10-03-2013, 11:30 PM
HIV and RNA interference
The original article in this thread points out some of the challenges associated with adopting an RNA interference-based approach to HIV therapy. These challenges include the high mutation rate of the virus and difficulties inherent in targeting therapeutic agents to the desired site of action.
The high mutation rate of the virus supports the notion of targeting multiple genes of the virus. This also has the advantage of allowing gene expression to be targeted at critical time points in the viral replication pathway. A group from the Beckman Research Institute in Duarte in the USA examined the potential of intronic MCM7 (minichromosome maintenance complex component-7) platform as a way of expressing small inhibitory RNAs against HIV. This platform normally harbours endogenous microRNAa (miRNAs) and these were replaced with multiple anti-HIV small RNAs targeting genes including tat and rev. The study found that three of the combinatorial constructs tested were able to potently suppress viral replication in HIV-1-infected CEM T lymphocytes when compared with cells that had not been transduced with a construct. One of the most effective constructs combined anti-HIV siRNA with a nucleolar- targeting U5 ribozyme and a trans-activation response (TAR) decoy designed to sequester HIV-1 Tat and Rev proteins inside the nucleolus. The group maintained that their constructs represent ‘a new paradigm for combinatorial RNA-based gene therapy applications’.
Another study from the same institute addressed the issue of which small interfering RNA strand is chosen by the RNA-induced silencing complex (RISC) for gene silencing and how it is targeted. It is important that the intended strand is selected and that the unintended strand is blocked to prevent off-target effects and increase potency of the silencing effect. The group used the technique of unlocked nucleic acid (UNA) modification of the 5' end of canonical siRNA, which abrogates gene silencing of the modified strand and demonstrated that modifying the unintended strand in their HIV siRNA resulted in improved targeting by the intended antisense strand in otherwise poorly targeting siRNA.
Much more work is needed to continue to develop RNA interference in HIV therapy but the signs are promising.
Sources
CHUNG, J. et al., 2012. Endogenous MCM7 microRNA cluster as a novel platform to multiplex small interfering and nucleolar RNAs for combinational HIV-1 gene therapy. Human Gene Therapy, 23(11), pp. 1200-1208
SNEAD, N.M. et al., 2013. 5' Unlocked Nucleic Acid Modification Improves siRNA Targeting. Molecular Therapy.Nucleic Acids, 2, pp. e103-e103
The original article in this thread points out some of the challenges associated with adopting an RNA interference-based approach to HIV therapy. These challenges include the high mutation rate of the virus and difficulties inherent in targeting therapeutic agents to the desired site of action.
The high mutation rate of the virus supports the notion of targeting multiple genes of the virus. This also has the advantage of allowing gene expression to be targeted at critical time points in the viral replication pathway. A group from the Beckman Research Institute in Duarte in the USA examined the potential of intronic MCM7 (minichromosome maintenance complex component-7) platform as a way of expressing small inhibitory RNAs against HIV. This platform normally harbours endogenous microRNAa (miRNAs) and these were replaced with multiple anti-HIV small RNAs targeting genes including tat and rev. The study found that three of the combinatorial constructs tested were able to potently suppress viral replication in HIV-1-infected CEM T lymphocytes when compared with cells that had not been transduced with a construct. One of the most effective constructs combined anti-HIV siRNA with a nucleolar- targeting U5 ribozyme and a trans-activation response (TAR) decoy designed to sequester HIV-1 Tat and Rev proteins inside the nucleolus. The group maintained that their constructs represent ‘a new paradigm for combinatorial RNA-based gene therapy applications’.
Another study from the same institute addressed the issue of which small interfering RNA strand is chosen by the RNA-induced silencing complex (RISC) for gene silencing and how it is targeted. It is important that the intended strand is selected and that the unintended strand is blocked to prevent off-target effects and increase potency of the silencing effect. The group used the technique of unlocked nucleic acid (UNA) modification of the 5' end of canonical siRNA, which abrogates gene silencing of the modified strand and demonstrated that modifying the unintended strand in their HIV siRNA resulted in improved targeting by the intended antisense strand in otherwise poorly targeting siRNA.
Much more work is needed to continue to develop RNA interference in HIV therapy but the signs are promising.
Sources
CHUNG, J. et al., 2012. Endogenous MCM7 microRNA cluster as a novel platform to multiplex small interfering and nucleolar RNAs for combinational HIV-1 gene therapy. Human Gene Therapy, 23(11), pp. 1200-1208
SNEAD, N.M. et al., 2013. 5' Unlocked Nucleic Acid Modification Improves siRNA Targeting. Molecular Therapy.Nucleic Acids, 2, pp. e103-e103
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