Immune Escape Strategies in Head and Neck Cancer: Evade, Resist, Inhibit, Recruit

Head and neck cancers (HNCs) arise from the mucosal lining of the aerodigestive tract and are often associated with alcohol use, tobacco use, and/or human papillomavirus (HPV) infection. Over 600,000 new cases of HNC are diagnosed each year, making it the sixth most common cancer worldwide. Historically, treatments have included surgery, radiation, and chemotherapy, and while these treatments are still the backbone of current therapy, several immunotherapies have recently been approved by the Food and Drug Administration (FDA) for use in HNC. The role of the immune system in tumorigenesis and cancer progression has been explored since the early 20th century, eventually coalescing into the current three-phase model of cancer immunoediting. During each of the three phases-elimination, equilibrium, and escape-cancer cells develop and utilize multiple strategies to either reach or remain in the final phase, escape, at which point the tumor is able to grow and metastasize with little to no detrimental interference from the immune system. In this review, we summarize the many strategies used by HNC to escape the immune system, which include ways to evade immune detection, resist immune cell attacks, inhibit immune cell functions, and recruit pro-tumor immune cells.

Radiation Sensitivity: The Rise of Predictive Patient-Derived Cancer Models

Patient-derived cancer models have been used for decades to improve our understanding of cancer and test anticancer treatments. Advances in radiation delivery have made these models more attractive for studying radiation sensitizers and understanding an individual patient's radiation sensitivity. Advances in the use of patient-derived cancer models lead to a more clinically relevant outcome, although many questions remain regarding the optimal use of patient-derived xenografts and patient-derived spheroid cultures. The use of patient-derived cancer models as personalized predictive avatars through mouse and zebrafish models is discussed, and the advantages and disadvantages of patient-derived spheroids are reviewed. In addition, the use of large repositories of patient-derived models to develop predictive algorithms to guide treatment selection is discussed. Finally, we review methods for establishing patient-derived models and identify key factors that influence their use as both avatars and models of cancer biology.

Circulating tumor cell abundance in head and neck squamous cell carcinoma decreases with successful chemoradiation and cetuximab treatment

Head and neck squamous cell carcinoma (HNSCC) is a common and deadly cancer. Circulating tumor cell (CTC) abundance may a valuable, prognostic biomarker in low- and intermediate-risk patients. However, few technologies have demonstrated success in detecting CTCs in these populations. We prospectively collected longitudinal CTC counts from two cohorts of patients receiving treatments at our institution using a highly sensitive device that purifies CTCs using biomimetic cell rolling and dendrimer-conjugated antibodies. In patients with intermediate risk human papillomavirus (HPV)-positive HNSCC, elevated CTC counts were detected in 13 of 14 subjects at screening with a median of 17 CTC/ml (range 0.2-2986.5). A second cohort of non-metastatic, HPV- HNSCC subjects received cetuximab monotherapy followed by surgical resection. In this cohort, all subjects had elevated baseline CTC counts median of 73 CTC/ml (range 5.4-332.9) with statistically significant declines during treatment. Interestingly, two patients with recurrent disease had elevated CTC counts during and following treatment, which also correlated with growth of size and ki67 expression in the primary tumor. The results suggest that our device may be a valuable tool for evaluating the success of less intensive treatment regimens.

Dual Axl/MerTK inhibitor INCB081776 creates a proinflammatory tumor immune microenvironment and enhances anti-PDL1 efficacy in head and neck cancer

BACKGROUND

The tyrosine kinase receptors Axl and MerTK are highly overexpressed in head and neck cancer (HNC) cells, where they are critical drivers of survival, proliferation, metastasis, and therapeutic resistance.

METHODS

We investigated the role of Axl and MerTK in creating an immunologically "cold" tumor immune microenvironment (TIME) by targeting both receptors simultaneously with a small molecule inhibitor of Axl and MerTK (INCB081776). Effects of INCB081776 and/or anti-PDL1 on mouse oral cancer (MOC) cell growth and on the TIME were evaluated.

RESULTS

Targeting Axl and MerTK can reduce M2 and induce M1 macrophage polarization. In vivo, INCB081776 treatment alone or with anti-PDL1 appears to slow MOC tumor growth, increase proinflammatory immune infiltration, and decrease anti-inflammatory immune infiltration.

CONCLUSIONS

This data indicates that simultaneous targeting of Axl and MerTK with INCB081776, either alone or in combination with anti-PDL1, slows tumor growth and creates a proinflammatory TIME in mouse models of HNC.

Active recruitment of anti-PD-1-conjugated platelets through tumor-selective thrombosis for enhanced anticancer immunotherapy

Immune checkpoint inhibitors (ICIs) can reinvigorate T cells to eradicate tumor cells, showing great potential in combating various types of tumors. We propose a delivery strategy to enhance tumor-selective ICI accumulation, which leverages the responsiveness of platelets and platelet-derivatives to coagulation cascade signals. A fused protein tTF-RGD targets tumor angiogenic blood vessel endothelial cells and initiates the coagulation locoregionally at the tumor site, forming a "cellular hive" to recruit anti-PD-1 antibody (aPD-1)-conjugated platelets to the tumor site and subsequently activating platelets to release aPD-1 antibody to reactivate T cells for improved immunotherapy. Moreover, on a patient-derived xenograft breast cancer model, the platelet membrane-coated nanoparticles can also respond to the coagulation signals initiated by tTF-RGD, thus enhancing the accumulation and antitumor efficacy of the loaded chemotherapeutics. Our study illustrates a versatile platform technology to enhance the local accumulation of ICIs and chemodrugs by taking advantage of the responsiveness of platelets and platelet derivatives to thrombosis.

Targeting HER3-dependent activation of nuclear AKT improves radiotherapy of non-small cell lung cancer

BACKGROUND

AKT1 must be present and activated in the nucleus immediately after irradiation to stimulate AKT1-dependent double-strand breaks (DSB) repair through the fast non-homologous end-joining (NHEJ) repair process. We investigated the subcellular distribution of AKT1 and the role of HER family receptor members on the phosphorylation of nuclear AKT and radiation response.

MATERIALS AND METHODS

Using genetic approaches and pharmacological inhibitors, we investigated the subcellular distribution of AKT1 and the role of HER family receptor members on the activation of nuclear AKT in non-small cell lung cancer (NSCLC) cells in vitro. ɤH2AX foci assay was applied to investigate the role of AKT activating signaling pathway on DSB repair. A mouse tumor xenograft model was used to study the impact of discovered signaling pathway activating nuclear AKT on the radiation response of tumors in vivo.

RESULTS

Our data suggests that neither ionizing radiation (IR) nor stimulation with HER family receptor ligands induced rapid nuclear translocation of endogenous AKT1. GFP-tagged exogenous AKT1 translocated to the nucleus under un-irradiated conditions and IR did not stimulate this translocation. Nuclear translocation of GFP-AKT1 was impaired by the AKT inhibitor MK2206 as shown by its accumulation in the cytoplasmic fraction. IR-induced phosphorylation of nuclear AKT was primarily dependent on HER3 expression and tyrosine kinase activation of epidermal growth factor receptor. In line with the role of AKT1 in DSB repair, the HER3 neutralizing antibody patritumab as well as HER3-siRNA diminished DSB repair in vitro. Combination of patritumab with radiotherapy improved the effect of radiotherapy on tumor growth delay in a xenograft model.

CONCLUSION

IR-induced activation of nuclear AKT occurs inside the nucleus that is mainly dependent on HER3 expression in NSCLC. These findings suggest that targeting HER3 in combination with radiotherapy may provide a logical treatment option for investigation in selected NSCLC patients.

Abstract 3535: Simultaneous inhibition of Axl and MerTK enhances anti-PDL1 efficacy and creates a pro-inflammatory tumor immune microenvironment in head and neck cancer

The tyrosine kinase receptors Axl and MerTK, known for their role on macrophages in regulating clearance of apoptotic cells, are highly overexpressed in head and neck cancer (HNC). Previous studies in our laboratory have shown that Axl is a critical driver of survival, proliferation, metastasis, and therapeutic resistance in HNC, and that MerTK is functionally redundant to Axl. In this study, we investigated the cooperative role of Axl and MerTK in creating an immunologically cold tumor immune microenvironment (TIME) by targeting both receptors simultaneously with a small molecule inhibitor of Axl and MerTK (INCB081776). Because Axl and MerTK are expressed on both macrophages and HNC cancer cells, we examined the effect of INCB081776 treatment on each cell type. In macrophages, Axl and MerTK signaling leads to M2-type polarization, an anti-inflammatory state that leads to the resolution of inflammation and, in cancer settings, promotes tumor growth. Our experiments suggest that treatment with INCB081776 can reduce M2 polarization and increase M1-type polarization, a pro-inflammatory state that promotes inflammation and tumor cell killing. Next, to determine the efficacy of INCB081776 on HNC cancer cells, mouse oral cancer (MOC) tumors were implanted in syngeneic mice and treated with INCB081776 alone or in combination with a monoclonal antibody against PDL1 (anti-PDL1), thereby mimicking current standard-of-care immune checkpoint inhibitor treatment. The results showed a marked effect of INCB081776 single-agent treatment on MOC tumor growth and an increase in several pro-inflammatory cell types (M1 macrophages, CD8+ T cells, total infiltrating leukocytes), suggesting that INCB081776 treatment can create an immunologically hot TIME. Further, in-depth analysis of tumor infiltrating leukocytes following INCB081776 treatment in both immunologically hot (MOC1) and cold (MOC2) HNC tumors suggested that INCB081776 has a greater effect in cold tumors. In cold tumors, levels of pro-inflammatory cells (CD8+ T cells, M1 macrophages, etc.) increased, and levels of anti-inflammatory cells (M2 macrophages, regulatory T cells, etc.) decreased, both to a greater extent than in hot tumors. Finally, the combination of INCB081776 and anti-PDL1 was superior to either treatment alone in slowing tumor growth. Together, these studies indicate that INCB081776 cooperates with anti-PDL1 in a syngeneic mouse model of HNC to slow tumor growth and create a pro-inflammatory environment, especially in immunologically cold tumors, thereby highlighting the potential clinical benefit of this therapeutic combination.

