Molecular mechanisms of radiation-induced accelerated repopulation

Radiosensitization and Radioprotection by Curcumin in Glioblastoma and Other Cancers

Radiation therapy plays an important role in almost every cancer treatment. However, radiation toxicity to normal tissues, mainly due to the generation of reactive free radicals, has limited the efficacy of radiotherapy in clinical practice. Curcumin has been reported to possess significant antitumor properties. Although curcumin can sensitize cancer cells to irradiation, healthy cells are much less sensitive to this effect, and thus, curcumin is thought to be a potent, yet safe anti-cancer agent. In this review, a summary of the role of curcumin as both a radiosensitizer and radioprotector has been presented, based on the most recent data from the experimental and clinical evaluation of curcumin in different cancer cell lines, animal models, and human patients.

Celecoxib and Afatinib synergistic enhance radiotherapy sensitivity on human non-small cell lung cancer A549 cells

PURPOSE

Radioresistance is highly correlated with radiotherapy failure in clinical cancer treatment. In the current study, we sought to examine the efficacy of Celecoxib and Afatinib co-treatment as radiosensitizers in the management of non-small cell lung cancer (NSCLC) A549 cells.

MATERIALS AND METHODS

Generally, A549 cells were cultured with the treatment of Celecoxib and/or Afatinib for 24 h. Then, the cells were exposed to irradiation at 2 Gy/min for 1 min. After the end of treatment, cell viability, clonogenic survival, apoptosis and Prostaglandin E2 (PGE2) Elisa assays were performed. Transcriptional levels of Cyclooxygenase-2 (COX-2) affected by Celecoxib and/or Afatinib were measured by RT-qPCR. Posttranscriptional level of epidermal growth factor receptor (EGFR)-related gene was measured by Western blotting analysis.

RESULTS

Here, we, for the first time, reported that the co-treatment of Celecoxib and Afatinib regulates the resistance of NSCLC A549 cells to radiation. The co-treatment of Celecoxib and Afatinib sensitized radiotherapy through the radiation-induced loss of cell viability and colony formation, as well as apoptosis. Mechanistically, Celecoxib and Afatinib-treated cells showed the inhibition of COX-2 and EGFR expression, which may be responsible for the A549 cells' increased resistance to radiation.

CONCLUSION

Our results suggested that Celecoxib and Afatinib regulate cell sensitivity to apoptosis, and thus modulate the resistance of NSCLC to radiation.

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.

Retrospective comparison of standard and escalated doses of radiotherapy in newly diagnosed glioblastoma patients treated with concurrent and adjuvant temozolomide

BACKGROUND

To compare the efficacies of standard dose-(SDRT) and escalated dose radiotherapy (EDRT) in newly diagnosed glioblastoma (GBM) with concurrent and adjuvant temozolomide (TMZ).

MATERIALS AND METHODS

Outcomes of 126 newly diagnosed GBM patients who received SDRT (60 Gy, 30 fractions) or EDRT (70 Gy, 30 fractions) with concurrent plus adjuvant TMZ were retrospectively analyzed. Both groups received concurrent TMZ (75 mg/m²) during the course of RT and at least one course of adjuvant TMZ (150-200 mg/m²), thereafter. Overall survival (OS) and local progression free survival (LPFS) constituted the primary and secondary endpoints, respectively.

RESULTS

At median 14.2 months follow-up, 26 (20.6%) patients were alive. Median LPFS and OS were 9.2 [95% confidence interval (CI); 8.4-10.0] and 15.4 months (95% CI; 12.1-18.8), respectively, for the entire cohort. Although the median OS was numerically superior in the EDRT this difference could not reach statistical significance (22.0 vs. 14.9 months; P = 0.45), Likewise, LPFS was also (9.9 vs. 8.9 months; P = 0.89) not different between the two treatment groups. In multivariate analysis, better recursive partitioning analysis class (3-4 vs. 5; P = 0.044) and extensive surgery (gross total resection vs. subtotal resection/biopsy only; P= 0.021) were identified to associate significantly with superior OS times, irrespective of the RT protocol.

CONCLUSIONS

Although the current median OS of 22 months of the EDRT group is promising, no statistically significant survival advantage for EDRT was observed even in the presence of TMZ. Randomized studies with larger population sizes and available genetic markers are warranted to conclude more reliably on the fate of EDRT plus TMZ.

