Preparation, cytotoxicity, and in vivo antitumor efficacy of 111In-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 In-111 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 In-111 in high specific activity. Cytotoxicity of the In-111-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 In-111-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 In-111 delivered by these MNTs was greatly enhanced on receptor-expressing cancer cells compared with In-111 nontargeted control. In mice with B16-F1 tumors, prolonged retention of I-111(n) 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 In-111-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-argeted In-111-NOTA-MNT suggests further applications of the MNT delivery strategy should be explored.