Background

Buntanetap, previously known as posiphen or ANVS-401, is the pure (+) enantiomer, i.e. mirror image, of phenserine. Both compounds derive from the intramural research program at NIH and were licensed to Axonyx, Inc., which developed both enantiomers into the clinic. Axonyx merged with Torrey Pines Therapeutics, which licensed posiphen to QR Pharma in 2008.

Both posiphen and phenserine reduce production of amyloid precursor protein by blocking translation of its mRNA (Shaw et al., 2001). Phenserine also inhibits acetylcholinesterase, while posiphen does not. Both are dosed by mouth and enter the brain. Posiphen and phenserine are considered separate therapeutics, as there is no chiral switching between the two, or between their metabolites. Posiphen and phenserine, and their respective metabolites, differ in their pharmacokinetics.

They share a number of common actions and, additionally, have separate actions. Posiphen and phenserine act on iron-response element sequences in the 5' untranslated region of APP mRNA to inhibit APP protein synthesis. They reduced APP and Aβ in neuronal cultures and brains of wild-type and AD transgenic mice (Lahiri et al., 2007; Marutle et al., 2007). Both drugs were reported to be neuroprotective and neurotrophic in AD mouse models (Lilja et al., 2013; Lilja et al., 2013), and posiphen was reported to normalize memory impairment, learning, and synaptic function (Teich et al., 2018). Posiphen was also tested in the APP-overexpressing Ts65DN mouse model of Down's syndrome, where 50 mg/kg for 26 days lowered expression of APP and its C-terminal fragments, corrected deficits in axonal transport, and normalized neurotrophin signaling (Chen et al., 2021).

Posiphen and phenserine reportedly also block translation of α-synuclein mRNA, implying potential application in Parkinson’s disease (Rogers et al., 2011; Mikkilineni et al., 2012; Yu et al., 2013). Posiphen reduced α-synuclein expression in brain and gut, and improved intestinal function in the A53T α-synuclein transgenic mouse model of PD (Kuo et al., 2019).

Posiphen was reported to improve outcomes in rodent stroke models (Yu et al., 2020) and to augment neurogenesis post stroke (Turcato et al., 2018). Pharmacokinetic data are published (Maccecchini and Mould, 2024).

Findings

Results of three Phase 1 studies of posiphen are published (Maccecchini et al., 2012). They include single and multiple dosing in 120 healthy adults and a small proof-of-concept study in five people with MCI. Most common side effects were dizziness, nausea, and vomiting that increased with dose. Adverse effects did not increase significantly at doses of up to 60 mg four times a day for 10 days, at which point posiphen reached brain concentrations presumed sufficient to inhibit APP production. Ten days of treatment in people with MCI led to statistically significant reductions in CSF of APP cleavage fragments sAPPα and β, as well as of both total- and phosphorylated-tau, and the inflammation markers YKL-40, complement C3, and MCP-1. A trend for reduction was evident in CSF levels of Aβ42 (-51.4 percent, p=0.0533).

In March 2017, QR Pharma started a Phase 1/2 trial to study the effect of posiphen on APP synthesis in people with early AD. The study recruited 18 participants with a diagnosis of amnestic MCI or probable mild AD, and CSF levels of Aβ42 consistent with AD. They were randomized to receive 60 mg once, twice, or three times daily, or placebo for 23 to 25 days. Primary endpoints are safety, pharmacokinetics in plasma and CSF, and the rate of turnover of CSF Aβ40 using the stable isotope labeling kinetics (SILK) technique (see Paterson et al., 2019). The Alzheimer Disease Cooperative Study group ran the trial at five academic medical centers in the U.S. As of February 2020, 11 participants had enrolled, and no adverse effects were reported (company press release). The trial was paused from March to October 2020 due to COVID19, then completed in December 2021. Results are posted on clinicaltrials.gov and were published after peer review (Galasko et al., 2024). The drug was safe, with side effects mainly attributed to CSF catheterization for the SILK analysis. Posiphen did not alter the rate of synthesis of Aβ compared to placebo, nor did it change cognitive measures or CSF biomarkers.

