The combination of BET and PARP inhibitors is synergistic in models of cholangiocarcinoma

Combining Data-Driven and Structure-Based Approaches in Designing Dual PARP1-BRD4 Inhibitors for Breast Cancer Treatment

Poly(ADP-ribose) polymerase 1 (PARP1) inhibitors have revolutionized the treatment of many cancers with DNA-repairing deficiencies via synthetic lethality. Advocated by the polypharmacology concept, recent evidence discovered that a significantly synergistic effect in increasing the death of cancer cells was observed by simultaneously perturbating the enzymatic activities of bromodomain-containing protein 4 (BRD4) and PARP1. Here, we developed a novel cheminformatics approach combined with a structure-based method aiming to facilitate the design of dual PARP1-BRD4 inhibitors. Instead of linking pharmacophores, the developed approach first identified merged pharmacophores (a pool of amide-containing ring systems), from which phenanthridin-6(5H)-one was further prioritized. Based on this starting point, several small molecules were rationally designed, among which HF4 exhibited low micromolar inhibitory activity against BRD4 and PARP1, particularly exhibiting strong inhibition of BRD4 BD1 with an IC50 value of 204 nM. Furthermore, it demonstrated potent antiproliferative effects against breast cancer gene-deficient and proficient breast cancer cell lines by arresting cell cycle progression and impeding DNA damage repair. Collectively, our systematic efforts to design lead-like molecules have the potential to open doors for the exploration of dual PARP1-BRD4 inhibitors as a promising avenue for breast cancer treatment. Furthermore, the developed approach can be extended to systematically design inhibitors targeting PARP1 and other related targets.

PLK1 inhibition leads to mitotic arrest and triggers apoptosis in cholangiocarcinoma cells

Cholangiocarcinoma (CCA) is a lethal cancer originating from the epithelial cells within the bile duct and ranks as the second most prevalent form of liver cancer in Thailand. Polo-like kinase 1 (PLK1), a protein serine/threonine kinase, regulates a number of steps in cell mitosis and is upregulated in several types of cancer, including CCA. Our previous study identified PLK1 as a biomarker of the C1 subtype, correlating with poor prognosis in intrahepatic CCA. The present study aimed to examine the effect of PLK1 inhibition on CCA cells. Different CCA cell lines developed from Thai patients, HuCCA1, KKU055, KKU100 and KKU213A, were treated with two PLK1 inhibitors, BI2536 and BI6727, and were transfected with small interfering RNA, followed by analysis of cell proliferation, cell cycle distribution and cell apoptosis. It was discovered that BI2536 and BI6727 inhibited cell proliferation and caused G2/M-phase arrest in CCA cells. Furthermore, the number of total apoptotic cells was increased in PLK1 inhibitor-treated CCA cells. The expression levels of mitotic proteins, aurora kinase A, phosphorylated PLK1 (T210) and cyclin B1, were augmented in PLK1-inhibited CCA cells. Additionally, inhibition of PLK1 led to increased DNA damage, as determined by the upregulated levels of γH2AX and increased cleavage of poly (ADP-ribose) polymerase, an apoptotic marker. These results suggested that inhibiting PLK1 prolonged mitotic arrest and subsequently triggered cell apoptosis. Validation of the antiproliferative effects of PLK1 inhibition was accomplished through silencing of the PLK1 gene. In conclusion, targeting PLK1 provided promising results for further study as a potential candidate for targeted therapy in CCA.

