Antimalarial and antioxidant activities of novel artesunate-ellagic acid hybrid compound in vitro and in vivo.

Introduction: Emergence of drug resistant strains of Plasmodium species has necessitated the search for novel antimalarials with unique mechanisms of action. Synthesis of hybrid compounds has been one approach to tackling this challenge. In this study, the synthesis of artesunate-ellagic acid hybrid compound (EA31) from ellagic acid and artesunate and its evaluation for antimalarial and antioxidant activities using in vitro and in vivo models were carried out. Method: EA31 was synthesized from artesunate and ellagic acid. The activities of the hybrid compound against Plasmodium falciparum W2 and P. berghei NK65 were evaluated, and its antioxidant activities were also determined. Results: The results revealed that EA31 was more active against P. falciparum W2 (chloroquine resistant) clone and less cytotoxic to buffalo green monkey kidney cell line compared to artesunate. EA31 was also active against Plasmodium berghei NK65 in vivo. The results revealed inhibition of ß-hematin formation as one of the mechanisms of action of EA31. EA31 also exhibited antioxidant activities. Conclusion: The results revealed that EA31 may exert dual action of killing malaria parasite and mopping the reactive oxygen species that mediate the secondary complications of malaria.

Novel 2,5-Diketopiperazines with In Vitro Activities against Protozoan Parasites of Tropical Diseases.

Malaria, Chagas disease, and leishmaniasis are tropical diseases caused by protozoan parasites of the genera Plasmodium, Trypanosoma and Leishmania, respectively. These diseases constitute a major burden on public health in several regions worldwide, mainly affecting low-income populations in economically poor countries. Severe side effects of currently available drug treatments and the emergence of resistant parasites need to be addressed by the development of novel drug candidates. Natural 2,5-Diketopiperazines (2,5-DKPs) constitute N-heterocyclic secondary metabolites with a wide range of biological activities of medicinal interest. Its structural and physicochemical properties make the 2,5-DKP ring a versatile, peptide-like, and stable pharmacophore attractive for synthetic drug design. In the present work, twenty-three novel synthetic 2,5-DKPs, previously synthesized through the versatile Ugi multicomponent reaction, were assayed for their anti-protozoal activities against P. falciparum, T. cruzi, and L. infantum. Some of the 2,5-DKPs have shown promising activities against the target protozoans, with inhibitory concentrations (IC50) ranging from 5.4 to 9.5 µg/mL. The most active compounds also show low cytotoxicity (CC50), affording selectivity indices ≥ 15. Results allowed for observing a clear relationship between the substitution pattern at the aromatic rings of the 2,5-DKPs and their corresponding anti-Plasmodium activity. Finally, calculated drug-like properties of the compounds revealed points for further structure optimization of promising drug candidates.

Fighting Plasmodium chloroquine resistance with acetylenic chloroquine analogues.

Malaria is among the tropical diseases that cause the most deaths in Africa. Around 500,000 malaria deaths are reported yearly among African children under the age of five. Chloroquine (CQ) is a low-cost antimalarial used worldwide for the treatment of Plasmodium vivax malaria. Due to resistance mechanisms, CQ is no longer effective against most malaria cases caused by P. falciparum. The World Health Organization recommends artemisinin combination therapies for P. falciparum malaria, but resistance is emerging in Southeast Asia and some parts of Africa. Therefore, new medicines for treating malaria are urgently needed. Previously, our group identified the 4-aminoquinoline DAQ, a CQ analog containing an acetylenic bond in its side chain, which overcomes CQ resistance in K1 P. falciparum strains. In this work, the antiplasmodial profile, drug-like properties, and pharmacokinetics of DAQ were further investigated. DAQ showed no cross-resistance against standard CQ-resistant strains (e.g., Dd2, IPC 4912, RF12) nor against P. falciparum and P. vivax isolates from patients in the Brazilian Amazon. Using drug pressure assays, DAQ showed a low propensity to generate resistance. DAQ showed considerable solubility but low metabolic stability. The main metabolite was identified as a mono N-deethylated derivative (DAQM), which also showed significant inhibitory activity against CQ-resistant P. falciparum strains. Our findings indicated that the presence of a triple bond in CQ-analogues may represent a low-cost opportunity to overcome known mechanisms of resistance in the malaria parasite.

