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. 2020 Oct 20;10(63):38601-38611.
doi: 10.1039/d0ra04494f. eCollection 2020 Oct 15.

Deuteration versus ethylation - strategies to improve the metabolic fate of an 18F-labeled celecoxib derivative

Markus Laube  1 , Cemena Gassner  1   2 , Christin Neuber  1 , Robert Wodtke  1 , Martin Ullrich  1 , Cathleen Haase-Kohn  1 , Reik Löser  1 , Martin Köckerling  3 , Klaus Kopka  1 , Torsten Kniess  1 , Evamarie Hey-Hawkins  4 , Jens Pietzsch  1   2
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Deuteration versus ethylation - strategies to improve the metabolic fate of an 18F-labeled celecoxib derivative

Markus Laube et al. RSC Adv. .

Abstract

The inducible isoenzyme cyclooxygenase-2 (COX-2) is closely associated with chemo-/radioresistance and poor prognosis of solid tumors. Therefore, COX-2 represents an attractive target for functional characterization of tumors by positron emission tomography (PET). In this study, the celecoxib derivative 3-([18F]fluoromethyl)-1-[4-(methylsulfonyl)phenyl]-5-(p-tolyl)-1H-pyrazole ([18F]5a) was chosen as a lead compound having a reported high COX-2 inhibitory potency and a potentially low carbonic anhydrase binding tendency. The respective deuterated analog [D2,18F]5a and the fluoroethyl-substituted derivative [18F]5b were selected to study the influence of these modifications with respect to COX inhibition potency in vitro and metabolic stability of the radiolabeled tracers in vivo. COX-2 inhibitory potency was found to be influenced by elongation of the side chain but, as expected, not by deuteration. An automated radiosynthesis comprising 18F-fluorination and purification under comparable conditions provided the radiotracers [18F]5a,b and [D2,18F]5a in good radiochemical yields (RCY) and high radiochemical purity (RCP). Biodistribution and PET studies comparing all three compounds revealed bone accumulation of 18F-activity to be lowest for the ethyl derivative [18F]5b. However, the deuterated analog [D2,18F]5a turned out to be the most stable compound of the three derivatives studied here. Time-dependent degradation of [18F]5a,b and [D2,18F]5a after incubation in murine liver microsomes was in accordance with the data on metabolism in vivo. Furthermore, metabolites were identified based on UPLC-MS/MS.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. Schematic presentation of selected radiolabeled celecoxib derivatives reported in the literature and the aim of this work. The generalized structure shows the vicinal diphenyl-substituted pyrazole as the core structure of celecoxib derivatives. The black dots indicate only the position of the radiolabel in the respective study. Beside the radiolabel, author and year are given as a reference.
Scheme 1
Scheme 1. Synthesis of labeling precursors and reference compounds. Reagents and conditions: (a) 4-methylsulfonylphenylhydrazine hydrochloride, MeOH, 70 °C, 21 h; (b) LiAlH4, THF, 70 °C, 1.5 h or r.t., 0.5 h; (c) LiAlD4, THF, 70 °C, 1.5 h; (d) (Ts)2O, DMAP, pyridine, DCM, −10 °C → r.t., 1–2 d; (e) DAST, DCM, r.t., 2 d.
Fig. 2
Fig. 2. Molecular structures of compounds 2e (left) and 5c (right) in the crystal (ORTEP plot with atom labeling scheme, displacement thermal ellipsoids are drawn at 50% probability level. Only one of the two independent molecules of the asymmetric unit of 5c is shown).
Scheme 2
Scheme 2. Radiosynthesis of the 18F-labeled celecoxib derivatives [18F]5a,b and [D2,18F]5a. Reagents and conditions: (a) [18F]fluoride/K2CO3/Kryptofix® 222 (K222), MeCN, 80 °C, 15 min.
Fig. 3
Fig. 3. Representative cellular binding and uptake of [18F]5a,b and [D2,18F]5a in COX-2-negative Mel-Juso and COX-2-positive A2058 cells at 37 °C. Blocking was performed by preincubation with 100 μM celecoxib. Results are shown as mean ± SD of one representative experiment performed in quadruplicate.
Fig. 4
Fig. 4. Biodistribution of [18F]5a,b and [D2,18F]5a in healthy rats at 5 min (A) and 60 min p.i. (B). Results are shown as mean ± SD of two independent experiments each performed in quadruplicate (8 animals for each time point and tracer).
Fig. 5
Fig. 5. Maximum intensity projections of small animal PET imaging after i.v. injection of [18F]5a, [D2,18F]5a, and [18F]5b in healthy rats. Tracer distribution was investigated for 60 min p.i. in dynamic mode (A) and, afterwards, the whole animal was scanned in static mode (B). Different organs are marked as H-heart, V-vein, K-kidney, L-liver, I-intestine, and B-bladder. For better visualization, PET images (scaled to SUVmax = 7.0) are overlayed with CT images (scaled between 400 and 6000 Houndsfield Units (HU)).
Fig. 6
Fig. 6. (A) Blood clearance rate (% ID per mL of intact compound) after i.v. injection of [18F]5a,b and [D2,18F]5a. (B) Radioactivity distribution in blood components with and without TCA precipitation. (C) Analytical radio-HPLC chromatograms of rat blood plasma at 60 min p.i. (D) Ratio of [18F]fluoride, intact compound, and radiometabolites at 20 and 60 min p.i. determined by radio-TLC (*) and radio-HPLC (**).
Fig. 7
Fig. 7. (A) Analytical radio-HPLC chromatograms of [18F]5a, [D2,18F]5a, and [18F]5b incubated for 60 min with murine liver microsomes and structure of metabolites determined by UPLC-MS/MS; (B) time dependency of metabolism of intact tracer and formation of [18F]fluoride and 18F-metabolites based on radio-TLC.
Fig. 8
Fig. 8. Comparison of 18F-defluorination and 18F-bearing metabolite formation tendency obtained for [18F]5a, [D2,18F]5a, and [18F]5bin vitro and in vivo based on selected results of this study. Formation of [18F]fluoride in vivo (left, orange bars) refers to SUV values for femur obtained in biodistribution studies 60 min p.i. Formation of 18F-bearing metabolites in vivo (right, orange bars) refers to % of activity in blood plasma samples as analyzed by radio-TLC and radio-HPLC 60 min p.i. Formation of [18F]fluoride and 18F-bearing metabolites in vitro (blue bars) refers to % of activity as analyzed by radio-TLC after 60 min incubation with murine liver microsomes.
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References

    1. Marnett L. J. Annu. Rev. Pharmacol. Toxicol. 2009;49:265–290. doi: 10.1146/annurev.pharmtox.011008.145638. - DOI - PubMed
    1. Carullo G. Galligano F. Aiello F. MedChemComm. 2017;8:492–500. doi: 10.1039/C6MD00569A. - DOI - PMC - PubMed
    1. Laube M. Kniess T. Pietzsch J. Antioxidants. 2016;5:14. doi: 10.3390/antiox5020014. - DOI - PMC - PubMed
    1. Sharma V. Bhatia P. Alam O. Javed Naim M. Nawaz F. Ahmad Sheikh A. Jha M. Bioorg. Chem. 2019;89:103007. doi: 10.1016/j.bioorg.2019.103007. - DOI - PubMed
    1. Dubois R. N. Abramson S. B. Crofford L. Gupta R. A. Simon L. S. Van De Putte L. B. A. Lipsky P. E. FASEB J. 1998;12:1063–1073. doi: 10.1096/fasebj.12.12.1063. - DOI - PubMed