Spontaneous Axonal Dystrophy in the Brain and Spinal Cord in Naïve Beagle Dogs.

Axonal dystrophy (AD) is a common age-related neurohistological finding in vertebrates that can be congenital or induced by xenobiotics, vitamin E deficiency, or trauma/compression. To understand the incidence and location of AD as a background finding in Beagle dogs used in routine toxicity studies, we examined central nervous system (CNS) and selected peripheral nervous system (PNS) tissues in twenty 18- to 24-month-old and ten 4- to 5-year-old control males and females. Both sexes were equally affected. The cuneate, gracile, and cochlear nuclei and the cerebellar white matter (rostral vermis) were the most common locations for AD. Incidence of AD increased with age in the cuneate nucleus, cerebellar white matter (rostral vermis), trigeminal nuclei/tracts, and lumbar spinal cord. Axonal dystrophy in the CNS was not accompanied by neuronal degeneration/necrosis, nerve fiber degeneration, and/or glial reaction. Axonal dystrophy was not observed in the PNS (sciatic nerve, vagus nerve branches, or gastrointestinal mural autonomic plexuses).

Rational approach to highly potent and selective apoptosis signal-regulating kinase 1 (ASK1) inhibitors.

Many diseases are believed to be driven by pathological levels of reactive oxygen species (ROS) and oxidative stress has long been recognized as a driver for inflammatory disorders. Apoptosis signal-regulating kinase 1 (ASK1) has been reported to be activated by intracellular ROS and its inhibition leads to a down regulation of p38-and JNK-dependent signaling. Consequently, ASK1 inhibitors may have the potential to treat clinically important inflammatory pathologies including renal, pulmonary and liver diseases. Analysis of the ASK1 ATP-binding site suggested that Gln756, an amino acid that rarely occurs at the GK+2 position, offered opportunities for achieving kinase selectivity for ASK1 which was applied to the design of a parallel medicinal chemistry library that afforded inhibitors of ASK1 with nanomolar potency and excellent kinome selectivity. A focused optimization strategy utilizing structure-based design resulted in the identification of ASK1 inhibitors with low nanomolar potency in a cellular assay, high selectivity when tested against kinase and broad pharmacology screening panels, and attractive physicochemical properties. The compounds we describe are attractive tool compounds to inform the therapeutic potential of ASK1 inhibition.

Drug design structural alert: formation of trifluoroacetaldehyde through N-dealkylation is linked to testicular lesions in rat.

In the process of drug design, it is important to consider potential structural alerts that may lead to toxicosis. This work illustrates how using trifluoroethane as a part of a novel chemical entity led to cytochrome P450 - mediated N-dealkylation and the formation of trifluoroacetaldehyde, a known testicular toxicant, in exploratory safety studies in rats. Testicular toxicosis was noted microscopically in a dose-dependent manner as measured by testicular spermatocytic degeneration and necrosis and excessive intratubular cellular debris in the epididymis. This apparent toxic effect correlated well with the dose-dependent formation of trifluoroacetaldehyde, identified from in vitro rat liver microsome metabolism studies. A similar safety study performed with an N-tetrazole substitution in place of the N-trifluoroethane showed no evidence of testicular injury, implicating further the role of trifluoroacetaldehyde in the testicular lesion observed. These results highlight the relevance of early metabolic and safety testing in assessing potential structural alerts in drug design.

Reduction of a 7,12-dimethylbenz[a]anthracene DNA adduct in rat mammary tissue in vivo when pretreated with tamoxifen.

Tamoxifen (TAM), an antiestrogenic compound, has been approved for the treatment of breast cancer in high risk women. TAM has been shown to be an effective agent for prevention of breast cancer in women of varying degrees of risk and has been proposed to be used prophylactically in women whose genetic background suggests a high risk for breast cancer. However, it is not known whether TAM given prophylactically will alter the response of women to carcinogens from common environmental exposures such as tobacco smoke. Therefore, we studied the effects of TAM pretreatment on mammary DNA adducts of the model carcinogen, 7,12-dimethylbenz[a]anthracene (DMBA), in the female rats to assess whether TAM would alter the adduct pattern of DMBA. TAM (0.3 mg/day) was given for 7 days prior to a single 20 mg DMBA gavage treatment that is considered a carcinogenic dose in the rat. At 7 days post-DMBA, there was a reduction in the major DMBA-DNA adduct and a significant reduction in the minor DMBA-DNA adduct in mammary glands (P=0.002) of TAM pretreated rats compared to control rats. These data indicate that TAM may alter either metabolic steps in the formation of DNA binding species and/or enhance adduct removal. These data suggest that TAM given to women prior to the development of breast cancer may modulate the impact of environmental exposures, for example, tobacco smoke. Furthermore, research is needed to determine if modulation will be positive, or negative as in the current study.