Rhone Akee | National Institutes of Health (original) (raw)
Papers by Rhone Akee
ACS Infectious Diseases, May 10, 2023
Molecular Pharmacology, Nov 27, 2007
Human apurinic/apyrimidinic endonuclease (Ape1) plays an important role by processing the >10,000... more Human apurinic/apyrimidinic endonuclease (Ape1) plays an important role by processing the >10,000 highly toxic abasic sites generated in the genome of each cell every day. Ape1 has recently emerged as a target for inhibition as its overexpression in tumors has been linked with poor response to both radiation and chemotherapy and lower overall patient survival. Inhibition of Ape1 using siRNA or the expression of a dominant-negative form of the protein have been shown to sensitize cells to DNA-damaging agents, including various chemotherapeutic agents. However, potent small molecule inhibitors of Ape1 remain to be found. To this end, we screened Ape1 against the NCI Diversity Set of small molecules and discovered aromatic nitroso, carboxylate, sulfonamide and arylstibonic acid compounds with micromolar affinities for the protein. A further screen of a 37compound arylstibonic acid sublibrary identified ligands with IC 50 values in the range 4 to 300 nM. The negatively charged stibonic acids act by a partial-mixed mode, and likely serve as DNA phosphate mimics. These compounds provide a useful scaffold for development of chemotherapeutic agents against Ape1. Every day, over 10,000 abasic sites are formed in each cell due to the spontaneous depurination of DNA bases (Lindahl and Nyberg, 1972). Without repair, these abasic sites are both mutagenic and cytotoxic (Boiteux and Guillet, 2004). Human apurinic/apyrimidinic endonuclease (Ape1) plays the important role of processing these lesions so that they may be recognized by subsequent enzymes and repaired. Ape1 accounts for more than 95% of the abasic site cleavage activity within the cell (Wilson and Barsky, 2001). This protein cleaves the DNA 5' to the abasic site, producing a 5' deoxyribose phosphate (dRP) group and a 3' hydroxyl. The 5' dRP is a substrate for DNA polymerase β, which removes this blocking group and adds the correct nucleotide. The remaining nick in the DNA is then closed by DNA ligase, consummating repair of the site (Dianov et al., 2003). Ape1 is also a pivotal component of the base excision repair (BER) pathway, which is responsible for removing aberrant bases from the genome. This pathway is initiated by enzymatic removal of a damaged or incorrect base by a DNA glycosylase, also producing an abasic site. Following cleavage of this abasic site by Ape1, the DNA is repaired through the action of the same enzymes as described above (Dianov et al., 2003). In addition to its role in DNA repair, Ape1 has been shown to be an important facilitator of both redox-dependent and independent DNA-transcription factor binding, giving the protein the alternative name of redox factor-1 (Ref-1
ACS Medicinal Chemistry Letters
Journal of The Chemical Society-perkin Transactions 1, 1994
In 1983 leptomycin A (LPT A) and leptomycin B (LPT B) were discovered at the University of Tokyo ... more In 1983 leptomycin A (LPT A) and leptomycin B (LPT B) were discovered at the University of Tokyo as potent anti-fungal agents against schizosaccharomyces pombe Mucor racemosus and Mucor rouxiannus (ref 1). In 1985 LPT A LPT B and the monohydroxylated derivatives kazusamycin A (30-hydroxyleptomycin B HLPT B) and kasuzamycin B (29-hydroxyleptomycin A HLPT A) were isolated and reported as antitumor compounds (ref 2).
ACS Chemical Biology, 2020
An automated, high-capacity, and high-throughput procedure for the rapid isolation and identifica... more An automated, high-capacity, and high-throughput procedure for the rapid isolation and identification of biologically active natural products from a prefractionated library is presented. The semipreparative HPLC method uses 1 mg of the primary hit fraction and produces 22 subfractions in an assay-ready format. Following screening, all active fractions are analyzed by NMR, LCMS, and FTIR, and the active principle structural classes are elucidated. In the proof-of-concept study, we show the processes involved in generating the subfractions, the throughput of the structural elucidation work, as well as the ability to rapidly isolate and identify new and biologically active natural products. Overall, the rapid second-stage purification conserves extract mass, requires much less chemist time, and introduces knowledge of structure early in the isolation workflow.
