Synthesis, cytotoxicity, and antiplasmodial and antitrypanosomal activity of new neocryptolepine derivatives.
On the basis of the original lead neocryptolepine or 5-methyl-5H-indolo[2,3-b]quinoline, an alkaloid from Cryptolepis sanguinolenta, derivatives were prepared using a biradical cyclization methodology. Starting from easily accessible educts, this approach allowed the synthesis of hitherto unknown compounds with a varied substitution pattern. As a result of steric hindrance, preferential formation of the 3-substituted isomers over the 1-substituted isomers was observed when cyclizing N-(3-substituted-phenyl)-N'-[2-(2-trimethylsilylethynyl)phenyl]carbodiimides. All compounds were evaluated for their activity against chloroquine-sensitive as well as chloroquine-resistant Plasmodium falciparum strains, for their activity against Trypanosoma brucei and T. cruzi, and for their cytotoxicity on human MRC-5 cells. Mechanisms of action were investigated by testing heme complexation using ESI-MS, inhibition of beta-hematin formation, DNA interactions (DNA-methyl green assay and linear dichroism), and inhibition of human topoisomerase II. Neocryptolepine derivatives with a higher antiplasmodial activity and a lower cytotoxicity than the original lead have been obtained. This selective antiplasmodial activity was associated with inhibition of beta-hematin formation. 2-Bromoneocryptolepine was the most selective compound with an IC(50) value against chloroquine-resistant P. falciparum of 4.0 microM in the absence of cytotoxicity (IC(50) > 32 microM). Although cryptolepine, a known lead for antimalarials also originally isolated from Cryptolepis sanguinolenta, was more active (IC(50) = 2.0 microM), 2-bromoneocryptolepine showed a low affinity for DNA and no inhibition of human topoisomerase II, in contrast to cryptolepine. Although some neocryptolepine derivatives showed a higher antiplasmodial activity than 2-bromocryptolepine, these compounds also showed a higher affinity for DNA and/or a more pronounced cytotoxicity. Therefore, 2-bromoneocryptolepine is considered as the most promising lead from the present work for new antimalarial agents. In addition, 2-bromo-, 2-nitro-, and 2-methoxy-9-cyanoneocryptolepine exhibited antitrypanosomal activity in the micromolar range in the absence of obvious cytotoxicity.
Department of Pharmaceutical Sciences, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium.
Tim H M
TH
Jonckers
Sabine
S
van Miert
Kanyanga
K
Cimanga
Christian
C
Bailly
Pierre
P
Colson
Marie-Claire
MC
De Pauw-Gillet
Hilde
H
van den Heuvel
Magda
M
Claeys
Filip
F
Lemière
Eddy L
EL
Esmans
Jef
J
Rozenski
Ludo
L
Quirijnen
Louis
L
Maes
Roger
R
Dommisse
Guy L F
GL
Lemière
Arnold
A
Vlietinck
Luc
L
Pieters
D000470:Alkaloids / Q000138:chemical synthesis* / Q000494:pharmacology / Q000633:toxicity; D000818:Animals; D000962:Antimalarials / Q000138:chemical synthesis* / Q000494:pharmacology / Q000633:toxicity; D002460:Cell Line; D004247:DNA / Q000737:chemistry; D006418:Heme / Q000737:chemistry; D006427:Hemin / Q000737:chemistry; D006801:Humans; D007364:Intercalating Agents / Q000138:chemical synthesis / Q000494:pharmacology / Q000633:toxicity; D010963:Plasmodium falciparum / Q000187:drug effects; D011108:Polymers; D011804:Quinolines / Q000138:chemical synthesis* / Q000494:pharmacology / Q000633:toxicity; D021241:Spectrometry, Mass, Electrospray Ionization; D013329:Structure-Activity Relationship; D059005:Topoisomerase II Inhibitors; D014344:Trypanocidal Agents / Q000138:chemical synthesis* / Q000494:pharmacology / Q000633:toxicity; D014346:Trypanosoma brucei brucei / Q000187:drug effects; D014349:Trypanosoma cruzi / Q000187:drug effects
D000470:Alkaloids; D000962:Antimalarials; D007364:Intercalating Agents; D011108:Polymers; D011804:Quinolines; D059005:Topoisomerase II Inhibitors; D014344:Trypanocidal Agents; C414982:neocryptolepine; D006418:Heme; D006427:Hemin; D004247:DNA