Enhanced therapeutic efficacy against an ovarian tumor xenograft of immunotoxins used in conjunction with recombinant alpha-interferon.

Abstract

The antitumor effects of two immunotoxins were evaluated in vitro and in vivo against the human ovarian carcinoma cell line, OVCAR-3. The immunotoxins used were composed of recombinant ricin A chain (rRTA) covalently attached to a monoclonal antibody directed toward the human transferrin receptor (45412/rRTA, also called 454A12 MAB-rRTA by Cetus Corporation) or Pseudomonas exotoxin coupled to an anticarcinoma monoclonal antibody (NR-LU-10/PE). Preliminary characterization of the NR-LU-10 antigen by immunoprecipitation and cellular fluorescence demonstrated two dominant cell surface polypeptide moieties with molecular weights of 40,000 and 45,000 and a minor component with a molecular weight of 33,000. The immunotoxins were used alone or in combination with recombinant human alpha-interferon (rhIFN-alpha). Protein synthesis was inhibited in a dose-dependent manner in OVCA-3 cells incubated in vitro with either NR-LU-10/PE or 454A12/rRTA (50% inhibitory concentrations, 1 and 75 ng/ml, respectively). Unconjugated NR-LU-10 or 454A12 abrogated the activity of the relevant immunotoxins. Concomitant incubation in vitro of OVCAR-3 cells with NR-LU-10/PE or 454A12/rRTA and a noncytotoxic concentration of rhIFN-alpha potentiated the inhibitory activity of the immunotoxins via a mechanism independent of antigenic upregulation. This potentially synergistic combination was then tested in vivo. The median survival time (MST) of mice given injections i.p. of 4 x 10(6) OVCAR-3 cells was 46 days. Cohorts of mice that received intracavitary treatment beginning 5 days posttumor cell inoculation with either 0.25 or 0.5 microgram of NR-LU-10/PE every other day for a total of 10 treatments exhibited a significantly increased MST of 63 and 104 days, respectively (P less than 0.0001). Likewise, the i.p. injection of either 2.5 or 10 micrograms of 454A12/rRTA given in an identical schedule resulted in a MST of 89 and greater than 120 days, respectively (P less than 0.0001). When rhIFN-alpha was administered i.p. in conjunction with those doses of either immunotoxin, a significant increase in the MST was observed in comparison with mice given immunotoxin alone. The combination of 5 x 10(4) units of rhIFN-alpha and 0.25 microgram of NR-LU-10/PE resulted in 67% long-term survivors (greater than 120 days) compared with only 13% survival of mice given the immunotoxin alone. Similarly, 2.5 micrograms of 454A12/rRTA plus rhIFN-alpha resulted in an enhanced therapeutic response (89% long-term survivors) when compared with 454A12/rRTA alone (29%).(ABSTRACT TRUNCATED AT 400 WORDS)