Citation Format: Kourtney L. Kostecki, Mari Iida, Anne L. Wiley, Seungpyo Hong, Ravi Salgia, Paul M. Harari, Deric L. Wheeler. Simultaneous inhibition of Axl and MerTK enhances anti-PDL1 efficacy and creates a pro-inflammatory tumor immune microenvironment in head and neck cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3535.

Abstract 1334: MerTK tumorigenesis and immune evasion mechanisms in triple negative breast cancer

Triple negative breast cancer (TNBC) cells lack estrogen, progesterone, and HER2 receptors. TNBC tends to be more aggressive than most types of breast cancer and is more likely to recur even after surgery and treatment. Recently, a few targeted therapies were approved for TNBC, but additional molecular targeting agents are still needed. Previous studies have found that activated MerTK is associated with many types of human cancers, including breast cancer. In this study, we focused on MerTK expression and its tumorigenesis and immunoregulatory functions in TNBC. We first examined MerTK expression levels in human TNBC tissue samples by analyzing tissue microarrays (TMA) using immunohistochemistry (IHC). IHC revealed that ~40% of TNBC samples expressed high levels of MerTK. We further examined MerTK expression levels in ten TNBC cell lines by immunoblot analysis. Three cell lines (BT549, MDAMB231 and MDAMB436) showed strong MerTK expression levels. Next, to evaluate MerTK’s effect on cell proliferation, we treated MDAMB231 cells with MerTK siRNA, which inhibited cell proliferation by 20% compared to siNon-target (siNT). These data indicate that TNBC cells remain dependent on MerTK-activated signaling pathways for proliferation and survival. To further investigate the impact of MerTK expression in TNBC cells, we stably overexpressed MerTK in the TNBC cell line SUM102, which naturally has very low MerTK levels. The results indicated that overexpression of MerTK in SUM102 cells led to: 1) increased proliferation in vitro 2) robust tumor growth, 3) marked migration potential and 4) increased metastasis in mice. Collectively, these results demonstrate that activation of a MerTK-driven pathway could be involved in tumorigenesis in TNBC. To understand the role of MerTK in cell signaling and pro-tumor immunity, we utilized a cytokine array to examine which molecules were impacted in MerTK-overexpressing SUM102 cells. The results showed that production of CXCL4, CD74, and IL-1α was increased, and production of CXCL10 was decreased in MerTK-overexpressing SUM102 cells as compared to control cells. Interestingly, PD-L1 was upregulated and MHC class I was downregulated in MerTK-overexpressing SUM102 cells as compared to control cells. These preliminary findings suggested that MerTK-overexpressing TNBC could be creating a favorable immune microenvironment for proliferation of tumor cells. To further explore the cytokine, PD-L1, and MHC class I results, we overexpressed MerTK in 4T1 murine TNBC-like cells. Immunoblot analysis showed that PD-L1 was upregulated in MerTK-overexpressing 4T1 cells. We will utilize this cell line to evaluate tumor growth and immunosuppression in the tumor microenvironment in BALB/C mice.

Citation Format: Mari Iida, Kourtney Kostecki, Carlene A. Kranjac, Christine Glitchev, David T. Yang, Deric L. Wheeler. MerTK tumorigenesis and immune evasion mechanisms in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1334.

AXL regulates neuregulin1 expression leading to cetuximab resistance in head and neck cancer

BACKGROUND

The receptor tyrosine kinase (RTK) epidermal growth factor receptor (EGFR) is overexpressed and an important therapeutic target in Head and Neck cancer (HNC). Cetuximab is currently the only EGFR-targeting agent approved by the FDA for treatment of HNC; however, intrinsic and acquired resistance to cetuximab is a major problem in the clinic. Our lab previously reported that AXL leads to cetuximab resistance via activation of HER3. In this study, we investigate the connection between AXL, HER3, and neuregulin1 (NRG1) gene expression with a focus on understanding how their interdependent signaling promotes resistance to cetuximab in HNC.

METHODS

Plasmid or siRNA transfections and cell-based assays were conducted to test cetuximab sensitivity. Quantitative PCR and immunoblot analysis were used to analyze gene and protein expression levels. Seven HNC patient-derived xenografts (PDXs) were evaluated for protein expression levels.

RESULTS

We found that HER3 expression was necessary but not sufficient for cetuximab resistance without AXL expression. Our results demonstrated that addition of the HER3 ligand NRG1 to cetuximab-sensitive HNC cells leads to cetuximab resistance. Further, AXL-overexpressing cells regulate NRG1 at the level of transcription, thereby promoting cetuximab resistance. Immunoblot analysis revealed that NRG1 expression was relatively high in cetuximab-resistant HNC PDXs compared to cetuximab-sensitive HNC PDXs. Finally, genetic inhibition of NRG1 resensitized AXL-overexpressing cells to cetuximab.

CONCLUSIONS

The results of this study indicate that AXL may signal through HER3 via NRG1 to promote cetuximab resistance and that targeting of NRG1 could have significant clinical implications for HNC therapeutic approaches.

Activation of EPHA2-ROBO1 Heterodimer by SLIT2 Attenuates Non-canonical Signaling and Proliferation in Squamous Cell Carcinomas

The tyrosine kinase receptor ephrin receptor A2 (EPHA2) is overexpressed in lung (LSCC) and head and neck (HNSCC) squamous cell carcinomas. Although EPHA2 can inhibit tumorigenesis in a ligand-dependent fashion via phosphorylation of Y588 and Y772, it can promote tumorigenesis in a ligand-independent manner via phosphorylation of S897. Here, we show that EPHA2 and Roundabout Guidance Receptor 1 (ROBO1) interact to form a functional heterodimer. Furthermore, we show that the ROBO1 ligand Slit Guidance Ligand 2 (SLIT2) and ensartinib, an inhibitor of EPHA2, can attenuate growth of HNSCC cells and act synergistically in LSCC cells. Our results suggest that patients with LSCC and HNSCC may be stratified and treated based on their EPHA2 and ROBO1 expression patterns. Although ~73% of patients with LSCC could benefit from SLIT2+ensartinib treatment, ~41% of patients with HNSCC could be treated with either SLIT2 or ensartinib. Thus, EPHA2 and ROBO1 represent potential LSCC and HNSCC theranostics.

Blocking Y-Box Binding Protein-1 through Simultaneous Targeting of PI3K and MAPK in Triple Negative Breast Cancers

Simple Summary

Triple-negative breast cancer (TNBC) is associated with the high rates of relapse and metastasis and poor survival. YB-1 is overexpressed in TNBC tumor tissues. In the present study, we demonstrated that S102 phosphorylation of YB-1 in TNBC cell lines depend on the mutation status of the components of the MAPK/ERK and PI3K/Akt pathways. Simultaneous targeting of MEK and PI3K was found to be the most effective approach to block YB-1 phosphorylation and to inhibit YB-1 dependent cell proliferation. YBX1 knockout was sufficient to block TNBC tumor growth.

Abstract

The multifunctional protein Y-box binding protein-1 (YB-1) regulates all the so far described cancer hallmarks including cell proliferation and survival. The MAPK/ERK and PI3K/Akt pathways are also the major pathways involved in cell growth, proliferation, and survival, and are the frequently hyperactivated pathways in human cancers. A gain of function mutation in KRAS mainly leads to the constitutive activation of the MAPK pathway, while the activation of the PI3K/Akt pathway occurs either through the loss of PTEN or a gain of function mutation of the catalytic subunit alpha of PI3K (PIK3CA). In this study, we investigated the underlying signaling pathway involved in YB-1 phosphorylation at serine 102 (S102) in KRAS(G13D)-mutated triple-negative breast cancer (TNBC) MDA-MB-231 cells versus PIK3CA(H1047R)/PTEN(E307K) mutated TNBC MDA-MB-453 cells. Our data demonstrate that S102 phosphorylation of YB-1 in KRAS-mutated cells is mainly dependent on the MAPK/ERK pathway, while in PIK3CA/PTEN-mutated cells, YB-1 S102 phosphorylation is entirely dependent on the PI3K/Akt pathway. Independent of the individual dominant pathway regulating YB-1 phosphorylation, dual targeting of MEK and PI3K efficiently inhibited YB-1 phosphorylation and blocked cell proliferation. This represents functional crosstalk between the two pathways. Our data obtained from the experiments, applying pharmacological inhibitors and genetic approaches, shows that YB-1 is a key player in cell proliferation, clonogenic activity, and tumor growth of TNBC cells through the MAPK and PI3K pathways. Therefore, dual inhibition of these two pathways or single targeting of YB-1 may be an effective strategy to treat TNBC.

AXL Mediates Cetuximab and Radiation Resistance Through Tyrosine 821 and the c-ABL Kinase Pathway in Head and Neck Cancer

PURPOSE

Radiation and cetuximab are therapeutics used in management of head and neck squamous cell carcinoma (HNSCC). Despite clinical success with these modalities, development of both intrinsic and acquired resistance is an emerging problem in the management of this disease. The purpose of this study was to investigate signaling of the receptor tyrosine kinase AXL in resistance to radiation and cetuximab treatment.

EXPERIMENTAL DESIGN

To study AXL signaling in the context of treatment-resistant HNSCC, we used patient-derived xenografts (PDXs) implanted into mice and evaluated the tumor response to AXL inhibition in combination with cetuximab or radiation treatment. To identify molecular mechanisms of how AXL signaling leads to resistance, three tyrosine residues of AXL (Y779, Y821, Y866) were mutated and examined for their sensitivity to cetuximab and/or radiation. Furthermore, reverse phase protein array (RPPA) was employed to analyze the proteomic architecture of signaling pathways in these genetically altered cell lines.

RESULTS

Treatment of cetuximab- and radiation-resistant PDXs with AXL inhibitor R428 was sufficient to overcome resistance. RPPA analysis revealed that such resistance emanates from signaling of tyrosine 821 of AXL via the tyrosine kinase c-ABL. In addition, inhibition of c-ABL signaling resensitized cells and tumors to cetuximab or radiotherapy even leading to complete tumor regression without recurrence in head and neck cancer models.

CONCLUSIONS

Collectively, the studies presented herein suggest that tyrosine 821 of AXL mediates resistance to cetuximab by activation of c-ABL kinase in HNSCC and that targeting of both EGFR and c-ABL leads to a robust antitumor response.

