Parasites resistant to the antimalarial atovaquone fail to transmit by mosquitoes

Malaria-related mortality has slowly decreased over the past decade; however, eradication of malaria requires the development of new antimalarial chemotherapies that target liver stages of the parasite and combat the emergence of drug resistance. The diminishing arsenal of anti-liver-stage compounds sparked our interest in reviving the old and previously abandoned compound menoctone. In support of these studies, we developed a new convergent synthesis method that was facile, required fewer steps, produced better yields, and utilized less expensive reagents than the previously published method. Menoctone proved to be highly potent against liver stages of Plasmodium berghei (50 percent inhibitory concentration [IC 50 ] ϭ 0.41 nM) and erythrocytic stages of Plasmodium falciparum (113 nM). We selected for resistance to menoctone and found M133I mutations in cytochrome b of both P. falciparum and P. berghei. The same mutation has been observed previously in atovaquone resistance, and we confirmed cross-resistance between menoctone and atovaquone in vitro (for P. falciparum) and in vivo (for P. berghei). Finally, we assessed the transmission potential of menoctone-resistant P. berghei and found that the M133I mutant parasites were readily transmitted from mouse to mosquitoes and back to mice. In each step, the M133I mutation in cytochrome b, inducing menoctone resistance, was confirmed. In summary, this study is the first to show the mechanism of resistance to menoctone and that menoctone and atovaquone resistance is transmissible through mosquitoes.

Section: Discussionsupporting

confidence: 82%

Section: Discussioncontrasting

confidence: 51%

See 1 more Smart Citation

Menoctone Resistance in Malaria Parasites Is Conferred by M133I Mutations in Cytochrome b That Are Transmissible through Mosquitoes

Blake

Johnson

Siegel

et al. 2017

“…Because both ATV and ELQ-300 act on a single protein, the development of simultaneous Q o and Q i site mutations would be exceedingly rare, and the fact that the mitochondrial genome is carried in only female gametocytes would prevent any dual-site resistance secondary to genetic recombination at the sexual stage. Even if rare ATV r /ELQ-300 r mutants were to arise, recent work suggests that these parasites would likely be incapable of transmission by mosquitoes; the McFadden group has recently shown that multiple ATV r mutations (including Y268C and Y268N) are associated with arrested oocyst development within the mosquito midgut and with a failure to produce the infectious sporozoites necessary for transmission to mammalian hosts (26). Ultimately, we believe that ATV and ELQ-300 could be ideal partner drugs with a low propensity for drug resistance and with the remarkable potency characteristic of cyt bc 1 inhibitors.…”

mentioning

confidence: 99%

Atovaquone and ELQ-300 Combination Therapy as a Novel Dual-Site Cytochrome bc ₁ Inhibition Strategy for Malaria

Stickles

Smilkstein

Morrisey

et al. 2016

cAntimalarial combination therapies play a crucial role in preventing the emergence of drug-resistant Plasmodium parasites. Although artemisinin-based combination therapies (ACTs) comprise the majority of these formulations, inhibitors of the mitochondrial cytochrome bc 1 complex (cyt bc 1 ) are among the few compounds that are effective for both acute antimalarial treatment and prophylaxis. There are two known sites for inhibition within cyt bc 1 : atovaquone (ATV) blocks the quinol oxidase (Q o ) site of cyt bc 1 , while some members of the endochin-like quinolone (ELQ) family, including preclinical candidate ELQ-300, inhibit the quinone reductase (Q i ) site and retain full potency against ATV-resistant Plasmodium falciparum strains with Q o site mutations. Here, we provide the first in vivo comparison of ATV, ELQ-300, and combination therapy consisting of ATV plus ELQ-300 (ATV:ELQ-300), using P. yoelii murine models of malaria. In our monotherapy assessments, we found that ATV functioned as a single-dose curative compound in suppressive tests whereas ELQ-300 demonstrated a unique cumulative dosing effect that successfully blocked recrudescence even in a high-parasitemia acute infection model. ATV:ELQ-300 therapy was highly synergistic, and the combination was curative with a single combined dose of 1 mg/kg of body weight. Compared to the ATV: proguanil (Malarone) formulation, ATV:ELQ-300 was more efficacious in multiday, acute infection models and was equally effective at blocking the emergence of ATV-resistant parasites. Ultimately, our data suggest that dual-site inhibition of cyt bc 1 is a valuable strategy for antimalarial combination therapy and that Q i site inhibitors such as ELQ-300 represent valuable partner drugs for the clinically successful Q o site inhibitor ATV.

