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[18F]FBEM-Z(HER2:342)-Affibody molecule-a new molecular tracer for in vivo monitoring of HER2 expression by positron emission tomography.

Kramer-Marek G, Kiesewetter DO, Martiniova L, Jagoda E, Lee SB, Capala J - Eur. J. Nucl. Med. Mol. Imaging (2007)

Bottom Line: The in vitro binding of the resulting radioconjugate was characterized by receptor saturation and competition assays.The animals were sacrificed at different times post-injection, and the radioactivity in selected tissues was measured.PET images were obtained using an animal PET scanner.

View Article: PubMed Central - PubMed

Affiliation: National Cancer Institute, National Institutes of Health, 10 Center Drive, Bldg. 10, Rm. 1B-37A, Bethesda, MD 20892, USA.

ABSTRACT

Purpose: The expression of human epidermal growth factor receptor-2 (HER2) receptors in cancers is correlated with a poor prognosis. If assessed in vivo, it could be used for selection of appropriate therapy for individual patients and for monitoring of the tumor response to targeted therapies. We have radiolabeled a HER2-binding Affibody molecule with fluorine-18 for in vivo monitoring of the HER2 expression by positron emission tomography (PET).

Materials and methods: The HER2-binding Z(HER2:342)-Cys Affibody molecule was conjugated with N-2-(4-[18F]fluorobenzamido)ethyl]maleimide ([18F]FBEM). The in vitro binding of the resulting radioconjugate was characterized by receptor saturation and competition assays. For in vivo studies, the radioconjugate was injected into the tail vein of mice bearing subcutaneous HER2-positive or HER2-negative tumors. Some of the mice were pre-treated with non-labeled Z(HER2:342)-Cys. The animals were sacrificed at different times post-injection, and the radioactivity in selected tissues was measured. PET images were obtained using an animal PET scanner.

Results: In vitro experiments indicated specific, high-affinity binding to HER2. PET imaging revealed a high accumulation of the radioactivity in the tumor as early as 20 min after injection, with a plateau being reached after 60 min. These results were confirmed by biodistribution studies demonstrating that, as early as 1 h post-injection, the tumor to blood concentration ratio was 7.5 and increased to 27 at 4 h. Pre-saturation of the receptors with unlabeled Z(HER2:342)-Cys lowered the accumulation of radioactivity in HER2-positive tumors to the levels observed in HER2-negative ones.

Conclusion: Our results suggest that the [18F]FBEM-Z(HER2:342) radioconjugate can be used to assess HER2 expression in vivo.

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Synthetic route used for labeling of the ZHER2:342-Cys Affibody molecule with 18F. DECP Diethyl cyanophosphonate, DIPEA N,N-diisoproplyethylamine
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Fig1: Synthetic route used for labeling of the ZHER2:342-Cys Affibody molecule with 18F. DECP Diethyl cyanophosphonate, DIPEA N,N-diisoproplyethylamine

Mentions: Affibody molecule with a C-terminal cysteine provided functionality for site-specific labeling using maleimide chemistry. We prepared N-(2-(4-[18F]fluorobenzamido)ethyl)maleimide [18F]FBEM using a similar method (Fig. 1) to that utilized to prepare [18F]fluoropaclitaxel [28]. An alternative synthesis of [18F]FBEM has been previously reported [26]. 4-[18F]Fluorobenzoic acid was obtained by reaction of pentamethylbenzyl 4-trimethylaniliniumbenzoate trifluoromethanesulfonate with [18F]fluoride followed by cleavage of the ester function with TFA. 2-Aminoethylmaleimide was coupled to [18F]fluorobenzoic acid using diethyl cyanophosphonate as the coupling reagent. [18F]FBEM was obtained in 22.0 ± 4.7% radiochemical yield (n = 44, uncorrected). The [18F]FBEM was purified by HPLC and, because of the complexity of the overall synthesis, was not commonly evaluated for purity. However, in the limited number of radiochemical purity assays of the isolated [18F]FBEM, we consistently observed values greater than 95%.Fig. 1


[18F]FBEM-Z(HER2:342)-Affibody molecule-a new molecular tracer for in vivo monitoring of HER2 expression by positron emission tomography.

