Anti-EGFR–mediated radiosensitization as a result of augmented EGFR expression

EGFR-amplification plus gene expression profiling predicts response to combined radiotherapy with EGFR-inhibition: A preclinical trial in 10 HNSCC-tumour-xenograft models

BACKGROUND AND PURPOSE

Improvement of the results of radiotherapy by EGFR inhibitors is modest, suggesting significant intertumoural heterogeneity of response. To identify potential biomarkers, a preclinical trial was performed on ten different human squamous cell carcinoma xenografts of the head and neck (HNSCC) studying in vivo and ex vivo the effect of fractionated irradiation and EGFR inhibition. Local tumour control and tumour growth delay were correlated with potential biomarkers, e.g. EGFR gene amplification and radioresponse-associated gene expression profiles.

MATERIAL AND METHODS

Local tumour control 120days after end of irradiation was determined for fractionated radiotherapy alone (30f, 6weeks) or after simultaneous EGFR-inhibition with cetuximab. The EGFR gene amplification status was determined using FISH. Gene expression analyses were performed using an in-house gene panel.

RESULTS

Six out of 10 investigated tumour models showed a significant increase in local tumour control for the combined treatment of cetuximab and fractionated radiotherapy compared to irradiation alone. For 3 of the 6 responding tumour models, an amplification of the EGFR gene could be demonstrated. Gene expression profiling of untreated tumours revealed significant differences between amplified and non-amplified tumours as well as between responder and non-responder tumours to combined radiotherapy and cetuximab.

CONCLUSION

The EGFR amplification status, in combination with gene expression profiling, may serve as a predictive biomarker for personalized interventional strategies regarding combined treatment of cetuximab and fractionated radiotherapy and should, as a next step, be clinically validated.

Current and Emerging Clinical Applications of Multispectral Optoacoustic Tomography (MSOT) in Oncology

Accurate detection and characterization of cancers are key for providing timely intervention and effective treatments. Current imaging technologies are particularly limited when it comes to detecting very small tumors in vivo, i.e., very early cancers or metastases, differentiating viable tumor from surrounding dead tumor tissue, and evaluating tumor metabolism within tissue. Optoacoustic imaging offers potential solutions to these imaging problems because of its ability to image optical absorption properties of both intrinsic tissue chromophores and exogenous contrast agents without the involvement of ionizing radiation. Optoacoustic imaging uses pulsed laser to induce localized thermoelastic expansion that generates acoustic waves detectable by an ultrasound transducer. To date, multispectral optoacoustic tomography (MSOT) has primarily been used in preclinical research; however, its use in translational and clinical research is expanding. This review focuses on current and emerging applications of optoacoustic imaging for molecular imaging of cancer using both exogenous and endogenous contrast agents and sheds light on potential future clinical applications. Clin Cancer Res; 22(14); 3432-9. ©2016 AACR.

Preoperative chemoradiation therapy in combination with panitumumab for patients with resectable esophageal cancer: the PACT study

PURPOSE

Preoperative chemoradiation therapy (CRT) has become the standard treatment strategy for patients with resectable esophageal cancer. This multicenter phase 2 study investigated the efficacy of the addition of the epidermal growth factor receptor (EGFR) inhibitor panitumumab to a preoperative CRT regimen with carboplatin, paclitaxel, and radiation therapy in patients with resectable esophageal cancer.

METHODS AND MATERIALS

Patients with resectable cT1N1M0 or cT2-3N0 to -2M0 tumors received preoperative CRT consisting of panitumumab (6 mg/kg) on days 1, 15, and 29, weekly administrations of carboplatin (area under the curve [AUC] = 2), and paclitaxel (50 mg/m(2)) for 5 weeks and concurrent radiation therapy (41.4 Gy in 23 fractions, 5 days per week), followed by surgery. Primary endpoint was pathologic complete response (pCR) rate. We aimed at a pCR rate of more than 40%. Furthermore, we explored the predictive value of biomarkers (EGFR, HER 2, and P53) for pCR.

RESULTS

From January 2010 until December 2011, 90 patients were enrolled. Patients were diagnosed predominantly with adenocarcinoma (AC) (80%), T3 disease (89%), and were node positive (81%). Three patients were not resected due to progressive disease. The primary aim was unmet, with a pCR rate of 22%. Patients with AC and squamous cell carcinoma reached a pCR of 14% and 47%, respectively. R0 resection was achieved in 95% of the patients. Main grade 3 toxicities were rash (12%), fatigue (11%), and nonfebrile neutropenia (11%). None of the biomarkers was predictive for response.

