gms | German Medical Science

Objective: Tyrosine kinase receptor AXL (AXL) plays a role in tumor progression and therapy resistance in cancer. Targeted AXL inhibition is leading to decreased proliferation, migration and neo-vascularization of glioblastoma in vitro and in vivo. Previous studies show that AXL might play a role in chemo-resistance. With this study we want to investigate the role of AXL in therapy resistant glioma cell lines.

Methods: Human glioma cell lines U118MG and SF126 were exposed to increasing dosage of temozolomide (TMZ, 10, 50, 100, 150µM) over a period of 3-6 month to achieve chemo-resistance. Cell viability and chemo-sensitivity was measured with MTT assay. Polymerase chain reaction (qPCR), Western blot (WB) and Immunoprecipitation (IP) was performed to determine full-length AXL (FL-AXL), C-terminal AXL (CT-AXL) phosphorylation of FL-AXL and CT-AXL. Activation grade of multiple kinase receptors was detected with Proteome Profiler Human Phospho-Kinase Array.

Results: U118MG and SF126 showed increasing AXL mRNA and AXL protein expression under long-term TMZ treatment (10, 50, 100 and 150µM). Exposure of U118MG to therapeutic TMZ dosages (10 and 50 µM) resulted to an increase of AXL activation (P-AXL), whereas high TMZ dosages (100 and 150 µM) were reducing FL-AXL expression and increasing CT-AXL on protein level. AXL mRNA remained unchanged under 10, 50, 100 and 150 µM TMZ. Besides P-AXL, EGFR, PDGFR and ALK were up regulated under long-term TMZ exposure.

Conclusion: Long-term TMZ exposure is leading to chemo-resistance of glioma cells, resulting in an increasing of AXL expression and activation (P-AXL). In context of chemo-resistance AXL expression underlies mostly posttranslational modifications. Our results are indicating that AXL inhibition might be a suitable strategy to restore chemo-sensitivity in TMZ resistant glioma cells.