DISTAMYCIN-A DERIVATIVES POTENTIATE TUMOR-NECROSIS-FACTOR ACTIVITY VIA THE MODULATION OF TYROSINE PHOSPHORYLATION

The cytotoxic activities of 2 novel distamycin-A derivatives, FCE 2451 7 and FCE 25450A, alone and in combination with tumor-necrosis factor- alpha (TNF), were studied. Both drugs, especially FCE 25450A, analyzed extensively here, inhibited the growth of HL60 promyelocytic cells, a nd human SV80 and murine L929 transformed fibroblasts in a dose-depend ent manner. The growth-inhibitory potential of sequential exposure to the distamycin-A analogs and TNF was determined. A 4-hr treatment of L 929 fibroblasts with 100-1,000 ng/ml FCE 25450A, followed by 2 ng/ml T NF, resulted in a synergistic anti-proliferative effect, The synergism of FCE 24517 with TNF was less profound. Experiments to elucidate the mechanism underlying the cooperation revealed that FCE 25450A pre-tre atment almost completely abolished the elevated tyrosine phosphorylati on of a 137-kDa and other membranal proteins and prevented the de-phos phorylation of another protein band observed in L929 cells in the pres ence of TNF. FCE 25450A alone induced no changes in the phosphotyrosin e profile of the cells. The effect of FCE 25450A was counteracted by t he tyrosine-phosphatase inhibitor orthovanadate. In parallel, the inhi bitor also diminished the antiproliferative action of the FCE 25450A/T NF combination. These findings suggest that, beyond their cytotoxic ef fects as single agents, the distamycin derivatives increase the sensit ivity of cells to TNF. This effect is governed via the inhibition of T NF-induced tyrosine phosphorylation of specific proteins which are pro bably involved in the development of TNF resistance. Thus, protein de- phosphorylation might provide an additional mechanism of action of the se novel distamycin-A-derived drugs. (C) 1997 Wiley-Liss, Inc.