Combined inhibition of PARP and EZH2 for cancer treatment: Current status, opportunities, and challenges

Epigenetic targeting of PGBD5-dependent DNA damage in SMARCB1-deficient sarcomas

Despite the potential of targeted epigenetic therapies, most cancers do not respond to current epigenetic drugs. The Polycomb repressive complex EZH2 inhibitor tazemetostat was recently approved for the treatment of SMARCB1-deficient epithelioid sarcomas, based on the functional antagonism between PRC2 and loss of SMARCB1. Through the analysis of tazemetostat-treated patient tumors, we recently defined key principles of their response and resistance to EZH2 epigenetic therapy. Here, using transcriptomic inference from SMARCB1-deficient tumor cells, we nominate the DNA damage repair kinase ATR as a target for rational combination EZH2 epigenetic therapy. We show that EZH2 inhibition promotes DNA damage in epithelioid and rhabdoid tumor cells, at least in part via its induction of the transposase-derived PGBD5. We leverage this collateral synthetic lethal dependency to target PGBD5-dependent DNA damage by inhibition of ATR but not CHK1 using elimusertib. Consequently, combined EZH2 and ATR inhibition improves therapeutic responses in diverse patient-derived epithelioid and rhabdoid tumors in vivo. This advances a combination epigenetic therapy based on EZH2-PGBD5 synthetic lethal dependency suitable for immediate translation to clinical trials for patients.

Computational exploration in search for novel natural product-derived EZH2 inhibitors for advancing anti-cancer therapy

Epigenetic regulation intricately governs cellular mechanisms, including proliferation, death, differentiation, and cell cycle orchestration. One such target, Enhancer of zeste homolog 2 (EZH2), is essential for epigenetic regulation. EZH2 trimethylates histone H3 lys27 (H3K27me3), inhibiting target gene transcription and promoting chromatin condensation, thereby initiating tumorigenesis, thus a potentially plausible target to disrupt cancer progression. In this virtual screening study, we utilized two large, open-source natural product libraries, NPASS and LOTUS, to search for potential natural product scaffolds capable of EZH2 inhibition. The merged library was filtered through increasingly rigorous criteria at each stage, including Medchem-based rule filters, 2D Tanimoto similarity, sequential rounds of docking, rescoring via ML-based functions, and binding pose visualization, funneling down to the most promising candidates for further pharmacokinetics and toxicological profiles. The best hits were analyzed for their binding stability through molecular dynamics simulation and their binding free energy estimations. Exploratory chemical analysis was conducted to understand the similarity of hits with known EZH2 chemical space. This comprehensive workflow identified one potential inhibitor, LTS0131784, which exhibited favorable pharmacokinetic toxicity profiling with binding stability and free energy better than the FDA-approved EZH2 inhibitor, Tazemetostat. Furthermore, the plausible binding mechanism was also elucidated by analyzing the per residue-free decomposition of the simulated trajectories, which indicated the involvement of the LTS0131784 with the key residues TYR:111, TRP:521, CYS:560, ASN:585, and SER:561.

EZH2 inhibition sensitizes MYC-high medulloblastoma cancers to PARP inhibition by regulating NUPR1-mediated DNA repair

MYC-driven medulloblastomas (MB) are highly aggressive pediatric brain tumors with poor outcomes, and effective therapies remain limited despite intensive multimodal treatments. Targeting MYC directly is challenging, but exploiting MYC-mediated synthetic lethality holds promise. In this study, we investigated the combined effects of EZH2 and PARP inhibitors in MYC-high medulloblastoma and demonstrated that EZH2 inhibition significantly increased the sensitivity of MYC-high MB tumor cells to PARP inhibitors. This effect occurs through the upregulation of NUPR1, which promotes error-prone non-homologous end-joining (NHEJ) DNA repair by facilitating the recruitment of the XRCC4-LIG4 complex to DNA damage sites. This amplification of error-prone NHEJ DNA repair leads to genetic instability and eventual cell death in cells treated with the PARP inhibitor. The synergistic effect of EZH2 and PARP inhibitors was further validated in both in vitro and in vivo MB models without observed toxicity. These findings reveal a novel therapeutic strategy for MYC-high MB by co-targeting EZH2 and PARP, suggesting that this combination could potentially overcome the clinical challenges associated with this aggressive tumor subtype and warrants further investigation in clinical trials.

