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Hayes TR, Chao CK, Blecha JE, Huynh TL, VanBrocklin HF, Zinn KR, Gerdes JM, Thompson CM. [ 11C]Paraoxon: Radiosynthesis, Biodistribution and In Vivo Positron Emission Tomography Imaging in Rat. J Pharmacol Exp Ther 2024; 388:333-346. [PMID: 37770203 PMCID: PMC10801775 DOI: 10.1124/jpet.123.001832] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2023] [Revised: 08/31/2023] [Accepted: 09/05/2023] [Indexed: 10/03/2023] Open
Abstract
Synthesis of the acetylcholinesterase inhibitor paraoxon (POX) as a carbon-11 positron emission tomography tracer ([11C]POX) and profiling in live rats is reported. Naïve rats intravenously injected with [11C]POX showed a rapid decrease in parent tracer to ∼1%, with an increase in radiolabeled serum proteins to 87% and red blood cells (RBCs) to 9%. Protein and RBC leveled over 60 minutes, reflecting covalent modification of proteins by [11C]POX. Ex vivo biodistribution and imaging profiles in naïve rats had the highest radioactivity levels in lung followed by heart and kidney, and brain and liver the lowest. Brain radioactivity levels were low but observed immediately after injection and persisted over the 60-minute experiment. This showed for the first time that even low POX exposures (∼200 ng tracer) can rapidly enter brain. Rats given an LD50 dose of nonradioactive paraoxon at the LD50 20 or 60 minutes prior to [11C]POX tracer revealed that protein pools were blocked. Blood radioactivity at 20 minutes was markedly lower than naïve levels due to rapid protein modification by nonradioactive POX; however, by 60 minutes the blood radioactivity returned to near naïve levels. Live rat tissue imaging-derived radioactivity values were 10%-37% of naïve levels in nonradioactive POX pretreated rats at 20 minutes, but by 60 minutes the area under the curve (AUC) values had recovered to 25%-80% of naïve. The live rat imaging supported blockade by nonradioactive POX pretreatment at 20 minutes and recovery of proteins by 60 minutes. SIGNIFICANCE STATEMENT: Paraoxon (POX) is an organophosphorus (OP) compound and a powerful prototype and substitute for OP chemical warfare agents (CWAs) such as sarin, VX, etc. To study the distribution and penetration of POX into the central nervous system (CNS) and other tissues, a positron emission tomography (PET) tracer analog, carbon-11-labeled paraoxon ([11C]POX), was prepared. Blood and tissue radioactivity levels in live rats demonstrated immediate penetration into the CNS and persistent radioactivity levels in tissues indicative of covalent target modification.
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Affiliation(s)
- Thomas R Hayes
- Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, Montana (C.-K.C., J.M.G., C.M.T.); Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, California (T.R.H., J.E.B., T.L.H., H.F.V.); and Departments of Radiology, Small Animal Clinical Sciences, and Biomedical Engineering and Institute for Quantitative Health Science and Engineering, Michigan State University, East Lansing, Michigan (K.R.Z.)
| | - Chih-Kai Chao
- Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, Montana (C.-K.C., J.M.G., C.M.T.); Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, California (T.R.H., J.E.B., T.L.H., H.F.V.); and Departments of Radiology, Small Animal Clinical Sciences, and Biomedical Engineering and Institute for Quantitative Health Science and Engineering, Michigan State University, East Lansing, Michigan (K.R.Z.)
| | - Joseph E Blecha
- Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, Montana (C.-K.C., J.M.G., C.M.T.); Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, California (T.R.H., J.E.B., T.L.H., H.F.V.); and Departments of Radiology, Small Animal Clinical Sciences, and Biomedical Engineering and Institute for Quantitative Health Science and Engineering, Michigan State University, East Lansing, Michigan (K.R.Z.)
| | - Tony L Huynh
- Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, Montana (C.-K.C., J.M.G., C.M.T.); Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, California (T.R.H., J.E.B., T.L.H., H.F.V.); and Departments of Radiology, Small Animal Clinical Sciences, and Biomedical Engineering and Institute for Quantitative Health Science and Engineering, Michigan State University, East Lansing, Michigan (K.R.Z.)