Fitoterapia, 2019
Botanical-based natural products are an important resource for medicinal drug discovery and conti... more Botanical-based natural products are an important resource for medicinal drug discovery and continue to provide diverse pharmacophores with therapeutic potential against cancer and other human diseases. A prototype Traditional Chinese Medicine (TCM) plant extract library has been established at the US National Cancer Institute, which contains both the organic and aqueous extracts of 132 authenticated medicinal plant species that collectively represent the potential therapeutic contents of most commonly used TCM herbal prescriptions. This library is publicly available in 96-and 384-well plates for high throughput screening across a broad array of biological targets, as well as in larger quantities for isolation of active chemical ingredients. Herein, we present the methodology used to generate the library and the preliminary assessment of the anti-proliferative activity of this crude extract library in NCI-60 human cancer cell lines screen. Particularly, we report the chemical profiling and metabolome comparison analysis of four commonly used TCM plants, namely Brucea javanica, Dioscorea nipponica, Cynanchum atratum, and Salvia miltiorrhiza. Bioassayguided isolation resulted in the identification of the active compounds, and different extraction methods were compared for their abilities to extract cytotoxic compounds and to concentrate biologically active natural products.
Bioorganic & Medicinal Chemistry Letters, 2018
Two new cassaine-type diterpenoids, namely erythrofordins D (1) and E (2), sourced from a Cameroo... more Two new cassaine-type diterpenoids, namely erythrofordins D (1) and E (2), sourced from a Cameroon collection of Erythrophleum suaveolens were isolated and assessed for anti-tumor
ACS chemical biology, Jan 13, 2018
The US National Cancer Institute's (NCI) Natural Product Repository is one of the world's... more The US National Cancer Institute's (NCI) Natural Product Repository is one of the world's largest, most diverse collections of natural products containing over 230,000 unique extracts derived from plant, marine, and microbial organisms that have been collected from biodiverse regions throughout the world. Importantly, this national resource is available to the research community for the screening of extracts and the isolation of bioactive natural products. However, despite the success of natural products in drug discovery, compatibility issues that make extracts challenging for liquid handling systems, extended timelines that complicate natural product-based drug discovery efforts and the presence of pan-assay interfering compounds have reduced enthusiasm for the high-throughput screening (HTS) of crude natural product extract libraries in targeted assay systems. To address these limitations, the NCI Program for Natural Product Discovery (NPNPD), a newly launched, national p...
Molecular Pharmacology, 2007
Human apurinic/apyrimidinic endonuclease (Ape1) plays an important role by processing the >10,000... more Human apurinic/apyrimidinic endonuclease (Ape1) plays an important role by processing the >10,000 highly toxic abasic sites generated in the genome of each cell every day. Ape1 has recently emerged as a target for inhibition as its overexpression in tumors has been linked with poor response to both radiation and chemotherapy and lower overall patient survival. Inhibition of Ape1 using siRNA or the expression of a dominant-negative form of the protein have been shown to sensitize cells to DNA-damaging agents, including various chemotherapeutic agents. However, potent small molecule inhibitors of Ape1 remain to be found. To this end, we screened Ape1 against the NCI Diversity Set of small molecules and discovered aromatic nitroso, carboxylate, sulfonamide and arylstibonic acid compounds with micromolar affinities for the protein. A further screen of a 37compound arylstibonic acid sublibrary identified ligands with IC 50 values in the range 4 to 300 nM. The negatively charged stibonic acids act by a partial-mixed mode, and likely serve as DNA phosphate mimics. These compounds provide a useful scaffold for