Key molecular lesions in colorectal and other cancers cause beta-catenin-dependent transactivation of T cell factor (Tcf)-dependent genes. Disruption of this signal represents an opportunity for rational cancer therapy. To identify compounds that inhibit association between Tcf4 and beta-catenin, we screened libraries of natural compounds in a high-throughput assay for immunoenzymatic detection of the protein-protein interaction. Selected compounds disrupt Tcf/beta-catenin complexes in several independent in vitro assays and potently antagonize cellular effects of beta-catenin-dependent activities, including reporter gene activation, c-myc or cyclin D1 expression, cell proliferation, and duplication of the Xenopus embryonic dorsal axis. These compounds thus meet predicted criteria for disrupting Tcf/beta-catenin complexes and define a general standard to establish mechanism-based activity of small molecule inhibitors of this pathogenic protein-protein interaction.

Homeostasis under hypoxic conditions is maintained through a coordinated transcriptional response mediated by the hypoxia-inducible factor (HIF) pathway and requires coactivation by the CBP and p300 transcriptional coactivators. Through a target-based high-throughput screen, we identified chetomin as a disrupter of HIF binding to p300. At a molecular level, chetomin disrupts the structure of the CH1 domain of p300 and precludes its interaction with HIF, thereby attenuating hypoxia-inducible transcription. Systemic administration of chetomin inhibited hypoxia-inducible transcription within tumors and inhibited tumor growth. These results demonstrate a therapeutic window for pharmacological attenuation of HIF activity and further establish the feasibility of disrupting a signal transduction pathway by targeting the function of a transcriptional coactivator with a small molecule.

SummaryWith renewed calls for malaria eradication, next-generation antimalarials need be active against drug-resistant parasites and efficacious against both liver- and blood-stage infections. We screened a natural product library to identify inhibitors of Plasmodium falciparum blood- and liver-stage proliferation. Cladosporin, a fungal secondary metabolite whose target and mechanism of action are not known for any species, was identified as having potent, nanomolar, antiparasitic activity against both blood and liver stages. Using postgenomic methods, including a yeast deletion strains collection, we show that cladosporin specifically inhibits protein synthesis by directly targeting P. falciparum cytosolic lysyl-tRNA synthetase. Further, cladosporin is >100-fold more potent against parasite lysyl-tRNA synthetase relative to the human enzyme, which is conferred by the identity of two amino acids within the enzyme active site. Our data indicate that lysyl-tRNA synthetase is an attractive, druggable, antimalarial target that can be selectively inhibited.

Due to evolutionary conservation of biology, experimental knowledge captured from genetic studies in eukaryotic model organisms provides insight into human cellular pathways and ultimately physiology. Yeast chemogenomic profiling is a powerful approach for annotating cellular responses to small molecules. Using an optimized platform, we provide the relative sensitivities of the heterozygous and homozygous deletion collections for nearly 1800 biologically active compounds. The data quality enables unique insights into pathways that are sensitive and resistant to a given perturbation, as demonstrated with both known and novel compounds. We present examples of novel compounds that inhibit the therapeutically relevant fatty acid synthase and desaturase (Fas1p and Ole1p), and demonstrate how the individual profiles facilitate hypothesis-driven experiments to delineate compound mechanism of action. Importantly, the scale and diversity of tested compounds yields a dataset where the number of modulated pathways approaches saturation. This resource can be used to map novel biological connections, and also identify functions for unannotated genes. We validated hypotheses generated by global two-way hierarchical clustering of profiles for (i) novel compounds with a similar mechanism of action acting upon microtubules or vacuolar ATPases, and (ii) an un-annotated ORF, YIL060w, that plays a role in respiration in the mitochondria. Finally, we identify and characterize background mutations in the widely used yeast deletion collection which should improve the interpretation of past and future screens throughout the community. This comprehensive resource of cellular responses enables the expansion of our understanding of eukaryotic pathway biology.

