Abstract
Temozolomide (TMZ) is a drug of choice in glioblastoma treatment. Its therapeutic applications expand also beyond high grade gliomas. However, a significant number of recurrences and resistance to the drug is observed. The key factor in each chemotherapy is to achieve the therapeutic doses of a drug at the pathologic site. Nonetheless, the rate of temozolomide penetration from blood to cerebrospinal fluid is only 20–30%, and even smaller into brain intestinum. That makes a challenge for the therapeutic regimens to obtain effective drug concentrations with minimal toxicity and minor side effects. The aim of our research was to explore a novel epigenetic mechanism of temozolomide action in therapeutic conditions. We analyzed the epigenetic effects of TMZ influence on different glioblastoma cell lines in therapeutically achieved TMZ concentrations through total changes of the level of 5-methylcytosine in DNA, the main epigenetic marker. That was done with classical approach of radioactive nucleotide post-labelling and separation on thin-layer chromatography. In the range of therapeutically achieved temozolomide concentrations we observed total DNA hypomethylation. The significant hypermethylating effect was visible after reaching TMZ concentrations of 10–50 μM (depending on the cell line). Longer exposure time promoted DNA hypomethylation. The demethylated state of the glioblastoma cell lines was overcome by repeated TMZ applications, where dose-dependent increase in DNA 5-methylcytosine contents was observed. Those effects were not seen in non-cancerous cell line. The increase of DNA methylation resulting in global gene silencing and consecutive down regulation of gene expression after TMZ treatment may explain better glioblastoma patients’ survival.
Highlights
The therapeutic potential of temozolomide (TMZ) in the treatment of primary and recurrent glioblastoma (GBM) has been proven [1,2]
We analyzed changes in 5-methylcytosine contents in DNA of three types of human glioblastoma cell lines (T98G, U138, U118), and one human keratinocyte cell line (HaCaT) after treatment with 0.5–100 μM of TMZ in the time range between 3 hrs and 7 days in different treatment regimens. These TMZ concentrations were chosen to cover the possible concentration of TMZ in the brain during chemotherapy (0.6±0.3μg/ml, corresponding to 3 ±1.5 μM) [19,21,22,23], and perform the observation after reaching the peak concentration in the brain (2.0±0.8 hrs) [23], as well as standard chemotherapy course time [1]
Analyzing the time factor in glioblastoma cell lines one can clearly see DNA demethylation in all glioblastoma cell lines increased with prolonging time, and evident extreme at 48 hrs
Summary
The therapeutic potential of temozolomide (TMZ) in the treatment of primary and recurrent glioblastoma (GBM) has been proven [1,2]. Its therapeutic applications expand beyond high grade gliomas [3,4,5]. TMZ is most effective in glioblastomas with hypermethylated promotor of the O6-methylguanine-DNA methyltransferase (MGMT) [1,6,7,8]. Temozolomide effects in therapeutic conditions questions about its efficacy, patient selection, outcome, and prognosis still remain, and therapy failures are observed in the vast majority of glioblastoma patients. The changing of dosing regimens didn’t fulfill the expectations to increase the treatment effectivity [9]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