development of chemotherapeutic agents against Ape1. Every day, over 10,000 abasic sites are formed in each cell due to the spontaneous depurination of DNA bases (Lindahl and Nyberg, 1972). Without repair, these abasic sites are both mutagenic and cytotoxic (Boiteux and Guillet, 2004). Human apurinic/apyrimidinic endonuclease (Ape1) plays the important role of processing these lesions so that they may be recognized by subsequent enzymes and repaired. Ape1 accounts for more than 95% of the abasic site cleavage activity within the cell (Wilson and Barsky, 2001). This protein cleaves the DNA 5' to the abasic site, producing a 5' deoxyribose phosphate (dRP) group and a 3' hydroxyl. The 5' dRP is a substrate for DNA polymerase β, which removes this blocking group and adds the correct nucleotide. The remaining nick in the DNA is then closed by DNA ligase, consummating repair of the site (Dianov et al., 2003). Ape1 is also a pivotal component of the base excision repair (BER) pathway, which is responsible for removing aberrant bases from the genome. This pathway is initiated by enzymatic removal of a damaged or incorrect base by a DNA glycosylase, also producing an abasic site. Following cleavage of this abasic site by Ape1, the DNA is repaired through the action of the same enzymes as described above (Dianov et al., 2003). In addition to its role in DNA repair, Ape1 has been shown to be an important facilitator of both redox-dependent and independent DNA-transcription factor binding, giving the protein the alternative name of redox factor-1 (Ref-1
Tetrahedron Letters, 1987
The structures of a dimeric and a tetrameric degraded dipeptide. derivable from bromotyrosine and... more The structures of a dimeric and a tetrameric degraded dipeptide. derivable from bromotyrosine and cysteine, have been elucidated. Both compounds inhibit the growth of Bacillus subtiZis and Staphylococcus aLLI-eus. Bromotyrosine-derived secondary metabolites are characteristic of sponges of the order Verongida. 2 The compounds that have been encountered may be simple tyrosine degradation products, as e.g. aerothionin (1) 3 or they may be complex, as e.g. the psammaplysins (_2).4 which may have arisen from condensation of tyrosine with homoserine or its equivalent.
Journal of Natural Products, 2012
A series of chlorinated englerins (3-9), were isolated from Phyllanthus engleri and shown to sele... more A series of chlorinated englerins (3-9), were isolated from Phyllanthus engleri and shown to selectively inhibit the growth of renal cancer cells. The compounds were shown to be extraction artifacts produced by exposure to chloroform decomposition products during their isolation. The most active compound, 3, was synthesized from englerin A (1). Our group recently reported the isolation of two new sesquiterpenes, englerins A (1) and B (2), from the root bark and stem bark of Phyllanthus engleri Pax (Euphorbiaceae). 1 Englerin A displayed remarkable potency and selectivity in its inhibition of renal cancer cell line growth. Consequently, englerin A (1) has been under intensive preclinical investigation at the National Cancer Institute, and several groups have published the synthesis of englerin A 2-7 and analogues. 8,9 At an early stage of this project, seven related bioactive compounds (3-9) were isolated, with these considered to be artifacts produced during the isolation procedure. Reported here are their structures and biological activity, and the synthesis from 1 of the most active compound. Results and Discussion An organic extract of stem bark was separated using batch elution from a diol-bonded phase medium to give five fractions of increasing polarity. The methylene chloride-soluble fraction was separated via flash chromatography over silica gel, using mixtures of chloroform and methanol, to yield three fractions, which potently inhibited the growth of UO-31 renal cancer cells, but were inactive against SF-295 CNS cancer cells. It was determined that it was at this stage when the natural compounds were modified by chloroform that had apparently spontaneously generated Cl 2 on standing, since later attempts to purify the same fractions with newly purchased chloroform yielded only 1 and 2.
