Dinesh Mohanakrishnan

Stilbene–Chalcone Hybrids: Design, Synthesis, and Evaluation as a New Class of Antimalarial Scaffolds That Trigger Cell Death through Stage Specific Apoptosis

Novel stilbene-chalcone (S-C) hybrids were synthesized via a sequential Claisen-Schmidt-Knoevenagel-Heck approach and evaluated for antiplasmodial activity in in vitro red cell culture using SYBR Green I assay. The most potent hybrid (11) showed IC(50) of 2.2, 1.4, and 6.4 μM against 3D7 (chloroquine sensitive), Indo, and Dd2 (chloroquine resistant) strains of Plasmodium falciparum, respectively. Interestingly, the respective individual stilbene (IC(50) > 100 μM), chalcone (IC(50) = 11.5 μM), or an equimolar mixture of stilbene and chalcone (IC(50) = 32.5 μM) were less potent than 11. Studies done using specific stage enriched cultures and parasite in continuous culture indicate that 11 and 18 spare the schizont but block the progression of the parasite life cycle at the ring or the trophozoite stages. Further, 11 and 18 caused chromatin condensation, DNA fragmentation, and loss of mitochondrial membrane potential in Plasmodium falciparum, thereby suggesting their ability to cause apoptosis in malaria parasite.

Reinvestigation of structure-activity relationship of methoxylated chalcones as antimalarials: synthesis and evaluation of 2,4,5-trimethoxy substituted patterns as lead candidates derived from abundantly available natural β-asarone.

We have examined the antimalarial structure-activity relationship of a series of methoxylated chalcones (A-CHCH-CO-B) against Plasmodium falciparum (3D7 strain) using fluorescence-based SYBR Green assay. Our study has revealed that electron releasing methoxy groups on ring A and electron withdrawing groups on ring B increases antimalarial potency while the positional interchange of these groups causes a decrease. In particular, 2,4,5-trimethoxy substitution pattern at ring A provided potent analogues which were easily derived from abundantly available natural β-asarone rich Acorus calamus oil. Cytotoxic evaluation indicated that the most active compounds 27 (IC(50): 1.8 μM) and 26 (IC(50): 2 μM) were also relatively non-toxic. Furthermore, compound 12 showed excellent resistance index of 1.1 against chloroquine resistant Dd2 strain of P. falciparum.

Antimalarial activities of medicinal plants traditionally used in the villages of Dharmapuri regions of South India.

ETHNOPHARMACOLOGICAL RELEVANCE An ethnopharmacological investigation of medicinal plants traditionally used to treat diseases associated with fevers in Dharmapuri region of South India was undertaken. Twenty four plants were identified and evaluated for their in vitro activity against Plasmodium falciparum and assessed for cytotoxicity against HeLa cell line. AIM OF THE STUDY This antimalarial in vitro study was planned to correlate and validate the traditional usage of medicinal plants against malaria. MATERIALS AND METHODS An ethnobotanical survey was made in Dharmapuri region, Tamil Nadu, India to identify plants used in traditional medicine against fevers. Selected plants were extracted with ethyl acetate and methanol and evaluated for antimalarial activity against erythrocytic stages of chloroquine (CQ)-sensitive 3D7 and CQ-resistant INDO strains of Plasmodium falciparum in culture using the fluorescence-based SYBR Green I assay. Cytotoxicity was determined against HeLa cells using MTT assay. RESULTS Promising antiplasmodial activity was found in Aegle marmelos [leaf methanol extract (ME) (IC(50)=7 μg/mL] and good activities were found in Lantana camara [leaf ethyl acetate extract (EAE) IC(50)=19 μg/mL], Leucas aspera (flower EAE IC(50)=12.5 μg/mL), Momordica charantia (leaf EAE IC(50)=17.5 μg/mL), Phyllanthus amarus (leaf ME IC(50)=15 μg/mL) and Piper nigrum (seed EAE IC(50)=12.5 μg/mL). The leaf ME of Aegle marmelos which showed the highest activity against Plasmodium falciparum elicited low cytotoxicity (therapeutic index>13). CONCLUSION These results provide validation for the traditional usage of some medicinal plants against malaria in Dharmapuri region, Tamil Nadu, India.

