Dendrimer-Conjugated Glutamine Antagonist, D-TTM020, Ameliorates Brain Immune Dysregulation and Improves Neurobehavioral Deficits in the Mecp2-Deficient Mouse Model

Rett Syndrome (RTT) is a neurodevelopmental disorder characterized by mutations in the MeCP2 gene, predominantly affecting females. Recent work with MeCP2-deficient mouse models showed a significant role in glutamatergic transmission, specifically microglia-produced glutamate and glutaminase upregulation, in RTT pathology. The glutamine antagonist 6-diazo-5-oxo-L-norleucine (DON) is a potent glutaminase inhibitor; however, its use is limited due to systemic toxicities arising from its non-specific inhibition of glutamine-utilizing reactions. In this work, we determined whether dendrimer conjugation of a DON analog, TTM020 (or D-TTM020), results in targeted microglial glutaminase inhibition and behavioral changes in <i>Mecp2</i> KO and heterozygous mice upon systemic administration. D-TTM020 at 1 mg/kg (drug basis) selectively and significantly inhibits glutaminase enzyme activity in the microglia of <i>Mecp2</i> KO mice. Biweekly systemic treatment with 1 mg/kg of D-TTM020 improved the neurobehavioral phenotype in symptomatic <i>Mecp2</i> KO and het mice. D-TTM020 also restored long-term retrieval of conditioned fear memory and improved cue responses during fear extinction after 8 weeks of treatment in symptomatic <i>Mecp2</i> het mice. Our data indicate that selectively targeting glutamine metabolism in dysregulated glia using dendrimers represents a promising strategy that may offer a therapeutic approach for addressing glutamate dysregulation in RTT.