CONCLUSIONS

The addition of panitumumab to CRT with carboplatin and paclitaxel was safe and well tolerated but could not improve pCR rate to the preset criterion of 40%.

The anti-EGFR antibody cetuximab sensitizes human head and neck squamous cell carcinoma cells to radiation in part through inhibiting radiation-induced upregulation of HIF-1α

In this study, we investigated the mechanisms underlying cetuximab-mediated radiosensitization of HNSCC. Irradiation of HNSCC cells upregulated hypoxia-inducible factor-1 alpha (HIF-1α) via a mechanism involving de novo synthesis of HIF-1α protein. Radiation-induced upregulation of HIF-1α was completely abolished by concurrent treatment of HNSCC cells with cetuximab. Experimental elevation of constitutively expressed HIF-1α abolished cetuximab-mediated radiosensitization in HNSCC cells, whereas downregulation of HIF-1α by siRNA or a small molecule inhibitor enhanced responses of cetuximab-resistant HNSCC cells to cetuximab plus radiation. Our data suggest that cetuximab sensitizes cancer cells to ionizing radiation in part through inhibition of radiation-induced upregulation of HIF-1α.

Thrombospondin-1 opens the paracellular pathway in pulmonary microvascular endothelia through EGFR/ErbB2 activation

Thrombospondin-1 (TSP1) is a multidomain protein that contains epidermal growth factor (EGF)-like repeats that indirectly activate the EGF receptor (EGFR) and selected downstream signaling pathways. In these studies, we show that TSP1 opens the paracellular pathway in human lung microvascular endothelial cells (HMVEC-Ls) in a dose-, time-, and protein tyrosine kinase (PTK)-dependent manner. TSP1 increased tyrosine phosphorylation of proteins enriched to intercellular boundaries including the zonula adherens (ZA) proteins, vascular endothelial-cadherin, γ-catenin, and p120 catenin. In HMVEC-Ls, EGFR and ErbB2 are expressed at low levels, and both heterodimerize and tyrosine autophosphorylate in response to TSP1. Prior EGFR-selective PTK inhibition with AG1478 or ErbB2-selective PTK inhibition with AG825 protected against TSP1-induced tyrosine phosphorylation of ZA proteins and barrier disruption. Preincubation of HMVEC-Ls with an EGFR ectodomain-blocking antibody also prevented TSP1-induced opening of the paracellular pathway. Therefore, in HMVEC-Ls, TSP1 increases tyrosine phosphorylation of ZA proteins and opens the paracellular pathway, in part, through EGFR/ErbB2 activation. Surprisingly, recombinant TSP1 EGF-like repeats 1-3 and the high-affinity EGFR ligands, EGF, TGF-α, and amphiregulin, each failed to increase paracellular permeability. However, HMVEC-Ls in which EGFR was overexpressed became responsive to the EGF-like repeats of TSP1 as well as to EGF. These studies indicate that TSP1 disrupts the endothelial barrier through EGFR/ErbB2 activation although additional signals are necessary in cells with low receptor expression.

Targeted human serum albumin nanoparticles for specific uptake in EGFR-Expressing colon carcinoma cells

The specific application and transport of drugs into malignant tissue is a critical point during diagnosis and therapy. Nanoparticles are known as excellent drug carrier systems and offer the possibility of surface modification with targeting ligands, leading to a specific accumulation in the targeted tissue. First, the specificity of such a carrier system has to be proven. In this study, cetuximab-modified nanoparticles based on biodegradable human serum albumin (HSA) are investigated regarding their cellular binding and intracellular accumulation. Different EGFR-expressing colon carcinoma cells were used to test possible cytotoxic potential, specific binding and intracellular accumulation. A specific accumulation targeting the EGFR could be shown. These results emphasize that cetuximab-modified HSA-nanoparticles are a promising carrier system for later drug transport. To our knowledge, this is the first study investigating the specific accumulation of HSA nanoparticles into different EGFR-expressing colon carcinoma cells.

FROM THE CLINICAL EDITOR

In this study, cetuximab-modified nanoparticles based on human serum albumin (HSA) are investigated regarding their cellular binding and intracellular accumulation. The results suggest that these nanoparticles are a promising carrier system for EGFR overexpressing colon carcinoma cells.

