Preparation, cytotoxicity, and in vivo antitumor efficacy of (111)In-labeled modular nanotransporters

PURPOSE: Modular nanotransporters (MNTs) are a polyfunctional platform designed to achieve receptor-specific delivery of short-range therapeutics into the cell nucleus by receptor-mediated endocytosis, endosome escape, and targeted nuclear transport. This study evaluated the potential utility of the MNT platform in tandem with Auger electron emitting (111)In for cancer therapy. METHODS: Three MNTs developed to target either melanocortin receptor-1 (MC1R), folate receptor (FR), or epidermal growth factor receptor (EGFR) that are overexpressed on cancer cells were modified with p-SCN-Bn-NOTA and then labeled with (111)In in high specific activity. Cytotoxicity of the (111)In-labeled MNTs was evaluated on cancer cell lines bearing the appropriate receptor target (FR: HeLa, SK-OV-3; EGFR: A431, U87MG.wtEGFR; and MC1R: B16-F1). In vivo micro-single-photon emission computed tomography/computed tomography imaging and antitumor efficacy studies were performed with intratumoral injection of MC1R-targeted (111)In-labeled MNT in B16-F1 melanoma tumor-bearing mice. RESULTS: The three NOTA-MNT conjugates were labeled with a specific activity of 2.7 GBq/mg with nearly 100% yield, allowing use without subsequent purification. The cytotoxicity of (111)In delivered by these MNTs was greatly enhanced on receptor-expressing cancer cells compared with (111)In nontargeted control. In mice with B16-F1 tumors, prolonged retention of (111)In by serial imaging and significant tumor growth delay (82% growth inhibition) were found. CONCLUSION: The specific in vitro cytotoxicity, prolonged tumor retention, and therapeutic efficacy of MC1R-targeted (111)In-NOTA–MNT suggest that this Auger electron emitting conjugate warrants further evaluation as a locally delivered radiotherapeutic, such as for ocular melanoma brachytherapy. Moreover, the high cytotoxicity observed with FR- and EGFR-targeted (111)In-NOTA–MNT suggests further applications of the MNT delivery strategy should be explored.