Deficiency in the Repair of DNA Damage by Homologous Recombination and Sensitivity to Poly(ADP-Ribose) Polymerase Inhibition

Cutibacterium acnes invades prostate epithelial cells to induce BRCAness as a possible pathogen of prostate cancer

BACKGROUND

Abundant evidence suggests that chronic inflammation is linked to prostate cancer and that infection is a possible cause of prostate cancer.

METHODS

To identify microbiota or pathogens associated with prostate cancer, we investigated the transcriptomes of 20 human prostate cancer tissues. We performed de novo assembly of nonhuman sequences from RNA-seq data.

RESULTS

We identified four bacteria as candidate microbiota in the prostate, including Moraxella osloensis, Uncultured chroococcidiopsis, Cutibacterium acnes, and Micrococcus luteus. Among these, C. acnes was detected in 19 of 20 prostate cancer tissue samples by immunohistochemistry. We then analyzed the gene expression profiles of prostate epithelial cells infected in vitro with C. acnes and found significant changes in homologous recombination (HR) and the Fanconi anemia pathway. Notably, electron microscopy demonstrated that C. acnes invaded prostate epithelial cells and localized in perinuclear vesicles, whereas analysis of γH2AX foci and HR assays demonstrated impaired HR repair. In particular, BRCA2 was significantly downregulated in C. acnes-infected cells.

CONCLUSIONS

These findings suggest that C. acnes infection in the prostate could lead to HR deficiency (BRCAness) which promotes DNA double-strand breaks, thereby increasing the risk of cancer development.

FANCM promotes PARP inhibitor resistance by minimizing ssDNA gap formation and counteracting resection inhibition

Poly(ADP-ribose) polymerase inhibitors (PARPis) exhibit remarkable anticancer activity in tumors with homologous recombination (HR) gene mutations. However, the role of other DNA repair proteins in PARPi-induced lethality remains elusive. Here, we reveal that FANCM promotes PARPi resistance independent of the core Fanconi anemia (FA) complex. FANCM-depleted cells retain HR proficiency, acting independently of BRCA1 in response to PARPis. FANCM depletion leads to increased DNA damage in the second S phase after PARPi exposure, driven by elevated single-strand DNA (ssDNA) gap formation behind replication forks in the first S phase. These gaps arise from both 53BP1- and primase and DNA directed polymerase (PRIMPOL)-dependent mechanisms. Notably, FANCM-depleted cells also exhibit reduced resection of collapsed forks, while 53BP1 deletion restores resection and mitigates PARPi sensitivity. Our results suggest that FANCM counteracts 53BP1 to repair PARPi-induced DNA damage. Furthermore, FANCM depletion leads to increased chromatin bridges and micronuclei formation after PARPi treatment, elucidating the mechanism underlying extensive cell death in FANCM-depleted cells.

Is the Homologous Recombination Repair Mutation Defined by a 15-Gene Panel Associated with the Prognosis of Epithelial Ovarian Cancer?

BACKGROUND

There is no consensus regarding the specific genes included in the homologous recombination repair (HRR) gene panel for identifying the HRR deficiency (HRD) status and predicting the prognosis of epithelial ovarian cancer (EOC) patients.

OBJECTIVE

We aimed to explore a 15-gene panel involving the HRR pathway as a predictive prognostic indicator in Chinese patients newly diagnosed with EOC.

PATIENTS AND METHODS

We reviewed the previously published reports about different HRR gene panels and prespecified the 15-gene panel. The genetic testing results in a 15-gene panel from 308 EOC patients diagnosed between 2014 and 2022 from six centers were collected. The association of clinicopathologic characteristics, the use of poly (adenosine diphosphate-ribose) polymerase inhibitors (PARPis) and progression-free survival (PFS) with 15-gene panel HRR mutations (HRRm) status was assessed.

RESULTS

43.2% (133/308) of patients were determined to carry 144 deleterious HRRm, among which 68.1% (98/144) were germline mutations and 32.8% (101/308) were BRCA1/2 gene lethal mutations. The hazard ratio (HR) (95% confidence interval, CI) for PFS (HRRm v HRR wild type, HRRwt) using the 15-gene panel HRRm was 0.42 (0.28-0.64) at all stages and 0.42 (0.27-0.65) at stages IIIC-IV. However, a prognostic difference was observed only between the BRCA mutation group and the HRRwt group, not between the non-BRCA HRRm group and the HRRwt group. For the subgroups of patients not using PARPis, the HR (95% CI) was 0.41 (0.24-0.68) at stages IIIC-IV.

CONCLUSIONS

This study provides evidence that 15-gene panel HRRm can predict the prognosis of EOC, of these only the BRCA1/2 mutations, not non-BRCA HRRm, contribute to prognosis prediction. Among patients without PARPis, the HRRm group presented a better PFS. This is the first study of this kind in the Chinese population.

New Horizons of Synthetic Lethality in Cancer: Current Development and Future Perspectives

In recent years, synthetic lethality has been recognized as a solid paradigm for anticancer therapies. The discovery of a growing number of synthetic lethal targets has led to a significant expansion in the use of synthetic lethality, far beyond poly(ADP-ribose) polymerase inhibitors used to treat BRCA1/2-defective tumors. In particular, molecular targets within DNA damage response have provided a source of inhibitors that have rapidly reached clinical trials. This Perspective focuses on the most recent progress in synthetic lethal targets and their inhibitors, within and beyond the DNA damage response, describing their design and associated therapeutic strategies. We will conclude by discussing the current challenges and new opportunities for this promising field of research, to stimulate discussion in the medicinal chemistry community, allowing the investigation of synthetic lethality to reach its full potential.

FLT1 activation in cancer cells promotes PARP-inhibitor resistance in breast cancer

Acquired resistance to PARP inhibitors (PARPi) remains a treatment challenge for BRCA1/2-mutant breast cancer that drastically shortens patient survival. Although several resistance mechanisms have been identified, none have been successfully targeted in the clinic. Using new PARPi-resistance models of Brca1- and Bard1-mutant breast cancer generated in-vivo, we identified FLT1 (VEGFR1) as a driver of resistance. Unlike the known role of VEGF signaling in angiogenesis, we demonstrate a novel, non-canonical role for FLT1 signaling that protects cancer cells from PARPi in-vivo through a combination of cell-intrinsic and cell-extrinsic pathways. We demonstrate that FLT1 blockade suppresses AKT activation, increases tumor infiltration of CD8+ T cells, and causes dramatic regression of PARPi-resistant breast tumors in a T-cell-dependent manner. Moreover, PARPi-resistant tumor cells can be readily re-sensitized to PARPi by targeting Flt1 either genetically (Flt1-suppression) or pharmacologically (axitinib). Importantly, a retrospective series of breast cancer patients treated with PARPi demonstrated shorter progression-free survival in cases with FLT1 activation at pre-treatment. Our study therefore identifies FLT1 as a potential therapeutic target in PARPi-resistant, BRCA1/2-mutant breast cancer.

Methylation synthetic lethality: Exploiting selective drug targets for cancer therapy

In cancer, synthetic lethality refers to the drug-induced inactivation of one gene and the inhibition of another in cancer cells by a drug, resulting in the death of only cancer cells; however, this effect is not present in normal cells, leading to targeted killing of cancer cells. Recent intensive epigenetic research has revealed that aberrant epigenetic changes are more frequently observed than gene mutations in certain cancers. Recently, numerous studies have reported various methylation synthetic lethal combinations involving DNA damage repair genes, metabolic pathway genes, and paralogs with significant results in cellular models, some of which have already entered clinical trials with promising results. This review systematically introduces the advantages of methylation synthetic lethality and describes the lethal mechanisms of methylation synthetic lethal combinations that have recently demonstrated success in cellular models. Furthermore, we discuss the future opportunities and challenges of methylation synthetic lethality in targeted anticancer therapies.

TP53-specific mutations serve as a potential biomarker for homologous recombination deficiency in breast cancer: a clinical next-generation sequencing study

Background

TP53 mutations and homologous recombination deficiency (HRD) occur frequently in breast cancer. However, the characteristics of TP53 pathogenic mutations in breast cancer patients with/without HRD are not clear.

