Design, synthesis, and characterization of novel system x_C⁻ transport inhibitors: inhibition of microglial glutamate release and neurotoxicity

Neuroinflammation appears to involve some degree of excitotoxicity promulgated by microglia, which release glutamate via the system x_C⁻ (Sx_C⁻) cystine-glutamate antiporter. With the aim of mitigating this source of neuronal stress and toxicity, we have developed a panel of inhibitors of the Sx_C⁻ antiporter. The compounds were based on l-tyrosine, as elements of its structure align with those of glutamate, a primary physiological substrate of the Sx_C⁻ antiporter. In addition to 3,5-dibromotyrosine, ten compounds were synthesized via amidation of that parent molecule with a selection of acyl halides. These agents were tested for the ability to inhibit release of glutamate from microglia activated with lipopolysaccharide (LPS), an activity exhibited by eight of the compounds. To confirm that the compounds were inhibitors of Sx_C⁻, two of them were further tested for the ability to inhibit cystine uptake. Finally, these agents were shown to protect primary cortical neurons from the toxicity exhibited by activated microglia. These agents may hold promise in reducing the neurodegenerative effects of neuroinflammation in conditions, such as encephalitis, traumatic brain injury, stroke, or neurodegenerative diseases.