4-aminoquinoline Antimalarials Research Articles

Abstract 1890: Chloroquine synergizes with MEK1/2 targeted therapy through dual YAP and lysosomal inhibition in GNAQ/11 mutant uveal melanoma

Abstract GNAQ and GNA11 (GNAQ/11) mutations are found in less than 2% of all melanoma, but more than 80% of uveal melanoma. Mutations in these Gα proteins lead to constitutive activation of multiple oncogenic pathways, including MAPK (RAF->MEK1/2->ERK1/2) and YAP signaling. Metastatic uveal melanoma is refractory to all forms of pharmacologic treatment, such as FDA-approved targeted therapies inhibiting MEK1/2 (i.e. trametinib and binimetinib). We show that combining MEK1/2 inhibitors with 4-aminoquinoline antimalarials, chloroquine or hydroxychloroquine, resulted in synergistic and apoptosis-mediated cytotoxicity in GNAQ/11 mutant uveal melanoma cell lines. Interestingly, in contrast to our previous work in pancreatic and other RAS-driven cancers, the lysosomotropic role of chloroquine was not sufficient to promote cytotoxicity with MEK1/2 inhibitors, as neither lysosome inhibition with Bafilomycin A1 nor autophagy-specific and macropinocytosis-specific inhibition yielded enhanced cell death in combination with MEK1/2 inhibition. We then found that chloroquine prevented nuclear localization of the transcriptional coactivator, YAP, suggesting a novel mechanism of chloroquine. YAP inhibition combined with MEK1/2 inhibition enhanced cell death only in the presence of Bafilomycin A1. Gα-specific inhibition (inhibiting YAP and MAPK) combined with Bafilomycin A1 yielded similar results. This implies that the ability of chloroquine to inhibit both YAP signaling and lysosome function is required for promoting cell death in the presence of MEK1/2 inhibition. For in vivostudies, we utilized a hepatic colonization model using luciferized human metastatic uveal melanoma cell lines, OMM2.5 and OMM1. Daily treatment of trametinib with hydroxychloroquine in combination resulted in delayed tumor growth and increased overall survival compared to either treatment as monotherapy or chemotherapy. These findings were also recapitulated in an immunocompetent mouse model in which immortalized mouse melanocytes (Melan-A) with either a GNAQ or GNA11 activating mutation were implanted into syngeneic C57BL/6 mice. Our findings identify a novel mechanism of chloroquine and suggest a potentially effective strategy combining two FDA-approved drugs for the treatment of metastatic uveal melanoma. Citation Format: Amanda Truong, Michael Scherzer, Conan Kinsey, John Michael Sanchez, Jae Hyuk Yoo, Jackson Richards, Donghan Shin, Phaedra Ghazi, Michael Onken, Kendall Blumer, Shannon Odelberg, Martin McMahon. Chloroquine synergizes with MEK1/2 targeted therapy through dual YAP and lysosomal inhibition in GNAQ/11 mutant uveal melanoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1890.

RETRACTED: Chloroquine or hydroxychloroquine for COVID-19: why might they be hazardous?

The 4-aminoquinoline antimalarials chloroquine and hydroxychloroquine have been promoted and sometimes used in the treatment of COVID-19, alone or combined with azithromycin, based on their immunomodulatory and antiviral properties, despite an absence of methodologically appropriate proof of their efficacy. The global community awaits the results of ongoing, well powered randomised controlled trials showing the effects of chloroquine and hydroxychloroquine on COVID-19 clinical outcomes. These drugs, however, might be associated with cardiac toxicity.

Relapse of porphyria cutanea tarda after treatment with phlebotomy or 4-aminoquinoline antimalarials: a meta-analysis.

