New targets for cancer chemotherapy--poly(ADP-ribosylation) processing and polyisoprene metabolism

Veliparib for the treatment of ovarian cancer

INTRODUCTION

Ovarian cancer represents the sixth most commonly diagnosed cancer among women, with an incidence of 6.1 cases per 100.000 women and a cumulative lifetime risk of 0.5%. Treatment is based on debulking surgery and platinum-based chemotherapy, with the potential combination with taxane. However, the recently available data on the genetic basis and aetiology of ovarian cancer has led to the development of new anticancer drugs. Poly(ADP-ribose) polymerase (PARP) inhibitors are one of the most promising new classes of targeted agents currently under investigation for the treatment of ovarian cancer. Veliparib is a small molecule that inhibits both PARP-1 and PARP-2 and was originally shown to be efficacious in BRCA-associated tumors.

AREAS COVERED

This manuscript reviews the Phase I and II studies investigating the use of veliparib in ovarian cancer. This article also provides and discusses the pharmacokinetics and pharmacodynamics of veliparib.

EXPERT OPINION

It is still being discussed whether PARP inhibitors should be used in a front-line or relapsed setting, alone or in combination with cytotoxic chemotherapy or as maintenance treatment. In terms of veliparib, further investigations are needed to explore its full potential in ovarian cancer. It is hoped that the ongoing phase 3 trials will help to further elucidate it potential as a treatment option.

A Phase I study of veliparib (ABT-888) in combination with low-dose fractionated whole abdominal radiation therapy in patients with advanced solid malignancies and peritoneal carcinomatosis

PURPOSE

The combination of low-dose radiotherapy with PARP inhibition has been shown to enhance antitumor efficacy through potentiating DNA damage. We combined low-dose fractionated whole abdominal radiation (LDFWAR) with escalating doses of veliparib (ABT-888), a small-molecule PARP inhibitor, in patients with peritoneal carcinomatosis from advanced solid tumor malignancies.

EXPERIMENTAL DESIGN

Patients were treated with veliparib (80-320 mg daily) for a total of 3 cycles. LDFWAR consisted of 21.6 Gy in 36 fractions, 0.6 Gy twice daily on days 1 and 5 for weeks 1-3 of each cycle. Circulating tumor cells (CTC) were collected and evaluated for γ-H2AX. Quality of life (QoL) was assessed using the EORTC-QLQ-C30 questionnaire.

RESULTS

Twenty-two patients were treated. Treatment-related grade 3 and 4 toxicities included lymphopenia (68%), anemia (9%), thrombocytopenia (14%), neutropenia (4%), leukopenia (9%), ascites (4%), vomiting (4%), and dyspnea (4%). No objective responses were observed. Disease stabilization (≥24 weeks) was observed in 7 patients (33%). Median progression-free survival (mPFS) was 4.47 months and median overall survival (mOS) was 13.04 months. In the subset of 8 ovarian and fallopian cancers, mPFS was 6.77 months and mOS was 17.54 months compared with mPFS 2.71 months and mOS 13.01 months in others. Patients with ovarian and fallopian cancers had better QoL over time than those with other cancers. An increased percentage of γ-H2AX-positive CTCs was observed in a subset of patients (3/6 with >2 CTCs at baseline).

CONCLUSIONS

Combined veliparib and LDFWAR is a well-tolerated regimen that resulted in prolonged disease stability for some patients with advanced solid tumors and carcinomatosis, particularly in the ovarian and fallopian cancer subpopulation.

Taxanes in combination with biologic agents for ovarian and breast cancers

Taxane-based cytotoxic therapy is commonly prescribed for breast and ovarian cancers. Although these cancers are often sensitive to such therapy, clinical benefit and overall survival are limited owing to the development of chemoresistance and recurrence. Biologic agents that specifically target proteins of growth factor signaling pathways, which are hyperactivated in cancers, offer attractive targets for cancer therapeutics and may work synergistically with standard taxane-based chemotherapy to improve patient outcomes. We review clinical trials of biologic agents--angiogenic, tyrosine kinase, and antibody inhibitors--in combination with taxane-based therapy for ovarian and breast cancers. Many clinical trials have shown promising results. However, some biologic agents still need larger trials to assess safety and efficacy. As research into the heterogeneity and complexity of ovarian and breast cancers improves our understanding of the molecular pathways involved, there is no question that targeted therapies with biologic agents will expand the future array of available cancer therapeutics.

