessed with patient-derived xenograft (PDX) models of PDAC. Changes in protein expression were detected by immunohistochemistry and immunoblot. In vitro growth inhibition and mechanistic studies were done using alamarBlue, qRT-PCR, immunoblot, immunofluorescence, ChIP, and shRNA knockdown assays.

FINDINGS

Tumors exposed in vivo to JQ1 had higher levels of the DNA damage marker γH2AX than tumors exposed to vehicle only. Increases in γH2AX was concomitant with decreased expression of DNA repair proteins Ku80 and RAD51. JQ1 + olaparib inhibited the growth of PDX tumors greater than either drug alone. Mechanistically, ChIP assays demonstrated that JQ1 decreased the association of BRD4 and BRD2 with promoter loci of Ku80 and RAD51, and shRNA data showed that expression of Ku80 and RAD51 was BRD4- and BRD2-dependent in PDAC cell lines.

INTERPRETATION

The data are consistent with the hypothesis that JQ1 confers a repair deficient phenotype and the consequent accumulation of DNA damage sensitizes PDAC cells to PARPi. Combinations of BET inhibitors with PARPi may provide a novel strategy for treating PDAC. FUND: NIH grants R01CA208272 and R21CA205501; UAB CMB T32 predoctoral training grant.

Stress responses in stromal cells and tumor homeostasis

In most (if not all) solid tumors, malignant cells are outnumbered by their non-malignant counterparts, including immune, endothelial and stromal cells. However, while the mechanisms whereby cancer cells adapt to microenvironmental perturbations have been studied in great detail, relatively little is known on stress responses in non-malignant compartments of the tumor microenvironment. Here, we discuss the mechanisms whereby cancer-associated fibroblasts and other cellular components of the tumor stroma react to stress in the context of an intimate crosstalk with malignant, endothelial and immune cells, and how such crosstalk influences disease progression and response to treatment.

Inhibition of Triple-Negative Breast Cancer Cell Aggressiveness by Cathepsin D Blockage: Role of Annexin A1

Triple-negative breast cancers (TNBCs) are more aggressive than other breast cancer (BC) subtypes and lack effective therapeutic options. Unraveling marker events of TNBCs may provide new directions for development of strategies for targeted TNBC therapy. Herein, we reported that Annexin A1 (AnxA1) and Cathepsin D (CatD) are highly expressed in MDA-MB-231 (TNBC lineage), compared to MCF-10A and MCF-7. Since the proposed concept was that CatD has protumorigenic activity associated with its ability to cleave AnxA1 (generating a 35.5 KDa fragment), we investigated this mechanism more deeply using the inhibitor of CatD, Pepstatin A (PepA). Fourier Transform Infrared (FTIR) spectroscopy demonstrated that PepA inhibits CatD activity by occupying its active site; the OH bond from PepA interacts with a CO bond from carboxylic acids of CatD catalytic aspartate dyad, favoring the deprotonation of Asp³³ and consequently inhibiting CatD. Treatment of MDA-MB-231 cells with PepA induced apoptosis and autophagy processes while reducing the proliferation, invasion, and migration. Finally, in silico molecular docking demonstrated that the catalytic inhibition comprises Asp²³¹ protonated and Asp³³ deprotonated, proving all functional results obtained. Our findings elucidated critical CatD activity in TNBC cell trough AnxA1 cleavage, indicating the inhibition of CatD as a possible strategy for TNBC treatment.

Targeting Epigenetic Aberrations in Pancreatic Cancer, a New Path to Improve Patient Outcomes?

