Abstract LB-369: In vivo imaging of tumor senescence with a novel beta-galactosidase specific PET tracer
Authors: Krueger Marcel A. , Cotton Jonathan M. , Zhou Benyuan , Wolter Katharina , Kuehn Anna , Schwenck Johannes , Fuchs Kerstin , Maurer Andreas , Fougere Christian la , Zender Lars , Pichler Bernd 
Published: August 2018

Abstract
Senescence is a response to cellular stress and induces a durable cell cycle arrest, which has essential effects on metabolism as well as treatment outcome in cancer. Therefore the development of a diagnostic tool to detect senescent cells in vivo in cancer patients is of great interest. Here, the development of a novel PET tracer for non-invasive imaging of beta-galactosidase as a surrogate marker for senescence is described. Three different in vitro models were used to test the tracer. In HCT116 cells senescence was induced by doxorubicin, while in an HRas driven liver progenitor cell line it was induced by a doxycycline-dependent p53-specific shRNA. Finally, in a hepatocellular carcinoma cell line a ribosomal checkpoint inhibitor (RCI) was used for senescence induction. After incubation of the senescent cell lines with the tracer, we measured the activity of the cells in a gamma-counter, to assess the tracer uptake. For in vivo studies, the in vitro tested cells lines were injected s.c. in mice. These xenograft tumor bearing mice were treated with doxorubicin, doxycycline or RCI for senescence induction, depending on the cell line used. After i.v. injection of the tracer, PET/MR scans were performed to assess tracer uptake in the tumors (% of the injected dose/cc; %ID/cc) and tumor-to-muscle ratios. In vitro tracer uptake was significantly increased in all three cellular models used, compared to the respective control cells. The strongest increase was observed in the hepatocellular carcinoma cell line with an increase from 0.06 %ID/106 cells in control cells to 0.21 %ID/106 cells in senescent cells. In vivo PET/MRI revealed an enhanced tracer uptake in mice bearing HCT116 tumors after senescence induction (1.7 %ID/cc) compared to mice without senescence inducing treatment (1.1 %ID/cc). In the HRas model, the tracer uptake in senescent tumors was increased from 0.9 %ID/cc in control tumors to 1.5 %ID/cc in senescent tumors and in the hepatocellular carcinoma model we could observe an increase from 0.6 %ID/cc in control mice to 1.1 %ID/cc in treated mice. Ex vivo beta-galactosidase staining and immunohistology of tumor tissue confirmed induction of senescence. In this study we were able to show an increased uptake of our novel beta-galactosidase specific PET tracer in vitro in senescent cells as well as in vivo in murine xenograft tumor models. Therefore our tracer could become the first tool for non-invasive detection of senescence in patients. First-in-man studies are currently being prepared.
Citation Format: Marcel A. Krueger, Jonathan M. Cotton, Benyuan Zhou, Katharina Wolter, Anna Kuehn, Johannes Schwenck, Kerstin Fuchs, Andreas Maurer, Christian la Fougere, Lars Zender, Bernd Pichler. In vivo imaging of tumor senescence with a novel beta-galactosidase specific PET tracer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-369.