Decreased repopulation as well as increased reoxygenation contribute to the improvement in local control after targeting of the EGFR by C225 during fractionated irradiation

Genomic biomarkers to guide precision radiotherapy in prostate cancer

Our ability to prognosticate the clinical course of patients with cancer has historically been limited to clinical, histopathological, and radiographic features. It has long been clear however, that these data alone do not adequately capture the heterogeneity and breadth of disease trajectories experienced by patients. The advent of efficient genomic sequencing has led to a revolution in cancer care as we try to understand and personalize treatment specific to patient clinico-genomic phenotypes. Within prostate cancer, emerging evidence suggests that tumor genomics (e.g., DNA, RNA, and epigenetics) can be utilized to inform clinical decision making. In addition to providing discriminatory information about prognosis, it is likely tumor genomics also hold a key in predicting response to oncologic therapies which could be used to further tailor treatment recommendations. Herein we review select literature surrounding the use of tumor genomics within the management of prostate cancer, specifically leaning toward analytically validated and clinically tested genomic biomarkers utilized in radiotherapy and/or adjunctive therapies given with radiotherapy.

Molecular Response to Combined Molecular- and External Radiotherapy in Head and Neck Squamous Cell Carcinoma (HNSCC)

Simple Summary

Our previous preclinical trial in a head and neck squamous cell carcinoma (HNSCC) xenograft model showed a high potential for the improvement of curative treatment outcome upon the combination treatment of a radiolabeled (Yttrium-90) anti-EGFR antibody (Cetuximab) and external radiotherapy. We aim to elucidate the molecular response of HNSCC tumors upon this combination. Here, we show that the combination treatment leads to an increasing number and complexity of DNA double strand breaks. The upregulation of p21^cip1/waf1 expression and cleaved caspase-3 suggest a blockage of cell cycle transition and an induction of programmed cell death. Collectively, a complex interplay between molecular mechanisms involved in cell death induction, cell cycle arrest, and DNA double strand break repair accounts for the beneficial potential using Yttrium-90-Cetuximab in combination with external radiotherapy.

Abstract

Combination treatment of molecular targeted and external radiotherapy is a promising strategy and was shown to improve local tumor control in a HNSCC xenograft model. To enhance the therapeutic value of this approach, this study investigated the underlying molecular response. Subcutaneous HNSCC FaDu_DD xenografts were treated with single or combination therapy (X-ray: 0, 2, 4 Gy; anti-EGFR antibody (Cetuximab) (un-)labeled with Yttrium-90 (⁹⁰Y)). Tumors were excised 24 h post respective treatment. Residual DNA double strand breaks (DSB), mRNA expression of DNA damage response related genes, immunoblotting, tumor histology, and immunohistological staining were analyzed. An increase in number and complexity of residual DNA DSB was observed in FaDu_DD tumors exposed to the combination treatment of external irradiation and ⁹⁰Y-Cetuximab relative to controls. The increase was observed in a low oxygenated area, suggesting the expansion of DNA DSB damages. Upregulation of genes encoding p21^cip1/waf1 (CDKN1A) and GADD45α (GADD45A) was determined in the combination treatment group, and immunoblotting as well as immunohistochemistry confirmed the upregulation of p21^cip1/waf1. The increase in residual γH2AX foci leads to the blockage of cell cycle transition and subsequently to cell death, which could be observed in the upregulation of p21^cip1/waf1 expression and an elevated number of cleaved caspase-3 positive cells. Overall, a complex interplay between DNA damage repair and programmed cell death accounts for the potential benefit of the combination therapy using ⁹⁰Y-Cetuximab and external radiotherapy.

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.

Combination of chemotherapy and radiotherapy: A thirty years evolution

Chemoradiotherapy is now considered the standard of care for many locally advanced diseases. Cytotoxic drugs have been largely evaluated in this setting, with cisplatin and 5FU the most often used drugs. A large amount of pre-clinical studies has demonstrated the synergy between both modalities. Concomitant administration seems the more beneficial in many diseases. Emergence of new approaches, combining targeted therapies and radiotherapy (RT) is now a reality. The main example is the association of cetuximab and RT in head and neck carcinomas, even if, 14 years after the initial publication, the best way to use it is still unknown. New compounds as inhibitors of DNA-repair or immune checkpoints are under investigation and showed early promising results.

