Phase I Safety, Pharmacokinetic, and Pharmacodynamic Study of the Poly(ADP-ribose) Polymerase (PARP) Inhibitor Veliparib (ABT-888) in Combination with Irinotecan in Patients with Advanced Solid Tumors

Translational Research Opportunities Regarding Homologous Recombination in Ovarian Cancer

Homologous recombination (HR) is a DNA repair pathway that is deficient in 50% of high-grade serous ovarian carcinomas (HGSOC). Deficient HR (DHR) constitutes a therapeutic opportunity for these patients, thanks to poly (ADP-ribose) polymerases (PARP) inhibitors (PARPi; olaparib, niraparib, and rucaparib are already commercialized). Although initially, PARPi were developed for patients with BRCA1/2 mutations, robust clinical data have shown their benefit in a broader population without DHR. This breakthrough in daily practice has raised several questions that necessitate further research: How can populations that will most benefit from PARPi be selected? At which stage of ovarian cancer should PARPi be used? Which strategies are reasonable to overcome PARPi resistance? In this paper, we present a summary of the literature and discuss the present clinical research involving PARPi (after reviewing ClinicalTrials.gov) from a translational perspective. Research into the functional biomarkers of DHR and clinical trials testing PARPi benefits as first-line setting or rechallenge are currently ongoing. Additionally, in the clinical setting, only secondary restoring mutations of BRCA1/2 have been identified as events inducing resistance to PARPi. The clinical frequency of this and other mechanisms that have been described in preclinics is unknown. It is of great importance to study mechanisms of resistance to PARPi to guide the clinical development of drug combinations.

Pharmacometabolomics Reveals Irinotecan Mechanism of Action in Cancer Patients

The purpose of this study was to identify early circulating metabolite changes implicated in the mechanism of action of irinotecan, a DNA topoisomerase I inhibitor, in cancer patients. A liquid chromatography-tandem mass spectrometry-based targeted metabolomic platform capable of measuring 254 endogenous metabolites was applied to profile circulating metabolites in plasma samples collected pre- and post-irinotecan treatment from 13 cancer patients. To gain further mechanistic insights, metabolic profiling was also performed for the culture medium of human primary hepatocytes (HepatoCells) and 2 cancer cell lines on exposure to SN-38 (an active metabolite of irinotecan). Intracellular reactive oxygen species (ROS) was detected by dihydroethidium assay. Irinotecan induced a global metabolic change in patient plasma, as represented by elevations of circulating purine/pyrimidine nucleobases, acylcarnitines, and specific amino acid metabolites. The plasma metabolic signature was well replicated in HepatoCells medium on SN-38 exposure, whereas in cancer cell medium SN-38 induced accumulation of pyrimidine/purine nucleosides and nucleobases while having no impact on acylcarnitines and amino acid metabolites. SN-38 induced ROS in HepatoCells, but not in cancer cells. Distinct metabolite signatures of SN-38 exposure in HepatoCells medium and cancer cell medium revealed different mechanisms of drug action on hepatocytes and cancer cells. Elevations in circulating purine/pyrimidine nucleobases may stem from nucleotide degradation following irinotecan-induced DNA double-strand breaks. Accumulations of circulating acylcarnitines and specific amino acid metabolites may reflect, at least in part, irinotecan-induced mitochondrial dysfunction and oxidative stress in the liver. The plasma metabolic signature of irinotecan exposure provides early insights into irinotecan mechanism of action in patients.

Development of a quantitative pharmacodynamic assay for apoptosis in fixed tumor tissue and its application in distinguishing cytotoxic drug-induced DNA double strand breaks from DNA double strand breaks associated with apoptosis

DNA double strand breaks (DSBs) induced by cancer therapeutic agents can lead to DNA damage repair or persistent DNA damage, which can induce apoptotic cell death; however, apoptosis also induces DSBs independent of genotoxic insult. γH2AX is an established biomarker for DSBs but cannot distinguish between these mechanisms. Activated cleaved caspase-3 (CC3) promotes apoptosis by enhancing nuclear condensation, DNA fragmentation, and plasma membrane blebbing. Here, we describe an immunofluorescence assay that distinguishes between apoptosis and drug-induced DSBs by measuring coexpression of γH2AX and membrane blebbing−associated CC3 to indicate apoptosis, and γH2AX in the absence of CC3 blebbing to indicate drug-induced DNA damage. These markers were examined in xenograft models following treatment with topotecan, cisplatin, or birinapant. A topotecan regimen conferring tumor regression induced tumor cell DSBs resulting from both apoptosis and direct DNA damage. In contrast, a cisplatin regimen yielding tumor growth delay, but not regression, resulted in tumor cell DSBs due solely to direct DNA damage. MDA-MB-231 xenografts exposed to birinapant, which promotes apoptosis but does not directly induce DSBs, exhibited dose-dependent increases in colocalized γH2AX/CC3 blebbing in tumor cells. Clinical feasibility was established using formalin-fixed, paraffin-embedded biopsies from a canine cancer clinical trial; γH2AX/CC3 colocalization analysis revealed apoptosis induction by two novel indenoisoquinoline topoisomerase I inhibitors, which was consistent with pathologist-assessed apoptosis and reduction of tumor volume. This assay is ready for use in clinical trials to elucidate the mechanism of action of investigational agents and combination regimens intended to inflict DNA damage, apoptotic cell death, or both.

