A Prodrug Form of a Plasmodium falciparum Glutathione Reductase Inhibitor Conjugated with a 4-Anilinoquinoline

Abstract

Glutathione (GSH), which is known to guard Plasmodium falciparum from oxidative damage, may have an additional protective role by promoting heme catabolism. An elevation of GSH content in parasites leads to increased resistance to chloroquine (CQ), while GSH depletion in resistant P. falciparum strains is expected to restore the sensitivity to CQ. High intracellular GSH levels depend inter alia on the efficient reduction of GSSG by glutathione reductase (GR). On the basis of this hypothesis, we have developed a new strategy for overcoming glutathione-dependent 4-aminoquinoline resistance. To direct both a 4-aminoquinoline and a GR inhibitor to the parasite, double-drugs were designed and synthesized. Quinoline-based alcohols (with known antimalarial activity) were combined with a GR inhibitor via a metabolically labile ester bond to give double-headed prodrugs. The biochemically most active double-drug 7 of this series was then evaluated as a growth inhibitor against six Plasmodium falciparum strains that differed in their degree of resistance to CQ; the ED(50) values for CQ ranged from 14 to 183 nM. While the inhibitory activity of the original 4-aminoquinoline-based alcohol followed that of CQ in these tests, the double-drug exhibited similar efficiency against all strains, the ED(50) being as low as 28 nM. For the ester 7, a dose-dependent decrease in glutathione content and GR activity and an increase in glutathione-S-transferase activity were determined in treated parasites. The drug was subsequently tested for its antimalarial action in vivo using murine malaria models infected with P. berghei. A 178% excess mean survival time was determined for the animals treated with 40 mg/kg 7 for 4 days. No cytotoxicity due to this compound was observed. Work is in progress to extend and validate the strategy outlined here.

The role of glutathione-S-transferase in anti-cancer drug resistance

“…Many antiparasitic drugs (for example, chloroquinone (CQ), an antimalarial agent) form free radicals that may be inactivated by parasitic GST-mediated conjugation to GSH. (DeCampo and Moreno, 1984;Davioud-Charvet et al, 2001). The efficacy of CQ can be enhanced by GSH depletion and GST inhibition.…”

“…The efficacy of CQ can be enhanced by GSH depletion and GST inhibition. Hence, inhibition of parasitic GSTs or destabilization of intraparasitic pools of GSH provide two means of combination therapy with CQ (Davioud-Charvet et al, 2001;Harwaldt et al, 2002). Investigations are underway to utilize the X-ray crystal structure of the malarial parasite's GST in the development of a structure-based drug design (Harwaldt et al, 2002).…”

Thioredoxin-2 but Not Thioredoxin-1 Is a Substrate of Thioredoxin Peroxidase-1 from Drosophila melanogaster

“…Not only in the human host, but also in the insect vector, oxidative compounds like peroxynitrite are produced and launched against the parasite (36,37). Analogous to GR inhibitors as antiparasitic drugs in man (38), TrxR inhibitors would be promising agents against the insect stages of the parasite and could also be used as insecticides. This perspective is supported by the fact that there are great structural and functional differences among the thioredoxin-reducing centers of the TrxRs from insects, malarial parasites, and mammals (15).…”

In Vitro Assessment of Methylene Blue on Chloroquine-Sensitive and -Resistant Plasmodium falciparum Strains Reveals Synergistic Action with Artemisinins

“…In Plasmodium, GSH is likely to be involved in buffering the reducing milieu, in antioxidant defense, redox signaling, DNA synthesis, and heme degradation, and in detoxification reactions catalyzed by glutathione S-transferase (3,4,14,18). Furthermore, the combination of CQ derivatives with the selective P. falciparum GR inhibitor 6-[2-(3-methyl)-naphthoquinolyl]hexanoic acid as a double-drug conjugate inhibited the growth of CQ-resistant Plasmodium species both in vitro and in vivo (7). These and other observations suggest that the combination of CQ with MB-as a P. falciparum GR inhibitor and thus CQ sensitizer-might be useful.…”