Sym004 represents a novel EGFR targeting approach comprised of a mixture of two anti-EGFR antibodies directed against distinct epitopes of EGFR. In contrast to single anti-EGFR antibodies, Sym004 induces rapid and highly efficient degradation of EGFR. In the current study, we examine the capacity of Sym004 to augment radiation response in lung cancer and head and neck (H&N) cancer model systems. We first examined the anti-proliferative effect of Sym004 and confirmed 40∼60% growth inhibition by Sym004. Using clonogenic survival analysis, we identified that Sym004 potently increased cell kill by up to 10-fold following radiation exposure. A significant increase of γH2AX foci resulting from DNA double strand breaks was observed in Sym004-treated cells following exposure to radiation. Mechanistic studies further demonstrated that Sym004 enhanced radiation response via induction of cell cycle arrest followed by induction of apoptosis and cell death reflecting inhibitory effects on DNA damage repair. The expression of several critical molecules involved in radiation-induced DNA damage repair were significantly inhibited by Sym004, including DNAPK, NBS1, RAD50, and BRCA1. Using single and fractionated radiation in human tumor xenograft models, we confirmed that the combination of Sym004 and radiation resulted in significant tumor regrowth delay and superior anti-tumor effects compared to treatment with Sym004 or radiation alone. Taken together, these data reveal the strong capacity of Sym004 to augment radiation response in lung and H&N cancers. The unique action mechanism of Sym004 warrants further investigation as a promising EGFR targeting agent combined with radiotherapy in cancer therapy.
Sym004; EGFR; Antibody; Radiation; Repair
To develop a clinically relevant model system to study head and neck squamous cell carcinoma (HNSCC), we have established and characterized a direct-from-patient, tumorgraft model of Human Papillomavirus (HPV)-positive and HPV-negative cancers.
Patients with newly diagnosed or recurrent HNSCC were consented for donation of tumor specimens. Surgically obtained tissue was implanted subcutaneously into immunodeficient mice. During subsequent passages, both formalin-fixed/paraffin embedded as well as flash frozen tissues were harvested. Tumors were analyzed for a variety of relevant tumor markers. Tumor growth rates and response to radiation, cisplatin, or cetuximab were assessed and early passage cell strains were developed for rapid testing of drug sensitivity.
Tumorgrafts have been established in 22 of 26 patients to date. Significant diversity in tumorgraft tumor differentiation was observed with good agreement in degree of differentiation between patient tumor and tumorgraft (Kappa 0.72). Six tumorgrafts were HPV-positive on the basis of p16 staining. A strong inverse correlation between tumorgraft p16 and p53 or Rb was identified (Spearman correlations p=0.085 and p=0.002, respectively). Significant growth inhibition of representative tumorgrafts was demonstrated with cisplatin, cetuximab or radiation treatment delivered over a two-week period. Early passage cell strains showed high consistency in response to cancer therapy between tumorgraft and cell strain.
We have established a robust human tumorgraft model system for investigating HPV-positive and HPV-negative HNSCC. These tumorgrafts show strong correlation with the original tumor specimens and provide a powerful resource for investigating mechanisms of therapeutic response as well as preclinical testing.
Head and neck cancer; animal models of cancer; DNA tumor viruses
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 immunofluo-rescence. 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.
There is presently great interest in mechanisms of acquired resistance to EGFR inhibitors that are now being used widely in the treatment of a variety of common human cancers. To investigate these mechanisms we established EGFR inhibitor resistant clones from non-small cell lung cancer cells. A comparative analysis revealed that acquired resistance to EGFR inhibitors was associated consistently with the loss of p53 and cross-resistance to radiation. To examine the role of p53, we first knocked down p53 in sensitive parental cells and found a reduction in sensitivity to both EGFR inhibitors and radiation. Conversely, restoration of functional p53 in EGFR inhibitor resistant cells was sufficient to resensitize them to EGFR inhibitors or radiation in vitro and in vivo. Further studies indicate that p53 may enhance sensitivity to EGFR inhibitors and radiation via induction of cell cycle arrest, apoptosis and DNA damage repair. Taken together, these findings suggest a central role of p53 in the development of acquired resistance to EGFR inhibitors and prompt consideration to apply p53 restoration strategies in future clinical trials that combine EGFR inhibitors and radiation.