Overexpression of chromatin assembly factor-1 p60, poly(ADP-ribose) polymerase 1 and nestin predicts metastasizing behaviour of oral cancer

Aims

The natural history of oral squamous cell carcinomas (OSCCs) is variable and difficult to predict. This study aimed to assess the value of the expression of poly(ADP-ribose) polymerase 1 (PARP-1), chromatin assembly factor-1 (CAF-1)/p60 and the stem cell markers CD133, CD166, CD44, CD44v6 and nestin as markers of outcome and progression-free survival in OSCC patients.

Methods

Clinical data were collected from 66 patients (41 male and 25 female, aged 29–92 years) who underwent surgery for OSCC of the tongue, floor, lips, and palate. During follow-up (range: 12–131 months), 14 patients experienced relapse/metastasis and/or death. The study was performed by immunohistochemistry on paraffin-embedded tumour tissues, western blot analysis of tumour protein lysates and human cell lines, and RNA silencing assays. In addition, the human papillomavirus (HPV) status of primary tumours was evaluated by immunohistochemistry and viral subtyping. Univariate and multivariate analyses were performed to determine the correlation between these parameters and the clinical and pathological variables of the study population.

Results and conclusions

We found that a PARP-1^high/CAF-1 p60^high/nestin^high phenotype characterized the OSCCs with the worst prognosis (all HPV-negative). This may be of benefit in clinical management, since radio-enhancing anti-PARP-1 and/or anti-CAF-1/p60 agents may allow radioresistance to be bypassed in the nestin-overexpressing, metastasizing OSCC cells.

Poly(adp-ribose) polymerase inhibitors: a novel drug class with a promising future

Poly(ADP-ribose) polymerase inhibitors are an exciting new class of antineoplastic agents that impair the ability of cells to recover from DNA damage. They are most effective in the setting of inherent DNA repair defects, such as in cancers resulting from BRCA gene mutations, or in the setting of DNA-damaging chemotherapeutic agents. This article reviews the background and development of these agents in the laboratory, as well as the rationale for the biologic correlative studies used in clinical trials. The most recent data from the clinical trials of olaparib (AZD2281, KU-0059436), BSI-201, AG014699, ABT-888, and INO-1001 and descriptions of ongoing studies are also presented.

Plasma and cerebrospinal fluid pharmacokinetics of ABT-888 after oral administration in non-human primates

PURPOSE

ABT-888 inhibits poly(ADP-ribose) polymerase (PARP) and may enhance the efficacy of chemotherapy and radiation in CNS tumors. We studied the plasma and cerebrospinal fluid (CSF) pharmacokinetics (PK) of ABT-888 in a non-human primate (NHP) model that is highly predictive of human CSF penetration.

METHODS

ABT-888, 5 mg/kg, was administered orally to three NHPs. Serial blood and CSF samples were obtained. Plasma and CSF concentrations of ABT-888 were measured using LC/MS/MS, and the resulting concentration versus time data were evaluated using non-compartmental and compartmental PK methods.

RESULTS

The CSF penetration of ABT-888 was 57+/-7% (mean+/-SD). The peak ABT-888 concentration in the plasma was 0.62+/-0.18 microM. Plasma and CSF AUC0-infinity were 3.7+/-1.7 and 2.1+/-0.8 microM h. PARP inhibition in peripheral blood mononuclear cells was evident 2 h after ABT-888 administration.

CONCLUSION

The CSF penetration of ABT-888 after oral administration was 57%. Plasma and CSF concentrations were in the range that has been shown to inhibit PARP activity in vivo in humans.

PARP1 expression in pediatric central nervous system tumors

BACKGROUND

Despite advances in therapy, outcome in many high-grade pediatric central nervous system (CNS) tumors remains poor. The focus of neuro-oncology research has thus turned towards identifying novel therapeutic targets. Poly(ADP-ribose) polymerase-1 (PARP1) is a DNA repair protein that has been studied in a variety of malignancies and may interfere with therapy-induced DNA damage, however expression in pediatric CNS tumors is unknown.

PROCEDURE

We evaluated PARP1 mRNA expression in 81 pediatric CNS tumors using microarray technology. Protein expression was examined by Western blot.

RESULTS

PARP1 mRNA is highly expressed in high-grade tumors (P < 0.0001). PARP1 mRNA expression was greater in high-grade glioma than pilocytic astrocytoma (P = 3.5 x 10(-5)) and in large cell medulloblastoma over classic medulloblastoma (P = 0.0053). PARP1 protein was also prominent in high-grade tumors (P = 0.022).

