Molecular targeting in radiotherapy of lung cancer

Dielectrophoretic analysis of treated cancer cells for rapid assessment of treatment efficacy

Whilst personalized medicine (where interventions are precisely tailored to a patient's genotype and phenotype, as well as the nature and state of the disease) is regarded as an optimal form of treatment, the time and cost associated with it means it remains inaccessible to the greater public. A simpler alternative, stratified medicine, identifies groups of patients who are likely to respond to a given treatment. This allows appropriate treatments to be selected at the start of therapy, avoiding the common "trial and error" approach of replacing a therapy only once it is demonstrated to be ineffective in the patient. For stratification to be effective, tests are required that rapidly predict treatment effectiveness. Most tests use genetic analysis to identify drug targets, but these can be expensive and may not detect changes in the phenotype that affect drug sensitivity. An alternative method is to assess the whole-cell phenotype by evaluating drug response using cells from a biopsy. We assessed dielectrophoresis to assess drug efficacy on short timescales and at low cost. To explore the principle of assessing drug efficacy we examined two cell lines (one expressing EGFR, one not) with the drug Iressa. We then further explored the sensitive cells using combinations of chemotherapeutic and radiotherapeutic therapies. Our results compare with known effects of these cell/treatment combination, and offer the additional benefit over methods such as TUNEL of detecting drug effects such as cell cycle arrest, which do not cause cell death.

Long Noncoding RNA GAS5 Inhibits Tumorigenesis and Enhances Radiosensitivity by Suppressing miR-135b Expression in Non-Small Cell Lung Cancer

Growth arrest-specific transcript 5 (GAS5) has been demonstrated to correlate with clinicopathological characteristics and serve as a tumor suppressor in non-small cell lung cancer (NSCLC). However, the underlying mechanism of the competing endogenous RNA (ceRNA) regulatory network involving GAS5 in NSCLC remains to be elucidated. In this study, qRT-PCR results showed that GAS5 was downregulated and miR-135b was upregulated in NSCLC tissues and cells. The expressions of GAS5 and miR-135b changed inversely in response to irradiation. Gain-of-function experiments revealed that GAS5 overexpression and miR-135b downregulation significantly suppressed tumorigenesis by repressing cell proliferation and invasion, and enhanced the radiosensitivity of NSCLC cells by reducing colony formation rates. Luciferase reporter assay confirmed that GAS5 could directly target miR-135b and negatively regulate its expression. Moreover, rescue experiments demonstrated that miR-135b upregulation markedly abolished GAS5 overexpression-induced tumorigenesis inhibition and radiosensitivity improvement. Furthermore, xenograft model analysis validated that GAS5 overexpression suppressed tumor growth and improved radiosensitivity of NSCLC cells in vivo. Taken together, GAS5 inhibits tumorigenesis and enhances radiosensitivity by suppressing miR-135b expression in NSCLC cells, deepening our understanding of the mechanism of miRNA-lncRNA interaction and providing a novel therapeutic strategy for NSCLC.

Rhamnetin and cirsiliol induce radiosensitization and inhibition of epithelial-mesenchymal transition (EMT) by miR-34a-mediated suppression of Notch-1 expression in non-small cell lung cancer cell lines

Radioresistance is a major cause of decreasing the efficiency of radiotherapy for non-small cell lung cancer (NSCLC). To understand the radioresistance mechanisms in NSCLC, we focused on the radiation-induced Notch-1 signaling pathway involved in critical cell fate decisions by modulating cell proliferation. In this study, we investigated the use of Notch-1-regulating flavonoid compounds as novel therapeutic drugs to regulate radiosensitivity in NSCLC cells, NCI-H1299 and NCI-H460, with different levels of radioresistance. Rhamnetin and cirsiliol were selected as candidate Notch-1-regulating radiosensitizers based on the results of assay screening for activity and pharmacological properties. Treatment with rhamnetin or cirsiliol reduced the proliferation of NSCLC cells through the suppression of radiation-induced Notch-1 expression. Indeed, rhamnetin and cirsiliol increased the expression of tumor-suppressive microRNA, miR-34a, in a p53-dependent manner, leading to inhibition of Notch-1 expression. Consequently, reduced Notch-1 expression promoted apoptosis through significant down-regulation of the nuclear factor-κB pathway, resulting in a radiosensitizing effect on NSCLC cells. Irradiation-induced epithelial-mesenchymal transition was also notably attenuated in the presence of rhamnetin and cirsiliol. Moreover, an in vivo xenograft mouse model confirmed the radiosensitizing and epithelial-mesenchymal transition inhibition effects of rhamnetin and cirsiliol we observed in vitro. In these mice, tumor volume was significantly reduced by combinational treatment with irradiation and rhamnetin or cirsiliol compared with irradiation alone. Taken together, our findings provided evidence that rhamnetin and cirsiliol can act as promising radiosensitizers that enhance the radiotherapeutic efficacy by inhibiting radiation-induced Notch-1 signaling associated with radioresistance possibly via miR-34a-mediated pathways.

