Abstract 2660: Synergistic effect of PI3Kδ inhibitor CAL-101 and JNK inhibitor SP600125 on glioblastoma cell proliferation

Abstract

Abstract Glioblastoma multiform (GBM) is the most aggressive malignant primary tumor in the central nervous system. Due to the hyperactivation of phosphatidylinositol 3-kinase (PI3K) and c-Jun N-terminal kinase (JNK) pathways in GBM, their respective inhibitors become promising and actively researched therapeutic agents. Our previous study showed that the PI3K catalytic isoform p110δ is highly expressed in GBM cell lines, indicating that p110δ may be a potential target for therapy. However, a single drug may not be sufficient to affect all pathogenic processes such as proliferation, migration and invasion in GBM cells. Therefore, we aimed to evaluate the combination effect of PI3Kδ inhibitor CAL-101 and JNK inhibitor SP600125 on glioma cells. The half maximal inhibitory concentration (IC50) of CAL-101 and SP600125 was first determined by the MTT method in GBM cell line U-87 MG. The combination effect of these 2 inhibitors on cell proliferation was analyzed using Compusyn software and the combination index (CI) was calculated. CI <0.9 indicates a synergistic effect, whereas CI >1.1 indicates an antagonistic effect, and CI between 0.9 and 1.1 indicates an additive effect. Cell migration and invasion capacity of U-87 MG cells were then evaluated under combined treatment with CAL-101 and SP600125. Our results showed that the effect of CAL-101 or SP600125 on cell proliferation was dose- and time-dependent. The IC50 of CAL-101 and SP600125 were 10.15 μM and 19.60 μM respectively. Treatment with SP600125 alone significantly suppressed U-87 MG cell proliferation, and combining 10 μM of CAL-101 and 20 μM of SP600125 showed a moderate synergistic effect. The cytotoxicity of CAL-101 or SP600125 alone, as well as combining them together was low on normal astrocytes. Western blot analysis of the PI3K/Akt and JNK pathways indicated that CAL-101 inhibited Akt phosphorylation at Ser473 and Thr308, whereas SP600125 suppressed JNK activity and Akt phosphorylation at Thr308. Combination of CAL-101 and SP600125 further inhibited Akt phosphorylation at Thr308, but showed no effect on the inhibition of Akt phosphorylation at Ser473 and c-Jun phosphorylation. CAL-101 significantly reduced migration but had no effect on invasion of U-87 MG cells, whereas SP600125 significantly suppressed both their migration and invasion abilities. Combining CAL-101 and SP600125 augmented the inhibitory effect on migration but showed no enhancement on invasion. In conclusion, combination treatment with CAL-101 and SP600125 showed a moderate synergistic effect on GBM cell proliferation, and enhanced the inhibition of cell migration. Our results suggest that GBM patients may benefit from combination therapy targeting both PI3Kδ and JNK. Citation Format: Hua-Fu ZHAO, Jing WANG, Shing-Shun Tony TO. Synergistic effect of PI3Kδ inhibitor CAL-101 and JNK inhibitor SP600125 on glioblastoma cell proliferation. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2660. doi:10.1158/1538-7445.AM2015-2660