Plakevulin A induces apoptosis and suppresses IL-6-induced STAT3 activation in HL60 cells.

(+)-Plakevulin A (1), an oxylipin isolated from an Okinawan sponge Plakortis sp. inhibits enzymatic inhibition of DNA polymerases (pols) α and δ and exhibits cytotoxicity against murine leukemia (L1210) and human cervix carcinoma (KB) cell lines. However, the half-maximal inhibitory concentration (IC50) value for cytotoxicity significantly differed from those observed for the enzymatic inhibition of pols α and ß, indicating the presence of target protein(s) other than pols. This study demonstrated cytotoxicity against human promyelocytic leukemia (HL60), human cervix epithelioid carcinoma (HeLa), mouse calvaria-derived pre-osteoblast (MC3T3-E1), and human normal lung fibroblast (MRC-5) cell lines. This compound had selectivity to cancer cells over normal ones. Among these cell lines, HL60 exhibited the highest sensitivity to (+)-plakevulin A. (+)-Plakevulin A induced DNA fragmentation and caspase-3 activation in HL60 cells, indicating its role in apoptosis induction. Additionally, hydroxysteroid 17-ß dehydrogenase 4 (HSD17B4) was isolated from the HL60 lysate as one of its binding proteins through pull-down experiments using its biotinylated derivative and neutravidin-coated beads. Moreover, (+)-plakevulin A suppressed the activation of interleukin 6 (IL-6)-induced signal transducer and activator of transcription 3 (STAT3). Because the knockdown or inhibition of STAT3 induces apoptosis and HSD17B4 regulates STAT3 activation, (+)-plakevulin A may induce apoptosis in HL60 cell lines by suppressing STAT3 activation, potentially by binding to HSD17B4. The present findings provide valuable information for the mechanism of its action.

Synthesis of 3-octadecanoxypropyl 6-deoxy-6-sulfo-α-d-glucopyranoside (ODSG) as a lipase-resistant SQAP derivative.

Sulfoquynovosylacyl propanediol (SQAP; 1) has been developed as a radiosensitizer (anti-cancer agent) for solid tumors, but it was easily cleaved in vivo and had a problem of short residence time. We synthesized a novel compound of a SQAP derivative (3-octadecanoxypropyl 6-deoxy-6-sulfo-α-d-glucopyranoside: ODSG; 2) to solve these problems not easily cleaved by lipase. ODSG (2) cytotoxicity was investigated in vitro, resulting in low toxicity like SQAP (1).

Epo-C12 inhibits peroxiredoxin 1 peroxidase activity.

Epo-C12 is a synthetic derivative of epolactaene, isolated from Penicillium sp. BM 1689-P. Epo-C12 induces apoptosis in human acute lymphoblastoid leukemia BALL-1 cells. In our previous studies, seven proteins that bind to Epo-C12 were identified by a combination of pull-down experiments using biotinylated Epo-C12 (Bio-Epo-C12) and mass spectrometry. In the present study, the effect of Epo-C12 on peroxiredoxin 1 (Prx 1), one of the proteins that binds to Epo-C12, was investigated. Epo-C12 inhibited Prx 1 peroxidase activity. However, it did not suppress its chaperone activity. Binding experiments between Bio-Epo-C12 and point-mutated Prx 1s suggest that Epo-C12 binds to Cys52 and Cys83 in Prx 1. The present study revealed that Prx 1 is one of the target proteins through which Epo-C12 exerts an apoptotic effect in BALL-1 cells.

SQAP, an acyl sulfoquinovosyl derivative, suppresses expression of histone deacetylase and induces cell death of cancer cells under hypoxic conditions.

Sulfoglycolipid, SQAP, is a radiosensitizing agent that makes tumor cells more sensitive to radiation therapy. A previous study revealed that SQAP induced the degradation of hypoxia-inducible factor-1α (HIF-1α) and inhibited angiogenesis in a hepatoma model mouse. Herein, we examined the biological activities of SQAP against hepatocarcinoma cells under low oxygen conditions. Cell growth inhibition of SQAP under hypoxic conditions was significantly higher than that under normoxic conditions. In addition, SQAP was found to impair the expression of histone deacetylase (HDAC) under low oxygen conditions. Our present data suggested that SQAP induced the degradation of HIF-1α and then decreased the expression of HDAC1. Unlike known HDAC inhibitors, SQAP increased the acetylation level of histone in cells without inhibition of enzymatic activity of HDACs. Our data demonstrated hypoxia-specific unique properties of SQAP.

