Exploring the modulatory influence on the antimalarial activity of amodiaquine using scaffold hybridisation with ferrocene integration.

Amodiaquine (AQ) is a potent antimalarial drug used in combination with artesunate as part of artemisinin-based combination therapies (ACTs) for malarial treatment. Due to the rising emergence of resistant malaria parasites, some of which have been reported for ACT, the usefulness of AQ as an efficacious therapeutic drug is threatened. Employing the organometallic hybridisation approach, which has been shown to restore the antimalarial activity of chloroquine in the form of an organometallic hybrid clinical candidate ferroquine (FQ), the present study utilises this strategy to modulate the biological performance of AQ by incorporating ferrocene. Presently, we have conceptualised ferrocenyl AQ derivatives and have developed facile, practical routes for their synthesis. A tailored library of AQ derivatives was assembled and their antimalarial activity evaluated against chemosensitive (NF54) and multidrug-resistant (K1) strains of the malaria parasite, Plasmodium falciparum. The compounds generally showed enhanced or comparable activities to those of the reference clinical drugs chloroquine and AQ, against both strains, with higher selectivity for the sensitive phenotype, mostly in the double-digit nanomolar IC50 range. Moreover, representative compounds from this series show the potential to block malaria transmission by inhibiting the growth of stage II/III and V gametocytes in vitro. Preliminary mechanistic insights also revealed hemozoin inhibition as a potential mode of action.

Amodiaquine Nonspecifically Binds Double Stranded and Three-Way Junction DNA Structures.

The 4-aminoquinoline class of compounds includes the important antimalarial compounds amodiaquine and chloroquine. Despite their medicinal importance, the mode of action of these compounds is poorly understood. In a previous study we observed these compounds, as well as quinine and mefloquine, tightly bind the DNA cocaine-binding aptamer. Here, we further explore the range of nucleic acid structures bound by these compounds. To gauge a wide range of binding affinities, we used isothermal titration calorimetry to explore high affinity binding (nM to tens of µM) and NMR spectroscopy to assay weak binding biding in the hundreds of micromolar range. We find that amodiaquine tightly binds all double stranded DNA structures explored. Mefloquine binds double stranded DNA duplex molecules tightly and weakly associates with a three-way junction DNA construct. Quinine and chloroquine only weakly bind duplex DNA but do not tightly bind any of the DNA constructs explored. A simulation of the free energy of binding of these ligands to the Dickerson-Drew dodecamer resulted in an excellent agreement between the simulated and experimental free energy. These results provide new insight into the DNA binding of clinically important antimalarial compounds and may play a role in future development of new antimalarials.

Effects of Replacing Oxygenated Functionality with Fluorine on Lipophilicity.

The replacement of oxygenated functionality (hydroxy and alkoxy) with a fluorine atom is a commonly used bioisosteric replacement in medicinal chemistry. In this paper, we use molecular matched-pair analysis to better understand the effects of this replacement on lipophilicity. It seems that the reduced log P of the oxygenated compound is normally dominant in determining the size of this difference. We observe that the presence of additional electron-donating groups on an aromatic ring generally increases the difference in lipophilicity between an oxygenated compound and its fluorinated analogue, while electron-withdrawing groups lead to smaller differences. Ortho-substituted compounds generally display a reduced difference in log P compared to para- and meta-substituted compounds, particularly if an ortho-substituent can form an intramolecular hydrogen bond. Hydrogen-bond acceptors remote to an aromatic ring containing fluorine/oxygen can also reduce the difference in log P between oxygen- and fluorine-substituted compounds.

Assessment of NR4A Ligands That Directly Bind and Modulate the Orphan Nuclear Receptor Nurr1.

