Carbazole-based fluorescent probes for G-quadruplex DNA targeting with superior selectivity and low cytotoxicity.

G-quadruplex DNA plays a very important role in clinical diagnosis and fluorescence analysis has attracted extensive attention. A class of carbazole-based fluorescent probes for the detection of G-quadruplex DNA was established in this work. In this system, the installation of an oligo(ethylene glycol) chain on the scaffold will improve the water-solubility and biocompatibility. The presence of styrene-like different side groups could tune the selectivity toward G-quadruplex DNA binding. Results revealed that the substitution pattern and position gave a great influence on the ability for the discrimination of the G-quadruplex from other DNA structures. Especially, probe E1 bound to G-quadruplex DNA with superior selectivity, which exhibiting almost no fluorescence response in the presence of non-G-quadruplex DNA structures. Comprehensive analyses revealed that E1 could bind both ends of the G-quadruplex, resulting in a significant increase of fluorescence emission intensity. Cellular uptake assay suggested that E1 could pass through membrane and enter living cells with low cytotoxicity.

Optimization of antimalarial, and anticancer activities of (E)-methyl 2-(7-chloroquinolin-4-ylthio)-3-(4-hydroxyphenyl) acrylate.

Chemically modified versions of bioactive substances, are particularly useful in overcoming barriers associated with drug formulation, drug delivery and poor pharmacokinetic properties. In this study, a series of fourteen (E)-methyl 2-(7-chloroquinolin-4-ylthio)-3-(4-hydroxyphenyl) acrylate (2-15) were prepared by using a one step synthesis from 1 previously described by us as potential antimalarial and antitumor agent. Molecules were evaluated as inhibitors of ß-hematin formation, where most of them showed a significant inhibition value (% > 70). The best inhibitors were tested in vivo as potential antimalarials in mice infected with P. berghei ANKA, chloroquine susceptible strain. Three of them (5, 6, and 15) displayed antimalarial activity comparable to that of chloroquine. Also, molecules were evaluated for their cytotoxic activity against two human cancer cell lines (Jurkat E6.1 and HL60) and primary culture of human lymphocytes. Most of the synthesized compounds, except for analogs 2-6, 8, and 10-12, displayed cytotoxicity against cancer cell lines without affecting normal cells. The potency of the compounds was 15 ≫ 1, and 14 > 7, 9, and 13. Flow cytometry analysis demonstrated an increase in apoptotic cell death after 24 h. The compounds may affect tumor cell autophagy and consequently increase cell apoptosis.

Hemoglobin pretreatment endows rat cortical astrocytes resistance to hemin-induced toxicity via Nrf2/HO-1 pathway.

Oxidative stress mediated secondary injury contributes to neurological deterioration after intracerebral hemorrhage (ICH). Astrocytes, the most dominant cells in the central nervous system (CNS), play key roles in maintaining redox homeostasis by providing oxidative stress defense. Hemoglobin (Hb), the primary component released by hemolysis, is an effective activator of astrocytes. Hemin, the product of Hb degradation, is highly toxic due to the induction of reactive oxygen species (ROS). We speculate that Hb-activated astrocytes are resistant to hemin-induced toxicity. To verify our speculation, Hb-pretreated astrocytes were exposed to hemin, intracellular ROS accumulation and cell apoptosis were evaluated. Heme oxygenase 1 (HO-1) and nuclear transcription factor-erythroid 2 related factor (Nrf2) expression were observed to explore the potential mechanism. The results demonstrated that Hb induced upregulation and nuclear translocation of Nrf2 in astrocytes, resulted in HO-1 upregulation, which contributed to reduced ROS accumulation and apoptosis rate. Knocking down Nrf2 expression by siRNA suppressed Hb-induced upregulation of HO-1 expression and increased the susceptibility of Hb-pretreated astrocytes to hemin-induced toxicity. Taken together, Hb-activated astrocytes acquired resistance to hemin-induced toxicity via Nrf2/HO-1 pathway. This phenomenon can be considered as the adaptive self-defense in the pathological process of ICH. Hb pre-warned astrocytes and enhanced their capability of handling the coming hemin "flood". Nrf2/HO-1 may be employed as a target for neuroprotection after ICH.

