Gaik-Lean Chee

Reproducible and high-speed separation of basic drugs by capillary zone electrophoresis

The complete separation of a mixture of seventeen basic drugs of different classes was achieved with capillary zone electrophoresis in 11 min. The migration time reproducibility for individual components was between 0.5 and 1.7% relative standard deviation (R.S.D.). Peak detection was achieved by ultraviolet absorption, with peak-area reproducibility ranging from 1.5 to 6.3% R.S.D. The pH of the running buffer was critical in determining the separation of the mixture of basic drugs. The detection of most of these components in urine and plasma is also illustrated.

A diazirine-based photoaffinity etoposide probe for labeling topoisomerase II

Etoposide is a widely used anticancer drug that targets topoisomerase II, an essential nuclear enzyme. However, despite the fact that it has been in use and studied for more than 30years the specific site on the enzyme to which it binds is unknown. In order to identify the etoposide binding site(s) on topoisomerase II, a diazirine-based photoaffinity etoposide analog probe has been synthesized and its photoreactivity and biological activities have been characterized. Upon UV irradiation, the diazirine probe rapidly produced a highly reactive carbene species that formed covalent adducts containing stable carbon-based bonds indicating that it should also be able to form stable covalent adducts with amino acid residues on topoisomerase II. The human leukemia K562 cell growth and topoisomerase II inhibitory properties of the diazirine probe suggest that it targets topoisomerase II in a manner similar to etoposide. The diazirine probe was also shown to act as a topoisomerase II poison through its ability to cause topoisomerase IIalpha-mediated double-strand cleavage of DNA. Additionally, the diazirine probe significantly increased protein-DNA covalent complex formation upon photoirradiation of diazirine probe-treated K562 cells, as compared to etoposide-treated cells. This result suggests that the photoactivated probe forms a covalent adduct with topoisomerase IIalpha. In conclusion, the present characterization of the chemical, biochemical, and biological properties of the newly synthesized diazirine-based photoaffinity etoposide analog indicates that use of a proteomics mass spectrometry approach will be a tractable strategy for future identification of the etoposide binding site(s) on topoisomerase II through covalent labeling of amino acid residues.

Design, synthesis and biological evaluation of a novel series of anthrapyrazoles linked with netropsin-like oligopyrrole carboxamides as anticancer agents

Anticancer drugs that bind to DNA and inhibit DNA-processing enzymes represent an important class of anticancer drugs. Combilexin molecules, which combine DNA minor groove binding and intercalating functionalities, have the potential for increased DNA binding affinity and increased selectivity due to their dual mode of DNA binding. This study describes the synthesis of DNA minor groove binder netropsin analogs containing either one or two N-methylpyrrole carboxamide groups linked to DNA-intercalating anthrapyrazoles. Those hybrid molecules which had both two N-methylpyrrole groups and terminal (dimethylamino)alkyl side chains displayed submicromolar cytotoxicity towards K562 human leukemia cells. The combilexins were also evaluated for DNA binding by measuring the increase in DNA melting temperature, for DNA topoisomerase IIalpha-mediated double strand cleavage of DNA, for inhibition of DNA topoisomerase IIalpha decatenation activity, and for inhibition of DNA topoisomerase I relaxation of DNA. Several of the compounds stabilized the DNA-topoisomerase IIalpha covalent complex indicating that they acted as topoisomerase IIalpha poisons. Some of the combilexins had higher affinity for DNA than their parent anthrapyrazoles. In conclusion, a novel group of compounds combining DNA intercalating anthrapyrazole groups and minor groove binding netropsin analogs have been designed, synthesized and biologically evaluated as possible novel anticancer agents.

The cardioprotective and DNA topoisomerase II inhibitory agent dexrazoxane (ICRF-187) antagonizes camptothecin-mediated growth inhibition of Chinese hamster ovary cells by inhibition of DNA synthesis.

