Abstract CT325: Combination of the PARP inhibitor veliparib (ABT888) with irinotecan in patients with triple negative breast cancer: Preliminary activity and signature of response

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.

Pharmacodynamic endpoints as clinical trial objectives to answer important questions in oncology drug development

Analyzing the molecular interplay between malignancies and therapeutic agents is rarely a straightforward process, but we hope that this special issue of Seminars has highlighted the clinical value of such endeavors as well as the relevant theoretical and practical considerations. Here, we conclude with both an overview of the various high-value applications of clinical pharmacodynamics (PD) in developmental therapeutics and an outline of the framework for incorporating PD analyses into the design of clinical trials. Given the increasingly recognized importance of determining and administering the biologically effective dose (BED) and schedule of targeted agents, we explain how clinical PD biomarkers specific to the agent mechanism of action (MOA) can be used for the development of pharmacodynamics-guided biologically effective dosage regimens (PD-BEDR) to maximize the efficacy and minimize the toxicity of targeted therapies. In addition, we discuss how MOA-based PD biomarker analyses can be used both as patient selection diagnostic tools and for designing novel drug combinations targeting the specific mutational signature of a given malignancy. We also describe the role of PD analyses in clinical trials, including for MOA confirmation and dosage regimen optimization during phase 0 trials as well as for correlating molecular changes with clinical efficacy when establishing proof-of-concept in phase I/II trials. Finally, we outline the critical technological developments that are needed to enhance the quality and quantity of future clinical PD data collection, broaden the types of molecular questions that can be answered in the clinic, and, ultimately, improve patient outcomes.

The PARP family: insights into functional aspects of poly (ADP-ribose) polymerase-1 in cell growth and survival

PARP family members can be found spread across all domains and continue to be essential molecules from lower to higher eukaryotes. Poly (ADP-ribose) polymerase 1 (PARP-1), newly termed ADP-ribosyltransferase D-type 1 (ARTD1), is a ubiquitously expressed ADP-ribosyltransferase (ART) enzyme involved in key cellular processes such as DNA repair and cell death. This review assesses current developments in PARP-1 biology and activation signals for PARP-1, other than conventional DNA damage activation. Moreover, many essential functions of PARP-1 still remain elusive. PARP-1 is found to be involved in a myriad of cellular events via conservation of genomic integrity, chromatin dynamics and transcriptional regulation. This article briefly focuses on its other equally important overlooked functions during growth, metabolic regulation, spermatogenesis, embryogenesis, epigenetics and differentiation. Understanding the role of PARP-1, its multidimensional regulatory mechanisms in the cell and its dysregulation resulting in diseased states, will help in harnessing its true therapeutic potential.

Advances in PARP inhibitors for the treatment of breast cancer

INTRODUCTION

Poly(ADP-Ribose) polymerases (PARPs) are one of the important components of base excision repair pathway for single strand DNA breaks. Currently accepted hypothesis for the mechanism of action for PARP inhibitors in tumors with homologous recombination deficiency is synthetic lethality, as the simultaneous blockage of both pathways prevents the tumor cells from repairing DNA damage. Other proposed mechanisms include PARP trapping, defective BRCA1 and POLQ recruitment to sites of DNA repair. Breast cancer subgroups with germline BRCA mutations or non-mutational functional defects in BRCA proteins exemplify potential targets for PARP inhibitors.

AREAS COVERED

Promising results have been achieved with PARP inhibitors in BRCA associated cancers, particularly in ovarian and breast cancer. Olaparib is the only PARP inhibitor approved by FDA in the treatment of patients with germline BRCA mutated advanced ovarian cancer pretreated with ≥3 prior lines of chemotherapy. In this article, we reviewed the current status of PARP inhibitors, completed and ongoing trials, safety and resistance issues in patients with breast cancer.

EXPERT OPINION

PARP inhibitors show promise in cancers with BRCA mutation and in the treatment of sporadic cancers with defective homologous recombination. Predictors of response, strategies to overcome resistance, combination with other chemotherapies and targeted agents, optimum dose and schedule of administration should be investigated in future trials.