CONCLUSION

These findings indicate that PARP1 is expressed in high-grade pediatric CNS tumors, implicating PARP1 inhibition as a potential therapeutic target.

Phase 0 clinical trial of the poly (ADP-ribose) polymerase inhibitor ABT-888 in patients with advanced malignancies

PURPOSE

We conducted the first phase 0 clinical trial in oncology of a therapeutic agent under the Exploratory Investigational New Drug Guidance of the US Food and Drug Administration. It was a first-in-human study of the poly (ADP-ribose) polymerase (PARP) inhibitor ABT-888 in patients with advanced malignancies.

PATIENTS AND METHODS

ABT-888 was administered as a single oral dose of 10, 25, or 50 mg to determine the dose range and time course over which ABT-888 inhibits PARP activity in tumor samples and peripheral blood mononuclear cells, and to evaluate ABT-888 pharmacokinetics. Blood samples and tumor biopsies were obtained pre- and postdrug administration for evaluation of PARP activity and pharmacokinetics. A novel statistical approach was developed and utilized to study pharmacodynamic modulation as the primary end point for trials of limited sample size.

RESULTS

Thirteen patients with advanced malignancies received the study drug; nine patients underwent paired tumor biopsies. ABT-888 demonstrated good oral bioavailability and was well tolerated. Statistically significant inhibition of poly (ADP-ribose) levels was observed in tumor biopsies and peripheral blood mononuclear cells at the 25-mg and 50-mg dose levels.

CONCLUSION

Within 5 months of study activation, we obtained pivotal biochemical and pharmacokinetic data that have guided the design of subsequent phase I trials of ABT-888 in combination with DNA-damaging agents. In addition to accelerating the development of ABT-888, the rapid conclusion of this trial demonstrates the feasibility of conducting proof-of-principle phase 0 trials as part of an alternative paradigm for early drug development in oncology.

The potential of PARP inhibitors in genetic breast and ovarian cancers

The abundant nuclear enzyme poly(ADP-ribose) polymerase-1 (PARP-1), represents an important novel target in cancer therapy. PARP-1 is essential to the repair of DNA single-strand breaks via the base excision repair pathway. Inhibitors of PARP-1 have been shown to enhance the cytotoxic effects of ionizing radiation and DNA damaging chemotherapy agents, such as the methylating agents and topoisomerase I inhibitors. There are currently at least five PARP inhibitors in clinical trial development. Recent in vitro and in vivo evidence suggests that PARP inhibitors could be used not only as chemo/radiotherapy sensitizers, but as single agents to selectively kill cancers defective in DNA repair, specifically cancers with mutations in the breast cancer associated (BRCA) 1 and 2 genes. This theory of selectively exploiting cells defective in one DNA repair pathway by inhibiting another is a major breakthrough in the treatment of cancer. BRCA1/2 mutations are responsible for the majority of genetic breast/ovarian cancers, known as the hereditary breast ovarian cancer syndrome. This review summarizes the preclinical and clinical evidence for the potential of PARP inhibitors in genetic breast and ovarian cancers.

Current development of clinical inhibitors of poly(ADP-ribose) polymerase in oncology

Poly(ADP-ribose) polymerase (PARP) is a nuclear enzyme that signals the presence of DNA damage by catalyzing the addition of ADP-ribose units to DNA, histones, and various DNA repair enzymes and by facilitating DNA repair. PARP has been gaining increasing interest as a therapeutic target for many diseases and especially for cancer. Inhibition of PARP potentiates the activity of DNA-damaging agents, such as alkylators, platinums, topoisomerase inhibitors, and radiation in in vitro and in vivo models. In addition, tumors with DNA repair defects, such as those arising from patients with BRCA mutations, may be more sensitive to PARP inhibition. At least five different companies have now initiated oncology clinical trials with PARP inhibitors, ranging in stage from phase 0 to phase 2. This review summarizes the preclinical and clinical data currently available for these agents and some of the challenges facing the clinical development of these agents.

Enhanced polyadenosine diphosphate-ribosylation in cirrhotic liver and carcinoma tissues in patients with hepatocellular carcinoma

AIM

The aim of this study is to assess the poly ADP-ribosylation activity in human hepatocellular carcinoma (HCC) and in liver cirrhosis (LC) as compared to the activity in normal livers (NL).