A phase 1 dose-escalation study of veliparib with bimonthly FOLFIRI in patients with advanced solid tumours

Background

Veliparib is a potent poly(ADP-ribose) polymerase inhibitor. This phase 1 study aimed to establish the maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D) of veliparib combined with various FOLFIRI regimens in patients with solid tumours.

Methods

Patients received veliparib (10–270 mg BID, days 1–5, 15–19) and FOLFIRI (days 1–3, 15–17) in three regimens containing 5-fluorouracil 2,400 mg/m²: irinotecan 150 mg/m² and folinic acid 400 mg/m² (part 1); irinotecan 180 mg/m², folinic acid 400 mg/m², and 5-fluorouracil 400 mg/m² bolus (part 2), or irinotecan 180 mg/m² (part 3). The RP2D was further evaluated in safety expansion cohorts. Preliminary antitumour activity was also assessed.

Results

Ninety-two patients received ≥1 veliparib dose. MTD was not reached; RP2D was set at 200 mg BID veliparib plus FOLFIRI (without 5-fluorouracil bolus). Most common treatment-emergent adverse events were neutropenia (66.3%), diarrhoea, and nausea (60.9% each). Dose-limiting toxicities (n = 4) were grade 3 gastritis and grade 4 neutropenia and febrile neutropenia. Veliparib exposure was dose-proportional, with no effects on the pharmacokinetics of FOLFIRI components. Fifteen patients had a partial response (objective response rate, 17.6%).

Conclusions

The acceptable safety profile and preliminary antitumour activity of veliparib plus FOLFIRI support further evaluation of this combination.

Molecular Pharmacodynamics-Guided Scheduling of Biologically Effective Doses: A Drug Development Paradigm Applied to MET Tyrosine Kinase Inhibitors

The development of molecularly targeted agents has benefited from use of pharmacodynamic markers to identify "biologically effective doses" (BED) below MTDs, yet this knowledge remains underutilized in selecting dosage regimens and in comparing the effectiveness of targeted agents within a class. We sought to establish preclinical proof-of-concept for such pharmacodynamics-based BED regimens and effectiveness comparisons using MET kinase small-molecule inhibitors. Utilizing pharmacodynamic biomarker measurements of MET signaling (tumor pY1234/1235MET/total MET ratio) in a phase 0-like preclinical setting, we developed optimal dosage regimens for several MET kinase inhibitors and compared their antitumor efficacy in a MET-amplified gastric cancer xenograft model (SNU-5). Reductions in tumor pY1234/1235MET/total MET of 95%-99% were achievable with tolerable doses of EMD1214063/MSC2156119J (tepotinib), XL184 (cabozantinib), and XL880/GSK1363089 (foretinib), but not ARQ197 (tivantinib), which did not alter the pharmacodynamic biomarker. Duration of kinase suppression and rate of kinase recovery were specific to each agent, emphasizing the importance of developing customized dosage regimens to achieve continuous suppression of the pharmacodynamic biomarker at the required level (here, ≥90% MET kinase suppression). The customized dosage regimen of each inhibitor yielded substantial and sustained tumor regression; the equivalent effectiveness of customized dosage regimens that achieve the same level of continuous molecular target control represents preclinical proof-of-concept and illustrates the importance of proper scheduling of targeted agent BEDs. Pharmacodynamics-guided biologically effective dosage regimens (PD-BEDR) potentially offer a superior alternative to pharmacokinetic guidance (e.g., drug concentrations in surrogate tissues) for developing and making head-to-head comparisons of targeted agents. Mol Cancer Ther; 17(3); 698-709. ©2018 AACR.

