TY - JOUR
AU - Kwon, Ho Jeong
AB - Abstract Natural products are valuable resources that provide a variety of bioactive compounds and natural pharmacophores in modern drug discovery. Discovery of biologically active natural products and unraveling their target proteins to understand their mode of action have always been critical hurdles for their development into clinical drugs. For effective discovery and development of bioactive natural products into novel therapeutic drugs, comprehensive screening and identification of target proteins are indispensable. In this review, a systematic approach to understanding the mode of action of natural products isolated using phenotypic screening involving chemical proteomics-based target identification is introduced. This review highlights three natural products recently discovered via phenotypic screening, namely glucopiericidin A, ecumicin, and terpestacin, as representative case studies to revisit the pivotal role of natural products as powerful tools in discovering the novel functions and druggability of targets in biological systems and pathological diseases of interest. Special Issue: Natural Product Discovery and Development in the Genomic Era. Dedicated to Professor Satoshi Ōmura for his numerous contributions to the field of natural products. Introduction Phenotypic screening for bioactive natural product discovery Phenotypic screening of bioactive natural products by perturbing biological systems Natural products from microbes, plants and animals have long been utilized as therapeutic agents and chemical probes. However, the application to drug discovery of natural products has been diminished owing to their incompatibility with molecular target-based high-throughput screening (HTS), an major approach of drug development generally applied with combinatorial chemistry in the past 20 years [21, 69]. Although the target-based screening has allowed many advances in modern drug discovery, high attrition rates in Phase II and III clinical trials mainly resulted from lack of drug efficacy have limited the approach [69]. Therefore, in the post-genomic era, phenotypic screening has been empowered and renewed as an approach for drug discovery because of its biological relevance as opposed to target-based screening [61, 69]. The bioactivities of natural products can be evaluated at the cellular, tissue, or whole organism level using unbiased phenotypic screening. In addition, phenotypic screening identifies various compounds with different structures that possess potentially diverse unknown target proteins and unexpected mechanisms. To this end, a number of biological entities have been phenotypically screened owing to curiosity and pharmaceutical needs [48, 61]. Various phenotypic events associated with diseases are exploited in the phenotypic screening of natural products, and are summarized in (Table 1). In specific, romidepsin, an US Food and Drug Administration (FDA)-approved anti-tumor bicyclic depsipeptide, was identified among microbial metabolites using a cytotoxicity screen in tumor cell lines [63]. Romidepsin is also known as a potent histone deacetylase inhibitor (HDACi) [48, 49]. Salinosporamide A and pateamine were also identified from phenotypic screening against cell proliferation. A famous HDAC inhibitor, trichostatin A was found by its cell cycle arrest activity. The immunosuppressive activity of a well-known drug, FK506, was also identified by phenotypic screening, which involves examining the inhibition of T cell activation and production of lymphokines, including interleukin (IL)-2 and interferon (IFN) [36, 37]. Further biological investigations identified cis-trans peptidyl-prolyl isomerase FKBP, as a target protein of FK506 [19]. To search for antibiotics with anti-tumor effects, a set of screenings for detransformation activity of tumor cells was performed, which led to the identification of trapoxin [25] and depeudecin [59] from microbial metabolites as hits. Later, the identification of the target of these natural products led to the discovery that histone deacetylases play key roles in detransformation as well as epigenetic regulation [35, 40]. Fumagillin was isolated from fungal metabolites that induced endothelial cell rounding and inhibited angiogenesis [24]. Fumagillin exhibits anti-angiogenic activity by inhibiting the methionine aminopeptidase (MetAP-2) [58]. The natural products manassantin and sesquicillin were identified from a phenotypic screen in zebrafish embryos using a natural product library [41]. The compounds caused developmental arrest without necrosis and inhibited the electron transport chain. Acyldepsipeptides (ADEPs), a new class of antibiotics isolated from microbial broth, showed potent antimicrobial activity through dysregulation of bacterial proteolytic machinery. Lysosomal cholesterol accumulation in cells is representative of Niemann–Pick disease type C1 (NPC1) phenotype. δ-Tocopherol was identified using a phenotypic screen that evaluated lysosomal cholesterol accumulation in NPC1 fibroblasts [67]. δ-Tocopherol effectively reduced cholesterol accumulation and alleviated pathological phenotypes in NPC1 cells, implying a potential for use in the treatment of lysosomal storage diseases. In particular, glucopiericidin A, ecumicin, and terpestacin were also identified from phenotypic screening of interest and will be introduced in detail. Examples of natural products isolated from phenotypic screens HDAC histone deacetylase, eIF4A eukaryotic initiation factor 4A, FABP FK506 binding protein, CaN calcineurin, MetAP-2 methionyl aminopeptidase 2, GLUT1 glucose transporter 1, UQCRB ubiquinol-cytochrome c reductase binding protein, ClpC1 ATP-dependent Clp protease ATP binding subunit ClpC1 Open in new tab Examples of natural products isolated from phenotypic screens HDAC histone deacetylase, eIF4A eukaryotic initiation factor 4A, FABP FK506 binding protein, CaN calcineurin, MetAP-2 methionyl aminopeptidase 2, GLUT1 glucose transporter 1, UQCRB ubiquinol-cytochrome c reductase binding protein, ClpC1 ATP-dependent Clp protease ATP binding subunit ClpC1 Open in new tab Summary of highlighted representative cases including their approaches from phenotypic screening to target identification Natural product . Glucopiericidin A . Ecumicin . Terpestacin . Phenotypic screen Filopodial protrusion inhibition Anti-tuberculosis activity Angiogenesis inhibition Target identification approach Chemical genomic screening of target-identified inhibitors Whole-genome sequencing of spontaneous drug-resistant