Chemogenomic study of gemcitabine using Saccharomyces cerevisiae as model cell-molecular insights about chemoresistance.

Gemcitabine (GEM) is the drug used as first line to treat pancreatic cancer, one of the most devastating human tumors. This peculiar type of tumor develops resistance to several drugs, including GEM, due to its desmoplastic reaction and other features. The GEM chemoresistance has been investigated at molecular level aiming to find a pathway whose inhibition or activation should overcome it. Through next-generation sequencing was performed a chemogenomic assay of GEM using Saccharomyces cerevisiae as model cell and the results showed that more than 40% of genes related to GEM response in yeast possess unknown or dubious function. We choose two yeast mutants to individually validate the fitness defect results observed by chemogenomic assay, Δhmt1 and Δcsi1, and it was found that in addition to some already described pathways involved in GEM resistance, cells deficient in deneddylation enzyme Cop9 Signalosome Interactor 1 (Csi1p) presented a high sensitivity to GEM. This was confirmed by individual growth analyses of Δcsi1 cells exposed to GEM, and this phenotype was reverted with CSI1 complementation gene. Csi1p is a well-characterized homolog equivalent to human Csn6 subunit of COP9 signalosome (CSN) involved in deneddylation process. We highlighted too that epigenetic alterations, such as methylation mediated by protein arginine methyltransferase 1, play an important role in regulating gemcitabine treatment resistance. Our results point out new unexplored molecular pathways that can be used to overcome GEM resistance: the inhibition of CSN and the arginine methyltransferase activities.