We report that
Aplidin, a novel
antitumor agent of marine origin presently undergoing Phase II clinical trials, induced growth arrest and apoptosis in human MDA-MB-231
breast cancer cells at nanomolar concentrations.
Aplidin induced a specific cellular stress response program, including sustained activation of the
epidermal growth factor receptor (EGFR), the non-
receptor protein-tyrosine kinase Src, and the
serine/threonine kinases JNK and
p38 MAPK.
Aplidin-induced apoptosis was only partially blocked by the general
caspase inhibitor benzyloxycarbonyl-VAD-fluoromethyl
ketone and was also sensitive to
AG1478 (an EGFR inhibitor), PP2 (an Src inhibitor), and
SB203580 (an inhibitor of JNK and
p38 MAPK) in MDA-MB-231 cells. Supporting a role for EGFR in
Aplidin action, EGFR-deficient mouse embryo fibroblasts underwent apoptosis upon treatment more slowly than wild-type EGFR fibroblasts and also showed delayed JNK and reduced
p38 MAPK activation.
N-Acetylcysteine and
ebselen (but not other
antioxidants such as
diphenyleneiodonium,
Tiron,
catalase,
ascorbic acid, and
vitamin E) reduced EGFR activation by
Aplidin.
N-Acetylcysteine and PP2 also partially inhibited JNK and
p38 MAPK activation. The intracellular level of GSH affected
Aplidin action; pretreatment of cells with GSH or
N-acetylcysteine inhibited, whereas GSH depletion caused, hyperinduction of EGFR, Src, JNK, and
p38 MAPK. Remarkably,
Aplidin also induced apoptosis and activated EGFR, JNK, and
p38 MAPK in two cell lines (A-498 and ACHN) derived from human
renal cancer, a
neoplasia that is highly refractory to
chemotherapy. These data provide a molecular basis for the anticancer activity of
Aplidin.