mutants T7 phage display biopanning CE-TOFMS-based metabolomics Identified molecular target GLUT1 ClpC1 UQCRB Validation of drug-target binding Drug sensitivity test to GLUT1 overexpressed cells DARTS assay SPR analysis Subcellular localization Genome-wide gene expression profiling Natural product . Glucopiericidin A . Ecumicin . Terpestacin . Phenotypic screen Filopodial protrusion inhibition Anti-tuberculosis activity Angiogenesis inhibition Target identification approach Chemical genomic screening of target-identified inhibitors Whole-genome sequencing of spontaneous drug-resistant mutants T7 phage display biopanning CE-TOFMS-based metabolomics Identified molecular target GLUT1 ClpC1 UQCRB Validation of drug-target binding Drug sensitivity test to GLUT1 overexpressed cells DARTS assay SPR analysis Subcellular localization Genome-wide gene expression profiling CE-TOFMS capillary electrophoresis time-of-flight mass spectrometry, GLUT1 glucose transporter 1, ClpC1 ATP-dependent Clp protease ATP binding subunit ClpC1, DARTS drug affinity responsive target stability, UQCRB ubiquinol-cytochrome c reductase binding protein, SPR surface plasmon resonance Open in new tab Summary of highlighted representative cases including their approaches from phenotypic screening to target identification Natural product . Glucopiericidin A . Ecumicin . Terpestacin . Phenotypic screen Filopodial protrusion inhibition Anti-tuberculosis activity Angiogenesis inhibition Target identification approach Chemical genomic screening of target-identified inhibitors Whole-genome sequencing of spontaneous drug-resistant mutants T7 phage display biopanning CE-TOFMS-based metabolomics Identified molecular target GLUT1 ClpC1 UQCRB Validation of drug-target binding Drug sensitivity test to GLUT1 overexpressed cells DARTS assay SPR analysis Subcellular localization Genome-wide gene expression profiling Natural product . Glucopiericidin A . Ecumicin . Terpestacin . Phenotypic screen Filopodial protrusion inhibition Anti-tuberculosis activity Angiogenesis inhibition Target identification approach Chemical genomic screening of target-identified inhibitors Whole-genome sequencing of spontaneous drug-resistant mutants T7 phage display biopanning CE-TOFMS-based metabolomics Identified molecular target GLUT1 ClpC1 UQCRB Validation of drug-target binding Drug sensitivity test to GLUT1 overexpressed cells DARTS assay SPR analysis Subcellular localization Genome-wide gene expression profiling CE-TOFMS capillary electrophoresis time-of-flight mass spectrometry, GLUT1 glucose transporter 1, ClpC1 ATP-dependent Clp protease ATP binding subunit ClpC1, DARTS drug affinity responsive target stability, UQCRB ubiquinol-cytochrome c reductase binding protein, SPR surface plasmon resonance Open in new tab Target identification and validation of natural products Small molecules from natural products as chemical probes for proteins Small molecules derived from natural products and chemical syntheses are invaluable sources for probing multiple molecular target proteins with varying biological activities [3, 50]. Through the identification of small-molecule target proteins, the mode of action of compounds and interactions between their target proteins within the cells can be elucidated. In this context, they are pivotal to identifying unknown target proteins of bioactive compounds with appropriate target identification methodologies (Fig. 2). In this review, three representative cases are introduced using the approach of isolating bioactive compounds from natural products and then deconvoluting their mode of action by target identification. The compounds we have specifically focused on are (1) glucopiericidin A (GPA), (2) ecumicin, and (3) terpestacin. These compounds were elected on the basis of distinctive target identification and validation methodologies which are plausible for identifying the mode of action of natural products. Case 1—GPA a natural microbial product that inhibits filopodial protrusion Isolation of GPA from a phenotypic screening in search of a filopodial protrusion inhibitor Filopodia are cell membrane projections, which contribute to tumor metastasis [1, 47]. Therefore, identifying new chemical inhibitors of filopodial protrusion, which can be applied to treat tumor metastasis, as well as uncovering the molecular mechanisms of the involvement of filopodia in tumor metastasis, would be beneficial. To this end, over 3000 microbial broth samples were adapted to a phenotypic screening in human epidermal carcinoma A431 cells [38]. Owing to the highly expressed epidermal growth factor (EGF) receptors, A431 cells are highly susceptible to EGF treatment and exhibit filopodial protrusion within 30 min. GPA [46] and piericidin A (PA) [17] were isolated (Fig. 1a) from a microbial broth with strong inhibitory activity against filopodial protrusion (Table 2) [38]. Interestingly, GPA and PA synergistically blocked EGF-induced filopodial protrusion. Fig. 1 Open in new tabDownload slide Structures of isolated natural products presented in this review a glucopiericidin A, piericidin A, b ecumicin, and c terpestacin Unraveling mechanisms underlying the synergistic effect of GPA and PA: Identification of metabolomic target of GPA PA was previously known as a mitochondrial complex I inhibitor [16]. Although GPA is a glucopyranoside derivative of PA, it showed considerably weaker inhibitory activity against mitochondrial respiration. These findings suggested that PA contributes to the synergistic inhibition of filopodia by suppression of mitochondrial respiration while GPA contributes via a different unknown mechanism. Therefore, chemical genomic screening was used to elucidate the mode of action of GPA. In this screening, about 200 target-identified inhibitors were tested against EGF-induced filopodial protrusion in the presence of PA, and then the biological profile of the inhibitors was compared with that of GPA. As a result, a known glycolysis suppressor 2-deoxyglucose (2DG) was the only compound that inhibited protrusion. Although the anti-cancer activity of 2DG does not seem to be entirely from inhibition of glycolysis [55], additional analysis revealed that the synergistic inhibition of filopodial protrusion by PA and 2DG was due to the simultaneous blockade of two ATP-producing metabolic pathways including glycolysis and mitochondrial respiration. As expected, GPA also decreased cellular ATP levels, implying that it inhibits protrusion by perturbing glycolysis. Notably, a metabolomics approach with capillary electrophoresis