PARP1 and phospho-p65 protein expression is increased in human HER2-positive breast cancers

Novel Molecular Classification of Breast Cancer with PET Imaging

Breast cancer is a heterogeneous disease characterized by a wide range of biomarker expressions, resulting in varied progression, behavior, and prognosis. While traditional biopsy-based molecular classification is the gold standard, it is invasive and limited in capturing tumor heterogeneity, especially in deep or metastatic lesions. Molecular imaging, particularly positron emission tomography (PET) imaging, offering a non-invasive alternative, potentially plays a crucial role in the classification and management of breast cancer by providing detailed information about tumor location, heterogeneity, and progression. This narrative review, which focuses on both clinical patients and preclinical studies, explores the latest advancements in PET imaging for breast cancer, emphasizing the development of new tracers targeting hormone receptors such as the estrogen alpha receptor, progesterone receptor, androgen receptor, estrogen beta receptor, as well as the ErbB family of receptors, VEGF/VEGFR, PARP1, PD-L1, and markers for indirectly assessing Ki-67. These innovative radiopharmaceuticals have the potential to guide personalized treatment approaches based on the unique tumor profiles of individual patients. Additionally, they may improve the assessment of treatment efficacy, ultimately leading to better outcomes for those diagnosed with breast cancer.

Poly(ADP-ribose) polymerase1 (PARP1) and PARP inhibitors: New frontiers in cervical cancer

Cervical cancer affects more than half a million women and treatment options for advanced disease and recurrence is limited. Poly (ADP-ribose) polymerase1 (PARP1) is a critical nuclear protein regulating several components and functions of cellular machinery, including cancer. PARP1 expression and activity plays a crucial dynamics in the tumor microenvironment. PARP inhibitors are being considered as a viable option for treating BRCA deficient ovarian and breast cancer patients. However, the role of PARP1 in cervical cancer tumorigenesis is less known. The aim of the present review is to provide a comprehensive insight about the role of PARP1 in cervical cancer pathogenesis in context to PARP1 expression as a molecular marker for identifying cancer and in predicting treatment response and prognosis. PARP1 expression is found to be elevated in cervical cancer tissues in comparison to that in the normal surrounding tissues. The cellular proteins linked with PARP1 have been described along with the association of SNPs in PARP1 gene with cervical cancer. Promising results of PARP inhibitors with immunotherapy and clinical trials with cisplatin have also been discussed. This review provides an up-to-date description of PARP1 expression, its role in cervical cancer pathogenesis and reported clinical trials of PARP inhibitors in adjuvant therapy.

Analysis of the PARP1, ADP-Ribosylation, and TRIP12 Triad With Markers of Patient Outcome in Human Breast Cancer

PARP inhibitors (PARPi) are increasingly used in breast cancer therapy, including high-grade triple-negative breast cancer (TNBC) treatment. Varying treatment responses and PARPi resistance with relapse currently pose limitations to the efficacy of PARPi therapy. The pathobiological reasons why individual patients respond differently to PARPi are poorly understood. In this study, we analyzed expression of PARP1, the main target of PARPi, in normal breast tissue, breast cancer, and its precursor lesions using human breast cancer tissue microarrays covering a total of 824 patients, including more than 100 TNBC cases. In parallel, we analyzed nuclear adenosine diphosphate (ADP)-ribosylation as a marker of PARP1 activity and TRIP12, an antagonist of PARPi-induced PARP1 trapping. Although we found PARP1 expression to be generally increased in invasive breast cancer, PARP1 protein levels and nuclear ADP-ribosylation were lower in higher tumor grade and TNBC samples than non-TNBCs. Cancers with low levels of PARP1 and low levels of nuclear ADP-ribosylation were associated with significantly reduced overall survival. This effect was even more pronounced in cases with high levels of TRIP12. These results indicate that PARP1-dependent DNA repair capacity may be compromised in aggressive breast cancers, potentially fueling enhanced accumulation of mutations. Moreover, the results revealed a subset of breast cancers with low PARP1, low nuclear ADP-ribosylation, and high TRIP12 levels, which may compromise their response to PARPi, suggesting a combination of markers for PARP1 abundance, enzymatic activity, and trapping capabilities might aid patient stratification for PARPi therapy.

