INHIBITION OF AMYLOID OLIGOMER FORMATION BY ENDOGENOUS METABOLITE OF ALZ-801/TRAMIPROSATE IN THE HUMAN BRAIN: DISCOVERY AND CHARACTERIZATION OF 3-SPA IN NORMAL SUBJECTS AND ALZHEIMER’S DISEASE PATIENTS

ALZ-801 is an oral, small molecule inhibitor of beta amyloid (Aβ) oligomer formation with improved pharmacokinetic and gastrointestinal tolerability properties in development for Alzheimer's disease (AD). We discovered that the metabolite of tramiprosate and its prodrug ALZ-801, 3-sulfopropanoic acid (3-SPA), is an endogenous molecule in brain of normal subjects and patients with AD (https://doi.org/10.1007/s40263-018-0554-0). Lumbar CSF samples were analyzed from drug-naïve patients with cognitive deficits, AD patients treated with 150 mg BID of tramiprosate in Phase 3 trial, and cognitively normal drug-naïve subjects. We used LC-MS/MS for structural molecular identity confirmation of endogenous 3-SPA and IMS-MS with molecular dynamics to characterize interactions of 3-SPA with Aβ42 monomers. Absorption and PK characteristics of 3-SPA were evaluated in rat studies. We confirmed the presence of 3-SPA in the CSF of drug-naïve patients with cognitive deficits (mean 11.8 ± 4.3 NM, n=64) and cognitively normal, drug-naïve adults (mean 15.0 ± 8.2 nM). The concentration of 3-SPA in AD patients treated with tramiprosate was 135 ± 51 nM. In AD patients receiving tramiprosate, 3-SPA levels were ∼13-fold greater than naïve patients. Investigations into 3-SPA activity in vitro revealed an inhibitory effect on aggregation of Aβ42 into soluble oligomers. In rat studies, 3-SPA was well absorbed and readily crossed the blood-brain barrier. These Results confirm that 3-SPA, the primary metabolite of ALZ-801 and tramiprosate, is an endogenous anti-Aβ oligomer agent in CSF of patients with AD and other neurodegenerative disorders. Brain 3-SPA levels are markedly increased after patients receive oral ALZ-801/tramiprosate. High brain levels of 3-SPA after oral ALZ-801 likely Results from brain penetration from plasma. In addition, 3-SPA displays potent anti-Aβ oligomer activity, inhibiting aggregation of Aβ42 into soluble oligomers. These findings suggest that 3-SPA is a protective endogenous agent that inhibits formation of soluble toxic Aβ oligomers in human brain, thereby preventing the initial pathogenic step in Alzheimer's disease. Clinical improvements observed in tramiprosate Phase 3 studies may be due in part to increased brain levels of 3-SPA in AD patients. The potential protective role of 3-SPA in AD pathogenesis warrants further investigation.