Predictive value of hypoxia, proliferation and tyrosine kinase receptors for EGFR-inhibition and radiotherapy sensitivity in head and neck cancer models

BACKGROUND AND PURPOSE

EGFR-inhibitor Cetuximab (C225) improves the efficacy of radiotherapy in only a subgroup of HNSCC patients. Identification of predictive tumor characteristics is essential to improve patient selection.

MATERIAL AND METHODS

Response to C225 and/or radiotherapy was assessed with tumor growth delay assays in 4 HNSCC xenograft models with varying EGFR-expression levels. Hypoxia and proliferation were quantified with immunohistochemistry and the expression of proteins involved in C225-resistance with Western blot.

RESULTS

EGFR-expression did not predict response to C225 and/or radiotherapy. Reduction of hypoxia by C225 was only observed in SCCNij202, which was highly sensitive to C225. Proliferation changes correlated with response to C225 and C225 combined with radiotherapy, as proliferation decreased after C225 treatment in C225-sensitive SCCNij202 and after combined treatment in SCCNij185, which showed a synergistic effect to combined C225-radiotherapy. Furthermore, C225-resistant SCCNij153 tumors expressed high levels of (activated) HER3 and MET.

CONCLUSIONS

EGFR-expression is needed for C225-response, but is not sufficient to predict response to C225 with or without radiotherapy. However, basal expression of additional growth factor receptors and effects on proliferation, but not hypoxia, correlated with response to combined C225-radiotherapy treatment and are potential clinically relevant predictive biomarkers.

Yes and Lyn play a role in nuclear translocation of the epidermal growth factor receptor

The epidermal growth factor receptor (EGFR) is a central regulator of tumor progression in human cancers. Cetuximab is an anti-EGFR antibody that has been approved for use in oncology. Previously we investigated mechanisms of resistance to cetuximab using a model derived from the non-small cell lung cancer line NCI-H226. We demonstrated that cetuximab-resistant clones (Ctx(R)) had increased nuclear localization of the EGFR. This process was mediated by Src family kinases (SFKs), and nuclear EGFR had a role in resistance to cetuximab. To better understand SFK-mediated nuclear translocation of EGFR, we investigated which SFK member(s) controlled this process as well as the EGFR tyrosine residues that are involved. Analyses of mRNA and protein expression indicated upregulation of the SFK members Yes (v-Yes-1 yamaguchi sarcoma viral oncogene) and Lyn (v-yes-1 Yamaguchi sarcoma viral-related oncogene homolog) in all Ctx(R) clones. Further, immunoprecipitation analysis revealed that EGFR interacts with Yes and Lyn in Ctx(R) clones, but not in cetuximab-sensitive (Ctx(S)) parental cells. Using RNAi interference, we found that knockdown of either Yes or Lyn led to loss of EGFR translocation to the nucleus. Conversely, overexpression of Yes or Lyn in low nuclear EGFR-expressing Ctx(S) parental cells led to increased nuclear EGFR. Chromatin immunoprecipitation (ChIP) assays confirmed nuclear EGFR complexes associated with the promoter of the known EGFR target genes B-Myb and iNOS. Further, all Ctx(R) clones exhibited upregulation of B-Myb and iNOS at the mRNA and protein levels. siRNAs directed at Yes or Lyn led to decreased binding of EGFR complexes to the B-Myb and iNOS promoters based on ChIP analyses. SFKs have been shown to phosphorylate EGFR on tyrosines 845 and 1101 (Y845 and Y1101), and mutation of Y1101, but not Y845, impaired nuclear entry of the EGFR. Taken together, our findings demonstrate that Yes and Lyn phosphorylate EGFR at Y1101, which influences EGFR nuclear translocation in this model of cetuximab resistance.

Activation of multiple ERBB family receptors mediates glioblastoma cancer stem-like cell resistance to EGFR-targeted inhibition

Epidermal growth factor receptor (EGFR) signaling is strongly implicated in glioblastoma (GBM) tumorigenesis. However, molecular agents targeting EGFR have demonstrated minimal efficacy in clinical trials, suggesting the existence of GBM resistance mechanisms. GBM cells with stem-like properties (CSCs) are highly efficient at tumor initiation and exhibit therapeutic resistance. In this study, GBMCSC lines showed sphere-forming and tumor initiation capacity after EGF withdrawal from cell culture media, compared with normal neural stem cells that rapidly perished after EGF withdrawal. Compensatory activation of related ERBB family receptors (ERBB2 and ERBB3) was observed in GBM CSCs deprived of EGFR signal (EGF deprivation or cetuximab inhibition), suggesting an intrinsic GBM resistance mechanism for EGFR-targeted therapy. Dual inhibition of EGFR and ERBB2 with lapatinib significantly reduced GBM proliferation in colony formation assays compared to cetuximab-mediated EGFR-specific inhibition. Phosphorylation of downstream ERBB signaling components (AKT, ERK1/2) and GBM CSC proliferation were inhibited by lapatinib. Collectively, these findings show that GBM therapeutic resistance to EGFR inhibitors may be explained by compensatory activation of EGFR-related family members (ERBB2, ERBB3) enabling GBM CSC proliferation, and therefore simultaneous blockade of multiple ERBB family members may be required for more efficacious GBM therapy.