Simultaneous targeting of EGFR, HER2, and HER4 by afatinib overcomes intrinsic and acquired cetuximab resistance in head and neck squamous cell carcinoma cell lines

The epidermal growth factor receptor (EGFR, HER1) is a therapeutic target in head and neck squamous cell carcinoma (HNSCC). After initial promising results with EGFR-targeted therapies such as cetuximab, therapeutic resistance has become a major clinical problem, and new treatment options are therefore necessary. Moreover, the relationship between HER receptors, anti-EGFR therapies, and the human papillomavirus (HPV) status in HNSCC is not fully understood. In contrast to first-generation EGFR inhibitors, afatinib irreversibly inhibits multiple HER receptors simultaneously. Therefore, treatment with afatinib might result in a more pronounced therapeutic benefit, even in patients experiencing cetuximab resistance. In this study, the cytotoxic effect of afatinib as single agent and in combination with cisplatin was investigated in cetuximab-sensitive, intrinsically cetuximab-resistant, and acquired cetuximab-resistant HNSCC cell lines with different HPV status under normoxia and hypoxia. Furthermore, the influence of cetuximab resistance, HPV, and hypoxia on the expression of HER receptors was investigated. Our results demonstrated that afatinib was able to establish cytotoxicity in cetuximab-sensitive, intrinsically cetuximab-resistant, and acquired cetuximab-resistant HNSCC cell lines, independent of the HPV status. However, cross-resistance between cetuximab and afatinib might be possible. Treatment with afatinib caused a G₀ /G₁ cell cycle arrest as well as induction of apoptotic cell death. Additive to antagonistic interactions between afatinib and cisplatin could be observed. Neither cetuximab resistance nor HPV status significantly influenced the expression of HER receptors in HNSCC cell lines. In contrast, the expression of EGFR, HER2, and HER3 was significantly altered under hypoxia. Oxygen deficiency is a common characteristic of HNSCC tumors, and these hypoxic tumor regions often contain cells that are more resistant to treatment. However, we observed that afatinib maintained its cytotoxic effect under hypoxia. In conclusion, our preclinical data support the hypothesis that afatinib might be a promising therapeutic strategy to treat patients with HNSCC experiencing intrinsic or acquired cetuximab resistance.

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.

Radiosensitization by gold nanoparticles: Will they ever make it to the clinic?

The utilization of gold nanoparticles (AuNPs) as radiosensitizers has shown great promise in pre-clinical research. In the current review, the physical, chemical, and biological pathways via which AuNPs enhance the effects of radiation are presented and discussed. In particular, the impact of AuNPs on the 5 Rs in radiobiology, namely repair, reoxygenation, redistribution, repopulation, and intrinsic radiosensitivity, which determine the extent of radiation enhancement effects are elucidated. Key findings from previous studies are outlined. In addition, crucial parameters including the physicochemical properties of AuNPs, route of administration, dosing schedule of AuNPs and irradiation, as well as type of radiation therapy, are highlighted; the optimal selection and combination of these parameters enable the achievement of a greater therapeutic window for AuNP sensitized radiotherapy. Future directions are put forward as a means to provide guidelines for successful translation of AuNPs to clinical applications as radiosensitizers.

Radiation oncology in the era of precision medicine

Technological advances and clinical research over the past few decades have given radiation oncologists the capability to personalize treatments for accurate delivery of radiation dose based on clinical parameters and anatomical information. Eradication of gross and microscopic tumours with preservation of health-related quality of life can be achieved in many patients. Two major strategies, acting synergistically, will enable further widening of the therapeutic window of radiation oncology in the era of precision medicine: technology-driven improvement of treatment conformity, including advanced image guidance and particle therapy, and novel biological concepts for personalized treatment, including biomarker-guided prescription, combined treatment modalities and adaptation of treatment during its course.

Molecular Targeting of Growth Factor Receptor Signaling in Radiation Oncology

Ionizing radiation has been shown to activate and interact with multiple growth factor receptor pathways that can influence tumor response to therapy. Among these receptor interactions, the epidermal growth factor receptor (EGFR) has been the most extensively studied with mature clinical applications during the last decade. The combination of radiation and EGFR-targeting agents using either monoclonal antibody (mAb) or small-molecule tyrosine kinase inhibitor (TKI) offers a promising approach to improve tumor control compared to radiation alone. Several underlying mechanisms have been identified that contribute to improved anti-tumor capacity after combined treatment. These include effects on cell cycle distribution, apoptosis, tumor cell repopulation, DNA damage/repair, and impact on tumor vasculature. However, as with virtually all cancer drugs, patients who initially respond to EGFR-targeted agents may eventually develop resistance and manifest cancer progression. Several potential mechanisms of resistance have been identified including mutations in EGFR and downstream signaling molecules, and activation of alternative member-bound tyrosine kinase receptors that bypass the inhibition of EGFR signaling. Several strategies to overcome the resistance are currently being explored in preclinical and clinical models, including agents that target the EGFR T790 M resistance mutation or target multiple EGFR family members, as well as agents that target other receptor tyrosine kinase and downstream signaling sites. In this chapter, we focus primarily on the interaction of radiation with anti-EGFR therapies to summarize this promising approach and highlight newly developing opportunities.

