Adriamycin and daunomycin semiquinone membrane/buffer partition constants using the spin-broadening technique.

Membrane/buffer partition constants have been determined for the semiquinones of adriamycin, Adrsq, and daunomycin, Daunosq, as a function of ionic strength and cholesterol content in phosphatidylcholine multilamellar vesicles using the spin-broadening technique. The partition constants corresponding to Adrsq were essentially similar to those of Daunosq under any of the conditions studied. These constants increase with ionic strength increase and decrease with an increase in cholesterol concentration at the membrane. These observations could have implications in the Adr and Dauno cytotoxicities where their corresponding semiquinones are postulated as important intermediates and consequently their interactions with biological membranes should also be considered as important.