title: A platelet biomarker for assessing phosphoinositide 3-kinase inhibition during cancer chemotherapy.
abstract: 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.
authors.affiliation: Lilly Research Laboratories, Indianapolis, Indiana, USA . bowers_rita_k@lilly.com
authors.forename: Rita K
authors.initials: RK
authors.lastname: Bowers
authors.forename: Philip
authors.initials: P
authors.lastname: Marder
authors.forename: Lisa J
authors.initials: LJ
authors.lastname: Green
authors.forename: Candice L
authors.initials: CL
authors.lastname: Horn
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Faber
authors.forename: James E
authors.initials: JE
authors.lastname: Thomas
mesh_terms: D000730:Androstadienes / Q000494:pharmacology*; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects* / Q000201:enzymology; D002867:Chromones / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009025:Morpholines / Q000494:pharmacology*; D009369:Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D015539:Platelet Activation / Q000187:drug effects*; D044463:Receptor, PAR-1 / Q000378:metabolism; D015398:Signal Transduction; D014183:Transplantation, Heterologous; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D002867:Chromones; D004791:Enzyme Inhibitors; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D044463:Receptor, PAR-1; D000077191:Wortmannin; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one