Methods

Clinical next-generation sequencing (NGS) of both tumor and paired blood DNA from 119 breast cancer patients (BRCA-119 cohort) was performed with a 520-gene panel. Mutations, tumor mutation burden (TMB), and genomic HRD scores were assessed from NGS data. NGS data from 47 breast cancer patients in the HRD test cohort were analyzed for further verification.

Results

All TP53 pathogenic mutations in patients had somatic origin, which was associated with the protein expression of estrogen receptor and progestogen receptor. Compared to patients without TP53 pathologic mutations, patients with TP53 pathologic mutations had higher levels of HRD scores and different genomic alterations. The frequency of TP53 pathologic mutation was higher in the HRD-high group (HRD score ≥ 42) relative to that in the HRD-low group (HRD score < 42). TP53 has different mutational characteristics between the HRD-low and HRD-high groups. TP53-specific mutation subgroups had diverse genomic features and TMB. Notably, TP53 pathogenic mutations predicted the HRD status of breast cancer patients with an area under the curve (AUC) of 0.61. TP53-specific mutations, namely HRD-low mutation, HRD-high mutation, and HRD common mutation, predicted the HRD status of breast cancer patients with AUC values of 0.32, 0.72, and 0.58, respectively. Interestingly, TP53 HRD-high mutation and HRD common mutation combinations showed the highest AUC values (0.80) in predicting HRD status.

Conclusions

TP53-specific mutation combinations predict the HRD status of patients, indicating that TP53 pathogenic mutations could serve as a potential biomarker for poly-ADP-ribose polymerase (PARP) inhibitors in breast cancer patients .

Germline Mutational Landscape and Novel Targetable RAD51D Variant in Chinese Patients With Ovarian Cancer

PURPOSE

Genetic variants of ovarian cancer (OV) show ethnic differences, but data from the Chinese population are still insufficient. Here, we elucidate the inheritance landscape in Chinese patients with OV and examine the functional implications of a Chinese-enriched RAD51D variant.

METHODS

Between 2015 and 2018, 373 consecutive patients with OV were prospectively enrolled. Variants of BRCA1/2, other homologous recombination repair (HRR) genes, and DNA mismatch repair (MMR) genes were analyzed using next-generation sequencing. An enriched RAD51D variant was identified, and its functional effects were examined using Cell Counting Kit-8, colony formation, transwell migration, and drug sensitivity assays.

RESULTS

Overall, 31.1% (116/373) of patients had at least one pathogenic or likely pathogenic germline variant. BRCA1 and BRCA2 accounted for 16.09% and 5.36%, respectively, with one patient having both variants. In addition, 32 (8.58%) patients carried other HRR gene variants, whereas three (0.8%) patients had MMR gene variants. The RAD51D variant ranked third (8/373, 2.1%), and its rate was much higher than that in other populations. Remarkably, all eight patients harbored the RAD51D K91fs variant (c.270_271dup, p.Lys91Ilefs*13) and demonstrated satisfactory platinum response and favorable prognosis. This variant confers enhanced sensitivity to poly (ADP-ribose) polymerase inhibitors in OV cells. However, the effects on platinum sensitivity were inconsistent across different cell lines. Against the background of the TP53 variant, RAD51D K91fs variant showed increased sensitivity to cisplatin.

CONCLUSION

Our study revealed the inheritance landscape of OV and identified an enriched RAD51D variant in Chinese patients with OV. This can serve as an important reference for OV management and a potential therapeutic target.

DNA damage response defects in hematologic malignancies: mechanistic insights and therapeutic strategies

ABSTRACT

The DNA damage response (DDR) encompasses the detection and repair of DNA lesions and is fundamental to the maintenance of genome integrity. Germ line DDR alterations underlie hereditary chromosome instability syndromes by promoting the acquisition of pathogenic structural variants in hematopoietic cells, resulting in increased predisposition to hematologic malignancies. Also frequent in hematologic malignancies are somatic mutations of DDR genes, typically arising from replication stress triggered by oncogene activation or deregulated tumor proliferation that provides a selective pressure for DDR loss. These defects impair homology-directed DNA repair or replication stress response, leading to an excessive reliance on error-prone DNA repair mechanisms that results in genomic instability and tumor progression. In hematologic malignancies, loss-of-function DDR alterations confer clonal growth advantage and adverse prognostic impact but may also provide therapeutic opportunities. Selective targeting of functional dependencies arising from these defects could achieve synthetic lethality, a therapeutic concept exemplified by inhibition of poly-(adenosine 5'-diphosphate ribose) polymerase or the ataxia telangiectasia and Rad 3 related-CHK1-WEE1 axis in malignancies harboring the BRCAness phenotype or genetic defects that increase replication stress. Furthermore, the role of DDR defects as a source of tumor immunogenicity, as well as their impact on the cross talk between DDR, inflammation, and tumor immunity are increasingly recognized, thus providing rationale for combining DDR modulation with immune modulation. The nature of the DDR-immune interface and the cellular vulnerabilities conferred by DDR defects may nonetheless be disease-specific and remain incompletely understood in many hematologic malignancies. Their comprehensive elucidation will be critical for optimizing therapeutic strategies to target DDR defects in these diseases.

Preclinical Characterization of AZD9574, a Blood-Brain Barrier Penetrant Inhibitor of PARP1

PURPOSE

We evaluated the properties and activity of AZD9574, a blood-brain barrier (BBB) penetrant selective inhibitor of PARP1, and assessed its efficacy and safety alone and in combination with temozolomide (TMZ) in preclinical models.

EXPERIMENTAL DESIGN

AZD9574 was interrogated in vitro for selectivity, PARylation inhibition, PARP-DNA trapping, the ability to cross the BBB, and the potential to inhibit cancer cell proliferation. In vivo efficacy was determined using subcutaneous as well as intracranial mouse xenograft models. Mouse, rat, and monkey were used to assess AZD9574 BBB penetration and rat models were used to evaluate potential hematotoxicity for AZD9574 monotherapy and the TMZ combination.

RESULTS

AZD9574 demonstrated PARP1-selectivity in fluorescence anisotropy, PARylation, and PARP-DNA trapping assays and in vivo experiments demonstrated BBB penetration. AZD9574 showed potent single agent efficacy in preclinical models with homologous recombination repair deficiency in vitro and in vivo. In an O6-methylguanine-DNA methyltransferase (MGMT)-methylated orthotopic glioma model, AZD9574 in combination with TMZ was superior in extending the survival of tumor-bearing mice compared with TMZ alone.

CONCLUSIONS

The combination of three key features-PARP1 selectivity, PARP1 trapping profile, and high central nervous system penetration in a single molecule-supports the development of AZD9574 as the best-in-class PARP inhibitor for the treatment of primary and secondary brain tumors. As documented by in vitro and in vivo studies, AZD9574 shows robust anticancer efficacy as a single agent as well as in combination with TMZ. AZD9574 is currently in a phase I trial (NCT05417594). See related commentary by Lynce and Lin, p. 1217.

A synergistic two-drug therapy specifically targets a DNA repair dysregulation that occurs in p53-deficient colorectal and pancreatic cancers

The tumor-suppressor p53 is commonly inactivated in colorectal cancer and pancreatic ductal adenocarcinoma, but existing treatment options for p53-mutant (p53Mut) cancer are largely ineffective. Here, we report a therapeutic strategy for p53Mut tumors based on abnormalities in the DNA repair response. Investigation of DNA repair upon challenge with thymidine analogs reveals a dysregulation in DNA repair response in p53Mut cells that leads to accumulation of DNA breaks. Thymidine analogs do not interrupt DNA synthesis but induce DNA repair that involves a p53-dependent checkpoint. Inhibitors of poly(ADP-ribose) polymerase (PARPis) markedly enhance DNA double-strand breaks and cell death induced by thymidine analogs in p53Mut cells, whereas p53 wild-type cells respond with p53-dependent inhibition of the cell cycle. Combinations of trifluorothymidine and PARPi agents demonstrate superior anti-neoplastic activity in p53Mut cancer models. These findings support a two-drug combination strategy to improve outcomes for patients with p53Mut cancer.

