Stability of doxorubicin in relation to chemosensitivity determinations: Loss of lethality and retention of antiproliferative activity

The chemical stability of doxorubicin in a variety of tissue culture media has been studied by thin layer chromatography (TLC). In all the media examined, authentic doxorubicin was converted to a chemically distinct form as evidenced by the failure of this form to migrate on TLC plates. The rates of conversion were rapid enough (t_1/2 3 hr) to be of consequence in chemosensitivity determinations, especially if working solutions of doxorubicin were to be routineh made and stored in tissue culture media. The addition of certain antioxidants to media did not prevent the conversion of authentic doxorubicin. However, doxorubicin was quite stable in distilled water. No single component of media was found to be responsible for the conversion of authentic doxorubicin, although arginine, histidine, tyrosine, NaHCO₃and Fe(NO:₃):₃ could each generate a form of doxorubicin which did not migrate in TLC analysis. Purification of the non-migrating form of doxorubicin demonstrated that in vitro conversion resulted in considerable loss of lethality while antiproliferative activity was retained. These observations provide possible explanations for the variability in chemosensitivity determinations and may explain some of the failures to predict clinical responsiveness.