Abstract
Radionuclide molecular imaging of human epidermal growth factor receptor 3 (HER3) expression using affibody molecules could be used for patient stratification for HER3-targeted cancer therapeutics. We hypothesized that the properties of HER3-targeting affibody molecules might be improved through modification of the radiometal-chelator complex. Macrocyclic chelators NOTA (1,4,7-triazacyclononane-N,N′,N′′-triacetic acid), NODAGA (1-(1,3-carboxypropyl)-4,7-carboxymethyl-1,4,7-triazacyclononane), DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid), and DOTAGA (1,4,7,10-tetraazacyclododececane,1-(glutaric acid)−4,7,10-triacetic acid) were conjugated to the C-terminus of anti-HER3 affibody molecule Z08698 and conjugates were labeled with indium-111. All conjugates bound specifically and with picomolar affinity to HER3 in vitro. In mice bearing HER3-expressing xenografts, no significant difference in tumor uptake between the conjugates was observed. Presence of the negatively charged 111In-DOTAGA-complex resulted in the lowest hepatic uptake and the highest tumor-to-liver ratio. In conclusion, the choice of chelator influences the biodistribution of indium-111 labeled anti-HER3 affibody molecules. Hepatic uptake of anti-HER3 affibody molecules could be reduced by the increase of negative charge of the radiometal-chelator complex on the C-terminus without significantly influencing the tumor uptake.
Highlights
Radionuclide molecular imaging of human epidermal growth factor receptor 3 (HER3) expression using affibody molecules could be used for patient stratification for HER3-targeted cancer therapeutics
The HER3-binding affibody Z08698 was recombinantly produced in E. coli, recovered with cation exchange chromatography, coupled to maleimide derivatives of NOTA, NODAGA, DOTA and DOTAGA and subjected to reverse-phase high performance liquid chromatography (RP-HPLC) as a final step for remnant chelator removal and separation from unconjugated protein
The conjugates were dissolved in ammonium acetate (0.2 M, pH 5.5) and incubated with 20 MBq indium-chloride for 40 minutes at 85 °C. 111In-Z08698-NODAGA and 111In-Z08698-DOTAGA were successfully labeled with almost quantitative yields
Summary
Radionuclide molecular imaging of human epidermal growth factor receptor 3 (HER3) expression using affibody molecules could be used for patient stratification for HER3-targeted cancer therapeutics. Hepatic uptake of anti-HER3 affibody molecules could be reduced by the increase of negative charge of the radiometal-chelator complex on the C-terminus without significantly influencing the tumor uptake. During recent years, targeting of the human epidermal growth factor receptor type 3 (HER3) has become an important and promising approach for anti-cancer therapy. Conventional methods for identification of target expression are complicated: HER3 is not shedded at a sufficiently high amount to be a reliable biomarker in blood[12] and biopsies are invasive procedures associated with risk of false negative results due to tumor heterogeneity. Such molecular imaging modalities are non-invasive and repeatable methods for detection of target expression in primary tumors and metastases as well as for monitoring of therapy response[13]. Substantial endogenous expression, in liver, decreases imaging contrast and complicates image interpretation
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