A Phase I Clinical Trial of the Poly(ADP-ribose) Polymerase Inhibitor Veliparib and Weekly Topotecan in Patients with Solid Tumors

Purpose: To determine the dose limiting toxicities (DLT), maximum tolerated dose (MTD), and recommended phase II dose (RP2D) of veliparib in combination with weekly topotecan in patients with solid tumors. Correlative studies were included to assess the impact of topotecan and veliparib on poly(ADP-ribose) levels in peripheral blood mononuclear cells, serum pharmacokinetics of both agents, and potential association of germline repair gene mutations with outcome.Experimental Design: Eligible patients had metastatic nonhematologic malignancies with measurable disease. Using a 3 + 3 design, patients were treated with veliparib orally twice daily on days 1-3, 8-10, and 15-17 and topotecan intravenously on days 2, 9, and 16 every 28 days. Tumor responses were assessed by RECIST.Results: Of 58 patients enrolled, 51 were evaluable for the primary endpoint. The MTD and RP2D was veliparib 300 mg twice daily on days 1-3, 8-10, and 15-17 along with topotecan 3 mg/m2 on days 2, 9, and 16 of a 28-day cycle. DLTs were grade 4 neutropenia lasting >5 days. The median number of cycles was 2 (1-26). The objective response rate was 10%, with 1 complete and 4 partial responses. Twenty-two patients (42%) had stable disease ranging from 4 to 26 cycles. Patients with germline BRCA1, BRCA2, or RAD51D mutations remained on study longer than those without homologous recombination repair (HRR) gene mutations (median 4 vs. 2 cycles).Conclusions: Weekly topotecan in combination with veliparib has a manageable safety profile and appears to warrant further investigation. Clin Cancer Res; 24(4); 744-52. ©2017 AACR.

Pilot trial of CRLX101 in patients with advanced, chemotherapy-refractory gastroesophageal cancer

Background

CRLX101 is an investigational nanoparticle-drug conjugate with a camptothecin payload. Preclinical evidence indicated preferential uptake in tumors, and tumor xenograft models demonstrate superiority of CRLX101 over irinotecan. A pilot trial was conducted at recommended phase 2 dosing (RP2D) using the bimonthly schedule to assess preferential uptake of CRLX101 in tumor vs. adjacent normal tissue in endoscopically accessible tumors in chemotherapy-refractory gastroesophageal cancer. Results from the biopsies were previously reported and herein we present the clinical outcomes.

Methods

Patients initiated CRLX101 dosed at RP2D (15 mg/m²) on days 1 and 15 of a 28-day cycle. Detection of preferential CRLX101 tumor uptake was the primary endpoint and objective response rate (ORR) was a secondary endpoint. With a sample size of ten patients, the study had 90% power to detect ≥1 responder if the true response rate is ≥21%.

Results

Between Dec. 2012 and Dec. 2014, ten patients with chemotherapy-refractory (median 2 prior lines of therapy, range 1-4) gastric adenocarcinoma were enrolled. The median time-to-progression was 1.7 months. Best response was seen in one patient with stable disease (SD) for 8 cycles. Only ≥ grade 3 drug-related toxicity occurred in one patient with grade 3 cardiac chest pain who was able to resume therapy after CRLX101 was reduced to 12 mg/m².

Conclusions

Bimonthly CRLX101 demonstrated minimal activity with SD as best response in this heavily pretreated population. Future efforts with CRLX101 in gastric cancer should focus on combination and more dose-intensive strategies given its favorable toxicity profile and evidence of preferential tumor uptake.

Improved pharmacodynamic (PD) assessment of low dose PARP inhibitor PD activity for radiotherapy and chemotherapy combination trials

BACKGROUND

PARP inhibitors are currently evaluated in combination with radiotherapy and/or chemotherapy. As sensitizers, PARP inhibitors are active at very low concentrations therefore requiring highly sensitive pharmacodynamic (PD) assays. Current clinical PD-assays partly fail to provide such sensitivities. The aim of our study was to enable sensitive PD evaluation of PARP inhibitors for clinical sensitizer development.

MATERIAL AND METHODS

PBMCs of healthy individuals and of olaparib and radiotherapy treated lung cancer patients were collected for ELISA-based PD-assays.

RESULTS

PAR-signal amplification by ex vivo irradiation enabled an extended quantification range for PARP inhibitory activities after ex vivo treatment with inhibitors. This "radiation-enhanced-PAR" (REP) assay provided accurate IC50 values thereby also revealing differences among healthy individuals. Implemented in clinical radiotherapy combination Phase I trials, the REP-assay showed sensitive detection of PARP inhibition in patients treated with olaparib and establishes strong PARP inhibitory activities at low daily doses.

CONCLUSIONS

Combination trials of radiotherapy and novel targeted agent(s) often require different and more sensitive PD assessments than in the monotherapy setting. This study shows the benefit and relevance of sensitive and adapted PD-assays for such combination purposes and provides proof of clinically relevant cellular PARP inhibitory activities at low daily olaparib doses.

