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18F-glutathione conjugate as a PET tracer for imaging tumors that overexpress L-PGDS enzyme.

Huang HL, Huang YC, Lee WY, Yeh CN, Lin KJ, Yu CS - PLoS ONE (2014)

Bottom Line: The inhibition percentage of the production of PGD2 from PGH2 at the presence of 200 µM of FBuEA-GS and 4-Dibenzo[a,d]cyclohepten-5-ylidene-1-[4-(2H-tetrazol-5-yl)butyl]piperidine (AT-56) were 74.1 ± 4.8% and 97.6 ± 16.0%, respectively. [18F]FBuEA-GS bound L-PGDS (16.3-21.7%) but not the isoform, microsomal prostaglandin E synthase 1.No binding to GST-alpha and GST-pi was observed.The contrasted images indicated that the radiotracer accumulation in tumor lesions is probably related to the overexpression of L-PGDS.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering and Environmental Sciences, National Tsinghua University, Hsinchu, Taiwan.

ABSTRACT
Lipocalin-type prostaglandin D synthase (L-PGDS) has been correlated with the progression of neurological disorders. The present study aimed at evaluating the imaging potency of a glutathione conjugate of fluorine-18-labeled fluorobutyl ethacrynic amide ([18F]FBuEA-GS) for brain tumors. Preparation of [18F]FBuEA-GS has been modified from the -4-tosylate derivative via radiofluorination in 5% radiochemical yield. The mixture of nonradioactive FBuEA-GS derived from a parallel preparation has be resolved to two isomers in a ratio of 9:1 using analytic chiral reversed phase high performance liquid chromatography (RP-HPLC). The two fluorine-18-labeled isomers purified through nonchiral semipreparative RP-HPLC as a mixture were studied by assessing the binding affinity toward L-PGDS through a gel filtration HPLC, by analyzing radiotracer accumulation in C6 glioma cells, and by evaluating the imaging of radiotracer in a C6 glioma rat with positron emission tomography. The inhibition percentage of the production of PGD2 from PGH2 at the presence of 200 µM of FBuEA-GS and 4-Dibenzo[a,d]cyclohepten-5-ylidene-1-[4-(2H-tetrazol-5-yl)butyl]piperidine (AT-56) were 74.1 ± 4.8% and 97.6 ± 16.0%, respectively. [18F]FBuEA-GS bound L-PGDS (16.3-21.7%) but not the isoform, microsomal prostaglandin E synthase 1. No binding to GST-alpha and GST-pi was observed. The binding strength between [18F]FBuEA-GS and L-PGDS has been evaluated using analytic gel filtration HPLC at the presence of various concentrations of the cold competitor FBuEA-GS. The contrasted images indicated that the radiotracer accumulation in tumor lesions is probably related to the overexpression of L-PGDS.

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HPLC chromatograms for the mixture of [18F]FBuEA-GS 3 with different enzymes.(a) mPGES-1, (b) L-PGDS (lipocalin-type; rat recombinant), (c) PGDS (lipocalin-type; human recombinant), (d) PGDS (lipocalin-type; mouse recombinant), (e) COX-1 (ovine), (f) COX-2 (ovine), (g) GSTA1-1 and (h) GSTP1. (b′)∼(f′) are chromatograms resolved from the radioactivity signals of (b)∼(f) using Origin software.
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pone-0104118-g004: HPLC chromatograms for the mixture of [18F]FBuEA-GS 3 with different enzymes.(a) mPGES-1, (b) L-PGDS (lipocalin-type; rat recombinant), (c) PGDS (lipocalin-type; human recombinant), (d) PGDS (lipocalin-type; mouse recombinant), (e) COX-1 (ovine), (f) COX-2 (ovine), (g) GSTA1-1 and (h) GSTP1. (b′)∼(f′) are chromatograms resolved from the radioactivity signals of (b)∼(f) using Origin software.

Mentions: Based on the results of the binding study (Fig. 4 and Table 1), COX enzymes tolerated the substrate with structural variation. The binding ratios of 52% and 75% for COX-1 and COX-2 enzymes, respectively, were significantly higher than those of the other enzymes. The specific activities of the three L-PGDS were significantly lower than those of the COX enzymes, and substantial binding was observed across all three species. Interestingly, mPGES-1 with a 1000-fold greater specific activity than that of L-PGDS did not show any binding affinity. The weak binding affinities of GSTA1-1 and GSTP1 could not be rationalized by lower specific activities because L-PGDS had similar specific activities (5-fold excess) and exhibited substantial binding. Thus, the binding sites of both mPGES-1 and GSTs may be restricted to GSH by the substrates, whereas COX and L-PGDS tolerate structural variances of substrates. Furthermore, L-PGDS recognized diversified thiol-containing structures as cofactors, enhancing the binding. The weak binding of both GSTs to [18F]FBuEA-GS 3 was consistent with our hypothesis.


