Mei-Lin Go

Antimalarial activity of ferrocenyl chalcones.

A series of ferrocenyl chalcones were synthesized and evaluated for in vitro antimalarial activity against a chloroquine-resistant strain of Plasmodium falciparum. The most active compounds were 1-(3-pyridyl)-3-ferrocenyl-2-propen-1-one (6) and 1-ferrocenyl-3-(4-nitrophenyl)-2-propen-1-one (28) with IC(50) of 4.5 and 5.1 microM, respectively. Differences in activity were not readily explained by the size and lipophilicity characteristics of these compounds.

Antiplasmodial Chalcones Inhibit Sorbitol-Induced Hemolysis of Plasmodium falciparum -Infected Erythrocytes

ABSTRACT A series of alkoxylated and hydroxylated chalcones previously reported to have antiplasmodial activities in vitro were investigated for their effects on the new permeation pathways induced by the malaria parasite in the host erythrocyte membrane. Of 21 compounds with good antiplasmodial activities (50% inhibitory concentrations [IC50s], ≤20 μM), 8 members were found to inhibit sorbitol-induced lysis of parasitized erythrocytes to a significant extent (≤40% of control values) at a concentration (10 μM) that was close to their antiplasmodial IC50s. Qualitative structure-activity analysis suggested that activity was governed to a greater extent by a substitution on ring B than on ring A of the chalcone template. Most of the active compounds had methoxy or dimethoxy groups on ring B. Considerable variety was permitted on ring A in terms of the electron-donating or -withdrawing property. Lipophilicity did not appear to be an important determinant for activity. Although they are not exceptionally potent as inhibitors (lowest IC50, 1.9 μM), the chalcones compare favorably with other more potent inhibitors in terms of their selective toxicities against plasmodia and their neutral character.

A Small Molecule Inhibitor of Isoprenylcysteine Carboxymethyltransferase Induces Autophagic Cell Death in PC3 Prostate Cancer Cells

A number of proteins involved in cell growth control, including members of the Ras family of GTPases, are modified at their C terminus by a three-step posttranslational process termed prenylation. The enzyme isoprenylcysteine carboxylmethyl-transferase (Icmt) catalyzes the last step in this process, and genetic and pharmacological suppression of Icmt activity significantly impacts on cell growth and oncogenesis. Screening of a diverse chemical library led to the identification of a specific small molecule inhibitor of Icmt, cysmethynil, that inhibited growth factor signaling and tumorigenesis in an in vitro cancer cell model (Winter-Vann, A. M., Baron, R. A., Wong, W., dela Cruz, J., York, J. D., Gooden, D. M., Bergo, M. O., Young, S. G., Toone, E. J., and Casey, P. J. (2005) Proc. Natl. Acad. Sci. U. S. A. 102, 4336–4341). To further evaluate the mechanisms through which this Icmt inhibitor impacts on cancer cells, we developed both in vitro and in vivo models utilizing PC3 prostate cancer cells. Treatment of these cells with cysmethynil resulted in both an accumulation of cells in the G1 phase and cell death. Treatment of mice harboring PC3 cell-derived xenograft tumors with cysmethynil resulted in markedly reduced tumor size. Analysis of cell death pathways unexpectedly showed minimal impact of cysmethynil treatment on apoptosis; rather, drug treatment significantly enhanced autophagy and autophagic cell death. Cysmethynil-treated cells displayed reduced mammalian target of rapamycin (mTOR) signaling, providing a potential mechanism for the excessive autophagy as well as G1 cell cycle arrest observed. These results identify a novel mechanism for the antitumor activity of Icmt inhibition. Further, the dual effects of cell death and cell cycle arrest by cysmethynil treatment strengthen the rationale for targeting Icmt in cancer chemotherapy.