Effect of cetuximab treatment in squamous cell carcinomas

The purpose of this study was to assess the effects of the monoclonal antibody cetuximab in a panel of cultured squamous cell carcinoma cell lines. This antibody, targeting the epidermal growth factor receptor (EGFR), is emerging as a promising agent for treatment of several cancers. As this antibody comes into clinical use, the identification of predictive markers of therapeutic benefit remains a pressing issue. Cells were first characterized according to EGFR expression, cell doubling time, and BRAF and K-ras mutations. The effects of cetuximab on cell-cycle distribution, proliferation, as well as cell growth rate were then evaluated. Cetuximab decreased cell proliferation in three out of four cell lines in a time-dependent manner, and all cell lines were found to exhibit wild type K-ras and BRAF genes. A possible correlation between EGFR expression and cetuximab effect on growth inhibition rate was observed, whereas reduction of cell doubling time seemed to be more dependent on initial growth rate. In addition, other factors may further influence the long-term treatment response of cetuximab. Moreover, the time-dependent manner of cetuximab response demonstrates the importance of long-term measurements for this substance.

Multiplexed Five-Color Molecular Imaging of Cancer Cells and Tumor Tissues with Carbon Nanotube Raman Tags in the Near-Infrared

Single-walled carbon nanotubes (SWNTs) with five different C13/C12 isotope compositions and well-separated Raman peaks have been synthesized and conjugated to five targeting ligands in order to impart molecular specificity. Multiplexed Raman imaging of live cells has been carried out by highly specific staining of cells with a five-color mixture of SWNTs. Ex vivo multiplexed Raman imaging of tumor samples uncovers a surprising up-regulation of epidermal growth factor receptor (EGFR) on LS174T colon cancer cells from cell culture to in vivo tumor growth. This is the first time five-color multiplexed molecular imaging has been performed in the near-infrared (NIR) region under a single laser excitation. Near zero interfering background of imaging is achieved due to the sharp Raman peaks unique to nanotubes over the low, smooth autofluorescence background of biological species.

Inhibition of STAT-3 results in radiosensitization of human squamous cell carcinoma

BACKGROUND

Signal transducer and activator of transcription-3 (STAT-3) is a downstream component of the Epidermal Growth Factor Receptor (EGFr) signaling process that may facilitate the resistance of tumor cells to conventional cancer treatments. Studies were performed to determine if inhibition of this downstream protein produces radiosensitization.

METHODS/RESULTS

A431 cells (human squamous cell carcinoma cells with EGFr overexpression) were found to be sensitized to radiation after treatment with STAT-3 small interfering RNA (siRNA). Therefore, a short hairpin RNA (shRNA) against STAT-3 was designed and cloned into a pBABE vector system modified for shRNA expression. Following transfection, clone 2.1 was selected for further study as it showed a dramatic reduction of STAT-3 protein (and mRNA) when compared to A431 parental cells or a negative control shRNA cell line (transfected with STAT-3 shRNA with 2 base pairs mutated). A431 2.1 showed doubling times of 25-31h as compared to 18-24h for the parental cell line. The A431 shRNA knockdown STAT-3 cells A431 were more sensitive to radiation than A431 parental or negative STAT-3 control cells.

CONCLUSION

A431 cells stably transfected with shRNA against STAT-3 resulted in enhanced radiosensitivity. Further work will be necessary to determine whether the inhibition of STAT-3 phosphorylation is a necessary step for the radiosensitization that is induced by the inhibition of EGFr.

Radiosensitisation of U87MG brain tumours by anti-epidermal growth factor receptor monoclonal antibodies

As epidermal growth factor receptor (EGFR) has been reported to be a radiation response modulator, HER inhibitors are regarded to act as potential radiosensitisers. Our study examined the role of nimotuzumab and cetuximab both, the two monoclonal antibodies (mAbs) to EGFR, as radiosensitisers in a murine glioma model in vivo. Co-administration of both the antibodies with radiation increased the radiosensitivity of U87MG, resulting in a significant delay of subcutaneous (s.c.) tumour growth. Furthermore, the addition of antibodies to the radiation decreased brain tumour sizes and is inhibited by 40–80% the increased tumour cell invasion provoked by radiotherapy, although promoted tumour cell apoptosis. Whereas nimotuzumab led to a reduction in the size of tumour blood vessels and proliferating cells in s.c. tumours, cetuximab had no significant antiangiogenic nor antiproliferative activity. In contrast, cetuximab induced a more marked inhibition of EGFR downstream signalling compared with nimotuzumab. Moreover, both antibodies reduced the total number of radioresistant CD133+ cancer stem cells (CSCs). These results were encouraging, and showed the superiority of combined treatment of mAbs to EGFR and radiation over each single therapy against glioblastoma multiforme (GBM), confirming the role of these drugs as radiosensitisers in human GBM. In addition, we first showed the ability of mAb specifics against EGFR to target radioresistant glioma CSC, supporting the potential use in patients.

