Diverse effects of combined radiotherapy and EGFR inhibition with antibodies or TK inhibitors on local tumour control and correlation with EGFR gene expression

The value of subcutaneous xenografts for individualised radiotherapy in HNSCC: Robust gene signature correlates with radiotherapy outcome in patients and xenografts

PURPOSE

To assess the robustness of prognostic biomarkers and molecular tumour subtypes developed for patients with head and neck squamous cell carcinoma (HNSCC) on cell-line derived HNSCC xenograft models, and to develop a novel biomarker signature by combining xenograft and patient datasets.

MATERIALS AND METHODS

Mice bearing xenografts (n = 59) of ten HNSCC cell lines and a retrospective, multicentre patient cohort (n = 242) of the German Cancer Consortium-Radiation Oncology Group (DKTK-ROG) were included. All patients received postoperative radiochemotherapy (PORT-C). Gene expression analysis was conducted using GeneChip Human Transcriptome Arrays. Xenografts were stratified based on their molecular subtypes and previously established gene classifiers. The dose to control 50 % of tumours (TCD50) was compared between these groups. Using differential gene expression analyses combining xenograft and patient data, a gene signature was developed to define risk groups for the primary endpoint loco-regional control (LRC).

RESULTS

Tumours of mesenchymal subtype were characterized by a higher TCD50 (xenografts, p < 0.001) and lower LRC (patients, p < 0.001) compared to the other subtypes. Similar to previously published patient data, hypoxia- and radioresistance-related gene signatures were associated with high TCD50 values. A 2-gene signature (FN1, SERPINE1) was developed that was prognostic for TCD50 (xenografts, p < 0.001) and for patient outcome in independent validation (LRC: p = 0.007).

CONCLUSION

Genetic prognosticators of outcome for patients after PORT-C and subcutaneous xenografts after primary clinically relevant irradiation show similarity. The identified robust 2-gene signature may help to guide patient stratification, after prospective validation. Thus, xenografts remain a valuable resource for translational research towards the development of individualized radiotherapy.

Prognostic biomarkers for the response to the radiosensitizer nimorazole combined with RCTx: a pre-clinical trial in HNSCC xenografts

BACKGROUND

Tumor hypoxia is associated with resistance to radiotherapy and chemotherapy. In head and neck squamous cell carcinoma (HNSCC), nimorazole, an oxygen mimic, combined with radiotherapy (RT) enabled to improve loco-regional control (LRC) in some patients with hypoxic tumors but it is unknown whether this holds also for radiochemotherapy (RCTx). Here, we investigated the impact of nimorazole combined with RCTx in HNSCC xenografts and explored molecular biomarkers for its targeted use.

METHODS

Irradiations were performed with 30 fractions in 6 weeks combined with weekly cisplatin. Nimorazole was applied before each fraction, beginning with the first or after ten fractions. Effect of RCTx with or without addition of nimorazole was quantified as permanent local control after irradiation. For histological evaluation and targeted gene expression analysis, tumors were excised untreated or after ten fractions. Using quantitative image analysis, micromilieu parameters were determined.

RESULTS

Nimorazole combined with RCTx significantly improved permanent local control in two tumor models, and showed a potential improvement in two additional models. In these four models, pimonidazole hypoxic volume (pHV) was significantly reduced after ten fractions of RCTx alone. Our results suggest that nimorazole combined with RCTx might improve TCR compared to RCTx alone if hypoxia is decreased during the course of RCTx but further experiments are warranted to verify this association. Differential gene expression analysis revealed 12 genes as potential for RCTx response. When evaluated in patients with HNSCC who were treated with primary RCTx, these genes were predictive for LRC.

CONCLUSIONS

Nimorazole combined with RCTx improved local tumor control in some but not in all HNSCC xenografts. We identified prognostic biomarkers with the potential for translation to patients with HNSCC.

Preclinical trial comparing radiotherapy alone versus standard radiochemotherapy in three human papilloma virus (HPV) negative and three HPV-positive head and neck squamous cell carcinoma (HNSCC) xenograft tumour models

PURPOSE

To perform a preclinical trial comparing the efficacy of fractionated radiotherapy versus radiochemotherapy with cisplatin in HPV-positive and negative human head and neck squamous cell carcinoma (HNSCC) xenografts.

MATERIAL AND METHODS

Three HPV-negative and three HPV-positive HNSCC xenografts in nude mice were randomized to radiotherapy (RT) alone or to radiochemotherapy (RCT) with weekly cisplatin. To evaluate tumour growth time, 20 Gy radiotherapy (±cisplatin) were administered in 10 fractions over 2 weeks. Dose-response curves for local tumour control were generated for RT with 30 fractions over 6 weeks to different dose levels given alone or combined with cisplatin (RCT).

RESULTS

One of three investigated HPV-negative and two out of three HPV-positive tumour models showed a significant increase in local tumour control after RCT compared to RT alone. Pooled analysis of the HPV-positive tumour models showed a statistically significant and substantial benefit of RCT versus RT alone, with an enhancement ratio of 1.34. Although heterogeneity in response to both RT and RCT was also observed between the different HPV-positive HNSCC, these overall were more RT and RCT sensitive than HPV-negative models.

CONCLUSION

The impact of adding chemotherapy to fractionated radiotherapy on local control was heterogenous, both in HPV-negative and in HPV-positive tumours, calling for predictive biomarkers. RCT substantially increased local tumour control in the pooled group of all HPV-positive tumours whereas this was not found in HPV-negative tumours. Omission of chemotherapy in HPV-positive HNSCC as part of a treatment de-escalation strategy is not supported by this preclinical trial.

Screening and Validation of Molecular Targeted Radiosensitizers

The development of molecular targeted drugs with radiation and chemotherapy are critically important for improving the outcomes of patients with hard-to-treat, potentially curable cancers. However, too many preclinical studies have not translated into successful radiation oncology trials. Major contributing factors to this insufficiency include poor reproducibility of preclinical data, inadequate preclinical modeling of inter-tumoral genomic heterogeneity that influences treatment sensitivity in the clinic, and a reliance on tumor growth delay instead of local control (TCD50) endpoints. There exists an urgent need to overcome these barriers to facilitate successful clinical translation of targeted radiosensitizers. To this end, we have employed 3D cell culture assays to better model tumor behavior in vivo. Examples of successful prediction of in vivo effects with these 3D assays include radiosensitization of head and neck cancers by inhibiting epidermal growth factor receptor or focal adhesion kinase signaling, and radioresistance associated with oncogenic mutation of KRAS. To address the issue of tumor heterogeneity we leveraged institutional resources that allow high-throughput 3D screening of radiation combinations with small molecule inhibitors across genomically characterized cell lines from lung, head and neck, and pancreatic cancers. This high-throughput screen is expected to uncover genomic biomarkers that will inform the successful clinical translation of targeted agents from the NCI CTEP portfolio and other sources. Screening "hits" need to be subjected to refinement studies that include clonogenic assays, addition of disease-specific chemotherapeutics, target/biomarker validation, and integration of patient-derived tumor models. The chemoradiosensitizing activities of the most promising drugs should be confirmed in TCD50 assays in xenograft models with/without relevant biomarker and utilizing clinically relevant radiation fractionation. We predict that appropriately validated and biomarker-directed targeted therapies will have a higher likelihood than past efforts to be successfully incorporated into the standard management of hard-to-treat tumors.

