Development and validation of a drug activity biomarker that shows target inhibition in cancer patients receiving enzastaurin, a novel protein kinase C-β inhibitor

Lisa J. Green, Philip Marder, Chad Ray, Carolyn A. Cook, Susan Jaken, Luna C. Musib, Roy S. Herbst, Michael Carducci, Carolyn D. Britten, Michele Basche, S. Gail Eckhardt, Donald Thornton

Research output: Contribution to journalArticle

Abstract

Purpose: To evaluate the effects of the novel protein kinase C (PKC) inhibitor enzastaurin on intracellular phosphoprotein signaling using flow cytometry and to use this approach to measure enzastaurin effects on surrogate target cells taken from cancer patients that were orally dosed with this agent. Experimental Design: The activity of PKC was assayed in intact cells using a modification of published techniques. The U937 cell line and peripheral blood mononuclear cells were stimulated with phorbol ester, fixed, permeabilized, and reacted with an antibody specific for the phosphorylated forms of PKC substrates. The processed samples were quantitatively analyzed using flow cytometry. The assay was validated for selectivity, sensitivity, and reproducibility. Finally, blood was obtained from volunteer cancer patients before and after receiving once daily oral doses of enzastaurin. These samples were stimulated ex vivo with phorbol ester and were assayed for PKC activity using this approach. Results: Assay of U937 cells confirmed the selectivity of the antibody reagent and enzastaurin for PKC. Multiparametric analysis of peripheral blood mononuclear cells showed monocytes to be the preferred surrogate target cell. Day-to-day PKC activity in normal donors was reproducible. Initial results showed that five of six cancer patients had decreased PKC activity following enzastaurin administration. In a following study, a group of nine patients displayed a significant decrease in PKC activity after receiving once daily oral doses of enzastaurin. Conclusion: An inhibition of surrogate target cell PKC activity was observed both in vitro and ex vivo after exposure to the novel kinase inhibitor, enzastaurin.

Original languageEnglish (US)
Pages (from-to)3408-3415
Number of pages8
JournalClinical Cancer Research
Volume12
Issue number11 I
DOIs
StatePublished - Jun 1 2006

ASJC Scopus subject areas

  • Oncology
  • Cancer Research

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    Green, L. J., Marder, P., Ray, C., Cook, C. A., Jaken, S., Musib, L. C., Herbst, R. S., Carducci, M., Britten, C. D., Basche, M., Eckhardt, S. G., & Thornton, D. (2006). Development and validation of a drug activity biomarker that shows target inhibition in cancer patients receiving enzastaurin, a novel protein kinase C-β inhibitor. Clinical Cancer Research, 12(11 I), 3408-3415. https://doi.org/10.1158/1078-0432.CCR-05-2231