GRB2 stabilizes RAD51 at reversed replication forks suppressing genomic instability and innate immunity against cancer

Growth factor receptor-bound protein 2 (GRB2) is a cytoplasmic adapter for tyrosine kinase signaling and a nuclear adapter for homology-directed-DNA repair. Here we find nuclear GRB2 protects DNA at stalled replication forks from MRE11-mediated degradation in the BRCA2 replication fork protection axis. Mechanistically, GRB2 binds and inhibits RAD51 ATPase activity to stabilize RAD51 on stalled replication forks. In GRB2-depleted cells, PARP inhibitor (PARPi) treatment releases DNA fragments from stalled forks into the cytoplasm that activate the cGAS-STING pathway to trigger pro-inflammatory cytokine production. Moreover in a syngeneic mouse metastatic ovarian cancer model, GRB2 depletion in the context of PARPi treatment reduced tumor burden and enabled high survival consistent with immune suppression of cancer growth. Collective findings unveil GRB2 function and mechanism for fork protection in the BRCA2-RAD51-MRE11 axis and suggest GRB2 as a potential therapeutic target and an enabling predictive biomarker for patient selection for PARPi and immunotherapy combination.

New clinical trial design in precision medicine: discovery, development and direction

In the era of precision medicine, it has been increasingly recognized that individuals with a certain disease are complex and different from each other. Due to the underestimation of the significant heterogeneity across participants in traditional "one-size-fits-all" trials, patient-centered trials that could provide optimal therapy customization to individuals with specific biomarkers were developed including the basket, umbrella, and platform trial designs under the master protocol framework. In recent years, the successive FDA approval of indications based on biomarker-guided master protocol designs has demonstrated that these new clinical trials are ushering in tremendous opportunities. Despite the rapid increase in the number of basket, umbrella, and platform trials, the current clinical and research understanding of these new trial designs, as compared with traditional trial designs, remains limited. The majority of the research focuses on methodologies, and there is a lack of in-depth insight concerning the underlying biological logic of these new clinical trial designs. Therefore, we provide this comprehensive review of the discovery and development of basket, umbrella, and platform trials and their underlying logic from the perspective of precision medicine. Meanwhile, we discuss future directions on the potential development of these new clinical design in view of the "Precision Pro", "Dynamic Precision", and "Intelligent Precision". This review would assist trial-related researchers to enhance the innovation and feasibility of clinical trial designs by expounding the underlying logic, which be essential to accelerate the progression of precision medicine.

A review of poly(ADP-ribose)polymerase-1 (PARP1) role and its inhibitors bearing pyrazole or indazole core for cancer therapy

Cancer is a disease with a high mortality rate characterized by uncontrolled proliferation of abnormal cells. The hallmarks of cancer evidence the acquired cells characteristics that promote the growth of malignant tumours, including genomic instability and mutations, the ability to evade cellular death and the capacity of sustaining proliferative signalization. Poly(ADP-ribose) polymerase-1 (PARP1) is a protein that plays key roles in cellular regulation, namely in DNA damage repair and cell survival. The inhibition of PARP1 promotes cellular death in cells with homologous recombination deficiency, and therefore, the interest in PARP protein has been rising as a target for anticancer therapies. There are already some PARP1 inhibitors approved by Food and Drug Administration (FDA), such as Olaparib and Niraparib. The last compound presents in its structure an indazole core. In fact, pyrazoles and indazoles have been raising interest due to their various medicinal properties, namely, anticancer activity. Derivatives of these compounds have been studied as inhibitors of PARP1 and presented promising results. Therefore, this review aims to address the importance of PARP1 in cell regulation and its role in cancer. Moreover, it intends to report a comprehensive literature review of PARP1 inhibitors, containing the pyrazole and indazole scaffolds, published in the last fifteen years, focusing on structure-activity relationship aspects, thus providing important insights for the design of novel and more effective PARP1 inhibitors.

The power and the promise of synthetic lethality for clinical application in cancer treatment

Synthetic lethality is a phenomenon wherein the simultaneous deficiency of two or more genes results in cell death, while the deficiency of any individual gene does not lead to cell death. In recent years, synthetic lethality has emerged as a significant topic in the field of targeted cancer therapy, with certain drugs based on this concept exhibiting promising outcomes in clinical trials. Nevertheless, the presence of tumor heterogeneity and the intricate DNA repair mechanisms pose challenges to the effective implementation of synthetic lethality. This review aims to explore the concepts, development, and ethical quandaries surrounding synthetic lethality. Additionally, it will provide an in-depth analysis of the clinical application and underlying mechanism of synthetic lethality.

Comparison of Adverse Events Between PARP Inhibitors in Patients with Epithelial Ovarian Cancer: A Nationwide Propensity Score Matched Cohort Study

BACKGROUND

Despite improvement in progression-free survival (PFS) with poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) as maintenance treatment for patients with epithelial ovarian cancer (EOC), a comparative analysis of clinical events of interest (CEIs) of different PARPi is scarce.

OBJECTIVE

This study aimed to compare the safety of different PARPi in patients with EOC.

PATIENTS AND METHODS

Through analyzing the Korean National Health Insurance Service from January 2009 to January 2022, this study involved BRCA-mutated, platinum-sensitive patients with EOC treated with olaparib (tablet), niraparib, and olaparib (capsule) as first-line or second-line maintenance treatment. CEIs were identified using International Statistical Classification of Diseases (ICD) 9/10 codes, with additional outcomes being dose modification and persistence.

RESULTS

In the first-line maintenance treatment [118 niraparib, 104 olaparib (tablet) patients], no significant differences were noted in CEIs, dose reduction, or 6-month discontinuation rate. For second-line maintenance treatment [303 niraparib, 126 olaparib (tablet), and 675 olaparib (capsule) patients], niraparib was associated with a higher risk of hematologic CEIs, particularly anemia, compared with olaparib (tablet) (0.51 [0.26-0.98] and 0.09 [0.01-0.74], respectively), and higher rate of discontinuation rate at 6 months. Of note, patients over 60 years old showed an increased risk of CEIs with niraparib, as indicated by the hazard ratio divergence in restricted cubic spline plots.

CONCLUSIONS

No differences were observed among the PARPi during first-line maintenance treatment. However, in the second-line maintenance treatment, significant differences were observed in the risk of experiencing CEIs, dose alteration possibilities, and discontinuation of PARPi between niraparib and olaparib (tablets). Moreover, our findings suggest that an age of 60 years may be a critical factor in selecting PARPi to reduce CEI incidence.

From clinical management to personalized medicine: novel therapeutic approaches for ovarian clear cell cancer

Ovarian clear-cell cancer is a rare subtype of epithelial ovarian cancer with unique clinical and biological features. Despite optimal cytoreductive surgery and platinum-based chemotherapy being the standard of care, most patients experience drug resistance and a poor prognosis. Therefore, novel therapeutic approaches have been developed, including immune checkpoint blockade, angiogenesis-targeted therapy, ARID1A synthetic lethal interactions, targeting hepatocyte nuclear factor 1β, and ferroptosis. Refining predictive biomarkers can lead to more personalized medicine, identifying patients who would benefit from chemotherapy, targeted therapy, or immunotherapy. Collaboration between academic research groups is crucial for developing prognostic outcomes and conducting clinical trials to advance treatment for ovarian clear-cell cancer. Immediate progress is essential, and research efforts should prioritize the development of more effective therapeutic strategies to benefit all patients.

Genetic Basis of Breast and Ovarian Cancer: Approaches and Lessons Learnt from Three Decades of Inherited Predisposition Testing

Germline variants occurring in BRCA1 and BRCA2 give rise to hereditary breast and ovarian cancer (HBOC) syndrome, predisposing to breast, ovarian, fallopian tube, and peritoneal cancers marked by elevated incidences of genomic aberrations that correspond to poor prognoses. These genes are in fact involved in genetic integrity, particularly in the process of homologous recombination (HR) DNA repair, a high-fidelity repair system for mending DNA double-strand breaks. In addition to its implication in HBOC pathogenesis, the impairment of HR has become a prime target for therapeutic intervention utilizing poly (ADP-ribose) polymerase (PARP) inhibitors. In the present review, we introduce the molecular roles of HR orchestrated by BRCA1 and BRCA2 within the framework of sensitivity to PARP inhibitors. We examine the genetic architecture underneath breast and ovarian cancer ranging from high- and mid- to low-penetrant predisposing genes and taking into account both germline and somatic variations. Finally, we consider higher levels of complexity of the genomic landscape such as polygenic risk scores and other approaches aiming to optimize therapeutic and preventive strategies for breast and ovarian cancer.

