This study describes the development of a rapid and practical real-time RT-PCR method to quantify ribonucleotide reductase M2 (RRM2) mRNA in tumor and peripheral white blood cells (WBCs) from patients treated with GTI-2040, an antisense drug currently in clinical trials. In order to assess target down-regulation by GTI-2040, RRM2 mRNA expression levels were analyzed in pre- and post-treatment samples from a phase II clinical trial of GTI-2040 combined with capecitabine in patients with metastatic breast cancer. Target gene RRM2 mRNA levels were evaluated using quantitative RT-PCR method: real-time PCR (TaqMan®) with fluorescein labeled probes on an ABI 7900HT instrument, with additional post-processing of the data to adjust for differences in total RNA in-put across the samples. Data are presented from a patient for whom both biopsy and PBMC samples were available, demonstrating applicability of this reproducible, highly sensitive real-time RT-PCR method for the detection and quantification of mRNAs for RRM2 in human WBC and tissue samples. By providing quantitative measurement of changes in target gene expression, this method may provide an opportunity to determine the correlation between target response to GTI-2040 antisense and clinical response in patients. Furthermore this assay may assess whether WBC samples are an appropriate surrogate tissue for approximating target down-regulation in the tumor.

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