Sample-size calculation for preclinical dose-response experiments using heterogeneous tumour models

BACKGROUND

In preclinical radio-oncological research, local tumour control is considered the most relevant endpoint as it reflects the inactivation of cancer stem cells. Preclinical tumour-control assays may compare dose-response curves between different radiotherapy strategies, e.g., assessing additional targeted drugs and immunotherapeutic interventions, or between different radiation modalities. To mimic the biological heterogeneity of human tumour populations and to accommodate for approaches of personalized oncology, preclinical studies are increasingly performed combining larger panels of tumour models. For designing the study protocols and to obtain reliable results, prospective sample-size planning has to be developed that accounts for such heterogeneous cohorts.

METHODS

A Monte-Carlo-based method was developed to estimate the sample size of a comparative 1:1 two-arm prospective tumour-control assay. Based on repeated logistic regression analysis, pre-defined dose levels, assumptions on the dose-response curves of the included tumour models and on the dose-modifying factors (DMF), the power is calculated for a given number of animals per dose group.

RESULTS

Two applications are presented: (i) For a simple tumour-control assay with the head and neck squamous cell carcinoma (HNSCC) model FaDu, 10 animals would be required for each of 7 dose levels per arm to reveal a DMF of 1.25 with a power of 0.82 without drop out (total: 140 animals). (ii) In a more complex experiment combining six different lung tumour models to a heterogeneous population, 21 animals would be required for each of 11 dose levels per arm to reveal a DMF of 1.25 with a power of 0.81 without drop out (total: 462 animals). Analyzing the heterogeneous cohort reduces the required animal number by more than 50% compared to six individual tumour-control assays.

CONCLUSION

An approach for estimating the required animal number for comparative tumour-control assays in a heterogeneous population is presented, allowing also the inclusion of different treatments as a personalized approach in the experimental arm. The software is publicly available and can be applied to plan comparisons of sigmoidal dose-response curves based on logistic regression.

Value of functional in-vivo endpoints in preclinical radiation research

BACKGROUND

Cancer research faces the problem of high rates of clinical failure of new treatment approaches after positive preclinical data. We hypothesize that a major confounding factor to this problem in radiooncology is the choice of the preclinical endpoint.

METHODS

We present a comprehensive re-evaluation of large-scale preclinical in-vivo data on fractionated irradiation alone or simultaneously with Epidermal Growth Factor Receptor inhibition. Taking the permanent local tumour control assay as a gold standard, we evaluated different tumour volume dependent endpoints that are widely used for preclinical experiments.

RESULTS

The analysis showed the highest correlations between volume related and local tumour control endpoints after irradiation alone. For combined treatments, wide inter-tumoural variations were observed with reduced correlation between the endpoints. Evaluation of growth delay per Gray (GD/Gy) based on two or more dose levels showed closest correlation with local tumour control dose 50% (TCD₅₀).

CONCLUSIONS

GD/Gy with at least two dose groups correlates with TCD₅₀, but cannot replace the latter as the goldstandard.

Restoration of circPSMC3 sensitizes gefitinib-resistant esophageal squamous cell carcinoma cells to gefitinib by regulating miR-10a-5p/PTEN axis

Circular RNAs (circRNAs) has been shown to play an important role in the progression of various cancers. However, the function and underlying mechanisms of circRNAs affecting chemotherapy resistance in esophageal squamous cell carcinoma (ESCC) remain largely unknown. In this study, we used gefitinib-resistant (GR) ESCC cells to investigate the function of circPSMC3 and clarify the underlying mechanism in chemotherapy resistance in ESCC. The results suggested that circPSMC3 expression was downregulated, but miR-10a-5p was upregulated in ESCC tissues and cells, as well as in GR ESCC cells. CircPSMC3 overexpression increased the sensitivity of ESCC cells to gefitinib, as indicated by reduced half maximal inhibitory concentration value, increased apoptosis rate and cleaved caspase-3 protein expression. CircPSMC3 directly interacted with miR-10a-5p and inhibited the expression of miR-10a-5p. Phosphatase and tensin homolog (PTEN) was a direct target of miR-10a-5p and circPSMC3 promoted PTEN expression via decreasing miR-10a-5p level. Moreover, the effect of circPSMC3 on resistance of GR ESCC cells to gefitinib was remarkably reduced by restoration of miR-10a-5p and downregultion of PTEN. Taken together, these observations suggested that upregulation of circPSMC3 overcame resistance of GR ESCC cells to gefitinib by modulating the miR-10a-5p/PTEN axis, which provide a new therapeutic strategy for overcoming gefitinib resistance in ESCC.

Inhibition of lncRNA PART1 Chemosensitizes Wild Type but Not KRAS Mutant NSCLC Cells

Background

Lung cancer has the highest incidence among solid tumors in men and is the third most common cancer in women. Despite improved understanding of genomic and mutational landscape in non-small cell lung cancer (NSCLC), the five-year survival in these patients has remained stagnant at a dismal 15%. The first line of treatment commonly adapted for NSCLC patients with somatic mutation in EGFR is tyrosine kinase inhibitor gefitinib or erlotinib. EGFR mutant cells seem to be intrinsically sensitive to tyrosine kinase inhibitors; however, the remaining 20-30% patients are resistant to tyrosine kinase inhibitor.

Materials and Methods

Here we show, using in vitro normal and NSCLS cell lines, that the lncRNA Prostate androgen-regulated transcript 1 (PART1) is expressed at higher levels in NSCLC cells compared to normal lung epithelial cell line, corroborating two earlier studies.

Results

We additionally show that these cells are resistant to erlotinib which is reversed in some, but not all, cell lines following suppression of PART1 expression. The differential response to erlotinib following siRNA-mediated knockdown of PART1 was found to be related to the mutational status of KRAS. Only in cells with wild-type KRAS suppression of PART1 sensitized them to erlotinib. Knockdown of mutant KRAS did not sensitize those cell lines to erlotinib. But knockdown of mutant KRAS along with suppression of PART1 sensitized the cells to treatment with erlotinib. The results from the study reveal a yet undefined and important role of lncRNA PART1 in defining sensitivity to erlotinib. This action is mediated by mutation status of KRAS.

Conclusion

Even though preliminary, our results indicate PART1 might be a potential candidate for targeted therapy or used as a predictor of chemosensitivity in patients with NSCLC.

Radioresistance of KRAS/TP53-mutated lung cancer can be overcome by radiation dose escalation or EGFR tyrosine kinase inhibition in vivo

Recent clinical data have linked KRAS/TP53 comutation (mut) to resistance to radiotherapy (RT), but supporting laboratory in vivo evidence is lacking. In addition, the ability of different radiation doses, with/without epidermal growth factor receptor (EGFR)-directed treatment, to achieve local tumor control as a function of KRAS status is unknown. Here, we assessed clonogenic radiation survival of a panel of annotated lung cancer cell lines. KRASmut/TP53mut was associated with the highest radioresistance in nonisogenic and isogenic comparisons. To validate these findings, isogenic TP53mut NCI-H1703 models, KRASmut or wild-type (wt), were grown as heterotopic xenografts in nude mice. A clinical RT schedule of 30 fractions over 6 weeks was employed. The dose that controlled 50% of tumors (TCD₅₀ ) was calculated. The TCD₅₀ for KRASwt/TP53mut xenografts was 43.1 Gy whereas KRASmut/TP53mut tumors required a 1.9-fold higher TCD₅₀ of 81.4 Gy. The EGFR inhibitor erlotinib radiosensitized KRASmut but not KRASwt cells and xenografts. The TCD₅₀ associated with adding erlotinib to RT was 58.8 Gy for KRASmut, that is, a ~1.4-fold dose enhancement. However, the EGFR antibody cetuximab did not have a radiosensitizing effect. In conclusion, we demonstrate for the first time that KRASmut in a TP53mut background confers radioresistance when studying a clinical RT schedule and local control rather than tumor growth delay. Despite the known unresponsiveness of KRASmut tumors to EGFR inhibitors, erlotinib radiosensitized KRASmut tumors. Our data highlight KRAS/TP53 comutation as a candidate biomarker of radioresistance that can be at least partially reversed by dose escalation or the addition of a targeted agent.