In 2019, QR Pharma became Annovis Bio.

In August 2020, Annovis began a Phase 1/2 dose-finding biomarker study in early AD and Parkinson’s disease patients. In Part 1, 14 AD and 14 PD patients were to be randomized roughly 2:1 to 80 mg posiphen or placebo, taken daily for 23 to 27 days. At the last dose, participants undergo blood and CSF sampling. In Part 2 of the study, 40 PD patients will receive 5, 10, 20, 40 or 80 mg posiphen, under the same design as in Part 1. The primary outcome is adverse events. Other endpoints include pharmacokinetic, functional, and cognitive endpoints. A panel of CSF biomarkers to be measured spans amyloid and tau pathology, inflammation, and neuronal death.

Part 1 finished in early 2021, and Annovis presented results at the 2021 AAIC on July 28. There were no serious adverse events. On exploratory efficacy measures, the company claimed a statistically significant within-subject improvement in the ADAS-Cog11 from baseline to 25 days, but the comparison with placebo group fell short of significance. Posiphen-treated PD patients improved on the WAIS coding task, a paper-and-pencil test measuring motor dexterity and cognitive speed compared to placebo. The AD patients had a decrease in all amyloid/tau biomarkers, with a 12 percent reduction in pTau, and improvement in the Aβ42/40 ratio. The neurodegeneration biomarker NfL had 13 percent lower levels in AD and 9 percent in PD, but the change was not statistically significant. The company reported significant reductions by 43 and 28 percent in inflammatory markers sTREM2 and GFAP in treated PD patients; a 55 percent YKL40 reduction did not meet statistical significance. The study finished in January 2022. Full results report improvement on the MDS-UPDRS and WAIS coding in PD patients, with optimal responses occurring at 10-20 mg (Fang et al., 2023).

In August 2022, the company began a Phase 3 study in people with early PD. The study intended to enroll 450 participants for six months of 10 or 20 mg buntanetap daily, or placebo, with a primary outcome of MDS-UPDRS Parts 2 and 3 (activities of daily living and motor exam), and safety. Other outcomes include total MDS-UPDRS total score, clinician and patient impression of change, WAIS, and biomarkers. The study, at approximately 100 locations in the U.S. and Europe, ended in December 2023 with a final enrollment of 523. The primary outcome was modified to the MDS-UPDRS Part 2. On July 2, 2024, the company announced some results (press release). The company did not report on the primary endpoint in the group as a whole. It reported improvement on the MDS-UPRDS for a subgroup of patients with more advanced PD. It also claimed effects on the MMSE, which was not listed as a study outcome. In the study group as a whole, the placebo group declined by a fraction of a point on the MMSE, while the treatment group was reported to have stayed the same.

In April 2023, the company started a Phase 2/3 trial in mild to moderate AD. The dose ranging study randomized 353 participants to 7.5, 15, or 30 mg buntanetap or placebo, once daily for three months. Participants had MMSE scores between 14 and 24, and a clinical diagnosis of AD. No biomarkers were used to confirm diagnosis. Primary outcomes are ADAS-Cog11 and the ADSC-CGIC. Other outcomes include the ADCS-ADL, MMSE, and the Digit Symbol Substitution Test. The trial ran at more than 50 sites in the U.S. until February 2024. On April 29, 2024, the company announced results on a subset of 202 patients with retrospectively confirmed AD pathology based on plasma pTau/tau measurements. In 90 of these participants who had MMSEs between 21-24, the company claimed ADAS-Cog improvement at all three doses, compared to placebo (press release). The highest-dose group did three points better than placebo. In participants with MMSE between 14-20, the buntanetap group reportedly did worse than placebo by 1.79 points. More results are to be presented at the July 2024 AAIC.

For details on posiphen trials, see clinicaltrials.gov.