Abstract LB-063: Anti-tumor activity of the novel dual p70S6KAKT inhibitor M2698 in glioma stem cell mouse models
Authors: piao yuji , Thomas Craig , Henry Verlene , Tiao Ningyi , park Soon Young , Juan Martinez-ledesma , Dong Jianwen , groot John frank de 
Published: July 2017

Abstract
The efficacy of the dual p70S6K/AKT inhibitor M2698 was evaluated in a panel of patient-derived glioma stem cell (GSC) lines. The IC50 was determined from a 7-dose cell viability assay using Celltiter Glo. GSCs were classified as sensitive (IC50 ≤ 1µM) or resistant (IC50 &gt;1µM). Two sensitive cell lines (GSC17 and GSC231) and two resistant cell lines (GSC272 and GSC20) were selected for in vivo experiments.
To determine the efficacy of M2698 in orthotopic models of glioblastoma, GSCs were implanted into the basal ganglia of nude mice. After four days, mice were treated with vehicle (control) or M2698 at 20 mg/kg daily M-F. In the cell line GSC231 (sensitive in vitro), the median animal survival time was 47 days in the control-treated mice and 62 days in the M2698-treated mice (p=0.0288). The tumor volumes at 6, 7.5, 10 weeks were 4.98 ± 6.17 mm3, 48.48 ± 10.57 mm3, and 61.38 ± 28.00 mm3, respectively, in the control-treated mice and 0.33 ± 0.45 mm3, 9.96 ± 6.89 mm3, and 18.00 ± 5.59 mm3, respectively, in the M2698 -treated mice (p=0.322, p&lt;0.001, and p=0.05, respectively). To determine the pharmacodynamic effect of the drug in mouse xenografts, the phospho-S6 (P-S6) expression level was evaluated over time (7.5 and 10 weeks). At 7.5 weeks, the P-S6 staining was 11.65 ± 1.17% per field in the control group and 2.61 ± 1.21% per field in the M2698 alone treated group (p&lt;0.004). At 10 weeks , the P-S6 staining was 13.93 ± 3.46% per field in the control group and 3.10 ± 1.23% per field in the M2698 alone treated group (p=0.020).
In the GSC272 (resistant line) xenograft mouse model, the median survival time was 72 days in the control-treated mice and 76 days in the M2698-treated mice. Although this difference was statistically significant (p=0.0022), the 4 day improvement in survival was minimal compared to the sensitive line GSC231. The tumor volumes at 6, 7.5, 10 weeks were 7.48 ± 4.10 mm3, 126.37 ± 41.98 mm3, and 158.79 ± 39.53 mm3, respectively in the control mice and 0.54 ± 0.47 mm3, 8.62 ± 3.88 mm3, and 64.3 ± 5.55 mm3, respectively in the M2698-treated mice (p=0.014, p&lt;0.001, and p=0.008, respectively). The P-S6 expression level at 6 weeks, 7.5 weeks, and 10 weeks was 4.27 ± 3.27% per field, 13.83 ± 4.13% per field, and 22.3 ± 7.67% per field, respectively, in the control-
treated mice and 1.40 ± 1.06% per field, 4.30 ± 2.26% per field, and 5.13 ± 1.02% per field, respectively, in the M2698-treated mice (p=0.302, p=0.005, and p=0.036, respectively).
GSC17 and GSC20 lines that were resistant to M2698 were further evaluated to elucidate potential mechanisms of resistance to p70S6K/AKT inhibitor treatment. Reverse Phase Protein Array (RPPA) assay was performed 24 hours after treatment with M2698 in GSC17 and GSC20 in vitro. M2698 successfully prevented S6 phosphorylation, but also resulted in an increase in P-ERK1/2 and P-MAPK expression suggesting compensatory activation of the Ras/MEK/ERK signaling pathway. To validate these results in vivo, we performed immunohistochemistry staining of P-S6 and P-ERK1/2 in tumor tissue from the GSC17 xenograft model at the latest time points. The data revealed that tumors from M2698-treated mice had lower levels of P-S6 expression and high level of P-ERK1/2 expression compared with the untreated control group. These results suggest that tumors not responsive to p70S6K/AKT inhibitor monotherapy might benefit from combination treatment with a MEK inhibitor.
Citation Format: yuji piao, Craig Thomas, Verlene Henry, Ningyi Tiao, Soon Young park, Martinez-ledesma Juan, Jianwen Dong, John frank de groot. Anti-tumor activity of the novel dual p70S6KAKT inhibitor M2698 in glioma stem cell mouse models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-063. doi:10.1158/1538-7445.AM2017-LB-063