A comparison of non-biologically active truncated EGF (EGFt) and full-length hEGF for delivery of Auger electron-emitting In-111 to EGFR-positive breast cancer cells and tumor xenografts in athymic mice

作者：Panosa Clara; Fonge Humphrey; Ferrer Batalle Montserrat; Menendez Javier A; Massaguer Anna; De Llorens Rafael^*; Reilly Raymond M

来源：Nuclear Medicine and Biology, 2015, 42(12): 931-938.

DOI：10.1016/j.nucmedbio.2015.08.003

• Breast cancer
• Indium-111
• EGF
• EGFR
• Radiopharmaceuticals
• Theranostics

Introduction: EGFt is a truncated form of human epidermal growth factor (hEGF) that is non-biologically active but retains binding and internalization into EGFR-positive cells. Our aim was to compare EGFt and hEGF for delivery of In-111 to human breast cancer (BC) cells and tumors and evaluate its cytotoxicity against EGFR-positive BC cells, mediated by the Auger electron emissions of In-111.
Methods: The binding, internalization and nuclear localization of EGFt and hEGF in MDA-MB-468 human BC cells were first assessed by confocal fluorescence microscopy. Subcellular fractionation was then used to quantify the cellular and nuclear uptake of In-111-EGFt and In-111-hEGF in MDA-MB-468 cells. The effect of exposure in vitro to In-111-EGFt or In-111-hEGF on the clonogenic survival of MDA-MB-468 (10(6) EGFR/cell) or MCF-7 cells (10(4) EGFR/cell) was determined. The pharmacokinetics and tumor and normal tissue biodistribution of In-111-EGFt was compared to In-111-hEGF in CD-1 athymic mice with s.c. MDA-MB-468 and MCF-7 tumors. Nuclear importation in MDA-MB-468 tumors was determined ex vivo by subcellular fractionation.
Results: Fluorescently-labeled EGFt and hEGF were bound, internalized and localized in the nucleus of MDA-MB-468 cells. Binding of In-111-EGFt to MDA-MB-468 cells was 8-fold lower than In-111-hEGF, but nuclear importation as a proportion of cell-bound In-111 was 3.6-fold greater than In-111-hEGF. Nuclear uptake of In-111-EGFt was lower than In-111-hEGF when differences in cell binding were taken into account. The cytotoxicity of In-111-EGFt (1.0 MBq/mL; 10 nmols/L) against MDA-MB-468 cells was 9-fold lower than In-111-hEGF but only 2-fold lower at a higher concentration (1.85 MBq/mL; 40 nmols/L). In-111-EGFt and In-111-hEGF exhibited greater cytotoxicity against MDA-MB-468 cells than MCF-7 cells. In-111-EGFt was eliminated more slowly from the blood of tumor-bearing mice and exhibited lower liver uptake but higher kidney accumulation. Uptake of In-111-EGFt in MDA-MB-468 tumors was 2.2-fold lower than In-111-hEGF, and was blocked by anti-EGFR monoclonal antibody, nimotuzumab. Nuclear uptake into MDA-MB-468 tumor cells was higher for In-111-EGFt than In-111-hEGF, but when the lower tumor uptake of In-111-EGFt was considered, there were no overall differences.
Conclusion: We conclude that the absence of biological activity of EGFt makes it attractive for delivery of Auger electron-emitting In-111 to EGFR-overexpressing BC, but its lower cellular and tumor uptake would limit its effectiveness compared to In-111-hEGF.
Advances in Knowledge and Implications for Patient Care: In-111-EGFt may reduce the adverse effects previously observed in patients administered In-111-hEGF since it is not biologically active, but its lower uptake by BC cells and tumors would limit its effectiveness for treatment of breast cancer.

• 出版日期2015-12