METHODS

Hepatocellular carcinoma and LC tissues were sampled from 19 patients with HCC. Normal liver tissue was obtained from 19 patients with metastatic liver cancer. Poly ADP-ribosylation activity of these tissues was measured by using [32P]-adenylate nicotinamide adenine dinucleotide (NAD)-incorporation into the 116-kDa protein. Nicotinamide adenine dinucleotide glycohydrolase activity of these tissues was determined with thin layer chromatography. The immunohistochemical expression of Ki-67 was also assessed as a parameter of cell proliferative activity.

RESULTS

The poly ADP-ribosylation of the 116 kDa protein was significantly increased in patients with HCC and LC as compared with NL (P<0.0001, P<0.05, respectively) and was inhibited by poly (ADP-ribose) polymerase inhibitors in a dose-dependent manner. There was no significant difference in NAD glycohydrolase activity among the three groups. A significant correlation was found between the Ki-67 positive cell rate and the relative radioactivity of poly ADP-ribosylation in HCC patients (r=0.794, P<0.0001). The poly ADP-ribosylation of the 116 kDa protein of LC was significantly higher in patients who had recurrences of HCC after hepatic resection than in patients without recurrence (P<0.05).

CONCLUSION

Poly ADP-ribosylation of the 116 kDa protein in HCC patients might be enhanced with its proliferative activity, and poly ADP-ribosylation of the same protein in LC patients might be a useful parameter of carcinogenic potential for predicting HCC recurrence after hepatectomy in patients who have had HCC.

Arecoline-induced changes of poly-ADP-ribosylation of cellular proteins and its influence on chromatin organization

Arecoline, the major alkaloid of betel nut (Areca catechu L.) and a suspected carcinogen, has been implicated in human cancers of various sites. A considerable portion of the world's population is constantly exposed to arecoline due to the habit of masticating betel nuts. The present work relates to the study of early molecular events following chronic arecoline exposure at a dose of 10 microg/ml to Swiss albino mice. Poly-ADP-ribosylation of all cellular proteins, histones and poly-ADP-ribose polymerase were studied in bone marrow and spleen cells and correlated with the organizational status of the chromatin. While most proteins showed lowering of their poly-ADP-ribosylation following arecoline treatment, only histone protein H1 in spleen cells and H2B in bone marrow cells exhibited an increase. The chromatin of both the tissues was progressively relaxed upon arecoline exposure. The implications of these changes have been discussed regarding the process of initiation of arecoline-induced carcinogenesis.

Cell culture of tumors alters endogenous poly(ADPR)polymerase expression and activity

Poly(ADP-ribose)polymerase, a chromatin-bound enzyme, actively participates in processes such as cell proliferation, differentiation, and DNA repair and replication. This enzyme is also implicated in cell transformation, and its inhibition has been proposed to potentiate anti-cancer drug activity. Since cells prepared from tumor biopsies and established tumor cell lines are commonly used to evaluate the efficiency of anticancer therapies, we have compared poly(ADP-ribose)polymerase activity in animal tumor cells growing in vivo and in cell culture. Three tumor types were tested: a mastocytoma (P815), a lymphoma (RDM4), and a glioma (C6). Our results show that cell culture alters poly(ADP-ribose)polymerase levels and activity. Endogenous poly(ADP-ribose) activity was several fold higher in exponentially growing cells than in cells freshly recovered from solid or ascitic tumors. Moreover, polymerase activity increased with culture time, reaching a maximum when cells became confluent. Measurements of poly(ADP-ribose)polymerase gene expression and protein amount indicate that lower enzyme activity in tumors grown in vivo are sustained by decreases in poly(ADP-ribose)polymerase mRNA and protein amount. In contrast, the increase in endogenous poly(ADP-ribose)polymerase activity observed in cultured cells was due to enzyme activation and not to de novo protein synthesis. Such differences must be considered when assessing the applicability of cell-culture results to in vivo situations.

Hexamethylenebisacetamide selectively inhibits the proliferation of human and rat vascular smooth-muscle cells

Hexamethylenebisacetamide (HMBA) selectively and reversibly inhibited proliferation of human and rat vascular smooth-muscle cells (VSMCs) compared with endothelial cells, fibroblasts or lymphocytes. Half-maximal inhibition of VSMC proliferation occurred at 2-5 mM-HMBA, and at 30- greater than 50 mM for other cell types. HMBA also prevented de-differentiation, defined by the loss of smooth-muscle-specific myosin heavy chain, of primary rat VSMCs and caused partial re-differentiation of subcultured cells. Other inhibitors of ADP-ribosyltransferase were also selective inhibitors of VSMC proliferation.