Factors determining the stability, size distribution, and cellular accumulation of small, monodisperse chitosan nanoparticles as candidate vectors for anticancer drug delivery: application to the passive encapsulation of [14C]-doxorubicin

Development of parameters for the fabrication of nanosized vectors is pivotal for its successful administration in therapeutic applications. In this study, homogeneously distributed chitosan nanoparticles (CNPs) with diameters as small as 62 nm and a polydispersity index (PDI) of 0.15 were synthesized and purified using a simple, robust method that was highly reproducible. Nanoparticles were synthesized using modified ionic gelation of the chitosan polymer with sodium tripolyphosphate. Using this method, larger aggregates were mechanically isolated from single particles in the nanoparticle population by selective efficient centrifugation. The presence of disaggregated monodisperse nanoparticles was confirmed using atomic force microscopy. Factors such as anions, pH, and concentration were found to affect the size and stability of nanoparticles directly. The smallest nanoparticle population was ∼62 nm in hydrodynamic size, with a low PDI of 0.15, indicating high particle homogeneity. CNPs were highly stable and retained their monodisperse morphology in serum-supplemented media in cell culture conditions for up to 72 hours, before slowly degrading over 6 days. Cell viability assays demonstrated that cells remained viable following a 72-hour exposure to 1 mg/mL CNPs, suggesting that the nanoparticles are well tolerated and highly suited for biomedical applications. Cellular uptake studies using fluorescein isothiocyanate-labeled CNPs showed that cancer cells readily accumulate the nanoparticles 30 minutes posttreatment and that nanoparticles persisted within cells for up to 24 hours posttreatment. As a proof of principle for use in anticancer therapeutic applications, a [14C]-radiolabeled form of the anticancer agent doxorubicin was efficiently encapsulated within the CNP, confirming the feasibility of using this system as a drug delivery vector.