Although Dox retention in both shERK1 and shERK2 groups was simi lar, the increased toxicity of Dox in the shERK2 group could be attributed to additional factors. Figure 3B confirms selleck chem inhibitor the patterns of Dox accumu lation by fluorescence microscopy in MM cells. Note the lack of Dox in the 0 and the dose related increases in intracellular fluorescence present in the shERK1 and shERK2 cells. Effect of ERK1 or ERK2 inhibition on ATP binding cassette genes in MM cells Inhibitors,Modulators,Libraries Based on data above and in Table 1, we next hypothe sized that ERKs modulated endogenous expression of ABC cassette genes that function to pump Dox and other chemotherapeutic drugs out of tumor cells, result ing in their decreased drug sensitivity. To address this hypothesis, we performed microarray analysis on shERK1, shERK2 and shControl HMESO cells.

Table 2 provides a list of 7 ABC genes that had decreased mRNA levels in shERK1 and shERK2 cell lines. Valida tion of several changes Inhibitors,Modulators,Libraries in gene expression was per formed using qRT PCR. We also examined endogenous levels of ABC transporter genes in HMESO MM cells as com pared to nontransformed human mesothelial cells LP9/ TERT 1. These results showed that HMESOs showed striking decreases in mRNA levels of ABCG2 and ABCA1 as well as signifi cant decreases in ABCA8, ABCC3, ABCB1, ABCG1 and ABCC4 expression, whereas other genes were upregulated. Tumors developing from shERK1 and shERK2 MM lines in a mouse xenograft model show decreased tumor growth rate after treatment with Dox To verify the functional effects of ERK inhibition and Dox treatment on tumor cell killing, we injected stable shERK1, shERK2 or shControl HMESO MM cells sub cutaneously into SCID mice, and treated various groups with Dox or saline at the tumor site as soon as tumors appeared for a 6 wk period.

As shown in Figure 4, Dox significantly reduced the rate of tumor growth in all three animal Inhibitors,Modulators,Libraries groups compared to saline treatment, with the largest reduction occurring in Inhibitors,Modulators,Libraries the shControl group. In addition, Dox treated animals in the shERK1 or shERK2 groups had significantly slower tumor growth than the Dox treated animals in the shControl group. The differences between the shControl Dox treated and shERK1 Dox treated tumor growth rates occurred prior to 21 days post MM cell injection. All conclusions were derived by statistical analysis performed on different groups to compare alterations in tumor growth rate and not tumor volume.

Discussion Treatment of various MM lines with doses of Dox much lower than LD50 concentrations resulted Inhibitors,Modulators,Libraries in phosphoryla tion of ERK1 and 2, the most abundant http://www.selleckchem.com/products/Tipifarnib(R115777).html ERKs in mamma lian cells. In addition to Dox, many other anti cancer drugs such as paclitaxel and cisplatin induce activation of ERKs in different tumor types. However, taxol inhibits ERK activation in different cell types depending upon experimental conditions.