Activation of AKT by hypoxia: a potential target for hypoxic tumors of the head and neck

BACKGROUND

Only a minority of cancer patients benefits from the combination of EGFR-inhibition and radiotherapy in head and neck squamous cell carcinoma (HNSCC). A potential resistance mechanism is activation of EGFR and/or downstream pathways by stimuli in the microenvironment. The aim of this study was to find molecular targets induced by the microenvironment by determining the in vitro and in vivo expression of proteins of the EGFR-signaling network in 6 HNSCC lines. As hypoxia is an important microenvironmental parameter associated with poor outcome in solid tumors after radiotherapy, we investigated the relationship with hypoxia in vitro and in vivo.

METHODS

Six human HNSCC cell lines were both cultured as cell lines (in vitro) and grown as xenograft tumors (in vivo). Expression levels were determined via western blot analysis and localization of markers was assessed via immunofluorescent staining. To determine the effect of hypoxia and pAKT-inhibition on cell survival, cells were incubated at 0.5% O(2) and treated with MK-2206.

RESULTS

We observed strong in vitro-in vivo correlations for EGFR, pEGFR and HER2 (rs = 0.77, p = 0.10, rs = 0.89, p = 0.03) and rs = 0.93, p = 0.02, respectively), but not for pAKT, pERK1/2 or pSTAT3 (all r(s)<0.55 and p>0.30). In vivo, pAKT expression was present in hypoxic cells and pAKT and hypoxia were significantly correlated (rs = 0.51, p = 0.04). We confirmed in vitro that hypoxia induces activation of AKT. Further, pAKT-inhibition via MK-2206 caused a significant decrease in survival in hypoxic cells (p<0.01), but not in normoxic cells.

CONCLUSIONS

These data suggest that (p)EGFR and HER2 expression is mostly determined by intrinsic features of the tumor cell, while the activation of downstream kinases is highly influenced by the tumor microenvironment. We show that hypoxia induces activation of AKT both in vitro and in vivo, and that hypoxic cells can be specifically targeted by pAKT-inhibition. Targeting pAKT is thus a potential way to overcome therapy resistance induced by hypoxia and improve patient outcome.

Abstract 5726: Human epidermal growth factor 3 (HER3) blockade with U3-1287/AMG888 modulates radiosensitivity in the lung and head and neck carcinomas

The epidermal growth factor receptor (EGFR) family consists of four members including HER1 (EGFR), HER2 (ErbB2), HER3 (ErbB3) and HER4 (ErbB4). Collectively this family of receptor tyrosine kinases (RTKs) play critical roles in the etiology of several human cancers as well as a role in resistance to radiation therapy. In 2006, a study in head and neck squamous cell carcinoma (HNSCC) indicated that using the anti-EGFR antibody cetuximab in combination with radiation resulted in a 10% advantage of 3-year overall survival rate when compared to radiotherapy alone. This study highlighted the therapeutic utility of RTK blockade in combination with radiation. Studies investigating the role of HER3 in radiation response are limited. In the present study, we investigated whether or not HER3 blockade could enhance radiation therapy using the HER3 antibody U3-1287/AMG888. We screened a battery of cell lines from lung, HNSCC and colorectal tumor lines for HER3 expression. The results indicated that all 15 cell lines tested showed expression of HER3. In addition, U3-1287/AMG888 was able to block basal HER3 activity and radiation induced HER3 activation. Further, proliferation assays, using U3-1287/AMG888, indicated that HER3 blockade could block proliferation in SCC6, SCC1483, H226 cell lines, highlighting the importance of HER3 in these tumor cells. Clonogenic assays showed that U3-1287/AMG888 could sensitize these lines to radiation. Furthermore, γ-H2AX analyses, detected by immunofluorescence, lead to a statistically significant increase in apoptotic cells. Cell cycle analysis, 24 and 48 hours after U3-1287/AMG888 and radiation treatments resulted in a significant G1 and G2 cell cycle arrest. Annexin-V binding assays showed a significant increase in apoptosis in the U3-1287/AMG888 plus radiation group as compared to either agent alone. To determine if HER3 blockade using U3-1287/AMG888 could enhance radiation therapy in vivo we performed tumor growth delay experiments using SCC6, SCC1483 and H226 xenografts in nude mice. Mice were inoculated and treated with 1) IgG, 2) U3-1287/AMG888, 3) radiation or 4) the combination. The results of these experiments indicated that the combination of U3-1287/AMG888 and radiation had a strong impact on tumor growth in studies using single dose or fractionated dosing. Tumor analysis indicated that radiation treatment activated HER3 in vivo and U3-1287/AMG888 could abrogate this activation. Collectively our findings in vitro and in vivo suggest that U3-1287/AMG888 in combination with radiation has an impact on cell and tumor growth by impacting cell cycle progression, increasing apoptosis and increasing DNA damage. These findings suggest that HER3 may play a critical role in response to radiation therapy and blocking its activity may be of strong therapeutic benefit in human tumors.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5726. doi:1538-7445.AM2012-5726

