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Comparison of tumor?targeting properties of directly and indirectly radioiodinated designed ankyrin repeat protein (DARPin) G3 variants for molecular imaging of HER2.

ABSTRACT: Evaluation of human epidermal growth factor receptor 2 (HER2) expression levels in breast and gastroesophageal cancer is used for the stratification of patients for HER2?targeting therapies. The use of radionuclide molecular imaging may facilitate such evaluation in a non?invasive way. Designed ankyrin repeat proteins (DARPins) are engineered scaffold proteins with high potential as probes for radionuclide molecular imaging. DARPin G3 binds with high affinity to HER2 and may be used to visualize this important therapeutic target. Studies on other engineered scaffold proteins have demonstrated that selection of the optimal labeling approach improves the sensitivity and specificity of radionuclide imaging. The present study compared two methods of labeling G3, direct and indirect radioiodination, to select an approach providing the best imaging contrast. G3?H6 was labeled with iodine?124, iodine?125 and iodine?131 using a direct method. A novel construct bearing a C?terminal cysteine, G3?GGGC, was site?specifically labeled using [125I]I?iodo?[(4?hydroxyphenyl)ethyl]maleimide (HPEM). The two radiolabeled G3 variants preserved binding specificity and high affinity to HER2?expressing cells. The specificity of tumor targeting in vivo was demonstrated. Biodistribution comparison of [131I]I?G3?H6 and [125I]I?HPEM?G3?GGGC in mice, bearing HER2?expressing SKOV3 xenografts, demonstrated an appreciable contribution of hepatobiliary excretion to the clearance of [125I]I?HPEM?G3?GGGC and a decreased tumor uptake compared to [131I]I?G3?H6. The direct label provided higher tumor?to?blood and tumor?to?organ ratios compared with the indirect label at 4 h post?injection. The feasibility of high contrast PET/CT imaging of HER2 expression in SKOV3 xenografts in mice using [124I]I?G3?H6 was demonstrated. In conclusion, direct radioiodination is the preferable approach for labeling DARPin G3 with iodine?123 and iodine?124 for clinical single photon emission computed tomography and positron emission tomography imaging.

SUBMITTER: Vorobyeva A

PROVIDER: S-EPMC6411343 | biostudies-literature | 2019 Apr

REPOSITORIES: biostudies-literature

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Comparison of tumor‑targeting properties of directly and indirectly radioiodinated designed ankyrin repeat protein (DARPin) G3 variants for molecular imaging of HER2.

Vorobyeva Anzhelika A Sсhulga Alexey A Konovalova Elena E Güler Rezan R Mitran Bogdan B Garousi Javad J Rinne Sara S Löfblom John J Orlova Anna A Deyev Sergey S Tolmachev Vladimir V

International journal of oncology 20190211 4

Evaluation of human epidermal growth factor receptor 2 (HER2) expression levels in breast and gastroesophageal cancer is used for the stratification of patients for HER2‑targeting therapies. The use of radionuclide molecular imaging may facilitate such evaluation in a non‑invasive way. Designed ankyrin repeat proteins (DARPins) are engineered scaffold proteins with high potential as probes for radionuclide molecular imaging. DARPin G3 binds with high affinity to HER2 and may be used to visualize ...[more]

PMID: 30968147

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Project description:PurposeHuman epidermal growth factor receptor-2 (HER2) overexpression is a predictor of response to anti-HER2 therapy in breast and gastric cancer. Currently, HER2 status is assessed by tumour biopsy, but this may not be representative of the larger tumour mass or other metastatic sites, risking misclassification and selection of suboptimal therapy. The designed ankyrin repeat protein (DARPin) G3 binds HER2 with high affinity at an epitope that does not overlap with trastuzumab and is biologically inert. We hypothesized that radiolabelled DARPin G3 would be capable of selectively imaging HER2-positive tumours, and aimed to identify a suitable format for clinical application.MethodsG3 DARPins tagged with hexahistidine (His6) or with histidine glutamate (HE)3 and untagged G3 DARPins were manufactured using a GMP-compatible Pichia pastoris protocol and radiolabelled with (125)I, or with (111)In via DOTA linked to a C-terminal cysteine. BALB/c mice were injected with radiolabelled G3 and tissue biodistribution was evaluated by gamma counting. The lead construct ((HE)3-G3) was assessed in mice bearing HER2-positive human breast tumour (BT474) xenografts.ResultsFor both isotopes, (HE)3-G3 had significantly lower liver uptake than His6-G3 and untagged G3 counterparts in non-tumour-bearing mice, and there was no significantly different liver uptake between His6-G3 and untagged G3. (HE)3-G3 was taken forward for evaluation in mice bearing HER2-positive tumour xenografts. The results demonstrated that radioactivity from (111)In-(HE)3-G3 was better maintained in tumours and cleared faster from serum than radioactivity from (125)I-(HE)3-G3, achieving superior tumour-to-blood ratios (343.7 ± 161.3 vs. 22.0 ± 11.3 at 24 h, respectively). On microSPECT/CT, (111)In-labelled and (125)I-labelled (HE)3-G3 could image HER2-positive tumours at 4 h after administration, but there was less normal tissue uptake of radioactivity with (111)In-(HE)3-G3. Preadministration of trastuzumab did not affect the uptake of (HE)3-G3 by HER2-positive tumours.ConclusionRadiolabelled DARPin (HE)3-G3 is a versatile radioligand with potential to allow the acquisition of whole-body HER2 scans on the day of administration.

Dataset Information

Comparison of tumor?targeting properties of directly and indirectly radioiodinated designed ankyrin repeat protein (DARPin) G3 variants for molecular imaging of HER2.

Publications

Comparison of tumor‑targeting properties of directly and indirectly radioiodinated designed ankyrin repeat protein (DARPin) G3 variants for molecular imaging of HER2.

Similar Datasets

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