Radiometals in Imaging and Therapy: Highlighting Two Decades of Research

177Lu-Labeled Iron Oxide Nanoparticles Functionalized with Doxorubicin and Bevacizumab as Nanobrachytherapy Agents against Breast Cancer

The use of conventional methods for the treatment of cancer, such as chemotherapy or radiotherapy, and approaches such as brachytherapy in conjunction with the unique properties of nanoparticles could enable the development of novel theranostic agents. The aim of our current study was to evaluate the potential of iron oxide nanoparticles, coated with alginic acid and polyethylene glycol, functionalized with the chemotherapeutic agent doxorubicin and the monoclonal antibody bevacizumab, to serve as a nanoradiopharmaceutical agent against breast cancer. Direct radiolabeling with the therapeutic isotope Lutetium-177 (177Lu) resulted in an additional therapeutic effect. Functionalization was accomplished at high percentages and radiolabeling was robust. The high cytotoxic effect of our radiolabeled and non-radiolabeled nanostructures was proven in vitro against five different breast cancer cell lines. The ex vivo biodistribution in tumor-bearing mice was investigated with three different ways of administration. The intratumoral administration of our functionalized radionanoconjugates showed high tumor accumulation and retention at the tumor site. Finally, our therapeutic efficacy study performed over a 50-day period against an aggressive triple-negative breast cancer cell line (4T1) demonstrated enhanced tumor growth retention, thus identifying the developed nanoparticles as a promising nanobrachytherapy agent against breast cancer.

Evaluation of a novel hexadentate 1,2-hydroxypyridinone-based acyclic chelate, HOPO-O6-C4, for 43Sc/47Sc, 68Ga, and 45Ti radiopharmaceuticals

INTRODUCTION

Chelators play a crucial role in the development of metal-based radiopharmaceuticals, and with the continued interest in 68Ga and increasing availability of new radiometals such as 43Sc/47Sc and 45Ti, there is a growing demand for tailored chelators that can form stable complexes with these metals. This work reports the synthesis and characterization of a hexadentate tris-1,2-hydroxypyridonone chelator HOPO-O6-C4 and its in vitro and in vivo evaluation with the above mentioned radiometals.

METHODS

To investigate the affinity of HOPO-O6-C4, macroscopic studies were performed with Sc3+, and Ga3+ followed by DFT structural optimization of the Sc3+, Ga3+ and Ti4+ complexes. Further tracer studies with 43Sc (and 47Sc), 45Ti, and 68Ga were performed to determine the potential for positron emission tomography (PET) imaging with these complexes. In vitro stability studies followed by in vivo imaging and biodistribution studies were performed to understand the kinetic stability of the resultant radiometal-complexes of HOPO-O6-C4.

RESULTS

Promising radiolabeling results with HOPO-O6-C4 were obtained with 43Sc, 47Sc, 45Ti, and 68Ga radionuclides; rapid radiolabeling was observed at 37 °C and pH 7 in under 30-min. Apparent molar activity measurements were performed for radiolabeling of HOPO-O6-C4 with 43Sc (4.9 ± 0.26 GBq/μmol), 47Sc (1.58 ± 0.01 GBq/μmol), 45Ti (11.5 ± 1.6 GBq/μmol) and 68Ga (5.74 ± 0.7 GBq/μmol), respectively. Preclinical in vivo imaging studies resulted in promising results with [68Ga]Ga-HOPO-O6-C4 indicating a rapid clearance through hepatic excretion route and no decomplexation whereas [43Sc]Sc-HOPO-O6-C4, [47Sc]Sc-HOPO-O6-C4 and [45Ti]Ti-HOPO-O6-C4 showed modest and significant evidence of decomplexation, respectively.

CONCLUSIONS

The tris-1,2-HOPO chelator HOPO-O6-C4 is a promising scaffold for elaboration into a 68Ga- based radiopharmaceutical.