Pharmacological inhibition of glioblastoma cell proliferation, migration and invasion

Abstract

Glioblastoma multiforme is the most aggressive and malignant primary brain tumor, characterized by rapid growth,extensive infiltration to neighboring normal brain parenchyma,and angiogenesis. Patients with glioblastoma have poor prognosis since the whole tumor is barely completely removed. Thus,identification of novel molecules or more effective drugs targeting glioblastoma migration and invasion is urgently needed.The phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway plays a pivotal role in the development and survival of many cancers including glioblastoma. Selective inhibitors against class IA PI3K catalytic isoforms (p110α, p110β and p110δ) are attractive options for glioblastoma treatment because they display less off-target effects and toxicities. Considering that the inhibition of PI3K isoforms might be compensated by other signaling pathways, and subsequently compromise their inhibitory effects, combination treatment strategies on glioblastoma cells were also investigated. Since JNK pathway is also essential to cancer cell viability and motility, and has a crosstalk with the PI3K/Akt pathway, concurrent inhibition of PI3K and JNK may exhibit synergism. Firstly, this study investigated the roles of p110α, p110β and p110δ in glioblastoma cells using their respective inhibitors PIK-75, TGX-221 and CAL-101. Combination effects of p110 isoforms and JNK inhibition on glioblastoma cell proliferation, migration and invasion were then evaluated. Results showed that p110α, p110β and p110δ have distinct roles in the pathological processes in glioblastoma. PIK-75 was sufficient to suppress glioblastoma cell viability, migration and invasion,whereas TGX-221 only reduced migration, and CAL-101 just moderately inhibited proliferation and migration. Compared with CAL-101, siRNA-induced knockdown of PIK3CD significantly suppressed glioblastoma cell proliferation, migration and invasion without affecting Akt phosphorylation level. According to these results, a competition model of p110α, p110β and p110δ was proposed, in which p110β and p110δ may compete with p110α for RTK binding sites. Furthermore, PIK-75 antagonized with JNK inhibitor SP600125, whereas TGX-221 and CAL-101 displayed synergistic inhibitory effects with SP600125 on glioblastoma cell proliferation and migration through inactivation of Akt, zyxin and FAK, leading to the blockade of lamellipodia and membrane ruffles formation. No synergistic effect on invasion was observed in all combinations. And a crosstalk model between PI3K isoforms and JNK was also proposed based on the competition model. Myricetin is a natural flavonoid that exhibits potent anti-oxidative, anti-inflammatory, anti-diabetic and anti-cancer activities. It targets Akt, MEK1, MKK4, JAK1, RSK2 and Fyn and inhibits their activation in an ATP-competitive or -noncompetitive manner. These suggest that myricetin may be a safe and potent therapeutic drug for glioblastoma treatment. However, the role of myricetin in the regulation of glioblastoma cell viability and motility is not fully clarified. This study showed that myricetin was sufficient to suppress glioblastoma cell proliferation, whereas it displayed lower cytotoxicity to normal astrocytes. It also significantly inhibited migration and invasion capacities of glioblastoma cells by targeting class IA PI3K catalytic isoforms and JNK. However, Myricetin was not able to sensitize glioblastoma cells to low concentrations of temozolomide. Nevertheless, it is still a promising therapeutic approach for treating glioblastoma multiforme. In summary, combined inhibition of p110β/p110δ and JNK, as well as myricetin can suppress proliferation and motility of glioblastoma cells, indicating that they may be attractive options for glioblastoma treatment.