Studies on Activities and Chemical Characterization of Medicinal Plants in Search for New Antimalarials: A Ten Year Review on Ethnopharmacology.

Malaria is an endemic disease that affected 229 million people and caused 409 thousand deaths, in 2019. Disease control is based on early diagnosis and specific treatment with antimalarial drugs since no effective vaccines are commercially available to prevent the disease. Drug chemotherapy has a strong historical link to the use of traditional plant infusions and other natural products in various cultures. The research based on such knowledge has yielded two drugs in medicine: the alkaloid quinine from Cinchona species, native in the Amazon highland rain forest in South America, and artemisinin from Artemisia annua, a species from the millenary Chinese medicine. The artemisinin-based combination therapies (ACTs), proven to be highly effective against malaria parasites, and considered as "the last bullet to fight drug-resistant malaria parasites," have limited use now due to the emergence of multidrug resistance. In addition, the limited number of therapeutic options makes urgent the development of new antimalarial drugs. This review focuses on the antimalarial activities of 90 plant species obtained from a search using Pubmed database with keywords "antimalarials," "plants" and "natural products." We selected only papers published in the last 10 years (2011-2020), with a further analysis of those which were tested experimentally in malaria infected mice. Most plant species studied were from the African continent, followed by Asia and South America; their antimalarial activities were evaluated against asexual blood parasites, and only one species was evaluated for transmission blocking activity. Only a few compounds isolated from these plants were active and had their mechanisms of action delineated, thereby limiting the contribution of these medicinal plants as sources of novel antimalarial pharmacophores, which are highly necessary for the development of effective drugs. Nevertheless, the search for bioactive compounds remains as a promising strategy for the development of new antimalarials and the validation of traditional treatments against malaria. One species native in South America, Ampelozyzyphus amazonicus, and is largely used against human malaria in Brazil has a prophylactic effect, interfering with the viability of sporozoites in in vitro and in vivo experiments.

Antimalarial and anti-inflammatory activities of new chloroquine and primaquine hybrids: Targeting the blockade of malaria parasite transmission.

Malaria is a disease that requires new drugs not only to fight Plasmodium but also to reduce symptoms of infection such as fever and inflammation. A series of 21 hybrid compounds were designed from chloroquine (CQ) and primaquine (PQ) linked to the pharmacophoric group present in phenylacetic anti-inflammatory drugs. These compounds were designed to have dual activity: namely, to be capable of killing Plasmodium and still act on the inflammatory process caused by malaria infection. The compounds were assayed with nine different biological methods. The carbonylated CQ derivative 6 (n = 3; R1 = Cl) was more potent than CQ in vitro, and 8 (n = 4; R1 = H) reduced P. berghei parasitemia up to 37% on day 7. The carbonylated PQ derivative 17 (R = Br) was slightly less potent than PQ. The gem-difluoro PQ derivative 20 (R = Cl) exhibited high transmission blockade of the malaria sporogonic cycle in mosquitoes. Compounds 6 and 20 dose-dependently reduced nitric oxide (NO) production and inhibited TNFα production by LPS-stimulated J774A.1 macrophages. Our results indicate a viable and interesting approach in planning new chemical entities that act as transmission-blocking drugs for treating malaria caused by P. falciparum and P. vivax and the anti-inflammatory process related to this disease.

New hybrid trifluoromethylquinolines as antiplasmodium agents.

