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Although microsampling of blood is recommended to promote the 3Rs in toxicokinetic (TK) evaluation, there are few reports applying microsampling in actual toxicity evaluation. Here, we assessed the effects of microsampling on toxicological evaluation of methapyrilene hydrochloride, a hepatotoxic substance. Female SD rats received methapyrilene hydrochloride orally at dose levels of 0 (vehicle), 10, and 30 mg/kg BW, once daily for 4 weeks. Each dose level included a microsampling group and a non-microsampling group (n = 5). In the microsampling groups, blood sampling (50 µL/time point) was performed at 6 time points on day 1 of administration and 7 time points on day 27-28; all the animals underwent necropsy on day 29. Toxicity studies and TK analysis were performed, and through these studies in 2 organizations, cross-organization validation of the effect on toxicity evaluation was conducted. In one organization, microsampling obscured changes in some parameters in hematology due to the administration of methapyrilene hydrochloride. In the other organization, although the relationship between the developing pattern of histopathological findings in the liver and the blood sampling was suspected, it was associated with poor reproducibility; this was considered as a change within a variation range of biological reactions. Each of these phenomena was observed in only one organization without consistency. In both organizations, no effect of blood microsampling was observed in other endpoints. In conclusion, microsampling is considered to be a technique applicable to safety studies of drugs showing hepatotoxicity, as it did not show a marked influence on the toxicological evaluation of methapyrilene hydrochloride.

Post-transplant lymphoproliferative disorder (PTLD) and other iatrogenic immunodeficiency-associated lymphoproliferative disorders (OIIA-LPD) are iatrogenic lymphoproliferative disorders (LPD) that develop in association with immunosuppressive treatment in the setting of organ transplantation and autoimmune disease, respectively. Each has a spectrum of pathologies ranging from lymphoid hyperplasia to lymphoma. To clarify the characteristics of the diffuse large B-cell lymphoma (DLBCL) subtype in a cohort of 25 patients with PTLD or OIIA-LPD from our institute, we selected 13 with a histological subtype of DLBCL, including 2 cases of PTLD and 11 of OIIA-LPD. The median patient age at diagnosis was 70 years, with a female predominance. Both PTLD cases developed after kidney transplant. Of the patients with OIIA-LPD, 10 had rheumatoid arthritis, 1 had mixed connective tissue disease, and 8 were treated using methotrexate. Both of the PTLD patients and 6 of the OIIA-LPD patients had extranodal manifestations. All patients except for one were classified as having the non-germinal center B-cell (non-GCB) subtype according to the Hans algorithm. Tissue samples from 8 patients were positive for CD30 and 8 were positive for Epstein-Barr virus (EBV)-encoded small RNA. Seven patients had MYC-positive tissue samples, but none had MYC translocation. Our study suggests that extranodal manifestations and the non-GCB subtype are common, that EBV is associated with the DLBCL subtype of PTLD and OIIA-LPD, and that anti-CD30 therapy is applicable. In addition, our patients with the DLBCL subtype of PTLD and OIIA-LPD exhibited MYC overexpression without MYC translocation, suggesting an alternative mechanism of MYC upregulation.