A silyl porphyrin derivative conjugated with 6-deoxy-6-sulfo-α-d-glucopyranose functions as an efficient photosensitizer for photodynamic therapy

We synthesized a new silyl porphyrin derivative conjugated with 6-deoxy-6-sulfo-α-d-glucopyranose (SGlc). Conjugation with SGlc improved A549 cellular uptake without significant changes in the photophysical and photochemical properties and subcellular localization. This improved cellular uptake led to enhanced photodynamic activity. Furthermore, conjugation with SGlc suppressed dark toxicity. These advantages were not observed for a conjugate with a glucose molecule. These results indicated that the conjugation with SGlc is a promising strategy for enhancing photodynamic efficacy.

Isolation, structural determination, and antiviral activities of metabolites from vanitaracin A-producing Talaromyces sp

Vanitaracin A, an anti-hepatitis B virus polyketide, has been previously isolated from Talaromyces sp. In the present study, we searched for novel compounds in the culture broth obtained from a vanitaracin A-producing fungus under various conditions. Three novel compounds (vanitaracin C, vanitaraphilone A, and 2-hydroxy-4-(hydroxymethyl)-6-methylbenzaldehyde) were isolated, and their structures were determined using spectroscopic methods (1D/2D NMR and MS). In addition, the antiviral spectrum of vanitaracin A was examined by measuring its antiviral activities against rabies virus, Borna disease virus 1, and bovine leukemia virus. This compound exhibited antiviral activity against bovine leukemia virus, which is the causative agent of enzootic bovine leukosis. The anti-bovine leukemia virus effects of other compounds isolated from the vanitaracin A-producing fungus, namely, vanitaracins B and C, vanitaraphilone A, and 2-hydroxy-4-(hydroxymethyl)-6-methylbenzaldehyde, were also evaluated. Vanitaracin B, vanitaraphilone A and 2-hydroxy-4-(hydroxymethyl)-6-methylbenzaldehyde were also found to exhibit activity against bovine leukemia virus. These findings reveal the broad-spectrum antiviral activity of the vanitaracin scaffold and suggest several candidates for the development of anti-bovine leukemia virus drugs.

Anticancer agent α-sulfoquinovosyl-acylpropanediol enhances the radiosensitivity of human malignant mesothelioma in nude mouse models

Malignant pleural mesothelioma (MPM) is a highly malignant disease that develops after asbestos exposure. Although the number of MPM cases is predicted to increase, no effective standard therapies have been established. The novel radiosensitizer α-sulfoquinovosyl-acylpropanediol (SQAP) enhances the effects of γ-radiation in human lung and prostate cancer cell lines and in animal models. In this study, we explored the radiosensitizing effect of SQAP and its mechanisms in MPM. The human MPM cell lines MSTO-211H and MESO-4 were implanted subcutaneously into the backs and thoracic cavities of immunodeficient KSN/Slc mice, then 2 mg/kg SQAP was intravenously administered with or without irradiation with a total body dose of 8 Gy. In both the orthotopic and ectopic xenograft murine models, the combination of irradiation plus SQAP delayed the implanted human MSTO-211H tumor growth. The analysis of the changes in the relative tumor volume of the MSTO-211H indicated a statistically significant difference after 8 Gy total body combined with 2 mg/kg SQAP, compared to both the untreated control (P = 0.0127) and the radiation treatment alone (P = 0.0171). After the treatment in each case, immunostaining of the harvested tumors revealed decreased cell proliferation, increased apoptosis and normalization of tumor blood vessels in the SQAP- and irradiation-treated group. Furthermore, hypoxia-inducible factor (HIF) 1 mRNA and protein expression were decreased, indicating reoxygenation in this group. In conclusion, SQAP improved hypoxic conditions in tumor tissue and may elicit a radiosensitizing effect in malignant mesothelioma models.

Determining the absolute configuration of vanitaracin A, an anti-hepatitis B virus agent

Vanitaracin A is an anti-hepatitis B virus (anti-HBV) compound isolated from the culture broth of the fungus Talaromyces sp. Vanitaracin A inhibits the entry of HBV into target cells with sub-micromolar IC₅₀ values. While a structure-activity relationship study is highly desirable, a synthetic approach still needs to be developed, which is difficult because the absolute configurations of the six stereogenic centers in the structure of vanitaracin A have not yet been determined. In the present study, we used the crystalline sponge method to clarify the configuration of the compound after determining the absolute configuration of the secondary alcohol using a modified Mosher ester method. Combining these analyses with the NOESY spectrum of vanitaracin A and NMR analyses of the crude side-chain carboxylic acid obtained by the alkaline hydrolysis of vanitaracin A revealed the absolute configurations of all stereogenic centers in this important compound.

