title: Dose-response relationship of temozolomide, determined by the Pig-a, comet, and micronucleus assay.
abstract: Temozolomide (TMZ), a monofunctional alkylating agent, was selected as a model compound to determine its quantitative genotoxic dose-response relationship in different tissues (blood, liver, and jejunum) and endpoints [Pig-a-, comet-, and micronucleus assay (MNT)] in male rats. TMZ was administered p.o. over 5 consecutive days (day 1-5), followed by a treatment-free period of 50 days (day 6-56) and a final administration prior to necropsy (day 57-59). TMZ showed a dose-dependent increase in DNA damage in all interrogated endpoints. A statistically significant increase in Pig-a mutant phenotypes was observed on day 44 starting at 7.5 mg/kg/day for mutant reticulocytes (for RETCD59-) and at 3.75 mg/kg/day for mutant red blood cells (RBCCD59-), respectively. In addition, a statistically significant increase in cytogenetic damage, as measured by micronucleated reticulocytes, was observed starting at 3.75 mg/kg/day on day 3 and 1.5 mg/kg/day on day 59. DNA strand breaks, as detected by the comet assay, showed a dose-dependent and statistically significant increase in liver, blood, and jejunum starting at doses of 3.75, 3.75, and 7.5 mg/kg/day, respectively. The dose-response relationships of the Pig-a, MNT, and comet data were analyzed for possible points of departure (PoD) using the benchmark-dose (BMD) software PROAST with different critical effect sizes (CES) (BMD0.1, BMD0.5, BMD1, and BMD1SD). Overall, PoD values show a high concordance between different tissues and endpoints, underlining the suitability of this experimental design to explore quantitative dose-response relationships in a variety of different tissues and endpoints, while minimizing animal use.
authors.affiliation: Pharmaceutical Sciences, Roche Innovation Center Basel, F. Hoffmann La Roche Ltd., Grenzacherstrasse 124, 4070, Basel, Switzerland. melanie.guerard@roche.com.
authors.forename: M
authors.initials: M
authors.lastname: Guérard
authors.affiliation: Institute of Life Science, Swansea University Medical School, Singleton Park, Swansea, SA3 5DE, UK.
authors.forename: G
authors.initials: G
authors.lastname: Johnson
authors.affiliation: Litron Laboratories, 3500 Winton Place, Rochester, NY, USA.
authors.forename: S
authors.initials: S
authors.lastname: Dertinger
authors.affiliation: Pharmaceutical Sciences, Roche Innovation Center Basel, F. Hoffmann La Roche Ltd., Grenzacherstrasse 124, 4070, Basel, Switzerland.
authors.forename: G
authors.initials: G
authors.lastname: Duran-Pacheco
authors.affiliation: Pharmaceutical Sciences, Roche Innovation Center Basel, F. Hoffmann La Roche Ltd., Grenzacherstrasse 124, 4070, Basel, Switzerland.
authors.forename: J
authors.initials: J
authors.lastname: Funk
authors.affiliation: Pharmaceutical Sciences, Roche Innovation Center Basel, F. Hoffmann La Roche Ltd., Grenzacherstrasse 124, 4070, Basel, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Zeller
mesh_terms: D000818:Animals; D020552:Comet Assay; D004249:DNA Damage; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000633:toxicity; D004305:Dose-Response Relationship, Drug; D004912:Erythrocytes / Q000187:drug effects* / Q000473:pathology; D007583:Jejunum / Q000187:drug effects / Q000473:pathology; D008099:Liver / Q000187:drug effects / Q000473:pathology; D008297:Male; D048629:Micronuclei, Chromosome-Defective / Q000139:chemically induced*; D015162:Micronucleus Tests; D009153:Mutagens / Q000633:toxicity*; D017208:Rats, Wistar; D012156:Reticulocytes / Q000187:drug effects / Q000473:pathology; D000077204:Temozolomide
chemical_list: D009153:Mutagens; D003606:Dacarbazine; D000077204:Temozolomide
keywords: Dose–response relationship; Multiendpoint; Pig-a; Temozolomide