Epidermal growth factor receptor-targeted therapy

High epidermal growth factor receptor (EGFR) expression is a feature of human tumours and is an adverse prognostic factor for radiotherapy outcome. High expression is associated with benefit from accelerated radiotherapy in patients with head and neck squamous cell carcinoma. Anti-EGFR strategies potentiate the effects of radiotherapy and the inhibition of deoxyribonucleic acid repair appears to be important amongst a wide range of mechanisms, which include effects on angiogenesis, differentiation and the immunological response. There is considerable interest in exploring combined modality therapies involving radiation and EGFR antagonists for the curative treatment of cancer patients. Important issues in designing new trials are to investigate optimal scheduling and to establish biobanks to develop biomarkers for future patient selection.

The efficacy and toxicity of EGFR in the settings of radiotherapy: Focus on published clinical trials

Basic research in solid malignant tumours has led to a wealth of knowledge about this disease process and about novel ways to more effectively target our therapies. Laboratory research continues to identify novel therapeutic targets and moreover, clinical research is identifying effective new treatment regimens. Many preclinical studies in this area have targeted the epidermal growth factor receptor (EGFR) signalling pathway to increase radiosensitivity. The in vitro rationale for targeting EGFR and concurrent ionising radiation is well established, but to date, rare clinical data could provide proof-of-principle. Here we report all the different published clinical trials focusing on efficacy and toxicity in order to clarify and to summarise the present state-of-the-art of this particularly promising combination in solid tumour management.

Enhancement of the antitumor activity of ionising radiation by nimotuzumab, a humanised monoclonal antibody to the epidermal growth factor receptor, in non-small cell lung cancer cell lines of differing epidermal growth factor receptor status

The expression and activity of the epidermal growth factor receptor (EGFR) are determinants of radiosensitivity in several tumour types, including non-small cell lung cancer (NSCLC). However, little is known of whether genetic alterations of EGFR in NSCLC cells affect the therapeutic response to monoclonal antibodies (mAbs) to EGFR in combination with radiation. We examined the effects of nimotuzumab, a humanised mAb to EGFR, in combination with ionising radiation on human NSCLC cell lines of differing EGFR status. Flow cytometry revealed that H292 and Ma-1 cells expressed high and moderate levels of EGFR on the cell surface, respectively, whereas H460, H1299, and H1975 cells showed a low level of surface EGFR expression. Immunoblot analysis revealed that EGFR phosphorylation was inhibited by nimotuzumab in H292 and Ma-1 cells but not in H460, H1299, or H1975 cells. Nimotuzumab augmented the cytotoxic effect of radiation in H292 and Ma-1 cells in a clonogenic assay in vitro, with a dose enhancement factor of 1.5 and 1.3, respectively. It also enhanced the antitumor effect of radiation on H292 and Ma-1 cell xenografts in nude mice, with an enhancement factor of 1.3 and 4.0, respectively. Nimotuzumab did not affect the radioresponse of H460 cells in vitro or in vivo. Nimotuzumab enhanced the antitumor efficacy of radiation in certain human NSCLC cell lines in vitro and in vivo. This effect may be related to the level of EGFR expression on the cell surface rather than to EGFR mutation.

Stimulated PI3K-AKT signaling mediated through ligand or radiation-induced EGFR depends indirectly, but not directly, on constitutive K-Ras activity