Molecular Pharmacology, 2012
Several basic leucine zipper (B-ZIP) transcription factors have been implicated in cancer, substa... more Several basic leucine zipper (B-ZIP) transcription factors have been implicated in cancer, substance abuse, and other pathological conditions. We previously identified arylstibonic acids that bind to B-ZIP proteins and inhibit their interaction with DNA. In this study, we used electrophoretic mobility shift assay to analyze 46 arylstibonic acids for their activity to disrupt the DNA binding of three B-ZIP [CCAAT/enhancer-binding protein ␣, cyclic AMP-response element-binding protein (CREB), and vitellogenin gene-binding protein (VBP)] and two basic helixloop-helix leucine zipper (B-HLH-ZIP) [USF (upstream stimulating factor) and Mitf] proteins. Twenty-five arylstibonic acids showed activity at micromolar concentrations. The most active compound, P6981 [2-(3-stibonophenyl)malonic acid], had halfmaximal inhibition at ϳ5 nM for CREB. Circular dichroism thermal denaturation studies indicated that P6981 binds both the B-ZIP domain and the leucine zipper. The crystal structure of an arylstibonic acid, NSC13778, bound to the VBP leucine zipper identified electrostatic interactions between both the stibonic and carboxylic acid groups of NSC13778 [(E)-3-(3stibonophenyl)acrylic acid] and arginine side chains of VBP, which is also involved in interhelical salt bridges in the leucine zipper. P6981 induced GFP-B-ZIP chimeric proteins to partially localize to the cytoplasm, demonstrating that it is active in cells. P6981 inhibited the growth of a patient-derived clear cell sarcoma cell line whose oncogenic potential is driven by a chimeric protein EWS-ATF1 (Ewing's sarcoma protein-activating transcription factor 1), which contains the DNA binding domain of ATF1, a B-ZIP protein. NSC13778 inhibited the growth of xenografted clear cell sarcoma, and no toxicity was observed. These experiments suggest that antimony containing arylstibonic acids are promising leads for suppression of DNA binding activities of B-ZIP and B-HLH-ZIP transcription factors.
Bioorganic Chemistry, 2008
Human topoisomerase IB (hTopo) forms a covalent phosphotyrosyl linkage with the DNA backbone, and... more Human topoisomerase IB (hTopo) forms a covalent phosphotyrosyl linkage with the DNA backbone, and controls genomic DNA topology by relaxing DNA supercoils during the processes of DNA replication, transcription, chromosome condensation and decondensation. The essential role of hTopo in these processes has made it a preeminent anticancer drug target. We have screened a small library of arylstibonic acids for their effects on plasmid supercoil relaxation catalyzed by hTopo. Despite the similar structures of the library compounds, some compounds were found to be effective competitive inhibitors, and others, nonessential activators. Some arylstibonic acids show selectivity in their action against hTopo and the related enzyme from poxvirus (vTopo). Structure-activity relationships and structural modeling suggest that competitive inhibition may result from positioning of the negatively charged stibonic acid and carboxylate groups of the inhibitors into DNA phosphate binding pockets on hTopo. The hTopo activators act by a surprising allosteric mechanism without interfering with DNA binding or binding of the widely used hTopo poison camptothecin. Arylstibonic acid competitive inhibitors may become useful small molecules for elucidating the cellular functions of hTopo.
Biochemical and Biophysical Research Communications, 2002
The crucial functions of HIV-1 nucleocapsid-p7 protein (NC-p7) at different stages of HIV replica... more The crucial functions of HIV-1 nucleocapsid-p7 protein (NC-p7) at different stages of HIV replication are dependent on its nucleic acid binding properties. In this study, a search has been made to identify antagonists of the interaction between NC-p7 and d(TG) 4 . A chemical library of $2000 small molecules (the NCI Diversity Set) was screened, of the 26 active inhibitors that were identified, five contained a xanthenyl ring structure. Further analysis of 63 structurally related compounds led to the identification of 2,3,4,5-tetrachloro-6-(4 0 ,5 0 ,6 0 -trihydroxy-3 0 -oxo-3H-xanthen-9 0 -yl)benzoic acid, which binds to NC-p7 stoichiometrically. This compound exerted a significant anti-HIV activity in vitro with an IC 50 of 16:6 AE 4:3 lM (means AE SD). Synthetic variants lacking the two hydroxyls at positions 4 0 and 5 0 in the xanthenyl ring system failed to bind NC-p7 and showed significantly less protection against HIV infection. Molecular modeling predicts that these hydroxyl groups would bind to the amide nitrogen of Gly 35 with other contacts at the carbonyl oxygens of Gly 40 and Lys 33 . Ó 2002 Elsevier Science (USA). All rights reserved.