| | - Henry F VanBrocklin
- Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, Montana (C.-K.C., J.M.G., C.M.T.); Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, California (T.R.H., J.E.B., T.L.H., H.F.V.); and Departments of Radiology, Small Animal Clinical Sciences, and Biomedical Engineering and Institute for Quantitative Health Science and Engineering, Michigan State University, East Lansing, Michigan (K.R.Z.)
| | - Kurt R Zinn
- Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, Montana (C.-K.C., J.M.G., C.M.T.); Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, California (T.R.H., J.E.B., T.L.H., H.F.V.); and Departments of Radiology, Small Animal Clinical Sciences, and Biomedical Engineering and Institute for Quantitative Health Science and Engineering, Michigan State University, East Lansing, Michigan (K.R.Z.)
| | - John M Gerdes
- Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, Montana (C.-K.C., J.M.G., C.M.T.); Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, California (T.R.H., J.E.B., T.L.H., H.F.V.); and Departments of Radiology, Small Animal Clinical Sciences, and Biomedical Engineering and Institute for Quantitative Health Science and Engineering, Michigan State University, East Lansing, Michigan (K.R.Z.)
| | - Charles M Thompson
- Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, Montana (C.-K.C., J.M.G., C.M.T.); Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, California (T.R.H., J.E.B., T.L.H., H.F.V.); and Departments of Radiology, Small Animal Clinical Sciences, and Biomedical Engineering and Institute for Quantitative Health Science and Engineering, Michigan State University, East Lansing, Michigan (K.R.Z.)
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Hayes TR, Chao CK, Blecha JE, Huynh TL, Zinn KR, Thompson CM, Gerdes JM, VanBrocklin HF. Biological Distribution and Metabolic Profiles of Carbon-11 and Fluorine-18 Tracers of VX- and Sarin-Analogs in Sprague-Dawley Rats. Chem Res Toxicol 2020; 34:63-69. [PMID: 33373198 PMCID: PMC7818893 DOI: 10.1021/acs.chemrestox.0c00237] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Organophosphorus esters (OPs) were originally developed as pesticides but were repurposed as easily manufactured, inexpensive, and highly toxic chemical warfare agents. Acute OP toxicity is primarily due to inhibition of acetylcholinesterase (AChE), an enzyme in the central and peripheral nervous system. OP inhibition of AChE can be reversed using oxime reactivators but many show poor CNS penetration, indicating a need for new clinically viable reactivators. However, challenges exist on how to best measure restored AChE activity in vivo and assess the reactivating agent efficacy. This work reports the development of molecular imaging tools using radiolabeled OP analog tracers that are less toxic to handle in the laboratory, yet inhibit AChE in a similar fashion to the actual OPs. Carbon-11 and fluorine-18 radiolabeled analog tracers of VX and sarin OP agents were prepared. Following intravenous injection in normal Sprague-Dawley rats (n = 3-4/tracer), the tracers were evaluated and compared using noninvasive microPET/CT imaging, biodistribution assay, and arterial blood analyses. All showed rapid uptake and stable retention in brain, heart, liver, and kidney tissues determined by imaging and biodistribution. Lung uptake of the sarin analog tracers was elevated, 2-fold and 4-fold higher uptake at 5 and 30 min, respectively, compared to that for the VX analog tracers. All tracers rapidly bound to red blood cells (RBC) and blood proteins as measured in the biodistribution and arterial blood samples. Analysis of the plasma soluble activity (nonprotein/cell bound activity) showed only 1-6% parent tracer and 88-95% of the activity in the combined solid fractions (RBC and protein bound) as early as 0.5 min post injection. Multivariate analysis of tracer production yield, molar activity, brain uptake, brain area under the curve over 0-15 min, and the amount of parent tracer in the plasma at 5 min revealed the [18F]VX analog tracer had the most favorable values for each metric. This tracer was considered the more optimal tracer relative to the other tracers studied and suitable for future in vivo OP exposure and reactivation studies.