The natural sulfoglycolipid derivative SQAP improves the therapeutic efficacy of tissue factor-targeted radioimmunotherapy in the stroma-rich pancreatic cancer model BxPC-3

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SQAP enhanced tumor uptake and the therapeutic efficacy of radiolabeled anti-tissue factor antibody 1849.

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SQAP allows for a reduction of the dose of the therapeutic agent ⁹⁰Y-labeled 1849 to half.

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SQAP did not affect hematologic parameters, or gastrointestinal and respiratory systems in mice.

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⁹⁰Y-labeled 1849 with SQAP potentially increases exposure of tumors to radiation.

α-Sulfoquinovosylacyl-1,3-propanediol (SQAP) is a semi-synthetic derivative of natural sulfoglycolipid that sensitizes tumors to external-beam radiotherapy. How SQAP affects internal radiotherapy, however, is not known. Here, we investigated the effects of SQAP for radioimmunotherapy (RIT) targeting tissue factor (TF) in a stroma-rich refractory pancreatic cancer mouse model, BxPC-3. A low dose of SQAP (2 mg/kg) increased tumor uptake of the ¹¹¹In-labeled anti-TF antibody 1849, indicating increased tumor perfusion. The addition of SQAP enhanced the growth-inhibitory effect of ⁹⁰Y-labeled 1849 without leading to severe body weight changes, allowing for the dose of ⁹⁰Y-labeled 1849 to be reduced to half that when used alone. Histologic analysis revealed few necrotic and apoptotic cells, but Ki-67–positive proliferating cells and increased vascular formation were detected. These results suggest that the addition of a low dose of SQAP may improve the therapeutic efficacy of TF-targeted RIT by increasing tumor perfusion, even for stroma-rich refractory pancreatic cancer.

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).

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.

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.

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.

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.

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.

Chloramphenicol inhibits eukaryotic Ser/Thr phosphatase and infection-specific cell differentiation in the rice blast fungus

Chloramphenicol (Cm) is a broad-spectrum classic antibiotic active against prokaryotic organisms. However, Cm has severe side effects in eukaryotes of which the cause remains unknown. The plant pathogenic fungus Magnaporthe oryzae, which causes rice blast, forms an appressorium to infect the host cell via single-cell differentiation. Chloramphenicol specifically inhibits appressorium formation, which indicates that Cm has a novel molecular target (or targets) in the rice blast fungus. Application of the T7 phage display method inferred that MoDullard, a Ser/Thr-protein phosphatase, may be a target of Cm. In animals Dullard functions in cell differentiation and protein synthesis, but in fungi its role is poorly understood. In vivo and in vitro analyses showed that MoDullard is required for appressorium formation, and that Cm can bind to and inhibit MoDullard function. Given that human phosphatase CTDSP1 complemented the MoDullard function during appressorium formation by M. oryzae, CTDSP1 may be a novel molecular target of Cm in eukaryotes.

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

endo-β-1,2-Glucanase (SGL) is an enzyme that hydrolyzes β-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 β-1,2-glucans to sophorose (Glc-β-1,2-Glc) as a main product. TfSGLr hydrolyzed reducing-end-modified β-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 β-1,2-glucoheptasaccharide. Mutational analysis and action pattern analysis of β-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.

High-Power Abiotic Direct Glucose Fuel Cell Using a Gold-Platinum Bimetallic Anode Catalyst

We developed a high-power abiotic direct glucose fuel cell system using a Au-Pt bimetallic anode catalyst. The high power generation (95.7 mW cm^-2) was attained by optimizing operating conditions such as the composition of a bimetallic anode catalyst, loading amount of the metal catalyst on a carbon support, ionomer/carbon weight ratio when the catalyst was applied to the anode, glucose and KOH concentrations in the fuel solution, and operating temperature and flow rate of the fuel solution. It was found that poly(N-vinyl-2-pyrrolidone)-stabilized Au₈₀Pt₂₀ nanoparticles (mean diameter 1.5 nm) on a carbon (Ketjen Black 600) support function as a highly active anode catalyst for the glucose electrooxidation. The ionomer/carbon weight ratio also greatly affects the cell properties, which was found to be optimal at 0.2. As for the glucose concentration, a maximum cell power was derived at 0.4-0.6 mol dm^-3. A high KOH concentration (4.0 mol dm^-3) was preferable for deriving the maximum power. The cell power increased with the increasing flow rate of the glucose solution up to 50 cm³ min^-1 and leveled off thereafter. At the optimal condition, the maximum power density and corresponding cell voltage of 58.2 mW cm^-2 (0.36 V) and 95.7 mW cm^-2 (0.34 V) were recorded at 298 and 328 K, respectively.