Malaria remains a major public health problem worldwide, and it is responsible for high rates of morbidity and mortality. Resistance to current antimalarial drugs has been identified, and new drugs are urgently needed. In this study, we designed and synthesized seventeen novel quinolines based on the structures of mefloquine ((2,8-bis(trifluoromethyl)quinolin-4-yl)(piperidin-2-yl)methanol) and amodiaquine (4-((7-chloroquinolin-4-yl)amino)-2-((diethylamino)methyl)phenol) using ring bioisosteric replacement and molecular hybridization of the functional groups. The compounds were evaluated in vitro against Plasmodium falciparum and in vivo in mice infected with P. berghei. All derivatives presented anti-P. falciparum activity with IC50 values ranging from 0.083 to 33.0 µM. The compound with the best anti-P. falciparum activity was N-(5-methyl-4H-1,2,4-triazol-3-yl)-2,8-bis(trifluoromethyl)quinolin-4-amine (12) which showed an IC50 of 0.083 µM. The three most active compounds were selected for antimalarial activity tests against P. berghei-infected mice. Compound 12 was the most active on the 5th day after infection, reducing parasitemia by 66%, which is consistent with its in vitro activity. This is an important result as 12, a simpler molecule than mefloquine, does not contain the stereogenic center, and consequently, its synthesis in the laboratory is easier and less expensive. This system proved promising for the design of potential antimalarial compounds.

Aspidosperma pyrifolium, a medicinal plant from the Brazilian caatinga, displays a high antiplasmodial activity and low cytotoxicity.

BACKGROUND: Several species of Aspidosperma plants are referred to as remedies for the treatment of malaria, especially Aspidosperma nitidum. Aspidosperma pyrifolium, also a medicinal plant, is used as a natural anti-inflammatory. Its fractionated extracts were assayed in vitro for activity against malaria parasites and for cytotoxicity. METHODS: Aspidosperma pyrifolium activity was evaluated against Plasmodium falciparum using extracts in vitro. Toxicity towards human hepatoma cells, monkey kidney cells or human monocytes freshly isolated from peripheral blood was also assessed. Anti-malarial activity of selected extracts and fractions that presented in vitro activity were tested in mice with a Plasmodium berghei blood-induced infection. RESULTS: The crude stem bark extract and the alkaloid-rich and ethyl acetate fractions from stem extract showed in vitro activity. None of the crude extracts or fractions was cytotoxic to normal monkey kidney and to a human hepatoma cell lines, or human peripheral blood mononuclear cells; the MDL50 values of all the crude bark extracts and fractions were similar or better when tested on normal cells, with the exception of organic and alkaloidic-rich fractions from stem extract. Two extracts and two fractions tested in vivo caused a significant reduction of P. berghei parasitaemia in experimentally infected mice. CONCLUSION: Considering the high therapeutic index of the alkaloidic-rich fraction from stem extract of A. pyrifolium, it makes the species a candidate for further investigation aiming to produce a new anti-malarial, especially considering that the active extract has no toxicity, i.e., no mutagenic effects in the genototoxicity assays, and that it has an in vivo anti-malarial effect. In its UPLC-HRMS analysis this fraction was shown to have two major components compatible with the bisindole alkaloid Leucoridine B, and a novel compound, which is likely to be responsible for the activity against malaria parasites demonstrated in in vitro tests.

Chloroquine analogs as antimalarial candidates with potent in vitro and in vivo activity.

In spite of recent efforts to eradicate malaria in the world, this parasitic disease is still considered a major public health problem, with a total of 216 million cases of malaria and 445,000 deaths in 2016. Artemisinin-based combination therapies remain effective in most parts of the world, but recent cases of resistance in Southeast Asia have urged for novel approaches to treat malaria caused by Plasmodium falciparum. In this work, we present chloroquine analogs that exhibited high activity against sensitive and chloroquine-resistant P. falciparum blood parasites and were also active against P. berghei infected mice. Among the compounds tested, DAQ, a chloroquine analog with a more linear side chain, was shown to be the most active in vitro and in vivo, with low cytotoxicity, and therefore may serve as the basis for the development of more effective chloroquine analogs to aid malaria eradication.

