Statistical analysis Statistical analysis was conducted using Students t test. A p value of 0. 05 was considered statistically significant. Results Generation of drug resistant cell lines The drug sensitive OV90 ovarian cancer cell line was used as a parental line to generate a series of drug resistant cell lines through repeated cycles of drug expo sure followed by recovery periods. Using this approach, we generated drug resistant OV90 sublines through exposure to cisplatin, doxorubicin, or paclitaxel. The lines derived through exposure to cisplatin, doxorubicin, and paclitaxel all exhibited significant resistance to their corresponding drugs compared to the parental OV90 cell. When cross resistance was investigated, we found that the cisplatin derived resistant lines were not cross resistant to doxorubicin or paclitaxel.

In contrast, the doxorubicin derived resistant cells exhibited significant cross resistance to pacli taxel, and the paclitaxel derived resistant cells were resistant to both cisplatin and dox selelck kinase inhibitor orubicin. Microarray analysis of gene expression in drug resistant ovarian cancer cell lines To identify genes and pathways important in the devel opment of drug resistance, we performed gene expres sion profiling analysis on the OV90 drug sensitive cell line and on the resistant cell lines using Illumina Sentrix microarrays. For each of the resistance types two independent sublines were profiled in duplicate. The raw data were deposited in the Gene Expression Omni bus database.

Multidimensional scal ing analysis based on gene expression data showed that the cell lines clustered according to the drug used in generating the resistance, demonstrating selleck chemical that the selection for resistance to differ ent drugs led to overall different patterns of gene expression changes. This suggested different mechan isms of resistance for the different drugs. Comparison of gene expression between sensitive and resistant lines revealed numerous genes differentially expressed. A total of 845 genes were found altered in at least one drug resistance phenotype. Looking at each resistance phe notype individually, 460, 366, and 337 genes were significantly altered in the development of resistance to cisplatin, doxorubicin, and paclitaxel, respectively. We identified 18 genes simultaneously elevated in all three drug resistant phenotypes and 44 were downregulated in all three.

Table 1 shows the top 20 most differentially expressed genes in each one of the three resistance phenotypes. When examining the downregulated genes, only CCL26 was found in the top 20 genes in all three resistance phenotypes. None of the top 20 up regulated genes was found in common between all 3 resistant phenotypes. Interestingly, several genes of the serine protease family were differentially expressed, although the direction of change was variable.