ИСТИНА

Objectives. Modular nanotransporters (MNTs) are vehicles designed to transport drugs via cell surface receptor-mediated endocytosis and endosomal escape to nucleus. They are designed for use with cytotoxins such as Auger electron emitters including 67Ga that require nuclear uptake to achieve efficient cell killing. Our objective was to evaluate the feasibility of using MNT as a platform for targeted radiotherapy with Auger electron emitting radionuclides. Methods. NOTA was selected for labeling MNT with 67Ga and EGF was chosen as the targeting ligand on the MNT. A major obstacle was that the pI of 5.7 of the MNT caused its precipitation in the pH range (4.5-5.5) normally used for 67Ga labeling. Uptake of 67Ga-NOTA-MNT by EGFR expressing A431 human epidermoid carcinoma cells was measured and its cytotoxicity was compared with that of 67Ga-EDTA and 67Ga-NOTA-BSA in clonogenic assays. Finally, a preliminary biodistribution study in normal mice was performed. Results. In the optimized labeling approach precipitation of MNT was minimized by dilution at the end of incubation to a 5% DMSO pH 8 phosphate buffer, giving 67Ga-NOTA-MNT in 79% yield with a maximum specific activity of 1270 MBq/mg. At 24 h, the fraction of 67Ga found in the intracellular compartment of A431 cells in vitro was more than 10-fold higher than on the cell membrane, with significant uptake in the cell nucleus. The D37 value for 67Ga-NOTA-MRT on A431 cells was 9.25±1.91 μCi/mL while for the two control compounds, D37 was not reached even at the highest dose used, 140 μCi/mL. In normal mice, the biodistribution of 67Ga-NOTA-MNT was similar to that previously reported for directly radiolabeled hEGF, where liver is the main accumulation organ. Conclusions. These results demonstrate the feasibility of using MNT as a platform for targeted radiotherapy using Auger electron emitting radionuclides.