Nurr1/NR4A2 is an orphan nuclear receptor transcription factor implicated as a drug target for neurological disorders including Alzheimer's and Parkinson's diseases. Previous studies identified small-molecule NR4A nuclear receptor modulators, but it remains unclear if these ligands affect transcription via direct binding to Nurr1. We assessed 12 ligands reported to affect NR4A activity for Nurr1-dependent and Nurr1-independent transcriptional effects and the ability to bind the Nurr1 ligand-binding domain (LBD). Protein NMR structural footprinting data show that amodiaquine, chloroquine, and cytosporone B bind the Nurr1 LBD; ligands that do not bind include C-DIM12, celastrol, camptothecin, IP7e, isoalantolactone, ethyl 2-[2,3,4-trimethoxy-6-(1-octanoyl)phenyl]acetate (TMPA), and three high-throughput screening hit derivatives. Importantly, ligands that modulate Nurr1 transcription also show Nurr1-independent effects on transcription in a cell type-specific manner, indicating that care should be taken when interpreting the functional response of these ligands in transcriptional assays. These findings should help focus medicinal chemistry efforts that desire to optimize Nurr1-binding ligands.

Beneficial Effect of Chloroquine and Amodiaquine on Type 1 Diabetic Tubulopathy by Attenuating Mitochondrial Nox4 and Endoplasmic Reticulum Stress.

BACKGROUND: Oxidative stress induced by chronic hyperglycemia is recognized as a significant mechanistic contributor to the development of diabetic kidney disease (DKD). Nonphagocytic nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4) is a major source of reactive oxygen species (ROS) in many cell types and in the kidney tissue of diabetic animals. We designed this study to explore the therapeutic potential of chloroquine (CQ) and amodiaquine (AQ) for inhibiting mitochondrial Nox4 and diabetic tubular injury. METHODS: Human renal proximal tubular epithelial cells (hRPTCs) were cultured in high-glucose media (30 mM D-glucose), and diabetes was induced with streptozotocin (STZ, 50 mg/kg i.p. for 5 days) in male C57BL/6J mice. CQ and AQ were administered to the mice via intraperitoneal injection for 14 weeks. RESULTS: CQ and AQ inhibited mitochondrial Nox4 and increased mitochondrial mass in hRPTCs under high-glucose conditions. Reduced mitochondrial ROS production after treatment with the drugs resulted in decreased endoplasmic reticulum (ER) stress, suppressed inflammatory protein expression and reduced cell apoptosis in hRPTCs under high-glucose conditions. Notably, CQ and AQ treatment diminished Nox4 activation and ER stress in the kidneys of STZ-induced diabetic mice. In addition, we observed attenuated inflammatory protein expression and albuminuria in STZ-induced diabetic mice after CQ and AQ treatment. CONCLUSION: We substantiated the protective actions of CQ and AQ in diabetic tubulopathy associated with reduced mitochondrial Nox4 activation and ER stress alleviation. Further studies exploring the roles of mitochondrial Nox4 in the pathogenesis of DKD could suggest new therapeutic targets for patients with DKD.

Development of pharmaceutically scalable inhaled anti-cancer nanotherapy - Repurposing amodiaquine for non-small cell lung cancer (NSCLC).

