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Antimicrobial Agents and Chemotherapy, Sep 1997, 1859-1866, Vol 41, No. 9
JA Silverman, ML Hayes, BJ Luft and KA Joiner
The immunosuppressive agent cyclosporin A (CsA) also possesses broad-
spectrum antimicrobial activity. Previous investigators have reported that
the obligate intracellular protozoan Toxoplasma gondii is sensitive to CsA.
We have measured the sensitivity of Toxoplasma to 26 CsA derivatives that
maintain only a subset of the parent compound's activity. We identified one
compound, SDZ 215-918, that is a particularly potent inhibitor of parasite
invasion and replication, with a 50% inhibitory concentration of 0.45
microg/ml, which is 10-fold lower than that of CsA. Kinetic studies
demonstrate that activity has a rapid onset (half-life, < or = 20 min)
and is initially reversible, although long-term exposure (> 24 h) to 5
microg/ml is lethal; in contrast, this concentration had no effect on host
cell protein synthesis or cell division. SDZ 215-918 acts directly on the
parasite, as demonstrated by inhibition of macromolecular synthesis in
host-free extracellular parasites. Inhibition of invasion is due to a
reduction in parasite motility. SDZ 215-918 does not bind to cyclophilins,
the ubiquitous cyclosporin-binding proteins, but is a potent inhibitor of
the mammalian P glycoprotein, a member of the ATP binding cassette
transporter superfamily and the pump responsible for multidrug resistance
in cancer and parasite cell lines. SDZ 215-918 blocks the efflux of
rhodamine 123 from extracellular parasites, consistent with inhibition of a
P glycoprotein-like pump. We suggest that a P glycoprotein or a related
transporter plays a crucial role in the biology of Toxoplasma and may be a
novel target for antiparasitic compounds. Preliminary studies with animals
indicate that SDZ 215-918 inhibits parasite growth in vivo; its
relationship to CsA may make it suitable for clinical development.
Copyright © 1997 by the American Society for Microbiology. All rights reserved.
Characterization of anti-Toxoplasma activity of SDZ 215-918, a cyclosporin derivative lacking immunosuppressive and peptidyl-prolyl- isomerase-inhibiting activity: possible role of a P glycoprotein in Toxoplasma physiology
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520-8022, USA.
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