Profile of veliparib and its potential in the treatment of solid tumors

DNA damage targeted therapy for advanced breast cancer

Breast cancer (BC) is the most prevalent malignancy affecting women worldwide, including Portugal. While the majority of BC cases are sporadic, hereditary forms account for 5-10% of cases. The most common inherited mutations associated with BC are germline mutations in the BReast CAncer (BRCA) 1/2 gene (gBRCA1/2). They are found in approximately 5-6% of BC patients and are inherited in an autosomal dominant manner, primarily affecting younger women. Pathogenic variants within BRCA1/2 genes elevate the risk of both breast and ovarian cancers and give rise to distinct clinical phenotypes. BRCA proteins play a key role in maintaining genome integrity by facilitating the repair of double-strand breaks through the homologous recombination (HR) pathway. Therefore, any mutation that impairs the function of BRCA proteins can result in the accumulation of DNA damage, genomic instability, and potentially contribute to cancer development and progression. Testing for gBRCA1/2 status is relevant for treatment planning, as it can provide insights into the likely response to therapy involving platinum-based chemotherapy and poly[adenosine diphosphate (ADP)-ribose] polymerase inhibitors (PARPi). The aim of this review was to investigate the impact of HR deficiency in BC, focusing on BRCA mutations and their impact on the modulation of responses to platinum and PARPi therapy, and to share the experience of Unidade Local de Saúde Santa Maria in the management of metastatic BC patients with DNA damage targeted therapy, including those with the Portuguese c.156_157insAlu BRCA2 founder mutation.

Spatiotemporal Concurrent PARP Inhibitor Sensitization Based on Radiation-Responsive Nanovesicles for Lung Cancer Chemoradiotherapy

The implementation of chemoradiation combinations has gained great momentum in clinical practices. However, the full utility of this paradigm is often restricted by the discordant tempos of action of chemotherapy and radiotherapy. Here, a gold nanoparticle-based radiation-responsive nanovesicle system loaded with cisplatin and veliparib, denoted as CV-Au NVs, is developed to augment the concurrent chemoradiation effect in a spatiotemporally controllable manner of drug release. Upon irradiation, the in situ generation of •OH induces the oxidation of polyphenylene sulfide from being hydrophobic to hydrophilic, resulting in the disintegration of the nanovesicles and the rapid release of the entrapped cisplatin and veliparib (the poly ADP-ribose polymerase (PARP) inhibitor). Cisplatin-induced DNA damage and the impairment of the DNA repair mechanism mediated by veliparib synergistically elicit potent pro-apoptotic effects. In vivo studies suggest that one-dose injection of the CV-Au NVs and one-time X-ray irradiation paradigm effectively inhibit tumor growth in the A549 lung cancer model. This study provides new insight into designing nanomedicine platforms in chemoradiation therapy from a vantage point of synergizing both chemotherapy and radiation therapy in a spatiotemporally concurrent manner.

Novel Fluorescent Benzimidazole-Hydrazone-Loaded Micellar Carriers for Controlled Release: Impact on Cell Toxicity, Nuclear and Microtubule Alterations in Breast Cancer Cells

Fluorescent micellar carriers with controlled release of a novel anticancer drug were developed to enable intracellular imaging and cancer treatment simultaneously. The nanosized fluorescent micellar systems were embedded with a novel anticancer drug via the self-assembling behavior of well-defined block copolymers based on amphiphilic poly(acrylic acid)-block-poly(n-butyl acrylate) (PAA-b-PnBA) copolymer obtained by Atom Transfer Radical Polymerization (ATRP) and hydrophobic anticancer benzimidazole-hydrazone drug (BzH). Through this method, well-defined nanosized fluorescent micelles were obtained consisting of a hydrophilic PAA shell and a hydrophobic PnBA core embedded with the BzH drug due to the hydrophobic interactions, thus reaching very high encapsulation efficiency. The size, morphology, and fluorescent properties of blank and drug-loaded micelles were investigated using dynamic light scattering (DLS), transmission electron microscopy (TEM), and fluorescent spectroscopy, respectively. Additionally, after 72 h of incubation, drug-loaded micelles released 3.25 μM of BzH, which was spectrophotometrically determined. The BzH drug-loaded micelles were found to exhibit enhanced antiproliferative and cytotoxic effects on MDA-MB-231 cells, with long-lasting effects on microtubule organization, with apoptotic alterations and preferential localization in the perinuclear space of cancer cells. In contrast, the antitumor effect of BzH alone or incorporated in micelles on non-cancerous cells MCF-10A was relatively weak.

DNA repair pathways in breast cancer: from mechanisms to clinical applications

BACKGROUND

Breast cancer (BC) is a complex disease with various subtypes and genetic alterations that impact DNA repair pathways. Understanding these pathways is essential for developing effective treatments and improving patient outcomes.

AREA COVERED

This study investigates the significance of DNA repair pathways in breast cancer, specifically focusing on various pathways such as nucleotide excision repair, base excision repair, mismatch repair, homologous recombination repair, non-homologous end joining, fanconi anemia pathway, translesion synthesis, direct repair, and DNA damage tolerance. The study also examines the role of these pathways in breast cancer resistance and explores their potential as targets for cancer treatment.

CONCLUSION

Recent advances in targeted therapies have shown promise in exploiting DNA repair pathways for BC treatment. However, much research is needed to improve the efficacy of these therapies and identify new targets. Additionally, personalized treatments that target specific DNA repair pathways based on tumor subtype or genetic profile are being developed. Advances in genomics and imaging technologies can potentially improve patient stratification and identify biomarkers of treatment response. However, many challenges remain, including toxicity, resistance, and the need for more personalized treatments. Continued research and development in this field could significantly improve BC treatment.

Synthesis of Veliparib Prodrugs and Determination of Drug-Release-Dependent PARP-1 Inhibition

Poly(ADP-ribose) polymerase (PARP) plays a key role in repairing DNA damage, and several PARP inhibitors have been approved as treatments in BRCA1/2 mutated breast and ovarian cancers. Mounting evidence also supports their application as neuroprotective agents since PARP overactivation compromises the mitochondrial homeostasis by consumption of NAD⁺ reserves, leading to an increase in reactive oxygen and nitrogen species and a spike in intracellular Ca²⁺ levels. Herein, we present the synthesis and preliminary evaluation of new mitochondria-targeting PARP inhibitor prodrugs of (±)-veliparib, with the goal to advance potential neuroprotective properties without impairing the repair of damaged DNA in the nucleus.

Clinical efficacy of PARP inhibitors in breast cancer

BRCA1 and BRCA2 are key tumor suppressor genes that are essential for the homologous recombination DNA repair pathway. Loss of function mutations in these genes result in hereditary breast and ovarian cancer syndromes, which comprise approximately 5% of cases. BRCA1/2 mutations are associated with younger age of diagnosis and increased risk of recurrences. The concept of synthetic lethality led to the development of PARP inhibitors which cause cell cytotoxicity via the inhibition of PARP1, a key DNA repair protein, in cells with germline BRCA1/2 mutations. Although still poorly understood, the most well-acknowledged proposed mechanisms of action of PARP1 inhibition include the inhibition of single strand break repair, PARP trapping, and the upregulation of non-homologous end joining. Olaparib and talazoparib are PARP inhibitors that have been approved for the management of HER2-negative breast cancer in patients with germline BRCA1/2 mutations. This review article highlights the clinical efficacy of PARP inhibitors in patients with HER2-negative breast cancer in early and advanced settings.