New drug and dosage form development faces significant challenges, especially in oncology, due to longer development cycle and associated scale-up complexities. Repurposing of existing drugs with potential anti-cancer activity into new therapeutic regimens provides a feasible alternative. In this project, amodiaquine (AQ), an anti-malarial drug, has been explored for its anti-cancer efficacy through formulating inhalable nanoparticulate systems using high-pressure homogenization (HPH) with scale-up feasibility and high reproducibility. A 32 multifactorial design was employed to better understand critical processes (probe homogenization speed while formulating coarse emulsion) and formulation parameters (concentration of cationic polymer in external aqueous phase) so as to ensure product quality with improved anticancer efficacy in non-small cell lung cancer (NSCLC). Optimized AQ loaded nanoparticles (AQ NP) were evaluated for physicochemical properties, stability profile, in-vitro aerosol deposition behavior, cytotoxic potential against NSCLC cells in-vitro and in 3D simulated tumor spheroid model. The highest probe homogenization speed (25,000 rpm) resulted in lower particle size. Incorporation of cationic polymer, polyethylenimine (0.5% w/v) resulted in high drug loading efficiencies at optimal drug quantity of 5 mg. Formulated nanoparticles (liquid state) exhibited an aerodynamic diameter of 4.7 ± 0.1 µm and fine particle fraction of 81.0 ± 9.1%, indicating drug deposition in the respirable airways. Cytotoxicity studies in different NSCLC cell lines revealed significant reduction in IC50 values with AQ-loaded nanoparticles compared to plain drug, along with significant cell migration inhibition (scratch assay) and reduced % colony growth (clonogenic assay) in A549 cells with AQ NP. Moreover, 3D simulated spheroid studies revealed efficacy of nanoparticles in penetration to tumor core, and growth inhibition. AQ's autophagy inhibition ability significantly increased (increased LC3B-II levels) with nanoparticle encapsulation, along with moderate improvement in apoptosis induction (Caspase-3 levels). No impact was observed on HUVEC angiogenesis suggesting alternative anticancer mechanisms. To conclude, amodiaquine can be a promising candidate for repurposing to treat NSCLC while delivering inhalable nanoparticles developed using a scalable HPH process. Despite the involvement of complex parameters, application of DoE has simplified the process of product and process optimization.

Investigation of Some Antiviral N-Heterocycles as COVID 19 Drug: Molecular Docking and DFT Calculations.

The novel coronavirus, COVID-19, caused by SARS-CoV-2, is a global health pandemic that started in December 2019. The effective drug target among coronaviruses is the main protease Mpro, because of its essential role in processing the polyproteins that are translated from the viral RNA. In this study, the bioactivity of some selected heterocyclic drugs named Favipiravir (1), Amodiaquine (2), 2'-Fluoro-2'-deoxycytidine (3), and Ribavirin (4) was evaluated as inhibitors and nucleotide analogues for COVID-19 using computational modeling strategies. The density functional theory (DFT) calculations were performed to estimate the thermal parameters, dipole moment, polarizability, and molecular electrostatic potential of the present drugs; additionally, Mulliken atomic charges of the drugs as well as the chemical reactivity descriptors were investigated. The nominated drugs were docked on SARS-CoV-2 main protease (PDB: 6LU7) to evaluate the binding affinity of these drugs. Besides, the computations data of DFT the docking simulation studies was predicted that the Amodiaquine (2) has the least binding energy (-7.77 Kcal/mol) and might serve as a good inhibitor to SARS-CoV-2 comparable with the approved medicines, hydroxychloroquine, and remdesivir which have binding affinity -6.06 and -4.96 Kcal/mol, respectively. The high binding affinity of 2 was attributed to the presence of three hydrogen bonds along with different hydrophobic interactions between the drug and the critical amino acids residues of the receptor. Finally, the estimated molecular electrostatic potential results by DFT were used to illustrate the molecular docking findings. The DFT calculations showed that drug 2 has the highest of lying HOMO, electrophilicity index, basicity, and dipole moment. All these parameters could share with different extent to significantly affect the binding affinity of these drugs with the active protein sites.

Synthesis of stable isotope-labeled chloroquine and amodiaquine and their metabolites.

Anti-malaria drugs chloroquine and amodiaquine and their metabolites were synthesized to incorporate 13 C and 15 N starting from U-13 C-labeled benzene to give M + 7 isotopomers. Chloroquine and its metabolites were prepared from 7-chloro-1,2,3,4-tetrahydroquinolin-4-one through an aryl substitution with the corresponding amines; and the amodiaquine and its metabolites were prepared from 4,7-dichloroquinoline in a similar fashion.

Selective adsorption and removal of drug contaminants by using an extremely stable Cu(II)-based 3D metal-organic framework.

