Mouse Model of Cervicovaginal Toxicity and Inflammation for Preclinical Evaluation of Topical Vaginal Microbicides

Abstract

Clinical trials evaluating the efficacy of nonoxynol-9 (N-9) as a topical microbicide concluded that N-9 offers no in vivo protection against human immunodeficiency virus type 1 (HIV-1) infection, despite demonstrated in vitro inactivation of HIV-1 by N-9. These trials emphasize the need for better model systems to determine candidate microbicide effectiveness and safety in a preclinical setting. To that end, time-dependent in vitro cytotoxicity, as well as in vivo toxicity and inflammation, associated with N-9 exposure were characterized with the goal of validating a mouse model of microbicide toxicity. In vitro studies using submerged cell cultures indicated that human cervical epithelial cells were inherently more sensitive to N-9-mediated damage than human vaginal epithelial cells. These results correlated with in vivo findings obtained by using Swiss Webster mice in which intravaginal inoculation of 1% N-9 or Conceptrol gel (containing 4% N-9) resulted in selective and acute disruption of the cervical columnar epithelial cells 2 h postapplication accompanied by intense inflammatory infiltrates within the lamina propria. Although damage to the cervical epithelium was apparent out to 8 h postapplication, these tissues resembled control tissue by 24 h postapplication. In contrast, minimal damage and infiltration were associated with both short-and long-term exposure of the vaginal mucosa to either N-9 or Conceptrol. These analyses were extended to examine the relative toxicity of polyethylene hexamethylene biguanide (PEHMB), a polybiguanide compound under evaluation as a candidate topical microbicide. In similar studies, in vivo exposure to 1% PEHMB caused minimal damage and inflammation of the genital mucosa, a finding consistent with the demonstration that PEHMB was >350-fold less cytotoxic than N-9 in vitro. Collectively, these studies highlight the murine model of toxicity as a valuable tool for the preclinical assessment of toxicity and inflammation associated with exposure to candidate topical microbicides.

Efficacy and Toxicity of Zinc Salts as Candidate Topical Microbicides against Vaginal Herpes Simplex Virus Type 2 Infection

“…Thus, to be accepted, they will need to not only to show efficacy but also to have outstanding safety profiles. The increased emphasis on early evaluation of microbicide safety that accompanied the nonoynol-9 findings is shown by recent reports describing a number of preclinical models for safety evaluation (5,13,15). In animals treated with zinc salts during the efficacy studies, there were no outward signs of adverse effects, such as irritation around the vaginal opening or altered behavior.…”

Candidate Sulfonated and Sulfated Topical Microbicides: Comparison of Anti-Human Immunodeficiency Virus Activities and Mechanisms of Action

“…Despite its in vitro antiviral activity, N-9 can be damaging to tissues both in vivo and in vitro. A recent paper by Catalone et al using a mouse model of cervicovaginal toxicity and inflammation showed that 1% N-9 intravaginal inoculation of Swiss Webster mice resulted in acute disruption of cervical epithelial cells (3). Another study utilizing an in vitro model demonstrated that a KY-N-9 formulation was 20 to 50 times more toxic than other candidate microbicides, including PRO 2000 and cellulose acetate phthalate (CAP) (6).…”

Quantification of Poly(I:C)-Mediated Protection against Genital Herpes Simplex Virus Type 2 Infection

“…Microbicides can be applied locally to the vaginal or rectal mucosa prior to or just following a high-risk sexual encounter. The term microbicide implies that the compound kills microorganisms; this is somewhat misleading, because microbicides may work in a variety of ways, including disrupting the pathogen's membrane or envelope, blocking receptor interactions essential for infection, inhibiting intra-or extracellular pathogen replication, or enhancing local, mucosal immune responses, thereby reducing susceptibility (10,22,26,30). A recent experimental microbicide strategy used CpG-containing oligonucleotides (CpG-ODN) delivered topically to the vaginal mucosa to induce a local immune response that protected against HSV-2 infection (21).…”