Antitumour efficacy of MEK inhibitors in human lung cancer cells and their derivatives with acquired resistance to different tyrosine kinase inhibitors

Chemosensitization of non-small cell lung cancer to sorafenib via non-hydroxamate s-triazinedione-based MMP-9/10 inhibitors

Non-small cell lung cancer (NSCLC) continues to be a leading cause of cancer death. Its fatality is associated with angiogenesis and metastasis. While VEGFR inhibitors are expected to be the central pillar for halting lung cancer, several clinical reports declared their subpar activities as monotherapy. These results directed combination studies of VEGFR inhibitors, especially sorafenib (Nexavar®), with various chemotherapeutic agents. Matrix metalloproteinase (MMP) inhibitors are seldom utilized in such combinations despite the expected complementary therapeutic outcome. This could be attributed to the clinical unsuitability of MMP inhibitors from the hydroxamate family. Herein, we report new non-hydroxamate s-triazinedione-based inhibitors of MMP-9 (6b; IC50 = 0.112 μM), and MMP-10 (6e; IC50 = 0.076 μM) surpassing the hydroxamate inhibitor NNGH for chemosensitization of NSCLC to sorafenib. MMPs inhibition profiling of the hits revealed MMP-9 over -2 and MMP-10 over -13 selectivity. 6b and 6e were potent (IC50 = 0.139 and 0.136 µM), safe (SI up to 6.77) and superior to sorafenib (IC50 = 0.506 µM, SI = 6.27) against A549 cells. When combined with sorafenib, the studied MMP inhibitors enhanced its cytotoxic efficacy up to 26 folds as confirmed by CI and DRI values for 6b (CI = 0.160 and DRI = 22.175) and 6e (CI = 0.096 and DRI = 29.060). 6b and 6e exerted anti-invasive activities in A549 cells as single agents (22.66 and 39.67 %) and in sorafenib combinations (29.96 and 91.83 %) compared to untreated control. Both compounds downregulated VEGF in A549 cells by approximately 70 % when combined with sorafenib, highlighting enhanced anti-angiogenic activities. Collectively, combinations of 6b and 6e with sorafenib demonstrated synergistic NSCLC cytotoxicity with pronounced anti-invasive and anti-angiogenic activities introducing a promising start point for preclinical studies.

HIF-1 Inhibitor YC-1 Reverses the Acquired Resistance of EGFR-Mutant HCC827 Cell Line with MET Amplification to Gefitinib

Background

Acquired resistance occurred in the majority of nonsmall cell lung cancer (NSCLC) patients receiving epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) therapy, and this may be related to the activation of the HIF-1 pathway. Therefore, we examined the influence of the hypoxia-inducible factor-1 (HIF-1) pathway inhibition on the sensitivity of HCC827 gefitinib-resistant (HCC827 GR) cells with MET amplification to gefitinib.

Methods

We established HCC827 GR cell line with MET amplification and set four groups with different treatment. An MTT assay, a colony formation analysis, and a wound healing assay were performed to determine the sensitivity change of HCC827 GR cells after different treatments. HIF-1α, p-EGFR, and p-Met levels were detected with western blot. Correlations among HIF-1α, p-EGFR, and p-Met levels of HCC827 GR cells with different treatments were analyzed with Pearson's correlation analysis.

Results

HIF-1 inhibitor YC-1 enhanced the sensitivity of HCC827 GR cells to gefitinib. p-Met level was correlated with HIF-1α level, while there was no correlation between p-Met level and p-EGFR level.

Conclusion

HIF-1 inhibitor YC-1 is able to reverse the acquired resistance of HCC827 GR to gefitinib, and the regulation of the HIF-1 pathway on MET may be one of the mechanisms.

High expression of hypoxia inducible factor 1α related with acquired resistant to EGFR tyrosine kinase inhibitors in NSCLC

The acquired resistance of the first generation epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) is a main factor leading to poor prognosis of non-small cell lung cancer (NSCLC), so we researched whether the high expression of hypoxia-inducible factor-1α (HIF-1α) in EGFR-TKIs sensitive NSCLC tissue tends to induce the acquired resistance. We detected the HIF-1α in normal lung tissue, EGFR-TKIs sensitive NSCLC tissue, the first generation EGFR-TKIs acquired resistant NSCLC tissue and acquired EGFR T790M mutation NSCLC tissue with the method of immunohistochemistry. Then, we compared the expression of HIF-1α in these tissues, and evaluate the effect of HIF-1α expression to the occurrence of acquired resistance. The expression of HIF-1α was much higher in the EGFR-TKIs sensitive NSCLC tissue than that in normal lung tissue. HIF-1α level became higher after the occurrence acquired resistance. There was negative correlation between HIF-1α level before receiving treatment and the time of acquired resistance occurring as well as the acquired EGFR T790M mutation occurring. As the treatment going on, EGFR-TKIs sensitivity rate of low HIF-1α level group was much higher than that of high level group. The high expression of HIF-1α related with the acquired resistance of the first generation EGFR-TKIs, and HIF-1α can be a biomarker to predict the early occurrence of acquired resistance.

Antitumor activity of dual blockade of PD-L1 and MEK in NSCLC patients derived three-dimensional spheroid cultures

BACKGROUND

Anti-PD-1/PD-L1 drugs are effective as monotherapy in a proportion of NSCLC patients and there is a strong rationale for combining them with targeted therapy. Inhibition of MAPK pathway may have pleiotropic effects on the microenvironment. This work investigates the efficacy of combining MEK and PD-L1 inhibition in pre-clinical and ex-vivo NSCLC models.

METHODS

We studied the effects of MEK inhibitors (MEK-I) on PD-L1 and MCH-I protein expression and cytokine production in vitro in NSCLC cell lines and in PBMCs from healthy donors and NSCLC patients, the efficacy of combining MEK-I with anti-PD-L1 antibody in ex-vivo human spheroid cultures obtained from fresh biopsies from NSCLC patients in terms of cell growth arrest, cytokine production and T-cell activation by flow cytometry.

RESULTS

MEK-I modulates in-vitro the immune micro-environment through a transcriptionally decrease of PD-L1 expression, enhance of MHC-I expression on tumor cells, increase of the production of several cytokines, like IFNγ, IL-6, IL-1β and TNFα. These effects trigger a more permissive anti-tumor immune reaction, recruiting immune cells to the tumor sites. We confirmed these data on ex-vivo human spheroids, showing a synergism of MEK and PD-L1 inhibition as result of both direct cancer cell toxicity of MEK-I and its immune-stimulatory effect on cytokine secretion profile of cancer cells and PBMCs with the induction of the ones that sustain an immune-reactive and inflammatory micro-environment.

