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Clinical Investigation |
1 Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania; 2 Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, Tennessee; 3 Department of Neurology, Alzheimer's Disease Center, and Center of Excellence for Research on Neurodegenerative Diseases, University of Pennsylvania, Philadelphia, Pennsylvania; and 4 Avid Radiopharmaceuticals, Inc., Philadelphia, Pennsylvania
Correspondence: For correspondence or reprints contact: Andrew B. Newberg, 110 Donner Building, H.U.P., 3400 Spruce St., Philadelphia, PA 19104. E-mail: andrew.newberg{at}uphs.upenn.edu
123I-IMPY (6-iodo-2-(4'-dimethylamino-)phenyl-imidazo[1,2-a]pyridine) is a novel radiopharmaceutical that selectively binds to Alzheimer's disease (AD) amyloid plaques. As a first step toward validating this radiopharmaceutical as an imaging biomarker for AD, we measured the whole-body biokinetics and radiation dosimetry of 123I-IMPY in AD patients and cognitively normal control subjects. The pharmacologic safety profile of the compound was simultaneously assessed. Methods: The sample included 9 subjects ranging in age from 44 to 80 y. Whole-body images were obtained for each subject (mean ± SD, 9.0 ± 3.2 scans per subject) for up to 48 h after the intravenous administration of 185 MBq (5 mCi) of 123I-IMPY. The fraction of administered activity in 12 regions of interest was quantified from the attenuation-corrected geometric mean counts in conjugate views. Multiexponential functions were iteratively fit to each time–activity curve using a nonlinear, least-squares regression algorithm. These curves were numerically integrated to yield cumulated activity values for source organs. Radiation doses were then estimated with the MIRD technique. Results: The radiotracer had no pharmacologic effects (produced no changes in heart rate, blood pressure, or laboratory results) on any of the subjects. Radiation dosimetry estimates indicated that the dose-limiting organ was the gallbladder, which received an average of 0.135 mGy/MBq (range, 0.075–0.198 mGy/MBq). The effective dose equivalent and effective dose for 123I-IMPY were 0.042 ± 0.003 mSv/MBq and 0.035 ± 0.001 mSv/MBq, respectively. The mean effective dose for 123I-IMPY was similar to that for 111In-diethylenetriaminepentaacetic acid (0.035 mGy/MBq), less than half that for 111In-pentetreotide (0.81 mGy/MBq), and approximately twice that for 123I-IMP (0.018 mGy/MBq). No significant differences were found between men and women or between AD patients and control subjects. Conclusion: 123I-IMPY may be a safe radiotracer with appropriate biokinetics for imaging amyloid plaques in AD patients.
Key Words: neurology • 123I-IMPY • amyloid plaque • Alzheimer's disease • dosimetry • SPECT
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