Studies on the tumor-promoting activity of polyurethanes: depletion of inhibitory action of metabolic cooperation on the surface of a polyalkyleneurethane but not a polyetherurethane.

Methanol extracts prepared from three polyetherurethanes (PEUs), namely PU4, PU6, and PU8, which were synthesized using 4,4'-diphenylmethanediisocyanate, poly(tetramethylene oxide), and 1,4-butanediol, showed an inhibitory action on the gap-junctional intercellular communication in a V79 metabolic cooperation (MC) test system. However, the inhibitory potentials of methanol extracts did not correlate with the tumorigenic potential of the polyurethanes in 1-year rat implantation studies. When the MC test was carried out using glass dishes partly coated with low molecular weight PEU, the inhibitory activity was clearly detected on the surface of the polyurethane coating but not on that of the noncoated glass area. The inhibitory activity of the three PEUs investigated using polyurethane-coated dishes correlated with the values of the polyurethane's tumorigenic potential in the rat implantation study. Various polyurethanes containing polybutadiene (PBD), hydrogenated polybutadiene (HPBD), or a fluoropolyether glycol (FPEG) as the soft segment were also tested using coated dishes in the MC assay. The threshold inhibitory response of FPEG-PU was 10-fold less than that of PU4, and neither PBD-PU nor HPBD-PU showed any inhibition in the MC test system. Both the FPEG and aliphatic soft segment containing polyurethanes decreased, and had minimal influence on the gap junctional intercellular communication. Thus, the tumor-promoting potential of PBD-PU, HPBD-PU, and FPEG-PU was considered to be lower than those of the PEUs based on these in vitro test results.