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.

A Multimodal Molecular Imaging Study Evaluates Pharmacological Alteration of the Tumor Microenvironment to Improve Radiation Response

: Hypoxic zones in solid tumors contribute to radioresistance, and pharmacologic agents that increase tumor oxygenation prior to radiation, including antiangiogenic drugs, can enhance treatment response to radiotherapy. Although such strategies have been applied, imaging assessments of tumor oxygenation to identify an optimum time window for radiotherapy have not been fully explored. In this study, we investigated the effects of α-sulfoquinovosylacyl-1,3-propanediol (SQAP or CG-0321; a synthetic derivative of an antiangiogenic agent) on the tumor microenvironment in terms of oxygen partial pressure (pO₂), oxyhemoglobin saturation (sO₂), blood perfusion, and microvessel density using electron paramagnetic resonance imaging, photoacoustic imaging, dynamic contrast-enhanced MRI with Gd-DTPA injection, and T2*-weighted imaging with ultrasmall superparamagnetic iron oxide (USPIO) contrast. SCCVII and A549 tumors were grown by injecting tumor cells into the hind legs of mice. Five days of daily radiation (2 Gy) combined with intravenous injection of SQAP (2 mg/kg) 30 minutes prior to irradiation significantly delayed growth of tumor xenografts. Three days of daily treatment improved tumor oxygenation and decreased tumor microvascular density on T2*-weighted images with USPIO, suggesting vascular normalization. Acute effects of SQAP on tumor oxygenation were examined by pO₂, sO₂, and Gd-DTPA contrast-enhanced imaging. SQAP treatment improved perfusion and tumor pO₂ (ΔpO₂: 3.1 ± 1.0 mmHg) and was accompanied by decreased sO₂ (20%-30% decrease) in SCCVII implants 20-30 minutes after SQAP administration. These results provide evidence that SQAP transiently enhanced tumor oxygenation by facilitating oxygen dissociation from oxyhemoglobin and improving tumor perfusion. Therefore, SQAP-mediated sensitization to radiation in vivo can be attributed to increased tumor oxygenation. SIGNIFICANCE: A multimodal molecular imaging study evaluates pharmacological alteration of the tumor microenvironment to improve radiation response.

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.

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.

MA026, an anti-hepatitis C virus compound, opens tight junctions of the epithelial cell membrane

MA026 is an antiviral natural compound against hepatitis C virus (HCV). It was recently reported that MA026 binds claudin-1 (CLDN1) and inhibits HCV infection. Although CLDN1 is an important component of tight junctions (TJ) in the epithelial cell layer, the effects of MA026 on the TJ barrier function remained to be revealed. Here we report that MA026 irreversibly opens the TJ. MA026 irreversibly increased FD4 permeability and decreased transepithelial electrical resistance (TER) for at least 5 h. Although MA026 increased Ca²⁺ influx in layered MDCKII cells, the Ca²⁺ influx was less than that of capsaicin, a reversible TJ opener. Moreover, MA026 did not induce the dephosphorylation of cofilin and reorganization of F-actin structure. Although the mechanism is left to be disclosed, these results suggest that MA026 is a novel irreversible TJ opener probably by targeting CLDN1.

Low doses of the mycotoxin citrinin protect cortical neurons against glutamate-induced excitotoxicity

Citrinin, a natural mycotoxin that is found in fermented foods, is known as a cytotoxin and nephrotoxin. Exposure to high doses of citrinin result in apoptosis; however, the effects of low doses are not fully understood. Glutamate excitotoxicity is responsible for neuronal death in acute neurological disorders including stroke, trauma and other neurodegenerative diseases. Here, we show the neuroprotective effect of low doses of citrinin against glutamate-induced excitotoxicity. We examined the effect of citrinin exposure on glutamate-induced cell death in cultured rat cortical neurons under two conditions: simultaneous treatment with citrinin 0.1 to 1,000 nM and glutamate (30 μM) for 1, 3 hr; the same simultaneous treatment for 3 hr after pretreatment with citrinin for 21 hr. Both the MTT and immunocytochemical assay showed significant neuroprotective effects at several doses and exposure times tested. All concentrations of citrinin tested showed no remarkable cell death following 14-day exposure, and no marked alterations to synapses. These data suggest that low doses of citrinin can be used as a neuroprotective agent against glutamate-induced excitotoxicity without additional harmful cellular alterations.

