Abstract 4914: AKT- and ERK signaling inhibition does not sensitize GBM cells to chemo-/radiation in vitro

A common feature of Glioblastoma Multiforme (GBM) is an augmented RTK/RAS/PI3K pathway signaling. This pathway has been shown to be involved in DNA repair by both NHEJ and HR in various tumor types and is thought thereby to interfere with its chemo- and radioresistance. Targeting this pathway to sensitize GBM to chemo- and radiotherapy seems to be an attractive therapeutic approach. Proliferation and clonogenic survival of U251, U87 and T98 GBM cells were assessed following exposure to, BKM120 (pan class I PI3K inhibitor), RAD001 (mTORC1 inhibitor), MK-2206 (AKT inhibitor) and/or MEK162 (ERK inhibitor) alone and in combination with either irradiation or Temozolomide (TMZ). Effectivity of each compound on its target pathway was assessed by westernblot. BEZ235 (PI3K/mTOR/DNA-PK inhibitor) was used as a positive control for radiosensitization. Our data show BKM120 and MK-2206 to effectively inhibit AKT phosphorylation at 1 uM and leads to growth inhibition in all tested cell lines. However, these compounds are not toxic on clonogenic cell survival and do not sensitize the cells to TMZ or irradiation. Increasing the dose to 5 uM and 10 uM for BKM120 and MK-2206 respectively an antagonistic effect was found in the combination with TMZ and irradiation. Effectively inhibiting mTOR, the downstream effector of AKT, by 100 nM RAD001 also does not radiosensitize GBM cells. Inhibiting the parallel ERK-pathway by 1 uM MEK162, dephosphorylates ERK1/2 and leads to a slight increase in AKT phosphorylation. Inhibiting both pathways with BKM120 and MEK162 resulted in a synergistic growth inhibition of U251 cells however no radiosensitizing effect was found in a clonogenic assay. In conclusion, selective targeting of key components in the AKT- and/or ERK signaling pathway effectively inhibits proliferation of GBM cells yet does not sensitize them to either TMZ or radiotherapy, indicating that GBM does not depend on the RTK/RAS/PI3K pathway for its DNA-repair. Citation Format: Ravi Narayan, Rogier Dik, Jaap van den Berg, Lukas J.A. Stalpers, Brigitta G. Baumert, Ben J. Slotman, Peter Sminia. AKT- and ERK signaling inhibition does not sensitize GBM cells to chemo-/radiation in vitro . [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4914. doi:10.1158/1538-7445.AM2014-4914