Radiolabeling and in vitro evaluation of 67Ga-NOTA-modular nanotransporter - A potential Auger electron emitting EGFR-targeted radiotherapeutic

Introduction: Modular nanotransporters (MNTs) are vehicles designed to transport drugs from the cell surface via receptor-mediated endocytosis and endosomal escape to nucleus. Hence their conjugation to Auger electron emitters, can cause severe cell killing, by nuclear localization. Herein we evaluate the use of MNT as a platform for targeted radiotherapy with Ga-67. Methods: EGF was the targeting ligand on the MNT, and NOTA was selected for its radiolabeling with Ga-67. In the radiolabeling study we dealt with the precipitation of MNT (pI 5.7) at the labeling pH (4.5-5.5) of 67Ga. Cellular and nuclei uptake of Ga-67-NOTA-MNT by the A431 cell line was determined. Its specific cytotoxicity was compared to that of Ga-67-EDTA, Ga-67-NOTA-BSA and Ga-67-NOTA-hEGF, in A431 and U87MGWTT, cell lines, by clonogenic assay. Dosimetry studies were also performed. Results: 67Ga-NOTA-MNT was produced with 90% yield and specific activity of 25.6 mCi/mg. The in vitro kinetics revealed an increased uptake over 24 h. 55% of the internalized radioactivity was detected in the nuclei at 1 h. The cytotoxicity of Ga-67-NOTA-MNT on A431 cell line was 17 and 385-fold higher when compared to non-specific Ga-67-NOTA-BSA and 67Ga-EDTA. While its cytotoxic potency was 13 and 72-fold higher when compared to 67Ga-NOTA-hEGF in the A431 and the U87MGWIT cell lines, respectively, validating its nuclear localization. The absorbed dose, for 63% cell killing, was 8 Gy, confirming the high specific index of Ga-67. Conclusion: These results demonstrate the feasibility of using MNT as a platform for single cell kill targeted radiotherapy by Auger electron emitters. (C) 2014 Elsevier Inc. All rights reserved.