Heterogeneous drug penetrance of veliparib and carboplatin measured in triple negative breast tumors

BACKGROUND

Poly(ADP-ribose) polymerase inhibitors (PARPi), coupled to a DNA damaging agent is a promising approach to treating triple negative breast cancer (TNBC). However, not all patients respond; we hypothesize that non-response in some patients may be due to insufficient drug penetration. As a first step to testing this hypothesis, we quantified and visualized veliparib and carboplatin penetration in mouse xenograft TNBCs and patient blood samples.

METHODS

MDA-MB-231, HCC70 or MDA-MB-436 human TNBC cells were implanted in 41 beige SCID mice. Low dose (20 mg/kg) or high dose (60 mg/kg) veliparib was given three times daily for three days, with carboplatin (60 mg/kg) administered twice. In addition, blood samples were analyzed from 19 patients from a phase 1 study of carboplatin + PARPi talazoparib. Veliparib and carboplatin was quantified using liquid chromatography-mass spectrometry (LC-MS). Veliparib tissue penetration was visualized using matrix-assisted laser desorption/ionization mass spectrometric imaging (MALDI-MSI) and platinum adducts (covalent nuclear DNA-binding) were quantified using inductively coupled plasma-mass spectrometry (ICP-MS). Pharmacokinetic modeling and Pearson's correlation were used to explore associations between concentrations in plasma, tumor cells and peripheral blood mononuclear cells (PBMCs).

RESULTS

Veliparib penetration in xenograft tumors was highly heterogeneous between and within tumors. Only 35% (CI 95% 26-44%), 74% (40-97%) and 46% (9-37%) of veliparib observed in plasma penetrated into MDA-MB-231, HCC70 and MDA-MB-436 cell-based xenografts, respectively. Within tumors, penetration heterogeneity was larger with the 60 mg/kg compared to the 20 mg/kg dose (RSD 155% versus 255%, P = 0.001). These tumor concentrations were predicted similar to clinical dosing levels, but predicted tumor concentrations were below half maximal concentration values as threshold of response. Xenograft veliparib concentrations correlated positively with platinum adduct formation (R 2 = 0.657), but no PARPi-platinum interaction was observed in patients' PBMCs. Platinum adduct formation was significantly higher in five gBRCA carriers (ratio of platinum in DNA in PBMCs/plasma 0.64% (IQR 0.60-1.16%) compared to nine non-carriers (ratio 0.29% (IQR 0.21-0.66%, P < 0.0001).

CONCLUSIONS

PARPi/platinum tumor penetration can be measured by MALDI-MSI and ICP-MS in PBMCs and fresh frozen, OCT embedded core needle biopsies. Large variability in platinum adduct formation and spatial heterogeneity in veliparib distribution may lead to insufficient drug exposure in select cell populations.

Phase I Trial of Veliparib, a Poly ADP Ribose Polymerase Inhibitor, Plus Metronomic Cyclophosphamide in Metastatic HER2-negative Breast Cancer

BACKGROUND

Poly-ADP-ribose-polymerase is an essential nuclear enzyme, involved in base-excision repair of damaged DNA. Poly-ADP-ribose-polymerase inhibition sensitizes tumor cells to cytotoxic agents, which induce DNA damage, including cyclophosphamide (C), and metronomic dosing of C may optimize potential for synergy.

METHODS

The primary objective of this phase I trial was to determine the safety and identify the recommended phase II dose of the combination of low-dose oral C (50, 75, 100, and 125 mg) once daily in combination with veliparib (V) (100, 200, and 300 mg) administered twice a day (BID) for 21-day cycles using a standard 3 + 3 design in patients with metastatic human epidermal growth factor receptor 2/neu-negative breast cancer. Dose-limiting toxicity was defined as any grade 3 non-hematologic toxicity or grade 4 thrombocytopenia/neutropenia occurring during cycle 1.

RESULTS

A total of 31 patients were enrolled; 19 were treated with 50 mg of C and 12 were treated at higher doses (75, 100, or 125 mg), with V doses ranging from 50 to 300 mg BID. The recommended phase II dose of the combination was V 200 mg orally BID plus C 125 mg orally daily, with nausea and headache dose-limiting at higher V dose levels. Objective response or stable disease for at least 24 weeks occurred in 3 (43%) of 7 patients with known deleterious germline BRCA mutations and 2 (11%) of 19 patients with negative/unknown mutation status (P = .1).

CONCLUSION

The combination of oral continuous dosing of V (200 mg orally BID) with metronomic C (50, 75, 100, and 125 mg daily) is well-tolerated and shows antitumor activity in patients with BRCA-mutation-associated metastatic human epidermal growth factor receptor 2/neu-negative breast cancer.