The adsorption capacity of three representative pharmaceutical drugs and personal care products (PPCPs) viz. diclofenac sodium (DCF), chlorpromazine hydrochloride (CLF) and amodiaquin dihydrochloride (ADQ), were preliminarily studied using a water-stable Cu(II)-based metal organic framework (MOF) [Cu(BTTA)]n·2DMF (1) (H2BTTA = 1,4-bis(triazol-1-yl)terephthalic acid). We also investigated the factors influencing the adsorption such as concentration, pH, contact time, temperature and dosages. The results show that the adsorption capacity of 1 for DCF (650 mg g-1) from aqueous medium, which is higher in comparison to most of the reported MOFs. While the adsorption of CLF and ADQ are only 67 mg g-1 and 72 mg g-1, respectively. The adsorption isotherm and adsorption kinetics indicated that the adsorption of diclofenac sodium by 1 follows Freundlich model with R2 value of 0.9902 and pseudo-first-order kinetics with correlation coefficient 0.9939 and K1 value of 0.0058 min-1, respectively. Investigations indicate that 1 could become a potential material to adsorb DCF from aqueous medium.

Nanomolar binding affinity of quinine-based antimalarial compounds by the cocaine-binding aptamer.

An unusual feature of the cocaine-binding aptamer is that it binds quinine much tighter than the ligand it was selected for, cocaine. Here we expand the repertoire of ligands that this aptamer binds to include the quinine-based antimalarial compounds amodiaquine, mefloquine, chloroquine and primaquine. Using isothermal titration calorimetry (ITC) we show that amodiaquine is bound by the cocaine-binding aptamer with an affinity of (7 ±â€¯4) nM, one of the tightest aptamer-small molecule affinities currently known. Amodiaquine, mefloquine and chloroquine binding are driven by both a favorable entropy and enthalpy of binding, while primaquine, quinine and cocaine binding are enthalpy driven with unfavorable binding entropy. Using nuclear magnetic resonance (NMR) and ITC methods we show that these ligands compete for the same binding sites in the aptamer. Our identification of such a tight binding ligand for this aptamer should prove useful in developing new biosensor techniques and applications using the cocaine-binding aptamer as a model system.

Capillary zone electrophoresis for the determination of amodiaquine and three of its synthetic impurities in pharmaceutical formulations.

A simple and robust CZE method was developed for the separation and quantification of the antimalarial compound amodiaquine as well as three of its synthetic impurities at a concentration equal to or lower than 0.5%. For capillary electrophoresis, a fused-silica capillary, a background electrolyte of 100 mM sodium phosphate buffer at a pH value of 6.2, a voltage of +20 kV, and a detection wavelength of 220 nm were used, allowing the determination of the analytes within 20 min. The method was validated according to the guideline Q2(R1) of the International Council for Harmonization with respect to linearity, precision, accuracy, limit of detection and limit of quantification, and was successfully applied to evaluate the quality of drug samples collected in the Democratic Republic of the Congo. Quantitative analysis results obtained by the CZE method were compared to those obtained with the contemporary HPLC method described in The International Pharmacopoeia.

New phenylaniline derivatives as modulators of amyloid protein precursor metabolism.

The chloroquinoline scaffold is characteristic of anti-malarial drugs such as chloroquine (CQ) or amodiaquine (AQ). These drugs are also described for their potential effectiveness against prion disease, HCV, EBV, Ebola virus, cancer, Parkinson or Alzheimer diseases. Amyloid precursor protein (APP) metabolism is deregulated in Alzheimer's disease. Indeed, CQ modifies amyloid precursor protein (APP) metabolism by precluding the release of amyloid-beta peptides (Aß), which accumulate in the brain of Alzheimer patients to form the so-called amyloid plaques. We showed that AQ and analogs have similar effects although having a higher cytotoxicity. Herein, two new series of compounds were synthesized by replacing 7-chloroquinolin-4-amine moiety of AQ by 2-aminomethylaniline and 2-aminomethylphenyle moieties. Their structure activity relationship was based on their ability to modulate APP metabolism, Aß release, and their cytotoxicity similarly to CQ. Two compounds 15a, 16a showed interesting and potent effect on the redirection of APP metabolism toward a decrease of Aß peptide release (in the same range compared to AQ), and a 3-10-fold increased stability of APP carboxy terminal fragments (CTFα and AICD) without obvious cellular toxicity at 100 µM.