An Avidity-Based PD-L1 Antagonist Using Nanoparticle-Antibody Conjugates for Enhanced Immunotherapy

Upregulation of programmed death ligand 1 (PD-L1) allows cancer cells to evade antitumor immunity. Despite tremendous efforts in developing PD-1/PD-L1 immune checkpoint inhibitors (ICIs), clinical trials using such ICIs have shown inconsistent benefits. Here, we hypothesized that the ICI efficacy would be dictated by the binding strength of the inhibitor to the target proteins. To assess this, hyperbranched, multivalent poly(amidoamine) dendrimers were employed to prepare dendrimer-ICI conjugates (G7-aPD-L1). Binding kinetics measurements using SPR, BLI, and AFM revealed that G7-aPD-L1 exhibits significantly enhanced binding strength to PD-L1 proteins, compared to free aPD-L1. The binding avidity of G7-aPD-L1 was translated into in vitro efficiency and in vivo selectivity, as the conjugates improved the PD-L1 blockade effect and enhanced accumulation in tumor sites. Our results demonstrate that the dendrimer-mediated multivalent interaction substantially increases the binding avidity of the ICIs and thereby improves the antagonist effect, providing a novel platform for cancer immunotherapy.

Targeting AKT/PKB to improve treatment outcomes for solid tumors

The serine/threonine kinase AKT, also known as protein kinase B (PKB), is the major substrate to phosphoinositide 3-kinase (PI3K) and consists of three paralogs: AKT1 (PKBα), AKT2 (PKBβ) and AKT3 (PKBγ). The PI3K/AKT pathway is normally activated by binding of ligands to membrane-bound receptor tyrosine kinases (RTKs) as well as downstream to G-protein coupled receptors and integrin-linked kinase. Through multiple downstream substrates, activated AKT controls a wide variety of cellular functions including cell proliferation, survival, metabolism, and angiogenesis in both normal and malignant cells. In human cancers, the PI3K/AKT pathway is most frequently hyperactivated due to mutations and/or overexpression of upstream components. Aberrant expression of RTKs, gain of function mutations in PIK3CA, RAS, PDPK1, and AKT itself, as well as loss of function mutation in AKT phosphatases are genetic lesions that confer hyperactivation of AKT. Activated AKT stimulates DNA repair, e.g. double strand break repair after radiotherapy. Likewise, AKT attenuates chemotherapy-induced apoptosis. These observations suggest that a crucial link exists between AKT and DNA damage. Thus, AKT could be a major predictive marker of conventional cancer therapy, molecularly targeted therapy, and immunotherapy for solid tumors. In this review, we summarize the current understanding by which activated AKT mediates resistance to cancer treatment modalities, i.e. radiotherapy, chemotherapy, and RTK targeted therapy. Next, the effect of AKT on response of tumor cells to RTK targeted strategies will be discussed. Finally, we will provide a brief summary on the clinical trials of AKT inhibitors in combination with radiochemotherapy, RTK targeted therapy, and immunotherapy.

MERTK Mediates Intrinsic and Adaptive Resistance to AXL-targeting Agents

The TAM (TYRO3, AXL, MERTK) family receptor tyrosine kinases (RTK) play an important role in promoting growth, survival, and metastatic spread of several tumor types. AXL and MERTK are overexpressed in head and neck squamous cell carcinoma (HNSCC), triple-negative breast cancer (TNBC), and non-small cell lung cancer (NSCLC), malignancies that are highly metastatic and lethal. AXL is the most well-characterized TAM receptor and mediates resistance to both conventional and targeted cancer therapies. AXL is highly expressed in aggressive tumor types, and patients with cancer are currently being enrolled in clinical trials testing AXL inhibitors. In this study, we analyzed the effects of AXL inhibition using a small-molecule AXL inhibitor, a monoclonal antibody (mAb), and siRNA in HNSCC, TNBC, and NSCLC preclinical models. Anti-AXL-targeting strategies had limited efficacy across these different models that, our data suggest, could be attributed to upregulation of MERTK. MERTK expression was increased in cell lines and patient-derived xenografts treated with AXL inhibitors and inhibition of MERTK sensitized HNSCC, TNBC, and NSCLC preclinical models to AXL inhibition. Dual targeting of AXL and MERTK led to a more potent blockade of downstream signaling, synergistic inhibition of tumor cell expansion in culture, and reduced tumor growth in vivo Furthermore, ectopic overexpression of MERTK in AXL inhibitor-sensitive models resulted in resistance to AXL-targeting strategies. These observations suggest that therapeutic strategies cotargeting both AXL and MERTK could be highly beneficial in a variety of tumor types where both receptors are expressed, leading to improved survival for patients with lethal malignancies. Mol Cancer Ther; 17(11); 2297-308. ©2018 AACR.

Dual targeting of PI3K and MEK enhances the radiation response of K-RAS mutated non-small cell lung cancer

Despite the significant contribution of radiotherapy to non-small lung cancer (NSCLC), radioresistance still occurs. One of the major radioresistance mechanisms is the hyperactivation of the PI3K/Akt pathway in which Akt facilitates the repair of DNA double-strand breaks (DSBs) through the stimulation of DNA-PKcs. We investigated if targeting PI3K would be a potential approach for enhancing the radiosensitivity of K-RAS mutated (K-RASmut) NSCLC cell lines A549 and H460.

Short-term (1-2 h) pre-treatment of cells with the PI3K inhibitor PI-103 (1 μM) inhibited Akt/DNA-PKcs activity, blocked DSBs repair and induced radiosensitivity, while long-term (24 h) pre-treatment did not. Lack of an effect after 24 h of PI-103 pre-treatment was due to reactivation of K-Ras/MEK/ERK-dependent Akt. However, long-term treatment with the combination of PI-103 and MEK inhibitor PD98059 completely blocked reactivation of Akt and impaired DSBs repair through non-homologous end joining (NHEJ) leading to radiosensitization. The effect of PI3K inhibition on Akt signaling was also tested in A549 mouse xenografts. P-Akt and P-DNA-PKcs were inhibited 30 min post-irradiation in xenografts, which were pretreated by PI-103 30 min before irradiation. However, Akt was reactivated 30 min post-irradiation in tumors, which were pre-treated for 3 h with PI-103 before irradiation. After a 24 h pretreatment with PI-103, a significant reactivation of Akt was achieved 24 h after irradiation. Thus, due to MEK/ERK-dependent reactivation of Akt, targeting PI3K alone is not a suitable approach for radiosensitizing K-RASmut NSCLC cells, indicating that dual targeting of PI3K and MEK is an efficient approach to improve radiotherapy outcome.

Anti-Trop2 blockade enhances the therapeutic efficacy of ErbB3 inhibition in head and neck squamous cell carcinoma

ErbB3 has been widely implicated in treatment resistance, but its role as a primary treatment target is less clear. Canonically ErbB3 requires EGFR or ErbB2 for activation, whereas these two established treatment targets are thought to signal independently of ErbB3. In this study, we show that ErbB3 is essential for tumor growth of treatment-naive HNSCC patient-derived xenografts. This ErbB3 dependency occurs via ErbB3-mediated control of EGFR activation and HIF1α stabilization, which require ErbB3 and its ligand neuregulin-1. Here, we show that ErbB3 antibody treatment selects for a population of ErbB3-persister cells that express high levels of the transmembrane protein Trop2 that we previously identified as an inhibitor of ErbB3. Co-treatment with anti-ErbB3 and anti-Trop2 antibodies is synergistic and produces a greater anti-tumor response than either antibody alone. Collectively, these data both compel a revision of ErbB-family signaling and delineate a strategy for its effective inhibition in HNSCC.

Abstract A140: MERTK mediates intrinsic and adaptive resistance to AXL-targeting agents

The TAM family of receptor tyrosine kinases (RTKs) has been discovered to play a predominant role in promoting the growth, survival, and metastatic spread of several tumor types. AXL and MERTK are two TAM family RTKs that are overexpressed in head and neck squamous cell carcinoma (HNSCC), triple-negative breast cancer (TNBC), and non-small cell lung cancer (NSCLC), malignancies that are highly metastatic and lethal. The AXL receptor is the most well-characterized TAM receptor and has been found to mediate resistance to both conventional and targeted cancer therapies. Since AXL is overexpressed in aggressive tumor types, cancer patients are currently being enrolled in clinical trials testing AXL inhibitors. In the current study, we analyzed the efficacy of AXL inhibitors—both small molecule and monoclonal antibody therapy—in HNSCC, TNBC, and NSCLC preclinical models. We observed limited efficacy of anti-AXL targeting strategies across these different models, which was attributed to the upregulation of MERTK. MERTK was robustly overexpressed in cell lines and patient-derived xenografts treated with AXL inhibitors. Inhibition of MERTK sensitized HNSCC, TNBC, and NSCLC preclinical models to AXL inhibitors, leading to a more potent blockade of downstream signaling, decreased expansion of tumor cells in culture, and reduced tumor growth in vivo. Furthermore, ectopic overexpression of MERTK in AXL inhibitor-sensitive models resulted in resistance to AXL-targeting strategies. These results suggest that cotargeting both AXL and MERTK may be highly beneficial in a variety of tumor types where both receptors are expressed and may therefore prolong antitumor effects and improve the survival of patients with lethal malignancies.

Citation Format: Nellie K. McDaniel, Christopher T. Cummings, Toni M. Brand, Mari Iida, Justus Hulse, Hannah E. Pearson, Rachel A. Orbuch, Olivia J. Ondracek, Kurtis D. Davies, Parkash Gill, Xiaodong Wang, Stephen V. Frye, H. Shelton Earp, Randall J. Kimple, Paul M. Harari, Deborah DeRyckere, Douglas K. Graham, Deric L. Wheeler. MERTK mediates intrinsic and adaptive resistance to AXL-targeting agents [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A140.

Abstract 51: Potential and challenges in co-targeting mTORC and EGFR signaling as a therapeutic strategy in HNSCC

Background: Head and neck squamous cell carcinomas (HNSCCs) have high rates of mutation and other alterations along the PI3K/AKT/mTORC signaling axis. This has led to interest in the use of therapeutics targeting this pathway; however, identifying reliable predictive biomarkers to guide patient selection remains challenging. Despite excellent preclinical data, the use of these compounds as monotherapy has been underwhelming in initial clinical trials. The EGFR monoclonal antibody cetuximab remains the only approved targeted agent for HNSCC and with reasonable toxicity profiles, has potential use in combination therapy.

