Clinical Pharmacokinetics of Oral ALZ-801/Valiltramiprosate in a 2-Year Phase 2 Trial of APOE4 Carriers with Early Alzheimer’s Disease

Alzheimer’s disease (AD) remains an enormous medical and socioeconomic challenge with limited treatment options. The traditional symptomatic management paradigms, i.e., acetylcholinesterase inhibitors (AChEI; e.g., donepezil) and the N-methyl-d-aspartate (NMDA) receptor antagonist memantine, are known to have modest clinical effects with short efficacy duration, and do not slow the disease progression [1]. Recently, three anti-amyloid antibodies (aducanumab, lecanemab, and donanemab) have been approved by the Food and Drug Administration (FDA) for the treatment of AD [2‐4]. While the antibody agents have demonstrated potential for disease modification, they are associated with a high risk of developing amyloid-related imaging abnormalities (ARIA), including vasogenic edema (ARIA-E) and hemorrhagic complications (ARIA-H), which are especially prominent in apolipoprotein ε4 (APOE4) carrier patients with AD [5, 6]. Furthermore, antibody treatments require parenteral routes of administration, which increase the burden to patients. Therefore, better treatments are needed for patients with AD that could significantly improve cognitive or functional endpoints or slow disease progression, while maintaining a favorable safety profile and a convenient dosing regimen.

ALZ-801/valiltramiprosate is an orally bioavailable, small-molecule inhibitor of β-amyloid (Aβ) oligomer formation currently in clinical development as a potential disease-modifying treatment for AD. ALZ-801 was evaluated in a APOLLOE4 phase 3 placebo-controlled study in 325 APOE4/4 subjects with early AD (NCT04770220), with the main results being prepared for publication. ALZ-801 is also being evaluated in a long-term extension (LTE) of this recently completed phase 3 trial (NCT06304883), and in the LTE of a 2-year phase 2 biomarker study in APOE4 carrier patients with AD (NCT04693520). We recently reported that 2 years of oral treatment with ALZ-801 tablets resulted in a significant, 31% decrease of plasma p-tau₁₈₁, a reduction of hippocampal atrophy (measured by volumetric MRI), as well as stabilization of cognitive outcomes in 84 APOE4 carrier patients with early AD [7]. There was a significant correlation between reduced hippocampal atrophy and cognitive stability over 2 years. Additionally, using a quantitative systems pharmacology approach, we demonstrated that ALZ-801 treatment arrested the progressive decline in CSF Aβ₄₂ levels and plasma Aβ₄₂/Aβ₄₀ ratio, and stabilized the cognitive outcome Rey Auditory Verbal Learning Test (RAVLT) over 2 years of treatment [8]. These results support target engagement and suggest a disease-modifying effect of ALZ-801 treatment in patients with early AD. Together with the favorable safety profile without any events of ARIA, these data continue to support the development of ALZ-801 as a disease-modifying anti-amyloid therapy for AD [9].

ALZ-801, (S)−3-(2-amino-3-methylbutanamido) propane-1-sulfonic acid, is a valine-conjugated prodrug of tramiprosate. Following oral administration, ALZ-801 is efficiently absorbed and then rapidly converted to tramiprosate and the amino acid valine. The metabolism of tramiprosate in humans generates a single metabolite, 3-sulfopropanoic acid (3-SPA) [10]. Both tramiprosate and 3-SPA are pharmacologically active in inhibition of Aβ oligomer formation, which mediate ALZ-801’s mechanism of action (MOA), and both tramiprosate and 3-SPA readily penetrate the blood–brain barrier [10‐12].

The anti-Aβ aggregation effect of tramiprosate is well established [13‐22]. We have provided further elucidation on its molecular MOA as an inhibitor of Aβ oligomer formation, which is via a multiligand, enveloping, conformational modification mechanism [11]. In addition, 3-SPA exerts similar inhibition on Aβ oligomers [12]. Both tramiprosate and 3-SPA bind and stabilize soluble Aβ monomers in a semicyclic conformational state that prevents aggregation, resulting in reduced formation of toxic oligomers and inhibition of the subsequent neurotoxic amyloid cascade that is implicated in AD pathogenesis [11, 12, 21, 23, 24]. In vivo, repeated oral tramiprosate dosing produced a significant (∼ 30%) reduction in cerebral insoluble amyloid plaques, as well as both soluble and insoluble Aβ₄₀ and Aβ₄₂ in a transgenic AD mouse model [16]. This anti-Aβ oligomer MOA is consistent with the previously observed APOE4 gene dose-related efficacy in tramiprosate phase 3 clinical trials in patients with AD in prespecified subpopulation analyses [5, 25‐30].

