Physciosporin

Background: Physciosporin (PHY) is one of the potent anticancer lichen compound. Recently, PHY was shown to suppress colorectal cancer cell proliferation, motility, and tumorigenesis through novel mechanisms of action. Purpose: We investigated the effects of PHY on energy metabolism and tumorigenicity of the human breast cancer (BC) cells MCF-7 (estrogen and progesterone positive BC) and MDA-MB-231 (triple negative BC). Methods: The anticancer effect of PHY on cell viability, motility, cancer metabolism and tumorigenicity was evaluated by MTT assay, migration assay, clonogenic assay, anchorage-independent colony formation assay, glycolytic and mitochondrial metabolism analysis, qRT-PCR, flow cytometric analysis, Western blotting, immunohistochemistry in vitro; and by tumorigenicity study with orthotopic breast cancer xenograft model in vivo. Results: PHY markedly inhibited BC cell viability. Cell-cycle profiling and Annexin V-FITC/PI double staining showed that a toxic dosage of PHY triggered apoptosis in BC cell lines by regulating the B-cell lymphoma-2 (Bcl-2) family proteins and the activity of caspase pathway. At non-toxic concentrations, PHY potently decreased migration, proliferation, and tumorigenesis of BC cells in vitro. Metabolic studies revealed that PHY treatment significantly reduced the bioenergetic profile by decreasing respiration, ATP production, and glycolysis capacity. In addition, PHY significantly altered the levels of mitochondrial (PGC-1α) and glycolysis (GLUT1, HK2 and PKM2) markers, and downregulated transcriptional regulators involved in cancer cell metabolism, including β-catenin, c-Myc, HIF-1α, and NF-κB. An orthotopic implantation mouse model of BC confirmed that PHY treatment suppressed BC growth in vivo and target genes were consistently suppressed in tumor specimens. Conclusion: The findings from our in vitro as well as in vivo studies exhibit that PHY suppresses energy metabolism as well as tumorigenesis in BC. Especially, PHY represents a promising therapeutic effect against hormone-insensitive BC (triple negative) by targeting energy metabolism.

Secondary metabolites from fungi, algae and lichens have remarkable biological activities as antibiotics, fungicides, antiviral drugs, and cancer therapeutics. This review focuses on the lichen-derived metabolite gyrophoric acid and other select secondary metabolites (e.g., usnic acid, salazinic acid, physodic acid, vulpinic acid ceratinalone, flavicansone, ramalin, physciosporin, tumidulin, atranorin, parmosidone) that modulate a number of cellular pathways relevant to several biomedical diseases and disorders, including cancer, diabetes and cardiovascular disease. We discuss the chemical structure and biochemical activities of gyrophoric acid and other compounds relative to the molecular mechanisms and cellular processes that these metabolites target in a distinct human and rodent cell types. The therapeutic promise of gyrophoric acid and similar lichen derived metabolites is associated with the chemical versatility of these compounds as polyaromatic depsides with functional carboxyl and hydroxyl side-groups that may permit selective interactions with distinct enzymatic active sites. Gyrophoric acid has been examined in a series of studies as an effective anticancer drug because it impinges on topoisomerase 1 activity, as well as causes cell cycle arrest, comprises cell survival, and promotes apoptosis. Because gyrophoric acid has cytostatic properties, its biological roles and possible medicinal utility may extend beyond effects on cancer cells and be relevant to any process that is controlled by cell growth and differentiation.

Secondary metabolites of lichens are promising bioresources for candidate anti-cancer drugs. Accordingly, several approaches have been proposed for screening these molecules for novel anti-cancer lead compounds. In this study, we found that a non-toxic concentration of physciosporin, a compound isolated from Pseudocyphellaria granulata, significantly decreased colony formation on soft agar and spheroid formation by CSC221 cancer stem-like cells. Physciosporin also decreased spheroid formation in other colorectal cancer cell lines, including DLD1, Caco2, and HT29. Aldehyde dehydrogenase-1 (ALDH1), the most important cancer stem marker, was sharply downregulated at both the protein and mRNA level following treatment with physciosporin. Physciosporin also decreased the transcriptional activity of the glioma-associated oncogene homolog zinc finger protein (Gli), as well as the Hes1 and CSL promoters, in reporter assays. Moreover, the drug significantly suppressed spheroid formation in CSC221 cells overexpressing Gli1/2 or EN1 (an S2-cleaved but membrane-tethered form of human Notch1) but did not suppress spheroid formation in cells overexpressing both Gli1/2 and ∆EN1, suggesting that physciosporin suppresses colon cancer cell stemness through the Sonic hedgehog and Notch signaling pathways. Together, these results demonstrate for the first time that physciosporin is a potent inhibitor of colorectal cancer cell stemness.