PARP-1 Expression and BRCA1 Mutations in Breast Cancer Patients' CTCs

Simple Summary

Recent estimates have shown that approx. 70% of individuals with BRCA1 mutations will develop breast cancer by the age of 70. To make matters worse, breast cancer patients with BRCA1 mutations are more likely to have the more aggressive triple-negative breast cancer. PARPs, belong to a family of nuclear enzymes, which are involved in many cellular processes, including DNA repair. PARP inhibitors have been approved for the treatment of BRCA-mutated breast cancer. The aim of the study was the determination of PARP-1 expression in the context of the presence of BRCA1 mutations in circulating tumor cells of breast cancer patients. PARP-1 (nuclear) expression and BRCA1 mutations were mainly detected in triple negative breast cancer patients, and the latter were correlated with decreased survival. Our data suggest that PARP-1, in conjunction with BRCA1, could potentially be used as (a) biomarker(s) for patients’ stratification.

Abstract

BRCA1 and PARP are involved in DNA damage repair pathways. BRCA1 mutations have been linked to higher likelihood of triple negative breast cancer (TNBC). The aim of the study was to determine PARP-1 expression and BRCA1 mutations in circulating tumor cells (CTCs) of BC patients. Fifty patients were enrolled: 23 luminal and 27 TNBC. PARP expression in CTCs was identified by immunofluorescence. Genotyping was performed by PCR-Sanger sequencing in the same samples. PARP-1 expression was higher in luminal (61%) and early BC (54%), compared to TNBC (41%) and metastatic (33%) patients. In addition, PARP-1 distribution was mostly cytoplasmic in luminal patients (p = 0.024), whereas it was mostly nuclear in TNBC patients. In cytokeratin (CK)-positive patients, those with the CK⁺PARP⁺ phenotype had longer overall survival (OS, log-rank p = 0.046). Overall, nine mutations were detected; M1 and M2 were completely new and M4, M7 and M8 were characterized as pathogenic. M7 and M8 were predominantly found in metastatic TNBC patients (p = 0.014 and p = 0.002). Thus, PARP-1 expression and increased mutagenic burden in TNBC patients’ CTCs, could be used as an indicator to stratify patients regarding therapeutic approaches.

Prediction of Late Recurrence and Distant Metastasis in Early-stage Breast Cancer: Overview of Current and Emerging Biomarkers

Recently, a significant number of breast cancer (BC) patients have been diagnosed at an early stage. It is therefore critical to accurately predict the risk of recurrence and distant metastasis for better management of BC in this setting. Clinicopathologic patterns, particularly lymph node status, tumor size, and hormonal receptor status are routinely used to identify women at increased risk of recurrence. However, these factors have limitations regarding their predictive ability for late metastasis risk in patients with early BC. Emerging molecular signatures using gene expression-based approaches have improved the prognostic and predictive accuracy for this indication. However, the use of their based-scores for risk assessment has provided contradictory findings. Therefore, developing and using newly emerged alternative predictive and prognostic biomarkers for identifying patients at high- and low-risk is of great importance. The present review discusses some serum biomarkers and multigene profiling scores for predicting late recurrence and distant metastasis in early-stage BC based on recently published studies and clinical trials.

