Abstract
Melanoma is the most aggressive skin cancer and a serious health problem worldwide because of its increasing incidence and the lack of satisfactory chemotherapy for late stages of the disease. The marine depsipeptide Aplidin (plitidepsin) is an antitumoral agent under phase II clinical development against several neoplasias, including melanoma. We report that plitidepsin has a dual effect on the human SK-MEL-28 and UACC-257 melanoma cell lines; at low concentrations (≤45 nM), it inhibits the cell cycle by inducing G1 and G2/M arrest, whereas at higher concentrations it induces apoptosis as assessed by poly-(ADP-ribose) polymerase cleavage and the appearance of a hypodiploid peak in flow cytometry analyses. Plitidepsin activates Rac1 GTPase and c-Jun NH2-terminal kinase (JNK). In addition, it induces AKT and p38 mitogen-activated protein kinase (MAPK) phosphorylation. By using inhibitors, we found that JNK and p38 MAPK activation depends on Rac1 but not on phosphatidylinositol 3-kinase (PI3K), whereas AKT activation is independent of Rac1 but requires PI3K activity. Plitidepsin cytotoxicity diminishes by Rac1 inhibition or by the blockage of JNK and p38 MAPK using 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB203580), but not by PI3K inhibition using wortmannin or 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002). It is remarkable that plitidepsin and dacarbazine, the alkylating agent most active for treating metastatic melanoma, show a synergistic antiproliferative effect that was paralleled at the level of JNK activation. These results indicate that Rac1/JNK activation is critical for cell cycle arrest and apoptosis induction by plitidepsin in melanoma cells. They also support the combined use of plitidepsin and dacarbazine in in vivo studies.
Footnotes
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This work was supported by Grants SAF2004-01015 and SAF2007-60413 (to A.M.) and SAF2003-02604 and SAF2006-04247 (to J.M.R.) from Ministerio de Educación y Ciencia, and Intramural ISCIII (03/ESP27) (to J.M.R.) and RD06/002/0009 (to A.M.) from Instituto de Salud Carlos III of Spain.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.107.132662.
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ABBREVIATIONS: DTIC, dacarbazine; JNK, c-Jun NH2-terminal kinase; MAPK, mitogen-activated protein kinase; ROS, reactive oxygen species; VEGF, vascular endothelial growth factor; GSH, glutathione reduced ethyl ester; NSC23766, 1,2,6,7-tetrathiacyclodecane; LY294002, 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; SB203580, 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole; GST, glutathione transferase; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium; CI, combination index; ANOVA, analysis of variance; PARP, poly(ADP-ribose) polymerase; PI3K, phosphatidylinositol 3-kinase; Fa, fraction of cells affected.
- Received October 10, 2007.
- Accepted December 17, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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