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Affiliation(s)
- Thomas R Hayes
- Department of Radiology and Biomedical Imaging, University of California at San Francisco, San Francisco, California 94143, United States
| | - Chih-Kai Chao
- Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, Montana 59812, United States
| | - Joseph E Blecha
- Department of Radiology and Biomedical Imaging, University of California at San Francisco, San Francisco, California 94143, United States
| | - Tony L Huynh
- Department of Radiology and Biomedical Imaging, University of California at San Francisco, San Francisco, California 94143, United States
| | - Kurt R Zinn
- Departments of Radiology, Small Animal Clinical Sciences, and Biomedical Engineering; Institute for Quantitative Health Science and Engineering, Michigan State University, East Lansing, Michigan 48824, United States
| | - Charles M Thompson
- Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, Montana 59812, United States
| | - John M Gerdes
- Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, Montana 59812, United States
| | - Henry F VanBrocklin
- Department of Radiology and Biomedical Imaging, University of California at San Francisco, San Francisco, California 94143, United States
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Hayes TR, Blecha JE, Thompson CM, Gerdes JM, VanBrocklin HF. Divergent synthesis of organophosphate [ 11C]VX- and [ 11C]Sarin-surrogates from a common set of starting materials. Appl Radiat Isot 2019; 151:182-186. [PMID: 31202183 DOI: 10.1016/j.apradiso.2019.05.033] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2019] [Revised: 05/09/2019] [Accepted: 05/23/2019] [Indexed: 11/27/2022]
Abstract
Radiolabeled 1-[11C]ethyl, 4-nitrophenyl methylphosphonate (VX surrogate) and 2-[11C]-propanyl, 4-nitrophenyl methylphosphonate (sarin surrogate) were developed as organophosphate (OP) tracers. The [11C]ethyl- and [11C]isopropyl-iodide radiolabeled synthons were obtained by temperature controlled, in loop reactions of [11C]CO2 with MeMgBr followed by reduction with LiAlH4, then reaction with HI. Distillation of the [11C]alkyl iodides into a solution of hydrogen (4-nitrophenyl)methylphosphonate and cesium carbonate afforded the desired tracers in >95% radiochemical purity, yields from [11C]CO2 of 1-3% and 1.7-15.1 GBq/mmol molar activities.
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Affiliation(s)
- Thomas R Hayes
- Department of Radiology and Biomedical Imaging, University of California - San Francisco, 185 Berry St. Suite 350, San Francisco, CA, 94107, United States
| | - Joseph E Blecha
- Department of Radiology and Biomedical Imaging, University of California - San Francisco, 185 Berry St. Suite 350, San Francisco, CA, 94107, United States
| | - Charles M Thompson
- Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, MT, 59812, United States
| | - John M Gerdes
- Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, MT, 59812, United States
| | - Henry F VanBrocklin
- Department of Radiology and Biomedical Imaging, University of California - San Francisco, 185 Berry St. Suite 350, San Francisco, CA, 94107, United States.
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Thompson CM, Gerdes JM, VanBrocklin HF. Positron emission tomography studies of organophosphate chemical threats and oxime countermeasures. Neurobiol Dis 2019; 133:104455. [PMID: 31022458 DOI: 10.1016/j.nbd.2019.04.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2018] [Revised: 03/28/2019] [Accepted: 04/19/2019] [Indexed: 01/31/2023] Open
Abstract
There is a unique in vivo interplay involving the mechanism of inactivation of acetylcholinesterase (AChE) by toxic organophosphorus (OP) compounds and the restoration of AChE activity by oxime antidotes. OP compounds form covalent adducts to this critical enzyme target and oximes are introduced to directly displace the OP from AChE. For the most part, the in vivo inactivation of AChE leading to neurotoxicity and antidote-based therapeutic reversal of this mechanism are well understood, however, these molecular-level events have not been evaluated by dynamic imaging in living systems at millimeter resolution. A deeper understanding of these critically, time-dependent mechanisms is needed to develop new countermeasures. To address this void and to help accelerate the development of new countermeasures, positron-emission tomography (PET) has been investigated as a unique opportunity to create platform technologies to directly examine the interdependent toxicokinetic/pharmacokinetic and toxicodynamic/pharmacodynamic features of OPs and oximes in real time within live animals. This review will cover two first-in-class PET tracers representing an OP and an oxime antidote, including their preparation, requisite pharmacologic investigations, mechanistic interpretations, biodistribution and imaging.
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Affiliation(s)
- Charles M Thompson
- Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, MT 59812, USA.
| | - John M Gerdes
- Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, MT 59812, USA
| | - Henry F VanBrocklin
- Department of Radiology and Biomedical Imaging, University of California, San Francisco 185 Berry St. Suite 350, San Francisco, CA 94107, USA
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