Cysteine-stabilised peptide extract of Morinda lucida (Benth) leaf exhibits antimalarial activity and augments antioxidant defense system in P. berghei-infected mice.

ETHNOPHARMACOLOGICAL RELEVANCE: Cysteine-stabilised peptides (CSP) are majorly explored for their bioactivities with applications in medicine and agriculture. Morinda lucida leaf is used indigenously for the treatment of malaria; it also contains CSP but the role of CSP in the antimalarial activity of the leaf has not been evaluated. AIM OF THE STUDY: This study was therefore performed to evaluate the antimalarial activity of partially purified cysteine-stabilised peptide extract (PPCPE) of Morinda lucida leaf and its possible augmentation of the antioxidant systems of liver and erythrocytes in murine malaria. MATERIALS AND METHODS: PPCPE was prepared from Morinda lucida leaf. The activity of PPCPE was evaluated in vitro against Plasmodium falciparum W2 and its cytotoxicity against a BGM kidney cell line. PPCPE was also evaluated for its antimalarial activity and its effects on selected liver and erythrocyte antioxidant parameters in P. berghei NK65-infected mice. RESULTS: PPCPE was not active against P. falciparum W2 (IC50: >50µg/ml) neither was it cytotoxic (MLD50: >1000µg/ml). However, PPCPE was active against P. berghei NK65 in vivo, causing 51.52% reduction in parasitaemia at 31.25mg/Kg body weight on day 4 post-inoculation. PPCPE significantly reduced (P < 0.05) malondialdehyde concentrations in the liver and erythrocyte at higher doses compared to untreated controls. PPCPE increased glutathione concentration and activities of glutathione peroxidase, glutathione reductase, superoxide dismutase and catalase in a dose-dependent manner, which was significant (P < 0.05) at higher doses compared to the untreated controls. CONCLUSION: The results suggest that PPCPE may require bioactivation in vivo in order to exert its antimalarial effect and that PPCPE may augment the antioxidant defense system to alleviate the reactive oxygen species-mediated complications of malaria.

Primaquine-thiazolidinones block malaria transmission and development of the liver exoerythrocytic forms.

BACKGROUND: Primaquine is an anti-malarial used to prevent Plasmodium vivax relapses and malaria transmission. However, PQ metabolites cause haemolysis in patients deficient in the enzyme glucose-6-phosphate dehydrogenase (G6PD). Fifteen PQ-thiazolidinone derivatives, synthesized through one-post reactions from primaquine, arenealdehydes and mercaptoacetic acid, were evaluated in parallel in several biological assays, including ability to block malaria transmission to mosquitoes. RESULTS: All primaquine derivatives (PQ-TZs) exhibited lower cell toxicity than primaquine; none caused haemolysis to normal or G6PD-deficient human erythrocytes in vitro. Sera from mice pretreated with the test compounds thus assumed to have drug metabolites, caused no in vitro haemolysis of human erythrocytes, whereas sera from mice pretreated with primaquine did cause haemolysis. The ability of the PQ-TZs to block malaria transmission was evaluated based on the oocyst production and percentage of mosquitoes infected after a blood meal in drug pre-treated animals with experimental malaria caused by either Plasmodium gallinaceum or Plasmodium berghei; four and five PQ-TZs significantly inhibited sporogony in avian and in rodent malaria, respectively. Selected PQ-TZs were tested for their inhibitory activity on P. berghei liver stage development, in mice and in vitro, one compound (4m) caused a 3-day delay in the malaria pre-patent period. CONCLUSIONS: The compound 4m was the most promising, blocking malaria transmissions and reducing the number of exoerythrocytic forms of P. berghei (EEFs) in hepatoma cells in vitro and in mice in vivo. The same compound also caused a 3-day delay in the malaria pre-patent period.

Synthesis, antimalarial activity in vitro, and docking studies of novel neolignan derivatives.