Kramer-Marek G, Kiesewetter DO, Martiniova L, Jagoda E, Lee SB, Capala J - Eur. J. Nucl. Med. Mol. Imaging (2007)

Synthetic route used for labeling of the ZHER2:342-Cys Affibody molecule with 18F. DECP Diethyl cyanophosphonate, DIPEA N,N-diisoproplyethylamine
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2365742&req=5

Fig1: Synthetic route used for labeling of the ZHER2:342-Cys Affibody molecule with 18F. DECP Diethyl cyanophosphonate, DIPEA N,N-diisoproplyethylamine
Mentions: Affibody molecule with a C-terminal cysteine provided functionality for site-specific labeling using maleimide chemistry. We prepared N-(2-(4-[18F]fluorobenzamido)ethyl)maleimide [18F]FBEM using a similar method (Fig. 1) to that utilized to prepare [18F]fluoropaclitaxel [28]. An alternative synthesis of [18F]FBEM has been previously reported [26]. 4-[18F]Fluorobenzoic acid was obtained by reaction of pentamethylbenzyl 4-trimethylaniliniumbenzoate trifluoromethanesulfonate with [18F]fluoride followed by cleavage of the ester function with TFA. 2-Aminoethylmaleimide was coupled to [18F]fluorobenzoic acid using diethyl cyanophosphonate as the coupling reagent. [18F]FBEM was obtained in 22.0 ± 4.7% radiochemical yield (n = 44, uncorrected). The [18F]FBEM was purified by HPLC and, because of the complexity of the overall synthesis, was not commonly evaluated for purity. However, in the limited number of radiochemical purity assays of the isolated [18F]FBEM, we consistently observed values greater than 95%.Fig. 1

Bottom Line: The in vitro binding of the resulting radioconjugate was characterized by receptor saturation and competition assays.The animals were sacrificed at different times post-injection, and the radioactivity in selected tissues was measured.PET images were obtained using an animal PET scanner.

View Article: PubMed Central - PubMed

Affiliation: National Cancer Institute, National Institutes of Health, 10 Center Drive, Bldg. 10, Rm. 1B-37A, Bethesda, MD 20892, USA.

ABSTRACT

Purpose: The expression of human epidermal growth factor receptor-2 (HER2) receptors in cancers is correlated with a poor prognosis. If assessed in vivo, it could be used for selection of appropriate therapy for individual patients and for monitoring of the tumor response to targeted therapies. We have radiolabeled a HER2-binding Affibody molecule with fluorine-18 for in vivo monitoring of the HER2 expression by positron emission tomography (PET).

Materials and methods: The HER2-binding Z(HER2:342)-Cys Affibody molecule was conjugated with N-2-(4-[18F]fluorobenzamido)ethyl]maleimide ([18F]FBEM). The in vitro binding of the resulting radioconjugate was characterized by receptor saturation and competition assays. For in vivo studies, the radioconjugate was injected into the tail vein of mice bearing subcutaneous HER2-positive or HER2-negative tumors. Some of the mice were pre-treated with non-labeled Z(HER2:342)-Cys. The animals were sacrificed at different times post-injection, and the radioactivity in selected tissues was measured. PET images were obtained using an animal PET scanner.

Results: In vitro experiments indicated specific, high-affinity binding to HER2. PET imaging revealed a high accumulation of the radioactivity in the tumor as early as 20 min after injection, with a plateau being reached after 60 min. These results were confirmed by biodistribution studies demonstrating that, as early as 1 h post-injection, the tumor to blood concentration ratio was 7.5 and increased to 27 at 4 h. Pre-saturation of the receptors with unlabeled Z(HER2:342)-Cys lowered the accumulation of radioactivity in HER2-positive tumors to the levels observed in HER2-negative ones.

Conclusion: Our results suggest that the [18F]FBEM-Z(HER2:342) radioconjugate can be used to assess HER2 expression in vivo.

Show MeSH
Related in: MedlinePlus