Design, synthesis and antiplasmodial activity of novel imidazole derivatives based on 7-chloro-4-aminoquinoline.

A series of short chain 4-aminoquinoline-imidazole derivatives have been synthesized in one pot two step multicomponent reaction using van leusen standard protocol. The diethylamine function of chloroquine is replaced by substituted imidazole derivatives containing tertiary terminal nitrogen. All the synthesized compounds were screened against the chloroquine sensitive (3D7) and chloroquine resistant (K1) strains of Plasmodium falciparum. Some of the compounds (6, 8, 9 and 17) in the series exhibited comparable activity to CQ against K1 strain of P. falciparum. All the compounds displayed resistance factor between 0.09 and 4.57 as against 51 for CQ. Further, these analogues were found to form a strong complex with hematin and inhibit the ß-hematin formation, therefore these compounds act via heme polymerization target.

Quantitative proteomics reveals that miR-222 inhibits erythroid differentiation by targeting BLVRA and CRKL.

miR-222 plays an important role in erythroid differentiation, but the potential targets of miR-222 in the regulation of erythroid differentiation remain to be determined. The target genes of miR-222 were identified by proteomics combined with bioinformatics analysis in this study. Thirteen proteins were upregulated, and 13 were downregulated in K562 cells following transfection with miR-222 inhibitor for 24 and 48 hours. Among these proteins, BLVRA and CRKL were upregulated after transfection of miR-222 inhibitor in K562 cells and human CD34+ HPCs. Moreover, miR-222 mimics reduced and miR-222 inhibitor enhanced the mRNA and protein levels of both BLVRA and CRKL. Luciferase assay showed that miR-222 directly targeted 3'-UTR of BLVRA and CRKL. In addition, overexpression of either BLVRA or CRKL or both increased the erythroid differentiation of K562 cells, while silencing of either BLVRA or CRKL or both by siRNA significantly attenuated hemin-induced erythroid differentiation of K562 cells. Our results indicated that BLVRA and CRKL are targets of miR-222.

Mechanisms of hematin crystallization and inhibition by the antimalarial drug chloroquine.

Hematin crystallization is the primary mechanism of heme detoxification in malaria parasites and the target of the quinoline class of antimalarials. Despite numerous studies of malaria pathophysiology, fundamental questions regarding hematin growth and inhibition remain. Among them are the identity of the crystallization medium in vivo, aqueous or organic; the mechanism of crystallization, classical or nonclassical; and whether quinoline antimalarials inhibit crystallization by sequestering hematin in the solution, or by blocking surface sites crucial for growth. Here we use time-resolved in situ atomic force microscopy (AFM) and show that the lipid subphase in the parasite may be a preferred growth medium. We provide, to our knowledge, the first evidence of the molecular mechanisms of hematin crystallization and inhibition by chloroquine, a common quinoline antimalarial drug. AFM observations demonstrate that crystallization strictly follows a classical mechanism wherein new crystal layers are generated by 2D nucleation and grow by the attachment of solute molecules. We identify four classes of surface sites available for binding of potential drugs and propose respective mechanisms of drug action. Further studies reveal that chloroquine inhibits hematin crystallization by binding to molecularly flat {100} surfaces. A 2-µM concentration of chloroquine fully arrests layer generation and step advancement, which is ∼10(4)× less than hematin's physiological concentration. Our results suggest that adsorption at specific growth sites may be a general mode of hemozoin growth inhibition for the quinoline antimalarials. Because the atomic structures of the identified sites are known, this insight could advance the future design and/or optimization of new antimalarials.

