The genes for polyketide synthases (PKSs), enzymes that assemble the carbon backbones of many secondary metabolites, often cluster with other secondary pathway genes. We describe here the first lichen PKS cluster likely to be implicated in the biosynthesis of a depside and a depsidone, compounds in a class almost exclusively produced by lichen fungi (mycobionts). With degenerate PCR with primers biased toward presumed PKS genes for depsides and depsidones we identified among the many PKS genes in Cladonia grayi four (CgrPKS13-16) potentially responsible for grayanic acid (GRA), the orcinol depsidone characteristic of this lichen. To single out a likely GRA PKS we compared mRNA and GRA induction in mycobiont cultures using the four candidate PKS genes plus three controls; only CgrPKS16 expression closely matched GRA induction. CgrPKS16 protein domains were compatible with orcinol depside biosynthesis. Phylogenetically CgrPKS16 fell in a new subclade of fungal PKSs uniquely producing orcinol compounds. In the C. grayi genome CgrPKS16 clustered with a CytP450 and an o-methyltransferase gene, appropriately matching the three compounds in the GRA pathway. Induction, domain organization, phylogeny and cluster pathway correspondence independently indicated that the CgrPKS16 cluster is most likely responsible for GRA biosynthesis. Specifically we propose that (i) a single PKS synthesizes two aromatic rings and links them into a depside, (ii) the depside to depsidone transition requires only a cytochrome P450 and (iii) lichen compounds evolved early in the radiation of filamentous fungi.

Purpose Chronic Lymphocytic Leukemia (CLL), a malignancy of mature B-cells, is incurable with chemotherapy. Signals from the microenvironment support leukemic cell survival and proliferation, and may confer chemotherapy resistance. ON 01910.Na (Rigosertib) a multikinase PI3K inhibitor is entering phase III trials for myelodysplastic syndrome. Our aim was to analyze the efficacy of ON 01910.Na against CLL cells in vitro and investigate the molecular effects of this drug on tumor biology. Experimental design Cytotoxicity of ON 01910.Na against CLL cells from 34 patients was determined in vitro using flow cytometry of cells stained with Annexin V and CD19. Global gene expression profiling on Affymetrix microarrays, flow cytometry, western blotting, and co-cultures with stroma cells were used to delineate ON 01910.Na mechanism of action. Results ON 01910.Na induced apoptosis in CLL B-cells without significant toxicity against T-cells or normal B-cells. ON 01910.Na was equally active against leukemic cells associated with a more aggressive disease course (IGHV unmutated, adverse cytogenetics) than against cells without these features. Gene expression profiling revealed two main mechanisms of action: PI3K/AKT inhibition and induction of ROS that resulted in an oxidative stress response through activating protein 1 (AP-1), c-Jun NH2-terminal kinase, and ATF3 culminating in the upregulation of NOXA. ROS scavengers and shRNA mediated knockdown of ATF3 and NOXA protected cells from drug induced apoptosis. ON 01910.Na also abrogated the pro-survival effect of follicular dendritic cells on CLL cells and reduced SDF-1-induced migration of leukemic cells. Conclusions These data support the clinical development of ON 01910.Na in CLL.