Bromodomain and Extraterminal Domain Protein 2 in Multiple Human Diseases

Bromodomain and extraterminal domain protein 2 (BRD2), a member of the bromodomain and extraterminal domain (BET) protein family, is a crucial epigenetic regulator with significant function in various diseases and cellular processes. The central function of BRD2 is modulating gene transcription by binding to acetylated lysine residues on histones and transcription factors. This review highlights key findings on BRD2 in recent years, emphasizing its roles in maintaining genomic stability, influencing chromatin spatial organization, and participating in transcriptional regulation. BRD2's diverse functions are underscored by its involvement in diseases such as malignant tumors, neurologic disorders, inflammatory conditions, metabolic diseases, and virus infection. Notably, the potential role of BRD2 as a diagnostic marker and therapeutic target is discussed in the context of various diseases. Although pan inhibitors targeting the BET family have shown promise in preclinical studies, a critical need exists for the development of highly selective BRD2 inhibitors. In conclusion, this review offers insights into the multifaceted nature of BRD2 and calls for continued research to unravel its intricate mechanisms and harness its therapeutic potential. SIGNIFICANCE STATEMENT: BRD2 is involved in the occurrence and development of diseases through maintaining genomic stability, influencing chromatin spatial organization, and participating in transcriptional regulation. Targeting BRD2 through protein degradation-targeting complexes technology is emerging as a promising therapeutic approach for malignant cancer and inflammatory diseases.

ZNF432 stimulates PARylation and inhibits DNA resection to balance PARPi sensitivity and resistance

Zinc finger (ZNF) motifs are some of the most frequently occurring domains in the human genome. It was only recently that ZNF proteins emerged as key regulators of genome integrity in mammalian cells. In this study, we report a new role for the Krüppel-type ZNF-containing protein ZNF432 as a novel poly(ADP-ribose) (PAR) reader that regulates the DNA damage response. We show that ZNF432 is recruited to DNA lesions via DNA- and PAR-dependent mechanisms. Remarkably, ZNF432 stimulates PARP-1 activity in vitro and in cellulo. Knockdown of ZNF432 inhibits phospho-DNA-PKcs and increases RAD51 foci formation following irradiation. Moreover, purified ZNF432 preferentially binds single-stranded DNA and impairs EXO1-mediated DNA resection. Consequently, the loss of ZNF432 in a cellular system leads to resistance to PARP inhibitors while its overexpression results in sensitivity. Taken together, our results support the emerging concept that ZNF-containing proteins can modulate PARylation, which can be embodied by the pivotal role of ZNF432 to finely balance the outcome of PARPi response by regulating homologous recombination.

Bromodomain and extraterminal (BET) proteins: biological functions, diseases, and targeted therapy

BET proteins, which influence gene expression and contribute to the development of cancer, are epigenetic interpreters. Thus, BET inhibitors represent a novel form of epigenetic anticancer treatment. Although preliminary clinical trials have shown the anticancer potential of BET inhibitors, it appears that these drugs have limited effectiveness when used alone. Therefore, given the limited monotherapeutic activity of BET inhibitors, their use in combination with other drugs warrants attention, including the meaningful variations in pharmacodynamic activity among chosen drug combinations. In this paper, we review the function of BET proteins, the preclinical justification for BET protein targeting in cancer, recent advances in small-molecule BET inhibitors, and preliminary clinical trial findings. We elucidate BET inhibitor resistance mechanisms, shed light on the associated adverse events, investigate the potential of combining these inhibitors with diverse therapeutic agents, present a comprehensive compilation of synergistic treatments involving BET inhibitors, and provide an outlook on their future prospects as potent antitumor agents. We conclude by suggesting that combining BET inhibitors with other anticancer drugs and innovative next-generation agents holds great potential for advancing the effective targeting of BET proteins as a promising anticancer strategy.

Targeting SIRT1 synergistically improves the antitumor effect of JQ-1 in hepatocellular carcinoma