Differential Toxicity in Patients with and without DNA Repair Mutations: Phase I Study of Carboplatin and Talazoparib in Advanced Solid Tumors

Purpose: The PARP inhibitor (PARPi) talazoparib may potentiate activity of chemotherapy and toxicity in cells vulnerable to DNA damage.Experimental Design: This phase I study evaluated the safety, tolerability, pharmacokinetics, and efficacy of talazoparib and carboplatin. Pharmacokinetic modeling explored associations between DNA vulnerability and hematologic toxicity.Results: Twenty-four patients (eight males; 16 females) with solid tumors were enrolled in four cohorts at 0.75 and 1 mg daily talazoparib and weekly carboplatin (AUC 1 and 1.5, every 2 weeks or every 3 weeks), including 14 patients (58%) with prior platinum treatment. Dose-limiting toxicities included grade 3 fatigue and grade 4 thrombocytopenia; the MTD was not reached. Grade 3/4 toxicities included fatigue (13%), neutropenia (63%), thrombocytopenia (29%), and anemia (38%). After cycle 2's dose, delays/reductions were required in all patients. One complete and two partial responses occurred in germline BRCA1/2 (gBRCA1/2) patients. Four patients showed stable disease beyond 4 months, three of which had known mutations in DNA repair pathways. Pharmacokinetic toxicity modeling suggests that after three cycles of carboplatin AUC 1.5 every 3 weeks and talazoparib 1 mg daily, neutrophil counts decreased 78% [confidence interval (CI), 87-68] from baseline in gBRCA carriers and 63% (CI, 72-55) in noncarriers (P < 0.001). Pharmacokinetic toxicity modeling suggests an intermittent, pulse dosing schedule of PARP inhibition, differentiated by gBRCA mutation status, may improve the benefit/risk ratio of combination therapy.Conclusions: Carboplatin and talazoparib showed efficacy in DNA damage mutation carriers, but hematologic toxicity was more pronounced in gBRCA carriers. Carboplatin is best combined with intermittent talazoparib dosing differentiated by germline and somatic DNA damage mutation carriers. Clin Cancer Res; 23(21); 6400-10. ©2017 AACR.

Poly-(ADP-ribose)-polymerase inhibitors as radiosensitizers: a systematic review of pre-clinical and clinical human studies

BACKGROUND

Poly-(ADP-Ribose)-Polymerase (PARP) inhibitors are becoming important actors of anti-neoplasic agents landscape, with recent but narrow FDA's approvals for ovarian BRCA mutated cancers and prostatic cancer. Nevertheless, PARP inhibitors are also promising drugs for combined treatments particularly with radiotherapy. More than seven PARP inhibitors have been currently developed. Central Role of PARP in DNA repair, makes consider PARP inhibitor as potential radiosensitizers, especially for tumors with DNA repair defects, such as BRCA mutation, because of synthetic lethality. Furthermore the replication-dependent activity of PARP inhibitor helps to maintain the differential effect between tumoral and healthy tissues. Inhibition of chromatin remodeling, G2/M arrest, vasodilatory effect induced by PARP inhibitor, also participate to their radio-sensitization effect.

MATERIALS AND METHODS

Here, after highlighting mechanisms of PARP inhibitors radiosensitization we methodically searched PubMed, Google Scholar, Cochrane Databases and meeting proceedings for human pre-clinical and clinical studies that evaluated PARP inhibitor radiosensitizing effect. Enhancement ratio, when available, was systematically reported.

RESULTS

Sixty four studies finally met our selection criteria and were included in the analysis. Only three pre-clinical studies didn't find any radiosensitizing effect. Median enhancement ratio vary from 1,3 for prostate tumors to 1,5 for lung cancers. Nine phase I or II trials assessed safety data.

CONCLUSION

PARP inhibitors are promising radiosensitizers, but need more clinical investigation. The next ten years will be determining for judging their real potential.

The National Cancer Institute ALMANAC: A Comprehensive Screening Resource for the Detection of Anticancer Drug Pairs with Enhanced Therapeutic Activity

To date, over 100 small-molecule oncology drugs have been approved by the FDA. Because of the inherent heterogeneity of tumors, these small molecules are often administered in combination to prevent emergence of resistant cell subpopulations. Therefore, new combination strategies to overcome drug resistance in patients with advanced cancer are needed. In this study, we performed a systematic evaluation of the therapeutic activity of over 5,000 pairs of FDA-approved cancer drugs against a panel of 60 well-characterized human tumor cell lines (NCI-60) to uncover combinations with greater than additive growth-inhibitory activity. Screening results were compiled into a database, termed the NCI-ALMANAC (A Large Matrix of Anti-Neoplastic Agent Combinations), publicly available at https://dtp.cancer.gov/ncialmanac Subsequent in vivo experiments in mouse xenograft models of human cancer confirmed combinations with greater than single-agent efficacy. Concomitant detection of mechanistic biomarkers for these combinations in vivo supported the initiation of two phase I clinical trials at the NCI to evaluate clofarabine with bortezomib and nilotinib with paclitaxel in patients with advanced cancer. Consequently, the hypothesis-generating NCI-ALMANAC web-based resource has demonstrated value in identifying promising combinations of approved drugs with potent anticancer activity for further mechanistic study and translation to clinical trials. Cancer Res; 77(13); 3564-76. ©2017 AACR.