The absence of effective vaccines against malaria and the difficulties associated with controlling mosquito vectors have left chemotherapy as the primary control measure against malaria. However, the emergence and spread of parasite resistance to conventional antimalarial drugs result in a worrisome scenario making the search for new drugs a priority. In the present study, the activities of nine neolignan derivatives were evaluated as follows: (i) against blood forms of chloroquine-resistant Plasmodium falciparum (clone W2), using the tritiated hypoxanthine incorporation and anti-HRPII assays; (ii) for cytotoxic activity against cultured human hepatoma cells (HepG2); and (iii) for intermolecular interaction with the P. falciparum cysteine protease of falcipain-2 (F2) by molecular docking. The neolignan derivatives 9 and 10 showed activity against the blood form of the chloroquine-resistant P. falciparum clone W2 and were not cytotoxic against cultured human hepatoma cells. A molecular docking study of these two neolignans with FP2 revealed several intermolecular interactions that should guide the design of future analogs.

Evaluation of 7-arylaminopyrazolo[1,5-a]pyrimidines as anti-Plasmodium falciparum, antimalarial, and Pf-dihydroorotate dehydrogenase inhibitors.

Malaria remains one of the most serious global infectious diseases. An important target for antimalarial chemotherapy is the enzyme dihydroorotate dehydrogenase from Plasmodium falciparum (PfDHODH), which is responsible for the conversion of dihydroorotate to orotate in the de novo pyrimidine biosynthetic pathway. In this study, we have designed and synthesized fifteen 7-arylpyrazolo[1,5-a]pyrimidine derivatives using ring bioisosteric replacement and molecular hybridization of functional groups based on the highly active 5-methyl-N-(naphthalen-2-yl)-2-(trifluoromethyl)- [1,2,4]triazolo[1,5-a]pyrimidin-7-amine. The compounds were tested against Plasmodium falciparum, as antimalarials in mice with P. berghei, and as inhibitors of PfDHODH. Thirteen compounds were found to be active against P. falciparum, with IC50 values ranging from 1.2 ± 0.3 to 92 ± 26 µM in the anti-HRP2 and hypoxanthine assays. Four compounds showed the highest selective index (SI), which is a ratio between cytotoxicity and activity in vitro. The inhibition of PfDHODH showed that compound 30 (R2 = CH3; R5 = CF3; Ar = 7-ß-naphthyl) displayed higher and selective inhibitory activity, with IC50 = 0.16 ± 0.01 µM, followed by 25 (R2 = CH3; R5 = CH3; Ar = 7-ß-Naphthyl) and 19 (R2 = CF3; R5 = CF3; Ar = 7-ß-naphthyl), with IC50 = 4 ± 1 µM and 6 ± 1 µM, respectively. The trifluoromethyl group at the 2- or 5-positions of the pyrazolo[1,5-a]pyrimidine ring led to increased drug activity. The docking results agreed with the values obtained from enzymatic assays.

New pentasubstituted pyrrole hybrid atorvastatin-quinoline derivatives with antiplasmodial activity.

Cerebral malaria is caused by Plasmodium falciparum. Atorvastatin (AVA) is a pentasubstituted pyrrole, which has been tested as an adjuvant in the treatment of cerebral malaria. Herein, a new class of hybrids of AVA and aminoquinolines (primaquine and chloroquine derivatives) has been synthesized. The quinolinic moiety was connected to the pentasubstituted pyrrole from AVA by a linker group (CH2)n=2-4 units. The activity of the compounds increased with the size of the carbons chain. Compound with n=4 and 7-chloroquinolinyl has displayed better activity (IC50=0.40 µM) than chloroquine. The primaquine derivative showed IC50=1.41 µM, being less toxic and more active than primaquine.

In vitro and in vivo anti-malarial activity of plants from the Brazilian Amazon.