Synthesis of zinc-carboxylate metal-organic frameworks for the removal of emerging drug contaminant (amodiaquine) from aqueous solution.

We herein report the removal of amodiaquine, an emerging drug contaminant from aqueous solution using [Zn2(fum)2(bpy)] and [Zn4O(bdc)3] (fum=fumaric acid; bpy=4,4-bipyridine; bdc=benzene-1,4-dicarboxylate) metal-organic frameworks (MOFs) as adsorbents. The adsorbents were characterized by elemental analysis, Fourier transform infrared (FT-IR) spectroscopy, and powder X-ray diffraction (PXRD). Adsorption process for both adsorbents were found to follow the pseudo-first-order kinetics, and the adsorption equilibrium data fitted best into the Freundlich isotherm with the R2 values of 0.973 and 0.993 obtained for [Zn2(fum)2(bpy)] and [Zn4O(bdc)3] respectively. The maximum adsorption capacities foramodiaquine in this study were found to be 0.478 and 47.62mg/g on the [Zn2(fum)2(bpy)] and [Zn4O(bdc)3] MOFs respectively, and were obtained at pH of 4.3 for both adsorbents. FT-IR spectroscopy analysis of the MOFs after the adsorption process showed the presence of the drug. The results of the study showed that the prepared MOFs could be used for the removal of amodiaquine from wastewater.

Establishment of an antiviral assay system and identification of severe fever with thrombocytopenia syndrome virus inhibitors.

Aims Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease. SFTS is epidemic in Asia, and its fatality rate is around 30% in Japan. The causative virus severe fever with thrombocytopenia syndrome virus (SFTSV) is a phlebovirus of the family Phenuiviridae (the order Bunyavirales). Although effective treatments are required, there are no antiviral agents currently approved for clinical use. Ribavirin and favipiravir were examined for their anti-SFTSV activity and found to be selective inhibitors of SFTSV replication in vitro. However, their activity was not sufficient. Therefore, it is mandatory to identify novel compounds active against SFTSV. To this end, we have established a safe and rapid assay system for screening selective inhibitors of SFTSV. Methods The virus was isolated from SFTS patients treated in Kagoshima University Hospital. Vero cells were infected with SFTSV and incubated in the presence of various concentrations of test compounds. After three days, the cells were examined for their intracellular viral RNA levels by real-time reverse transcription-PCR without extracting viral RNA. The cytotoxicity of test compounds was determined by a tetrazolium dye method. Results Among the test compounds, the antimalarial agent amodiaquine was identified as a selective inhibitor of SFTSV replication. Its 50% effective concentration (EC50) and cytotoxic concentration (CC50) were 19.1 ± 5.1 and >100 µM, respectively. The EC50 value of amodiaquine was comparable to those of ribavirin and favipiravir. Conclusion Amodiaquine is considered to be a promising lead of novel anti-SFTSV agents, and evaluating the anti-SFTSV activity of its derivatives is in progress.

Characterization of stress degradation products of amodiaquine dihydrochloride by liquid chromatography with high-resolution mass spectrometry and prediction of their properties by using ADMET Predictor™.

