Low susceptibility to N-ethyl-N-nitrosourea-induced transplacental carcinogenesis in Long-Evans Cinnamon (LEC) rats

The Long-Evans Cinnamon (LEC) rat, an animal model of Wilson’s disease, is resistant to a variety of chemical carcinogenesis except liver and colon. In the present study, N-ethyl-N-nitrosourea (ENU)-induced transplacental carcinogenesis was examined in male and female LEC, Long-Evans Agouti (LEA), a sibling line of the LEC rat, and F344 rats (n=21). ENU was administered to pregnant rats as a single s.c. injection at a dose of 60 mg/kg body weight on the 17th day after conception. Cerebral/spinal gliomas and trigeminal/spinal nerve schwannomas developed in both LEA and F344 rats at 30 weeks of age, but no nervous system tumors developed in LEC rats, the difference being statistically significant. Lung adenomas also developed in LEA and F344 rats, but not in LEC rats. Semiquantitative RT-PCR demonstrated that metallothionein (MT)1a, MT2 and O6-methylguanine-DNA methyltransferase (MGMT) mRNA levels in the liver of LEC rats were higher than those in F344 and LEA rats. In addition, Western blot analysis showed that MT (MT1 plus MT2) in the liver of LEC rats was also higher than that in other strains. Present results suggest that high levels of MT and/or MGMT contribute to the resistance to nitrosamine-induced carcinogenesis in LEC rats

A CASE OF ACUTE LIVER FAILURE CAUSED BY THE INGESTION OF GALERINA FASCICULATA

A 76-year-old man presented to another hospital with a two-day history of severe diarrhea andvomiting. A laboratory analysis revealed liver dysfunction. He was admitted to that hospital,but the laboratory data showed the exacerbation of patient’s liver dysfunction and renal dysfunction.He was therefore transferred to our hospital for multidisciplinary treatment. According topatient’s laboratory data and medical history, he was diagnosed with acute liver failure due tomushroom poisoning. This mushroom was identified as Galerina fasciculata. An investigationat the prefecture’s agricultural center revealed that the mushroom contained amatoxin

Discovery of Potent and Centrally Active 6‑Substituted 5‑Fluoro-1,3-dihydro-oxazine β‑Secretase (BACE1) Inhibitors via Active Conformation Stabilization

β-Secretase (BACE1) has an essential role in the production of amyloid β peptides that accumulate in patients with Alzheimer’s disease (AD). Thus, inhibition of BACE1 is considered to be a disease-modifying approach for the treatment of AD. Our hit-to-lead efforts led to a cellular potent 1,3-dihydro-oxazine <b>6</b>, which however inhibited hERG and showed high P-gp efflux. The close analogue of 5-fluoro-oxazine <b>8</b> reduced P-gp efflux; further introduction of electron withdrawing groups at the 6-position improved potency and also mitigated P-gp efflux and hERG inhibition. Changing to a pyrazine followed by optimization of substituents on both the oxazine and the pyrazine culminated in <b>24</b> with robust Aβ reduction in vivo at low doses as well as reduced CYP2D6 inhibition. On the basis of the X-ray analysis and the QM calculation of given dihydro-oxazines, we reasoned that the substituents at the 6-position as well as the 5-fluorine on the oxazine would stabilize a bioactive conformation to increase potency

Discovery of Potent and Centrally Active 6‑Substituted 5‑Fluoro-1,3-dihydro-oxazine β‑Secretase (BACE1) Inhibitors via Active Conformation Stabilization

β-Secretase (BACE1) has an essential role in the production of amyloid β peptides that accumulate in patients with Alzheimer’s disease (AD). Thus, inhibition of BACE1 is considered to be a disease-modifying approach for the treatment of AD. Our hit-to-lead efforts led to a cellular potent 1,3-dihydro-oxazine <b>6</b>, which however inhibited hERG and showed high P-gp efflux. The close analogue of 5-fluoro-oxazine <b>8</b> reduced P-gp efflux; further introduction of electron withdrawing groups at the 6-position improved potency and also mitigated P-gp efflux and hERG inhibition. Changing to a pyrazine followed by optimization of substituents on both the oxazine and the pyrazine culminated in <b>24</b> with robust Aβ reduction in vivo at low doses as well as reduced CYP2D6 inhibition. On the basis of the X-ray analysis and the QM calculation of given dihydro-oxazines, we reasoned that the substituents at the 6-position as well as the 5-fluorine on the oxazine would stabilize a bioactive conformation to increase potency

Rational Design of Novel 1,3-Oxazine Based β‑Secretase (BACE1) Inhibitors: Incorporation of a Double Bond To Reduce P‑gp Efflux Leading to Robust Aβ Reduction in the Brain

Accumulation of Aβ peptides is a hallmark of Alzheimer’s disease (AD) and is considered a causal factor in the pathogenesis of AD. β-Secretase (BACE1) is a key enzyme responsible for producing Aβ peptides, and thus agents that inhibit BACE1 should be beneficial for disease-modifying treatment of AD. Here we describe the discovery and optimization of novel oxazine-based BACE1 inhibitors by lowering amidine basicity with the incorporation of a double bond to improve brain penetration. Starting from a 1,3-dihydrooxazine lead <b>6</b> identified by a hit-to-lead SAR following HTS, we adopted a p<i>K</i>_a lowering strategy to reduce the P-gp efflux and the high hERG potential leading to the discovery of <b>15</b> that produced significant Aβ reduction with long duration in pharmacodynamic models and exhibited wide safety margins in cardiovascular safety models. This compound improved the brain-to-plasma ratio relative to <b>6</b> by reducing P-gp recognition, which was demonstrated by a P-gp knockout mouse model