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Disruption of vitellogenesis and spermatogenesis by triclabendazole (TCBZ) in a TCBZ-resistant isolate of Fasciola hepatica following incubation in vitro with a P-glycoprotein inhibitor

Published online by Cambridge University Press:  24 April 2014

J. SAVAGE ,
M. MEANEY ,
G. P. BRENNAN ,
E. HOEY ,
A. TRUDGETT  and
I. FAIRWEATHER
J. SAVAGE
Affiliation:
Parasite Therapeutics Research Group, School of Biological Sciences, Medical Biology Centre, The Queen's University of Belfast, 97 Lisburn Road, Belfast, BT9 7BL, Northern Ireland
M. MEANEY
Affiliation:
Parasite Therapeutics Research Group, School of Biological Sciences, Medical Biology Centre, The Queen's University of Belfast, 97 Lisburn Road, Belfast, BT9 7BL, Northern Ireland
G. P. BRENNAN
Affiliation:
Parasite Therapeutics Research Group, School of Biological Sciences, Medical Biology Centre, The Queen's University of Belfast, 97 Lisburn Road, Belfast, BT9 7BL, Northern Ireland
E. HOEY
Affiliation:
Parasite Therapeutics Research Group, School of Biological Sciences, Medical Biology Centre, The Queen's University of Belfast, 97 Lisburn Road, Belfast, BT9 7BL, Northern Ireland
A. TRUDGETT
Affiliation:
Parasite Therapeutics Research Group, School of Biological Sciences, Medical Biology Centre, The Queen's University of Belfast, 97 Lisburn Road, Belfast, BT9 7BL, Northern Ireland
I. FAIRWEATHER*
Affiliation:
Parasite Therapeutics Research Group, School of Biological Sciences, Medical Biology Centre, The Queen's University of Belfast, 97 Lisburn Road, Belfast, BT9 7BL, Northern Ireland
*
* Corresponding author: School of Biological Sciences, Medical Biology Centre, The Queen's University of Belfast, 97 Lisburn Road, Belfast, BT9 7BL, Northern Ireland. E-mail: i.fairweather@qub.ac.uk
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Summary

A study has been carried out to investigate whether the action of triclabendazole (TCBZ) against Fasciola hepatica is altered by inhibition of P-glycoprotein (Pgp)-linked drug efflux pumps. The Sligo TCBZ-resistant fluke isolate was used for these experiments and the Pgp inhibitor selected was R(+)-verapamil [R(+)-VPL]. In the first experiment, flukes were initially incubated for 2 h in R(+)-VPL (100 μ m), then incubated in R(+)-VPL+triclabendazole sulphoxide (TCBZ.SO) (50 μg mL−1, or 133·1 μ m) until flukes ceased movement (at 9 h post-treatment). In a second experiment, flukes were incubated in TCBZ.SO alone and removed from the incubation medium following cessation of motility (after 15 h). In the third experiment, flukes were incubated for 24 h in R(+)-VPL on its own. Changes to the testis tubules and vitelline follicles following drug treatment and following Pgp inhibition were assessed by means of light microscope histology and transmission electron microscopy. Incubation of the Sligo isolate in either R(+)-VPL or TCBZ.SO on their own had a limited impact on the morphology of the two tissues. Greater disruption was observed when the drugs were combined, in terms of the block in development of the spermatogenic and vitelline cells and the apoptotic breakdown of the remaining cells. Sperm formation was severely affected and abnormal. Large spaces appeared in the vitelline follicles and synthesis of shell protein was disrupted. The results of this study support the concept of altered drug efflux in TCBZ-resistant flukes and indicate that drug transporters may play a role in the development of drug resistance.

