Abstract B12: Understanding the role of the tumor microenvironment in mediating resistance to anti-MET drugs
Authors: Corso Simona , Apicella Maria , Giordano Silvia 
Published: May 2015

Abstract
Resistance to targeted therapy represents a major challenge to the treatment of cancer patients. Many data support the role of tumor stroma in modulating tumor progression, but little is known about its potential role in drug resistance. This is mostly due to the fact that resistance to targeted therapies has been mainly studied in vitro; thus in vivo tumor models that better mimic human tumors are absolutely needed.
Since MET, the tyrosine kinase receptor for Hepatocyte Growth Factor, is frequently implicated in resistance to kinase-targeted therapies and MET Tyrosine kinase inhibitors (TKIs) are currently in advanced phases of clinical trials, our aim was to investigate a possible role of non-cell-autonomous (microenvironment-mediated) mechanisms of resistance to MET-TKIs.
We generated in vivo models of MET-addicted tumors resistant to anti-MET treatment, subcutaneously injecting the non–small cell lung carcinoma cell line-EBC-1 and the gastric carcinoma cells GTL16 in NOD-SCID mice and treating them with MET inhibitors (JNJ-38877605 or CRIZOTINIB) until resistance onset. In parallel, untreated tumors were used as control.
We analyzed both tumors and cells (tumor cells and murine fibroblasts) isolated and put in culture from WT and resistant (RES) tumors. Through cell viability assays we demonstrated that six out of seven xeno-derived tumor cell lines were not or poorly resistant in vitro to MET inhibitors, suggesting a possible involvement of microenvironment in sustaining resistance.
We reasoned that the stroma of the resistant tumors could be qualitatively and/or quantitatively different from that of the wild-type tumors. To support this idea murine-gene arrays showed a significantly different gene expression profile between WT and resistant murine stroma. Gene-annotation enrichment analysis showed that inflammatory pathways and cancer-associated fibroblast (CAF) genes were particularly up-regulated in resistant versus wt tumors.
In order to understand whether the stroma may confer resistance to MET TKIs, we started to perform in vitro- and in vivo- co-colture experiments. In vitro experiments suggest that tumor cells co-cultured with fibroblasts were less sensitive to the MET inhibitors. We also performed preliminary in vivo experiments to demonstrate that the stroma of resistant tumors can induce resistance. We injected wild-type EBC1 cells (highly sensitive to MET inhibitors), transduced with the luciferase gene, into pre-existing wild-type or resistant tumors. Then we treated mice with the MET inhibitor JNJ-38877605 and monitored the luciferase signal. At the end of the experiment, by IVIS imaging analysis, we observed a decrease of the EBC1 luciferase signal (that is death of the WT labeled injected cells) in WT tumors treated with the MET inhibitor, but an increased luciferase signal in the resistant tumors (meaning that luciferase-labeled WT cells did not die in the presence of the MET inhibitor when in the contest of resistant tumors).
All together our experiments suggest that the microenvironment of resistant tumors can induce resistance to targeted therapies, protecting tumor cells from the effect of the drug.
Citation Format: Simona Corso, Maria Apicella, Silvia Giordano. Understanding the role of the tumor microenvironment in mediating resistance to anti-MET drugs. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Drug Sensitivity and Resistance: Improving Cancer Therapy; Jun 18-21, 2014; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(4 Suppl): Abstract nr B12.