Abstract C260: Dual targeting of the PI3K/Akt/mTOR pathway significantly delays chondrosarcoma progression and relapse.
Authors: Jury Delphine , Decouvelaere Anne Valerie , Pasquier Amandine , Belvin Marcia , Friedman Lorie , Langlois Jean Baptiste , Michot Jean Philippe , Blay Jean Yves , Dutour Aurelie 
Published: August 2014

Abstract
Chondrosarcoma is a rare and usually slow growing sarcoma. This tumor is notoriously resistant to chemotherapy and radiation treatment. To improve survival rates in patients with chondrosarcoma exploring targeted therapies approaches seems promising. Thus we performed a preclinical study evaluating the efficacy of mTOR inhibitor everlimus in an orthotopic rat chondrosarcoma model and showed the potential of this mTORC 1 inhibitor to significantly delay tumor progression and relapse. Based on these data, we initiated preclinical studies in the same chondrosarcoma model to investigate how mTOR inhibition can be optimized. We first evaluated the antitumor effect of a PI3K (GDC-0941), an Akt (G-594) and a dual PI3K/mTOR inhibitor (GDC-0980). In a second step and in order to overcome forms of resistance we combined inhibition of PI3K to Akt or PI3K to the one of mTOR. GDC-0941 based drug combinations (GDC-0941+G-594; GDC-0941+RAD001) potency to inhibit tumor progression was compared to the one of each agent alone. For each setting, the effect of each treatment on mTOR and ERK pathways, apoptosis and cell proliferation was also tested.
Results: As monotherapy, PI3K inhibitor (GDC-0941) was found to be the most efficient inducing an inhibition of tumor progression of 58 % whereas RAD001 induced a 49 % inhibition. The comparison of therapeutic efficiency of GDC-0941 based combinations showed an additive effect of G-594 or RAD001 to GDC-0941. Each of these combination caused an inhibition &gt;60% in chondrosarcoma progression, whereas each agent alone induced a 22% to 45 % inhibition of tumor progression. GDC-0941 exposure inhibited chondrosarcoma proliferation as evaluated by Ki67 staining and induced Caspase 3/7 mediated apoptosis when used as single agent or in combined therapies. Our data reveal that all combination treatments blocked Akt activation, and inhibited phosphorylation of both 4EBP1 and S6K1 which resulted in. The tested treatments induced a similar inhibition of mTOR mediated signaling. Chondrosarcoma exposure to GDC-0941 or G-594 caused a 20% inhibition of p70S6K and 4EBP activation similar to the one induced by the rapalog RAD001. The PI3K inhibitor GDC-0941 caused an activation of Erk Pathway as noted by the strong increase in bRaf phosphorylation.
Taken together these data confirm that targeting the PI3K/mTOR pathway is an efficient treatment for chondrosarcoma and combined therapy best way to cause inhibition of tumor progression. The effect noted on Erk pathway suggests that new combination approaches targeting the mTOR and Erk pathway could be of interest.
Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C260.
Citation Format: Delphine Jury, Anne Valerie Decouvelaere, Amandine Pasquier, Marcia Belvin, Lorie Friedman, Jean Baptiste Langlois, Jean Philippe Michot, Jean Yves Blay, Aurelie Dutour. Dual targeting of the PI3K/Akt/mTOR pathway significantly delays chondrosarcoma progression and relapse. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C260.