The hypoxic tumor microenvironment and drug resistance against EGFR inhibitors: preclinical study in cetuximab-sensitive head and neck squamous cell carcinoma cell lines

Background

Increased expression of the epidermal growth factor receptor (EGFR) is observed in more than 90% of all head and neck squamous cell carcinomas (HNSCC). Therefore, EGFR has emerged as a promising therapeutic target. Nevertheless, drug resistance remains a major challenge and an important potential mechanism of drug resistance involves the hypoxic tumor microenvironment. Therefore, we investigated the cytotoxic effect of the EGFR-targeting agents cetuximab and erlotinib under normoxia versus hypoxia.

Findings

Three cetuximab-sensitive HNSCC cell lines (SC263, LICR-HN2 and LICR-HN5) were treated with either cetuximab or erlotinib. Cells were incubated under normal or reduced oxygen conditions (<0.1% O₂) for 24 or 72 h immediately after drug addition. Cell survival was assessed with the sulforhodamine B assay. Cetuximab and erlotinib established a dose-dependent growth inhibition under both normal and prolonged reduced oxygen conditions in all three HNSCC cell lines. However, a significantly increased sensitivity to cetuximab was observed in SC263 cells exposed to hypoxia for 72 h (p = 0.05), with IC₅₀ values of 2.38 ± 0.59 nM, 0.64 ± 0.38 nM, and 0.10 ± 0.05 nM under normoxia, hypoxia for 24 h and hypoxia for 72 h, respectively. LICR-HN5 cells showed an increased sensitivity towards erlotinib when cells were incubated under hypoxia for 24 h (p = 0.05).

Conclusions

Our results suggest that both EGFR-inhibitors cetuximab and erlotinib maintain their growth inhibitory effect under hypoxia. These results suggest that resistance to anti-EGFR therapy in HNSCC is probably not the result of hypoxic regions within the tumor and other mechanisms are involved.

Targeting EGFR-PI3K-AKT-mTOR signaling enhances radiosensitivity in head and neck squamous cell carcinoma

INTRODUCTION

Head and neck squamous cell carcinoma (HNSCC) is frequently characterized by high resistance to radiotherapy, which critically depends on both altered signaling pathways within tumor cells and their dynamic interaction with the tumor microenvironment.

AREAS COVERED

This review covers EGFR-phosphoinositide 3-kinase (PI3K)-protein kinase B (AKT)-mechanistic target of rapamycin (mTOR) signaling in HNSCC. The role of each pathway node in radioresistance is discussed. Preclinical and clinical innovative aspects of targeting EGFR-PI3K-AKT and mTOR are demonstrated. Ongoing clinical trials and future perspectives are presented.

EXPERT OPINION

Different cellular signaling pathways seem to mediate radioresistance in advanced HNSCC and various molecular targeted therapies are currently being investigated to sensitize tumor cells to radiotherapy. Recently, new insights in the mutational landscape of HNSCC unraveled critical alterations in putative oncogenes and tumor suppressor genes and have emphasized the importance of PI3K and the corresponding upstream and downstream signaling pathways in pathogenesis and treatment response. The frequent activation of the EGFR-PI3K-AKT-mTOR pathway in HNSCC and its implication in the context of radiosensitivity make this pathway one of the most promising targets in the therapy of HNSCC patients. Clinical studies targeting EGFR and mTOR in combination with radiotherapy are under investigation.

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.

Effects of the administration of epidermal growth factor receptor specific inhibitor cetuximab, alone and in combination with cisplatin, on proliferation and apoptosis of Hep-2 laryngeal cancer cells

BACKGROUND

Epidermal growth factor receptor (EGFR) overexpression and prognostic value in head and neck squamous cell cancer is the basis for targeting by anti-EGFR antibodies, which increase the efficacy of radiotherapy. In order to evaluate the best therapeutic schedule, the effects of cetuximab (C225) on Hep-2 cell proliferation, alone and in combination with cisplatin, were studied.

METHODS

Hep-2 cells were treated with cetuximab alone or in combination with cisplatin. After determining cell viability with trypan blue, morphological features of apoptotic degeneration were analysed by fluorescence microscopy with Hoechst 33258 stain.

RESULTS

Cetuximab alone mildly inhibited Hep-2 proliferation and showed no pro-apoptotic effects. When administered concomitantly with cisplatin, cetuximab synergistically increased inhibition of proliferation and apoptosis.

CONCLUSION

The antiproliferative activity of cetuximab is consistent with its hypothesised role in inhibiting repopulation. However, the increase in the effects of pro-apoptotic agents induced by cetuximab may be even more relevant to its clinical effectiveness than the inhibition of repopulation.

