3-D tissue culture systems for the evaluation and optimization of nanoparticle-based drug carriers

Abstract

Nanoparticle carriers are attractive vehicles for a variety of drug delivery applications. In order to evaluate nanoparticle formulations for biological efficacy, monolayer cell cultures are typically used as in vitro testing platforms. However, these studies sometimes poorly predict the efficacy of the drug in vivo. The poor in vitro and in vivo correlation may be attributed in part to the inability of two-dimensional cultures to reproduce extracellular barriers, and may also be due to differences in cell phenotype between cells cultured as monolayers and cells in native tissue. In order to more accurately predict in vivo results, it is desirable to test nanoparticle therapeutics in cells cultured in three-dimensional (3-D) models that mimic in vivo conditions. In this review, we discuss some 3-D culture systems that have been used to assess nanoparticle delivery and highlight several implications for nanoparticle design garnered from studies using these systems. While our focus will be on nanoparticle drug formulations, many of the systems discussed here could, or have been, used for the assessment of small molecule or peptide/protein drugs. We also offer some examples of advancements in 3-D culture that could provide even more highly predictive data for designing nanoparticle therapeutics for in vivo applications.

Fig 1

3-D culture systems include additional extracellular barriers encountered by delivery vehicles that are not accounted for in 2-D monolayer cultures.

Fig 2

Penetration of model nanoparticles into multicellular spheroids. Phase contrast of multicellular spheroids shows intact spheroids prior to treatment with 40 nm fluorescent polystyrene nanoparticles (A). Cryosections of untreated spheroids (B) showed poor particle association compared to spheroids co-incubated with collagenase (C). Scale bar is 200 μm.

Fig 3

Examples of advanced 3-D models. (a) Some variations of co-culture models: (1) spheroid co-culture models, (2) cell-cell co-culture in ECM and (3) cell-monolayer on 3-D cell-ECM co-culture model; (b) Ex-vivo models: one version where samples of tissues such as the liver were harvested, sectioned and cultured on 2-D substrates for screening; (c) A typical set up of 3-D perfusion cell-ECM culture models where media flow is driven over the cell-ECM by a pump from a reservoir; and (d) A short-term perfusion system developed by Ng and Pun for nanoparticle penetration studies.