Identification, characterization, and structural analyses of a fungal endo-ß-1,2-glucanase reveal a new glycoside hydrolase family.

endo-ß-1,2-Glucanase (SGL) is an enzyme that hydrolyzes ß-1,2-glucans, which play important physiological roles in some bacteria as a cyclic form. To date, no eukaryotic SGL has been identified. We purified an SGL from Talaromyces funiculosus (TfSGL), a soil fungus, to homogeneity and then cloned the complementary DNA encoding the enzyme. TfSGL shows no significant sequence similarity to any known glycoside hydrolase (GH) families, but shows significant similarity to certain eukaryotic proteins with unknown functions. The recombinant TfSGL (TfSGLr) specifically hydrolyzed linear and cyclic ß-1,2-glucans to sophorose (Glc-ß-1,2-Glc) as a main product. TfSGLr hydrolyzed reducing-end-modified ß-1,2-gluco-oligosaccharides to release a sophoroside with the modified moiety. These results indicate that TfSGL is an endo-type enzyme that preferably releases sophorose from the reducing end of substrates. Stereochemical analysis demonstrated that TfSGL is an inverting enzyme. The overall structure of TfSGLr includes an (α/α)6 toroid fold. The substrate-binding mode was revealed by the structure of a Michaelis complex of an inactive TfSGLr mutant with a ß-1,2-glucoheptasaccharide. Mutational analysis and action pattern analysis of ß-1,2-gluco-oligosaccharide derivatives revealed an unprecedented catalytic mechanism for substrate hydrolysis. Glu-262 (general acid) indirectly protonates the anomeric oxygen at subsite -1 via the 3-hydroxy group of the Glc moiety at subsite +2, and Asp-446 (general base) activates the nucleophilic water via another water. TfSGLr is apparently different from a GH144 SGL in the reaction and substrate recognition mechanism based on structural comparison. Overall, we propose that TfSGL and closely-related enzymes can be classified into a new family, GH162.

Synthesis of nucleotide analogues, EFdA, EdA and EdAP, and the effect of EdAP on hepatitis B virus replication.

4'-Ethynyl-2-fluoro-2'-deoxyadenosine (EFdA) and 4'-ethynyl-2'-deoxyadenosine (EdA) are nucleoside analogues which inhibit human immunodeficiency virus type 1 (HIV-1) reverse transcriptase. EdAP, a cyclosaligenyl (cycloSal) phosphate derivative of EdA, inhibits the replication of the influenza A virus. The common structural feature of these compounds is the ethynyl group at the 4'-position. In this study, these nucleoside analogues were prepared by a common synthetic strategy starting from the known 1,2-di-O-acetyl-D-ribofuranose. Biological evaluation of EdAP revealed that this compound reduced hepatitis B virus (HBV) replication dose-dependently without cytotoxicity against host cells tested in this study.

The aryl hydrocarbon receptor-cytochrome P450 1A1 pathway controls lipid accumulation and enhances the permissiveness for hepatitis C virus assembly.

Viruses hijack and modify host cell functions to maximize viral proliferation. Hepatitis C virus (HCV) reorganizes host cell metabolism to produce specialized membrane structures and to modify organelles such as double-membrane vesicles and enlarged lipid droplets (LDs), thereby enabling virus replication and assembly. However, the molecular bases of these host-HCV interactions are largely unknown. Here, using a chemical screen, we demonstrate that the benzamide derivative flutamide reduces the host capacity to produce infectious HCV. Flutamide disrupted the formation of enlarged LDs in HCV-infected cells, thereby abolishing HCV assembly. We also report that aryl hydrocarbon receptor (AhR), a known flutamide target, plays a key role in mediating LD accumulation and HCV production. This AhR function in lipid production was also observed in HCV-uninfected Huh-7 cells and primary human hepatocytes, suggesting that AhR signaling regulates lipid accumulation independently of HCV infection. We further observed that a downstream activity, that of cytochrome P450 1A1 (CYP1A1), was the primary regulator of AhR-mediated lipid production. Specifically, blockade of AhR-induced CYP1A1 up-regulation counteracted LD overproduction, and overproduction of CYP1A1, but not of CYP1B1, in AhR-inactivated cells restored lipid accumulation. Of note, HCV infection up-regulated the AhR-CYP1A1 pathway, resulting in the accumulation of enlarged LDs. In conclusion, we demonstrate that the AhR-CYP1A1 pathway has a significant role in lipid accumulation, a hallmark of HCV infection that maximizes progeny virus production. Our chemical-genetic analysis reveals a new strategy and lead compounds to control hepatic lipid accumulation as well as HCV infection.

