Efflux transporters at the blood-brain barrier limit delivery and efficacy of cyclin-dependent kinase 4/6 inhibitor palbociclib (PD-0332991) in an orthotopic brain tumor model.
6-Acetyl-8-cyclopentyl-5-methyl-2-([5-(piperazin-1-yl)pyridin-2-yl]amino)pyrido(2,3-d)pyrimidin-7(8H)-one [palbociclib (PD-0332991)] is a cyclin-dependent kinase 4/6 inhibitor approved for the treatment of metastatic breast cancer and is currently undergoing clinical trials for many solid tumors. Glioblastoma (GBM) is the most common primary brain tumor in adults and has limited treatment options. The cyclin-dependent kinase 4/6 pathway is commonly dysregulated in GBM and is a promising target in treating this devastating disease. The blood-brain barrier (BBB) limits the delivery of drugs to invasive regions of GBM, where the efflux transporters P-glycoprotein and breast cancer resistance protein can prevent treatments from reaching the tumor. The purpose of this study was to examine the mechanisms limiting the effectiveness of palbociclib therapy in an orthotopic xenograft model. The in vitro intracellular accumulation results demonstrated that palbociclib is a substrate for both P-glycoprotein and breast cancer resistance protein. In vivo studies in transgenic mice confirmed that efflux transport is responsible for the limited brain distribution of palbociclib. There was an ∼115-fold increase in brain exposure at steady state in the transporter deficient mice when compared with wild-type mice, and the efflux inhibitor elacridar significantly increased palbociclib brain distribution. Efficacy studies demonstrated that palbociclib is an effective therapy when GBM22 tumor cells are implanted in the flank, but ineffective in an orthotopic (intracranial) model. Moreover, doses designed to mimic brain exposure were ineffective in treating flank tumors. These results demonstrate that efflux transport in the BBB is involved in limiting the brain distribution of palbociclib and this has critical implications in determining effective dosing regimens of palbociclib therapy in the treatment of brain tumors.
Department of Pharmaceutics, Brain Barriers Research Center, University of Minnesota, Minneapolis, Minnesota (K.E.P., R.K.M., W.F.E.); and Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota (J.P., K.B., J.N.S.).
Karen E
KE
Parrish
Department of Pharmaceutics, Brain Barriers Research Center, University of Minnesota, Minneapolis, Minnesota (K.E.P., R.K.M., W.F.E.); and Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota (J.P., K.B., J.N.S.).
Jenny
J
Pokorny
Department of Pharmaceutics, Brain Barriers Research Center, University of Minnesota, Minneapolis, Minnesota (K.E.P., R.K.M., W.F.E.); and Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota (J.P., K.B., J.N.S.).
Rajendar K
RK
Mittapalli
Department of Pharmaceutics, Brain Barriers Research Center, University of Minnesota, Minneapolis, Minnesota (K.E.P., R.K.M., W.F.E.); and Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota (J.P., K.B., J.N.S.).
Katrina
K
Bakken
Department of Pharmaceutics, Brain Barriers Research Center, University of Minnesota, Minneapolis, Minnesota (K.E.P., R.K.M., W.F.E.); and Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota (J.P., K.B., J.N.S.).
Jann N
JN
Sarkaria
Department of Pharmaceutics, Brain Barriers Research Center, University of Minnesota, Minneapolis, Minnesota (K.E.P., R.K.M., W.F.E.); and Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota (J.P., K.B., J.N.S.) elmqu011@umn.edu.
William F
WF
Elmquist
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism*; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000166:Acridines / Q000494:pharmacology; D000818:Animals; D000970:Antineoplastic Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D001812:Blood-Brain Barrier / Q000378:metabolism*; D001932:Brain Neoplasms / Q000188:drug therapy / Q000378:metabolism*; D045744:Cell Line, Tumor; D051358:Cyclin-Dependent Kinase 4 / Q000037:antagonists & inhibitors*; D051361:Cyclin-Dependent Kinase 6 / Q000037:antagonists & inhibitors*; D004285:Dogs; D019008:Drug Resistance, Neoplasm; D004357:Drug Synergism; D005260:Female; D005909:Glioblastoma / Q000188:drug therapy / Q000378:metabolism*; D064593:Heterografts; D061985:Madin Darby Canine Kidney Cells; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D010879:Piperazines / Q000493:pharmacokinetics / Q000494:pharmacology*; D011725:Pyridines / Q000493:pharmacokinetics / Q000494:pharmacology*; D044005:Tetrahydroisoquinolines / Q000494:pharmacology
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; C501412:Abcg2 protein, mouse; D000166:Acridines; D000970:Antineoplastic Agents; D010879:Piperazines; D011725:Pyridines; D044005:Tetrahydroisoquinolines; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; C500026:palbociclib; C083501:Elacridar