PARP inhibitors for prostate cancer

Poly(ADP-ribose) polymerase (PARP) inhibitors have transformed the treatment landscape for patients with metastatic castration-resistant prostate cancer (mCRPC) and alterations in DNA damage response genes. This has also led to widespread use of genomic testing in all patients with mCRPC. The current review will give an overview of (1) the current understanding of the interplay between DNA damage response and PARP enzymes; (2) the clinical landscape of PARP inhibitors, including the combination of PARP inhibitors with other agents such as androgen-receptor signaling agents; (3) biomarkers related to PARP inhibitor response and resistance; and (4) considerations for interpreting genomic testing results and treating patients with PARP inhibitors.

Beyond BRCA: Diagnosis and management of homologous recombination repair deficient pancreatic cancer

Approximately 4%-7% of patients diagnosed with pancreatic adenocarcinoma (PDAC) are found to harbor deleterious germline mutations in BRCA1 and/or BRCA2. Loss of function of BRCA1 and/or BRCA2 results in deficiency in homologous recombination repair (HRR), a critical DNA repair pathway, and confers sensitivity to certain DNA damaging agents, including platinum chemotherapy and PARP inhibitors. The PARP inhibitor olaparib is food and drug administration (FDA) approved for use in pancreatic cancer based on the POLO trial, which found that maintenance olaparib significantly prolonged progression free survival compared to placebo among patients with germline BRCA1 or BRCA2 mutations and metastatic PDAC that had not progressed following frontline platinum-based chemotherapy. Recently, there has been considerable interest in identifying patients without BRCA inactivation whose tumors also exhibit properties of HRR deficiency and thus may be susceptible to therapies with proven benefit in cancers harboring BRCA mutations. Here, we discuss methods for identification of HRR-deficiency and review the management of HRR-deficient cancers with a focus on HRR-deficient PDAC.

Synergistic antitumor efficacy of rMV-Hu191 and Olaparib in pancreatic cancer by generating oxidative DNA damage and ROS-dependent apoptosis

BACKGROUND

Malignancies with BRCA1/2 deficiencies are particularly sensitive to PARP inhibitors. Thus, combining PARP inhibitors with agents that impair DNA damage repair to treat BRCA1/2 wild-type PDAC could broaden the clinical use of these promising PARP inhibitors. Here we examined the synergism and mechanism of oncolytic measles virus (rMV-Hu191) with a PARP inhibitor (Olaparib) in vitro and in vivo.

METHODS

The cell viability assay, cell cycle analysis, colony formation assay, TCID 50 method, western blotting, flow cytometry, DNA comet assay, Mice bearing PDAC xenografts, IF, IHC and TUNEL assay were performed to explore the antitumor efficacy and underlying mechanisms.

RESULTS

In this study, we explored the antitumor activities of rMV-Hu191 and Olaparib in two PDAC cell lines harboring wild-type BRCA1/2 genes. Compared to monotherapy, the combination of rMV-Hu191 and Olaparib was able to synergistically cause growth arrest, apoptotic cell death and DNA damage, accompanying with excessive oxidative stress. Mechanistically, the data indicated that the observed synergy depended on the oxidative DNA damage and ROS-dependent apoptosis generating by rMV-Hu191 combined with Olaparib in human PDAC cells. Tumor inhibition and prolonged survival of PDAC mice xenografts in vivo confirmed the synergism of combinational treatment with trivial side-effects.

CONCLUSIONS

Our findings firstly suggested that combination treatment with rMV-Hu191 and Olaparib had a profound and synergistic therapeutic effect against human PDAC through synthetic lethality. In conclusion, we recommend combining oncolytic rMV-Hu191 with a PARP inhibitor (Olaparib) as a novel therapeutic strategy and provided a potential mechanism for advanced PDAC regardless of BRCA mutation status.

Germline Genetic Associations for Hepatobiliary Cancers

Hepatobiliary cancers (HBCs) include hepatocellular carcinoma, cholangiocarcinoma, and gallbladder carcinoma, which originate from the liver, bile ducts, and gallbladder, respectively. They are responsible for a substantial burden of cancer-related deaths worldwide. Despite knowledge of risk factors and advancements in therapeutics and surgical interventions, the prognosis for most patients with HBC remains bleak. There is evidence from familial aggregation and case-control studies to suggest a familial risk component in HBC susceptibility. Recent progress in genomics research has led to the identification of germline variants including single nucleotide polymorphisms (SNPs) and pathogenic or likely pathogenic (P/LP) variants in cancer-associated genes associated with HBC risk. These findings emerged from genome-wide association studies and next-generation sequencing techniques such as whole-exome sequencing. Patients with other cancer types, including breast, colon, ovarian, prostate, and pancreatic cancer, are recommended by guidelines to undergo germline genetic testing, but similar recommendations are lagging in HBC. This prompts the question of whether multi-gene panel testing should be integrated into clinical guidelines for HBC management. Here, we review the hereditary genetics of HBC, explore studies investigating SNPs and P/LP variants in HBC patients, discuss the clinical implications and potential for personalized treatments and impact on patient's family members, and conclude that additional studies are needed to examine how genetic testing can be applied clinically.

Inhibition of p300 increases cytotoxicity of cisplatin in pancreatic cancer cells

Pancreatic cancer is a notoriously deadly disease with a five-year survival rate around 10 percent. Since early detection of these tumors is difficult, pancreatic cancers are often diagnosed at advanced stages. At this point, genotoxic chemotherapeutics can be used to manage tumor growth. However, side effects of these drugs are severe, limiting the amount of treatment that can be given and resulting in sub-optimal dosing. Thus, there is an urgent need to identify chemo-sensitizing agents that can lower the effective dose of genotoxic agents and as a result reduce the side effects. Here, we use transformed and non-transformed pancreatic cell lines to evaluate DNA repair inhibitors as chemo-sensitizing agents. We used a novel next generation sequencing approach to demonstrate that pancreatic cancer cells have a reduced ability to faithfully repair DNA damage. We then determine the extent that two DNA repair inhibitors (CCS1477, a small molecule inhibitor of p300, and ART558, a small molecule inhibitor of polymerase theta) can exploit this repair deficiency to make pancreatic cancer cells more sensitive to cisplatin, a commonly used genotoxic chemotherapeutic. Immunofluorescence microscopy and cell viability assays show that CCS1477 delayed repair and significantly sensitized pancreatic cancer cells to cisplatin. The increased toxicity was not seen in a non-transformed pancreatic cell line. We also found that while ART558 sensitizes pancreatic cancer cells to cisplatin, it also sensitized non-transformed pancreatic cancer cells.

PARP inhibitor combinations with high-dose vitamin C in the treatment of Ewing sarcoma: two case reports and mechanistic overview

Ewing's sarcoma (ES) is a bone and soft tissue tumor that mainly occurs at a young age. The underlying cause of Ewing's sarcoma is the formation of fusion proteins between FET family genes and ETS family genes. Tumors with FET/ETS fusion genes can have defects in the DNA damage response and are sensitive to PARP inhibitors (PARPi). However, several studies have shown that PARPi alone is not sufficient to induce a meaningful antitumor response and that combinations of DNA-damaging agents with PARPi are required to achieve efficacy. Accordingly, preclinical studies have reported dramatic responses to PARPi treatment in combination with DNA-damaging agents such as temozolomide or irinotecan. Similarly, it has been previously reported that by generating reactive oxygen species, high-dose intravenous vitamin C (IVC) can induce DNA damage. This suggests that the combination of IVC with PARPi may increase genotoxic stress and enhance the antitumor response. In addition, unlike chemotherapeutic agents, IVC induces DNA damage selectively in cancer cells, and the side effects are significantly milder than those of chemotherapy. As ETS fusion-positive ES is deficient in faithful DNA repair, partly due to the interaction between ETS fusion products and PARP1, a PARPi plus IVC seems to be a logical and effective combination for the treatment of ETS fusion-positive ES. This paper reports significant responses to IVC (1-1.5 g/kg) in combination with PARPi (olaparib 300 mg BID or talazoparib 1 mg/day) in two patients with metastatic Ewing's sarcoma. The observations highlight an unmet therapeutic need for patients with advanced metastatic ES. The combination of PARPi with a selective DNA-damaging agent was effective in these cases. This case experience suggests that IVC may be incorporated into PARPi-based therapeutic strategies. Further studies are needed to confirm the efficacy of this combination in the treatment of Ewing sarcoma with ETS fusions.

