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Retargeting azithromycin-like compounds as antimalarials with dual modality

ABSTRACT: Resistance to front-line antimalarials (artemisinin combination therapies) is spreading, and development of new drug treatment strategies to rapidly kill Plasmodium parasites that cause malaria are urgently needed. Here, we show that azithromycin—a clinically used macrolide antibiotic that targets the bacterium-like ribosome of the malaria parasites apicoplast organelle and causes a slow-killing ‘delayed death’ phenotype—can also rapidly kill parasites throughout the asexual blood-stages of the lifecycle via a ‘quick-killing’ mechanism of action. Investigation of 84 azithromycin analogues revealed nanomolar quick-killing potency that is directed against the very earliest stage of parasite development within red blood cells. Indeed, the best analogue exhibited 1600-fold higher potency than azithromycin for in vitro treatment windows less than 48 hours. Analogues were also effective against the zoonotic malaria parasite P. knowlesi, and against both multi-drug and artemisinin resistant P. falciparum lines. Metabolomic profiles of azithromycin analogue treated parasites were similar to those of chloroquine treated parasites, suggesting that the quick-killing mechanism of action may in part be localised to the parasite food vacuole. However, metabolomic signatures associated with mitochondrial disruption were also present. In addition, unlike chloroquine, azithromycin and analogues were active across blood stage development, including merozoite invasion, suggesting that these macrolides have a multi-factorial mechanism of quick-killing activity. The positioning of functional groups added to azithromycin and its quick-killing analogues altered their activity against bacterial-like ribosomes but had minimal change on quick-killing activity, which suggests that apicoplast-targeting, delayed-death activity can either be preserved or removed independently of quick-killing. Apicoplast minus parasites remained susceptible to both azithromycin and its analogues, further demonstrating that quick-killing is independent of apicoplast-targeting, delayed-death activity. Therefore, development of azithromycin and analogues as antimalarials offers the possibility of targeting parasites through both a quick-killing and delayed death mechanism of action in a single, multifactorial chemotype.

ORGANISM(S): Plasmodium Falciparum

TISSUE(S): Blood

DISEASE(S): Malaria

SUBMITTER: Ghizal Siddiqui

PROVIDER: ST001315 | MetabolomicsWorkbench | Thu Feb 06 00:00:00 GMT 2020

REPOSITORIES: MetabolomicsWorkbench

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Project description:Plasmodium falciparum, the most pathogenic human malaria parasite, infects millions of human beings and causes a serious public health threat. Currently, the most potent anti-malarial drugs are artemisinin and its derivatives1,2. Artemisinin is a sesquiterpene lactone with an endoperoxide bridge3. The activation of artemisinin requires the cleavage of the endoperoxide bridge in the presence of iron sources4. Once activated, artemisinins are converted into highly reactive carbon-centered radicals5,6 that attack macromolecules through alkylation and propagate a series of damages, eventually leading to parasite death7,8. Even though several parasite proteins have been reported as the targets of artemisinin9,10, the exact mechanism of artemisinin action is still controversial and its high potency and specificity against the malaria parasite could not be fully accounted. Here, we have developed an unbiased chemical proteomics approach to directly probe the mechanism of action of artemisinin in P. falciparum in situ. An alkyne-tagged artemisinin analogue coupled with biotin enables selective purification and identification of 124 artemisinin covalent-binding protein targets, many of which are involved in essential biological processes of the parasite. In vitro assays confirm the specific artemisinin binding and inhibition of selected targets. Such a broad targeting spectrum disrupts the biochemical landscape of the parasite and causes its death. Furthermore, using the alkyne-tagged artemisinin coupled with a fluorescent dye to monitor its protein binding, we showed that heme, rather than free ferrous iron, is predominantly responsible for artemisinin activation. The extremely high level of heme released from the hemoglobin digestion by the parasite make artemisinin exceptionally potent against late-stage parasites (trophozoite and schizont stages) compared to parasites at early ring stage, which have low level of heme, mainly from endogenous synthesis. The ‘blood eating’ nature of the parasite with the release of large amounts of heme confers artemisinin with extremely high specificity against the parasites, with minimum side effects towards healthy red blood cells. Taken together, our results established a unifying model to explain the action and specificity of artemisinin in parasite killing. Our findings could facilitate the development of better alternative strategies to treat malaria in times of emerging artemisinin resistance11,12.

Project description:Mechanisms regulating gene expression in malaria parasites are not well understood. Little is known about how this parasite regulates its gene expression during transition from one developmental stage to another and in response to various environmental conditions. Parasites in a diseased host face environments which differ from the static, well adapted in vitro conditions in culture. Parasites thus need to adapt quickly and effectively to these conditions by establishing transcriptional states which is best suited for better survival. With the discovery of natural antisense transcripts (NATs) in this parasite and considering the various proposed mechanisms by which NATs might regulate gene expression, it has been speculated that these might be playing a critical role in gene regulation. We report here the diversity of NATs that exist in this parasite, using isolates taken directly from patients with differing clinical symptoms caused by malaria infection. A total of 797 NATs targeted against annotated loci have been detected using a custom designed strand specific microarray. Out of these, 545 are unique to this study. The majority of NATs were positively correlated with the expression pattern of the sense transcript. Many were found to be differentially regulated in response to disease conditions. Antisense transcripts mapped to a wide variety of biochemical/ metabolic pathways, especially pathways pertaining to the central carbon metabolism and stress related pathways. Our data strongly suggests that a large group of NATs detected here are unannotated transcription units antisense to annotated gene models. The results reveal a previously unknown set of NATs that prevails in this parasite, their differential regulation in disease conditions and mapping to functionally well annotated genes. The results detailed here call for studies to deduce the possible mechanism of action, which would help in understanding the in vivo pathological adaptations of these parasites. Plasmodium falciparum isolates were collected from patients (n = 11) with differing clinical conditions.The patients exhibited symptoms categorized as un-complicated (n =2) or complicated malaria (n = 9). Criteria for determination of complicated disease were based on World Health Organization year 2000 guidelines. Microarray array based transcriptional profiling was carried out to detect prevalence of natural antisense transcript.

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Retargeting azithromycin-like compounds as antimalarials with dual modality

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