Time-dependent changes in drug sensitivity expressed by mammalian cells after exposure to trypsin.

Immediately after a 5-minute exposure to 0.025% trypsin, Chinese hamster ovary cells treated with anticancer drugs exhibited changes in drug sensitivity. Depending on the drug, cells immediately became more sensitive, less sensitive, or showed no change in sensitivity at all. The deviation from normally expected survival values ranged from fourfold to fifty-fold and varied with time (of drug treatment) after trypsinization. By the 12th hour post trypsinization, the drug survival responses had returned to values obtained with untrypsinized cells.