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