Tandem allylic oxidation–condensation/esterification catalyzed by silica gel: an expeditious approach towards antimalarial diaryldienones and enones from natural methoxylated phenylpropenes

A new one-pot strategy has been developed, wherein abundantly available methoxylated phenylpropenes are directly transformed into corresponding dienones (1,5-diarylpenta-2,4-dien-1-ones) and enones (chalcones and cinnamic esters) via allylic oxidation-condensation or allylic oxidation-esterification sequences. Preliminary antimalarial activity studies of the above synthesized diaryldienones and enones against Plasmodium falciparum (Pf3D7) have shown them to be promising lead candidates for developing newer and economical antimalarial agents. In particular, two enones (12b and 13b) were found to possess comparatively better activity (IC(50) = 4.0 and 3.4 μM, respectively) than licochalcone (IC(50) = 4.1 μM), a well known natural antimalarial compound.

Antiplasmodial potential of selected medicinal plants from Eastern Ghats of South India

Malaria caused by the protozoan parasite Plasmodium falciparum, is a major health problem of the developing world. In the present study medicinal plants from Eastern Ghats of South India have been extracted with ethyl acetate and assayed for growth inhibition of asexual erythrocytic stages of chloroquine (CQ)-sensitive (3D7) and (CQ)-resistant (INDO) strains of P. falciparum in culture using the fluorescence-based SYBR Green I assay. Studied extracts showed a spectrum of antiplasmodial activities ranging from (a) very good (IC(50)<10-10 μg/mL: Cyperus rotundus and Zingiber officinale); (b) good (IC(50), >10-15 μg/mL: Ficus religiosa and Murraya koenigii); (c) moderate (IC(50)>15-25 μg/mL: Ficus benghalensis); (d) poor activity (IC(50)>25-60 μg/mL) and (e) inactive (IC(50)>60 μg/mL). Resistance indices ranging from 0.78 to 1.28 suggest that some of these extracts had equal promise against the CQ resistant INDO strain of P. falciparum. Cytotoxicity assessment of the extracts against HeLa cell line using MTT assay revealed that the selectivity indices in the range of 3-15 suggesting a good margin of safety.

Antiplasmodial activity of medicinal plants from Chhotanagpur plateau, Jharkhand, India.

BACKGROUND The alarmingly increasing problem of drug resistance in treatment of malaria has led to an urgent need for identifying new anti-malarial drugs for both prophylaxis and chemotherapy. AIM OF THE STUDY The present study presents a systematic exploration of the ex vivo blood stage antiplasmodial potential of medicinal plants to corroborate their traditional usage against malaria in Jharkhand, India. METHODS An ethnobotanical survey in and around Ranchi was done to grasp the traditional knowledge of medicinal plants used by local healers for malaria, other fevers and for other medicinal purposes like, antiamoebic, antihelmenthic, antidote to poisons, etc. Following the survey, the selected 22 plant samples were extracted in ethanol for studying ex vivo SYBR Green I fluorescence assay based anti-plasmodial activity against both chloroquine-sensitive Pf3D7 and chloroquine resistant PfINDO strains of Plasmodium falciparum grown in human red blood cell cultures. Cytotoxicity was determined against HeLa and L929 cells using MTT assay. Further the most potent extract was chromatographed on reverse phase HPLC towards antiplasmodial activity guided purification of metabolites. RESULTS Of the 22 plant species assayed, the highest antiplasmodial activity (Pf3D7IC50 ≤ 5 µg/ml) was seen in leaf ethanol extracts of Corymbia citriodora (Hook.) K.D.Hill & L.A.S.Johnson, Calotropis procera (Aiton) Dryand. and Annona squamosa L. and bark ethanol extract of Holarrhena pubescens Wall. ex G.Don. Leaf ethanol extract of H. pubescens, bark ethanol extract of Pongamia pinnata (L.) Pierre and whole plant ethanol extract of Partheniumhysterophorus L. showed promising activity (IC50 6-10 µg/ml). Good antiplasmodial activity (IC50: 11-20 µg/ml) was observed in leaf ethanol extract of Bryophyllum pinnatum (Lam.) Oken and whole plant ethanol extract of Catharanthus roseus (L.) G.Don. The extracts of plants showing highest to good antiplasmodial activity exhibited HeLa/Pf3D7 selectivity indices of the order of 20-45. Bioassay guided fractionation of P. hysterophorus led to fivefold enrichment of antiplasmodial activities (IC50 ~450 ng/ml) in some fractions. CONCLUSION These results provide confirmation to the traditional usage of some medicinal plants against malaria in areas around Ranchi, Jharkhand.

