RT Journal Article
SR Electronic
T1 In Vitro and In Vivo Evidence for Active Brain Uptake of the GHB Analog HOCPCA by the Monocarboxylate Transporter Subtype 1
JF Journal of Pharmacology and Experimental Therapeutics
JO J Pharmacol Exp Ther
FD American Society for Pharmacology and Experimental Therapeutics
SP 166
OP 174
DO 10.1124/jpet.115.224543
VO 354
IS 2
A1 Louise Thiesen
A1 Jan Kehler
A1 Rasmus P. Clausen
A1 Bente Frølund
A1 Christoffer Bundgaard
A1 Petrine Wellendorph
YR 2015
UL http://jpet.aspetjournals.org/content/354/2/166.abstract
AB γ-Hydroxybutyric acid (GHB) is a recreational drug, a clinically prescribed drug in narcolepsy and alcohol dependence, and an endogenous substance that binds to both high- and low-affinity sites in the brain. For studying the molecular mechanisms and the biologic role of the GHB high-affinity binding sites, ligands with high and specific affinity are essential. The conformationally restricted GHB analog HOCPCA (3-hydroxycyclopent-1-enecarboxylic acid) is one such compound. The objective of this study was to investigate the transport of HOCPCA across the blood-brain barrier in vitro and in vivo and to investigate the hypothesis that HOCPCA, like GHB, is a substrate for the monocarboxylate transporters (MCTs). For in vitro uptake studies, MCT1, -2, and -4 were recombinantly expressed in Xenopus laevis oocytes, and the previously reported radioligand [3H]HOCPCA was used as substrate. HOCPCA inhibited the uptake of the endogenous MCT substrate l-[14C]lactate, and [3H]HOCPCA was shown to act as substrate for MCT1 and 2 (Km values in the low- to mid-millimolar range). Introducing single-point amino acid mutations into positions essential for MCT function supported that HOCPCA binds to the endogenous substrate pocket of MCTs. MCT1-mediated brain entry of HOCPCA (10 mg/kg s.c.) was further confirmed in vivo in mice by coadministration of increasing doses of the MCT inhibitor AR-C141990 [(R)-5-(3-hydroxypyrrolidine-1-carbonyl)-1-isobutyl-3-methyl-6-(quinolin-4-ylmethyl)thieno[2,3-d]pyrimidine-2,4(1H,3H)-dione], which inhibited brain penetration of HOCPCA in a dose-dependent manner (ID50 = 4.6 mg/kg). Overall, our study provides evidence that MCT1 is an important brain entry site for HOCPCA and qualifies for future in vivo studies with HOCPCA.