RESUMO
BACKGROUND: Glioblastoma (GBM) is the most common and aggressive primary brain tumor. Prognosis remains poor despite multimodal therapy. Developing alternative treatments is essential. Drugs targeting kinases within the phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) effectors of receptor tyrosine kinase (RTK) signaling represent promising candidates. METHODS: We previously developed a non-germline genetically engineered mouse model of GBM in which PI3K and MAPK are activated via Pten deletion and KrasG12D in immortalized astrocytes. Using this model, we examined the influence of drug potency on target inhibition, alternate pathway activation, efficacy, and synergism of single agent and combination therapy with inhibitors of these 2 pathways. Efficacy was then examined in GBM patient-derived xenografts (PDX) in vitro and in vivo. RESULTS: PI3K and mitogen-activated protein kinase kinase (MEK) inhibitor potency was directly associated with target inhibition, alternate RTK effector activation, and efficacy in mutant murine astrocytes in vitro. The kinomes of GBM PDX and tumor samples were heterogeneous, with a subset of the latter harboring MAPK hyperactivation. Dual PI3K/MEK inhibitor treatment overcame alternate effector activation, was synergistic in vitro, and was more effective than single agent therapy in subcutaneous murine allografts. However, efficacy in orthotopic allografts was minimal. This was likely due to dose-limiting toxicity and incomplete target inhibition. CONCLUSION: Drug potency influences PI3K/MEK inhibitor-induced target inhibition, adaptive kinome reprogramming, efficacy, and synergy. Our findings suggest that combination therapies with highly potent, brain-penetrant kinase inhibitors will be required to improve patient outcomes.
Assuntos
Neoplasias Encefálicas/tratamento farmacológico , Resistencia a Medicamentos Antineoplásicos , Glioblastoma/tratamento farmacológico , Proteínas Quinases Ativadas por Mitógeno/antagonistas & inibidores , Inibidores de Fosfoinositídeo-3 Quinase , Inibidores de Proteínas Quinases/farmacologia , Animais , Apoptose/efeitos dos fármacos , Neoplasias Encefálicas/metabolismo , Neoplasias Encefálicas/patologia , Proliferação de Células/efeitos dos fármacos , Sinergismo Farmacológico , Glioblastoma/metabolismo , Glioblastoma/patologia , Humanos , Camundongos , Fosforilação , Transdução de Sinais/efeitos dos fármacos , Células Tumorais Cultivadas , Ensaios Antitumorais Modelo de XenoenxertoAssuntos
Antineoplásicos/farmacologia , Duplicação Gênica , Leucemia/genética , Metiltransferases/antagonistas & inibidores , Proteína de Leucina Linfoide-Mieloide/genética , Sequências de Repetição em Tandem , Apoptose/efeitos dos fármacos , Apoptose/genética , Linhagem Celular Tumoral , Proliferação de Células/efeitos dos fármacos , Sobrevivência Celular/efeitos dos fármacos , Sobrevivência Celular/genética , Resistencia a Medicamentos Antineoplásicos/genética , Inibidores Enzimáticos/farmacologia , Histona-Lisina N-Metiltransferase , Histonas/metabolismo , Humanos , Leucemia/metabolismo , Leucemia/patologiaRESUMO
The establishment and maintenance of centromeric heterochromatin in fission yeast require the RITS complex. Comprised of centromeric siRNAs, the chromodomain protein Chp1, Argonaute (Ago1), and Tas3, RITS couples the cellular RNAi pathway with assembly of constitutive heterochromatin. However, the mechanisms governing RITS-dependent establishment versus maintenance of centromeric heterochromatin remain unresolved. Here, we report that a mutant Tas3 protein that cannot bind Ago1 supports the maintenance of centromeric heterochromatin but cannot mediate efficient de novo establishment from cells transiently depleted for the histone H3 lysine 9 methyltransferase Clr4. In contrast, centromeric heterochromatin efficiently assembles in mutant cells transiently depleted for dicer. This mutant therefore allows ordering of the events leading to establishment of centromeric heterochromatin and places lysine 9 methylation of histone H3 upstream of dicer function.
