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

Abstract

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 specificity 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 complexes with melanin and melanins are abundant constituents of the skin, we determined whether daunorubicin interacts with melanin and how this process affects collagen biosynthesis in cultured human skin fibroblasts. Results indicated that daunorubicin forms complexes with melanin. Scatchard analysis showed that the binding of daunorubicin to melanin was heterogeneous, suggesting the presence of two classes of independent binding sites with K 1=1.83×10 5 M −1 and K 2=5.52×10 3 M −1. The number of strong binding sites was calculated as n 1=0.158 μmol/mg of melanin and the number of weak binding sites as n 2=0.255 μmol/mg of melanin. We have suggested that prolidase, an enzyme involved in collagen metabolism, may be one of the targets for anthracycline-induced inhibition of collagen synthesis. We found that daunorubicin induced inhibition of prolidase activity (IC 50=10 μM), collagen biosynthesis (IC 50=70 μM) and DNA biosynthesis (IC 50=10 μM) in human skin fibroblasts. Melanin (100 μg/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 μg/ml) to daunorubicin-treated cells (at IC 50 concentration) augmented the inhibitory action of daunorubicin on collagen and DNA biosynthesis without having any effect on prolidase activity. The same effect was achieved when the cells were treated with daunorubicin at one-fourth of the IC 50 given at 0, 6, 12 and 18 h during a 24-h incubation. The data suggest that the melanin-induced augmentation of the inhibitory effects of daunorubicin on collagen and DNA biosynthesis may result from: (i) accumulation of the drug in the extracellular matrix, (ii) gradual dissociation of the complex, and (iii) constant action of the released drug on cell metabolism. The phenomenon may explain the potential mechanism for the organ specificity of daunorubicin-induced poor wound healing in patients administered this drug.