Methods: Both catalytic mTORC (AZD8055) and PI3K/mTORC(NVP-BEZ-235) inhibitors were tested +/- cetuximab in several in vitro and in vivo pre-clinical models. A panel of HNSCC cell lines and patient derived xenografts (PDX) were evaluated for PI3K/AKT/mTORC pathway mutation by sequencing and potential protein biomarker by immunoblot and IHC. Cell lines were assayed for sensitivity to all three agents by growth inhibition and clonogenic survival assay. DNA replication (BrdU uptake) and apoptosis (Capase 3/7 activity) were investigated to assess the mechanism of inhibition. The specificity of the molecular targeted effects was confirmed by siRNA knockdown. Five unique PDX models that presented PIK3CA mutation or intrinsic cetuximab resistance were treated with a combination of cetuximab and the dual mTORC inhibitor AZD8055 in a nude mouse model. Matched PDX derived cell strains were generated to investigate differences in response observed in in vitro and in vivo settings.

Results: Assessment of the panel of HNSCC cell lines by mutational hotspot sequencing did not reveal any obvious sensitizing mutations, whereas putative protein biomarkers (e.g. PIK3CA, pAKT) were elevated in some cell lines. All cell lines showed modest response to both PI3K/mTORC and dual mTORC inhibition. The addition of cetuximab to either agent produced modest additive effect. Mechanistic studies revealed that growth inhibition rather than death induction was the major anticancer effect. SiRNA knockdown showed similar molecular signaling and functional effects to drug inhibition. Using the PDX models, in vivo single agent mTORC inhibition inhibited growth of a PIK3CA mutant cancer, but had no effect on any PIK3CAWT or a second PIK3CA mutant model. In all models the combination therapy showed greater growth delay than monotherapy. In matched PDX derived cell strains, in vitro responses were similar when grown in 3D culture but cells displayed greater sensitivity when grown in 2D culture, suggesting that tumor microenvironment contributes to response.

Conclusions: The uniform ability of PI3K/mTORC and mTORC inhibition to suppress the growth of HNSCC cells highlights the role of this signaling pathway to drive the proliferation. In vivo, despite some PDX models meeting likely selection criteria, the single agent therapy was largely ineffective. Conversely, the combination treatment produced growth delay and suggests the potential for adding a catalytic mTORC inhibitor to cetuximab therapy for HNSCC patients. Overall, these results add to a growing body of evidence suggesting approaches that attempt to match genetic alternation or other biomarker to the optimal therapy in HNSCC remain complex and challenging.

Citation Format: Adam D. Swick, Prashanth J. Prabakaran, Margot C. Miller, Amal M. Javaid, Michael M. Fisher, Emmanuel Sampene, Irene M. Ong, Mari Iida, Deric L. Wheeler, Kwangok P. Nickel, Justine Y. Bruce, Randall J. Kimple. Potential and challenges in co-targeting mTORC and EGFR signaling as a therapeutic strategy in HNSCC [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; April 23-25, 2017; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(23_Suppl):Abstract nr 51.

Overcoming Resistance to Cetuximab with Honokiol, A Small-Molecule Polyphenol

Overexpression and activation of the EGFR have been linked to poor prognosis in several human cancers. Cetuximab is a mAb against EGFR that is used for the treatment in head and neck squamous cell carcinoma (HNSCC) and metastatic colorectal cancer. Unfortunately, most tumors have intrinsic or will acquire resistance to cetuximab during the course of therapy. Honokiol is a natural compound found in the bark and leaves of the Chinese Magnolia tree and is established to have several anticancer properties without appreciable toxicity. In this study, we hypothesized that combining cetuximab and honokiol treatments could overcome acquired resistance to cetuximab. We previously developed a model of acquired resistance to cetuximab in non-small cell lung cancer H226 cell line. Treatment of cetuximab-resistant clones with honokiol and cetuximab resulted in a robust antiproliferative response. Immunoblot analysis revealed the HER family and their signaling pathways were downregulated after combination treatment, most notably the proliferation (MAPK) and survival (AKT) pathways. In addition, we found a decrease in phosphorylation of DRP1 and reactive oxygen species after combination treatment in cetuximab-resistant clones, which may signify a change in mitochondrial function. Furthermore, we utilized cetuximab-resistant HNSCC patient-derived xenografts (PDX) to test the benefit of combinatorial treatment in vivo There was significant growth delay in PDX tumors after combination treatment with a subsequent downregulation of active MAPK, AKT, and DRP1 signaling as seen in vitro Collectively, these data suggest that honokiol is a promising natural compound in overcoming acquired resistance to cetuximab. Mol Cancer Ther; 17(1); 204-14. ©2017 AACR.

Abstract 4176: Targeting TAM family members with antibody or small molecule inhibitors enhances therapeutic modalities of HNSCC

Radiation, cisplatin, and cetuximab are clinical therapeutics used in the treatment of head and neck squamous cell carcinoma (HNSCC). Despite clinical success with these modalities, development of both intrinsic and acquired resistance is an emerging problem in the management of HNSCC. Thus, identifying and targeting molecules driving this drug resistance is essential for improving efficacy of treatment approaches.

Recent studies have identified a role for the TAM family of receptor tyrosine kinases (Tyro, Axl, and Mer) in tumor biology, especially the Axl receptor in promoting tumor growth and metastasis. Previously, we identified Axl as a logical molecular target in HNSCC and indicated that it may play a pivotal role in resistance to radiation, cisplatin, and cetuximab. In the current study, we advanced these early findings into pre-clinical models using patient-derived xenografts (PDXs). We have shown that small molecules targeting Axl can enhance therapy in PDXs that express high levels of Axl and have been identified as resistant to radiation, cisplatin, and cetuximab. Current studies are focusing on antibody-based targeting of Axl using PDXs and genetically-modified models of resistance. Furthermore, studies focused on co-targeting of Axl and Mer in vitro and in vivo have shown striking results and denote the importance of establishing logical approaches to target TAMs in the management of HNSCC.

Finally, investigations into the molecular mechanisms of how Axl signaling can lead to resistance have underscored the importance of tyrosine 821 (Y821) of Axl. Overexpression of Axl rendered cetuximab sensitive lines resistant, but cell lines overexpressing Axl-Y821F retained their sensitivity to cetuximab. Advancing this line of study in vivo indicated that tumors expressing Axl were resistant to cetuximab whereas tumors harboring the Y821 mutation were sensitive demonstrating that signals emanating from Y821 may be critical for cetuximab resistant pathways.

Collectively, the studies presented herein identify the TAM family of receptors as key players in radiation, cisplatin, and cetuximab resistance. These results provide rationale for the clinical targeting of TAM receptors to enhance the therapeutic modalities used in treating HNSCC.

Citation Format: Nellie K. Black, Mari Iida, Tamara S. Rodems, Toni M. Brand, Randall J. Kimple, Deric L. Wheeler. Targeting TAM family members with antibody or small molecule inhibitors enhances therapeutic modalities of HNSCC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4176. doi:10.1158/1538-7445.AM2017-4176

Abstract 3333: The receptor tyrosine kinase AXL mediates nuclear translocation of the epidermal growth factor receptor

The epidermal growth factor receptor (EGFR) is an important therapeutic target in patients with various cancers. Unfortunately, resistance to anti-EGFR therapeutics is common. Previous studies in our laboratory identified two mechanisms of resistance to the EGFR monoclonal antibody cetuximab: First, the nuclear translocation of EGFR bypasses the inhibitory effects of cetuximab; and second, the receptor tyrosine kinase AXL mediates cetuximab resistance by maintaining EGFR activation and downstream signaling. On the basis of these findings, we hypothesized that AXL could mediate the nuclear translocation of EGFR in the setting of cetuximab resistance. We found that NSCLC cetuximab-resistant clones and patient-derived xenografts (PDXs) had increased abundance of nuclear EGFR (nEGFR) and AXL. Cellular fractionation techniques, super resolution microscopy, and electron microcopy revealed that genetic loss of AXL diminished the nuclear translocation and accumulation of EGFR. Building on previous studies indicating that SRC family kinases (SFKs) and HER family ligands mediate the nuclear translocation of EGFR, we found that AXL knockdown down-regulated the expression of the SFKs YES and LYN, and the ligand neuregulin-1 (NRG1). Furthermore, AXL knockdown decreased the interaction between EGFR and HER3 and the nuclear abundance of HER3. Nuclear localization of EGFR could be rescued only upon simultaneous overexpression of Lyn and NRG1 in cells depleted of AXL. Collectively, these data uncover a previously unrecognized role for AXL in regulating the nuclear translocation of EGFR and suggest that AXL-mediated SFK activation and NRG1 expression are necessary and sufficient to regulate this process.

Citation Format: Toni M. Brand, Mari Iida, Kelsey L. Corrigan, Cara M. Braverman, John P. Coan, Bailey G. Flanigan, Andrew P. Stein, Ravi Salgia, Jana Rolff, Randall J. Kimple, Deric L. Wheeler. The receptor tyrosine kinase AXL mediates nuclear translocation of the epidermal growth factor receptor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3333. doi:10.1158/1538-7445.AM2017-3333

Cotargeting mTORC and EGFR Signaling as a Therapeutic Strategy in HNSCC

Head and neck squamous cell carcinomas (HNSCC) are frequently altered along the PI3K/AKT/mTORC signaling axis. Despite excellent preclinical data, the use of compounds targeting this pathway as monotherapy has been underwhelming in initial clinical trials, and identification of predictive biomarkers remains challenging. To investigate mTORC-specific inhibition, we tested catalytic mTORC (AZD8055) and PI3K/mTORC (NVP-BEZ-235) inhibitors ± cetuximab in a panel of HNSCC cell lines and patient-derived xenografts (PDX). Cell lines were assayed for response to all agents and siRNA knockdown of targets by multiple approaches. All cell lines showed similar response to both drug and siRNA inhibition of both PI3K and mTORC pathways, with anti-EGFR combination producing modest additive effect. Five PDX models that presented PIK3CA mutation or intrinsic cetuximab resistance were treated with a combination of cetuximab and AZD8055. In vivo single-agent mTORC inhibition inhibited growth of one PIK3CA-mutant cancer, but had little effect on any PIK3CA^WT or a second PIK3CA-mutant model. In all models, the combination therapy showed greater growth delay than monotherapy. The uniform ability of PI3K and mTORC inhibition to suppress the growth of HNSCC cells highlights the pathway's role in driving proliferation. Although single-agent therapy was largely ineffective in vivo, improved response of combination treatment in an array of PDXs suggests the potential for adding a catalytic mTORC inhibitor to cetuximab therapy. Overall, these results add to a growing body of evidence, suggesting that approaches that attempt to match biomarkers to the optimal therapy in HNSCC remain complex and challenging. Mol Cancer Ther; 16(7); 1257-68. ©2017 AACR.