CONCLUSIONS

Our work shows the biological rationale for combining immunotherapy with MEK-I in a reproducible ex-vivo 3D-culture model, useful to predict sensitivity of patients to such therapies.

Hypoxia-inducible factor-1 signaling pathway influences the sensitivity of HCC827 cells to gefitinib

The majority of patients with non-small cell lung cancer (NSCLC) with activating epidermal growth factor receptor (EGFR) mutations inevitably progress in stage despite an initial substantial and rapid response to EGFR-tyrosine kinase inhibitors (EGFR-TKIs). Previous research indicates that hypoxia may be associated with resistance to EGFR-TKIs in EGFR mutation-positive NSCLC. Therefore, the present study regulated the activity of hypoxia-inducible factor-1 (HIF-1) signaling pathway to observe if it is able to alter the sensitivity of lung cancer cells to gefitinib. The present study selected 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (YC-1) and dimethyloxalylglycine (DMOG) as a HIF-1 signaling pathway inhibitor and activator, respectively, on HCC827 cells. Cells were incubated with different treatments for different durations: A blank control, DMOG, gefitinib, or DMOG and gefitinib combined, for 36 and 48 h; and then a blank control, YC-1, gefitinib, or YC-1 and gefitinib combined, for 16 and 28 h. A western blot analysis assay was performed to evaluate the protein expression levels of HIF-1α and phosphorylated hepatocyte growth factor receptor (p-MET), an MTT assay was used to determine cell proliferation, a colony formation assay was used to investigate the colony-forming ability and a wound healing assay was used to test the cell migration ability. Additionally, Pearson's correlation analysis was used to evaluate the correlation between p-Met and HIF-1α expression levels. Finally, it was identified that gefitinib and DMOG combined notably improve the growth and cell migration ability of HCC827 cells, compared with gefitinib alone. When gefitinib and YC-1 were combined, the inhibiting effect on the growth and cell migration ability of HCC827 cells was substantially enhanced, compared with the control cells. Pearson's correlation analysis revealed that the p-Met expression level had a strong positive correlation with HIF-1α expression levels. Thus, it was concluded that the HIF-1 signaling pathway influences the sensitivity of HCC827 cells to gefitinib. The positive correlation between p-Met and HIF-1α expression levels may be the underlying mechanism of the HIF-1 signaling pathway influencing the sensitivity of HCC827 cells to gefitinib.

LXR ligands induce apoptosis of EGFR-TKI-resistant human lung cancer cells in vitro by inhibiting Akt-NF-κB activation

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) are efficient in treating patients with non-small cell lung cancer (NSCLC) harboring EGFR activating mutations. Unfortunately, nearly all patients ultimately acquire resistance to EGFR-TKI treatment. Liver X receptors (LXRs) can regulate tumor growth in various cancer cell lines. The present study indicated that LXR agonist combined with gefitinib weakened Akt-nuclear factor (NF)-κB activation and inhibited the expression levels of apoptosis-related proteins in vitro. By contrast, LXR ligands alone exhibited no significant effect on gefitinib-resistant lung cells. In conclusion, the study provided evidence for the combination treatment of acquired TKI resistance in NSCLC.

IGF1R depletion facilitates MET-amplification as mechanism of acquired resistance to erlotinib in HCC827 NSCLC cells

EGFR-mutated non-small cell lung cancer patients experience relapse within 1-2 years of treatment with EGFR-inhibitors, such as erlotinib. Multiple resistance mechanisms have been identified including secondary EGFR-mutations, MET-amplification, and epithelial-mesenchymal transition (EMT). Previous studies have indicated a role of Insulin-like growth factor 1 receptor (IGF1R) in acquired resistance to EGFR-directed drugs as well as in EMT. In the present study, we have investigated the involvement of IGF1R in acquired high-dose erlotinib resistance in the EGFR-mutated lung adenocarcinoma cell line HCC827. We observed that IGF1R was upregulated in the immediate response to erlotinib and hyperactivated in erlotinib resistant HCC827 cells. Resistant cells additionally acquired features of EMT, whereas MET-amplification and secondary EGFR-mutations were absent. Using CRISPR/Cas9, we generated a HCC827(IGFR1-/-) cell line and subsequently investigated resistance development in response to high-dose erlotinib. Interestingly, HCC827(IGFR1-/-) cells were now observed to specifically amplify the MET gene. Additionally, we observed a reduced level of mesenchymal markers in HCC827(IGFR1-/-) indicating an intrinsic enhanced epithelial signature compared to HCC827 cells. In conclusion, our data show that IGF1R have an important role in defining selected resistance mechanisms in response to high doses of erlotinib.

Efficacy of continuous EGFR-inhibition and role of Hedgehog in EGFR acquired resistance in human lung cancer cells with activating mutation of EGFR

Purpose

The aim of this work was to investigate the efficacy of sequential treatment with first-, second- and third-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors and the mechanisms of acquired resistance occurring during the sequential use of these inhibitors.

Experimental design

We developed an in vivo model of acquired resistance to EGFR-inhibitors by treating nude mice xenografted with HCC827, a human non-small-cell lung cancer (NSCLC) cell line harboring EGFR activating mutation, with a sequence of first-generation EGFR tyrosine kinase inhibitors (EGFR-TKIs) (erlotinib and gefitinib), of second-generation EGFR-TKI (afatinib) plus/minus the anti-EGFR monoclonal antibody cetuximab, and of third-generation EGFR-TKI (osimertinib).

Results

HCC827-derived xenografts and with acquired resistance to EGFR-inhibitors were sensitive to the sequential use of first-, second- and third-generation EGFR-TKIs. Continuous EGFR inhibition of first-generation resistant tumors by sequential treatment with afatinib plus/minus cetuximab, followed by osimertinib, represented an effective therapeutic strategy in this model. Whereas T790M resistance mutation was not detected, a major mechanism of acquired resistance was the activation of components of the Hedgehog (Hh) pathway. This phenomenon was accompanied by epithelial-to-mesenchymal transition. Cell lines established in vitro from gefitinib-, or afatinib- or osimertinib-resistant tumors showed metastatic properties and maintained EGFR-TKIs resistance in vitro, that was reverted by the combined blockade of Hh, with the selective SMO inhibitor sonidegib, and EGFR.

Conclusions

EGFR-mutant NSCLC can benefit from continuous treatment with EGFR-inhibitors, indepenently from mechanisms of resistance. In a complex and heterogenous scenario, Hh showed an important role in mediating resistance to EGFR-inhibitors through the induction of mesenchymal properties.