Benzimidazole and its derivatives as cancer therapeutics: The potential role from traditional to precision medicine

Cancer is the second leading cause of mortality globally which remains a continuing threat to human health today. Drug insensitivity and resistance are critical hurdles in cancer treatment; therefore, the development of new entities targeting malignant cells is considered a high priority. Targeted therapy is the cornerstone of precision medicine. The synthesis of benzimidazole has garnered the attention of medicinal chemists and biologists due to its remarkable medicinal and pharmacological properties. Benzimidazole has a heterocyclic pharmacophore, which is an essential scaffold in drug and pharmaceutical development. Multiple studies have demonstrated the bioactivities of benzimidazole and its derivatives as potential anticancer therapeutics, either through targeting specific molecules or non-gene-specific strategies. This review provides an update on the mechanism of actions of various benzimidazole derivatives and the structure‒activity relationship from conventional anticancer to precision healthcare and from bench to clinics.

Cellular and molecular basis of therapeutic approaches to breast cancer

In recent decades, there has been a significant amount of research into breast cancer, with some important breakthroughs in the treatment of both primary and metastatic breast cancers. It's a well-known fact that treating breast cancer is still a challenging endeavour even though physicians have a fantastic toolset of the latest treatment options at their disposal. Due to limitations of current clinical treatment options, traditional chemotherapeutic drugs, and surgical options are still required to address this condition. In recent years, there have been several developments resulting in a wide range of treatment options. This review article discusses the cellular and molecular foundation of chemotherapeutic drugs, endocrine system-based treatments, biological therapies, gene therapy, and innovative techniques for treating breast cancer.

Combining Poly (ADP-Ribose) Polymerase (PARP) Inhibitors with Chemotherapeutic Agents: Promise and Challenges

Better understanding of molecular drivers and dysregulated pathways has furthered the concept of precision oncology and rational drug development. The role of DNA damage response (DDR) pathways has been extensively studied in carcinogenesis and as potential therapeutic targets to improve response to chemotherapy or overcome resistance. Treatment with small molecule inhibitors of PARP has resulted in clinical response and conferred survival benefit to patients with ovarian cancer, BRCA-mutant breast cancer, HRD-deficient prostate cancer and BRCA-mutant pancreatic cancer, leading to US Food and Drug Administration (FDA) approvals. However, the observed clinical benefit with single agent PARP inhibitors is limited to few tumor types within the relevant genetic context. Since DDR pathways are essential for repair of damage caused by cytotoxic agents, PARP inhibitors have been evaluated in combination with various chemotherapeutic agents to broaden the therapeutic application of this class of drugs. In this chapter, we discuss the combination of PARP inhibitors with different chemotherapeutics agents, clinical experience to date, lessons learnt, and future directions for this approach.

An epithelial-mesenchymal transition-related mRNA signature associated with the prognosis, immune infiltration and therapeutic response of colon adenocarcinoma

Background: Epithelial-mesenchymal transition (EMT) is closely associated with cancer cell metastasis. Colon adenocarcinoma (COAD) is one of the most common malignancies in the world, and its metastasis leading to poor prognosis remains a challenge for clinicians. The purpose of this study was to explore the prognostic value of EMT-related genes (EMTRGs) by bioinformatics analysis and to develop a new EMTRGs prognostic signature for COAD. Methods: The TCGA-COAD dataset was downloaded from the TCGA portal as the training cohort, and the GSE17538 and GSE29621 datasets were obtained from the GEO database as the validation cohort. The best EMTRGs prognostic signature was constructed by differential expression analysis, Cox, and LASSO regression analysis. Gene set enrichment analysis (GSEA) is used to reveal pathways that are enriched in high-risk and low-risk groups. Differences in tumor immune cell levels were analyzed using microenvironmental cell population counter and single sample gene set enrichment analysis. Subclass mapping analysis and Genomics of Drug Sensitivity in Cancer were applied for prediction of immunotherapy response and chemotherapy response, respectively. Results: A total of 77 differentially expressed EMTRGs were identified in the TCGA-COAD cohort, and they were significantly associated with functions and pathways related to cancer cell metastasis, proliferation, and apoptosis. We constructed EMTRGs prognostic signature with COMP, MYL9, PCOLCE2, SCG2, and TIMP1 as new COAD prognostic biomarkers. The high-risk group had a poorer prognosis with enhanced immune cell infiltration. The GSEA demonstrated that the high-risk group was involved in "ECM Receptor Interaction," "WNT Signaling Pathway" and "Colorectal Cancer." Furthermore, patients with high risk scores may respond to anti-CTLA4 therapy and may be more resistant to targeted therapy agents BI 2536 and ABT-888. Conclusion: Together, we developed a new EMTRGs prognostic signature that can be an independent prognostic factor for COAD. This study has guiding implications for individualized counseling and treatment of COAD patients.

Role of PARP Inhibitors in Glioblastoma and Perceiving Challenges as Well as Strategies for Successful Clinical Development

Glioblastoma multiform is the most aggressive primary type of brain tumor, representing 54% of all gliomas. The average life span for glioblastoma multiform is around 14-15 months instead of treatment. The current treatment for glioblastoma multiform includes surgical removal of the tumor followed by radiation therapy and temozolomide chemotherapy for 6.5 months, followed by another 6 months of maintenance therapy with temozolomide chemotherapy (5 days every month). However, resistance to temozolomide is frequently one of the limiting factors in effective treatment. Poly (ADP-ribose) polymerase (PARP) inhibitors have recently been investigated as sensitizing drugs to enhance temozolomide potency. However, clinical use of PARP inhibitors in glioblastoma multiform is difficult due to a number of factors such as limited blood-brain barrier penetration of PARP inhibitors, inducing resistance due to frequent use of PARP inhibitors, and overlapping hematologic toxicities of PARP inhibitors when co-administered with glioblastoma multiform standard treatment (radiation therapy and temozolomide). This review elucidates the role of PARP inhibitors in temozolomide resistance, multiple factors that make development of these PARP inhibitor drugs challenging, and the strategies such as the development of targeted drug therapies and combination therapy to combat the resistance of PARP inhibitors that can be adopted to overcome these challenges.

Glioblastoma: Current Status, Emerging Targets, and Recent Advances

Glioblastoma (GBM) is a highly malignant brain tumor characterized by a heterogeneous population of genetically unstable and highly infiltrative cells that are resistant to chemotherapy. Although substantial efforts have been invested in the field of anti-GBM drug discovery in the past decade, success has primarily been confined to the preclinical level, and clinical studies have often been hampered due to efficacy-, selectivity-, or physicochemical property-related issues. Thus, expansion of the list of molecular targets coupled with a pragmatic design of new small-molecule inhibitors with central nervous system (CNS)-penetrating ability is required to steer the wheels of anti-GBM drug discovery endeavors. This Perspective presents various aspects of drug discovery (challenges in GBM drug discovery and delivery, therapeutic targets, and agents under clinical investigation). The comprehensively covered sections include the recent medicinal chemistry campaigns embarked upon to validate the potential of numerous enzymes/proteins/receptors as therapeutic targets in GBM.