Previous results showed an inducible radiation sensitivity selectively observable for K-RAS-mutated cell lines as a function of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor blockade of phosphatidylinositol 3-kinase (PI3K)-AKT signaling. Therefore, the role of K-Ras activity for a direct (i.e., through activation of PI3K by K-Ras) or an indirect stimulation of PI3K-AKT signaling (through K-Ras activity-dependent EGFR ligand production) was investigated by means of small interfering RNA and inhibitor approaches as well as ELISA measurements of EGFR ligand production. K-RASmt tumor cells presented a constitutively activated extracellular signal-regulated kinase-1/2 signaling, resulting in enhanced production and secretion of the EGFR ligand amphiregulin (AREG). Medium supernatants conditioned by K-RASmt tumor cells equally efficiently stimulated EGFR signaling into the PI3K-AKT and mitogen-activated protein kinase pathways. Knocking down K-Ras expression by specific small interfering RNA markedly affected autocrine production of AREG, but not PI3K-AKT signaling, after treatment of K-RAS-mutated or wild-type cells with EGFR ligands or exposure to ionizing radiation. These results indicate that PI3K-mediated activation of AKT in K-RASmt human tumor cells as a function of EGFR ligand or radiation stimulus is independent of a direct function of K-Ras enzyme activity but depends on a K-Ras-mediated enhanced production of EGFR ligands (i.e., most likely AREG) through up-regulated extracellular signal-regulated kinase-1/2 signaling. The data provide new differential insight into the importance of K-RAS mutation in the context of PI3K-AKT-mediated radioresistance of EGFR-overexpressing or EGFR-mutated tumors.

Biology of Interactions: Antiepidermal Growth Factor Receptor Agents

Epidermal growth factor receptor (EGFR) signaling inhibition represents a highly promising arena for the application of molecularly targeted cancer therapies. Evolving from several decades of systematic research in cancer cell biology, a series of EGFR inhibitors from both the monoclonal antibody (mAb) and tyrosine kinase inhibitor (TKI) class have been developed and promoted into clinical application. Several EGFR inhibitors have recently gained US Food and Drug Administration approval for cancer therapy in the United States (and many other countries), including the mAbs cetuximab and panitumumab, and the small molecule TKIs gefitinib, erlotinib, and lapatinib. The rapidly expanding preclinical and clinical data contributing to these US Food and Drug Administration drug registrations validates a central role of the EGFR as an important molecular target in epithelial malignancies. In this review, we focus primarily on the biology of EGFR interactions. Through improved understanding of EGFR biology in human cancers, there is anticipation that more tumor-selective therapy approaches with diminished collateral normal tissue toxicity can be advanced. Many questions remain to be answered, particularly with regard to how best combine EGFR inhibitors with conventional cancer therapies, and how to select those patients (tumors) most likely to benefit from EGFR inhibition strategies.

Targeting EGFR with metabolically biotinylated fiber-mosaic adenovirus

Adenovirus (Ad)-based vectors are useful gene delivery vehicles for a variety of applications. Despite their attractive properties, many in vivo applications require modulation of the viral tropism. Targeting approaches applied to adenoviral vectors included genetic modification of the viral capsid, controlled expression of the transgene and combinatorial approaches that combine two or more targeting elements in single vectors. Most of these studies confirmed successful retargeting in cell cultures, however, in vivo gains of targeted adenoviral vectors have not been widely demonstrated. We have developed a combinatorial retargeting approach utilizing metabolically biotinylated Ad, where the biotin acceptor peptide was incorporated in one of the fibers in a dual fiber viral particle resulting in metabolically biotinylated fiber-mosaic Ad (mBfMAd). We have utilized this vector in complex with epidermal growth factor (EGF)-Streptavidin to retarget fiber-mosaic virus to EGF receptor (EGFR) expressing cells in vitro and confirmed an increased infectivity of the retargeting complex. Most importantly, the utility of this strategy was demonstrated in vivo in two distinct animal models. In both models tested, retargeted mBfMAd demonstrated an increased ratio of gene expression in target tissues compared to the liver expression profile. Thus, metabolically biotinylated fiber-mosaic virus in combination with appropriate adapters can be successfully exploited for adenoviral retargeting strategies.

Cetuximab in the treatment of metastatic colorectal cancer

Cetuximab is a chimeric monoclonal antibody that binds to the epidermal growth factor receptor and thereby inhibits cell proliferation, metastasis and angiogenesis. Preclinical studies indicate that cetuximab induces synergistic antitumor activity when combined with chemotherapy or radiation. This observation is supported by clinical trials demonstrating that cetuximab improves tumor response when used in conjunction with modern chemotherapy in patients with metastatic colorectal cancer. Improved treatment efficacy may help to increase the rate of hepatic metastasis resection after downsizing of initially unresectable lesions. In pretreated patients, cetuximab may restore the sensitivity to irinotecan and, therefore, has been registered in this setting. Ongoing studies are investigating the integration of anti-epidermal growth factor receptor and anti-vascular endothelial growth factor strategies into new treatment regimens. Promising results have already been obtained in a trial combining irinotecan, bevacizumab and cetuximab.