ACS Infectious Diseases, May 10, 2023
Molecular Pharmacology, Nov 27, 2007
Human apurinic/apyrimidinic endonuclease (Ape1) plays an important role by processing the >10,000... more Human apurinic/apyrimidinic endonuclease (Ape1) plays an important role by processing the >10,000 highly toxic abasic sites generated in the genome of each cell every day. Ape1 has recently emerged as a target for inhibition as its overexpression in tumors has been linked with poor response to both radiation and chemotherapy and lower overall patient survival. Inhibition of Ape1 using siRNA or the expression of a dominant-negative form of the protein have been shown to sensitize cells to DNA-damaging agents, including various chemotherapeutic agents. However, potent small molecule inhibitors of Ape1 remain to be found. To this end, we screened Ape1 against the NCI Diversity Set of small molecules and discovered aromatic nitroso, carboxylate, sulfonamide and arylstibonic acid compounds with micromolar affinities for the protein. A further screen of a 37compound arylstibonic acid sublibrary identified ligands with IC 50 values in the range 4 to 300 nM. The negatively charged stibonic acids act by a partial-mixed mode, and likely serve as DNA phosphate mimics. These compounds provide a useful scaffold for development of chemotherapeutic agents against Ape1. Every day, over 10,000 abasic sites are formed in each cell due to the spontaneous depurination of DNA bases (Lindahl and Nyberg, 1972). Without repair, these abasic sites are both mutagenic and cytotoxic (Boiteux and Guillet, 2004). Human apurinic/apyrimidinic endonuclease (Ape1) plays the important role of processing these lesions so that they may be recognized by subsequent enzymes and repaired. Ape1 accounts for more than 95% of the abasic site cleavage activity within the cell (Wilson and Barsky, 2001). This protein cleaves the DNA 5' to the abasic site, producing a 5' deoxyribose phosphate (dRP) group and a 3' hydroxyl. The 5' dRP is a substrate for DNA polymerase β, which removes this blocking group and adds the correct nucleotide. The remaining nick in the DNA is then closed by DNA ligase, consummating repair of the site (Dianov et al., 2003). Ape1 is also a pivotal component of the base excision repair (BER) pathway, which is responsible for removing aberrant bases from the genome. This pathway is initiated by enzymatic removal of a damaged or incorrect base by a DNA glycosylase, also producing an abasic site. Following cleavage of this abasic site by Ape1, the DNA is repaired through the action of the same enzymes as described above (Dianov et al., 2003). In addition to its role in DNA repair, Ape1 has been shown to be an important facilitator of both redox-dependent and independent DNA-transcription factor binding, giving the protein the alternative name of redox factor-1 (Ref-1
ACS Medicinal Chemistry Letters
Journal of The Chemical Society-perkin Transactions 1, 1994
In 1983 leptomycin A (LPT A) and leptomycin B (LPT B) were discovered at the University of Tokyo ... more In 1983 leptomycin A (LPT A) and leptomycin B (LPT B) were discovered at the University of Tokyo as potent anti-fungal agents against schizosaccharomyces pombe Mucor racemosus and Mucor rouxiannus (ref 1). In 1985 LPT A LPT B and the monohydroxylated derivatives kazusamycin A (30-hydroxyleptomycin B HLPT B) and kasuzamycin B (29-hydroxyleptomycin A HLPT A) were isolated and reported as antitumor compounds (ref 2).
ACS Chemical Biology, 2020
An automated, high-capacity, and high-throughput procedure for the rapid isolation and identifica... more An automated, high-capacity, and high-throughput procedure for the rapid isolation and identification of biologically active natural products from a prefractionated library is presented. The semipreparative HPLC method uses 1 mg of the primary hit fraction and produces 22 subfractions in an assay-ready format. Following screening, all active fractions are analyzed by NMR, LCMS, and FTIR, and the active principle structural classes are elucidated. In the proof-of-concept study, we show the processes involved in generating the subfractions, the throughput of the structural elucidation work, as well as the ability to rapidly isolate and identify new and biologically active natural products. Overall, the rapid second-stage purification conserves extract mass, requires much less chemist time, and introduces knowledge of structure early in the isolation workflow.