Pyrenocine A induces monopolar spindle formation and suppresses proliferation of cancer cells.

Pyrenocine A, a phytotoxin, was found to exhibit cytotoxicity against cancer cells with an IC50 value of 2.6-12.9 µM. Live cell imaging analysis revealed that pyrenocine A arrested HeLa cells at the M phase with characteristic ring-shaped chromosomes. Furthermore, as a result of immunofluorescence staining analysis, we found that pyrenocine A resulted in the formation of monopolar spindles in HeLa cells. Monopolar spindles are known to be induced by inhibitors of the kinesin motor protein Eg5 such as monastrol and STLC. Monastrol and STLC induce monopolar spindle formation and M phase arrest via inhibition of the ATPase activity of Eg5. Interestingly, our data revealed that pyrenocine A had no effect on the ATPase activity of Eg5 in vitro, which suggested the compound induces a monopolar spindle by an unknown mechanism. Structure-activity relationship analysis indicates that the enone structure of pyrenocine A is likely to be important for its cytotoxicity. An alkyne-tagged analog of pyrenocine A was synthesized and suppressed proliferation of HeLa cells with an IC50 value of 2.3 µM. We concluded that pyrenocine A induced monopolar spindle formation by a novel mechanism other than direct inhibition of Eg5 motor activity, and the activity of pyrenocine A may suggest a new anticancer mechanism.

Distribution and metabolism of 14C-sulfoquinovosylacylpropanediol (14C-SQAP) after a single intravenous administration in tumor-bearing mice.

Sulfoquinovosylacylpropanediol (SQAP) is a novel potent radiosensitizer that inhibits angiogenesis in vivo and results in increased oxigenation and reduced tumor volume. We investigated the distribution, metabolism, and excretion of SQAP in male KSN-nude mice transplanted with a human pulmonary carcinoma, Lu65. For the metabolism analysis, a 2 mg (2.98 MBq)/kg of [glucose-U-14C]-SQAP (CP-3839) was intravenously injected. The injected SQAP was decomposed into a stearic acid and a sulfoquinovosylpropanediol (SQP) in the body. The degradation was relatively slow in the carcinoma tissue.1,3-propanediol[1-14C]-SQAP (CP-3635) was administered through intravenous injection of a 1 mg (3.48 MBq)/kg dose followed by whole body autoradiography of the mice. The autoradiography analysis demonstrated that SQAP rapidly distributed throughout the whole body and then quickly decreased within 4 hours except the tumor and excretion organs such as liver, kidney. Retention of SQAP was longer in tumor parts than in other tissues, as indicated by higher levels of radioactivity at 4 hours. The radioactivity around the tumor had also completely disappeared within 72 hours.

Design, Synthesis, and Biological Evaluation of EdAP, a 4'-Ethynyl-2'-Deoxyadenosine 5'-Monophosphate Analog, as a Potent Influenza a Inhibitor.

Influenza A viruses leading to infectious respiratory diseases cause seasonal epidemics and sometimes periodic global pandemics. Viral polymerase is an attractive target in inhibiting viral replication, and 4'-ethynyladenosine, which has been reported as a highly potent anti-human immunodeficiency virus (HIV) nucleoside derivative, can work as an anti-influenza agent. Herein, we designed and synthesized a 4'-ethynyl-2'-deoxyadenosine 5'-monophosphate analog called EdAP (5). EdAP exhibited potent inhibition against influenza virus multiplication in Madin-Darby canine kidney (MDCK) cells transfected with human α2-6-sialyltransferase (SIAT1) cDNA and did not show any toxicity toward the cells. Surprisingly, this DNA-type nucleic acid analog (5) inhibited the multiplication of influenza A virus, although influenza virus is an RNA virus that does not generate DNA.

Identification of proteins that bind to the neuroprotective agent neoechinulin A.