Keywords

Fasciola hepaticaliver fluketriclabendazole resistanceR(+)-verapamilP-glycoproteintransmission electron microscopy
Type
Research Article
Information
Parasitology , Volume 141 , Issue 8 , July 2014 , pp. 1064 - 1079
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Copyright
Copyright © Cambridge University Press 2014 

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References

REFERENCES

Alvarez, L. I., Solana, H. D., Mottier, M. L., Virkel, G. L., Fairweather, I. and Lanusse, C. E. (2005). Altered drug influx/efflux and enhanced metabolic activity in triclabendazole resistant liver flukes. Parasitology 131, 501–510.Google Scholar
Bartley, D. J., McAllister, H., Bartley, Y., Dupuy, J., Menez, C., Alvinerie, M., Jackson, F. and Lespine, A. (2009). P-glycoprotein interfering agents potentiate ivermectin susceptibility in ivermectin sensitive and resistant isolates of Teladorsagia circumcinta and Haemonchus contortus . Parasitology 136, 1081–1088.Google Scholar
Bartley, D. J., Morrison, A. A., Dupuy, J., Bartley, Y., Sutra, J. F., Menez, C., Alvineire, M., Jackson, F., Devin, L. and Lespine, A. (2012). Influence of Pluronic 85 and ketoconazole on disposition and efficacy of ivermectin in sheep infected with a multiple resistant Haemonchus contortus isolate. Veterinary Parasitology 187, 464–472.Google Scholar
Biscardi, M., Teodori, E., Caporale, R., Budriesi, R., Balestri, F., Scappini, B., Gavazzi, S. and Grossi, A. (2006). Multidrug reverting activity toward leukemia cells in a group of new verapamil analogues with low cardiovascular activity. Leukemia Research 30, 1–8.Google Scholar
Choi, S. U., Lee, C. O., Kim, K. H., Choi, E. J., Park, S. H., Shin, H. S., Yoo, S. E., Jung, N. P. and Lee, B. H. (1998). Reversal of multidrug resistance by novel verapamil analogs in cancer cells. Anti-Cancer Drugs 9, 157–165.Google Scholar
Colhoun, L. M., Fairweather, I. and Brennan, G. P. (1998). Observations on the mechanism of eggshell formation in the liver fluke, Fasciola hepatica . Parasitology 116, 555–567.Google Scholar
Devine, C., Brennan, G. P., Lanusse, C. E., Alvarez, L. I., Trudgett, A., Hoey, E. M. and Fairweather, I. (2011). Enhancement of triclabendazole action in vivo against a triclabendazole-resistant isolate of Fasciola hepatica by co-treatment with ketoconazole. Veterinary Parasitology 177, 305–315.CrossRefGoogle ScholarPubMed
Devine, C., Brennan, G. P., Lanusse, C. E., Alvarez, L. I., Trudgett, A., Hoey, E. and Fairweather, I. (2012). Potentiation of triclabendazole action in vivo against a triclabendazole-resistant isolate of Fasciola hepatica following its co-administration with the metabolic inhibitor, ketoconazole. Veterinary Parasitology 184, 37–47.Google Scholar
Echizen, H., Brecht, T., Niedergesass, S., Vogelgesang, B. and Eichelbaum, M. (1985). The effect of dextro-, levo-, and racemic verapamil on atrioventricular conduction in humans. American Heart Journal 109, 210–217.Google Scholar
Fairweather, I. (2011). Liver fluke isolates: a question of provenance. Veterinary Parasitology 176, 1–8.Google Scholar
Fairweather, I., Anderson, H. R. and Threadgold, L. T. (1988). Fasciola hepatica: morphological changes in vitelline cells following treatment in vitro with the deacetylated (amine) metabolite of diamphenethide (DAMD). International Journal for Parasitology 18, 1061–1069.Google Scholar
Fairweather, I., McShane, D. D., Shaw, L., Ellison, S. E., O'Hagan, N. T., York, E. A., Trudgett, A. and Brennan, G. P. (2012). Development of an in vitro egg hatch assay for the diagnosis of triclabendazole resistance in Fasciola hepatica: proof of concept. Veterinary Parasitology 183, 249–259.CrossRefGoogle Scholar