Bromodomain and extraterminal domain protein inhibitors have shown therapeutic promise in hepatocellular carcinoma. However, resistance to bromodomain and extraterminal domain protein inhibitors has emerged in preclinical trials, presenting an immense clinical challenge, and the mechanisms are unclear. In this study, we found that overexpression of SIRT1 induced by JQ-1, a bromodomain and extraterminal domain protein inhibitor, may confer resistance to JQ-1 in hepatocellular carcinoma. SIRT1 protein expression was higher in hepatocellular carcinoma tissues than in normal tissues, and this phenotype was correlated with a poor prognosis. Cotreatment with JQ-1 and the SIRT1 inhibitor EX527 synergistically suppressed proliferation and blocked cell cycle progression in hepatocellular carcinoma cells. Combined administration of JQ-1 and EX527 successfully reduced the tumor burden in vivo. In addition, JQ-1 mediated AMPK/p-AMPK axis activation to upregulate SIRT1 protein expression and enhanced autophagy to inhibit cell apoptosis. Activation of AMPK could alleviate the antitumor effect of the combination of JQ-1 and EX527 on hepatocellular carcinoma cells. Furthermore, inhibition of SIRT1 further enhanced the antitumor effect of JQ-1 by blocking protective autophagy in hepatocellular carcinoma. Our study proposes a novel and efficacious therapeutic strategy of a BET inhibitor combined with a SIRT1 inhibitor for hepatocellular carcinoma.

Dual-target inhibitors of PARP1 in cancer therapy: a drug discovery perspective

Poly (ADP-ribose) polymerase 1 (PARP1), a key enzyme in DNA repair, has emerged as a promising anticancer druggable target. An increasing number of PARP1 inhibitors have been discovered to treat cancer, most notably those characterized by BRCA1/2 mutations. Although PARP1 inhibitors have achieved great clinical success, their cytotoxicity, development of drug resistance, and restriction of indication have weakened their clinical therapeutic effects. To address these issues, dual PARP1 inhibitors have been documented as a promising strategy. Here, we review recent progress in the development of dual PARP1 inhibitors, summarize the different designs of dual-target inhibitors, and introduce their antitumor pharmacology, shedding light on the discovery of dual PARP1 inhibitors for cancer treatment.

BET proteins: Biological functions and therapeutic interventions

Bromodomain and extra-terminal (BET) family member proteins (BRD2, BRD3, BRD4 and BRDT) play a pivotal role in interpreting the epigenetic information of histone Kac modification, thus controlling gene expression, remodeling chromatin structures and avoid replicative stress-induced DNA damages. Abnormal activation of BET proteins is tightly correlated to various human diseases, including cancer. Therefore, BET bromodomain inhibitors (BBIs) were considered as promising therapeutics to treat BET-related diseases, raising >70 clinical trials in the past decades. Despite preliminary effects achieved, drug resistance and adverse events represent two major challenges for current BBIs development. In this review, we will introduce the biological functions of BET proteins in both physiological and pathological conditions; and summarize the progress in current BBI drug development. Moreover, we will also discuss the major challenges in the front of BET inhibitor development and provide rational strategies to overcome these obstacles.

Therapeutic strategies of dual-target small molecules to overcome drug resistance in cancer therapy

Despite some advances in targeted therapeutics of human cancers, curative cancer treatment still remains a tremendous challenge due to the occurrence of drug resistance. A variety of underlying resistance mechanisms to targeted cancer drugs have recently revealed that the dual-target therapeutic strategy would be an attractive avenue. Compared to drug combination strategies, one agent simultaneously modulating two druggable targets generally shows fewer adverse reactions and lower toxicity. As a consequence, the dual-target small molecule has been extensively explored to overcome drug resistance in cancer therapy. Thus, in this review, we focus on summarizing drug resistance mechanisms of cancer cells, such as enhanced drug efflux, deregulated cell death, DNA damage repair, and epigenetic alterations. Based upon the resistance mechanisms, we further discuss the current therapeutic strategies of dual-target small molecules to overcome drug resistance, which will shed new light on exploiting more intricate mechanisms and relevant dual-target drugs for future cancer therapeutics.

Rational Combinations of PARP Inhibitors with HRD-Inducing Molecularly Targeted Agents

Cancers with wild-type BRCA, homologous recombination proficiency, or de novo or acquired resistance to PARP inhibition represent a growing population of patients who may benefit from combinatorial PARP inhibitor strategies. We review targeted inhibitors of angiogenesis, epigenetic regulators, and PI3K, MAPK, and other cellular signaling pathways as inducers of homologous recombination deficiency, providing support for the use of PARP inhibitors in contexts not previously considered susceptible to PARP inhibition.

