ABSTRACT
New inhibitors of the enzyme thymidylate synthase (TS) are now reaching clinical application. Alteration of the dUTP: dTTP ratio may be critical to TS inhibition-induced tumor cell death. The DNA polymerase assay with modification was used to rapidly and sensitively measure dUTP, dTTP, and dUTP:dTTP ratios in cell extracts of HT29 human colon carcinoma cells treated with the specific TS inhibitor ZD1694 [N-(5-[N-(3,4-dihydro-2-methyl-4-oxoquinazolin-6-ylmethyl)-N-methylamino]-2-thenoyl)-L-glutamic acid]. These results revealed an increase in the dUTP:dTTP ratio at 2 hr after a 2-hr exposure to ZD1694 at concentrations of 0.05 to 0.2 microM with significant normalization at 16 hr after a 2-hr exposure despite evidence of continued TS inhibition. This assay is highly sensitive and reproducible for levels of dUTP and is less labor intensive than traditional assays.
Subject(s)
Antimetabolites, Antineoplastic/pharmacology , Deoxyuracil Nucleotides/metabolism , Quinazolines/pharmacology , Thiophenes/pharmacology , Thymidylate Synthase/antagonists & inhibitors , Thymine Nucleotides/metabolism , Adenocarcinoma , Colonic Neoplasms , DNA-Directed DNA Polymerase/metabolism , Deoxyuracil Nucleotides/analysis , Dose-Response Relationship, Drug , Enzyme Inhibitors/pharmacology , Humans , Kinetics , Pyrophosphatases/metabolism , Templates, Genetic , Thymine Nucleotides/analysis , Tumor Cells, CulturedABSTRACT
We have used pulsed-field gel electrophoresis to examine 5-fluorouracil (5FU)-induced DNA double-strand breaks (DSBs), both with and without modulation by IFN-alpha2a (IFNalpha), in HT29 human colon adenocarcinoma cells. Although 24-h treatment with either 10 microM 5FU or 500 units/ml IFNalpha did not result in significant DNA fragmentation, the combination of 5FU + IFNalpha resulted in a significant increase in DNA DSBs versus either drug alone (P < 0.05). The pattern of fragmentation induced by treatment with 5FU + IFNalpha was compared to that induced by gamma-radiation, which generates lesions at random sites, digestion with NotI restriction endonuclease, which cleaves at the specific sequence 5' ellipsis GCGGCCGCellipsis 3', and HhaI restriction endonuclease, which cleaves at the specific sequence 5'ellipsis GCGCellipsis 3'. 5FU + IFNalpha resulted in a specific pattern characterized by the accumulation of fragments of <3 Mb in the absence of fragments of >3 Mb, which differed from that of gamma-radiation and restriction endonuclease digestion. Because neither morphological nor DNA fragmentation characteristic of apoptosis was observed after 5FU + IFNalpha treatment, the nonrandom pattern of DSBs that was observed did not appear to be the result of the initiation of programmed cell death within these cells.
Subject(s)
Apoptosis/drug effects , DNA Fragmentation/drug effects , Fluorouracil/toxicity , Interferon-alpha/toxicity , Base Sequence , Cesium Radioisotopes , Combined Modality Therapy , DNA Damage/drug effects , DNA Damage/radiation effects , DNA, Neoplasm/chemistry , DNA, Neoplasm/metabolism , Deoxyribonucleases, Type II Site-Specific/metabolism , HT29 Cells , Humans , Interferon alpha-2 , Recombinant Proteins , Substrate SpecificityABSTRACT
Irinotecan (CPT-11) is a derivative of the chemotherapeutic agent camptothecin. CPT-11 inhibits the nuclear enzyme topoisomerase I. It has demonstrated a broad spectrum of antitumor activity in preclinical tumor model systems. Significant advances have been made toward the understanding of the pharmacokinetics and schedule dependency of this agent. CPT-11 has demonstrated significant clinical activity in the treatment of patients with gastrointestinal, pulmonary, gynecologic, and lymphoid malignancies. Further study of this agent to determine its role in combination chemotherapeutic regimens is currently underway.
