Integration of the rat liver micronucleus assay into a 28-day treatment protocol: testing the genotoxicity of four small-molecule nitrosamines with different carcinogenic potencies and tumor target specificities.

Several potent carcinogenic nitrosamines, including N-nitrosodiethylamine (NDEA) and N-nitrosodimethylamine (NDMA), induce micronuclei in the micronucleated hepatocyte (MNHEP) assay but not in the micronucleated reticulocyte (MNRET) assay. However, the MNHEP assay is not as frequently used as the MNRET assay for evaluating in vivo genotoxicity. The present study evaluated MN formation in the liver of Big Blue transgenic rats exposed to four small-molecule nitrosamines, NDMA, N-nitrosodiisopropylamine (NDIPA), N-nitrosoethylisoporpylamine (NEIPA), and N-nitrosomethylphenylamine (NMPA), using a repeat-dose protocol typically used for in vivo mutagenicity studies.

Mutagenicity and genotoxicity evaluation of 15 nitrosamine drug substance-related impurities in human TK6 cells.

Nitrosamine drug substance-related impurities (NDSRIs) are a sub-category of N-nitrosamine drug impurities that share structural similarity to the corresponding active pharmaceutical ingredient. The mutagenicity of NDSRIs is poorly understood. We previously tested a series of NDSRIs using the Enhanced Ames Test (EAT).

Optimizing the detection of N-nitrosamine mutagenicity in the Ames test.

Accurately determining the mutagenicity of small-molecule N-nitrosamine drug impurities and nitrosamine drug substance-related impurities (NDSRIs) is critical to identifying mutagenic and cancer hazards. In the current study we have evaluated several approaches for enhancing assay sensitivity for evaluating the mutagenicity of N-nitrosamines in the bacterial reverse mutagenicity (Ames) test. Preincubation assays were conducted using five activation conditions: no exogenous metabolic activation and metabolic activation mixes employing both 10% and 30% liver S9 from hamsters and rats pretreated with inducers of enzymatic activity.

Genotoxicity assessment of eight nitrosamines using 2D and 3D HepaRG cell models.

N-nitrosamine impurities have been increasingly detected in human drugs. This is a safety concern as many nitrosamines are mutagenic in bacteria and carcinogenic in rodent models. Typically, the mutagenic and carcinogenic activity of nitrosamines requires metabolic activation by cytochromes P450 enzymes (CYPs), which in many in vitro models are supplied exogenously using rodent liver homogenates.

Revisiting the mutagenicity and genotoxicity of N-nitroso propranolol in bacterial and human in vitro assays.

Propranolol is a widely used β-blocker that can generate a nitrosated derivative, N-nitroso propranolol (NNP). NNP has been reported to be negative in the bacterial reverse mutation test (the Ames test) but genotoxic in other in vitro assays. In the current study, we systematically examined the in vitro mutagenicity and genotoxicity of NNP using several modifications of the Ames test known to affect the mutagenicity of nitrosamines, as well as a battery of genotoxicity tests using human cells.