Inhibition of NF-κB improves sensitivity to irradiation and EGFR-TKIs and decreases irradiation-induced lung toxicity

Resistance to radiotherapy and to EGFR tyrosine kinase inhibitors (EGFR-TKIs), as well as therapy-related lung toxicity, are serious problems in the treatment of lung cancer. NF-κB has been reported to be associated with radioresistance. Therefore, we evaluated its effects on sensitivity to irradiation and to EGFR-TKIs; irradiation-induced lung toxicity; and the effects of irradiation on sensitivity to EGFR-TKIs. We used IKKβ inhibitor IMD 0354 or p65 depletion to explore their effects on sensitivity to irradiation and to EGFR-TKIs in vitro and in vivo. We evaluated the efficacy of IMD 0354 in a radiation-induced pulmonary-fibrosis mouse model. Irradiation enhanced activation and expression of MET and therefore suppressed the sensitivity of lung cancer cells to irradiation or EGFR-TKIs. Inhibition of NF-κB by IMD 0354 or by p65 depletion reversed irradiation-induced MET activation and increased the sensitivity of lung cancer cells to irradiation, to EGFR-TKIs and to the combination thereof in vitro and in vivo. In addition, IMD 0354 significantly reduced lung toxicity in a murine model of irradiation-induced pneumonia and lung fibrosis. These findings indicated that NF-κB inhibition can improve sensitivity to irradiation and to EGFR-TKIs and can decrease irradiation-induced lung toxicity in lung cancer.

EGFR-directed monoclonal antibodies in combination with chemotherapy for treatment of non-small-cell lung cancer: an updated review of clinical trials and new perspectives in biomarkers analysis

Lung cancer still represents one of the most common and fatal neoplasm, accounting for nearly 30% of all cancer-related deaths. Targeted therapies based on molecular tumor features and programmed death-1 (PD-1)/programmed death ligand-1 (PDL-1) blockade immunotherapy have offered new therapeutic options for patients with advanced non-small-cell lung cancer (NSCLC). Activation of the epidermal growth factor receptor (EGFR)-pathway promotes tumor growth and progression, including angiogenesis, invasion, metastasis and inhibition of apoptosis, providing a strong rationale for targeting this pathway. EGFR expression is detected in up to 85% of NSCLC and has been demonstrated to be associated with poor prognosis. Two approaches for blocking EGFR signaling are available: prevention of ligand binding to the extracellular domain with monoclonal antibodies (mAbs) and inhibition of the intracellular tyrosine kinase activity with small molecules. There is a strong rationale to consider the tumor's level of EGFR expression as one of the most significant predictive biomarkers in this setting. In this paper we provide an update focusing on the current status of EGFR-directed mAbs use for the treatment of patients with advanced NSCLC, through a review of all clinical trials involving anti-EGFR mAbs in combination with chemotherapy (CT) for advanced disease and with chemo-radiotherapy for stage III disease. Here we also discuss the current status of predictive biomarkers for anti-EGFR mAbs when added to first-line CT in patients with advanced NSCLC. Finally, we focused on the relevance of EGFR fluorescence in situ hybridization (FISH)+ and immunohistochemistry (IHC)-Score ≥ 200 as predictive biomarkers for the selection of patients who would be most likely to derive a clinical benefit from treatment with CT in combination with anti-EGFR mAbs, with particular reference also to histology.

Barriers affecting adherence to radiation treatment and strategies to overcome those barriers

BACKGROUND

The WHO defines adherence as the extent to which a patient's behavior coincides with recommendations from a health-care provider. Nonadherence to cancer treatment has a major impact on the therapeutic outcome.

AIM OF THE STUDY

To assess the prevalence of nonadherence to radiation regimen and to analyze the factors that affect adherence to cancer treatment.

MATERIALS AND METHODS

Patients receiving radiation treatment in our hospital were screened for adherence to appointment keeping and to the prescribed radiation regimen and patients who had unplanned treatment breaks during treatment were interviewed. Between January and July 2013, we identified 61 patients who had unplanned breaks during treatment. We analyzed the social, emotional, educational, economic, and therapeutic barriers that led to nonadherence.

RESULTS

Of the 61 patients who had unplanned breaks during treatment, 54% were males and 46% were females. Fifty-seven percent of patients had head and neck cancers and 25% had gynecological cancers. Seventy-one percent of patients were planned for concurrent chemoradiation. The number of days of unplanned treatment breaks ranged from 3 to 27 days. Social and therapeutic barriers were found to be the most common factor that led to nonadherence in these patients.

CONCLUSION

Identification of barriers that lead to nonadherence, designing strategies to overcome such barriers and effective communication becomes imperative to ensure uninterrupted treatment. Based on the above analysis, we have designed several strategies to improve adherence to treatment among our patients.

PET imaging of zirconium-89 labelled cetuximab: A phase I trial in patients with head and neck and lung cancer

BACKGROUND AND PURPOSE

PET imaging of cetuximab uptake may help selecting cancer patients with the highest chance of benefit. The aim of this phase I trial was to determine the safety of the tracer ⁸⁹Zr-cetuximab and to assess tumour uptake.