Modeling long-term tumor growth and kill after combinations of radiation and radiosensitizing agents

PURPOSE

Radiation therapy, whether given alone or in combination with chemical agents, is one of the cornerstones of oncology. We develop a quantitative model that describes tumor growth during and after treatment with radiation and radiosensitizing agents. The model also describes long-term treatment effects including tumor regrowth and eradication.

METHODS

We challenge the model with data from a xenograft study using a clinically relevant administration schedule and use a mixed-effects approach for model-fitting. We use the calibrated model to predict exposure combinations that result in tumor eradication using Tumor Static Exposure (TSE).

RESULTS

The model is able to adequately describe data from all treatment groups, with the parameter estimates taking biologically reasonable values. Using TSE, we predict the total radiation dose necessary for tumor eradication to be 110 Gy, which is reduced to 80 or 30 Gy with co-administration of 25 or 100 mg kg^-1 of a radiosensitizer. TSE is also explored via a heat map of different growth and shrinkage rates. Finally, we discuss the translational potential of the model and TSE concept to humans.

CONCLUSIONS

The new model is capable of describing different tumor dynamics including tumor eradication and tumor regrowth with different rates, and can be calibrated using data from standard xenograft experiments. TSE and related concepts can be used to predict tumor shrinkage and eradication, and have the potential to guide new experiments and support translations from animals to humans.

Cetuximab-radiotherapy combination in the management of locally advanced cutaneous squamous cell carcinoma

INTRODUCTION

We report the outcomes of using a combination of cetuximab with radiation therapy (Cetux-RT) to treat a selected group of patients with locally advanced (unresectable) cutaneous squamous cell carcinoma (LA-cSCC). This study presents two-year efficacy and safety data for 8 patients with LA-cSCC treated within a single institution.

METHODS

Between 2014 and 2017 a total of eight patients (seven males, one female) with LA-cSCC received curative intent treatment with Cetux-RT. All patients received an initial loading dose of cetuximab at 400 mg/m² seven days prior to radiotherapy, followed by weekly treatment with 250 mg/m² , continuing through the end of radiotherapy. Radiation doses were 6600 cGy/30 fr (n = 2), 6300 cGy/30fr (n = 2) and 5500 cGy/22 fr (n = 4).

RESULTS

The median age was 81 years (range, 55-87). The ECOG performance status of all patients was between 0 and 2. With a median duration of follow-up of 25 months (range 10-48 months), five patients remain in a complete response. After a partial response, another patient has relapsed and is receiving palliative chemotherapy, while two patients have died during the period of follow up (one of whom died following progression of disease, the other of an unrelated cause). Treatment in this group of patients was well tolerated, with most toxicities ≤ grade 2, and no toxicities of grade 4/5 reported.

CONCLUSIONS

Cetux-RT was well tolerated and provided durable disease control within this patient sample. Our data support the use of the Cetux-RT regimen for selected patients with inoperable LA-cSCC and adequate performance status.

Exosome-mediated transfer of lncRNA PART1 induces gefitinib resistance in esophageal squamous cell carcinoma via functioning as a competing endogenous RNA

BACKGROUND

Currently, resistance to tyrosine kinase inhibitors, such as gefitinib, has become a major obstacle in improving the clinical outcome of patients with metastatic and advanced-stage esophageal squamous cell carcinoma (ESCC). While cell behavior can be modulated by long non-coding RNAs (lncRNAs), the roles of lncRNAs within extracellular vesicles (exosomes) are largely unknown. Therefore, we investigated the involvement and regulatory functions of potential lncRNAs enclosed in exosomes during formation of chemoresistance in human ESCC.

METHODS

Gefitinib-resistant cell lines were established by continuously grafting TE1 and KYSE-450 cells into gefitinib-containing culture medium. LncRNA microarray assay followed by RT-qPCR were used to verify the differential expression of lncRNA Prostate Androgen-Regulated Transcript 1 (PART1) between gefitinib resistant and parental cell lines. RNA fluorescence in situ hybridization (FISH) was used to investigate whether extracellular PART1 could be incorporated into exosomes and transmitted to recipient cells. Subsequently, a series of in vitro assays and a xenograft tumor model were used to observe the functions of lncRNA PART1 in ESCC cells. A signal transduction reporter array, bioinformatics analysis, western blotting, and immunofluorescence were carried out to verify the regulation of PART1 and its downstream Bcl-2 signaling pathway.

RESULTS

lncRNA PART1 was upregulated in gefitinib-resistant cells when compared to parental ESCC cells. It was found that STAT1 can bind to the promoter region of lncRNA PART1, resulting in its activation. Knockdown of lncRNA PART1 potently promoted the gefitinib-induced cell death, while elevated PART1 promoted gefitinib resistance by competitively binding to miR-129 to facilitate Bcl-2 expression in ESCC cells. In addition, extracellular PART1 could be incorporated into exosomes and transmitted to sensitive cells, thus disseminating gefitinib resistance. Clinically, high levels of serum lncRNA PART1 in exosome were associated with poor response to gefitinib treatment in ESCC patients.

CONCLUSIONS

LncRNA PART1 promotes gefitinib resistance by regulating miR-129/Bcl-2 pathway, and may serve as a therapeutic target for ESCC patients.

Toward A variable RBE for proton beam therapy

In the clinic, proton beam therapy (PBT) is based on the use of a generic relative biological effectiveness (RBE) of 1.1 compared to photons in human cancers and normal tissues. However, the experimental basis for this RBE lacks any significant number of representative tumor models and clinically relevant endpoints for dose-limiting organs at risk. It is now increasingly appreciated that much of the variations of treatment responses in cancers are due to inter-tumoral genomic heterogeneity. Indeed, recently it has been shown that defects in certain DNA repair pathways, which are found in subsets of many cancers, are associated with a RBE increase in vitro. However, there currently exist little in vivo or clinical data that confirm the existence of similarly increased RBE values in human cancers. Furthermore, evidence for variable RBE values for normal tissue toxicity has been sparse and conflicting to date. If we could predict variable RBE values in patients, we would be able to optimally use and personalize PBT. For example, predictive tumor biomarkers may facilitate selection of patients with proton-sensitive cancers previously ineligible for PBT. Dose de-escalation may be possible to reduce normal tissue toxicity, especially in pediatric patients. Knowledge of increased tumor RBE may allow us to develop biologically optimized therapies to enhance local control while RBE biomarkers for normal tissues could lead to a better understanding and prevention of unusual PBT-associated toxicity. Here, we will review experimental data on the repair of proton damage to DNA that impact both RBE values and biophysical modeling to predict RBE variations. Experimental approaches for studying proton sensitivity in vitro and in vivo will be reviewed as well and recent clinical findings discussed. Ultimately, therapeutically exploiting the understudied biological advantages of protons and developing approaches to limit treatment toxicity should fundamentally impact the clinical use of PBT.