KRAS mutant colorectal tumors: past and present

The treatment of metastatic colorectal cancer (mCRC) remains one of the largest hurdles in cancer therapeutics to date. The most advanced treatment option for mCRC patients are anti-epidermal growth factor receptor (EGFR) monoclonal antibodies (mAbs) that bind to and inhibit the activity of EGFR. While the use of anti-EGFR mABs has had great impact in the treatment of mCRC, it has now been widely accepted that mCRC tumors with a mutation in the small GTPase KRAS do not respond to these therapies. KRAS mutations allow for EGFR independent activation of various oncogenic signaling cascades. In attempts to inhibit KRAS mutant tumor growth, BRAF, MEK and farsenyltransferase inhibitors have been used, however, their clinical efficacy is still accruing in the setting of CRC. Recent data suggests that various other inhibitors, including inhibitors of Src family kinases (SFK) and hepatocyte growth factor receptor (MET), may have potential preclinical and clinical success in KRAS mutant tumors. Additionally, it is becoming increasingly clear that different KRAS missense mutations may have varied biological responses to cetuximab, suggesting that cetuximab may still be a potential therapeutic option in some KRAS mutant tumors. In this review, we highlight the importance for both improved multimodality approaches for treating KRAS mutant mCRC tumors and stratification of KRAS mutations in response to different treatment regimes in order to optimize the best possible care for mCRC patients.

Abstract A146: Targeting AKT signaling overcomes acquired resistance to cetuximab in non-small lung cancer cells

The epidermal growth factor receptor (EGFR) is a central regulator of tumor progression in human cancers. Cetuximab is an anti-EGFR antibody that has been approved by FDA for the treatment of patients with head and neck squamous cell carcinoma and metastatic colorectal cancer. However, increasing evidence suggests that the vast majority of patients do not respond to cetuximab and those who initially respond subsequently acquire resistance. To determine how tumor cells acquire resistance to cetuximab we developed models of acquired resistance using the non-small cell lung cancer line NCI-H226. During investigations into the molecular mechanisms of acquired resistance we found that cetuximab-resistant clones manifested strong activation of HER3 through transphosphorylation by the EGFR and constitutive PI(3)K/AKT activity and ultimate escape from cetuximab therapy. To determine the extent of AKT signaling in cetuximab-resistant clones, we analyzed the activation of the AKT pathway using a human AKT phospho-antibody array, which measured the activity of 137 proteins in the AKT pathway. Results showed strong activation of several key AKT substrates including GSK3β, eIF4E, S6, IKKα, IRS-1, Bad, β-catenin and Raf1 in cetuximab-resistant clones. To determine if cetuximab-resistant clones had dependence on AKT signaling we utilized RNAi technology to knockdown AKT expression. The results demonstrated that loss of AKT signaling in cetuximab-resistant clones resulted in decreased proliferative potential. To determine if AKT inhibition could be a therapeutic approach to overcome cetuximab resistance we investigated the AKT inhibitor MK-2206, a recently developed allosteric inhibitor, in this model of acquired resistance to cetuximab. We treated cetuximab-resistant clones with 2.5 μM of MK2206 and interrogated the AKT pathway using the human AKT phospho-antibody array. Results from this antibody array showed that MK-2206 inhibited multiple downstream AKT targets including GSK3β, eIF4E, S6, IKKα, IRS-1, β-catenin and Raf1. We next measured the effects of MK2206 on cellular proliferation and apoptosis. We found that cetuximab-resistant clones treated with MK-2206 showed robust inhibition of cell proliferation and increased apoptosis as compared to vehicle controls. Furthermore, the combination of cetuximab and MK-2206 resulted in further decreases in proliferation and increased apoptosis than either drug alone. Thus, MK-2206 treatment of cetuximab-resistant clones re-sensitized resistant clones to cetuximab. This combinatorial treatment resulted in decreased phospho-AKT and phospho-MAPK, highlighting the importance of these two pathways in cetuximab-resistance cells. These results indicate that dual targeting of the EGFR and AKT might produce greater impact than either drug alone. Collectively, our findings indicate that AKT activation is an important pathway in acquired resistance to cetuximab and suggest a rationale for clinical strategies that investigate combinatorial therapy directed at both the EGFR and AKT in patients with acquired resistance to cetuximab.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A146.

p53 modulates acquired resistance to EGFR inhibitors and radiation

There is presently great interest in mechanisms of acquired resistance to epidermal growth factor receptor (EGFR) inhibitors that are now being used widely in the treatment of a variety of common human cancers. To investigate these mechanisms, we established EGFR inhibitor-resistant clones from non-small cell lung cancer cells. A comparative analysis revealed that acquired resistance to EGFR inhibitors was associated consistently with the loss of p53 and cross-resistance to radiation. To examine the role of p53, we first knocked down p53 in sensitive parental cells and found a reduction in sensitivity to both EGFR inhibitors and radiation. Conversely, restoration of functional p53 in EGFR inhibitor-resistant cells was sufficient to resensitize them to EGFR inhibitors or radiation in vitro and in vivo. Further studies indicate that p53 may enhance sensitivity to EGFR inhibitors and radiation via induction of cell-cycle arrest, apoptosis, and DNA damage repair. Taken together, these findings suggest a central role of p53 in the development of acquired resistance to EGFR inhibitors and prompt consideration to apply p53 restoration strategies in future clinical trials that combine EGFR inhibitors and radiation.