A P53-Independent DNA Damage Response Suppresses Oncogenic Proliferation and Genome Instability

The Mre11-Rad50-Nbs1 complex is a DNA double-strand break sensor that mediates a tumor-suppressive DNA damage response (DDR) in cells undergoing oncogenic stress, yet the mechanisms underlying this effect are poorly understood. Using a genetically inducible primary mammary epithelial cell model, we demonstrate that Mre11 suppresses proliferation and DNA damage induced by diverse oncogenic drivers through a p53-independent mechanism. Breast tumorigenesis models engineered to express a hypomorphic Mre11 allele exhibit increased levels of oncogene-induced DNA damage, R-loop accumulation, and chromosomal instability with a characteristic copy number loss phenotype. Mre11 complex dysfunction is identified in a subset of human triple-negative breast cancers and is associated with increased sensitivity to DNA-damaging therapy and inhibitors of ataxia telangiectasia and Rad3 related (ATR) and poly (ADP-ribose) polymerase (PARP). Thus, deficiencies in the Mre11-dependent DDR drive proliferation and genome instability patterns in p53-deficient breast cancers and represent an opportunity for therapeutic exploitation.

An open-label, pilot study of veliparib and lapatinib in patients with metastatic, triple-negative breast cancer

BACKGROUND

Poly (ADP-ribose)-polymerase inhibitors (PARPi) have been approved for cancer patients with germline BRCA1/2 (gBRCA1/2) mutations, and efforts to expand the utility of PARPi beyond BRCA1/2 are ongoing. In preclinical models of triple-negative breast cancer (TNBC) with intact DNA repair, we have previously shown an induced synthetic lethality with combined EGFR inhibition and PARPi. Here, we report the safety and clinical activity of lapatinib and veliparib in patients with metastatic TNBC.

METHODS

A first-in-human, pilot study of lapatinib and veliparib was conducted in metastatic TNBC (NCT02158507). The primary endpoint was safety and tolerability. Secondary endpoints were objective response rates and pharmacokinetic evaluation. Gene expression analysis of pre-treatment tumor biopsies was performed. Key eligibility included TNBC patients with measurable disease and prior anthracycline-based and taxane chemotherapy. Patients with gBRCA1/2 mutations were excluded.

RESULTS

Twenty patients were enrolled, of which 17 were evaluable for response. The median number of prior therapies in the metastatic setting was 1 (range 0-2). Fifty percent of patients were Caucasian, 45% African-American, and 5% Hispanic. Of evaluable patients, 4 demonstrated a partial response and 2 had stable disease. There were no dose-limiting toxicities. Most AEs were limited to grade 1 or 2 and no drug-drug interactions noted. Exploratory gene expression analysis suggested baseline DNA repair pathway score was lower and baseline immunogenicity was higher in the responders compared to non-responders.

CONCLUSIONS

Lapatinib plus veliparib therapy has a manageable safety profile and promising antitumor activity in advanced TNBC. Further investigation of dual therapy with EGFR inhibition and PARP inhibition is needed.

TRIAL REGISTRATION

ClinicalTrials.gov , NCT02158507 . Registered on 12 September 2014.

Trastuzumab-Resistant HER2+ Breast Cancer Cells Retain Sensitivity to Poly (ADP-Ribose) Polymerase (PARP) Inhibition

HER2-targeted therapies, such as trastuzumab, have increased the survival rates of HER2⁺ breast cancer patients. However, despite these therapies, many tumors eventually develop resistance to these therapies. Our lab previously reported an unexpected sensitivity of HER2⁺ breast cancer cells to poly (ADP-ribose) polymerase inhibitors (PARPi), agents that target homologous recombination (HR)-deficient tumors, independent of a DNA repair deficiency. In this study, we investigated whether HER2⁺ trastuzumab-resistant (TR) breast cancer cells were susceptible to PARPi and the mechanism behind PARPi induced cytotoxicity. We demonstrate that the PARPi ABT-888 (veliparib) decreased cell survival in vitro and tumor growth in vivo of HER2⁺ TR breast cancer cells. PARP-1 siRNA confirmed that cytotoxicity was due, in part, to PARP-1 inhibition. Furthermore, PARP-1 silencing had variable effects on the expression of several NF-κB-regulated genes. In particular, silencing PARP-1 inhibited NF-κB activity and reduced p65 binding at the IL8 promoter, which resulted in a decrease in IL8 mRNA and protein expression. Our results provide insight in the potential mechanism by which PARPi induces cytotoxicity in HER2⁺ breast cancer cells and support the testing of PARPi in patients with HER2⁺ breast cancer resistant to trastuzumab. Mol Cancer Ther; 17(5); 921-30. ©2018 AACR.

