Abstract 4258: Molecular spectral CT imaging of Hsp70 positive solid tumors
Authors: Stangl Stefan , Shevtsov Maxim , Werner Caroline , Sievert Wolfgang , Multhoff Gabriele 
Published: September 2020

Abstract
Computed tomography (CT) imaging techniques play a major role in clinical imaging of malignant lesions. In recent years, this technique was expanded by the development of spectral CT techniques, offering the possibility to extract detailed information from spectral parameters of the imaged specimen. In particular, utilizing metal based contrast agent probes offer considerable advantages for tumor diagnosis and prognosis. Therefore, metal nanoparticle platforms enable effective payload delivery. In this work, we demonstrate the feasibility of anti plasmamembrane Heat shock protein 70 antibody conjugated spherical gold nanoparticles (cmHsp70.1-AuNP) for tumor specific in vivo spectral CT imaging, following intravenous application. The membrane associated form of Hsp70 (mHsp70) is exclusively presented on the plasma membrane of malignant cells of multiple tumor entities, but not on corresponding normal tissue cells, predestining this target epitope for tumor-selective in vivo targeting. Following incubation in vitro, the cmHsp70.1-AuNP were detectable in the cytoplasma of two cell lines being internalized via the endosomal-lysosomal pathway. In contrast, very low binding and internalization of isotype-labeled or blank NP were detectable. For characterization of the cell lines, cytoplasmatic and membrane-localized Hsp70 content was determined by flow cytometry, in-cell ELISA and Western Blot. Binding and internalization of the NP were investigated by Transition Electron Microscopy (TEM) and Mass Spectrometry (MS). In vivo, 24h after i.v. application in orthotopically and subcutaneously tumor bearing mice, the biodistribution as well as the intratumoral enrichment of AuNP were examined. AuNP were analyzed qualitatively and quantitatively by Silver enhancement technique of gold surfaces on histological slides, as well as by spectral CT analysis. Next to a minor enrichment in the tumor-associated Macrophages (due to camouflage by PEGylation), significant enrichment and explicit tumor delineation of cmHsp70.1-AuNP in tumors was detectable. Overall enrichment of the Isotype control mAb labelled AuNP was significantly lower. In contrast, the blank AuNP were found predominantly in tumor associated Macrophages near the main supplying blood vessels at the tumor borders.In summary, utilizing mHsp70 as target structure for guidance of Hsp70 functionalized Nanoparticles enables sufficient enrichment as well as uniform distribution of the cmHsp70.1-AuNP, adequate for spectral CT based tumor delineation. The study was supported by TaGoNaX DFG project № 336532926, STA1520/1-1 and the DFG grant SFB824/3 (TUM). Additional financial support was provided by RFBR 20-38-70039.
Citation Format: Stefan Stangl, Maxim Shevtsov, Caroline Werner, Wolfgang Sievert, Gabriele Multhoff. Molecular spectral CT imaging of Hsp70 positive solid tumors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4258.