Design, synthesis and anthelmintic activity of 7-keto-sempervirol analogues

Abstract

The plant-derived, diterpenoid 7-keto-sempervirol was recently reported to display moderate activity against larval stages of Schistosoma mansoni (IC = 19.1 μM) and Fasciola hepatica (IC = 17.7 μM), two related parasitic blood and liver flukes responsible for the neglected tropical diseases schistosomiasis and fascioliasis, respectively. Here, we aimed to increase the potency of 7-keto-sempervirol by total synthesis of 30 structural analogues. Subsequent screening of these new diterpenoids against juvenile and adult lifecycle stages of both parasites as well as the human HepG2 liver cell line and the bovine MDBK kidney cell line revealed structure-activity relationship trends. The most active analogue, 7d, displayed improved dual anthelmintic activity over 7-keto-sempervirol (IC ≈ 6 μM for larval blood flukes; IC ≈ 3 μM for juvenile liver flukes) and moderate selectivity (SI ≈ 4-5 for blood flukes, 8-13 for liver flukes compared to HepG2 and MDBK cells, respectively). Phenotypic studies using scanning electron microscopy revealed substantial tegumental alterations in both helminth species, supporting the hypothesis that the parasite surface is one of the main targets of this family of molecules. Further modifications of 7d could lead to greater potency and selectivity metrics resulting in a new class of broad-spectrum anthelmintic.

Quorum sensing N-Acyl homoserine lactones are a new class of anti-schistosomal

“…Biomphalaria glabrata (NMRI and the previously described pigmented strains [23]) snails infected with S. mansoni (Puerto Rican strain) were shed for 2 hrs under light at 26 o C. Cercariae were collected, mechanically transformed into schistosomula [24] and subsequently prepared for high throughput screening (HTS) on the Roboworm platform as previously described [25]. Compounds were initially tested at a final concentration of 10 M and those that were active were further titrated at concentrations of 10, 5, 2.5, 1.25 and 0.625 µM.…”

“…The cytotoxicity of each compound was assessed on human HepG2 cells as described previously [25]. Briefly, 2…”

“…At 72hrs, schistosomula were scored using the Roboworm platform for both motility and phenotype as previously described [17,25]. A) Of the 14 compounds evaluated, two fell within the hit region.…”

“…Towards this goal, our group has recently identified several diverse starting points for anti-schistosomal drug discovery. These include diterpenoids [16,17], triterpenoids [18], and epigenetic probes/inhibitors [19,20]. While the primary focus of these investigations evaluated compound-induced activity on Schistosoma mansoni (the schistosome species responsible for both Old and New world schistosomiasis), parallel studies were also conducted to quantify anti-infective activities against other NTD-causing pathogens including Fasciola hepatica (liver fluke) [16][17][18] or NTD models such as Mycobacterium smegmatis (related to Mycobacterium leprae) [21].…”

The repositioning of epigenetic probes/inhibitors identifies new anti-schistosomal lead compounds and chemotherapeutic targets

“…Due to our (and other research groups) continued interest in deciphering how schistosome epigenetic processes shape schistosome lifecycle progression [17–27] and the SGC’s ability to supply epigenetic probes (EPs)/epigenetic inhibitors (EIs) (compounds that have been designed to modulate human epigenetic targets) [28, 29], we herein have conducted a repositioning campaign focused on the anti-schistosomal activity (against S. mansoni ) of thirty-four SGC-supplied EPs (compounds that display in vitro potency of < 100 nM, > 30 fold selectivity vs other subfamilies and on-target cellular activity at 1 µM) and three EIs (compounds that do not display these specific epigenetic probe traits) [30]. Using both a high-throughput platform for measuring schistosomula motility and phenotype as well as a low-throughput assay for quantifying adult schistosome viability and egg production [31–33], we have determined that compounds targeting bromodomain (BRD) – containing proteins, histone methyltransferases (HMTs) and histone demethylases (HDMs) are amongst the most potent anti-schistosomals within the tested SGC epigenetic probe collection. As the schistosome histone methylation machinery has recently been shown to be critical for schistosome developmental processes including egg production, miracidium to sporocyst transformation and adult worm motility [34–36], we specifically pursued the SGC epigenetic probes (LLY-507/BAY-598 and GSK-J4) involved in HMT/HDM inhibition for follow-on functional investigations.…”