Fuchs, M., Ryan, L., Brennan, G., Trudgett, A., Fairweather, I. and Hoey, E. (2008). Triclabendazole resistance in the liver fluke, Fasciola hepatica: scanning candidate genes for mutations and mRNA-expression levels. In Proceedings of the Tenth European Multicolloquium of Parasitology (EMOP X), Paris, France, abstract no. SY04/0605, p. 49.Google Scholar
Griswold, M. D. and McLean, D. (2006). The sertoli cell. In Knobil and Neill's Physiology of Reproduction (ed. Neill, J. D.), pp. 949–975. Academic Press, London, UK.Google Scholar
Halferty, L., O'Neill, J. F., Brennan, G. P., Keiser, J. and Fairweather, I. (2009). Electron microscopical study to assess the in vitro effects of the synthetic trioxolane OZ78 against the liver fluke, Fasciola hepatica . Parasitology 136, 1325–1337.CrossRefGoogle ScholarPubMed
Hanna, R. E. B., Edgar, H., Moffett, D., McConnell, S., Fairweather, I., Brennan, G. P., Trudgett, A., Hoey, E. M., Cromie, L., Taylor, S. M. and Daniel, R. (2008). Fasciola hepatica: histology of the testis in egg-laying adults of several laboratory-maintained isolates of flukes grown to maturity in cattle and sheep and in flukes from naturally infected hosts. Veterinary Parasitology 157, 222–234.Google Scholar
Hanna, R. E. B., Edgar, H. W. J., McConnell, S., Toner, E., McConville, M., Brennan, G. P., Devine, C., Flanagan, A., Halferty, L., Meaney, M., Shaw, L., Moffett, D., McCoy, M. and Fairweather, I. (2010). Fasciola hepatica: histological changes in the reproductive structures of triclabendazole (TCBZ)-sensitive and TCBZ-resistant flukes after treatment in vivo with TCBZ and the related benzimidazole derivative, compound alpha. Veterinary Parasitology 168, 240–254.Google Scholar
Hanna, R. E. B., Scarcella, S., Solana, H., McConnell, S. and Fairweather, I. (2012 a). Early onset of changes to the reproductive system of Fasciola hepatica following in vivo treatment with triclabendazole. Veterinary Parasitology 184, 341–347.Google Scholar
Hanna, R. E. B., Moffett, D., Brennan, G. P. and Fairweather, I. (2012 b). Fasciola hepatica: a light and electron microscope study of sustentacular tissue and heterophagy in the testis. Veterinary Parasitology 187, 168–182.CrossRefGoogle ScholarPubMed
Hanna, R. E. B., Forster, F. I., Brennan, G. P. and Fairweather, I. (2013). Fasciola hepatica: histological demonstration of apoptosis in the reproductive organs of flukes of triclabendazole-sensitive and triclabendazole-resistant isolates, and in field-derived flukes from triclabendazole-treated hosts, using in situ hybridization to visualize endonuclease strand breaks. Veterinary Parasitology 191, 240–251.Google Scholar
Höllt, V., Kouba, M., Dietel, M. and Vogt, G. (1992). Stereoisomers of calcium antagonists which differ markedly in their potencies as calcium blockers are equally effective in modulating drug transport by P-glycoprotein. Biochemical Pharmacology 43, 2601–2608.Google Scholar
Holmes, S. D. (1983). In vitro studies into the mode of action of anthelmintics on the liver fluke, Fasciola hepatica L. Ph.D. thesis. The Queen's University of Belfast, Belfast, Northern Ireland.Google Scholar
Irwin, S. W. B. and Threadgold, L. T. (1970). Electron-microscope studies on Fasciola hepatica VIII. The development of the vitelline cells. Experimental Parasitology 28, 399–411.Google Scholar
James, C. E., Hudson, A. L. and Davey, M. W. (2009). An update on P-glycoprotein and drug resistance in Schistosoma mansoni . Trends in Parasitology 25, 538–539.CrossRefGoogle ScholarPubMed
Kasinathan, R. S. and Greenberg, R. M. (2012). Pharmacology and potential physiological significance of schistosome multidrug resistance transporters. Experimental Parasitology 132, 2–6.CrossRefGoogle ScholarPubMed
Kasinathan, R. S., Goronga, T., Messerli, S. M., Webb, T. R. and Greenberg, R. M. (2010 a). Modulation of a Schistosoma mansoni multidrug transporter by the antischistosomal drug praziquantel. FASEB Journal 24, 128–135.Google Scholar
