Betulinic acid, a potent inhibitor of eukaryotic topoisomerase I: Identification of the inhibitory step, the major functional group responsible and development of more potent derivatives

Arnab Roy Chowdhury, Suparna Mandal, Bidyottam Mittra, Shalini Sharma, Sibabrata Mukhopadhyay, Hemanta K. Majumder

Research output: Contribution to journalArticle

100 Citations (Scopus)

Abstract

Background: Betulinic acid, a naturally abundant, plant derived, pentacyclic triterpenoid possesses anti-HIV, anti-malarial and anti-inflammatory properties and has recently emerged as a potent anti-tumor compound. This study explores the mode of action of betulinic acid on eukaryotic topoisomerase I and identifies the major functional group responsible along with more potent derivatives, Material/Methods: Topoisomerase I relaxation activity was electrophoretically measured by the decreased mobility of the relaxed monomers followed by ethidium bromide staining. DNA cleavage was studied by electrophoretic separation of the nicked monomers from the relaxed and supercoiled monomers in presence of ethidium bromide. In-vivo DNA cleavage was studied in blasted mouse splenocytes by the SDS-K+ trapping of 3H-DNA-topoisomerase I-camptothecin ternary complex. Results: Betulinic acid exerts its inhibitory effect by preventing topoisomerase I-DNA interaction as a result of which the 'cleavable complex' is not formed. In consequence, it also acts as an antagonist to camptothecin-mediated cleavage. A series of analogues modified at C-3, C-17 and C-20 positions of betulinic acid were subsequently assayed for inhibition of topoisomerase I catalytic activity. Replacement of the 17-carboxylic group reduces the inhibitory effect and decarboxylation leads to the complete loss of inhibitory effect. Conclusion: This study is the first detail report of betulinic acid as a very potent inhibitior of eukaryotic topoisomerase I and highlights the necessity of the carboxylic functional group. Dihydro betulinic acid is the most potent (IC50=0.5 μM) pentacyclic triterpenoid to inhibit eukaryotic topoisomerase I till date and can be exploited as a strong candidate for anti-tumor drug designing.

Original languageEnglish (US)
JournalMedical Science Monitor
Volume8
Issue number7
StatePublished - 2002
Externally publishedYes

Fingerprint

Topoisomerase I Inhibitors
Type I DNA Topoisomerase
Camptothecin
DNA Cleavage
Ethidium
Decarboxylation
Antimalarials
betulinic acid
Inhibitory Concentration 50
Neoplasms
Anti-Inflammatory Agents
HIV
Staining and Labeling

Keywords

  • Anti-tumor compound
  • Betulinic acid
  • Catalytic Inhibitor
  • Cleavage antagonist
  • Topoisomerase I

ASJC Scopus subject areas

  • Medicine(all)

Cite this

Betulinic acid, a potent inhibitor of eukaryotic topoisomerase I : Identification of the inhibitory step, the major functional group responsible and development of more potent derivatives. / Chowdhury, Arnab Roy; Mandal, Suparna; Mittra, Bidyottam; Sharma, Shalini; Mukhopadhyay, Sibabrata; Majumder, Hemanta K.

In: Medical Science Monitor, Vol. 8, No. 7, 2002.

Research output: Contribution to journalArticle

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AU - Majumder, Hemanta K.

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N2 - Background: Betulinic acid, a naturally abundant, plant derived, pentacyclic triterpenoid possesses anti-HIV, anti-malarial and anti-inflammatory properties and has recently emerged as a potent anti-tumor compound. This study explores the mode of action of betulinic acid on eukaryotic topoisomerase I and identifies the major functional group responsible along with more potent derivatives, Material/Methods: Topoisomerase I relaxation activity was electrophoretically measured by the decreased mobility of the relaxed monomers followed by ethidium bromide staining. DNA cleavage was studied by electrophoretic separation of the nicked monomers from the relaxed and supercoiled monomers in presence of ethidium bromide. In-vivo DNA cleavage was studied in blasted mouse splenocytes by the SDS-K+ trapping of 3H-DNA-topoisomerase I-camptothecin ternary complex. Results: Betulinic acid exerts its inhibitory effect by preventing topoisomerase I-DNA interaction as a result of which the 'cleavable complex' is not formed. In consequence, it also acts as an antagonist to camptothecin-mediated cleavage. A series of analogues modified at C-3, C-17 and C-20 positions of betulinic acid were subsequently assayed for inhibition of topoisomerase I catalytic activity. Replacement of the 17-carboxylic group reduces the inhibitory effect and decarboxylation leads to the complete loss of inhibitory effect. Conclusion: This study is the first detail report of betulinic acid as a very potent inhibitior of eukaryotic topoisomerase I and highlights the necessity of the carboxylic functional group. Dihydro betulinic acid is the most potent (IC50=0.5 μM) pentacyclic triterpenoid to inhibit eukaryotic topoisomerase I till date and can be exploited as a strong candidate for anti-tumor drug designing.

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