The nuclear epidermal growth factor receptor signaling network and its role in cancer

The epidermal growth factor receptor (EGFR) is a member of the EGFR family of receptor tyrosine kinases (RTKs). EGFR activation via ligand binding results in signaling through various pathways ultimately resulting in cellular proliferation, survival, angiogenesis, invasion, and metastasis. Aberrant expression or activity of EGFR has been strongly linked to the etiology of several human epithelial cancers including but not limited to head and neck squamous cell carcinoma (HNSCC), non-small cell lung cancer (NSCLC), colorectal cancer (CRC), breast cancer, pancreatic cancer, and brain cancer. Thus intense efforts have been made to inhibit the activity of EGFR by designing antibodies against the ligand binding domains (cetuximab and panitumumab) or small molecules against the tyrosine kinase domain (erlotinib, gefitinib, and lapatinib). Although targeting membrane-bound EGFR has shown benefit, a new and emerging role for EGFR is now being elucidated. In this review we will summarize the current knowledge of the nuclear EGFR signaling network, including how it is trafficked to the nucleus, the functions it serves in the nucleus, and how these functions impact cancer progression, survival, and response to chemotherapeutics.

Erlotinib is a viable treatment for tumors with acquired resistance to cetuximab

The epidermal growth factor receptor (EGFR) is a ubiquitously expressed receptor tyrosine kinase (RTK) and is recognized as a key mediator of tumorigenesis in many human tumors. Currently there are five EGFR inhibitors used in oncology, two monoclonal antibodies (panitumumab, and cetuximab) and three tyrosine kinase inhibitors (erlotinib, gefitinib, and lapatinib). Both strategies of EGFR inhibition have demonstrated clinical successes, however many tumors remain non-responsive or acquire resistance during therapy. To explore potential molecular mechanisms of acquired resistance to cetuximab we previously established a series of cetuximab-resistant clones by chronically exposing the NCI-H226 NSCLC cell line to escalating doses of cetuximab. Cetuximab-resistant clones exhibited a dramatic increase in steady-state expression of EGFR, HER2, and HER3 receptors as well as increased signaling through the MAPK and AKT pathways. RNAi studies demonstrated dependence of cetuximab-resistant clones on the EGFR signaling network. These findings prompted investigation on whether or not cells with acquired resistance to cetuximab would be sensitive to the EGFR targeted TKI erlotinib. In vitro, erlotinib was able to decrease signaling through the EGFR axis, decrease cellular proliferation, and induce apoptosis. To determine if erlotinib could have therapeutic benefit in vivo, we established cetuximab-resistant NCI-H226 mouse xenografts, and subsequently treated them with erlotinib. Mice harboring cetuximab-resistant tumors treated with erlotinib exhibited either a tumor regression or growth delay as compared to vehicle controls. Analysis of the erlotinib treated tumors demonstrated a decrease in cell proliferation and increase rates of apoptosis. The work presented herein suggests that 1) cells with acquired resistance to cetuximab maintain their dependence on EGFR and 2) tumors developing resistance to cetuximab can benefit from subsequent treatment with erlotinib, providing rationale for its use in the setting of cetuximab resistance.

Molecular mechanisms of resistance to the EGFR monoclonal antibody cetuximab

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase belonging to the HER family of receptor tyrosine kinases. Receptor activation upon ligand binding leads to down stream activation of the PI3K/AKT, RAS/RAF/MEK/ERK and PLCγ/PKC pathways that influence cell proliferation, survival and the metastatic potential of tumor cells. Increased activation by gene amplification, protein overexpression or mutations of the EGFR has been identified as an etiological factor in a number of human epithelial cancers (e.g., NSCLC, CRC, glioblastoma and breast cancer). Therefore, targeting the EGFR has been intensely pursued as a cancer treatment strategy over the last two decades. To date, five EGFR inhibitors, including three small molecule tyrosine kinase inhibitors (TKIs) and two monoclonal antibodies have gained FDA approval for use in oncology. Both approaches to targeting the EGFR have shown clinical promise and the anti-EGFR antibody cetuximab is used to treat HNSCC and CRC. Despite clinical gains arising from use of cetuximab, both intrinsic resistance and the development of acquired resistance are now well recognized. In this review we focus on the biology of the EGFR, the role of EGFR in human cancer, the development of antibody-based anti-EGFR therapies and a summary of their clinical successes. Further, we provide an in depth discussion of described molecular mechanisms of resistance to cetuximab and potential strategies to circumvent this resistance.

The use of single-agent dasatinib in molecularly unselected non-small-cell lung cancer patients

A Phase II study of the Src family kinase (SFK) inhibitor dasatinib was recently reported in molecularly unselected patients with metastatic NSCLC. SFK inhibition has a strong rationale as a clinical strategy in NSCLC. The reviewed study unfortunately showed disappointing activity as monotherapy in this molecularly unselected patient cohort and toxicity in terms of pleural effusion was problematic. Therefore, dasatinib as monotherapy in this setting does not appear promising. Nonetheless, the reviewed study may be used in conjunction with other studies of dasatinib in NSCLC to identify patients more likely to benefit from dasatinib either as monotherapy or in combination with other agents. Future studies of dasatinib in NSCLC should examine the agent in combination with EGFR inhibitors and/or cytotoxic chemotherapies.

