Chemosensitization potential of P-glycoprotein inhibitors in malaria parasites

Recent developments in antimalarial drug discovery

Although malaria remains a big burden to many countries that it threatens their socio-economic stability, particularly in the countries where malaria is endemic, there have been great efforts to eradicate this disease with both successes and failures. For example, there has been a great improvement in malaria prevention and treatment methods with a net reduction in infection and mortality rates. However, the disease remains a global threat in terms of the number of people affected because it is one of the infectious diseases that has the highest prevalence rate, especially in Africa where the deadly Plasmodium falciparum is still widely spread. Methods to fight malaria are being diversified, including the use of mosquito nets, the target candidate profiles (TCPs) and target product profiles (TPPs) of medicine for malarial venture (MMV) strategy, the search for newer and potent drugs that could reverse chloroquine resistance, and the use of adjuvants such as rosiglitazone and sevuparin. Although these adjuvants have no antiplasmodial activity, they can help to alleviate the effects which result from plasmodium invasion such as cytoadherence. The list of new antimalarial drugs under development is long, including the out of ordinary new drugs MMV048, CDRI-97/78 and INE963 from South Africa, India and Novartis, respectively.

Antimalarial activity and sensitization of chrysosplenetin against artemisinin-resistant genotype Plasmodium berghei K173 potentially via dual-mechanism of maintaining host P-glycoprotein homeostasis mediated by NF-κB p52 or PXR/CAR signaling pathways and regulating heme/haemozoin metabolism

This study investigated antimalarial efficacy and sensitization of chrysosplenetin against artemisinin-resistant Plasmodium berghei K173 and potential molecular mechanism. Our data indicated a risk of artemisinin resistance because a higher parasitaemia% and lower inhibition% under artemisinin treatment against resistant parasites than those in the sensitive groups were observed. Two non-antimalarial components, verapamil and chrysosplentin, being P-gp inhibitors, possessed a strong efficacy against resistant parasites but it was not the case for Bcrp inhibitor novobiocin. Artemisinin-chrysosplenetin combination improved artemisinin susceptibility of resistant P. berghei. Artemisinin activated intestinal P-gp and Abcb1/Abcg2 expressions and suppressed Bcrp whereas chrysosplenetin reversed them. Resistant parasite infection led to a decreased haemozoin in organs or an increased heme in peripheral bloods compared with the sensitives; however, that in Abcb1-deficient knockout (KO)-resistant mice reversely got increased or decreased versus wild type (WT)-resistant animals. Chrysosplenetin as well as rifampin (nuclear receptor agonist) increased the transcription levels of PXR/CAR while showed a versatile regulation on hepatic and enternal PXR/CAR in WT- or KO-sensitive or -resistant parasites. Oppositely, hepatic and enteric NF-κB p52 mRNA decreased conformably in WT but increased in KO-resistant mice. NF-κB pathway potentially involved in the mechanism of chrysosplenetin on inhibiting P-gp expressions while PXR/CAR play a more complicated role in this mechanism.

Identifying Protein Features Responsible for Improved Drug Repurposing Accuracies Using the CANDO Platform: Implications for Drug Design

Drug repurposing is a valuable tool for combating the slowing rates of novel therapeutic discovery. The Computational Analysis of Novel Drug Opportunities (CANDO) platform performs shotgun repurposing of 2030 indications/diseases using 3733 drugs/compounds to predict interactions with 46,784 proteins and relating them via proteomic interaction signatures. The accuracy is calculated by comparing interaction similarities of drugs approved for the same indications. We performed a unique subset analysis by breaking down the full protein library into smaller subsets and then recombining the best performing subsets into larger supersets. Up to 14% improvement in accuracy is seen upon benchmarking the supersets, representing a 100⁻1000-fold reduction in the number of proteins considered relative to the full library. Further analysis revealed that libraries comprised of proteins with more equitably diverse ligand interactions are important for describing compound behavior. Using one of these libraries to generate putative drug candidates against malaria, tuberculosis, and large cell carcinoma results in more drugs that could be validated in the biomedical literature compared to using those suggested by the full protein library. Our work elucidates the role of particular protein subsets and corresponding ligand interactions that play a role in drug repurposing, with implications for drug design and machine learning approaches to improve the CANDO platform.

