G-quadruplex DNA motifs in the malaria parasite Plasmodium falciparum and their potential as novel antimalarial drug targets [PublishAheadOfPrint]

G-quadruplexes are DNA or RNA secondary structures that can be formed from guanine-rich nucleic acids. These four-stranded structures, composed of stacked quartets of guanine bases, can be highly stable and have been demonstrated to occur in vivo in the DNA of human cells and other systems, where they play important biological roles, influencing processes such as telomere maintenance, DNA replication and transcription, or in the case of RNA G-quadruplexes, RNA translation and processing. We report for the first time that DNA G-quadruplexes can be detected in the nuclei of the malaria parasite Plasmodium falciparum, which has one of the most A/T-biased genomes sequenced and therefore possesses few guanine-rich sequences with the potential to form G-quadruplexes. We show that despite this paucity of putative G-quadruplex-forming sequences, P. falciparum parasites are sensitive to several G-quadruplex-stabilizing drugs, including quarfloxin which previously reached Phase-2 clinical trials as an anticancer drug. Quarfloxin has a rapid initial rate of kill and is active against ring stages as well as replicative stages of intraerythrocytic development. We show that several G-quadruplex-stabilising drugs including quarfloxin can suppress the transcription of a G-quadruplex-containing reporter gene in P. falciparum, but that quarfloxin does not appear to disrupt the transcription of rRNAs, which was proposed as its mode of action in both human cells and trypanosomes. These data suggest that quarfloxin has potential for repositioning as an antimalarial with a novel mode of action. Furthermore, G-quadruplex biology in P. falciparum may present a target for development of other new antimalarial drugs.

IMPORTANCE

The malaria parasite Plasmodium falciparum has historically become resistant to every antimalarial drug deployed, leading to a constant demand for new drugs and novel molecular targets for their development. G-quadruplex DNA motifs have been studied as a possible target for anti-cancer drugs, yielding an abundance of G-quadruplex-binding compounds, several of which have undergone clinical trials although none has yet reached the clinic. Here, we examine the existence and function of G-quadruplex motifs in the P. falciparum genome, and investigate the possibility of repurposing G-quadruplex-binding compounds as novel antiplasmodial agents. We show that G-quadruplex DNA motifs can be detected in the P. falciparum genome, and can modulate expression of a G-quadruplex-containing reporter gene. We also show that one G-quadruplex-binding drug, which previously underwent Phase-2 clinical trials, is potent and fast-acting against the intraerythrocytic stages of the parasite in vitro. G-quadruplexes thus constitute a possible new drug target in P. falciparum.

http://ift.tt/2AGWCk1