Multi-therapies Based on PARP Inhibition: Potential Therapeutic Approaches for Cancer Treatment

The nuclear enzymes called poly(ADP-ribose)polymerases (PARPs) are known to catalyze the process of PARylation, which plays a vital role in various cellular functions. They have become important targets for the discovery of novel antitumor drugs since their inhibition can induce significant lethality in tumor cells. Therefore, researchers all over the world have been focusing on developing novel and potent PARP inhibitors for cancer therapy. Studies have shown that PARP inhibitors and other antitumor agents, such as EZH2 and EGFR inhibitors, play a synergistic role in cancer cells. The combined inhibition of PARP and the targets with synergistic effects may provide a rational strategy to improve the effectiveness of current anticancer regimens. In this Perspective, we sum up the recent advance of PARP-targeted agents, including single-target inhibitors/degraders and dual-target inhibitors/degraders, discuss the fundamental theory of developing these dual-target agents, and give insight into the corresponding structure-activity relationships of these agents.

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

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

Targeting the Heterogeneous Genomic Landscape in Triple-Negative Breast Cancer through Inhibitors of the Transcriptional Machinery

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer defined by lack of the estrogen, progesterone and human epidermal growth factor receptor 2. Although TNBC tumors contain a wide variety of oncogenic mutations and copy number alterations, the direct targeting of these alterations has failed to substantially improve therapeutic efficacy. This efficacy is strongly limited by interpatient and intratumor heterogeneity, and thereby a lack in uniformity of targetable drivers. Most of these genetic abnormalities eventually drive specific transcriptional programs, which may be a general underlying vulnerability. Currently, there are multiple selective inhibitors, which target the transcriptional machinery through transcriptional cyclin-dependent kinases (CDKs) 7, 8, 9, 12 and 13 and bromodomain extra-terminal motif (BET) proteins, including BRD4. In this review, we discuss how inhibitors of the transcriptional machinery can effectively target genetic abnormalities in TNBC, and how these abnormalities can influence sensitivity to these inhibitors. These inhibitors target the genomic landscape in TNBC by specifically suppressing MYC-driven transcription, inducing further DNA damage, improving anti-cancer immunity, and preventing drug resistance against MAPK and PI3K-targeted therapies. Because the transcriptional machinery enables transcription and propagation of multiple cancer drivers, it may be a promising target for (combination) treatment, especially of heterogeneous malignancies, including TNBC.

Case Report: Sustained complete remission on combination therapy with olaparib and pembrolizumab in BRCA2-mutated and PD-L1-positive metastatic cholangiocarcinoma after platinum derivate

Cholangiocarcinoma (CCA) still has a poor prognosis and remains a major therapeutic challenge. When curative resection is not possible, palliative systemic chemotherapy with gemcitabine and platinum derivate as first line followed by a 5-FU doublet combination as second line is the standard therapy. Recently, targeted therapy and immunotherapy have rapidly emerged as personalized therapeutic approaches requiring previous tumor sequencing and molecular profiling. BRCA mutations are well-characterized targets for poly (ADP-ribose) polymerase inhibitors (PARPi). However, BRCA gene mutations in CCA are rare and few data of PARPi in the treatment of CCA are available. Immunotherapy with programmed death receptor-1 (PD-1) has been shown to be effective in combination with chemotherapy or in PD-L1-positive CCA. However, data from immunotherapy combined with targeted therapy, including PARPi, are lacking. In this report, we present the case of a male patient with PD-L1-positive and BRCA2-mutated metastatic intrahepatic cholangiocarcinoma, who was treated with a combined therapy with PARP (PARPi), olaparib, and a PD-1 antibody, pembrolizumab, as second-line therapy after gemcitabine/platinum derivate failure. Combined therapy was able to induce a long-lasting complete remission for over 15 months. The combined therapy was feasible and well tolerated. Only mild anemia and immune-related thyroiditis were observed, which were easily manageable and did not result in discontinuation of olaparib and pembrolizumab.

