Trophoblast cell surface antigen 2 (TROP2) is highly expressed on various epithelial tumors and correlates with poor prognosis. We developed the novel TROP2-directed antibody-drug conjugate (ADC), datopotamab deruxtecan (Dato-DXd, DS-1062a), with a potent DNA topoisomerase I inhibitor (DXd), and evaluated its antitumor activity and safety profiles in preclinical models.The pharmacologic activity and mechanism of action of Dato-DXd were investigated in several human cancer cell lines and xenograft mouse models including patient-derived xenograft (PDX) models. Safety profiles were also assessed in rats and cynomolgus monkeys.Dato-DXd bound specifically to TROP2 and was internalized into tumor cells followed by intracellular trafficking to lysosome and DXd release, which induced DNA damage and apoptosis in TROP2expressing tumor cells in vitro. Dato-DXd exhibited in vivo antitumor activity with DNA damage induced by the accumulated DXd in TROP2-expressing xenograft tumors, but neither isotype control IgG-ADC nor anti-TROP2 antibody had this effect. Dato-DXd also showed potent antitumor activity with tumor regression in several TROP2-expressing xenograft tumors including NSCLC PDX models. Safety profiles of Dato-DXd in rats and cynomolgus monkeys were acceptable.Dato-DXd demonstrated potent antitumor activity against TROP2-expressing tumors by efficient payload delivery into tumors and acceptable safety profiles in preclinical models. These results suggest Dato-DXd could be a valuable treatment option for patients with TROP2-expressing tumors in the clinical setting. delivery into tumors Binding to TROP2, internalization into cancer cells and payload release Dato-DXd (Anti-TROP2 ADC) TROP2 Cancer cell Nucleus DNA topoisomerase I inhibition leading to DNA damage and apoptosis Tumor regression Cancer cell

In order to evaluate a short-term carcinogenicity testing system using CB6F1 -Tg rasH2 (rasH2-Tg) mice carrying a human prototype c-Ha-ras gene, 26-week studies were conducted in 12 different facilities as a part of an International Life Science Institute Health and Environmental Science Institute (ILSI HESI) international collaborative project. In each study N-methyl-N-nitrosourea (MNU) was administered to a separate group of rasH2-Tg mice by single intraperitoneal injection (75 mg/kg) as a positive control. We herein have summarized the mortality, body weight change, and neoplastic and nonneoplastic lesions detected in these positive control groups as representative historical positive control data. Also, we performed an interlaboratory comparison of the response of rasH2-Tg mice to MNU based on the data of 11 positive control groups from these studies. Although the body weight of rasH2-Tg mice showed lower values than that of non-Tgmice during the experimental period, body weight gain in the rasH2-Tg mice was similar to that in non-Tg mice. The mortality of rasH2-Tg mice during the study period was very low, the same as for the non-Tg mice. Incidences of spontaneous alveolar/bronchiolar adenomas and splenic hemangiomas/hemangiosarcomas were also low in the rasH2-Tg mice. Nonneoplastic lesions detected in the rasH2-Tg mice were similar to those in non-Tg mice, excluding the incidence of myopathy. There were interlaboratory differences in mortality and incidence of some lesions in the MNU-treated groups. However, the causes of death were common among the 11 laboratories and almost all the MNU-treated rasH2-Tg mice developed forestomach squamous cell papillomas/carcinomas or malignant lymphomas. This suggests that there is no appreciable difference in the response of the rasH2-Tg mouse to MNU used as a positive control. Therefore, it is concluded that MNU would be an adequate positive control compound in this testing system.

Gap junctional intercellular communication (GJIC), by which glutathione (GSH) and inorganic ions are transmitted to neighboring cells, is recognized as being largely involved in toxic processes of chemicals. We examined acetaminophen (APAP)-induced hepatotoxicity clinicopathologically using male wild-type mice and mice lacking the gene for connexin32, a major gap junction protein in the liver [knockout (Cx32KO) mice]. When APAP was intraperitoneally administered at doses of 100, 200, or 300mg/kg, hepatic centrilobular necrosis with elevated plasma aminotransferase activities was observed in wild-type mice receiving 300mg/kg, and in Cx32KO mice given 100mg/kg or more. At 200mg/kg or more, hepatic GSH and GSSG contents decreased significantly and the effect was more severe in wild-type mice than in Cx32KO mice. On the other hand, markedly decreased GSH staining was observed in the hepatic centrilobular zones of Cx32KO mice compared to that of wild-type mice. These results demonstrate that Cx32KO mice are more susceptible to APAP hepatotoxicity than wild-type mice, and indicate that the distribution of GSH of the centrilobular zones in the hepatic lobules, rather than GSH and GSSG contents in the liver, is important in APAP hepatotoxicity. In conclusion, Cx32 protects against APAP-induced hepatic centrilobular necrosis in mice, which may be through the GSH transmission to neighboring hepatocytes by GJIC.

The attenuated PhNR and histopathology of the retina indicated that RGCs were markedly damaged, both functionally and morphologically in monkeys with ethambutol-induced optic neuropathy. These results implied that RGCs are predominantly affected in the retina of patients with ethambutol-induced optic neuropathy.