Radiosensitization of HNSCC cells by EGFR inhibition depends on the induction of cell cycle arrests

The increase in cellular radiosensitivity by EGF receptor (EGFR) inhibition has been shown to be attributable to the induction of a G1-arrest in p53-proficient cells. Because EGFR targeting in combination with radiotherapy is used to treat head and neck squamous cell carcinomas (HNSCC) which are predominantly p53 mutated, we tested the effects of EGFR targeting on cellular radiosensitivity, proliferation, apoptosis, DNA repair and cell cycle control using a large panel of HNSCC cell lines. In these experiments EGFR targeting inhibited signal transduction, blocked proliferation and induced radiosensitization but only in some cell lines and only under normal (pre-plating) conditions. This sensitization was not associated with impaired DNA repair (53BP1 foci) or induction of apoptosis. However, it was associated with the induction of a lasting G2-arrest. Both, the radiosensitization and the G2-arrest were abrogated if the cells were re-stimulated (delayed plating) with actually no radiosensitization being detectable in any of the 14 tested cell lines. Therefore we conclude that EGFR targeting can induce a reversible G2 arrest in p53 deficient HNSCC cells, which does not consequently result in a robust cellular radiosensitization. Together with recent animal and clinical studies our data indicate that EGFR inhibition is no effective strategy to increase the radiosensitivity of HNSCC cells.

Inhibition of GRP78 abrogates radioresistance in oropharyngeal carcinoma cells after EGFR inhibition by cetuximab

The EGFR-specific mAb cetuximab is one of the most effective treatments for oropharyngeal carcinoma, while patient responses to EGFR inhibitors given alone are modest. Combination treatment with radiation can improve the efficacy of treatment through increasing radiosensitivity, while resistance to radiation after administration of cetuximab limits its efficiency. Radiation and drugs can damage the endoplasmic reticulum (ER) homeostatic state and result in ER stress (ERS), subsequently causing resistance to radiation and drugs. Whether the ERS pathway is involved in radioresistance after administration of cetuximab has not been reported. Herein, we show that cetuximab could increase the radiosensitivity of FaDu cells but not Detroit562 cells. In addition, cetuximab inhibited the radiation-induced activation of the ERS signalling pathway IRE1α/ATF6-GRP78 in FaDu cells, while this effect was absent in Detroit562 cells. Silencing GRP78 increased the radiosensitivity of oropharyngeal carcinoma cells and inhibited radiation-induced DNA double-strand-break (DSB) repair and autophagy. More interestingly, silencing GRP78 abrogated resistance to cetuximab and radiation in Detroit562 cells and had a synergistic effect with cetuximab in increasing the radiosensitivity of FaDu cells. Immunohistochemistry showed that overexpression of both GRP78 and EGFR was associated with a poor prognosis in oropharyngeal carcinoma patients (P<0.05). Overall, the results of this study show that radioresistance after EGFR inhibition by cetuximab is mediated by the ERS signalling pathway IRE1α/ATF6-GRP78. This suppression was consequently unable to inhibit radiation-induced DSB repair and autophagy in oropharyngeal carcinoma cells, which conferred resistance to radiotherapy and cetuximab. These results suggest that the cooperative effects of radiotherapy and cetuximab could be further improved by inhibiting GRP78 in non-responsive oropharyngeal carcinoma patients.

Afatinib radiosensitizes head and neck squamous cell carcinoma cells by targeting cancer stem cells

The dismal prognosis of locally advanced and metastatic squamous cell carcinoma of the head and neck (HNSCC) is primarily due to the development of resistance to chemoradiation therapy (CRT). Deregulation of Epidermal Growth Factor Receptor (EGFR) signaling is involved in HNSCC pathogenesis by regulating cell survival, cancer stem cells (CSCs), and resistance to CRT. Here we investigated the radiosensitizing activity of the pan-EGFR inhibitor afatinib in HNSCC in vitro and in vivo. Our results showed strong antiproliferative effects of afatinib in HNSCC SCC1 and SCC10B cells, compared to immortalized normal oral epithelial cells MOE1a and MOE1b. Comparative analysis revealed stronger antitumor effects with afatinib than observed with erlotinib. Furthermore, afatinib enhanced in vitro radiosensitivity of SCC1 and SCC10B cells by inducing mesenchymal to epithelial transition, G1 cell cycle arrest, and the attenuating ionizing radiation (IR)-induced activation of DNA double strand break repair (DSB) ATM/ATR/CHK2/BRCA1 pathway. Our studies also revealed the effect of afatinib on tumor sphere- and colony-forming capabilities of cancer stem cells (CSCs), and decreased IR-induced CSC population in SCC1 and SCC10B cells. Furthermore, we observed that a combination of afatinib with IR significantly reduced SCC1 xenograft tumors (median weight of 168.25 ± 20.85 mg; p = 0.05) compared to afatinib (280.07 ± 20.54 mg) or IR alone (324.91 ± 28.08 mg). Immunohistochemical analysis of SCC1 tumor xenografts demonstrated downregulation of the expression of IR-induced pEGFR1, ALDH1 and upregulation of phosphorylated γH2AX by afatinib. Overall, afatinib reduces tumorigenicity and radiosensitizes HNSCC cells. It holds promise for future clinical development as a novel radiosensitizer by improving CSC eradication.

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.

Personalized Radiation Oncology: Epidermal Growth Factor Receptor and Other Receptor Tyrosine Kinase Inhibitors

Molecular biomarkers are currently evaluated in preclinical and clinical studies in order to establish predictors for treatment decisions in radiation oncology. The receptor tyrosine kinases (RTK) are described in the following text. Among them, the most data are available for the epidermal growth factor receptor (EGFR) that plays a major role for prognosis of patients after radiotherapy, but seems also to be involved in mechanisms of radioresistance, specifically in repopulation of tumour cells between radiotherapy fractions. Monoclonal antibodies against the EGFR improve locoregional tumour control and survival when applied during radiotherapy, however, the effects are heterogeneous and biomarkers for patient selection are warranted. Also other RTK´s such as c-Met and IGF-1R seem to play important roles in tumour radioresistance. Beside the potential to select patients for molecular targeting approaches combined with radiotherapy, studies are also needed to evluate radiotherapy adaptation approaches for selected patients, i.e. adaptation of radiation dose, or, more sophisticated, of target volumes.

Assessment of pulmonary 18F-FDG-PET uptake and cytokine profiles in non-small cell lung cancer patients treated with radiotherapy and erlotinib

Purpose

To investigate effects of radiotherapy (RT) and erlotinib on pulmonary glucose uptake using 2-deoxy-2-(18F)fluoro-D-glucose (¹⁸F-FDG) positron emission tomography (PET) during and after treatment of non-small cell lung cancer (NSCLC) and to identify associations between serum cytokine levels and lung glucose uptake.

Material and methods

Twenty-seven patients with advanced NSCLC, receiving RT alone or concomitant RT and erlotinib therapy, were examined by ¹⁸F-FDG PET before, during, and after treatment. A total of 57 ¹⁸F-FDG PET scans were analyzed. Pulmonary ¹⁸F-FDG uptake and radiotherapy dose mapping were used to acquire dose-response curves for each patient, where subsequent linear regression gave a glucose uptake level in the un-irradiated parts of the lungs (SUV₀) and a response slope (ΔSUV). Serum cytokine levels at corresponding time points were assessed using a multiplex bioassay. Correlations between the most robust cytokines and lung ¹⁸F-FDG dose response parameters were further investigated.

