Abstract
Toward developing antileishmanial agents with mode of action targeted to DNA topoisomerases of Leishmania donovani, we have synthesized a large number of derivatives of betulin. The compound, a natural triterpene isolated from the cork layer of Betula spp. plants exhibits several pharmacological properties. Three compounds (disuccinyl betulin, diglutaryl dihydrobetulin, and disuccinyl dihydrobetulin) inhibit growth of the parasite as well as relaxation activity of the enzyme type IB topoisomerase [Leishmania donovani topoisomerase I (LdTOP1LS)] of the parasite. Mechanistic studies suggest that these compounds interact with the enzyme in a reversible manner. The stoichiometry of these compounds binding to LdTOP1LS is 1:1 (mole/mole) with a dissociation constant on the order of ∼10−6 M. Unlike CPT, these compounds do not stabilize the cleavage complex; rather, they abrogate the covalent complex formation. In processive mode of relaxation assay condition, these compounds slow down the strand rotation event, which ultimately affects the relaxation of supercoiled DNA. It is noteworthy that these compounds reduce the intracellular parasite burden in macrophages infected with wild-type L. donovani as well as with sodium antimony gluconate resistant parasite (GE1). Taken together, our data suggest that these betulin derivatives can be exploited as potential drug candidates against threatening drug resistant leishmaniasis.
Footnotes
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The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
This work was supported by the Network Project from Council of Scientific and Industrial Research (CSIR), Government of India [Grant NWP-0038]; and by a Senior Research Fellowship from Council of Scientific and Industrial Research, Government of India (to S.C.).
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.111.072785.
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ABBREVIATIONS:
- LdTOP1L
- Leishmania donovani topoisomerase I large subunit
- LdTOP1S
- Leishmania donovani topoisomerase I small subunit
- CPT
- camptothecin
- DMSO
- dimethyl sulfoxide
- DTT
- dithiothreitol
- pBS
- pBluescript
- BSA
- bovine serum albumin
- EtBr
- ethidium bromide
- FBS
- fetal bovine serum
- RPMI-FBS
- RPMI 1640 medium (supplemented with 100 IU/ml penicillin and 100 μg/ml streptomycin) containing 10% (v/v) heat-inactivated FBS
- DiSB
- 3-O,28-O-disuccinyl betulin (4)
- DiGDHB
- 3-O,28-O-diglutaryl dihydrobetulin (8)
- DiSDHB
- 3-O,28-O-disuccinyl dihydrobetulin (10)
- LdTOP1LS
- Leishmania donovani type IB topoisomerase
- SbS
- antimony-sensitive
- SbR
- antimony-resistant
- Lk
- Linking number.
- Received April 6, 2011.
- Accepted July 12, 2011.
- Copyright © 2011 The American Society for Pharmacology and Experimental Therapeutics
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