Antimalarial and antiplasmodial activity of husk extract and fractions of Zea mays

Abstract Context: Zea mays L. (Poacae) husk decoctions are traditionally used in the treatment of malaria by various tribes in Nigeria. Objective: To assess the antimalarial and antiplasmodial potentials of the husk extract and fractions on malaria parasites using in vivo and in vitro models. Materials and methods: The ethanol husk extract and fractions (187–748 mg/kg, p.o.) of Zea mays were investigated for antimalarial activity against Plasmodium berghei using rodent (mice) malaria models and in vitro activity against chloroquine sensitive (Pf 3D7) and resistant (Pf INDO) strains of Plasmodium falciparum using the SRBR green assay method. Median lethal dose and cytotoxic activities against HeLa and HEKS cells were also carried out. The GCMS analysis of the most active fraction was carried out. Results: The husk extract (187–748 mg/kg, p.o.) with LD50 of 1874.83 mg/kg was found to exert significant (p < 0.05–0.001) antimalarial activity against P. berghei infection in suppressive, prophylactive and curative tests. The crude extract and fractions also exerted prominent activity against both chloroquine sensitive (Pf 3D7) and resistant (Pf INDO) strains of P. falciparum with the ethyl acetate fraction exerting the highest activity with IC50 values of 9.31 ± 0.46 μg/mL (Pf 3D7) and 3.69 ± 0.66 μg/mL (Pf INDO). The crude extract and fractions were not cytotoxic to the two cell lines tested with IC50 values of >100 μg/mL against both HeLa and HEKS cell lines. Discussion and conclusion: These results suggest that the husk extract/fractions of Zea mays possesses antimalarial and antiplasmodial activities and these justify its use in ethnomedicine to treat malaria infections.

Synthesis, mechanistic and synergy studies of diarylidenecyclohexanone derivatives as new antiplasmodial pharmacophores

Diarylidenecyclohexanone (DAC) derivatives (Ia-i, IIa-c and IIIa-b) were synthesized, characterized and screened for their invitro antiplasmodial activities against erythrocytic stages of chloroquine (CQ) sensitive and resistant strains of P. falciparum by using SYBR green I fluorescence assay. SAR studies of DAC derivatives showed antiplasmodial activity in the order of 3-NO2 (Ib, IC50 0.95 µM) > 3-chloro (Id, IC50 3 µM) > 4-chloro (Ie, IC50 8.5 µM) > 2-chloro (Ic, IC50 13 µM). Further Ib and Id exhibited nearly equal potencies against CQ-resistant strains P. falciparum Dd2, {IC50 1 µM (Ib) and 2.7 µM (Id)} and PfINDO {IC50 1.1 µM (Ib) and 2.5 µM (Id)}. Drug exposure followed by drug withdrawal-based stage-specific kill kinetic studies showed that Ib is shizonticidal within 3 h while the earliest killing actions against Trophozoites and Rings were seen at >3 h and >6 h, respectively. Combination studies of the most potent leads viz. Ib and Id showed strong to moderate synergistic effects with Artemisinin (ƩFIC50: 0.34 to 0.63) whereas no interaction (ƩFIC50: 0.65 to 2.36) was observed with Chloroquine. The DACs showed significant insilico binding affinity with β-haematin and P. falciparum lactate dehydrogenase (PfLDH) suggesting these to be the targets of their antiplasmodial action. High compliance with Lipinski rule of 5 and high selectivity index of Ib (105.3) and Id (8.3) against HeLa cell line indicated that Diarylidenecyclohexanones could serve as structural templates towards lead optimization of compounds for discovery of novel, potent, safe and affordable drugs against malaria.