18F-glutathione conjugate as a PET tracer for imaging tumors that overexpress L-PGDS enzyme.

Huang HL, Huang YC, Lee WY, Yeh CN, Lin KJ, Yu CS - PLoS ONE (2014)

HPLC chromatograms for the mixture of [18F]FBuEA-GS 3 with different enzymes.(a) mPGES-1, (b) L-PGDS (lipocalin-type; rat recombinant), (c) PGDS (lipocalin-type; human recombinant), (d) PGDS (lipocalin-type; mouse recombinant), (e) COX-1 (ovine), (f) COX-2 (ovine), (g) GSTA1-1 and (h) GSTP1. (b′)∼(f′) are chromatograms resolved from the radioactivity signals of (b)∼(f) using Origin software.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4128654&req=5

pone-0104118-g004: HPLC chromatograms for the mixture of [18F]FBuEA-GS 3 with different enzymes.(a) mPGES-1, (b) L-PGDS (lipocalin-type; rat recombinant), (c) PGDS (lipocalin-type; human recombinant), (d) PGDS (lipocalin-type; mouse recombinant), (e) COX-1 (ovine), (f) COX-2 (ovine), (g) GSTA1-1 and (h) GSTP1. (b′)∼(f′) are chromatograms resolved from the radioactivity signals of (b)∼(f) using Origin software.
Mentions: Based on the results of the binding study (Fig. 4 and Table 1), COX enzymes tolerated the substrate with structural variation. The binding ratios of 52% and 75% for COX-1 and COX-2 enzymes, respectively, were significantly higher than those of the other enzymes. The specific activities of the three L-PGDS were significantly lower than those of the COX enzymes, and substantial binding was observed across all three species. Interestingly, mPGES-1 with a 1000-fold greater specific activity than that of L-PGDS did not show any binding affinity. The weak binding affinities of GSTA1-1 and GSTP1 could not be rationalized by lower specific activities because L-PGDS had similar specific activities (5-fold excess) and exhibited substantial binding. Thus, the binding sites of both mPGES-1 and GSTs may be restricted to GSH by the substrates, whereas COX and L-PGDS tolerate structural variances of substrates. Furthermore, L-PGDS recognized diversified thiol-containing structures as cofactors, enhancing the binding. The weak binding of both GSTs to [18F]FBuEA-GS 3 was consistent with our hypothesis.

Bottom Line: The inhibition percentage of the production of PGD2 from PGH2 at the presence of 200 µM of FBuEA-GS and 4-Dibenzo[a,d]cyclohepten-5-ylidene-1-[4-(2H-tetrazol-5-yl)butyl]piperidine (AT-56) were 74.1 ± 4.8% and 97.6 ± 16.0%, respectively. [18F]FBuEA-GS bound L-PGDS (16.3-21.7%) but not the isoform, microsomal prostaglandin E synthase 1.No binding to GST-alpha and GST-pi was observed.The contrasted images indicated that the radiotracer accumulation in tumor lesions is probably related to the overexpression of L-PGDS.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering and Environmental Sciences, National Tsinghua University, Hsinchu, Taiwan.

ABSTRACT
Lipocalin-type prostaglandin D synthase (L-PGDS) has been correlated with the progression of neurological disorders. The present study aimed at evaluating the imaging potency of a glutathione conjugate of fluorine-18-labeled fluorobutyl ethacrynic amide ([18F]FBuEA-GS) for brain tumors. Preparation of [18F]FBuEA-GS has been modified from the -4-tosylate derivative via radiofluorination in 5% radiochemical yield. The mixture of nonradioactive FBuEA-GS derived from a parallel preparation has be resolved to two isomers in a ratio of 9:1 using analytic chiral reversed phase high performance liquid chromatography (RP-HPLC). The two fluorine-18-labeled isomers purified through nonchiral semipreparative RP-HPLC as a mixture were studied by assessing the binding affinity toward L-PGDS through a gel filtration HPLC, by analyzing radiotracer accumulation in C6 glioma cells, and by evaluating the imaging of radiotracer in a C6 glioma rat with positron emission tomography. The inhibition percentage of the production of PGD2 from PGH2 at the presence of 200 µM of FBuEA-GS and 4-Dibenzo[a,d]cyclohepten-5-ylidene-1-[4-(2H-tetrazol-5-yl)butyl]piperidine (AT-56) were 74.1 ± 4.8% and 97.6 ± 16.0%, respectively. [18F]FBuEA-GS bound L-PGDS (16.3-21.7%) but not the isoform, microsomal prostaglandin E synthase 1. No binding to GST-alpha and GST-pi was observed. The binding strength between [18F]FBuEA-GS and L-PGDS has been evaluated using analytic gel filtration HPLC at the presence of various concentrations of the cold competitor FBuEA-GS. The contrasted images indicated that the radiotracer accumulation in tumor lesions is probably related to the overexpression of L-PGDS.

Show MeSH
Related in: MedlinePlus