Institution: | aCentre for Addiction and Mental Health, 250 College Street, Toronto, Ont., Canada M5T 1R8 bDepartment of Psychiatry, University of Toronto, 250 College Street, Toronto, Ont., Canada M5T 1R8 cLaro Chemicals, 218 Queens Quay W., Suite 902, Toronto, Ont., Canada M5J 2Y6 dDepartment of Medical Biophysics, University of Toronto, 1 King’s College Circle, Toronto, Ont., Canada M5S 1A8 eOntario Cancer Institute/Princess Margaret Hospital, 610 University Avenue, Toronto, Ont., Canada M5G 2M9 |
Abstract: | Protein kinase A (PKA) is an important signal transduction target for drug development because it influences critical cellular processes implicated in neuropsychiatric illnesses such as major depressive disorder. The goal of the present study was to develop the first imaging agent for measuring the levels of PKA with positron emission tomography (PET). By rational derivatization of 5-isoquinoline sulfonamides, it was found that the introduction of a methyl group to the sulphonamidic nitrogen on the known PKA inhibitors N-(2-aminoethyl)isoquinoline-5-sulfonamide (H-9, 1) and N-(2-(4-bromocinnamylamino)ethyl)isoquinoline-5-sulfonamide (H-89, 2), (yielding N-(2-aminoethyl)-N-methyl-isoquinoline-5-sulfonamide (4) and N-(2-(4-bromocinnamylamino)ethyl)-N-methyl-isoquinoline-5-sulfonamide (5), respectively) does not appreciably reduce in vitro potency toward PKA. We have facilitated the synthesis of 4 by reacting isoquinoline-5-sulfonyl chloride with N-methylethylenediamine (20% yield). Several techniques were used to thoroughly characterize 4 including multi (1H, 13C and 15N) NMR spectroscopy and X-ray crystallography. Compound 4 and 1-(4-bromophenyl)-1-propen-3-yl bromide were reacted to produce 5 in 16% yield. Compound 2 was reacted with 11C]CH3I to prepare N-(2-(4-bromocinnamylamino) ethyl)-N-11C]methyl-isoquinoline-5-sulfonamide (11C]5), with a decay-corrected radiochemical yield of 32%, based on 11C]CO2. 11C]5 was produced with >98% radiochemical purity and 1130 mCi/μmol specific activity after 40 min (end of synthesis). Conscious rats were administered 11C] 5 and sacrificed at 5, 15, 30 and 60 min after injection. Radioactivity from all excised brain regions was <0.2%ID/g at all time points. The modest brain penetration of 11C]5 may limit its use for studying PKA in the central nervous system. |