Chrysosplenetin inhibits artemisinin efflux in P-gp-over-expressing Caco-2 cells and reverses P-gp/MDR1 mRNA up-regulated expression induced by artemisinin in mouse small intestine

CONTEXT

CYP3A4 and P-gp together form a highly efficient barrier for orally absorbed drugs and always share the same substrates. Our previous work revealed that chrysosplenetin (CHR) significantly augmented the rat plasma level and anti-malarial efficacy of artemisinin (ART), partially due to the uncompetitive inhibition effect of CHR on rat CYP3A. But the impact of CHR on P-gp is still unknown.

OBJECTIVE

The present study investigates whether CHR interferes with P-gp-mediated efflux of ART and elucidates the underlying mechanism.

MATERIALS AND METHODS

P-gp-over-expressing Caco-2 cells were treated with ART (10 μM) or ART-CHR (1:2, 10:20 μM) in ART bidirectional transport experiment. ART concentration was determined by UHPLC-MS/MS method. Healthy male ICR mice were randomly divided into nine groups (n = 6) including negative control (0.5% CMC-Na solution, 13 mL/kg), ART alone (40 mg/kg), verapamil (positive control, 40 mg/kg), ART-verapamil (1:1, 40:40 mg/kg), CHR alone (80 mg/kg), ART-CHR (1:0.1, 40:4 mg/kg), ART-CHR (1:1, 40:40 mg/kg), ART-CHR (1:2, 40:80 mg/kg) and ART-CHR (1:4, 40:160 mg/kg). The drugs were administrated intragastrically for seven consecutive days. MDR1 and P-gp expression levels in mice small intestine were examined by performing RT-PCR and western blot analysis. ABC coupling ATPase activity was also determined.

RESULTS

After combined with CHR (1:2), Papp (AP-BL) and Papp (BL-AP) of ART changed to 4.29 × 10 - 8 (increased 1.79-fold) and 2.85 × 10 - 8 cm/s (decreased 1.24-fold) from 2.40 × 10 - 8 and 3.54 × 10 - 8 cm/s, respectively. Efflux ratio (PBA/PAB) declined 2.21-fold (p < 0.01) versus to ART alone. ART significantly up-regulated both MDR1 mRNA and P-gp levels compared with vehicle, while CHR in combination ratio of 0:1, 0.1:1, 1:1, 2:1 and 4:1 with ART, reversed them to normal levels as well as negative control (p < 0.05). The ATPase activities in ART-CHR 1:4 and CHR alone groups achieved a slight increase (p < 0.05) when compared with ART alone.

DISCUSSION AND CONCLUSION

These results confirm that CHR inhibited P-gp activity and reverse the up-regulated P-gp and MDR1 levels induced by ART. It suggested that CHR potentially can be used as a P-gp reversal agent to obstruct ART multidrug resistance.

Oridonin induces apoptosis and reverses drug resistance in cisplatin resistant human gastric cancer cells

Gastric cancer is the third most frequent cause of cancer-associated mortality and almost all patients who respond initially to cisplatin (DDP) later develop drug resistance, indicating multi-drug resistance (MDR) is an essential aspect of the failure of treatment. The natural diterpenoid component Oridonin (Ori) has exhibited efficient inhibition in several types of human cancer. However, the effect and potential mechanism of Ori-reversed MDR in human gastric cancer has not been fully elucidated. In the present study, it was found that Ori significantly suppressed DDP-resistant human SGC7901/DDP cell proliferation, growth and colony formation, causing increased caspase-dependent apoptosis, decreased expression of P-glycoprotein (P-gp), encoded by the MDR gene, multi-drug resistance-associated protein (MRP1), and cyclin D1. SGC7901/DDP cells were cultured with different groups of drugs (Ori, DDP alone, or the combination of Ori and DDP). The drug sensitivity, cell apoptosis and effects on MDR were detected by MTT assay and western blot analysis. The results revealed that Ori is able to reverse the DDP resistance and has a clear synergistic effect with DDP in SGC7901/DDP cells by decreasing the levels of P-gp, MRP1, cyclin D1 and cancerous inhibitor of protein phosphatase 2A. Thus, Ori may be a novel effective candidate to treat DDP-resistant human gastric cancer cells.