Synthesis and Evaluation of Chirally Defined Side Chain Variants of 7-Chloro-4-Aminoquinoline To Overcome Drug Resistance in Malaria Chemotherapy.

A novel 4-aminoquinoline derivative [(S)-7-chloro-N-(4-methyl-1-(4-methylpiperazin-1-yl)pentan-2-yl)-quinolin-4-amine triphosphate] exhibiting curative activity against chloroquine-resistant malaria parasites has been identified for preclinical development as a blood schizonticidal agent. The lead molecule selected after detailed structure-activity relationship (SAR) studies has good solid-state properties and promising activity against in vitro and in vivo experimental malaria models. The in vitro absorption, distribution, metabolism, and excretion (ADME) parameters indicate a favorable drug-like profile.

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.

Phenanthrolines protect astrocytes from hemin without chelating iron.

Hemin, the degradation product of hemoglobin, contributes to the neurodegeneration that occurs in the weeks following a hemorrhagic stroke. The breakdown of hemin in cells releases redox-active iron that can facilitate the production of toxic hydroxyl radicals. The present study used 3-week old primary cultures of mouse astrocytes to compare the toxicity of 33 µM hemin in the presence of the iron chelator 1,10-phenanthroline or its non-chelating analogue, 4,7-phenanthroline. This concentration of hemin killed approximately 75 % of astrocytes within 24 h. Both isoforms of phenanthroline significantly decreased the toxicity of hemin, with the non-chelating analogue providing complete protection at concentrations of 33 µM and above. The decrease in toxicity was associated with less cellular accumulation of hemin. Approximately 90 % of the hemin accumulated was not degraded, irrespective of treatment condition. These observations indicate that chelatable iron is not the cause of hemin toxicity. Cell-free experiments demonstrated that hemin can inactivate a molar excess of hydrogen peroxide (H2O2), and that the rate of inactivation is halved in the presence of either isoform of phenanthroline. We conclude that phenanthrolines may protect astrocytes by limiting hemin uptake and by impairing the capacity of intact hemin to interact with endogenous H2O2.

Synthesis, ß-haematin inhibition, and in vitro antimalarial testing of isocryptolepine analogues: SAR study of indolo[3,2-c]quinolines with various substituents at C2, C6, and N11.

A series of indolo[3,2-c]quinolines were synthesized by modifying the side chains of the ω-aminoalkylamines at the C6 position and introducing substituents at the C2 position, such as F, Cl, Br, Me, MeO and NO2, and a methyl group at the N11 position for an SAR study. The in vitro antiplasmodial activities of the derivative agents against two different strains (CQS: NF54 and CQR: K1) and the cytotoxic activity against normal L6 cells were evaluated. The test results showed that compounds 6k and 6l containing the branched methyl groups of 3-aminopropylamino at C6 with a Cl atom at C2 exhibited a very low cytotoxicity with IC50 values above 4000 nM, high antimalarial activities with IC50 values of about 11 nM for CQS (NF54), IC50 values of about 17 nM for CQR (K1), and RI resistance indices of 1.6. Furthermore, the compounds were tested for ß-haematic inhibition, and QSAR revealed an interesting linear correlation between the biological activity of CQS (NF54) and three contributing factors, namely solubility, hydrophilic surface area, and ß-haematin inhibition for this series. In vivo testing of 6l showed a reduction in parasitaemia on day 4 with an activity of 38%.

Hemin therapy suppresses inflammation and retroperitoneal adipocyte hypertrophy to improve glucose metabolism in obese rats co-morbid with insulin-resistant type-2 diabetes.