The Relationship Between Single-Nucleotide Polymorphisms, the Expression of DNA Damage Response Genes, and Hepatocellular Carcinoma in a Polish Population

The molecular mechanism of hepatocellular carcinoma (HCC) is related to DNA damage caused by oxidative stress products induced by hepatitis B virus (HBV) or C (HCV) infection and exposure to environmental pollutants. Single-nucleotide polymorphisms (SNPs) of DNA damage response (DDR) genes may influence individual susceptibility to environmental risk factors and affect DNA repair efficacy, which, in turn, can influence the risk of HCC. The study evaluates a panel of 15 SNPs in 11 DDR genes (XRCC1, XRCC3, XPD, MUTYH, LIG1, LIG3, hOGG1, PARP1, NFIL1, FEN1, and APEX1) in 65 HCC patients, 50 HBV- and 50 HCV-infected non-cancerous patients, and 50 healthy controls. It also estimates the mRNA expression of nine DDR genes in cancerous and adjacent healthy liver tissues. Two of the investigated polymorphisms (rs1052133 and rs13181) were associated with HCC risk. For all investigated genes, the level of mRNA was significantly lower in HCC cancer tissue than in non-cancerous liver tissue. Seven of the investigated polymorphisms were statistically related to gene expression in cancer tissues. The disruption of DDR genes may be responsible for hepatocellular transformation in HCV-infected patients.

Prediction of therapy response in ovarian cancer: Where are we now?

Therapy resistance is a major challenge in the management of ovarian cancer (OC). Advances in detection and new technology validation have led to the emergence of biomarkers that can predict responses to available therapies. It is important to identify predictive biomarkers to select resistant and sensitive patients in order to reduce important toxicities, to reduce costs and to increase survival. The discovery of predictive and prognostic biomarkers for monitoring therapy is a developing field and provides promising perspectives in the era of personalized medicine. This review article will discuss the biology of OC with a focus on targetable pathways; current therapies; mechanisms of resistance; predictive biomarkers for chemotherapy, antiangiogenic and DNA-targeted therapies, and optimal cytoreductive surgery; and the emergence of liquid biopsy using recent studies from the Medline database and ClinicalTrials.gov.

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.

PARP1 expression drives the synergistic antitumor activity of trabectedin and PARP1 inhibitors in sarcoma preclinical models

Background

Enhancing the antitumor activity of the DNA-damaging drugs is an attractive strategy to improve current treatment options. Trabectedin is an isoquinoline alkylating agent with a peculiar mechanism of action. It binds to minor groove of DNA inducing single- and double-strand-breaks. These kinds of damage lead to the activation of PARP1, a first-line enzyme in DNA-damage response pathways. We hypothesized that PARP1 targeting could perpetuate trabectedin-induced DNA damage in tumor cells leading finally to cell death.

Methods

We investigated trabectedin and PARP1 inhibitor synergism in several tumor histotypes both in vitro and in vivo (subcutaneous and orthotopic tumor xenografts in mice). We searched for key determinants of drug synergism by comparative genomic hybridization (aCGH) and gene expression profiling (GEP) and validated their functional role.

Results

Trabectedin activated PARP1 enzyme and the combination with PARP1 inhibitors potentiated DNA damage, cell cycle arrest at G2/M checkpoint and apoptosis, if compared to single agents. Olaparib was the most active PARP1 inhibitor to combine with trabectedin and we confirmed the antitumor and antimetastatic activity of trabectedin/olaparib combination in mice models. However, we observed different degree of trabectedin/olaparib synergism among different cell lines. Namely, in DMR leiomyosarcoma models the combination was significantly more active than single agents, while in SJSA-1 osteosarcoma models no further advantage was obtained if compared to trabectedin alone. aCGH and GEP revealed that key components of DNA-repair pathways were involved in trabectedin/olaparib synergism. In particular, PARP1 expression dictated the degree of the synergism. Indeed, trabectedin/olaparib synergism was increased after PARP1 overexpression and reduced after PARP1 silencing.

Conclusions

PARP1 inhibition potentiated trabectedin activity in a PARP1-dependent manner and PARP1 expression in tumor cells might be a useful predictive biomarker that deserves clinical evaluation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-017-0652-5) contains supplementary material, which is available to authorized users.