Previously, we reported the phase 1 pharmacokinetics (PK) and safety of ALZ-801 in healthy male and female adult and elderly volunteers, including a single ascending dose (SAD) study, a multiple ascending dose (MAD) study, and a single-dose tablet food-effect study [10]. Overall, these results demonstrate that ALZ-801 exhibits improved oral tolerability and PK characteristics versus tramiprosate and represents a novel prodrug approach to achieving optimal delivery of tramiprosate into the brain [10]. Furthermore, we evaluated steady-state PK profiles following 2 weeks of oral ALZ-801 tablet 265 mg BID in APOE4 carrier subjects with early AD in a phase 1b clinical trial (ALZ-801-106ADPK study). These data show that oral ALZ-801 tablet delivers consistent steady-state plasma exposures for the active agents, tramiprosate and 3-SPA, after 2 weeks of treatment in APOE4 carrier subjects with AD.

In the present report, we summarize the phase 2 plasma steady-state PK profiles of the prodrug ALZ-801 and the active molecules, tramiprosate and 3-SPA, in APOE4 carrier subjects with early AD following oral ALZ-801 tablets 265 mg administered BID over 104 weeks. Considering that the phase 2 dose regimen is same as the earlier ALZ-801-106ADPK phase 1b study, we also include the 2-week steady-state PK data from that study as a reference.

The development of safe and effective disease-modifying treatments for AD remains a major unmet need, although there has been substantial progress in the past several years. To date, three anti-amyloid monoclonal antibody therapies (i.e., aducanumab, lecanemab, and donanemab) have been approved by the FDA for AD treatment [2‐4]. However, antibody therapies are associated with serious complications of brain edema and microhemorrhage called ARIA, which occur more frequently in APOE4 homozygote and heterozygote patients owing to a higher burden of amyloid deposition in cerebral vessels in these patients (i.e., cerebral amyloid angiopathy, CAA), which upon active removal renders the vessels leaky and prone to hemorrhage [5, 6, 32, 33]. These agents also require monthly or biweekly parenteral administration (e.g., intravenous) and are, therefore, burdensome to patients. These limitations have been a barrier to broad adoption and clinical use.

Importantly, the advent of anti-amyloid antibody therapies for AD has provided much needed clinical proof-of-concept evidence to support the amyloid hypothesis [34, 35], stating that the toxicity of soluble amyloid aggregates plays a central role in AD pathogenesis initiation and progression, and targeting this pathway is a validated approach for development of disease-modifying treatments for AD [23, 24]. Specifically, a growing body of evidence supports a central and causative role of Aβ oligomers in the pathogenesis of AD, and inhibition of the formation of Aβ oligomers, especially the highly aggregation-prone Aβ₄₂ species, constitutes a highly desirable target for the next-generation therapeutics for this disease [5, 23, 24, 30].

ALZ-801/valiltramiprosate is in phase 3 development as an oral, small-molecule inhibitor of Aβ oligomer formation with potential disease-modification effects for the treatment of AD. As a valine conjugated prodrug, ALZ-801 achieves its pharmacologic action via the two active moieties, tramiprosate and its sole metabolite 3-SPA. Both tramiprosate and 3-SPA inhibit the formation of Aβ oligomers in the brain at the PK exposure achieved following administration of ALZ-801 265 mg BID [10‐12]. Previously, we have shown that the projected steady-state brain exposure of tramiprosate after ALZ-801 265 mg BID dose maintains over three orders of magnitude in excess of brain concentration of soluble Aβ₄₂ [36‐39], which is sufficient to block the formation of toxic oligomers and amyloid aggregation [11].

ALZ-801 was developed to exploit this important efficacy attribute of tramiprosate in APOE4 carrier patients with AD [5, 23‐30], while circumventing its two limitations: gastrointestinal side effects (i.e., nausea and vomiting) and high intersubject variability. Similar to the ALZ-801 phase 1 trial [10] and the ALZ-801-106ADPK phase 1b study, the present phase 2 trial evaluated ALZ-801 tablets at the 265 mg BID dose in APOE4 carrier subjects with AD, with the goal of achieving a plasma drug exposure comparable to that of the previous tramiprosate phase 3 trials in patients with AD [5, 23‐30] and to support the ALZ-801 phase 3 trials.

We recently reported that ALZ-801 was well tolerated by APOE4 carrier subjects with early AD over 2 years of treatment at the 265 mg BID dose, without drug-related severe or serious adverse events or laboratory findings. The safety profile of ALZ-801 in subjects with AD remained favorable with no events of ARIA on MRI monitoring [7], which contrasts with the well-established safety risks of anti-amyloid antibodies in APOE4 carriers or patients with AD with CAA [2‐4]. This favorable safety profile is consistent with the profile of the active moiety, tramiprosate, in the earlier 78-week phase 3 studies [28], with no new safety signals identified. The most common adverse events were transient mild nausea and some instances of vomiting, which showed an improvement over tramiprosate [28] and development of tolerance over time.