The complexity of targeting EGFR signalling in cancer: from expression to turnover

The epidermal growth factor receptor (ErbB1 or EGFR) has been found to be altered in a variety of human cancers. A number of agents targeting these receptors, including specific antibodies directed against the ligand-binding domain of the receptor and small molecules that inhibit kinase activity are either in clinical trials or are already approved for clinical treatment. However, identifying patients that are likely to respond to such treatments has been challenging. As a consequence, it still remains important to identify additional alterations of the tumor cell that contribute to the response to EGFR-targeted agents. While EGFR-mediated signalling pathways have been well established, there is still a rather limited understanding of how intracellular protein-protein interactions, ubiquitination, endocytosis and subsequent degradation of EGFR contribute to the determination of sensitivity to EGFR targeting agents and are emerging areas of investigation. This review primarily focuses on the basic signal transduction pathways mediated through activated membrane bound and/or endosomal EGFR and emphasizes the need to co-target additional proteins that function either upstream or downstream of EGFR to improve cancer therapy.

Impact of viral E2-gene status on outcome after radiotherapy for patients with human papillomavirus 16-positive cancer of the uterine cervix

PURPOSE

Integration of high-risk papillomavirus DNA has been considered an important step in oncogenic progression to cervical carcinoma. Disruption of the human papillomavirus (HPV) genome within the E2 gene is frequently a consequence. This study investigated the influence of episomal viral DNA on outcome in patients with advanced cervical cancer treated with primary radiotherapy.

METHODS AND MATERIALS

Paraffin-embedded biopsies of 82 women with locally advanced cervical cancer could be analyzed for HPV infection by multiplex polymerase chain reaction (PCR) by use of SPF1/2 primers. E2-gene intactness of HPV-16-positive samples was analyzed in 3 separate amplification reactions by use of the E2A, E2B, E2C primers. Statistical analyses (Kaplan-Meier method; log-rank test) were performed for overall survival (OS), disease-free survival (DFS), local progression-free survival (LPFS), and distant metastases-free survival (DMFS).

RESULTS

Sixty-one (75%) of 82 carcinomas were HPV positive, 44 of them for HPV-16 (72%). Seventeen of the 44 HPV-16-positive tumors (39%) had an intact E2 gene. Patients with a HPV-16-positive tumor and an intact E2 gene showed a trend for a better DFS (58% vs. 38%, p = 0.06) compared with those with a disrupted E2 gene. A nonsignificant difference occurred regarding OS (87% vs. 66%, p = 0.16) and DMFS (57% vs. 48%, p = 0.15).

CONCLUSION

E2-gene status may be a promising new target, but more studies are required to elucidate the effect of the viral E2 gene on outcome after radiotherapy in HPV-positive tumors.

Radioresistance of K-Ras mutated human tumor cells is mediated through EGFR-dependent activation of PI3K-AKT pathway

BACKGROUND AND PURPOSE

In the context of EGFR-targeting strategies we investigated autocrine/paracrine factors leading to in vitro radioresistance of K-Ras mutated tumor cells through activation of EGFR mediated signal transduction.

PATIENTS AND METHODS

Ras mutated (Rasmt) and normal Ras (Raswt) presenting human tumor cell lines were used to analyze the potential of conditioned media (CM) of both cell types to mediate radioresistance and to activate EGFR-signaling cascades. Therefore, clonogenic assays as well as SDS-PAGE combined with immunoblotting was performed. Additionally, Ras-mutated cells were transfected with K-Ras-siRNA to investigate, how downregulation of mutated K-Ras affects secretion of EGFR-ligands, stimulation of EGFR-signaling and modulation of radiation response.

RESULTS

TGFalpha, Amphiregulin (ARG) and CM from Rasmt cells (Rasmt-CM) resulted in an increased clonogenic survival of irradiated Raswt cells. Both, EGFR ligands as well as Rasmt-CM led to a strong phosphorylation of EGFR and activation of downstream pathways, i.e. PI3K-AKT. However, neutralization of TGFalpha or ARG in Rasmt-CM led to a marked reduction of P-AKT. Furthermore, Rasmt-CM from K-Ras-siRNA transfected Rasmt-cells markedly inhibited phosphorylation of AKT in Raswt cells and enhanced radiation sensitivity of A549 cells transfected with the siRNA.

