[Proc Amer Assoc Cancer Res, Volume 47, 2006]
Experimental and Molecular Therapeutics 42: Circumventing Drug Resistance
Is cytoplasmic localization of topoisomerase I (topo I) a mechanism of resistance for topo I inhibitors? Results from an NCCN sponsored phase II trial of gemcitabine and irinotecan in metastatic breast cancer.
Stacy L. Moulder,
Caio Rocha Lima and
University of Texas, M.D. Anderson Cancer Center, Houston, TX, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, Sylvester Cancer Center, Miami, FL
Background: Preclinical data indicate that the incorporation of gemcitabine into DNA enhances cleavage complexes in vitro when combined with a topo I inhibitor. Since topo I requires nuclear localization to exert its activity, predominate localization of topo I within the cytoplasm may predict for drug resistance. Methods: After obtaining informed consent, 48 patients with anthracycline refractory MBC received therapy with gemcitabine at 1000mg/m2 and irinotecan at 100mg/m2 on days 1 and 8 of a 21day cycle. Response was measured using RECIST criteria. Optional tumor biopsies were obtained by FNA in 9 patients prior to initiation of therapy. Topo I was detected by immunofluorescence using the C-21 murine monoclonal IgM antibody directed against an epitope in the C-terminal 67 kDa. A monoclonal antibody that recognizes a conserved epitope in all 5 histones was used to identify nuclei and function as an internal control for sample variation. Quantification of topo I was performed on 50 randomly selected tumor cells/sample with measurements confirmed by Adobe Photoshop 7.0. Each cellular compartment was quantified separately in pixels and nuclear/cytoplasmic ratios were calculated for each individual cell. Results: Of the 48 patients enrolled, 45 have been evaluated for response with an overall response rate of 25% (CR=0, PR=11). 3 patients had SD for >6 months for a clinical benefit rate of 32%. 7/9 tissue biopsies were assessable for top1 and are listed in the table below. Conclusion: Gemcitabine and irinotecan is an active combination for metastatic breast cancer. Topo I localization can be measured in breast tumors using FNA. In this data set, the two lowest nuclear to cytoplasmic ratios were associated with lack of response to irinotecan. Further validation is needed.
Copyright © 2006 by the American Association for Cancer Research.