The amyloid-ß protein (Aß), strongly implicated
in the etiology of Alzheimer's disease (AD), is formed from
the amyloid-ß precursor protein (APP) through sequential
proteolysis by ß- and
-secretases. Cleavage by
-secretase
takes place within the middle of the single transmembrane region
of APP and results primarily in 40- and 42-amino acid Aß
C-terminal variants, Aß
40 and Aß
42. The
latter form of Aß is highly fibrillogenic, is invariably
elevated in autosomal-dominant forms of AD, and is the major
Aß component found presymptomatically in cerebral
deposits. Thus, blocking production of Aß in general
and Aß
42 in particular is considered an important
therapeutic goal. We have developed transition-state analogue
inhibitors of
-secretase as molecular probes for characterizing
the active site of this enzyme, as pharmacological tools for
understanding its role in biology, and as affinity labels toward
its definitive identification. Specifically, we found that:
(1) difluoro ketone and difluoro alcohol peptidomimetics are
effective inhibitors of
-secretase activity in APP-transfected
cells, strongly suggesting an aspartyl protease mechanism; (2)
-secretases that form Aß
40 and Aß
42 are
pharmacologically distinct but are nevertheless closely similar;
(3) large hydrophobic P1 substituents increase the inhibitory
potency of these peptidomimetics, suggesting a large complementary
S1 pocket for
-secretases; (4) Aß
42 production is
increased several fold over control by these
-secretase inhibitors
after replacement with inhibitor-free media; (5) a bromoacetamide
derivative of one of these analogues continues to inhibit total
Aß and Aß
42 production hours after replacement
with compound-free media and should help identify the target(s)
of these protease transition-state mimics.
-Secretases Using Transition-state Analogue Inhibitors