Combining targeted agents and hypo- and hyper-fractionated radiotherapy in NSCLC

Radical radiotherapy remains the cornerstone of treatment for patients with unresectable locally advanced non small cell lung cancer (NSCLC) either as single modality treatment for poor performance status patients or with sequential or concomitant chemotherapy for good performance status patients. Advances in understanding of tumour molecular biology, targeted drug development and experiences of novel agents in the advanced disease setting have brought targeted agents into the NSCLC clinic. In parallel experience using modified accelerated fractionation schedules in locally advanced disease have demonstrated improved outcomes compared to conventional fractionation in the single modality and sequential chemo-radiotherapy settings. Early studies of targeted agents combined with (chemo-) radiotherapy in locally advanced disease in different clinical settings are discussed below and important areas for future studies are high-lighted.

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.

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.

The hallmarks of cancer and the radiation oncologist: updating the 5Rs of radiobiology

A comprehensive, mechanistic understanding of radiobiological phenomena that can be integrated within the broader context of cancer biology offers the prospect of transforming clinical practice in radiation oncology. In this review, we revisit the six established biological hallmarks of cancer and examine how they have provided insights into novel therapeutic strategies. In addition, we discuss the potential of two emerging hallmarks to continue to expand our understanding beyond the narrow confines of the traditional 5Rs of radiobiology.

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.

Basic mechanisms of therapeutic resistance to radiation and chemotherapy in lung cancer

In recent years, there have been multiple breakthroughs in our understanding of lung cancer biology. Despite significant advances in molecular targeted therapies, DNA-damaging cytotoxic therapies will remain the mainstay of lung cancer management for the near future. Similar to the concept of personalized targeted therapies, there is mounting evidence that perturbations in DNA repair pathways are common in lung cancers, altering the resistance of the affected tumors to many chemotherapeutics as well as radiation. Defects in DNA repair may be due to a multitude of mechanisms including gene mutations, epigenetic events, and alterations in signal transduction pathways such as epidermal growth factor receptor and phosphoinositide 3-kinase/AKT. Functional biomarkers that assess the subcellular localization of central repair proteins in response to DNA damage may prove useful for individualization of cytotoxic therapies including poly(adenosine diphosphate-ribose) polymerase inhibitors. A better mechanistic understanding of cellular sensitivity and resistance to DNA damaging agents should facilitate the development of novel, individualized treatment approaches. Absolute resistance to radiation therapy, however, does not exist. To some extent, radiation therapy will always have to remain unselective and indiscriminant to eradicate persistent, drug-resistant tumor stem cell pools.

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.

Emerging developments of chemoradiotherapy in stage III NSCLC

Over the past decade, concomitant chemotherapy and radiotherapy has become the established treatment for patients with stage III non-small-cell lung cancer (NSCLC). Unfortunately, many patients with NSCLC are too old or have multiple comorbidities to withstand such aggressive treatments. Attempts to improve outcomes have included studies of radiotherapy dose escalation and new chemotherapy combinations, as well as adding biological agents and cancer vaccines to existing regimens. Technical radiotherapy modifications, including intensity-modulated radiotherapy and particle beam therapy, have also been investigated. Given the number of potential advances to current models of treatment development, phase III trials of any single new treatment can take years to complete, which is inadequate. To advance research within shorter timescales to improve patient outcomes, we need methods of improving clinical trial accrual, which might require changes in models of research governance, cooperative group activity, trial design and patient consent.

The clinical development of molecularly targeted agents in combination with radiation therapy: a pharmaceutical perspective

This paper explores historical and current roles of pharmaceutical industry sponsorship of clinical trials testing radiation therapy combinations with molecularly targeted agents and attempts to identify potential solutions to expediting further combination studies. An analysis of clinical trials involving a combination of radiation therapy and novel cancer therapies was performed. Ongoing and completed trials were identified by searching the clinicaltrials.gov Web site, in the first instance, with published trials of drugs of interest identified through American Society of Clinical Oncology, European CanCer Organisation/European Society for Medical Oncology, American Society for Radiation Oncology/European Society for Therapeutic Radiology and Oncology, and PubMed databases and then cross-correlated with clinicaltrials.gov protocols. We examined combination trials involving radiation therapy with novel agents and determined their distribution by tumor type, predominant molecular mechanisms examined in combination to date, timing of initiation of trials relative to a novel agent's primary development, and source of sponsorship of such trials. A total of 564 studies of targeted agents in combination with radiation therapy were identified with or without concomitant chemotherapy. Most studies were in phase I/II development, with only 36 trials in phase III. The tumor site most frequently studied was head and neck (26%), followed by non-small cell lung cancer. Pharmaceutical companies were the sponsors of 33% of studies overall and provided support for only 16% of phase III studies. In terms of pharmaceutical sponsorship, Genentech was the most active sponsor of radiation therapy combinations (22%), followed by AstraZeneca (14%). Most radiation therapy combination trials do not appear to be initiated until after drug approval. In phase III studies, the most common (58%) primary endpoint was overall survival. Collectively, this analysis suggests that such trials are not given priority by pharmaceutical companies. The potential reasons for this and some challenges and possible solutions are discussed.