Dasatinib sensitizes KRAS mutant colorectal tumors to cetuximab

KRAS mutation is a predictive biomarker for resistance to cetuximab (Erbitux®) in metastatic colorectal cancer (mCRC). This study sought to determine if KRAS mutant CRC lines could be sensitized to cetuximab using dasatinib (BMS-354825, sprycel®) a potent, orally bioavailable inhibitor of several tyrosine kinases, including the Src Family Kinases. We analyzed 16 CRC lines for: 1) KRAS mutation status, 2) dependence on mutant KRAS signaling, 3) expression level of EGFR and SFKs. From these analyses, we selected three KRAS mutant (LS180, LoVo, and HCT116) cell lines, and two KRAS wild type cell lines (SW48 and CaCo2). In vitro, using Poly-D-Lysine/laminin plates, KRAS mutant cell lines were resistant to cetuximab whereas parental controls showed sensitivity to cetuximab. Treatment with cetuximab and dasatinib showed a greater anti-proliferative effect on KRAS mutant line as compared to either agent alone both in vitro and in vivo. To investigate potential mechanisms for this anti-proliferative response in the combinatorial therapy we performed Human Phospho-kinase Antibody Array analysis measuring the relative phosphorylation levels of phosphorylation of 39 intracellular proteins in untreated, cetuximab, dasatinib or the combinatorial treatment in LS180, LoVo and HCT116 cells. The results of this experiment showed a decrease in a broad spectrum of kinases centered on the β-catenin pathway, the classical MAPK pathway, AKT/mTOR pathway and the family of STAT transcription factors when compared to the untreated control or monotherapy treatments. Next we analyzed tumor growth with cetuximab, dasatinib or the combination in vivo. KRAS mutant xenografts showed resistance to cetuximab therapy, whereas KRAS wild type demonstrated an anti-tumor response when treated with cetuximab. KRAS mutant tumors exhibited minimal response to dasatinib monotherapy. However, as in vitro, KRAS mutant lines exhibited a response to the combination of cetuximab and dasatinib. Combinatorial treatment of KRAS mutant xenografts resulted in decreased cell proliferation as measured by Ki67 and higher rates of apoptosis as measured by TUNEL. The data presented herein indicate that dasatinib can sensitize KRAS mutant CRC tumors to cetuximab and may do so by altering the activity of several key-signaling pathways. Further, these results suggest that signaling via the EGFR and SFKs may be necessary for cell proliferation and survival of KRAS mutant CRC tumors. This data strengthen the rationale for clinical trials in this genetic setting combining cetuximab and dasatinib.

Regulation of heparin-binding EGF-like growth factor by miR-212 and acquired cetuximab-resistance in head and neck squamous cell carcinoma

Background

We hypothesized that chronic inhibition of epidermal growth factor receptor (EGFR) by cetuximab, a monoclonal anti-EGFR antibody, induces up-regulation of its ligands resulting in resistance and that microRNAs (miRs) play an important role in the ligand regulation in head and neck squamous cell carcinoma (HNSCC).

Methodology/Principal Findings

Genome-wide changes in gene and miR expression were determined in cetuximab-sensitive cell line, SCC1, and its resistant derivative 1Cc8 using DNA microarrays and RT-PCR. The effects of differentially expressed EGFR ligands and miRs were examined by MTS, colony formation, ELISA, and western blot assays. Heparin-binding EGF-like growth factor (HB-EGF) and its regulator, miR-212, were differentially expressed with statistical significance when SCC1 and 1Cc8 were compared for gene and miR expression. Stimulation with HB-EGF induced cetuximab resistance in sensitive cell lines. Inhibition of HB-EGF and the addition of miR-212 mimic induced cetuximab sensitivity in resistant cell lines. MicroRNA-212 and HB-EGF expression were inversely correlated in an additional 33 HNSCC and keratinocyte cell lines. Six tumors and 46 plasma samples from HNSCC patients were examined for HB-EGF levels. HB-EGF plasma levels were lower in newly diagnosed HNSCC patients when compared to patients with recurrent disease.

Conclusions/Significance

Increased expression of HB-EGF due to down-regulation of miR-212 is a possible mechanism of cetuximab resistance. The combination of EGFR ligand inhibitors or miR modulators with cetuximab may improve the clinical outcome of cetuximab therapy in HNSCC.

Understanding resistance to EGFR inhibitors-impact on future treatment strategies

EGFR is a tyrosine kinase that participates in the regulation of cellular homeostasis. Following ligand binding, EGFR stimulates downstream cell signaling cascades that influence cell proliferation, apoptosis, migration, survival and complex processes, including angiogenesis and tumorigenesis. EGFR has been strongly implicated in the biology of human epithelial malignancies, with therapeutic applications in cancers of the colon, head and neck, lung, and pancreas. Accordingly, targeting EGFR has been intensely pursued, with the development of a series of promising molecular inhibitors for use in clinical oncology. As is common in cancer therapy, challenges with respect to treatment resistance emerge over time. This situation is certainly true of EGFR inhibitor therapies, where intrinsic and acquired resistance is now well recognized. In this Review, we provide a brief overview regarding the biology of EGFR, preclinical and clinical development of EGFR inhibitors, and molecular mechanisms that underlie the development of treatment resistance. A greater understanding of the mechanisms that lead to EGFR resistance may provide valuable insights to help design new strategies that will enhance the impact of this promising class of inhibitors for the treatment of cancer.

Augmentation of radiation response by motesanib, a multikinase inhibitor that targets vascular endothelial growth factor receptors

BACKGROUND

Motesanib is a potent inhibitor of vascular endothelial growth factor receptors (VEGFR) 1, 2, and 3, platelet-derived growth factor receptor, and Kit receptors. In this report we examine the interaction between motesanib and radiation in vitro and in head and neck squamous cell carcinoma (HNSCC) xenograft models.

