RESUMEN
The 2-[(18)F]fluoro-3-pent-4-yn-1-yloxypyridine ([(18)F]FPyKYNE) analog of the potent non-peptide angiotensin II type 1 receptor (AT1R) blocker losartan was produced via click chemistry linking [(18)F]FPyKYNE to azide-modified tetrazole-protected losartan followed by TFA deprotection. Preliminary small animal imaging with positron emission tomography (PET) in rats displayed high uptake in the kidneys with good contrast to surrounding tissue. Rat metabolism displayed the presence of 23% unchanged tracer in plasma at 30 min. Upon co-administration with AT1R blocker candesartan (2.5, 5 and 10 mg/kg), a dose-dependent reduction (47-65%) in tracer uptake was observed in the kidney, while no difference was observed following AT2R blocker PD123,319 (5 mg/kg), indicating binding selectivity for AT1R over AT2R and potential for imaging AT1R using PET.
Asunto(s)
Bloqueadores del Receptor Tipo 1 de Angiotensina II/síntesis química , Losartán/química , Receptor de Angiotensina Tipo 1/química , Bloqueadores del Receptor Tipo 1 de Angiotensina II/química , Bloqueadores del Receptor Tipo 1 de Angiotensina II/farmacología , Animales , Bencimidazoles/farmacología , Compuestos de Bifenilo , Radioisótopos de Flúor/química , Riñón/diagnóstico por imagen , Riñón/efectos de los fármacos , Riñón/metabolismo , Losartán/síntesis química , Losartán/farmacología , Masculino , Tomografía de Emisión de Positrones , Piridinas/química , Radiofármacos/síntesis química , Radiofármacos/química , Ratas , Ratas Sprague-Dawley , Receptor de Angiotensina Tipo 1/metabolismo , Tetrazoles/química , Tetrazoles/farmacologíaRESUMEN
Most physiologic effects of the renin angiotensin system (RAS) are mediated via the angiotensin (Ang) type 1 receptor (AT1R). The 18F-FPyKYNE derivative of the clinically used AT1R blocker losartan exhibits high binding selectivity for kidney AT1R and rapid metabolism in rats. The aim of this study was to further assess the binding profile of this novel PET agent for imaging AT1R in rats and pigs. METHODS: In vitro binding assays were performed with 18F-FPyKYNE-losartan in rat kidneys. Male Sprague-Dawley rats were used to assess dosimetry, antagonistic efficacy via blood pressure measurements, and presence of labeled metabolites in kidneys. Test-retest PET imaging, blocking with AT1R antagonist candesartan (10 mg/kg), and plasma metabolism analysis were performed in female Yorkshire pigs. RESULTS: 18F-FPyKYNE-losartan bound with high affinity (dissociation constant of 49.4 ± 18.0 nM and maximal binding of 348 ± 112 fmol/mm2) to rat kidney AT1R. It bound strongly to plasma proteins in rats (97%), and its labeled metabolites displayed minimal interference on renal AT1R binding. FPyKYNE-losartan fully antagonized the Ang II pressor effect, albeit with 4-fold potency reduction (the effective dose inhibiting 50% of the Ang II-induced maximal pressor response of 25.5 mg/kg) relative to losartan. PET imaging exhibited high kidney-to-blood contrast and slow renal clearance, with an SUV of 14.1 ± 6.2. Excellent reproducibility was observed in the calculated test-retest variability (7.2% ± 0.75%). Only hydrophilic-labeled metabolites were present in plasma samples, and renal retention was reduced (-60%) at 10-15 min after blockade with candesartan. CONCLUSION: 18F-FPyKYNE-losartan has a favorable binding profile and displays high potential for translational work in humans as an AT1R PET imaging agent.