Incidence and risk of endocrine and metabolic abnormalities linked to PARP inhibitors in solid tumors: a meta-analysis

BACKGROUND

Poly (ADP-ribose) polymerase inhibitors (PARPi) serve as crucial therapeutic agents in solid tumor treatment. Preclinical investigations suggest a potential protective function of PARPi against endocrine and metabolic impairments. Nevertheless, the existing body of evidence remains inconclusive on this aspect.

PURPOSE

Our aim was to evaluate the potential impact of PARPi on endocrine and metabolic disruptions in clinical trials.

DATA SOURCES

We conducted a comprehensive search across the Medline, EMBASE, PubMed, and Web of Science databases, along with the ClinicalTrials.gov registry.

STUDY SELECTION

Phase II/III randomized controlled trials (RCTs) investigating the effects of PARPi in metabolic and endocrine processes were selected for inclusion in patients with solid tumors.

DATA EXTRACTION

The primary outcomes of interest encompassed metabolic and endocrine dysfunctions.

DATA SYNTHESIS

A total of 26 trials (n = 9,590 patients) were included in our meta-analysis. Niraparib demonstrated an increased risk of any-grade hyperglycemia (OR = 2.15, 95% CI 1.28-3.62), with patients receiving PARPi for metastatic pancreatic cancer showing a higher susceptibility to any-grade hyperglycemia (OR = 1.78, 95% CI 1.04-3.04). Conversely, rucaparib exhibited a potential ameliorative effect on hyperglycemia (OR = 0.54, 95% CI 0.30-0.97). No statistically significant disparities were observed for other outcomes associated with PARPi utilization.

LIMITATIONS

Among these RCTs included, 50% were assessed as low qualities due to high risk of bias.

CONCLUSIONS

Our meta-analysis demonstrated that PARPi may exert adverse effects on endocrine and metabolic pathways. Close monitoring of hyperglycemia is recommended for patients undergoing niraparib therapy, especially those with pancreatic cancer.

TRIAL REGISTRATION

This meta-Analysis was prospectively registered in the PROSPERO database with ID CRD42023457959.

Combined strategies with PARP inhibitors for the treatment of BRCA wide type cancer

Genomic instability stands out as a pivotal hallmark of cancer, and PARP inhibitors (PARPi) emerging as a groundbreaking class of targeted therapy drugs meticulously crafted to inhibit the repair of DNA single-strand breaks(SSB) in tumor cells. Currently, PARPi have been approved for the treatment of ovarian cancer, pancreatic cancer, breast cancer, and prostate cancer characterized by homologous recombination(HR) repair deficiencies due to mutations in BRCA1/2 or other DNA repair associated genes and acquiring the designation of breakthrough therapy. Nonetheless, PARPi exhibit limited efficacy in the majority of HR-proficient BRCA1/2 wild-type cancers. At present, the synergistic approach of combining PARPi with agents that induce HR defects, or with chemotherapy and radiotherapy to induce substantial DNA damage, significantly enhances the efficacy of PARPi in BRCA wild-type or HR-proficient patients, supporting extension the use of PARPi in HR proficient patients. Therefore, we have summarized the effects and mechanisms of the combined use of drugs with PARPi, including the combination of PARPi with HR defect-inducing drugs such as ATRi, CHKi, HR indirectly inducing drugs like VEGFRi, CDKi, immune checkpoint inhibitors and drugs instigating DNA damage such as chemotherapy or radiotherapy. In addition, this review discusses several ongoing clinical trials aimed at analyzing the clinical application potential of these combined treatment strategies.

PROTAC EZH2 degrader-1 overcomes the resistance of podophyllotoxin derivatives in refractory small cell lung cancer with leptomeningeal metastasis

BACKGROUND

Leptomeningeal metastasis (LM) of small cell lung cancer (SCLC) is a highly detrimental occurrence associated with severe neurological disorders, lacking effective treatment currently. Proteolysis-targeting chimeric molecules (PROTACs) may provide new therapeutic avenues for treatment of podophyllotoxin derivatives-resistant SCLC with LM, warranting further exploration.

