Dual targeting of EWS-FLI1 activity and the associated DNA damage response with trabectedin and SN38 synergistically inhibits Ewing sarcoma cell growth.

[werner syndrome]

The goal of this study is to optimize the activity of trabectedin for Ewing sarcoma by developing a molecularly targeted combination therapy .We have recently shown that trabectedin interferes with the activity of EWS-FLI 1 in Ewing sarcoma cells . In this report , we build on this work to develop a trabectedin-based combination therapy with improved EWS-FLI 1 suppression that also targets the drug-associated DNA damage to Ewing sarcoma cells .We demonstrate by siRNA experiments that EWS-FLI 1 drives the expression of the Werner syndrome protein (WRN ) in Ewing sarcoma cells . Because WRN -deficient cells are known to be hypersensitive to camptothecins , we utilize trabectedin to block EWS-FLI 1 activity , suppress WRN expression , and selectively sensitize Ewing sarcoma cells to the DNA-damaging effects of SN 38 . We show that trabectedin and SN 38 are synergistic , demonstrate an increase in DNA double -strand breaks , an accumulation of cells in S-phase and a low picomolar IC 50 . In addition , SN 38 cooperates with trabectedin to augment the suppression of EWS-FLI 1 downstream targets , leading to an improved therapeutic index in vivo . These effects translate into the marked regression of two Ewing sarcoma xenografts at a fraction of the dose of camptothecin used in other xenograft studies .These results provide the basis and rationale for translating this drug combination to the clinic . In addition , the study highlights an approach that utilizes a targeted agent to interfere with an oncogenic transcription factor and then exploits the resulting changes in gene expression to develop a molecularly targeted combination therapy .