Kreshnik Zejnullahu

MET Amplification Leads to Gefitinib Resistance in Lung Cancer by Activating ERBB3 Signaling

The epidermal growth factor receptor (EGFR) kinase inhibitors gefitinib and erlotinib are effective treatments for lung cancers with EGFR activating mutations, but these tumors invariably develop drug resistance. Here, we describe a gefitinib-sensitive lung cancer cell line that developed resistance to gefitinib as a result of focal amplification of the MET proto-oncogene. inhibition of MET signaling in these cells restored their sensitivity to gefitinib. MET amplification was detected in 4 of 18 (22%) lung cancer specimens that had developed resistance to gefitinib or erlotinib. We find that amplification of MET causes gefitinib resistance by driving ERBB3 (HER3)–dependent activation of PI3K, a pathway thought to be specific to EGFR/ERBB family receptors. Thus, we propose that MET amplification may promote drug resistance in other ERBB-driven cancers as well.

Preexistence and Clonal Selection of MET Amplification in EGFR Mutant NSCLC

MET amplification activates ERBB3/PI3K/AKT signaling in EGFR mutant lung cancers and causes resistance to EGFR kinase inhibitors. We demonstrate that MET activation by its ligand, HGF, also induces drug resistance, but through GAB1 signaling. Using high-throughput FISH analyses in both cell lines and in patients with lung cancer, we identify subpopulations of cells with MET amplification prior to drug exposure. Surprisingly, HGF accelerates the development of MET amplification both in vitro and in vivo. EGFR kinase inhibitor resistance, due to either MET amplification or autocrine HGF production, was cured in vivo by combined EGFR and MET inhibition. These findings highlight the potential to prospectively identify treatment naive, patients with EGFR-mutant lung cancer who will benefit from initial combination therapy.

EML4-ALK fusion gene and efficacy of an ALK kinase inhibitor in lung cancer

Purpose: The EML4-ALK fusion gene has been detected in ∼7% of Japanese non-small cell lung cancers (NSCLC). We determined the frequency of EML4-ALK in Caucasian NSCLC and in NSCLC cell lines. We also determined whether TAE684, a specific ALK kinase inhibitor, would inhibit the growth of EML4-ALK-containing cell lines in vitro and in vivo. Experimental Design: We screened 305 primary NSCLC [both U.S. (n = 138) and Korean (n = 167) patients] and 83 NSCLC cell lines using reverse transcription-PCR and by exon array analyses. We evaluated the efficacy of TAE684 against NSCLC cell lines in vitro and in vivo. Results: We detected four different variants, including two novel variants, of EML4-ALK using reverse transcription-PCR in 8 of 305 tumors (3%) and 3 of 83 (3.6%) NSCLC cell lines. All EML4-ALK-containing tumors and cell lines were adenocarcinomas. EML4-ALK was detected more frequently in NSCLC patients who were never or light (<10 pack-years) cigarette smokers compared with current/former smokers (6% versus 1%; P = 0.049). TAE684 inhibited the growth of one of three (H3122) EML4-ALK-containing cell lines in vitro and in vivo, inhibited Akt phosphorylation, and caused apoptosis. In another EML4-ALK cell line, DFCI032, TAE684 was ineffective due to coactivation of epidermal growth factor receptor and ERBB2. The combination of TAE684 and CL-387,785 (epidermal growth factor receptor/ERBB2 kinase inhibitor) inhibited growth and Akt phosphorylation and led to apoptosis in the DFCI032 cell line. Conclusions:EML4-ALK is found in the minority of NSCLC. ALK kinase inhibitors alone or in combination may nevertheless be clinically effective treatments for NSCLC patients whose tumors contain EML4-ALK.