Expression of EGFR under tumor hypoxia: identification of a subpopulation of tumor cells responsible for aggressiveness and treatment resistance

PURPOSE

Overexpression of epidermal growth factor receptor (EGFR) and tumor hypoxia have been shown to correlate with worse outcome in several types of cancer including head-and-neck squamous cell carcinoma. Little is known about the combination and possible interactions between the two phenomena.

METHODS AND MATERIALS

In this study, 45 cases of histologically confirmed squamous cell carcinomas of the head and neck were analyzed. All patients received intravenous infusions of the exogenous hypoxia marker pimonidazole prior to biopsy. Presence of EGFR, pimonidazole binding, and colocalization between EGFR and tumor hypoxia were examined using immunohistochemistry.

RESULTS

Of all biopsies examined, respectively, 91% and 60% demonstrated EGFR- and pimonidazole-positive areas. A weak but significant association was found between the hypoxic fractions of pimonidazole (HFpimo) and EGFR fractions (F-EGFR) and between F-EGFR and relative vascular area. Various degrees of colocalization between hypoxia and EGFR were found, increasing with distance from the vasculature. A high fraction of EGFR was correlated with better disease-free and metastasis-free survival, whereas a high degree of colocalization correlated with poor outcome.

CONCLUSIONS

Colocalization of hypoxia and EGFR was demonstrated in head-and-neck squamous cell carcinomas, predominantly at longer distances from vessels. A large amount of colocalization was associated with poor outcome, which points to a survival advantage of hypoxic cells that are also able to express EGFR. This subpopulation of tumor cells might be indicative of tumor aggressiveness and be partly responsible for treatment resistance.

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

PURPOSE

To compare functional effects of combined irradiation and EGFR inhibition in different HNSCC tumour models in vivo with the results of molecular evaluations, aiming to set a basis for the development of potential biomarkers for local tumour control.

MATERIAL AND METHODS

In five HNSCC tumour models, all wild-type for EGFR and KRAS, the effect of radiotherapy alone (30 fractions/6 weeks) and with simultaneous cetuximab or erlotinib treatment on local tumour control were evaluated and compared with molecular data on western blot, immunohistochemistry and fluorescence-in situ-hybridisation (FISH).

RESULTS

Erlotinib and cetuximab alone significantly prolonged tumour growth time in 4/5 tumour models. Combined irradiation and cetuximab treatment significantly improved local tumour control in 3/5 tumour models, whereas erlotinib did not alter local tumour control in any of the tumour models. The amount of the cetuximab-effect on local tumour control significantly correlated with the EGFR/CEP-7 ratios obtained by FISH.

CONCLUSION

Both drugs prolonged growth time in most tumour models, but only application of cetuximab during irradiation significantly improved local tumour control in 3/5 tumour models. The significant correlation of this curative effect with the genetic EGFR expression measured by FISH will be further validated in preclinical and clinical studies.

Effect of cetuximab and fractionated irradiation on tumour micro-environment

BACKGROUND AND PURPOSE

Previous experiments have shown that application of the anti-EGFR monoclonal antibody C225 (cetuximab) improves local tumour control after irradiation in FaDu human squamous cell carcinoma (hSCC) due to the combined effect of decreased repopulation and improved reoxygenation. The present study investigates early changes of the pimonidazole hypoxic fraction of FaDu tumours and the expression and phosphorylation of the EGFR and its downstream signal transduction molecules after treatment with C225 alone or in combination with irradiation.

MATERIAL AND METHODS

FaDu tumour xenografts were irradiated with up to 3×3Gy with or without additional C225 treatment and excised at different time points. Tumour hypoxia was evaluated using pimonidazole. EGFR expression and phosphorylation and intratumoural distribution of C225 were assessed by immunofluorescence analysis. Western blots were performed to evaluate expression and phosphorylation of EGFR, ErbB2, AKT and MAPK (ERK1/2).

RESULTS

Hypoxia did not change during the 4days of treatment in the tumours treated with C225 alone or combined with irradiation. C225 treatment led to downregulation of the total EGFR in FaDu tumours, accompanied by a change of the spatial distribution of the receptor favouring the membranous expression. An induction of phosphorylation of the EGFR (tyr992, tyr1173) was observed with C225 alone or combined with irradiation. AKT phosphorylation was decreased, whereas MAPK phosphorylation remained unchanged. C225 membrane staining was homogeneously distributed over the whole tumour with no differences between hypoxic and non-hypoxic tumour cells.

CONCLUSION

Pimonidazole-hypoxia of FaDu tumours during the initial part of fractionated irradiation is not influenced by C225, indicating that external hypoxia markers may not be promising as biomarkers for tumour response to combined treatment. The downregulation of the total EGFR, but at the same time higher membrane staining, as well as the changes in downstream signal transduction molecules, warrants further investigation in other tumour models.

