Diffusely infiltrating gliomas are among the most prognostically discouraging neoplasia in human. Temozolomide (TMZ) in combination with radiotherapy is currently used for the treatment of glioblastoma (GBM) patients, but less than half of the patients respond to therapy and chemoresistance develops rapidly. Epigenetic silencing of the O6-methylguanine-DNA methyltransferase (MGMT) has been associated with longer survival in GBM patients treated with TMZ, but nuclear factor κB (NF-κB)-mediated survival signaling and TP53 mutations contribute significantly to TMZ resistance. Enhanced NF-κB is in part owing to downregulation of negative regulators of NF-κB activity, including Tumor necrosis factor alpha-induced protein 3 (TNFAIP3) and NF-κB inhibitor interacting RAS-like 2 (NKIRAS2). Here we provide a novel mechanism independent of TP53 and MGMT by which oncogenic miR-125b confers TMZ resistance by targeting TNFAIP3 and NKIRAS2. GBM cells overexpressing miR-125b showed increased NF-κB activity and upregulation of anti-apoptotic and cell cycle genes. This was significantly associated with resistance of GBM cells to TNFα- and TNF-related inducing ligand-induced apoptosis as well as resistance to TMZ. Conversely, overexpression of anti-miR-125b resulted in cell cycle arrest, increased apoptosis and increased sensitivity to TMZ, indicating that endogenous miR-125b is sufficient to control these processes. GBM cells overexpressing TNFAIP3 and NKIRAS2 were refractory to miR-125b-induced apoptosis resistance as well as TMZ resistance, indicating that both genes are relevant targets of miR-125b. In GBM tissues, high miR-125b expression was significantly correlated with nuclear NF-κB confirming that miR-125b is implicated in NF-κB signaling. Most remarkably, miR-125b overexpression was clearly associated with shorter overall survival of patients treated with TMZ, suggesting that this microRNA is an important predictor of response to therapy.

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a b s t r a c tThe MET receptor tyrosine kinase is deregulated primarily via overexpression or point mutations in various human cancers and different strategies for MET inhibition are currently evaluated in clinical trials. We observed by Western blot analysis and by Flow cytometry that MET inhibition by different MET small molecule inhibitors surprisingly increases in a dose-dependent manner total MET levels in treated cells. Mechanistically, this inhibition-related MET accumulation was associated with reduced Tyr1003 phosphorylation and MET physical association with the CBL ubiquitin ligase with concomitant decrease in MET ubiquitination. These data may suggest careful consideration for design of anti-MET clinical protocols. Structured summary of protein interactions:Cbl physically interacts with Met by anti bait coimmunoprecipitation (1, 2)

Increasing evidence suggests that interference with growth factor receptor tyrosine kinase (RTK) signaling can affect DNA damage response (DDR) networks, with a consequent impact on cellular responses to DNA-damaging agents widely used in cancer treatment. In that respect, the MET RTK is deregulated in abundance and/or activity in a variety of human tumors. Using two proteomic techniques, we explored how disrupting MET signaling modulates global cellular phosphorylation response to ionizing radiation (IR). Following an immunoaffinity-based phosphoproteomic discovery survey, we selected candidate phosphorylation sites for extensive characterization by targeted proteomics focusing on phosphorylation sites in both signaling networks. Several substrates of the DDR were confirmed to be modulated by sequential MET inhibition and IR, or MET inhibition alone. Upon combined treatment, for two substrates, NUMA1 S395 and CHEK1 S345, the gain and loss of phosphorylation, respectively, were recapitulated using invivo tumor models by immunohistochemistry, with possible utility in future translational research. Overall, we have corroborated phosphorylation sites at the intersection between MET and the DDR signaling networks, and suggest that these represent a class of proteins at the interface between oncogene-driven proliferation and genomic stability.Abbreviations ATM, ataxia telangiectasia mutated; ATR, ataxia telangiectasia and Rad3-related protein; CDK, cell cycle-dependent kinase; CHEK1, checkpoint kinase 1; CHEK2, checkpoint kinase 2; DDA, DNA-damaging agent; DDR, DNA damage response; DNA-PKcs, catalytic subunit of the DNA-dependent protein kinase

Signaling via the MET receptor tyrosine kinase has been implicated in crosstalk with cellular responses to DNA damage. Our group previously demonstrated that MET inhibition in tumor cells with deregulated MET activity results in radiosensitization via downregulation of the ATR-CHK1-CDC25 pathway, a major signaling cascade responsible for intra-S and G 2 -M cell-cycle arrest following DNA damage. Here we aimed at studying the potential therapeutic application of ionizing radiation in combination with a MET inhibitor, EMD-1214063, in p53-deficient cancer cells that harbor impaired G 1 -S checkpoint regulation upon DNA damage. We hypothesized that upon MET inhibition, p53-deficient cells would bypass both G 1 -S and G 2 -M checkpoints, promoting premature mitotic entry with substantial DNA lesions and cell death in a greater extent than p53-proficient cells. Our data suggest that p53-deficient cells are more susceptible to EMD-1214063 and combined treatment with irradiation than wild-type p53 lines as inferred from elevated gH2AX expression and increased cytotoxicity. Furthermore, cell-cycle distribution profiling indicates constantly lower G 1 and higher G 2 -M population as well as higher expression of a mitotic marker p-histone H3 following the dual treatment in p53 knockdown isogenic variant, compared with the parental counterpart.Implications: The concept of MET inhibition-mediated radiosensitization enhanced by p53 deficiency is of high clinical relevance, as p53 is frequently mutated in numerous types of human cancer. The current data point for a therapeutic advantage for an approach combining MET targeting along with DNA-damaging agents for MET-positive/p53-negative tumors.