time-of-flight mass spectrometry (CE-TOFMS) was used to evaluate the effect of GPA on glycolysis and to compare control and GPA-treated cells. The CE-TOFMS-based metabolomics analysis has been applied in the detection of altered metabolic profiles in various biological states [23, 39, 51]. The analysis of the quantitatively identified peaks showed that GPA inhibited glycolysis. Moreover, the specific reaction step in glycolysis was determined using CE-MS with incorporation of labeled glucose, to identify the target of GPA. In the additional in vitro experiments, GPA inhibited glucose uptake in a range of concentration that is required to inhibit filopodial protrusion, and the glucose transporter 1 (GLUT1) was finally identified as a functional target of GPA. In addition, GLUT1 was overexpressed in A431 cells to elucidate the relationship between GPA and GLUT1 and the sensitivity of glucose uptake in response to GPA treatment was estimated. GLUT1 overexpression decreased cell sensitive to GPA, suggesting that GPA abrogated the glycolysis inhibiting function of GLUT1. Notably, this is the first report of a target identification of a natural product using a metabolomics approach. Case 2—Ecumicin a microbial cyclic peptide effective against tuberculosis (TB) Isolation of ecumicin from a phenotypic screening for new anti-tuberculosis (TB) drugs Tuberculosis (TB) is a common and in many cases lethal infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis (M. tuberculosis) [28]. The emergence of multiple-drug-resistant (MDR) and extensively drug-resistant (XDR) TB prompted an increase in development of new anti-TB drugs and targets, and the discovery of additional drug candidates is clearly still in demand [6, 62]. To find a new anti-TB drug with a novel mode of action, a high-throughput screening of over 65,000 actinomycete extracts was conducted against M. tuberculosis [14]. As a result, the macrocyclic tridecapeptide, ecumicin was isolated [14, 15], and it exerted potent and selective bactericidal activity against both replicating and non-replicating M. tuberculosis, as well as strains that are resistant to the existing actinomycete-derived antibiotics (Fig. 1b and Table 2). Furthermore, ecumicin possessed strong bactericidal activity within host cells. To investigate the anti-TB activity of ecumicin in vivo, a polymeric micelle formulation was used because of its poor water solubility. After administration of ecumicin in M. tuberculosis-infected mice, the compound appeared to accumulate in the lung tissue and inhibit the growth of M. tuberculosis in there. Identification of the molecular target of ecumicin To identify the specific target of ecumicin, four spontaneously ecumicin-resistant mutants of M. tuberculosis were selected for whole-genome sequencing. Compared to the parental strain, the mutants possessed a distinct mutation in the N-terminal repeat II of ClpC1, conferring resistance against ecumicin. As a result, the ClpC1 ATPase was identified as a putative target of ecumicin. To validate the binding of ecumicin and ClpC1, a drug affinity responsive target stability (DARTS) assay was conducted with recombinant E. coli BL21 isolates overexpressing the wild-type or mutant M. tuberculosis ClpC1. DARTS assay is a proteomics-based target identification method without an immobilization approach, based on the premise that a target protein, which binds to a compound, might be more stable against proteolysis [9, 43, 44]. As expected, the wild-type but not the mutant ClpC1 was protected against proteolysis by ecumicin, dose dependently. Additionally, MS analysis confirmed the presence of ClpC1 in the protected band, indicating that it is a molecular target of ecumicin. Elucidation of molecular mechanisms of ecumicin ClpC1 is an ATPase, which plays an essential role specifically in M. tuberculosis and not in other bacteria. In addition, ClpC1 mediates ATP-dependent protein degradation with the ClpP1P2 protease complex. Treatment with ecumicin specifically stimulated the ATPase activity of the wild-type ClpC1 and suppressed that of the mutants. In addition, ecumicin strongly inhibited the ClpC1-dependent protein degradation, suggesting that the compound uncoupled ATP hydrolysis from protein proteolysis. Clearly, ClpC1 is an authentic target of ecumicin and therefore, the potent bactericidal activity of ecumicin might be mediated by its inhibitory activity against ATP-dependent proteolysis of cellular proteins. Case 3—Terpestacin, a natural microbial product that inhibits angiogenesis Isolation of terpestacin from a phenotypic screening to discover new angiogenesis inhibitors Angiogenesis is a multi-step process of new blood vessel growth and remodeling by endothelial cells, which is a prerequisite for many biological events including development, reproduction, and tissue repair [5]. However, pathological states of angiogenesis are responsible for several diseases such as tumor growth and metastasis, diabetic retinopathy, and rheumatoid arthritis [12, 53, 65]. Therefore, basic and biomedical research interests highlight the need for regulation of angiogenesis [12, 13]. Although several cellular angiogenic target proteins and regulators have been identified, discovering novel therapeutic targets of anti-angiogenesis is regarded as a crucial gateway to improving the success rate of drug development targeting angiogenesis-related diseases. To discover new angiogenesis inhibitors, a phenotypic screening of microbial metabolites inhibiting invasion and tube formation of endothelial cells (ECs) was performed in the presence of pro-angiogenic stimulation [33]. As a result, the known compound terpestacin [52] was identified from a culture extract of the fungus Embellisia chlamydospora (Table 2) [33]. Terpestacin is a small molecule with a unique bicyclo sesterterpene structure (Fig. 1c) and was previously known for its inhibitory activity against syncytium formation in human immunodeficiency virus infection [52]. However, the large-scale phenotypic screening of microbial extracts first demonstrated the anti-angiogenic activity of the compound. Terpestacin showed effective anti-angiogenic activity by inhibiting invasion, in vitro tube formation, and in vivo chorioallantoic membrane (CAM) angiogenesis. Although terpestacin showed prominent therapeutic anti-angiogenic effects, identification of its molecular target and mechanism of action remained elusive. Therefore, efficient target identification for terpestacin was conducted following the phenotypic screening. Target identification