Mucosal Delivery of RNAi Therapeutics - RNA Interference from Biology to Therapeutics - page 114

5.6 Intravaginal Delivery

Advantages such as an established therapeutic route, marketed products for sus-
tained drug release, low enzymatic activity and possible avoidance of the first-pass
effect [ 129 ] promote vaginal administration of siRNA. Poor systemic absorption of
polar high molecular weight molecules across the epithelium, however, seemingly
restricts siRNA-based therapies to local vaginal treatments.

5.6.1 Vaginal Studies

A number of studies have utilised acute infection of mice with herpes simplex virus
2 (HSV-2) as a model for the development of antiviral siRNA-based therapeutics. In
this setting, the capacity of the treatment to inhibit viral spread across the genital
mucosa after HSV-2 challenge is evaluated. In 2006, a study by Palliser et al. [ 94 ]
assessed the protection provided by lipid-complexed siRNA (~7 m g/dose) targeting
essential HSV-2 viral genes. Two siRNA (UL27.2 and UL29.2) conferred significant
protection with considerable reduction in the lethality and severity of the lesions,
when administrated in a double regime 2 h prior and 4 h after an otherwise lethal
HSV-2 vaginal challenge. The protection was, however, transient and a post-expo-
sure treatment (3 and 6 h after the viral challenge) was only effective when both
siRNA were administrated in combination but not individually. No inflammatory
response or interferon induction was detected by histological and expression analy-
sis respectively in this study. More exhaustive follow-up studies have revealed,
however, several undesirable features and toxic side effects related to lipid formula-
tions [ 95, 96 ] .
A chemically modified siRNA approach has been also used for the treatment of
HSV-2 [ 95 ]. The cholesterol (Chol)-siRNA conjugate, stabilised with phosphoro-
thioate residues, was used to knockdown viral and host gene expression. Consistent
with previous results [ 94 ], targeting an essential viral gene (UL29) exclusively con-
ferred protection when the siRNA was administrated within a few hours of the viral
challenge. Interestingly, this protection could not be replicated if a too high siRNA
dose (~135 mg) was employed, a matter that requires further investigation. In con-
trast, targeting of nectin-1, the receptor used by HSV-2 to penetrate in the cells,
conferred protection only when administrated 1-7 days prior, but not immediately
before or after the HSV-2 challenge. Treatment of the mice with two doses (~27 m g/
dose) of Chol-siRNA combining the targeting of nectin-1 and viral genes provided
significant protection for 1 week irrespective of the time of challenge.
Woodrow et al. [ 96 ] developed a delivery system based on a siRNA/polyamine
(spermidine) core encapsulated into PLGA nanoparticles. A single dose (~7 m g) of
these particles induced sustained GFP mRNA silencing throughout the female