In order to evaluate a short-term carcinogenicity testing system using CB6F1 -Tg rasH2 (rasH2-Tg) mice carrying a human prototype c-Ha-ras gene, 26-week studies were conducted in 12 different facilities as a part of an International Life Science Institute Health and Environmental Science Institute (ILSI HESI) international collaborative project. In each study N-methyl-N-nitrosourea (MNU) was administered to a separate group of rasH2-Tg mice by single intraperitoneal injection (75 mg/kg) as a positive control. We herein have summarized the mortality, body weight change, and neoplastic and nonneoplastic lesions detected in these positive control groups as representative historical positive control data. Also, we performed an interlaboratory comparison of the response of rasH2-Tg mice to MNU based on the data of 11 positive control groups from these studies. Although the body weight of rasH2-Tg mice showed lower values than that of non-Tgmice during the experimental period, body weight gain in the rasH2-Tg mice was similar to that in non-Tg mice. The mortality of rasH2-Tg mice during the study period was very low, the same as for the non-Tg mice. Incidences of spontaneous alveolar/bronchiolar adenomas and splenic hemangiomas/hemangiosarcomas were also low in the rasH2-Tg mice. Nonneoplastic lesions detected in the rasH2-Tg mice were similar to those in non-Tg mice, excluding the incidence of myopathy. There were interlaboratory differences in mortality and incidence of some lesions in the MNU-treated groups. However, the causes of death were common among the 11 laboratories and almost all the MNU-treated rasH2-Tg mice developed forestomach squamous cell papillomas/carcinomas or malignant lymphomas. This suggests that there is no appreciable difference in the response of the rasH2-Tg mouse to MNU used as a positive control. Therefore, it is concluded that MNU would be an adequate positive control compound in this testing system.

PURPOSE. The purpose of this study was to investigate both functional and morphologic alteration of the retina acutely induced by N-methyl-N-nitrosourea (MNU) in monkeys.METHODS. The MNU was administered intravenously at a single dose of 40 mg/kg to six cynomolgus monkeys, and standard full-field electroretinograms (ERGs) were recorded 1, 3, and 7 days after dosing. In addition, the rod and cone a-waves in response to high-intensity flashes were analyzed by the a-wave fitting model (a-wave analysis). The photopic negative response (PhNR) was also recorded at the same time points. Furthermore, the retinas of two animals each were examined histopathologically 1, 3, or 7 days after dosing. RESULTS.The MNU attenuated all the standard full-field ERGs including the rod-driven and cone-driven responses; in the combined rod-cone response, the b-wave was more affected than the a-wave. In the a-wave analysis, the sensitivity parameters (S) of the rod and cone awaves had decreased on the day after dosing and remained unchanged thereafter. The maximum response parameter (R max ) of the rod a-wave gradually decreased. On the other hand, the R max in the cone a-wave transiently increased on the day after dosing and decreased thereafter; the PhNR amplitude showed a similar time course change. Histopathologically, the retinal lesion on the day after dosing mainly consisted of pyknosis and karyorrhexis in the photoreceptor nucleus. Depletion of some photoreceptor nuclei, and shortening and disorientation of the photoreceptor segments became prominent at 3 and 7 days after dosing. Localization of degenerated photoreceptors was consistent with that of rhodopsin-positive photoreceptors, resulting in a well-preserved central fovea. CONCLUSIONS.Our results indicated that MNU acutely induced rod-dominant photoreceptor degeneration in monkey retinas, but the photoreceptor function was impaired in both the rods and cones. Functional involvement of the postreceptoral components was also indicated.

B7-H3 is overexpressed in various solid tumors and has been considered as an attractive target for cancer therapy. Here, we report the development of DS-7300a, a novel B7-H3–targeting antibody–drug conjugate with a potent DNA topoisomerase I inhibitor, and its in vitro profile, pharmacokinetic profiles, safety profiles, and in vivo antitumor activities in nonclinical species. The target specificity and species cross-reactivity of DS-7300a were assessed. Its pharmacologic activities were evaluated in several human cancer cell lines in vitro and xenograft mouse models, including patient-derived xenograft (PDX) mouse models in vivo. Pharmacokinetics was investigated in cynomolgus monkeys. Safety profiles in rats and cynomolgus monkeys were also assessed. DS-7300a specifically bound to B7-H3 and inhibited the growth of B7-H3–expressing cancer cells, but not that of B7-H3–negative cancer cells, in vitro. Additionally, treatment with DS-7300a and DXd induced phosphorylated checkpoint kinase 1, a DNA damage marker, and cleaved PARP, an apoptosis marker, in cancer cells. Moreover, DS-7300a demonstrated potent in vivo antitumor activities in high–B7-H3 tumor xenograft models, including various tumor types of high–B7-H3 PDX models. Furthermore, DS-7300a was stable in circulation with acceptable pharmacokinetic profiles in monkeys, and well tolerated in rats and monkeys. DS-7300a exerted potent antitumor activities against B7-H3–expressing tumors in in vitro and in vivo models, including PDX mouse models, and showed acceptable pharmacokinetic and safety profiles in nonclinical species. Therefore, DS-7300a may be effective in treating patients with B7-H3–expressing solid tumors in a clinical setting.

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