Malformin A is a cyclopentapeptide fungal metabolite that has been found in A. niger and has diverse biological activities. It is a plant growth regulator that induces malformations in plant structure. Malformin A inhibits replication of tobacco mosaic virus (TMV) in local lesion and leaf-disc assays (IC50s = 19.7 and 45.4 μg/ml, respectively). It is cytotoxic to NCI-H460, MIA PaCa-2, MCF-7, SF-268, and WI-38 cancer cells (IC50s = 70, 50, 100, 70, and 100 nM, respectively), inhibits proliferation of PC3 and LNCaP cells (IC50s = 130 and 90 nM, respectively), and induces apoptosis and necrosis in PC3 and LNCaP cells. Malformin A also increases the accumulation of reactive oxygen species, decreases the mitochondrial membrane potential, and induces autophagy in PC3 and LNCaP cells. It is toxic to mice when administered intraperitoneally (LD50 = 3.1 mg/kg) but not orally up to doses of 50 mg/kg.
Lobaric acid is a depsidone metabolite that has been isolated from Stereocaulon lichen species with antioxidant, antiproliferative, antiviral, and enzyme inhibitory activites. It scavenges superoxide radicals in a cell-free assay (IC50 = 97.9 μmol) and inhibits proliferation in a panel of leukemia, colorectal, gastric, breast, ovarian, prostate, pancreatic, and lung cancer cell lines (EC50s = 15.2-63.9 μg ml). Lobaric acid inhibits protein tyrosine phosphatase 1B (PTP1B; IC50 = 0.87 μM for the human recombinant enzyme) and production of 12(S)-HETE (Item No. 34570) by 12(S)-lipoxygenase (IC50 = 28.5 μM). In vivo, lobaric acid (250 μM) decreases lesion number, but not lesion diameter, in tobacco leaves infected with tobacco mosaic virus (TMV).