Activation of Focal Adhesion Kinase and Src Mediates Acquired Sorafenib Resistance in A549 Human Lung Adenocarcinoma Xenografts

Despite encouraging clinical results with sorafenib monotherapy in patients with KRAS-mutant non-small-cell lung cancer (NSCLC), the overall survival benefit of this drug is limited by the inevitable development of acquired resistance. The exact mechanism underlying acquired sorafenib resistance in KRAS-mutant NSCLC is unclear. In this study, the mechanism of acquired sorafenib resistance was explored using a biologically relevant xenograft model, which was established by using the A549 human lung adenocarcinoma cell line and an in vivo-derived, sorafenib-resistant A549 subline (A549/SRFres). Results from the initial study demonstrated that sorafenib treatment significantly decreased E-cadherin (P < 0.05) levels but significantly increased matrix metallopeptidase 9 (MMP9) levels (P < 0.01) in A549/SRFres tumors, whereas expression levels of phospho-protein kinase B (AKT), phospho-focal adhesion kinase (FAK), and phospho-Src were elevated in sorafenib-treated A549 and A549/SRFres tumors. We next examined whether concomitant dasatinib treatment could overcome acquired sorafenib resistance by blocking the FAK/Src escape route that mediates resistance. Despite the observed in vitro synergy between sorafenib and dasatinib, the in vivo antitumor effect of half-dose sorafenib-dasatinib combination therapy was inferior to that of the full-dose sorafenib treatment. Although the sorafenib-dasatinib combination effectively inhibited Src and AKT phosphorylation, it did not block the Y576/577-FAK phosphorylation, nor did it decrease vimentin protein expression; unexpectedly, it increased Y397-FAK phosphorylation and MMP9 protein expression in tumors. These results suggest that acquired sorafenib resistance in KRAS-mutant A549 xenografts involves the compensatory activation of FAK and Src, and Src inhibition alone is insufficient to diminish sorafenib-promoted epithelial-mesenchymal transition process and invasive potentials in tumors.

The Challenges of Modeling Drug Resistance to Antiangiogenic Therapy

Drug resistance remains an ongoing challenge for the majority of patients treated with inhibitors of the vascular endothelial growth factor (VEGF) pathway, a key regulator of tumor angiogenesis. Preclinical models have played a significant role in identifying multiple complex mechanisms of antiangiogenic treatment failure. Yet questions remain about the optimal methodology to study resistance that may assist in making clinically relevant choices about alternative or combination treatment strategies. The origins of antiangiogenic treatment failure may stem from the tumor vasculature, the tumor itself, or both together, and preclinical methods that define resistance are diverse and rarely compared. We performed a literature search of the preclinical methodologies used to examine resistance to VEGF pathway inhibitors and identified 109 papers from more than 400 that use treatment failure as the starting point for mechanistic study. We found that definitions of resistance are broad and inconsistent, involve only a small number of reagents, and derive mostly from in vitro and in vivo methodologies that often do not represent clinically relevant disease stages or progression. Together, this literature analysis highlights the challenges of studying inhibitors of the tumor microenvironment in the preclinical setting and the need for improved methodology to assist in qualifying (and quantifying) treatment failure to identify mechanisms that will help predict alternative strategies in patients.

Activation of an AKT/FOXM1/STMN1 pathway drives resistance to tyrosine kinase inhibitors in lung cancer

Background:

Tyrosine kinase inhibitors (TKIs) have demonstrated clinical benefits in the treatment of several tumour types. However, the emergence of TKI resistance restricts the therapeutic effect. This study uses non-small cell lung cancer (NSCLC) to explore the mechanisms contributing to TKI resistance in tumours.

Methods:

Biological phenotypes and RNA microarray expression data were analysed in NSCLC cells with and without TKI pretreatment. Specific inhibitors and siRNAs were used to validate the direct involvement of an AKT/FOXM1/STMN1 pathway in TKI resistance. Patients’ tissues were analysed to explore the clinical importance of FOXM1 and STMN1.

Results:

In vitro and in vivo studies showed that TKIs induced the enrichment of cancer stem cells (CSC), promoted epithelial to mesenchymal transition (EMT), and conferred multidrug resistance on NSCLC cells in a cell type- and TKI class-dependent manner. Mechanistically, TKIs activated an AKT/FOXM1/STMN1 pathway. The crucial role of this pathway in TKI-induced enrichment of CSC and drug resistance was verified by silencing FOXM1 and STMN1 or blocking the AKT pathway. Additionally, overexpression of STMN1 was associated with upregulation of FOXM1 in advanced NSCLC patients, and STMN1/FOXM1 upregulation predicted a poor outcome.

Conclusions:

Our findings elucidate an additional common mechanism for TKI resistance and provide a promising therapeutic target for reversing TKI resistance in NSCLC.

Therapeutic efficacy of SYM004, a mixture of two anti-EGFR antibodies in human colorectal cancer with acquired resistance to cetuximab and MET activation

Purpose

Cetuximab and panitumumab have an effective therapeutic response in a subset of RAS Wild-Type (WT) metastatic colorectal cancers (mCRCs). Despite molecular-driven selection, all patients do not respond to epidermal growth factor receptor (EGFR) inhibitors and the onset of secondary resistance limits their clinical benefit.

Experimental Design

We tested, in vitro and in vivo, the effect of SYM004, a 1:1 mixture of two recombinant human-mouse chimeric monoclonal antibodies (mAbs) directed against non-overlapping epitopes of the EGFR, on CRC models with acquired resistance to cetuximab.

Results

SYM004 showed a potent growth inhibitory effect in CRC cell lines with acquired resistance to cetuximab and MET activation. SYM004 treatment determined a significant induction of apoptosis and a strong inhibition of MET, AKT and MAPK phosphorilation in these resistant models. The data may further suggest SYM004 -driven induced internalization and degradation of the antibody-receptor complex, which prevents cross-interaction between EGFR and MET even in the presence of TGFα. Moreover, in vivo xenograft studies demonstrated that SYM004 has stronger antitumor activity than cetuximab in CRC models. Importantly, in the current work we observed a response to therapy in all cetuximab resistant tumors mice treated with SYM004. More importantly, four out of seven mice continue to respond to SYM004 after 30 weeks of treatment underling the prolonged effect of the drug.

Conclusion

These results suggest that the treatment with SYM004 could be a strategy to overcome acquired resistance to first generation of anti-EGFR therapies in mCRC as a result of MET activation.