Sulfoquinovosyl acylpropanediol (SQAP): Inhibition of poly(ADP-ribose) metabolism and enhanced cytotoxicity in homologous recombination repair-deficient Chinese hamster-derived cells

Sulfoquinovosyl acylpropanediol (SQAP; a synthetic derivative of the sulfoglycolipid natural product sulfoquinovosyl acylglycerol, SQAG), has anti-tumor and radiosensitizing activities in tumor xenograft mouse models. Here, we have studied the PARP inhibitory activity of SQAP and synthetic lethality in BRCA2-deficient cells. In initial screening studies with DNA repair-deficient Chinese hamster ovary cells, homologous recombination repair-deficient cell lines showed increased sensitivity to SQAP, compared to wild-type cells or other DNA repair-deficient mutants. Chinese hamster lung V79 cells and the derivative cell lines V-C8 (BRCA2-deficient) and V-C8 + BRCA2 gene corrections were used to test the role of BRCA2 in SQAP cytotoxicity. The findings were confirmed in studies of the human colon cancer cell lines DLD-1 and its BRCA2-knockout derivative. SQAP inhibited the enzymes poly(ADP-ribose) polymerase (PARP) and poly(ADP-ribose) glycohydrolase (PARG). SQAP pretreatment decreased H2O2induced poly(ADP-ribose) formation in V79 cells. SQAP caused DNA double-strand breaks and chromosome aberrations in V79 BRCA2-mutated cells but did not affect cells in the G2 phase. We have demonstrated that SQAP induces synthetic lethality in BRCA2-deficient Chinese hamster-derived cells via its effects on poly(ADP-ribose) metabolism, motivating further examination of its therapeutic potential, especially against tumors that are deficient in homologous recombination repair due to mutations in BRCA2 or other genes.

A Review of PARP-1 Inhibitors: Assessing Emerging Prospects and Tailoring Therapeutic Strategies

Eukaryotic organisms contain an enzyme family called poly (ADP-ribose) polymerases (PARPs), which is responsible for the poly (ADP-ribosylation) of DNA-binding proteins. PARPs are members of the cell signaling enzyme class. PARP-1, the most common isoform of the PARP family, is responsible for more than 90% of the tasks carried out by the PARP family as a whole. A superfamily consisting of 18 PARPs has been found. In order to synthesize polymers of ADP-ribose (PAR) and nicotinamide, the DNA damage nick monitor PARP-1 requires NAD+ as a substrate. The capability of PARP-1 activation to boost the transcription of proinflammatory genes, its ability to deplete cellular energy pools, which leads to cell malfunction and necrosis, and its involvement as a component in the process of DNA repair are the three consequences of PARP-1 activation that are of particular significance in the process of developing new drugs. As a result, the pharmacological reduction of PARP-1 may result in an increase in the cytotoxicity toward cancer cells.

A genetic mosaic mouse model illuminates the pre-malignant progression of basal-like breast cancer

Basal-like breast cancer (BLBC) is highly aggressive, and often characterized by BRCA1 and p53 deficiency. Although conventional mouse models enabled the investigation of BLBC at malignant stages, its initiation and pre-malignant progression remain understudied. Here, we leveraged a mouse genetic system known as mosaic analysis with double markers (MADM) to study BLBC initiation by generating rare GFP+Brca1, p53-deficient mammary cells alongside RFP+ wild-type sibling cells. After confirming the close resemblance of mammary tumors arising in this model to human BLBC at both transcriptomic and genomic levels, we focused our studies on the pre-malignant progression of BLBC. Initiated GFP+ mutant cells showed a stepwise pre-malignant progression trajectory from focal expansion to hyper-alveolarization and then to micro-invasion. Furthermore, despite morphological similarities to alveoli, hyper-alveolarized structures actually originate from ductal cells based on twin-spot analysis of GFP-RFP sibling cells. Finally, luminal-to-basal transition occurred exclusively in cells that have progressed to micro-invasive lesions. Our MADM model provides excellent spatiotemporal resolution to illuminate the pre-malignant progression of BLBC, and should enable future studies on early detection and prevention for this cancer.

CRISPR/Cas9-mediated knock-in of BRCA1/2 mutations restores response to olaparib in pancreatic cancer cell lines

Pancreatic cancer is one of the most aggressive diseases with a very poor outcome. Olaparib, a PARP inhibitor, as maintenance therapy showed benefits in patients with metastatic pancreatic adenocarcinoma bearing germline BRCA1/2 mutations. However, germline BRCA mutation has been described in only 4-7% of patients with pancreatic adenocarcinoma. A CRISPR/Cas9-mediated system was used to knock-in the c.763G > T p.(Glu255*) and c.2133C > A p.(Cys711*) mutations in cell lines to obtain truncated BRCA1 and BRCA2 proteins, respectively. A CRISPR/Cas9 ribonucleoprotein complex was assembled for each mutation and transfected into two pancreatic cell lines (T3M4 and Capan-2) and into a breast cancer cell lines (MCF7) as control. BRCA protein levels were significantly decreased in all BRCA-depleted cells (P < 0.05), proving the transfection efficiency of our CRISPR/Cas9 systems. As expected, the calculated olaparib IC50 were significantly reduced for all cell lines harbored BRCA1 or BRCA2 mutations compared to wild-type BRCA1/2 cells (P < 0.01). Furthermore, we observed a higher induction of apoptosis after 72 h olaparib treatment in BRCA-depleted cells than in wild-type cells. This strategy might offer new insights into the management of patients with pancreatic cancer and open up new perspectives based on the in vivo use of CRISPR/Cas9 strategy.

Targeting MALAT1 Augments Sensitivity to PARP Inhibition by Impairing Homologous Recombination in Prostate Cancer

PARP inhibitors (PARPi) have emerged as a promising targeted therapeutic intervention for metastatic castrate-resistant prostate cancer (mCRPC). However, the clinical utility of PARPi is limited to a subset of patients who harbor aberrations in the genes associated with the homologous recombination (HR) pathway. Here, we report that targeting metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), an oncogenic long noncoding RNA (lncRNA), contrives a BRCAness-like phenotype, and augments sensitivity to PARPi. Mechanistically, we show that MALAT1 silencing reprograms the homologous recombination (HR) transcriptome and makes prostate cancer cells more vulnerable to PARPi. Particularly, coinhibition of MALAT1 and PARP1 exhibits a decline in clonogenic survival, delays resolution of γH2AX foci, and reduces tumor burden in mice xenograft model. Moreover, we show that miR-421, a tumor suppressor miRNA, negatively regulates the expression of HR genes, while in aggressive prostate cancer cases, miR-421 is sequestered by MALAT1, leading to increased expression of HR genes. Conclusively, our findings suggest that MALAT1 ablation confers sensitivity to PARPi, thus highlighting an alternative therapeutic strategy for patients with castration-resistant prostate cancer (CRPC), irrespective of the alterations in HR genes.

SIGNIFICANCE

PARPi are clinically approved for patients with metastatic CRPC carrying mutations in HR genes, but are ineffective for HR-proficient prostate cancer. Herein, we show that oncogenic lncRNA, MALAT1 is frequently overexpressed in advanced stage prostate cancer and plays a crucial role in maintaining genomic integrity. Importantly, we propose a novel therapeutic strategy that emphasizes MALAT1 inhibition, leading to HR dysfunction in both HR-deficient and -proficient prostate cancer, consequently augmenting their susceptibility to PARPi.