Neoechinulin A is an indole alkaloid with several biological activities. We previously reported that this compound protects neuronal PC12 cells from cytotoxicity induced by the peroxynitrite generator 3-morpholinosydnonimine (SIN-1), but the target proteins and precise mechanism of action of neoechinulin A were unclear. Here, we employed a phage display screen to identify proteins that bind directly with neoechinulin A. Our findings identified two proteins, chromogranin B and glutaredoxin 3, as candidate target binding partners for the alkaloid. QCM analyses revealed that neoechinulin A displays high affinity for both chromogranin B and glutaredoxin 3. RNA interference-mediated depletion of chromogranin B decreased the sensitivity of PC12 cells against SIN-1. Our results suggested chromogranin B is a plausible target of neoechinulin A.

Fungus-Derived Neoechinulin B as a Novel Antagonist of Liver X Receptor, Identified by Chemical Genetics Using a Hepatitis C Virus Cell Culture System.

UNLABELLED: Cell culture systems reproducing virus replication can serve as unique models for the discovery of novel bioactive molecules. Here, using a hepatitis C virus (HCV) cell culture system, we identified neoechinulin B (NeoB), a fungus-derived compound, as an inhibitor of the liver X receptor (LXR). NeoB was initially identified by chemical screening as a compound that impeded the production of infectious HCV. Genome-wide transcriptome analysis and reporter assays revealed that NeoB specifically inhibits LXR-mediated transcription. NeoB was also shown to interact directly with LXRs. Analysis of structural analogs suggested that the molecular interaction of NeoB with LXR correlated with the capacity to inactivate LXR-mediated transcription and to modulate lipid metabolism in hepatocytes. Our data strongly suggested that NeoB is a novel LXR antagonist. Analysis using NeoB as a bioprobe revealed that LXRs support HCV replication: LXR inactivation resulted in dispersion of double-membrane vesicles, putative viral replication sites. Indeed, cells treated with NeoB showed decreased replicative permissiveness for poliovirus, which also replicates in double-membrane vesicles, but not for dengue virus, which replicates via a distinct membrane compartment. Together, our data suggest that LXR-mediated transcription regulates the formation of virus-associated membrane compartments. Significantly, inhibition of LXRs by NeoB enhanced the activity of all known classes of anti-HCV agents, and NeoB showed especially strong synergy when combined with interferon or an HCV NS5A inhibitor. Thus, our chemical genetics analysis demonstrates the utility of the HCV cell culture system for identifying novel bioactive molecules and characterizing the virus-host interaction machinery. IMPORTANCE: Hepatitis C virus (HCV) is highly dependent on host factors for efficient replication. In the present study, we used an HCV cell culture system to screen an uncharacterized chemical library. Our results identified neoechinulin B (NeoB) as a novel inhibitor of the liver X receptor (LXR). NeoB inhibited the induction of LXR-regulated genes and altered lipid metabolism. Intriguingly, our results indicated that LXRs are critical to the process of HCV replication: LXR inactivation by NeoB disrupted double-membrane vesicles, putative sites of viral replication. Moreover, NeoB augmented the antiviral activity of all known classes of currently approved anti-HCV agents without increasing cytotoxicity. Thus, our strategy directly links the identification of novel bioactive compounds to basic virology and the development of new antiviral agents.

A Novel Tricyclic Polyketide, Vanitaracin A, Specifically Inhibits the Entry of Hepatitis B and D Viruses by Targeting Sodium Taurocholate Cotransporting Polypeptide.