Cancer resistance to therapies against the EGFR-RAS-RAF pathway: The role of MEK

The mitogen-activated protein kinases (MAPKs) mediate intracellular signals activated by a wide variety of extracellular stimuli. The activation of the RAS-RAF-MEK-MAPK cascade culminates in the regulation of gene transcription promoting cancer cell proliferation, survival, migration and angiogenesis. MEK (mitogen-activated protein kinase kinase-MAPKK) 1/2 is a transducer of the growth factor receptor-RAS-RAF-MAPK signalling cascade and plays a relevant role in development and progression of human cancers, such as colorectal cancer (CRC), non small cell lung cancer (NSCLC). Direct inhibition of MEK is a promising strategy and several inhibitors are currently under evaluation in clinical trials showing initial clinical activity in different tumours. MEK activation, by different genetic mechanisms, has been described for both intrinsic and acquired resistance to drugs targeting the EGFR (Epidermal Growth Factor Receptor)-RAS-RAF pathway in CRC, NSCLC. Combination therapies with chemotherapy and/or with molecular targeted agents are warranted and biomarkers studies are needed to identify those tumours dependent on MEK signalling.

Metformin increases antitumor activity of MEK inhibitors through GLI1 downregulation in LKB1 positive human NSCLC cancer cells

PURPOSE

Metformin, widely used as antidiabetic drug, showed antitumoral effects expecially in combination with chemotherapy. Our group recently has demonstrated that metformin and gefitinib are synergistic in LKB1-wild-type NSCLC cells. In these models, metformin as single agent induced an activation and phosphorylation of mitogen-activated-protein-kinase (MAPK) through an increased C-RAF/B-RAF heterodimerization.

EXPERIMENTAL DESIGN

Since single agent metformin enhances proliferating signals through the RAS/RAF/MAPK pathway, and several MEK inhibitors (MEK-I) demonstrated clinical efficacy in combination with other agents in NSCLC, we tested the effects of metformin plus MEK-I (selumetinib or pimasertib) on proliferation, invasiveness, migration abilities in vitro and in vivo in LKB1 positive NSCLC models harboring KRAS wild type and mutated gene.

RESULTS

The combination of metformin with MEK-I showed a strong anti-proliferative and proapoptotic effect in Calu-3, H1299, H358 and H1975 human NSCLC cell lines, independently from the KRAS mutational status. The combination reduced the metastatic behaviour of NSCLC cells, via a downregulation of GLI1 trascritional activity, thus affecting the transition from an epithelial to a mesenchymal phenotype. Metformin and MEK-Is combinations also decreased the production and activity of MMP-2 and MMP-9 by reducing the NF-jB (p65) binding to MMP-2 and MMP-9 promoters.

CONCLUSIONS

Metformin potentiates the antitumor activity of MEK-Is in human LKB1-wild-type NSCLC cell lines, independently from the KRAS mutational status, through GLI1 downregulation and by reducing the NF-jB (p65)-mediated transcription of MMP-2 and MMP-9.

Therapeutic value of EGFR inhibition in CRC and NSCLC: 15 years of clinical evidence

Epidermal growth factor receptor (EGFR) plays a key role in tumour evolution, proliferation and immune evasion, and is one of the most important targets for biological therapy, especially for non-small-cell lung cancer (NSCLC) and colorectal cancer (CRC). In the past 15 years, several EGFR antagonists have been approved for the treatment of NSCLC and metastatic CRC (mCRC). To optimise the use of anti-EGFR agents in clinical practice, various clinical and molecular biomarkers have been investigated, thus moving their indication from unselected to selected populations. Nowadays, anti-EGFR drugs represent a gold-standard therapy for metastatic NSCLC harbouring EGFR activating mutation and for RAS wild-type mCRC. Their clinical efficacy is limited by the presence of intrinsic resistance or the onset of acquired resistance. In this review, we provide an overview of the antitumour activity of EGFR inhibitors in NSCLC and CRC and of mechanisms of resistance, focusing on the development of a personalised approach through 15 years of preclinical and clinical research.

Src inhibitors act through different mechanisms in Non-Small Cell Lung Cancer models depending on EGFR and RAS mutational status

Resistance to the EGFR tyrosine kinase inhibitors (TKIs) gefitinib and erlotinib, often related to Ras or secondary EGFR mutations, is a relevant clinical issue in Non-Small Cell Lung Cancer (NSCLC). Although Src TK has been involved in such resistance, clinical development of its inhibitors has been so far limited.

To better define the molecular targets of the Src TKIs saracatinib, dasatinib and bosutinib, we used a variety of in vitro/in vivo studies.

Kinase assays supported by docking analysis demonstrated that all the compounds directly inhibit EGFR TK variants. However, in live cells only saracatinib efficiently reduced EGFR activation, while dasatinib was the most effective agent in inhibiting Src TK. Consistently, a pronounced anti-proliferative effect was achieved with saracatinib, in EGFR mutant cells, or with dasatinib, in wt EGFR/Ras mutant cells, poorly dependent on EGFR and erlotinib-resistant. We then identified the most effective drug combinations to overcome resistance to EGFR inhibitors, both in vitro and in nude mice: in T790M EGFR erlotinib-resistant cells, saracatinib with the anti-EGFR mAb cetuximab; in Ras mutant erlotinib-resistant models, dasatinib with the MEK inhibitor selumetinib.

Src inhibitors may act with different mechanisms in NSCLCs, depending on EGFR/Ras mutational profile, and may be integrated with EGFR or MEK inhibitors for different cohorts of NSCLCs.

The role of epithelial to mesenchymal transition in resistance to epidermal growth factor receptor tyrosine kinase inhibitors in non-small cell lung cancer

Inhibition of the epidermal growth factor receptor (EGFR) is an important strategy when treating non-small cell lung cancer (NSCLC) patients. However, intrinsic resistance or development of resistance during the course of treatment constitutes a major challenge. The knowledge on EGFR-directed tyrosine kinase inhibitors (TKIs) and their biological effect keeps increasing. Within the group of patients with EGFR mutations some benefit to a much higher degree than others, and for patients lacking EGFR mutations a subset experience an effect. Up to 70% of patients with EGFR mutations and 10-20% of patients without EGFR mutations initially respond to the EGFR-TKI erlotinib, but there is a severe absence of good prognostic markers. Despite initial effect, all patients acquire resistance to EGFR-TKIs. Multiple mechanisms have implications in resistance development, but much is still to be explored. Epithelial to mesenchymal transition (EMT) is a transcriptionally regulated phenotypic shift rendering cells more invasive and migratory. Within the EMT process lays a need for external or internal stimuli to give rise to changes in central signaling pathways. Expression of mesenchymal markers correlates to a bad prognosis and an inferior response to EGFR-TKIs in NSCLC due to the contribution to a resistant phenotype. A deeper understanding of the role of EMT in NSCLC and especially in EGFR-TKI resistance-development constitute one opportunity to improve the benefit of TKI treatment for the individual patient. Many scientific studies have linked the EMT process to EGFR-TKI resistance in NSCLC and our aim is to review the role of EMT in both intrinsic and acquired resistance to EGFR-TKIs.