EXPERIMENTAL DESIGN

In vitro assays were done to assess the impact of motesanib on VEGFR2 signaling pathways in human umbilical vein endothelial cells (HUVEC). HNSCC lines grown as tumor xenografts in athymic nude mice were utilized to assess the in vivo activity of motesanib alone and in combination with radiation.

RESULTS

Motesanib inhibited VEGF-stimulated HUVEC proliferation in vitro, as well as VEGFR2 kinase activity. Additionally, motesanib and fractionated radiation showed additive inhibitory effects on HUVEC proliferation. In vivo combination therapy with motesanib and radiation showed increased response compared with drug or radiation alone in UM-SCC1 (P < 0.002) and SCC-1483 xenografts (P = 0.001); however, the combination was not significantly more efficacious than radiation alone in UM-SCC6 xenografts. Xenografts treated with motesanib showed a reduction of vessel penetration into tumor parenchyma, compared with control tumors. Furthermore, triple immunohistochemical staining for vasculature, proliferation, and hypoxia showed well-defined spatial relationships among these parameters in HNSCC xenografts. Motesanib significantly enhanced intratumoral hypoxia in the presence and absence of fractionated radiation.

CONCLUSIONS

These studies identify a favorable interaction when combining radiation and motesanib in HNSCC models. The data presented suggest that motesanib reduces blood vessel penetration into tumors and thereby increases intratumoral hypoxia. These findings suggest that clinical investigations examining combinations of radiation and motesanib are warranted in HNSCC.

Abstract 338: Enhanced cetuximab and radiosensitization with src inhibition in head and neck cancer

The epidermal growth factor receptor (EGFR) is a ubiquitously expressed receptor tyrosine kinase (RTK) that initiates a spectrum of signaling pathways that promote cell proliferation, differentiation, migration, motility, and metastasis. The EGFR has been strongly linked to the etiology of head and neck squamous cell carcinoma (HNSCC). The first major phase III clinical trial combining cetuximab with radiation in HNSCC confirmed a strong survival advantage for patients on the cetuximab arm. It has recently been reported, however, that cetuximab and radiation can induce EGFR to the nucleus where it can enhance resistance to both of these therapeutic modalities. In this report we sought to determine how to block cetuximab and radiation induced translocation of EGFR to the nucleus to increase the efficacy of this therapeutic regimen in HNSCC.

We utilized three established HNSCC lines, SCC1, SCC6 and SCC1483 and measured nuclear translocation of the EGFR after treatment with cetuximab, radiation or the combination. Both cetuximab and radiation treatment could induce nuclear translocation of the EGFR in all SCC lines tested. Strikingly, time course analysis indicated that cetuximab could stimulate movement of the EGFR to the nucleus within one hour where it maintained its present for greater than 96 hours. Conversely, radiation could stimulate EGFR translocation to the nucleus within 0.5 hours, but returned to baseline levels within four hours. Both cetuximab and radiation treatment of SCC lines led to the phosphorylation of tyrosine 845 (Y845) of the EGFR. Y845 is phosphorylated specifically by the non-receptor tyrosine kinase Src and/or its family of kinases (SFKs). Blockade of SFKs by dasatinib could abrogate cetuximab and radiation induced EGFR translocation to the nucleus indicating that SFKs are crucial for the movement of the EGFR to the nucleus. In addition, pre-treatment of HNSCC cells with dasatinib, followed by cetuximab and radiation enhanced the suppression of ERK activity in all three SCC cell lines. Furthermore, combining dasatinib with cetuximab/radiation treatment exhibited additive inhibitory effects on cell growth or clonogenic formation. These data suggest that both cetuximab and radiation can induce EGFR to the nucleus and blockade of SFKs using dasatinib can abrogate this translocation. Collectively these findings may suggest that dasatinib can limit EGFR translocation to the nucleus and may enhance radiotherapy plus cetuximab in HNSCC.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 338.

Abstract 5151: Protein kinase Cε, which is linked to development of squamous cell carcinomas, potentiates ultraviolet radiation-induced proliferation of hair follicle putative stem cells

