Abstract 3872: Quantitative measurement of immune-modulatory mediators within tumors of freely moving mice utilizing in vivo microdialysis
Authors: Morisot Nadege , Roeser Julien , Schiewe Hajo , Janssens Holden Brown , Hart Marieke van der , Rassoulpour Arash 
Published: August 2018

Abstract
Monitoring changes in biochemical elements within tumors is crucial to understanding cancer biology and to helping with the development of novel therapies. Yet to date, experimental techniques enabling sensitive and quantitative measurement of the levels of small molecules contributing to tumor development have been limited in preclinical oncology models. In the current set of experiments, we implemented in vivo microdialysis to measure signaling molecules and oncometabolites in the tumor microenvironment of freely moving rodents. To this aim, a small dialysis probe is implanted in syngeneic tumors in mice. Probes are perfused with artificial dialysate fluid and dialysate containing molecules from the tumor microenvironment is collected at regular intervals. Levels of biochemicals in the dialysate are then quantified by liquid chromatography-mass spectrometry (LC-MS), a robust and sensitive quantitative technique. We report here proof-of-concept results supporting the use of in vivo microdialysis coupled to LC-MS in cancer research. First, we tested whether implantation of dialysis probe affects in vivo tumor growth. To do so, tumor volume from probe-implanted and non-implanted MC38 allografts in mice was monitored daily for up to 10 days following probe implantation. We found that the growth curve from probe-bearing MC38 tumors was similar to probe-free tumors, revealing that probe implantation did not influence tumor size progression. Next, the levels of metabolites that are known to be involved in tumor development were measured in tumor allografts of freely-moving mice using in vivo microdialysis. Relevant levels of arginine, ornithine and putrescine were quantified by LC-MS. Levels of key molecules of the adenosine signaling and tryptophan/kynurenine pathway metabolites in MC38 tumors were also quantified. To better understand the homogeneity of this particular allograft model, we measured the concentration of the above-mentioned molecules in different regions of a tumor. To this end, two separate probes were implanted in the center and the peripheral area of the same 300 mm3 MC38 allograft. We found that levels of measured molecules were similar in dialysates collected from both probe locations, suggesting homogenous levels of biochemicals throughout the microenvironment of these non-necrotic tumors. Our proposed experimental approach allows for a quantitative and sensitive measurement of key biochemical mediators of tumor progression. In vivo microdialysis in murine tumor models may be used to elucidate the mechanisms by which therapies, such as chemotherapy and immune checkpoint inhibitors, modulate the tumor microenvironment. Our efforts in preclinical cancer research has the potential to bring new insights on the mechanisms underlying cancer development and help the discovery of next-generation therapies for cancer
Citation Format: Nadege Morisot, Julien Roeser, Hajo Schiewe, Holden Brown Janssens, Marieke van der Hart, Arash Rassoulpour. Quantitative measurement of immune-modulatory mediators within tumors of freely moving mice utilizing in vivo microdialysis [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 3872.