Functionalized 3-benzylidene-indolin-2-ones: Inducers of NAD(P)H-quinone oxidoreductase 1 (NQO1) with antiproliferative activity

Functionalized benzylidene-indolin-2-ones are widely associated with antiproliferative activity. The scaffold is not normally associated with chemoprevention in spite of the presence of a nitrogen-linked Michael acceptor moiety that may predispose members to induction of NQO1, a widely used biomarker of chemopreventive potential. To investigate this possibility, we have synthesized and evaluated a series of functionalized 3-benzylidene-indolin-2-ones for induction of NQO1 in murine Hepa1c1c7 cells as well as antiproliferative activity against two human cancer cell lines (MCF-7, HCT116). The benzylideneindolinones were found to be good inducers of NQO1 activity, with 85% of test compounds able to increase basal NQO1 activity by more than twofold at concentrations of 10 microM. By contrast, fewer compounds (11%) tested at the same concentration were able to reduce cell viability by more than 50%. Structure activity relationships showed that the nitrogen linked Michael acceptor moiety was an essential requirement for both activities. This common feature notwithstanding, substitution of the 3-benzylidene-indolin-2-one core structure affected NQO1 induction and antiproliferative activities in dissimilar ways, underscoring different structural requirements for these two activities. Nonetheless, promising compounds (10, 42, 45-48) were identified that combine selective induction of NQO1 with potent antiproliferative activity. A potential advantage of such agents would be the ability to provide added protection to normal cells by the up-regulation of NQO1 and other phase II enzymes while simultaneously targeting neoplastic cells.

Functionalized aurones as inducers of NAD(P)H:quinone oxidoreductase 1 that activate AhR/XRE and Nrf2/ARE signaling pathways: synthesis, evaluation and SAR.

The chemopreventive potential of functionalized aurones and related compounds as inducers of NAD(P)H:quinone oxidoreductase 1 (NQO1, EC 1.6.99.2) are described. Several 4,6-dimethoxy and 5-hydroxyaurones induced NQO1 activity of Hepa1c1c7 cells by 2-fold at submicromolar concentrations, making these the most potent inducers to be identified from this class. Mechanistically, induction of NQO1 was mediated by the activation of AhR/XRE and Nrf2/ARE pathways, indicating that aurones may be mixed activators of NQO1 induction or agents capable of exploiting the proposed cross-talk between the AhR and Nrf2 gene batteries. QSAR analysis by partial least squares projection to latent structures (PLS) identified size parameters, in particular those associated with non-polar surface areas, as an important determinant of induction activity. These were largely determined by the substitution on rings A and B. A stereoelectronic role for the exocyclic double bond as reflected in the E(LUMO) term was also identified. The electrophilicity of the double bond or its effect on the conformation of the target compound are possible key features for induction activity.

Modulation of breast cancer resistance protein (BCRP/ABCG2) by non-basic chalcone analogues.

Chalcones are biosynthetic precursors of flavonoids found to possess cytotoxic and chemopreventive activities. In this study, 17 non-basic chalcone analogues were synthesized and evaluated for their ability to modulate the function of either the human wild-type (482R) or mutant (482T) breast cancer resistance protein (BCRP/ABCG2) stably expressed in breast cancer MDA-MB-231 cells. At 5microM, chalcones with 2,4-dimethoxy groups or 2,4-dihydroxyl groups on ring A were found to increase mitoxantrone accumulation to a greater extent than an established BCRP inhibitor, fumitremorgin C. At the same time, these chalcones had negligible effect on calcein accumulation in P-glycoprotein overexpressing MDCKII cells, indicating their potential as selective BCRP inhibitors. Functionally, these compounds were able to increase the sensitivity of BCRP-overexpressing cancer cells to mitoxantrone by 2-5-fold. The effect of chalcone compounds on both wild-type and mutant BCRP ATPase activity was also examined and variable effects were observed. A stimulatory effect was mostly observed with chalcones with 2,4-dimethoxy substitution on ring A which were earmarked as good BCRP inhibitors in the MX accumulation and cytotoxicity assays. These findings underscore the potential of methoxylated and hydroxylated chalcones as selective and potent inhibitors of BCRP whose mode of action may not involve the inhibition of ATPase activity.

Caffeine and nicotinamide enhances the aqueous solubility of the antimalarial agent halofantrine.

