title: Enhanced therapeutic efficacy of an immunotoxin in combination with chemotherapy against an intraperitoneal human tumor xenograft in athymic mice.
abstract: A mouse IgG2b anti-pan carcinoma monoclonal antibody, NR-LU-10, was shown to bind homogeneously to ascites xenografts of both ovarian and colon carcinoma. Following linkage to a highly potent holotoxin, Pseudomonas exotoxin A (PE), NR-LU-10 demonstrated high potency and selectivity in vitro (ID50 = 100 pg/ml; elimination of greater than or equal to 4.5 logs of cells). The conjugate was evaluated for therapeutic efficacy against a human colon tumor (HT-29) transplantable in the peritoneal cavity of nude mice. Beginning 3 days after HT-29 injection, mice received either three or six i.p. injections of 0.5 micrograms of unconjugated NR-LU-10 or immunotoxin conjugate (NR-LU-10/PE) every other day. Mice that received three or six treatments of NR-LU-10 alone had median survival times (MSTs) of 39 and 40 days, respectively, which did not differ significantly from the MST observed for the untreated control groups (MST = 35 days). In contrast, treatment with three or six injections of 0.5 micrograms NR-LU-10/PE exhibited significantly increased MSTs (P = 0.002) of 50 and 60 days, respectively. Coinjection of unconjugated NR-LU-10 (20 micrograms) and 0.5 micrograms of NR-LU-10/PE blocked the therapeutic effect of the immunotoxin (MST = 33 days). The therapeutic efficacy of NR-LU-10/PE was further enhanced against HT-29 when administered i.p. during and after cytoreductive chemotherapy. The i.p. administration of 300 mg/lg of cyclophosphamide plus 100 mg/kg of the chemoprotective drug, WR-2721, 10 and 17 days posttumor cell inoculation induced a significant increase in MST from 36 days to 59 days (P = 0.002). Interestingly, groups of mice that received either two, four, or seven treatments of NR-LU-10/PE following cytoreductive therapy exhibited a further significant increase (P = 0.001) in MSTs of 89, 97, and 105 days, respectively. Therefore, the use of immunotoxin therapy following cytoreductive chemotherapy significantly prolonged survival time of mice bearing the HT-29 colon tumor over that observed with chemotherapy or NR-LU-10/PE alone.
authors.affiliation: Laboratory of Experimental Immunology, NCI-Frederick Cancer Research Facility, Maryland 21701.
authors.forename: J W
authors.initials: JW
authors.lastname: Pearson
authors.forename: G
authors.initials: G
authors.lastname: Sivam
authors.forename: R
authors.initials: R
authors.lastname: Manger
authors.forename: R H
authors.initials: RH
authors.lastname: Wiltrout
authors.forename: A C
authors.initials: AC
authors.lastname: Morgan
authors.forename: D L
authors.initials: DL
authors.lastname: Longo
mesh_terms: D036002:ADP Ribose Transferases; D000818:Animals; D000911:Antibodies, Monoclonal / Q000627:therapeutic use; D000951:Antigens, Neoplasm / Q000032:analysis; D001427:Bacterial Toxins; D002460:Cell Line; D003110:Colonic Neoplasms / Q000628:therapy*; D005098:Exotoxins; D005434:Flow Cytometry; D006801:Humans; D000922:Immunotoxins / Q000627:therapeutic use*; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D011550:Pseudomonas aeruginosa; D014183:Transplantation, Heterologous; D014410:Tumor Stem Cell Assay; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A
chemical_list: D036002:ADP Ribose Transferases; D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm; D001427:Bacterial Toxins; D005098:Exotoxins; D000922:Immunotoxins; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A