A chemically-modified miR-21 inhibitor (ADM-21) as a novel potential therapy in bladder cancer.

Abstract

335 Background: MicroRNAs are key regulators of cancer signaling pathways.Targeting their expression has therapeutic potential. MicroRNA-21 (miR-21) acts as an oncogene in several cancers. Here we describe its functional significance in bladder oncogenesis and the therapeutic properties of a novel chemically-modified miR-21 inhibitor (ADM-21). Methods: MiR-21 expression was assessed by RT-PCR in a panel of human bladder cancer tissues and cell lines. Transcriptomic profiling of 28 bladder cancer cell lines performed to identify miR-21-dependent gene signatures. ADM-21 is a chemically-modified (phosphorothioate backbone and locked-nuclei-acid) antisense oligo against miR-21 with high potency and stability.The efficacy of ADM-21 treatment was evaluated in vitro and in vivo. Results: MiR-21 was up-regulated by 5-fold in bladder tumors relatively to normal tissue and by 3-fold in advanced compared to early stage bladder cancers. The 28 cancer cell lines were stratified in 3 groups (high, intermediate, low) according to miR-21 levels. Transcriptomic analysis revealed a 15-gene signature that negatively correlated with miR-21 levels. Protein Phosphatase 2 Regulatory Subunit B Isoform A (PPP2R2A) displayed tumor suppressive properties in bladder cancer. Moreover, PPP2R2A represents a novel miR-21 direct target gene and a negative regulator of the AKT/mTOR pathway. ADM-21 (10uM) treatment suppressed 43.5% the growth and 90% the invasiveness of 5367 bladder cancer cells. Also, intravenous (I.V.) administration of ADM-21 was proven more effective than intraperitoneal (I.P.) administration in mouse xenografts. Specifically, 15mg/kg of ADM-21 (I.V.) every 5 days for 3 cycles reduced 37% and 47% (day 16) the growth rate of tumors originating from injections of 5367 and RT-112 cells, respectively. Conclusions: Integrative analysis of human bladder tumors and cell lines revealed a novel 15-gene signature that correlates with miR-21 levels. PPP2R2A is a miR-21 direct target and regulator of the AKT/mTOR pathway. ADM-21effectively reduces bladder cancer growth in vitro and in vivo. Upon completion of ADM-21 toxicology studies and confirm safety we will design phase I clinical trial for advanced bladder cancer.