A platelet biomarker for assessing phosphoinositide 3-kinase inhibition during cancer chemotherapy

• Published in: Molecular cancer therapeutics Vol. 6; no. 9; pp. 2600 - 2607
• Main Authors: Bowers, Rita K, Marder, Philip, Green, Lisa J, Horn, Candice L, Faber, Andrew L, Thomas, James E
• Format: Journal Article
• Language: English
• Published: United States American Association for Cancer Research 01.09.2007
• Subjects: Androstadienes - pharmacology; Animals; biomarkers; Blood Platelets - drug effects; Blood Platelets - enzymology; Chromones - pharmacology; Enzyme Inhibitors - pharmacology; Female; Flow Cytometry; Humans; Mice; Mice, Nude; Morpholines - pharmacology; Neoplasms - drug therapy; Neoplasms - enzymology; Neoplasms - pathology; Phosphatidylinositol 3-Kinases - antagonists & inhibitors; Phosphatidylinositol 3-Kinases - metabolism; phosphoinositide 3-kinase; Phosphorylation - drug effects; Platelet Activation - drug effects; platelets; Receptor, PAR-1 - metabolism; Signal Transduction; Transplantation, Heterologous; wortmannin
• ISSN: 1535-7163; 1538-8514
• DOI: 10.1158/1535-7163.MCT-06-0746

Thrombin cleavages of selective proteinase-activated receptors (PAR) as well as PAR-activating peptide ligands can initiate the phosphoinositide 3-kinase (PI3K) signaling cascade in platelets. Downstream to this event, fibrinogen receptors on platelets undergo conformational changes that enhance fibrinogen binding. In our study, we used this phenomenon as a surrogate biomarker for assessing effects on PI3K activity. Our method, using flow cytometric measurement of fluorescent ligand and antibody binding, uncovered a 16- to 45-fold signal window after PAR-induced platelet activation. Pretreatment ( in vitro ) with the PI3K inhibitors wortmannin and LY294002 resulted in concentration-dependent inhibition at predicted potencies. In addition, platelets taken from mice treated with wortmannin were blocked from PAR-induced ex vivo activation concomitantly with a decrease in phosphorylation of AKT from excised tumor xenografts. This surrogate biomarker assay was successfully tested ( in vitro ) on blood specimens received from volunteer cancer patients. Our results indicate that measurement of platelet activation could serve as an effective drug activity biomarker during clinical evaluation of putative PI3K inhibitors. [Mol Cancer Ther 2007;6(9):2600–7]