Molecularly targeted therapies in locally advanced non-small-cell lung cancer

Approximately a third of the patients with non-small cell lung cancer (NSCLC) present with locally advanced disease not amenable to curative resection. Concurrent chemoradiation is currently the treatment of choice for these patients. Outcomes in patients with locally advanced NSCLC treated with concurrent chemoradiation are modest at best. No significant progress has been made over the past decade in this subset of patients with NSCLC. Several trials have examined the role of molecular targeted therapies in this setting. We review the results of these trials and present the outline of a proposed prospective clinical trial to evaluate targeted drugs in molecularly selected group of patients with locally advanced NSCLC.

Phosphorylation of ribosomal protein S3 and antiapoptotic TRAF2 protein mediates radioresistance in non-small cell lung cancer cells

Radioresistance is considered as a main factor restricting efficacy of radiotherapy. However, the exact molecular mechanism of radioresistance has not been explained yet. In this study, to elucidate radioresistance mechanism in lung cancer, we compared radiation responses in two types of non-small cell lung cancer (NSCLC) cells with different radiosensitivity and identified key molecules conferring radioresistance. In radioresistant NSCLC cells, ionizing radiation (IR) led to casein kinase 2α (CK2α)- and PKC-mediated phosphorylation of rpS3 and TRAF2, respectively, which induced dissociation of rpS3-TRAF2 complex and NF-κB activation, resulting in significant up-regulation of prosurvival genes (cIAP1, cIAP2, and survivin). Also, dissociated phospho-rpS3 translocated into nucleus and bound with NF-κB complex (p65 and p50), contributing to p65 DNA binding property and specificity. However, in radiosensitive NSCLC cells, IR-mediated rpS3 phosphorylation was not detected due to the absence of CK2α overexpression. Consequently, IR-induced rpS3-TRAF2 complex dissociation, NF-κB activation, and prosurvival gene expression were not presented. Taken together, our findings revealed a novel radioresistance mechanism through functional orchestration of rpS3, TRAF2, and NF-κB in NSCLC cells. Moreover, we provided the first evidence for the function of rpS3 as a new TRAF2-binding protein and demonstrated that phosphorylation of both rpS3 and TRAF2 is a key control point of radioresistance in NSCLC cells. These results suggest that regulation of rpS3 and TRAF2 in combination with radiotherapy could have high pharmacological therapeutic potency for radioresistance of NSCLC.

Potent anti-tumor activity of telomerase-dependent and HSV-TK armed oncolytic adenovirus for non-small cell lung cancer in vitro and in vivo

BACKGROUND

Non-small cell lung cancer (NSCLC) is the leading cause of cancer related mortality, any improvements in therapeutic strategies are urgently required. In this study we generated a novel 'suicide gene' armed oncolytic adenoviral vector and investigated its antitumor effect both in vitro and in vivo.

METHODS

Since the up-regulated expression of human telomerase reverse transcriptase (hTERT) is a hallmark of alltypes of NSCLC, we chose hTERT promoter to transcriptionally control E1A gene expression to obtain adenoviral replication in NSCLC. In order to further enhance anti-tumor effect of this oncolytic adenoviral vector, we inserted a 'suicide gene' i.e. Herpes Simplex Virus Thymidine Kinase (HSV-TK) into oncolytic adenoviral vector to engineer a novel armed oncolytic adenoviral vector 'Ad.hTERT-E1A-TK'.

RESULTS

Ad.hTERT-E1A-TK efficiently killed different types of tumor cells including two types of NSCLC cells in vitro, causing no damage to normal primary fibroblasts. Furthermore, Ad.hTERT-E1A-TK infection combined with administration of prodrug gancyclovir (GCV) resulted in more potent cytotoxicity on NSCLC cells, and synergistically suppressed human NSCLC tumor growth in nude mice.