for terpestacin using reverse chemical proteomics approach Various methods have been applied in target identification based on genomics, proteomics, metabolomics, and bioinformatics approaches guided by the chemical properties of small molecules. Among them, the phage display biopanning, which is an approach involving reverse chemical proteomics, was applied in target identification for terpestacin. The phage display system is an affinity-based target identification method using human cDNA libraries expressed on the surface of bacteriophages and immobilized small molecules as probes. The target proteins for several bioactive small molecules, including FK506 [56], doxorubicin [27], kahalalide F [54], and HBC [57] were successfully identified using this method. Based on this approach, ubiquinol-cytochrome c reductase binding protein (UQCRB) was identified as a direct binding target of terpestacin [34]. UQCRB is a 13.4 kDa subunit of complex III in the mitochondrial electron transport chain (ETC), which participates in the assembly of complex III [60]. The specific molecular interaction between terpestacin and intact human UQCRB was further confirmed by biophysical analysis using surface plasmon resonance (BIAcore) analysis. Additionally, the interaction was still maintained at the cellular level, as confirmed by the subcellular localization of coumarin-tagged terpestacin. The binding mode of terpestacin to UQCRB was also revealed from the docking modeling. Furthermore, a significant correlation between terpestacin and UQCRB genetic knockdown was validated by genome-wide transcriptional profiling, suggesting that UQCRB is a biologically relevant target protein of terpestacin. Mechanism of action study of terpestacin The anti-angiogenic activity of terpestacin is the major biological implication of its binding to UQCRB. The interaction between terpestacin and UQCRB decreased the mitochondrial membrane potential without inhibiting mitochondrial respiration. Furthermore, molecular validation showed that terpestacin inhibited hypoxia-induced angiogenesis [34] as well as vascular endothelial growth factor 2 (VEGFR2)-stimulated angiogenesis [31] by suppression of mitochondrial reactive oxygen species (mROS) generation, followed by inhibition of the hypoxia-inducible factor (HIF)-1α-mediated VEGF expression in vitro and in vivo. Remarkably, combination treatment with terpestacin and VEGF-signaling inhibitors such as bevacizumab, a VEGF blocker or DPI, an NADPH oxidase inhibitor increased the anti-angiogenic effect in human umbilical vein endothelial cells (HUVECs). Collectively, these findings suggest that terpestacin showed prominent anti-angiogenic activity by the inhibition of UQCRB-mediated mROS generation in tumor cells and ECs. More importantly, identification of the target protein and mode of action of terpestacin revealed UQCRB to be the new player in angiogenesis. Decoding biological role of mitochondrial UQCRB in angiogenesis It was inferred from the biological activities of terpestacin that UQCRB may play an important role in modulating mROS- and HIF-mediated angiogenesis during hypoxia. Indeed, overexpression of UQCRB induces mROS generation and HIF-1α stability, whereas suppression of UQCRB with siUQCRB inhibits hypoxia-induced angiogenesis. In addition, UQCRB enhances VEGFR2 signaling by increasing ROS generation in ECs. Furthermore, functional inhibition of UQCRB with UQCRB morpholino showed dose-dependent inhibition of angiogenesis and VEGF levels in a zebrafish model, which phenocopied the effects of terpestacin treatment [10]. These findings, therefore, clearly demonstrate that UQCRB is a critical player in hypoxia- or VEGF-induced angiogenesis via mROS-mediated signaling [32]. Further validation and application of UQCRB in angiogenesis Recent studies have highlighted the presence of various genetic variations of UQCRB in several cancers including hepatocellular carcinoma [26], ovarian [66], pancreatic ductal adenocarcinoma [18], and colorectal [42]. Notably, the hereditary defect of the UQCRB gene was identified in a Turkish girl with hypoglycemia and lactic acidosis [22]. To elucidate the pathological role of UQCRB, its mutant stable cell lines were recently established according to a human case report [7]. Interestingly, these cell lines exhibited glycolytic and pro-angiogenic activities via mROS-mediated HIF-1α signal transduction. In addition, the proliferative effect of the UQCRB mutant was significantly regulated by terpestacin. Therefore, it is conceivable that inhibition of mROS by terpestacin could affect cell growth. Accordingly, these data demonstrate a molecular basis for UQCRB-mediated biological processes and reveal the pathophysiological link between mitochondrial abnormalities caused by mutations in UQCRB and angiogenesis- or mitochondria-related diseases. Moreover, these findings can provide new options for correcting the pathological effects of UQCRB mutations using UQCRB inhibitors. The UQCRB overexpression experiments demonstrated its pro-angiogenic activity. However, the effect of UQCRB replenishment by direct delivery remains unknown. Therefore, a protein transduction domain (PTD)-conjugated UQCRB fusion protein was newly generated to verify the potential role of UQCRB as a pro-angiogenic factor [8]. The cell permeable PTD-UQCRB fusion protein specifically localized to the mitochondria, where endogenous UQCRB protein exists. Treatment with PTD-UQCRB increased mROS generation without cytotoxicity following HIF-1α stabilization and VEGF expression. Consequently, PTD-UQCRB potently induced angiogenesis in in vitro and in vivo matrigel plug assays. Moreover, PTD-UQCRB facilitated cutaneous wound healing in a mouse model. Accordingly, this study clearly verifies the biological role of UQCRB in angiogenesis and for the first time, provides evidence that an intracellular mitochondrial protein can be used as an activator of angiogenesis. Discovery of new anti-angiogenesis inhibitors regulating UQCRB In recent drug discovery processes, many new chemical entities have been derived from natural substances. In addition, the biologically validated scaffolds of natural products can serve as structural starting points for the development of synthetic small molecules with enhanced chemical properties, as well as biological activities [21, 64]. Hence, the acquisition of novel candidate compounds inspired by terpestacin and UQCRB is a promising approach for the discovery of novel angiogenesis inhibitors. UQCRB has proved to be a promising therapeutic target