Porphyria cutanea tarda (PCT) is the most common human porphyria. It is caused by hepatic deficiency of uroporphyrinogen decarboxylase activity, which is acquired in the presence of multiple susceptibility factors. PCT presents clinically with cutaneous blistering photosensitivity and is readily treatable with either repeated phlebotomy or 4-aminoquinoline antimalarials. To perform a systematic review and meta-analysis to compare the effectiveness of these quite different treatment approaches, especially on relapse rates (RRs) after achieving remission. Published studies that included follow-up for at least 1year after treatment of PCT were included. The primary study outcome was PCT relapse. Pooled data are reported as the RRs per person-year of follow-up with 95% confidence intervals (CIs). Of 375 articles identified as pertaining to PCT treatment, 12 were eligible for analysis. Of these, five used high-dose 4-aminoquinoline regimens (two combined with phlebotomy and three without phlebotomy), five used low-dose 4-aminoquinoline regimens and three used phlebotomy. RRs during the year after treatment were similar for the high- and low-dose 4-aminoquinoline groups (35-36%) and lower in the phlebotomy group (20%). The pooled RRs with their 95% CIs were 8·6 (3·9-13·3) per 100 person-years in the high-dose 4-aminoquinoline group, 17·1 (8·9-25·3) per 100 person-years in the low-dose 4-aminoquinoline group and 5·1 (0·5-10·6) per 100 person-years in the phlebotomy group. Subgroup and sensitivity analyses showed similar results. Clinical or biochemical RRs ranged from 5 to 17 per 100 person-years after remission of PCT. Relapses were somewhat more frequent after remission with 4-aminoquinoline regimens than after remission following phlebotomy. Prospective studies are needed to define better how often relapses occur with these treatments after documenting both clinical and biochemical remission of PCT.

4-Aminoquinoline Antimalarials Containing a Benzylmethylpyridylmethylamine Group Are Active against Drug Resistant Plasmodium falciparum and Exhibit Oral Activity in Mice.

Emergence of drug resistant Plasmodium falciparum including artemisinin-tolerant parasites highlights the need for new antimalarials. We have previously shown that dibemequines, 4-amino-7-chloroquinolines with dibenzylmethylamine (dibemethin) side chains, are efficacious. In this study, analogues in which the terminal phenyl group of the dibemethin was replaced with a 2-pyridyl group and in which the 4-amino-7-chloroquinoline was either maintained or replaced with a 4-aminoquinoline-7-carbonitrile were synthesized in an effort to improve druglikeness. These compounds exhibited significantly improved solubility and decreased lipophilicity and were potent against chloroquine-sensitive (NF54) and -resistant (Dd2 and 7G8) P. falciparum strains with 5/6 having IC50 < 100 nM against the NF54 strain. All inhibited both β-hematin (synthetic hemozoin) formation and hemozoin formation in the parasite. Parasitemia was reduced by over 90% in P. berghei infected mice in 3/6 derivatives following oral dosing at 4 × 30 mg/kg, with microsomal metabolic stability data suggesting that this could be attributed to highly active metabolites.

Modulation of Antimalarial Activity at a Putative Bisquinoline Receptor In Vivo Using Fluorinated Bisquinolines.

Antimalarials can interact with heme covalently, by π⋅⋅⋅π interactions or by hydrogen bonding. Consequently, the prototropy of 4-aminoquinolines and quinoline methanols was investigated by using quantum mechanics. Calculations showed mefloquine protonated preferentially at the piperidine and was impeded at the endocyclic nitrogen because of electronic rather than steric factors. In gas-phase calculations, 7-substituted mono- and bis-4-aminoquinolines were preferentially protonated at the endocyclic quinoline nitrogen. By contrast, compounds with a trifluoromethyl substituent on both the 2- and 8-positions, reversed the order of protonation, which now favored the exocyclic secondary amine nitrogen at the 4-position. Loss of antimalarial efficacy by CF3 groups simultaneously occupying the 2- and 8-positions was recovered if the CF3 group occupied the 7-position. Hence, trifluoromethyl groups buttressing the quinolinyl nitrogen shifted binding of antimalarials to hematin, enabling switching from endocyclic to the exocyclic N. Both theoretical calculations (DFT calculations: B3LYP/BS1) and crystal structure of (±)-trans-N1 ,N2 -bis-(2,8-ditrifluoromethylquinolin-4-yl)cyclohexane-1,2-diamine were used to reveal the preferred mode(s) of interaction with hematin. The order of antimalarial activity in vivo followed the capacity for a redox change of the iron(III) state, which has important implications for the future rational design of 4-aminoquinoline antimalarials.