A Novel Classification Model for Lower-Grade Glioma Patients Based on Pyroptosis-Related Genes

Recent studies demonstrated that pyroptosis plays a crucial role in shaping the tumor-immune microenvironment. However, the influence of pyroptosis on lower-grade glioma regarding immunotherapy and targeted therapy is still unknown. This study analyzed the variations of 33 pyroptosis-related genes in lower-grade glioma and normal tissues. Our study found considerable genetic and expression alterations in heterogeneity among lower-grade gliomas and normal brain tissues. There are two pyroptosis phenotypes in lower-grade glioma, and they exhibited differences in cell infiltration characteristics and clinical characters. Then, a PyroScore model using the lasso-cox method was constructed to measure the level of pyroptosis in each patient. PyroScore can refine the lower-grade glioma patients with a stratified prognosis and a distinct tumor immune microenvironment. Pyscore may also be an effective factor in predicting potential therapeutic benefits. In silico analysis showed that patients with a lower PyroScore are expected to be more sensitive to targeted therapy and immunotherapy. These findings may enhance our understanding of pyroptosis in lower-grade glioma and might help optimize risk stratification for the survival and personalized management of lower-grade glioma patients.

Long-term efficacy and safety of addition of carboplatin with or without veliparib to standard neoadjuvant chemotherapy in triple-negative breast cancer: 4-year follow-up data from BrighTNess, a randomized phase 3 trial

BACKGROUND

Primary analyses of the phase 3 BrighTNess trial showed addition of carboplatin with/without veliparib to neoadjuvant chemotherapy significantly improved pathological complete response (pCR) rates with manageable acute toxicity in patients with triple-negative breast cancer (TNBC). Here, we report 4.5-year follow-up data from the trial.

DESIGN

Women with untreated stage II-III TNBC were randomized (2:1:1) to paclitaxel (weekly for 12 doses) plus either: (a) carboplatin (every 3 weeks for four cycles) plus veliparib (twice daily); (b) carboplatin plus veliparib placebo; or (c) carboplatin placebo plus veliparib placebo. All patients then received doxorubicin and cyclophosphamide (AC) every 2‒3 weeks for four cycles. The primary endpoint was pCR. Secondary endpoints included event-free survival (EFS), overall survival (OS), and safety. Since the co-primary endpoint of increased pCR with carboplatin plus veliparib with paclitaxel versus carboplatin with paclitaxel was not met, secondary analyses are descriptive.

RESULTS

Of 634 patients, 316 were randomized to carboplatin plus veliparib with paclitaxel, 160 to carboplatin with paclitaxel, and 158 to paclitaxel. With median follow-up of 4.5 years, the hazard ratio [HR] for EFS for carboplatin plus veliparib with paclitaxel versus paclitaxel was 0.63 (95% confidence interval [CI] 0.43‒0.92, P=0.02), but 1.12 (95% CI 0.72‒1.72, P=0.62) for carboplatin plus veliparib with paclitaxel versus carboplatin with paclitaxel. In post hoc analysis, HR for EFS was 0.57 (95% CI 0.36‒0.91, P=0.02) for carboplatin with paclitaxel versus paclitaxel. OS did not differ significantly between treatment arms, nor did rates of myelodysplastic syndromes, acute myeloid leukemia, or other secondary malignancies.

CONCLUSION

Improvement in pCR with addition of carboplatin was associated with long-term EFS benefit with a manageable safety profile, and without increasing the risk of second malignancies, while adding veliparib did not impact EFS. These findings support the addition of carboplatin to weekly paclitaxel followed by AC neoadjuvant chemotherapy for early stage TNBC.

Effect and Safety of Therapeutic Regimens for Patients With Germline BRCA Mutation-Associated Breast Cancer: A Network Meta-Analysis

Purpose

Breast cancer type 1 susceptibility (BRCA) mutations not only increase breast cancer (BC) risk but also result in poor survival and prognosis for BC patients. This study will analyze the effect and safety of therapeutic regimens for the treatment of BC patients with germline BRCA (gBRCA) mutations by network meta-analysis.

Methods

Public databases were searched from inception to 29 April 2021. Frequentist network meta-analysis was conducted to analyze the benefit of chemotherapy and targeted drug-related strategies.

Results

Seventeen articles were included in the analysis. For progression-free survival (PFS), olaparib (hazard ratio (HR): 0.58; 95% confidence interval (CI): 0.43 – 0.79), platinum (HR: 0.45; 95% CI: 0.22 – 0.89), and talazoparib (HR: 0.54; 95% CI: 0.41 – 0.71) were significantly better than platinum-free chemotherapy (Chemo). The results based on indirect comparisons showed that veliparib (Vel) + platinum + Chemo was also significantly better than Chemo (HR: 0.37; 95% CI: 0.20 – 0.69). For overall survival (OS), olaparib was significantly better than Chemo only in the population who did not receive prior chemotherapy. For pathologic complete response (pCR), bevacizumab+Chemo had a significant advantage over platinum agents (OR: 3.64; 95% CI: 1.07 - 12.39). Olaparib and talazoparib both showed significantly higher objective response rates (ORRs) than Chemo.

Conclusion

The PFS results suggested that olaparib, talazoparib, and Vel+platinum agent+Chemo were ideal regimens for overall, TNBC, and advanced BC patients with gBRCA mutations. Whether PARPis are suitable for patients with gBRCA mutations who have received prior platinum therapy still needs to be clarified.

Exploiting DNA Damage Repair in Precision Cancer Therapy: BRCA1 as a Prime Therapeutic Target

Simple Summary

Chemical inhibition of central DNA damage repair (DDR) proteins has become a promising approach in precision cancer therapy. In particular, BRCA1 and its DDR-associated proteins constitute important targets for developing DNA repair inhibiting drugs. This review provides relevant insights on DDR biology and pharmacology, aiming to boost the development of more effective DDR targeted therapies.

Abstract

Precision medicine aims to identify specific molecular alterations, such as driver mutations, allowing tailored and effective anticancer therapies. Poly(ADP)-ribose polymerase inhibitors (PARPi) are the prototypical example of targeted therapy, exploiting the inability of cancer cells to repair DNA damage. Following the concept of synthetic lethality, PARPi have gained great relevance, particularly in BRCA1 dysfunctional cancer cells. In fact, BRCA1 mutations culminate in DNA repair defects that can render cancer cells more vulnerable to therapy. However, the efficacy of these drugs has been greatly affected by the occurrence of resistance due to multi-connected DNA repair pathways that may compensate for each other. Hence, the search for additional effective agents targeting DNA damage repair (DDR) is of crucial importance. In this context, BRCA1 has assumed a central role in developing drugs aimed at inhibiting DNA repair activity. Collectively, this review provides an in-depth understanding of the biology and regulatory mechanisms of DDR pathways, highlighting the potential of DDR-associated molecules, particularly BRCA1 and its interconnected partners, in precision cancer medicine. It also affords an overview about what we have achieved and a reflection on how much remains to be done in this field, further addressing encouraging clues for the advance of DDR targeted therapy.

