BOVINE SERUM ALBUMIN-DOXORUBICIN CONJUGATE OVERCOMES MULTIDRUG-RESISTANCE IN A RAT HEPATOMA

A bovine serum albumin-conjugated doxorubicin via the glutaraldehyde b ridge (BSA-DXR conjugate) showed potent dose-dependent inhibition of c ell growth against daunorubicin-resistant AH66 (AH66DR) cells as well as parental AH66 (AH66P) cells in vitro as compared to treatment with DXR or BSA-glutaraldehyde conjugate without DXR (BSA-GA). In the cultu re of AH66DR with BSA-DXR conjugate, drug accumulation in the AH66DR c ells increased as a function of time up to 24 h reaching approximately the same drug level as AH66P cells treated with DXR. The intracellula r accumulation of the BSA-DXR conjugate was inhibited by the addition of ammonium chloride, while that of DXR alone was not inhibited. Intra cellular DXR was effluxed rapidly from AH66DR cells, but BSA-DXR conju gate or pharmacologically active DXR adduct remained in the cells at a relatively high concentration over a 36-h time period. The life-prolo nging effect of the conjugate was assessed using rats inoculated i.p. with AH66P or AH66DR. The rats were treated with the BSA-DXR conjugate , DXR, a mixture of DXR with BSA, or BSA-GA by either the i.p. or i.v. route. Treatment with DXR had no significant surviving effect as comp ared to that with saline in AH66P-bearing rats. By contrast, BSA-DXR c onjugate showed a significant life-prolonging effect as compared with DXR alone in the same degree both in AH66P- and AH66DR-bearing rats. B SA-GA did not show any toxicity in vivo as well as in vitro. These res ults indicate that the BSA-DXR conjugate allows DXR to escape from the multidrug resistance mechanism.