Results

From the dose response analysis, SUV₀ at post-therapy was significantly higher (P < 0.001) than at mid- and pre-therapy (45% and 58%, respectively) for the group receiving RT + erlotinib. Also, SUV₀ at post-therapy was higher for patients receiving RT + erlotinib compared to RT alone (42%; P < 0.001). No differences in ΔSUV were seen with treatments or time. SUV₀ was positively associated (r = 0.47, P = 0.01) with serum levels of the chemokine C-C motif ligand 21 (CCL21) for patients receiving RT + erlotinib.

Conclusions

Concomitant RT and erlotinib causes an elevation in pulmonary ¹⁸F-FDG uptake post treatment compared to RT alone. Pulmonary glucose uptake is associated with an upregulation of a chemokine (CCL21) involved in inflammatory reactions.

Radiation Resistance in KRAS-Mutated Lung Cancer Is Enabled by Stem-like Properties Mediated by an Osteopontin-EGFR Pathway

Lung cancers with activating KRAS mutations are characterized by treatment resistance and poor prognosis. In particular, the basis for their resistance to radiation therapy is poorly understood. Here, we describe a radiation resistance phenotype conferred by a stem-like subpopulation characterized by mitosis-like condensed chromatin (MLCC), high CD133 expression, invasive potential, and tumor-initiating properties. Mechanistic investigations defined a pathway involving osteopontin and the EGFR in promoting this phenotype. Osteopontin/EGFR-dependent MLCC protected cells against radiation-induced DNA double-strand breaks and repressed putative negative regulators of stem-like properties, such as CRMP1 and BIM. The MLCC-positive phenotype defined a subset of KRAS-mutated lung cancers that were enriched for co-occurring genomic alterations in TP53 and CDKN2A. Our results illuminate the basis for the radiation resistance of KRAS-mutated lung cancers, with possible implications for prognostic and therapeutic strategies. Cancer Res; 77(8); 2018-28. ©2017 AACR.

Resistance of Nonmelanoma Skin Cancer to Nonsurgical Treatments. Part II: Photodynamic Therapy, Vismodegib, Cetuximab, Intralesional Methotrexate, and Radiotherapy

A wide range of treatments is now available for nonmelanoma skin cancer, including 5-fluorouracil, ingenol mebutate, imiquimod, diclofenac, photodynamic therapy, methotrexate, cetuximab, vismodegib, and radiotherapy. All are associated with high clinical and histologic response rates. However, some tumors do not respond due to resistance, which may be primary or acquired. Study of the resistance processes is a broad area of research that aims to increase our understanding of the nature of each tumor and the biologic features that make it resistant, as well as to facilitate the design of new therapies directed against these tumors. In this second article, having covered the topical treatments of nonmelanoma skin cancer, we review resistance to other nonsurgical treatments, such as monoclonal antibodies against basal and squamous cell carcinomas, intralesional chemotherapy, photodynamic therapy, and radiotherapy.

Improving external beam radiotherapy by combination with internal irradiation

The efficacy of external beam radiotherapy (EBRT) is dose dependent, but the dose that can be applied to solid tumour lesions is limited by the sensitivity of the surrounding tissue. The combination of EBRT with systemically applied radioimmunotherapy (RIT) is a promising approach to increase efficacy of radiotherapy. Toxicities of both treatment modalities of this combination of internal and external radiotherapy (CIERT) are not additive, as different organs at risk are in target. However, advantages of both single treatments are combined, for example, precise high dose delivery to the bulk tumour via standard EBRT, which can be increased by addition of RIT, and potential targeting of micrometastases by RIT. Eventually, theragnostic radionuclide pairs can be used to predict uptake of the radiotherapeutic drug prior to and during therapy and find individual patients who may benefit from this treatment. This review aims to highlight the outcome of pre-clinical studies on CIERT and resultant questions for translation into the clinic. Few clinical data are available until now and reasons as well as challenges for clinical implementation are discussed.

Adapting a drug screening platform to discover associations of molecular targeted radiosensitizers with genomic biomarkers

Large collections of annotated cancer cell lines are powerful tools for precisely matching targeted drugs with genomic alterations that can be tested as biomarkers in the clinic. Whether these screening platforms, which utilize short-term cell survival to assess drug responses, can be applied to precision radiation medicine is not established. To this end, 32 cancer cell lines were screened using 18 targeted therapeutic agents with known or putative radiosensitizing properties (227 combinations). The cell number remaining after drug exposure with or without radiation was assessed by nonclonogenic assays. We derived short-term radiosensitization factors (SRF2Gy) and calculated clonogenic survival assay-based dose enhancement factors (DEFSF0.1). Radiosensitization was characterized by SRF2Gy values of mostly ∼1.05 to 1.2 and significantly correlated with drug-induced changes in apoptosis and senescence frequencies. SRF2Gy was significantly correlated with DEFSF0.1, with a respective sensitivity and specificity of 91.7% and 81.5% for a 3-day endpoint, and 82.8% and 84.2% for a robotic 5-day assay. KRAS mutations (codons 12/13) were found to be a biomarker of radiosensitization by midostaurin in lung cancer, which was pronounced under conditions that enriched for stem cell-like cells. In conclusion, although short-term proliferation/survival assays cannot replace the gold-standard clonogenic survival assay for measuring cellular radiosensitivity, they capture with high accuracy the relative change in radiosensitivity that is caused by a radiosensitzing targeted agent.

IMPLICATIONS

This study supports a paradigm shift regarding the utility of short-term assays for precision radiation medicine, which should facilitate the identification of genomic biomarkers to guide the testing of novel drug/radiation combinations.

Effect of combined irradiation and EGFR/Erb-B inhibition with BIBW 2992 on proliferation and tumour cure in cell lines and xenografts

BACKGROUND AND PURPOSE

In previous experiments an enhanced anti-proliterative effect of the EGFR/ErbB tyrosine kinase inhibitor (TKI) BIBW 2992 with single dose irradiation was observed in FaDu tumour xenografts. Aim of the present experiment was to determine if this effect can also be seen in combination with a fractionated radiotherapy. Secondly we investigate the efficacy of BIBW 2992 on local tumour control for UT-SCC-15.

MATERIAL AND METHODS

Tumour pieces of FaDu, UT-SCC-14, A431, UT-SCC-15 (squamous cell carcinomas) and A7 (glioma) tumour models were transplanted onto the right hind leg of NMRI (nu/nu) nude mice. For evaluation of tumour growth mice were either treated daily orally with BIBW 2992 (30 mg/kg body weight), or carrier up to a final tumour size of 15 mm or with a fractionated radiotherapy (15f/15d, 30 Gy) with simultaneous application of BIBW 2992 or carrier. For local tumour control UT-SCC-15 tumours were treated with a fractionated radiotherapy (30f/6weeks) or received 30f/6 weeks in combination with daily orally BIBW 2992 (22.5 mg/kg b.w.) during RT.

