Abstract 1462: Characterization of patient-derived bladder cancer xenografts: role of xCT in response to cisplatin

Background: A major challenge in cancer drug development has been largely attributed to the inability of cell lines to recapitulate the heterogeneity of human tumors. Patient derived xenografts (PDX) represent a major advance as they are more representative of the clinical setting. However, appropriate characterization of PDXs is necessary to guide biomarker driven drug discovery research. Methods: H&E staining was used to compare the original patient tumors with PDX developed from cystectomy specimens to validate morphological similarity. Immunohistochemical (IHC) staining for cytokeratins (CK) 5/6 & 20 and EMT markers E cadherin and vimentin were used to identify whether these tumors represent a basal or a luminal subtype. In addition, Western blot and RT-PCR analysis were performed to assess markers of epithelial-to-mesenchymal transition (EMT). Therapeutic response to cisplatin was evaluated both in vitro and in vivo. Furthermore, expression of xCT (cystine transporter), one of the known cisplatin resistance markers, was determined by RT-PCR, Western blot and IHC in PDXs and cells. Results: Morphologically, we observed that our PDX models (RP-B-01 and RP-B-02) did not drift from the original patient tumors and they still retained their characteristic stromal features. Based on cytokeratin (CK) staining, we found both models to be CK 5/6 positive and CK 20 negative, suggesting a basal subtype of bladder cancer. Both PDXs, similarly to the original tumors, were E cadherin positive. However, cells derived from these tumors and cultured in vitro lost E cadherin and acquired vimentin expression, suggesting an EMT phenotype. When cells from PDX were transplanted back into mice they re-expressed E cadherin and lost vimentin expression, suggesting a reversion to MET. Despite no difference in cytokeratins and EMT markers between the two models, both PDX and cells isolated from PDXs had differential expression of xCT and possessed differential response to cisplatin treatment. RP-B01 expressed higher levels of xCT and was less responsive to cisplatin as compared to RP-B-02 which expressed lower levels of xCT. Conclusion: Differential expression of xCT in bladder cancer PDXs and cells correlated with cisplatin response, suggesting that pharmacological targeting of xCT in combination therapies will enhance cisplatin efficacy in bladder cancer. Citation Format: May F. Elbanna, Eric Ciamporcero, Swathi Ramakrishnan, Remi Adelaiye, Li Shen, Ashley Orillion, Sheng-Yu Ku, Sreenivasulu Chintala, Roberto Pili. Characterization of patient-derived bladder cancer xenografts: role of xCT in response to cisplatin. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1462. doi:10.1158/1538-7445.AM2015-1462