The aqueous solubility of the antimalarial agent halofantrine in phosphate buffers pH 5.9 and 7.0 (ionic strength 0.08) is increased by the addition of caffeine and nicotinamide. Solubility is increased to a greater extent in the presence of caffeine (12.5-125 mM) than nicotinamide (125 mM -2.0 M). The greatest increase in solubility was observed at pH 5.9 where the basal solubility of halofantrine rose from 0.91 to 435 microM when 125 mM caffeine was added. Phase solubility studies support the formation of a 1:1 complex between caffeine and halofantrine which is characterised by a K(1:1) constant of 2.75x10(3) M(-1) (pH 5.9). A less stable 1:1 complex is formed at pH 7.0 (K(1:1)=6.37x10(3) M(-1)). Differential scanning calorimetry of solid mixtures of caffeine and halofantrine showed the absence of the endotherms of the two drugs and the appearance of a distinct endotherm (with a smaller enthalpy) characteristic of the complex. An analysis of the 1H-NMR spectra of mixtures of caffeine and halofantrine revealed perturbations in the chemical shifts of the methyl group and proton at positions 4 and 8 of caffeine, and a change in splitting pattern of the H(9) proton of the phenanthrene ring in halofantrine.

Aurones as modulators of ABCG2 and ABCB1: synthesis and structure-activity relationships.

The ability of aurones to modulate the efflux activities of ABCG2 and ABCB1 was investigated by quantifying their effects on the accumulation of pheophorbide A (PhA) in ABCG2‐overexpressing MDA‐MB‐231/R cells and calcein AM in ABCB1‐overexpressing MDCKII/MDR1 cells. Key structural features for interactions at both ABCG2 and ABCB1 are a methoxylated ring A, an intact exocyclic double bond, and the location of the carbonyl bond on ring C. Modifications on rings B and C were less critical and served primarily to moderate activity and selectivity for one or both transporters. These SAR trends were quantified by Free–Wilson analyses and are reflected in a pharmacophore model for PhA accumulation. Several compounds were found to be equipotent with fumitremorgin C (FTC) in promoting PhA accumulation, and they also demonstrated strong affinities for ABCB1. These compounds were disubstituted on ring B with methoxy or a combination of methoxy and hydroxy groups. Taken together, our findings highlight the versatility of the aurone template as a lead scaffold for the design of dual‐targeting ABCG2 and ABCB1 modulators.

Antiprion activity of functionalized 9-aminoacridines related to quinacrine.

A library of functionalized 6-chloro-2-methoxy-(N(9)-substituted)acridin-9-amines structurally related to quinacrine were synthesized and evaluated for antiprion activity on four different cell models persistently infected with scrapie prion strains (ScN2a, N167, Ch2) or a human disease prion strain (F3). Most of the compounds were distinguished by the side chain attached to 9-amino of the acridine ring. These were dialkylaminoalkyl and phenyl with basic groups on the phenyl ring. The most promising compound was 6-chloro-2-methoxy-N-(4-(4-methylpiperazin-1-yl)phenyl)acridin-9-amine (15) which had submicromolar EC(50) values (0.1-0.7microM) on all cell models, was able to clear PrP(Sc) at non-toxic concentrations of 1.2-2.5microM, and was more active than quinacrine in terms of EC(50) values. Other promising compounds were 14 (a regioisomer of 15) and 17 which had a 1-benzylpiperidin-4-yl substituent attached to the 9-amino function. Activity was strongly dependent on the presence of a substituted acridine ring, which in this library comprised 6-chloro-2-methoxy substituents on the acridine ring. The side chains of 14, 15, and 17 have not been previously associated with antiprion activity and are interesting leads for further optimization of antiprion activity.

Structure-activity relationships of some indolo[3,2-c]quinolines with antimalarial activity.

The synthesis, physicochemical characterization and in vitro antimalarial activity of a series of indolo[3,2-c]quinolines (9a-f) are described. There is only a poor correlation between the activity and hydrophobicity. In contrast, 33% of the observed variation in antimalarial activity can be attributed to the size of the side chain attached to position 9 of the indoloquinoline ring. An increase in the size of this dibasic side chain generally results in a reduction in activity, suggesting that it is accommodated in a site/cavity of limited size on the receptor. More significantly, the charge on the distal nitrogen (N3) on the side chain, located 10-11 A from the quinoline N, could account for 75% of the observed variation. Since a large charge on N3 is associated with improved antimalarial activity, it is suggested that N3 is protonated and functions as a H bond donor in the drug-receptor interaction.