Neuroblastoma is the second most common solid tumour during childhood, characterized by rapid
disease progression. Most children with metastasized
neuroblastoma die despite intensive
chemotherapy due to an intrinsic or acquired
chemotherapy resistance. Thus, new therapeutic strategies are urgently needed. Here, we demonstrate that the novel compound
nemorosone isolated from alcoholic extracts of Clusia rosea resins by reverse phase high pressure liquid chromatography (RP-HPLC) exerts cytotoxic activity in neuroblas-toma cell lines both parental and their clones selected for resistance against
adriamycin,
cisplatin,
etoposide or
5-fluorouracil. Cell cycle studies revealed that
nemorosone induces an accumulation in G0/G1- with a reduction in S-phase population combined with a robust up-regulation of p21Cip1. Furthermore, a dose-dependent apoptotic
DNA laddering accompanied by an activation of
caspase-3 activity was detected.
Nemorosone induced a significant dephosphorylation of ERK1/2 in LAN-1 parental cells probably by the inhibition of its upstream
kinase MEK1/2. No significant modulation of signal transducers JNK,
p38 MAPK and Akt/PKB was detected. The enzymatic activity of immunoprecipitated Akt/PKB was strongly inhibited in vitro, suggesting that
nemorosone exerts its anti-proliferative activity at least in part by targeting Akt/PKB in the cell lines studied. In addition, a synergistic effect with Raf-1 inhibitor
BAY 43-9006 was found. Finally,
nemorosone induced a considerable down-regulation of
N-myc protein levels in parental LAN-1 and an
etoposide resistant sub-line at the same
drug-concentrations.