Lovastatin inhibits EGFR dimerization and AKT activation in squamous cell carcinoma cells: potential regulation by targeting rho proteins

Abstract

We recently showed the ability of lovastatin to inhibit the function of the epidermal growth factor receptor (EGFR) and its downstream signaling of the phosphatidylinositol-3 kinase/ AKT pathway. Combining lovastatin with gefitinib, a potent EGFR inhibitor, induced synergistic cytotoxicity in various tumor-derived cell lines. In this study, lovastatin treatment was found to inhibit ligand-induced EGFR dimerization in squamous cell carcinoma cells and its activation of AKT and its downstream targets 4E-binding protein 1 and S6 kinase 1. This inhibition was associated with global protein translational inhibition shown by a decrease in RNA associated polysome fractions. The effects of lovastatin on EGFR function were reversed by the addition of geranylgeranyl pyrophosphate, which functions as a protein membrane anchor. Lovastatin treatment induced actin cytoskeletal disorganization and the expression of geranylgeranylated rho family proteins that regulate the actin cytoskeleton, including rhoA. Lovastatin-induced rhoA was inactive as EGF stimulation failed to activate rhoA and inhibition of the rho-associated kinase, a target and mediator of rhoA function, with Y-27632 also showed inhibitory effects on EGFR dimerization. The ability of lovastatin to inhibit EGFR dimerization is a novel exploitable mechanism regulating this therapeutically relevant target. To explore the potential clinical significance of this combination, we evaluated the effect of statin on the overall survival (OS) and disease-specific survival (DSS) of patients with advanced nonsmall-cell lung cancer enrolled in the NCIC Clinical Trials Group phase III clinical trials BR21 (EGFR tyrosine kinase inhibitor erlotinib versus placebo) and BR18 (carboplatin and paclitaxel with or without the metalloproteinase inhibitor BMS275291). In BR18, use of statin did not affect OS or DSS. In BR21, patients showed a trend for improvement in OS (HR: 0.69, P ¼ 0.098) and DSS (HR: 0.62, P ¼ 0.048), but there was no statin  treatment interaction effect (P ¼ 0.34 and P ¼ 0.51 for OS and DSS, respectively).

A Randomized Phase II Study of Gefitinib Plus Simvastatin Versus Gefitinib Alone in Previously Treated Patients with Advanced Non–Small Cell Lung Cancer

“…Furthermore, they retrospectively evaluated the effect of statin on the OS and disease-specific survival (DSS) of NSCLC patients enrolled in the NCIC Clinical Trials Group phase III clinical trial BR21 (erlotinib vs. placebo). Although it was not statistically significant, erlotinib-treated patients with statin use showed a trend toward improved OS and DSS compared with patients without statin use (22). In our study, patients with wild-type EGFR nonadenocarcinomas treated with GS showed higher response rates and longer PFS compared with G. Although the number of these patients was small, these clinical observations may support the preclinical evidence of the effective EGFR-inhibitory activity of statins in wild-type EGFR non-adenocarcinoma tumors.…”

“…The impact of statins on EGFR function and signaling and in vivo activity against tumor cells has generated interest in studying statins as a potential EGFRtargeted therapeutic intervention. Some in vitro studies have reported that the combination of gefitinib and lovastatin has synergistic cytotoxicity and enhances EGFR inhibition in squamous cell head and neck carcinoma, NSCLC, and colon carcinoma cell lines (20)(21)(22). Interestingly, not all of the studied cell lines possess EGFR mutations, which confer increased sensitivity to gefitinib.…”

Monensin Inhibits Epidermal Growth Factor Receptor Trafficking and Activation: Synergistic Cytotoxicity in Combination with EGFR Inhibitors

“…The synergistic effects of lovastatin in combination with EGFR-TKIs that we previously reported were due to its ability to inhibit EGFR activity (30) and to induce the integrated stress response; particularly, the ATF3 that regulates the apoptosis induction of this pathway (35,36). We first evaluated the effect of monensin treatment alone and in combination with erlotinib on ligand-induced EGFR activation and its downstream signaling pathways by Western blot analysis.…”

“…Our previous studies demonstrated that lovastatininduced inhibition of EGFR activity results from its ability to inhibit ligand-induced receptor trafficking and dimerization (30). Monensin is a recognized inhibitor of intracellular trafficking, including the ability to inhibit trafficking of the EGFR (37,38), thus, may share a common mechanism with lovastatin.…”

“…We then demonstrated the potential of lovastatin to induce synergistic cytotoxicity in combination with EGFR-TKIs (29). The mechanism of action revolves around the ability of lovastatin to target the activity of EGFR and other RTKs enhancing the cytotoxicity of EGFR-TKIs in HNSCC cells (30,31). These studies eventually led to a phase I clinical trial of rosuvastatin and erlotinib at our Institute that showed disease stabilization, although the high dose of statins used had undesirable muscle pathologies in a significant number of patients (ClinicalTrials.gov Identifier: NCT00966472), suggesting an alternative approach to improve cancer targeting while minimizing the side effects of the treatment regimen.…”