Kasinathan, R. S., Morgan, W. M. and Greenberg, R. M. (2010 b). Schistosoma mansoni express higher levels of multidrug resistance-associated protein 1 (SmMRP1) in juvenile worms and in response to praziquantel. Molecular and Biochemical Parasitology 173, 25–31.Google Scholar
Kasinathan, R. S., Morgan, W. M. and Greenberg, R. M. (2011). Genetic knockdown and pharmacological inhibition of parasite multidrug resistance transporters disrupts egg production in Schistosoma mansoni . PLoS Neglected Tropical Diseases 5, e1425.Google Scholar
Kerboeuf, D. and Riou, M. (2011). Efflux pump inhibitors: a progress in parasitic nematode control. Bulletin de l'Académie Vétérinaire de France 164, 257–264.Google Scholar
Kerboeuf, D., Chambrier, P., Le Vern, Y. and Aycardi, J. (1999). Flow cytometry analysis of drug transport mechanisms in Haemonchus contortus susceptible or resistant to anthelmintics. Parasitology Research 85, 118–123.Google Scholar
Kerboeuf, D., Blackhall, W., Kaminsky, R. and Von Samson-Himmelstjerna, G. (2003 a). P-glycoprotein in helminths: function and perspectives for anthelmintic treatment and reversal of resistance. International Journal of Antimicrobial Agents 22, 332–346.Google Scholar
Kerboeuf, D., Guénard, F. and Le Vern, Y. (2003 b). Detection of P-glycoprotein-mediated multidrug resistance against anthelmintics in Haemonchus contortus using anti-human mdr1 monoclonal antibodies. Parasitology Research 91, 79–85.Google Scholar
Kumar, V., Abbas, A. K. and Fausto, N. (2005). Cellular responses to stress and toxic insults: adaptation, injury and death. In Robbins and Cotran Pathologic Basis of Disease, 7th Edn, pp. 26–32. Elsevier Saunders, Philadelphia, PA, USA.Google Scholar
Lespine, A., Alvinerie, M., Vercruysse, J., Prichard, R. K. and Geldhof, P. (2008). ABC transporter modulation: a strategy to enhance the activity of macrocyclic lactone anthelmintics. Trends in Parasitology 24, 293–298.Google Scholar
Lespine, A., Ménez, C., Bourguinat, C. and Prichard, R. K. (2012). P-glycoproteins and other multidrug resistance transporters in the pharmacology of anthelmintics: prospects for reversing transport-dependent anthelmintic resistance. International Journal for Parasitology: Drugs and Drug Resistance 2, 58–75.Google ScholarPubMed
Lifschitz, A., Entrocasso, C., Alvarez, L., Lloberas, M., Ballent, M., Manazza, G., Virkel, G., Borda, B. and Lanusse, C. (2010 a). Interference with P-glycoprotein improves ivermectin activity against adult resistant nematodes in sheep. Veterinary Parasitology 172, 291–298.CrossRefGoogle ScholarPubMed
Lifschitz, A., Suarez, V. H., Sallovitz, J., Cristel, S. L., Imperiale, F., Ahoussou, S., Schiavi, C. and Lanusse, C. (2010 b). Cattle nematodes resistant to macrocyclic lactones: comparative effects of P-glycoprotein modulation on the efficacy and disposition kinetics of ivermectin and moxidectin. Experimental Parasitology 125, 172–178.Google Scholar
McConville, M., Hanna, R. E. B., Brennan, G. P., McCoy, M., Edgar, H. W. J., McConnell, S., Castillo, R., Hernández-Campos, A. and Fairweather, I. (2010). Fasciola hepatica: disruption of spermatogenesis by the fasciolicide compound alpha. Parasitology Research 106, 311–323.Google Scholar
Meaney, M., Savage, J., Brennan, G. P., Hoey, E., Trudgett, A. and Fairweather, I. (2013). Increased susceptibility of a triclabendazole (TCBZ)-resistant isolate of Fasciola hepatica to TCBZ following co-incubation in vitro with the P-glycoprotein inhibitor, R(+)-verapamil. Parasitology 140, 1286–1302.Google Scholar
Melaine, N., Liénard, M.-O., Dorval, I., Le Goascogne, C., Lejeune, H. and Jégou, B. (2002). Multidrug resistance genes and P-glycoprotein in the testis of the rat, mouse, guinea pig, and human. Biology of Reproduction 67, 1699–1707.Google Scholar