Dexrazoxane (ICRF-187), which is clinically used to reduce doxorubicin-induced cardiotoxicity, has cell growth inhibitory properties through its ability to inhibit the catalytic activity of DNA topoisomerase II. A study was undertaken to investigate whether preincubating Chinese hamster ovary cells (CHO) with dexrazoxane prior to camptothecin treatment resulted in potentiation. Camptothecin is a DNA topoisomerase I poison. It was found that pretreating CHO cells with concentrations of dexrazoxane sufficient to strongly inhibit topoisomerase II for periods from 18 to 96 h resulted in significant antagonism of camptothecin-mediated growth inhibition. Lower concentrations that were sufficient to cause partial inhibition of topoisomerase II and partial dexrazoxane-mediated cell growth inhibition had little effect on camptothecin-mediated growth inhibition. Neither topoisomerase I protein levels nor camptothecin-induced topoisomerase I-DNA covalent complexes were affected by dexrazoxane concentrations that were sufficient to cause antagonism of camptothecin-induced growth inhibition. However, under these experimental conditions, dexrazoxane caused a decrease in DNA synthesis. Therefore, results presented here confirm the importance of the DNA synthesis-dependent replication fork interaction with topoisomerase I-DNA covalent complexes for the expression of camptothecin activity. It is concluded that dexrazoxane and camptothecin analogs should be used with caution in combination chemotherapy.

Synthesis of chiral esters of acetylenedicarboxylic acid

A general method for the preparation of acetylenedicarboxylic acid esters has been investigated and several esters have been prepared in excellent yield. The bis-(methyl (S)-lactyl), bis-(methyl (R)-mandelyl), and bis-menthyl esters were prepared, as well as achiral diaryl and dialkyl esters. The esters were synthesized from the corresponding dibromofumarates by 2,3-dibromo elimination using zinc or zinc amalgam in THF at room temperature or at reflux. The dibromofumarates were prepared by the esterification of dibromofumaryl chloride with the corresponding alcohols.

Efficient Synthesis of Bifenazate

Abstract The synthesis of bifenazate using a two‐step procedure has been accomplished with an overall yield of 26%. The procedure involved the Lewis acid–catalyzed electrophilic aromatic substitution of 4‐methoxybiphenyl with diisopropyl azodicarcoxylate (DIAD) to give a hydrazinedicarboxylate intermediate that was then subjected to a decarboxylation reaction to give bifenazate.Abstract The synthesis of bifenazate using a two‐step procedure has been accomplished with an overall yield of 26%. The procedure involved the Lewis acid–catalyzed electrophilic aromatic substitution of 4‐methoxybiphenyl with diisopropyl azodicarcoxylate (DIAD) to give a hydrazinedicarboxylate intermediate that was then subjected to a decarboxylation reaction to give bifenazate.

Synthesis and biological activity of a photoaffinity etoposide probe.

The epipodophyllotoxin etoposide is a potent and widely used anticancer drug that targets DNA topoisomerase II. The synthesis, photochemical, and biological testing of a photoactivatable aromatic azido analogue of etoposide also containing an iodo group is described. This azido analogue should prove useful for identifying the etoposide interaction site on topoisomerase II. Irradiation of the azido analogue and an aldehyde-containing azido precursor with UV light produced changes in their UV--visible spectra that were consistent with photoactivation. The azido analogue strongly inhibited topoisomerase II and inhibited the growth of Chinese Hamster Ovary cells. Azido analogue-induced topoisomerase II--DNA covalent complexes were significantly increased subsequent to UV irradiation of drug-treated human leukemia K562 cells as compared to etoposide-treated cells. These results suggest that the photoactivated form of etoposide is a more effective topoisomerase II poison either by interacting directly with the enzyme or with DNA subsequent to topoisomerase II-mediated strand cleavage.

