Narendra K. Vaish

RNAi-based Therapeutics Targeting Survivin and PLK1 for Treatment of Bladder Cancer

Harnessing RNA interference (RNAi) to silence aberrant gene expression is an emerging approach in cancer therapy. Selective inhibition of an overexpressed gene via RNAi requires a highly efficacious, target-specific short interfering RNA (siRNA) and a safe and efficient delivery system. We have developed siRNA constructs (UsiRNA) that contain unlocked nucleobase analogs (UNA) targeting survivin and polo-like kinase-1 (PLK1) genes. UsiRNAs were encapsulated into dialkylated amino acid-based liposomes (DiLA(2)) containing a nor-arginine head group, cholesteryl hemisuccinate (CHEMS), cholesterol and 1, 2-dimyristoyl-phosphatidylethanolamine-polyethyleneglycol 2000 (DMPE-PEG2000). In an orthotopic bladder cancer mouse model, intravesical treatment with survivin or PLK1 UsiRNA in DiLA(2) liposomes at 1.0 and 0.5 mg/kg resulted in 90% and 70% inhibition of survivin or PLK1 mRNA, respectively. This correlated with a dose-dependent decrease in tumor volumes which was sustained over a 3-week period. Silencing of survivin and PLK1 mRNA was confirmed to be RNA-induced silencing complex mediated as specific cleavage products were detected in bladder tumors over the duration of the study. This report suggests that intravesical instillation of survivin or PLK1 UsiRNA can serve as a potential therapeutic modality for treatment of bladder cancer.

An Amino Acid-based Amphoteric Liposomal Delivery System for Systemic Administration of siRNA

We demonstrate a systematic and rational approach to create a library of natural and modified, dialkylated amino acids based upon arginine for development of an efficient small interfering RNA (siRNA) delivery system. These amino acids, designated DiLA₂ compounds, in conjunction with other components, demonstrate unique properties for assembly into monodisperse, 100-nm small liposomal particles containing siRNA. We show that DiLA₂-based liposomes undergo a pH-dependent phase transition to an inverted hexagonal phase facilitating efficient siRNA release from endosomes to the cytosol. Using an arginine-based DiLA₂, cationic liposomes were prepared that provide high in vivo siRNA delivery efficiency and are well-tolerated in both cell and animal models. DiLA₂-based liposomes demonstrate a linear dose-response with an ED₅₀ of 0.1 mg/kg against liver-specific target genes in BALB/c mice.

Structure—function studies of the hammerhead ribozyme

Elucidation of the catalytic mechanism and structure-function relationship studies of the hammerhead ribozyme continue to be an area of intensive research. A combination of diverse approaches, such as X ray crystallography, spectral studies, chemical modifications, sequence variations and kinetic analyses, have provided valuable insight into the cleavage mechanism of this ribozyme. The hammerhead ribozyme crystal structures have provided valuable insight into conformational deformations needed to attain the catalytically active structure. Similarly, determination of ribozyme solution structure by spectroscopic analyses and the effect of divalent metal ions on RNA folding has further aided in the construction of a model for hammermead catalysis.

Abstract 581: Development of RNA interference-based therapeutics for bladder cancer and hepatocellular carcinoma

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Bladder cancer and hepatocellular carcinoma are two of many cancers refractory to current treatments. Small interfering RNAs (siRNAs) are a new therapeutic modality able to specifically silence expression of targets not accessible via current small molecule and antibody options. MDRNA is developing UsiRNAs, a novel siRNA construct containing unlocked nucleobase analogs, with improved specificity for RNA interference (RNAi). Delivery of UsiRNAs to target tissues is achieved using proprietary Di-alkylated Amino Acid (DiLA2)-based liposomes. Survivin, overexpressed in many cancers, is involved in cell division and inhibition of apoptosis. In orthotopic and xenograft models of liver cancer, systemic administration of survivin UsiRNA-DiLA2 liposomes resulted in approximately 60% and 70% reductions in survivin mRNA, respectively, and > 50% decreases in tumor weight. Local intravesical administration in an orthotopic bladder cancer model resulted in 90% inhibition of mRNA expression and substantial tumor growth inhibition. Polo-like kinase 1 (PLK-1), also elevated in many tumors, regulates cell cycle progression and mitosis. Treatment of bladder cancer and liver cancer cell lines with PLK-1 UsiRNA/DiLA2 liposomes leads to significant caspase activation and corresponding apoptotic cell death. In vivo studies with PLK-1 UsiRNA are in progress. These UsiRNAs and UsiRNAs directed against additional targets are being evaluated in vitro and in orthotopic and xenograft models of cancer as single agents, in combinations of target-specific UsiRNAs, and with existing small molecule and antibody therapeutics. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 581.