Targeting the MEK signaling pathway in non-small cell lung cancer (NSCLC) patients with RAS aberrations

With the advancement in understanding the biology of non-small cell lung cancer (NSCLC), therapies focused on novel molecular pathways have come to the forefront of NSCLC treatment. This review focuses on the preclinical and clinical aspects underlying the targeting of RAS aberrations in NSCLC with special focus on MEK inhibitors which work by inhibiting the principal downstream mediator of RAS aberrations with a view on how to optimize outcomes with these agents. Preclinical evidence of the activity of MEK inhibitors in KRAS-mutant NSCLC has pushed forward the clinical development of these agents (namely selumetinib and trametinib) in KRAS-mutant NSCLC particularly in combination with other agents. A number of randomized studies have been launched to confirm the activity of these agents and to establish their position in the treatment armamentarium of NSCLC.

MicroRNA-122 confers sorafenib resistance to hepatocellular carcinoma cells by targeting IGF-1R to regulate RAS/RAF/ERK signaling pathways

Sorafenib is the first-line treatment for advanced hepatocellular carcinoma (HCC), but the clinical response to sorafenib is seriously limited by drug resistance. In this study, we investigated the molecular mechanisms of sorafenib resistance in HCC cells. Our miRNA microarray data indicate that liver-specific miR-122 expression was significantly reduced in sorafenib-resistant cells. Overexpression of miR-122 made drug-tolerant cells sensitive to sorafenib and induced apoptosis. Insulin-like growth factor 1 receptor (IGF-1R) was validated as a target of miR-122 and was repressed by this miRNA. miR-122-induced apoptosis was repressed by the IGF-1R activator IGFI or IGFII. Conversely, the IGF-1R inhibitor PPP or NVP-AEW541 in combination with sorafenib significantly induced cell apoptosis and disrupted tolerance to drugs in vitro. These results indicated that activation of IGF-1R by ectopic down-regulation of miR-122 counteracted the effects of sorafenib-induced apoptosis, thus conferring sorafenib resistance. Further study revealed that activation of IGF-1R by miR-122 down-regulation contributed to activation of RAS/RAF/ERK signaling, which was associated with drug resistance. Our data imply that an intimate correlation between miR-122 and IGF-1R abnormal expression is a critical determinant of sorafenib tolerance.

Targeting the KRAS variant for treatment of non-small cell lung cancer: potential therapeutic applications

Lung cancer is the leading cause of cancer deaths worldwide, with non-small cell lung cancer (NSCLC) accounting for 80% of all lung cancers. Kirsten rat sarcoma viral oncogene homolog (KRAS) is one of the deadliest cancer-related proteins and plays a pivotal role in the most aggressive and lethal human cancers, including lung adenocarcinoma where it represents one of the most frequently mutated oncogene. Although therapeutic progresses have made an impact over the last decade, median survival for patients with advanced lung cancer remains disappointing, with a 5-year worldwide survival rate of <15%. For more than 20 years it has been recognized that constitutively active signaling downstream of KRAS is a fundamental driver of lung tumorigenesis. However, years of pursuit have failed to yield a drug that can safely curb KRAS activity; up to now no approved therapies exist for KRAS-mutant NSCLC. The aim of this review is to discuss the current knowledge of KRAS-mutated NSCLC, touching upon KRAS clinical relevance as a prognostic and predictive biomarker, with an emphasis on novel therapeutic approaches for the treatment of KRAS-variant NSCLC.

SMO Gene Amplification and Activation of the Hedgehog Pathway as Novel Mechanisms of Resistance to Anti-Epidermal Growth Factor Receptor Drugs in Human Lung Cancer

PURPOSE

Resistance to tyrosine kinase inhibitors (TKI) of EGF receptor (EGFR) is often related to activation of other signaling pathways and evolution through a mesenchymal phenotype.

EXPERIMENTAL DESIGN

Because the Hedgehog (Hh) pathway has emerged as an important mediator of epithelial-to-mesenchymal transition (EMT), we studied the activation of Hh signaling in models of EGFR-TKIs intrinsic or acquired resistance from both EGFR-mutated and wild-type (WT) non-small cell lung cancer (NSCLC) cell lines.

RESULTS

Activation of the Hh pathway was found in both models of EGFR-mutated and EGFR-WT NSCLC cell line resistant to EGFR-TKIs. In EGFR-mutated HCC827-GR cells, we found SMO (the Hh receptor) gene amplification, MET activation, and the functional interaction of these two signaling pathways. In HCC827-GR cells, inhibition of SMO or downregulation of GLI1 (the most important Hh-induced transcription factor) expression in combination with MET inhibition exerted significant antitumor activity.In EGFR-WT NSCLC cell lines resistant to EGFR inhibitors, the combined inhibition of SMO and EGFR exerted a strong antiproliferative activity with a complete inhibition of PI3K/Akt and MAPK phosphorylation. In addition, the inhibition of SMO by the use of LDE225 sensitizes EGFR-WT NSCLC cells to standard chemotherapy.

CONCLUSIONS

This result supports the role of the Hh pathway in mediating resistance to anti-EGFR-TKIs through the induction of EMT and suggests new opportunities to design new treatment strategies in lung cancer.

Tumor heterogeneity: evolution through space and time in EGFR mutant non small cell lung cancer patients

NSCLC patients with mutations in epidermal growth factor receptor (EGFR) gene have dramatic responses with the EGFR tyrosine kinase inhibitors (TKI) in the majority of patients. However, all patients will eventually present progression of disease because of both primary and acquired resistance to EGFR TKI. In the recent years several studies have identified mechanisms involved in primary and secondary resistance to EGFR TKI treatment that can also be potential therapeutic strategies, although up to 30% of cases of acquired resistance to EGFR TKI are still unexplained. In this review we describe the mechanisms of resistance to EGFR TKIs in NSCLC patients that have been discovered and potential therapeutic strategies to overcome EGFR TKI resistance. Additionally we highlight the importance of performing additional biopsies not only at time of acquired resistance to EGFR TKI but also immediately after initiation of therapy to discover the remaining unknown mechanisms of acquired resistance to EGFR TKI as well as the underlying molecular basis of the heterogeneity in response to EGFR TKI.

Targeting of MEK in lung cancer therapeutics

The MAP-kinase pathway, consisting of the kinases RAS, RAF, MEK, and ERK, is crucial for cell proliferation, inhibition of apoptosis, and migration of cells. Direct inhibition of RAS is not yet possible, whereas inhibition of RAF is already established in malignant melanoma and under investigation in non-small-cell lung cancer (NSCLC). Due to their structure and function, the MEK proteins are attractive targets for cancer therapy and are also under investigation in NSCLC. We discuss strategies of targeting the RAS-RAF-MEK-ERK pathway with emphasis on MEK inhibition, either alone or in combination with other targets or conventional chemotherapy.