EGFR; Inhibitor; Radiation; Resistance; p53
Vascular endothelial growth factor (VEGF) plays a critical role in tumor angiogenesis. Bevacizumab is a humanized monoclonal antibody that neutralizes VEGF. We examined the impact on radiation response by blocking VEGF signaling with bevacizumab.
Human umbilical vein endothelial cell (HUVEC) growth inhibition and apoptosis were examined by crystal violet assay and flow cytometry, respectively. In vitro HUVEC tube formation and in vivo Matrigel assays were performed to assess the anti-angiogenic effect. Finally, a series of experiments of growth inhibition on head and neck (H&N) SCC1 and lung H226 tumor xenograft models were conducted to evaluate the impact of bevacizumab on radiation response in concurrent as well as sequential therapy.
The anti-angiogenic effect of bevacizumab appeared to derive not only from inhibition of endothelial cell growth (40%) but also by interfering with endothelial cell function including mobility, cell-to-cell interaction and the ability to form capillaries as reflected by tube formation. In cell culture, bevacizumab induced a 2 ~ 3 fold increase in endothelial cell apoptosis following radiation. In both SCC1 and H226 xenograft models, the concurrent administration of bevacizumab and radiation reduced tumor blood vessel formation and inhibited tumor growth compared to either modality alone. We observed a siginificant tumor reduction in mice receiving the combination of bevacizumab and radiation in comparison to mice treated with bevacizumab or radiation alone. We investigated the impact of bevacizumab and radiation treatment sequence on tumor response. In the SCC1 model, tumor response was strongest with radiation followed by bevacizumab with less sequence impact observed in the H226 model.
Overall, these data demonstrate enhanced tumor response when bevacizumab is combined with radiation, supporting the emerging clinical investigations that are combining anti-angiogenic therapies with radiation.
Anti-angiogenesis; VEGF; Bevacizumab; Radiation
Motesanib is a potent inhibitor of VEGFR1, 2 and 3, PDGFR and Kit receptors. In this report we examine the interaction between motesanib and radiation in vitro and in head and neck squamous cell carcinoma (HNSCC) xenograft models.
In vitro assays were performed to assess the impact of motesanib on VEGFR2 signaling pathways in human umbilical vein endothelial cells (HUVECs). HNSCC lines grown as tumor xenografts in athymic nude mice were utilized to assess the in vivo activity of motesanib alone and in combination with radiation.
Motesanib inhibited VEGF-stimulated HUVEC proliferation in vitro, as well as VEGFR2 kinase activity. Additionally motesanib and fractionated radiation showed additive inhibitory effects on HUVEC proliferation. In vivo combination therapy with motesanib and radiation showed increased response compared to drug or radiation alone in UM-SCC1 (p<0.002) and SCC-1483 xenografts (p=0.001); however the combination was not significantly more efficacious than radiation alone in UM-SCC6 xenografts. Xenografts treated with motesanib demonstrated a reduction of vessel penetration into tumor parenchyma, compared to control tumors. Furthermore, triple immunohistochemical staining for vasculature, proliferation, and hypoxia demonstrated well-defined spatial relationships between these parameters in HNSCC xenografts. Motesanib significantly enhanced intratumoral hypoxia in the presence and absence of fractionated radiation.
These studies identify a favorable interaction when combining radiation and motesanib in HNSCC models. Data presented suggest that motesanib reduces blood vessel penetration into tumors and thereby increases intratumoral hypoxia. These findings suggest that clinical investigations examining combinations of radiation and motesanib are warranted in HNSCC.
