PO-278 Assessment of the influence of stellate cells on primary pancreatic cancer cell growth and drug resistance in a spheroid model: MET inhibitors to the rescue

Introduction Pancreatic ductal adenocarcinoma has one of the lowest 5 year survival rates among all cancers and it is going to be the 2nd leading cause of cancer death in 2030. Drug resistance and early metastasis are among the main causes of this dismal prognosis and tumour microenvironment may give a considerable contribution to this aggressive behaviour. Pancreatic stellate cells (PSCs) are the main source of cancer-associated fibroblasts in stroma, and are suspected to induce drug resistance by paracrine secretion of hepatocyte growth factor (HGF) and activation of the MET receptor in cancer cells. Material and methods We first examined the effect of human PSC conditioned medium on the growth and drug resistance of six different primary cell cultures isolated from PDAC patients by sulforhodamine B (SRB) assay growing as monolayers. Further, we developed a spheroid 3D-co-culture with PDAC5-SSEA4 and immortalised or primary PSC cells and examined the effects of different drugs by luciferase assay, immunofluoresence and confocal microscopy. Results and discussions Conditioned medium of stimulated PSC cells, i.e., primed with PDAC conditioned medium, gave growth advantage to different primary PDAC cells and made them several times more resistant to gemcitabine and oxaliplatin. PDAC5-SSEA4/PSC spheroids were much more resistant to gemcitabine and oxaliplatin compared to PDAC5-SSEA4 spheroids. However, MET inhibitors such as tivantinib and PHA-665752 were equally effective in homo and heterospheroids. Of note, immortalised and primary PSC cells had similar influences on the behaviour of PDAC cells in spheroids. Conclusion We successfully developed a 3D-spheroid model to evaluate the interaction of primary PDAC cells with PSCs. Pharmacological studies provided evidence that spheroids containing PSCs are much more resistant to cytotoxic drugs. Conversely MET inhibitors seem to be valuable tools to overcome the drug resistance of PDAC cells caused by the presence of PSC cells.