PARP Inhibitors in Reproductive System Cancers: Current Use and Developments

The repair of DNA damage is a critical cellular process governed by multiple biochemical pathways that are often found to be defective in cancer cells. The poly(ADP-ribose) polymerase (PARP) family of proteins controls response to single-strand DNA breaks by detecting these damaged sites and recruiting the proper factors for repair. Blocking this pathway forces cells to utilize complementary mechanisms to repair DNA damage. While PARP inhibition may not, in itself, be sufficient to cause tumor cell death, inhibition of DNA repair with PARP inhibitors is an effective cytotoxic strategy when it is used in patients who carry other defective DNA-repair mechanisms, such as mutations in the genes BRCA 1 and 2. This discovery has supported the development of PARP inhibitors (PARPi), agents that have proven effective against various types of tumors that carry BRCA mutations. With the application of next-generation sequencing of tumors, there is increased interest in looking beyond BRCA mutations to identify genetic and epigenetic aberrations that might lead to similar defects in DNA repair, conferring susceptibility to PARP inhibition. Identification of these genetic lesions and the development of screening assays for their detection may allow for the selection of patients most likely to respond to this class of anticancer agents. This article provides an overview of clinical trial results obtained with PARPi and describes the companion diagnostic assays being established for patient selection. In addition, we review known mechanisms for resistance to PARPi and potential strategies for combining these agents with other types of therapy.

Synthetic Lethality Exploitation by an Anti-Trop-2-SN-38 Antibody-Drug Conjugate, IMMU-132, Plus PARP Inhibitors in BRCA1/2-wild-type Triple-Negative Breast Cancer

Purpose: Both PARP inhibitors (PARPi) and sacituzumab govitecan (IMMU-132) are currently under clinical evaluation in triple-negative breast cancer (TNBC). We sought to investigate the combined DNA-damaging effects of the topoisomerase I (Topo I)-inhibitory activity of IMMU-132 with PARPi disruption of DNA repair in TNBC.Experimental Design:In vitro, human TNBC cell lines were incubated with IMMU-132 and various PARPi (olaparib, rucaparib, or talazoparib) to determine the effect on growth, double-stranded DNA (dsDNA) breaks, and cell-cycle arrest. Mice bearing BRCA1/2-mutated or -wild-type human TNBC tumor xenografts were treated with the combination of IMMU-132 and PARPi (olaparib or talazoparib). Study survival endpoint was tumor progression to >1.0 cm³ and tolerability assessed by hematologic changes.Results: Combining IMMU-132 in TNBC with all three different PARPi results in synergistic growth inhibition, increased dsDNA breaks, and accumulation of cells in the S-phase of the cell cycle, regardless of BRCA1/2 status. A combination of IMMU-132 plus olaparib or talazoparib produces significantly improved antitumor effects and delay in time-to-tumor progression compared with monotherapy in mice bearing BRCA1/2-mutated HCC1806 TNBC tumors. Furthermore, in mice bearing BRCA1/2-wild-type tumors (MDA-MB-468 or MDA-MB-231), the combination of IMMU-132 plus olaparib imparts a significant antitumor effect and survival benefit above that achieved with monotherapy. Most importantly, this combination was well tolerated, with no substantial changes in hematologic parameters.Conclusions: These data demonstrate the added benefit of combining Topo I inhibition mediated by IMMU-132 with synthetic lethality provided by PARPi in TNBC, regardless of BRCA1/2 status, thus supporting the rationale for such a combination clinically. Clin Cancer Res; 23(13); 3405-15. ©2017 AACR.

Role of Protein Linked DNA Breaks in Cancer

Topoisomerases are a group of specialized enzymes that function to maintain DNA topology by introducing transient DNA breaks during transcription and replication. As a result of abortive topoisomerases activity, topoisomerases catalytic intermediates may be trapped on the DNA forming topoisomerase cleavage complexes (Topcc). Topoisomerases trapping on the DNA is the mode of action of several anticancer drugs, it lead to formation of protein linked DAN breaks (PDBs). PDBs are now considered as one of the most dangerous forms of endogenous DNA damage and a major threat to genomic stability. The repair of PDBs involves both the sensing and repair pathways. Unsuccessful repair of PDBs leads to different signs of genomic instabilities such as chromosomal rearrangements and cancer predisposition. In this chapter we will summarize the role of topoisomerases induced PDBs, identification and signaling, repair, role in transcription. We will also discuss the role of PDBs in cancer with a special focus on prostate cancer.

