Photoinactivation of Anthracyclines*

When adriamycin or daunomycin is irradiated at 366 nm, the drug loses its cytotoxic activity against Sarcoma 180 cells in culture. The half‐time for inactivation is about 9 h. Laboratory fluorescent lights also inactivate these anthracyclines with a half‐time of about one day. The photoinactivated drugs do not interact effectively with the anthracycline transport system and consequently are not taken up into the cell. Fluorescence and NMR spectroscopy yield spectra identical to native drug but with reduced peak intensities. Likewise, high pressure liquid chromatographic analysis does not reveal any new chemical species in photolyzed anthracyline solutions. Gel filtration chromatography, however, shows that the photoinactivation process is accompanied by the formation of drug polymers which are suggested to be the inactive species.