Epithelial-to-mesenchymal transition and c-myc expression are the determinants of cetuximab-induced enhancement of squamous cell carcinoma radioresponse

PURPOSE

Radiation therapy cures malignant tumors of the head and neck region more effectively when it is combined with application of the anti-EGFR monoclonal antibody cetuximab. Despite the successes achieved, we still do not know how to select patients who will respond to this combination of anti-EGFR monoclonal antibody and radiation. This study was conducted to elucidate possible mechanisms which cause the combined treatment with cetuximab and irradiation to fail in some cases of squamous cell carcinomas.

METHODS AND MATERIALS

Mice bearing FaDu and A431 squamous cell carcinoma xenograft tumors were treated with cetuximab (total dose 3 mg, intraperitoneally), irradiation (10 Gy) or their combination at the same doses. Treatment was applied when tumors reached 8mm in size. To collect samples for further protein analysis (two-dimensional differential gel electrophoresis (2-D DIGE), mass spectrometry MALDI-TOF/TOF, Western blot analysis, and ELISA), mice from each group were sacrificed on the 8th day after the first injection of cetuximab. Other mice were subjected to tumor growth delay assay.

RESULTS

In FaDu xenografts, treatment with cetuximab alone was nearly as effective as cetuximab combined with ionizing radiation, whereas A431 tumors responded to the combined treatment with significantly enhanced delay in tumor growth. Tumors extracted from the untreated FaDu and A431 xenografts were analysed for protein expression, and 34 proteins that were differently expressed in the two tumor types were identified. The majority of these proteins are closely related to intratumoral angiogenesis, cell adhesion, motility, differentiation, epithelial-to-mesenchymal transition (EMT), c-myc signaling and DNA repair.

CONCLUSIONS

The failure of cetuximab to enhance radiation response in FaDu xenografts was associated with the initiation of the program of EMT and with c-myc up-regulation in the carcinoma cells. For this reason, c-myc and EMT-related proteins (E-cadherin, vimentin) may be considered as potential biomarkers to predict squamous cell carcinoma response after treatment with cetuximab in combination with radiation.

Cancer stem cells at the crossroads of current cancer therapy failures--radiation oncology perspective

Despite continuous improvements in cancer management, locoregional recurrence or metastatic spread still occurs in a high proportion of patients after radiotherapy or combined treatments. One underlying reason might be a low efficacy of current treatments on eradication of cancer stem cells (CSCs). It has been recognised for a long time, that only the small subpopulation of CSCs can cause recurrences and that all CSCs need to be killed for permanent tumour cure. However, only recently novel technologies have allowed to enrich CSCs and to investigate their biology. An emerging experimental and clinical database provides first hints that cell populations accumulated by putative stem cell markers or tumours that highly express such markers may be more radioresistant than their marker-negative counterparts. Other data support a higher tolerance of CSCs to hypoxia and preferential location in specific microenvironmental niches. However, conflicting data, methodological problems of the assays and a generally small database on only few tumour types necessitate further large and well-designed prospective experimental and clinical investigations that specifically address this question to corroborate this hypothesis. If such investigations confirm biological differences between CSCs and non-CSCs, this would imply that novel treatment strategies need to be tested specifically for their effect on CSCs. Another implication is that also biomarkers for prediction of local tumour control after radiotherapy or combined treatments need to reflect the behaviour of CSCs and not of the bulk of all cancer cells. This review discusses the importance of CSCs for treatment failure and challenges occurring from the CSC concept for cancer diagnosis, treatment and prediction of outcome. It is concluded that CSC-based endpoints and biomarkers are eventually expected to considerably improve tumour cure rates in the clinics through individualised tailoring of treatment.

Modulating the tumor microenvironment to increase radiation responsiveness

Radiosensitivity can be influenced both by factors intrinsic and extrinsic to the cancer cell. One of the factors in the tumor microenvironment (TME) extrinsic to the cancer cell that can affect radiosensitivity is oxygenation. Severely hypoxic cells require a 2-3 fold higher dose of radiation to achieve the same level of cell killing as do well-oxygenated cells. Other elements in the microenvironment that may influence tumor radiosensitivity are the response of stromal cells to radiation and the expression of factors such as vascular endothelial growth factor (VEGF) and hypoxia inducible factor-1 (HIF-1). There are currently several classes of agents that may increase tumor radiosensitivity by modulating the TME. Pre-clinical evidence indicates that inhibition of VEGF may increase local control after radiation. Several mechanisms have been postulated to explain this including radiosensitization of tumor endothelial cells, prevention of the establishment of new vasculature post-radiation, and increased oxygenation secondary to vascular normalization. Agents targeting HIF-1 also increase local control after radiation in pre-clinical models. This may occur via indirect inhibition of VEGF, which is a downstream target of HIF-1, or by VEGF-independent means. When combined with radiation, the EGFR inhibitor cetuximab improves local control and survival in patients with head and neck cancer. Pre-clinical data indicate that EGFR inhibitors can increase the intrinsic radiosensitivity of cancer cells. They can also improve tumor blood flow and oxygenation, which may increase extrinsic radiosensitivity. One of the pathways downstream of EGFR that may contribute to this effect is the PI3K/Akt pathway. Agents that directly inhibit this pathway improve blood flow and increase tumor oxygenation in pre-clinical models. The challenge remains to obtain clinical data from patients showing that modulation of the TME is an important mechanism by which biological agents can radiosensitize tumors and then to utilize this information to optimize therapy.