RETRACTED: The receptor tyrosine kinase AXL mediates nuclear translocation of the epidermal growth factor receptor

The epidermal growth factor receptor (EGFR) is a therapeutic target in patients with various cancers. Unfortunately, resistance to EGFR-targeted therapeutics is common. Previous studies identified two mechanisms of resistance to the EGFR monoclonal antibody cetuximab. Nuclear translocation of EGFR bypasses the inhibitory effects of cetuximab, and the receptor tyrosine kinase AXL mediates cetuximab resistance by maintaining EGFR activation and downstream signaling. Thus, we hypothesized that AXL mediated the nuclear translocation of EGFR in the setting of cetuximab resistance. Cetuximab-resistant clones of non-small cell lung cancer in culture and patient-derived xenografts in mice had increased abundance of AXL and nuclear EGFR (nEGFR). Cellular fractionation analysis, super-resolution microscopy, and electron microscopy revealed that genetic loss of AXL reduced the accumulation of nEGFR. SRC family kinases (SFKs) and HER family ligands promote the nuclear translocation of EGFR. We found that AXL knockdown reduced the expression of the genes encoding the SFK family members YES and LYN and the ligand neuregulin-1 (NRG1). AXL knockdown also decreased the interaction between EGFR and the related receptor HER3 and accumulation of HER3 in the nucleus. Overexpression of LYN and NRG1 in cells depleted of AXL resulted in accumulation of nEGFR, rescuing the deficit induced by lack of AXL. Collectively, these data uncover a previously unrecognized role for AXL in regulating the nuclear translocation of EGFR and suggest that AXL-mediated SFK and NRG1 expression promote this process.

Targeting the HER Family with Pan-HER Effectively Overcomes Resistance to Cetuximab

Cetuximab, an antibody against the EGFR, has shown efficacy in treating head and neck squamous cell carcinoma (HNSCC), metastatic colorectal cancer, and non-small cell lung cancer (NSCLC). Despite the clinical success of cetuximab, many patients do not respond to cetuximab. Furthermore, virtually all patients who do initially respond become refractory, highlighting both intrinsic and acquired resistance to cetuximab as significant clinical problems. To understand mechanistically how cancerous cells acquire resistance, we previously developed models of acquired resistance using the H226 NSCLC and UM-SCC1 HNSCC cell lines. Cetuximab-resistant clones showed a robust upregulation and dependency on the HER family receptors EGFR, HER2, and HER3. Here, we examined pan-HER, a mixture of six antibodies targeting these receptors on cetuximab-resistant clones. In cells exhibiting acquired or intrinsic resistance to cetuximab, pan-HER treatment decreased all three receptors' protein levels and downstream activation of AKT and MAPK. This correlated with decreased cell proliferation in cetuximab-resistant clones. To determine whether pan-HER had a therapeutic benefit in vivo, we established de novo cetuximab-resistant mouse xenografts and treated resistant tumors with pan-HER. This regimen resulted in a superior growth delay of cetuximab-resistant xenografts compared with mice continued on cetuximab. Furthermore, intrinsically cetuximab-resistant HNSCC patient-derived xenograft tumors treated with pan-HER exhibited significant growth delay compared with vehicle/cetuximab controls. These results suggest that targeting multiple HER family receptors simultaneously with pan-HER is a promising treatment strategy for tumors displaying intrinsic or acquired resistance to cetuximab. Mol Cancer Ther; 15(9); 2175-86. ©2016 AACR.

Abstract 247: Understanding the role of tyrosine 1101 in the nuclear translocation of the epidermal growth factor receptor

Triple-negative breast cancer (TNBC) is a subclass of breast cancers that are negative for the estrogen receptor, the progesterone receptor, and HER2. Currently, TNBCs have poor prognosis and very few proven molecular targets. One promising target in TNBC has been the epidermal growth factor receptor (EGFR), as it is overexpressed in as many as 80% of TNBCs. Strikingly, however, antibody-based therapy directed against the EGFR (cetuximab) in TNBCs has had modest clinical impact. Over the last decade, advances in EGFR biology have established that the EGFR functions in two distinct signaling pathways: classical membrane-bound signaling and the nuclear EGFR signaling pathway. We previously demonstrated that EGFR nuclear translocation is dependent on Src Family Kinases (SFKs) and phosphorylation of tyrosine 1101 (Y1101) on the cytoplasmic tail of the EGFR. In these studies, translocation of the EGFR to the nucleus led to activation of the nuclear EGFR signaling pathway, which resulted in cetuximab resistance. Resistance could be reversed by simultaneously targeting both the nuclear EGFR signaling pathway and the classical EGFR signaling pathway through the inhibition of its nuclear transport (blockade of SFKs) and with cetuximab, respectively. Despite the identification of nuclear EGFR as a functional molecular target in TNBC, the role of Y1101 in EGFR translocation has yet to be identified.

In this study, we seek to better understand the role of Y1101 in the nuclear translocation of EGFR in TNBC. Using a battery of TNBC cell lines, we have created isogenic pairs that overexpress either wild type EGFR (EGFR-WT) or EGFR with a mutant Y1101 (EGFR-Y110F). Using electron and super-resolution confocal microscopy as well as cellular fractionation, we have shown that EGFR-Y1101 undergoes normal endocytosis upon EGF stimulation in multiple cell lines, but unlike EGFR-WT, EGFR-Y1101F deposits around the perinuclear region. These data suggest that EGFR-Y1101F is able to undergo normal translocation to the perinuclear space, but that amino acid Y1101 is necessary for direct nuclear entry, potentially due to its interactions with nucleoporins. Current work is focused on the identification of nucleoporins with which EGFR-Y1101 may interact. In addition, continued work focuses on allelic mutation using CrisprCas9. Ultimately, the long-term goal of this project is to understand how Y1101 mediates EGFR nuclear translocation. With this information, we will then aim to develop allosteric inhibitors of Y1101 that may abrogate EGFR nuclear translocation and lead to a novel therapeutic which targets the nuclear EGFR signaling pathway in TNBC.

Citation Format: Bailey G. Flanigan, Mari Iida, Toni M. Brand, Deric L. Wheeler. Understanding the role of tyrosine 1101 in the nuclear translocation of the epidermal growth factor receptor. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 247.

Verticillium dahliae Infects, Alters Plant Biomass, and Produces Inoculum on Rotation Crops

Verticillium wilt, caused by Verticillium dahliae, reduces yields of potato and mint. Crop rotation is a potential management tactic for Verticillium wilt; however, the wide host range of V. dahliae may limit the effectiveness of this tactic. The hypothesis that rotation crops are infected by V. dahliae inoculum originating from potato and mint was tested by inoculation of mustards, grasses, and Austrian winter pea with eight isolates of V. dahliae. Inoculum density was estimated from plants and soil. Typical wilt symptoms were not observed in any rotation crop but plant biomass of some crops was reduced, not affected, or increased by infection of specific isolates. Each isolate was host-specific and infected a subset of the rotation crops tested but microsclerotia from at least one isolate were observed on each rotation crop. Some isolates were host-adapted and differentially altered plant biomass or produced differential amounts of inoculum on rotation crops like arugula and Austrian winter pea, which supported more inoculum of specific isolates than potato. Evidence of asymptomatic and symptomatic infection and differential inoculum formation of V. dahliae on rotation crops presented here will be useful in designing rotations for management of Verticillium wilt.

Adaptive responses to antibody based therapy

Receptor tyrosine kinases (RTKs) represent a large class of protein kinases that span the cellular membrane. There are 58 human RTKs identified which are grouped into 20 distinct families based upon their ligand binding, sequence homology and structure. They are controlled by ligand binding which activates intrinsic tyrosine-kinase activity. This activity leads to the phosphorylation of distinct tyrosines on the cytoplasmic tail, leading to the activation of cell signaling cascades. These signaling cascades ultimately regulate cellular proliferation, apoptosis, migration, survival and homeostasis of the cell. The vast majority of RTKs have been directly tied to the etiology and progression of cancer. Thus, using antibodies to target RTKs as a cancer therapeutic strategy has been intensely pursued. Although antibodies against the epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2) have shown promise in the clinical arena, the development of both intrinsic and acquired resistance to antibody-based therapies is now well appreciated. In this review we provide an overview of the RTK family, the biology of EGFR and HER2, as well as an in-depth review of the adaptive responses undertaken by cells in response to antibody based therapies directed against these receptors. A greater understanding of these mechanisms and their relevance in human models will lead to molecular insights in overcoming and circumventing resistance to antibody based therapy.

Genetic deletion of TNFα inhibits ultraviolet radiation-induced development of cutaneous squamous cell carcinomas in PKCε transgenic mice via inhibition of cell survival signals

Protein kinase C epsilon (PKCε), a Ca(2+)-independent phospholipid-dependent serine/threonine kinase, is among the six PKC isoforms (α, δ, ε, η, μ, ζ) expressed in both mouse and human skin. Epidermal PKCε level dictates the susceptibility of PKCε transgenic (TG) mice to the development of cutaneous squamous cell carcinomas (SCC) elicited either by repeated exposure to ultraviolet radiation (UVR) or by using the DMBA initiation-TPA (12-O-tetradecanoylphorbol-13-acetate) tumor promotion protocol (Wheeler,D.L. et al. (2004) Protein kinase C epsilon is an endogenous photosensitizer that enhances ultraviolet radiation-induced cutaneous damage and development of squamous cell carcinomas. Cancer Res., 64, 7756-7765). Histologically, SCC in TG mice, like human SCC, is poorly differentiated and metastatic. Our earlier studies to elucidate mechanisms of PKCε-mediated development of SCC, using either DMBA-TPA or UVR, indicated elevated release of cytokine TNFα. To determine whether TNFα is essential for the development of SCC in TG mice, we generated PKCε transgenic mice/TNFα-knockout (TG/TNFαKO) by crossbreeding TNFαKO with TG mice. We now present that deletion of TNFα in TG mice inhibited the development of SCC either by repeated UVR exposures or by the DMBA-TPA protocol. TG mice deficient in TNFα elicited both increase in SCC latency and decrease in SCC incidence. Inhibition of UVR-induced SCC development in TG/TNFαKO was accompanied by inhibition of (i) the expression levels of TNFα receptors TNFRI and TNFRII and cell proliferation marker ornithine decarboxylase and metastatic markers MMP7 and MMP9, (ii) the activation of transcription factors Stat3 and NF-kB and (iii) proliferation of hair follicle stem cells and epidermal hyperplasia. The results presented here provide the first genetic evidence that TNFα is linked to PKCε-mediated sensitivity to DMBA-TPA or UVR-induced development of cutaneous SCC.