for anti-angiogenic drug development and, therefore, efforts to discover new small molecules that can specifically modulate its function are escalating. Indeed, 6-((1-hydroxynaphthalen-4-ylamino)dioxysulfone)-2H-naphtho[1,8-bc]thiophen-2-one (HDNT), a novel synthetic small molecule targeting UQCRB, was isolated from the smart chemical library constructed using a pharmacophore-based virtual screening with structural information on the binding mode of terpestacin and UQCRB [30]. Subsequent biological assays demonstrated the potent anti-angiogenic activity of HDNT mediated by the suppression of mROS-induced hypoxic signal transduction following binding to the hydrophobic pocket of UQCRB. Furthermore, HDNT was used as a viable lead compound, and its pharmacological properties were improved for medical application. This resulted in the development of a series of HDNT derivatives with a sulfonylamide backbone. Several derivatives exhibited potent inhibition of angiogenesis without cytotoxicity. Moreover, a salt form of the most prominent derivative showed significant anti-tumor activity with increased aqueous solubility in a glioblastoma mouse xenograft model [29]. Collectively, these findings imply that the new class of UQCRB regulators inspired from the binding mode of terpestacin and UQCRB could be applied as new therapeutic drugs targeting angiogenesis. Conclusions Natural products have been an invaluable source of drug discovery and development, especially because of their structural diversity. In addition, their wide range of pharmacophores and biologically pre-validated structures in chemical space have been a valuable tool as well [4]. Nevertheless, the presence of natural products in the drug discovery industry has declined owing to several reasons. For example, there is a lack of mechanistic understanding of their mode of action and the processes for their synthesis are often uneconomical. However, natural product screening has been revisited by virtue of the development of new technologies and approaches in the post-genomic era [21]. Phenotypic screening has emerged as a complementary approach to the discovery of first-in-class drugs rather than target-based screening [48, 61]. Phenotypic screening has advantages including the fact that small bioactive molecules can be identified without preconceived molecular mechanisms or chemical entities. This enables the expansion of the compounds available as leads for new drug discovery. The target identification and elucidation of selected hit compounds from phenotypic screening are still fraught with obstacles and challenges. However, the recent development of efficient target identification and validation approaches makes phenotypic screening still attractive [20]. In this review, we highlighted three case studies of natural small molecules obtained by phenotypic screening and deconvolution of their molecular mechanisms using target identification. Firstly, a new inhibitor of filopodial protrusion, GPA was isolated by natural product screening [38]. The indirect target identification approach involving, in particular, CE-TOFMS-based metabolomics technologies was applied to GPA following chemical genomic screening. As a result, the glucose transporter GLUT1 was identified as a functional target of GPA, responsible for its bioactivity against ATP-dependent filopodial protrusion, in combination with PA. Accordingly, GPA can be used as a glucose transporter chemical probe. Most importantly, this case was the first report of the identification of natural product using metabolomics. Secondly, a new potent and selective anti-TB agent, ecumicin was identified from a whole cell-based high-throughput screening of actinomycetes extracts against M. tuberculosis [14]. A whole-genome sequencing of spontaneous ecumicin-resistant M. tuberculosis strains, followed by DARTS analysis, confirmed ClpC1 ATPase complex as the biologically relevant target of ecumicin. Accordingly, the cytotoxic effect of ecumicin against M. tuberculosis was revealed, which is induced by the uncoupling of ClpC1-mediated ATP hydrolysis from ClpP1P2 proteolysis, thereby inhibiting cellular protein degradation. Taken together, ClpC1 has emerged as a druggable target in M. tuberculosis. Moreover, the potential of ecumicin as a drug lead for anti-TB drug development has been demonstrated. Lastly, a potent angiogenesis inhibitor, terpestacin was also isolated by phenotypic screening of microbial extracts against EC invasion and tube formation [33]. The direct binding target protein of terpestacin was identified as UQCRB using several approaches such as reverse chemical proteomics, biophysical analysis, and transcriptome profiling [34]. Terpestacin is the first small molecule targeting the UQCRB of mitochondrial complex III. Many reports have demonstrated the involvement of various mitochondrial proteins in angiogenesis-related diseases such as cancers and metabolic diseases. However, information on the relationship between UQCRB and angiogenesis has been limited prior to the target identification and deconvolution of terpestacin. Recently, UQCRB has emerged as a new therapeutic target for angiogenesis. Therefore, in an effort to discover novel candidate compounds regulating UQCRB, new synthetic UQCRB modulators were identified as promising anti-angiogenic leads. Collectively, as shown in these recent cases, a combination of phenotypic screening and the target identification methods from multi-omics-based technologies has provided new gateways for discovering unique natural products as chemical probes and therapeutic leads. In addition, their target proteins can be used to explore new biological possibilities for developing novel therapeutics (Fig. 2). Fig. 2 Open in new tabDownload slide Schematic summary of the review. The unbiased phenotypic screening of natural products can provide a number of unique bioactive small molecules. Target identification of these bioactive natural products with omics-based methods including chemical genomics, proteomics, and metabolomics uncovers new therapeutic target genes or protein candidates. This enables the deconvolution of the mode of action of the natural product and functional annotation of the target proteins in specific biological systems. Based on the newly identified structural and biological information on bioactive natural products, new synthetic small molecules can be discovered. Collectively, this approach will raise the availability of natural products for therapeutic applications Acknowledgments This work was partly