A New Class of Antifilarial Compounds

Pyrvinium Pamoate: Past, Present, and Future as an Anti-Cancer Drug

Pyrvinium, a lipophilic cation belonging to the cyanine dye family, has been used in the clinic as a safe and effective anthelminthic for over 70 years. Its structure, similar to some polyaminopyrimidines and mitochondrial-targeting peptoids, has been linked with mitochondrial localization and targeting. Over the past two decades, increasing evidence has emerged showing pyrvinium to be a strong anti-cancer molecule in various human cancers in vitro and in vivo. This efficacy against cancers has been attributed to diverse mechanisms of action, with the weight of evidence supporting the inhibition of mitochondrial function, the WNT pathway, and cancer stem cell renewal. Despite the overwhelming evidence demonstrating the efficacy of pyrvinium for the treatment of human cancers, pyrvinium has not yet been repurposed for the treatment of cancers. This review provides an in-depth analysis of the history of pyrvinium as a therapeutic, the rationale and data supporting its use as an anticancer agent, and the challenges associated with repurposing pyrvinium as an anti-cancer agent.

Studies on the metabolism of the filarial worm, Litomosoides carinii

The filarial worm, Litomosoides carinii, has a high rate of aerobic and anaerobic glucose metabolism. Aerobically 30 to 45 per cent of the glucose utilized was converted to lactic acid, 25 to 35 per cent to acetic acid, and 10 to 20 per cent to a polysaccharide. Anaerobically over 80 per cent of the total carbohydrate removed by the filariae was metabolized to lactic acid, the remainder was accounted for by the production of acetic acid. The high rates of aerobic and anaerobic lactic acid production and of aerobic polysaccharide synthesis, as well as the absence of a postanaerobic increase of the oxygen uptake, differentiate the filarial worm, L. carinii, from the known metabolic characteristics of all other helminths and of most other invertebrates. The rate of aerobic lactate and pyruvate utilization by the filariae appears to be much slower than that of glucose. Anaerobically, dismutation of two moles of pyruvate to one mole of lactate, one mole of acetate, and one mole of CO(2), occurred. Aerobically, acetate production from pyruvate exceeded that of lactate. A significant proportion of the pyruvate metabolized aerobically by the filariae was not oxidized to acetate. In the presence of fluoroacetate, aerobic incubation of the filariae in a glucose-containing medium produced a marked decrease in the respiration of the organisms, an accumulation of pyruvate, a decreased formation of acetate, and an increase in aerobic glycolysis. Low concentrations of fluoroacetate (1 x 10(-3)M) inhibited the oxidative metabolism of pyruvate which did not result in the conversion of pyruvate to acetate; higher concentrations of this inhibitor produced also a decreased oxidation of pyruvate to acetate. No evidence has been obtained that fluoroacetate inhibits the respiration of the filariae because of a competitive inhibition of acetate oxidation. Respiration and glycolysis of filariae were markedly decreased by low concentrations of p-chloromercuric benzoate. This inhibition could not be reversed by a large excess of thioglycollate, cystein, glutathione, or H(2)S. Respiration of the filariae was completely inhibited by cyanide (2 x 10(-4)M). The cyanine dyes, a group of compounds possessing high chemotherapeutic activity in filariasis of the cotton rat, inhibited in low concentrations (6.5 x 10(-8)M) the oxygen uptake of the filarial worms. This decrease in oxidative metabolism was associated with a compensatory increase in aerobic glycolysis of the worms and with decreased rates of acetate production and of polysaccharide synthesis. The same metabolic changes were observed in filariae removed from cotton rats to which subcurative doses of a cyanine dye had been administered. Concentrations of cyanine dyes which produced an almost complete inhibition of filarial respiration had no effect on the rate of anaerobic glycolysis of the worms nor on the activity of cytochrome C or of cytochrome oxidase. It is concluded that, in contrast to many other parasitic invertebrates, oxidative metabolism is essential for the survival of the filarial worm, L. carinii, and that the chemotherapeutic activity of the cyanine dyes in filariasis of the cotton rat is due to the inhibitory effect of this group of compounds on the respiratory metabolism of the parasite.

Carbohydrate metabolism of schistosoma mansoni

1. Schistosoma mansoni utilizes in 1 hour an amount of glucose equivalent to one-sixth to one-fifth of its dry weight. Over 80 per cent of the metabolized glucose is converted to lactic acid by this organism. 2. The rates of glucose utilization and of lactic acid production by S. mansoni are the same under aerobic and under anaerobic conditions. 3. A high rate of lactic acid production and the absence of a postanaerobic increase in the oxygen uptake differentiate S. mansoni from most other parasitic helminths whose metabolism has been studied. 4. Arsenite and p-chloromercuric benzoate inhibit in low concentrations the oxygen uptake and the rate of glycolysis of S. mansoni. This inhibition is not prevented or reversed by an excess of glutathione or of thioglycollate. 5. Fluoride inhibits the removal of glucose and the production of lactic acid by S. mansoni to the same degree. 6. Low concentrations of quinacrine (atabrine) do not affect the respiration or the carbohydrate metabolism of the schistosomes. 7. The inhibitory effect of aldehydes on the metabolism of S. mansoni has been measured. Among this group of compounds dl-glyceraldehyde and o-nitrobenzaldehyde are the most effective inhibitors of glycolysis. 8. In a concentration of 2.6 x 10^–6M (1:1,000,000) a cyanine dye inhibits almost completely the respiration of the schistosomes, but has no effect on their rate of glycolysis. The oxygen uptake of the worms is inhibited by fuadin to a greater degree than their rate of glycolysis. 2-methyl-1,4-napthoquinone is a much more effective inhibitor of glycolysis than of the respiration of S. mansoni. The latter compound interacts with plasma albumin and, therefore, its inhibitory action on the metabolism of the schistosomes is greatly reduced in human serum or plasma. 9. Evidence is discussed which indicates that, in contrast to glycolysis, respiratory metabolism is not essential for the survival of S. mansoni.