Cancer stem cells and tumor response to therapy: current problems and future prospects

The presence of a subpopulation of cells within tumors, so-called cancer stemlike cells, that is uniquely capable of reestablishing the tumor during and after definitive radio(chemo)therapy and must be effectively controlled for a long-term cure is being increasingly appreciated. The existence and physiology of a rare cancer cell population, termed cancer cell clonogens, with similar properties has been extensively described in the radiobiology literature for several decades based on studies using tumor cells transplanted into syngeneic or immunodeficient animals. The earlier studies have identified important features that govern tumor establishment; tumor growth and homeostasis; and therapeutic resistance, including clonogen number, tumor type, vascular status, hypoxia, repopulation dynamics during treatment, and immunologic and microenvironmental status. These discoveries led to therapeutic strategies, some of which have shown efficacy and have become current standard clinical practice (eg, concomitant boost and concurrent radio chemotherapy). Although the identity of cancer stemlike cells and cancer cell clonogens has not been definitively shown, recent characterization of molecular signaling pathways controlling stem cells and their microenvironmental niche combined with the earlier findings on clonogen physiology may now lead to the development of molecularly targeted strategies to overcome therapeutic resistance of this rare subpopulation of tumor cells. Along these lines, we describe 3 unique treatment settings (ie, before, during, and after definitive radio[chemo]therapy) in which molecularly targeted approaches might specifically counteract cancer stemlike cell resistance mechanisms and enhance the curative efficiency of radio(chemo)therapy.

Epidermal growth factor receptor inhibition modulates the microenvironment by vascular normalization to improve chemotherapy and radiotherapy efficacy

Background

Epidermal growth factor receptor (EGFR) inhibitors have shown only modest clinical activity when used as single agents to treat cancers. They decrease tumor cell expression of hypoxia-inducible factor 1-α (HIF-1α) and vascular endothelial growth factor (VEGF). Hypothesizing that this might normalize tumor vasculature, we examined the effects of the EGFR inhibitor erlotinib on tumor vascular function, tumor microenvironment (TME) and chemotherapy and radiotherapy sensitivity.

Methodology/Principal Findings

Erlotinib treatment of human tumor cells in vitro and mice bearing xenografts in vivo led to decreased HIF-1α and VEGF expression. Treatment altered xenograft vessel morphology assessed by confocal microscopy (following tomato lectin injection) and decreased vessel permeability (measured by Evan's blue extravasation), suggesting vascular normalization. Erlotinib increased tumor blood flow measured by Power Doppler ultrasound and decreased hypoxia measured by EF5 immunohistochemistry and tumor O₂ saturation measured by optical spectroscopy. Predicting that these changes would improve drug delivery and increase response to chemotherapy and radiation, we performed tumor regrowth studies in nude mice with xenografts treated with erlotinib and either radiotherapy or the chemotherapeutic agent cisplatin. Erlotinib therapy followed by cisplatin led to synergistic inhibition of tumor growth compared with either treatment by itself (p<0.001). Treatment with erlotinib before cisplatin led to greater tumor growth inhibition than did treatment with cisplatin before erlotinib (p = 0.006). Erlotinib followed by radiation inhibited tumor regrowth to a greater degree than did radiation alone, although the interaction between erlotinib and radiation was not synergistic.

Conclusions/Significance

EGFR inhibitors have shown clinical benefit when used in combination with conventional cytotoxic therapy. Our studies show that targeting tumor cells with EGFR inhibitors may modulate the TME via vascular normalization to increase response to chemotherapy and radiotherapy. These studies suggest ways to assess the response of tumors to EGFR inhibition using non-invasive imaging of the TME.

Receptor signaling as a regulatory mechanism of DNA repair

Radiotherapy plays a crucial role in the treatment of many malignancies; however, locoregional disease progression remains a critical problem. This has stimulated laboratory research into understanding the basis for tumor cell resistance to radiation and the development of strategies for overcoming such resistance. We know that some cell signaling pathways that respond to normal growth factors are abnormally activated in human cancer and that these pathways also invoke cell survival mechanisms that lead to resistance to radiation. For example, abnormal activation of the epidermal growth factor receptor (EGFR) promotes unregulated growth and is believed to contribute to clinical radiation resistance. Molecular blockade of EGFR signaling is an attractive strategy for enhancing the cytotoxic effects of radiotherapy and, as shown in numerous reports, the radiosensitizing effects of EGFR antagonists correlate with a suppression of the ability of the cells to repair radiation-induced DNA double strand breaks (DSBs). The molecular connection between the EGFR and its governance of DNA repair capacity appears to be mediated by one or more signaling pathways downstream of this receptor. The purpose of this review is to highlight what is currently known regarding EGFR signaling and the processes responsible for repairing radiation-induced DNA lesions that would explain the radiosensitizing effects of EGFR antagonists.