Fitoterapia, 2019
Botanical-based natural products are an important resource for medicinal drug discovery and conti... more Botanical-based natural products are an important resource for medicinal drug discovery and continue to provide diverse pharmacophores with therapeutic potential against cancer and other human diseases. A prototype Traditional Chinese Medicine (TCM) plant extract library has been established at the US National Cancer Institute, which contains both the organic and aqueous extracts of 132 authenticated medicinal plant species that collectively represent the potential therapeutic contents of most commonly used TCM herbal prescriptions. This library is publicly available in 96-and 384-well plates for high throughput screening across a broad array of biological targets, as well as in larger quantities for isolation of active chemical ingredients. Herein, we present the methodology used to generate the library and the preliminary assessment of the anti-proliferative activity of this crude extract library in NCI-60 human cancer cell lines screen. Particularly, we report the chemical profiling and metabolome comparison analysis of four commonly used TCM plants, namely Brucea javanica, Dioscorea nipponica, Cynanchum atratum, and Salvia miltiorrhiza. Bioassayguided isolation resulted in the identification of the active compounds, and different extraction methods were compared for their abilities to extract cytotoxic compounds and to concentrate biologically active natural products.
Bioorganic & Medicinal Chemistry Letters, 2018
Two new cassaine-type diterpenoids, namely erythrofordins D (1) and E (2), sourced from a Cameroo... more Two new cassaine-type diterpenoids, namely erythrofordins D (1) and E (2), sourced from a Cameroon collection of Erythrophleum suaveolens were isolated and assessed for anti-tumor
ACS chemical biology, Jan 13, 2018
The US National Cancer Institute's (NCI) Natural Product Repository is one of the world's... more The US National Cancer Institute's (NCI) Natural Product Repository is one of the world's largest, most diverse collections of natural products containing over 230,000 unique extracts derived from plant, marine, and microbial organisms that have been collected from biodiverse regions throughout the world. Importantly, this national resource is available to the research community for the screening of extracts and the isolation of bioactive natural products. However, despite the success of natural products in drug discovery, compatibility issues that make extracts challenging for liquid handling systems, extended timelines that complicate natural product-based drug discovery efforts and the presence of pan-assay interfering compounds have reduced enthusiasm for the high-throughput screening (HTS) of crude natural product extract libraries in targeted assay systems. To address these limitations, the NCI Program for Natural Product Discovery (NPNPD), a newly launched, national p...
Molecular Pharmacology, 2007
Human apurinic/apyrimidinic endonuclease (Ape1) plays an important role by processing the >10,000... more Human apurinic/apyrimidinic endonuclease (Ape1) plays an important role by processing the >10,000 highly toxic abasic sites generated in the genome of each cell every day. Ape1 has recently emerged as a target for inhibition as its overexpression in tumors has been linked with poor response to both radiation and chemotherapy and lower overall patient survival. Inhibition of Ape1 using siRNA or the expression of a dominant-negative form of the protein have been shown to sensitize cells to DNA-damaging agents, including various chemotherapeutic agents. However, potent small molecule inhibitors of Ape1 remain to be found. To this end, we screened Ape1 against the NCI Diversity Set of small molecules and discovered aromatic nitroso, carboxylate, sulfonamide and arylstibonic acid compounds with micromolar affinities for the protein. A further screen of a 37compound arylstibonic acid sublibrary identified ligands with IC 50 values in the range 4 to 300 nM. The negatively charged stibonic acids act by a partial-mixed mode, and likely serve as DNA phosphate mimics. These compounds provide a useful scaffold for