Figure 5B shows that these cell http://www.selleckchem.com/products/SB-203580.html lines express the long 50 UTR MDR1 mRNA and, furthermore, that TSA treatment decreased the levels of expression of the long 50 UTR MDR1 mRNA in all of them. Even more, we used K 562 cell sublines resistant to different con centrations of daunomycin that have been generated in our laboratory by selective pressure with increasing con centrations of the drug. We have previously shown that resistance to daunomycin in this sublines was related to the active expression of P glycoprotein, and that this ex pression correlates with the expression of the long 50 UTR MDR1 mRNA. As shown in Figure 5C, TSA was able to increase daunomycin accumulation in the K 562 d20, a subline that expresses P glycoprotein and the long 50 UTR MDR1 mRNA associated with the USP promoter.

This result suggests that TSA decreases P glycoprotein ex pression leading to an increased accumulation of dauno mycin in these cells. Futhermore, as shown in Figure 5C, TSA downregulated MDR1 mRNA, as determined by real time PCR in K 562 d450, a cell subline which expresses high levels of P glycoprotein and also the long 50 UTR MDR1 mRNA. Meanwhile, TSA increased the expression of the MDR1 mRNA in the parental K562 that does not express P glycoprotein and expresses the short 50 UTR MDR1 mRNA. TSA effect on RUNDC3B mRNA levels The ABCB1 gene is located in a genetic locus with the nested gene RUNDC3B in the complementary DNA strand . Based on this special localization, we investigated whether the expression of RUNDC3B mRNA was regulated by TSA and whether the expression of this mRNA was related to the expres sion of the short or the long 50UTR of the MDR1 mRNA.

As shown in Figure 6B, TSA upregulates RUNDC3B mRNA expression levels independently of the MDR1 mRNA isoform expressed in the different cell lines. Discussion In the present study, we demonstrate that the increase in MDR 1 mRNA levels induced by iHDACs inhibitors in pancreatic adenocarcinoma cell lines does not parallel an increase in Pgp protein or in Pgp activity. Anacetrapib This obser vation is important since we and others have reported that the histone deacetylase inhibitors TSA and SAHA induce two major effects in several drug resistant cell lines down regulation of Pgp and induction of apop tosis. In that sense, we have demonstrated that TSA markedly reduced Pgp expression in the L1210R drug resistant murine cell line and sensitized these cells to daunomycin, as shown in Figure 1C, where TSA treatment increases DNM accumulation in L1210R cells, suggesting that iHDACs might have a therapeutic potential against chemoresistant tumours.