AIM: Visceral adiposity and impaired glucose metabolism are common patho-physiological features in patients co-morbid with obesity and type-2 diabetes. We investigated the effects of the heme-oxygenase (HO) inducer hemin and the HO blocker stannous-mesoporphyrin (SnMP) on glucose metabolism, adipocyte hypertrophy and pro-inflammatory cytokines/mediators in Zucker diabetic fatty (ZDF) rats, a model characterized by obesity and type-2 diabetes. METHODS: Histological, morphological/morphometrical, Western immunoblotting, enzyme immunoassay, ELISA and spectrophotometric analysis were used. RESULTS: Treatment with hemin enhanced HO-1, HO activity and cGMP, but suppressed retroperitoneal adiposity and abated the elevated levels of macrophage-chemoattractant protein-1 (MCP-1), ICAM-1, tumour necrosis factor-alpha (TNF-α), interleukin 6 (IL-6), IL-1ß, NF-κB, c-Jun-NH2-terminal-kinase (JNK) and activating-protein (AP-1), with parallel reduction of adipocyte hypertrophy. Correspondingly, important proteins of lipid metabolism and insulin-signalling such as lipoprotein lipase (LPL), insulin-receptor substrate-1 (IRS-1), GLUT4, PKB/Akt, adiponectin, the insulin-sensitizing and anti-inflammatory protein and adenosine-monophosphate-activated protein kinase (AMPK) were significantly enhanced in hemin-treated ZDF rats. CONCLUSION: Elevated retroperitoneal adiposity and the high levels of MCP-1, ICAM-1, TNF-α, IL-6, IL-1ß, NF-κB, JNK and AP-1 in untreated ZDF are patho-physiological factors that exacerbate inflammatory insults, aggravate adipocyte hypertrophy, with corresponding reduction of adiponectin and deregulation of insulin-signalling and lipid metabolism. Therefore, the suppression of MCP-1, ICAM-1, TNF-α, IL-6, IL-1ß, NF-κB, JNK, AP-1 and adipocyte hypertrophy, with the associated enhancement of LPL, adiponectin, AMPK, IRS-1, GLUT4, PKB/Akt and cGMP in hemin-treated ZDF are among the multifaceted mechanisms by which the HO system combats inflammation to potentiate insulin signalling and improve glucose and lipid metabolism. Thus, HO inducers may be explored in the search of novel remedies against the co-morbidities of obesity, dysfunctional lipid metabolism and impaired glucose metabolism.

Synthesis and biological evaluation of 1,4-naphthoquinones and quinoline-5,8-diones as antimalarial and schistosomicidal agents.

Improving the solubility of polysubstituted 1,4-naphthoquinone derivatives was achieved by introducing nitrogen in two different positions of the naphthoquinone core, at C-5 and at C-8 of menadione through a two-step, straightforward synthesis based on the regioselective hetero-Diels-Alder reaction. The antimalarial and the antischistosomal activities of these polysubstituted aza-1,4-naphthoquinone derivatives were evaluated and led to the selection of distinct compounds for antimalarial versus antischistosomal action. The Ag(II)-assisted oxidative radical decarboxylation of the phenyl acetic acids using AgNO(3) and ammonium peroxodisulfate was modified to generate the 3-picolinyl-menadione with improved pharmacokinetic parameters, high antimalarial effects and capacity to inhibit the formation of ß-hematin.

Thrombin and hemin as central factors in the mechanisms of intracerebral hemorrhage-induced secondary brain injury and as potential targets for intervention.

Intracerebral hemorrhage (ICH) is a subtype of stoke that may cause significant morbidity and mortality. Brain injury due to ICH initially occurs within the first few hours as a result of mass effect due to hematoma formation. However, there is increasing interest in the mechanisms of secondary brain injury as many patients continue to deteriorate clinically despite no signs of rehemorrhage or hematoma expansion. This continued insult after primary hemorrhage is believed to be mediated by the cytotoxic, excitotoxic, oxidative, and inflammatory effects of intraparenchymal blood. The main factors responsible for this injury are thrombin and erythrocyte contents such as hemoglobin. Therapies including thrombin inhibitors, N-methyl-D-aspartate antagonists, chelators to bind free iron, and antiinflammatory drugs are currently under investigation for reducing this secondary brain injury. This review will discuss the molecular mechanisms of brain injury as a result of intraparenchymal blood, potential targets for therapeutic intervention, and treatment strategies currently in development.