UNLABELLED: Anti-hepatitis B virus (HBV) drugs are currently limited to nucleos(t)ide analogs (NAs) and interferons. A challenge of drug development is the identification of small molecules that suppress HBV infection from new chemical sources. Here, from a fungus-derived secondary metabolite library, we identify a structurally novel tricyclic polyketide, named vanitaracin A, which specifically inhibits HBV infection. Vanitaracin A inhibited the viral entry process with a submicromolar 50% inhibitory concentration (IC50) (IC50 = 0.61 ± 0.23 µM), without evident cytotoxicity (50% cytotoxic concentration of >256 µM; selectivity index value of >419) in primary human hepatocytes. Vanitaracin A did not affect the HBV replication process. This compound was found to directly interact with the HBV entry receptor sodium taurocholate cotransporting polypeptide (NTCP) and impaired its bile acid transport activity. Consistent with this NTCP targeting, antiviral activity of vanitaracin A was observed with hepatitis D virus (HDV) but not hepatitis C virus. Importantly, vanitaracin A inhibited infection by all HBV genotypes tested (genotypes A to D) and clinically relevant NA-resistant HBV isolate. Thus, we identified a fungal metabolite, vanitaracin A, which was a potent, well-tolerated, and broadly active inhibitor of HBV and HDV entry. This compound, or its related analogs, could be part of an antiviral strategy for preventing reinfection with HBV, including clinically relevant nucleos(t)ide analog-resistant virus. IMPORTANCE: For achieving better treatment and prevention of hepatitis B virus (HBV) infection, anti-HBV agents targeting a new molecule are in great demand. Although sodium taurocholate cotransporting polypeptide (NTCP) has recently been reported to be an essential host factor for HBV entry, there is a limited number of reports that identify new compounds targeting NTCP and inhibiting HBV entry. Here, from an uncharacterized chemical library, we isolated a structurally new compound, named vanitaracin A, which inhibited the process of entry of HBV and hepatitis D virus (HDV). This compound was suggested to directly interact with NTCP and inhibit its transporter activity. Importantly, vanitaracin A inhibited the entry of all HBV genotypes examined and of a clinically relevant nucleos(t)ide analog-resistant HBV isolate.

Anti-hepatitis C Virus Natural Product from a Fungus, Penicillium herquei.

New diazabicyclo[2.2.2]octane derivatives, peniciherquamides A-C (1-3), and a novel herqueinone derivative, neoherqueinone (5), were isolated from a fungal culture broth of Penicillium herquei. The structures of these novel compounds were determined by interpretation of spectroscopic data (1D/2D NMR, MS, and IR). Four known compounds, preparaherquamide (4), peniciherqueinone (6), and herqueinone/isoherqueinone (7/7a), were also obtained. The isolated compounds were tested for anti-hepatitis C virus (HCV) activity, and peniciherquamide C (3) was found to display an IC50 value of 5.1 µM. To our knowledge, this is the first report of a diazabicyclo[2.2.2]octane derivative with anti-HCV activity.

EpsinR, a target for pyrenocine B, role in endogenous MHC-II-restricted antigen presentation.

While the presentation mechanism of antigenic peptides derived from exogenous proteins by MHC class II molecules is well understood, relatively little is known about the presentation mechanism of endogenous MHC class II-restricted antigens. We therefore screened a chemical library of 200 compounds derived from natural products to identify inhibitors of the presentation of endogenous MHC class II-restricted antigens. We found that pyrenocine B, a compound derived from the fungus Pyrenochaeta terrestris, inhibits presentation of endogenous MHC class II-restricted minor histocompatibility antigen IL-4 inducible gene 1 (IL4I1) by primary dendritic cells (DCs). Phage display screening and surface plasmon resonance (SPR) analysis were used to investigate the mechanism of suppressive action by pyrenocine B. EpsinR, a target molecule for pyrenocine B, mediates endosomal trafficking through binding of soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs). Lentiviral-mediated short hairpin (sh) RNA downregulation of EpsinR expression in DCs resulted in a decrease in the responsiveness of CD4+ T cells. Our data thus suggest that EpsinR plays a role in antigen presentation, which provides insight into the mechanism of presentation pathway of endogenous MHC class II-restricted antigen.

Promotion of crystalline cellulose degradation by expansins from Oryza sativa.

MAIN CONCLUSION: Enzymatic activities of Oryza sativa expansins, which were heterologously overexpressed in Escherichia coli , were analyzed. Results suggested that expansins promote degradation of cellulose by cellulase in a synergistic manner. Sustainable production of future biofuels is dependent on efficient saccharification of lignocelluloses. Expansins have received a lot of attention as proteins promoting biological degradation of cellulose using cellulase. The expansins are a class of plant cell wall proteins that induce cell wall loosening without hydrolysis. In this study, the expansins from Oryza sativa were classified using phylogenetic analysis and five proteins were selected for functional evaluation. At low cellulose loading, the cellulase in expansin mixtures was up to 2.4 times more active than in mixtures containing only cellulase, but at high cellulose loading the activity of cellulase in expansin mixtures and cellulase only mixtures did not differ. Furthermore, expansin activity was greater in cellulase mixtures compared with cellulase-deficient mixtures. Therefore, the expansins showed significant synergistic activity with cellulase. Expansin may play an important role in efficient saccharification of cellulose.

Isolation and structure of vanitaracin A, a novel anti-hepatitis B virus compound from Talaromyces sp.

