Investigating Pharmacological Targeting of G-Quadruplexes in the Human Malaria Parasite

Abstract

The unique occurrence of G-quadruplexes in the AT-rich genome of human malaria parasite Plasmodium falciparum provides hints about their critical roles in parasite survival, pathogenesis, and host immune evasion. An intriguing question is whether these noncanonical structures can serve as molecular targets for small molecule-based interventions against malaria. In this study, we have investigated the pharmacological targeting of G-quadruplexes for parasite inhibition. We observed that bisquinolinium derivatives of 1,8-naphthyridine and pyridine affected the stability and molecular recognition properties of G-quadruplexes in telomeric and subtelomeric regions in P. falciparum. Parasite inhibition and cytotoxicity assays revealed that these ligands effectively inhibit parasite growth with minimal toxic effects in human cells. G-quadruplex interacting ligands caused degeneration and shortening of parasite telomeres. Ligand-induced perturbations in telomere homeostasis also affected transcriptional state of the subtelomeric region harboring antigenic variation genes. Taken together, our results suggest that quadruplex-ligand interaction disturbs telomeric/subtelomeric chromatin organization and induces DNA damage that consequently leads to parasite death. Our findings also draw attention to the striking differences in telomere dynamics in the protozoan parasite and human host that can be exploited for selective targeting of the telomeric quadruplex of the parasite as a potential antimalarial strategy.

PfGBP2is a novel G‐quadruplex binding protein inPlasmodium falciparum

“…Several computational and experimental studies unveiled the existence of G4s in the genomes of P. falciparum (Anas et al, 2017; Calvo & Wasserman, 2016; De Cian et al, 2008; Gazanion et al, 2020; Harris et al, 2018; Marsico et al, 2019; Smargiasso et al, 2009; Stanton et al, 2016). However, there is a lack of information on the proteins that can interact or support the G4 formation within these parasites.…”

“…The G4s are associated with telomeric maintenance and mitotic recombination events among var genes of these parasites (Calvo & Wasserman, 2016; De Cian et al, 2008; Gazanion et al, 2020; Stanton et al, 2016). Several G4 ligands such as naphthalene di‐imide, TMPyP4 and telomestatin affect the parasite growth, thus targeting G4‐associated processes might represent new strategies for malaria intervention (Anas et al, 2017; Belmonte‐Reche et al, 2018; Calvo & Wasserman, 2016; Harris et al, 2018).…”

Genome wide distribution of G-quadruplexes and their impact on gene expression in malaria parasites

“…Some studies have used a limited set of genes, including rifin and var genes [36,37]. However, the two rifin genes tested did not contain a G4 in the promoter but rather in the coding sequence [36] and no difference was observed in the level of expression when a G4 was present or not in the promoter of var genes [37]. Here we measured the effect of pyridostatin, a high affinity G4 ligand, on the expression of the var members.…”

“…In several viruses including HIV, Herpes viruses and Epstein-Barr, viral G4s present in promoters have been shown to modulate promoter activity [33][34][35]. Interestingly, several G4-stabilizing molecules that were initially developed as potential anticancer agents displayed antimalarial activity, although their precise molecular mode of action remains unknown [28,[36][37][38].…”

Parasitic Protozoa: Unusual Roles for G-Quadruplexes in Early-Diverging Eukaryotes

“…It is important to note that G4-targetting was not proven and telomestatin activity could interfere with other pathways inside the parasite [57]. However, three other G4-binding compounds were subsequently tested by another research group, and showed significant P. falciparum telomere erosion, suggesting a common mode of interference with telomerase activity [58].…”