gms | German Medical Science

We have characterized a polyisoprenylated benzophenone isolated from Clusia rosea, collected in Florida, USA. This novel substance, called CLU-502, was isolated from methanolic extracts of the plant using RP-HPLC coupled to a PDA-detector. In the SRB proliferation assay, CLU-502 demonstrated a potent cytotoxic activity in a panel of human tumor cell lines such as neuroblastoma and leukemia. Both, wild-type cell lines and sub-lines resistant to doxorubicin, cis-platin, etoposide or 5-fluorouracil were highly sensitive to CLU-502. Interestingly, normal fibroblasts were more resistant to this compound than cancer cells. CLU-502 inhibits the unwinding activity of topoisomerase I in a relaxation of pBR322l plasmid, as well as the decatenation of kinetoplasmids by human topoisomerase II. In addition, CLU-502 induce a dose-dependent inhibition of telomerase activity in vitro. A dose-dependent effect on the phosphorylation of ERK1/2, the cytosolic downstream enzymes of the MAP-kinase pathway, was also detected in Western blot analyses. The interaction of CLU-502 with PD98059, a specific inhibitor of ERK1/2 phosphorylation, resulted in a synergistic cytotoxic effect when both drugs were administered to tumor cells simultaneously. As the result of the exposure of cell cultures to CLU-502, a cell cycle arrest of the G1 phase was detected. Finally, an apoptosis/DNA-damage in tumor cells was observed in agarose gels after the exposure of CLU-502 at different concentrations. CLU-502 inhibits Akt/PKB in NB cells. Initial toxicological studies in a nude mouse model revealed that treatment with CLU-502 was well tolerated up to 100 mg/kg. The antitumoral effect are currently analyzed in vivo in a neuroblastoma nude mouse model.