Synthesis and biological evaluation of benzimidazole-5-carbohydrazide derivatives as antimalarial, cytotoxic and antitubercular agents.

A series of N'-substituted-2-(5-nitrofuran or 5-nitrothiophen-2-yl)-3H-benzo[d]imidazole-5-carbohydrazide derivatives were synthesized and investigated for their abilities to inhibit ß-hematin formation, hemoglobin hydrolysis and in vivo for their antimalarial efficacy in rodent Plasmodium berghei. Selected analogues were screened for their antitubercular activity against sensitive MTB H(37)Rv and multidrug-resistant MDR-MTB strains, and cytotoxic activity against a panel of human tumor cell lines and two nontumourogenic cell lines. Compounds 3a, 5a, f, 6g were the most promising as inhibitors of ß-hematin formation, however, their effect as inhibitors of hemoglobin hydrolysis were marginal. The most active compounds to emerge from the in vitro and in vivo murine studies were 3a and 6i, suggesting an antimalarial activity via inhibition of ß-hematin formation and are as efficient as chloroquine. The cytotoxic and antitubercular activities of the present compounds were not comparable with those of the standard drugs employed. But, however, compound 5b showed better antitubercular activity compared to rifampin against multidrug-resistant MDR-MTB strains. Compounds 3a, 6i and 5b showed a good safety index.

Pervasive Genomic Damage in Experimental Intracerebral Hemorrhage: Therapeutic Potential of a Mechanistic-Based Carbon Nanoparticle.

Therapy for intracerebral hemorrhage (ICH) remains elusive, in part dependent on the severity of the hemorrhage itself as well as multiple deleterious effects of blood and its breakdown products such as hemin and free iron. While oxidative injury and genomic damage have been seen following ICH, the details of this injury and implications remain unclear. Here, we discovered that, while free iron produced mostly reactive oxygen species (ROS)-related single-strand DNA breaks, hemin unexpectedly induced rapid and persistent nuclear and mitochondrial double-strand breaks (DSBs) in neuronal and endothelial cell genomes and in mouse brains following experimental ICH comparable to that seen with γ radiation and DNA-complexing chemotherapies. Potentially as a result of persistent DSBs and the DNA damage response, hemin also resulted in senescence phenotype in cultured neurons and endothelial cells. Subsequent resistance to ferroptosis reported in other senescent cell types was also observed here in neurons. While antioxidant therapy prevented senescence, cells became sensitized to ferroptosis. To address both senescence and resistance to ferroptosis, we synthesized a modified, catalytic, and rapidly internalized carbon nanomaterial, poly(ethylene glycol)-conjugated hydrophilic carbon clusters (PEG-HCC) by covalently bonding the iron chelator, deferoxamine (DEF). This multifunctional nanoparticle, DEF-HCC-PEG, protected cells from both senescence and ferroptosis and restored nuclear and mitochondrial genome integrity in vitro and in vivo. We thus describe a potential molecular mechanism of hemin/iron-induced toxicity in ICH that involves a rapid induction of DSBs, senescence, and the consequent resistance to ferroptosis and provide a mechanistic-based combinatorial therapeutic strategy.

Ferroquine, an ingenious antimalarial drug: thoughts on the mechanism of action.

Ferroquine (FQ or SR97193) is a novel antimalarial drug candidate, currently in development at Sanofi-Aventis. In contrast to conventional drugs, FQ is the first organometallic drug: a ferrocenyl group covalently flanked by a 4-aminoquinoline and a basic alkylamine. FQ is able to overcome the CQ resistance problem, an important limit to the control of Plasmodium falciparum, the principal causative agent of malaria. After fifteen years of effort, it is now possible to propose a multifactorial mechanism of action of FQ by its capacity to target lipids, to inhibit the formation of hemozoin and to generate reactive oxygen species.

