Synergistic activity of simvastatin and irinotecan chemotherapy against glioblastoma converges on TGF-β signaling.

PURPOSE

This study investigates the synergistic therapeutic potential of a novel combination of the repurposed drug simvastatin with irinotecan chemotherapy towards glioblastoma (GBM) and the underlying molecular mechanisms.

METHODS

In vitro efficacy of simvastatin and irinotecan alone and in combination against diverse GBM lines (U251MG, G34, SB28) was assessed using mechanistically distinct cell viability assays. RNA-Sequencing was performed to uncover the top pathways and genes affected by these drugs, followed by validation of promising pathways (TGF-β signaling and cell death) using targeted phosphoproteomics and in vitro genetic manipulation and functional assays.

RESULTS

We observed robust in vitro synergy at nanomolar concentrations between simvastatin and irinotecan across diverse GBM lines. Notably, irinotecan alone and in combination with simvastatin reduced mRNA expression of TGF-β family members. Targeted phosphoproteomics and functional experiments further showed significant inhibition of TGF-β signaling with both treatment types. Additionally, a role for apoptosis and enrichment of caspase-independent cell death pathways (autophagy, ferroptosis) as well as immunological (interferons, complement, inflammatory responses, TNF-α) and oncogenic (K-RAS/ERK) signaling pathways were observed with the combination treatment.

CONCLUSIONS

Besides the first detailed demonstration of a robust synergy between simvastatin and irinotecan against GBM lines, this study shows for the first time that both irinotecan and the combination treatment converge on inhibition of TGF-β signaling. This is notable given the lack of TGF-β inhibitors in the clinic. Collectively, this study provides preclinical data suggesting this novel drug combination be tested in patients with GBM and TGF-β driven cancers.