The BET Inhibitor JQ1 Potentiates the Anticlonogenic Effect of Radiation in Pancreatic Cancer Cells

We reported previously that the BET inhibitor (BETi) JQ1 decreases levels of the DNA repair protein RAD51 and that this decrease is concomitant with increased levels of DNA damage. Based on these findings, we hypothesized that a BETi would augment DNA damage produced by radiation and function as a radiosensitizer. We used clonogenic assays to evaluate the effect of JQ1 ± ionizing radiation (IR) on three pancreatic cancer cell lines in vitro. We performed immunofluorescence assays to assess the impact of JQ1 ± IR on DNA damage as reflected by levels of the DNA damage marker γH2AX, and immunoblots to assess levels of the DNA repair protein RAD51. We also compared the effect of these agents on the clonogenic potential of transfectants that expressed contrasting levels of the principle molecular targets of JQ1 (BRD2, BRD4) to determine whether levels of these BET proteins affected sensitivity to JQ1 ± IR. The data show that JQ1 + IR decreased the clonogenic potential of pancreatic cancer cells more than either modality alone. This anticlonogenic effect was associated with increased DNA damage and decreased levels of RAD51. Further, lower levels of BRD2 or BRD4 increased sensitivity to JQ1 and JQ1 + IR, suggesting that pre-treatment levels of BRD2 or BRD4 may predict sensitivity to a BETi or to a BETi + IR. We suggest that a BETi + IR merits evaluation as therapy prior to surgery for pancreatic cancer patients with borderline resectable disease.

DNA Damage Response Inhibitors in Cholangiocarcinoma: Current Progress and Perspectives

Cholangiocarcinoma (CCA) is a poorly treatable type of cancer and its incidence is dramatically increasing. The lack of understanding of the biology of this tumor has slowed down the identification of novel targets and the development of effective treatments. Based on next generation sequencing profiling, alterations in DNA damage response (DDR)-related genes are paving the way for DDR-targeting strategies in CCA. Based on the notion of synthetic lethality, several DDR-inhibitors (DDRi) have been developed with the aim of accumulating enough DNA damage to induce cell death in tumor cells. Observing that DDRi alone could be insufficient for clinical use in CCA patients, the combination of DNA-damaging regimens with targeted approaches has started to be considered, as evidenced by many emerging clinical trials. Hence, novel therapeutic strategies combining DDRi with patient-specific targeted drugs could be the next level for treating cholangiocarcinoma.

TNKS inhibitors potentiate proliferative inhibition of BET inhibitors via reducing β-Catenin in colorectal cancer cells

Colorectal cancer (CRC) is an aggressive malignancy with limited options for treatment. Targeting the bromodomain and extra terminal domain (BET) proteins by using BET inhibitors (BETis) could effectively interrupt the interaction with acetylated histones, inhibit genes transcription and have shown a certain effect on CRC inhibition. To improve the efficacy, the inhibitors of Tankyrases, which cause accumulation of AXIN through dePARsylation, in turn facilitate the degradation of β-Catenin and suppress the growth of adenomatous polyposis coli (APC)-mutated CRCs, were tested together with BETi as a combination treatment. We examined the effects of BETi and Tankyrases inhibitor (TNKSi) together on the proliferation, cell cycle and apoptosis of human CRCs cell lines with APC or CTNNB1 mutation, and elucidated the underlying molecular mechanisms affected by the double treatment. The result showed that the TNKSi could sensitize all tested CRC cell lines to BETi, and the synergistic effect was not only seen in cell proliferation inhibition, but also confirmed in decreased colony-forming ability and weaken EdU incorporation compared with monotherapy. Combined treatment resulted in enhanced G1 cell cycle arrest and increased apoptosis. In addition, we found β-Catenin was potentially inhibited by the combination and revealed that both BETi-induced transcriptional inhibition and TNKSi-mediated protein degradation all reduced the β-Catenin accumulation. In all, the synergistic effects suggest that combination of BETi and TNKSi could provide novel treatment opportunities for CRC, but both TNKSi and combination strategy need to be optimized.