Comprehensive review on various strategies for antimalarial drug discovery

The resistance of malaria parasites to existing drugs carries on growing and progressively limiting our ability to manage this severe disease and finally lead to a massive global health burden. Till now, malaria control has relied upon the traditional quinoline, antifolate and artemisinin compounds. Very few new antimalarials were developed in the past 50 years. Among recent approaches, identification of novel chemotherapeutic targets, exploration of natural products with medicinal significance, covalent bitherapy having a dual mode of action into a single hybrid molecule and malaria vaccine development are explored heavily. The proper execution of these approaches and proper investment from international agencies will accelerate the discovery of drugs that provide new hope for the control or eventual eradication of this global infectious disease. This review explores various strategies for assessment and development of new antimalarial drugs. Current status and scientific value of previous approaches are systematically reviewed and new approaches provide a pragmatic forecast for future developments are introduced as well.

A self-contrast approach to evaluate the inhibitory effect of chrysosplenetin, in the absence and presence of artemisinin, on the in vivo P-glycoprotein-mediated digoxin transport activity

In this study, we used a self-contrast method, which excluded the individual difference, to evaluate the inhibitory effect of chrysosplentin (CHR) in the presence or absence of artemisinin (ART) on the P-glycoprotein (P-gp) transport activity. A sensitive and rapid UHPLC-MS/MS method was applied for quantification of digoxin, a P-gp-specific substrate, in rat plasma. A pharmacokinetic study was carried out: first after an oral administration of digoxin at a dose of 0.09 mg/kg (first period), followed by a 20-day wash-out, then after another administration of digoxin (second period). During the second period, test compounds were orally given three times per day for seven consecutive days. Results showed that the t1/2 of digoxin in all the groups had no significant difference between the first and second periods. The AUC0-24 , Cmax , tmax , and Clz /F of the negative control and ART alone groups showed no difference. However, the AUC0-24 and Cmax in the CHR alone, CHR-ART (1:2) and verapamil (positive control) groups showed 2.34-, 3.04-, 1.79-, and 1.81-, 1.99-, 2.06-fold increases along with 3.50-, 3.84- and 4.76-fold decreases for CLz /F, respectively. The tmax in the CHR-ART (1:2) group increased 3.73-fold. In conclusion, our self-contrast study suggested that CHR, especially when combined with ART in a ratio of 1:2, inhibited P-gp activity while ART alone has no effect. Copyright © 2016 John Wiley & Sons, Ltd.

Reemergence of chloroquine (CQ) analogs as multi-targeting antimalarial agents: a review

Amongst several communicable diseases (CDs), malaria is one of the deadliest parasitic disease all over the world, particularly in African and Asian countries. To curb this menace, numbers of antimalarial agents are being sold as over the counter (OTC) drugs. Chloroquine (CQ) is one of them and is one of the oldest, cheapest, and easily available synthetic agents used to curb malaria. Unfortunately, after the reports of CQ-resistance against different strains of malarial parasite strains worldwide, scientist are continuously modifying the core structure of CQ to get an efficient drug. Interestingly, several new drugs have been emerged in due course having unique and enhanced properties (like dual stage inhibitors, resistance reversing ability etc.) and are ready to enter into the clinical trial. In this course, some new agents have also been discovered which are; though inactive against CQS strain, highly active against CQR strains. The present article describes the role of modification of the core structure of CQ and its effects on the biological activities. Moreover, the attempt has also been made to predict the future prospects of such drugs to reemerge as antimalarial agents.