Pancreatic cancer has one of the highest mortality rates among all types of cancers. The disease is highly aggressive and typically diagnosed in late stage making it difficult to treat. Currently, the vast majority of therapeutic regimens have only modest curative effects, and most of them are in the surgical/neo-adjuvant setting. There is a great need for new and more effective treatment strategies in common clinical practice. Previously, pathogenesis of pancreatic cancer was attributed solely to genetic mutations; however, recent advancements in the field have demonstrated that aberrant activation of epigenetic pathways contributes significantly to the pathogenesis of the disease. The identification of these aberrant activated epigenetic pathways has revealed enticing targets for the use of epigenetic inhibitors to mitigate the phenotypic changes driven by these cascades. These pathways have been found to be responsible for overactivation of growth signaling pathways and silencing of tumor suppressors and other cell cycle checkpoints. Furthermore, new miRNA signatures have been uncovered in pancreatic ductal adenocarcinoma (PDAC) patients, further widening the window for therapeutic opportunity. There has been success in preclinical settings using both epigenetic inhibitors as well as miRNAs to slow disease progression and eliminate diseased tissues. In addition to their utility as anti-proliferative agents, the pharmacological inhibitors that target epigenetic regulators (referred to here as readers, writers, and erasers for their ability to recognize, deposit, and remove post-translational modifications) have the potential to reconfigure the epigenetic landscape of diseased cells and disrupt the cancerous phenotype. The potential to “reprogram” cancer cells to revert them to a healthy state presents great promise and merits further investigation.

Image-Based Profiling of Patient-Derived Pancreatic Tumor-Stromal Cell Interactions Within a Micropatterned Tumor Model

Pancreatic cancer is one of the most aggressive cancers with a 5-year patient survival rate of 8.2% and limited availability of therapeutic agents to target metastatic disease. Pancreatic cancer is characterized by a dense stromal cell population with unknown contribution to the progression or suppression of tumor growth. In this study, we describe a microengineered tumor stromal assay of patient-derived pancreatic cancer cells to study the heterotypic interactions of patient pancreatic cancer cells with different types of stromal fibroblasts under basal and drug-treated conditions. The population dynamics of tumor cells in terms of migration and viability were visualized as a functional end point. Coculture with cancer-associated fibroblasts increased the migration of cancer cells when compared to dermal fibroblasts. Finally, we imaged the response of a bromodomain and extraterminal inhibitor on the viability of pancreatic cancer clusters surrounding by stroma in microengineered tumor stromal assay. We visualized a codynamic reduction in both cancer and stromal cells with bromodomain and extraterminal treatment compared to the dimethyl sulfoxide-treated group. This study demonstrates the ability to engineer tumor–stromal assays with patient-derived cells, study the role of diverse types of stromal cells on cancer progression, and precisely visualize a coculture during the screening of therapeutic compounds.

Pharmacotherapeutic Management of Pancreatic Ductal Adenocarcinoma: Current and Emerging Concepts

Pancreatic ductal adenocarcinoma is a devastating malignancy, which is the result of late diagnosis, aggressive disease, and a lack of effective treatment options. Thus, pancreatic ductal adenocarcinoma is projected to become the second leading cause of cancer-related death by 2030. This review summarizes recent developments of oncological therapy in the palliative setting of metastatic pancreatic ductal adenocarcinoma. It further compiles novel targets and therapeutic approaches as well as promising treatment combinations, which are presently in preclinical evaluation, covering several aspects of the hallmarks of cancer. Finally, challenges to the implementation of an individualized therapy approach in the context of precision medicine are discussed.

Tumor engraftment in patient-derived xenografts of pancreatic ductal adenocarcinoma is associated with adverse clinicopathological features and poor survival

