The Anticholinesterase Phenserine and Its Enantiomer Posiphen as 5^′Untranslated-Region-Directed Translation Blockers of the Parkinson’s Alpha Synuclein Expression

Abstract

There is compelling support for limiting expression of alpha-synuclein (α-syn) in the brains of Parkinson's disease (PD) patients. An increase of SNCA gene copy number can genetically cause familial PD where increased dose of this pathogenic protein correlates with severity of symptoms (triplication of the SNCA gene causes dementia in PD patients). Gene promoter polymorphisms were shown to increase α-synuclein expression as a risk for PD. Cholinesterase inhibitors can clinically slow cognitive decline in the later stages of PD etiology similar to their widespread use in Alzheimer's disease (AD). Pertinent to this, we identified that the well-tolerated anticholinesterase, phenserine, blocked neural SNCA mRNA translation and tested for targeting via its 5′untranslated region (5′UTR) in a manner similar to its action to limit the expression of the AD-specific amyloid precursor protein (APP). Posiphen, its better-tolerated (+) enantiomer (devoid of anticholinesterase action), repressed neural α-synuclein translation. Primary metabolic analogs of posiphen were, likewise, characterized using primary fetal neurons grown ex vivo from the brains of Parkinson's transgenic mice expressing the human SNCA gene.

A Synopsis on the Role of Tyrosine Hydroxylase in Parkinson’s Disease

“…Common features between targets across diseases permit the repositioning of already developed drugs effective for one disease to be assessed in another, as epitomized by exendin-4 – an efficacious drug in type 2 diabetes mellitus [184-186, 188] presently being assessed in early efficacy studies in PD and AD. Even for drugs with a different target, such as the experimental AD agents posiphen and phenserine that lower the rate of synthesis of amyloid-β precursor protein and thereby reduces the generation of the AD toxic species amyloid-β peptide [242], the molecular mechanism via it is achieved (translational regulation mediated via an iron response element) within the 5’-untranslated region of amyloid-β precursor protein mRNA [242, 243] is present within the 5’-untranslated region of α-synuclein [244, 245] and thereby providing a basis for the assessment of these agents in PD [246, 247]. Pioglitazone represents a further potential example [248].…”

Synthesis of the Alzheimer Drug Posiphen into its Primary Metabolic Products (+)-N1-norPosiphen, (+)-N8-norPosiphen and (+)-N1, N8-bisnorPosiphen, their Inhibition of Amyloid Precursor Protein, α -Synuclein Synthesis, Interleukin-1β Release, and Cholinergic Action.

“…Human SH-SY5Y neuroblastoma cells were acquired from from the American Type Culture Collection (Manassas, VA) and cultured as previously described [10,53,54]. Cells were grown in complete media (10% fetal calf serum, 2 mM glutamine in DMEM and an antibiotic cocktail (Invitrogen)) to 70% confluence.…”

Amyloid‐β precursor protein synthesis inhibitors for Alzheimer's disease treatment

“…[1] Unlike outcomes in neuronal cells,[4, 5] we found phenserine relatively inactive using CHO clones (unpublished data). Phenserine is also highly lipophilic (clog P n-octanol/water partition value = 2.22 (vs. 0.925 for 2-PAM) ((i.e., a 160-fold preference for the lipid vs. aqueous phase for phenserine vs. 8-fold for 2-PAM)).…”

“…We expect Asuni and colleagues would have recognized and explained this discrepancy for readers, because they cite Lahiri et al,[4] in which we reported the nonchiral phenserine extracellular and intracellular median inhibition concentration (IC50) values for APP synthesis in neurons (0.64–1.0 and 1.14–1.5μM, respectively) (this data derived from a concentration-dependent study to define the IC50 [4], albeit higher phenserine doses have been used in earlier studies). The literature also documents for Asuni and colleagues the relevant rapid chiral metabolism of (−)-phenserine,[6] the cellular IC50 of 100nM for the resulting active N1,N8-bisnor-metabolite,[5] and, of most importance, the lowering of cerebrospinal fluid APP and key AD markers in humans with mild cognitive impairment (i.e., clinical studies rather than cell culture ones). [7] Each of these is inconsistent with the implications to be drawn from Asuni and colleagues’ reported values, which require explanation to avoid misleading readers.…”