Expression Microarray Analysis and Oligo Array Comparative Genomic Hybridization of Acquired Gemcitabine Resistance in Mouse Colon Reveals Selection for Chromosomal Aberrations

Abstract

Gemcitabine is a commonly used therapy for many solid tumors. Acquired resistance to this nucleoside analogue, however, diminishes the long-term effectiveness in a majority of patients. To better define the molecular background of gemcitabine resistance, a mouse colon tumor was selected during successive rounds of transplantation with continued treatment of gemcitabine. Expression microarray analysis was applied to determine which genes are consistently and highly overexpressed or underexpressed in the resistant versus the nonresistant tumor. For the statistical interpretation of the microarray data, a parametric model was implemented, which returns model-based differential gene expression (log-) ratios and their uncertainties. This defined a set of 13 genes, putatively responsible for the gemcitabine resistance in solid tumors. One of these, RRM1, was previously identified as an important marker for gemcitabine resistance in human cell lines. Five of the 13 genes, including RRM1, are located within a 3 Mb region at chromosome 7E1 of which four are highly overexpressed, suggesting a chromosomal amplification. Therefore, chromosomal copy number changes were measured, using oligo array comparative genomic hybridization. A narrow and high amplification area was identified on 7E1 that encompassed all five genes. In addition, reduced RNA expression of two other genes at 8E1 encoding COX4I1 and RPL13 could be explained by a decrease in chromosomal copy number on chromosome 8. In conclusion, the array comparative genomic hybridization biologically validates our statistical approach and shows that gemcitabine is capable to select for chromosomally aberrant tumor cells, where changed gene expression levels lead to drug resistance. (Cancer Res 2005; 65(22): 10208-13)

Bexarotene (LGD1069, Targretin), a Selective Retinoid X Receptor Agonist, Prevents and Reverses Gemcitabine Resistance in NSCLC Cells by Modulating Gene Amplification

“…Although we have not directly determined whether, as for rrm1, this is also due to increased DNA copy number, the high concentration of overexpressed genes together with the measured increase in rrm1 DNA locus suggests a general amplification of this region. This is also in agreement with amplification of the mouse 7E1 locus, as measured by comparative genomic hybridization and observed with gemcitabine resistance in a mouse colon tumor model (25). The mouse 7E1 region corresponds to the human chr11p15.5 locus and also contains rrm1 as well as several other homologues contained in the human chr11p15.5 locus.…”

Expression Profiling of Rectal Tumors Defines Response to Neoadjuvant Treatment Related Genes

“…Moreover, there has been little agreement between signatures, with scarce overlap in the reported genes [4]–[16]. Only two genes, MMP4 and FLNA, have been reported in more than one paper [7], [8], [13] and one of the 257 genes reported in this study RRM1 (an important marker for chemotherapy resistance in colon tumors [17]), was also identified by Nishioka [13]. This could be due to variations in the inclusions criteria, schedule of neoadjuvancy, sample collection, patient characteristics, definition of response, types of platform used and data analysis.…”

In vivo Induction of Resistance to Gemcitabine Results in Increased Expression of Ribonucleotide Reductase Subunit M1 as the Major Determinant

“…The used microarray and real-time PCR assays do not give insight in mutations, genomic polymorphisms, and posttranslational modifications such as protein phosphorylation, although other genes are coamplified or deleted (36). In addition, it is also known that P53 can regulate ribonucleotide reductase expression and activity (37).…”