CONCLUSION

The results from this study showed that Ad.hTERT-E1A-TK/GCV could be a potent but safe anti-tumor strategy for NSCLC biotherapy.

[18F]galacto-RGD positron emission tomography for imaging of alphavbeta3 expression on the neovasculature in patients with squamous cell carcinoma of the head and neck

PURPOSE

[(18)F]Galacto-RGD has been developed for positron emission tomography (PET)-imaging of alphavbeta3 expression, a receptor involved in angiogenesis and metastasis. Our aim was to study the feasibility of PET imaging with [(18)F]Galacto-RGD in patients with squamous cell carcinoma of the head and neck (SCCHN).

EXPERIMENTAL DESIGN

Eleven patients with primary diagnosis of SCCHN were examined. After injection of 140 to 200 MBq [(18)F]Galacto-RGD, static emission scans 60 min post injection from the head to the abdomen (n = 11) and dynamic scans >60 min covering the tumor region (n = 6) for kinetic modeling were acquired. Standardized uptake values (SUV) were measured in tumors, muscle and oral mucosa. Immunohistochemistry was done using an alphavbeta3-specific antibody (n = 7). Image fusion with magnetic resonance imaging and/or computed tomography (CT) scans (n = 8) and calculation of tumor subvolumes based on SUVs was done using the iPlan software (BrainLAB).

RESULTS

[(18)F]Galacto-RGD PET identified 10 of 12 tumors, with SUVs ranging from 2.2 to 5.8 (mean, 3.4 +/- 1.2). Two tumors <5 mm were missed. Tumor/blood and tumor/muscle ratios were 2.8 +/- 1.1 and 5.5 +/- 1.6, respectively. Tumor kinetics was consistent with a two-tissue compartmental model with reversible specific binding. Immunohistochemistry confirmed alphavbeta3 expression in all tumors with alphavbeta3 being located on the microvessels in all specimens and additionally on tumor cells in one specimen. Image fusion of [(18)F]Galacto-RGD PET with magnetic resonance imaging/multislice CT and definition of tumor subvolumes was feasible in all cases.

CONCLUSIONS

[(18)F]Galacto-RGD PET allows for specific imaging of alphavbeta3 expression in SCCHN with good contrast. Image fusion and definition of tumor subvolumes is feasible. This technique might be used for the assessment of angiogenesis and for planning and response evaluation of alphavbeta3-targeted therapies.

Radiosensitivity enhancement by combined treatment of celecoxib and gefitinib on human lung cancer cells

PURPOSE

To characterize the radiation-enhancing effects and underlying mechanisms of combined treatment with celecoxib, a cyclooxygenase-2 selective inhibitor, and gefitinib, an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, in human lung cancer cells.

EXPERIMENTAL DESIGN

Clonogenic cytotoxicity assays and clonogenic radiation survival assays after treatments with celecoxib and gefitinib with or without radiation were done on three human lung cancer cell lines. Synergisms after combined treatment with celecoxib, gefitinib, and radiation were investigated using isobologram and statistical analyses according to an independent action model. Alterations in apoptosis and cell cycle were measured to identify the mechanisms underlying the cell killing or radiation-enhancing effects of celecoxib and gefitinib combination treatment. Western blots for phosphorylated EGFR, EGFR, cyclooxygenase-2, and G(2) checkpoint molecules were conducted after treatment with celecoxib and/or gefitinib with or without radiation.

RESULTS

Combination celecoxib, gefitinib, and radiation treatments were shown to be synergistic in causing clonogenic cell deaths in all cell lines tested, but the nature of synergism was cell type specific. The combined drug treatments induced apoptosis in an additive manner in A549 cells and in a synergistic manner in NCI-H460 and VMRC-LCD cells. Celecoxib or gefitinib attenuated radiation-induced G(2)-M arrest, and combined drug treatment additively attenuated radiation-induced G(2)-M arrest in all cell lines. Radiation-induced checkpoint kinase (Chk) 1 and Chk2 phosphorylation were inhibited by celecoxib and gefitinib treatment, respectively.

