Requirements to assess feasibility of phase 0 trials during major abdominal surgery: variability of PARP activity

Promise and limits of the CellSearch platform for evaluating pharmacodynamics in circulating tumor cells

Circulating tumor cells (CTCs), which are captured from blood with anti-epithelial cell adhesion molecule (EpCAM) antibodies, have established prognostic value in specific epithelial cancers, but less is known about their utility for assessing patient response to molecularly targeted agents via measurement of pharmacodynamic (PD) endpoints. We discuss the use of CellSearch (Janssen Diagnostics, LLC, Raritan, NJ) CTC isolation technology for monitoring PD response in early phase trials. We present representative data from three clinical trials with the poly(ADP-ribose) polymerase (PARP) inhibitor veliparib (ABT-888) suggesting that CTCs can be used to measure PD effects. However, while often leading to hypothesis-generating information, our experience points to the difficulty in obtaining sufficient EpCAM-expressing CTCs from patients with advanced disease to reach statistically significant conclusions about PD effects from each trial. Overall, the level of phenotypic heterogeneity observed in specimens from patients with advanced carcinomas suggests caution in the use of cell-surface differentiation marker-based methods for isolating CTCs.

Pharmacodynamic analyses in a multi-laboratory network: lessons from the poly(ADP-ribose) assay

Clinical pharmacodynamic assays need to meet higher criteria for sensitivity, precision, robustness, and reproducibility than those expected for research-grade assays because of the long duration of clinical trials and the potentially unpredictable number of laboratories running the assays. This report describes the process of making an immunoassay based on commercially available reagents "clinically ready". The assay was developed to quantify poly(ADP-ribose) (PAR) levels as a marker of PAR polymerase inhibitor activity for a proof-of-concept phase 0 clinical trial at the National Cancer Institute (NCI) and subsequent clinical trials. In this publication, we retrospectively examine the measures taken to validate the published PAR immunoassay and outline key lessons learned during the development and implementation of these procedures at both internal and external clinical trial sites; these measures included optimizing PAR measurements in tumor biopsies and peripheral blood mononuclear cells (PBMCs), reagent qualification, analytical validation and assay quality control, instrument qualification and method quality control, and support for external laboratories.

Implementation of validated pharmacodynamic assays in multiple laboratories: challenges, successes, and limitations

There is a "life cycle" of pharmacodynamic (PD) biomarker assays that guides the development and clinical implementation in our laboratories. The well-recognized elements of analytical assay validation and demonstration of fitness-for-purpose of the biomarker, specimen collection, handling, and assay methods are only a part of the required activities. Assay transfer across laboratories and testing on actual human clinical specimens are vital for understanding assay performance and robustness. In our experience, this patient specimen-centered approach has required assay method modifications, some unexpected, but which were critical to successful implementation in clinical trials. In addition, dispersing assays throughout the National Cancer Institute's clinical trials network has required the development of calibrator and control materials as well as formal training courses for smooth implementation. One measure of success of this approach has been that a number of the assays developed at NCI's Frederick National Laboratory have ultimately reached the stage of commercialization, enabling wide accessibility of the PD biomarker assays by the research community. See all articles in this ccr focus section, "Progress in pharmacodynamic endpoints."