The antiplasmodial activity of a series of spirotetrahydro beta-carbolines is described. Racemic spiroazepineindole (1) was identified from a phenotypic screen on wild type Plasmodium falciparum with an in vitro IC(50) of 90 nM. Structure-activity relationships for the optimization of 1 to compound 20a (IC(50) = 0.2 nM) including the identification of the active 1R,3S enantiomer and elimination of metabolic liabilities is presented. Improvement of the pharmacokinetic profile of the series translated to exceptional oral efficacy in the P. berghei infected malaria mouse model where full cure was achieved in four of five mice with three daily doses of 30 mg/kg.

Unstimulated monocytes rapidly undergo physiological changes resulting in programmed cell death (apoptosis) while stimuli promoting differentiation of these cells into macrophages were shown to inhibit apoptotic processes. In the present study, we report that the platelet-derived -chemokine platelet factor 4 (PF4) induces the differentiation of monocytes into macrophages, as is evident from morphological changes as well as from the up-regulation of differentiation markers (carboxypeptidase M/MAX1 and CD71). Significant alterations of the phenotype were observed after 72 hours of culture in the presence of the chemokine and required a minimal concentration of 625 nmol/L PF4. PF4-induced macrophages were characterized by a lack of HLA-DR antigen on their surface but showed a strong increase in the expression of the CD28 ligand B7-2. Furthermore, PF4 stimulation prevented monocytes from undergoing spontaneous apoptosis during 72 hours of culture as determined in an annexin-V–binding assay. Although PF4 induced the secretion of relevant amounts of TNF-, neutralizing antibodies directed against TNF- or granulocyte-macrophage colony–stimulating factor (GM-CSF) did not revert PF4-induced rescue from programmed cell death, suggesting that PF4 exerts its antiapoptotic effects in a TNF-– or GM-CSF–independent fashion. On the basis of these results, we propose a novel role for PF4 in the control of monocyte differentiation during an inflammatory process in vivo.

The recruitment of neutrophil granulocytes to sites of tissue injury is one of the earliest events during host defense. Several chemotactic cytokines belonging to the CXC subfamily of chemokines are thought to be implicated in this kind of response. Especially those CXC chemokines that are stored in blood platelets and become immediately released upon activation are likely to dominate neutrophil-dependent host defense at the onset of inflammation. The major platelet-derived CXC chemokines are the ␤-thromboglobulins and platelet factor 4 (PF-4), which are both released into the blood at micromolar concentrations. The availability as well as the functional activity of these mediators appear to be subject to tight control by diverse regulatory mechanisms. These include proteolytic processing of chemokine precursors, oligomer formation, and the differential usage of neutrophil-expressed receptors. Herein we review our work on early neutrophil regulation by PF-4, the ␤-thromboglobulin neutrophil-activating peptide 2 (NAP-2) and its major precursor connective tissueactivating peptide III (CTAP-III). We moreover propose a model to assess the contribution by either of these chemokines to coordinated recruitment and activation of neutrophils in response to acute tissue injury. J. Leukoc. Biol. 67: 471-478; 2000.

Although platelet factor 4 (PF-4) and the beta-thromboglobulin (beta-TG) proteins represent the first chemokines to be discovered, their functional roles in host defense became clear only recently. Residing in platelets as storage proteins and becoming released into the blood at very high concentrations, these mediators appear to fulfill different and complementary tasks as first-line mediators in the recruitment and activation of leukocytes, as well in the regulation of tissue repair. Whereas both proteins are structurally closely related members of the CXC chemokine subfamily, they are subject to quite dissimilar regulatory mechanisms controlling their generation and their spectrum of biological activities. Thus, proteolytic processing of inactive precursors plays a decisive role in whether the beta-TG proteins will act as stimulatory or inhibitory agents in neutrophil activation via the G protein-coupled receptors CXCR-1 and 2. PF-4, existing as a single molecular form, is largely resistant to proteolytic modification, but its interaction with an unusual receptor(s) on leukocytes (a proteoglycan) appears to depend on its oligomeric state. There is growing evidence that both chemokines may interfere with each other at various regulatory levels to promote coordinated cell activation. Moreover, recent findings suggest novel and unexpected activities for these chemokines, which may extend our view on early host defense.