RESULTS

A significant effect on tumour growth time was observed in all tumour models for BIBW 2992 application alone. However, substantial intertumoural heterogeneity could be seen. In the UT-SCC-14, UT-SCC-15 and A431 tumour models a total regression of the tumours and no recurrence during treatment time (73 days) were determined where as for the A7 tumour only a slight effect was noticeable. For the combined treatment of fractionated radiotherapy (15f/15d) and BIBW 2992 administration a significant effect on tumour growth time was seen compared to irradiation alone for A7, UT-SCC-15 and A431 (ER 1.2 - 3.7), this advantage could not be demonstrated for FaDu and UT-SCC-14. However, the local tumour control was not altered for the UT-SCC-15 tumour model when adding BIBW 2992 to fractionated irradiation (30f/6weeks).

CONCLUSION

A heterogeneous effect on tumour growth time of BIBW 2992 alone as well as in combination with fractionated irradiation could be demonstrated for all tumour models. However, the significant effect on tumour growth time did not translate into an improvement of local tumour control for the UT-SCC-15 tumour model.

Tomotherapy concomitant with cetuximab, followed by cetuximab as single-agent therapy for unresectable squamous cell carcinoma of the skin: a case report

BACKGROUND

Cutaneous squamous cell carcinoma (SCC) is the second most frequency of all skin tumors. Incidence of SCC has risen significantly due to an increased sun exposure and the number of immunodeficient patients. Cutaneous SCC is characterized by high Epidermal growth factor receptor (EGFR) expression with low frequency of RAS mutations. Generally, locoregional surgery is curative and systemic therapy is not indicated. We evaluated the activity and toxicity profile of tomotherapy concomitant with Cetuximab, followed by Cetuximab as single agent therapy in a patient affected by unresectable, locally advanced cutaneous SCC.

CASE PRESENTATION

At our institution, on March 2012 we treated a 45 years-old patient affected by locally advanced, unresectable G1 SCC of the lumbar region. At our first observation, the patient was asthenic, with severe pain and functional limitations. There was also a superinfection due to Pseudomonas Aeruginosa resistant to antibiotics, and a G3 anemia secondary to the bleeding lesion. ECOG Performance Status was 2. Tomotherapy has been performed concomitant with the Cetuximab (400 mg/m2, followed by weekly doses of 250 mg/m2) at the total dose of 60 Gy (2 Gy/fx), followed by Cetuximab monotherapy.The lesion reduced progressively until disappear even after the suspension of the treatment and the patient achieved complete response. Toxicity resulted in G1 cutaneous rash and G2 toxicity to the nails, appeared after 5 months of treatment, typical toxicity profile of the anti-EGFR therapies. After one month of therapy the Pseudomonas Aeruginosa superinfection totally disappeared. Quality of life resulted significantly improved with reduction until discontinuation of the anti-pain drugs, and progressive increase of the hemoglobin levels. At follow up of 15 months there was no evidence of active disease and the ECOG Performance Status was 0 (zero).

CONCLUSION

The treatment was effective and feasible. Considering these excellent results, further studies about concomitant tomotherapy with Cetuximab for advanced/inoperable SCC of the skin are needed.

Focal adhesion signaling and therapy resistance in cancer

Interlocking gene mutations, epigenetic alterations and microenvironmental features perpetuate tumor development, growth, infiltration and spread. Consequently, intrinsic and acquired therapy resistance arises and presents one of the major goals to solve in oncologic research today. Among the myriad of microenvironmental factors impacting on cancer cell resistance, cell adhesion to the extracellular matrix (ECM) has recently been identified as key determinant. Despite the differentiation between cell adhesion-mediated drug resistance (CAMDR) and cell adhesion-mediated radioresistance (CAMRR), the underlying mechanisms share great overlap in integrin and focal adhesion hub signaling and differ further downstream in the complexity of signaling networks between tumor entities. Intriguingly, cell adhesion to ECM is per se also essential for cancer cells similar to their normal counterparts. However, based on the overexpression of focal adhesion hub signaling receptors and proteins and a distinct addiction to particular integrin receptors, targeting of focal adhesion proteins has been shown to potently sensitize cancer cells to different treatment regimes including radiotherapy, chemotherapy and novel molecular therapeutics. In this review, we will give insight into the role of integrins in carcinogenesis, tumor progression and metastasis. Additionally, literature and data about the function of focal adhesion molecules including integrins, integrin-associated proteins and growth factor receptors in tumor cell resistance to radio- and chemotherapy will be elucidated and discussed.

EGFR expression and survival in patients given cetuximab and chemoradiation for stage III non-small cell lung cancer: a secondary analysis of RTOG 0324

PURPOSE

We investigated whether expression of epidermal growth factor receptor (EGFR) was associated with survival and disease control in this secondary analysis of a phase II trial of cetuximab+chemoradiation for stage III non-small cell lung cancer.

METHODS

Patients received cetuximab weekly before and during radiation (63 Gy/35 fractions/7 weeks) with weekly carboplatin + paclitaxel. We analyzed EGFR expression by immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) in pretreatment biopsy specimens and compared findings with overall and progression-free survival (OS, PFS) and time to progression (TTP).

RESULTS

Specimens for IHC and FISH were collected from 51 and 45 of 87 evaluable patients. Pretreatment characteristics did not differ for patients with (n = 51) or without (n= 36) EGFR IHC data, or with (n = 45) or without (n = 42) FISH data. However, patients without IHC data had worse OS (HR = 1.63, P = 0.05), worse PFS (HR = 1.88, P = 0.008), and worse TTP [HR = 1.99, P = 0.01] than those with IHC data. EGFR protein expression was not related to pretreatment characteristics or OS; FISH-positive disease was associated with better performance status but not with OS, PFS, or TTP.

CONCLUSIONS

Surprisingly, outcomes differed not by EGFR expression but by the availability of samples for analysis, underscoring the importance of obtaining biopsy samples in such trials.

Radiolabeled Cetuximab Conjugates for EGFR Targeted Cancer Diagnostics and Therapy

The epidermal growth factor receptor (EGFR) has evolved over years into a main molecular target for the treatment of different cancer entities. In this regard, the anti-EGFR antibody cetuximab has been approved alone or in combination with: (a) chemotherapy for treatment of colorectal and head and neck squamous cell carcinoma and (b) with external radiotherapy for treatment of head and neck squamous cell carcinoma. The conjugation of radionuclides to cetuximab in combination with the specific targeting properties of this antibody might increase its therapeutic efficiency. This review article gives an overview of the preclinical studies that have been performed with radiolabeled cetuximab for imaging and/or treatment of different tumor models. A particularly promising approach seems to be the treatment with therapeutic radionuclide-labeled cetuximab in combination with external radiotherapy. Present data support an important impact of the tumor micromilieu on treatment response that needs to be further validated in patients. Another important challenge is the reduction of nonspecific uptake of the radioactive substance in metabolic organs like liver and radiosensitive organs like bone marrow and kidneys. Overall, the integration of diagnosis, treatment and monitoring as a theranostic approach appears to be a promising strategy for improvement of individualized cancer treatment.