Two new tricyclic polyketides, vanitaracin A (1) and B (2), together with three novel compounds 3, 4 and 5, were isolated from a culture broth of a fungus, Talaromyces sp. The chemical structures of these compounds were determined from spectroscopic data (1D/2D NMR, MS and IR). The five isolated compounds were then tested for anti-hepatitis B virus (HBV) activity and vanitaracin A was found to exhibit an IC50 value of 10.5 µM using a HBV-susceptible cell line. By contrast, the derivative 2 displayed weak anti-HBV action, which suggested that the substituents at C-9 in 1 are likely to be important for its antiviral activity. We believe the two vanitaracin derivatives constitute a new class of anti-HBV agents.

Ridaifen G, tamoxifen analog, is a potent anticancer drug working through a combinatorial association with multiple cellular factors.

Ridaifen-G (RID-G), a tamoxifen analog that we previously synthesized, has potent growth inhibitory activity against various cancer cell lines. Tamoxifen is an anticancer drug known to act on an estrogen receptor (ER) and other proteins. However, our previous studies interestingly suggested that the mechanism of action of RID-G was different from that of tamoxifen. In order to investigate the molecular mode of action of RID-G, we developed a novel chemical genetic approach that combined a phage display screen with a statistical analysis of drug potency and gene expression profiles in thirty-nine cancer cell lines. Application of this method to RID-G revealed that three proteins, calmodulin (CaM), heterogeneous nuclear ribonucleoproteins A2/B1 (hnRNP A2/B1), and zinc finger protein 638 (ZNF638) were the candidates of direct targets of RID-G. Moreover, cell lines susceptible to RID-G show similar expression profiles of RID-G target genes. These results suggest that RID-G involves CaM, hnRNP A2/B1, and ZNF638 in its growth inhibitory activity.

Formosusin A, a novel specific inhibitor of mammalian DNA polymerase ß from the fungus Paecilomyces formosus.

Variotin (1) and three novel compounds, formosusin A (2), B (3), and C (4), were isolated from the cultures of the fungus Paecilomyces formosus, and their structures were determined by spectroscopic analyses. Compound 2 is (6Z,8E,10E)-variotin, a new cis-olefin analog of compound 1. Compound 2 selectively inhibited the activity of mammalian DNA polymerase ß (pol ß) in vitro, with an IC50 of 35.6µM. By contrast, compounds 1, 3, and 4 did not influence the activity of pol ß. These four compounds showed no effect on the activities of other 10 mammalian pols (i.e., pols α, γ, δ, ε, η, ι, κ, λ, and µ, and terminal deoxynucleotidyl transferase). These compounds also did not inhibit the activities of fish, insect, plant, and prokaryotic pols and other DNA metabolic enzymes tested. These results suggested that compound 2 could be a selective inhibitor of mammalian pol ß. The compound 2-induced inhibition of rat pol ß activity was competitive and non-competitive with respect to the DNA template-primer substrate and the dNTP substrate, respectively. On the basis of these results, the relationship between the three-dimensional structure and pol ß inhibitory mechanism of compound 2 is discussed.

Cytotoxic alkylated hydroquinone, phenol, and cyclohexenone derivatives from Aspergillus violaceofuscus Gasperini.

New alkylated hydroquinones violaceoid A (1), violaceoid B (2), and violaceoid C (3), an alkylated phenol violaceoid D (4), and a cyclohexenoid violaceoid E (5) were isolated from a culture broth of Aspergillus violaceofuscus Gasperini isolated from moss. The structures were identified by interpretation of spectroscopic data (1D and 2D NMR, MS, and IR). Two known compounds, the cyclohexenoid 6 and eupenoxide (7), were also isolated. Compound 6 was isolated for the first time as a natural product and named violaceoid F. Isolated compounds were tested for cytotoxic activity against five human cancer cell lines and a mouse macrophage cell line. Violaceoid A was the most potent of the seven compounds against all cell lines. Violaceoid C and D exhibited cytotoxicity against the leukemia cell lines with LD50 values 5.9-8.3 µM, while violaceoid F was found to be cytotoxic against HCT116 and RAW264.7 with LD50 values of 6.4 and 6.5 µM, respectively. These results demonstrate that violaceoid derivatives are a new class of cytotoxic hydroquinones with a hydroxymethyl and a linear alkyl substituent.