The Antimalarial Ferroquine: Role of the Metal and Intramolecular Hydrogen Bond in Activity and Resistance

Inhibition of hemozoin biocrystallization is considered the main mechanism of action of 4-aminoquinoline antimalarials including chloroquine (CQ) but cannot fully explain the activity of ferroquine (FQ) which has been related to redox properties and intramolecular hydrogen bonding. Analogues of FQ, methylferroquine (Me-FQ), ruthenoquine (RQ), and methylruthenoquine (Me-RQ), were prepared. Combination of physicochemical and molecular modeling methods showed that FQ and RQ favor intramolecular hydrogen bonding between the 4-aminoquinoline NH group and the terminal amino group in the absence of water, suggesting that this structure may enhance its passage through the membrane. This was further supported by the use of Me-FQ and Me-RQ where the intramolecular hydrogen bond cannot be formed. Docking studies suggest that FQ can interact specifically with the {0,0,1} and {1,0,0} faces of hemozoin, blocking crystal growth. With respect to the structure-activity relationship, the antimalarial activity on 15 different P. falciparum strains showed that the activity of FQ and RQ were correlated with each other but not with CQ, confirming lack of cross resistance. Conversely, Me-FQ and Me-RQ showed significant cross-resistance with CQ. Mutations or copy number of pfcrt, pfmrp, pfmdr1, pfmdr2, or pfnhe-1 did not exhibit significant correlations with the IC(50) of FQ or RQ. We next showed that FQ and Me-FQ were able to generate hydroxyl radicals, whereas RQ and me-RQ did not. Ultrastructural studies revealed that FQ and Me-FQ but not RQ or Me-RQ break down the parasite digestive vacuole membrane, which could be related to the ability of the former to generate hydroxyl radicals.

Synthesis of new 4-aminoquinolines and quinoline–acridine hybrids as antimalarial agents

Despite emergence of resistance to CQ and other 4-aminoquinoline drugs in most of the endemic regions, research findings provide considerable support that there is still significant potential to discover new affordable, safe, and efficacious 4-aminoquinoline antimalarials. In present study, new side chain modified 4-aminoquinoline derivatives and quinoline–acridine hybrids were synthesized and evaluated in vitro against NF 54 strain of Plasmodium falciparum. Among the evaluated compounds, compound 17 (MIC = 0.125 μg/mL) was equipotent to standard drug CQ (MIC = 0.125 μg/mL) and compound 21 (MIC = 0.031 μg/mL) was four times more potent than CQ. Compound 17 showed the curative response to all the treated swiss mice infected with CQ-resistant N-67 strain of Plasmodium yoelii at the doses 50 mg/kg and 25 mg/kg for four days by intraperitoneal route and was found to be orally active at the dose of 100 mg/kg for four days. The promising antimalarial potency of compound 17 highlights the significance of exploring the privileged 4-aminoquinoline class for new antimalarials.

Comparative preclinical drug metabolism and pharmacokinetic evaluation of novel 4-aminoquinoline anti-malarials

The disposition of three 4-aminoquinoline leads, namely isoquine (ISO), des-ethyl isoquine (DEI) and N-tert-butyl isoquine (NTBI), were studied in a range of in vivo and in vitro assays to assist in selecting an appropriate candidate for further development. Analogous to amodiaquine (ADQ), ISO undergoes oxidative N-dealkylation to form DEI in vivo. Blood clearance of DEI was as much as 10-fold lower than that of ISO in animals and after oral administration, metabolite exposure exceeded that of parent by as much as 14-fold. Replacement of the N-ethyl with an N-tert-butyl substituent substantially reduced N-dealkylation as blood clearance of NTBI was ~2 to 3-fold lower than DEI in mouse, rat, dog and monkey. Mean NTBI oral bioavailability was generally higher than the other leads (≥68%). Blood cell association was substantial for NTBI, particularly in dog and monkey, where blood to plasma concentration ratios >4 were observed. Human plasma protein binding was similar for NTBI, DEI, and des-ethyl amodiaquine (DEA). Allometric scaling predicted human blood clearance (CL) for NTBI to be low (~12% liver blood flow). All the 4-aminoquinolines inhibited recombinant human cytochrome P450 2D6 with similar potency; DEI also inhibited 1A2. On balance, NTBI appeared the most promising lead to progress towards full development.