The degradation behavior of amodiaquine dihydrochloride, an antimalarial drug, was investigated in solution as well as solid states. The drug was subjected to hydrolytic, photolytic, oxidative, and thermal stress conditions, according to International Conference on Harmonization guideline Q1A(R2). It showed extensive hydrolysis in acidic, alkaline, and neutral solutions both with and without light, while it proved to be stable to thermal and oxidative conditions. In total, six degradation products were formed, which were separated on a C8 column, employing a gradient reversed-phase high-performance liquid chromatography method in which acetonitrile and 10 mM ammonium formate (pH 3.0) were used in the mobile phase. To characterize the degradation products, mass fragmentation behavior of the drug was established by direct infusion of solution to quadrupole time-of-flight and multiple-stage mass spectrometry systems. Liquid chromatography with high-resolution mass spectrometry studies were subsequently carried out on the stressed samples using the same gradient high-performance liquid chromatography method employed for the separation of the degradation products. Hydrogen/deuterium exchange studies were additionally conducted to determine the number of labile hydrogen atoms. The degradation pathway of the drug was delineated, justified by mechanistic explanation. Lastly, ADMET Predictor™ software was employed to predict relevant physicochemical and toxicity data for the degradation products.

TiO2 Photocatalysis-DESI-MS Rotating Array Platform for High-Throughput Investigation of Oxidation Reactions.

We present a new high-throughput platform for studying titanium dioxide (TiO2) photocatalytic oxidation reactions by performing reactions on a TiO2-coated surface, followed by direct analysis of oxidation products from the surface by desorption electrospray ionization mass spectrometry (DESI-MS). For this purpose, we coated a round glass wafer with photocatalytically active anatase-phase TiO2 using atomic layer deposition. Approximately 70 aqueous 1 µL samples can be injected onto the rim of the TiO2-coated glass wafer, before the entire wafer is exposed to UV irradiation. After evaporation of water, the oxidation products can be directly analyzed from the sample spots by DESI-MS, using a commercial rotating sample platform. The method was shown to provide fast photocatalytic oxidation reactions and analysis with throughput of about four samples per minute. The feasibility of the method was examined for mimicking phase I metabolism reactions of amodiaquine, buspirone and verapamil. Their main photocatalytic reaction products were mostly similar to the products observed earlier in TiO2 photocatalysis and in in vitro phase I metabolism assays performed using human liver microsomes.

From malaria to cancer: Computational drug repositioning of amodiaquine using PLIP interaction patterns.

Drug repositioning identifies new indications for known drugs. Here we report repositioning of the malaria drug amodiaquine as a potential anti-cancer agent. While most repositioning efforts emerge through serendipity, we have devised a computational approach, which exploits interaction patterns shared between compounds. As a test case, we took the anti-viral drug brivudine (BVDU), which also has anti-cancer activity, and defined ten interaction patterns using our tool PLIP. These patterns characterise BVDU's interaction with its target s. Using PLIP we performed an in silico screen of all structural data currently available and identified the FDA approved malaria drug amodiaquine as a promising repositioning candidate. We validated our prediction by showing that amodiaquine suppresses chemoresistance in a multiple myeloma cancer cell line by inhibiting the chaperone function of the cancer target Hsp27. This work proves that PLIP interaction patterns are viable tools for computational repositioning and can provide search query information from a given drug and its target to identify structurally unrelated candidates, including drugs approved by the FDA, with a known safety and pharmacology profile. This approach has the potential to reduce costs and risks in drug development by predicting novel indications for known drugs and drug candidates.

Deconstructing Quinoline-Class Antimalarials to Identify Fundamental Physicochemical Properties of Beta-Hematin Crystal Growth Inhibitors.

A versatile approach to control crystallization involves the use of modifiers, which are additives that interact with crystal surfaces and alter their growth rates. Elucidating a modifier's binding specificity to anisotropic crystal surfaces is a ubiquitous challenge that is critical to their design. In this study, we select hematin, a byproduct of malaria parasites, as a model system to examine the complementarity of modifiers (i.e., antimalarial drugs) to ß-hematin crystal surfaces. We divide two antimalarials, chloroquine and amodiaquine, into segments consisting of a quinoline base, common to both drugs, and side chains that differentiate their modes of action. Using a combination of scanning probe microscopy, bulk crystallization, and analytical techniques, we show that the base and side chain work synergistically to reduce the rate of hematin crystallization. In contrast to general observations that modifiers retain their function upon segmentation, we show that the constituents do not act as modifiers. A systematic study of quinoline isomers and analogues shows how subtle rearrangement and removal of functional moieties can create effective constituents from previously ineffective modifiers, along with tuning their inhibitory modes of action. These findings highlight the importance of specific functional moieties in drug compounds, leading to an improved understanding of modifier-crystal interactions that could prove to be applicable to the design of new antimalarials.