Potential of a Cetuximab-based radioimmunotherapy combined with external irradiation manifests in a 3-D cell assay

Targeting epidermal growth factor receptor (EGFR)-overexpressing tumors with radiolabeled anti-EGFR antibodies is a promising strategy for combination with external radiotherapy. In this study, we evaluated the potential of external plus internal irradiation by [(90) Y]Y-CHX-A″-DTPA-C225 (Y-90-C225) in a 3-D environment using FaDu and SAS head and neck squamous cell carcinoma (HNSCC) spheroid models and clinically relevant endpoints such as spheroid control probability (SCP) and spheroid control dose 50% (SCD50 , external irradiation dose inducing 50% loss of spheroid regrowth). Spheroids were cultured using a standardized platform. Therapy response after treatment with C225, CHX-A"-DTPA-C225 (DTPA-C225), [(90) Y]Y-CHX-A"-DTPA (Y-90-DTPA) and Y-90-C225 alone or in combination with X-ray was evaluated by long-term monitoring (60 days) of spheroid integrity and volume growth. Penetration kinetics into spheroids and EGFR binding capacities on spheroid cells were identical for unconjugated C225 and Y-90-C225. Spheroid-associated radioactivity upon exposure to the antibody-free control conjugate Y-90-DTPA was negligible. Determination of the SCD50 demonstrated higher intrinsic radiosensitivity of FaDu as compared with SAS spheroids. Treatment with unconjugated C225 alone did not affect spheroid growth and cell viability. Also, C225 treatment after external irradiation showed no additive effect. However, the combination of external irradiation with Y-90-C225 (1 µg/ml, 24 hr) resulted in a considerable benefit as reflected by a pronounced reduction of the SCD50 from 16 Gy to 9 Gy for SAS spheroids and a complete loss of regrowth for FaDu spheroids due to the pronounced accumulation of internal dose caused by the continuous exposure to cell-bound radionuclide upon Y-90-C225-EGFR interaction.

Radiolabeled anti-EGFR-antibody improves local tumor control after external beam radiotherapy and offers theragnostic potential

PURPOSE

The effect of radioimmunotherapy (RIT) using the therapeutic radionuclide Y-90 bound to the anti-EGFR antibody cetuximab combined with external beam irradiation (EBRT) (EBRIT) on permanent local tumor control in vivo was examined.

METHODS

Growth delay was evaluated in three human squamous cell carcinoma models after RIT with [(90)Y]Y-(CHX-A''-DTPA)₄-cetuximab (Y-90-cetuximab). The EBRT dose required to cure 50% of the tumors (TCD₅₀) for EBRT alone or EBRIT was evaluated in one RIT-responder (FaDu) and one RIT-non-responder (UT-SCC-5). EGFR expression and microenvironmental parameters were evaluated in untreated tumors, bioavailability was visualized by PET using ([(86)Y]Y-(CHX-A''-DTPA)₄-cetuximab (Y-86-cetuximab) and biodistribution using Y-90-cetuximab.

RESULTS

In UT-SCC-8 and FaDu but not in UT-SCC-5 radiolabeled cetuximab led to significant tumor growth delay. TCD₅₀ after EBRT was significantly decreased by EGFR-targeted RIT in FaDu but not in UT-SCC-5. In contrast to EGFR expression, parameters of the tumor micromilieu and in particular the Y-90-cetuximab biodistribution or Y-86-cetuximab visualization in PET correlated with the responsiveness to RIT or EBRIT.

CONCLUSION

EGFR-targeted EBRIT can improve permanent local tumor control compared to EBRT alone. PET imaging of bioavailability of labeled cetuximab appears to be a suitable predictor for response to EBRIT. This theragnostic approach should be further explored for clinical translation.

Epidermal growth factor receptor targeted nuclear delivery and high-resolution whole cell X-ray imaging of Fe3O4@TiO2 nanoparticles in cancer cells

Sequestration within the cytoplasm often limits the efficacy of therapeutic nanoparticles that have specific subcellular targets. To allow for both cellular and subcellular nanoparticle delivery, we have created epidermal growth factor receptor (EGFR)-targeted Fe3O4@TiO2 nanoparticles that use the native intracellular trafficking of EGFR to improve internalization and nuclear translocation in EGFR-expressing HeLa cells. While bound to EGFR, these nanoparticles do not interfere with the interaction between EGFR and karyopherin-β, a protein that is critical for the translocation of ligand-bound EGFR to the nucleus. Thus, a portion of the EGFR-targeted nanoparticles taken up by the cells also reaches cell nuclei. We were able to track nanoparticle accumulation in cells by flow cytometry and nanoparticle subcellular distribution by confocal fluorescent microscopy indirectly, using fluorescently labeled nanoparticles. More importantly, we imaged and quantified intracellular nanoparticles directly, by their elemental signatures, using X-ray fluorescence microscopy at the Bionanoprobe, the first instrument of its kind in the world. The Bionanoprobe can focus hard X-rays down to a 30 nm spot size to map the positions of chemical elements tomographically within whole frozen-hydrated cells. Finally, we show that photoactivation of targeted nanoparticles in cell nuclei, dependent on successful EGFR nuclear accumulation, induces significantly more double-stranded DNA breaks than photoactivation of nanoparticles that remain exclusively in the cytoplasm.

Simultaneous PLK1 inhibition improves local tumour control after fractionated irradiation

PURPOSE

Polo-like kinase 1 (PLK1) plays an important role in mitotic progression, is frequently overexpressed and associated with a poor prognosis of cancer patients, thus providing a promising target in anticancer treatment. Aim of the current project was to evaluate the effect of the novel PLK1 inhibitor BI 6727 in combination with irradiation.

MATERIAL AND METHODS

In vitro proliferation and radiation cell survival assays as well as in vivo local tumour control assays after single treatment and combined radiation and drug application were carried out using the squamous cell carcinoma models A431 and FaDu. In addition, cell cycle phases were monitored in vitro and in vivo.

RESULTS

BI 6727 showed a dose-dependent antiproliferative effect and an increase in the mitotic fraction. BI 6727 alone reduced clonogenic cell survival, while radiosensitivity in vitro (SF2) and in vivo (single-dose TCD(50) under clamped hypoxia) was not affected. In contrast, local tumour control was significantly improved after application of BI 6727 simultaneously to fractionated irradiation (A431: TCD(50) = 60.5 Gy [95% C.I. 57; 63] after IR alone and <30 Gy after combined treatment; FaDu: 49.5 Gy [43; 56 Gy] versus 32.9 Gy [26; 40]).

CONCLUSIONS

Despite the lack of direct cellular radiosensitisation, PLK1 inhibition with BI 6727 during fractionated irradiation significantly improves local tumour control when compared to irradiation alone. This result is likely explained by a considerable effect on cell cycle and an independent cytotoxic potential of BI 6727.

Cetuximab attenuates its cytotoxic and radiosensitizing potential by inducing fibronectin biosynthesis

Inherent and acquired resistance to targeted therapeutics continues to emerge as a major clinical obstacle. For example, resistance to EGF receptor targeting occurs commonly, more so than was expected, on the basis of preclinical work. Given emerging evidence that cancer cell-substrate interactions are important determinants of therapeutic sensitivity, we examined the impact of cell-fibronectin interactions on the efficacy of the EGF receptor antibody cetuximab, which is used widely for lung cancer treatment. Our results revealed the potential for cell-fibronectin interactions to induce radioresistance of human non-small cell lung cancer cells. Cell adhesion to fibronectin enhanced tumor cell radioresistance and attenuated the cytotoxic and radiosensitizing effects of cetuximab. Both in vitro and in vivo, we found that cetuximab treatment led to a remarkable induction of fibronectin biosynthesis. Mechanistic analyses revealed the induction was mediated by a p38-MAPK-ATF2 signaling pathway and that RNAi-mediated inhibition of fibronectin could elevate the cytotoxic and radiosensitizing potential of cetuximab. Taken together, our findings show how cell adhesion blunts cetuximab, which, by inducing fibronectin, generates a self-attenuating mechanism of drug resistance.