Pyrazole-pyrazoline as promising novel antimalarial agents: A mechanistic study.

A series of pyrazole-pyrazoline substituted with benzenesulfonamide were synthesized and evaluated for their antimalarial activity in vitro and in vivo. The compounds were active against both chloroquine (CQ) sensitive (3D7) and CQ resistant (RKL-9) strains of Plasmodium falciparum. Seven compounds (7e, 7i, 7j, 7l, 7m, 7o and 7p) exhibiting EC50 less than 2 µM. A mechanistic study of compound 7o revealed that these compound act through the inhibition of ß-hematin. The study indicated that these compounds can serve as lead compounds for further development of potent antimalarial drugs.

Effect of hemin, baicalein and heme oxygenase-1 (HO-1) enzyme activity inhibitors on Cd-induced accumulation of HO-1, HSPs and aggresome-like structures in Xenopus kidney epithelial cells.

Cadmium is a highly toxic environmental pollutant that can cause many adverse effects including cancer, neurological disease and kidney damage. Aquatic amphibians are particularly susceptible to this toxicant as it was shown to cause developmental abnormalities and genotoxic effects. In mammalian cells, the accumulation of heme oxygenase-1 (HO-1), which catalyzes the breakdown of heme into CO, free iron and biliverdin, was reported to protect cells against potentially lethal concentrations of CdCl2. In the present study, CdCl2 treatment of A6 kidney epithelial cells, derived from the frog, Xenopus laevis, induced the accumulation of HO-1, heat shock protein 70 (HSP70) and HSP30 as well as an increase in the production of aggregated protein and aggresome-like structures. Treatment of cells with inhibitors of HO-1 enzyme activity, tin protoporphyrin (SnPP) and zinc protoporphyrin (ZnPP), enhanced CdCl2-induced actin cytoskeletal disorganization and the accumulation of HO-1, HSP70, aggregated protein and aggresome-like structures. Treatment of cells with hemin and baicalein, which were previously shown to provide cytoprotection against various stresses, induced HO-1 accumulation in a concentration-dependent manner. Also, treatment of cells with hemin and baicalein suppressed CdCl2-induced actin dysregulation and the accumulation of aggregated protein and aggresome-like structures. This cytoprotective effect was inhibited by SnPP. These results suggest that HO-1-mediated protection against CdCl2 toxicity includes the maintenance of actin cytoskeletal and microtubular structure and the suppression of aggregated protein and aggresome-like structures.

Reinvestigating Old Pharmacophores: Are 4-Aminoquinolines and Tetraoxanes Potential Two-Stage Antimalarials?

The syntheses and antiplasmodial activities of various substituted aminoquinolines coupled to an adamantane carrier are described. The compounds exhibited pronounced in vitro and in vivo activity against Plasmodium berghei in the Thompson test. Tethering a fluorine atom to the aminoquinoline C(3) position afforded fluoroaminoquinolines that act as intrahepatocytic parasite inhibitors, with compound 25 having an IC50 = 0.31 µM and reducing the liver load in mice by up to 92% at 80 mg/kg dose. Screening our peroxides as inhibitors of liver stage infection revealed that the tetraoxane pharmacophore itself is also an excellent liver stage P. berghei inhibitor (78: IC50 = 0.33 µM). Up to 91% reduction of the parasite liver load in mice was achieved at 100 mg/kg. Examination of tetraoxane 78 against the transgenic 3D7 strain expressing luciferase under a gametocyte-specific promoter revealed its activity against stage IV-V Plasmodium falciparum gametocytes (IC50 = 1.16 ± 0.37 µM). To the best of our knowledge, compounds 25 and 78 are the first examples of either an 4-aminoquinoline or a tetraoxane liver stage inhibitors.

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.