Discovery, Synthesis,
Pharmacological Profiling, and
Biological Characterization of Brintonamides A–E, Novel Dual
Protease and GPCR Modulators from a Marine Cyanobacterium
Five
novel modified linear peptides named brintonamides A–E
(<b>1</b>–<b>5</b>) were discovered from a marine
cyanobacterial sample collected from Brinton Channel, Florida Keys.
The total synthesis of <b>1</b>–<b>5</b> in addition
to two other structurally related analogues (<b>6</b> and <b>7</b>) was achieved, which provided more material to allow rigorous
biological evaluation and SAR studies. Compounds were subjected to
cancer-focused phenotypic cell viability and migration assays and
orthogonal target-based pharmacological screening platforms to identify
their protease and GPCR modulatory activity profiles. The cancer related
serine protease kallikrein 7 (KLK7) was inhibited to similar extents
with an IC<sub>50</sub> near 20 μM by both representative members <b>1</b> and <b>4</b>, which differed in the presence or lack
of the N-terminal unit. In contrast to the biochemical protease profiling
study, clear SAR was observed in the functional GPCR screens, where
five GPCRs in antagonist mode (CCR10, OXTR, SSTR3, TACR2) and agonist
mode (CXCR7) were modulated by compounds <b>1</b>–<b>7</b> to varying extents. Chemokine receptor type 10 (CCR10) was
potently modulated by brintonamide D (<b>4</b>) with an IC<sub>50</sub> of 0.44 μM. We performed in silico modeling to understand
the structural basis underlying the differences in the antagonistic
activity among brintonamides toward CCR10. Because of the significance
of KLK7 and CCR10 in cancer progression and metastasis, we demonstrated
the ability of brintonamide D (<b>4</b>) at 10 μM to significantly
target downstream cellular substrates of KLK7 (Dsg-2 and E-cad) in
vitro and to inhibit CCL27-induced CCR10-mediated proliferation and
the migration of highly invasive breast cancer cells