KRAS mutation is a predictive biomarker for resistance to cetuximab (Erbitux®) in metastatic colorectal cancer (mCRC). This study sought to determine if KRAS mutant CRC lines could be sensitized to cetuximab using dasatinib (BMS-354825, sprycel®) a potent, orally bioavailable inhibitor of several tyrosine kinases, including the Src Family Kinases. We analyzed 16 CRC lines for: 1) KRAS mutation status, 2) dependence on mutant KRAS signaling, 3) expression level of EGFR and SFKs. From these analyses, we selected three KRAS mutant (LS180, LoVo, and HCT116) cell lines, and two KRAS wild type cell lines (SW48 and CaCo2). In vitro, using Poly-D-Lysine/laminin plates, KRAS mutant cell lines were resistant to cetuximab whereas parental controls showed sensitivity to cetuximab. Treatment with cetuximab and dasatinib showed a greater anti-proliferative effect on KRAS mutant line as compared to either agent alone both in vitro and in vivo. To investigate potential mechanisms for this anti-proliferative response in the combinatorial therapy we performed Human Phospho-kinase Antibody Array analysis measuring the relative phosphorylation levels of phosphorylation of 39 intracellular proteins in untreated, cetuximab, dasatinib or the combinatorial treatment in LS180, LoVo and HCT116 cells. The results of this experiment showed a decrease in a broad spectrum of kinases centered on the β-catenin pathway, the classical MAPK pathway, AKT/mTOR pathway and the family of STAT transcription factors when compared to the untreated control or monotherapy treatments. Next we analyzed tumor growth with cetuximab, dasatinib or the combination in vivo. KRAS mutant xenografts showed resistance to cetuximab therapy, whereas KRAS wild type demonstrated an anti-tumor response when treated with cetuximab. KRAS mutant tumors exhibited minimal response to dasatinib monotherapy. However, as in vitro, KRAS mutant lines exhibited a response to the combination of cetuximab and dasatinib. Combinatorial treatment of KRAS mutant xenografts resulted in decreased cell proliferation as measured by Ki67 and higher rates of apoptosis as measured by TUNEL. The data presented herein indicate that dasatinib can sensitize KRAS mutant CRC tumors to cetuximab and may do so by altering the activity of several key-signaling pathways. Further, these results suggest that signaling via the EGFR and SFKs may be necessary for cell proliferation and survival of KRAS mutant CRC tumors. This data strengthen the rationale for clinical trials in this genetic setting combining cetuximab and dasatinib.
Cetuximab; resistance; KRAS mutation; dasatinib; EGFR; SRC; colorectal cancer
In this report, we examine the interaction between panitumumab, a fully human anti-EGFR monoclonal antibody, and radiation in head and neck squamous cell carcinoma (HNSCC) and non-small cell lung cancer (NSCLC) cell lines and xenografts.
Methods and Materials
HNSCC lines UM-SCC-1 and SCC-1483 as well as the NSCLC line H226 were studied. Tumor xenografts in athymic nude mice were utilized to assess the in vivo activity of panitumumab alone and in combination with radiation. In vitro assays were performed to assess the impact of panitumumab on radiation-induced cell signaling, apoptosis, and DNA damage.
Panitumumab increased radiosensitivity as measured by clonogenic survival assay. Radiation-induced EGFR phosphorylation and downstream signaling through MAPK and STAT3 was inhibited by panitumumab. Panitumumab augmented radiationinduced DNA damage by 1.2–1.6-fold in each of the cell lines studied as assessed by residual γ-H2AX foci after radiation. Radiation-induced apoptosis was increased 1.4–1.9-fold by panitumumab, as evidenced by Annexin V-FITC staining and flow cytometry. In vivo, combination therapy with panitumumab and radiation was superior to panitumumab or radiation alone in H226 xenografts (p=0.01) and showed a similar trend in SCC-1483 xenografts (p=0.08). These in vivo findings correlated with immunohistochemistry examination of PCNA; panitumumab with radiation markedly reduced PCNA staining in tumor xenografts.
These studies identify a favorable interaction when combining radiation and panitumumab in upper aerodigestive tract tumor models, both in vitro and in vivo. These data suggest that clinical investigations examining the combination of radiation and panitumumab in the treatment of epithelial tumors warrant further pursuit.
Panitumumab; radiation; EGFR
The epidermal growth factor receptor (EGFR) is recognized as a key mediator of proliferation and progression in many human tumors. A series of EGFR specific inhibitors have recently gained FDA approval in oncology. These strategies of EGFR inhibition have demonstrated major tumor regressions in approximately 10–20% of advanced cancer patients. However, many tumors eventually manifest resistance to treatment. Efforts to better understand the underlying mechanisms of acquired resistance to EGFR inhibitors, and potential strategies to overcome resistance, are highly needed.
