Structure–Activity Relationships of Potent, Targeted Covalent Inhibitors That Abolish Both the Transamidation and GTP Binding Activities of Human Tissue Transglutaminase

Human tissue transglutaminase (hTG2)
is a multifunctional enzyme.
It is primarily known for its calcium-dependent transamidation activity
that leads to formation of an isopeptide bond between glutamine and
lysine residues found on the surface of proteins, but it is also a
GTP binding protein. Overexpression and unregulated hTG2 activity
have been associated with numerous human diseases, including cancer
stem cell survival and metastatic phenotype. Herein, we present a
series of targeted covalent inhibitors (TCIs) based on our previously
reported Cbz-Lys scaffold. From this structure–activity relationship
(SAR) study, novel irreversible inhibitors were identified that block
the transamidation activity of hTG2 and allosterically abolish its
GTP binding ability with a high degree of selectivity and efficiency
(kinact/KI > 105 M–1 min–1).
One optimized inhibitor (VA4) was also shown to inhibit
epidermal cancer stem cell invasion with an EC50 of 3.9
μM, representing a significant improvement over our previously
reported “hit” NC9.