AXL Is a Logical Molecular Target in Head and Neck Squamous Cell Carcinoma

PURPOSE

Head and neck squamous cell carcinoma (HNSCC) represents the eighth most common malignancy worldwide. Standard-of-care treatments for patients with HNSCC include surgery, radiation, and chemotherapy. In addition, the anti-EGFR monoclonal antibody cetuximab is often used in combination with these treatment modalities. Despite clinical success with these therapeutics, HNSCC remains a difficult malignancy to treat. Thus, identification of new molecular targets is critical.

EXPERIMENTAL DESIGN

In the current study, the receptor tyrosine kinase AXL was investigated as a molecular target in HNSCC using established cell lines, HNSCC patient-derived xenografts (PDX), and human tumors. HNSCC dependency on AXL was evaluated with both anti-AXL siRNAs and the small-molecule AXL inhibitor R428. Furthermore, AXL inhibition was evaluated with standard-of-care treatment regimens used in HNSCC.

RESULTS

AXL was found to be highly overexpressed in several models of HNSCC, where AXL was significantly associated with higher pathologic grade, presence of distant metastases, and shorter relapse-free survival in patients with HNSCC. Further investigations indicated that HNSCC cells were reliant on AXL for cellular proliferation, migration, and invasion. In addition, targeting AXL increased HNSCC cell line sensitivity to chemotherapy, cetuximab, and radiation. Moreover, radiation-resistant HNSCC cell line xenografts and PDXs expressed elevated levels of both total and activated AXL, indicating a role for AXL in radiation resistance.

CONCLUSIONS

This study provides evidence for the role of AXL in HNSCC pathogenesis and supports further preclinical and clinical evaluation of anti-AXL therapeutics for the treatment of patients with HNSCC.

Overcoming acquired resistance to cetuximab by dual targeting HER family receptors with antibody-based therapy

Background

Cetuximab, an anti-EGFR monoclonal antibody, is used to treat several cancers. However, many patients who initially respond to cetuximab acquire resistance. To examine mechanisms of acquired resistance, we developed a series of cetuximab-resistant (Ctx^R) clones derived from the cetuximab sensitive (Ctx^S) non-small cell lung cancer (NSCLC) cell line H226. Previous studies characterizing this model revealed that: 1) EGFR was robustly overexpressed in Ctx^R clones due to decreased EGFR ubiquitination and degradation and 2) Ctx^R clones expressed increased HER2 and HER3 activation resulting in constitutive activation of the PI3K/AKT signaling axis. These findings suggest that dual targeting HER family receptors would be highly beneficial in the Ctx^R setting.

Results

Since HER3 has been implicated in resistance to EGFR inhibitors, the efficacy of dually targeting both EGFR and HER3 in Ctx^R models was evaluated. First, EGFR and HER3 expression were knocked down with siRNAs. Compared to the Ctx^S parental cell line (HP), all Ctx^R clones exhibited robust decreases in cell proliferation upon dual knockdown. Analysis of Ctx^R clones indicated that neuregulin-1 was highly overexpressed compared to HP cells. Incubation of HP cells with neuregulin-1 rendered them resistant to cetuximab. Next, dual treatment of Ctx^R clones with cetuximab and the HER3 neutralizing monoclonal antibody (mAb) U3-1287 led to potent anti-proliferative effects. Blockade of EGFR with cetuximab resulted in inactivation of MAPK, while blockade of HER3 with U3-1287 resulted in the inactivation of AKT. Treatment with both mAbs resulted in knockdown of both signaling pathways simultaneously. HER2 was also strongly inactivated upon dual mAb therapy, suggesting that this treatment regimen can diminish signaling from three HER family receptors. De novo Ctx^R H226 mouse xenografts were established to determine if dual therapy could overcome acquired resistance to cetuximab in vivo. Tumors that had acquired resistance to cetuximab were significantly growth delayed upon dual treatment of U3-1287 and cetuximab compared to those continued on cetuximab only. Combinatorial-treated xenograft tumors expressed decreased Ki67 and increased cleaved caspase-3 levels compared to tumors treated with either monotherapy.

Conclusions

These studies demonstrate that dually targeting HER family receptors with antibody-based therapies can overcome acquired resistance to cetuximab.

Abstract LB-215: The TAM family of receptor tyrosine kinases play a role in acquired resistance to cetuximab

Cetuximab is an anti-epidermal growth factor receptor (EGFR) monoclonal antibody that has shown efficacy in metastatic colorectal cancer, head and neck squamous cell carcinoma (HNSCC) and non-small cell lung cancer (NSCLC). Clinical data suggests that patients whom initially respond to cetuximab eventually acquire resistance, highlighting the importance of understanding resistant mechanisms for the development of better treatment regimes for cancer patients. Recent studies have identified a role for the TAM family of receptor tyrosine kinases (Tyro, Axl, and Mer) in tumor biology, and more specifically the Axl receptor as playing a key role in promoting tumor growth and metastasis. In the current study, we utilized NSCLC and HNSCC models of acquired resistance to cetuximab and found that Axl was overexpressed, activated, and highly associated with EGFR as compared parental controls. Further, using siRNA technology and novel Axl targeting agents (antibody and tyrosine kinase inhibitor), Axl was found to regulate proliferation, EGFR activation, and MAPK signaling in cetuximab resistant clones (CtxR). Additionally, Axl mRNA expression was regulated by EGFR induced MAPK activation in resistant cells. To investigate the role of Axl in in vivo models of acquired resistance to cetuximab, de novo acquired resistance was created by prolonged treatment of cetuximab sensitive (CtxS) tumor xenografts with cetuximab. Analysis of resultant CtxR tumors demonstrated that Axl was hyperactivated and highly associated with EGFR as compared to vehicle treated tumors. In addition, CtxR tumors expressing the highest levels of phosphorylated Axl also expressed hyperactivated EGFR, supporting the role of Axl in EGFR activation. Finally, to expand these findings to other members of the TAM family, Tyro, Axl, or Mer were stably overexpressed in CtxS parental NSCLC cells and tested for cetuximab response. The results of this experimentation indicated that stable overexpression of each TAM receptor rendered CtxS cells resistant to cetuximab therapy. Collectively, the studies presented herein identify the TAM family of receptors as key players in acquired resistance to cetuximab and provide rationale for the clinical evaluation of anti-TAM receptor therapeutics in the resistant setting.

Citation Format: Toni Michel Brand, Mari Iida, Kelsey L. Corrigan, Neha Luthar, Megan Hornung, Mahmoud Toulany, Parkash Gill, Ravi Salgia, Deric L. Wheeler. The TAM family of receptor tyrosine kinases play a role in acquired resistance to cetuximab. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-215. doi:10.1158/1538-7445.AM2014-LB-215

AXL mediates resistance to cetuximab therapy

The EGFR antibody cetuximab is used to treat numerous cancers, but intrinsic and acquired resistance to this agent is a common clinical outcome. In this study, we show that overexpression of the oncogenic receptor tyrosine kinase AXL is sufficient to mediate acquired resistance to cetuximab in models of non-small cell lung cancer (NSCLC) and head and neck squamous cell carcinoma (HNSCC), where AXL was overexpressed, activated, and tightly associated with EGFR expression in cells resistant to cetuximab (Ctx(R) cells). Using RNAi methods and novel AXL-targeting agents, we found that AXL activation stimulated cell proliferation, EGFR activation, and MAPK signaling in Ctx(R) cells. Notably, EGFR directly regulated the expression of AXL mRNA through MAPK signaling and the transcription factor c-Jun in Ctx(R) cells, creating a positive feedback loop that maintained EGFR activation by AXL. Cetuximab-sensitive parental cells were rendered resistant to cetuximab by stable overexpression of AXL or stimulation with EGFR ligands, the latter of which increased AXL activity and association with the EGFR. In tumor xenograft models, the development of resistance following prolonged treatment with cetuximab was associated with AXL hyperactivation and EGFR association. Furthermore, in an examination of patient-derived xenografts established from surgically resected HNSCCs, AXL was overexpressed and activated in tumors that displayed intrinsic resistance to cetuximab. Collectively, our results identify AXL as a key mediator of cetuximab resistance, providing a rationale for clinical evaluation of AXL-targeting drugs to treat cetuximab-resistant cancers. Cancer Res; 74(18); 5152-64. ©2014 AACR.

Nuclear epidermal growth factor receptor is a functional molecular target in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a subclass of breast cancers (i.e., estrogen receptor-negative, progesterone receptor-negative, and HER2-negative) that have poor prognosis and very few identified molecular targets. Strikingly, a high percentage of TNBCs overexpresses the EGF receptor (EGFR), yet EGFR inhibition has yielded little clinical benefit. Over the last decade, advances in EGFR biology have established that EGFR functions in two distinct signaling pathways: (i) classical membrane-bound signaling and (ii) nuclear signaling. Previous studies have demonstrated that nuclear EGFR (nEGFR) can enhance resistance to anti-EGFR therapies and is correlated with poor overall survival in breast cancer. On the basis of these findings, we hypothesized that nEGFR may promote intrinsic resistance to cetuximab in TNBC. To examine this question, a battery of TNBC cell lines and human tumors were screened and found to express nEGFR. Knockdown of EGFR expression demonstrated that TNBC cell lines retained dependency on EGFR for proliferation, yet all cell lines were resistant to cetuximab. Furthermore, Src Family Kinases (SFKs) influenced nEGFR translocation in TNBC cell lines and in vivo tumor models, where inhibition of SFK activity led to potent reductions in nEGFR expression. Inhibition of nEGFR translocation led to a subsequent accumulation of EGFR on the plasma membrane, which greatly enhanced sensitivity of TNBC cells to cetuximab. Collectively, these data suggest that targeting both the nEGFR signaling pathway, through the inhibition of its nuclear transport, and the classical EGFR signaling pathway with cetuximab may be a viable approach for the treatment of patients with TNBC.