Neoechinulin A induced memory improvements and antidepressant-like effects in mice

Neoechinulin A is an isoprenyl indole alkaloid that exhibits scavenging, neurotrophic factor-like, and anti-apoptotic activities. However, the effectiveness of neoechinulin A in animal models of disease has not yet been explored. In the present study, we investigated the effects of neoechinulin A on memory impairment in lipopolysaccharide (LPS)-treated mice and its antidepressant-like effects in mice. In the Y-maze test, the intracerebroventicular (i.c.v.) administration of LPS (10μg/mouse) significantly decreased spontaneous alternation behavior, which was prevented by the prior administration of neoechinulin A (300ng/mouse, i.c.v.). None of the treatments altered the locomotor activity of mice. Moreover, the administration of neoechinulin A decreased the immobility time in the forced-swim test or tail suspension test, which was prevented by the prior administration of WAY100635 (an antagonist of 5-HT1A receptors) and parachlorophenylalanine (an inhibitor of tryptophan hydroxylase). These results suggest that neoechinulin A improves memory functions in LPS-treated mice, and also exerts antidepressant-like effects through changes in the 5-HT system.

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.

Novel anticancer agent, SQAP, binds to focal adhesion kinase and modulates its activity

SQAP is a novel and promising anticancer agent that was obtained by structural modifications from a natural compound. SQAP inhibits angiogenesis in vivo resulting in increased hypoxia and reduced tumor volume. In this study, the mechanism by which SQAP modifies the tumor microenvironment was revealed through the application of a T7 phage display screening. This approach identified five SQAP-binding proteins including sterol carrier protein 2, multifunctional enzyme type 2, proteasomal ubiquitin receptor, UV excision repair protein and focal adhesion kinase (FAK). All the interactions were confirmed by surface plasmon resonance analysis. Since FAK plays an important role in cell turnover and angiogenesis, the influence of SQAP on FAK was the principal goal of this study. SQAP decreased FAK phosphorylation and cell migration in human umbilical vein endothelial cells and A549 cancer cells. These findings suggest that inhibition of FAK phosphorylation works as the mechanism for the anti-angiogenesis activity of SQAP.

Multimodal biopanning of T7 phage-displayed peptides reveals angiomotin as a potential receptor of the anti-angiogenic macrolide Roxithromycin

Roxithromycin (RXM) is a semi-synthetic fourteen-membered macrolide antibiotic that shows anti-angiogenic activity in solid tumors. In the present study, we conducted biopanning of T7 phage-displayed peptides either on a 96-well formatted microplate, a flow injection-type quartz-crystal microbalance (QCM) biosensor, or a cuvette-type QCM. RXM-selected peptides of different sequence, length and number were obtained from each mode of screening. Subsequent bioinformatics analysis of the RXM-selected peptides consistently gave positive scores for the extracellular domain (E458-T596) of angiomotin (Amot), indicating that this may comprise a binding region for RXM. Bead pull down assay and QCM analysis confirmed that RXM directly interacts with Amot via the screen-guided region, which also corresponds to the binding site for the endogenous anti-angiogenic inhibitor angiostatin (Anst). Thus, multimodal biopanning of T7PD revealed that RXM binds to the extracellular domain on Amot as a common binding site with Anst, leading to inhibition of angiogenesis-dependent tumor growth and metastasis. These data might explain the molecular basis underlying the mechanism of action for the anti-angiogenic activity of RXM.

Promotion of crystalline cellulose degradation by expansins from Oryza sativa

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.

Bioactive dihydronaphthoquinone derivatives from Fusarium solani

New dihydronaphthoquinone derivatives, karuquinone A (1), karuquinone B (2), and karuquinone C (3), were isolated from a fungal culture broth of Fusarium solani. The structures were determined by interpretation of spectroscopic data (1D/2D NMR, MS, and IR). Three known compounds, javanicin (4), 2,3-dihydro-5-hydroxy-8-methoxy-2,4-dimethylnaphtho[1,2-b]furan-6,9-dione (5), and 5-hydroxydihydrofusarubin C (6), were also isolated. The six isolated compounds were tested for cytotoxicity against three human cancer cell lines and a human umbilical vein endothelial cell (HUVEC) line. Of these, karuquinone A exhibited the strongest cytotoxic activity. Karuquinone B did not affect the proliferation of the cancer cell lines but did inhibit the proliferation of HUVEC. Additionally, we demonstrated that karuquinone A induces apoptosis in cancer cells through the generation of reactive oxygen species (ROS).

