Phase I Study of Thiotepa in Combination with the Glutathione Transferase Inhibitor Ethacrynic Acid

Peter J. O'Dwyer, Frank LaCreta, Sherri Nash, Peter W. Tinsley, Russell Schilder, Margie L. Clapper, Kenneth D. Tew, Lisa Panting, Samuel Litwin, Robert L. Comis, Robert F. Ozols

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158 Scopus citations

Abstract

The glutathione transferases comprise a family of isoenzymes, one or more of which are involved in the conjugation of alkylating agents to glutathione (GSH). Increased GSH transferase activity has been shown to underlie acquired resistance to several alkylating agents. Ethacrynic acid inhibits the isoenzymes of GSH transferase with 50% inhibitoryconcentration values ranging from 0.3 to 6.0 MMand has been shown to restore sensitivity to alkylating agents in drug-resistant animal tumor models. \Ve entered 27 previously treated patients with advanced cancer on a study of ethacrynic acid (25 to 75 mg/m2 p.o. every 6 h for 3 doses) and thiotepa (30 to 55 mg/m2 i.v. l h after the second dose of ethacrynic acid). The major toxicity of ethacrynic acid was diuresis, which was observed at every dose level; in addition, severe metabolic abnormalities occurred at 75 mg/m2. At 50 mg/m2, the diuretic effects were manageable. Myelosuppression was the most important effect of the combination. Two of seven courses of ethacrynic acid, 50 mg/m2, and thiotepa, 55 mg/ m2, were associated with grade 3 or 4 neutropenia and/or thrombocytopenia. Nausea/vomiting ≥grade 2 was observed in 16% of courses. GSH transferase activity was assayed spectrophotometrically in the peripheral mononuclear cells of all patients. At each dose level, activity decreased following ethacrynic acid administration, with recovery by 6 h. Adminis tration of ethacrynic acid, 50 mg/m2, resulted in a mean nadir of trans ferase activity of 37% of control. The pharmacokinetics of thiotepa and its principal metabolite TEPA were studied in 23 patients. The plasma disappearance of thiotepa fit a two-compartment open model with a terminal half-life of approximately 2 h. Plasma TEPA levels peaked at a mean of 2.16 h following thiotepa administration. The harmonic mean terminal half-life of TEPA was 10.4 h, and the TEPA area under the curve (AUC) did not increase with increasing thiotepa dose. The AUC of thiotepa was approximately twice, and the clearance about one-half, of the values obtained in a previous study of single agent thiotepa. The AUC of TEPA was lower than that previously observed. The data suggest that ethacrynic acid inhibits enzymes involved in the metabolic disposition of thiotepa, including its oxidative desulfuration to TEPA. The severity of the platelet toxicity was correlated with the AUC of thiotepa, but not with that of TEPA. This combination of thiotepa and ethacrynic acid will be tested further in Phase II trials.

Original languageEnglish
Pages (from-to)6059-6065
Number of pages7
JournalCancer Research
Volume51
Issue number22
StatePublished - Nov 1991

Keywords

  • Adult
  • Aged
  • Antineoplastic Combined Chemotherapy Protocols/therapeutic use
  • Drug Evaluation
  • Drug Tolerance
  • Ethacrynic Acid/administration & dosage
  • Female
  • Glutathione Transferase/antagonists & inhibitors
  • Humans
  • Male
  • Middle Aged
  • Neoplasms/drug therapy
  • Thiotepa/administration & dosage

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