Co-Encapsulation of Methylene Blue and PARP-Inhibitor into Poly(Lactic-Co-Glycolic Acid) Nanoparticles for Enhanced PDT of Cancer

The development of resistance against photodamage triggered by photodynamic therapy (PDT) is ascribed mainly to the cellular redox defenses and repair. If the tumor tissue is not promptly eliminated by the first few PDT sessions, PDT-resistance can be favored, challenging the efficacy of the treatment. Although the mechanism of PDT resistance is still unclear, in vitro assays have evidenced that it can be developed through the PARP damage-repair signaling pathway. Therefore, inhibition of poly(adenosine diphosphate (ADP)-ribose) polymerase (PARP) has the potential to increase PDT efficacy. This work reports on the synthesis of a controlled release system of a photosensitizer, methylene blue (MB) and a PARP-inhibitor, the veliparib. MB and veliparib were co-encapsulated in poly(lactic-co-glycolic acid) (PLGA) nanoparticles (VMB-NPs). A colloidal stable aqueous suspension of nanoparticles was obtained. The average hydrodynamic diameter was 90 nm and a narrow size distribution was obtained, with a polydispersity index (PDI) of 0.08. The release kinetics of MB and veliparib from VMB-NPs showed an initial burst of 8.7% and 58.3% release of the total amounts of MB and veliparib respectively, in the first 6 h, and a delayed release of up to 11.3% and 70%, in 19 days, for MB and veliparib, respectively. The VMB-NPs showed no cytotoxicity in the dark but the viability of B16F10-Nex2 cells decreased by 36% when the cells were irradiated (102 J/cm², 660 nm) and treated with VMB-NPs containing 1.0 µM of MB and 8.3 µM of veliparib. Considering the increased photoactivity even at low MB and veliparib concentrations and the absence of cytotoxicity in dark, the co-encapsulation of MB and veliparib was shown to be a promising strategy to improve the PDT efficacy.

BENZIMIDAZOLE AS A PROMISING ANTIVIRAL HETEROCYCLIC SCAFFOLD: A REVIEW

Heterocyclic derivatives are unavoidable in many fields of natural disciplines. These derivatives play numerous significant roles in research, medication, and nature. Nitrogenous heterocyclic derivatives extremely are the main target of concern in synthetic chemistry to ensue active natural products with pharmaceuticals and agrochemicals interest. Benzimidazole skeleton is another example of some active heterocyclic moiety that significantly contributes in the numerous bioactive of essential compounds. Benzimidazole skeleton is studied as a prominent moiety of biologically active compounds with various activities including antimicrobial, antiprotozoal, anticancer, antiviral, acetylcholinesterase, antihistaminic, anti-inflammatory, antimalarial, analgesic, anti-HIV and antitubercular. Therefore, in this review we summarize the various antiviral activities of several benzimidazole derivatives and outline the correlation among the structures of different benzimidazoles scaffold with their therapeutic significance.

Super-resolution visualization of distinct stalled and broken replication fork structures

Endogenous genotoxic stress occurs in healthy cells due to competition between DNA replication machinery, and transcription and topographic relaxation processes. This causes replication fork stalling and regression, which can further collapse to form single-ended double strand breaks (seDSBs). Super-resolution microscopy has made it possible to directly observe replication stress and DNA damage inside cells, however new approaches to sample preparation and analysis are required. Here we develop and apply multicolor single molecule microscopy to visualize individual replication forks under mild stress from the trapping of Topoisomerase I cleavage complexes, a damage induction which closely mimics endogenous replicative stress. We observe RAD51 and RAD52, alongside RECQ1, as the first responder proteins to stalled but unbroken forks, whereas Ku and MRE11 are initially recruited to seDSBs. By implementing novel super-resolution imaging assays, we are thus able to discern closely related replication fork stress motifs and their repair pathways.

Differential immunomodulatory effect of PARP inhibition in BRCA1 deficient and competent tumor cells

Poly-ADP-ribose polymerase (PARP) inhibitors are active against cells and tumors with defects in homology-directed repair as a result of synthetic lethality. PARP inhibitors (PARPi) have been suggested to act by either catalytic inhibition or by PARP localization in chromatin. In this study, we treat BRCA1 mutant cells derived from a patient with triple negative breast cancer and control cells for three weeks with veliparib, a PARPi, to determine if treatment with this drug induces increased levels of mutations and/or an inflammatory response. We show that long-term treatment with PARPi induces an inflammatory response in HCC1937 BRCA1 mutant cells. The levels of chromatin-bound PARP1 in the BRCA1 mutant cells correlate with significant upregulation of inflammatory genes and activation of the cyclic GMP-AMP synthase (cGAS)/signaling effector stimulator of interferon genes (STING pathway). In contrast, an increased mutational load is induced in BRCA1-complemented cells treated with a PARPi. Our results suggest that long-term PARP inhibitor treatment may prime both BRCA1 mutant and wild-type tumors for positive responses to immune checkpoint blockade, but by different underlying mechanisms.

A therapeutic update on PARP inhibitors: implications in the treatment of glioma

Central nervous system (CNS) cancers are among the most aggressive and devastating. Further, due to unavailability of neuro-oncologists and neurosurgeons, the specialized treatment options of CNS cancers are still not completely available in most parts of the world. Among various strategies of inducing death in cancer cells, inhibition of poly(ADP-ribose) polymerase (PARP) has emerged as a beneficial therapy when combined with other anticancer agents. In this review, we provide a detailed therapeutic update of PARP inhibitors that have shown clinical activity against glioma.

The Effects of Doxorubicin, Ethanol Extract and Flavonoid-rich Fraction of Euphorbia Splendida Mobayen on the PARP Level, and APC Gene Expression in HT-29 Human Colon Cancer Cell Line

Background: Natural products derived from various sources are being used to develop chemotherapeutic drugs. Euphorbiaceae is widely used to treat different types of cancers. Colorectal cancer (CRC) is the second and third cause of cancer in women and men, respectively. CRC is strongly associated with the deregulation of the Adenomatous polyposis coli (APC) gene and Poly [ADP-ribose] polymerase (PPAR) protein. Objectives: The current study aimed to examine the effect of doxorubicin, ethanol extract, and the flavonoid-rich fraction of Euphorbia Splendida Mobayen on colon cancer HT-29 cell line death, APC gene expression, and PPAR concentration. Methods: Following treatment of cells by Euphorbia ethanol extract, Euphorbia flavonoid-rich fraction, and doxorubicin, cell viability assay was used to investigate the viability status of the HT-29 cell line. Total RNA was isolated from the cell line and converted into cDNA. The expression level of the APC gene was determined by quantitative real-time PCR. Poly (ADP-ribose) polymerase (PPAR) protein was detected by the ELIZA method. Results: We found that Euphorbia ethanol extract, Euphorbia flavonoid-rich fraction, and doxorubicin can stimulate dose-dependent cell death in the HT-29 cell line, increase ACP gene expression (P = 0.001, P = 0.041, P = 0.019), and decrease PARP level (P = 0.001, P = 0.001, P = 0.001, respectively). Conclusions: The findings indicated that doxorubicin, ethanol extract, and the flavonoid-rich fraction of Euphorbia Splendida Mobayen had cytotoxic effects on human colon cancer HT-29 cell line by possibly stimulating apoptosis.

