Poly( N-isopropylacrylamide) co-polymer films as potential vehicles for delivery of an antimitotic agent to vascular smooth muscle cells

Abstract

Introduction: Local delivery of antimitotic agents is a potential therapeutic strategy for protection of injured coronary vasculature against intimal hyperplasia and restenosis. This study sought to establish the principle that thermoresponsive poly( N-isopropylacrylamide) co-polymer films can be used to deliver, in a controlled manner, an antimitotic agent to vascular smooth muscle cells (VSMC). Methods: A series of co-polymer films was prepared, using varying ratios (w/w) of N-isopropylacrylamide (NiPAAm) monomer to N- tert-butylacrylamide (NtBAAm) and loaded with the antimitotic agent colchicine (100 nmol/film) at room temperature. Results: The extent of colchicine release at 37 °C was inversely proportional to the amount of NtBAAm in co-polymer films: release after 48 h from 85:15, 65:35 and 50:50 (NiPAAm:NtBAAm) films was 26, 17 and 0.5 nmol, respectively. In cytotoxicity studies, when medium incubated with co-polymers for 24 h (in the absence of colchicine) was further incubated with target bovine aortic smooth muscle cells (BASMC), no loss of cell viability occurred. Colchicine released from all three co-polymer films significantly inhibited proliferation and random migration of BASMC: 100 nM colchicine (released from 65:35 NiPAAm:NtBAAm) reduced cell proliferation to 25.7±1.7% of levels seen in the absence of colchicine (control) and random cell migration to 37.7±5.7% of control (mean±S.E.M., n=3, P<.01 and P<.05, respectively). The magnitudes of these effects were comparable to those seen in separate experiments with native colchicine and were observed in samples of released colchicine which had been stored at −20 °C for up to 6 months. Conclusions: This study has shown that the release of the antimitotic agent colchicine, from NiPAAm/NtBAAm co-polymer films can be manipulated by changes in co-polymer composition. Furthermore, such drug released at 37 °C retains comparable bioactivity to that of native colchicine.