METHODS

The SCLC cell line H128 expressing luciferase were mutated by MNNG to generate H128-Mut cell line. After subcutaneous inoculation of H128-Mut into nude mice, H128-LM and H128-BPM (brain parenchymal metastasis) cell lines were primarily cultured from LM and BPM tissues individually, and employed to in vitro drug testing. The SCLC-LM mouse model was established by inoculating H128-LM into nude mice via carotid artery and subjected to in vivo drug testing. RNA-seq and immunoblotting were conducted to uncover the molecular targets for LM.

RESULTS

The SCLC-LM mouse model was successfully established, confirmed by in vivo live imaging and histological examination. The upregulated genes included EZH2, SLC44A4, VEGFA, etc. in both BPM and LM cells, while SLC44A4 was particularly upregulated in LM cells. When combined with PROTAC EZH2 degrader-1, the drug sensitivity of cisplatin, etoposide (VP16), and teniposide (VM26) for H128-LM was significantly increased in vitro. The in vivo drug trials with SCLC-LM mouse model demonstrated that PROTAC EZH2 degrader-1 plus VM26 or cisplatin/ VP16 inhibited H128-LM tumour significantly compared to VM26 or cisplatin/ VP16 alone (P < 0.01).

CONCLUSION

The SCLC-LM model effectively simulates the pathophysiological process of SCLC metastasis to the leptomeninges. PROTAC EZH2 degrader-1 overcomes chemoresistance in SCLC, suggesting its potential therapeutic value for SCLC LM.

Novel therapies for metastatic prostate cancer

INTRODUCTION

Patients with metastatic prostate cancer, especially in the castrate-resistant setting, have a poor prognosis. Many agents have been approved for metastatic prostate cancer, such as androgen receptor pathway inhibitors, taxane-based chemotherapy, radiopharmaceuticals, and immunotherapy. However, prostate cancer remains the leading cause of cancer deaths in nonsmoking men. Fortunately, many more novel agents are under investigation.

AREAS COVERED

We provide an overview of the broad group of novel therapies for metastatic prostate cancer, with an emphasis on active and recruiting clinical trials that have been recently published and/or presented at national or international meetings.

EXPERT OPINION

The future for patients with metastatic prostate cancer is promising, with further development of novel therapies such as radiopharmaceuticals. Based on a growing understanding of prostate cancer biology, novel agents are being designed to overcome resistance to approved therapies. There are many trials using novel agents either as monotherapy or in combination with already approved agents with potential to further improve outcomes for men with advanced prostate cancer.

PARP Inhibitors and Proteins Interacting with SLX4

PARP inhibitors are small molecules currently used with success in the treatment of certain cancer patients. Their action was first shown to be specific to cells with DNA repair deficiencies, such as BRCA-mutant cancers. However, recent work has suggested clinical interest of these drugs beyond this group of patients. Preclinical data on relationships between the activity of PARP inhibitors and other proteins involved in DNA repair exist, and this review will only highlight findings on the SLX4 protein and its interacting protein partners. As suggested from these available data and depending on further validations, new treatment strategies could be developed in order to broaden the use for PARP inhibitors in cancer patients.

Clinical application of PARP inhibitors in ovarian cancer: from molecular mechanisms to the current status

As a kind of gynecological tumor, ovarian cancer is not as common as cervical cancer and breast cancer, but its malignant degree is higher. Despite the increasingly mature treatment of ovarian cancer, the five-year survival rate of patients is still less than 50%. Based on the concept of synthetic lethality, poly (ADP- ribose) polymerase (PARP) inhibitors target tumor cells with defects in homologous recombination repair(HRR), the most significant being the target gene Breast cancer susceptibility genes(BRCA). PARP inhibitors capture PARP-1 protein at the site of DNA damage to destroy the original reaction, causing the accumulation of PARP-DNA nucleoprotein complexes, resulting in DNA double-strand breaks(DSBs) and cell death. PARP inhibitors have been approved for the treatment of ovarian cancer for several years and achieved good results. However, with the widespread use of PARP inhibitors, more and more attention has been paid to drug resistance and side effects. Therefore, further research is needed to understand the mechanism of PARP inhibitors, to be familiar with the adverse reactions of the drug, to explore the markers of its efficacy and prognosis, and to deal with its drug resistance. This review elaborates the use of PARP inhibitors in ovarian cancer.