Synthesis and Antimalarial Activity of New Isotebuquine Analogues

Amodiaquine (AQ) and tebuquine are 4-aminoquinoline antimalarials with Mannich base side chain and are highly effective against chloroquine (CQ)-resistant strains of Plasmodium falciparum. Clinical use of AQ has been severely restricted due to hepatoxicity and agranulocytosis side effects associated with its long term use. Lysosomal accumulation and bioactivation to generate reactive quinoneimine metabolite are implicated to be the cause of the observed AQ toxicities. To avoid the quinoneimine formation and thus the toxicity, a series of isotebuquine analogues and their Nomega-oxides with hydroxy group meta to the amino rather than in para position of the aniline moiety were prepared. The new Mannich bases are highly active against both CQ-sensitive (D6) and -resistant (W2 and TM91C235) clones of P. falciparum with IC50 in the range of 0.3-120 ng/mL. New compounds are1000-fold less toxic (IC50 = 0.7-6 microg/mL) to mouse macrophage cell line than to parasite cell lines. Mono-Mannich bases are more active than bis-Mannich bases. Mono-Mannich base 1a (IC50 = 0.3 ng/mL) is 20-fold more active than the corresponding trifluoromethyl analogue 1b. No appreciable difference in either toxicity or efficacy were observed between the new Mannich bases (m-hydroxyaniline derivatives) 1a or 2a and the corresponding p-hydroxyaniline derivatives.

Mapping Antimalarial Pharmacophores as a Useful Tool for the Rapid Discovery of Drugs Effective in Vivo: Design, Construction, Characterization, and Pharmacology of Metaquine

Resistant strains of Plasmodium falciparum and the unavailability of useful antimalarial vaccines reinforce the need to develop new efficacious antimalarials. This study details a pharmacophore model that has been used to identify a potent, soluble, orally bioavailable antimalarial bisquinoline, metaquine (N,N'-bis(7-chloroquinolin-4-yl)benzene-1,3-diamine) (dihydrochloride), which is active against Plasmodium berghei in vivo (oral ID(50) of 25 micromol/kg) and multidrug-resistant Plasmodium falciparum K1 in vitro (0.17 microM). Metaquine shows strong affinity for the putative antimalarial receptor, heme at pH 7.4 in aqueous DMSO. Both crystallographic analyses and quantum mechanical calculations (HF/6-31+G) reveal important regions of protonation and bonding thought to persist at parasitic vacuolar pH concordant with our receptor model. Formation of drug-heme adduct in solution was confirmed using high-resolution positive ion electrospray mass spectrometry. Metaquine showed strong binding with the receptor in a 1:1 ratio (log K = 5.7 +/- 0.1) that was predicted by molecular mechanics calculations. This study illustrates a rational multidisciplinary approach for the development of new 4-aminoquinoline antimalarials, with efficacy superior to chloroquine, based on the use of a pharmacophore model.

Isoquine and related amodiaquine analogues: a new generation of improved 4-aminoquinoline antimalarials.

Amodiaquine (AQ) (2) is a 4-aminoquinoline antimalarial that can cause adverse side effects including agranulocytosis and liver damage. The observed drug toxicity is believed to involve the formation of an electrophilic metabolite, amodiaquine quinoneimine (AQQI), which can bind to cellular macromolecules and initiate hypersensitivity reactions. We proposed that interchange of the 3' hydroxyl and the 4' Mannich side-chain function of amodiaquine would provide a new series of analogues that cannot form toxic quinoneimine metabolites via cytochrome P450-mediated metabolism. By a simple two-step procedure, 10 isomeric amodiaquine analogues were prepared and subsequently examined against the chloroquine resistant K1 and sensitive HB3 strains of Plasmodium falciparum in vitro. Several analogues displayed potent antimalarial activity against both strains. On the basis of the results of in vitro testing, isoquine (ISQ1 (3a)) (IC(50) = 6.01 nM +/- 8.0 versus K1 strain), the direct isomer of amodiaquine, was selected for in vivo antimalarial assessment. The potent in vitro antimalarial activity of isoquine was translated into excellent oral in vivo ED(50) activity of 1.6 and 3.7 mg/kg against the P. yoelii NS strain compared to 7.9 and 7.4 mg/kg for amodiaquine. Subsequent metabolism studies in the rat model demonstrated that isoquine does not undergo in vivo bioactivation, as evidenced by the complete lack of glutathione metabolites in bile. In sharp contrast to amodiaquine, isoquine (and Phase I metabolites) undergoes clearance by Phase II glucuronidation. On the basis of these promising initial studies, isoquine (ISQ1 (3a)) represents a new second generation lead worthy of further investigation as a cost-effective and potentially safer alternative to amodiaquine.

Structure-function relationships in chloroquine and related 4-aminoquinoline antimalarials.