CONCLUSION

The data suggest that constitutively upregulated autocrine/paracrine secretion of EGF receptor ligands, especially ARG from K-Ras mutated cells, mediates radioresistance in Rasmt-cells through stimulation of EGFR-PI3K-AKT pathway.

Mechanisms of resistance to Erbitux (anti-epidermal growth factor receptor) combination therapy in pancreatic adenocarcinoma cells

We previously demonstrated that pancreatic adenocarcinoma BxPC-3 xenografts display resistance to treatment with Erbitux, gemcitabine, and radiation, whereas MIA PaCa-2 xenografts are highly sensitive to the same therapy. Here, we elucidate in vitro mechanisms that may explain the observed differential response of epidermal growth factor receptor (EGFR) expressing pancreatic adenocarcinoma xenografts to Erbitux-based combination therapy in vivo. MIA PaCa-2 and BxPC-3 protein lysates were probed with antibodies to EGFR, ErbB2, ErbB3, and ErbB4. Constitutive ErbB3 activity was visualized by immunoblot analysis using anti-phosphotyrosine antibodies and receptor-specific immunoprecipitates. erbB2 and erbB3 gene expression in both cell lines was quantified with real-time polymerase chain reaction. Erbitux-induced internalization of EGFR was determined by flow cytometry following Erbitux treatment for different incubation times at 0 degrees C and 37 degrees C. MIA PaCa-2 and BxPC-3 protein extracts were also probed with anti-phospho-mitogen-activated protein kinase antibody after stimulation with EGF and in the presence of Erbitux. Although both cell lines expressed EGFR and ErbB2 protein, ErbB3 protein was selectively expressed by BxPC-3 cells, where it also showed evidence of constitutive phosphorylation. There was a 10-fold increase of erbB3 transcript levels in BxPC-3 cells compared with MIA PaCa-2. ErbB4 protein was not detectable in either cell line. Erbitux mediated EGFR internalization in MIA PaCa-2 cells after 2 hours of incubation, whereas it did not promote EGFR internalization in BxPC-3 cells. Likewise, EGF-dependent phosphorylation of MAPK p44/42 was blocked by Erbitux treatment in MIA PaCa-2 but not BxPC-3 cells. Erbitux selectively interfered with EGF-induced MAPK activation in MIA PaCa-2 but not BxPC-3 cells. Persistent MAPK activation and impaired in vitro internalization of EGFR by BxPC-3 pancreatic cancer cells may be due to constitutive ErbB3 signaling, facilitated by heterodimerization with EGFR, which may explain resistance to Erbitux-based combination therapy in vivo.

Adenoviral vector-mediated augmentation of epidermal growth factor receptor (EGFr) enhances the radiosensitization properties of anti-EGFr treatment in prostate cancer cells

PURPOSE

To determine whether an adenoviral vector approach to the augmentation of epidermal growth factor receptor (EGFr) expression results in increased antiproliferative and radiosensitization properties of anti-EGFr antibody therapy in prostate cancer cells.

METHODS AND MATERIALS

DU145 and LNCaP human prostate cancer cells were used to test the above question in vitro. An adenoviral vector was utilized to transduce cells with an EGFr transgene (AdEGFr). Immunoblots were performed to measure EGFr expression and EGFr tyrosine phosphorylation. Radiolabeled ligand studies were employed to test binding of epidermal growth factor to EGFr. Scatchard analyses allowed for quantification of the number of EGFrs. Standard immunohistochemistry was performed to assess EGFr expression. Cellular proliferation was assessed after various combinations of treatment.

RESULTS

Studies of prostate carcinoma cells infected with AdEGFr demonstrated an increase in EGFr expression. This increase in expression correlated with increased function of EGFr. Specifically, increased EGFr expression also resulted in increased ligand binding, ligand-induced internalization of EGFr, and ligand-induced EGFr tyrosine kinase activity that could be blocked with pre-exposure to IMC-C225 (an anti-EGFr monoclonal antibody). Transduction of the LNCaP cells with AdEGFr did not increase the antiproliferative effects of IMC-C225, but did significantly increase IMC-C225-induced radiosensitization as determined by cell proliferation.

CONCLUSIONS

Augmentation of EGFr expression, through an adenoviral vector approach in prostate carcinoma cells, resulted in cells that demonstrated greater IMC-C225-induced radiosensitization compared to cells that were not treated with AdEGFr.