Antiviral activities of selected antimalarials against dengue virus type 2 and Zika virus.

In a previous study, twelve antimalarial compounds, amodiaquine (AQ) and derivatives, were shown to have potent anti-dengue viral (DENV) activity by using the stable DENV2 Renilla luciferase reporter replicon expressing BHK-21 cells, infectivity (plaque), and the qRT-PCR assays. In this study, we performed molecular modeling on these compounds to determine their stereo-electronic properties required for optimal antiviral activity. Based on the similarity of calculated stereo-electronic profiles, specifically the electrostatic potential profiles of the compounds, and in silico screening of related compounds from literature, we identified three additional compounds, Quinacrine (QC), Mefloquine (MQ), and GSK369796. Analysis of their antiviral activities indicated that all three compounds have high anti-DENV activity in the DENV2 replicon expressing cells with EC50 values of 5.30 ± 1.31 µM (QC), 3.22 ± 0.37 µM (MQ), and 5.06 ± 0.86 µM (GSK369796). The infectivity assays revealed the EC50 values of 7.09 ± 1.67 µM (QC), 4.36 ± 0.31 µM (MQ) and 3.03 ± 0.35 µM (GSK369796). The mode of action of these compounds is through inhibition of autophagy, thereby affecting DENV2 replication. Moreover, these compounds also showed antiviral activity against the rapidly emerging Zika virus (ZIKV) with EC50 values of 2.27 ± 0.14 µM (QC), 3.95 ± 0.21 µM (MQ), and 2.57 ± 0.09 µM (GSK369796).

Influence of LAR and VAR on Para-Aminopyridine Antimalarials Targetting Haematin in Chloroquine-Resistance.

Antimalarial chloroquine (CQ) prevents haematin detoxication when CQ-base concentrates in the acidic digestive vacuole through protonation of its p-aminopyridine (pAP) basic aromatic nitrogen and sidechain diethyl-N. CQ export through the variant vacuolar membrane export channel, PFCRT, causes CQ-resistance in Plasmodium falciparum but 3-methyl CQ (sontochin SC), des-ethyl amodiaquine (DAQ) and bis 4-aminoquinoline piperaquine (PQ) are still active. This is determined by changes in drug accumulation ratios in parasite lipid (LAR) and in vacuolar water (VAR). Higher LAR may facilitate drug binding to and blocking PFCRT and also aid haematin in lipid to bind drug. LAR for CQ is only 8.3; VAR is 143,482. More hydrophobic SC has LAR 143; VAR remains 68,523. Similarly DAQ with a phenol substituent has LAR of 40.8, with VAR 89,366. In PQ, basicity of each pAP is reduced by distal piperazine N, allowing very high LAR of 973,492, retaining VAR of 104,378. In another bis quinoline, dichlorquinazine (DCQ), also active but clinically unsatisfactory, each pAP retains basicity, being insulated by a 2-carbon chain from a proximal nitrogen of the single linking piperazine. While LAR of 15,488 is still high, the lowest estimate of VAR approaches 4.9 million. DCQ may be expected to be very highly lysosomotropic and therefore potentially hepatotoxic. In 11 pAP antimalarials a quadratic relationship between logLAR and logResistance Index (RI) was confirmed, while log (LAR/VAR) vs logRI for 12 was linear. Both might be used to predict the utility of structural modifications.