RNA interference-based therapeutics for human immunodeficiency virus HIV-1 treatment: synthetic siRNA or vector-based shRNA?

Abstract

Importance of the field: Despite the clinical benefits of highly active antiretroviral therapy (HAART), the prospect of life-long antiretroviral treatment poses significant problems, which has spurred interest in developing new drugs and strategies to treat HIV infection and eliminate persistent viral reservoirs. RNAi has emerged as a therapeutic possibility for HIV.

Areas covered in this review: We discuss progress in overcoming hurdles to translating transient and stable RNAi enabling technologies to clinical application for HIV; covering the past 2 - 3 years.

What the reader will gain: HIV inhibition can be achieved by transfection of chemically or enzymatically synthesized siRNAs or by DNA-based vector systems expressing short hairpin RNAs (shRNAs) that are processed intracellularly into siRNA. We compare these approaches, focusing on technical and safety issues that will guide the choice of strategy for clinical use.

Take home message: Introduction of synthetic siRNA into cells or its stable endogenous production using vector-driven shRNA have been shown to suppress HIV replication in vitro and, in some instances, in vivo. Each method has advantages and limitations in terms of ease of delivery, duration of silencing, emergence of escape mutants and potential toxicity. Both appear to have potential as future therapeutics for HIV, once the technical and safety issues of each approach are overcome.

Figure 1. Promising strategies for using si/shRNA for HIV infection

The most favored method for expressing shRNA is infection with self inactivating lentiviral particles (generated using transfection with a three-plasmid system (shRNA expression cassette, packaging construct and an envelope construct). After infection, the shRNA expression cassette integrates in the cell’s genome leading to long-term production of shRNA that is processed in the cytoplasm into siRNA. The most promising targeted siRNA delivery strategy consists of a targeting and a cargo moiety. Examples include gp120 Fab-protamine, CD7ScFv-9R protein and siRNA-encapsulated immunoliposome coated with LFA-1 antibody. After delivery, the targeting complex is endocytosed and siRNA released from the endosome is taken up by RISC to mediate gene silencing.

Figure 2. si/shRNA design to enhance potency and reduce toxicity

Short and long siRNA triggers and chemical modifications of siRNA are depicted on the left. Strategies for conventional shRNA, shRNAmiRs and conditional shRNA expression are depicted on the right