Combined transcriptional and translational targeting of EWS/FLI-1 in Ewing's sarcoma.

PURPOSE To show the efficacy of targeting EWS/FLI-1 expression with a combination of specific antisense oligonucleotides and rapamycin for the control of Ewing's sarcoma (EWS) cell proliferation in vitro and the treatment of mouse tumor xenografts in vivo. EXPERIMENTAL DESIGN EWS cells were simultaneously exposed to EWS/FLI-1-specific antisense oligonucleotides and rapamycin for various time periods. After treatment, the following end points were monitored and evaluated: expression levels of the EWS/FLI-1 protein, cell proliferation, cell cycle distribution, apoptotic cell death, caspase activation, and tumor growth in EWS xenografts implanted in nude mice. RESULTS Simultaneous exposure of EWS cells in culture to an EWS/FLI-1-targeted suppression therapy using specific antisense oligonucleotides and rapamycin resulted in the activation of a caspase-dependent apoptotic process that involved the restoration of the transforming growth factor-beta-induced proapoptotic pathway. In vivo, individual administration of either antisense oligonucleotides or rapamycin significantly delayed tumor development, and the combined treatment with antisense oligonucleotides and rapamycin caused a considerably stronger inhibition of tumor growth. CONCLUSIONS Concurrent administration of EWS/FLI-1 antisense oligonucleotides and rapamycin efficiently induced the apoptotic death of EWS cells in culture through a process involving transforming growth factor-beta. In vivo experiments conclusively showed that the combined treatment with antisense oligonucleotides and rapamycin caused a significant inhibition of tumor growth in mice. These results provide proof of principle for further exploration of the potential of this combined therapeutic modality as a novel strategy for the treatment of tumors of the Ewing's sarcoma family.