To develop cell lines with acquired resistance to EGFR inhibitors we utilized the human head and neck squamous cell carcinoma (HNSCC) tumor cell line SCC-1. Cells were treated with increasing concentrations of cetuximab, gefitinib or erlotinib and characterized for the molecular changes in the EGFR-inhibitor resistant lines relative to the EGFR-inhibitor sensitive lines.
EGFR inhibitor-resistant lines were able to maintain their resistant phenotype in both drug-free medium and in athymic nude mouse xenografts. In addition, EGFR inhibitor-resistant lines showed a markedly increased proliferation rate. EGFR inhibitor-resistant lines had elevated levels of phosphorylated EGFR, MAPK, AKT and STAT3 which were associated with reduced apoptotic capacity. Subsequent in vivo experiments indicated enhanced angiogenic potential in EGFR inhibitor-resistant lines. Finally, EGFR inhibitor-resistant lines demonstrated cross resistance to ionizing radiation.
We have developed EGFR inhibitor-resistant HNSCC cell lines. This model provides a valuable preclinical tool to investigate molecular mechanisms of acquired resistance to EGFR blockade.
EGFR; Cetuximab; Gefitinib; Erlotinib; Resistance
The epidermal growth factor receptor (EGFR) is a central regulator of proliferation and progression in human cancers. Five EGFR inhibitors, two monoclonal antibodies and three TKIs, have recently gained FDA approval in oncology (cetuximab, panitumumab, erlotinib, gefitinib and lapatinib). These strategies of EGFR inhibition demonstrate major tumor regressions in approximately 10–20% of advanced cancer patients. However, many tumors eventually manifest acquired resistance to treatment. In this study we established and characterized a model to study molecular mechanisms of acquired resistance to the EGFR monoclonal antibody cetuximab. Using high-throughput screening we examined the activity of 42 receptor tyrosine kinases in resistant tumor cells following chronic exposure to cetuximab. Cells developing acquired resistance to cetuximab exhibited increased steady-state EGFR expression secondary to alterations in trafficking and degradation. In addition, cetuximab-resistant cells manifested strong activation of HER2, HER3 and cMET. EGFR upregulation promoted increased dimerization with HER2 and HER3 leading to their transactivation. Blockade of EGFR and HER2 led to loss of HER3 and PI(3)K/Akt activity. These data suggest that acquired-resistance to cetuximab is accompanied by dysregulation of EGFR internalization/degradation and subsequent EGFR-dependent activation of HER3. Taken together these findings suggest a rationale for the clinical evaluation of combinatorial anti-HER targeting approaches in tumors manifesting acquired resistance to cetuximab.
EGFR; cetuximab; acquired-resistance
The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that plays a major role in oncogenesis. Cetuximab is an EGFR-blocking antibody that is FDA approved for use in patients with metastatic colorectal cancer (mCRC) and head and neck squamous cell carcinoma (HNSCC). Although cetuximab has shown strong clinical benefit for a subset of cancer patients, most become refractory to cetuximab therapy. We reported that cetuximab-resistant NSCLC line NCI-H226 cells have increased steady-state expression and activity of EGFR secondary to altered trafficking/degradation and this increase in EGFR expression and activity lead to hyper-activation of HER3 and down stream signals to survival. We now present data that Src family kinases (SFKs) are highly activated in cetuximab-resistant cells and enhance EGFR activation of HER3 and PI(3)K/Akt. Studies using the Src kinase inhibitor dasatinib decreased HER3 and PI(3)K/Akt activity. In addition, cetuximab-resistant cells were resensitized to cetuximab when treated with dasatinib. These results indicate that SFKs and EGFR cooperate in acquired resistance to cetuximab and suggest a rationale for clinical strategies that investigate combinatorial therapy directed at both the EGFR and SFKs in patients with acquired resistance to cetuximab.
EGFR; cetuximab; resistance; Src-family kinases; dasatinib