RESUMO
PURPOSE: Apoptotic dysregulation, redox adaptive mechanisms, and resilience to hypoxia are major causes of glioblastoma (GBM) resistance to therapy. Commonly known as crucial factors in energy metabolism, OCTN2 (SLC22A5) and its substrate L-carnitine (LC) are increasingly recognized as actors in cytoprotection. This study provides a comprehensive expression and survival analysis of the OCTN2/LC system in GBM and clarifies the system's impact on GBM progression. EXPERIMENTAL DESIGN: OCTN2 expression and LC content were measured in 121 resected human GBM specimens and 10 healthy brain samples and analyzed for prognostic significance. Depending on LC administration, the effects of hypoxic, metabolic, and cytotoxic stress on survival and migration of LN18 GBM cells were further studied in vitro. Finally, an orthotopic mouse model was employed to investigate inhibition of the OCTN2/LC system on in vivo GBM growth. RESULTS: Compared with healthy brain, OCTN2 expression was increased in primary and even more so in recurrent GBM on mRNA and protein level. High OCTN2 expression was associated with a poor overall patient survival; the unadjusted HR for death was 2.7 (95% CI, 1.47-4.91; P < 0.001). LC administration to GBM cells increased their tolerance toward cytotoxicity, whereas siRNA-mediated OCTN2 silencing led to a loss of tumor cell viability. In line herewith, OCTN2/LC inhibition by meldonium resulted in reduced tumor growth in an orthotopic GBM mouse model. CONCLUSIONS: Our data indicate a potential role of the OCTN2/LC system in GBM progression and resistance to therapy, and suggests OCTN2 as a prognostic marker in patients with primary GBM.
Assuntos
Biomarcadores Tumorais/metabolismo , Carnitina/metabolismo , Proliferação de Células , Citoproteção , Glioblastoma/mortalidade , Recidiva Local de Neoplasia/mortalidade , Membro 5 da Família 22 de Carreadores de Soluto/metabolismo , Adolescente , Adulto , Idoso , Idoso de 80 Anos ou mais , Animais , Apoptose , Biomarcadores Tumorais/genética , Estudos de Casos e Controles , Movimento Celular , Criança , Pré-Escolar , Feminino , Seguimentos , Regulação Neoplásica da Expressão Gênica , Glioblastoma/metabolismo , Glioblastoma/patologia , Glioblastoma/cirurgia , Humanos , Lactente , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Pessoa de Meia-Idade , Recidiva Local de Neoplasia/metabolismo , Recidiva Local de Neoplasia/patologia , Recidiva Local de Neoplasia/cirurgia , Prognóstico , Membro 5 da Família 22 de Carreadores de Soluto/genética , Taxa de Sobrevida , Células Tumorais Cultivadas , Ensaios Antitumorais Modelo de Xenoenxerto , Adulto JovemRESUMO
Patients with glioblastoma multiforme (GBM) are at high risk to develop a relapse despite multimodal therapy. Assumedly, glioma stem cells (GSCs) are responsible for treatment resistance of GBM. Identification of specific GSC markers may help to develop targeted therapies. Here, we performed expression analyses of stem cell (ABCG2, CD44, CD95, CD133, ELF4, Nanog, and Nestin) as well as differentiation and microglia markers (GFAP, Iba1, and Sparc) in GBM compared to nonmalignant brain. Furthermore, the role of these proteins for patient survival and their expression in LN18 stem-like neurospheres was analyzed. At mRNA level, ABCG2 and CD95 were reduced, GFAP was unchanged; all other investigated markers were increased in GBM. At protein level, CD44, ELF4, Nanog, Nestin, and Sparc were elevated in GBM, but only CD133 and Nestin were strongly associated with survival time. In addition, ABCG2 and GFAP expression was decreased in LN18 neurospheres whereas CD44, CD95, CD133, ELF4, Nanog, Nestin, and Sparc were upregulated. Altogether only CD133 and Nestin were associated with survival rates. This raises concerns regarding the suitability of the other target structures as prognostic markers, but makes both CD133 and Nestin candidates for GBM therapy. Nevertheless, a search for more specific marker proteins is urgently needed.