Inhibition of mammalian DNA polymerases and the suppression of inflammatory and allergic responses by tyrosol from used activated charcoal waste generated during sake production

The components adsorbed onto activated charcoal following the fermentation process of the Japanese rice wine "sake" have been studied with the aim of identifying suitable applications for this industrial food waste product. The absorbed materials were effectively extracted from the charcoal, and inhibited the activity of several mammalian DNA polymerases (pols). Subsequent purification of the extract afforded tyrosol [4-(2-hydroxyethyl)phenol] as the active component, which selectively inhibited the activity of 11 mammalian pols with IC50 values in the range of 34.3-46.1 μM. In contrast, this compound did not influence the activities of plant or prokaryotic pols or any of the other DNA metabolic enzymes tested. Tyrosol suppressed both anti-inflammatory and antiallergic effects in vivo, including 12-O-tetradecanoylphorbol-13-acetate-induced inflammatory mouse ear edema, and immunoglobulin E-induced passive cutaneous anaphylactic reaction in mice. These results suggested that this byproduct formed during the sake-brewing process could be used as an anti-inflammatory and/or antiallergic agent.

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.

Formosusin A, a novel specific inhibitor of mammalian DNA polymerase β 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 β (pol β) in vitro, with an IC50 of 35.6μM. By contrast, compounds 1, 3, and 4 did not influence the activity of pol β. 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 β. The compound 2-induced inhibition of rat pol β 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 β inhibitory mechanism of compound 2 is discussed.

Total synthesis and anti-hepatitis C virus activity of MA026

The first total synthesis of MA026 and the identification of its candidate target protein for anti-hepatitis C virus activity are presented. MA026, a novel lipocyclodepsipeptide isolated from the fermentation broth of Pseudomonas sp. RtIB026, consists of a cyclodepsipeptide, a chain peptide, and an N-terminal (R)-3-hydroxydecanoic acid. The first subunit, side chain 2, was prepared by coupling fatty acid moiety 4 with tripeptide 5. The key macrocyclization of the decadepsipeptide at L-Leu(10)-D-Gln(11) provided the second subunit, cyclodepsipeptide 3. Late-stage condensation of the two key subunits and final deprotection afforded MA026. This convergent, flexible, solution-phase synthesis will be invaluable in generating MA026 derivatives for future structure-activity relationship studies. An infectious hepatitis C virus (HCV) cell culture assay revealed that MA026 suppresses HCV infection into host hepatocytes by inhibiting the entry process in a dose-dependent manner. Phage display screening followed by surface plasmon resonance (SPR) binding analyses identified claudin-1, an HCV entry receptor, as a candidate target protein of MA026.

Specific inhibition of hepatitis C virus entry into host hepatocytes by fungi-derived sulochrin and its derivatives

Hepatitis C virus (HCV) is a major causative agent of hepatocellular carcinoma. Although various classes of anti-HCV agents have been under clinical development, most of these agents target RNA replication in the HCV life cycle. To achieve a more effective multidrug treatment, the development of new, less expensive anti-HCV agents that target a different step in the HCV life cycle is needed. We prepared an in-house natural product library consisting of compounds derived from fungal strains isolated from seaweeds, mosses, and other plants. A cell-based functional screening of the library identified sulochrin as a compound that decreased HCV infectivity in a multi-round HCV infection assay. Sulochrin inhibited HCV infection in a dose-dependent manner without any apparent cytotoxicity up to 50 μM. HCV pseudoparticle and trans-complemented particle assays suggested that this compound inhibited the entry step in the HCV life cycle. Sulochrin showed anti-HCV activities to multiple HCV genotypes 1a, 1b, and 2a. Co-treatment of sulochrin with interferon or a protease inhibitor telaprevir synergistically augmented their anti-HCV effects. Derivative analysis revealed anti-HCV compounds with higher potencies (IC50<5 μM). This is the first report showing an antiviral activity of methoxybenzoate derivatives. Thus, sulochrin derivatives are anti-HCV lead compounds with a new mode of action.

Synthesis, structure, and cytotoxicity studies of some fungal isochromanes

Ustusorane D and penicisochromans B-D are natural isochromans isolated from Aspergillus ustus 094102 and Penicillium sp. PSU-F40, respectively. Herein, we report the syntheses of (-)-ustusorane D and (+)-penicisochroman B and the structures of penicisochromans C and D. The relative configuration of natural ustusorane D and the absolute configuration of natural penicisochroman B were determined. Two plausible structures for penicisochroman C were evaluated through synthesis, but their ¹H and ¹³C NMR data were not in agreement with those of the natural product. The structural revision and the determination of the absolute configuration of natural penicisochroman D were achieved. Structure-activity relationship studies of the synthetic compounds as well as a series of related isochromans indicated that the enone of the furanone moiety was essential for the cytotoxicity of these compounds toward HCT116 human colon cancer cells. Pseudodeflectusin, the related natural isochroman, suppressed cell growth and induced apoptosis in HCT116 cells.