Histone-dependent PARP-1 inhibitors: A novel therapeutic modality for the treatment of prostate and renal cancers

Clinical interest in poly(ADP-ribose) polymerase 1 (PARP-1) has increased over the past decade with the recognition of its roles in transcription regulation, DNA repair, epigenetic bookmarking, and chromatin restructuring. A number of PARP-1 inhibitors demonstrating clinical efficacy against tumors of various origins have emerged in recent years. These inhibitors have been essentially designed as nicotinamide adenine dinucleotide (NAD⁺) mimetics. However, because NAD⁺ is utilized by many enzymes other than PARP-1, NAD⁺ competitors tend to produce certain off-target effects. To overcome the limitation of NAD-like PARP-1 inhibitors, we have developed a new class of PARP-1 inhibitors that specifically targets the histone-dependent route of PARP-1 activation, a mechanism of activation that is unique to PARP-1. Novel histone-dependent inhibitors are highly specific for PARP-1 and demonstrate promising in vitro and in vivo efficacy against prostate and renal tumors. Our findings suggest that novel PARP-1 inhibitors have strong therapeutic potential for the treatment of urological tumors.

Targeting therapeutic vulnerabilities with PARP inhibition and radiation in IDH-mutant gliomas and cholangiocarcinomas

Mutations in isocitrate dehydrogenase (IDH) genes occur in multiple cancer types, lead to global changes in the epigenome, and drive tumorigenesis. Yet, effective strategies targeting solid tumors harboring IDH mutations remain elusive. Here, we demonstrate that IDH-mutant gliomas and cholangiocarcinomas display elevated DNA damage. Using multiple in vitro and preclinical animal models of glioma and cholangiocarcinoma, we developed treatment strategies that use a synthetic lethality approach targeting the reduced DNA damage repair conferred by mutant IDH using poly(adenosine 5'-diphosphate) ribose polymerase inhibitors (PARPis). The therapeutic effects are markedly enhanced by cotreatment with concurrent, localized radiation therapy. PARPi-buttressed multimodality therapies may represent a readily applicable approach that is selective for IDH-mutant tumor cells and has potential to improve outcomes in multiple cancers.

PARP1 Inhibition Augments UVB-Mediated Mitochondrial Changes-Implications for UV-Induced DNA Repair and Photocarcinogenesis

Keratinocytes provide the first line of defense of the human body against carcinogenic ultraviolet (UV) radiation. Acute and chronic UVB-mediated cellular responses were widely studied. However, little is known about the role of mitochondrial regulation in UVB-induced DNA damage. Here, we show that poly (ADP-ribose) polymerase 1 (PARP1) and ataxia-telangiectasia-mutated (ATM) kinase, two tumor suppressors, are important regulators in mitochondrial alterations induced by UVB. Our study demonstrates that PARP inhibition by ABT-888 upon UVB treatment exacerbated cyclobutane pyrimidine dimers (CPD) accumulation, cell cycle block and cell death and reduced cell proliferation in premalignant skin keratinocytes. Furthermore, in human keratinocytes UVB enhanced oxidative phosphorylation (OXPHOS) and autophagy which were further induced upon PARP inhibition. Immunoblot analysis showed that these cellular responses to PARP inhibition upon UVB irradiation strongly alter the phosphorylation level of ATM, adenosine monophosphate-activated kinase (AMPK), p53, protein kinase B (AKT), and mammalian target of rapamycin (mTOR) proteins. Furthermore, chemical inhibition of ATM led to significant reduction in AMPK, p53, AKT, and mTOR activation suggesting the central role of ATM in the UVB-mediated mitochondrial changes. Our results suggest a possible link between UVB-induced DNA damage and metabolic adaptations of mitochondria and reveal the OXPHOS-regulating role of autophagy which is dependent on key metabolic and DNA damage regulators downstream of PARP1 and ATM.

Veliparib: a new therapeutic option in ovarian cancer?

The role of poly ADP ribose polymerase inhibitors in ovarian cancer is rapidly evolving. Three different poly ADP ribose polymerase inhibitors (olaparib, niraparib and rucaparib) have been already approved as maintenance after response to platinum-based chemotherapy; two of them (olaparib and rucaparib) also as single agents. Veliparib, a novel PARPI, showed promising results in preclinical and early clinical settings. The aim of this review is to discuss veliparib’s mechanisms of action, to provide a clinical update on its safety and activity in ovarian cancer, and to highlight future perspectives for its optimal use. Veliparib favorable toxicity profile encourages its use either as monotherapy or in combination. Its peculiar neuroprotective and radio-sensitizing effect warrant further investigation.

PARP1 inhibition alleviates injury in ARH3-deficient mice and human cells

Poly(ADP-ribosyl)ation refers to the covalent attachment of ADP-ribose to protein, generating branched, long chains of ADP-ribose moieties, known as poly(ADP-ribose) (PAR). Poly(ADP-ribose) polymerase 1 (PARP1) is the main polymerase and acceptor of PAR in response to DNA damage. Excessive intracellular PAR accumulation due to PARP1 activation leads cell death in a pathway known as parthanatos. PAR degradation is mainly controlled by poly(ADP-ribose) glycohydrolase (PARG) and ADP-ribose-acceptor hydrolase 3 (ARH3). Our previous results demonstrated that ARH3 confers protection against hydrogen peroxide (H2O2) exposure, by lowering cytosolic and nuclear PAR levels and preventing apoptosis-inducing factor (AIF) nuclear translocation. We identified a family with an ARH3 gene mutation that resulted in a truncated, inactive protein. The 8-year-old proband exhibited a progressive neurodegeneration phenotype. In addition, parthanatos was observed in neurons of the patient's deceased sibling, and an older sibling exhibited a mild behavioral phenotype. Consistent with the previous findings, the patient's fibroblasts and ARH3-deficient mice were more sensitive, respectively, to H2O2 stress and cerebral ischemia/reperfusion-induced PAR accumulation and cell death. Further, PARP1 inhibition alleviated cell death and injury resulting from oxidative stress and ischemia/reperfusion. PARP1 inhibitors may attenuate the progression of neurodegeneration in affected patients with ARH3 deficiency.

Population pharmacokinetics and exposure-response assessment of veliparib co-administered with temozolomide in patients with myeloid leukemias

PURPOSE

Veliparib is an oral inhibitor of poly(ADP-ribose) polymerase enzyme. Combination of veliparib and temozolomide was well-tolerated and demonstrated clinical activity in older patients with relapsed or refractory acute myeloid leukemia (AML) or AML arising from pre-existing myeloid malignancies. We aimed to perform quantitative assessments of pharmacokinetics, efficacy, and safety of veliparib in this patient population to inform future trial design.

METHODS

Population pharmacokinetic analysis was performed using Phoenix^® NLME with pharmacokinetic data obtained from 37 subjects after oral administration of veliparib in a Phase I study with and without temozolomide. Effect of covariates (age, sex, BMI, creatinine clearance (CL_CR), and co-administration of temozolomide) on the pharmacokinetics of veliparib were evaluated, as well as impact of veliparib exposure on mucositis (dose-limiting toxicity), objective response rate (ORR), and overall survival.

RESULTS

A two-compartment model with first-order elimination and a first-order absorption with lag-time adequately described veliparib pharmacokinetics. CL_CR and body weight were clinically significant covariates for veliparib disposition. The proportion of subjects with all grade mucositis increased with veliparib exposure (AUC). However, no trend in ORR and overall survival was observed with increasing exposure.

CONCLUSIONS

Veliparib with temozolomide presents a promising combination for older patients with myeloid leukemias. An exposure-safety relationship was established for this combination. Further clinical investigations aimed at elucidating the veliparib exposure-efficacy/safety relationship and optimizing dosing recommendations for maximizing benefit-risk in patients with advanced myeloid malignancies should study veliparib doses ranging up to 120 mg in combination with temozolomide.

