title: The potential of enzastaurin to enhance platelet aggregation and growth factor secretion: implications for cancer cell survival.
abstract: BACKGROUND
  Enzastaurin is a protein kinase C (PKC)β inhibitor with antiproliferative and proapoptotic effects that was in clinical development for the treatment of a variety of cancers. However, the primary endpoints in several clinical trials of enzastaurin were not met, and thrombosis was reported as an adverse effect in some trials. While investigating the role of PKC in regulating growth factor release from platelets, we found that, unlike other PKC inhibitors, enzastaurin may potentiate platelet aggregation.
  
  
  OBJECTIVE
  To investigate the effects of enzastaurin on platelet aggregation, growth factor secretion from α-granules and cancer cell apoptosis in the presence of platelets.
  
  
  METHODS
  Prostacyclin-washed platelets and platelet-rich plasma were isolated from the blood of healthy human volunteers. Platelet light-aggregometry was performed in the presence and absence of enzastaurin and acetylsalicylic acid (ASA). P-selectin was measured by flow cytometry, and vascular endothelial growth factor (VEGF) release was measured by ELISA. A549 lung carcinoma cells were treated with releasates from enzastaurin-titrated platelets. A cell death ELISA was performed to measure A549 apoptosis.
  
  
  CONCLUSIONS
  Enzastaurin (10(-8) -10(-6)  m) potentiated aggregation of prostacyclin-washed platelets and caused an increase in VEGF release from α-granules that, in turn, promoted cancer cell survival. In platelet-rich plasma, 10(-6)  m enzastaurin inhibited platelet aggregation, but not 10(-7)  m enzastaurin, which also failed to suppress VEGF secretion. ASA abrogated enzastaurin-potentiated washed-platelet aggregation and VEGF release. These findings indicate that, at high plasma protein-free drug concentrations, enzastaurin potentiates platelet aggregation and growth factor secretion, an effect that may counteract its anticancer activity. ASA nullifies this effect.
authors.affiliation: Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, AB, Canada.|Cardiovascular Research Centre, University of Alberta, Edmonton, AB, Canada.
authors.forename: G
authors.initials: G
authors.lastname: Lesyk
authors.affiliation: Department of Pharmacology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada.
authors.forename: T
authors.initials: T
authors.lastname: Fong
authors.affiliation: Department of Leukemia Research, MD Anderson Cancer Center, University of Texas, Houston, TX, USA.
authors.forename: P P
authors.initials: PP
authors.lastname: Ruvolo
authors.affiliation: Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, AB, Canada.|Cardiovascular Research Centre, University of Alberta, Edmonton, AB, Canada.|Department of Pharmacology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada.|Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, AB, Canada.
authors.forename: P
authors.initials: P
authors.lastname: Jurasz
mesh_terms: D000970:Antineoplastic Agents / Q000633:toxicity*; D017209:Apoptosis / Q000187:drug effects; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007211:Indoles / Q000633:toxicity*; D008175:Lung Neoplasms / Q000188:drug therapy / Q000201:enzymology / Q000473:pathology; D010974:Platelet Aggregation / Q000187:drug effects*; D064546:Protein Kinase C beta / Q000037:antagonists & inhibitors / Q000097:blood; D047428:Protein Kinase Inhibitors / Q000633:toxicity*; D022142:Secretory Vesicles / Q000187:drug effects / Q000378:metabolism; D013997:Time Factors; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D007211:Indoles; D047428:Protein Kinase Inhibitors; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; C579054:PRKCB protein, human; D064546:Protein Kinase C beta; C504878:enzastaurin
keywords: drug therapy; neoplasms; pharmacology; platelet aggregation; vascular endothelial growth factor A