development of chemotherapeutic agents against Ape1. Every day, over 10,000 abasic sites are formed in each cell due to the spontaneous depurination of DNA bases (Lindahl and Nyberg, 1972). Without repair, these abasic sites are both mutagenic and cytotoxic (Boiteux and Guillet, 2004). Human apurinic/apyrimidinic endonuclease (Ape1) plays the important role of processing these lesions so that they may be recognized by subsequent enzymes and repaired. Ape1 accounts for more than 95% of the abasic site cleavage activity within the cell (Wilson and Barsky, 2001). This protein cleaves the DNA 5' to the abasic site, producing a 5' deoxyribose phosphate (dRP) group and a 3' hydroxyl. The 5' dRP is a substrate for DNA polymerase β, which removes this blocking group and adds the correct nucleotide. The remaining nick in the DNA is then closed by DNA ligase, consummating repair of the site (Dianov et al., 2003). Ape1 is also a pivotal component of the base excision repair (BER) pathway, which is responsible for removing aberrant bases from the genome. This pathway is initiated by enzymatic removal of a damaged or incorrect base by a DNA glycosylase, also producing an abasic site. Following cleavage of this abasic site by Ape1, the DNA is repaired through the action of the same enzymes as described above (Dianov et al., 2003). In addition to its role in DNA repair, Ape1 has been shown to be an important facilitator of both redox-dependent and independent DNA-transcription factor binding, giving the protein the alternative name of redox factor-1 (Ref-1
Tetrahedron Letters, 1987
The structures of a dimeric and a tetrameric degraded dipeptide. derivable from bromotyrosine and... more The structures of a dimeric and a tetrameric degraded dipeptide. derivable from bromotyrosine and cysteine, have been elucidated. Both compounds inhibit the growth of Bacillus subtiZis and Staphylococcus aLLI-eus. Bromotyrosine-derived secondary metabolites are characteristic of sponges of the order Verongida. 2 The compounds that have been encountered may be simple tyrosine degradation products, as e.g. aerothionin (1) 3 or they may be complex, as e.g. the psammaplysins (_2).4 which may have arisen from condensation of tyrosine with homoserine or its equivalent.
Journal of Natural Products, 2012
A series of chlorinated englerins (3-9), were isolated from Phyllanthus engleri and shown to sele... more A series of chlorinated englerins (3-9), were isolated from Phyllanthus engleri and shown to selectively inhibit the growth of renal cancer cells. The compounds were shown to be extraction artifacts produced by exposure to chloroform decomposition products during their isolation. The most active compound, 3, was synthesized from englerin A (1). Our group recently reported the isolation of two new sesquiterpenes, englerins A (1) and B (2), from the root bark and stem bark of Phyllanthus engleri Pax (Euphorbiaceae). 1 Englerin A displayed remarkable potency and selectivity in its inhibition of renal cancer cell line growth. Consequently, englerin A (1) has been under intensive preclinical investigation at the National Cancer Institute, and several groups have published the synthesis of englerin A 2-7 and analogues. 8,9 At an early stage of this project, seven related bioactive compounds (3-9) were isolated, with these considered to be artifacts produced during the isolation procedure. Reported here are their structures and biological activity, and the synthesis from 1 of the most active compound. Results and Discussion An organic extract of stem bark was separated using batch elution from a diol-bonded phase medium to give five fractions of increasing polarity. The methylene chloride-soluble fraction was separated via flash chromatography over silica gel, using mixtures of chloroform and methanol, to yield three fractions, which potently inhibited the growth of UO-31 renal cancer cells, but were inactive against SF-295 CNS cancer cells. It was determined that it was at this stage when the natural compounds were modified by chloroform that had apparently spontaneously generated Cl 2 on standing, since later attempts to purify the same fractions with newly purchased chloroform yielded only 1 and 2.