PF00299804, an Irreversible Pan-ERBB Inhibitor, Is Effective in Lung Cancer Models with EGFR and ERBB2 Mutations that Are Resistant to Gefitinib

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors gefitinib and erlotinib are effective treatments for a subset of non-small cell lung cancers. In particular, cancers with specific EGFR-activating mutations seem to be the most sensitive to these agents. However, despite their initial response, such cancers almost invariably develop resistance. In 50% of such cancers, a secondary EGFR mutation, T790M, has been identified that renders gefitinib and erlotinib ineffective inhibitors of EGFR kinase activity. Thus, there is a clinical need to develop novel EGFR inhibitors that can effectively inactivate T790M-containing EGFR proteins. In this study, we evaluate the effectiveness of a novel compound, PF00299804, an irreversible pan-ERBB inhibitor. The results from these studies show that PF00299804 is a potent inhibitor of EGFR-activating mutations as well as the EGFR T790M resistance mutation both in vitro and in vivo. Additionally, PF00299804 is a highly effective inhibitor of both the wild-type ERBB2 and the gefitinib-resistant oncogenic ERBB2 mutation identified in lung cancers. These preclinical evaluations support further clinical development of PF00299804 for cancers with mutations and/or amplifications of ERBB family members.

Allelic dilution obscures detection of a biologically significant resistance mutation in EGFR -amplified lung cancer

EGFR is frequently mutated and amplified in lung adenocarcinomas sensitive to EGFR inhibitors gefitinib and erlotinib. A secondary mutation, T790M, has been associated with acquired resistance but has not been shown to be sufficient to render EGFR mutant/amplified lung cancers resistant to EGFR inhibitors. We created a model for studying acquired resistance to gefitinib by prolonged exposure of a gefitinib-sensitive lung carcinoma cell line (H3255; EGFR mutated and amplified) to gefitinib in vitro. The resulting resistant cell line acquired a T790M mutation in a small fraction of the amplified alleles that was undetected by direct sequencing and identified only by a highly sensitive HPLC-based technique. In gefitinib-sensitive lung cancer cells with EGFR mutations and amplifications, exogenous introduction of EGFR T790M effectively conferred resistance to gefitinib and continued ErbB-3/PI3K/Akt signaling when in cis to an activating mutation. Moreover, continued activation of PI3K signaling by the PIK3CA oncogenic mutant, p110alpha E545K, was sufficient to abrogate gefitinib-induced apoptosis. These findings suggest that allelic dilution of biologically significant resistance mutations may go undetected by direct sequencing in cancers with amplified oncogenes and that restoration of PI3K activation via either a T790M mutation or other mechanisms can provide resistance to gefitinib.

Activation of ERBB2 Signaling Causes Resistance to the EGFR-Directed Therapeutic Antibody Cetuximab

Several cancers become resistant to cetuximab by activating a bypass signaling pathway and preventing cetuximab inhibition of ERK1/2-stimulated growth. Combating Resistance to an EGF Receptor Inhibitor Many promising anticancer drugs are effective only for a limited time, because the tumor cells develop resistance. Cetuximab, directed against the epidermal growth factor receptor (EGFR), is no exception, and patients with colorectal, head and neck, or non–small cell lung cancer eventually cease to respond to the drug. Yonesaka and colleagues have determined that cetuximab-resistant cancer cells—both in culture and in patients—can up-regulate signaling through the ERBB2 growth factor receptor in several ways, permanently turning on extracellular signal–regulated kinase 1/2 (ERK1/2)–mediated growth, differentiation, and survival. They further show that interference with the ERBB2 pathway restores the ability of cetuximab to control these cancers, pointing to a promising resistance-fighting approach. The authors generated clones of cetuximab-resistant non–small cell lung and colorectal cancer cell lines by exposing the cells to increasing concentration of the drug. In some of these resistant clones, the ERBB2 receptor oncogene was genetically amplified, resulting in activated ERK1/2 signaling. Down-regulation of ERBB2 with a small interfering RNA or antibody restored sensitivity. Other clones did not have amplified ERBB2 genes but did make excess heregulin, an activating ligand for the ERBB2 receptor. Heregulin depletion or ERBB2 inhibition restored cetuximab sensitivity. After replicating these studies in xenografts in mice, the authors also looked for evidence that these resistance-associated alterations pertain to human tumors. In several groups of patients with colorectal cancer, they saw decreased survival or decreased sensitivity to cetuximab in those who exhibited amplified ERBB2 gene or higher heregulin concentrations. The concordance of their cellular data with patient experience improves confidence that concomitant treatment of certain lung, head and neck, or colorectal cancers with cetuximab and an anti-ERBB2 drug may prevent or delay the development of drug resistance. These studies add to other successes for this approach, which has also been used for analysis of other molecular targeted therapies, including EGFR kinase inhibitors. Cetuximab, an antibody directed against the epidermal growth factor receptor, is an effective clinical therapy for patients with colorectal, head and neck, and non–small cell lung cancer, particularly for those with KRAS and BRAF wild-type cancers. Treatment in all patients is limited eventually by the development of acquired resistance, but little is known about the underlying mechanism. Here, we show that activation of ERBB2 signaling in cell lines, either through ERBB2 amplification or through heregulin up-regulation, leads to persistent extracellular signal–regulated kinase 1/2 signaling and consequently to cetuximab resistance. Inhibition of ERBB2 or disruption of ERBB2/ERBB3 heterodimerization restores cetuximab sensitivity in vitro and in vivo. A subset of colorectal cancer patients who exhibit either de novo or acquired resistance to cetuximab-based therapy has ERBB2 amplification or high levels of circulating heregulin. Collectively, these findings identify two distinct resistance mechanisms, both of which promote aberrant ERBB2 signaling, that mediate cetuximab resistance. Moreover, these results suggest that ERBB2 inhibitors, in combination with cetuximab, represent a rational therapeutic strategy that should be assessed in patients with cetuximab-resistant cancers.

