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Microglia-targeted dendrimer-2PMPA therapy robustly inhibits GCPII and improves cognition in a mouse model of multiple sclerosis

Hollinger, KR;Sharma, A;Tallon, C;Lovell, L;

Roughly half of all individuals with multiple sclerosis (MS) experience cognitive impairment, but there are no approved treatments that target this aspect of the disease. Recent studies link reduced brain N-acetylaspartylglutamate (NAAG) levels to impaired cognition in various neurological diseases, including MS. NAAG levels are regulated by glutamate carboxypeptidase II (GCPII), which hydrolyzes the neuropeptide to N-acetyl-aspartate (NAA) and glutamate. Although several GCPII inhibitors, such as 2-(phosphonomethyl)-pentanedioic acid (2-PMPA), elevate brain NAAG levels and restore cognitive function in preclinical studies when given at high systemic doses or via direct brain injection, no GCPII inhibitors are clinically available due to poor bioavailability and limited brain penetration. Systemic hydroxyl dendrimers (~4 nm) have been successfully used to enhance brain delivery of drugs selectively to activated glia. We recently discovered that GCPII is highly upregulated in activated microglia after brain injury. To determine if dendrimer conjugation could enhance the brain delivery of GCPII inhibitors, specifically in the context of MS, we attached 2-PMPA to hydroxyl polyamidoamicne (PAMAM) dendrimers (D-2PMPA) using a highly efficient click chemistry approach. Targeted uptake of D-2PMPA into activated glia was subsequently confirmed in glial cultures where it showed robust anti-inflammatory activity, including an elevation in TGF and a reduction in TNF. Given these positive effects, D-2PMPA (20mg/kg) or vehicle dendrimer were dosed twice weekly to experimental autoimmune encephalomyelitis (EAE)-immunized mice starting at disease onset (therapeutic paradigm). D-2PMPA significantly improved cognition in EAE as assessed by Barnes maze performance, even though physical severity was not impacted. Glial target engagement was confirmed, as CD11b+ enriched cells isolated from hippocampi in D-2PMPA-treated mice exhibited almost complete loss of GCPII activity. These data demonstrate the utility of hydroxyl dendrimers to enhance brain penetration and support the development of D-2PMPA to treat cognitive impairment in MS.