On 2014 Apr 02, GREGORY CROWTHER commented:

“The discovery and biochemical characterization of Plasmodium thioredoxin reductase inhibitors from an antimalarial set” is a very nice paper showing progress in the important but challenging task of following up on hits from a high-throughput screen against Plasmodium cells. Expression and purification of full-length, untagged TrxR from multiple species was achieved, a huge accomplishment for Plasmodium proteins, which are notoriously hard to express in E. coli. A clever assay is reported, in which the substrate concentrations may be maintained at their Km’s (or some other desired level) for screening purposes. And inhibition of TrxR by the hit compounds was characterized in some detail.

In my view, the main limitation of this paper is the odd way in which it dances around the issue of the mechanism of action (MoA) of the hit compounds. The Abstract, Introduction, and beginning of the Discussion all emphasize the value of knowing the MoA by which a given compound or series kills a pathogen, and this study was apparently done to investigate whether any compounds in the TCAMS set act through inhibition of TrxR. Yet in the end, no direct opinion is offered as to whether the seven compounds are likely to kill Plasmodium cells via their inhibition of TrxR! Moreover, the challenges of inferring MoA from biochemical inhibition are not discussed. For example, if a particular protein target does indeed represent a compound’s MoA, it is generally expected that the compound’s IC50 against the protein will be less than its IC50 against whole cells, but that was not true for the newly discovered TrxR inhibitors. Is this IC50 reasoning appropriate here? If not, why not? In light of these issues, the following sentence from the Discussion seems awfully vague: “only experimental verification by testing the compounds in an appropriate biochemical screen of an essential target can provide a definitive link between the observed whole cell inhibition and a specific antimalarial mode of action." By "definitive link," I don't know if the authors mean something like a correlation, or whether they see their evidence as stronger than that. In the end, I can't really tell whether they believe that inhibition of TrxR is a primary MoA of their compounds.

On 2014 Apr 02, GREGORY CROWTHER commented:

“The discovery and biochemical characterization of Plasmodium thioredoxin reductase inhibitors from an antimalarial set” is a very nice paper showing progress in the important but challenging task of following up on hits from a high-throughput screen against Plasmodium cells. Expression and purification of full-length, untagged TrxR from multiple species was achieved, a huge accomplishment for Plasmodium proteins, which are notoriously hard to express in E. coli. A clever assay is reported, in which the substrate concentrations may be maintained at their Km’s (or some other desired level) for screening purposes. And inhibition of TrxR by the hit compounds was characterized in some detail.

In my view, the main limitation of this paper is the odd way in which it dances around the issue of the mechanism of action (MoA) of the hit compounds. The Abstract, Introduction, and beginning of the Discussion all emphasize the value of knowing the MoA by which a given compound or series kills a pathogen, and this study was apparently done to investigate whether any compounds in the TCAMS set act through inhibition of TrxR. Yet in the end, no direct opinion is offered as to whether the seven compounds are likely to kill Plasmodium cells via their inhibition of TrxR! Moreover, the challenges of inferring MoA from biochemical inhibition are not discussed. For example, if a particular protein target does indeed represent a compound’s MoA, it is generally expected that the compound’s IC50 against the protein will be less than its IC50 against whole cells, but that was not true for the newly discovered TrxR inhibitors. Is this IC50 reasoning appropriate here? If not, why not? In light of these issues, the following sentence from the Discussion seems awfully vague: “only experimental verification by testing the compounds in an appropriate biochemical screen of an essential target can provide a definitive link between the observed whole cell inhibition and a specific antimalarial mode of action." By "definitive link," I don't know if the authors mean something like a correlation, or whether they see their evidence as stronger than that. In the end, I can't really tell whether they believe that inhibition of TrxR is a primary MoA of their compounds.