Cysteine protease inhibitors as chemotherapy: Lessons from a parasite target

Cysteine protease inhibitors as chemotherapy: Lessons from a parasite target

Departments of ^*Pathology, ^**Pharmaceutical Chemistry, ^¶Biochemistry, and ^‡Medicine, University of California, San Francisco, CA 94143; ^‖Washington University, St. Louis, MO 63110; and ^§I. Frauenklinik, Klinikum Innenstadt, Ludwig-Maximilians Universität München, 80337 Munich, Germany

Abstract

Papain family cysteine proteases are key factors in the pathogenesis of cancer invasion, arthritis, osteoporosis, and microbial infections. Targeting this enzyme family is therefore one strategy in the development of new chemotherapy for a number of diseases. Little is known, however, about the efficacy, selectivity, and safety of cysteine protease inhibitors in cell culture or in vivo. We now report that specific cysteine protease inhibitors kill Leishmania parasites in vitro, at concentrations that do not overtly affect mammalian host cells. Inhibition of Leishmania cysteine protease activity was accompanied by defects in the parasite’s lysosome/endosome compartment resembling those seen in lysosomal storage diseases. Colocalization of anti-protease antibodies with biotinylated surface proteins and accumulation of undigested debris and protease in the flagellar pocket of treated parasites were consistent with a pathway of protease trafficking from flagellar pocket to the lysosome/endosome compartment. The inhibitors were sufficiently absorbed and stable in vivo to ameliorate the pathology associated with a mouse model of Leishmania infection.

Footnotes

↵ † To whom reprint requests may be addressed at present address: Hoechst Roussel Vet GmbH, Research Pharmaceuticals, Building H 811, D-65926 Frankfurt/Main, Germany. E-mail: PSelzer{at}hrvet.com.
↵ ‡‡ To whom reprint requests may be addressed at: Department of Pathology, University of California, Tropical Disease Research Unit, VAMC, 4150 Clement Street 113B, San Francisco, CA 94121. E-mail: jmck{at}cgl.ucsf.edu.
This paper was presented at the National Academy of Sciences colloquium “Proteolytic Processing and Physiological Regulation” held February 20–21, 1999, at the Arnold and Mabel Beckman Center in Irvine, CA.
ABBREVIATIONS:

cpL,

cathepsin L-like cysteine protease;

cpB,

cathepsin B-like cysteine protease;

AMC,

7-amino-4-methylcoumarin