Small RNAs: The Qualified Candidates for Gene Manipulation in Diverse Clinical Pathologies

Abstract

In recent years, RNA interference (RNAi) has become a tool of choice to analyze and target the in vitro and in vivo function of mammalian genes. RNAi down-regulates gene expression by inducing enzyme-dependent degradation of targeted mRNA. This can be achieved using small double-stranded RNAs (dsRNAs), including small interfering RNAs (siRNAs), micro RNAs, and piwi RNAs. These active, small dsRNAs can regulate endogenous genes in both somatic and germ cells such that they can defend the genome from invasive nucleic acids. Extension of the concept of RNAi to preclinical studies indicates its probable application in the treatment of cancers, viral infections, arterial stenosis, and genetic disorders. Exciting results from ongoing clinical trials have raised the expectations of the scientific community for the use of RNAi in "real cures". Rational pharmaceutical design of these molecules can further open a Pandora's box of newer therapeutic options. However, efficient delivery of these small dsRNAs to target tissues or cells and their unanticipated nonspecific effects comprise a few important issues that still need to be addressed. In this review, we offer an overview of different small dsRNAs, their biogenesis, and their applicability in therapeutics. Current delivery strategies and formulation techniques to achieve the desired transfection capability and RNAi products in clinical trials are also discussed.

Cell-Penetrating Peptides

“…The family of protein-derived CPPs quickly expanded including novel highly cationic peptides deduced from vascular epithelial cadherin (pVEC) [ 42 ], herpes (VP22) [ 43 ] and other viruses [ 44 ], and homeoproteins Islet-1 [ 45 ], Engrailed-2 [ 46 ], and others [ 47 ]. The sequences from human calcitonin [ 48 , 49 ] and lactoferrin [ 50 ] have also been intensely investigated and developed as well as peptides from toxins crotamine [ 51 ] and maurocalcine [ 52 , 53 ]. The family of protein-derived CPPs is still the largest, and since the quest for novel cell-penetrating sequences continues, it continues expanding.…”

“…The selection was further refined by removing sequences that contain negatively charged amino acids. From the candidates eight were selected and tested and seven performed equal to or better than the positive control, tat (48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60). Futaki and colleagues [21] tested ten arginine-rich peptides derived from RNA-binding domain of proteins.…”

“…Such modifi cations have potential to change the targets of AMPs and improve the stability of AMPs against proteases [ 45 ]. Despite these advantageous features of AMPs, there are still some challenges to their applications, such as potential toxicity to humans [ 46 ], sensitivity to harsh environmental conditions (susceptibility to proteases and extreme pH) [ 47 ], lack of selectivity against specifi c strains [ 48 ], high production costs [ 49 ], folding issues of some large AMPs [ 50 ], reduced activity when used for surface coating, and bacterial resistance to some AMPs [ 51 ].…”

“…Jones et al, compared the toxicities of rhodamine-labeled and unlabeled pAntp (43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58), pTAT (48-60), TP10, and Arg 11 , and their conjugates with NBD peptide cargo in A549 cells [ 5 ]. The CPP-NBD or its scrambled sequence increased the toxicity of TP10 and pTAT (48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60), decreased the toxicity of Arg 11 and had no effect on pAntp (43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58) response. Several reports demonstrated that the conjugation of the carboxyfl uorescein to CPP increases the cytotoxicity of the peptide [ 6 , 7 ].…”

“…First, in 1988, two independent research groups demonstrated the shuttling properties for an HIV tat trans-activator protein [2,3]. Second, in 1991, the group of Alain Prochiantz reported [4] on cellular internalization of the 60 aa homeodomain of Antennapedia (a Drosophila homeoprotein), followed in 1994 by the report on a short 16 aa peptide, pAntp (43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58), later named penetratin, which was necessary and suffi cient for this translocation [5].…”