Abstract 3120: RUNX2 rescues the inhibitory effect of FGFR-2 silencing and increases the metastatic potential of IBH-6 human breast cancer xenografts

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Carcinoma associated fibroblasts participate in the regulation of breast cancer growth. We have shown that FGF2 is one of the growth factors involved in tumor progression that activates FGFR-2 and progesterone receptors (PR) increasing the proliferation of breast cancer cells (Cerliani et al, Cancer Res 2011). In addition, we have also shown an increased expression of RUNX2 in tumor cells with acquired hormone independence. It has been suggested that RUNX2 regulates the expression of FGFR2, and on the other hand that FGF2 increases RUNX2 expression. The aim of this study was to evaluate the interplay between FGFR-2 and RUNX2 using a human breast cancer xenograft model. IBH-6 cells express ERα, PR, FGFR 1 to 4 and RUNX2 and grow in vivo in immunocompromised mice without hormone supply giving rise to invasive carcinomas. IBH-6 cells were stably transfected with a specific plasmid designed to knock down the expression of FGFR-2 (shFGFR-2) or with a control plasmid (Scrambled, SC). The decrease of FGFR-2 was confirmed by Western Blot and immunohistochemistry. No differences were found between both cell lines in the proliferation assays performed in vitro. For the in vivo experiments, 3.106 cells were s.c. inoculated into the flank of nude mice (nu/nu). The shFGFR-2 tumors were significantly smaller than control tumors (p<0.001), showed a less aggressive phenotype, a lower proliferation index (Ki67, p<0.01), diminished ratio of pErk/Erk and pAkt/Akt (p<0.05) and a decrease in CCND1 and RUNX2 expression as compared with control SC tumor samples. In order to evaluate if RUNX2 was able to bypass the inhibitory effect of shFGFR-2, cells were cotransfected with the expression plasmid for RUNX2 and were then inoculated in mice as previously described. An increase in tumor size and in aggressiveness associated with higher levels of CCND1 was observed in shFGFR-2/RUNX2 as compared with control (p<0.05) or shFGFR-2 (p<0.01) tumors. Interestingly, a high number of lung and liver metastases were observed in all the shFGFR-2/RUNX2 animals. Our results indicate that FGFR-2 is a key protein involved in mammary tumor growth. The fact that no changes were registered between shFGFR-2 and control cells growing in plastic lends support to our hypothesis postulating a paracrine effect between stromal and parenchymal tissue involving FGFR-2. Since RUNX2 bypasses the inhibitory effect induced by shFGFR-2 we propose that the signaling pathways involved are FGFR-2-independent supporting the hypothesis that FGF2 activates FGFR-2 and in turn RUNX2. Currently we are studying the signaling pathways involved in RUNX2 mediated tumor growth. The results reported here emphasize the use of FGFR-2 inhibitors in combination with standard therapy in breast cancer. Citation Format: Cecilia Perez Pinero, Maria May, Isabel A. Luthy, Claudia Lanari. RUNX2 rescues the inhibitory effect of FGFR-2 silencing and increases the metastatic potential of IBH-6 human breast cancer xenografts. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3120. doi:10.1158/1538-7445.AM2014-3120