MiR-92a and miR-486 are potential diagnostic biomarkers for mercury poisoning and jointly sustain NF-κB activity in mercury toxicity

Occupational and environmental exposure to mercury is a public health concern worldwide. Although the altered epigenetic regulatory features, such as microRNA, have been associated with mercury exposure, the underlying molecular mechanism is not well illuminated. This study aimed to confirm that hsa-miR-92a and hsa-miR-486 are novel diagnostic biomarkers of occupational mercury poisoning, and to explore the underlying mechanism of miR-92a and miR-486 in mercury toxicity. RT-qPCR assays and receiver operating characteristics curve analyses were conducted to confirm the diagnostic value of miR-92a and miR-486 as biomarkers of occupational mercury poisoning. Dual-luciferase assay was applied to confirm the target gene of miR-92a and miR-486 in vitro. Then, we established an in-vitro model where miR-92a and miR-486 were overexpressed or knocked down in HEK-293 and HUVEC cells. RT-qPCR and western blotting were used to analyze gene and protein expression levels. Cell apoptosis was determined by flow cytometry. Results show that miR-92a and miR-486 expression levels were up-regulated in workers exposed to occupational mercury. Upregulation of miR-92a and miR-486 may play a crucial role in mercury toxicity by jointly activating the NF-κB signaling pathway via targeting KLF4 and Cezanne, respectively.

RBR-type E3 ubiquitin ligase RNF144A targets PARP1 for ubiquitin-dependent degradation and regulates PARP inhibitor sensitivity in breast cancer cells

Poly(ADP-ribose) polymerase 1 (PARP1), a critical DNA repair protein, is frequently upregulated in breast tumors with a key role in breast cancer progression. Consequently, PARP inhibitors have emerged as promising therapeutics for breast cancers with DNA repair deficiencies. However, relatively little is known about the regulatory mechanism of PARP1 expression and the determinants of PARP inhibitor sensitivity in breast cancer cells. Here, we report that ring finger protein 144A (RNF144A), a RING-between-RING (RBR)-type E3 ubiquitin ligase with an unexplored functional role in human cancers, interacts with PARP1 through its carboxy-terminal region containing the transmembrane domain, and targets PARP1 for ubiquitination and subsequent proteasomal degradation. Moreover, induced expression of RNF144A decreases PARP1 protein levels and renders breast cancer cells resistant to the clinical-grade PARP inhibitor olaparib. Conversely, knockdown of endogenous RNF144A increases PARP1 protein levels and enhances cellular sensitivity to olaparib. Together, these findings define RNF144A as a novel regulator of PARP1 protein abundance and a potential determinant of PARP inhibitor sensitivity in breast cancer cells, which may eventually guide the optimal use of PARP inhibitors in the clinic.

Therapeutic Targeting of Poly(ADP-Ribose) Polymerase-1 (PARP1) in Cancer: Current Developments, Therapeutic Strategies, and Future Opportunities

Poly(ADP-ribose) polymerase-1 (PARP-1) plays a central role in numerous cellular processes including DNA repair, replication, and transcription. PARP interacts directly, indirectly or via PARylation with various oncogenic proteins and regulates several transcription factors thereby modulating carcinogenesis. Therapeutic inhibition of PARP is therefore perceived as a promising anticancer strategy and a number of PARP inhibitors (PARPi) are currently under development and clinical evaluation. PARPi inhibit the DNA repair pathway and thus form the concept of synthetic lethality in cancer therapeutics. Preclinical and clinical studies have shown the potential of PARPi as chemopotentiator, radiosensitizer, or as adjuvant therapeutic agents. Recent studies have shown that PARP-1 could be either oncogenic or tumor suppressive in different cancers. PARP inhibitor resistance is also a growing concern in the clinical setting. Recently, changes in the levels of PARP-1 activity or expression in cancer patients have provided the basis for consideration of PARP-1 regulatory proteins as potential biomarkers. This review focuses on the current developments related to the role of PARP in cancer progression, therapeutic strategies targeting PARP-associated oncogenic signaling, and future opportunities in use of PARPi in anticancer therapeutics.