Biomarkers of Response and Resistance to DNA Repair Targeted Therapies

Drugs targeting DNA damage repair (DDR) pathways are exciting new agents in cancer therapy. Many of these drugs exhibit synthetic lethality with defects in DNA repair in cancer cells. For example, ovarian cancers with impaired homologous recombination DNA repair show increased sensitivity to poly(ADP-ribose) polymerase (PARP) inhibitors. Understanding the activity of different DNA repair pathways in individual tumors, and the correlations between DNA repair function and drug response, will be critical to patient selection for DNA repair targeted agents. Genomic and functional assays of DNA repair pathway activity are being investigated as potential biomarkers of response to targeted therapies. Furthermore, alterations in DNA repair function generate resistance to DNA repair targeted agents, and DNA repair states may predict intrinsic or acquired drug resistance. In this review, we provide an overview of DNA repair targeted agents currently in clinical trials and the emerging biomarkers of response and resistance to these agents: genetic and genomic analysis of DDR pathways, genomic signatures of mutational processes, expression of DNA repair proteins, and functional assays for DNA repair capacity. We review biomarkers that may predict response to selected DNA repair targeted agents, including PARP inhibitors, inhibitors of the DNA damage sensors ATM and ATR, and inhibitors of nonhomologous end joining. Finally, we introduce emerging categories of drugs targeting DDR and new strategies for integrating DNA repair targeted therapies into clinical practice, including combination regimens. Generating and validating robust biomarkers will optimize the efficacy of DNA repair targeted therapies and maximize their impact on cancer treatment. Clin Cancer Res; 22(23); 5651-60. ©2016 AACR.

The PARP inhibitor ABT-888 potentiates dacarbazine-induced cell death in carcinoids

Monoagent DNA-alkylating chemotherapies like dacarbazine are among a paucity of medical treatments for advanced carcinoid tumors, but are limited by host toxicity and intrinsic chemoresistance through the base excision repair (BER) pathway via poly (ADP-ribose) polymerase (PARP). Hence, inhibitors of PARP may potentiate DNA-damaging agents by blocking BER and DNA restoration. We show that the PARP inhibitor ABT-888 (Veliparib) enhances the cytotoxic effects of dacarbazine in carcinoids. Two human carcinoid cell lines (BON and H727) treated with a combination of ABT-888 and dacarbazine resulted in synergistic growth inhibition signified by combination indices <1 on the Chou-Talalay scale. ABT-888 administered prior to varying dacarbazine doses promoted the suppression of neuroendocrine biomarkers of malignancy ASCL1 and CgA, shown by Western analysis. ATM phosphorylation and p21^Waf1/Cip1 activation, indicative of DNA damage, were increased by ABT-888 when combined with dacarbazine treatment, suggesting BER pathway attenuation by ABT-888. PE Annexin V/7-AAD staining and sorting revealed a profound induction of apoptosis following combination treatment, which was further confirmed by increased PARP cleavage. These results demonstrate that ABT-888 synergizes dacarbazine treatment in carcinoids. Therefore, ABT-888 may help treat carcinoids unresponsive or refractory to mainstay therapies.

Theory and practice of clinical pharmacodynamics in oncology drug development

The clinical development of molecularly targeted cancer therapies is enhanced by proof of mechanism of action as well as proof of concept, which relate molecular pharmacodynamics to efficacy via changes in cancer cell biology and physiology resulting from drug action on its intended target. Here, we present an introduction to the field of clinical pharmacodynamics, its medical and laboratory aspects, and its practical incorporation into clinical trials. We also describe key success factors that are useful for judging the quality of clinical pharmacodynamic studies, including biopsy quality and suitability, specimen handling, assay fitness-for-purpose, and reagent quality control. This introduction provides not only context for the following articles in this issue, but also an appreciation of the role of well-conducted clinical pharmacodynamic studies in oncology drug development.

γ-H2AX and other histone post-translational modifications in the clinic

Chromatin is a dynamic complex of DNA and proteins that regulates the flow of information from genome to end product. The efficient recognition and faithful repair of DNA damage, particularly double-strand damage, is essential for genomic stability and cellular homeostasis. Imperfect repair of DNA double-strand breaks (DSBs) can lead to oncogenesis. The efficient repair of DSBs relies in part on the rapid formation of foci of phosphorylated histone H2AX (γ-H2AX) at each break site, and the subsequent recruitment of repair factors. These foci can be visualized with appropriate antibodies, enabling low levels of DSB damage to be measured in samples obtained from patients. Such measurements are proving useful to optimize treatments involving ionizing radiation, to assay in vivo the efficiency of various drugs to induce DNA damage, and to help diagnose patients with a variety of syndromes involving elevated levels of γ-H2AX. We will survey the state of the art of utilizing γ-H2AX in clinical settings. We will also discuss possibilities with other histone post-translational modifications. The ability to measure in vivo the responses of individual patients to particular drugs and/or radiation may help optimize treatments and improve patient care. This article is part of a Special Issue entitled: Chromatin in time and space.