Mapping a disordered portion of the Brz2001-binding site on a plant monooxygenase, DWARF4, using a quartz-crystal microbalance biosensor-based T7 phage display

In small-molecule/protein interaction studies, technical difficulties such as low solubility of small molecules or low abundance of protein samples often restrict the progress of research. Here, we describe a quartz-crystal microbalance (QCM) biosensor-based T7 phage display in combination use with a receptor-ligand contacts (RELIC) bioinformatics server for application in a plant Brz2001/DWARF4 system. Brz2001 is a brassinosteroid biosynthesis inhibitor in the less-soluble triazole series of compounds that targets DWARF4, a cytochrome P450 (Cyp450) monooxygenase containing heme and iron. Using a Brz2001 derivative that has higher solubility in 70% EtOH and forms a self-assembled monolayer on gold electrode, we selected 34 Brz2001-recognizing peptides from a 15-mer T7 phage-displayed random peptide library using a total of four sets of one-cycle biopanning. The RELIC/MOTIF program revealed continuous and discontinuous short motifs conserved within the 34 Brz2001-selected 15-mer peptide sequences, indicating the increase of information content for Brz2001 recognition. Furthermore, an analysis of similarity between the 34 peptides and the amino-acid sequence of DWARF4 using the RELIC/MATCH program generated a similarity plot and a cluster diagram of the amino-acid sequence. Both of these data highlighted an internally located disordered portion of a catalytic site on DWARF4, indicating that this portion is essential for Brz2001 recognition. A similar trend was also noted by an analysis using another 26 Brz2001-selected peptides, and not observed using the 27 gold electrode-recognizing control peptides, demonstrating the reproducibility and specificity of this method. Thus, this affinity-based strategy enables high-throughput detection of the small-molecule-recognizing portion on the target protein, which overcomes technical difficulties such as sample solubility or preparation that occur when conventional methods are used.

Neoechinulin a imparts resistance to acute nitrosative stress in PC12 cells: a potential link of an elevated cellular reserve capacity for pyridine nucleotide redox turnover with cytoprotection

Treatment of PC12 cells with fungus-derived alkaloid neoechinulin A for more than 12 h renders the cells resistant to subsequent superoxide (O₂⁻)/nitric oxide (NO) insults derived from 3-morpholinosydnonimine (SIN-1). However, the underlying mechanism(s) remains largely unclear. To elucidate the mechanism(s), we assessed the specificity of the cytoprotection afforded by neoechinulin A treatment using other cytocidal stressors and also clarified the resulting cellular alterations, focusing on the antioxidant and metabolic enzymes systems. Neoechinulin A treatment for more than 12 h endowed PC12 cells with significant resistance to transient NO toxicity, but not persistent NO toxicity, bolus H₂O₂ toxicity, or oxidative insult from the redox cycling quinone menadione. Cellular antioxidant system profiling revealed no substantial potentiation of the activity of any antioxidant enzyme in lysate from the neoechinulin A-treated cells excluding glutathione (GSH) content, which was significantly decreased (>50%), resulting in a proportional compromise in the thiol-reducing activity of the intact cells. In addition, no differences were observed in the activity for any nicotinamide adenine dinucleotide (phosphate) reduced form (NAD(P)H)-generating enzyme, steady-state NAD(P)H/nicotinamide adenine dinucleotide (phosphate) oxidized form (NAD(P)⁺) ratios, or the levels of total NAD(P)H. Nevertheless, the neoechinulin A-treated intact cells exhibited increased NAD(P)H redox turnover when driven by extracellular tetrazolium. The structurally inactive analog preechinulin failed to protect cells against NO toxicity or induce these alterations, suggesting their link with the cytoprotective mechanism. These results suggest that neoechinulin A, despite disabling the GSH defense system, confers cytoprotection against nitrosative stresses by elevating the cellular reserve capacity for NAD(P)H generation, which could offset crippling of energy-supplying systems due to nitrosative stress.

Ridaifen B, a tamoxifen derivative, directly binds to Grb10 interacting GYF protein 2

Ridaifen B (RID-B) is a tamoxifen derivative that potently inhibits breast tumor growth. RID-B was reported to show anti-proliferating activity for a variety of estrogen receptor (ER)-positive human cancer cells. Interestingly, RID-B was also reported to possess higher potency than that of tamoxifen even for some ER-negative cells, suggesting an ER-independent mechanism of action. In this study, a T7 phage display screen and subsequent binding analyses have identified Grb10 interacting GYF protein 2 (GIGYF2) as a RID-B-binding protein. Using a cell-based assay, the Akt phosphorylation level mediated by GIGYF2 was found to have decreased in the presence of RID-B.

