Antiproliferative effect of mTOR inhibitor everolimus (EV) alone or in combination with multikinase inhibitor (MK-I) sorafenib (SOR) in preclinical models of osteosarcoma (OS).

Abstract

10058 Background: Targeting pathways involved in progression and metastatization might be a suitable way to overcome chemoresistance in OS. Monoclonal antibodies (anti-IGF1R) andMK-I (SOR, dasatinib) are investigated in the clinical setting. Since mTOR is involved in OS progression [Zhou Q, 2009], the activity of EV, SOR and their combination was explored in vitro and in vivo. Methods: In vitro effects of EV (from 500 to 15.125 nM) and SOR (from 10 to 0.3125 μM) were assessed on 7 human OS cell lines evaluating cell proliferation (Cell Titre GLO assay), cell cycle (flow cytometry) and apoptosis (Annexin V/propidium iodide assay). Synergism (SOR+EV) was assessed through normalized isobologram and combination index (CI) by CalcuSyn software. For in vivo experiments 106 OS cells were injected in SCID mice. After tumor establishment (500 mm3), mice were treated by oral gavage for 3 wks with SOR (5 mg/kg/day) or EV (1 mg/kg/day) and their combination. Tumor volumes were compared between the 3 treatment groups and vehicle (DMSO) treatment control and p- values calculated. Results: SOR showed a dose-dependent inhibition effect. EV alone was able to affect around 40% of cell proliferation. The combination displayed synergism in the interval of 30-70% of fractions affected (CI<1) and antagonism at higher doses (CI>1). SOR IC50 was reduced from 2.7 to 1.3 mM in presence of EV, with a marked increase in apoptotic cells compared to both single agents. In vivo each treatment strikingly inhibited tumor growth with relative tumor proliferation rate (T/C) values of 0.34 (SOR) 0.46 (EV) 0.29 (combination). Survival was increased from 12 to 20 days, (p<0.05). Conclusions: This work shows the in vitro and in vivo antiproliferative effect of SOR, EV and their combination. Whilst molecular mechanisms are investigated, the combination of SOR and EV warrants to be tested in OS clinical setting. No significant financial relationships to disclose.