Simultaneous targeting PI3K/Akt/mTOR and MEK/RAF/ERK pathways results in a synergis6c an6-prolifera6ve effect in an adrenocor6cal carcinoma model

<p>Introduction:</p> <p>Adrenocortical carcinoma (ACC) is a rare disease with a poor prognosis and limited therapeutic options.</p> <p>Aim:</p> <p>The aim of this study was to assess the anti-proliferative effect of combinatorial targeting of the PI3K/Akt/mTOR pathway with different drugs and simultaneous targeting of the MEK/Raf/ERKpathway in H295R adrenocortical cancer cells.</p> <p>Material and Methods:</p> <p>The cytotoxicity of LY294002 (pan-PI3K inhibitor), everolimus (mTOR inhibitor), BEZ235 (dual PI3K/mTOR inhibitor) and U0126 (MEK1/2 inhibitor) was assessed by Alamar blue assay in the H295R cell line. After finding the maximal cytotoxic concentrations for all inhibitors, we used suboptimal concentrations for experiments where multiple agents were used simultaneously. Everolimus and BEZ235 were kindly provided by Novartis, Switzerland; LY294002 and U0126 were commercially available.</p> <p>Results:</p> <p>While everolimus, BEZ235 and LY294002 caused 20±6%, 15.6±6% and 11±1% cytotoxicity when used as single agents, co-treatment of cells with everolimus and BEZ235 showed a synergistic cytotoxic effect of 54±9% (p=0.007) (the strongest effect for combination of two inhibitors in our system, N=3 independent experiments). Addition of LY294002 to everolimus and BEZ235 increased the effect further to 65±7%.</p> <p>We also explored the potential benefit of combined inhibition of PI3K/mTOR and MEK1/2. Addition of U0126 to BEZ235 had a synergistic effect (42±3% vs 14±5% and 15±5.6% alone, respectively, N=3 independent experiments). We observed only an additive effect if the MEK1/2 inhibitor was added to everolimus alone or in combination with BEZ235.</p> <p>Conclusions:</p> <p>The combination of agents inhibiting PI3K/Akt/mTOR and MEK/Raf/ERK pathways results in a synergistic cytotoxic effect. Our results suggest also that multiple mode of inhibition of the same pathway may result in a greater cytotoxic effect in adrenocortical cancer cells which cannot be achieved by simple dose escalation. We suggest that new combinations targeting those pathways require further investigation to improve the treatment of ACC patients.</p