We reported that
iron influx drives the translational expression of the neuronal
amyloid precursor
protein (APP), which has a role in
iron efflux. This is via a classic release of repressor interaction of APP
mRNA with
iron-regulatory protein-1 (IRP1) whereas IRP2 controls the mRNAs encoding the L- and H-subunits of the
iron storage
protein,
ferritin. Here, we identified thirteen potent APP translation blockers that acted selectively towards the uniquely configured
iron-responsive
element (IRE)
RNA stem loop in the
5' untranslated region (UTR) of APP
mRNA. These agents were 10-fold less inhibitory of
5'UTR sequences of the related
prion protein (PrP)
mRNA. Western blotting confirmed that the 'ninth' small molecule in the series selectively reduced neural APP production in SH-SY5Y cells at picomolar concentrations without affecting viability or the expression of α-
synuclein and
ferritin.
APP blocker-9 (JTR-009), a
benzimidazole, reduced the production of toxic Aβ in SH-SY5Y neuronal cells to a greater extent than other well tolerated APP 5'UTR-directed translation blockers, including
posiphen, that were shown to limit
amyloid burden in mouse models of
Alzheimer's disease (AD).
RNA binding assays demonstrated that
JTR-009 operated by preventing IRP1 from binding to the IRE in APP
mRNA, while maintaining IRP1 interaction with the
H-ferritin IRE
RNA stem loop. Thus,
JTR-009 constitutively repressed translation driven by APP
5'UTR sequences.
Calcein staining showed that
JTR-009 did not indirectly change
iron uptake in neuronal cells suggesting a direct interaction with the APP
5'UTR. These studies provide key data to develop small molecules that selectively reduce neural APP and Aβ production at 10-fold lower concentrations than related previously characterized translation blockers. Our data evidenced a novel therapeutic strategy of potential impact for people with
trisomy of the APP gene on chromosome 21, which is a phenotype long associated with
Down syndrome (DS) that can also cause familial
Alzheimer's disease.