Antileishmanial activity of synthetic analogs of the naturally occurring quinolone alkaloid N-methyl-8-methoxyflindersin

Leishmaniasis is a neglected, parasitic tropical disease caused by an intracellular protozoan from the genus Leishmania. Quinoline alkaloids, secondary metabolites found in plants from the Rutaceae family, have antiparasitic activity against Leishmania sp. N-methyl-8-methoxyflindersin (1), isolated from the leaves of Raputia heptaphylla and also known as 7-methoxy-2,2-dimethyl-2H,5H,6H-pyran[3,2-c]quinolin-5-one, shows antiparasitic activity against Leishmania promastigotes and amastigotes. This study used in silico tools to identify synthetic quinoline alkaloids having structure similar to that of compound 1 and then tested these quinoline alkaloids for their in vitro antiparasitic activity against Leishmania (Viannia) panamensis, in vivo therapeutic response in hamsters suffering from experimental cutaneous leishmaniasis (CL), and ex vivo immunomodulatory potential in healthy donors’ human peripheral blood (monocyte)-derived macrophages (hMDMs). Compounds 1 (natural), 2 (synthetic), and 8 (synthetic) were effective against intracellular promastigotes (9.9, 3.4, and 1.6 μg/mL medial effective concentration [EC50], respectively) and amastigotes (5.07, 7.94, and 1.91 μg/mL EC50, respectively). Compound 1 increased nitric oxide production in infected hMDMs and triggered necrosis-related ultrastructural alterations in intracellular amastigotes, while compound 2 stimulated oxidative breakdown in hMDMs and caused ultrastructural alterations in the parasite 4 h posttreatment, and compound 8 failed to induce macrophage modulation but selectively induced apoptosis of infected hMDMs and alterations in the intracellular parasite ultrastructure. In addition, synthetic compounds 2 and 8 improved the health of hamsters suffering from experimental CL, without evidence of treatment-associated adverse toxic effects. Therefore, synthetic compounds 2 and 8 are potential therapeutic candidates for topical treatment of CL.


Dear Dr Schallig,
Thank you for your kindly response about the process of submission of the manuscript entitled "Antileishmanial activity of synthetic analogues of the naturally occurring quinolone alkaloid N-methyl-8-methoxyflindersin" by Torres et al.
We have done the corrections indicated by the reviewer, and all the changes and the respective response on each point raised by the reviewer are exposed in the following table:

General comments
1 This manuscript has improved with respect to structure and readability when compared to the first version. However, even though the authors have a native English speaker review the manuscript before resubmitting it, there are still some linguistic issues that must taken care of. The authors may consider asking a native English speaker for a second opinion.
The English of the article has been reviewed by a new official translator native to the language (Enago).

Specific comments TITLE
2 Change title to: "Antileishmanial activity of synthetic analogues of the naturally occurring quinolone alkaloid N-methyl-8methoxyflindersin" The title of the article was changed from "Antileishmanial activity of synthetic analogues of the quinolone alkaloid N-methyl-8methoxyflindersin" to The short title of the article was changed from "Quinoline alkaloid and its potential antileishmanial activity" to "Potential antileishmanial activity of quinoline alkaloids" ABSTRACT 4 This section is okay, but the mistakes in lines 31-32 and 41-42 must be corrected Indicate in lines 33-35 that these were in vitro studies.
Suggested corrections have made, and emphasis has made in In vitro studies Lines 56-59. Make two separate sentences. Thus: "The first therapeutic choice for CL patients is based on the intravenous or intralesional administration of pentavalent antimony [refs]. Oral administration of miltefosine or intravenous administration of amphotericin B have also been recommended as second therapeutic possibilities [5,6]." The change proposed has made. The references "Oliveira LF y cols. Acta Tropica. 2011", "Monge-Maillo B y cols. Drugs. 2013" y "Ponte-Sucre A y cols. PLoS Neglected Tropical Diseases. 2017", were added.

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Lines 59-63. Make two separate sentences, improve the language, and clearer express the relationship between the statements in both sentences. Thus: "Nonetheless However, these drugs could produce adverse effects associated with such as cardiotoxicity, liver damage, nephrotoxicity, or even teratogenic effects in the case of miltefosine [7,8]. These drawbacks along with prolonged treatment schemes, and parenteral administration, can lead to noncompliance, and abandonment of prescribed treatment, and the consequent emergence of drug-resistant parasites could therefore occur [6,7,9]." The change proposed has made. 7 Line 65. "….. and safer for patients (better adherence and less toxic effects) [10,11]." The authors must properly phrase this.
The changes were made by the paragraph: There is thus a need for new therapeutic alternatives that are more effective and efficient in terms of parasite elimination and disease resolution and safer for patients reflected in better adherence and less toxic effects there. The change has made. Relevant information was given related to the structure, as well as the activity of quinolinic alkaloid compounds, therefore the paragraph conforms to "Using natural molecules and their synthetic derivatives is the main strategy followed in the search for new therapeutic options [7]. Of these, quinoline alkaloids, which are secondary metabolites found mainly in plants from the Rutaceae family, are biosynthesized from anthranilic acid and comprise carboxyl groups of anthranilic acid with an acetate group (malonate) and their subsequent cyclization of the quinolinic ring [12,13]. [12,13]. Quinoline alkaloids are effective against CL caused by L. amazonensis and L. venezuelensis in BALB/c mice [14]. In addition, 2substituted quinoline alkaloids chimanine D and B isolated from the Galipea longiflora K. Krause stem bark act against L. braziliensis and L. donovani promastigotes [15,16]." 9 Line 80. The authors should connect this alinea with the previous one by using, for instance, the expressions "Therefore, ……" or For this reason,"……..".
The change proposed has made. Therefore the paragraph is set to "For this reason, in silico tools ...".

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The authors may consider substituting the title of the first subsection by "Screening for synthetic analogues of N-methyl-8methoxyflindersine" The change proposed has made, therefore the title changes from "Screening for synthetic compounds analogous to the natural quinoline alkaloid" to " Screening for synthetic analogs of compound 1".

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The authors may consider combining the "subsection "Isolating human monocytederived macrophages" with the subsection "Antileishmanial activity in L. (V.) panamensis intracellular amastigotes" It is considered not to make changes in the order of the subsections, to make it easier to read separately, the requirements of cell culture and each technical apart; because they all share the same cellular model (hMDMs). But we change the title to "Isolating hMDMs".