Review 2: "A Fast-Acting Inhibitor of Blood-Stage P. falciparum with Mechanism Distinct from Artemisinin and Chloroquine"

RR\ID Evidence Scale rating by reviewer:

• Reliable. The main study claims are generally justified by its methods and data. The results and conclusions are likely to be similar to the hypothetical ideal study. There are some minor caveats or limitations, but they would/do not change the major claims of the study. The study provides sufficient strength of evidence on its own that its main claims should be considered actionable, with some room for future revision.

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Review: The authors characterize a new blood-stage Plasmodium falciparum inhibitor (MMV1580853) with a mechanism distinct from artemisinin and chloroquine. The compound had been previously  been identified from a previous screening of the open-access Pandemic Response Box provided by Medicines for Malaria Venture (MMV).  The authors convincingly demonstrate that MMV1580853 is a potent asexual blood-stage P. falciparum inhibitor with a unique mechanism of action. The rapid in vitro killing rate, comparable to dihydroartemisinin, suggests that MMV1580853 has the potential to be a fast-acting artemisinin alternative.

The methodology was comprehensive, including in vitro assays to compare growth inhibition and mechanistic studies. The data support the claim that MMV1580853 operates differently from established antimalarial agents like artemisinin and chloroquine. Cross-resistance assays against different artemisinin-resistant strains showed the compound maintains its potency.

From an impact perspective, much of the data is negative and a variety of additional assays could provide more insights into the unique mechanism responsible for the rapid killing rate, thus aiding the development of fast-acting antimalarials while addressing the growing problem of resistance to current treatments.

Notes:

• There is a mislabeling in the units in the paragraph: “Moreover, artemisinin-resistant strains, Dd2 Kelch13 C580Y and R539T, remained susceptible to MMV158053 with EC50= 0.0107 nM (0.0098–0.0117 nM) and 0.0114 nM (0.0105–0.0124 nM), respectively, comparable to the parent Dd2 EC50= 0.0128 nM (0.0124–0.0132 nM) (Fig S1) [21].” Should it be microM instead of nM?

• There is a mislabeling in Figure 2C. MMV019313 should be more potent against the parasites treated with 5 nM aTC.

• The authors conclusions that resistant parasites could not be obtained would be better supported if the authors provided more information/data on what they actually did and for how many generations the parasites were grown in the presence of drug. 

• The work would be strengthened if the authors could provide evidence that the compound is what they think it is.  Mixups have been known to occur.  The authors do not describe the source of the compound.