In vitro inhibition of nitrogen mustard efficacy by postincubation of treated cells in serum protein

Lettre-Ehrlich cells were loaded with sufficient HN 2 to produce about a 98% cell kill. Postincubation of the HN 2 -loaded cells in PBS resulted in the loss of about 40% of their HN 2 without changing the cytolytic effect, supporting the proposal that only bound drug was effective. Postincubation of the HN 2 -loaded cells in PBS which contained 2% bovine serum albumin or in cell-free mouse ascitic fluid (1.8% protein) resulted in the same relative cellular HN 2 loss as well as a 79% decrease in the cell kill