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：Lymphoma is the third most common cancer diagnosed in children, and T-cell lymphoma has the worst prognosis based on clinical observations. To date, a lymphoma model with uniform penetrance has not yet been developed. In this study, we generated a p53 deficient mouse model by targeting embryonic stem cells derived from a C57BL/6J mouse strain. Homozygous p53 deficient mice exhibited a higher rate of spontaneous tumorigenesis, with a high spontaneous occurrence rate (93.3%) of malignant lymphoma.Because tumor models with high phenotypic consistency are currently needed, we generated a lymphoma model by a single intraperitoneal injection of 37.5 or 75 mg/kg N-methyl-N-nitrosourea to p53 deficient mice. Lymphoma and retinal degeneration occurred in 100% of p53 +/mice administered with higher concentrations of N-methyl-N-nitrosourea, a much greater response than those of previously reported models. The main anatomic sites of lymphoma were the thymus, spleen, bone marrow, and lymph nodes. Both induced and spontaneous lymphomas in the thymus and spleen stained positive for CD3 antigen, and flow cytometry detected positive CD4 and/or CD8 cells. Based on our observations and previous data, we hypothesize that mice with a B6 background are prone to lymphomagenesis.

It is important to establish the safety of impurities in drug substances or drug products. The assessment of genotoxicity of impurities and the determination of acceptable limits for genotoxic impurities was addressed in some recent guidances as a difficult issue. Descarboxyl levofloxacin is an impurity isolated from levofloxacin, which may impose a risk without associated benefit. However, there is insufficient toxic information about descarboxyl levofloxacin. This study investigated the genotoxicity of this impurity by in silico and in vitro methods. We used Derek, a commercial structure-activity relationship software package, as an in silico tool. The results showed that there was a structural alert (quinoline) in this impurity. Then, the in vitro genotoxicity of descarboxyl levofloxacin was investigated by a modified Ames test and by a chromosomal aberration test, using Chinese hamster lung (CHL) cells. Both assays were conducted in the presence or absence of S-9 mix. The results showed that the test impurity was not mutagenic in the Ames test (31.25-500 μg/plate). Whereas there was a statistically significant increase in the number of metaphase CHL cells with structural aberrations at the concentration of 1 mg/mL with S-9 mix, the aberrations rate was 7.5%. It did not significantly increase the number of structural aberration in CHL cells in the presence (at 250 and 500 μg/mL) or absence of S-9 mix. Based on these assays, descarboxyl levofloxacin could be controlled as a nongenotoxic impurity.

Impurities in drug substances and drug products generally do not have beneficial effects and may impose a risk without associated benefit. Levofloxacin n-oxide is an impurity isolated from levofloxacin. However there is insufficient toxic information about levofloxacin n-oxide. This study investigates the genotoxicity of this impurity by in silico and in vitro methods. We used Derek, a commercial structure-activity relationship software package as an in silico tool. The results showed that there was a structural alert (quinolone-3-carboxylic acid or naphthyridine analogue) in this impurity. Then the mouse lymphoma assay (MLA) and chromosome aberration assay in Chinese hamster lung (CHL) cells were conducted in vitro. Both assays were conducted in the presence or absence of S-9 mix. The test impurity was not mutagenic in the test of MLA. While there was a statistically significant increase in the number of metaphase CHL cells with structural aberrations at the concentration of 1 mg/mL with S-9 mix, and the aberrations rate is 6.5%. It did not significantly increase the number of structural aberration in CHL cells in the presence (at other two doses) or absence of S-9 mix. Based on these assays, levofloxacin n-oxide could be controlled as a non-genotoxic impurity despite the DEREK alert for quinolone-3-carboxylic acid or naphthyridine analogue.