Use of phage display technology for the determination of the targets for small-molecule therapeutics

IMPORTANCE OF THE FIELD

Target discovery of drug-like small-molecules contributes to our understanding of biological phenomena at the molecular level as well as elucidating the mode of action of bioactive compounds. Research in this field is of high value because, in addition to basic observations, the data can be used to directly identify molecular targets or investigate pharmacokinetic characteristics of drugs in clinical use.

AREAS COVERED IN THIS REVIEW

In addition to providing a brief overview of phage display (PD) technology, we discuss screening platforms, different types of phage libraries and the application of this method to the determination of targets for small-molecule therapeutics over the past decade.

WHAT THE READER WILL GAIN

Readers will gain an understanding of the basis of PD technology through successful examples of the use of this method for the determination of targets for small-molecule therapeutics. They will learn what kinds of small-molecules were used to identify their binding partner, what characteristics and drawbacks are present in the use of small-molecule as bait, and what kinds of approaches were introduced in order to improve the technique to overcome the limitations of conventional strategies.

TAKE HOME MESSAGE

A suitable combination of diverse technologies from various different fields can act synergistically to increase throughput and enhance the efficiency of PD technology for the determination of targets for small-molecule therapeutics. The most suitable method for successful target identification of small-molecules of interest using PD technology can often be determined by referring to past examples.

Anti-angiogenesis effect of 3'-sulfoquinovosyl-1'-monoacylglycerol via upregulation of thrombospondin 1

We previously reported that 3'-sulfoquinovosyl-1'-monoacylglycerol (SQMG) effectively suppresses the growth of solid tumors, likely via its anti-angiogenic activity. To investigate how SQMG affects angiogenesis, we performed DNA microarray analysis and quantitative real-time polymerase chain reaction. Consequently, upregulation of thrombospondin 1 (TSP-1) in SQMG-treated tumors in vitro and in vivo was confirmed. To address the mechanisms of TSP-1 upregulation by SQMG, we established stable TSP-1-knockdown transformants (TSP1-KT) by short hairpin RNA induction and performed reporter assay and in vivo assessment of anti-tumor assay. On the reporter assay, transcriptional upregulation of TSP-1 in TSP1-KT could not be induced by SQMG, thus suggesting that TSP-1 upregulation by SQMG occurred via TSP-1 molecule. In addition, growth of TSP1-KT xenografted tumors in vivo was not inhibited by SQMG, thus suggesting that anti-angiogenesis via TSP-1 upregulation induced by SQMG did not occur, as the SQMG target molecule TSP-1 was knocked down in TSP1-KT transformants. These data provide that SQMG is a promising candidate for the treatment of tumor-induced angiogenesis via TSP-1 upregulation.

Pinophilins A and B, inhibitors of mammalian A-, B-, and Y-family DNA polymerases and human cancer cell proliferation

Pinophilins A (1) and B (2), new hydrogenated azaphilones, and Sch 725680 (3) were isolated from cultures of a fungus (Penicillium pinophilum Hedgcok) derived from a seaweed, and their structures were determined using spectroscopic analyses. These compounds selectively inhibited the activities of mammalian DNA polymerases (pols), A (pol γ), B (pols α, δ, and ε), and Y (pols η, ι, and κ) families, but did not influence the activities of the four X-family pols (pols β, λ, μ, and terminal deoxynucleotidyl transferase). Compound 1 was the strongest inhibitor, with IC₅₀ values of 48.6 to 55.6 μM. Kinetic analysis showed that compound 1 is a noncompetitive inhibitor of both pol α and κ activities with the DNA template-primer substrate, and a competitive inhibitor with the nucleotide substrate. In contrast, compounds 1-3 showed no effect on the activities of plant and prokaryotic pols or any other DNA metabolic enzymes tested. The compounds suppressed cell proliferation and growth in five human cancer cell lines, but had no effect on the viability of normal human cell lines.