PARP inhibitors as precision medicine for cancer treatment

Personalized or precision medicine is an emerging treatment approach tailored to individuals or certain groups of patients based on their unique characteristics. These types of therapies guided by biomarkers tend to be more effective than traditional approaches, especially in cancer. The inhibitor against poly (ADP-ribose) polymerase (PARP), olaparib (Lynparza, AstraZeneca), which was approved by the US Food and Drug Administration (FDA) in 2014, demonstrated efficacy specifically for ovarian cancer patients harboring mutations in BRCA genes, which encode proteins in DNA double-strand break repairs. However, the response to PARP inhibitors has been less encouraging in other cancer types that also carry defects in the BRCA genes. Thus, furthering our understanding of the underlying mechanism of PARP inhibitors and resistance is critical to improve their efficacy. In this review, we summarize the results of preclinical studies and the clinical application of PARP inhibitors, and discuss the future direction of PARP inhibitors as a potential marker-guided personalized medicine for cancer treatment.

PARP-1 Expression Quantified by [18F]FluorThanatrace: A Biomarker of Response to PARP Inhibition Adjuvant to Radiation Therapy

INTRODUCTION

Poly (ADP-ribose) polymerase 1 (PARP-1) is the major target of clinical PARP inhibitors and is a potential predictive biomarker for response to therapy. Due to the limited success of PARP inhibitors as monotherapy, investigators have shifted the clinical role of PARP inhibitors to the adjuvant setting. In this study, we evaluate the radiotracer [¹⁸F]FluorThanatrace ([¹⁸F]FTT) as a marker of PARP expression in vitro and the associated biological implications of PARP-1 expression in PARP inhibitor treatment adjuvant to radiation therapy.

MATERIALS AND METHODS

SNU-251 (BRCA1-mutant) and SKOV3 (BRCA1-WT) cell lines were evaluated in vitro by using the radiotracer [¹⁸F]FTT. Pharmacological binding assays were performed at baseline and were correlated with PARP-1 protein expression measured by Western blot protein analysis. Cell viability and clonogenic assays were used to characterize in vitro cytotoxicity for treatments, including: PARP inhibitors alone, radiation alone, and PARP inhibitor adjuvant to radiation. Western blot protein analysis was used to assess response to treatment by using γH2AX to measure DNA damage and PAR to measure the catalytic inhibition of PARP.

RESULTS

[¹⁸F]FTT was capable of measuring PARP-1 protein expression in vitro and corresponded to Western blot protein analysis at baseline. The addition of a PARP inhibitor enhanced radiation effects in both cell lines; however, a greater synergy was observed in the SNU-251 cell line that expresses a BRCA1 mutation and homologous recombination deficiency. Western blot protein analysis showed that the addition of a PARP inhibitor adjuvant to radiation increases DNA damage in both cell lines and reduces PARP enzymatic activity as measured by PAR.

CONCLUSIONS

In this work, we found that PARP-1 expression positively corresponds in vitro to the response of PARP inhibitors in combination with radiation therapy in ovarian cancer.

Let-7 Status Is Crucial for PARP1 Expression in HER2-Overexpressing Breast Tumors