Poor oxygenation is a common hallmark of solid cancers that strongly associates with aggressive tumor progression and treatment resistance. While a hypoxia-inducible factor 1α (HIF-1α)-associated transcriptional overexpression of the hepatocyte growth factor (HGF) receptor tyrosine kinase (RTK) MET has been previously documented, any regulation of the HIF-1α system through MET downstream signaling in hypoxic tumors has not been yet described. By using MET-driven in vitro as well as ex vivo tumor organotypic fresh tissue models we report that MET targeting results in depletion of HIF-1α and its various downstream targets. Mechanistically, we provide evidence that MET regulates HIF-1α levels through a protein translation mechanism that relies on phosphorylation modulation of the eukaryotic initiation factor 4G1 (eIF4G1) on serine 1232 (Ser-1232). Targeted phosphoproteomics data demonstrate a significant drop in eIF4G1 Ser-1232 phosphorylation following MET targeting, which is linked to an increased affinity between eIF4G1 and eIF4E. Since phosphorylation of eIF4G1 on Ser-1232 is largely mediated through mitogen-activated protein kinase (MAPK), we show that expression of a constitutively active K-RAS variant is sufficient to abrogate the inhibitory effect of MET targeting on the HIF-1α pathway with subsequent resistance of tumor cells to MET targeting under hypoxic conditions. Analysis of The Cancer Genome Atlas data demonstrates frequent co-expression of MET, HIF-1α and eIF4G1 in various solid tumors and its impact on disease-free survival of non-small cell lung cancer patients. Clinical relevance of the MET-eIF4G1-HIF-1α pathway is further supported by a co-occurrence of their expression in common tumor regions of individual lung cancer patients.

Background: The Wee1 tyrosine kinase is activated upon DNA damage and regulates the G2-M cell cycle checkpoint. Inhibition of Wee1, in conjunction with additional genetic alterations and/or addition of a DNA damaging agent, results in mitotic catastrophe and apoptosis of cancer cells, offering an attractive approach to treating cancer. The aim of the present study was to characterize the pharmacological properties of the newly discovered, orally available, and highly selective Wee1 inhibitor Debio 0123. Methods: Profiling of Debio 0123 was performed on 465 selected kinases in a cell-free system. Effects of Debio 0123 on downstream signaling were analyzed by ELISA and western blot in HT29 (colorectal adenocarcinoma) and A427 (lung carcinoma) cell lines. The in vitro growth inhibition activity of Debio 0123 was defined in a broad number of human cancer cell lines after 72h using a proliferation monolayer assay. Debio 0123 in vivo anti-tumoral activity was assessed in an A427 subcutaneous xenograft model in athymic nude mice. Debio 0123 pharmacodynamic effects were also evaluated after oral dosing in surrogate tissues of mice, rats and monkeys by immunohistochemistry. Results: Debio 0123 is a highly selective ATP-competitive Wee1 inhibitor with an IC50 in the low nanomolar range. Debio 0123 inhibited Cdk1 (Cdc2) phosphorylation at Y15, a direct substrate of Wee1 in cells. Debio 0123 also induced dose- and time-dependent increased mitosis and unrepaired DNA damage shown by increased phosphorylation of histone H3 and γH2AX foci formation. In vitro activity was further studied in a large panel of cancer cell lines. Debio 0123 demonstrated submicromolar cytotoxic activity on multiple cell lines from various histotypes. In vivo, Debio 0123 was shown to inhibit phosphorylation of Cdk1 in tissues of multiple species and induction of DNA damage in a xenograft model. When administered orally once daily for 28 consecutive days, Debio 0123 induced dose-dependent anti-tumor activity and was well tolerated at all doses tested. At 30 mg/kg, treatment with Debio 0123 resulted in tumor regression. Conclusion: Altogether these results demonstrate that Debio 0123 is a highly selective and potent Wee1 inhibitor able to prevent Cdk1 phosphorylation in multiple species and to induce apoptosis through accumulation of unrepaired DNA damage both in vitro and in vivo that result in tumor regression. The advancement of Debio 0123 into clinical studies may provide improved therapeutic outcomes for patients with cancer. Citation Format: Colin O'Dowd, Gerald Gavory, Frank Burkamp, Adam Treder, Caroline Boyd, Tim Harrison, Frederic Massière, Astrid Glück, Christophe Chardonnens, Andrea Zaffalon, Stefania Rigotti, Robert Mader, Grégoire Vuagniaux, Anne Vaslin Chessex. Antitumor activity of the novel oral highly selective Wee1 inhibitor Debio 0123 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4423.

Deregulated expression of the MET receptor tyrosine kinase has been reported in up to 50% of patients with hepatocellular carcinoma, the most abundant form of liver cancers, and is associated with decreased survival. Consequently, MET is considered as a molecular target in this malignancy, whose progression is highly dependent on extensive angiogenesis. Here we studied the impact of MET small molecule inhibitors on angiogenesis-associated parameters and growth of xenograft liver models consisting of cells expressing MET-mutated variants M1268T and Y1248H, which exhibit constitutive kinase activity. We demonstrate that MET mutations expression is associated with significantly increased production of vascular endothelial growth factor, which is blocked by MET targeting only in cells expressing the M1268T inhibitor-sensitive but not in the Y1248H inhibitor-resistant variant. Decrease in vascular endothelial growth factor production is also associated with reduction of tyrosine phopshorylation of the vascular endothelial growth factor receptor 2 expressed on primary liver sinusoidal endothelial cells and with inhibition of vessel formation. Furthermore, MET inhibition demonstrated an efficient anti-tumor activity and considerable reduction in microvessel density only against the M1268T-derived intrahepatic tumors. Collectively, our data support the role of targeting METassociated angiogenesis as a major biological determinant for liver tumor growth control.