Clinical and laboratory studies to support the first-in-human trial of a novel poly(ADP-ribose) polymerase inhibitor in combination with temozolomide

Abstract

Poly(ADP-ribose)polymerase (PARP) is a nuclear enzyme involved in the repair of DNA single strand breaks via the Base Excision Repair pathway (BER). Temozolomide, a DNA alkylating agent recently licensed for the treatment of gliomas and melanoma, produces DNA lesions which are targets for BER. Preclinical studies demonstrate that PARP inhibitors increase the cytotoxicity and antitumour activity of temozolomide suggesting that PARP inhibitors may have a clinical role as chemopotentiating agents. This thesis describes the protocol development of a First-in-Human phase I clinical trial of AGO14699, a potent PARP inhibitor, in combination with temozolomide in patients with advanced solid malignancies discussing the rationale for the study design, definition of pharmacodynamic (PD) endpoints and starting dose. A two part trial escalating first the dose of AG014699 then that oftemozolomide was designed with PD endpoints for part 1 and classical toxicity endpoints for part 2. The development and validation of two PARP activity assays to measure enzyme activity and inhibition in human peripheral blood lymphocytes (PBLs) and homogenised tumour biopsies are discussed. An established tumour cell line (L1210) was evaluated to provide Quality Assurance, and preparation, storage and transport stability of samples investigated. The first assay developed relied upon measuring incorporation ofe2p] NAD+ into poly(ADP-ribose) (PAR), this assay proved robust but depended upon the availability of large numbers of PBLs, limiting its clinical application. An alternative assay based on detection of PAR with a monoclonal antibody and electronic digitisation of the chemiluminescence signal was validated and then assessed in a phase II mechanistic study of temozolomide alone in patients with advanced malignant melanoma. This small study provided additional validation for the assay and also data on DNA damage and repair after temozolomide which can be used as control data to interpret the pharmacodynamic results of the First-inHuman study.