HER2⁺ breast tumors have been shown to express elevated levels of PARP1 protein. Yet, the mechanism by which PARP1 is upregulated in HER2⁺ breast cancer is unknown. Here, knockdown of HER2 (ERBB2) in HER2⁺ breast cancer cells resulted in a reduction in PARP1 protein. Conversely, ectopic overexpression of HER2 in a non-HER2-overexpressing cell line resulted in increased PARP1 protein levels. Alterations in HER2 expression had no significant effect on PARP1 transcript levels. Instead, HER2 mRNA status was inversely correlated with let-7a miRNA levels in breast cancer cells. Ectopic expression of let-7a miRNA resulted in downregulation of PARP1 protein, whereas expression of the let-7a anti-miRNA increased PARP1 protein. Furthermore, luciferase assays demonstrate that let-7a regulates PARP1 via its 3'UTR. Importantly, let-7a was significantly lower in human HER2⁺ breast tumors compared with HER2^- breast tumors and inversely correlated with PARP1 protein levels. Finally, HER2⁺ breast cancer cells exhibited similar cytotoxicity to ectopic let-7a expression as the PARP inhibitor veliparib (ABT-888). Collectively, these results reveal that increased PARP1 expression in HER2⁺ breast cancers is regulated by the let-7a miRNA, and that let-7a is a potential strategy to suppress PARP1 activity.Implications: This study reports the novel findings that HER2 increases PARP1 protein via suppression of the let-7a miRNA, which regulates the PARP1 3'-UTR. Moreover, HER2 status correlates with high PARP1 and low let-7a in breast cancer clinical specimens. Mol Cancer Res; 15(3); 340-7. ©2016 AACR.

Detection and delineation of oral cancer with a PARP1 targeted optical imaging agent

Earlier and more accurate detection of oral squamous cell carcinoma (OSCC) is essential to improve the prognosis of patients and to reduce the morbidity of surgical therapy. Here, we demonstrate that the nuclear enzyme Poly(ADP-ribose)Polymerase 1 (PARP1) is a promising target for optical imaging of OSCC with the fluorescent dye PARPi-FL. In patient-derived OSCC specimens, PARP1 expression was increased 7.8 ± 2.6-fold when compared to normal tissue. Intravenous injection of PARPi-FL allowed for high contrast in vivo imaging of human OSCC models in mice with a surgical fluorescence stereoscope and high-resolution imaging systems. The emitted signal was specific for PARP1 expression and, most importantly, PARPi-FL can be used as a topical imaging agent, spatially resolving the orthotopic tongue tumors in vivo. Collectively, our results suggest that PARP1 imaging with PARPi-FL can enhance the detection of oral cancer, serve as a screening tool and help to guide surgical resections.

Nuclear PARP1 expression and its prognostic significance in breast cancer patients

Poly(adenosine diphosphate [ADP]-ribose) polymerase 1 (PARP1) plays important roles in DNA damage response pathways and is often overexpressed in various human tumors. Currently, the use of PARP inhibitors for breast cancer (BC) therapy is the subject of debate, and there is an urgent need to understand much the expression and prognostic role of the PARP1 protein. The aim was to investigate the clinicopathological and prognostic significance of PARP1 in BC patients. The PARP1 and breast cancer susceptibility gene 1 (BRCA1) protein expressions were evaluated in 114 BCs by immunohistochemistry. Disease-free survival (DFS) and overall survival (OS) were determined based on the Kaplan-Meier method. Our results showed that nuclear PARP1 expression was significantly associated with peritumoral vascular invasion (P = 0.046), chemotherapeutic treatment (P = 0.026), oestrogen receptor (ER; P = 0.013), human epidermal growth factor receptor 2 (HER2; P = 0.003) and BRCA1 (P < 0.001) expression. Survival analyses showed a significant association with clinical outcome in the subgroup of ER-negative patients (P = 0.017 for DFS and P = 0.048 for OS) and in the subgroup of patients treated with chemotherapeutic agents (P = 0.042 for DFS and P = 0.046 for OS). A significant correlation was also found for DFS in patients characterized by tumors without peritumoral vascular invasion (P = 0.022). More importantly, multivariate analyses revealed that high nuclear PARP1 expression was associated with decreased DFS (P = 0.012) and OS (P = 0.026). In conclusion, PARP1 expression may be used as an independent prognostic factor in BC patients. In addition, this study demonstrated that high PARP1 expression may represent a marker of poorer prognosis both for patients with worse clinical outcome and in less aggressive clinical conditions.