Host cell metabolism contributes to delayed-death kinetics of apicoplast inhibitors in Toxoplasma gondii

Abstract

15Toxoplasma gondii and related human parasites contain an essential plastid 16 organelle called the apicoplast. Clinically-used antibiotics and other inhibitors that 17 disrupt apicoplast biogenesis cause a mysterious "delayed-death" phenotype, in which 18 parasite growth is unaffected during the first lytic cycle of inhibitor treatment but is 19 severely inhibited in the second lytic cycle even after drug removal. Critical to 20 understanding the complex downstream cellular effects of these drug classes is the timing 21 of apicoplast loss during inhibitor treatment and how it relates to this peculiar growth 22phenotype. Here we show that, upon treatment with diverse classes of apicoplast 23 . CC-BY-NC-ND 4.0 International license It is made available under a was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint (which . http://dx.doi.org/10.1101/384123 doi: bioRxiv preprint first posted online Aug. 3, 2018; 2 inhibitors, newly-replicated T. gondii parasites in the first lytic cycle initially form 24 apicoplasts with defects in protein import or genome replication and eventually fail to 25 inherit the apicoplast altogether. Despite the accumulation of parasites with defective or 26 missing apicoplasts, growth is unaffected during the first lytic cycle, as previously 27 observed. Strikingly, concomitant inhibition of host cell isoprenoid biosynthesis results in 28 growth inhibition in the first lytic cycle and unmasks the apicoplast defects. These results 29 suggest that defects in and even complete loss of the apicoplast in T. gondii are partially 30 rescued by scavenging of host cell metabolites leading to death that is delayed. Our 31 findings uncover host cell interactions that can alleviate apicoplast inhibition and 32 highlight key differences in "delayed-death" inhibitors between T. gondii and 33 Plasmodium falciparum. 34 35Introduction 36

Antimalarial Agents as Therapeutic Tools Against Toxoplasmosis—A Short Bridge between Two Distant Illnesses

“…Among them, one which deserves distinctive attention is the apical complex, the hallmark of the Apicomplexa phylum, an indispensable structure for the recognition and subsequent invasion of host cells [25]. Most of these parasites also contain the apicoplast, an essential plastid organelle derived from an endosymbiotic process with a seaweed, which is crucial for the biosynthesis of essential parasitic biomolecules, like fatty acids (type II fatty acid pathway), iron-sulfur clusters, the heme group, and isoprenoid precursors (the non-mevalonate pathway) [25,26]. The high similitude in morphology and biochemistry between T. gondii and Plasmodium spp.…”

“…makes them especially interesting from the therapeutic viewpoint, since common metabolic pathways and organelles may serve as targets for the same drugs, as happens with some of the currently available antitoxoplasmic drugs pyrimethamine, sulfonamides, and atovaquone, which were initially designed and developed for the treatment of malaria [27,28]. The apicoplast ribosome inhibitors, such as clindamycin and doxycycline, also fit these criteria, being currently used for the treatment of acute toxoplasmosis and malaria chemoprophylaxis [26]. Hence, drug repurposing stems as a useful approach for drug development in these parasitic illnesses.…”