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Paper 4 (0900)
MUC1 PLAYS A ROLE IN TUMOR MAINTENANCE IN AGGRESSIVE THYROID CARCINOMAS
Background: We recently identified MUC1 as a target of 1q21 amplification and validated it as an independent marker of aggressive behavior in thyroid cancer (TC) (Wreesmann V, et. al. Cancer Res. 2004;64:3780-9). The aims of this study were to determine if TC cell lines retain MUC1 expression patterns seen in primary tumors, assess the role of MUC1 in tumor maintenance and develop a virally delivered anti-MUC1 RNAi that is effective in decreasing MUC1 expression in vitro.
The 26th Annual Meeting of the American
Association of Endocrine Surgeons
April 3rd- 5th,2005 - Paradisus Riviera Cancun.
Kerstin Lorenz MD, Curd Behrmann MD; Carsten Sekulla PhD,
K. Patel, MD, E. Maghami, MD, V. Wreesmann, MD, A. Shaha, MD, J. Shah, MD, R. Ghossein, MD, B. Singh, MD, PhD.
Memorial Sloan-Kettering Cancer Center New York, NY, USA
Methods: Fifteen TC cell lines were screened for MUC1 expression by Western blot analysis. Cell lines with low (KAT5, KAT10), high (KAT4) and undetectable MUC1 expression (KAT18) were treated with increasing concentrations of anti-MUC1 monoclonal antibody (0.01-1.0ng/µl) and studied by MTT (3,[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) cell viability assays. Several short hairpin RNAi constructs against MUC1 were developed and cloned into a recombinant retroviral delivery system. Efficacy and optimal dosing of retrovirally delivered RNAi against MUC1 was established by infection and expression screening. Virus containing a scrambled construct was also developed for control experiments.
Results: Similar to expression patterns in primary tumors, increased MUC1 expression was found in aggressive TC cell lines (7/10) but not in classical papillary TC cell lines (0/5). Blocking MUC1 by antibody treatment resulted in a significant decrease in cell viability in all MUC1-expressing cell lines (p<0.02), but not in the cell line lacking MUC1 expression. The MUC1-779 RNAi construct showed excellent infection efficiency and reproducible silencing when delivered in 3 serial infections. In contrast, no MUC1 suppression was seen after infection with virus containing the control scrambled construct.
Conclusions: These data offer functional evidence implicating MUC1 over-expression as a key molecular event in the pathogenesis of aggressive TC. Moreover, it appears that certain TC cells are dependent on high levels of MUC1 protein, offering an opportunity for therapeutic targeting. Retrovirally delivered anti-MUC1 RNAi is effective in silencing MUC1 and merits further investigation to establish therapeutic efficacy and safety in anticipation of potential clinical application.