(127a) Real-Time Tracking of the Intracellular Path of Pla-Peg Polymeric Micelles in Live Cells

Topical delivery of drugs and genes to the cervical vaginal (CV) tract based on nanoparticle (NP) systems has potential clinical applications, such as treatment of cancer and prevention of sexually transmitted diseases (STDs). An often overlooked obstacle is the mucosal barrier lining the CV tract, which NPs must overcome in order to reach underlying cells and avoid clearance.

Previous methods provided only ensemble-averaged particle transport rates, thereby limiting the insight into complex transport phenomena that control NP transport in CV mucus. Multiple Particle Tracking allows for detailed quantitative analysis of individual NP movement in physiologically-relevant mucus samples. The measurements reported here were performed on cervicovaginal secretions present in the vagina, and therefore are more appropriate for vaginal delivery of NP than prior measurements that were performed on mucus obtained by vacuum extraction from the endocervical canal. In order to improve the transport of NP across the mucosal network, we investigated the effects of particle size, surface PEGylation, and presence of ligands on NP transport in undiluted human CV mucus.

The movement of hundreds of fluorescently labeled nanospheres of different sizes and surface modification was quantified using MPT within 4 hrs after sample collection. A high-speed axiovert camera was used to capture movies at 15 frames/sec and ~10nm resolution. Mean-square displacements (MSDs) and effective diffusivities (Deff) of nanospheres were obtained through analysis of the movies using particle tracking software.

PEGylation drastically reduced the number of immobile particles in CV mucus across all NP sizes (100-500nm), and increased the number of diffusive particles. PEGylation also improved the overall transport rates of particles undergoing subdiffusive transport for all particle sizes. 200nm particles exhibited the fastest transport properties overall in CV mucus, both in the form of minimized percentage of immobile particles and maximized percentage of diffusive particles. 200nm particles also had a higher transport rate compared to other particle sizes within the subdiffusive population. Accounting for both PEGylation and size, 200nm PS-PEG nanoparticles transport the fastest in CV mucus as demonstrated by the highest effective diffusivity over the entire population of NP.

PEGylation may enhance particle transport rates by reducing interactions between nanoparticles and the mucosal fiber network. By preventing protein adsorption and minimizing interactions with the fiber network, PEGylation eliminates virtually all immobilization via electrostatic and chemical means, as evident with 200nm and 500nm particles. The reduced interaction upon PEGylation leads to a decreased number of subdiffusive particles and an increased number of diffusive particles. The unexpected slower transport properties of 100nm particles compared to 200nm particles might be explained using principles from gel permeation chromatography (GPC). For particles of various sizes traveling in a network with heterogeneous pore sizes, smaller particles have a greater tendency to diffuse into small pores/pockets, resulting in an overall reduced transport.