MP66-15 INHIBITION OF ERG ACTIVITY IN PATIENT DERIVED PROSTATE CANCER XENOGRAFTS USING THE SMALL MOLECULE INHIBITOR YK-4-279

RESULTS: Previously, cFLIP was identified as an androgenresponsive gene. However, we show that cFLIP expression is increased in androgen-independent CaP cells. We provide evidence that (i) cFLIP-expressing CRPC cells exhibit higher proliferative index than cFLIP-deficient counterparts and (ii) cFLIP expression is high in prostatic tissues of castrated (ARR2.IkB-Myc) transgenic mice. The significance of cFLIP as an upstream of AR could be ascertained from the finding that suppressing cFLIP could decrease PSA levels and transcriptional activities of ARFL and ARv7 in CRPC cells. These data prompted to further investigate the correlation between Cflip, ARFL and ARv7. We show that cFLIP forms a complex with ARv-7 and ARFL in CRPC cells. We observed higher levels of cFLIP/ARv7 complex in nuclei than in cytoplasm suggesting the possibility of cFLIP as a protein-carrier. Using transfections with cFLIP-Long, cFLIP-short-variant and mutants (cFLIPL435mt/472mt/439mt), two sequences on C-terminus were identified for nuclear translocation that confirmed its protein-transporter property. These data were validated in PC3 cells (in which ARv7 was ectopically expressed). Next, we observed that b-catenin is required for complex formation and subsequent nuclear translocation of cFLIP/ARv7 in cells. Finally, using a xenograft mouse model, we established the significance of cFLIP/ARv7 complex as a therapeutic target and show that simultaneous targeting (by using nanoparticle-loaded cFLIP-siRNA þ ARv7siRNA) significantly inhibits CRPC-type tumor growth and improves the outcome of docetaxel therapy. We also identified a novel inhibitor of cFLIP/ARv. CONCLUSIONS: We identified a novel therapeutic approach of treating CRPC.