Targeting AKT with the allosteric AKT inhibitor MK-2206 in non-small cell lung cancer cells with acquired resistance to cetuximab

The epidermal growth factor receptor (EGFR) is a central regulator of tumor progression in human cancers. Cetuximab is an anti-EGFR monoclonal antibody that has been approved for use in oncology. Despite clinical success the majority of patients do not respond to cetuximab and those who initially respond frequently acquire resistance. To understand how tumor cells acquire resistance to cetuximab we developed a model of resistance using the non-small cell lung cancer line NCI-H226. We found that cetuximab-resistant (Ctx (R) ) clones manifested strong activation of EGFR, PI3K/AKT and MAPK. To investigate the role of AKT signaling in cetuximab resistance we analyzed the activation of the AKT pathway effector molecules using a human AKT phospho-antibody array. Strong activation was observed in Ctx (R) clones for several key AKT substrates including c-jun, GSK3β, eIF4E, rpS6, IKKα, IRS-1 and Raf1. Inhibition of AKT signaling by siAKT1/2 or by the allosteric AKT inhibitor MK-2206 resulted in robust inhibition of cell proliferation in all Ctx (R) clones. Moreover, the combinational treatment of cetuximab and MK-2206 resulted in further decreases in proliferation than either drug alone. This combinatorial treatment resulted in decreased activity of both AKT and MAPK thus highlighting the importance of simultaneous pathway inhibition to maximally affect the growth of Ctx (R) cells. Collectively, our findings demonstrate that AKT activation is an important pathway in acquired resistance to cetuximab and suggests that combinatorial therapy directed at both the AKT and EGFR/MAPK pathways may be beneficial in this setting.

Combined MET inhibition and topoisomerase I inhibition block cell growth of small cell lung cancer

Small cell lung cancer (SCLC) is a devastating disease, and current therapies have not greatly improved the 5-year survival rates. Topoisomerase (Top) inhibition is a treatment modality for SCLC; however, the response is short lived. Consequently, our research has focused on improving SCLC therapeutics through the identification of novel targets. Previously, we identified MNNG HOS transforming gene (MET) to be overexpressed and functional in SCLC. Herein, we investigated the therapeutic potential of combinatorial targeting of MET using SU11274 and Top1 using 7-ethyl-10-hydroxycamptothecin (SN-38). MET and TOP1 gene copy numbers and protein expression were determined in 29 patients with limited (n = 11) and extensive (n = 18) disease. MET gene copy number was significantly increased (>6 copies) in extensive disease compared with limited disease (P = 0.015). Similar TOP1 gene copy numbers were detected in limited and extensive disease. Immunohistochemical staining revealed a significantly higher Top1 nuclear expression in extensive (0.93) versus limited (0.15) disease (P = 0.04). Interestingly, a significant positive correlation was detected between MET gene copy number and Top1 nuclear expression (r = 0.5). In vitro stimulation of H82 cells revealed hepatocyte growth factor (HGF)-induced nuclear colocalization of p-MET and Top1. Furthermore, activation of the HGF/MET axis enhanced Top1 activity, which was abrogated by SU11274. Combination of SN-38 with SU11274 dramatically decreased SCLC growth as compared with either drug alone. Collectively, these findings suggest that the combinatorial inhibition of MET and Top1 is a potentially efficacious treatment strategy for SCLC.

Combining radiotherapy with MEK1/2, STAT5 or STAT6 inhibition reduces survival of head and neck cancer lines

BACKGROUND

Kinases downstream of growth factor receptors have been implicated in radioresistance and are, therefore, attractive targets to improve radiotherapy outcome in head and neck squamous cell carcinoma (HNSCC) patients.

METHODS

An antibody-based array was used to quantify the expression levels of multiple phospho-kinases involved in growth factor signaling in nine untreated or irradiated HNSCC lines. Radiosensitivity was assessed with clonogenic cell survival assays and correlated with the expression levels of the phospho-kinases. Inhibitors of the kinases that were associated with radiosensitivity were tested for their ability to increase radiosensitivity in the 3 most radioresistant HNSCC lines.

RESULTS

The basal expression of phosphorylated Yes, Src and STAT5A, and the expression after radiotherapy of phosphorylated AKT, MSK1/2, Src, Lyn, Fyn, Hck, and STAT6, were correlated with radiosensitivity in the panel of HNSCC lines. In combination with radiotherapy, inhibitors of AKT, p38 and Src Family Kinases (SFK) were variably able to reduce survival, whereas MEK1/2, STAT5 and STAT6 inhibition reduced survival in all cell lines. The combined effect of radiotherapy and the kinase inhibitors on cell survival was mostly additive, although also supra-additive effects were observed for AKT, MEK1/2, p38 and STAT5 inhibition.

CONCLUSIONS

Kinases of the AKT, MAPK, STAT and SFK pathways correlated with radiosensitivity in a panel of HNSCC lines. Particularly inhibitors against MEK1/2, STAT5 and STAT6 were able to decrease survival in combination with radiotherapy. Hence, inhibitors against these kinases have the potential to improve radiotherapy outcome in HNSCC patients and further research is warranted to confirm this in vivo.

Human epidermal growth factor receptor 3 (HER3) blockade with U3-1287/AMG888 enhances the efficacy of radiation therapy in lung and head and neck carcinoma

HER3 is a member of the epidermal growth factor receptor (EGFR) family of receptor tyrosine kinases. In the present study, we investigated the capacity of the HER3 blocking antibody, U3-1287/AMG888, to modulate the in vitro and in vivo radiation response of human squamous cell carcinomas of the lung and head and neck. We screened a battery of cell lines from these tumors for HER3 expression and demonstrated that all cell lines screened exhibited expression of HER3. Importantly, U3-1287/AMG888 treatment could block both basal HER3 activity and radiation induced HER3 activation. Proliferation assays indicated that HER3 blockade could decrease the proliferation of both HNSCC cell line SCC6 and NSCLC cell line H226. Further, we demonstrated that U3-1287/AMG888 can sensitize cells to radiation in clonogenic survival assays, in addition to increasing DNA damage as detected via λ-H2AX immunofluorescence. To determine if U3-1287/AMG888 could enhance radiation sensitivity in vivo we performed tumor growth delay experiments using SCC6, SCC1483, and H226 xenografts. The results of these experiments indicated that the combination of U3-1287/AMG888 and radiation could decrease tumor growth in studies using single or fractionated doses of radiation. Analysis of HER3 expression in tumor samples indicated that radiation treatment activated HER3 in vivo and that U3-1287/AMG888 could abrogate this activation. Immunohistochemistry analysis of SCC6 tumors treated with both U3-1287/AMG888 and a single dose of radiation demonstrated that various cell survival and proliferation markers could be reduced. Collectively our findings suggest that U3-1287/AMG888 in combination with radiation has an impact on cell and tumor growth by increasing DNA damage and cell death. These findings suggest that HER3 may play an important role in response to radiation therapy and blocking its activity in combination with radiation may be of therapeutic benefit in human tumors.

Nuclear EGFR as a molecular target in cancer

The epidermal growth factor receptor (EGFR) has been one of the most targeted receptors in the field of oncology. While anti-EGFR inhibitors have demonstrated clinical success in specific cancers, most patients demonstrate either intrinsic or acquired resistance within one year of treatment. Many mechanisms of resistance to EGFR inhibitors have been identified, one of these being attributed to alternatively localized EGFR from the cell membrane into the cell's nucleus. Inside the nucleus, EGFR functions as a co-transcription factor for several genes involved in cell proliferation and angiogenesis, and as a tyrosine kinase to activate and stabilize proliferating cell nuclear antigen and DNA dependent protein kinase. Nuclear localized EGFR is highly associated with disease progression, worse overall survival in numerous cancers, and enhanced resistance to radiation, chemotherapy, and the anti-EGFR therapies gefitinib and cetuximab. In this review the current knowledge of how nuclear EGFR enhances resistance to cancer therapeutics is discussed, in addition to highlighting ways to target nuclear EGFR as an anti-cancer strategy in the future.

Paxillin mutations affect focal adhesions and lead to altered mitochondrial dynamics: relevance to lung cancer

Cytoskeletal and focal adhesion abnormalities are observed in several types of cancer, including lung cancer. We have previously reported that paxillin (PXN) was mutated, amplified, and overexpressed in a significant number of lung cancer patient samples, that PXN protein was upregulated in more advanced stages of lung cancer compared with lower stages, and that the PXN gene was also amplified in some pre-neoplastic lung lesions. Among the mutations investigated, we previously found that PXN variant A127T in lung cancer cells enhanced cell proliferation and focal adhesion formation and colocalized with the anti-apoptotic protein B Cell Lymphoma 2 (BCL-2), which is known to localize to the mitochondria, among other sites. To further explore the effects of activating mutations of PXN on mitochondrial function, we cloned and expressed wild-type PXN and variants containing the most commonly occurring PXN mutations (P46S, P52L, G105D, A127T, P233L, T255I, D399N, E423K, P487L, and K506R) in a GFP-tagged vector using HEK-293 human embryonic kidney cells. Utilizing live-cell imaging to systematically study the effects of wild-type PXN vs. mutants, we created a model that recapitulates the salient features of the measured dynamics and conclude that compared with wild-type, some mutant clones confer enhanced focal adhesion and lamellipodia formation (A127T, P233L, and P487L) and some confer increased association with BCL-2, Dynamin-related Protein-1 (DRP-1), and Mitofusion-2 (MFN-2) proteins (P233L and D399N). Further, PXN mutants, through their interactions with BCL-2 and DRP-1, could regulate cisplatin drug resistance in human lung cancer cells. The data reported herein suggest that mutant PXN variants play a prominent role in mitochondrial dynamics with direct implications on lung cancer progression and hence, deserve further exploration as therapeutic targets.

