Synthesis, DNA cleavage and cytotoxicity of some novel cyclic peptide-2,6-dimethoxyhydroquinone-3-mercaptoacetic acid conjugates containing D-amino acids

Sen Liang Chen, Ricky N S WONG, Vivian Lo, Suzi Chang, Chi Der Chiang, Leung Sheh*

*Corresponding author for this work

Research output: Contribution to journalJournal articlepeer-review

5 Citations (Scopus)

Abstract

This paper reports an ongoing study of the use of small-ring-size cyclic peptides as carriers of a potential antitumor agent: 2,6-dimethoxyhydroquinone-3-mercaptoacetic acid (DMQ-MA). Three new cyclic tripeptide-DMQ-MA conjugates - cyclo[D-Val-Lys(DMQ-MA)-γ-aminobutyric acid (GABA)-], cyclo[Val-Lys(DMQ-MA)-GABA-] and cyclo[D-Val-D-Lys(DMQ-MA)-GABA-] - were synthesized. The isomeric cyclic tripeptide-DMQ-MA conjugates were designed and synthesized to study the effect of stereoisomerism of the conjugates on cytotoxicity. The cyclic peptides were synthesized by coupling protected amino acids in solution and the final cyclization performed by the pentafluorophenyl ester method as described previously. After removing the lysyl-Z protecting group of the cyclic peptides the conjugation was achieved by reacting with the pentafluorophenyl ester of DMQ-MA. Electron spin resonance (ESR) studies of these three cyclic tripeptide-DMQ-MA conjugates showed that hydroxyl radicals were generated as a non-linear function of L-ascorbic acid (AH2) concentration. The IC50 of the cyclic tripeptide-DMQ-MA conjugates against a human pulmonary carcinoma cell line (PC 9 cells) under the synergistic activation of AH2 ranges from 0.4 to 1.6 μM, which is significantly lower than the parent compound DMQ-MA (6.1 μM). Agarose gel electrophoresis showed that DMQ-MA and these cyclic peptide-DMQ-MA conjugates are capable of cleaving supercoiled plasmid DNA to open circular and linear forms, even in the absence of AH2. The effects of enantiomeric and diastereomeric variations of these cyclic tripeptide-DMQ-MA conjugates on the cytotoxicity against PC-9 cells were discussed.

Original languageEnglish
Pages (from-to)501-518
Number of pages18
JournalAnti-Cancer Drug Design
Volume13
Issue number5
Publication statusPublished - Jul 1998

Scopus Subject Areas

  • Biochemistry
  • Oncology
  • Biochemistry, Genetics and Molecular Biology(all)
  • Pharmacology
  • Drug Discovery
  • Organic Chemistry

User-Defined Keywords

  • DNA cleavage studies
  • Enantiomeric and diastereomeric cyclic tripeptide-cytotoxic agent conjugates
  • ESR studies
  • In vitro antitumor studies

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