The in vivo chromosomal aberration test is especially relevant to assessing mutagenic hazard in that it allows consideration of factors of in vivo metabolism, pharmacokinetics and DNA-repair processes. An in vivo test is also useful for further investigation of a mutagenic effect detected by an in vitro test. The objective of this assay is to evaluate the test article and its metabolites for their potential to cause chromosome aberrations in vivo in rodents. The study design follows the current OECD 475 Guideline “Mammalian Bone Marrow Chromosome Aberration Test”. The assay can be performed in accordance with Good Laboratory Practices.
Nucro-Technics typically conducts this test in mouse bone marrow as part of an acute or subchronic study. This is one of the tests which can be used as part of the ICH S2(R1) Guideline on Genotoxicity Testing and Data Interpretation for Pharmaceuticals Intended for Human Use / FDA Battery.
A preliminary toxicity test may be performed to help design three analyzable concentrations. In the main experiment, usually five female and five male healthy animals are randomly assigned to each control and treatment groups. Test substances are preferably administered as a single treatment, but may also be administered as a split dose. Positive and negative control groups will be treated with Cyclophosphamide and the vehicle, respectively. The sampling interval is 1.5 normal cell cycle length (12-18 hr) following treatment. After being sampled, animals are injected with a metaphase arresting agent (e.g. colchicine) at an appropriate time and cells are harvested from the bone marrow and analyzed from chromosome aberrations. Slides are prepared for analysis and coded. Well-spread metaphase cells with 2n ± 2 chromosomes will be analyzed for chromosome aberrations. At least 150 cells from each animal are examined.
A positive response shows a concentration-related response and a statistically significant increase in the percentage of cells with aberrations at one or more concentrations over that of the solvent controls. Positive results indicate that the test article induces chromosome aberrations in vivo. A negative response presents no statistically significant increase in the percentage of cells with aberrations. Negative results indicate that, under the test conditions, the test article does not induce chromosome aberrations in vivo. In the case of a negative result it is needed to perform a confirmatory experiment. In the confirmatory assay, cells are collected 24 hr after the first sample time is recommended. A positive result will not usually need confirmation.