Protein kinase C epsilon (PKCε) is among the six PKC isoforms (α, δ, ε, η, μ, ζ) expressed in both mouse and human skin. We have reported that epidermal PKCε levels dictate the susceptibility of PKCε transgenic (TG) mice to the development of squamous cell carcinomas (SCC) elicited either by repeated exposures to ultraviolet radiation (UVR) or initiation with 7,12-dimethylbenz[a]anthracene and tumor promotion with 12-O-tetradecanoylphorbol-13-acetate (TPA). Histologically, SCC in TG mice, like human SCC, is poorly differentiated and metastatic. To find clues about the mechanism by which PKCε may impart susceptibility to UVR-induced development of SCC, we compared the effects of UVR treatment of TG mice with their wildtype (WT) littermates on hair follicle putative stem cells (HSCs). HSCs in the mouse hair follicle are known to be the precursor cells for SCC in the mouse skin (Mol Carcinog. 46: 579-84, 2007). The cell surface markers CD34 and α6-integrin mark mouse hair follicle bulge cells, which have attributes of stem cells, including quiescence and multipotency. In this experiment, TG and WT mice were exposed to UVR (2kJ/m2, 3x weekly i.e, Monday, Wednesday, Friday) emitted by Kodacel-filtered FS-40 sun lamps. At 24 hr post last UVR (1, 2 or 4) exposures, mice were sacrificed and the dorsal skin removed for keratinocyte isolation. Keratinocytes were incubated for 30 minutes in the dark at 4oC with FITC-conjugated rat anti-human α6-integrin antibody at 10 μl per 106 cells and PE-conjugated rat anti-mouse CD34 antibody at 2 μg per 106 cells (FITC-α6-integrin and PE-CD34 antibodies; BD Biosciences). Flow cytometric analysis was done using a BD Biosciences FACS Calibur flow cytometer using a 488 nm laser as excitation. For both untreated and treated mice, the percent of double positive cells was higher in the TG than in WT mice. Both acute and chronic UVR treatment increased (2-fold) the number of double positive cell in both TG and WT mice. To examine the rate of proliferation of bulge region stem cells, a 5-bromo-2′-deoxyuridine labeling (BrdU) experiment was performed. Three-day old neonatal mice were injected twice daily for three days with 50 mg/kg of BrdU in PBS. At 8 weeks of age mice were sacrificed and the dorsal skin harvested for keratinocytes. The cells were stained for α6-integrin and CD34, fixed then stained for BrdU. In the WT mice, the percent of double positive cells maintaining BrdU label was 28.4 + 0.6% compared to 4.0 + 0.06% for the TG mice, an approximately 7-fold decrease in the TG mice. Similar results were obtained in a repeat experiment, indicating that the double positive cells in the TG mice cycle at a faster rate. This may contribute to the sensitivity of these transgenic animals to UVR-induced development of squamous cell carcinomas (Support: NIH grants CA102431 and CA35368 T32ES007015).

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5151.

Nuclear EGFR contributes to acquired resistance to cetuximab

Epidermal growth factor receptor (EGFR) is a ubiquitously expressed receptor tyrosine kinase involved in the etiology of several human cancers. Cetuximab is an EGFR-blocking antibody that has been approved for the treatment of patients with head and neck squamous cell carcinoma and metastatic colorectal cancer. Previous reports have shown that EGFR translocation to the nucleus is associated with cell proliferation. Here we investigated mechanisms of acquired resistance to cetuximab using a model derived from the non-small cell lung cancer line H226. We demonstrated that cetuximab-resistant cells overexpress HER family ligands including epidermal growth factor (EGF), amphiregulin, heparin-binding EGF and beta-cellulin. Overexpression of these ligands is associated with the nuclear translocation of the EGFR and this process was mediated by the Src family kinases (SFK). Treatment of cetuximab-resistant cells with the SFK inhibitor, dasatinib, resulted in loss of nuclear EGFR, increased membrane expression of the EGFR and resensitization to cetuximab. In addition, expression of a nuclear localization sequence-tagged EGFR in cetuximab-sensitive cells increased resistance to cetuximab both in vitro and in mouse xenografts. Collectively, these data suggest that nuclear expression of EGFR may be an important molecular determinant of resistance to cetuximab therapy and provides a rationale for investigating nuclear EGFR as a biomarker for cetuximab response. Further, these data suggest a rationale for the design of clinical trials that examine the value of treating patients with cetuximab-resistant tumors with inhibitors of SFKs in combination with cetuximab.

The role of Src in solid tumors

The proto-oncogene c-Src (Src) encodes a nonreceptor tyrosine kinase whose expression and activity are correlated with advanced malignancy and poor prognosis in a variety of human cancers. Nine additional enzymes with homology to Src have been identified and collectively are referred to as Src family kinases (SFKs). Together, SFKs represent the largest family of nonreceptor tyrosine kinases and interact directly with receptor tyrosine kinases, G-protein-coupled receptors, steroid receptors, signal transducers and activators of transcription, and molecules involved in cell adhesion and migration. These interactions lead to a diverse array of biological functions including proliferation, cell growth, differentiation, cell shape, motility, migration, angiogenesis, and survival. Studies investigating mutational activation of Src in human cancers suggest that this may be a rare event and that wild-type Src is weakly oncogenic. Thus, the role of Src in the development and progression of human cancer remains unclear. Recently, it was suggested that increased SFK protein levels and, more importantly, SFK tyrosine kinase activity are linked to cancer progression and metastatic disease by facilitating the action of other signaling proteins. This accumulating body of evidence indicates that SFKs may represent a promising therapeutic target for the treatment of solid tumors. This review discusses the role of SFKs in solid tumors and the recent therapeutic advances aimed at targeting this family of tyrosine kinases in cancer.

Epidermal growth factor receptor cooperates with Src family kinases in acquired resistance to cetuximab

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that plays a major role in oncogenesis. Cetuximab is an EGFR-blocking antibody that is FDA approved for use in patients with metastatic colorectal cancer (mCRC) and head and neck squamous cell carcinoma (HNSCC). Although cetuximab has shown strong clinical benefit for a subset of cancer patients, most become refractory to cetuximab therapy. We reported that cetuximab-resistant NSCLC line NCI-H226 cells have increased steady-state expression and activity of EGFR secondary to altered trafficking/degradation and this increase in EGFR expression and activity lead to hyper-activation of HER3 and down stream signals to survival. We now present data that Src family kinases (SFKs) are highly activated in cetuximab-resistant cells and enhance EGFR activation of HER3 and PI(3)K/Akt. Studies using the Src kinase inhibitor dasatinib decreased HER3 and PI(3)K/Akt activity. In addition, cetuximab-resistant cells were resensitized to cetuximab when treated with dasatinib. These results indicate that SFKs and EGFR cooperate in acquired resistance to cetuximab and suggest a rationale for clinical strategies that investigate combinatorial therapy directed at both the EGFR and SFKs in patients with acquired resistance to cetuximab.