Dual-target inhibitors based on PARP1: new trend in the development of anticancer research

PARP1 is a hot target, and its inhibitors have been approved for cancer therapy. However, some undesirable properties restrict the application of PARP1 inhibitors, including drug resistance, side effects and low efficiency. For multifactorial diseases, dual-target drugs have exhibited excellent synergistic effects, such as reduced drug resistance, low side effects and high therapeutic efficacy, by simultaneously regulating the main pathogenic and compensatory signal pathways of diseases. In recent years, several dual-target inhibitors based on PARP1 have been reported and have demonstrated unique advantages. In this review we summarize the research progress in dual-target inhibitors based on PARP1 and discuss the related drug design strategies and structure-activity relationships. This work is expected to provide references for the development of PARP1 inhibitors.

Precision Medicine for BRCA/PALB2-Mutated Pancreatic Cancer and Emerging Strategies to Improve Therapeutic Responses to PARP Inhibition

Simple Summary

For the small subset of pancreatic ductal adenocarcinoma (PDAC) patients with loss-of-function mutations to BRCA1/2 or PALB2, both first-line and maintenance therapy differs significantly. These mutations confer a loss of double-strand break DNA homologous recombination (HR), substantially altering drug sensitivities. In this review, we discuss the current treatment guidelines for PDAC tumors deficient in HR, as well as newly emerging strategies to improve drug responses in this population. We also highlight additional patient populations in which these strategies may also be effective, and novel strategies aiming to confer similar drug sensitivity to tumors proficient in HR repair.

Abstract

Pancreatic cancer is projected to become the second leading cause of cancer-related death by 2030. As patients typically present with advanced disease and show poor responses to broad-spectrum chemotherapy, overall survival remains a dismal 10%. This underscores an urgent clinical need to identify new therapeutic approaches for PDAC patients. Precision medicine is now the standard of care for several difficult-to-treat cancer histologies. Such approaches involve the identification of a clinically actionable molecular feature, which is matched to an appropriate targeted therapy. Selective poly (ADP-ribose) polymerase (PARP) inhibitors such as Niraparib, Olaparib, Talazoparib, Rucaparib, and Veliparib are now approved for several cancers with loss of high-fidelity double-strand break homologous recombination (HR), namely those with deleterious mutations to BRCA1/2, PALB2, and other functionally related genes. Recent evidence suggests that the presence of such mutations in pancreatic ductal adenocarcinoma (PDAC), the most common and lethal pancreatic cancer histotype, significantly alters drug responses both with respect to first-line chemotherapy and maintenance therapy. In this review, we discuss the current treatment paradigm for PDAC tumors with confirmed deficits in double-strand break HR, as well as emerging strategies to both improve responses to PARP inhibition in HR-deficient PDAC and confer sensitivity to tumors proficient in HR repair.

Discovery of Potent and Novel Dual PARP/BRD4 Inhibitors for Efficient Treatment of Pancreatic Cancer

Targeting poly(ADP-ribose) polymerase1/2 (PARP1/2) is a promising strategy for the treatment of pancreatic cancer with breast cancer susceptibility gene (BRCA) mutation. Inducing the deficiency of homologous recombination (HR) repair is an effective way to broaden the indication of PARP1/2 inhibitor for more patients with pancreatic cancer. Bromodomain-containing protein 4 (BRD4) repression has been reported to elevate HR deficiency. Therefore, we designed, synthetized, and optimized a dual PARP/BRD4 inhibitor III-16, with a completely new structure and high selectivity against PARP1/2 and BRD4. III-16 showed favorable synergistic antitumor efficacy in pancreatic cancer cells and xenografts by arresting cell cycle progression, inhibiting DNA damage repair, and promoting autophagy-associated cell death. Moreover, III-16 reversed Olaparib-induced acceleration of cell cycle progression and recovery of DNA repair. The advantages of III-16 over Olaparib suggest that dual PARP/BRD4 inhibitors are novel and promising agents for the treatment of advanced pancreatic cancer.