Follistatin is a novel biomarker for lung adenocarcinoma in humans

Background

Follistatin (FST), a single chain glycoprotein, is originally isolated from follicular fluid of ovary. Previous studies have revealed that serum FST served as a biomarker for pregnancy and ovarian mucinous tumor. However, whether FST can serve as a biomarker for diagnosis in lung adenocarcinoma of humans remains unclear.

Methods and Results

The study population consisted of 80 patients with lung adenocarcinoma, 40 patients with ovarian adenocarcinoma and 80 healthy subjects. Serum FST levels in patients and healthy subjects were measured using ELISA. The results showed that the positive ratio of serum FST levels was 51.3% (41/80), which was comparable to the sensitivity of FST in 40 patients with ovarian adenocarcinoma (60%, 24/40) using the 95th confidence interval for the healthy subject group as the cut-off value. FST expressions in lung adenocarcinoma were examined by immunohistochemical staining, we found that lung adenocarcinoma could produce FST and there was positive correlation between the level of FST expression and the differential degree of lung adenocarcinoma. Furthermore, the results showed that primary cultured lung adenocarcinoma cells could secrete FST, while cells derived from non-tumor lung tissues almost did not produce FST. In addition, the results of CCK8 assay and flow cytometry showed that using anti-FST monoclonal antibody to neutralize endogenous FST significantly augmented activin A-induced lung adenocarcinoma cells apoptosis.

Conclusions

These data indicate that lung adenocarcinoma cells can secret FST into serum, which may be beneficial to the survival of adenocarcinoma cells by neutralizing activin A action. Thus, FST can serve as a promising biomarker for diagnosis of lung adenocarcinoma and a useful biotherapy target for lung adenocarcinoma.

Blockade of EGFR and MEK intercepts heterogeneous mechanisms of acquired resistance to anti-EGFR therapies in colorectal cancer

Colorectal cancers (CRCs) that are sensitive to the anti-epidermal growth factor receptor (EGFR) antibodies cetuximab or panitumumab almost always develop resistance within several months of initiating therapy. We report the emergence of polyclonal KRAS, NRAS, and BRAF mutations in CRC cells with acquired resistance to EGFR blockade. Regardless of the genetic alterations, resistant cells consistently displayed mitogen-activated protein kinase kinase (MEK) and extracellular signal-regulated kinase (ERK) activation, which persisted after EGFR blockade. Inhibition of MEK1/2 alone failed to impair the growth of resistant cells in vitro and in vivo. An RNA interference screen demonstrated that suppression of EGFR, together with silencing of MEK1/2, was required to hamper the proliferation of resistant cells. Indeed, concomitant pharmacological blockade of MEK and EGFR induced prolonged ERK inhibition and severely impaired the growth of resistant tumor cells. Heterogeneous and concomitant mutations in KRAS and NRAS were also detected in plasma samples from patients who developed resistance to anti-EGFR antibodies. A mouse xenotransplant from a CRC patient who responded and subsequently relapsed upon EGFR therapy showed exquisite sensitivity to combinatorial treatment with MEK and EGFR inhibitors. Collectively, these results identify genetically distinct mechanisms that mediate secondary resistance to anti-EGFR therapies, all of which reactivate ERK signaling. These observations provide a rational strategy to overcome the multifaceted clonal heterogeneity that emerges when tumors are treated with targeted agents. We propose that MEK inhibitors, in combination with cetuximab or panitumumab, should be tested in CRC patients who become refractory to anti-EGFR therapies.

Primary and acquired resistance of colorectal cancer cells to anti-EGFR antibodies converge on MEK/ERK pathway activation and can be overcome by combined MEK/EGFR inhibition

PURPOSE

The EGFR-independent activation of the RAS/RAF/MEK/MAPK pathway is one of the resistance mechanisms to cetuximab.

EXPERIMENTAL DESIGN

We have evaluated, in vitro and in vivo, the effects of BAY 86-9766, a selective MEK1/2 inhibitor, in a panel of human colorectal cancer cell lines with primary or acquired resistance to cetuximab.

RESULTS

Among the colorectal cancer cell lines, five with a KRAS mutation (LOVO, HCT116, HCT15, SW620, and SW480) and one with a BRAF mutation (HT29) were resistant to the antiproliferative effects of cetuximab, whereas two cells (GEO and SW48) were highly sensitive. Treatment with BAY 86-9766 determined dose-dependent growth inhibition in all cancer cells, including two human colorectal cancer cells with acquired resistance to cetuximab (GEO-CR and SW48-CR), with the exception of HCT15 cells. Combined treatment with cetuximab and BAY 86-9766 induced a synergistic antiproliferative and apoptotic effects with blockade in the MAPK and AKT pathway in cells with either primary or acquired resistance to cetuximab. The synergistic antiproliferative effects were confirmed using other two selective MEK1/2 inhibitors, selumetinib and pimasertib, in combination with cetuximab. Moreover, inhibition of MEK expression by siRNA restored cetuximab sensitivity in resistant cells. In nude mice bearing established human HCT15, HCT116, SW48-CR, and GEO-CR xenografts, the combined treatment with cetuximab and BAY 86-9766 caused significant tumor growth inhibition and increased mice survival.

CONCLUSION

These results suggest that activation of MEK is involved in both primary and acquired resistance to cetuximab and the inhibition of EGFR and MEK could be a strategy for overcoming anti-EGFR resistance in patients with colorectal cancer.

Type III or allosteric kinase inhibitors for the treatment of non-small cell lung cancer

INTRODUCTION

In recent times, there has been much interest in the development of pharmacological kinase inhibitors that treat NSCLC. Furthermore, treatment options have been guided by the development of a wide panel of synthetic small molecule kinase inhibitors. Most of the molecules developed belong to the type I class of inhibitors that target the ATP-binding site in its active conformation. The high sequence similarity in the ATP-binding site among members of the kinase families often results in low selectivity and additional toxicities. Also, second mutations in the ATP-binding site, such as threonine to methionine at position 790, have been described as a mechanism of resistance to ATP-competitive kinase inhibitors. For these reasons, alternative drug development approaches targeting sites other than the ATP cleft are being pursued. The class III or allosteric inhibitors, which bind outside the ATP-binding site, have been shown to negatively modulate kinase activity.

AREAS COVERED

In this review, the authors discuss the most well-characterised allosteric inhibitors that have reached clinical development in NSCLC.

EXPERT OPINION

Great progress has made in developing inhibitors with entirely new modes of action. That being said, it is important to highlight that despite their apparent simplicity, biochemical assays will remain at the core of drug discovery activities to better explore these new opportunities.

