The acridonecarboxamide GF120918 potently reverses P-glycoprotein-mediatedresistance in human sarcoma MES-Dx5 cells

The doxorubicin-selected. P-glycoprotein (P-gp)-expressing human sarcoma ce ll line MES-Dx5 showed the following levers of resistance relative to the n on-P-gp-expressing parental MES-SA cells in a 72 h exposure to cytotoxic dr ugs: etoposide twofold, doxorubicin ninefold. vinblastine tenfold, taxotere 19-fold and taxol 94-fold. GF120918 potently reversed resistance completel y for all drugs. The EC(50)s of GF120918 to reverse resistance of MES-Dx5 c ells were: etoposide 7 +/- 2 nM, vinblastine 19 +/- 3 nM, doxorubicin 21 +/ - 6 nM, taxotere 57 +/- 14 nM and taxol 91 +/- 23 nM. MES-Dx5 cells exhibit ed an accumulation deficit relative to the parental MES-SA cells of 35% for [H-3]-vinblastine, 20% for [H-3]-taxol and [C-14]-doxorubicin. The EC, of GF120918, to reverse the accumulation deficit in MES-Dx5 cells, ranged from 37 to 64 nM for all three radiolabelled cytotoxics. [H-3]-vinblastine boun d saturably to membranes from MES-Dx5 cells with a K-D of 7.8 +/- 1.4 nM an d a B-max Of 5.2 +/- 1.6 pmol mg(-1) protein. Binding of [H-3]-vinblastine to P-gp in MES-Dx5 membranes was inhibited by GF120918 (K-i = 5 +/- 1 nM), verapamil (K-i = 660 +/- 350 nM) and doxorubicin (K-i = 6940 +/- 2100 nM). Taxol, an allosteric inhibitor of [H-3]-vinblastine binding to P-gp, could only displace 40% of PHI-vinblastine (K-i = 400 +/- 140 nar). The novel acr idonecarboxamide derivative GF120918 potently overcomes P-gp-mediated multi drug resistance in the human sarcoma cell line MES-Dx5. Detailed analysis r evealed that five times higher GF120918 concentrations were needed to rever se drug resistance to taxol in the cytotoxicity assay compared to doxorubic in, vinblastine and etoposide. An explanation for this phenomenon had not b een found. (C) 1999 Cancer Research Campaign.