In vitro studies on the absorption of WR-2721 by tumors and normal tissues

An attempt was made to develop single cell systems which would allow the study of absorption of WR-2721 by individual normal and malignant cells. Simple mechanical dissociation procedures provided adequate single cell suspensions for most normal tissues and these cells concentrated WR-2721 against a gradient. One apparent exception was bone marrow—while the tissue is very responsive to WR-2721 in vivo, our in vitro preparations absorbed the drug only very poorly. It was found, however, that lipid and red blood cell contaminants in the marrow cell preparation masked and interfered with the absorption of WR-2721, causing the anomolous results. In contrast with normal tissue, mechanical or enzymatic dissociation procedures failed to produce adequate single cell preparations from tumors. Problems encountered include low cell yield, contamination by non-tumor cells of host origin, and tumor cell membrane damage. Since published studies of WR-2721 protection of monolayer cultures have probably all been carried out using malignant cells, we repeated these experiments using normal human fibroblasts. As with malignant cells, however, we found only marginal radiation protection of these cultured normal cells by WR-2721. In addition, the drug produced no detectable protection against radiation-induced DNA strand breaks, either in normal fibroblasts or in HeLa cells. Thus, cultured fibroblasts do not appear to provide a useful model for studying the absorption of WR-2721 by normal tissue.