Enhancement of Vincristine Cytotoxicity in Drug-Resistant Cells by Simultaneous Treatment With Onconase, an Antitumor Ribonuclease

• Published in: JNCI : Journal of the National Cancer Institute 1996-06, Vol.88 (11), p.747-753
• Main Authors: Rybak, Susanna M., Pearson, John W., Fogler, William E., Volker, Kirk, Spence, Sally E., Newton, Dianne L., Mikulski, Stanislaw M., Ardelt, Wojciech, Riggs, Charles W., Kung, Hsiang-Fu, Longo, Dan L.
• Format: Article
• Language: English
• Subjects: Animals; Antineoplastic agents; Antineoplastic Agents - pharmacology; Antineoplastic Combined Chemotherapy Protocols - pharmacology; Biological and medical sciences; Colon cancer; Colonic Neoplasms - drug therapy; Drug Resistance; Drug therapy; Egg Proteins - pharmacology; Female; General aspects; Genes; Humans; Medical research; Medical sciences; Mice; Mice, Nude; Neoplasm Transplantation; Pharmacology. Drug treatments; Rana pipiens; Ribonucleases - pharmacology; Transplantation, Heterologous; Tumor Cells, Cultured; Vincristine - pharmacokinetics; Vincristine - pharmacology
• ISSN: 0027-8874; 1460-2105
• DOI: 10.1093/jnci/88.11.747

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-29par cells) were infected with a retrovirus containing human mdr1 (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-29mdr1 cells). Drug-resistant HT-29mdr1 cells and drug-sensitive HT-29par 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-29par or HT-29mdr1 intraperitoneal tumors. IC50 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 o