Pronounced antitumor efficacy of doxorubicin when given as the prodrug DOX-GA3 in combination with a monoclonal antibody beta-glucuronidase conjugate

Int J Cancer. 2001 Feb 15;91(4):550-4. doi: 10.1002/1097-0215(200002)9999:9999<::aid-ijc1075>;2-l.


A glucuronide doxorubicin prodrug N-[4-doxorubicin-N-carbonyl (oxymethyl) phenyl] O-beta-glucuronyl carbamate (DOX-GA3) has been developed to improve the antitumor effects of doxorubicin (DOX). The prodrug was originally designed to be activated into drug by human beta-glucuronidase (GUS) released from tumor cells in necrotic areas of tumor lesions. The aim of this study was to further improve the antitumor effects of DOX-GA3 by means of antibody-directed enzyme prodrug therapy (ADEPT). We thus investigated if the administration of an enzyme-immunoconjugate prepared from the pancarcinoma Ep-CAM specific monoclonal antibody (MAb) 323/A3 and beta-glucuronidase would result in improved antitumor effects because of additional enzyme localization in tumor tissue. In vitro, the prodrug DOX-GA3 was found to be 12-times less toxic than the parent drug DOX in a human ovarian cancer cell line. Immunospecific and complete activation of the prodrug took place when the cells were pretreated with 323/A3-beta-glucuronidase conjugate. In nude mice bearing s.c. human ovarian cancer xenografts (FMa) the maximum tolerated dose (MTD) of DOX-GA3 (500 mg/kg weekly x 2) was much higher when compared with that of DOX (8 mg/kg weekly x 2). In mice bearing well-established FMa xenografts, the standard treatment of DOX at the MTD (8 mg/kg weekly x 2) resulted in a tumor growth inhibition of 67%. Treatment with DOX-GA3 at a single dose of 500 mg/kg resulted in a better tumor growth inhibition of 87%. The combination of DOX-GA3 (500 mg/kg) with 323/A3-mGUS conjugate and anti-GUS MAb 105, to clear circulating conjugate, improved the antitumor effect even further to 98%. At the lower dose of 250 mg/kg DOX-GA3 tumor growth inhibition (34%) was not better than that of DOX. The combination, however, of DOX-GA3 at 250 mg/kg and 323/A3-mGUS conjugate plus MAb 105 again greatly improved the antitumor effect (growth inhibition of 93%). DOX given at 8 mg/kg weekly x 2 did not result in tumor regressions. As a result of ADEPT, the number of regressions of tumors improved from 0 out of 12 to 9 out of 11 at a dose of 250 mg/kg DOX-GA3. At the higher prodrug dose (500 mg/kg) the number of regressions improved from 2 out of 12 to 9 out of 10 as a result from the addition of enzyme-immunoconjugate. Our studies show that the efficacy of the widely used anti-cancer agent DOX may be improved by using the prodrug DOX-GA3, in combination with the tumor-specific enzyme-immunoconjugate 323/A3-mGUS and a conjugate clearing antibody.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibiotics, Antineoplastic / therapeutic use
  • Antibodies, Monoclonal / therapeutic use*
  • Antineoplastic Agents / therapeutic use
  • Body Weight / drug effects
  • Cell Division
  • Dose-Response Relationship, Drug
  • Doxorubicin / analogs & derivatives*
  • Doxorubicin / therapeutic use*
  • Female
  • Glucuronates / therapeutic use*
  • Glucuronidase / metabolism
  • Glucuronidase / therapeutic use*
  • Humans
  • Maximum Tolerated Dose
  • Membrane Glycoproteins / immunology
  • Mice
  • Mice, Nude
  • Models, Chemical
  • Necrosis
  • Neoplasm Transplantation
  • Neoplasms / drug therapy*
  • Ovarian Neoplasms / drug therapy
  • Ovarian Neoplasms / therapy
  • Prodrugs / therapeutic use*
  • Time Factors
  • Tumor Cells, Cultured


  • 323-A3 antigen, human
  • Antibiotics, Antineoplastic
  • Antibodies, Monoclonal
  • Antineoplastic Agents
  • Glucuronates
  • Membrane Glycoproteins
  • N-(4-doxorubicin-N-carbonyl(oxymethyl)phenyl)-O-glucuronyl carbamate
  • Prodrugs
  • Doxorubicin
  • Glucuronidase