Orally Effective Aminoalkyl 10H-Indolo-[3,2-b]quinoline-11-carboxamide Kills the Malaria Parasite by Inhibiting Host Hemoglobin Uptake

A series of indolo[3,2‐b]quinoline‐C11‐carboxamides were synthesized by incorporation of aminoalkyl side chains into the core of indolo[3,2‐b]quinoline‐C11‐carboxylic acid. Their in vitro antiplasmodial evaluation against Plasmodium falciparum led to the identification of a 2‐(piperidin‐1‐yl)ethanamine‐linked analogue {2‐bromo‐N‐[2‐(piperidin‐1‐yl)ethyl]‐10H‐indolo[3,2‐b]quinoline‐11‐carboxamide (3 g)} (IC50=1.3 μm) as the most promising compound exhibiting good selectivity indices against mammalian cell lines. The kill kinetics on erythrocytic‐stage parasites revealed that 3 g caused complete killing of only the trophozoite‐stage parasites. Mechanistic studies showed that 3 g targets the food vacuole of the parasite and inhibits hemoglobin uptake, β‐hematin formation, and the basic endocytic processes of the parasite. Analogue 3 g was found to be orally bioavailable, and its curative antimalarial studies at 50 mg per kg p.o. against a Plasmodium berghei (ANKA)‐infected mouse model revealed that mice treated with 3 g showed 27–35 % suppression of parasitemia with an increase in life span relative to untreated, control mice. Thus, the present work demonstrated a proof of concept for the oral efficacy of indolo[3,2‐b]quinoline‐C11‐carboxamides.

Antimalarial, antiplasmodial and analgesic activities of root extract of Alchornea laxiflora

Abstract Context: Alchornea laxiflora (Benth.) Pax. & Hoffman (Euphorbiaceae) root decoctions are traditionally used in the treatment of malaria and pain in Nigeria. Objective: To assess the antimalarial, antiplasmodial and analgesic potentials of root extract and fractions against malarial infections and chemically-induced pains. Material and methods: The root extract and fractions of Alchornea laxiflora were investigated for antimalarial activity against Plasmodium berghei infection in mice, antiplasmodial activity against chloroquine sensitive (Pf 3D7) and resistant (Pf INDO) strains of Plasmodium falciparum using SYBR green assay method and analgesic activity against experimentally-induced pain models. Acute toxicity study of the extract, cytotoxic activity against HeLa cells and GCMS analysis of the active fraction were carried out. Results: The root extract (75–225 mg/kg, p.o.) with LD50 of 748.33 mg/kg exerted significant (p < 0.05–0.001) antimalarial activity against P. berghei infection in suppressive, prophylactive and curative tests. The root extract and fractions also exerted moderate activity against chloroquine sensitive (Pf 3D7) and resistant (Pf INDO) strains of P. falciparum with the ethyl acetate fraction exerting the highest activity with IC50 value of 38.44 ± 0.89 μg/mL (Pf 3D7) and 40.17 ± 0.78 μg/mL (Pf INDO). The crude extract was not cytotoxic to HeLa cells with LC50 value >100 μg/mL. The crude extract and ethyl acetate fraction exerted significant (p < 0.05–0.001) analgesic activity in all pain models used. Discussion and conclusions: These results suggest that the root extract/fractions of A. laxiflora possess antimalarial, antiplasmodial and analgesic potentials and these justify its use in ethnomedicine to treat malaria and pain.