BACKGROUND: The anti-malarials quinine and artemisinin were isolated from traditionally used plants (Cinchona spp. and Artemisia annua, respectively). The synthetic quinoline anti-malarials (e.g. chloroquine) and semi-synthetic artemisinin derivatives (e.g. artesunate) were developed based on these natural products. Malaria is endemic to the Amazon region where Plasmodium falciparum and Plasmodium vivax drug-resistance is of concern. There is an urgent need for new anti-malarials. Traditionally used Amazonian plants may provide new treatments for drug-resistant P. vivax and P. falciparum. Herein, the in vitro and in vivo antiplasmodial activity and cytotoxicity of medicinal plant extracts were investigated. METHODS: Sixty-nine extracts from 11 plant species were prepared and screened for in vitro activity against P. falciparum K1 strain and for cytotoxicity against human fibroblasts and two melanoma cell lines. Median inhibitory concentrations (IC50) were established against chloroquine-resistant P. falciparum W2 clone using monoclonal anti-HRPII (histidine-rich protein II) antibodies in an enzyme-linked immunosorbent assay. Extracts were evaluated for toxicity against murine macrophages (IC50) and selectivity indices (SI) were determined. Three extracts were also evaluated orally in Plasmodium berghei-infected mice. RESULTS: High in vitro antiplasmodial activity (IC50 = 6.4-9.9 µg/mL) was observed for Andropogon leucostachyus aerial part methanol extracts, Croton cajucara red variety leaf chloroform extracts, Miconia nervosa leaf methanol extracts, and Xylopia amazonica leaf chloroform and branch ethanol extracts. Paullinia cupana branch chloroform extracts and Croton cajucara red variety leaf ethanol extracts were toxic to fibroblasts and or melanoma cells. Xylopia amazonica branch ethanol extracts and Zanthoxylum djalma-batistae branch chloroform extracts were toxic to macrophages (IC50 = 6.9 and 24.7 µg/mL, respectively). Andropogon leucostachyus extracts were the most selective (SI >28.2) and the most active in vivo (at doses of 250 mg/kg, 71% suppression of P. berghei parasitaemia versus untreated controls). CONCLUSIONS: Ethnobotanical or ethnopharmacological reports describe the anti-malarial use of these plants or the antiplasmodial activity of congeneric species. No antiplasmodial activity has been demonstrated previously for the extracts of these plants. Seven plants exhibit in vivo and or in vitro anti-malarial potential. Future work should aim to discover the anti-malarial substances present.

BbMP-1, a new metalloproteinase isolated from Bothrops brazili snake venom with in vitro antiplasmodial properties.

This study describes the biochemical and functional characterization of a new metalloproteinase named BbMP-1, isolated from Bothrops brazili venom. BbMP-1 was homogeneous on SDS-PAGE, presented molecular mass of 22,933Da and pI 6.4. The primary structure was partially elucidated with high identity with others metalloproteinases from Viperidae venoms. The enzymatic activity on azocasein was evaluated in different experimental conditions (pH, temperature). A significant reduction in enzyme activity after exposure to chelators of divalent cations (EDTA), reducing agents (DTT), pH less than 5.0 or temperatures higher than 45 °C was observed. BbMP-1 showed activity on fibrinogen degrading Aα chain quickly and to a lesser extent the Bß chain. Also demostrated to be weakly hemorrhagic, presenting however, significant myotoxic and edematogenic activity. The in vitro activity of BbMP-1 against Plasmodium falciparum showed an IC50 of 3.2 ± 2.0 µg/mL. This study may help to understand the pathophysiological effects induced by this group of toxin and their participation in the symptoms observed in cases of snake envenomation. Moreover, this result is representative for this group of proteins and shows the biotechnological potential of BbMP-1 by the demonstration of its antiplasmodial activity.

Ethnopharmacological evaluation of medicinal plants used against malaria by quilombola communities from Oriximiná, Brazil.

