New findings on Simalikalactone D, an antimalarial compound from Quassia amara L. (Simaroubaceae)

Antiplasmodial and cytotoxic effects of the methanol extract, canthinone alkaloids, squalene- and protolimonoid-type triterpenes from Homalolepis suffruticosa roots

ETHNOPHARMACOLOGICAL RELEVANCE

Different species of the Simaroubaceae family are used in traditional medicine to treat malaria. Among these is Homalolepis suffruticosa (syn. Simaba suffruticosa and Quassia suffruticosa), which is native to Central Brazil and popularly known as calunga. However, there is a lack of investigation concerning its antimalarial effects.

AIM OF THE STUDY

To investigate the antiplasmodial and cytotoxic effects of the isolated metabolites and methanol extract from H. suffruticosa roots as well as to conduct the dereplication of this extract aiming to characterize its metabolic profile by UPLC-DAD-ESI-MS/MS.

MATERIALS AND METHODS

Methanol extract of the H. suffruticosa roots and six isolated compounds were evaluated against chloroquine-resistant Plasmodium falciparum W2 strain by the PfLDH method and cytotoxicity in HepG2 cells by the MTT assay. Dereplication of the extract was performed by UPLC-DAD-ESI-MS/MS.

RESULTS

The six isolated compounds disclosed high to moderate antiplasmodial activity (IC₅₀ 0.0548 ± 0.0083 μg/mL to 26.65 ± 2.40 μg/mL) and cytotoxicity was in the range of CC₅₀ 0.62 ± 0.33 μg/mL to 56.43 ± 2.54 μg/mL, while 5-metoxycantin-6-one proved to be the most potent constituent of the six assayed ones. The methanol extract of the roots showed high in vitro antiplasmodial activity (IC₅₀ 1.88 ± 0.56 μg/mL), moderate cytotoxicity (CC₅₀ 41.93 ± 2.30 μg/mL), and good selectivity index (SI = 22.30). Finally, C₂₀ quassinoids and canthin-6-one alkaloids were putatively identified in the H. suffruticosa methanol extract by LC-MS.

CONCLUSIONS

Taken together, the isolated compounds, mainly the 5-metoxycantin-6-one and the methanol extract from H. suffruticosa roots, disclose good antiplasmodial activity, supporting the ethnopharmacological history of the Simaroubaceae species as traditional antimalarial drugs.

Antimalarial Natural Products

Natural products have made a crucial and unique contribution to human health, and this is especially true in the case of malaria, where the natural products quinine and artemisinin and their derivatives and analogues, have saved millions of lives. The need for new drugs to treat malaria is still urgent, since the most dangerous malaria parasite, Plasmodium falciparum, has become resistant to quinine and most of its derivatives and is becoming resistant to artemisinin and its derivatives. This volume begins with a short history of malaria and follows this with a summary of its biology. It then traces the fascinating history of the discovery of quinine for malaria treatment and then describes quinine's biosynthesis, its mechanism of action, and its clinical use, concluding with a discussion of synthetic antimalarial agents based on quinine's structure. The volume then covers the discovery of artemisinin and its development as the source of the most effective current antimalarial drug, including summaries of its synthesis and biosynthesis, its mechanism of action, and its clinical use and resistance. A short discussion of other clinically used antimalarial natural products leads to a detailed treatment of other natural products with significant antiplasmodial activity, classified by compound type. Although the search for new antimalarial natural products from Nature's combinatorial library is challenging, it is very likely to yield new antimalarial drugs. The chapter thus ends by identifying over ten natural products with development potential as clinical antimalarial agents.

Antiplasmodial natural products: an update

Background

Malaria remains a significant public health challenge in regions of the world where it is endemic. An unprecedented decline in malaria incidences was recorded during the last decade due to the availability of effective control interventions, such as the deployment of artemisinin-based combination therapy and insecticide-treated nets. However, according to the World Health Organization, malaria is staging a comeback, in part due to the development of drug resistance. Therefore, there is an urgent need to discover new anti-malarial drugs. This article reviews the literature on natural products with antiplasmodial activity that was reported between 2010 and 2017.

Methods

Relevant literature was sourced by searching the major scientific databases, including Web of Science, ScienceDirect, Scopus, SciFinder, Pubmed, and Google Scholar, using appropriate keyword combinations.

Results and Discussion

A total of 1524 compounds from 397 relevant references, assayed against at least one strain of Plasmodium, were reported in the period under review. Out of these, 39% were described as new natural products, and 29% of the compounds had IC₅₀ ≤ 3.0 µM against at least one strain of Plasmodium. Several of these compounds have the potential to be developed into viable anti-malarial drugs. Also, some of these compounds could play a role in malaria eradication by targeting gametocytes. However, the research into natural products with potential for blocking the transmission of malaria is still in its infancy stage and needs to be vigorously pursued.

Quassia "biopiracy" case and the Nagoya Protocol: A researcher's perspective

Biopiracy accusations are common in the world of biodiversity research. At the end of 2015, a French NGO accused researchers from the Institut de Recherche pour le Développement (IRD) of biopiracy. These researchers had applied for a patent for a natural bioactive molecule against malaria and cancer, the Simalikalactone E, isolated from Quassia amara L. (Simaroubaceae) leaves. This biopiracy allegation triggered a huge wave of attacks from the media and social networks, and vehement recrimination from political officials in French Guiana against researchers who have been accused of ethical misconduct, by stealing the traditional knowledge of indigenous people. These accusations were made in the contentious context of the ratification of the Nagoya Protocol in the frame of implementing the French law on biodiversity, nature and landscapes. So, in an atmosphere of heightened emotions it is crucial to understand the issues behind these accusations. We describe herein the genesis of our discovery, present the detractors' arguments, and discuss the consequences of such biopiracy denunciations for scientific research. We also address our concerns about the gap between rhetoric and reality and the real impact of the Nagoya Protocol on biodiversity conservation.