Application of Phi29 Motor pRNA for Targeted Therapeutic Delivery of siRNA Silencing Metallothionein-IIA and Survivin in Ovarian Cancers

Ovarian cancer is a highly metastatic and lethal disease, making it imperative to find treatments that target late-stage malignant tumors. The packaging RNA (pRNA) of bacteriophage phi29 DNA-packaging motor has been reported to function as a highly versatile vehicle to carry small interference RNA (siRNA) for silencing of survivin. In this article, we explore the potential of pRNA as a vehicle to carry siRNA specifically targeted to metallothionein-IIa (MT-IIA) messenger RNA (mRNA), and compare it to survivin targeting pRNA. These two anti-apoptotic cell survival factors promote tumor cell viability, and are over-expressed in recurrent tumors. We find that pRNA chimeras targeting MT-IIA are processed into double-stranded siRNA by dicer, are localized within the GW/P-bodies, and are more potent than siRNA alone in silencing MT-IIA expression. Moreover, knockdown of both survivin and MT-IIA expression simultaneously results in more potent effects on cell proliferation in the aggressive ovarian tumor cell lines than either alone, suggesting that therapeutic approaches that target multiple genes are essential for molecular therapy. The folate receptor-targeted delivery of siRNA by the folate-pRNA dimer emphasizes the cancer cell-specific aspect of this system. The pRNA system, which has the capability to assemble into multivalent nanoparticles, has immense promise as a highly potent therapeutic agent.