The BET Inhibitor JQ1 Augments the Antitumor Efficacy of Gemcitabine in Preclinical Models of Pancreatic Cancer

Gemcitabine is used to treat pancreatic cancer (PC), but is not curative. We sought to determine whether gemcitabine + a BET bromodomain inhibitor was superior to gemcitabine, and identify proteins that may contribute to the efficacy of this combination. This study was based on observations that cell cycle dysregulation and DNA damage augment the efficacy of gemcitabine. BET inhibitors arrest cells in G1 and allow increases in DNA damage, likely due to inhibition of expression of DNA repair proteins Ku80 and RAD51. BET inhibitors (JQ1 or I-BET762) + gemcitabine were synergistic in vitro, in Panc1, MiaPaCa2 and Su86 PC cell lines. JQ1 + gemcitabine was more effective in vivo than either drug alone in patient-derived xenograft models (P < 0.01). Increases in the apoptosis marker cleaved caspase 3 and DNA damage marker γH2AX paralleled antitumor efficacy. Notably, RNA-seq data showed that JQ1 + gemcitabine selectively inhibited HMGCS2 and APOC1 ~6-fold, compared to controls. These proteins contribute to cholesterol biosynthesis and lipid metabolism, and their overexpression supports tumor cell proliferation. IPA data indicated that JQ1 + gemcitabine selectively inhibited the LXR/RXR activation pathway, suggesting the hypothesis that this inhibition may contribute to the observed in vivo efficacy of JQ1 + gemcitabine.

The Role of PARP Inhibitors in the Treatment of Prostate Cancer: Recent Advances in Clinical Trials

Poly (adenosine diphosphate-ribose) polymerase inhibitors (PARPis) belong to a class of targeted drugs developed for the treatment of homologous recombination repair (HRR)-defective tumors. Preclinical and limited clinical data suggest that PARP inhibition is effective against prostate cancer (PC) in patients with HRR-deficient tumors and that PARPis can improve the mortality rate of PC in patients with BRCA1/2 mutations through a synthetic lethality. Olaparib has been approved by the FDA for advanced ovarian and breast cancer with BRCA mutations, and as a maintenance therapy for ovarian cancer after platinum chemotherapy. PARPis are also a new and emerging clinical treatment for metastatic castration-resistant prostate cancer (mCRPC). Although PARPis have shown great efficacy, their widespread use is restricted by various factors, including drug resistance and the limited population who benefit from treatment. It is necessary to study the combination of PARPis and other therapeutic agents such as anti-hormone drugs, USP7 inhibitors, BET inhibitors, and immunotherapy. This article reviews the mechanism of PARP inhibition in the treatment of PC, the progress of clinical research, the mechanisms of drug resistance, and the strategies of combination treatments.

Enhancer rewiring in tumors: an opportunity for therapeutic intervention

Enhancers are cis-regulatory sequences that fine-tune expression of their target genes in a spatiotemporal manner. They are recognized by sequence-specific transcription factors, which in turn recruit transcriptional coactivators that facilitate transcription by promoting assembly and activation of the basal transcriptional machinery. Their functional importance is underscored by the fact that they are often the target of genetic and nongenetic events in human disease that disrupt their sequence, interactome, activation potential, and/or chromatin environment. Dysregulation of transcription and addiction to transcriptional effectors that interact with and modulate enhancer activity are common features of cancer cells and are amenable to therapeutic intervention. Here, we discuss the current knowledge on enhancer biology, the broad spectrum of mechanisms that lead to their malfunction in tumor cells, and recent progress in developing drugs that efficaciously target their dependencies.