Establishment and characterization of a model of acquired resistance to epidermal growth factor receptor targeting agents in human cancer cells

PURPOSE

The epidermal growth factor receptor (EGFR) is recognized as a key mediator of proliferation and progression in many human tumors. A series of EGFR-specific inhibitors have recently gained Food and Drug Administration approval in oncology. These strategies of EGFR inhibition have shown major tumor regressions in approximately 10% to 20% of advanced cancer patients. Many tumors, however, eventually manifest resistance to treatment. Efforts to better understand the underlying mechanisms of acquired resistance to EGFR inhibitors, and potential strategies to overcome resistance, are greatly needed.

EXPERIMENTAL DESIGN

To develop cell lines with acquired resistance to EGFR inhibitors we utilized the human head and neck squamous cell carcinoma tumor cell line SCC-1. Cells were treated with increasing concentrations of cetuximab, gefitinib, or erlotinib, and characterized for the molecular changes in the EGFR inhibitor-resistant lines relative to the EGFR inhibitor-sensitive lines.

RESULTS

EGFR inhibitor-resistant lines were able to maintain their resistant phenotype in both drug-free medium and in athymic nude mouse xenografts. In addition, EGFR inhibitor-resistant lines showed a markedly increased proliferation rate. EGFR inhibitor-resistant lines had elevated levels of phosphorylated EGFR, mitogen-activated protein kinase, AKT, and signal transducer and activator of transcription 3, which were associated with reduced apoptotic capacity. Subsequent in vivo experiments indicated enhanced angiogenic potential in EGFR inhibitor-resistant lines. Finally, EGFR inhibitor-resistant lines showed cross-resistance to ionizing radiation.

CONCLUSIONS

We have developed EGFR inhibitor-resistant human head and neck squamous cell carcinoma cell lines. This model provides a valuable preclinical tool to investigate molecular mechanisms of acquired resistance to EGFR blockade.

Molecular target approaches in head and neck cancer: epidermal growth factor receptor and beyond

Approximately 50,000 new cases of head and neck squamous cell carcinoma (HNSCC) will be diagnosed in the United States in 2009. Although the gradual decline in smoking rates in the United States is a highly favorable trend, the future global HNSCC incidence will likely reflect the increased marketing and penetration of tobacco products across several of our most populous countries. Although modern surgery, radiation, and conventional chemotherapy strategies for HNSCC continue to provide gradual improvement in outcome, the first molecular targeting approach to show a survival advantage for HNSCC patients has recently emerged in the context of epidermal growth factor receptor biology. The scientific background and current challenges accompanying this recent advance are described in this article as are several additional promising molecular targets for HNSCC. There is cautious anticipation that the logical advancement of molecular targeting agents in conjunction with radiation may afford increased cure rates and diminished normal tissue toxicity profiles for HNSCC patients over the years to come.

Augmentation of radiation response by panitumumab in models of upper aerodigestive tract cancer

PURPOSE

To examine the interaction between panitumumab, a fully human anti-epidermal growth factor receptor monoclonal antibody, and radiation in head-and-neck squamous cell carcinoma and non-small-cell lung cancer cell lines and xenografts.

METHODS AND MATERIALS

The head-and-neck squamous cell carcinoma lines UM-SCC1 and SCC-1483, as well as the non-small-cell lung cancer line H226, were studied. Tumor xenografts in athymic nude mice were used to assess the in vivo activity of panitumumab alone and combined with radiation. In vitro assays were performed to assess the effect of panitumumab on radiation-induced cell signaling, apoptosis, and DNA damage.

RESULTS

Panitumumab increased the radiosensitivity as measured by the clonogenic survival assay. Radiation-induced epidermal growth factor receptor phosphorylation and downstream signaling through mitogen-activated protein kinase (MAPK) and signal transducer and activator of transcription 3 (STAT3) was inhibited by panitumumab. Panitumumab augmented radiation-induced DNA damage by 1.2-1.6-fold in each of the cell lines studied as assessed by residual gamma-H(2)AX foci after radiation. Radiation-induced apoptosis was increased 1.4-1.9-fold by panitumumab, as evidenced by Annexin V-fluorescein isothiocyanate staining and flow cytometry. In vivo, the combination therapy of panitumumab and radiation was superior to panitumumab or radiation alone in the H226 xenografts (p = 0.01) and showed a similar trend in the SCC-1483 xenografts (p = 0.08). In vivo, immunohistochemistry demonstrated the ability of panitumumab to augment the antiproliferative and antiangiogenic effects of radiation.

CONCLUSION

These studies have identified a favorable interaction in the combination of radiation and panitumumab in upper aerodigestive tract tumor models, both in vitro and in vivo. These data suggest that clinical investigations examining the combination of radiation and panitumumab in the treatment of epithelial tumors warrant additional pursuit.