Messerli, S. M., Kasinathan, R. S., Morgan, W., Spranger, S. and Greenberg, R. M. (2009). Schistosoma mansoni P-glycoprotein levels increase in response to praziquantel exposure and correlate with reduced praziquantel susceptibility. Molecular and Biochemical Parasitology 167, 54–59.Google Scholar
Molento, M. B. and Prichard, R. K. (1999). Effects of the multidrug-reversing agents verapamil and CL 347,099 on the efficacy of ivermectin or moxidectin against unselected and drug-selected strains of Haemonchus contortus in jirds. Parasitology Research 85, 1007–1011.Google Scholar
Mottier, L., Alvarez, L., Fairweather, I. and Lanusse, C. (2006). Resistance-induced changes in triclabendazole transport in Fasciola hepatica: ivermectin reversal effect. Journal of Parasitology 6, 1355–1360.Google Scholar
Pereira, E., Teodori, E., Dei, S., Gualtieri, F. and Garnier-Suillerot, A. (1995). Reversal of multidrug resistance by verapamil analogues. Biochemical Pharmacology 50, 451–457.Google Scholar
Prichard, R. K. and Roulet, A. (2007). ABC transporters and β-tubulin in macrocyclic lactone resistance: prospects for marker development. Parasitology 134, 1123–1132.Google Scholar
Riou, M., Koch, C., Delaleu, B., Berthon, P. and Kerboeuf, D. (2005). Immunolocalisation of an ABC transporter, P-glycoprotein, in the eggshells and cuticles of free-living and parasitic stages of Haemonchus contortus . Parasitology Research 96, 142–148.Google Scholar
Robillard, K. R., Hoque, M. T. and Bendayan, R. (2012). Expression of ATP-binding cassette membrane transporters in rodent and human Sertoli cells: relevance to the permeability of antiretroviral therapy at the blood-testis barrier. Journal of Pharmacology and Experimental Therapeutics 340, 96–108.Google Scholar
Robinson, M. W., Trudgett, A., Hoey, E. M. and Fairweather, I. (2002). Triclabendazole-resistant Fasciola hepatica: ß-tubulin and response to in vitro treatment with triclabendazole. Parasitology 124, 325–338.Google Scholar
Robinson, M. W., Lawson, J., Trudgett, A., Hoey, E. M. and Fairweather, I. (2004). The comparative metabolism of triclabendazole sulphoxide by triclabendazole-susceptible and triclabendazole-resistant Fasciola hepatica . Parasitology Research 92, 205–210.Google Scholar
Ryan, L., Hoey, E., Trudgett, A., Fairweather, I., Fuchs, M., Robinson, M. W., Chambers, E., Timson, D. J., Ryan, E., Feltwell, T., Ivens, A., Bentley, G. and Johnston, D. (2008). Fasciola hepatica expresses multiple α- and β-tubulin isotypes. Molecular and Biochemical Parasitology 159, 73–78.Google Scholar
Savage, J., Meaney, M., Brennan, G. P., Hoey, E., Trudgett, A. and Fairweather, I. (2013 a). Effect of the P-glycoprotein inhibitor, R(+)-verapamil on the drug susceptibility of a triclabendazole-resistant isolate of Fasciola hepatica . Veterinary Parasitology 195, 72–86.Google Scholar
Savage, J., Meaney, M., Brennan, G. P., Hoey, E., Trudgett, A. and Fairweather, I. (2013 b). Increased action of triclabendazole (TCBZ) in vitro against a TCBZ-resistant isolate of Fasciola hepatica following its co-incubation with the P-glycoprotein inhibitor, R(+)-verapamil. Experimental Parasitology 135, 642–653.Google Scholar
Scarcella, S., Fiel, C., Guzman, M., Alzola, R., Felipe, A., Hanna, R. E. B., Fairweather, I., McConnell, S. and Solana, H. (2011). Reproductive disruption in Fasciola hepatica associated with incomplete efficacy of a new experimental formulation of triclabendazole. Veterinary Parasitology 176, 157–164.CrossRefGoogle ScholarPubMed
Skuce, P. J. and Fairweather, I. (1988). Fasciola hepatica: perturbation of secretory activity in the vitelline cells by the sodium ionophore monensin. Experimental Parasitology 65, 20–30.CrossRefGoogle ScholarPubMed
Stitt, A. W. and Fairweather, I. (1990). Spermatogenesis and the fine structure of the mature spermatozoon of the liver fluke, Fasciola hepatica (Trematoda: Digenea). Parasitology 101, 395–407.Google Scholar