supported by grants from the National Research Foundation of Korea funded by the Korean Government (MSIP, 2010-0017984 and 2012M3A9D1054520), the Translational Research Center for Protein Function Control, NRF (2009-0083522), the Ministry of Health and Welfare (0620360-1), and the Brain Korea 21 Plus Project, Republic of Korea. References 1. Bacon C , Lakics V, Machesky L, Rumsby M N-WASP regulates extension of filopodia and processes by oligodendrocyte progenitors, oligodendrocytes, and Schwann cells-implications for axon ensheathment at myelination Glia 2007 55 844 858 10.1002/glia.20505 Google Scholar Crossref Search ADS PubMed WorldCat 2. Brotz-Oesterhelt H , Beyer D, Kroll HP, Endermann R, Ladel C, Schroeder W, Hinzen B, Raddatz S, Paulsen H, Henninger K, Bandow JE, Sahl HG, Labischinski H Dysregulation of bacterial proteolytic machinery by a new class of antibiotics Nat Med 2005 11 1082 1087 10.1038/nm1306 Google Scholar Crossref Search ADS PubMed WorldCat 3. Butler MS The role of natural product chemistry in drug discovery J Nat Prod 2004 67 2141 2153 10.1021/np040106y Google Scholar Crossref Search ADS PubMed WorldCat 4. Carlson EE Natural products as chemical probes ACS Chem Biol 2010 5 639 653 2926141 10.1021/cb100105c Google Scholar Crossref Search ADS PubMed WorldCat 5. Carmeliet P , Jain RK Molecular mechanisms and clinical applications of angiogenesis Nature 2011 473 298 307 4049445 10.1038/nature10144 Google Scholar Crossref Search ADS PubMed WorldCat 6. Chaisson RE , Nuermberger EL Confronting multidrug-resistant tuberculosis New Engl J Med 2012 366 2223 2224 10.1056/NEJMe1204478 Google Scholar Crossref Search ADS PubMed WorldCat 7. Chang J , Jung HJ, Jeong SH, Kim HK, Han J, Kwon HJ A mutation in the mitochondrial protein UQCRB promotes angiogenesis through the generation of mitochondrial reactive oxygen species Biochem Biophys Res Commun 2014 455 290 297 10.1016/j.bbrc.2014.11.005 Google Scholar Crossref Search ADS PubMed WorldCat 8. Chang J , Jung HJ, Park HJ, Cho SW, Lee SK, Kwon HJ Cell-permeable mitochondrial ubiquinol-cytochrome c reductase binding protein induces angiogenesis in vitro and in vivo Cancer Lett 2015 366 52 60 10.1016/j.canlet.2015.06.013 Google Scholar Crossref Search ADS PubMed WorldCat 9. Chin RM , Fu X, Pai MY, Vergnes L, Hwang H, Deng G, Diep S, Lomenick B, Meli VS, Monsalve GC, Hu E, Whelan SA, Wang JX, Jung G, Solis GM, Fazlollahi F, Kaweeteerawat C, Quach A, Nili M, Krall AS, Godwin HA, Chang HR, Faull KF, Guo F, Jiang M, Trauger SA, Saghatelian A, Braas D, Christofk HR, Clarke CF, Teitell MA, Petrascheck M, Reue K, Jung ME, Frand AR, Huang J The metabolite alpha-ketoglutarate extends lifespan by inhibiting ATP synthase and TOR Nature 2014 510 397 401 4263271 Google Scholar Crossref Search ADS PubMed WorldCat 10. Cho YS , Jung HJ, Seok SH, Payumo AY, Chen JK, Kwon HJ Functional inhibition of UQCRB suppresses angiogenesis in zebrafish Biochem Biophys Res Commun 2013 433 396 400 3691074 10.1016/j.bbrc.2013.02.082 Google Scholar Crossref Search ADS PubMed WorldCat 11. Feling RH , Buchanan GO, Mincer TJ, Kauffman CA, Jensen PR, Fenical W Salinosporamide A: a highly cytotoxic proteasome inhibitor from a novel microbial source, a marine bacterium of the new genus salinospora Angew Chem Int Ed Engl 2003 42 355 357 10.1002/anie.200390115 Google Scholar Crossref Search ADS PubMed WorldCat 12. Ferrara N , Kerbel RS Angiogenesis as a therapeutic target Nature 2005 438 967 974 10.1038/nature04483 Google Scholar Crossref Search ADS PubMed WorldCat 13. Folkman J Angiogenesis: an organizing principle for drug discovery? Nat Rev Drug Discov 2007 6 273 286 10.1038/nrd2115 Google Scholar Crossref Search ADS PubMed WorldCat 14. Gao W , Kim JY, Anderson JR, Akopian T, Hong S, Jin YY, Kandror O, Kim JW, Lee IA, Lee SY, McAlpine JB, Mulugeta S, Sunoqrot S, Wang Y, Yang SH, Yoon TM, Goldberg AL, Pauli GF, Suh JW, Franzblau SG, Cho S The cyclic peptide ecumicin targeting ClpC1 is active against Mycobacterium tuberculosis in vivo Antimicrob Agents Chemother 2015 59 880 889 4335914 10.1128/AAC.04054-14 Google Scholar Crossref Search ADS PubMed WorldCat 15. Gao W , Kim JY, Chen SN, Cho SH, Choi J, Jaki BU, Jin YY, Lankin DC, Lee JE, Lee SY, McAlpine JB, Napolitano JG, Franzblau SG, Suh JW, Pauli GF Discovery and characterization of the tuberculosis drug lead ecumicin Org Lett 2014 16 6044 6047 10.1021/ol5026603 Google Scholar Crossref Search ADS PubMed WorldCat 16. Gutman M , Singer TP, Beinert H, Casida JE Reaction sites of rotenone, piericidin A, and amytal in relation to the nonheme iron components of NADH dehydrogenase Proc Natl Acad Sci USA 1970 65 763 770 282972 10.1073/pnas.65.3.763 Google Scholar Crossref Search ADS PubMed WorldCat 17. Hall C , Wu M, Crane FL, Takahashi H, Tamura S, Folkers K Piericidin A: a new inhibitor of mitochondrial electron transport Biochem Biophys Res Commun 1966 25 373 377 10.1016/0006-291X(66)90214-2 Google Scholar Crossref Search ADS PubMed WorldCat 18. Harada T , Chelala C, Crnogorac-Jurcevic T, Lemoine NR Genome-wide analysis of pancreatic cancer using microarray-based techniques Pancreatology 2009 9 13 24 10.1159/000178871 Google Scholar Crossref Search ADS PubMed WorldCat 19. Harding MW , Galat A, Uehling DE, Schreiber SL A receptor for the immunosuppressant FK506 is a cis-trans peptidyl-prolyl isomerase Nature 1989 341 758 760 10.1038/341758a0 Google Scholar Crossref Search ADS PubMed WorldCat 20. Hart CP Finding the target after screening the phenotype Drug Discov Today 2005 10 513 519 10.1016/S1359-6446(05)03415-X Google Scholar Crossref Search ADS PubMed WorldCat 21. Harvey AL , Edrada-Ebel R, Quinn RJ The re-emergence of natural products for drug discovery in the genomics era Nat Rev Drug Discov 2015 14 111 129 10.1038/nrd4510 Google Scholar Crossref Search ADS PubMed WorldCat 22. Haut S , Brivet M, Touati G, Rustin P, Lebon S, Garcia-Cazorla A, Saudubray JM, Boutron A, Legrand A, Slama A A deletion in the human QP-C gene causes a complex III deficiency resulting in hypoglycaemia and lactic acidosis Hum Genet 2003 113 118 122 Google Scholar Crossref Search ADS PubMed WorldCat 23. Hirayama A , Kami K, Sugimoto M, Sugawara M, Toki N, Onozuka H, Kinoshita T, Saito N, Ochiai A, Tomita M, Esumi H, Soga T Quantitative metabolome profiling of colon and stomach cancer microenvironment by capillary electrophoresis time-of-flight mass spectrometry Cancer Res 2009 69 4918 4925 10.1158/0008-5472.CAN-08-4806 Google Scholar Crossref Search ADS PubMed WorldCat 24. Ingber D , Fujita T, Kishimoto S, Sudo K, Kanamaru T, Brem