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Background: Onconase, a protein isolated from oocytes and early embryos of the frog Rana pipiens, shares extensive homology with bovine pancreatic ribonuclease (RNase A) and possesses similar enzyme activity. Onconase is cytotoxic toward cancer cells in vitro and exhibits antitumor activity in animal models. In addition, Onconase has been shown to enhance the cytotoxic activity of some chemotherapeutic agents in vitro. Purpose: We studied interactions between the cytotoxic effects of Onconase and the chemotherapeutic agent vincristine (VCR) in the treatment of drug-sensitive and multidrug-resistant human colon carcinoma cells in vitro and in mice. Methods: Transplantable human colon carcinoma cells (HT-[29.sup.par] cells) were infected with a retrovirus containing human marl (also known as MDR1 and PGY1) complementary DNA (encoding P-glycoprotein [P-gp]), and clones that were cross-resistant to colchicine, doxorubicin, and vinblastine were selected (HT-[29.sup.mdr1] cells). Drug-resistant HT-[29.sup.mdr1] cells and drug-sensitive HT[29.sup.par] parental cells were treated with Onconase and/or VCR in vitro at varying concentrations to measure the effects on protein synthesis and cell viability. The impact of Onconase on VCR accumulation in both types of cells was determined in the presence or absence of MRK-16, an anti-P-gp monoclonal antibody capable of reversing the multidrug-resistant phenotype. The antitumor effects of onconase and/or VCR treatment were assessed in nude mice bearing established HT-[29.sup.par] or HT-[29.sup.mdr1] intraperitoneal tumors. [IC.sup.50] values (drug concentrations resulting in 50% inhibition of protein synthesis or cell viability) for Onconase and VCR were determined from semilogarithmic dose-response curves; interactions between the cytotoxic effects of these two agents were evaluated using data from protein synthesis inhibition experiments and a two-way analysis of variance. Survival distributions from in vivo experiments were compared using Cox proportional hazards models. Results: The combination of Onconase and VCR yielded enhanced cytotoxicity in vitro that was independent of P-gp expression. Evaluation of the effects of these two compounds on protein synthesis over a wide range of drug concentrations indicated possible synergistic interactions (i.e., greater than additive effects) in both drug-resistant and drug-sensitive cells. The enhancement of VCR cytotoxicity was dependent on onconase enzyme activity and was not associated with increased intracellular levels of VCR. Simultaneous treatment of mice bearing HT-[29.sup.par] tumors with Onconase and VCR did not extend their median survival time (MST) significantly (MST with VCR = 66 days; MST with VCR plus Onconase = 69 days; two-tailed P = .57); however, the MST of mice with HT-[29.sup.mdr1] tumors was extended significantly by this treatment (MST with VCR = 44 days; MST with VCR plus Onconase = 66 days; two-tailed P

The anti--P-glycoprotein monoclonal antibody MRK-16 mediates the reversal of multidrug resistance. Recombinant human interferon alfa (rHuIFN [alpha]) enhances the cytotoxic activity of diverse chemotherapeutics and may modulate multidrug resistance. Purpose: Our purpose was to determine the outcome of combination treatment with MRK-16, rHuIFN [alpha]-2a, and cytotoxic agents on tumor cells that express P-glycoprotein (Pgp). Methods: Three Pgp-expressing, multidrug-resistant human tumor cell lines were used: the MDR1 retrovirus-infected HT-29 colon adenocarcinoma (HT-[29.sup.mdr1]), the doxorubicin (Adriamycin)-resistant MCF-7 ([Adr.sup.R] MCF-7) breast carcinoma, and the de novo Pgp-acquired, HCT-15 colon carcinoma. The parental cell lines HT-[29.sup.par] and MCF-7 were used as controls. The in vitro effects of MRK-16 and rHuIFN [alpha]-2a were studied on: (a) chemosensitivity of parental and multidrug-resistant cell lines to vincristine, doxorubicin, or paclitaxel (Taxol); (b) intracellular drug concentrations; and (c) Pgp expression. The efficacy of vincristine alone or in combination with MRK-16 and/or rHuIFN [alpha]-2a was assessed against HT-[29.sup.mdr1] cells in female, athymic NCr-nu/nu mice. Results: For vincristine, the [IC.sub.50] (i.e., the concentration that causes 50% inhibition of cell growth) was 7.0 ng/mL in HT-[29.sup.mdr1] cells. Pretreatment of HT-[29.sup.mdr1] cells with MRK-16 partially restored vincristine sensitivity ([IC.sub.50] = 4.8 ng/mL), which was enhanced by noncytotoxic concentrations of rHuIFN [alpha]-2a ([IC.sub.50] = 2.9 ng/mL) via a mechanism independent of Pgp modulation or [[.sup.3.H]]vincristine efflux. rHuIFN [alpha]-2a potentiated MRK-16 reversal of multidrug resistance with both doxorubicin and paclitaxel on HT-[29.sup.mdra1] cells and with vincristine on [Adr.sup.R] MCF-7 and HCT-15 tumor cells. Treatment of mice with 1 mg/kg vincristine weekly for 3 weeks, beginning 10 days after tumor injection, significantly increased the median survival times of the HT-[29.sup.par] tumor-bearing mice (60 days versus 35 days; P