“…RIcT and RIaT therefore could be developed as useful tools to predict the potential emergence of resistance to antimalarials. In the case of atovaquone, the rapid within-host selection of resistance had not been followed by its spread in the population, presumably because parasites that are resistant to atovaquone are not transmissible by mosquitoes due to the resulting defective sexual cycle (12). However, information regarding the potential emergence of resistance to other antimalarials currently used, as well as newly introduced compounds, could provide knowledge essential for planning malaria control and devising strategies to delay the emergence of resistance.…”

Section: Dose-dependent Selection Of Atovaquone Resistance Antimicrobmentioning

confidence: 99%

Within-Host Selection of Drug Resistance in a Mouse Model Reveals Dose-Dependent Selection of Atovaquone Resistance Mutations

Nuralitha

Murdiyarso

Siregar

et al. 2017

Self Cite

The evolutionary selection of malaria parasites within an individual host plays a critical role in the emergence of drug resistance. We have compared the selection of atovaquone resistance mutants in mouse models reflecting two different causes of failure of malaria treatment, an inadequate subtherapeutic dose and an incomplete therapeutic dose. The two models are based on cycles of insufficient treatment of Plasmodium berghei-infected mice: repeated inadequate treatment associated with a subtherapeutic dose (RIaT) (0.1 mg kg Ϫ1 of body weight) and repeated incomplete treatment with a therapeutic dose (RIcT) (14.4 mg kg Ϫ1 of body weight). The number of treatment cycles for the development of a stable resistance phenotype during RIaT was 2.00 Ϯ 0.00 cycles (n ϭ 9), which is not statistically different from that during RIcT (2.57 Ϯ 0.85 cycles; combined n ϭ 14; P ϭ 0.0591). All mutations underlying atovaquone resistance selected by RIaT (M133I, T142N, and L144S) were found to be in the Qo1 (quinone binding 1) domain of the mitochondrial cytochrome b gene, in contrast to those selected by RIcT (Y268N/C, L271V, K272R, and V284F) in the Qo2 domain or its neighboring sixth transmembrane region. Exposure of mixed populations of resistant parasites from RIaT to the higher therapeutic dose of RIcT revealed further insights into the dynamics of within-host selection of resistance to antimalarial drugs. These results suggest that both inadequate subtherapeutic doses and incomplete therapeutic doses in malaria treatment pose similar threats to the emergence of drug resistance. RIcT and RIaT could be developed as useful tools to predict the potential emergence of resistance to newly introduced and less-understood antimalarials.KEYWORDS dose-dependent selection, mouse malaria model, repeated inadequate treatment, repeated incomplete treatment, within-host selection of atovaquone resistance T he evolutionary selection of malaria parasites within an individual host plays a critical role in the emergence of antimalarial drug resistance, a major problem in malaria control. The study of within-host selection of drug resistance benefits from animal models of malaria infection, as it allows pharmacological manipulations in vivo.We recently reported such a model, based on cycles of repeated incomplete treatment (RIcT) of Plasmodium berghei-infected mice with a constant therapeutic dose of an antimalarial drug, which mimics treatment failure in the human field situation (1). We showed that under these conditions, stable resistance of P. berghei to the antimalarial atovaquone developed rapidly, after only 2.5 cycles of treatment.