Identification of the first noncompetitive SARM1 inhibitors.

Sterile Alpha and Toll Interleukin Receptor Motif-containing protein 1 (SARM1) is a key therapeutic target for diseases that exhibit Wallerian-like degeneration; Wallerian degeneration is characterized by degeneration of the axon distal to the site of injury. These diseases include traumatic brain injury, peripheral neuropathy, and neurodegenerative diseases. SARM1 promotes neurodegeneration by catalyzing the hydrolysis of NAD+ to form a mixture of ADPR and cADPR. Notably, SARM1 knockdown prevents degeneration, indicating that SARM1 inhibitors will likely be efficacious in treating these diseases. Consistent with this hypothesis is the observation that NAD+ supplementation is axoprotective. To identify compounds that block the NAD+ hydrolase activity of SARM1, we developed and performed a high-throughput screen (HTS). This HTS assay exploits an NAD+ analog, etheno-NAD+ (ENAD) that fluoresces upon cleavage of the nicotinamide moiety. From this screen, we identified berberine chloride and zinc chloride as the first noncompetitive inhibitors of SARM1. Though modest in potency, the noncompetitive mode of inhibition, suggests the presence of an allosteric binding pocket on SARM1 that can be targeted for future therapeutic development. Additionally, zinc inhibition and site-directed mutagenesis reveals that cysteines 629 and 635 are critical for SARM1 catalysis, highlighting these sites for the design of inhibitors targeting SARM1.

Biomimetic deiodination of thyroid hormones and iodothyronamines - a structure-activity relationship study.

Mammalian selenoenzymes, iodothyronine deiodinases (DIOs), catalyze the tyrosyl and phenolic ring deiodination of thyroid hormones (THs) and play an important role in maintaining the TH concentration throughout the body. These enzymes also accept the decarboxylated thyroid hormone metabolites, iodothyronamines (TAMs), as substrates for deiodination. Naphthalene-based selenium and/or sulphur-containing small molecules have been shown to mediate the regioselective tyrosyl ring deiodination of thyroid hormones and their metabolites. Herein, we report on the structure-activity relationship studies of a series of peri-substituted selenium-containing naphthalene derivatives for the deiodination of thyroid hormones and iodothyronamines. Single crystal X-ray crystallographic and 77Se NMR spectroscopic studies indicated that the intramolecular SeX (X = N, O and S) interactions play an important role in the deiodinase activity of the synthetic mimics. Furthermore, the decarboxylated metabolites, TAMs, have been observed to undergo slower tyrosyl ring deiodination than THs by naphthyl-based selenium and/or sulphur-containing synthetic deiodinase mimics and this has been explained on the basis of the strength of SeI halogen bonding formed by THs and TAMs.

Selenium-Mediated Dehalogenation of Halogenated Nucleosides and its Relevance to the DNA Repair Pathway.

Halogenated nucleosides can be incorporated into the newly synthesized DNA of replicating cells and therefore are commonly used in the detection of proliferating cells in living tissues. Dehalogenation of these modified nucleosides is one of the key pathways involved in DNA repair mediated by the uracil-DNA glycosylase. Herein, we report the first example of a selenium-mediated dehalogenation of halogenated nucleosides. We also show that the mechanism for the debromination is remarkably different from that of deiodination and that the presence of a ribose or deoxyribose moiety in the nucleosides facilitates the deiodination. The results described herein should help in understanding the metabolism of halogenated nucleosides in DNA and RNA.