Discovery of a novel antitumor benzolactone enamide class that selectively inhibits mammalian vacuolar-type (H+)-atpases.
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.
Laboratory of Natural Products, Division of Basic Sciences, National Cancer Institute, Bldg. 1052, Rm. 121, Frederick, MD 21702-1201, USA. boyd@tdpax2.ncifcrf.gov
M R
MR
Boyd
C
C
Farina
P
P
Belfiore
S
S
Gagliardi
J W
JW
Kim
Y
Y
Hayakawa
J A
JA
Beutler
T C
TC
McKee
B J
BJ
Bowman
E J
EJ
Bowman
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002417:Cattle; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D009492:Neurospora crassa / Q000201:enzymology; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors*; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured; D014617:Vacuoles / Q000201:enzymology*
D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D006180:Proton-Translocating ATPases