title: Plasmodial surface anion channel-independent phloridzin resistance in Plasmodium falciparum.
abstract: The plasmodial surface anion channel (PSAC) is an unusual ion channel induced on the human red blood cell membrane after infection with the malaria parasite, Plasmodium falciparum. Because PSAC is permeant to small metabolic precursors essential for parasite growth and is present on red blood cells infected with geographically divergent parasite isolates, it may be an ideal target for future antimalarial development. Here, we used chemically induced mutagenesis and known PSAC antagonists that inhibit in vitro parasite growth to examine whether resistance mutations in PSAC can be readily induced. Stable mutants resistant to phloridzin were generated and selected within 3 weeks after treatment with 1-methyl-3-nitro-1-nitrosoguanidine. These mutants were evaluated with osmotic lysis and electrophysiological transport assays, which indicate that PSAC inhibition by phloridzin is complex with at least two different modes of inhibition. Mutants resistant to the growth inhibitory effects of phloridzin expressed PSAC activity indistinguishable from that on sensitive parasites, indicating selection of resistance via mutations in one or more other parasite targets. Failure to induce mutations in PSAC activity is consistent with a highly constrained channel protein less susceptible to resistance mutations; whether this protein is parasite- or host-encoded remains to be determined.
authors.affiliation: Laboratory of Malaria and Vector Research, NIAID, National Institutes of Health, Bethesda, Maryland 20892, USA. sdesai@niaid.nih.gov
authors.forename: Sanjay A
authors.initials: SA
authors.lastname: Desai
authors.forename: Abdulnaser
authors.initials: A
authors.lastname: Alkhalil
authors.forename: Myungsa
authors.initials: M
authors.lastname: Kang
authors.forename: Umar
authors.initials: U
authors.lastname: Ashfaq
authors.forename: My-Le
authors.initials: ML
authors.lastname: Nguyen
mesh_terms: D000465:Algorithms; D000495:Allosteric Site; D000818:Animals; D000838:Anions / Q000737:chemistry; D004232:Diuretics / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004351:Drug Resistance; D004594:Electrophysiology; D005665:Furosemide / Q000494:pharmacology; D007473:Ion Channels / Q000378:metabolism*; D007477:Ions; D007700:Kinetics; D008051:Lipid Bilayers / Q000378:metabolism; D008954:Models, Biological; D008956:Models, Chemical; D016296:Mutagenesis; D009153:Mutagens; D009154:Mutation; D009604:Nitrosoguanidines / Q000494:pharmacology; D009995:Osmosis; D010695:Phlorhizin / Q000494:pharmacology*; D010963:Plasmodium falciparum; D011485:Protein Binding; D013997:Time Factors
chemical_list: D000838:Anions; D004232:Diuretics; D007473:Ion Channels; D007477:Ions; D008051:Lipid Bilayers; D009153:Mutagens; D009604:Nitrosoguanidines; C505335:surface anion channel protein, Plasmodium falciparum; D005665:Furosemide; D010695:Phlorhizin