ETHNOPHARMACOLOGICAL RELEVANCE: Malaria is the most important parasitic disease in the world, including in the Amazon region, due to its high incidence. In addition, malaria is difficult to control because of the geographical characteristics of the endemic Amazon region. The quilombola communities of Oriximina, located in remote rainforest areas, have extensive experience with medicinal plants due to their close contact with and dependence on local biodiversity as a therapeutic resource. To search for active bioproducts against malaria, based on in vitro tests using blood culture-derived parasites and plants selected by an ethno-directed approach in traditional quilombola communities of Oriximiná, in the Amazon region of Brazil. MATERIALS AND METHODS: Ethnobotanical data were collected from 35 informants in the quilombola communities of Oriximiná, Brazil, by a free-listing method for the survey of species locally indicated to be effective against malaria and related symptoms. Data were analyzed by salience index (S) and major use agreement. The activity of extracts from 11 plants, selected based on their Salience values (four plants with S>1; seven plants with S<0.1), was measured in vitro in cultures of W2 clone Plasmodium falciparum parasites resistant to chloroquine. RESULTS: Thirty-five ethnospecies comprising 40 different plants belonging to 23 botanical families and 37 genera were listed as antimalarials by the ethno-directed approach. Among these, 11 species selected based on their S values were assayed against P. falciparum. The most active plant extracts, with an IC50 as low as 1.6µg/mL, were obtained from Aspidosperma rigidum (Apocynaceae), Bertholletia excelsa (Lecythidaceae) and Simaba cedron (Simaroubaceae), all of which displayed an S value>1. CONCLUSION: A strong correlation between the consensus of the informants from quilombola communities living in a malaria endemic area and the salience index indicating antiplasmodial activity was observed, where the ethnospecies mostly cited to be effective against malaria produced the most active plant extracts in vitro. It was also evident from the data that these groups approached the treatment of malaria with an holistic view, making use of purgative, depurative, emetic and adaptogen plants.

Anti-Plasmodium falciparum activity of quinoline-sulfonamide hybrids.

Fifteen quinoline-sulfonamide hybrids, with a 7-chloroquinoline moiety connected by a linker group to arylsulfonamide moieties with different substituents in the 4-position were synthesized and assayed against Plasmodium falciparum. The compounds displayed high schizonticidal blood activity in vitro, with IC50 values ranging from 0.05 to 1.63 µM, in the anti-HPR2 assay against clone W2-chloroquine-resistant; ten of them showed an IC50 (ranging from 0.05 to 0.40 µM) lower than that of chloroquine and sulfadoxine. Among them, two compounds inhibited Plasmodium berghei parasitemia by 47% and 49% on day 5 after mice inoculation. The most active, in vivo, hybrid 13 is considered to be a new prototype for the development of an antimalarial drug against chloroquine-resistant parasites.

Antiplasmodial activity of chloroquine analogs against chloroquine-resistant parasites, docking studies and mechanisms of drug action.

