Synthetic inhibition of SREBP2 and the mevalonate pathway blocks rhabdomyosarcoma tumor growth in vitro and in vivo and promotes chemosensitization.

By analyzing RNA datasets from rhabdomyosarcoma (RMS), a soft tissue tumor with a prevalence in young people, we found upregulation of sterol regulatory element-binding protein 2 (SREBP2) and mevalonate pathway (MVP) genes, including 3-Hydroxy-3-Methylglutaryl-CoA Reductase (HMGCR), farnesyl-diphosphate synthase (FDPS), squalene epoxidase (SQLE), which correlated with worse overall patient survival and predicted statin sensitivity. In human RD and RH30 lines, treatment with 0.01-1 μM doses of fatostatin (SREBP2 inhibitor), lovastatin and simvastatin (HMGCR inhibitors), and zoledronic acid (FDPS inhibitor) impaired cell growth and migration, which were conversely stimulated by 50-100 μM cholesterol (CHO) supplementation. Treatment of RMS lines with higher doses of SREBP2 and MVP inhibitors (5-50 μM) promoted oxidative cell death and chemosensitization in combination with actinomycin D. Administration of lovastatin or fatostatin to RD and RH30 cells produced a rapid attenuation of Erk1/2 and Akt1 phosphorylation, detectable after 4 hours of treatment. Furthermore, tumor mass growth of xenografted RD cells in NOD/SCID mice was reduced by oral administration of lovastatin. Lastly, we found the forced Akt1 activation in RD cells was sufficient to drive SREBP2, HMGCR and SQLE protein expression and enhance cell death susceptibility to MVP inhibitors. Taken together, these data suggest that the axis formed by Akt1, SREBP2 and MVP is critical for RMS tumor growth, migration, and oxidative stress protection mainly through the maintenance of CHO levels that ensure proper intracellular signaling. Therefore, targeting CHO levels by SREBP2 and MVP inhibition may represent a viable option to improve the combination therapy protocol in RMS.