Mucosal Delivery of RNAi Therapeutics - RNA Interference from Biology to Therapeutics - page 115

reproductive tract for at least 14 days in a transgenic GFP mouse model. Reduction
of fluorescence was maximal at day 10 in the vaginal tract, with only 30-40% of the
siRNA dose (~2.8 mg) released due to the slow degradation rate of the
nanoparticles.
In the aforementioned studies, thorough cleaning of the vaginal tract and/or pro-
gesterone treatment of the animals prior to particle administration was performed
[ 94- 96 ]. Whilst mucus removal eliminates one of the main barriers for vaginal epi-
thelial transfection, the hormone treatment arrests the oestrous cycle in the dioestrus
phase in which the epithelium is thin and porous that most probably contributed to
higher drug absorption [ 130 ]. In addition this treatment has been associated with a
reduced immune response in the vagina, which may mask potential undesirable side
effects of the evaluated drugs.
In a model more closely resembling the normal physiological conditions, Zhang
et al. [ 92 ] reported liposome-mediated transfection of the squamous epithelia layer
and submucosa. A single dose of siRNA (~53 mg siRNA) was sufficient to induce a
significant and consistent knockdown of the targeted gene (lamin A/C or CCR5)
over a 7-day period. Analysis of proinflammatory cytokines (IL-1, IL-10, TNF-a )
and interferon-related genes did not detect any significant changes in the treated
animals compared to controls.
In contrast, Wu et al. [ 97 ] suggested that vaginal epithelium transfection in
physiological conditions with conventional lipoplexes was unlikely, most probably
due to the combination of poor drug retention at the vaginal cavity and an inefficient
transport across the mucus layer. In order to overcome these limitations and achieve
sustained release of the entrapped therapeutic, the authors developed and character-
ised a system based on a biodegradable alginate scaffold. Upon exposure to sodium
ions, a common element of cells and body fluids, scaffold degradation occurs,
resulting in the slow release of incorporated PEGylated lipoplexes. PEGylated, but
not conventional, liposomes were capable of mucosal diffusion and induce siRNA-
mediated gene knockdown at the vaginal epithelium. Intra-vaginal administration
of the scaffold over 2 consecutive days (daily dose of 8 mg/animal) resulted in an
85% knockdown of lamin A/C mRNA. In this report, evaluation of proinflammatory
cytokine levels and unspecific interferon activation was not reported.
Encouraging results have been recently reported by Wheeler et al. [ 98 ] , who by
targeting viral ( gag and vif ) and host genes ( CCR5 ) could inhibit HIV vaginal trans-
mission in a humanised mouse model. Macrophage and CD4+ T-cell-specific tar-
geting was achieved by the fusion of the siRNAs to a CD4 receptor-specific aptamer.
The observed protection is probably due to the combination of selective gene knock-
down by the siRNAs ( CCR5 , gag and vif ) and a viral-aptamer competition for CD4
receptor binding. Despite the apparent absence of cellular toxicity or lymphocyte
activation, caution should be taken with molecules interacting with the CD4 recep-
tor due to its role in the host immune response and susceptibility for HIV infections
in activated T lymphocytes.