Synthesis and Evaluation of a Mitochondria-Targeting Poly(ADP-ribose) Polymerase-1 Inhibitor

The poly(ADP-ribose) polymerase (PARP) family of enzymes plays a crucial role in cellular and molecular processes including DNA damage detection and repair and transcription; indeed, PARP inhibitors are under clinical evaluation as chemotherapeutic adjuncts given their capacity to impede genomic DNA repair in tumor cells. Conversely, overactivation of PARP can lead to NAD⁺ depletion, mitochondrial energy failure, and cell death. Since PARP activation facilitates genomic but impedes mitochondrial DNA repair, nonselective PARP inhibitors are likely to have opposing effects in these cellular compartments. Herein, we describe the synthesis and evaluation of the mitochondria-targeting PARP inhibitor, XJB-veliparib. Attachment of the hemigramicidin S pentapeptide isostere for mitochondrial targeting using a flexible linker at the primary amide site of veliparib did not disrupt PARP affinity or inhibition. XJB-veliparib was effective at low nanomolar concentrations (10-100 nM) and more potent than veliparib in protection from oxygen-glucose deprivation (OGD) in primary cortical neurons. Both XJB-veliparib and veliparib (10 nM) preserved mitochondrial NAD⁺ after OGD; however, only XJB-veliparib prevented release of NAD⁺ into cytosol. XJB-veliparib (10 nM) appeared to inhibit poly(ADP-ribose) polymer formation in mitochondria and preserve mitochondrial cytoarchitecture after OGD in primary cortical neurons. After 10 nM exposure, XJB-veliparib was detected by LC-MS in mitochondria but not nuclear-enriched fractions in neurons and was observed in mitoplasts stripped of the outer mitochondrial membrane obtained from HT22 cells. XJB-veliparib was also effective at preventing glutamate-induced HT22 cell death at micromolar concentrations. Importantly, in HT22 cells exposed to H₂O₂ to produce DNA damage, XJB-veliparib (10 μM) had no effect on nuclear DNA repair, in contrast to veliparib (10 μM) where DNA repair was retarded. XJB-veliparib and analogous mitochondria-targeting PARP inhibitors warrant further evaluation in vitro and in vivo, particularly in conditions where PARP overactivation leads to mitochondrial energy failure and maintenance of genomic DNA integrity is desirable, e.g., ischemia, oxidative stress, and radiation exposure.

An efficient one-pot conversion of carboxylic acids into benzimidazoles via an HBTU-promoted methodology

Benzimidazole is a privileged, and routinely used pharmacophore in the drug discovery process. Herein, we report a mild, acid-free and one-pot synthesis of indole, alkyl and alpha-amino benzimidazoles through a novel HBTU-promoted methodology. An extensive library of indole-carboxylic acids, alkyl carboxylic acids and N-protected alpha-amino acids has been converted into the corresponding benzimidazoles in 80-99% yield. Since alpha-aminobenzimidazoles are highly useful synthons as chiral ligands for chemical catalysis, as well as for drug discovery endeavors, our reported method provides direct access to this scaffold in a simple, one-pot operation from commercially available carboxylic acids.

Effect of ABT-888 on the apoptosis, motility and invasiveness of BRAFi-resistant melanoma cells

Melanoma is a molecularly heterogeneous disease with many genetic mutations and altered signaling pathways. Activating mutations in the BRAF oncogene are observed in approximately 50% of cutaneous melanomas and the use of BRAF inhibitor (BRAFi) compounds has been reported to improve the outcome of patients with BRAF-mutated metastatic melanoma. However, the majority of these patients develop resistance within 6-8 months following the initiation of BRAFi treatment. In this study, we examined the possible use of the poly(ADP-ribose) polymerase 1 (PARP1) inhibitor, ABT-888 (veliparib), as a novel molecule that may be successfully employed in the treatment of BRAFi-resistant melanoma cells. Sensitive and resistant to BRAFi dabrafenib A375 cells were exposed to increasing concentrations of ABT-888. Cell viability and apoptosis were assessed by MTT assay and Annexin V-FITC analysis, respectively. The cell migratory and invasive ability was investigated using the xCELLigence technology and Boyden chamber assays, respectively. ABT-888 was found to reduce cell viability and exhibited pro-apoptotic activity in melanoma cell lines, independently from the BRAF/NRAS mutation status, in a dose-dependent manner, with the maximal effect being reached in the 25-50 µM concentration range. Moreover, ABT-888 promoted apoptosis in both the sensitive and resistant A375 cells, suggesting that ABT-888 may be useful in the treatment of BRAFi-resistant subsets of melanoma cells. Finally, in accordance with the involvement of PARP1 in actin cytoskeletal machinery, we found that the cytoskeletal organization, motility and invasive capability of both the A375 and A375R cells decreased upon exposure to 5 µM ABT-888 for 24 h. On the whole, the findings of this study highlight the pivotal role of PARP1 in the migration and invasion of melanoma cells, suggesting that ABT-888 may indeed be effective, not only as a pro-apoptotic drug for use in the treatment of BRAFi-resistant melanoma cells, but also in suppressing their migratory and invasive activities.

PARP inhibitor veliparib and HDAC inhibitor SAHA synergistically co-target the UHRF1/BRCA1 DNA damage repair complex in prostate cancer cells

Background

The poly ADP ribose polymerase (PARP) inhibitor olaparib has been approved for treating prostate cancer (PCa) with BRCA mutations, and veliparib, another PARP inhibitor, is being tested in clinical trials. However, veliparib only showed a moderate anticancer effect, and combination therapy is required for PCa patients. Histone deacetylase (HDAC) inhibitors have been tested to improve the anticancer efficacy of PARP inhibitors for PCa cells, but the exact mechanisms are still elusive.

Methods

Several types of PCa cells and prostate epithelial cell line RWPE-1 were treated with veliparib or SAHA alone or in combination. Cell viability or clonogenicity was tested with violet crystal assay; cell apoptosis was detected with Annexin V-FITC/PI staining and flow cytometry, and the cleaved PARP was tested with western blot; DNA damage was evaluated by staining the cells with γH2AX antibody, and the DNA damage foci were observed with a fluorescent microscopy, and the level of γH2AX was tested with western blot; the protein levels of UHRF1 and BRCA1 were measured with western blot or cell immunofluorescent staining, and the interaction of UHRF1 and BRCA1 proteins was detected with co-immunoprecipitation when cells were treated with drugs. The antitumor effect of combinational therapy was validated in DU145 xenograft models.

Results

PCa cells showed different sensitivity to veliparib or SAHA. Co-administration of both drugs synergistically decreased cell viability and clonogenicity, and synergistically induced cell apoptosis and DNA damage, while had no detectable toxicity to normal prostate epithelial cells. Mechanistically, veliparib or SAHA alone reduced BRCA1 or UHRF1 protein levels, co-treatment with veliparib and SAHA synergistically reduced BRCA1 protein levels by targeting the UHRF1/BRCA1 protein complex, the depletion of UHRF1 resulted in the degradation of BRCA1 protein, while the elevation of UHRF1 impaired co-treatment-reduced BRCA1 protein levels. Co-administration of both drugs synergistically decreased the growth of xenografts.

