title: DNA repair and cellular resistance to alkylating agents in chronic lymphocytic leukemia.
abstract: The time course of the formation and persistence of repair-induced DNA lesions such as single-strand breaks (SSBs) were determined in isolated lymphocytes derived from 32 patients with chronic lymphocytic leukemia (CLL) using the single-cell gel electrophoresis (SCGE, "comet") assay. After pulse-exposure to N-ethyl-N-nitrosourea (EtNU), the initial amount of SSBs (t0 SCGE values) and the time periods required to reduce DNA damage by 50% (t50% SCGE values) were determined in nuclear DNA of individual cells. The t0 SCGE and t50% SCGE values varied interindividually between CLL specimens by factors of 16.6 and 8.2, respectively. Regarding cell-to-cell variation, no major subpopulations with significantly different DNA repair capacities were observed in cell specimens from a given patient. In addition, a monoclonal antibody-based immunocytological assay was used to determine the elimination kinetics for the cytotoxic alkylation product O6-ethylguanine from nuclear DNA. A strong correlation was observed between the relative times for SSB repair and the elimination of O6-ethylguanine from nuclear DNA. Because SCGE and immunocytological assay measure different steps of DNA repair, this observation suggests coordinated regulation of the respective repair pathways. With regard to chemosensitivity profiles, a "fast" repair phenotype corresponded to enhanced in vitro resistance to EtNU, 1,3-bis(2-chloroethyl)-1-nitrosourea, or chlorambucil. Accelerated SSB repair and pronounced in vitro resistance to chlorambucil, 1,3-bis(2-chloroethyl)-1-nitrosourea, and EtNU were found in lymphocytes from CLL patients nonresponsive to chemotherapy with alkylating agents. Distinct DNA repair processes thus mediate resistance to alkylating agents in CLL lymphocytes.
authors.affiliation: Department of Internal Medicine (Cancer Research) and Institute of Cell Biology (Cancer Research), West German Cancer Center Essen, University of Essen Medical School, D-45122 Essen, Germany.
authors.forename: M R
authors.initials: MR
authors.lastname: Müller
authors.forename: C
authors.initials: C
authors.lastname: Buschfort
authors.forename: J
authors.initials: J
authors.lastname: Thomale
authors.forename: C
authors.initials: C
authors.lastname: Lensing
authors.forename: M F
authors.initials: MF
authors.lastname: Rajewsky
authors.forename: S
authors.initials: S
authors.lastname: Seeber
mesh_terms: D018906:Antineoplastic Agents, Alkylating / Q000633:toxicity*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D002330:Carmustine / Q000633:toxicity*; D002467:Cell Nucleus / Q000187:drug effects; D002699:Chlorambucil / Q000633:toxicity*; D003520:Cyclophosphamide / Q000008:administration & dosage; D004249:DNA Damage; D004260:DNA Repair; D004273:DNA, Neoplasm / Q000097:blood / Q000737:chemistry; D019008:Drug Resistance, Neoplasm; D005038:Ethylnitrosourea / Q000633:toxicity*; D006147:Guanine / Q000031:analogs & derivatives / Q000032:analysis; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000097:blood* / Q000188:drug therapy; D008214:Lymphocytes / Q000187:drug effects* / Q000473:pathology; D011241:Prednisone / Q000008:administration & dosage; D014750:Vincristine / Q000008:administration & dosage
chemical_list: D018906:Antineoplastic Agents, Alkylating; D004273:DNA, Neoplasm; D002699:Chlorambucil; C007673:6-ethylguanine; D014750:Vincristine; D006147:Guanine; D003520:Cyclophosphamide; D005038:Ethylnitrosourea; D002330:Carmustine; D011241:Prednisone