Figure 4.

Binding and intracellular retention of compounds 3–6 (PS 3–6) by human lung tumor fibroblasts. Subconfluent cultures of fibroblast were incubated in medium containing 3.2 µM of the indicated compunds. Binding to the cells was determined by 30-min exposure at 0°, uptake by incubation of the cells for 4 hours at 37° and retention by culturing in compound-free medium for 20 hours. Cell-associatied fluorescence of the compounds was visualized by microscopy (400× magnification).