Inactivation of the nuclear receptor TR3 as an important new drug target for treating RCC.

Abstract

e15618 Background: The high mortality of patients with RCC is due to poor performance of most chemotherapy. There is a critical need for development of new mechanism-based drugs.The nuclear orphan receptor NR4A1 (TR3, Nur77) are immediate early genes activated by various stressors. NR4A is highly expressed in multiple tumors. TR3 knockdown studies show that TR3 plays an important role in cancer cell growth and angiogenesis. The pro-oncogenic activity of this receptor is an excellent example of “non-oncogene addiction” which is essential for maintaining the cancer cell/tumor phenotype. Methods: Multiple RCC cell lines have been used. Several different classes of C-substituted DIMs summarized in Fig1 has been screened for TR3 deactivation in RCC cell lines using GAL4-TR3/UAS-luc constructs (Fig1). Effects of the C-DIM compounds on cancer cell growth and expression of Sp-regulated genes has been determined by cell counting, the MTT assay, western blot and activation of caspases 3 and 9 and directly compared to knockdown of TR3 by RNAi. Results: Knockdown of TR3 by RNAi has confirmed that TR3 is pro-oncogenic and we have focused on structure-activity relations (SARs) of C-DIM analogs to identify compounds that inactivate TR3. Renal cancer cells were treated with c-DIM TR3 inactivators and this significantly inhibited cell proliferation (Figs 2 and 3). Expression of TR3 in RCC cell lines has not previously been reported. Fig. 4 presents a western blot of cell lysates showing that TR3 is expressed in these cell lines. TR3 inactivators decreased expression of survivin and bcl-2 and this was accompanied by several apoptotic markers. These results show that RCC cells not only express TR3 but TR3 inactivators decrease the pro-survival genes and induce apoptosis which confirm that TR3 is also a target for renal cancer therapy. TR3 pro-oncogenic activity is due, in part, to the role of TR3 in constitutive expression of survivin and other Sp-regulated genes (VEGF, c-MET..). TR3 also involves in formation of a complex with p53 which inactivates the tumor suppressor gene. Thus inactivation of TR3 activates p53 pathway (Fig 5). Conclusions: TR3 is overexpressed in RCC. We have shown for the first time that TR3 is an important new drug target for treating RCC.