Structure-Based Design and Biological Evaluation of Novel Caspase‑2 Inhibitors Based on the Peptide AcVDVAD-CHO and the Caspase-2-Mediated Tau Cleavage Sequence YKPVD314

Alzheimer’s disease (AD) was
first described by Alois Alzheimer
over 100 years ago, but there is still no overarching theory that
can explain its cause in detail. There are also no effective therapies
to treat either the cause or the associated symptoms of this devastating
disease. A potential approach to better understand the pathogenesis
of AD could be the development of selective caspase-2 (Casp2) probes,
as we have shown that a Casp2-mediated cleavage product of tau (Δtau314)
reversibly impairs cognitive and synaptic function in animal models
of tauopathies. In this article, we map out the Casp2 binding site
through the preparation and assay of a series of 35 pentapeptide inhibitors
with the goal of gaining selectivity against caspase-3 (Casp3). We
also employed computational docking methods to understand the key
interactions in the binding pocket of Casp2 and the differences predicted
for binding at Casp3. Moreover, we crystallographically characterized
the binding of selected pentapeptides with Casp3. Furthermore, we
engineered and expressed a series of recombinant tau mutants and investigated
them in an in vitro cleavage assay. These studies resulted in simple
peptidic inhibitors with nanomolar affinity, for example, AcVDV­(Dab)­D-CHO
(24) with up to 27.7-fold selectivity against Casp3.
Our findings provide a good basis for the future development of selective
Casp2 probes and inhibitors that can serve as pharmacological tools
in planned in vivo studies and as lead compounds for the design of
bioavailable and more drug-like small molecules.