Targeted Nanocarrier Delivery of RNA Therapeutics to Control HIV Infection

Abstract

Our understanding of HIV infection has greatly advanced since the discovery of the virus in 1983. Treatment options have improved the quality of life of people living with HIV/AIDS, turning it from a fatal disease into a chronic, manageable infection. Despite all this progress, a cure remains elusive. A major barrier to attaining an HIV cure is the presence of the latent viral reservoir, which is established early in infection and persists for the lifetime of the host, even during prolonged anti-viral therapy. Different cure strategies are currently being explored to eliminate or suppress this reservoir. Several studies have shown that a functional cure may be achieved by preventing infection and also inhibiting reactivation of the virus from the latent reservoir. Here, we briefly describe the main HIV cure strategies, focussing on the use of RNA therapeutics, including small interfering RNA (siRNA) to maintain HIV permanently in a state of super latency, and CRISPR gRNA to excise the latent reservoir. A challenge with progressing RNA therapeutics to the clinic is achieving effective delivery into the host cell. This review covers recent nanotechnological strategies for siRNA delivery using liposomes, N-acetylgalactosamine conjugation, inorganic nanoparticles and polymer-based nanocapsules. We further discuss the opportunities and challenges of those strategies for HIV treatment.

Keywords: HIV; RNA therapeutics; delivery; latent reservoir; nanocarrier; siRNA.

Figure 1

Illustration of the delivery route of FDA-approved siRNA from injection to the liver through the circulation system. The drug enters the circulatory system after it is administered intravenously and reaches the liver where it targets hepatocytes. Created with BioRender.com.

Figure 2

Challenges associated with HIV infection. (A) Illustration showing the distribution of organs and tissues known to harbour latent HIV (B) Challenges in attaining HIV cure. Created with BioRender.com.

Figure 3

Mechanism of action of CRISPR-Cas9 gene editing. The CRISPR-Cas9 complex cleaves the target and creates a DSB. The DSB is then repaired via either the NHEJ or HDR pathway. The NHEJ pathway is error-prone, resulting in loss of gene function caused by indels in gene sequence. HDR results in precise modifications of the target. sgRNA, single guide RNA; PAM, protospacer-adjacent motif; NHEJ, nonhomologous end-joining; HDR, homology-directed repair; wt, wildtype. Created with BioRender.com.

Figure 4

Proposed combination of PTGS and TGS RNAi pathways to control HIV infection. Both RNAi pathways can be mediated by viral or non-viral delivery of RNA sequences. siRNA can achieve PTGS via RISC initiating specific cleavage of mRNA transcripts of cellular factors required for HIV infection or replication such as CCR5. A downregulation of CCR5 prevents entry of HIV into the cell. siRNA can also trigger TGS in the nucleus via the RITS complex. This initiates repressive epigenetic modifications, such as increased histone methylation and deacetylation, at the HIV promoter region, resulting in transcriptional silencing and abrogation of the replication cycle. PTGS, post-transcriptional gene silencing; TGS, transcriptional gene silencing; Ago1, Argonaute 1; Ago2, Argonaute 2; shRNA, short hairpin RNA; siRNA, small interfering RNA; RISC, RNA induced silencing complex; RITS, RNA induced transcriptional silencing complex; mRNA messenger RNA; CR5, C-C Motif Chemokine Receptor 5.

Figure 5

Summary of non-viral delivery systems currently used for nucleic acid delivery. Created with BioRender.com.

Figure 6

Methods used in conjugating ligands to nanocarriers. (A) Adsorption, (B) covalent conjugation, (C) use of adapters. EDC, 1-ethyl-3-(-3-dimethylaminopropyl) carbodiimide; sulfo-NHS, N-hydroxysulfosuccinimide. Created with BioRender.com.