Abstract LB-286: Use of circulating tumor cells to monitor pharmacodynamic responses of patients in early-stage clinical trials

Abstract

Abstract Circulating tumor cells (CTCs) in peripheral blood of cancer patients potentially represent a fraction of solid tumor cells available for more frequent pharmacodynamic assessment of drug action than is possible using tumor biopsy. We have developed and validated an assay that directly examines increases in the number of cells positive for the nuclear DNA-damage marker H2AX in individual CTCs of patients treated with DNA-damaging chemotherapeutic agents. The method uses AexaFluor 488-conjugated monoclonal anti- H2AX (JBW301), to stain putative CTCs collected from blood by the CellSearch AutoPrep instrument, followed by enumeration and fluorescence analysis on the CellTracks Analyzer. Patient baselining studies demonstrated that in the absence of treatment the number of CTCs per blood aliquot is relatively constant over short time periods (2 weeks off therapy). CTC measurements are currently in use supporting four NCI new agent trials, two with cytotoxic agents and two with targeted agents (aTOP1 inhibitor and a tyrosine kinase inhibitor, TKI). CTC changes in 40 patients have been monitored on therapy to date. H2AX positive cells increased in 7/14 patients on cytotoxic therapies, 3/14 were unchanged and 4/14 were unevaluable; the fraction of H2AX positive CTCs did not decrease in any patient on cytotoxic therapy, and did not change in patients treated with TKI. The increased H2AX signal in patients on cytotoxic agents appears definitive for the cycle of therapy in which it is measured. Interestingly, 10/40 patients had increased CTC numbers immediately post-therapy, and several of these patients had few or no CTC immediately prior to therapy, suggesting that the cells were mobilized or shed from the tumor as a consequence of drug exposure. Six patients had decreases in CTC number, 12 were unchanged and 12 were unevaluable due to low CTC numbers. These data show promise for monitoring dynamic changes in nuclear biomarkers in CTCs, in addition to a CTC count alone, to rapidly assess drug pharmacodynamic activity, in clinical trials of cytotoxic agents and targeted anti-cancer therapeutics, as well as for translational research. This method may have the potential to inform the development of new anti-cancer agents and enable longitudinal monitoring of target response. Funded by NCI Contract No. HHSN261200800001E. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-286.