Sensitivity of human lung adenocarcinoma cell lines to targeted inhibition of BET epigenetic signaling proteins.

Bromodomain and extra terminal domain (BET) proteins function as epigenetic signaling factors that associate with acetylated histones and facilitate transcription of target genes. Inhibitors targeting the activity of BET proteins have shown potent antiproliferative effects in hematological cancers through the suppression of c-MYC and downstream target genes. However, as the epigenetic landscape of a cell varies drastically depending on lineage, transcriptional coactivators such as BETs would be expected to have different targets in cancers derived from different cells of origin, and this may influence the activity and mechanism of action of BET inhibitors. To test this hypothesis, we treated a panel of lung adenocarcinoma (LAC) cell lines with the BET inhibitor JQ1 and found that a subset is acutely susceptible to BET inhibition. In contrast to blood tumors, we show that LAC cells are inhibited by JQ1 through a mechanism independent of c-MYC down-regulation. Through gene expression profiling, we discovered that the oncogenic transcription factor FOSL1 and its targets are suppressed by JQ1 in a dose-dependant manner. Knockdown of BRD4 also decreased FOSL1 levels, and inhibition of FOSL1 phenocopied the effects of JQ1 treatment, suggesting that loss of this transcription factor may be partly responsible for the cytotoxic effects of BET inhibition in LAC cells, although ectopic expression of FOSL1 alone did not rescue the phenotype. Together, these findings suggest that BET inhibitors may be useful in solid tumors and that cell-lineage–specific differences in transcriptional targets of BETs may influence the activity of inhibitors of these proteins in different cancer types.

Amplification of EGFR T790M causes resistance to an irreversible EGFR inhibitor

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors, gefitinib and erlotinib are effective therapies against mutant non-small cell lung cancers (NSCLCs). Treatment is limited by the development of resistance in part explained by the gain of a secondary EGFR mutation, T790M, at the gatekeeper residue. Irreversible EGFR inhibitors, including PF00299804, are effective in vitro and in vivo against EGFR mutant tumors that contain EGFR T790M and are currently under clinical development. In this study, we generate models of resistance to PF00299804, using cell lines with EGFR T790M and show that the PF00299804-resistant models develop focal amplification of EGFR that preferentially involves the T790M-containing allele. These PF00299804-resistant cell lines remain dependent on EGFR for growth as downregulation of EGFR by shRNA compromises their viability. We show that resistance to PF00299804 arises, at least in part, through selection of a pre-existing EGFR T790M-amplified clone both in vitro and using a xenograft model in vivo. Our findings show that EGFR T790M is a common resistance mechanism to both reversible, and when amplified, the irreversible EGFR kinase inhibitors further emphasizing the need to develop more potent therapies against EGFR T790M. These findings can be used to guide studies of patient tumor specimens from ongoing clinical trials of irreversible EGFR kinase inhibitors.