Stitt, A. W. and Fairweather, I. (1991). Fasciola hepatica: the effect of the microfilament inhibitor cytochalasin B on the ultrastructure of the adult fluke. Parasitology Research 77, 675–685.CrossRefGoogle ScholarPubMed
Stitt, A. W. and Fairweather, I. (1992). Spermatogenesis in Fasciola hepatica: an ultrastructural comparison of the effects of the anthelmintic, triclabendazole (“Fasinex”) and the microtubule inhibitor, tubulozole. Invertebrate Reproduction and Development 22, 139–150.Google Scholar
Stitt, A. W. and Fairweather, I. (1996). Fasciola hepatica: disruption of the vitelline cells in vitro by the sulphoxide metabolite of triclabendazole. Parasitology Research 82, 333–339.CrossRefGoogle ScholarPubMed
Stitt, L. E., Tompkins, J. B., Dooley, L. A. and Ardelli, B. F. (2011). ABC transporters influence sensitivity of Brugia malayi to moxidectin and have potential roles in drug resistance. Experimental Parasitology 129, 137–144.CrossRefGoogle ScholarPubMed
Su, L., Mruk, D. D. and Cheng, C. Y. (2011). Drug transporters, the blood-testis barrier and spermatogenesis. Journal of Endocrinology 208, 207–223.Google Scholar
Tiberghien, F. and Loor, F. (1996). Ranking of P-glycoprotein substrates and inhibitors by a calcein-AM fluorometry screening assay. Anti-Cancer Drugs 7, 568–578.Google Scholar
Toffoli, G., Simone, F., Corona, G., Raschack, M., Cappelletto, B., Gigante, M. and Boiocchi, M. (1995). Structure-activity relationship of verapamil analogs and reversal of multidrug resistance. Biochemical Pharmacology 50, 1245–1255.Google Scholar
Tompkins, J. B., Stitt, L. E., Morrissette, A. M. and Ardelli, B. F. (2011). The role of Brugia malayi ATP-binding cassette (ABC) transporters in potentiating drug sensitivity. Parasitology Research 109, 1311–1322.Google Scholar
Toner, E., Brennan, G. P., Wells, K., McGeown, J. G. and Fairweather, I. (2008). Physiological and morphological effects of genistein against the liver fluke, Fasciola hepatica . Parasitology 135, 1189–1203.Google Scholar
Toner, E., Brennan, G. P., Hanna, R. E. B., Edgar, H. W. J. and Fairweather, I. (2011 a). Disruption of egg formation by Fasciola hepatica following treatment in vivo with triclabendazole in the sheep host. Veterinary Parasitology 177, 79–89.Google Scholar
Toner, E., Brennan, G. P., Hanna, R. E. B., Edgar, H. W. J. and Fairweather, I. (2011 b). Fasciola hepatica: time-dependent disruption of spermatogenesis following in vivo treatment with triclabendazole. Parasitology Research 109, 1035–1043.Google Scholar
Varma, M. V. S., Ashkraj, Y., Dey, C. S. and Panchagnula, R. (2003). P-glycoprotein inhibitors and their screening: a perspective from bioavailability enhancement. Pharmacological Research 48, 347–359.Google Scholar
Wells, K. (2008). Ion channels and the control of motility in the liver fluke, Fasciola hepatica. Ph.D. thesis. The Queen's University of Belfast, Belfast, Northern Ireland.Google Scholar
Wilkinson, R., Law, C. J., Hoey, E. M., Fairweather, I., Brennan, G. P. and Trudgett, A. (2012). An amino acid substitution in Fasciola hepatica P-glycoprotein from triclabendazole-resistant and triclabendazole-susceptible populations. Molecular and Biochemical Parasitology 186, 69–72.Google Scholar
Wolstenholme, A. J., Fairweather, I., Prichard, R., Von Samson-Himmelstjerna, G. and Sangster, N. C. (2004). Drug resistance in veterinary helminths. Trends in Parasitology 20, 469–476.Google Scholar
Xu, M., Molento, M., Blackhall, W., Riberio, P., Beech, R. and Prichard, R. (1998). Ivermectin resistance in nematodes may be caused by alteration of P-glycoprotein homolog. Molecular and Biochemical Parasitology 91, 327–335.Google Scholar
Ye, Z. G. and Van Dyke, K. (1988). Reversal of chloroquine resistance in falciparum malaria independent of calcium channels. Biochemical and Biophysical Research Communications 30, 476–481.Google Scholar