Cancer chemotherapy may be improved by increasing antineoplastic drug specificity for tumor cells. We have synthesized a glucuronide prodrug that can be enzymatically converted to an antineoplastic agent at tumor cells that are able to bind β-glucuronidase-monoclonal antibody conjugates. The glucuronide prodrug BHAMG, the tetra-n-butyl ammonium salt of (p-di-2-chloroethylaminophenyl-β-d-glucopyranosid) uronic acid, was 150 times less toxic than the parent drug, N,N-di-(2-chloroethyl)-4-hydroxyaniline, to HepG2 human hepatoma cells and over 1000-fold less toxic than the parent drug to AS-30D rat hepatoma cells in vitro. In the presence of β-glucuronidase, BHAMG was activated and became as toxic as the parent drug N,N-di-(2-chloroethyl)4-hydroxyaniline. A conjugate (RH1-βG) was formed by linking β-glucuronidase to a monoclonal antibody which binds to an antigen expressed on the surface of AS-30D cells. The concentration of BHAMG causing 50% inhibition of AS-30D cellular protein synthesis was reduced over 1000-fold, from >770 µm to <0.74 µm after these cells were preincubated with RH1-βG. Specificity of BHAMG activation at antigen-positive cells was shown by monoclonal antibody RH1 blocking of RH1-βG conversion of BHAMG to toxic drug and by the inability of BHAMG to be converted to active drug when antigen-negative control cells were preincubated with RH1-βG. Our results show that the targeted-β-glucuronidase activation of BHAMG can increase the specificity of chemotherapy for rat hepatoma in vitro and suggest that the targeted activation of glucuronide prodrugs may be useful for cancer therapy.
Supported by grants and allocations from the National Science Council and Academia Sinica, Taipei, Taiwan, Republic of China.