Recent publication have provided strong evidence that activity and cellular uptake of 4-aminoquinoline antimalarials depends on vacuolar haemoglobin degradation and that haematin is the drug target. Studies on haematin-quinoline interactions have provided insight into the structural requirements for these interactions and indications are that 4-aminoquinolines may act by inhibiting haemozoin formation. Structural requirements for this activity have also been reported recently and have led to construction of an empirical structure-function relationship for 4-aminoquinolines.

The fate of ferriprotorphyrin IX in malaria infected erythrocytes in conjunction with the mode of action of antimalarial drugs

The intraerythrocytic malaria parasite digests considerable amounts of its host cell cytosol, which consists mostly of hemoglobin. In order to avert the toxicity of ferriprotorphyrin IX (FP) thus produced, it is generally accepted that FP is polymerized to the non-toxic hemozoin. Investigating the fate of FP in cultured Plasmodium falciparum-infected human red blood cells, revealed a straight correlation between amounts of digested hemoglobin and hemozoin, but the latter contained less FP than produced. The efficacy of FP polymerization is stage-dependent, increasing with parasite maturation. Different strains display dissimilar efficacy in hemozoin production. Unpolymerized FP possibly exits the food vacuole and is degraded by glutathione, thus accounting for the low levels of free FP found in infected cells. 4-aminoquinoline antimalarials demonstrably form complexes with FP and inhibit hemozoin production in vitro. Chloroquine, amodiaquine, quinine and mefloquine were found to inhibit hemozoin production in intact infected cells, but only the first two drugs caused a dose-dependent accumulation of FP in the membrane fraction of infected cells that correlated well with parasite killing, due to the permeabilization of membranes to ions. This differential effect is explained by the ability of chloroquine and amodiaquine to inhibit the degradation of membrane-associated FP by glutathione and the incapacity of quinine and mefloquine to do so. This discrepancy implies that the antimalarial mode of action of chloroquine and amodiaquine is different in its mechanistic details from that of quinine and mefloquine and is compatible with the diametric sensitivity of most strains to chloroquine and mefloquine and the disparate interaction of these drugs with enhancers of their antimalarial action.

4-Aminoquinoline antimalarials enhance UV-B induced c-jun transcriptional activation.

Previous work has documented that the earliest observable response in mammalian cells following ultraviolet (UV) irradiation is the activation of plasma membrane-associated Src tyrosine kinases. These molecules then trigger a signalling cascade that results in activation of the transcription factor AP-1 which subsequently transactivates the early immediate genes including c-jun. This pathway has been postulated to play a protective role against UV damage. As aminoquinoline antimalarials such as chloroquine are known to downregulate several photoinduced cutaneous disorders including LE-specific skin disease, we asked whether chloroquine might be capable of modulating this early limb of the UV light response. A431 cells (a human epidermal keratinocyte cell line) that had been transfected with a c-jun luciferase reporter gene construct were then treated with physiologically relevant concentrations of chloroquine followed by exposure to 0-125 J/m2 of UV-B from a bank of unfiltered FS20 lamps. Chloroquine pretreatment resulted in a dose-dependent increase in luciferase activity in permanently transfected A431 cells (luciferase activity was increased by 45% at 2.5 x 10(-5) M chloroquine and 125 J/m2 of UV-B). Hydroxychloroquine pretreatment also resulted in an increase in luciferase activity. Primaquine, an 8-aminoquinoline, did not influence the UV-B induced c-jun activity. Furthermore, chloroquine did not have a similar impact on HSP-70 gene activity during heat shock. These studies suggest that the beneficial effect of the 4-aminoquinoline antimalarials in various photodermatoses including cutaneous LE might result in part from the capacity of these drugs to enhance the protective early limb of the UV response.

Antimalarial drugs in pregnancy – the North American experience

The use of the 4-aminoquinoline antimalarials in pregnancy is controversial. The current practice of discontinuing these medications because of pregnancy makes little sense as the half-life of these medications is so long. Patients with SLE have increased fetal wastage and one of the factors known to contribute to this fetal wastage is disease activity. It is also known that discontinuing the 4-aminoquinoline antimalarial drugs can precipitate flares of disease in lupus patients. Mothers and their potential offspring are therefore at risk for flares of disease and pregnancy failure if these medications are discontinued because of pregnancy. This review addresses the North American experience of the use of antimalarial drugs in pregnant lupus patients. Unlike most centers in North America, we continue our patients on these medications throughout pregnancy and to date have documented 16 lupus patients who have taken these drugs throughout pregnancy. Our most recent study documents nine pregnancies in eight women. All of these pregnancies resulted in live births (five pre-term deliveries and four full-term deliveries). There were no congenital abnormalities in these infants and follow-up to date has revealed no evidence of ocular or oral deficits in any of these children. One patient experienced a flare of disease when her antimalarial therapy was temporarily discontinued.

