Development of an Infectious Cell Center Assay (ICCA) to Predict Appropriate Dosing of HIV Topical Microbicides

Abstract

With millions of people currently infected with human immunodeficiency virus (HIV), and with increasing rates of transmission around the world, the development of new and more potent HIV inhibitors is necessary. Along with development of new agents to treat existing infections, it is also important to consider products and methods to reduce the rates of transmission of HIV and prevent new infections from occurring. In light of the increasing burden of HIV infection in women especially in developing areas of the world, as well as the high transmissibility of HIV through anal sex with both women and men who have sex with men (MSM), one of the important types of products being developed are topically applied microbicides. Microbicides are formulated for use at the site of infection, so they must deliver a high enough concentration of inhibitor to be effective but be delivered without the possibility of unnecessary and potentially dangerous toxicity and systemic exposure. A critical requirement of microbicides is that the preventative agent must be present at the correct place (the site of infection) at the correct time and at the correct dose to prevent transmission of HIV. This research project was designed to determine if an in vitro assay designated the Infectious Cell Center Assay, or ICCA, could be used to determine the optimal and correct tissue concentration of a microbicide product which would be required to effectively prevent transmission from occurring in the vaginal or rectal epithelial tissue. It is hypothesized that the prevention product must totally inhibit the initial transmission and infection event such that a subsequent spreading infection from the locus of initial infection does not occur. Thus, we propose to utilize the ICCA to define the sterilizing concentration of a microbicide product and utilize this information to prioritize products for continued development in the microbicide pipeline. In developing the ICCA, the research performed effectively confirmed that the ICCA is able to determine the concentration of an antiretroviral (ARV) that is needed at the tissue level to prevent transmission and infection of HIV and thus result in sterilization of the cell culture. The ICCA was found to be more predictive than other in vitro assays due to the ability of the technology to quantify the number of infected cells present in each culture through the syncytium forming unit (SFU) assay. The ICCA was able to be used with various wild-type and drug resistant strains of HIV-1. To mimic the results of microbicide use by people, the effect of virus multiplicity of infection, drug pretreatment and delayed drug addition of compound were also simulated in the ICCA and defined as critical assay variables with importance to the development and use of microbicide products. The antiviral effect of combinations of antiretroviral agents was also able to be quantified in the ICCA. Most importantly, the ICCA defines sterilizing concentration of a microbicide product was able to be harmonized with concentrations of these same products shown to be effective in both ex vivo and in vivo research, suggesting that the in vitro defined sterilizing concentration is an important addition to the development of any topical microbicide product. We believe that with additional investigation, the ICCA might be validated as a more predictive in vitro assay used to define appropriate effective dosing concentrations of ARVs to be used as microbicide products in order to totally suppress HIV transmission and to prioritize products for further development in highly expensive and time consuming human clinical trials.