LAUSR

Introduction Cytotoxic drugs like doxorubicin remain as the most utilised agents in sarcoma treatment. However, advanced sarcomas often show resistance to these drugs, mainly through the overexpression of members of the ATP binding cassette (ABC) family which act as efflux pumps for drugs. Therefore, the development more effective treatments able to prevent drug resistance would improve sarcoma treatments. Multi-kinase inhibitors provided an efficient way to target several pro-tumorigenic pathways using a single agent and have shown anti-tumour activity in a range of tumours. Aberrant activation of pro-tumoral kinase is common in sarcoma, however the effect of multikinase inhibitors in sarcoma has been barely tested. Here, we aimed to study the anti-tumour effect of one of such inhibitors in cell-of-origin sarcoma models and sarcoma patient-derived primary cell lines, as well as its ability to prevent drug resistance and synergize with doxorubicin. Material and methods Cell survival, apoptotic induction, cell cycle progression and DNA damage were analysed after drug treatments. The existence of synergism between drugs was evaluated using statistic tools. Drug effect on signalling proteins was studied using phospho-antibody arrays and Western-blotting analysis. Interaction between drugs and ABC transporters were characterised using substrate and inhibition assays. Finally, in vivotumour growth and pharmacodynamic response after drug treatments were evaluated in xenografts models. Results and discussions Sarcoma cells were sensitive to sub-micromolar concentrations of the multikinase inhibitor, which induced cell cycle arrest, DNA damage and apoptosis. Evaluation of the phosphorylation status of signalling kinases evidenced that PI3K/AKT/mTOR and ERK1/2 were the most highly activated pathways in sarcoma cells and that the drug efficiently inhibited them in vitro and in vivo. By using specific mTOR inhibitors and agonists, we confirmed that the inhibition of this pathway contributed to the cytotoxic effect of the drug. In addition, this drug inhibited the expression and activity of ABC transporters and was not a substrate for them. In line with this ability, we found a synergistic cytotoxic effect when sarcoma cells were treated with combinations of the kinase inhibitor and doxorubicin both in vitro and in vivo. Conclusion A novel multikinase inhibitor induced a consistent cytotoxic effect and was able to counteract drug resistance in sarcoma cells, thus highlighting its therapeutic potential when combined with current treatments.