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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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Related in: MedlinePlus

a The [18F]FBEM-ZHER2:432-Affibody uptake 2 h post i.v. injection in athymic nude mice bearing either HER2-positive SKOV-3 cells after pretreatment with or without non-radioactive Affibody or HER2-negative U251 tumors (tissue type versus % ID/g tissue). Each bar represents an average ± SD from n = 3-6. b Blood kinetics of [18F]FBEM-ZHER2:342-Affibody. The squares represent % ID/g in the blood with an exponential curve fit. Insert Average HMW fractions of the plasma-associated radioactivity. Each point represents mean ± SD (three to four mice)
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Fig4: a The [18F]FBEM-ZHER2:432-Affibody uptake 2 h post i.v. injection in athymic nude mice bearing either HER2-positive SKOV-3 cells after pretreatment with or without non-radioactive Affibody or HER2-negative U251 tumors (tissue type versus % ID/g tissue). Each bar represents an average ± SD from n = 3-6. b Blood kinetics of [18F]FBEM-ZHER2:342-Affibody. The squares represent % ID/g in the blood with an exponential curve fit. Insert Average HMW fractions of the plasma-associated radioactivity. Each point represents mean ± SD (three to four mice)

Mentions: The specificity of binding in vivo was evaluated in two independent experiments. In each case, mice were sacrificed 2 h post-injection, and the radioactivity in the blood and major organs was measured. As expected, blocking the HER2 receptors in mice bearing HER2-positive SKOV-3 tumors with an excess of unlabeled Affibody resulted in a significant decrease of radioactivity in the tumor, as only tumors expressed high numbers of HER2 receptors. In the blood and the rest of organs examined, there was no significant change because of pre-treatment with non-labeled molecules (Fig. 4a). Receptor-mediated binding of radiotracer was confirmed by successful blocking with non-labeled Affibody molecules.Fig. 4


[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)

a The [18F]FBEM-ZHER2:432-Affibody uptake 2 h post i.v. injection in athymic nude mice bearing either HER2-positive SKOV-3 cells after pretreatment with or without non-radioactive Affibody or HER2-negative U251 tumors (tissue type versus % ID/g tissue). Each bar represents an average ± SD from n = 3-6. b Blood kinetics of [18F]FBEM-ZHER2:342-Affibody. The squares represent % ID/g in the blood with an exponential curve fit. Insert Average HMW fractions of the plasma-associated radioactivity. Each point represents mean ± SD (three to four mice)
© Copyright Policy
Related In: Results  -  Collection

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

Fig4: a The [18F]FBEM-ZHER2:432-Affibody uptake 2 h post i.v. injection in athymic nude mice bearing either HER2-positive SKOV-3 cells after pretreatment with or without non-radioactive Affibody or HER2-negative U251 tumors (tissue type versus % ID/g tissue). Each bar represents an average ± SD from n = 3-6. b Blood kinetics of [18F]FBEM-ZHER2:342-Affibody. The squares represent % ID/g in the blood with an exponential curve fit. Insert Average HMW fractions of the plasma-associated radioactivity. Each point represents mean ± SD (three to four mice)
Mentions: The specificity of binding in vivo was evaluated in two independent experiments. In each case, mice were sacrificed 2 h post-injection, and the radioactivity in the blood and major organs was measured. As expected, blocking the HER2 receptors in mice bearing HER2-positive SKOV-3 tumors with an excess of unlabeled Affibody resulted in a significant decrease of radioactivity in the tumor, as only tumors expressed high numbers of HER2 receptors. In the blood and the rest of organs examined, there was no significant change because of pre-treatment with non-labeled molecules (Fig. 4a). Receptor-mediated binding of radiotracer was confirmed by successful blocking with non-labeled Affibody molecules.Fig. 4

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