pd-184352 and Glioblastoma

The present studies were initiated to determine whether inhibitors of MEK1/2 or SRC signaling, respectively, enhance CHK1 inhibitor lethality in primary human glioblastoma cells. Multiple MEK1/2 inhibitors (CI-1040 (PD184352); AZD6244 (ARRY-142886)) interacted with multiple CHK1 inhibitors (UCN-01, AZD7762) to kill multiple primary human glioma cell isolates that have a diverse set of genetic alterations typically found in the disease. Inhibition of SRC family proteins also enhanced CHK1 inhibitor lethality. Combined treatment of glioma cells with (MEK1/2 + CHK1) inhibitors enhanced radiosensitivity. Combined (MEK1/2 + CHK1) inhibitor treatment led to dephosphorylation of ERK1/2 and S6 ribosomal protein, whereas the phosphorylation of JNK and p38 was increased. MEK1/2 + CHK1 inhibitor-stimulated cell death was associated with the cleavage of pro-caspases 3 and 7 as well as the caspase substrate (PARP). We also observed activation of pro-apoptotic BCL-2 effector proteins BAK and BAX and reduced levels of pro-survival BCL-2 family protein BCL-XL. Overexpression of BCL-XL alleviated but did not completely abolish MEK1/2 + CHK1 inhibitor cytotoxicity in GBM cells. These findings argue that multiple inhibitors of the SRC-MEK pathway have the potential to interact with multiple CHK1 inhibitors to kill glioma cells.

Topics: Antineoplastic Agents; Antineoplastic Combined Chemotherapy Protocols; bcl-2 Homologous Antagonist-Killer Protein; bcl-2-Associated X Protein; bcl-X Protein; Benzamides; Benzimidazoles; Checkpoint Kinase 1; Glioblastoma; Humans; MAP Kinase Kinase 1; MAP Kinase Kinase 2; MAP Kinase Kinase 4; Medulloblastoma; Phosphorylation; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerases; Protein Kinase Inhibitors; Protein Kinases; Radiation-Sensitizing Agents; src-Family Kinases; Staurosporine; Tumor Cells, Cultured

The Ras/Raf/MEK/extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin (mTOR) signaling pathways are aberrantly activated in many tumors, including highly proliferative glioblastomas, but how they are wired with the cell cycle remains imperfectly understood. Inhibitors of MEK/ERK and mTOR pathways are tested as anticancer agents. They are generally considered to induce a G(1) cell cycle arrest through down-regulation of D-type cyclins and up-regulation of p27(kip1). Here, we examined the effect of targeting mTOR by rapamycin and/or MEK by PD184352 in human glioblastoma cell lines. In combination, these drugs cooperatively and potently inhibited the G(1)-S transition and retinoblastoma protein phosphorylation. Their cooperation could not be explained by their partial and differential inhibitory effects on cyclin D1 or D3 but instead by their synergistic inhibition of the activating T172 phosphorylation of cyclin-dependent kinase (CDK) 4. This appeared independent of p27 and unrelated to weak modulations of the CDK-activating kinase activity. The T172 phosphorylation of CDK4 thus appears as a crucial node integrating the activity of both MEK/ERK and mTOR pathways. Combined inhibition of both pathways should be considered as a promising strategy for treatment of tumors harboring a deregulated CDK4 activity.

Topics: Adaptor Proteins, Signal Transducing; Benzamides; Cell Line, Tumor; Cell Proliferation; Cyclin-Dependent Kinase 4; DNA Replication; Drug Combinations; Drug Evaluation, Preclinical; Glioblastoma; Humans; MAP Kinase Kinase 1; MAP Kinase Kinase 2; Mechanistic Target of Rapamycin Complex 1; Multiprotein Complexes; Phosphorylation; Protein Kinase Inhibitors; Protein Kinases; Proteins; Regulatory-Associated Protein of mTOR; Retinoblastoma Protein; Sirolimus; TOR Serine-Threonine Kinases; Transcription Factors; Tumor Cells, Cultured