Abstract 4379: Role of Nanog in resistance of prostate cancer cells toward chemotherapy

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Drug resistance is a major barrier to efficacious chemotherapy. Cancer stem cells (CSCs) may pose resistance to chemo- or radio-therapy, but the mechanism remains unknown. Nanog is a transcription factor essential for self-renewal of embryonic stem cells. The expression of Nanog has been reported in some cancer cells but its role in resistance to chemotherapy has not been convincingly demonstrated. Herein, we report that Nanog is expressed in tumorigenic prostate cancer cells and further it contributes to chemoresistance. Nanog expression was detected in prostate cancer cells by Western blot and RT-PCR and confirmed by sequencing. In the surviving fractions of prostate cancer cells after chemo-treatments, we found increased levels of Nanog expression and activities when compared to vehicle control-treated group. To determine the role of Nanog in resistance of prostate cancer cells, we marked and enriched Nanog-expressing prostate cancer DU145 using a reporter gene under control of 2.5 kb hNanog1 promoter. When compared to the control, the prospectively enriched Nanog-expressing cells had enhanced endogenous Nanog expression, increased positivity for stem/progenitor markers (CD44 and CD133), and presented increased resistance to Taxol, vinblastine, and doxorubicin, but not camptothecin (CPT). In addition, Nanog-enriched DU145 cells showed reduced apoptosis in the response to Taxol treatment, whereas control cells had increased activation of effector caspases after treatment with Taxol. Colony formation assay revealed that prostate tumor cells with enriched Nanog expression displayed increased recurrent ability after chemotherapy. Knockdown of Nanog by tet-inducible shRNA sensitized prostate tumor cells to multiple drug treatments, suggesting its essential role in prostate cancer chemo-resistance. Profiling of genes in drug resistance and metabolism revealed a marked increase in the mRNA levels of ATP-binding cassette (ABC) efflux transporters B1 and G2 in tumor cells enriched with endogenous Nanog expression. The increased expression of ABCB1 and ABCG2 in Nanog expressing cells was confirmed by Western blot and immunocytochemistry. Inhibition of ABCB1 activities or knockdown of ABCB1 expression sensitized Nanog expressing cells toward Taxol and vinblastine, but not doxorubicin. Knockdown of ABCG2 sensitized Nanog expressing cells toward doxorubicin, and to lesser extent, vinblastine, but not Taxol. Knockdown of Nanog reduced the expression of ABCB1 and ABCG2 and reduced the resistance of tumor cells toward chemotherapy. In summary, Nanog expression is associated with tumor cells positive for stem/progenitor markers and resistant to chemotherapy. The gain-of-function and loss-of-function studies suggest an essential role of Nanog for prostate cancer cells to resist chemotherapy via regulating the expression of ABC transporters. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4379. doi:10.1158/1538-7445.AM2011-4379