Management of EGFR-mutant non-small-cell lung cancer patients after first-line reversible EGF receptor-tyrosine kinase inhibitors

SUMMARY Lung cancers harboring mutations in the EGFR respond to EGF receptor-tyrosine kinase inhibitor, which at present represent the most appropriate treatment for EGFR mutation-positive advanced non-small-cell lung cancer. Unfortunately drug resistance invariably emerges with different known mechanisms, including the EGFR T790M mutation, MET gene amplification, EGFR amplification, mutations in the PIK3CA gene, mutations in the HER2 gene, IGF1R amplification, transformation of non-small-cell lung cancer into small-cell lung cancer and moreover epithelial-to-mesenchymal transition. Various strategies to manage secondary resistance have been explored and in this review we will analyze scientific data in support of these different strategies to assess the most adequate to use in relation to the progression disease.

Metformin in lung cancer: rationale for a combination therapy

INTRODUCTION

Metformin is a widely used antidiabetic drug, which also displays significant growth inhibitory and proapoptotic effects in several cancer models, including lung cancer, alone or in combination with chemotherapeutic drugs.

AREAS COVERED

The role of metformin as a chemopreventive drug in lung cancer is still an object of debate as epidemiological studies have shown contrasting results. More preclinical data support its role as an adjuvant drug in the treatment of lung cancer, in combination with chemotherapy or targeted molecular drugs, although the complete mechanism of action of metformin is still unclear, and potentially may exert unexpected effects with contradictory clinical implications.

EXPERT OPINION

Future perspective studies are required in nonsmall-cell lung cancer (NSCLC) patients to better investigate the effect of metformin action on the RAS/RAF/MAPK pathway and the best context in which to use metformin in combination with molecularly targeted agents.

Notch-1 contributes to epidermal growth factor receptor tyrosine kinase inhibitor acquired resistance in non-small cell lung cancer in vitro and in vivo

Acquired resistance to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) occurs in non-small cell lung cancer (NSCLC) patients who initially respond to TKI treatment but whose cancer then progresses. Recent studies have shown that Notch signal is associated with drug resistance. However, the exact mechanism of Notch during acquisition of resistance to EGFR-TKI in human lung cancer remains unclear. In the present study, we showed that the expression of Notch-1 was highly upregulated in EGFR-TKI acquired resistant lung cancer cells. More importantly, Notch-1 contributed to the acquisition of the epithelial-mesenchymal transition (EMT) phenotype, which was critically associated with acquired resistance to EGFR-TKI. Silencing of Notch-1 using siRNA resulted in mesenchymal-epithelial transition (MET), which was associated with impaired invasion and anchorage-independent growth of lung cancer and resensitisation to gefitinib in acquired resistant NSCLC cells. Finally, gefitinib treatment of Balb/c nu/nu with acquired resistant lung cancer xenografts in combination with Notch inhibitor N-[N-(3,5-difluorophenacetyl)-L-alanyl]-(S)-phenylglycine t-butyl ester (DAPT) resulted in effective tumour growth retardation, with decreased proliferative activity and increased apoptotic activity. Collectively, these data suggest that Notch-1 might play a novel role in acquired resistance to gefitinib, which could be reversed by inhibiting Notch-1.

Antitumor activity of pimasertib, a selective MEK 1/2 inhibitor, in combination with PI3K/mTOR inhibitors or with multi-targeted kinase inhibitors in pimasertib-resistant human lung and colorectal cancer cells

The RAS/RAF/MEK/MAPK and the PTEN/PI3K/AKT/mTOR pathways are key regulators of proliferation and survival in human cancer cells. Selective inhibitors of different transducer molecules in these pathways have been developed as molecular targeted anti-cancer therapies. The in vitro and in vivo anti-tumor activity of pimasertib, a selective MEK 1/2 inhibitor, alone or in combination with a PI3K inhibitor (PI3Ki), a mTOR inhibitor (everolimus), or with multi-targeted kinase inhibitors (sorafenib and regorafenib), that block also BRAF and CRAF, were tested in a panel of eight human lung and colon cancer cell lines. Following pimasertib treatment, cancer cell lines were classified as pimasertib-sensitive (IC50 for cell growth inhibition of 0.001 µM) or pimasertib-resistant. Evaluation of basal gene expression profiles by microarrays identified several genes that were up-regulated in pimasertib-resistant cancer cells and that were involved in both RAS/RAF/MEK/MAPK and PTEN/PI3K/AKT/mTOR pathways. Therefore, a series of combination experiments with pimasertib and either PI3Ki, everolimus, sorafenib or regorafenib were conducted, demonstrating a synergistic effect in cell growth inhibition and induction of apoptosis with sustained blockade in MAPK- and AKT-dependent signaling pathways in pimasertib-resistant human colon carcinoma (HCT15) and lung adenocarcinoma (H1975) cells. Finally, in nude mice bearing established HCT15 and H1975 subcutaneous tumor xenografts, the combined treatment with pimasertib and BEZ235 (a dual PI3K/mTOR inhibitor) or with sorafenib caused significant tumor growth delays and increase in mice survival as compared to single agent treatment. These results suggest that dual blockade of MAPK and PI3K pathways could overcome intrinsic resistance to MEK inhibition.

Synergistic effects of metformin treatment in combination with gefitinib, a selective EGFR tyrosine kinase inhibitor, in LKB1 wild-type NSCLC cell lines

PURPOSE

EGF receptor (EGFR) tyrosine kinase inhibitors (TKI) have been found to be effective against lung cancer, but clinical resistance to these agents has developed as their usage has increased. Metformin is a widely used antidiabetic drug and also displays significant growth-inhibitory and proapoptotic effects in several cancer models, alone or in combination with chemotherapeutic drugs.

EXPERIMENTAL DESIGN

The effects of gefitinib, a selective EGFR-TKI, and metformin on a panel of non-small cell lung cancer (NSCLC) cell lines were assessed by using MTT, bromide assay, flow cytometry, anchorage-independent growth, coimmunoprecipitation, and Western blot analysis.

RESULTS

The combination of metformin with gefitinib induced a strong antiproliferative and proapoptotic effect in NSCLC cell lines that harbored wild-type LKB1 gene. Treatment with metformin as single agent, however, induced an activation and phosphorylation of mitogen-activated protein kinase (MAPK) through an increased C-RAF/B-RAF heterodimerization. The inhibition of EGFR phosphorylation and of downstream signaling by adding gefitinib to metformin treatment abrogated this phenomenon and induced a strong apoptotic effect in vitro and in vivo.

CONCLUSIONS

Metformin and gefitinib are synergistic in LKB1 wild-type NSCLC cells. However, further studies are required to investigate better the effect of metformin action on the RAS/RAF/MAPK pathway and the best context in which to use metformin in combination with molecular targeted agents.

Improving outcomes in colorectal cancer: where do we go from here?