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.

Epidermal growth factor receptor inhibitors for radiotherapy: biological rationale and preclinical results

Blocking the epidermal growth factor receptor (EGFR) represents a role model for a successful biological targeting approach to improving outcomes after radiotherapy. This review summarizes data from several local tumour control experiments in which EGFR inhibitors were combined with radiation in FaDu human squamous cell carcinomas xenografted into nude mice. BIBX1382BS is an oral bioavailable inhibitor of the intracellular tyrosine kinase domain of EGFR. It was administered in different experimental settings: concurrent with fractionated radiotherapy, following completion of irradiation, and in the period between surgery and adjuvant irradiation. Despite beneficial effects on tumour growth, in none of these experimental settings did BIBX1382BS improve local tumour control. In contrast, cetuximab (Erbitux), an IgG1 monoclonal antibody against the extracellular ligand-binding domain of EGFR, improved local tumour control when given concurrently with radiation. Results from a series of local tumour control experiments designed to elucidate the underlying mechanisms of cetuximab suggest that multiple radiobiological mechanisms might contribute to the observed effects: decreased number of clonogenic tumour cells, increased cellular radiation sensitivity, decreased repopulation and improved reoxygenation of clonogenic tumour cells during the combined treatment. In summary, the data suggest that different classes of EGFR inhibitors may have a different potential to improve local tumour control after fractionated irradiation.

Clinical biomarkers of kinase activity: examples from EGFR inhibition trials

INTRODUCTION

Tumor response and duration of patient survival after treatment with inhibitors of the epidermal growth factor receptor (EGFR) varies considerably between different kinds of EGFR inhibitors, different combination schedules, but also between individual patients.

DISCUSSION

Development and introduction of biomarkers into clinical practice is necessary to predict treatment response and thereby to individualize cancer therapy. Due to specific interactions of EGFR inhibitors with biological effects of irradiation, biomarkers are expected to differ for radiation oncology compared to application of the drugs alone or within chemotherapy treatment schedules and therefore need to be established and tested separately.

OBJECTIVES

The review summarizes the current status of potential predictors for the effect of EGFR inhibitors used as single agents or in combination with chemotherapy.

CONCLUSION

Based on this knowledge and on preclinical radiotherapy data, candidate biomarkers and further research strategies for radiation oncology are discussed.

Infusional 5-fluorouracil and ZD1839 (Gefitinib-Iressa) in combination with preoperative radiotherapy in patients with locally advanced rectal cancer: a phase I and II Trial (1839IL/0092)

PURPOSE

To report the final data of a Phase I and II study (1839IL/0092) on the combination of an anti-epidermal growth factor receptor drug (gefitinib), infusional 5-fluorouracil, and preoperative radiotherapy in locally advanced, resectable rectal cancer.

METHODS AND MATERIALS

Patients received 45 Gy in the posterior pelvis plus a boost of 5.4 Gy on the tumor and corresponding mesorectum. Infusional 5-fluorouracil (5-FU) and gefitinib (250 and 500 mg/day) were delivered during all radiotherapy course. An IORT boost of 10 Gy was allowed. The main endpoints of the study were to establish dose-limiting toxicity (DLT) and to evaluate the rate of pathologic response according to the tumor regression grade (TRG) Mandard score.

RESULTS

A total of 41 patients were enrolled. The DLT was not reached in the 6 patients enrolled in the dose-escalation part of the study. Of the 33 patients in the Phase II, TRG 1 was recorded in 10 patients (30.3%) and TRG 2 in 7 patients (21.2 %); overall 17 of 33 patients (51.5%) had a favorable endpoint. Overall, Grade 3+ toxicity was recorded in 16 patients (41%); these included Grade 3+ gastrointestinal toxicity in 8 patients (20.5%), Grade 3+ skin toxicity in 6 (15.3%), and Grade 3+ genitourinary toxicity in 4 (10.2%). A dose reduction of gefitinib was necessary in 24 patients (61.5%).

CONCLUSIONS

Gefitinib can be associated with 5-FU-based preoperative chemoradiation at the dose of 500 mg without any life-threatening toxicity and with a high pCR (30.3%). The relevant rate of Grade 3 gastrointestinal toxicity suggests that 250 mg would be more tolerable dose in a neaoadjuvant approach with radiotherapy and infusional 5-FU.