| Mucosal immunization has been demonstrated to convey protective immunity both systemically and at the mucosal surface. But in the female reproductive tract, intravaginal (ivag) drug delivery is limited by existing chemical and physical barriers. To achieve efficient delivery to the reproductive epithelium, a vehicle is necessary to protect therapeutic agents from the harsh environment and overcome the mucus gel, a diffusion-limiting barrier. Polymeric particles such as PLGA have been widely explored in drug delivery for their ability to encapsulate and transport various payloads, usually for systemic of subcutaneous delivery (i.e., protein, nucleic acids, and drugs). Furthermore, the surface of these particles can be modified to add functionalities such as increased transport or facilitate cell/tissue-specific uptake in vivo.To explore the application of polymer particles in ivag delivery, we formulated PLGA nanoparticles (d&sim 150--170 nm) that can encapsulate therapeutic payloads and quickly diffuse through the mucus gel. Surface modifications of nanoparticles were achieved by first functionalizing the particle surface with avidin (&sim420 molecules/nanoparticle), creating a robust and versatile platform that allows for controlled immobilization of biotinylated-PEG (MW=2, 5, and 10 kDa) at 100% or 10% surface density. This systematic PEGylation produced particle formulations with more net-neutral surface and low aggregation. PEG surface coating facilitates particle diffusion through human cervical mucus with diffusion coefficients up to 3--10x higher than unmodified or avidin-modified particles. For optimally PEGylated particles, diffusion in human cervical mucus is as rapid as diffusion in water.To assess the properties of nanoparticles that arc optimal for ivag delivery, the distributions of particles within the reproductive tract of mice were monitored after delivery by quantifying particle residence time, mucus-association, and tissue penetration. Negatively charged PLGA particles (NP) exhibited 5x shorter residence time compared to adhesive (avidin-coated or Avid-NP) or stealth (PEG-coated or PEG-NP) particles. Significant differences in mucus association were observed higher concentrations of Avid-NP formulations were measured (324 microg nanoparticle) in the lumen compared to NP (216 microg) and PEG-NP (171 microg) after 0.5 hrs. On average, PEG-NP penetrated the tissue more efficiently, especially at a longer time points (6 hrs), where up to 4x higher concentration in the tissue was detected over other formulations.Surface modification of PLGA particles also produced differences in release of protein and nucleic acid payloads. The presence of avidin-palmitate conjugate formed a monolayer coating on the surface of particles that prevented degradation, but also hindered release of protein and DNA (&sim2x reduction), and in a pH-dependent manner for DNA payloads (reduced at more acidic pH). This hindrance in release reduced the effectiveness of modified-particles as ivag vaccine delivery vehicles, such that no differences between antibody and IFN-gamma production were observed for animals treated with modified particles compared to untreated animals over 8 weeks.The interplay between efficiency of particle delivery into cell and payload release was further explored in vitro. PLGA particles with BSA on the surface were taken up &sim4x more efficiently and with specificity by OK cells that expresses the receptor megalin. However, due to the lower plasmid DNA (encoding luciferase gene) release from the particles, the resulting luciferase expression was 3--10 fold lower. Our findings demonstrated that systematic modification of PLGA particles can enhance delivery efficiency, by increasing transport through mucus barriers and into cells in the underlying epithelium, but may also negatively impact release of encapsulated therapeutic agents. Finding the optimum balance between these key factors through rational design of polymer carriers is an important step towards the rational development of an efficacious vehicle for ivag delivery. |
