Discovery of an Endogenous Metabolite of Tramiprosate and its Prodrug ALZ-801 that Inhibits Beta Amyloid Oligomer Formation In Human Brain

John A. Hey, Petr Kocis, Jakub Hort, Susan Abushakra, Aidan Power, Martin Vyhnálek, Jeremy Y. Yu, Martin Tolar
Abstract

Background
ALZ-801 is an oral, small molecule inhibitor of beta amyloid (Aβ) oligomer formation in clinical development for Alzheimer’s disease (AD). ALZ-801 is a prodrug of tramiprosate with improved pharmacokinetic properties and gastrointestinal tolerability. During clinical studies, we discovered that the primary metabolite of tramiprosate and its prodrug ALZ-801, 3-sulfopropanoic acid (3-SPA), is an endogenous molecule in the human brain and is found in cerebrospinal fluid (CSF) of patients with AD and other neurodegenerative diseases (Hey et al, 2018; https://doi.org/10.1007/s40263-018-0554-0).

Objectives
The objectives of the study were: 1) identify and confirm the presence of 3-SPA in human CSF samples from elderly, drug-naïve, patients with memory deficits, 2) quantify the levels of 3-SPA in the CSF of patients with AD from the tramiprosate Phase 3 trial, 3) evaluate the in vitro anti-Aβ42 oligomer activity of 3-SPA, and 4) characterize the pharmacokinetic (PK) and brain penetration properties of 3-SPA.

Methods
Lumbar CSF samples were analyzed from drug naïve patients with cognitive deficits (MMSE range: 15-30), patients with AD treated with 150 mg BID of tramiprosate in the Phase 3 trial at Week 78,  and normal drug naïve subjects. We used LC-MS/MS for structural molecular identity confirmation of endogenous 3-SPA with a 3-SPA reference standard, and ion mobility–mass spectrometry with molecular dynamics to characterize interactions of 3-SPA with Aβ42 monomers, and the resultant conformational alterations. Rat studies using 30 mg/kg oral and 10 mg/kg intravenous doses were conducted to characterize the PK properties and brain penetration of 3-SPA. 

Results
We confirmed the presence of 3-SPA in the CSF of drug naïve patients with cognitive deficits (mean concentration 11.8 ± 4.3 nM, n= 64, mean age 68.6 yr) and normal, drug naïve adults (mean concentration 15.0 ± 8.2 nM, mean age 49.9 yr). The mean concentration of 3-SPA in AD patients treated with tramiprosate was 135 ± 51 nM. In vitro investigations in to the activity of 3-SPA revealed a multi-ligand interaction with monomeric Aβ42 that inhibits the aggregation of Aβ42 into small soluble oligomers. Comparisons of the molecular interactions of tramiprosate and 3-SPA with Ab42 are also presented. Furthermore, in rat preclinical studies, 3-SPA displayed 100% oral bioavailability and 25% brain penetration, indicating that the metabolite is well absorbed and crosses the blood-brain barrier.

Conclusions
We have confirmed the endogenous presence of 3-SPA, the major metabolite of tramiprosate, in CSF of drug-naïve elderly patients with memory deficits due to a variety of neurodegenerative disorders. In patients with AD receiving tramiprosate, the levels of 3-SPA were up to 12.6-fold greater than in drug-naïve patients. In addition, 3-SPA displays potent anti-Aβ oligomer activity, inhibiting aggregation of Aβ42 into small soluble oligomers with efficacy comparable to tramiprosate. 3-SPA displays excellent oral availability and brain penetration in rats, suggesting that the higher CSF concentrations of 3-SPA in human brain after oral administration of ALZ-801 or tramiprosate and subsequent conversion to 3-SPA, result from the penetration of 3-SPA metabolite into the CNS. These data suggest that 3-SPA is an endogenous agent with potential activity stabilizing the conformational flexibility of Aβ monomers that, in turn, inhibits Aβ misfolding and formation of soluble toxic Aβ oligomers in humans, thereby preventing the initial pathogenic step in the progression of Alzheimer’s disease. Clinical improvements observed in AD patients in tramiprosate Phase 3 studies (Abushakra et al, 2018) may in part be explained by the therapeutic effects of excess levels of the metabolite in the brains of these patients. The potential protective role of 3-SPA in AD pathogenesis, disease progression, as well as its therapeutic role in AD and other neurodegenerative disorders, warrants further investigation.

 

References

  1. Hey, JA, Kocis, P, Hort, J et al. CNS Drugs 2018. https://doi.org/10.1007/s40263-018-0554-0

Abushakra S, Porsteinsson A, Scheltens P, et al. J Prev Alzheimers Dis 2017; 4:149–56

2019-02-02T13:53:35+00:00October 24th, 2018|