title: The effects of tumor treating fields and temozolomide in MGMT expressing and non-expressing patient-derived glioblastoma cells.
abstract: A recent Phase 3 study of newly diagnosed glioblastoma (GBM) demonstrated the addition of tumor treating fields (TTFields) to temozolomide (TMZ) after combined radiation/TMZ significantly increased survival and progression free survival. Preliminary data suggested benefit with both methylated and unmethylated O-6-methylguanine-DNA methyl-transferase (MGMT) promoter status. To date, however, there have been no studies to address the potential interactions of TTFields and TMZ. Thus, the effects of TTFields and TMZ were studied in vitro using patient-derived GBM stem-like cells (GSCs) including MGMT expressing (TMZ resistant: 12.1 and 22GSC) and non-MGMT expressing (TMZ sensitive: 33 and 114GSC) lines. Dose-response curves were constructed using cell proliferation and sphere-forming assays. Results demonstrated a ⩾10-fold increase in TMZ resistance of MGMT-expressing (12.1GSCs: IC50=160μM; 22GSCs: IC50=44μM) compared to MGMT non-expressing (33GSCs: IC50=1.5μM; 114GSCs: IC50=5.2μM) lines. TTFields inhibited 12.1 GSC proliferation at all tested doses (50-500kHz) with an optimal frequency of 200kHz. At 200kHz, TTFields inhibited proliferation and tumor sphere formation of both MGMT GSC subtypes at comparable levels (12.1GSC: 74±2.9% and 38±3.2%, respectively; 22GSC: 61±11% and 38±2.6%, respectively; 33GSC: 56±9.5% and 60±7.1%, respectively; 114 GSC: 79±3.5% and 41±4.3%, respectively). In combination, TTFields (200kHz) and TMZ showed an additive anti-neoplastic effect with equal efficacy for TTFields in both cell types (i.e., ± MGMT expression) with no effect on TMZ resistance. This is the first demonstration of the effects of TTFields on cancer stem cells. The expansion of such studies may have clinical implications.
authors.affiliation: Department of Neurological Surgery, University of Wisconsin School of Medicine and Public Health (UWSMPH), Madison, WI, United States.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Clark
authors.affiliation: Department of Neurological Surgery, University of Wisconsin School of Medicine and Public Health (UWSMPH), Madison, WI, United States.
authors.forename: Jordan T
authors.initials: JT
authors.lastname: Gaal
authors.affiliation: Department of Neurological Surgery, University of Wisconsin School of Medicine and Public Health (UWSMPH), Madison, WI, United States.
authors.forename: Joslyn K
authors.initials: JK
authors.lastname: Strebe
authors.affiliation: University of Wisconsin Carbone Cancer Center, UWSMPH, United States.
authors.forename: Cheri A
authors.initials: CA
authors.lastname: Pasch
authors.affiliation: University of Wisconsin Carbone Cancer Center, UWSMPH, United States; Division of Hematology and Oncology, Department of Medicine, UWSMPH, United States; McArdle Laboratory for Cancer Research, Department of Oncology, UWSMPH, United States; William S Middleton Memorial Veterans Hospital, Madison, WI, United States.
authors.forename: Dustin A
authors.initials: DA
authors.lastname: Deming
authors.affiliation: Department of Neurological Surgery, University of Wisconsin School of Medicine and Public Health (UWSMPH), Madison, WI, United States; University of Wisconsin Carbone Cancer Center, UWSMPH, United States; Department of Human Oncology, UWSMPH, United States.
authors.forename: John S
authors.initials: JS
authors.lastname: Kuo
authors.affiliation: University of Wisconsin Carbone Cancer Center, UWSMPH, United States; Division of Hematology and Oncology, Department of Medicine, UWSMPH, United States; William S Middleton Memorial Veterans Hospital, Madison, WI, United States; Department of Neurology, UWSMPH, United States; Department of Human Oncology, UWSMPH, United States. Electronic address: hirobins@wisc.edu.
authors.forename: H Ian
authors.initials: HI
authors.lastname: Robins
mesh_terms: D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects / Q000528:radiation effects; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D002478:Cells, Cultured; D015254:DNA Modification Methylases / Q000235:genetics / Q000378:metabolism*; D045643:DNA Repair Enzymes / Q000235:genetics / Q000378:metabolism*; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004574:Electromagnetic Fields; D005909:Glioblastoma / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D014411:Neoplastic Stem Cells / Q000187:drug effects / Q000528:radiation effects; D009474:Neurons / Q000187:drug effects / Q000528:radiation effects; D000077204:Temozolomide; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D018906:Antineoplastic Agents, Alkylating; D025521:Tumor Suppressor Proteins; D003606:Dacarbazine; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D045643:DNA Repair Enzymes; D000077204:Temozolomide
keywords: Cancer stem cells; Glioblastoma; MGMT methylation; Temozolomide; Tumor treating fields