H, Folkman J Synthetic analogues of fumagillin that inhibit angiogenesis and suppress tumour growth Nature 1990 348 555 557 10.1038/348555a0 Google Scholar Crossref Search ADS PubMed WorldCat 25. Itazaki H , Nagashima K, Sugita K, Yoshida H, Kawamura Y, Yasuda Y, Matsumoto K, Ishii K, Uotani N, Nakai Het al. Isolation and structural elucidation of new cyclotetrapeptides, trapoxins A and B, having detransformation activities as antitumor agents J Antibiot (Tokyo) 1990 43 1524 1532 10.7164/antibiotics.43.1524 Google Scholar Crossref Search ADS PubMed WorldCat 26. Jia HL , Ye QH, Qin LX, Budhu A, Forgues M, Chen Y, Liu YK, Sun HC, Wang L, Lu HZ, Shen F, Tang ZY, Wang XW Gene expression profiling reveals potential biomarkers of human hepatocellular carcinoma Clin Cancer Res 2007 13 1133 1139 10.1158/1078-0432.CCR-06-1025 Google Scholar Crossref Search ADS PubMed WorldCat 27. Jin Y , Yu J, Yu YG Identification of hNopp140 as a binding partner for doxorubicin with a phage display cloning method Chem Biol 2002 9 157 162 10.1016/S1074-5521(02)00096-0 Google Scholar Crossref Search ADS PubMed WorldCat 28. Johnson R , Streicher EM, Louw GE, Warren RM, van Helden PD, Victor TC Drug resistance in Mycobacterium tuberculosis Curr Issues Mol Biol 2006 8 97 111 Google Scholar PubMed OpenURL Placeholder Text WorldCat 29. Jung HJ , Cho M, Kim Y, Han G, Kwon HJ Development of a novel class of mitochondrial ubiquinol-cytochrome c reductase binding protein (UQCRB) modulators as promising antiangiogenic leads J Med Chem 2014 57 7990 7998 10.1021/jm500863j Google Scholar Crossref Search ADS PubMed WorldCat 30. Jung HJ , Kim KH, Kim ND, Han G, Kwon HJ Identification of a novel small molecule targeting UQCRB of mitochondrial complex III and its anti-angiogenic activity Bioorganic Med Chem Lett 2011 21 1052 1056 10.1016/j.bmcl.2010.12.002 Google Scholar Crossref Search ADS WorldCat 31. Jung HJ , Kim Y, Chang J, Kang SW, Kim JH, Kwon HJ Mitochondrial UQCRB regulates VEGFR2 signaling in endothelial cells J Mol Med 2013 91 1117 1128 10.1007/s00109-013-1049-6 Google Scholar Crossref Search ADS PubMed WorldCat 32. Jung HJ , Kwon HJ Exploring the role of mitochondrial UQCRB in angiogenesis using small molecules Mol BioSyst 2013 9 930 939 10.1039/c3mb25426g Google Scholar Crossref Search ADS PubMed WorldCat 33. Jung HJ , Lee HB, Kim CJ, Rho JR, Shin J, Kwon HJ Anti-angiogenic activity of terpestacin, a bicyclo sesterterpene from Embellisia chlamydospora J Antibiot (Tokyo) 2003 56 492 496 10.7164/antibiotics.56.492 Google Scholar Crossref Search ADS PubMed WorldCat 34. Jung HJ , Shim JS, Lee J, Song YM, Park KC, Choi SH, Kim ND, Yoon JH, Mungai PT, Schumacker PT, Kwon HJ Terpestacin inhibits tumor angiogenesis by targeting UQCRB of mitochondrial complex III and suppressing hypoxia-induced reactive oxygen species production and cellular oxygen sensing J Biol Chem 2010 285 11584 11595 2857036 10.1074/jbc.M109.087809 Google Scholar Crossref Search ADS PubMed WorldCat 35. Kijima M , Yoshida M, Sugita K, Horinouchi S, Beppu T Trapoxin, an antitumor cyclic tetrapeptide, is an irreversible inhibitor of mammalian histone deacetylase J Biol Chem 1993 268 22429 22435 Google Scholar Crossref Search ADS PubMed WorldCat 36. Kino T , Hatanaka H, Hashimoto M, Nishiyama M, Goto T, Okuhara M, Kohsaka M, Aoki H, Imanaka H FK-506, a novel immunosuppressant isolated from a Streptomyces. I. Fermentation, isolation, and physico-chemical and biological characteristics J Antibiot (Tokyo) 1987 40 1249 1255 10.7164/antibiotics.40.1249 Google Scholar Crossref Search ADS PubMed WorldCat 37. Kino T , Hatanaka H, Miyata S, Inamura N, Nishiyama M, Yajima T, Goto T, Okuhara M, Kohsaka M, Aoki Het al. FK-506, a novel immunosuppressant isolated from a Streptomyces. II. Immunosuppressive effect of FK-506 in vitro J Antibiot (Tokyo) 1987 40 1256 1265 10.7164/antibiotics.40.1256 Google Scholar Crossref Search ADS PubMed WorldCat 38. Kitagawa M , Ikeda S, Tashiro E, Soga T, Imoto M Metabolomic identification of the target of the filopodia protrusion inhibitor glucopiericidin A Chem Biol 2010 17 989 998 10.1016/j.chembiol.2010.06.017 Google Scholar Crossref Search ADS PubMed WorldCat 39. Kume S , Yamato M, Tamura Y, Jin G, Nakano M, Miyashige Y, Eguchi A, Ogata Y, Goda N, Iwai K, Yamano E, Watanabe Y, Soga T, Kataoka Y Potential biomarkers of fatigue identified by plasma metabolome analysis in rats PLoS One 2015 10 e0120106 4368560 10.1371/journal.pone.0120106 Google Scholar Crossref Search ADS PubMed WorldCat 40. Kwon HJ , Owa T, Hassig CA, Shimada J, Schreiber SL Depudecin induces morphological reversion of transformed fibroblasts via the inhibition of histone deacetylase Proc Natl Acad Sci USA 1998 95 3356 3361 19839 10.1073/pnas.95.7.3356 Google Scholar Crossref Search ADS PubMed WorldCat 41. Lai K , Selinger DW, Solomon JM, Wu H, Schmitt E, Serluca FC, Curtis D, Benson JD Integrated compound profiling screens identify the mitochondrial electron transport chain as the molecular target of the natural products manassantin, sesquicillin, and arctigenin ACS Chem Biol 2013 8 257 267 10.1021/cb300495e Google Scholar Crossref Search ADS PubMed WorldCat 42. Lascorz J , Bevier M, Schonfels WV, Kalthoff H, Aselmann H, Beckmann J, Egberts J, Buch S, Becker T, Schreiber S, Hampe J, Hemminki K, Forsti A, Schafmayer C Polymorphisms in the mitochondrial oxidative phosphorylation chain genes as prognostic markers for colorectal cancer BMC Med Genet 2012 13 31 3420261 10.1186/1471-2350-13-31 Google Scholar Crossref Search ADS PubMed WorldCat 43. Lomenick B , Hao R, Jonai N, Chin RM, Aghajan M, Warburton S, Wang J, Wu RP, Gomez F, Loo JA, Wohlschlegel JA, Vondriska TM, Pelletier J, Herschman HR, Clardy J, Clarke CF, Huang J Target identification using drug affinity responsive target stability (DARTS) Proc Natl Acad Sci USA 2009 106 21984 21989 2789755 10.1073/pnas.0910040106 Google Scholar Crossref Search ADS PubMed WorldCat 44. Lomenick B , Jung G, Wohlschlegel JA, Huang J Target identification using drug affinity responsive target stability (DARTS) Curr Protoc Chem Biol 2011 3 163 180 3251962 Google Scholar Crossref Search ADS PubMed WorldCat 45. Low WK , Dang Y, Schneider-Poetsch T, Shi Z, Choi NS, Merrick WC, Romo D, Liu JO Inhibition of eukaryotic translation initiation by the marine natural product pateamine A Mol Cell 2005 20 709 722 10.1016/j.molcel.2005.10.008 Google Scholar Crossref Search ADS PubMed WorldCat 46. Matsumoto M , Mogi K, Nagaoka K, Ishizeki S, Kawahara R, Nakashima T New piericidin glucosides, glucopiericidins A and B J Antibiot (Tokyo) 