STRONG BINDING OF DITRISARUBICIN B TO DNA

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DNA binding characteristics of ditrisarubicin B were studied by the fluorescence titration technique. Ditrisarubicin B bound to calf thymus DNA with an affinity higher than any we have ever seen among anthracyclines. The apparent association constant (K_app) of ditrisarubicin B was 2.36 × 10⁸ M^-1, which is 22.7 times larger than that of doxorubicin. The apparent number of binding sites (n_app) of ditrisarubicin B per nucleotide of DNA was 0.164, and this value is identical with that of doxorubicin. Betaclamycin A, which has a trisaccharide chain at C-7 but no carbohydrate at C-10 in the aglycone, interacted with DNA to give a K_app of 5.92 ×10⁶ M^-1 and n_app of 0.178. These results suggest to us that the high affinity of ditrisarubicin B for DNA is caused by the existence of a glycosidic chain at C-10.