Genomic analysis of advanced breast cancer tumors from talazoparib-treated gBRCA1/2mut carriers in the ABRAZO study

These analyses explore the impact of homologous recombination repair gene mutations, including BRCA1/2 mutations and homologous recombination deficiency (HRD), on the efficacy of the poly(ADP-ribose) polymerase (PARP) inhibitor talazoparib in the open-label, two-cohort, Phase 2 ABRAZO trial in germline BRCA1/2-mutation carriers. In the evaluable intent-to-treat population (N = 60), 58 (97%) patients harbor ≥1 BRCA1/2 mutation(s) in tumor sequencing, with 95% (53/56) concordance between germline and tumor mutations, and 85% (40/47) of evaluable patients have BRCA locus loss of heterozygosity indicating HRD. The most prevalent non-BRCA tumor mutations are TP53 in patients with BRCA1 mutations and PIK3CA in patients with BRCA2 mutations. BRCA1- or BRCA2-mutated tumors show comparable clinical benefit within cohorts. While low patient numbers preclude correlations between HRD and efficacy, germline BRCA1/2 mutation detection from tumor-only sequencing shows high sensitivity and non-BRCA genetic/genomic events do not appear to influence talazoparib sensitivity in the ABRAZO trial.ClinicalTrials.gov identifier: NCT02034916.

Patient Assessment and Therapy Planning Based on Homologous Recombination Repair Deficiency

Defects in genes involved in the DNA damage response cause homologous recombination repair deficiency (HRD). HRD is found in a subgroup of cancer patients for several tumor types, and it has a clinical relevance to cancer prevention and therapies. Accumulating evidence has identified HRD as a biomarker for assessing the therapeutic response of tumor cells to poly(ADP-ribose) polymerase inhibitors and platinum-based chemotherapies. Nevertheless, the biology of HRD is complex, and its applications and the benefits of different HRD biomarker assays are controversial. This is primarily due to inconsistencies in HRD assessments and definitions (gene-level tests, genomic scars, mutational signatures, or a combination of these methods) and difficulties in assessing the contribution of each genomic event. Therefore, we aim to review the biological rationale and clinical evidence of HRD as a biomarker. This review provides a blueprint for the standardization and harmonization of HRD assessments.

A review of strategies to overcome immune resistance in the treatment of advanced prostate cancer

Immunotherapy has become integral in cancer therapeutics over the past two decades and is now part of standard-of-care treatment in multiple cancer types. While various biomarkers and pathway alterations such as dMMR, CDK12, and AR-V7 have been identified in advanced prostate cancer to predict immunotherapy responsiveness, the vast majority of prostate cancer remain intrinsically immune-resistant, as evidenced by low response rates to anti-PD(L)1 monotherapy. Since regulatory approval of the vaccine therapy sipuleucel-T in the biomarker-unselected population, there has not been much success with immunotherapy treatment in advanced prostate cancer. Researchers have looked at various strategies to overcome immune resistance, including the identification of more biomarkers and the combination of immunotherapy with existing effective prostate cancer treatments. On the horizon, novel drugs using bispecific T-cell engager (BiTE) and chimeric antigen receptors (CAR) technology are being explored and have shown promising early efficacy in this disease. Here we discuss the features of the tumour microenvironment that predispose to immune resistance and rational strategies to enhance antitumour responsiveness in advanced prostate cancer.

A novel marker integrating multiple genetic alterations better predicts platinum sensitivity in ovarian cancer than HRD score

Introduction: Platinum-based chemotherapy is the first-line treatment strategy for ovarian cancer patients. The dismal prognosis of ovarian cancer was shown to be stringently associated with the heterogeneity of tumor cells in response to this therapy, therefore understanding platinum sensitivity in ovarian cancer would be helpful for improving patients' quality of life and clinical outcomes. HRDetect, utilized to characterize patients' homologous recombination repair deficiency, was used to predict patients' response to platinum-based chemotherapy. However, whether each of the single features contributing to HRD score is associated with platinum sensitivity remains elusive. Methods: We analyzed the whole-exome sequencing data of 196 patients who received platinum-based chemotherapy from the TCGA database. Genetic features were determined individually to see if they could indicate patients' response to platinum-based chemotherapy and prognosis, then integrated into a Pt-score employing LASSO regression model to assess its predictive performance. Results and discussion: Multiple genetic features, including bi-allelic inactivation of BRCA1/2 genes and genes involved in HR pathway, multiple somatic mutations in genes involved in DNA damage repair (DDR), and previously reported HRD-related features, were found to be stringently associated with platinum sensitivity and improved prognosis. Higher contributions of mutational signature SBS39 or ID6 predicted improved overall survival. Besides, arm-level loss of heterozygosity (LOH) of either chr4p or chr5q predicted significantly better disease-free survival. Notably, some of these features were found independent of HRD. And SBS3, an HRD-related feature, was found irrelevant to platinum sensitivity. Integrated all candidate markers using the LASSO model to yield a Pt-score, which showed better predictive ability compared to HRDetect in determining platinum sensitivity and predicting patients' prognosis, and this performance was validated in an independent cohort. The outcomes of our study will be instrumental in devising effective strategies for treating ovarian cancer with platinum-based chemotherapy.

Exceptional Response to Olaparib: A Case Report of Metastatic Esophageal Squamous Cell Carcinoma in a Patient With Fanconi Anemia, Germline FANCA Mutation, and Somatic BRCA2 Mutations

Exceptional response to olaparib in a case with Fanconi anemia and metastatic esophageal carcinoma

Poly(ADP-ribose) Polyremase-1 (PARP-1) Inhibition: A Promising Therapeutic Strategy for ETS-Expressing Tumours

ETS transcription factors are a highly conserved family of proteins involved in the progression of many cancers, such as breast and prostate carcinomas, Ewing's sarcoma, and leukaemias. This significant involvement can be explained by their roles at all stages of carcinogenesis progression. Generally, their expression in tumours is associated with a poor prognosis and an aggressive phenotype. Until now, no efficient therapeutic strategy had emerged to specifically target ETS-expressing tumours. Nevertheless, there is evidence that pharmacological inhibition of poly(ADP-ribose) polymerase-1 (PARP-1), a key DNA repair enzyme, specifically sensitises ETS-expressing cancer cells to DNA damage and limits tumour progression by leading some of the cancer cells to death. These effects result from a strong interplay between ETS transcription factors and the PARP-1 enzyme. This review summarises the existing knowledge of this molecular interaction and discusses the promising therapeutic applications.

Fanconi anemia associated protein 20 (FAAP20) plays an essential role in homology-directed repair of DNA double-strand breaks

FAAP20 is a Fanconi anemia (FA) protein that associates with the FA core complex to promote FANCD2/FANCI monoubiquitination and activate the damage response to interstrand crosslink damage. Here, we report that FAAP20 has a marked role in homologous recombination at a DNA double-strand break not associated with an ICL and separable from its binding partner FANCA. While FAAP20's role in homologous recombination is not dependent on FANCA, we found that FAAP20 stimulates FANCA's biochemical activity in vitro and participates in the single-strand annealing pathway of double-strand break repair in a FANCA-dependent manner. This indicates that FAAP20 has roles in several homology-directed repair pathways. Like other homology-directed repair factors, FAAP20 loss causes a reduction in nuclear RAD51 Irradiation-induced foci; and sensitizes cancer cells to ionizing radiation and PARP inhibition. In summary, FAAP20 participates in DNA double strand break repair by supporting homologous recombination in a non-redundant manner to FANCA, and single-strand annealing repair via FANCA-mediated strand annealing activity.

Relevance of ATM Status in Driving Sensitivity to DNA Damage Response Inhibitors in Patient-Derived Xenograft Models

Ataxia-telangiectasia mutated gene (ATM) is a key component of the DNA damage response (DDR) and double-strand break repair pathway. The functional loss of ATM (ATM deficiency) is hypothesised to enhance sensitivity to DDR inhibitors (DDRi). Whole-exome sequencing (WES), immunohistochemistry (IHC), and Western blotting (WB) were used to characterise the baseline ATM status across a panel of ATM mutated patient-derived xenograft (PDX) models from a range of tumour types. Antitumour efficacy was assessed with poly(ADP-ribose)polymerase (PARP, olaparib), ataxia- telangiectasia and rad3-related protein (ATR, AZD6738), and DNA-dependent protein kinase (DNA-PK, AZD7648) inhibitors as a monotherapy or in combination to associate responses with ATM status. Biallelic truncation/frameshift ATM mutations were linked to ATM protein loss while monoallelic or missense mutations, including the clinically relevant recurrent R3008H mutation, did not confer ATM protein loss by IHC. DDRi agents showed a mixed response across the PDX's but with a general trend toward greater activity, particularly in combination in models with biallelic ATM mutation and protein loss. A PDX with an ATM splice-site mutation, 2127T > C, with a high relative baseline ATM expression and KAP1 phosphorylation responded to all DDRi treatments. These data highlight the heterogeneity and complexity in describing targetable ATM-deficiencies and the fact that current patient selection biomarker methods remain imperfect; although, complete ATM loss was best able to enrich for DDRi sensitivity.