Nuclear EGFR protein expression predicts poor survival in early stage non-small cell lung cancer

INTRODUCTION

Nuclear EGFR (nEGFR) has been identified in various human tumor tissues, including cancers of the breast, ovary, oropharynx, and esophagus, and has predicted poor patient outcomes. We sought to determine if protein expression of nEGFR is prognostic in early stage non-small cell lung cancer (NSCLC).

METHODS

Resected stages I and II NSCLC specimens were evaluated for nEGFR protein expression using immunohistochemistry (IHC). Cases with at least one replicate core containing ≥5% of tumor cells demonstrating strong dot-like nucleolar EGFR expression were scored as nEGFR positive.

RESULTS

Twenty-three (26.1% of the population) of 88 resected specimens stained positively for nEGFR. Nuclear EGFR protein expression was associated with higher disease stage (45.5% of stage II vs. 14.5% of stage I; p = 0.023), histology (41.7% in squamous cell carcinoma vs. 17.1% in adenocarcinoma; p = 0.028), shorter progression-free survival (PFS) (median PFS 8.7 months [95% CI 5.1-10.7 mo] for nEGFR positive vs. 14.5 months [95% CI 9.5-17.4 mo] for nEGFR negative; hazard ratio (HR) of 1.89 [95% CI 1.15-3.10]; p = 0.011), and shorter overall survival (OS) (median OS 14.1 months [95% CI 10.3-22.7 mo] for nEGFR positive vs. 23.4 months [95% CI 20.1-29.4 mo] for nEGFR negative; HR of 1.83 [95% CI 1.12-2.99]; p = 0.014).

CONCLUSIONS

Expression of nEGFR protein was associated with higher stage and squamous cell histology, and predicted shorter PFS and OS, in this patient cohort. Nuclear EGFR serves as a useful independent prognostic variable and as a potential therapeutic target in NSCLC.

Abstract LB-219: Nuclear EGFR serves as a functional molecular target in triple-negative breast cancer

Triple negative breast cancer (TNBC) is a subclass of breast cancer (i.e. estrogen receptor negative, progesterone receptor negative, and HER-2 negative) that has poor prognosis and very few identified molecular targets. Strikingly the majority of TNBC's overexpress the epidermal growth factor receptor (EGFR), yet EGFR inhibition has had very little clinical benefit in this setting. This suggests a gap in our knowledge of EGFR function in TNBC.

Over the last decade, advances in the basic biology of EGFR in human cancer have established that the EGFR functions in two distinct signaling pathways: 1) Classical membrane bound signaling (classical EGFR pathway) and 2) nuclear signaling (nEGFR pathway). In the nEGFR pathway, published data from our laboratory suggests that the EGFR is phosphorylated by Src family kinases (SFKs) at tyrosine 1101 (Y1101) and this phosphorylation is a necessary and early event for trafficking EGFR from the membrane to the nucleus. Nuclear EGFR has been correlated with poor overall survival in breast cancer and has been shown to enhance resistance to the EGFR targeted therapies cetuximab and gefitinib.

In the current study we found that TNBC cell lines were: 1) dependent on EGFR expression for proliferation as indicated by RNAi techniques, 2) resistant to cetuximab therapy and 3) harbored high levels of nEGFR and SFK activity. Further, a TNBC tissue microarray indicated that a portion of human TNBCs express nEGFR. Using molecular approaches to investigate if nEGFR and SFKs play a role in resistance to cetuximab we demonstrate that the overexpression of constitutively active Src (ca-Src) enhanced the nuclear localization of EGFR, while the overexpression of a negative regulator of Src, src-like adaptor protein (SLAP) prevented EGFR nuclear localization. SLAP not only associated with the EGFR but also led to a decrease in its phosphorylation at Y1101. Further, stable overexpression of several SFK members (Yes, Lyn, Fyn, Hck, Blk, and Fgr) in the breast cancer cell line MCF-7 led to both the activation of EGFR at Y1101 and potent increases in EGFR nuclear localization, indicating that SFKs exhibit functional redundancy in their ability to influence the nuclear translocation of the EGFR. Treatment of various cetuximab resistant TNBC cell lines with the small molecule SFK inhibitor dasatinib resulted in: 1) loss of nuclear localized EGFR, 2) increased plasma-membrane levels of the EGFR and 3) statistically significant, increases in cetuximab sensitivity.

Taken together, these findings suggest targeting nEGFR, by abrogating its translocation to the nucleus via SFK inhibition, increases plasma-membrane levels of EGFR where it is susceptible to targeting by cetuximab. The combinatorial therapy of cetuximab and dasatinib results in the simultaneous targeting of both the classical and nEGFR signaling pathways, and therefore may enhance the therapeutic response of nEGFR expressing TNBCs to cetuximab.

Citation Format: Toni M. Brand, Mari Iida, Neha Luthar, Matthew Wleklinski, Kellie Kostopoulos, Deric L. Wheeler. Nuclear EGFR serves as a functional molecular target in triple-negative breast cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-219. doi:10.1158/1538-7445.AM2013-LB-219

Abstract 4276: Mapping C-terminal transactivation domains of nuclear HER family receptor tyrosine kinases

The HER family of receptor tyrosine kinases consist of four receptors, epidermal growth factor receptor (EGFR/ErbB1/HER1), HER2 (ErbB2), HER3 (ErbB3), and HER4 (ErbB4). Collectively, this family of receptors plays a critical role in initiating proliferation and survival signals in several human cancers. It is well established that the HER family receptors rely on two distinct compartments of signaling: 1) Classical membrane bound signaling and 2) nuclear signaling. In the nucleus, HER family receptors can serve as co-transcription factors, mediated by their C-terminal domains, to promote transcription of several genes essential for cell proliferation and cell cycle regulation, including regulation of the gene cyclin D1. However, the domains within the C-terminus of EGFR, HER2 and HER3 that confer this transcriptional potential (transactivation domains) have yet to be defined.

In the current study we aimed to minimally map the regions of the C-terminal domains of EGFR, HER2 and HER3 that function as transactivation domains. We first demonstrate that EGFR, HER2, and HER3 are nuclear localized in their full-length forms in various breast and lung cancer cell lines. Next, we fused various intracellular cytoplasmic domain regions of each receptor to the DNA binding domain of the yeast transcription factor Gal4, and measured the ability for each construct to transactivate Gal4 UAS-luciferase activity. This analysis demonstrated that the C-terminal region distal to the tyrosine kinase domain (CTD) of all HER family receptors have strong transactivation potential, with HER2 exhibiting the highest transactivation potential. Further deletion mapping analysis of each receptor's CTD identified two regions (bipartite) of approximately 25-40 amino acids in length that harbored the majority of the receptors transactivation potential. To understand how the identified bipartite C-terminal regions of each HER family receptor influenced their transcriptional functions we deleted these regions from each full-length receptor and performed cyclin D1 promoter-luciferase assays. While wild type EGFR, HER2, and HER3 overexpression was capable of transactivating cyclin D1-luciferase, bipartite deleted receptors were severely hindered in their ability to regulate the cyclin D1 promoter. Collectively, the findings presented herein suggest that the EGFR, HER2 and HER3 contain a bipartite C-terminal transactivation domain that may be responsible for their ability to function as co-transcription factors.

Citation Format: Toni M. Brand, Mari Iida, Matthew J. Wleklinski, Neha Luthar, Megan M. Starr, Deric L. Wheeler. Mapping C-terminal transactivation domains of nuclear HER family receptor tyrosine kinases. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4276. doi:10.1158/1538-7445.AM2013-4276

Abstract 5646: Overcoming acquired resistance to cetuximab by dual targeting of HER family members using antibody based therapy

The EGFR is recognized as a key mediator of proliferation and progression in many human tumors and strategies to inhibit EGFR signaling have emerged as highly promising cancer therapy approaches. However, many tumors do not show response to EGFR inhibition and some of the responders eventually manifest resistance to treatment. In an effort to examine mechanisms of acquired resistance to anti-EGFR monoclonal antibody we developed a series of cetuximab-resistant clones using the NSCLC line NCI-H226. During efforts to elucidate molecular pathways that are involved in acquired resistance to cetuximab we found that 1) EGFR ubiquitination and degradation is altered in cetuximab-resistant cells resulting in increased steady-state expression of the EGFR and 2) enhanced signaling from the EGFR to HER3 and the PI(3)K/Akt pathway indicating that activation of HER3 may lead to escape from cetuximab therapy.

To investigate the role of HER3 in acquired resistance to cetuximab we used both RNAi and targeted approaches using the anit-HER3 antibody U3-1287/AMG888. siRNA directed against HER3 indicated that resistant cells had a strong dependency on HER3. Further, targeting HER3 using U3-1287/AMG888 showed a dose-dependent anti-proliferative response in resistant cells. In studies using siRNA against the EGFR and HER3 resulted in robust inhibition of cell proliferation than did silencing of either receptor alone in resistant cells. Comparable effects on cell proliferation were observed after combinatorial treatment of cells by the EGFR antibody cetuximab and the HER3 antibody U3-1287/AMG888. In addition, combined EGFR and HER3 inhibition by either siRNAs or antibodies decreased the phosphorylation of downstream signaling pathways AKT and MAPK. Annexin-V binding assays showed a significant increase in apoptosis in U3-1287/AMG888 plus cetuximab treated cells as compared to either agent alone. To determine if U3-1287/AMG888 could have therapeutic benefit as a combination treatment with cetuximab in vivo, mice harboring NCI-H226 xenografts will be treated with cetuximab for approximately 70-100 days until cetuximab-resistant tumors develop. At this time mice with resistant tumors will be divided into two groups that will be treated with both cetuximab and U3-1287/AMG888 or cetuximab alone.

The work presented herein suggests that cells with acquired resistance to cetuximab maintain their dependence on EGFR and HER3 signaling via the AKT and MAPK pathways.

Citation Format: Mari Iida, Toni M. Brand, Megan M. Starr, Neha Luthar, Matthew J. Wleklinski, Deric L. Wheeler. Overcoming acquired resistance to cetuximab by dual targeting of HER family members using antibody based therapy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5646. doi:10.1158/1538-7445.AM2013-5646

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.