Conclusions

Our studies revealed that the synergistic lethality of HDAC and PARP inhibitors resulted from promoting DNA damage and inhibiting HR DNA damage repair pathways, in particular targeting the UHRF1/BRCA1 protein complex. The synergistic lethality of veliparib and SAHA shows great potential for future PCa clinical trials.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0810-7) contains supplementary material, which is available to authorized users.

Safety and pharmacokinetics of veliparib extended-release in patients with advanced solid tumors: a phase I study

The poly(ADP-ribose) polymerase-1/2 inhibitor veliparib is active against tumors deficient in homologous DNA damage repair. The pharmacokinetics and safety of veliparib extended-release (ER) were evaluated in patients with advanced solid tumors. This phase I study assessed veliparib-ER up to 800 mg once daily or 600 mg twice daily. Dose-limiting toxicities (DLTs), recommended phase II dose (RP2D), and maximum tolerated dose (MTD) were assessed in cycle 1 and safety/tolerability during continuous administration (28-day cycles). Seventy-one patients (n = 53 ovarian, n = 17 breast, n = 1 prostate carcinoma) received veliparib; 50 had deleterious breast cancer susceptibility (BRCA) gene mutations. Single-dose veliparib-ER 200 mg (fasting) led to 58% lower peak concentration and similar area under the concentration-time curve compared with veliparib immediate-release (IR). Three patients experienced DLTs (grade 2: asthenia; grade 3: nausea/vomiting, seizure). RP2D and MTD for veliparib-ER were 400 mg BID. The most frequent adverse events (AEs) were nausea (78.9%) and vomiting (50.7%). The most common grade 3/4 treatment-related AEs were as follows: thrombocytopenia (7.0%), nausea, and anemia (4.2% each). Overall, 12 (27.3%) patients with ovarian and 10 (62.5%) patients with breast carcinoma had a partial response. Veliparib-ER, versus veliparib-IR, exhibited an improved pharmacokinetic profile and was well tolerated in patients with ovarian and BRCA-mutated breast cancers.

Double-barreled gun: Combination of PARP inhibitor with conventional chemotherapy

DNA repair pathways are evolutionarily conserved molecular mechanisms that maintain the integrity of genomic DNA. In cancer therapies, the integrity and activity of DNA repair pathways predict therapy resistance and disease outcome. Members of the poly (ADP-ribose) polymerase (PARP) family initiate and organize the biologic process of DNA repair, which counteracts many types of chemotherapies. Since the first development in approximately 3 decades ago, PARP inhibitors have greatly changed the concept of cancer therapy, leading to encouraging improvements in tumor suppression and disease outcomes. Here we summaries both pre-clinical and clinical findings of PARP inhibitors applications, particularly for combination therapies.

Veliparib Monotherapy to Patients With BRCA Germ Line Mutation and Platinum-Resistant or Partially Platinum-Sensitive Relapse of Epithelial Ovarian Cancer: A Phase I/II Study

OBJECTIVE

A new treatment principle, which seems to radically change the treatment approach in ovarian cancer (OC), has developed over the past few years. Poly(ADP-ribose) polymerase inhibitors work by interfering with mechanisms important to DNA damage repair. Cancer cells that already have defects in the BRCA genes are particularly sensitive to treatment with poly(ADP-ribose) polymerase inhibitors. The main purpose of this study was to investigate the effect of veliparib in patients with known BRCA1/2 mutations and with a platinum-resistant or intermediate sensitive relapse of OC.

METHODS

Major eligibility criteria were primary epithelial ovarian/fallopian/peritoneal cancer patients with a platinum-resistant or intermediate sensitive relapse of OC and with evaluable disease by either Response Evaluation Criteria In Solid Tumors or Gynecological Cancer Intergroup CA-125 criteria. Patients were treated with oral veliparib twice daily on days 1 to 28.

RESULTS

Sixteen patients were enrolled in the phase I part, and a maximum tolerable dose of 300 mg twice daily was established. The phase II part enrolled 32 patients with a median of 4 previous treatment regimens. The overall response rate combining Response Evaluation Criteria In Solid Tumors and CA-125 response was 65% (6% complete response and 59% partial response). Progression-free and overall survival rates of the intention-to-treat population were 5.6 months (95% confidence interval, 5.2-7.3 months) and 13.7 months (95% confidence interval, 10.2-17.3 months), respectively. The most common phase II treatment-related grade 2 toxicities included fatigue (22%), nausea (22%), and vomiting (9%).

CONCLUSIONS

Treatment with veliparib in heavily pretreated patients with relapse of OC demonstrates a considerable efficacy with an acceptable toxicity profile.

Effects of Veliparib on Microglial Activation and Functional Outcomes after Traumatic Brain Injury in the Rat and Pig

The inflammation response induced by brain trauma can impair recovery. This response requires several hours to develop fully and thus provides a clinically relevant therapeutic window of opportunity. Poly(ADP-ribose) polymerase inhibitors suppress inflammatory responses, including brain microglial activation. We evaluated delayed treatment with veliparib, a poly(ADP-ribose) polymerase inhibitor, currently in clinical trials as a cancer therapeutic, in rats and pigs subjected to controlled cortical impact (CCI). In rats, CCI induced a robust inflammatory response at the lesion margins, scattered cell death in the dentate gyrus, and a delayed, progressive loss of corpus callosum axons. Pre-determined measures of cognitive and motor function showed evidence of attentional deficits that resolved after three weeks and motor deficits that recovered only partially over eight weeks. Veliparib was administered beginning 2 or 24 h after CCI and continued for up to 12 days. Veliparib suppressed CCI-induced microglial activation at doses of 3 mg/kg or higher and reduced reactive astrocytosis and cell death in the dentate gyrus, but had no significant effect on delayed axonal loss or functional recovery. In pigs, CCI similarly induced a perilesional microglial activation that was attenuated by veliparib. CCI in the pig did not, however, induce detectable persisting cognitive or motor impairment. Our results showed veliparib suppression of CCI-induced microglial activation with a delay-to-treatment interval of at least 24 h in both rats and pigs, but with no associated functional improvement. The lack of improvement in long-term recovery underscores the complexities in translating anti-inflammatory effects to clinically relevant outcomes.

Current status of poly(ADP-ribose) polymerase inhibitors and future directions

Inhibitors of poly(ADP-ribose) polymerases (PARPs), which play a key role in DNA damage/repair pathways, have been developed as antitumor agents based on the concept of synthetic lethality. Synthetic lethality is the idea that cell death would be efficiently induced by simultaneous loss of function of plural key molecules, for example, by exposing tumor cells with inactivating gene mutation of BRCA-mediated DNA repair to chemically induced inhibition of PARPs. Indeed, three PARP inhibitors, olaparib, rucaparib and niraparib have already been approved in the US or Europe, mainly for the treatment of BRCA-mutant ovarian cancer. Clinical trials of various combinations of PARP inhibitors with cytotoxic or molecular-targeted agents are also underway. In particular, expanded applications of PARP inhibitors are anticipated following recent reports that defects in homologous recombination repair (HRR) are associated with mutations in repair genes other than BRCA1/BRCA2, such as ATM, ATR, PALB2, RAD51, CHEK1 and CHEK2, as well as with epigenetic loss of BRCA1 function through promoter methylation or overexpression of the BRCA2-interacting transcriptional repressor EMSY. Current topics of interest include selection of the best agent in each clinical context, identification of new treatment targets for HRR-proficient cases, and development of PARP inhibitor-based regimens that are less toxic and that prolong overall survival as well as progression-free survival. In addition, potential long-term side effects and suitable biomarkers for predicting efficacy and mechanisms of clinical resistance are in discussion. This review summarizes representative preclinical and clinical data for PARP inhibitors and discusses their potential for future applications to treat various malignancies.