Combined PARP and WEE1 inhibition triggers anti-tumor immune response in BRCA1/2 wildtype triple-negative breast cancer

Novel therapeutic strategies that can effectively combine with immunotherapies are needed in the treatment of triple-negative breast cancer (TNBC). We demonstrate that combined PARP and WEE1 inhibition are synergistic in controlling tumour growth in BRCA1/2 wild-type TNBC preclinical models. The PARP inhibitor (PARPi) olaparib combined with the WEE1 inhibitor (WEE1i) adavosertib triggered increases in anti-tumour immune responses, including STING pathway activation. Combinations with a STING agonist resulted in further improved durable tumour regression and significant improvements in survival outcomes in murine tumour models of BRCA1/2 wild-type TNBC. In addition, we have identified baseline tumour-infiltrating lymphocyte (TIL) levels as a potential predictive biomarker of response to PARPi, WEE1i and immunotherapies in BRCA1/2 wild-type TNBC.

The intrinsically disordered, epigenetic factor RYBP binds to the citrullinating enzyme PADI4 in cancer cells

RYBP (Ring1 and YY 1 binding protein) is a multifunctional, intrinsically disordered protein (IDP), best described as a transcriptional regulator. It exhibits a ubiquitin-binding functionality, binds to other transcription factors, and has a key role during embryonic development. RYBP, which folds upon binding to DNA, has a Zn-finger domain at its N-terminal region. By contrast, PADI4 is a well-folded protein and it is one the human isoforms of a family of enzymes implicated in the conversion of arginine to citrulline. As both proteins intervene in signaling pathways related to cancer development and are found in the same localizations within the cell, we hypothesized they may interact. We observed their association in the nucleus and cytosol in several cancer cell lines, by using immunofluorescence (IF) and proximity ligation assays (PLAs). Binding also occurred in vitro, as measured by isothermal titration calorimetry (ITC) and fluorescence, with a low micromolar affinity (~1 μM). AlphaFold2-multimer (AF2) results indicate that PADI4's catalytic domain interacts with the Arg53 of RYBP docking into its active site. As RYBP sensitizes cells to PARP (Poly (ADP-ribose) polymerase) inhibitors, we applied them in combination with an enzymatic inhibitor of PADI4 observing a change in cell proliferation, and the hampering of the interaction of both proteins. This study unveils for the first time the possible citrullination of an IDP, and suggests that this new interaction, whether it involves or not citrullination of RYBP, might have implications in cancer development and progression.

Triumphs and challenges in exploiting poly(ADP-ribose) polymerase inhibition to combat triple-negative breast cancer

Poly(ADP-ribose) polymerase 1 (PARP1) regulates a myriad of DNA repair mechanisms to preserve genomic integrity following DNA damage. PARP inhibitors (PARPi) confer synthetic lethality in malignancies with a deficiency in the homologous recombination (HR) pathway. Patients with triple-negative breast cancer (TNBC) fail to respond to most targeted therapies because their tumors lack expression of the estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2. Certain patients with TNBC harbor mutations in HR mediators such as breast cancer susceptibility gene 1 (BRCA1) and breast cancer susceptibility gene 2 (BRCA2), enabling them to respond to PARPi. PARPi exploits the synthetic lethality of BRCA-mutant cells. However, de novo and acquired PARPi resistance frequently ensue. In this review, we discuss the roles of PARP in mediating DNA repair processes in breast epithelial cells, mechanisms of PARPi resistance in TNBC, and recent advances in the development of agents designed to overcome PARPi resistance in TNBC.

Transforming Growth Factor Beta and Epithelial to Mesenchymal Transition Alter Homologous Recombination Repair Gene Expression and Sensitize BRCA Wild-Type Ovarian Cancer Cells to Olaparib

Epithelial ovarian cancer (EOC) remains the most lethal gynecologic malignancy, largely due to metastasis and drug resistant recurrences. Fifteen percent of ovarian tumors carry mutations in BRCA1 or BRCA2, rendering them vulnerable to treatment with PARP inhibitors such as olaparib. Recent studies have shown that TGFβ can induce "BRCAness" in BRCA wild-type cancer cells. Given that TGFβ is a known driver of epithelial to mesenchymal transition (EMT), and the connection between EMT and metastatic spread in EOC and other cancers, we asked if TGFβ and EMT alter the susceptibility of EOC to PARP inhibition. Epithelial EOC cells were transiently treated with soluble TGFβ, and their clonogenic potential, expression, and function of EMT and DNA repair genes, and response to PARP inhibitors compared with untreated controls. A second epithelial cell line was compared to its mesenchymal derivative for EMT and DNA repair gene expression and drug responses. We found that TGFβ and EMT resulted in the downregulation of genes responsible for homologous recombination (HR) and sensitized cells to olaparib. HR efficiency was reduced in a dose-dependent manner. Furthermore, mesenchymal cells displayed sensitivity to olaparib, cisplatin, and the DNA-PK inhibitor Nu-7441. Therefore, the treatment of disseminated, mesenchymal tumors may represent an opportunity to expand the clinical utility of PARP inhibitors and similar agents.

Implementation of Nurse Navigation Improves Rate of Molecular Tumor Testing for Ovarian Cancer in a Gynecologic Oncology Practice

PURPOSE

The purpose of this study was to assess the impact of implementing a Nurse Navigator (NN) to improve the rate and timeliness of molecular tumor testing.

METHODS

This is an evaluation of the impact of education sessions, consensus building, and NN implementation for molecular tumor testing in patients with epithelial ovarian cancer. The NNs' responsibilities included attending tumor boards and ensuring Next Generation Sequencing (NGS) is ordered, reviewed, and coordinated for appropriate patients.

RESULTS

NNs significantly improved NGS testing rates from 35.29% to 77.27%, p = 0.002. Ordering a targeted panel test (TPT) was the most common reason for not ordering NGS in the pre-NN cohort (13/22, 59%). The total turnaround time for testing was reduced after the introduction of NNs from 145.2 days to 42.8 days, p < 0.0001. The post-NN group had a significantly higher rate of actionable mutations identified for the recurrent setting [67.6% versus 20.8% (p = 0.0005)] and a trend towards a higher rate of actionable mutations identified in the frontline setting [41.2% versus 33.3% (p = 0.41)].

CONCLUSION

NNs significantly improved somatic tumor testing rates and timeliness for patients with ovarian cancer. Discontinuing TPT in favor of NGS revealed a higher rate of actionable tumor mutations that would have been missed with TPT alone.

Tumor Microenvironment CD8 T and Treg Cells-related Genes Signature Distinguishes Distinct Prognosis and Targeted Therapies Response in Endometrial Cancer

Although most endometrial cancer (EC) patients have a favorable prognosis, the overall survival (OS) of metastatic and recurrent EC could hardly be improved by the current chemoradiotherapy. We aimed to reveal the tumor microenvironment immune infiltration characteristics to elucidate the underlying mechanism of EC progression and guide clinical decisions. In the Cancer Genome Atlas (TCGA) cohort, Kaplan-Meier survival curves confirmed Tregs and CD8 T cells were prognosis-protective factors in OS of EC ( P <0.05). Weighted gene coexpression network analysis identified 2 gene modules closely correlated with Tregs and CD8 T-cell infiltration. We randomly split the TCGA EC cohort into the training and testing cohorts at a ratio of 7:3. An immune-related prognosis risk index (IRPRI), including NR3C1, E2F1, OTOG, TTK, PPP1R16B, and FOXP3, was established by univariate, Least Absolute Shrinkage and Selection Operator, and multivariate Cox regression with area under the curve >0.67. Distinct clinical, immune, and mutation characteristics existed between IRPRI groups by multiomics analysis. Cell proliferation and DNA damage repair-related pathways were activated, and immune-related pathways were inactivated in the IRPRI-high group. Furthermore, patients in the IRPRI-high group had lower tumor mutation burden, programmed death-ligand 1 expression, and Tumor Immune Dysfunction and Exclusion scores, indicating a poor response to immune checkpoint inhibitors therapy ( P <0.05), which was also validated in the TCGA testing cohort and independent cohorts, GSE78200, GSE115821, and GSE168204. Also, the higher mutation frequencies of BRCA1, BRCA2, and genes enrolled in homologous recombination repair in the IRPRI-low group predicted a good response to PARP inhibitors. Finally, a nomogram integrating the IRPRI group and prognosis significant clinicopathological factors for EC OS prediction was developed and validated with good discrimination and calibration.