Mode of antimalarial effect of methylene blue and some of its analogues on Plasmodium falciparum in culture and their inhibition of P. vinckei petteri and P. yoelii nigeriensis in vivo.

The antimalarial action of methylene blue (MB) was first noted by Paul Ehrlich in the late 19th century. Although it has only sporadically been adopted as a serviceable drug, the resolution of its antimalarial action seems warranted, as it is currently used for the treatment of various methemoglobinemias. In this work we have used MB, and its analogues Azures A (AZA), B (AZB), C (AZC), and thionin (TH), as well as the oxazine Celestine blue (CB) and azine Phenosaphranin (PS). All MB analogues inhibit the growth of various strains of Plasmodium falciparum in culture with IC50s in the 2 x 10(-9)-1 x 10(-7) M range, with the rank order MB approximately AZA > AZB > AZC > TH > PS > CB. The IC50s for a mammalian cell line were in the 3 x 10(-6)-4 x 10(-5) M range, and the rank order was TH approximately AZB > AZA approximately PS > AZC approximately CB > MB. As MB could affect cell growth through the oxidation of NADPH, we tested the action of the various compounds on the hexose-monophosphate shunt activity. Appreciable activation of the shunt was observed at 1 x 10(-5) M in both cell types, thus accounting for inhibition of growth of mammalian cells but not of parasites. All compounds were found to complex with heme in a rank order similar to their antimalarial effect. It is therefore suggested that MB and its congeners act by preventing the polymerization of heme, which is produced during the digestion of host cell cytosol in the parasite food vacuole, into hemozoin. In this respect, these compounds seem to act similarly to the 4-aminoquinoline antimalarials. All compounds effectively suppressed the growth of P. vinckei petteri in vivo with IC50 in the 1.2-5.2 mg/kg range, and MB and AZB suppressed P. yoelii nigeriensis in the 9-11 mg/kg range (i.e. at doses similar to those of chloroquine). The potential toxicity of these compounds may restrict their clinical use, but their impressive antimalarial activities suggest that the phenothiazine structure could serve as a lead compound for further drug development.

Pharmacokinetics and cellular uptake of 4-aminoquinoline antimalarials.

Pharmacokinetics and cellular uptake of 4-aminoquinoline antimalarials.

Use and misuse of 4-aminoquinoline antimalarials in tropical Africa and re-examination of itch reaction to these drugs.

A total of 1059 persons from 14 different locations in Ibadan (the most populous city in tropical Africa) were interviewed to determine whether they had had itch reaction with each of the 12 4-aminoquinoline preparations (one amodiaquine hydrochloride, 11 chloroquine). The various trade and pharmacological names are listed in a table. Respondents were asked for what purpose the listed drugs were used: treatment of an attack of malaria fever; prevention of malaria; and other conditions or illnesses. The respondents were also asked how often each subject had an attack of malaria: monthly, every 3 months, every 6 months, once a year, once every 2-3 years, less often than this, never. Inquiry was made regarding details of the itch reaction since there was particular interest in the pruritus which, judging from previous studies, constitutes the 1 reaction most likely to make 4-aminoquinolines unpopular. Chloroquine sulphate tablets, the 8th most popular preparation, was the 6th on the list of itching incidence. There appeared to be no difference in the incidence of itching after chloroquine sulphate injection. Avloclor tablets, chloroquine phosphate injection tablets and Malarex and Aralen tablets gave a comparatively low incidence of itch reaction--3.4% and 1.4% respectively within the population studied. The incidence of itching after these 4-aminoquinoline preparations may also be estimated in the population sampled by finding the mean percentage of the subjects who itch within those who admitted taking each preparation mentioned in the questionnaire. The corrected percentage incidence gave an estimated mean of 28% compared with a mean incidence of 11% when projected to the whole population sampled. Most of the people (90%) used the 4-aminoquinoline antimalarials to treat an attack of malaria fever; 23% take them for prophylaxis and 7% in the population used the drugs for nonmalarial ailments. The misuse of the drugs for nonmalarial ailments may be related to their potency in treating malaria. In sum, the itch reaction failed to conform to a simple clinical pattern.

