Melanin potentiates daunorubicin-induced inhibition of collagen biosynthesis in human skin fibroblasts

One of the recognized side effects of antineoplastic anthracyclines is poor wound healing, resulting from an impairment of collagen biosynthesis. The most affected tissue is skin. The mechanism underlying the tissue specifici ty of the side effects of anthracyclines has not been established. In view of the fact that a number of pharmacologic agents are known to form complex es with melanin and melanins are abundant constituents of the skin, we dete rmined whether daunorubicin interacts with melanin and how this process aff ects collagen biosynthesis in cultured human skin fibroblasts. Results indi cated that daunorubicin forms complexes with melanin. Scatchard analysis sh owed that the binding of daunorubicin to melanin was heterogeneous, suggest ing the presence of two classes of independent binding sites with K-1 = 1.8 3 x 10(5) M-1 and K-2 = 5.52 x 10(3) M-1, The number of strong binding site s was calculated as n(1) = 0.158 mu mol/mg of melanin and the number of wea k binding sites as n(2) = 0.255 mu mol/mg of melanin. We have suggested tha t prolidase, an enzyme involved in collagen metabolism, may be one of the t argets for anthracycline-induced inhibition of collagen synthesis. We found that daunorubicin induced inhibition of prolidase activity (IC50 = 10 muM) , collagen biosynthesis (IC50 = 70 muM) and DNA biosynthesis (IC50 = 10 muM ) in human skin fibroblasts. Melanin (100 mug/ml) by itself produced about 25% inhibition of DNA synthesis and prolidase activity but it had no effect on collagen biosynthesis in cultured fibroblasts. However, the addition of melanin (100 mug/ml) to daunorubicin-treated cells (at IC50 concentration) augmented the inhibitory action of daunorubicin on collagen and DNA biosyn thesis without having any effect on prolidase activity. The same effect was achieved when the cells were treated with daunorubicin at one-fourth of th e IC50 given at 0, 6, 12 and 18 h during a 24-h incubation. The data sugges t that the melanin-induced augmentation of the inhibitory effects of daunor ubicin on collagen and DNA biosynthesis may result from: (i) accumulation o f the drug in the extracellular matrix, (ii) gradual dissociation of the co mplex, and (iii) constant action of the released drug on cell metabolism. T he phenomenon may explain the potential mechanism for the organ specificity of daunorubicin-induced poor wound healing in patients administered this d rug. (C) 2001 Published by Elsevier Science B.V.