Localized chemotherapy approaches and advanced drug delivery strategies: a step forward in the treatment of peritoneal carcinomatosis from ovarian cancer

Peritoneal carcinomatosis (PC) is a common outcome of epithelial ovarian carcinoma and is the leading cause of death for these patients. Tumor location, extent, peculiarities of the microenvironment, and the development of drug resistance are the main challenges that need to be addressed to improve therapeutic outcome. The development of new procedures such as HIPEC (Hyperthermic Intraperitoneal Chemotherapy) and PIPAC (Pressurized Intraperitoneal Aerosol Chemotherapy) have enabled locoregional delivery of chemotherapeutics, while the increasingly efficient design and development of advanced drug delivery micro and nanosystems are helping to promote tumor targeting and penetration and to reduce the side effects associated with systemic chemotherapy administration. The possibility of combining drug-loaded carriers with delivery via HIPEC and PIPAC represents a powerful tool to improve treatment efficacy, and this possibility has recently begun to be explored. This review will discuss the latest advances in the treatment of PC derived from ovarian cancer, with a focus on the potential of PIPAC and nanoparticles in terms of their application to develop new therapeutic strategies and future prospects.

MND1 and PSMC3IP control PARP inhibitor sensitivity in mitotic cells

The PSMC3IP-MND1 heterodimer promotes meiotic D loop formation before DNA strand exchange. In genome-scale CRISPR-Cas9 mutagenesis and interference screens in mitotic cells, depletion of PSMC3IP or MND1 causes sensitivity to poly (ADP-Ribose) polymerase inhibitors (PARPi) used in cancer treatment. PSMC3IP or MND1 depletion also causes ionizing radiation sensitivity. These effects are independent of PSMC3IP/MND1's role in mitotic alternative lengthening of telomeres. PSMC3IP- or MND1-depleted cells accumulate toxic RAD51 foci in response to DNA damage, show impaired homology-directed DNA repair, and become PARPi sensitive, even in cells lacking both BRCA1 and TP53BP1. Epistasis between PSMC3IP-MND1 and BRCA1/BRCA2 defects suggest that abrogated D loop formation is the cause of PARPi sensitivity. Wild-type PSMC3IP reverses PARPi sensitivity, whereas a PSMC3IP p.Glu201del mutant associated with D loop defects and ovarian dysgenesis does not. These observations suggest that meiotic proteins such as MND1 and PSMC3IP have a greater role in mitotic DNA repair.

Targeting DNA damage repair precision medicine strategies in cancer

DNA repair targeted therapeutics is a promising precision medicine strategy in cancer. The development and clinical use of PARP inhibitors has transformed lives for many patients with BRCA germline deficient breast and ovarian cancer as well as platinum sensitive epithelial ovarian cancers. However, lessons learnt from the clinical use of PARP inhibitors also confirm that not all patients respond either due to intrinsic or acquired resistance. Therefore, the search for additional synthetic lethality approaches is an active area of translational and clinical research. Here, we review the current clinical state of PARP inhibitors and other evolving DNA repair targets including ATM, ATR, WEE1 inhibitors and others in cancer.

A genetic mosaic mouse model illuminates the pre-malignant progression of basal-like breast cancer

Basal-like breast cancer is an aggressive breast cancer subtype, often characterized by a deficiency in BRCA1 function and concomitant loss of p53 . While conventional mouse models enable the investigation of its malignant stages, one that reveals its initiation and pre-malignant progression is lacking. Here, we leveraged a mouse genetic system known as M osaic A nalysis with D ouble M arkers (MADM) to generate rare GFP-labeled Brca1 , p53 -deficient cells alongside RFP+ wildtype sibling cells in the mammary gland. The mosaicism resembles the sporadic initiation of human cancer and enables spatially resolved analysis of mutant cells in comparison to paired wildtype sibling cells. Mammary tumors arising in the model show transcriptomic and genomic characteristics similar to human basal-like breast cancer. Analysis of GFP+ mutant cells at interval time points before malignancy revealed a stepwise progression of lesions from focal expansion to hyper-alveolarization and then to micro-invasion. These stereotyped morphologies indicate the pre-malignant stage irrespective of the time point at which it is observed. Paired analysis of GFP-RFP siblings during focal expansion suggested that hyper-alveolarized structures originate from ductal rather than alveolar cells, despite their morphological similarities to alveoli. Evidence for luminal-to-basal transition at the pre-malignant stages was restricted to cells that had escaped hyper-alveoli and progressed to micro-invasive lesions. Our MADM-based mouse model presents a useful tool for studying the pre-malignancy of basal-like breast cancer.

Summary statement

A mouse model recapitulates the process of human basal-like breast tumorigenesis initiated from sporadic Brca1, p53 -deficient cells, empowering spatially-resolved analysis of mutant cells during pre-malignant progression.

Mutations in Homologous Recombination Genes and Loss of Heterozygosity Status in Advanced-Stage Breast Carcinoma

Poly (adenosine diphosphate-ribose) polymerase inhibitors (PARPis) have demonstrated antitumor activity in cancers with a homologous recombination deficiency (HRD) and have recently been approved by the FDA for the treatment of germline BRCA1/2-mutation-associated breast cancer. PARPis have also been found to be efficacious in BRCA wild-type (BRCAwt) lesions with high genomic loss of heterozygosity (LOH-high). The goal of this study was to retrospectively investigate the tumor mutations in homologous recombination (HRR) genes and the LOH score in advanced-stage breast carcinomas (BCs). Sixty-three patients were included in our study, 25% of whom had HRR gene mutations in their tumors, including 6% BRCA1/2 and 19% non-BRCA-containing gene mutations. An HRR gene mutation was associated with a triple-negative phenotype. Twenty-eight percent of the patients had an LOH-high score, which, in turn, was associated with a high histological grade, a triple-negative phenotype, and a high tumor mutational burden (TMB). Among the six patients who received PARPi therapy, one had a tumor with a PALB2 mutation other than BRCA and had a clinical partial response. Twenty-two percent of the LOH-low tumors had BRCAwt-HRR gene mutations, compared with 11% of the LOH-high tumors. Comprehensive genomic profiling revealed a subset of breast cancer patients with a BRCAwt-HRR gene mutation that would be missed by an LOH test. The necessity of next-generation sequencing coupled with HRR gene analysis for PARPi therapy requires further investigation in clinical trials.

Inhibitors of Rho kinases (ROCK) induce multiple mitotic defects and synthetic lethality in BRCA2-deficient cells

The trapping of Poly-ADP-ribose polymerase (PARP) on DNA caused by PARP inhibitors (PARPi) triggers acute DNA replication stress and synthetic lethality (SL) in BRCA2-deficient cells. Hence, DNA damage is accepted as a prerequisite for SL in BRCA2-deficient cells. In contrast, here we show that inhibiting ROCK in BRCA2-deficient cells triggers SL independently from acute replication stress. Such SL is preceded by polyploidy and binucleation resulting from cytokinesis failure. Such initial mitosis abnormalities are followed by other M phase defects, including anaphase bridges and abnormal mitotic figures associated with multipolar spindles, supernumerary centrosomes and multinucleation. SL was also triggered by inhibiting Citron Rho-interacting kinase, another enzyme that, similarly to ROCK, regulates cytokinesis. Together, these observations demonstrate that cytokinesis failure triggers mitotic abnormalities and SL in BRCA2-deficient cells. Furthermore, the prevention of mitotic entry by depletion of Early mitotic inhibitor 1 (EMI1) augmented the survival of BRCA2-deficient cells treated with ROCK inhibitors, thus reinforcing the association between M phase and cell death in BRCA2-deficient cells. This novel SL differs from the one triggered by PARPi and uncovers mitosis as an Achilles heel of BRCA2-deficient cells.