111In-cetuximab-F(ab')2 SPECT imaging for quantification of accessible epidermal growth factor receptors (EGFR) in HNSCC xenografts

BACKGROUND AND PURPOSE

Immunohistochemical epidermal growth factor receptor (EGFR) expression does not correlate with treatment response in head and neck squamous cell carcinomas (HNSCC). Aim was to apply the tracer (111)In-cetuximab-F(ab')2 for EGFR microSPECT imaging and to investigate if tracer uptake correlated with response to EGFR-inhibition by cetuximab in HNSCC xenografts. Usage of F(ab)2 fragments allows for shorter interval between tracer injection and imaging.

MATERIALS AND METHODS

Mice with HNSCC xenografts, SCCNij202, 153, 185 and 167 were imaged with microSPECT using (111)In-cetuximab-F(ab')2. Subsequently, tumors were analyzed by autoradiography and immunohistochemistry and tracer concentration was determined. Tumor uptake was correlated with previously assessed response to cetuximab treatment.

RESULTS

MicroSPECT imaging showed preferential uptake in HNSCC xenografts. Tumor-to-liver ratios were 3.1 ± 0.2 (SCCNij202), 2.8 ± 0.4 (SCCNij153), 2.0 ± 0.8 (SCCNij185), 2.0 ± 0.4 (SCCNij167). Immunohistochemical EGFR fractions (fEGFR) differed significantly between xenografts; 0.77 ± 0.07 (SCCNij202), 0.66 ± 0.11 (SCCNij153), 0.57 ± 0.19 (SCCNij185), 0.16 ± 0.10 (SCCNij167) (p < 0.001). Tumor fEGFR correlated with (111)In-cetuximab-F(ab')2 tumor uptake (r = 0.6, p < 0.01) and tracer autoradiography (r = 0.7, p < 0.0001). Tumor uptake of (111)In-cetuximab-F(ab')2 was proportionally associated with cetuximab treatment response in three out of four xenograft models.

CONCLUSION

(111)In-cetuximab-F(ab')2 showed good tumor-to-background contrast on microSPECT imaging, allowing noninvasive assessment of EGFR expression in vivo, and possibly evaluation of treatment response to EGFR-inhibition.

Acquired resistance to cetuximab is associated with the overexpression of Ras family members and the loss of radiosensitization in head and neck cancer cells

PURPOSE

Cetuximab in combination with radiation therapy is used to treat patients with head and neck squamous cell carcinoma (HNSCC). In the present study, the mechanism of acquired resistance to cetuximab in HNSCC cells was investigated in vitro.

MATERIAL AND METHODS

The HNSCC cell lines UT5 and SAS and UT5 cells with acquired resistance to cetuximab (UT5R9) were used. The radiotoxicity potentials of cetuximab and inhibitors of PI3K, MAPK and farnesylation were tested using a clonogenic survival assay. Western blotting was used to evaluate protein expression. The levels of EGFR ligands were detected by ELISA.

RESULTS

Cetuximab inhibited proliferation and induced radiosensitization in UT5 cells but not in SAS cells. In comparison with UT5 cells, cetuximab-resistant SAS cells markedly overexpressed the K-Ras, H-Ras and N-Ras proteins, as detected by Western blotting. Resistance in UT5R9 cells was associated with the overexpression of the K-Ras, H-Ras and N-Ras proteins as well as an increase in the autocrine production of the EGFR ligands amphiregulin and transforming growth factor α (TGFα). UT5R9 cells were significantly more radioresistant than UT5 cells. Radioresistant UT5R9 cells were not radiosensitized by cetuximab, but knocking down H-RAS and N-RAS with siRNA and targeting Ras farnesylation using the farnesyltransferase inhibitor lonafarnib induced radiosensitization in these cells. Targeting PI3K and MEK revealed that the activation of the PI3K/Akt pathway but not the MAPK/ERK pathway is associated with radioresistance in UT5R9 cells.

CONCLUSION

Targeting Ras and PI3K activity improves the outcome of irradiation in cetuximab-resistant HNSCC cell lines in vitro.

Clinical perspectives of cancer stem cell research in radiation oncology

Radiotherapy has a proven potential to eradicate cancer stem cells which is reflected by its curative potential in many cancer types. Considerable progress has been made in identification and biological characterisation of cancer stem cells during the past years. Recent biological findings indicate significant inter- and intratumoural and functional heterogeneity of cancer stem cells and lead to more complex models which have potential implications for radiobiology and radiotherapy. Clinical evidence is emerging that biomarkers of cancer stem cells may be prognostic for the outcome of radiotherapy in some tumour entities. Perspectives of cancer stem cell based research for radiotherapy reviewed here include their radioresistance compared to the mass of non-cancer stem cells which form the bulk of all tumour cells, implications for image- and non-image based predictive bio-assays of the outcome of radiotherapy and a combination of novel systemic treatments with radiotherapy.

Interaction of EGFR with the tumour microenvironment: implications for radiation treatment

Treatment failure through radioresistance of tumours is associated with activation of the epidermal growth factor receptor (EGFR). Tumour cell proliferation, DNA-repair, hypoxia and metastases-formation are four mechanisms in which EGFR signalling has an important role. In clinical trials, a correlation has been demonstrated between high EGFR expression in tumours and poor outcome after radiotherapy. Inhibition of EGFR signalling pathways improves the effectiveness of radiotherapy of head and neck cancers by overcoming these main mechanisms of radioresistance. The fact that only a minority of the patients respond to EGFR inhibitors reflects the complexity of interactions between EGFR-dependent signalling pathways and the tumour microenvironment. Furthermore, many components of the microenvironment are potential targets for therapeutic interventions. Characterisation of the interaction of EGFR signalling and the tumour microenvironment is therefore necessary to improve the effectiveness of combined modality treatment with radiotherapy and targeted agents. Here, the current status of knowledge is reviewed and directions for future research are discussed.

Prediction of response to radiotherapy in the treatment of esophageal cancer using stem cell markers

BACKGROUND AND PURPOSE

In this study, we investigated whether cancer stem cell marker expressing cells can be identified that predict for the response of esophageal cancer (EC) to CRT.

MATERIALS AND METHODS

EC cell-lines OE-33 and OE-21 were used to assess in vitro, stem cell activity, proliferative capacity and radiation response. Xenograft tumors were generated using NOD/SCID mice to assess in vivo proliferative capacity and tumor hypoxia. Archival and fresh EC biopsy tissue was used to confirm our in vitro and in vivo results.

RESULTS

We showed that the CD44+/CD24- subpopulation of EC cells exerts a higher proliferation rate and sphere forming potential and is more radioresistant in vitro, when compared to unselected or CD44+/CD24+ cells. Moreover, CD44+/CD24- cells formed xenograft tumors faster and were often located in hypoxic tumor areas. In a study of archival pre-neoadjuvant CRT biopsy material from EC adenocarcinoma patients (N=27), this population could only be identified in 50% (9/18) of reduced-responders to neoadjuvant CRT, but never (0/9) in the complete responders (P=0.009).

CONCLUSION

These results warrant further investigation into the possible clinical benefit of CD44+/CD24- as a predictive marker in EC patients for the response to chemoradiation.

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.