Received for publication October 11, 2007.
Revised November 28, 2007.
Accepted for publication December 17, 2007.

Plitidepsin has a dual effect inhibiting cell cycle and inducing apoptosis via Rac1/JNK activation in human melanoma cells

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 plitidepsin (Aplidin^®) is an anti-tumoral 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 while at higher concentrations it induces apoptosis as assessed by PARP cleavage and the appearance of a hypodiploid peak in flow cytometry analyses. Plitidepsin activates Rac1 GTPase and c-Jun N-terminal kinase (JNK) and, in addition, it induces AKT and p38MAPK phosphorylation. By using inhibitors, we found that JNK and p38MAPK activation depends on Rac1 but not on PI3K, while AKT activation is independent of Rac1 but requires PI3K activity. Plitidepsin cytotoxicity diminishes by Rac1 inhibition or by the blockage of JNK and p38MAPK using SB203580, but not by PI3K inhibition using Wortmannin or LY294002. Remarkably, plitidepsin and dacarbazine, the alkylating agent most active for treating metastatic melanoma, show synergistic anti-proliferative 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.

Key words: Aplidin, JNK, anti-tumoral, apoptosis, cell-cycle arrest, melanoma