Dual inhibition of EGFR at protein and activity level via combinatorial blocking of PI4KIIα as anti-tumor strategy

Abstract

Our previous studies indicate that phosphatidylinositol 4-kinase IIα can promote the growth of multi-malignant tumors via HER-2/PI3K and MAPK pathways. However, the molecular mechanisms of this pathway and its potential for clinical application remain unknown. In this study, we found that PI4KIIα could be an ideal combinatorial target for EGFR treatment via regulating EGFR degradation. Results showed that PI4KIIα knockdown reduced EGFR protein level, and the expression of PI4KIIα shows a strong correlation with EGFR in human breast cancer tissues (r = 0.77, P < 0.01). PI4KIIα knockdown greatly prolonged the effects and decreased the effective dosage of AG-1478, a specific inhibitor of EGFR. In addition, it significantly enhanced AG1478-induced inhibition of tumor cell survival and strengthened the effect of the EGFR-targeting anti-cancer drug Iressa in xenograft tumor models. Mechanistically, we found that PI4KIIα suppression increased EGFR ligand-independent degradation. Quantitative proteomic analysis by stable isotope labeling with amino acids in cell culture (SILAC) and LC-MS/MS suggested that HSP90 mediated the effect of PI4KIIα on EGFR. Furthermore, we found that combined inhibition of PI4KIIα and EGFR suppressed both PI3K/AKT and MAPK/ERK pathways, and resulted in downregulation of multiple oncogenes like PRDX2, FASN, MTA2, ultimately leading to suppression of tumor growth. Therefore, we conclude that combined inhibition of PI4KIIα and EGFR exerts a multiple anti-tumor effect. Dual inhibition of EGFR at protein and activity level via combinatorial blocking of PI4KIIα presents a novel strategy to combat EGFR-dependent tumors.Electronic supplementary materialThe online version of this article (doi:10.1007/s13238-014-0055-y) contains supplementary material, which is available to authorized users.

Phosphatidylinositol 4-kinases: Function, structure, and inhibition

“…Based on this observation Li and colleagues demonstrated that suppression of PI4K IIα significantly decreased tumor growth in mice and identified this enzyme as novel tumor growth regulator [93]. They also showed that PI4K IIα knockdown can significantly enhance the antitumor effect of EGFR inhibitors, such as tyrphostin (AG 1478) [94]. However, more conclusive and convincing studies are needed to assess the role of PI4K IIα in tumorigenesis.…”

PI-273, a Substrate-Competitive, Specific Small-Molecule Inhibitor of PI4KIIα, Inhibits the Growth of Breast Cancer Cells

“…1D and 4D), we hypothesize that the effect of PI4KIIa inhibitors on AKT activity does not result from the direct regulation of the PI(4,5)P 2 and PI(3,4,5)P 3 levels. Instead, numerous studies have indicated that PI4KIIa is important for receptor activity via trafficking regulation (13,17,58,59). Therefore, it is possible that the regulation of PI4KIIa inhibitors on AKT activity is dependent on its receptor regulation effect, but this requires further validation.…”

“…4B), indicating that PI4KIIa is essential for the effect of PI-273 on cell viability. Because our previous works (4,17) and other studies indicated that PI4KIIa can regulate the AKT signaling pathway (3), we tested the effects of our compounds on AKT signaling. As shown in Fig.…”

“…PI4KIIa knockout mice develop late-onset neurologic features that resemble human hereditary spastic paraplegia (15). Recently, an increasing number of reports have identified PI4KIIa as a potential target for breast cancer therapy (3,4,(16)(17)(18)(19). We previously reported that increased PI4KIIa expression promotes tumor growth by altering the HER2/PI3-kinase (PI3K)/ERK signaling cascades (4) and that dual inhibition of EGFR and PI4KIIa represents a novel strategy to combat EGFR-dependent tumors (17).…”

Puzzle out the regulation mechanism of PI4KIIα activity

“…Future studies could be focused on the following directions: (i) Discovery of specific inhibitors based on the ADP binding pocket of PI4KII PI4KII has been proved as an oncoprotein and suppression of its expression level inhibits tumor growth [3]. Recently it was found that dual inhibition of EGFR at the protein and activity level via combinatorial blocking of PI4KII had a marked anti-tumor effect [4]. Thus PI4KII is undoubtedly an effective anti-tumor target.…”