Patient-derived xenograft (PDX) tumors are powerful tools to study cancer biology. However, the ability of PDX tumors to model the biological and histological diversity of pancreatic ductal adenocarcinoma (PDAC) is not well known. In this study, we subcutaneously implanted 133 primary and metastatic PDAC tumors into immunodeficient mice. Fifty-seven tumors were successfully engrafted and even after extensive passaging, the histology of poorly-, moderately-, and well-differentiated tumors was maintained in the PDX models. Moreover, the fibroblast and collagen contents in the stroma of patient tumors were recapitulated in the corresponding PDX models. Analysis of the clinicopathological features of patients revealed xenograft tumor engraftment was associated with lymphovascular invasion (P = 0.001) and worse recurrence-free (median, 7 vs. 16 months, log-rank P = 0.047) and overall survival (median, 13 vs. 21 months, log-rank P = 0.038). Among successful engraftments, median time of growth required for reimplantation into new mice was 151 days. Reflective of the inherent biological diversity between PDX tumors with rapid (<151 days) and slow growth, differences in their growth were maintained during extensive passaging. Rapid growth was additionally associated with lymph node metastasis (P = 0.022). The association of lymphovascular invasion and lymph node metastasis with PDX formation and rapid growth may reflect an underlying biological mechanism that allows these tumors to adapt and grow in a new environment. While the ability of PDX tumors to mimic the cellular and non-cellular features of the parental tumor stroma provides a valuable model to study the interaction of PDAC cells with the tumor microenvironment, the association of successful engraftment with adverse clinicopathological features suggests PDX models over represent more aggressive forms of this disease.

Selective inhibition of BET proteins reduces pancreatic damage and systemic inflammation in bile acid- and fatty acid ethyl ester- but not caerulein-induced acute pancreatitis

OBJECTIVES

To evaluate the therapeutic potential of I-BET-762, an inhibitor of the bromodomain and extra-terminal (BET) protein family, in experimental acute pancreatitis (AP).

METHODS

AP was induced by retrograde infusion of taurolithocholic acid sulphate into the biliopancreatic duct (TLCS-AP) or 2 intraperitoneal (i.p.) injections of ethanol and palmitoleic acid 1 h apart (FAEE-AP) or 12 hourly i.p. injections of caerulein (CER-AP). In all treatment groups, I-BET-762 (30 mg/kg, i.p.) was administered at the time of disease induction and again 12 h later. AP severity was assessed at 24 h by serum biochemistry, multiple cytokines and histopathology.

RESULTS

TLCS-AP, FAEE-AP and CER-AP resulted in characteristic elevations in serum amylase and cytokine levels, increased pancreatic trypsin and myeloperoxidase activity, typical pancreatic histopathological changes and lung injury. Treatment with I-BET-762 significantly reduced biochemical, cytokine and histopathological responses in TLCS-AP and FAEE-AP, but not CER-AP.

CONCLUSIONS

These results suggest that in different forms of AP there are significant differences in the epigenetic control of gene transcription contributing to the severity of disease responses. There is therapeutic potential in targeting bromodomains for the treatment of gallstone- and alcohol-related pancreatitis.

Epigenetic treatment of pancreatic cancer: is there a therapeutic perspective on the horizon?

Pancreatic ductal adenocarcinoma (PDAC) constitutes one of the most aggressive malignancies with a 5-year survival rate of <7%. Due to growing incidence, late diagnosis and insufficient treatment options, PDAC is predicted to soon become one of the leading causes of cancer-related death. Although intensified cytostatic combinations, particularly gemcitabine plus nab-paclitaxel and the folinic acid, fluorouracil, irinotecan, oxaliplatin (FOLFIRINOX) protocol, provide some improvement in efficacy and survival compared with gemcitabine alone, a breakthrough in the treatment of metastatic pancreatic cancer remains out of sight. Nevertheless, recent translational research activities propose that either modulation of the immune response or pharmacological targeting of epigenetic modifications alone, or in combination with chemotherapy, might open highly powerful therapeutic avenues in GI cancer entities, including pancreatic cancer. Deregulation of key epigenetic factors and chromatin-modifying proteins, particularly those responsible for the addition, removal or recognition of post-translational histone modifications, are frequently found in human pancreatic cancer and hence constitute particularly exciting treatment opportunities. This review summarises both current clinical trial activities and discovery programmes initiated throughout the biopharma landscape, and critically discusses the chances, hurdles and limitations of epigenetic-based therapy in future PDAC treatment.