Hyaluronic acid-modified bioadhesive liposomes as local drug depots: Effects of cellular and fluid dynamics on liposome retention at target sites

Bioadhesive liposomes, in which hyaluronic acid is the surface-anchored bioadhesive ligand, are being tested in vitro in order to evaluate their bioadhesivity. The first part of the test, binding to monolayers of cells modeling the in vivo designated sites under static conditions, was reported in a previous communication. This communication reports the results of the second and third parts of the test, which consist of evaluating the retention of bound liposomes in the face of tissue-related events such as cell migration, proliferation, and death, and under fluid flow. The in vivo- designated binding sites for the bioadhesive liposomes were modeled, as before, by monolayers of the A431 cell line served. A setup for perfusing a culture flask containing a monolayer of cells was devised for measuring the retention under fluid flow. The major findings are: (1) Over a selected tested period of 28 h, the cell cultures mimicked the tissue-related events described above, whether they did or did not receive a dose of liposomes. Over the same period and throughout these events, the bioadhesive liposomes remained bound at equilibrium-like levels, in the range of 0.03 ng lipid/10⁵ cells. (2) Fluid flowed over a cell monolayer dosed with bioadhesive liposomes swept away part of the dose. This loss was due mostly to that fraction of the dose which was in excess of the binding capacity of the monolayer, and occurred over the first 15 min of flow. Thereafter, the cell monolayer retained the bound liposomes, at equilibrium-like levels and with no further loss, even for the longest flow period tested (45 min of continuous flow) and under a flow rate of 0.64 ml/min. This study, together with previous results, shows that the hyaluronic acid-modified liposomes meet all parts of the bioadhesivity test. We therefore find merit in their further investigation.