PARP1 in Carcinomas and PARP1 Inhibitors as Antineoplastic Drugs

Poly (ADP-ribose) polymerase 1 (PARP1), the best-studied isoform of the nuclear enzyme PARP family, plays a pivotal role in cellular biological processes, such as DNA repair, gene transcription, and so on. PARP1 has been found to be overexpressed in various carcinomas. These all indicate the clinical potential of PARP1 as a therapeutic target of human malignancies. Additionally, multiple preclinical research studies and clinical trials demonstrate that inhibition of PARP1 can repress tumor growth and metastasis. Up until now, PARP1 inhibitors are clinically used not only for monotherapy to suppress various tumors, but also for adjuvant therapy, to maintain or enhance therapeutic effects of mature antineoplastic drugs, as well as protect patients from chemotherapy and surgery-induced injury. To supply a framework for understanding recent research progress of PARP1 in carcinomas, we review the structure, expression, functions, and mechanisms of PARP1, and summarize the clinically mature PARP1-related anticancer agents, to provide some ideas for the development of other promising PARP1 inhibitors in antineoplastic therapy.

Novel DNA targeted therapies for head and neck cancers: clinical potential and biomarkers

Head and neck squamous cell carcinoma is the sixth most common cancer worldwide and despite advances in treatment over the last years, there is still a relapse rate of 50%. New therapeutic agents are awaited to increase the survival of patients. DNA repair targeted agents in combination with standard DNA damaging therapies are a recent evolution in cancer treatment. These agents focus on the DNA damage repair pathways in cancer cells, which are often involved in therapeutic resistance. Interesting targets to overcome these cancer defense mechanisms are: PARP, DNA-PK, PI3K, ATM, ATR, CHK1/2, and WEE1 inhibitors. The application of DNA targeted agents in head and neck squamous cell cancer showed promising preclinical results which are translated to multiple ongoing clinical trials, although no FDA approval has emerged yet. Biomarkers are necessary to select the patients that can benefit the most from this treatment, although adequate biomarkers are limited and validation is needed to predict therapeutic response.

Small-Molecule Inhibitors Targeting DNA Repair and DNA Repair Deficiency in Research and Cancer Therapy

To maintain stable genomes and to avoid cancer and aging, cells need to repair a multitude of deleterious DNA lesions, which arise constantly in every cell. Processes that support genome integrity in normal cells, however, allow cancer cells to develop resistance to radiation and DNA-damaging chemotherapeutics. Chemical inhibition of the key DNA repair proteins and pharmacologically induced synthetic lethality have become instrumental in both dissecting the complex DNA repair networks and as promising anticancer agents. The difficulty in capitalizing on synthetically lethal interactions in cancer cells is that many potential targets do not possess well-defined small-molecule binding determinates. In this review, we discuss several successful campaigns to identify and leverage small-molecule inhibitors of the DNA repair proteins, from PARP1, a paradigm case for clinically successful small-molecule inhibitors, to coveted new targets, such as RAD51 recombinase, RAD52 DNA repair protein, MRE11 nuclease, and WRN DNA helicase.

Development of a Level A in Vitro-in Vivo Correlation for Veliparib (ABT-888) Extended Release Tablet Formulation

PURPOSE

The aim of the current manuscript is to develop and validate a level A in vitro-in vivo correlation (IVIVC) for veliparib extended-release (ER) tablet formulations.

METHODS

The in vitro release profiles of veliparib formulations were determined using USP Dissolution Apparatus 2 with 900 mL of 0.1 N HCl at 75 rpm. In a clinical study, 24 subjects with solid tumors received one of the ER formulations (200 mg): fast (Formulation A), intermediate (Formulation B), and slow (Formulation C), and two 100 mg immediate release capsules (Formulation D). Blood samples were collected over a period of 48 h and analyzed using LCMS/MS. A linear correlation model was developed using fraction absorbed and fraction dissolved data from formulations A and B. Besides assessing internal predictability, external predictability was evaluated using formation C. Prediction errors were estimated for maximum observed plasma concentration (C_max) and area under the plasma-concentration time curve from zero to last measured time point (AUC_t) to determine the predictive ability of the correlation.

RESULTS

There was a significant linear relationship (r² = 0.944) between the fraction of drug absorbed and the fraction of drug dissolved. The prediction error using the internal validation for C_max and AUC_t were below 15% for the individual formulations and below 10% for the average. The prediction error in AUC_t and C_max for formulation C was 5% and 11%, respectively.

CONCLUSIONS

A level A IVIVC for the veliparib ER tablet formulation was established. The IVIVC may allow the associated dissolution data to be used as a surrogate for bioavailability.

Novel poly(ADP-ribose) polymerase inhibitor veliparib: biophysical studies on its binding to calf thymus DNA

Veliparib, an new anticancer drug in the class of poly (ADP-ribose) polymerase inhibitors, intercalates partially and binds to ctDNA and induces moderate conformational perturbation of the DNA.

Adaptive mechanisms of resistance to anti-neoplastic agents

Intrinsic and acquired resistance to conventional and targeted therapeutics is a fundamental reason for treatment failure in many cancer patients. Targeted approaches to overcome chemoresistance as well as resistance to targeted approaches require in depth understanding of the underlying molecular mechanisms. The anti-cancer activity of a drug can be limited by a broad variety of molecular events at different levels of drug action in a cell-autonomous and non-cell-autonomous manner. This review summarizes recent insights into the adaptive mechanisms used by tumours to resist therapy including cellular phenotypic plasticity, dynamic alterations of the tumour microenvironment, activation of redundant signal transduction pathways, modulation of drug target expression levels, and exploitation of pro-survival responses.

BRCA somatic and germline mutation detection in paraffin embedded ovarian cancers by next-generation sequencing

BRCA mutated ovarian cancers respond better to platinum-based therapy and to the recently approved PARP-inhibitors. There is the need for efficient and timely methods to detect both somatic and germline mutations using formalin-fixed paraffin-embedded (FFPE) tissues and commercially available technology. We used a commercial kit exploring all exons and 50bp exon-intron junctions of BRCA1 and BRCA2 genes, and semiconductor next-generation sequencing (NGS) on DNA from 47 FFPE samples of high-grade serous ovarian cancers. Pathogenic mutations were found in 13/47 (28%) cancers: eight in BRCA1 and five in BRCA2. All BRCA1 and two BRCA2 mutations were germline; three BRCA2 mutations were somatic. All mutations were confirmed by Sanger sequencing. To evaluate the performance of the NGS panel, we assessed its capability to detect the 6,953 variants described for BRCA1 and BRCA2 in ClinVar and COSMIC databases using callability analysis. 6,059 (87.1%) variants were identified automatically by the software; 829 (12.0%) required visual verification. The remaining 65 (0.9%) variants were uncallable, and would require 15 Sanger reactions to be resolved. Thus, the sensitivity of the NGS-panel was 99.1%. In conclusion, NGS performed with a commercial kit is highly efficient for detection of germline and somatic mutations in BRCA genes using routine FFPE tissue.