Abstract
A series of naturally occurring compounds reported recently by multiple laboratories defines a new small-molecule class sharing a unique benzolactone enamide core structure and diverse biological actions, including inhibition of growth of tumor cells and oncogene-transformed cell lines. Here we show that representative members of this class, including salicylihalamide A, lobatamides A–F, and oximidines I and II inhibit mammalian vacuolar-type (H+)-ATPases (V-ATPases) with unprecedented selectivity. Data derived from the NCI 60-cell antitumor screen critically predicted the V-ATPase molecular target, while specific biochemical assays provided confirmation and further illumination. The compounds potently blocked representative V-ATPases from human kidney, liver, and osteoclastic giant-cell tumor of bone but were essentially inactive against V-ATPases of Neurospora crassa and Saccharomyces cerevisiae and other membrane ATPases. Essential regulation of pH in cytoplasmic, intraorganellar, and local extracellular spaces is provided by V-ATPases, which are ubiquitously distributed among eukaryotic cells and tissues. The most potent and selective V-ATPase inhibitors heretofore known were the bafilomycins and concanamycins, which do not discriminate between mammalian and nonmammalian V-ATPases. Numerous physiological processes are mediated by V-ATPases, and aberrant V-ATPase functions are implicated in many different human diseases. Previous efforts to develop therapeutic pharmacological modulators of V-ATPases have been frustrated by a lack of synthetically tractable and biologically selective leads. Therefore, availability of the unique benzolactone enamide inhibitor class may enable further elucidation of functional and architectural features of mammalian versus nonmammalian V-ATPase isoforms and provide new opportunities for targeting V-ATPase-mediated processes implicated in diverse pathophysiological phenomena, including cancer.
Footnotes
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Send reprint requests to: Michael R. Boyd, M.D., Ph.D., Laboratory of Natural Products, NCI-FCRDC, Bldg. 1052, Rm. 121, Frederick, MD 21702-1201. E-mail:boyd{at}dtpax2.ncifcrf.gov
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This article is dedicated to Professor George R. Pettit on the occasion of his 71st birthday.
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This project was funded in part with federal funds from the National Cancer Institute, National Institutes of Health, under contract number N01-C0-56000 and from the National Institute of General Medical Science Grant GM28703. The content of this article does not necessarily reflect the views of the Department of Health and Human Services, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government. The publisher or recipient acknowledges right of the U.S. Government to retain a nonexclusive royalty-free license in and to any copyright covering this article.
- Abbreviations:
- V-ATPase
- vacuolar-type (H+)-ATPase
- DMSO
- dimethyl sulfoxide
- hK
- human kidney
- hL
- human liver
- hOc
- human osteoclasts
- PIPES
- piperazine-N,N′-bis(2-ethanesulfonic acid)
- CDTA
- 1,2-cyclohexylenedinitrilotetraacetic acid
- MES
- 4-morpholineethanesulfonic acid
- SAR
- structure-activity relationship(s)
- Received November 6, 2000.
- Accepted December 19, 2000.
- U.S. Government
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