Anthracycline resistance and consequences of the in situ-in vitro transfer

Adriamycin-resistant and normal cells of the sarcoma 180 of the mouse undergo qualitatively different deflections from the in situ state when prepared for an experiment. Resistant cells perform a fast reactive decline in the proliferative activity. They are capable of quiescence as defined by the time needed for the induction of the proliferation. Sensitive cells seem to be unable to quiesce and are only slowed down. These facts must be taken into account in interpretation of similar results. Differences in experiments need not necessarily imply differences in situ. Such in vitro appearing differences between sensitive and adriamycin-resistant cells of the murine sarcoma 180 include the retention of the mitochondria-specific stain rhodamine 123 and the uptake of anthracyclines, both being reduced in resistant cells. After labeling sensitive cells with thymidine in vivo and sorting them according to their rhodamine 123-derived fluorescence, the label was only found in the major, highly fluorescing fraction. A small low-fluorescing fraction remained unlabeled. We were able to demonstrate similar results with labeled anthracyclines applied to both the sensitive and the resistant cells in a short period between the removal of the cells from the ascites and the cell sorting. The adriamycin resistance seems to be joined with the ability of the cells to reduce their proliferative activity following changes to unfavorable conditions in vitro. Quiescent cells of the resistant line demonstrate the "anthracycline pump." Substances which are known to increase the sensitivity of anthracycline-resistant cells (TWEEN, verapamil) also shift the cells from low to high rhodamine 123-fluorescence.