Behaviour of [11C]R(-)- and [11C]S(+)-rolipram in vitro and in vivo, and their use as PET radiotracers for the quantificative assay of PDE4.
Cyclic AMP (cAMP) is a continually produced nucleotide which is inactivated by hydrolysis to 5'AMP via phosphodiesterase 4 (PDE4) enzymes. Rolipram is a selective PDE4 inhibitor which exists in two enantiomeric forms, R(-) and S(+). Both of these enantiomers have previously been labelled with carbon-11 and used as positron emission tomography (PET) ligands for measuring PDE4 expression and function, and indirectly to explore the function of the cAMP second messenger, in vivo, using PET. The aim of these studies was to relate the in vitro affinities of the two rolipram enantiomers using standard pharmacological assays with the in vivo behaviour of the two enantiomers using PET. In vitro competition assays were performed using rat cortical membranes and [(3)H]R(-)- and [(3)H]S(+)-rolipram with increasing concentrations of either unlabelled R(-)- or S(+)-rolipram. In vivo, a series of PET studies were performed in the porcine brain using [(11)C]R(-)-rolipram with co-administration of increasing doses of either unlabelled R(-)- or S(+)-rolipram. Additional in vivo PET studies were performed using [(11)C]S(+)-rolipram with saturating doses of rolipram. In all studies, R(-)-rolipram exhibited a higher affinity for the PDE4 enzyme than S(+)-rolipram. The calculated affinity ratios were 7.97 from the in vitro studies; 12.5 from the in vivo studies using [(11)C]R(-)-rolipram; and 14.7 from the in vivo studies using [(11)C]S(+)-rolipram. To conclude, the in vitro affinities of R(-)- and S(+)-rolipram predict their apparent in vivo behaviour in the porcine brain, as measured by PET.
Parker
Christine A
CA
GlaxoSmithKline, ACCI Addenbrooke's Hospital, Hills Road, Cambridge, CB2 2GG, UK. Christine.2.Parker@gsk.com
Matthews
Julian C
JC
Gunn
Roger N
RN
Martarello
Laurent
L
Cunningham
Vincent J
VJ
Dommett
David
D
Knibb
Stephen T
ST
Bender
Dirk
D
Jakobsen
Steen
S
Brown
John
J
Gee
Antony D
AD
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000032:analysis* / Q000378:metabolism*; D000345:Affinity Labels / Q000378:metabolism / Q000493:pharmacokinetics; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects / Q000502:physiology; D001921:Brain / Q000033:anatomy & histology / Q000187:drug effects / Q000201:enzymology*; D002250:Carbon Radioisotopes; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4; D066298:In Vitro Techniques; D008297:Male; D010726:Phosphodiesterase Inhibitors / Q000378:metabolism* / Q000493:pharmacokinetics; D049268:Positron-Emission Tomography / Q000379:methods*; D051381:Rats; D017207:Rats, Sprague-Dawley; D020889:Rolipram / Q000378:metabolism* / Q000493:pharmacokinetics; D013237:Stereoisomerism; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D034421:Sus scrofa
D000345:Affinity Labels; D002250:Carbon Radioisotopes; D010726:Phosphodiesterase Inhibitors; D000242:Cyclic AMP; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4; D020889:Rolipram