Background, Previous studies in the literature have suggested that radiolabeled F(ab'), fragments might be superior to whole immunoglobulin G (IgG) for imaging and therapy of cancer because of their greater penetration in tumors. To test this hypothesis, the authors compared tumor and normal tissue uptake along with plasma clearance of[125] I-labeled monoclonal antibody (Moab) IMMU-4 whole IgG with its[131] I-labeled F(ab')[sub.2] fragment. Methods. Five patients with either liver metastases from colorectal cancer (n = 4) or intact primary tumors (n = 1) received a combination 1251_IMMU-4 IgG (2 mCi/1 mg) plus [131]I-IMMU-4 F(ab')[sub.2] (10 MCi/1 mg) as a single 1-hour intravenous infusion on day 1. Serial blood samples were taken for up to 72 hours postinfusion to determine plasma clearance of each Moab. On days 3-9, patients underwent exploratory laparotomy in which biopsies of tumor as well as normal tissues (liver, normal colon, lymph node, and blood) were obtained. Tissues were weighed and counted in a gamma counter, and the percent of injected dose per kilogram (%ID/kg) of each antibody, along with the radiolocalization index (RI), was computed RI = %ID/kg tumor. % ID/kg normal tissue). Results. Tumor uptake of both antibodies (2.3 [+ or -] 0.53 % ID/kg) was significantly higher than that of normal tissues (0.56 [+ or - ] 0.12; P < 0.001), except for blood (2.8 [+ or -] 0.83), resulting in an RI [greater than or equal to] 3. There were no significant differences in uptake %Id/g) between F(ab')[sub.2] and IgG (F[ab'][sub.2] = 2.0 [+ or -] 0.57; IgG = 2.6 [+ or - ] 0.94). The mean [+ or -] SD of plasma T 1/2 was slightly shorter for F(ab')[sub.2] (28.8 [+ or -] 7.2 hours) than for IgG (45.9 [+ or -] 16.7; P = 0.08). Conclusion. In short, the biodistribution and pharmacokinetics of IMMU-4 F(ab')[sub.2] were comparable to those of IMMU-4-IGG. Cancer 1994; 73:850-7.

Background: We have demonstrated that, in the human ovarian carcinoma cell line (OVCAR-3), recombinant human interferon [alpha] (rHuIFN-[alpha]) potentiated in vitro inhibition of protein synthesis by immunotoxins. The antitumor activity of intracavitary immunotoxin administered to nude mice 5 days after tumor cell injection was enhanced by a nontherapeutic dose of rHuIFN-[alpha], as evidenced by increased survival time. Purpose: Our purpose was to determine the outcome of treatment with immunotoxin and rHuIFN-[alpha] in xenografts of more advanced tumors. Methods: At 10 or 15 days after tumor cell injection, nude mice with peritoneal OVCAR-3 xenografts were treated intraperitoneally with immunotoxin or with 454A12 monoclonal antibody (Mab) recombinant ricin A chain (rRA), alone or combined with a nontherapeutic dose of rHuIFN-[alpha]. The immunotoxin was composed of rRA covalently bound to an anti-CD71 (transferrin receptor) MAb. In other experiments, mice were treated intraperitoneally with cyclophosphamide and cisplatin to reduce tumor size on days 20 and 27 after tumor cell inoculation and then, beginning on day 40, with immunotoxin alone or combined with rHuIFN-[alpha]. Results: Initiation of treatment 10 days after OVCAR-3 transplantation significantly increased median survival from 41 to 89 days (10% survivors on day 120) with 454A12 MAb rRA alone and to more than 120 days (70% survivors) with 454A12 MAb rRA combined with rHuIFN-[alpha] (P