Frequency and prognostic value of mutations associated with the homologous recombination DNA repair pathway in a large pan cancer cohort

PARP inhibitors have shown remarkable efficacy in the clinical management of several BRCA-mutated tumors. This approach is based on the long-standing hypothesis that PARP inhibition will impair the repair of single stranded breaks, causing synthetic lethality in tumors with loss of high-fidelity double-strand break homologous recombination. While this is now well accepted and has been the basis of several successful clinical trials, emerging evidence strongly suggests that mutation to several additional genes involved in homologous recombination may also have predictive value for PARP inhibitors. While this notion is supported by early clinical evidence, the mutation frequencies of these and other functionally related genes are largely unknown, particularly in cancers not classically associated with homologous recombination deficiency. We therefore evaluated the mutation status of 22 genes associated with the homologous recombination DNA repair pathway or PARP inhibitor sensitivity, first in a pan-cancer cohort of 55,586 patients, followed by a more focused analysis in The Cancer Genome Atlas cohort of 12,153 patients. In both groups we observed high rates of mutations in a variety of HR-associated genes largely unexplored in the setting of PARP inhibition, many of which were associated also with poor clinical outcomes. We then extended our study to determine which mutations have a known oncogenic role, as well as similar to known oncogenic mutations that may have a similar phenotype. Finally, we explored the individual cancer histologies in which these genomic alterations are most frequent. We concluded that the rates of deleterious mutations affecting genes associated with the homologous recombination pathway may be underrepresented in a wide range of human cancers, and several of these genes warrant further and more focused investigation, particularly in the setting of PARP inhibition and HR deficiency.

BRCA in Gastrointestinal Cancers: Current Treatments and Future Perspectives

A strong association between pancreatic cancer and BRCA1 and BRCA2 mutations is documented. Based on promising results of breast and ovarian cancers, several clinical trials with poly (ADP-ribose) polymerase inhibitors (PARPi) are ongoing for gastrointestinal (GI) malignancies, especially for pancreatic cancer. Indeed, the POLO trial results provide promising and awaited changes for the pancreatic cancer therapeutic landscape. Contrariwise, for other gastrointestinal tumors, the rationale is currently only alleged. The role of BRCA mutation in gastrointestinal cancers is the subject of this review. In particular, we aim to provide the latest updates about novel therapeutic strategies that, exploiting DNA repair defects, promise to shape the future therapeutic scenario of GI cancers.

PARP Inhibitors in Biliary Tract Cancer: A New Kid on the Block?

Poly adenosine diphosphate-ribose polymerase inhibitors (PARPi) represent an effective therapeutic strategy for cancer patients harboring germline and somatic aberrations in DNA damage repair (DDR) genes. BRCA1/2 mutations occur at 1–7% across biliary tract cancers (BTCs), but a broader spectrum of DDR gene alterations is reported in 28.9–63.5% of newly diagnosed BTC patients. The open question is whether alterations in genes that are well established to have a role in DDR could be considered as emerging predictive biomarkers of response to platinum compounds and PARPi. Currently, data regarding PARPi in BTC patients harboring BRCA and DDR mutations are sparse and anecdotal; nevertheless, a variety of clinical trials are testing PARPi as monotherapy or in combination with other anticancer agents. In this review, we provide a comprehensive overview regarding the genetic landscape of DDR pathway deficiency, state of the art and future therapeutic implications of PARPi in BTC, looking at combination strategies with immune-checkpoint inhibitors and other anticancer agents in order to improve survival and quality of life in BTC patients.

Make your best BET: The emerging role of BET inhibitor treatment in malignant tumors

Bromodomains are protein-protein interaction modules with a great diversity in terms of number of proteins and their function. The bromodomain and extraterminal protein (BET) represents a distinct subclass of bromodomain proteins mainly involved in transcriptional regulation via their interaction with acetylated chromatin. In cancer cells BET proteins are found to be altered in many ways such as overexpression, mutations and fusions of BET proteins or their interference with cancer relevant signaling pathways and transcriptional programs in order to sustain cancer growth and viability. Blocking BET protein function with small molecules is associated with therapeutic activity. Consequently, a variety of small molecules have been developed and a number of phase I clinical trials have explored their tolerability and efficacy in patients with solid tumors and hematological malignancies. We will review the rational for applying BET inhibitors in the clinic and we will discuss the toxicity profile as well as efficacy of this new class of protein inhibitors. We will also highlight the emerging problem of treatment resistance and the potential these drugs might have when combined with other anti-cancer therapies.