In vivo administration of the anticancer agent bryostatin 1 activates platelets and neutrophils and modulates protein kinase C activity.
Bryostatin 1 is a naturally occurring macrocyclic lactone which when applied to cells in culture activates protein kinase C (PKC). In vivo bryostatin 1 functions as an anticancer agent with activity against murine lymphomas, leukemias, and melanoma. Because all organs and tissues contain PKC, normal cells would also be a likely target for this agent. Here we demonstrate that in vivo administration of bryostatin 1 activates platelets over a dose range of 0.4 to 40 micrograms/kg with half-maximal activation occurring at 3 micrograms/kg and stimulation of neutrophils over a similar dose range. This in vivo activation of neutrophils is associated with a rapid decrease in measurable cytosolic PKC, a finding consistent with translocation of the enzyme to the membrane. In contrast, no statistically significant change in PKC location was found in liver, spleen, brain, or L10A B-cell lymphoma. However, in culture the L10A lymphoma did respond to bryostatin 1 with translocation of PKC. To evaluate whether the lack of effect of bryostatin 1 on PKC in organs was secondary to rapid degradation, we developed a bioassay to measure the levels of bryostatin 1 in the blood. To measure the presence of bryostatin 1, human neutrophils were incubated with plasma from mice given injections of different concentrations of bryostatin 1. Using this assay, bryostatin 1 at levels as low as 60 nM could be measured in the plasma. A time course with this bioassay demonstrated that less than 10% of the bryostatin 1 injected was detectable after 2.5 min. These results demonstrate that bryostatin 1 is capable of activating platelets and neutrophils and modulating PKC in vivo. The lack of effect of bryostatin 1 on specific organs may be secondary to the rapid clearance/degradation of this compound from the blood.
Division of Hematology/Oncology, University of Alabama, Birmingham 35294.
R L
RL
Berkow
L
L
Schlabach
R
R
Dodson
W H
WH
Benjamin
G R
GR
Pettit
P
P
Rustagi
A S
AS
Kraft
D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D001792:Blood Platelets / Q000187:drug effects / Q000201:enzymology; D054713:Bryostatins; D004789:Enzyme Activation / Q000187:drug effects; D007275:Injections, Intravenous; D007783:Lactones / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D016393:Lymphoma, B-Cell / Q000201:enzymology; D018942:Macrolides; D051379:Mice; D008810:Mice, Inbred C57BL; D009504:Neutrophils / Q000187:drug effects* / Q000502:physiology; D015539:Platelet Activation / Q000187:drug effects*; D011493:Protein Kinase C / Q000096:biosynthesis*; D016897:Respiratory Burst / Q000187:drug effects
D000970:Antineoplastic Agents; D054713:Bryostatins; D007783:Lactones; D018942:Macrolides; C046785:bryostatin 1; D011493:Protein Kinase C