CONCLUSIONS

Combined celecoxib and gefitinib treatments were shown to synergistically enhance the effect of radiation on lung cancer cells. The mechanisms underlying these synergistic effects seem to involve the synergistic enhancement of apoptosis and cooperative attenuation of radiation-induced G(2)-M arrest, possibly via Chk1 and Chk2 inhibition, by the combined drug treatments.

Preclinical evaluation of molecular-targeted anticancer agents for radiotherapy

The combination of molecular-targeted agents with irradiation is a highly promising avenue for cancer research and patient care. Molecular-targeted agents are in themselves not curative in solid tumours, whereas radiotherapy is highly efficient in eradicating tumour stem cells. Recurrences after high-dose radiotherapy are caused by only one or few surviving tumour stem cells. Thus, even if a novel agent has the potential to kill only few tumour stem cells, or if it interferes in mechanisms of radioresistance of tumours, combination with radiotherapy may lead to an important improvement in local tumour control and survival. To evaluate the effects of novel agents combined with radiotherapy, it is therefore necessary to use experimental endpoints which reflect the killing of tumour stem cells, in particular tumour control assays. Such endpoints often do not correlate with volume-based parameters of tumour response such as tumour regression and growth delay. This calls for radiotherapy specific research strategies in the preclinical testing of novel anti-cancer drugs, which in many aspects are different from research approaches for medical oncology.

Targeting the epidermal growth factor receptor in radiotherapy: radiobiological mechanisms, preclinical and clinical results

BACKGROUND AND PURPOSE

Inhibition of the epidermal growth factor receptor (EGFR) is a fastly developing field in preclinical and clinical cancer research. This review presents the current status of knowledge and discusses radiobiological mechanisms which may underly the efficacy of EGFR inhibitors combined with irradiation.

MATERIALS AND METHODS

Preclinical and clinical results on combined targeting of the EGFR and irradiation from the literature and from this laboratory are reviewed. Focus is given to the radiobiological rationale of this approach and to endpoints of experimental radiotherapy.

RESULTS

Overexpression of the EGFR is associated with decreased local tumour control after radiotherapy, especially when the overall treatment time is long. Inhibition of the EGFR either alone or in combination with irradiation decreases the growth rate of tumours expressing this receptor. Preclinical data provide proof-of-principle that local tumour control may be improved by combining irradiation with C225 mAb. In a randomised phase III clinical trial, simultaneous irradiation and treatment with the EGFR antibody Cetuximab (Erbitux; C225) in head and neck cancer patients resulted in significantly improved locoregional tumour control and survival compared to curative irradiation alone. Acute skin reactions increased in the experimental arm. The underlying mechanisms of enhanced radiation effects of combined EGFR inhibition with irradiation and of the partly conflicting results in different studies are poorly understood. There is increasing evidence, that important intertumoral heterogeneity in the response to EGFR inhibition alone and combined with irradiation exists, which appears to be at least partly dependent on specific mutations of the receptor as well as of molecules that are involved in the intracellular signal transduction pathway.

CONCLUSIONS AND OUTLOOK

Further investigations at all levels of the translational research chain exploring the mechanisms of EGFR inhibition in the context of radiotherapy are needed to fully exploit the potential of such combinations and to develop predictive tests that direct their use.

Molecular oncology — perspectives in lung cancer

Despite novel therapies in lung cancer treatment the 5-year survival rate still remains poor. Furthermore, screening concepts for early diagnosis, based on conventional sputum cytology and chest radiography, have so far not demonstrated an impact on decreasing lung-cancer mortality. More specific molecular markers allow new insights in the process of lung carcinogenesis. Furthermore they raise the hope that they provide new tools for early diagnosis and screening of high-risk individuals, determination of prognosis, and identification of innovative treatments. In this review, these perspectives of molecular targets in lung cancer will be discussed and summarised. Angiogenesis-stimulating factors (VEGF, FGF, MMP, etc.), parameters concerning tumour cell proliferation and apoptosis (EGFR, p53, K-ras, rb, bcl-2, etc.) are well known. Several of these genetic factors have already been investigated, but no single parameter has yet gained a sufficient selectivity regarding prognostic significance or therapeutic efficacy. New aspects in the complex tumour-stroma interaction and the interactive, cross-talking signal transduction pathways and recently developed functional genomic approaches, such as DNA microarrays and proteomics might lead to further progress in biological staging models and treatment concepts.