Gamma-ray emitting ¹¹¹In, which is extensively used for imaging, is also a source of short-range Auger electrons (AE). While exhibiting negligible effect outside cells, these AE become highly toxic near DNA within the cell nucleus. Therefore, these radionuclides can be used as a therapeutic anticancer agent if delivered precisely into the nuclei of tumor target cells. Modular nanotransporters (MNTs) designed to provide receptor-targeted delivery of short-range therapeutic cargoes into the nuclei of target cells are perspective candidates for specific intracellular delivery of AE emitters. The objective of this study was to evaluate the in vitro and in vivo efficacy of ¹¹¹In attached MNTs to kill human bladder cancer cells overexpressing epidermal growth factor receptor (EGFR). The cytotoxicity of ¹¹¹In delivered by the EGFR-targeted MNT (¹¹¹In-MNT) was greatly enhanced on EJ-, HT-1376-, and 5637-expressing EGFR bladder cancer cell lines compared with ¹¹¹In non-targeted control. In vivo microSPECT/CT imaging and antitumor efficacy studies revealed prolonged intratumoral retention of ¹¹¹In-MNT with t½ = 4.1 ± 0.5 days as well as significant dose-dependent tumor growth delay (up to 90% growth inhibition) after local infusion of ¹¹¹In-MNT in EJ xenograft-bearing mice.

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 ¹¹¹In 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 ¹¹¹In in high specific activity. Cytotoxicity of the ¹¹¹In-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 ¹¹¹In-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 ¹¹¹In delivered by these MNTs was greatly enhanced on receptor-expressing cancer cells compared with ¹¹¹In nontargeted control. In mice with B16-F1 tumors, prolonged retention of ¹¹¹In 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 ¹¹¹In-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 ¹¹¹In-NOTA–MNT suggests further applications of the MNT delivery strategy should be explored.

Photodynamic therapy and fluorescence diagnosis of malignant tumors have been actively developed over the last 15 years by the scientists participating in the Moscow Government-funded “Fight against...