Chemotherapeutic screening of compounds against Theileria annulata in tissue culture

Theileria annulata has been grown in tissue culture and these cultures have been used for screening compounds for chemotherapeutic activity against this parasite. The method described is simple and convenient for testing many compounds in a short time. Forty compounds, including antimalarials, trypanocides, and antibiotics, have been examined, but none has been found to be active.

Difference spectroscopic characterisation of the cytochrome complement in Acanthocheilonema viteae

(Dithionite-reduced) minus (ferricyanide-oxidised) difference spectra of 600 x g and 12,000 x g subcellular pellet fractions of adult male Acanthocheilonema viteae exhibited alpha-absorption maxima (296 K) attributable to Cyt c555, Cyt b562 and aa3 (600-605 nm). The gamma(Soret) maximum of both fractions was evident at 427 nm, with a shoulder at 432-434 nm. 600 x g and 12,000 x g pellet fractions of adult female and mixed-sex adult A. viteae exhibited similar absorption maxima. (Succinate-reduced)--(ferricyanide-oxidised) difference spectra of the 12,000 x g pellet fraction of mixed-sex adult A. viteae showed absorption maxima at 555 and 562 nm, 600 and 630 nm, suggesting the reduction of Cyt c555, Cyt b562, Cyt aa3 (600 nm) and an unidentified species (630 nm peak) Antimycin A (10(-6) M) induced the disappearance of the maxima at 555, 600 and 630 nm corresponding to Cyt c555, Cyt aa3 and the unidentified species; the maximum at 562 nm prevailed in the presence of antimycin A. These antimycin A induced changes can be cited as classical evidence for the functional involvement of these a, b and c type cytochromes in respiratory electron transport. (Dithionite reduced + CO)--(dithionite reduced) difference spectra suggest that adult A. viteae may have one or more CO-binding-species, one of which appears to be a low-spin-haemoprotein with a b-type or c-type haem, which has essentially an electron carrier function rather than a ligand binding function.

Evidence for the occurrence of respiratory electron transport in adult Brugia pahangi and Dipetalonema viteae

Mixed-sex adult stages of Brugia pahangi and Dipetalonema viteae, in the absence of exogenous substrate, consumed oxygen at rates of 4.18 +/- 0.38 and 2.12 +/- 0.20 ngatoms O2 min-1 mg-1 dry wt. respectively. When calculated on a unit dry weight basis the endogenous O2 consumption rates (E-QO2) of mature adult male macrofilariae of B. pahangi and D. viteae were significantly greater than those of mature females, although the E-QO2 calculated per individual worm was essentially similar irrespective of sex. When assayed as separate unisexual groups, the oxygen uptake of male and female macrofilariae of both species was inhibited by classical inhibitors of respiratory electron transport (RET), and showed classical substrate bypass phenomena in response to succinate and ascorbate, N,N,N',N'-tetramethyl-p-phenylenediamine with respect to the RET inhibitors rotenone (inhibitor of complex I) and antimycin A (inhibitor of complex III). Since male worms elicited similar responses to the classical RET inhibitors as did mixed-sex and/or adult female populations, the possibility that developmental stages contained within the female filariids were contributing in any significant manner to the overall responses observed with the RET inhibitors can be discounted. Such responses as observed with live-intact macrofilariae are normally elicited only by mitochondrial preparations and suggest that the cuticles of both species are permeable to rotenone, succinate, antimycin A, N,N,N',N'-tetramethyl-p-phenylenediamine, azide and cyanide. The uncoupler 2,4-dinitrophenol stimulated the endogenous rate of oxygen consumption (E-QO2) of intact B. pahangi at 33-160 microM, indicating the probable occurrence of RET-coupled oxidative phosphorylation. Higher concentrations of 2,4-dinitrophenol proved inhibitory. Respiratory studies on subcellular fractions substantiated the responses elicited by the intact parasites, suggesting the presence of antimycin A-sensitive and -insensitive RET pathways capable of utilising alpha-glycerophosphate, succinate, and malate as substrates. Both B. pahangi and D. viteae macrofilariae therefore probably possess branched RET-pathways bifurcating on the substrate side of RET-complex III. The rates of substrate oxidation in terms of QO2 mg-1 mitochondrial protein compare well with those observed with other nematode parasites.