In this study, the steady-state plasma PK results at 65 weeks following oral ALZ-801 tablet 265 mg BID treatment in APOE4 carrier subjects with AD are closely aligned with our findings of the 2-week PK data in the ALZ-801 phase 1b study in APOE4 carrier subjects with AD, as well as with the earlier 7-day PK data in the ALZ-801 phase 1 study in healthy elderly volunteers [10]. Following oral dosing, ALZ-801 was rapidly absorbed and efficiently converted to the active moieties, tramiprosate and 3-SPA. These results provide further support that the ALZ-801 tablets yield consistent tramiprosate and 3-SPA exposures in APOE4 carrier subjects with AD. In addition, in line with the ALZ-801 phase 1 study, individual PK analysis demonstrates very low intersubject variability in plasma drug levels as compared with the tramiprosate tablet at the dose of 150 mg BID in the earlier tramiprosate phase 3 trials [10, 28, 29].

We conducted correlation analyses of the PK exposures with the demographic and clinical characteristics of study subjects to understand whether any of the common variables might influence the PK behavior of ALZ-801. We found that the plasma exposures (both Cmax and AUC8h) of ALZ-801, tramiprosate, and 3-SPA were not affected by sex, age, BMI, APOE genotype, or concomitant use of AChEI. These data suggest that there is no need for dose adjustments for these baseline and clinical characteristics. Also, there is no apparent drug–drug interaction caused by concomitant AChEI use in this AD population.

We directly compared the PK profiles of the two GMP-manufactured tablet lots (with different API lots) in the 8-h PK substudy and found no differences. In addition, there was no significant PK difference between the current phase 2 study at 65 weeks and the earlier phase 1b study at 14 days (both at steady state) after ALZ-801 265 mg BID treatment. Since the two trials used different lots of tablets, these data suggest that the tablets have bioequivalent PK properties. Together, these results demonstrate comparable plasma PK performance across multiple ALZ-801 tablet lots.

A key finding of this analysis is that the plasma exposures (Cmax and AUC8h) of both tramiprosate and 3-SPA were inversely correlated with eGFR, an index of renal function, with higher exposures observed in subjects with lower eGFR values. These results are in line with renal clearance as a primary route of elimination for tramiprosate and 3-SPA and confirm the findings reported in healthy volunteers [10]. In contrast, there was no significant correlation between the plasma exposure of ALZ-801 and eGFR. Taken together, these results confirm the understanding that ALZ-801, as a prodrug, is efficiently and hepatically converted to the active moieties, tramiprosate and 3-SPA, after oral dosing [10].

The strengths of the phase 2 PK study include: (1) the low intersubject variability of PK exposures in the 8-h PK substudy, reflecting the quality of study conduct and bioanalysis, as well as the intrinsic and extrinsic drug properties; (2) the comparability and consistency of the present PK data with the earlier ALZ-801 phase 1 study in healthy elderly volunteers and the ALZ-801 phase 1b study in APOE4 carrier subjects with AD; and (3) the apparent divergent effect of renal function on plasma exposures of the prodrug versus the active molecules, which is in agreement with our knowledge of their elimination mechanisms.

There are a few limitations in this analysis. Firstly, our PK substudy was conducted at 65 weeks (steady state) over 8 h following oral ALZ-801 administration. This short, 8-h sampling duration did not allow us to derive the accurate terminal phase elimination kinetics for tramiprosate, because the calculation was confounded by the distribution phase. However, the present PK curves were almost overlapping with that of the previous phase 1b study in APOE4 carrier subjects with AD, which was obtained at steady state at 14 days after ALZ-801 265 mg BID and was sampled for 24 h. On the basis of this comparison, we believe that the true terminal phase elimination T1/2 for tramiprosate would be ~ 14 h. Similarly, the present PK curves for ALZ-801 and 3-SPA were nearly identical to those of the phase 1b study, and the calculated terminal phase elimination T1/2 values were comparable in both studies. Secondly, while the sparse PK data from this study were meant to offer an assessment of pre-dose trough drug levels immediately before the next dose, it was found that, in some of the subjects, the blood samples were apparently obtained shortly after an oral ALZ-801 tablet was taken, on the basis of the assessment of plasma drug levels of ALZ-801 and tramiprosate. Therefore, we used an estimated post-dose time (but not the nominal time) in the analysis, based on the relative concentration versus time relationship of the three analytes derived from the ALZ-801 phase 1b study. Thus, while the sparse data are a suitable surrogate for steady-state exposures, the 8-h PK data at 65 weeks represent a definitive assessment of steady-state PK profiles in this study.

ALZ-801/valiltramiprosate displays consistent PK performance with low intersubject variability in APOE4 carrier patients with AD that is devoid of interactions with sex, age, BMI or APOE genotype effect. There were no interactions with the AChEI, the symptomatic AD drugs approved for use in Mild, Moderate and Severe AD dementia. The favorable PK profile of ALZ-801 and comparable tablet properties support the continued development of oral ALZ-801 (265 mg BID dosing regimen) as a potential oral disease-modifying anti-amyloid agent for treatment of AD.