Molecular Pharmacology, 2012
Several basic leucine zipper (B-ZIP) transcription factors have been implicated in cancer, substa... more Several basic leucine zipper (B-ZIP) transcription factors have been implicated in cancer, substance abuse, and other pathological conditions. We previously identified arylstibonic acids that bind to B-ZIP proteins and inhibit their interaction with DNA. In this study, we used electrophoretic mobility shift assay to analyze 46 arylstibonic acids for their activity to disrupt the DNA binding of three B-ZIP [CCAAT/enhancer-binding protein ␣, cyclic AMP-response element-binding protein (CREB), and vitellogenin gene-binding protein (VBP)] and two basic helixloop-helix leucine zipper (B-HLH-ZIP) [USF (upstream stimulating factor) and Mitf] proteins. Twenty-five arylstibonic acids showed activity at micromolar concentrations. The most active compound, P6981 [2-(3-stibonophenyl)malonic acid], had halfmaximal inhibition at ϳ5 nM for CREB. Circular dichroism thermal denaturation studies indicated that P6981 binds both the B-ZIP domain and the leucine zipper. The crystal structure of an arylstibonic acid, NSC13778, bound to the VBP leucine zipper identified electrostatic interactions between both the stibonic and carboxylic acid groups of NSC13778 [(E)-3-(3stibonophenyl)acrylic acid] and arginine side chains of VBP, which is also involved in interhelical salt bridges in the leucine zipper. P6981 induced GFP-B-ZIP chimeric proteins to partially localize to the cytoplasm, demonstrating that it is active in cells. P6981 inhibited the growth of a patient-derived clear cell sarcoma cell line whose oncogenic potential is driven by a chimeric protein EWS-ATF1 (Ewing's sarcoma protein-activating transcription factor 1), which contains the DNA binding domain of ATF1, a B-ZIP protein. NSC13778 inhibited the growth of xenografted clear cell sarcoma, and no toxicity was observed. These experiments suggest that antimony containing arylstibonic acids are promising leads for suppression of DNA binding activities of B-ZIP and B-HLH-ZIP transcription factors.
Bioorganic Chemistry, 2008
Human topoisomerase IB (hTopo) forms a covalent phosphotyrosyl linkage with the DNA backbone, and... more Human topoisomerase IB (hTopo) forms a covalent phosphotyrosyl linkage with the DNA backbone, and controls genomic DNA topology by relaxing DNA supercoils during the processes of DNA replication, transcription, chromosome condensation and decondensation. The essential role of hTopo in these processes has made it a preeminent anticancer drug target. We have screened a small library of arylstibonic acids for their effects on plasmid supercoil relaxation catalyzed by hTopo. Despite the similar structures of the library compounds, some compounds were found to be effective competitive inhibitors, and others, nonessential activators. Some arylstibonic acids show selectivity in their action against hTopo and the related enzyme from poxvirus (vTopo). Structure-activity relationships and structural modeling suggest that competitive inhibition may result from positioning of the negatively charged stibonic acid and carboxylate groups of the inhibitors into DNA phosphate binding pockets on hTopo. The hTopo activators act by a surprising allosteric mechanism without interfering with DNA binding or binding of the widely used hTopo poison camptothecin. Arylstibonic acid competitive inhibitors may become useful small molecules for elucidating the cellular functions of hTopo.
Biochemical and Biophysical Research Communications, 2002
The crucial functions of HIV-1 nucleocapsid-p7 protein (NC-p7) at different stages of HIV replica... more The crucial functions of HIV-1 nucleocapsid-p7 protein (NC-p7) at different stages of HIV replication are dependent on its nucleic acid binding properties. In this study, a search has been made to identify antagonists of the interaction between NC-p7 and d(TG) 4 . A chemical library of $2000 small molecules (the NCI Diversity Set) was screened, of the 26 active inhibitors that were identified, five contained a xanthenyl ring structure. Further analysis of 63 structurally related compounds led to the identification of 2,3,4,5-tetrachloro-6-(4 0 ,5 0 ,6 0 -trihydroxy-3 0 -oxo-3H-xanthen-9 0 -yl)benzoic acid, which binds to NC-p7 stoichiometrically. This compound exerted a significant anti-HIV activity in vitro with an IC 50 of 16:6 AE 4:3 lM (means AE SD). Synthetic variants lacking the two hydroxyls at positions 4 0 and 5 0 in the xanthenyl ring system failed to bind NC-p7 and showed significantly less protection against HIV infection. Molecular modeling predicts that these hydroxyl groups would bind to the amide nitrogen of Gly 35 with other contacts at the carbonyl oxygens of Gly 40 and Lys 33 . Ó 2002 Elsevier Science (USA). All rights reserved.