Structural Diversity and Anticancer Activity of Marine‐Derived Elastase Inhibitors: Key Features and Mechanisms Mediating the Antimetastatic Effects in Invasive Breast Cancer

Abstract

Three new 3-amino-6-hydroxy-2-piperidone (Ahp)-containing cyclic depsipeptides, named loggerpeptins A-C (1-3), along with molassamide (4), were discovered from a marine cyanobacterium, extending the structural diversity of this prevalent scaffold of cyanobacterial serine protease inhibitors. Molassamide, which contains a 2-amino-butenoic (Abu) unit in the cyclic core, was the most potent and selective analogue against human neutrophil elastase (HNE). Given the growing evidence supporting the role of HNE in breast cancer progression and metastasis, we assessed the cellular effects of compounds 3 and 4 in the context of targeting invasive breast cancer. Both compounds inhibited cleavage of the elastase substrate CD40 in biochemical assays; however, only 4 exhibited significant cellular activity. As CD40 and other receptor proteolytic processing culminates in NFκB activation, we assessed the effects of 4 on the expression of target genes, including ICAM-1. ICAM-1 is also a direct target of elastase and, in our studies, compound 4 attenuated both elastase-induced ICAM-1 gene expression and ICAM-1 proteolytic processing by elastase, revealing a potential dual effect on migration through modulation of gene expression and proteolytic processing. Molassamide also specifically inhibited the elastase-mediated migration of highly invasive triple-negative breast cancer cells.

The Chemistry, Biochemistry and Pharmacology of Marine Natural Products from Leptolyngbya, a Chemically Endowed Genus of Cyanobacteria

“…Loggerpeptins A–C ( 25–27 ) are cyclic depsipeptides with 3-amino-6-hydroxy-2-piperidone (Ahp) residues ( Figure 6 ) that were isolated from a Florida cyanobacterial collection identified morphologically as Leptolyngbya sp. [ 40 ]. These compounds were screened for serine protease inhibitory activities to assess their antimetastatic effect against breast cancer cells.…”

“…These compounds were screened for serine protease inhibitory activities to assess their antimetastatic effect against breast cancer cells. Loggerpeptin A ( 25 ) and B ( 26 ) were more potent than loggerpeptin C ( 27 ) with IC 50 s of 0.24 and 0.22 µM against bovine pancreatic chymotrypsin and 0.24 and 0.28 µM against porcine pancreatic elastase [ 40 ]. Loggerpeptin A ( 25 ) was 2- and 3-fold more potent than loggerpeptin B ( 26 ) and C ( 27 ) against human neutrophil elastase (HNE) [ 40 ].…”

“…Loggerpeptin A ( 25 ) and B ( 26 ) were more potent than loggerpeptin C ( 27 ) with IC 50 s of 0.24 and 0.22 µM against bovine pancreatic chymotrypsin and 0.24 and 0.28 µM against porcine pancreatic elastase [ 40 ]. Loggerpeptin A ( 25 ) was 2- and 3-fold more potent than loggerpeptin B ( 26 ) and C ( 27 ) against human neutrophil elastase (HNE) [ 40 ]. All three compounds exhibited antiproteolytic activities, with IC 50 values under 1 µM.…”

“…All three compounds exhibited antiproteolytic activities, with IC 50 values under 1 µM. As the major component in the collection, loggerpeptin C ( 27 ) was subject to a detailed molecular study [ 40 ]. Molecular docking showed that the Leu and N-terminal Thr-1, Abu and Ala residues of loggerpeptin C ( 27 ) were binding to the subsites S1-S4 of HNE and porcine pancreatic elastase [ 40 ].…”

“…Molassamide ( 28 ) is another cyclic depsipeptide ( Figure 7 ) that was isolated along with loggerpeptins A–C ( 25–27 ) [ 40 ]. Compared to loggerpeptins ( 25–27 ), molassamide ( 28 ) exhibited much more potent inhibition activity against porcine pancreatic elastase, with an IC 50 value of 50 nM, indicating the Abu residue between Ahp and Thr-1 is important to the antiproteolytic selectivity [ 40 ].…”