Neoechinulin a impedes the progression of rotenone-induced cytotoxicity in PC12 cells

Neoechinulin A, an indole alkaloid from marine fungi, can protect PC12 cells from the cytotoxicity of 1-methyl-4-phenylpyridinium (MPP(+)), a Parkinson disease-inducing neurotoxin, by ameliorating downstream events resulting from mitochondrial complex I inactivation. However, the cytoprotective mechanisms remained unclear. In this study, by using rotenone, another parkinsonian-inducing neurotoxin targeting mitochondrial complex I, we investigated the cytoprotective mechanism of neoechinulin A. Rotenone-induced cell death was associated with accelerated glucose consumption, and excess glucose supplementation in the culture medium almost completely suppressed cell death, suggesting that glucose deficiency in the medium is critical for triggering cell death in this model. Co-treatment with neoechinulin A, but not neoechinulin A pre-treatment before rotenone exposure, significantly impeded cell death by rotenone. Although the presence of neoechinulin A did not affect the accelerated glycolytic turnover in rotenone-treated cells, it paradoxically decreased ATP levels in the cells, suggesting increased ATP consumption. Although the link between the decreased ATP levels and cytoprotection is not clear at present, it suggests that neoechinulin A may ameliorate rotenone toxicity by activating a cytoprotective machinery that requires ATP.

Characterization of marine X-family DNA polymerases and comparative analysis of base excision repair proteins

While mammalian DNA polymerase β (Pol β), which is a member of the Pol X family, play important roles in base excision repair (BER) that efficiently removes DNA base lesions arising from both endogenous and exogenous agents, this protein has been found only a subset of animals. To understand natural evolution of this enzyme, we isolated and characterized Pol β from jellyfish Aurelia sp.1. (AsPol β). Despite of phylogenetic distance and environmental differences between jellyfish and mammals, in vitro assays showed biochemical characteristics of AsPol β were very similar to those of a mammalian counterpart. We also searched two other homologs of mammalian genes that were involved in short patch (sp) BER in the nucleotide sequence database, and found that both of these homologs were encoded in the genomes of a lineage from Cnidarians through mammals and Arthropods. This study suggests that a DNA repair mechanism resembling mammalian sp-BER may be largely limited to a subset of animals. On the basis of our findings and previous reports, we discuss possible evolutional model of Pol β and the other members of the Pol X family.

Screening of a library of T7 phage-displayed peptides identifies alphaC helix in 14-3-3 protein as a CBP501-binding site

CBP501 is a chemically modified peptide composed of twelve unnatural d-amino acids, which inhibits Chk kinase and abrogates G2 arrest induced by DNA-damaging agents. Here we identified an alphaC helix in 14-3-3 protein as a CBP501-binding site using T7 phage display technology. An affinity selection of T7 phage-displayed peptide using biotinylated CBP501 identified a 14-mer peptide NSDCIISRKIEQKE. This peptide sequence showed similarity to a portion of the alphaC helix of human 14-3-3ε, suggesting that CBP501 may bind to this region. Surface plasmon resonance (SPR) and ELISA demonstrated that CBP501 interacts with 14-3-3ε specifically at the screen-guided region. An avidin-agarose bead pull-down assay showed that CBP501 also binds to other 14-3-3 isoforms in Jurkat cells. Among the other known Chk kinase inhibitors tested, CBP501 showed the strongest affinity for 14-3-3ε. Thus, we conclude that in addition to the direct inhibition of Chk kinase activity, CBP501 directly binds to cellular 14-3-3 proteins through alphaC helix.

Camptothecin (CPT) directly binds to human heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) and inhibits the hnRNP A1/topoisomerase I interaction

Camptothecin (CPT) is an anti-tumor natural product that forms a ternary complex with topoisomerase I (top I) and DNA (CPT-top I-DNA). In this study, we identified the direct interaction between CPT and human heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) using the T7 phage display technology. On an avidin-agarose bead pull down assay, hnRNP A1 protein was selectively pulled down in the presence of C20-biotinylated CPT derivative (CPT-20-B) both in vitro and in vivo. The interaction was also confirmed by an analysis on a quartz-crystal microbalance (QCM) device, yielding a K(D) value of 82.7 nM. A surface plasmon resonance (SPR) analysis revealed that CPT inhibits the binding of hnRNP A1 to top I (K(D): 260 nM) in a non-competitive manner. Moreover, an in vivo drug evaluation assay using Drosophila melanogaster showed that the knockout of the hnRNP A1 homolog Hrb87F gene showed high susceptibility against 5-50 μM of CPT as compared to a wild-type strain. Such susceptibility was specific for CPT and not observed after treatment with other cytotoxic drugs. Collectively, our data suggests that CPT directly binds to hnRNP A1 and non-competitively inhibits the hnRNP A1/top I interaction in vivo. The knockout strain loses the hnRNP A1 homolog as a both CPT-binding partner and naïve brakes of top I, which enhances the formation of the CPT-top I-DNA ternary complexes and subsequently sensitizes the growth inhibitory effect of CPT in D. melanogaster.