Characterization of the commercially-available fluorescent chloroquine-BODIPY conjugate, LynxTag-CQGREEN, as a marker for chloroquine resistance and uptake in a 96-well plate assay

Chloroquine was a cheap, extremely effective drug against Plasmodium falciparum until resistance arose. One approach to reversing resistance is the inhibition of chloroquine efflux from its site of action, the parasite digestive vacuole. Chloroquine accumulation studies have traditionally relied on radiolabelled chloroquine, which poses several challenges. There is a need for development of a safe and biologically relevant substitute. We report here a commercially-available green fluorescent chloroquine-BODIPY conjugate, LynxTag-CQ_GREEN, as a proxy for chloroquine accumulation. This compound localized to the digestive vacuole of the parasite as observed under confocal microscopy, and inhibited growth of chloroquine-sensitive strain 3D7 more extensively than in the resistant strains 7G8 and K1. Microplate reader measurements indicated suppression of LynxTag-CQ_GREEN efflux after pretreatment of parasites with known reversal agents. Microsomes carrying either sensitive- or resistant-type PfCRT were assayed for uptake; resistant-type PfCRT exhibited increased accumulation of LynxTag-CQ_GREEN, which was suppressed by pretreatment with known chemosensitizers. Eight laboratory strains and twelve clinical isolates were sequenced for PfCRT and Pgh1 haplotypes previously reported to contribute to drug resistance, and pfmdr1 copy number and chloroquine IC₅₀s were determined. These data were compared with LynxTag-CQ_GREEN uptake/fluorescence by multiple linear regression to identify genetic correlates of uptake. Uptake of the compound correlated with the logIC₅₀ of chloroquine and, more weakly, a mutation in Pgh1, F1226Y.

Conformational flexibility of the agonist binding jaw of the human P2X3 receptor is a prerequisite for channel opening

BACKGROUND AND PURPOSE

It is assumed that ATP induces closure of the binding jaw of ligand-gated P2X receptors, which eventually results in the opening of the membrane channel and the flux of cations. Immobilization by cysteine mutagenesis of the binding jaw inhibited ATP-induced current responses, but did not allow discrimination between disturbances of binding, gating, subunit assembly or trafficking to the plasma membrane.

EXPERIMENTAL APPROACH

A molecular model of the pain-relevant human (h)P2X3 receptor was used to identify amino acid pairs, which were located at the lips of the binding jaw and did not participate in agonist binding but strongly approached each other even in the absence of ATP.

KEY RESULTS

A series of cysteine double mutant hP2X3 receptors, expressed in HEK293 cells or Xenopus laevis oocytes, exhibited depressed current responses to α,β-methylene ATP (α,β-meATP) due to the formation of spontaneous inter-subunit disulfide bonds. Reducing these bonds with dithiothreitol reversed the blockade of the α,β-meATP transmembrane current. Amino-reactive fluorescence labelling of the His-tagged hP2X3 receptor and its mutants expressed in HEK293 or X. laevis oocytes demonstrated the formation of inter-subunit cross links in cysteine double mutants and, in addition, confirmed their correct trimeric assembly and cell surface expression.

CONCLUSIONS AND IMPLICATIONS

In conclusion, spontaneous tightening of the binding jaw of the hP2X3 receptor by inter-subunit cross-linking of cysteine residues substituted at positions not directly involved in agonist binding inhibited agonist-evoked currents without interfering with binding, subunit assembly or trafficking.

Probing the aurone scaffold against Plasmodium falciparum: design, synthesis and antimalarial activity

A library comprising 44 diversely substituted aurones derivatives was synthesized by straightforward aldol condensation reactions of benzofuranones and the appropriately substituted benzaldehydes. Microwave enhanced synthesis using palladium catalyzed protocols was introduced as a powerful strategy for extending the chemical space around the aurone scaffold. Additionally, Mannich-base derivatives, containing a 7-aminomethyl-6-hydroxy substitution pattern at ring A, were also prepared. Screening against the chloroquine resistant Plasmodium falciparum W2 strain identified novel aurones with IC50 values in the low micromolar range. The most potent compounds contained a basic moiety, with the ability to accumulate in acidic digestive vacuole of the malaria parasite. However, none of those aurones revealed significant activity against hemozoin formation and falcipain-2, two validated targets expressed during the blood stage of P. falciparum infection and functional in digestive vacuole of the parasite. Overall, this study highlight (i) the usefulness of aurones as platforms for synthetic procedures using palladium catalyzed protocols to rapidly deliver lead compounds for further optimization and (ii) the potential of novel aurone derivatives as promising antimalarial compounds.