Colorectal cancer (CRC) places a considerable burden on individuals and society in Europe, being the second most common cause of cancer-related death in the region. While earlier diagnosis and advances in treatment have considerably improved survival in recent years, further progress is needed. One of the greatest challenges associated with the treatment of CRC is the fact that current therapies for advanced disease are not curative, necessitating treatment for many years and placing a significant healthcare burden on society. To reduce the burden of CRC, care delivery must be more efficient and cost-effective. In particular, development of adequate screening programmes is needed, along with chemo-preventative strategies and newer, more active therapies. Further challenges include the lack of optimal selection of patients for adjuvant therapy, identification of the most appropriate target populations for current treatments and the optimum sequence for new molecular targeted agents. This article outlines current developments and unmet needs in CRC, and provides a detailed vision for improvements in the management of the disease. Implementation of some of these strategies will go some way to improving outcomes for patients with CRC.

Selumetinib: a promising pharmacologic approach for KRAS-mutant advanced non-small-cell lung cancer

Selumetinib is a potent and selective inhibitor of MEK1 and 2 that is currently being clinically developed for the treatment of several human malignancies. Initially administered as free-base suspension, a more convenient Hyd-sulfate capsule formulation has recently been developed. Phase I studies revealed that acneiform dermatitis was the dose-limiting toxicity of both the free-base and capsule formulation given two-times a day at the maximum tolerated doses of 100 and 75 mg, respectively, with the capsule formulation resulting into a significantly higher drug bioavailability. Importantly, as a MEK inhibitor, selumetinib could be particularly effective in tumors with a hyperactivated Ras/Raf/MEK/ERK pathway, which might be the case of KRAS-mutant non-small-cell lung cancers (NSCLCs). Accordingly, a recent randomized Phase II study evaluating docetaxel plus selumetinib or placebo in KRAS-mutant pretreated advanced NSCLC patients has demonstrated a significant improvement in terms of response rate, progression-free survival and patient-reported outcomes in favor of the combination arm. These positive results support further clinical evaluation of selumetinib in NSCLC, and confirmatory ongoing and future trials will assess its role according to KRAS-mutation status and in combination regimens with other targeted agents.

Mechanisms of acquired resistance to targeted cancer therapies

Drugs that target genomically defined vulnerabilities in human tumors have now been clinically validated as effective cancer therapies. However, the relatively rapid acquisition of resistance to such treatments that is observed in virtually all cases significantly limits their utility and remains a substantial challenge to the clinical management of advanced cancers. As molecular mechanisms of resistance have begun to be elucidated, new strategies to overcome or prevent the development of resistance have begun to emerge. In some cases, specific mutational mechanisms contribute directly to acquired drug resistance, and in other cases it appears that nonmutational and possibly epigenetic mechanisms play a significant role. This article discusses the various genetic and nongenetic mechanisms of acquired drug resistance that have been reported in the context of 'rationally targeted' drug therapies.

Long-term exposure to sorafenib of liver cancer cells induces resistance with epithelial-to-mesenchymal transition, increased invasion and risk of rebound growth

Sorafenib leads to a survival benefit in patients with advanced hepatocellular carcinoma but its use is hampered by the occurrence of drug resistance. To investigate the molecular mechanisms involved we developed five resistant human liver cell lines in which we studied morphology, gene expression and invasive potential. The cells changed their appearance, lost E-cadherin and KRT19 and showed high expression of vimentin, indicating epithelial-to-mesenchymal transition. Resistant cells showed reduced adherent growth, became more invasive and lost liver-specific gene expression. Furthermore, following withdrawal of sorafenib, the resistant cells showed rebound growth, a phenomenon also found in patients. This cell model was further used to investigate strategies for restoration of sensitivity to sorafenib.

Intrinsic resistance to selumetinib, a selective inhibitor of MEK1/2, by cAMP-dependent protein kinase A activation in human lung and colorectal cancer cells

Background:

MEK is activated in ∼40% colorectal cancer (CRC) and 20–30% non-small cell lung cancer (NSCLC). Selumetinib is a selective inhibitor of MEK1/2, which is currently in clinical development.

Methods:

We evaluated the effects of selumetinib in vitro and in vivo in CRC and NSCLC cell lines to identify cancer cell characteristics correlating with sensitivity to MEK inhibition.

Results:

Five NSCLC and six CRC cell lines were treated with selumetinib and classified according to the median inhibitory concentration (IC₅₀) values as sensitive (⩽1 μℳ) or resistant (>1 μℳ). In selumetinib-sensitive cancer cell lines, selumetinib treatment induced G1 cell-cycle arrest and apoptosis and suppression of tumour growth as xenografts in immunodeficient mice. Evaluation of intracellular effector proteins and analysis of gene mutations showed no correlation with selumetinib sensitivity. Microarray gene expression profiles revealed that the activation of cAMP-dependent protein kinase A (PKA) was associated with MEK inhibitor resistance. Combined targeting of both MEK and PKA resulted in cancer cell growth inhibition of MEK inhibitor-resistant cancer cell lines in vitro and in vivo.

Conclusion:

This study provides molecular insights to explain resistance to an MEK inhibitor in human cancer cell lines.

Acquisition of EMT phenotype in the gefitinib-resistant cells of a head and neck squamous cell carcinoma cell line through Akt/GSK-3β/snail signalling pathway

BACKGROUND

Epithelial mesenchymal transition (EMT) is known to be associated with chemoresistance as well as increased invasion/metastasis. However, the relationship between EMT and resistance to an epidermal growth factor receptor (EGFR) -targeting drug in head and neck squamous cell carcinoma (HNSCC) remains unknown. In this study, we investigated the acquisition of EMT by gefitinib in HNSCC cell line (UMSCC81B).

METHODS

We isolated fibroblastoid variant (81B-Fb) from gefitinib-resistant UMSCC81B-GR3 cells obtained after increasing the doses of gefitinib treatment in vitro and examined EMT and its underlying mechanism.

RESULT

81B-Fb cells exhibited fibroblast-like morphology, increased motility, loss of E-cadherin, acquisition of vimentin and snail expression. In 81B-Fb cells, downregulation of EGFR, which is mediated by increased ubiquitination, and activation of downstream protein kinase B (Akt), glycogen synthase kinase-beta (GSK-3β) signalling and upregulation of snail expression were observed compared with UMSCC81B cells. LY294002, but not U0126, suppressed foetal bovine serum or heregulin-β1-induced phosphorylation of Akt/GSK-3β and snail expression together with the inhibition of 81B-Fb cell motility. Furthermore, forced expression of EGFR resulted in partial restoration of gefitinib sensitivity and reversal of EMT.

CONCLUSION

These results suggest that EMT in the gefitinib-resistant cells is mediated by the downregulation of EGFR and compensatory activation of Akt/GSK-3β/snail pathway.