Non-synaptic Cell-Autonomous Mechanisms Underlie Neuronal Hyperactivity in a Genetic Model of PIK3CA-Driven Intractable Epilepsy

Patients harboring mutations in the PI3K-AKT-MTOR pathway-encoding genes often develop a spectrum of neurodevelopmental disorders including epilepsy. A significant proportion remains unresponsive to conventional anti-seizure medications. Understanding mutation-specific pathophysiology is thus critical for molecularly targeted therapies. We previously determined that mouse models expressing a patient-related activating mutation in PIK3CA, encoding the p110α catalytic subunit of phosphoinositide-3-kinase (PI3K), are epileptic and acutely treatable by PI3K inhibition, irrespective of dysmorphology. Here we report the physiological mechanisms underlying this dysregulated neuronal excitability. In vivo, we demonstrate epileptiform events in the Pik3ca mutant hippocampus. By ex vivo analyses, we show that Pik3ca-driven hyperactivation of hippocampal pyramidal neurons is mediated by changes in multiple non-synaptic, cell-intrinsic properties. Finally, we report that acute inhibition of PI3K or AKT, but not MTOR activity, suppresses the intrinsic hyperactivity of the mutant neurons. These acute mechanisms are distinct from those causing neuronal hyperactivity in other AKT-MTOR epileptic models and define parameters to facilitate the development of new molecularly rational therapeutic interventions for intractable epilepsy.

High in vitro and in vivo synergistic activity between mTORC1 and PLK1 inhibition in adenocarcinoma NSCLC

Significant rational is available for specific targeting of PI3K/AKT/mTOR pathway in the treatment of non-small cell lung cancer (NSCLC). However, almost all clinical trials that have evaluated Pi3K pathway-based monotherapies/combinations did not observe an improvement of patient’s outcome. The aim of our study was therefore to define combination of treatment based on the determination of predictive markers of resistance to the mTORC1 inhibitor RAD001/Everolimus. An in vivo study showed high efficacy of RAD001 in NSCLC Patient-Derived Xenografts (PDXs). When looking at biomarkers of resistance by RT-PCR study, three genes were found to be highly expressed in resistant tumors, i.e., PLK1, CXCR4, and AXL. We have then focused our study on the combination of RAD001 + Volasertib, a PLK1 inhibitor, and observed a high antitumor activity of the combination in comparison to each monotherapy; similarly, a clear synergistic effect between the two compounds was found in an in vitro study. Pharmacodynamics study demonstrated that this synergy was due to (1) tumor vascularization decrease, increase of the HIF1 protein expression and decrease of the intracellular pH, and (2) decrease of the Carbonic Anhydrase 9 (CAIX) protein that could not correct intracellular acidosis. In conclusion, all these preclinical data strongly suggest that the inhibition of mTORC1 and PLK1 proteins may be a promising therapeutic approach for NSCLC patients.

mTORC1 inhibitor RAD001 (everolimus) enhances non-small cell lung cancer cell radiosensitivity in vitro via suppressing epithelial-mesenchymal transition

Resistance to radiotherapy causes non-small cell lung cancer (NSCLC) treatment failure associated with local recurrence and metastasis. Thus, understanding the radiosensitization of NSCLC cells is crucial for developing new treatments and improving prognostics. mTORC1 has been shown to regulate tumor cell radiosensitivity, but the underlying mechanisms are unclear. Moreover, mTORC1 also regulates epithelial-mesenchymal transition (EMT) that is important to metastasis and recurrence. In this study we explored whether mTORC1 regulated NSCLC cell radiosensitivity by altering EMT. We performed immunohistichemical analysis using tumor, adjacent and normal tissues from 50 NSCLC patients, which confirmed significantly elevated mTOR protein expression in NSCLC tissue. Then we used NCI-H460 and NCI-H661 cell lines to examine the effects of the mTORC1 inhibitor RAD001 (everolimus) on in vitro radiosensitivity, protein expression and dose-survival curves. RAD001 (10 nmol/L) significantly inhibited the mTORC1 pathway in both the cell lines. Pretreatment with RAD001 (0.1 nmol/L) enhanced the radiosensitivity in NCI-H661 cells with wild-type PIK3CA and KRAS but not in NCI-H460 cells with mutant PIK3CA and KRAS; the sensitivity enhancement ratios in the two NSCLC cell lines were 1.40 and 1.03, respectively. Furthermore, pretreatment with RAD001 (0.1 nmol/L) significantly decreased the migration and invasion with altered expression of several EMT-associated proteins (significantly increased E-cadherin and decreased vimentin expression) in irradiated NCI-H661 cells. Publicly available expression data confirmed that irradiation affected mTOR and EMT-associated genes at the transcript level in NSCLC cells. These results suggest that mTORC1 inhibition enhances the in vitro radiosensitivity of NSCLC cells with wild-type PIK3CA and KRAS by affecting EMT. Our preclinical data may provide a potential new strategy for NSCLC treatment.

RAD001 (everolimus) enhances TRAIL cytotoxicity in human leukemic Jurkat T cells by upregulating DR5

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), either alone or in combination with other anti-cancer agents, is a promising new strategy for the treatment of cancer. However, aberrant PI3K/Akt/mTOR survival signaling may confer TRAIL resistance by altering the balance between pro- and anti-apoptotic proteins. In the present study, we showed that the Akt/mTOR inhibitor RAD001 (everolimus) induced cell death in a dose-dependent manner and enhanced TRAIL-induced apoptosis in human leukemic Jurkat T cells, which show PI3K/Akt/mTOR pathway activation and basal expression levels of death receptor (DR) 5 (TRAIL-R2). Investigation of the effect of RAD001 treatment on the expression of TRAIL receptors (TRAIL-Rs) in Jurkat T cells showed that RAD001 significantly upregulated DR5 by up to 51.22%, but not other TRAIL-Rs such as DR4 (TRAIL-R1), decoy receptor (DcR) 1 (TRAIL-R3), and DcR2 (TRAIL-R4). Pretreatment with DR5:Fc chimera abrogated the RAD001-induced increase of TRAIL cytotoxicity, indicating that the upregulation of DR5 by RAD001 plays a role in enhancing the susceptibility of Jurkat T cells to TRAIL. Our results indicate that combination treatment with RAD001 and TRAIL may be a novel therapeutic strategy in leukemia.