Purpose: One of the hallmarks of cancer cells is the excessive conversion of glucose to lactate under normoxic conditions, also known as the Warburg effect. Here, we tested whether the targeted inhibition of EGFR may revert this effect and reactivate mitochondrial oxidative phosphorylation in non–small cell lung cancer (NSCLC). Experimental Design: Sensitive (HCC827) and resistant (H1975 and H1993) NSCLC cells were treated with a panel of EGFR or MET inhibitors, and then tested for changes of EGFR signaling, glycolytic cascade, and mitochondrial function. Silencing of key glycolytic enzymes was then performed with targeted siRNAs. Furthermore, tumor-bearing nude mice treated with EGFR inhibitors were evaluated with 18F-FDG PET/CT and tumors were analyzed for glycolytic and mitochondrial proteins. Results: Effective inhibition of EGFR signaling in NSCLC cells induced a dramatic reduction of hexokinase II (HKII) and phospho-pyruvate kinase M2 (p-PKM2, Tyr105) levels as well as an upregulation of mitochondrial complexes subunits (OXPHOS). Accordingly, a decreased lactate secretion and increased intracellular ATP levels were also observed in response to EGFR inhibitors. Downregulation of HKII and PKM2 by targeted siRNA transfection did not cause upregulation of OXPHOS but enhanced the effects of EGFR TKIs. Conversely, selective inhibition of AKT and ERK1/2 caused OXPHOS upregulation and glycolysis inhibition, respectively. Similar findings were obtained in tumors from animals treated with appropriate EGFR inhibitors. Conclusions: Our findings indicate that EGFR inhibitors may reactivate oxidative phosphorylation of cancer cells and provide a mechanistic clue for the rational combination of agents targeting EGFR-dependent proliferation and glucose metabolism in cancer therapy. Clin Cancer Res; 21(22); 5110–20. ©2015 AACR.

Introduction: Src tyrosine kinase overactivation has been correlated with a poor response to human epidermal growth factor receptor 2 (HER2) inhibitors in breast cancer. To identify the mechanism by which Src overexpression sustains this resistance, we tested a panel of breast cancer cell lines either sensitive or resistant to lapatinib. Methods: To determine the role of Src in lapatinib resistance, we evaluated the effects of Src inhibition/silencing in vitro on survival, migration, and invasion of lapatinib-resistant cells. In vivo experiments were performed in JIMT-1 lapatinib-resistant cells orthotopically implanted in nude mice. We used artificial metastasis assays to evaluate the effect of Src inhibition on the invasiveness of lapatinib-resistant cells. Src-dependent signal transduction was investigated with Western blot and ELISA analyses. Results: Src activation was higher in lapatinib-resistant than in lapatinib-sensitive cells. The selective small-molecule Src inhibitor saracatinib combined with lapatinib synergistically inhibited the proliferation, migration, and invasion of lapatinib-resistant cells. Saracatinib combined with lapatinib significantly prolonged survival of JIMT-1-xenografted mice compared with saracatinib alone, and impaired the formation of lung metastases. Unexpectedly, in lapatinib-resistant cells, Src preferentially interacted with epidermal growth factor receptor (EGFR) rather than with HER2. Moreover, EGFR targeting and lapatinib synergistically inhibited survival, migration, and invasion of resistant cells, thereby counteracting Src-mediated resistance. These findings demonstrate that Src activation in lapatinib-resistant cells depends on EGFR-dependent rather than on HER2-dependent signaling. Conclusions: Complete pharmacologic EGFR/HER2 inhibition is required to reverse Src-dependent resistance to lapatinib in breast cancer.

Neutrophil extracellular traps (NETs), in addition to their function as a host defense mechanism, play a relevant role in thrombus formation and metastatic dissemination of cancer cells. Here we screened different cancer cell lines endogenously expressing a variety of integrins for their ability to bind to NETs. To this end, we used NETs isolated from neutrophil-like cells as a substrate for adhesion assays of HT1080, U-87 MG, H1975, DU 145, PC-3 and A-431 cells. Levels of α5, αIIb, αv, β1, β3 and β5 chains were determined by western blot analysis in all cell lines and levels of whole integrins on the plasma membrane were assessed by fluorescence-activated cell sorting (FACS) analysis. We found that high levels of α5β1, αvβ3 and αvβ5 enhance cell adhesion to NETs, whereas low expression of α5β1 prevents cell attachment to NETs. Excess of cyclic RGD peptide inhibited cell adhesion to NETs by competing with fibronectin within NETs. The maximal reduction of such adhesion was similar to that obtained by DNase 1 treatment causing DNA degradation. Our findings indicate that NETs from neutrophil-like cells may be used as a substrate for large screening of the adhesion properties of cancer cells expressing a variety of RGD-binding integrins.