1987 40 149 156 10.7164/antibiotics.40.149 Google Scholar Crossref Search ADS PubMed WorldCat 47. Mattila PK , Lappalainen P Filopodia: molecular architecture and cellular functions Nat Rev Mol Cell Biol 2008 9 446 454 10.1038/nrm2406 Google Scholar Crossref Search ADS PubMed WorldCat 48. Moffat JG , Rudolph J, Bailey D Phenotypic screening in cancer drug discovery—past, present and future Nat Rev Drug Discov 2014 13 588 602 10.1038/nrd4366 Google Scholar Crossref Search ADS PubMed WorldCat 49. Nakajima H , Kim YB, Terano H, Yoshida M, Horinouchi S FR901228, a potent antitumor antibiotic, is a novel histone deacetylase inhibitor Exp Cell Res 1998 241 126 133 10.1006/excr.1998.4027 Google Scholar Crossref Search ADS PubMed WorldCat 50. Newman DJ , Cragg GM Natural products as sources of new drugs over the last 25 years J Nat Prod 2007 70 461 477 10.1021/np068054v Google Scholar Crossref Search ADS PubMed WorldCat 51. Ohka F , Ito M, Ranjit M, Senga T, Motomura A, Motomura K, Saito K, Kato K, Kato Y, Wakabayashi T, Soga T, Natsume A Quantitative metabolome analysis profiles activation of glutaminolysis in glioma with IDH1 mutation Tumour Biol 2014 35 5911 5920 10.1007/s13277-014-1784-5 Google Scholar Crossref Search ADS PubMed WorldCat 52. Oka M , Iimura S, Tenmyo O, Sawada Y, Sugawara M, Ohkusa N, Yamamoto H, Kawano K, Hu SL, Fukagawa Yet al. Terpestacin, a new syncytium formation inhibitor from Arthrinium sp J Antibiot (Tokyo) 1993 46 367 373 10.7164/antibiotics.46.367 Google Scholar Crossref Search ADS PubMed WorldCat 53. Papetti M , Herman IM Mechanisms of normal and tumor-derived angiogenesis Am J Physiol Cell Physiol 2002 282 C947 C970 10.1152/ajpcell.00389.2001 Google Scholar Crossref Search ADS PubMed WorldCat 54. Piggott AM , Karuso P Rapid identification of a protein binding partner for the marine natural product kahalalide F by using reverse chemical proteomics Chem Bio Chem 2008 9 524 530 10.1002/cbic.200700608 Google Scholar Crossref Search ADS PubMed WorldCat 55. Ralser M , Wamelink MM, Struys EA, Joppich C, Krobitsch S, Jakobs C, Lehrach H A catabolic block does not sufficiently explain how 2-deoxy-d-glucose inhibits cell growth Proc Natl Acad Sci USA 2008 105 17807 17811 2584745 10.1073/pnas.0803090105 Google Scholar Crossref Search ADS PubMed WorldCat 56. Sche PP , McKenzie KM, White JD, Austin DJ Display cloning: functional identification of natural product receptors using cDNA-phage display Chem Biol 1999 6 707 716 10.1016/S1074-5521(00)80018-6 Google Scholar Crossref Search ADS PubMed WorldCat 57. Shim JS , Lee J, Park HJ, Park SJ, Kwon HJ A new curcumin derivative, HBC, interferes with the cell cycle progression of colon cancer cells via antagonization of the Ca2+/calmodulin function Chem Biol 2004 11 1455 1463 10.1016/j.chembiol.2004.08.015 Google Scholar Crossref Search ADS PubMed WorldCat 58. Sin N , Meng L, Wang MQ, Wen JJ, Bornmann WG, Crews CM The anti-angiogenic agent fumagillin covalently binds and inhibits the methionine aminopeptidase, MetAP-2 Proc Natl Acad Sci USA 1997 94 6099 6103 21008 10.1073/pnas.94.12.6099 Google Scholar Crossref Search ADS PubMed WorldCat 59. Sugita K , Yoshida H, Matsumoto M, Matsutani S A novel compound, depudecin, induces production of transformation to the flat phenotype of NIH3T3 cells transformed by ras-oncogene Biochem Biophys Res Commun 1992 182 379 387 10.1016/S0006-291X(05)80156-1 Google Scholar Crossref Search ADS PubMed WorldCat 60. Suzuki H , Hosokawa Y, Toda H, Nishikimi M, Ozawa T Cloning and sequencing of a cDNA for human mitochondrial ubiquinone-binding protein of complex III Biochem Biophys Res Commun 1988 156 987 994 10.1016/S0006-291X(88)80941-0 Google Scholar Crossref Search ADS PubMed WorldCat 61. Swinney DC , Anthony J How were new medicines discovered? Nat Rev Drug Discov 2011 10 507 519 10.1038/nrd3480 Google Scholar Crossref Search ADS PubMed WorldCat 62. Tomioka H , Namba K Development of antituberculous drugs: current status and future prospects Kekkaku 2006 81 753 774 Google Scholar PubMed OpenURL Placeholder Text WorldCat 63. Ueda H , Nakajima H, Hori Y, Fujita T, Nishimura M, Goto T, Okuhara M FR901228, a novel antitumor bicyclic depsipeptide produced by Chromobacterium violaceum no. 968. I. Taxonomy, fermentation, isolation, physico-chemical and biological properties, and antitumor activity J Antibiot (Tokyo) 1994 47 301 310 10.7164/antibiotics.47.301 Google Scholar Crossref Search ADS PubMed WorldCat 64. van Hattum H , Waldmann H Biology-oriented synthesis: harnessing the power of evolution J Am Chem Soc 2014 136 11853 11859 10.1021/ja505861d Google Scholar Crossref Search ADS PubMed WorldCat 65. Weis SM , Cheresh DA Tumor angiogenesis: molecular pathways and therapeutic targets Nat Med 2011 17 1359 1370 10.1038/nm.2537 Google Scholar Crossref Search ADS PubMed WorldCat 66. Wrzeszczynski KO , Varadan V, Byrnes J, Lum E, Kamalakaran S, Levine DA, Dimitrova N, Zhang MQ, Lucito R Identification of tumor suppressors and oncogenes from genomic and epigenetic features in ovarian cancer PLoS One 2011 6 e28503 3234280 10.1371/journal.pone.0028503 Google Scholar Crossref Search ADS PubMed WorldCat 67. Xu M , Liu K, Swaroop M, Porter FD, Sidhu R, Firnkes S, Ory DS, Marugan JJ, Xiao J, Southall N, Pavan WJ, Davidson C, Walkley SU, Remaley AT, Baxa U, Sun W, McKew JC, Austin CP, Zheng W Delta-Tocopherol reduces lipid accumulation in Niemann–Pick type C1 and Wolman cholesterol storage disorders J Biol Chem 2012 287 39349 39360 3501083 10.1074/jbc.M112.357707 Google Scholar Crossref Search ADS PubMed WorldCat 68. Yoshida M , Beppu T Reversible arrest of proliferation of rat 3Y1 fibroblasts in both the G1 and G2 phases by trichostatin A Exp Cell Res 1988 177 122 131 10.1016/0014-4827(88)90030-4 Google Scholar Crossref Search ADS PubMed WorldCat 69. Zheng W , Thorne N, McKew JC Phenotypic screens as a renewed approach for drug discovery Drug Discov Today 2013 18 1067 1073 4531371 10.1016/j.drudis.2013.07.001 Google Scholar Crossref Search ADS PubMed WorldCat © Society for Industrial Microbiology 2016 This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model) © Society for Industrial Microbiology 2016
TI - Discovery of novel drug targets and their functions using phenotypic screening of natural products
JF - Journal of Industrial Microbiology and Biotechnology
DO - 10.1007/s10295-015-1681-y
DA - 2016-03-01
UR - https://www.deepdyve.com/lp/oxford-university-press/discovery-of-novel-drug-targets-and-their-functions-using-phenotypic-w8cdJWEdh6
SP - 221
EP - 231
VL - 43
IS - 2-3
DP - DeepDyve
ER -