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Purpose: Plastics are used commonly in the world because of its convenience and cost-effectiveness. Microplastics, an environmental threat and human health risk, are widely detected in food, and consequently ingested. However degraded plastics are found everywhere, which cause environmental threat and human health risk. Therefore, real-time monitoring of orally administered microplastics is tremendously important to trace them in the body. Methods: In this study, to visualize their absorption path, we labeled polystyrene with [64Cu]Cu-DOTA. We prepared radiolabeled polystyrene with 64Cu after, [64Cu]Cu-DOTA-polystyrene was then orally administered to mice and evaluate its transit and absorption in mice using PET imaging. The absorption path and distribution of [64Cu]Cu-DOTA-polystyrene were determined using positron emission tomography (PET) over 48 h. Ex vivo tissue-radio thin-layer chromatography (Ex vivo-radioTLC) was used to demonstrate the existence of [64Cu]Cu-DOTA-polystyrene in tissue. Results: PET images demonstrated that [64Cu]Cu-DOTA-polystyrene began to transit to the intestine within 1 h. [64Cu]Cu-DOTA-polystyrene accumulation in the liver was also observed. Biodistribution of [64Cu]Cu-DOTA-polystyrene confirmed the observed distribution of [64Cu]Cu-DOTA-polystyrene from PET images. Ex vivo-radioTLC was used to demonstrate that the detected gamma rays originated from [64Cu]Cu-DOTA-polystyrene. Conclusion: This study provided evidence of microplastic accumulation and existence in tissue by using PET imaging, and cross confirmed by ex vivo-radioTLC. The information provided may be used as the basis for future studies on the toxicity of microplastics.

The epidermal growth factor receptor (EGFR) is a member of the erbB family of receptors and is overexpressed in many tumor types. A repebody is a newly designed nonantibody protein scaffold for tumor targeting that contains leucine-rich repeat modules. In this study, 3 64Cu-labeled anti-EGFR repebodies with different chelators were synthesized, and their biologic characteristics were assessed in cultured cells and tumor-bearing mice. Methods: Repebodies were synthesized with the chelators 2-(p-isothiocyanatobenzyl)-1,4,7-triazacyclononane-N,N',N,″-triacetic acid trihydrochloride ([p-SCN-Bn]-NOTA), 2,2',2″-(10-(2-(2,5-dioxopyrrolidin-1-yloxy)-2-oxoethyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl) triacetic acid (DOTA-N-hydroxysuccinimide ester), or 1-(p-isothiocyanatobenzyl)diethylenetriamine pentaacetic acid trihydrochloride ([p-SCN-Bn]-DTPA) in 1.0 M NaHCO3 buffer (pH 9.2) for 24 h. Purified NOTA-, DOTA-, and DTPA-conjugated repebody were radiolabeled with 64Cu in 0.1 M NH4OAc buffer (pH 5.5). To compare the EGFR-binding affinities of the repebodies, cellular uptake studies were performed with the human non-small cell lung cancer cell line H1650 (high expression of EGFR) and the human colon adenocarcinoma cell line SW620 (low expression of EGFR). Biodistribution and small-animal PET imaging studies were performed using H1650 tumor-bearing mice. Results: Radiochemical yields of the 64Cu-labeled repebodies were approximately 70%-80%. Cellular uptake of the NOTA-, DOTA-, and DTPA-repebodies was over 4-fold higher in H1650 cells than in SW620 cells at 1 h. The 3 repebodies had accumulated specifically in H1650 tumor-bearing nude mice by 1 h after intravenous injection and were retained for over 24 h, as measured by the percentage injected dose per gram of tissue (%ID/g). Tumor uptake of all repebodies increased from 1 to 6 h (at 1 h, 6.28, 8.46, and 6.91 %ID/g for NOTA-, DOTA-, and DTPA-repebody, respectively; at 6 h, 9.4, 8.28, and 10.1 %ID/g, respectively). H1650 tumors were clearly visible after injection of each repebody, with high tumor-to-background ratios (at 1 h, 3.43, 4.89, and 2.38 for NOTA-, DOTA-, and DTPA-repebody, respectively; at 6 h, 3.05, 4.36, and 2.08; at 24 h, 3.81, 4.58, and 2.86). Conclusion: The 3 64Cu-repebody complexes demonstrated specific and rapid uptake in EGFR-expressing tumors within 1 h and may have potential as novel EGFR imaging agents for PET.