Resistance to Irreversible EGF Receptor Tyrosine Kinase Inhibitors through a Multistep Mechanism Involving the IGF1R Pathway

The clinical efficacy of EGF receptor (EGFR) kinase inhibitors gefitinib and erlotinib is limited by the development of drug resistance. The most common mechanism of drug resistance is the secondary EGFR T790M mutation. Strategies to overcome EGFR T790M-mediated drug resistance include the use of mutant selective EGFR inhibitors, including WZ4002, or the use of high concentrations of irreversible quinazoline EGFR inhibitors such as PF299804. In the current study, we develop drug-resistant versions of the EGFR-mutant PC9 cell line, which reproducibly develops EGFR T790M as a mechanism of drug resistance to gefitinib. Neither PF299804-resistant nor WZ4002-resistant clones of PC9 harbor EGFR T790M. Instead, they have shown activated insulin-like growth factor receptor (IGF1R) signaling as a result of loss of expression of IGFBP3 with the IGF1R inhibitor, BMS 536924, restoring EGFR inhibitor sensitivity. Intriguingly, prolonged exposure to either PF299804 or WZ4002 results in the emergence of a more drug-resistant subclone that exhibits ERK activation. A MEK inhibitor, CI-1040, partially restores sensitivity to the EGFR/IGF1R inhibitor combination. Moreover, an IGF1R or MEK inhibitor used in combination with either PF299804 or WZ4002 completely prevents the emergence of drug-resistant clones in this model system. Our studies suggest that more effective means of inhibiting EGFR T790M will prevent the emergence of this common drug resistance mechanism in EGFR-mutant non-small cell lung cancer. However, multiple drug resistance mechanisms can still emerge. Preventing the emergence of drug resistance, by targeting pathways that become activated in resistant cancers, may be a more effective clinical strategy.

Autocrine Production of Amphiregulin Predicts Sensitivity to Both Gefitinib and Cetuximab in EGFR Wild-type Cancers

Purpose: Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors, gefitinib and erlotinib, lead to significant tumor regressions in 10% to 15% of non-small cell lung cancer (NSCLC) patients with EGFR activating mutations. However, 30% to 40% of NSCLC patients, majority of whom are EGFR wild-type, develop stable disease following EGFR tyrosine kinase inhibitor therapy. EGFR-directed antibodies (cetuximab) are effective treatments for head and neck squamous cell carcinomas, which seldom contain EGFR mutations. The determinant(s) of efficacy of EGFR-targeted therapies in EGFR wild-type cancers is not well defined. Experimental Design: We examined the relationship of EGFR ligands, EGF, transforming growth factor-α,and amphiregulin and the efficacy of gefitinib and cetuximab in EGFR wild-type NSCLC (n = 10) and head and neck squamous cell carcinoma (n = 4) cell lines. We compared amphiregulin expression using immunohistochemistry in EGFR wild-type NSCLC patients (n = 24) that developed either stable or progressive disease following erlotinib or gefitinib treatment. Results: Cell lines which produced ≥20 pmol/L amphiregulin, as detected by an ELISA, were significantly more likely to be growth inhibited by both gefitinib and cetuximab than those that produced minimal or no amphiregulin. In these cell lines, both cetuximab and gefitinib led to cell cycle arrest at the G1-S boundary and was associated with preferential inhibition of extracellular signal-regulated kinase 1/2 but not Akt signaling. Amphiregulin expression was significantly higher in NSCLC patients that developed stable disease compared with those that developed disease progression following gefitinib or erlotinib treatment. Conclusions: Amphiregulin expression may help select EGFR wild-type patients who are likely to develop stable disease from EGFR-targeted therapies.