Abstract 1358: Epithelioid and fibroblastic cell elements coexisting within the sarcomatoid renal carcinoma RCC52 cell line ensue divergent routes of tumor differentiation and progression

The immunobiology of sarcomatoid renal cell carcinoma and its transformation from and to the clear cell RCC cells are not fully understood. We analyzed a human sarcomatoid RCC cell line known as RCC52, derived from a primary lesion of clear cell RCC with extensive sarcomatoid differentiation. When grown as monolayers, RCC52 cells were all PAX-2 negative and consisted of mostly epithelioid cells and occasionally spindle/fibroblastic cells, suggestive of in vitro growth of the sarcomatoid, but not clear cell, component of the tumor. PAX-2 is a transcription factor found in all major RCC types including clear cell RCCs, but not in sarcomatoid RCCs. We next isolated and maintained a panel of epithelioid and fibroblastic clonal sublines. As determined by cDNA microarray analysis, cancer stem cell (CSC) marker genes, such as ALDH1L1, PSCA and ABCA2, were expressed greater in the epithelioid sublines, while mesenchymal-like cell marker genes including vimentin, snail, fibronectin and MMPs were expressed in much higher levels in the fibroblastic counterpart. Xenotransplantation in NOD/SCID mice showed that in contrast to fibroblastic sublines failing to developed tumors, epithelioid sublines invariably developed tumors at the injection sites. These results point to the existence of CSCs in the epithelioid, but not fibroblastic sublines. In order to investigate the self-renewal/colongenicity ability of these two types of clonal sublines, we used soft agar assay to assess their differential anchorage-independent colony forming abilities. Results showed the mean colony number in the parental RCC52 cells at day 28 was 293.3 ± 81.3 colonies/well, in the epithelioid sublines, the mean colony number was 322.2 ± 92.0 colonies/well. In contrast, no visible colonies were detected in any of the fibroblastic sublines tested. These results are consistent with those obtained in the xenotransplantation studies. Another important observation was that only epithelioid sublines developed xenografts in which clear cell component which was identified by its positive PAX-2 reactivity by immunostaining in some areas of tissue sections. Surprisingly, xenografts resulting from subcutaneous injection of RCC52 cells and the original patient tumor shared similar histopathology in that mostly sarcomatoid cells were noted with occasional clear cell areas. In conclusion, our results strongly point to the capability of sarcomatoid RCCs to undergo dedifferentiation or transdifferentiation. Further investigations into the molecular events responsible for sarcomatoid transformation from clear cell RCCs and for the progression of clear cell RCCs to sarcomatoid ones using additional tissues and cell lines of either types are warranted. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1358. doi:1538-7445.AM2012-1358