Structure-based design, synthesis and biological testing of piperazine-linked bis-epipodophyllotoxin etoposide analogs

Drugs that target DNA topoisomerase II, such as the epipodophyllotoxin etoposide, are a clinically important class of anticancer agents. A recently published X-ray structure of a ternary complex of etoposide, cleaved DNA and topoisomerase IIβ showed that the two intercalated etoposide molecules in the complex were separated by four DNA base pairs. Thus, using a structure-based design approach, a series of bis-epipodophyllotoxin etoposide analogs with piperazine-containing linkers was designed to simultaneously bind to these two sites. It was hypothesized that two-site binding would produce a more stable cleavage complex, and a more potent anticancer drug. The most potent bis-epipodophyllotoxin, which was 10-fold more growth inhibitory toward human erythroleukemic K562 cells than etoposide, contained a linker with eight methylene groups. All of the mono- and bis-epipodophyllotoxins, in a variety of assays, showed strong evidence that they targeted topoisomerase II. COMPARE analysis of NCI 60-cell GI50 endpoint data was also consistent with these compounds targeting topoisomerase II.

Abstract 3508: A diazirine-based photoaffinity etoposide probe for labeling topoisomerase II

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Etoposide is a widely used anticancer drug that targets topoisomerase II, an essential nuclear enzyme. However, despite the fact that it has been in use and studied for more than 30 years the specific site on the enzyme to which it binds is unknown. In order to identify the etoposide binding site(s) on topoisomerase II, a diazirine-based photoaffinity etoposide analog probe has been synthesized and its photoreactivity and biological activities have been characterized. Upon UV irradiation, the diazirine probe rapidly produced a highly reactive carbene species that formed covalent adducts containing stable carbon-based bonds indicating that it should also be able to form stable covalent adducts with amino acid residues on topoisomerase II. The human leukemia K562 cell growth and topoisomerase II inhibitory properties of the diazirine probe suggest that it targets topoisomerase II in a manner similar to etoposide. The diazirine probe was also shown to act as a topoisomerase II poison through its ability to cause topoisomerase IIα-mediated double-strand cleavage of DNA. Additionally, the diazirine probe significantly increased protein-DNA covalent complex formation upon photoirradiation of diazirine probe-treated K562 cells, as compared to etoposide-treated cells. This result suggests that the photoactivated probe forms a covalent adduct with topoisomerase IIα. In conclusion, the present characterization of the chemical, biochemical, and biological properties of the newly synthesized diazirine-based photoaffinity etoposide analog indicates that use of a proteomics mass spectrometry approach will be a tractable strategy for future identification of the etoposide binding site(s) on topoisomerase II through covalent labeling of amino acid residues. This work was supported by institutional grants from the University of Manitoba, Canadian Institutes of Health Research, National Institutes of Health grant CA090787 to J.C.Y. and a Canada Research Chair for Drug Development for B.B.H Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3508.

Abstract 3509: Design, synthesis and biological evaluation of a novel series of anthrapyrazoles linked with netropsin-like oligopyrrole carboxamides as anticancer agents

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Anticancer drugs that bind to DNA and inhibit DNA-processing enzymes represent an important class of anticancer drugs. Combilexin molecules, which combine DNA minor groove binder and intercalator functionalities, have the potential for increased DNA binding affinity and increased cytotoxicity due to their dual mode of DNA binding. In this study DNA minor groove binder netropsin analogs containing either a mono-N-methylpyrrole carboxamide or two units of N-methylpyrrole carboxamide linked to DNA intercalating anthrapyrazoles were synthesized. Two of the hybrid molecules which possessed bis-methylpyrrole moities and amine head groups displayed submicromolar cytotoxicity towards K562 human leukemia cells. The synthesized hybrids were also evaluated for DNA binding by measuring the increase in DNA melting temperature, for DNA topoisomerase IIα-mediated double strand cleavage of DNA, for inhibition of DNA topoisomerase IIα decatenation activity, and for inhibition DNA topoisomerase I relaxation of DNA. Several of the compounds stabilized the DNA-topoisomerase IIα covalent complex, indicating that they acted as topoisomerase IIα poisons. The results indicate that the hybrid agents have higher affinity for DNA than the parent compounds. In conclusion, a novel group of compounds combining DNA intercalating anthrapyrazoles and minor groove binding netropsin analogs have been designed, synthesized and biologically evaluated as possible novel anticancer agents. Support: CIHR, a Canada Research Chair in Drug Development, National Institutes of Health grant CA090787 to J.C.Y., the Dishman Foundation at Southwestern University and the Robert A. Welsh Foundation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3509.