Neutrophil extracellular traps (NETs), originally recognized as a host defense mechanism, were reported to promote thrombosis and metastatic dissemination of cancer cells. Here we tested the role of integrins α5β1 and ανβ3 in the adhesion of cancer cells to NETs. Neutrophil-like cells stimulated with calcium ionophore (A23187) were used as a stable source of cell-free NETs-enriched suspensions. Using NETs as an adhesion substrate, two human K562 cell lines, differentially expressing α5β1 and ανβ3 integrins, were subjected to adhesion assays in the presence or absence of DNAse 1, blocking antibodies against α5β1 or ανβ3, alone or in combination with DNAse 1, and Proteinase K. As expected DNAse 1 treatment strongly inhibited adhesion of both cell lines to NETs. An equivalent significant reduction of cell adhesion to NETs was obtained after treatment of cells with blocking antibodies against α5β1 or ανβ3 indicating that both integrins were able to mediate cell adhesion to NETs. Furthermore, the combination of DNAse 1 and anti-integrin antibody treatment almost completely blocked cell adhesion. Western blot analysis and immunoprecipitation experiments showed a dose-dependent increase of fibronectin levels in samples from stimulated neutrophil-like cells and a direct or indirect interaction of fibronectin with histone H3. Finally, co-immunolocalization studies with confocal microscopy showed that fibronectin and citrullinated histone H3 co-localize inside the web-structure of NETs. In conclusion, our study showed that α5β1 and ανβ3 integrins mediate cell adhesion to NETs by binding to their common substrate fibronectin. Therefore, in addition to mechanical trapping and aspecific adsorption of different cell types driven by DNA/histone complexes, NETs may provide specific binding sites for integrin-mediated cell adhesion of neutrophils, platelets, endothelial and cancer cells thus promoting intimate interactions among these cells.

Purpose: To test whether a novel bifunctional chimeric peptide comprising a cyclic Arg-Gly-Asp pentapeptide covalently bound to an echistatin domain can discriminate α_vβ₃ from α_vβ₅ integrin, thus allowing the in vivo selective visualization of α_vβ₃ expression by single-photon and positron emission tomography (PET) imaging.

Since many oncogenes, including BCR-ABL, may promote the acquisition and maintenance of the glycolytic phenotype, we tested whether treatment of BCR-ABL-driven human leukemia cells with imatinib, a selective BCR-ABL inhibitor, can modulate the expression of key glycolytic enzymes and mitochondrial complex subunits thus causing alterations of glucose metabolism. BCR-ABL-driven K562 and KCL-22 cells were incubated with increasing concentrations of imatinib to preliminarily test drug sensitivity. Then untreated and treated cells were analyzed for levels of BCR-ABL signaling mediators and key proteins of glycolytic cascade and oxidative phosphorylation. Effective inhibition of BCR-ABL caused a concomitant reduction of p-ERK1/2, p-AKT, phosphorylated form of STAT3 (at Tyr705 and Ser727), c-Myc and cyclin D1 along with an increase of cleaved PARP and caspase 3 at 48 h after treatment. Furthermore, a strong reduction of the hexokinase II (HKII), phosphorylated form of PKM2 (at Tyr105 and Ser37) and lactate dehydrogenase A (LDH-A) was observed in response to imatinib along with a strong upregulation of mitochondrial complexes (OXPHOS). According to these findings, a significant reduction of glucose consumption and lactate secretion along with an increase of intracellular ATP levels was observed in response to imatinib. Our findings indicate that imatinib treatment of BCR-ABL-driven human leukemia cells reactivates mitochondrial oxidative phosphorylation thus allowing potential co-targeting of BCR-ABL and OXPHOS.