BACKGROUND: Given the threat of resistance of human malaria parasites, including to artemisinin derivatives, new agents are needed. Chloroquine (CQ) has been the most widely used anti-malarial, and new analogs (CQAns) presenting alkynes and side chain variations with high antiplasmodial activity were evaluated. METHODS: Six diaminealkyne and diaminedialkyne CQAns were evaluated against CQ-resistant (CQ-R) (W2) and CQ-sensitive (CQ-S) (3D7) Plasmodium falciparum parasites in culture. Drug cytotoxicity to a human hepatoma cell line (HepG2) evaluated, allowed to calculate the drug selectivity index (SI), a ratio of drug toxicity to activity in vitro. The CQAns were re-evaluated against CQ-resistant and -sensitive P. berghei parasites in mice using the suppressive test. Docking studies with the CQAns and the human (HssLDH) or plasmodial lactate dehydrogenase (PfLDH) enzymes, and, a ß-haematin formation assay were performed using a lipid as a catalyst to promote crystallization in vitro. RESULTS: All tested CQAns were highly active against CQ-R P. falciparum parasites, exhibiting half-maximal inhibitory concentration (IC(50)) values below 1 µΜ. CQAn33 and CQAn37 had the highest SIs. Docking studies revealed the best conformation of CQAn33 inside the binding pocket of PfLDH; specificity between the residues involved in H-bonds of the PfLDH with CQAn37. CQAn33 and CQAn37 were also shown to be weak inhibitors of PfLDH. CQAn33 and CQAn37 inhibited ß-haematin formation with either a similar or a 2-fold higher IC(50) value, respectively, compared with CQ. CQAn37 was active in mice with P. berghei, reducing parasitaemia by 100%. CQAn33, -39 and -45 also inhibited CQ-resistant P. berghei parasites in mice, whereas high doses of CQ were inactive. CONCLUSIONS: The presence of an alkyne group and the size of the side chain affected anti-P. falciparum activity in vitro. Docking studies suggested a mechanism of action other than PfLDH inhibition. The ß-haematin assay suggested the presence of an additional mechanism of action of CQAn33 and CQAn37. Tests with CQAn34, CQAn37, CQAn39 and CQAn45 confirmed previous results against P. berghei malaria in mice, and CQAn33, 39 and 45 were active against CQ-resistant parasites, but CQAn28 and CQAn34 were not. The result likely reflects structure-activity relationships related to the resistant phenotype.

The use of an integrated molecular-, chemical- and biological-based approach for promoting the better use and conservation of medicinal species: a case study of Brazilian quinas.

ETHNOPHARMACOLOGICAL RELEVANCE: Quina is a popular name originally attributed to Cinchona pubescens Vahl (=Cinchona succirubra) and Cinchona. calisaya Wedd., species native from Peru that have the antimalarial alkaloid quinine. In Brazil, bitter barks substitutes for the Peruvian species began to be used centuries ago, and they still are sold in popular markets. To assess the authenticity and the conditions on which samples of quinas have been commercialized, using the DNA barcode, chemical and biological assays. MATERIALS AND METHODS: Starting with 28 samples of barks acquired on a popular market, 23 had their DNA extracted successfully. The regions matK and rbcL were amplified and sequenced for 15 and 23 samples, respectively. Phytochemical analyses were performed by chromatographic methods, and biological essays were done by antimalarial tests in vitro. RESULTS: The identified species belonged to six different families, many of them endangered or with no correlation with use in traditional medicine as a Brazilian quina. The absence of typical bitter chemical substances indicated that barks have been collected from other species or from very young trees. The results of biological essays confirm the lack of standardization of the sold materials. CONCLUSION: The integrated approaches proved to be efficient to evaluate medicinal plants sold in popular markets and can be useful for promoting their better use and conservation.

New compounds hybrids 1h-1,2,3-triazole-quinoline against Plasmodium falciparum.

Malaria is one of the most prevalent parasitic diseases in the world. The global importance of this disease, current vector control limitations, and the absence of an effective vaccine make the use of therapeutic antimalarial drugs the main strategy to control malaria. Chloroquine is a cost-effective antimalarial drug with a relatively robust safety profile, or therapeutic index. However, chloroquine is no longer used alone to treat patients with Plasmodium falciparum due to the emergence and spread of chloroquine-resistant strains, which have also been reported for Plasmodium vivax. However, the activity of 1,2,3-triazole derivatives against chloroquine-sensitive and chloroquine-resistant strains of P. falciparum has been reported in the literature. To enhance the anti-P. falciparum activity of quinoline derivatives, we synthesized 11 new quinoline-1H-1,2,3-triazole hybrids with different substituents in the 4-positions of the 1H-1,2,3-triazole ring, which were assayed against the W2-chloroquine-resistant P. falciparum clone. Six compounds exhibited activity against the P. falciparum W2 clone, chloroquine-resistant, with IC50 values ranging from 1.4 to 46 µm. None of these compounds was toxic to a normal monkey kidney cell line, thus exhibiting good selectivity indexes, as high 351 for one compound (11).