Electron microscopy of antibody-conjugated, lutetium-177 lanthanide gold-coated nanoparticles: Proof of concept of targeted loci—A potential theranostic agent

Benjamin Kogos,Douglas C Miller,Nicholas Sobol,J David Robertson,Vesna Sossi,Leona Cohen-Gould,Cristina Rodriguez-Rodriguez,Richard Johnson,Paul H Pevsner

doi:10.1063/5.0044515

Abstract

Following murine injection, the ultrastructural loci of nanoparticles (NPs) containing lutetium-177 (Lu-177) conjugated to an anti-thrombomodulin antibody (mAb-201b) were determined. The results confirmed prior work localizing NPs using Single Photon Emission Computed Tomography (SPECT) scans. The in vivo pharmacokinetics of these NPs were also identified. mAb-201b antibodies are primarily attracted to the thrombomodulin, a membrane protein in the endothelium of the lung vasculature. SPECT images demonstrated NPs in the lungs, liver, spleen, and proximal small bowel. Prior injection of clodronate liposomes reduced the number of circulating macrophages, which, in turn, reduced NP phagocytosis. At 24 h after injection of NPs and after final SPECT imaging, the lungs, liver, spleen, and kidneys were harvested for transmission electron microscopy. Although some NPs were found in all four organs, 85% of the injected dose was localized in type I and type II pneumocytes. Small concentrations were found in secondary lysosomes in hepatocytes, in splenic macrophages, and in an intravascular macrophage in a kidney. Importantly, there was no apoptosis or necrosis in any of the tissues, highlighting the relative safety of the radionuclide NP, whose primary interaction with non-targeted organs/tissues is in the filtration process. In addition to validating the biodistribution results of the SPECT scans carried out in our prior work, this study is proof of principle that NPs conjugated with appropriate antibodies can target specific antigens in vivo. From a theranostic perspective, these results suggest that radioactive nanoconjugates labeled with proper antigens should be able to target and destroy a variety of cancers with minimal harm to the surrounding healthy cells.

Highlights

Nanoparticles (NPs) are being investigated as a potentially very efficient medium for targeted drug delivery with direct relevance to cancer treatment.This study was undertaken to verify and prove the accuracy of the targeted NPs in our prior study1 and to document the pharmacokinetics in vivo by demonstrating the cellular loci of the injected NPs
Our findings correlate with prior work localizing NPs using Single Photon Emission Computed Tomography (SPECT) scans
We previously described the methods to make the NPs and how the SPECT scans demonstrated their biodistribution in the body via gamma spectroscopy of lung, liver, spleen, and kidney tissues.1 mAb-201b antibodies are attracted to the thrombomodulin, an integral membrane protein that is ubiquitous in the endothelium of the pulmonary vasculature

Summary

Introduction

Nanoparticles (NPs) are being investigated as a potentially very efficient medium for targeted drug delivery with direct relevance to cancer treatment. This study was undertaken to verify and prove the accuracy of the targeted NPs in our prior study and to document the pharmacokinetics in vivo by demonstrating the cellular loci of the injected NPs. In that report, the Single Photon Emission Computed Tomography (SPECT) scans revealed the NP uptake in the lung, liver, spleen, and small bowel. The electron microscopic (EM) images in this study demonstrate the unequivocal targeting of the NPs toward the thrombomodulin antigen loci in the lungs. The progression of the NPs from the lungs to liver to biliary tract to small bowel portrays the pharmacodynamics of the NPs in vivo, paving the way for their use as cancer theranostics. This study demonstrates the elegant juncture of biology, physics, and engineering

Results

Discussion

Conclusion