R. Jaskula Sztul1,3, G. Chen2, A. Harrison1, S. Gong2, H. Chen1,3 1University Of Wisconsin,Surgery,Madison, WI, USA 2University Of Wisconsin,Wisconsin Institutes For Discovery,Madison, WI, USA 3University Of Alabama,Surgery,Birmingham, Alabama, USA
Introduction: Although neuroendocrine tumors (NETs) are slow growing, they are frequently metastatic at the time of their discovery and no longer amenable to curative surgery. Therefore, there is a great need to develop novel therapeutic strategies both to reduce tumor burden and control the release of hormones. To address this need, we developed and optimized a family of novel multifunctional upconversion nanoparticle (UCNP)-based theranostic unimolecular micelles capable of delivering a newly reported anticancer drug AB3 for NET-targeted combination chemotherapy, photodynamic therapy (PDT), and bioimaging. These UCNP-based micelles conjugated with photosensitizer (Rose Bengal, RB) specifically target NET cells using somatostatin analog (KE108). In the current study we assessed the antitumor effects of the nanotheranostic micelles both in vitro and in vivo.
Methods: Stable UCNP-based micelles were prepared in an aqueous solution using multi-arm star amphiphilic block copolymer. KE108 was conjugated for active tumor-targeting. AB3 was loaded into the photosensitive hydrophobic core of the resulting micelles. The effect of 980nm on singlet oxygen generation and in vitro drug release of the UCNP-based micelles were studied. Cell proliferation was assessed by MTT assay in human medullary thyroid cancer cell line (MZ-CRC-1) treated with a family of AB3-loaded micelles (AB3 mM) for 48h with or without 980nm irradiation. The effect of the KE108 targeting ligands on the cellular uptake of the nanotheranostic micelles was measured by flow cytometry and confocal laser scanning microscope (CLSM). The antitumor efficacy of AB3-loaded micelles was determined in GI neuroendocrine (BON) xenografts after two intravenous injections performed with 7 day interval with a dose of 20 mg/kgBW. The group treated with UCNP-based micelles containing RB was irradiated for 15 min with 980nm laser at 4h post injection.
Results: The family of UCNP-based NET-targeting unimolecular micelles was developed for targeted delivery of AB3 and RB to NETs. UCNP-based micelles for targeted and combined chemotherapy with PDT exhibited the strongest antiproliferative effect. Moreover, the targeted micelles exhibited a much higher cellular uptake than non-targeted micelles based on flow cytometry and CLSM analyses. Additionally, AB3 loaded micelles conjugated with RB and KE108 (i.e., T-RB-AB3), enabling combined chemo-therapy and PDT, induced the best antitumor efficacy (82% reduction in tumor volume) and did not cause any significant changes in body weight or survival. Pathological assessment of H&E-stained sections of different organs of mice treated with T-RB-AB3 micelles did not indicate any signs of inflammation or necrotic regions.
Conclusion:The AB3-loaded UCNP-based micelles conjugated with both RB and KE108, offering combination chemotherapy and PDT, are more effective at suppressing NET cell growth while having minimal toxicity to non-NET cells.
