CURE OF MALIGNANT ASCITES AND GENERATION OF PROTECTIVE IMMUNITY BY MONOCLONAL ANTIBODY-TARGETED ACTIVATION OF A GLUCURONIDE PRODRUG IN RATS

We examined the in vivo efficacy of targeting beta-glucuronidase (beta G) to activate a glucuronide prodrug (BHAMG) of p-hydroxyaniline must ard (pHAM) at hepatoma ascites in Sprague-Dawley rats. Injection i.p. of 500 mu g RH1-beta G, a conjugate formed between recombinant beta G and monoclonal antibody RH1 with specificity for an antigen expressed on AS-30D rat hepatoma cells, into rats bearing AS-30D ascites resulte d in the accumulation of 54 mu g conjugate per 10(9) tumor cells after 2 hr. Ascites fluid and serum contained 0.53 and 0 mu g/ml, respectiv ely, RH1-beta G 2 hr after injection of the conjugate. Conjugate bindi ng to AS-30D cells was heterogeneous and non-saturated, as determined by flow cytometry. BHAMG was less toxic than pHAM to SD rats based on measures of animal mortality, weight loss and hematological toxicity. Treatment of rats bearing established hepatoma ascites with 500 mu g R H1-beta G followed 2 hr later with a single i.p. injection of 30 mg/kg BHAMG or 3 i.p. injections of 10 mg/kg BHAMG 2, 3 and 4 hr later resu lted in the cure of 6/8 and 8/8 animals, respectively, Treatment with BHAMG or pHAM alone did not produce cures, whereas treatment with a co ntrol antibody-beta G conjugate and BHAMG produced significantly great er hematological toxicity compared to treatment with RH1-beta G and BH AMG. All cured rats were completely protected from rechallenge with 2 x 10(7) AS-30D cells, indicating that successful treatment of animals induced protective immunity. (C) 1997 Wiley-Liss, Inc.