ABSTRACT
BACKGROUND: Anaplastic lymphoma kinase (ALK) is expressed in ~ 60% of glioblastomas and conveys tumorigenic functions. Therefore, ALK inhibitory strategies with alectinib are conceivable for patients with glioblastoma. The aims of this preclinical study were to investigate efficacy as well as to understand and potentially overcome primary and acquired resistance mechanisms of alectinib in glioblastoma. METHODS: Efficacy of alectinib was analyzed dependent on ALK expression in different glioblastoma initiating cells and after lentiviral knockdown of ALK. Alectinib resistant cells were generated by continuous treatment with increasing alectinib doses over 3 months. M-RNA, phospho-protein and protein regulation were analyzed to decipher relevant pathways associated to treatment or resistance and specifically inhibited to evaluate rational salvage therapies. RESULTS: Alectinib reduced clonogenicity and proliferation and induced apoptosis in ALK expressing glioblastoma initiating cells, whereas cells without ALK expression or after ALK depletion via knockdown showed primary resistance against alectinib. High expression of cMyc and activation of the ERK1/2 pathway conferred resistance against alectinib in ALK expressing glioblastoma cells. Pharmacological inhibition of these pathways by cMyc inhibitor or MEK inhibitor, trametinib, overcame alectinib resistance and re-sensitized resistant cells to continued alectinib treatment. The combination of alectinib with radiotherapy demonstrated synergistic effects in inhibition of clonogenicity in non-resistant and alectinib resistant glioblastoma cells. CONCLUSION: The data offer rationales for alectinib treatment in ALK expressing glioblastoma and for the use of ALK expression status as potential biomarker for alectinib treatment. In addition, the results propose MEK inhibition or radiotherapy as reasonable salvage treatments after acquired alectinib resistance.
Subject(s)
Anaplastic Lymphoma Kinase/antagonists & inhibitors , Carbazoles/pharmacology , Drug Resistance, Neoplasm , Glioblastoma/pathology , Mitogen-Activated Protein Kinase 1/metabolism , Mitogen-Activated Protein Kinase 3/metabolism , Piperidines/pharmacology , Proto-Oncogene Proteins c-myc/metabolism , Anaplastic Lymphoma Kinase/genetics , Apoptosis , Biomarkers, Tumor/genetics , Biomarkers, Tumor/metabolism , Cell Proliferation , Gene Expression Regulation, Neoplastic , Glioblastoma/drug therapy , Glioblastoma/genetics , Glioblastoma/metabolism , Humans , Mitogen-Activated Protein Kinase 1/genetics , Mitogen-Activated Protein Kinase 3/genetics , Mutation , Protein Kinase Inhibitors/pharmacology , Proto-Oncogene Proteins c-myc/genetics , Tumor Cells, CulturedABSTRACT
Background: Glioma therapy is challenged by the diffuse and invasive growth of glioma. Lysosomal protein transmembrane 5 (LAPTM5) was identified as an invasion inhibitor by an in vivo screen for invasion-associated genes. The aim of this study was to decipher the function of LAPTM5 in glioblastoma and its interaction with the CD40 receptor which is intensively evaluated as a target in the therapy of diverse cancers including glioma. Methods: Knockdown of LAPTM5 was performed in different glioma cell lines to analyze the impact on clonogenicity, invasiveness, sensitivity to temozolomide chemotherapy, and tumorigenicity in vitro and in vivo. An expression array was used to elucidate the underlying pathways. CD40 knockdown and overexpression were induced to investigate a potential crosstalk of LAPTM5 and CD40. LAPTM5 and CD40 were correlated with the clinical outcome of glioma patients. Results: Knockdown of LAPTM5 unleashed CD40-mediated NFκB activation, resulting in enhanced invasiveness, clonogenicity, and temozolomide resistance that was overcome by NFκB inhibition. LAPTM5 expression correlated with better overall survival in glioblastoma patients depending on CD40 expression status. Conclusion: We conclude that LAPTM5 conveyed tumor suppression and temozolomide sensitation in CD40-positive glioblastoma through the inhibition of CD40-mediated NFκB activation. Hence, LAPTM5 may provide a potential biomarker for sensitivity to temozolomide in CD40-positive glioblastoma.
ABSTRACT
PURPOSE: Resistance is an obstacle of glioma therapy. Despite targeted interventions, tumors harbor primary resistance or become resistant over short course of treatment. This study examined the mouse double minute 2 (MDM2) inhibitor RG7388 together with radiotherapy and analyzed strategies to overcome acquired MDM2 inhibitor resistance in glioblastoma. EXPERIMENTAL DESIGN: Effects of RG7388 and radiotherapy were analyzed in p53 wild-type glioblastoma cell lines and glioma-initiating cells. RG7388 resistant cells were generated by increasing RG7388 doses over 3 months. Regulated pathways were investigated by microarray, qRT-PCR, and immunoblot analysis and specifically inhibited to evaluate rational salvage therapies at RG7388 resistance. Effects of RG7388 and trametinib treatment were challenged in an orthotopical mouse model with RG7388 resistant U87MG glioblastoma cells. RESULTS: MDM2 inhibition required functional p53 and showed synergistic activity with radiotherapy in first-line treatment. Long-term exposure to RG7388 induced resistance by activation of the extracellular signal-regulated kinases 1/2 (ERK1/2)-insulin growth factor binding protein 1 (IGFBP1) signaling cascade, which was specifically overcome by ERK1/2 pathway inhibition with trametinib and knockdown of IGFBP1. Combining trametinib with continued RG7388 treatment enhanced antitumor effects at RG7388 resistance in vitro and in vivo. CONCLUSIONS: These data provide a rationale for combining RG7388 and radiotherapy as first-line therapy with a specific relevance for tumors insensitive to alkylating standard chemotherapy and for the addition of trametinib to continued RG7388 treatment as salvage therapy after acquired resistance against RG7388 for clinical practice.