Multistage Vectored siRNA Targeting Ataxia-Telangiectasia Mutated for Breast Cancer Therapy

The ataxia-telangiectasia mutated (ATM) protein plays a central role in DNA damage response and cell cycle checkpoints, and may be a promising target for cancer therapy if normal tissue toxicity could be avoided. The strategy presented here to target ATM for breast cancer therapy involves the use of liposomal-encapsulated, gene-specific ATM siRNA delivered with a well-characterized porous silicon-based multistage vector (MSV) delivery system (MSV/ATM). Biweekly treatment of MSV/ATM suppressed ATM expression in tumor tissues, and consequently inhibited growth of MDA-MB-231 orthotopic tumor in nude mice. At the therapeutic dosage, neither free liposomal ATM siRNA nor MSV/ATM triggered an acute immune response in BALB/c mice, including changes in serum cytokines, chemokines or colony-stimulating factors. Weekly treatments of mice with free liposomal ATM siRNA or MSV/ATM for 4 weeks did not cause significant changes in body weight, hematology, blood biochemistry, or major organ histology. These results indicate that MSV/ATM is biocompatible and efficacious in inhibiting tumor growth, and that further preclinical evaluation is warranted for the development of MSV/ATM as a potential therapeutic agent. Delivery of ataxia-telangiectasia mutated (ATM) siRNA to breast cancer is mediated by a multistage vector (MSV) system. This system consists of a porous silicon microparticle loaded with siRNA nanoparticles. The MSV particles settle at the tumor vasculature where the siRNA nanoparticles are released into the tumor interstitium. Uptake of siRNA by tumor cells results in knockdown of ATM expression, and subsequently tumor growth inhibition.