The Schizonticidal Activity of Hydroxynaphthoquinones against Plasmodium berghei Infections in Mice

Two decades ago 2-hydroxy-1,4-naphthoquinones were reported to have considerable suppressive and prophylactic activity against avian malaria. A few compounds were selected for clinical testing but were ineffective in human malarias presumably because of oxidation in the human body into inactive products. Recently homologs with longer n-alkyl side-chains than those of earlier compounds in the series have been synthesized and tested against rodent malarias. In four of the five series of 2-hydroxy-1,4-naphthoquinones reported in this study, peak activity occurred when the methylene groups adjacent to the alicyclic or terminal methyl group numbered 8 or 9. The higher members of the series have been demonstrated to possess not only schizonticidal activity at a dose level lower than that required for the older hydroxynaphthoquinones but also curative activity at high doses. The discovery of strains of Plasmodium falciparum refractory to either suppressive or therapeutic doses of 4-aminoquinolines (chloroquine, hydroxychloroquine, amodiaquine) and a-aminoacridines (quinacrine, propoquine) made reappraisal of malaria chemotherapy mandatory largely because of the known limitations of alternate drugs (chlorguanide, pyrimethamine, quinine, cycloguanil, primaquine, etc.). In an effort to discover new antimalarial drugs our attention was drawn to a group of 2-hydroxy-l,4-naphthoquinone compounds synthesized by Fieser and his associates at Harvard University's Chemical Laboratory as a part of the antimalarial survey conducted on a national scale during World War II. Two of these naphthoquinones (M-1916 and M-285) were shown to possess suppressive and curative effects against avian plasmodia (P. lophurae and P. gallinaceum), but they did not prove to have significant effects against P. vivax and P. falciparum infections of humans (Fieser et al., 1948a). These and other related naphthoquinone antimalarials received scant attention at that time because of the marked suppressive and therapeutic efficacy of 4aminoquinoline antimalarials at well tolerated dose levels. After the discovery of rodent plasmodial infections (P. berghei, P. vinckei, P. chabaudi), it became possible to screen drugs on a wide scale against mammalian rather than avian plasmodia. Several of the old and a few of the more recently synthesized hydroxynaphthoquinone antimalarials (Fieser et al., 1967a, Received for publication 12 March 1968. b) were screened and evaluated against bloodinduced rodent infections and were found to be effective following oral administration. The discovery by Yoeli and Most in 1960 of means for facilitating the transfer of P. berghei through the bites of infected anophelines under laboratory conditions made it possible for us to test the efficacy of the new hydroxynaphthoquinone derivatives against sporozoiteinduced as well as blood-induced P. berghei infections in mice. This paper describes the antimalarial screening procedures used and presents the activity of several compounds belonging to each of the various series of 3-substituted alkyl-2-hydroxy-1,4-naphthoquinones against blood-induced P. berghei infections in mice. A few selected derivatives from the various series of hydroxynaphthoquinones were administered to mice infected by injection of sporozoites of P. berghei. The details of these tests are the basis for a separate paper. MATERIALS AND METHODS Rodent plasmodia Four strains of Plasmodium berghei (NYU-2, NK-65, KSP-11, and subspecies yoelii), two other rodent plasmodia (P. vinckei and P. chabaudi), and a strain of P. berghei maintained under chloroquine pressure were used in our studies. In this paper the results of screening against two strains of P. berghei (NYU-2 and NK-65) will be presented. The NYU-2 strain was isolated on 6 January 1959 by Dr. Van Braeckel from infected salivary glands of Anopheles dureni caught in the vicinity of Kasapa (near Elizabethville, Congo). Dr. Yoeli of New York University obtained the strain from Professor Jadin of Belgium on 20 February 1959. Although originally a vigorous gametocyte producer, it gradually lost this ability through numer-

The Determination of 4-Aminoquinoline Antimalarials: Revaluation of the Induced Fluorescence Method, with Specific Application to Hydroxychloroquine Analysis

Various technical aspects of the procedure of Brodie, et al., for the determination of 4-aminoquinoline antimalarials in biological materials have been re-examined. Although it has not been possible to achieve any noteworthy increase in precision over that claimed by the original authors, the method has been materially shortened and simplified, thereby reducing the likelihood of technical errors. Specific procedures for the analysis of hydroxychloroquine are presented; the present widespread use of this compound in antimalarial therapy makes desirable the availability of an exact method for its determination in biological materials.