METHODS

Two dose schedules were used; two consecutive doses of 60MBq ⁸⁹Zr-cetuximab or a single dose of 120MBq, both preceded by 400mg/m² of unlabelled cetuximab. Toxicity (CTCAE 3.0) was scored twice weekly. PET-CT scans were acquired on days 4, 5 and 6 (step 1) or 5, 6, 7 (step 2). Because tumour uptake could not be assessed satisfactorily, a third step was added including EGFR overexpressing tumours.

RESULTS

Nine patients were included (6 NSCLC; 3 HNC). No additional toxicity was associated with administration of ⁸⁹Zr-cetuximab compared to standard cetuximab. A tumour to blood ratio (TBR)>1 was observed in all but one patient, with a maximum of 4.56. TBR was not different between dose schedules. There was a trend for higher TBR at intervals>5days after injection.

CONCLUSIONS

Both presented ⁸⁹Zr-cetuximab administration schedules are safe. The recommended dose for future trials is 60MBq, with a minimum time interval for scanning of 6days.

Comparison Between Concurrent EBRT and ICA with Conventional EBRT Followed by ICA in Cervical Cancer

INTRODUCTION

In carcinoma of cervix, if overall treatment time (OTT) is prolonged beyond 6 weeks, then the total dose required to achieve a given probability of tumor control is to be increased by 0.6 Gy for each day of prolongation, to control the accelerative repopulation of the cells, i.e., 1 % loss of tumor control, and to avoid increased treatment delays and drop outs due to the prolonged gap between EBRT and intracavitary brachytherapy (ICBT).

OBJECTIVES

To evaluate local disease control and early complications of concomitant HDR-ICBT with EBRT and thereby decrease the OTT in I B-III B stage carcinoma cervix.

METHODS

Fifty patients of carcinoma cervix (FIGO-I B/III B) were randomly divided into two groups: the study group treated with concomitant EBRT and HDR-ICBT (EBRT = 50-50.4 Gy/25-28 Fr, HDR 7 Gy in 3 Fr during the 3rd, 4th, and 5th weeks), EBRT and weekly cisplatin were not given on the day of HDR-ICBT; and the control group treated with EBRT followed by HDR-ICBT and weekly cisplatin. Acute reactions and local disease response were compared after treatment and at 6-month follow-up.

RESULTS

Medians of OTTs were 42 and 63 days in the study and the control groups, respectively. Dysuria and diarrhoea incidences were more in the study but manageable. At the completion of the treatment, there were 92 and 80 % complete responses; 4 and 4 % partial responses; and 4 and 16 % stable diseases in the study group and the control group, respectively. DFSs (disease free survivals) at 6-month follow-up were, respectively, 96 and 84 %, and most of the stable diseases were observed in stage III B.

CONCLUSIONS

Response was better in the study group but statistically insignificant, acute reactions were manageable, and there was decrease in drop outs due to completion of treatment at a stretch, but larger number of patients and longer follow-up are required to arrive at concrete conclusions.

Volume changes with stereotactic body radiation therapy in early lung cancer: Time trends and outcomes

INTRODUCTION

Tumour response during stereotactic body radiotherapy (SBRT) could be heterogeneous and the pattern of response may be used as an early predictor for outcome.

METHODS

Twenty-two consecutive patients with early lung cancer (ELC), treated with SBRT, were evaluated retrospectively for their gross tumour volume (GTV) changes during radiation therapy (RT). Kilo-voltage computed tomography scans (KVCTs) were acquired before every fraction and GTV was contoured manually on a total of 152 datasets. Tumour volume changes were noted with every fraction. The overall survival (OS), locoregional recurrence free survival (LRFS) and distant metastasis free survival (DMFS) were computed using the Kaplan-Meier method and comparisons were made using log-rank test.

RESULTS

Of the 22 patients, six had T1 tumours and 16 had T2 tumours. Median GTV was 40.6 cc (range 7.3-140.2 cc) on CT1 (KVCT at first fraction) and 33.3 cc (range 4.1-83.4 cc) on CTlast (KVCT at last fraction), suggesting a 17.9% median volume reduction at RT completion. Increase in tumour volume was noted in 18 (81.8%) patients at some point during RT. In the mid-treatment scan, 12 (54.5%) patients had higher tumour volumes than in CT1, however, only six (27.3%) patient's GTV remained larger compared to the baseline at the end of treatment. The median follow-up was 12.4 months. The OS, LRFS and DMFS rate at 12 and 18 months were 86.4%, 88.2%, 62% and 64.8%, 75.6% and 37.2% respectively. Tumours that regressed in volume by >17.9% (median volume reduction at RT completion) had significantly worse OS and LRFS compared to those that regressed <17.9% (P = 0.03 and 0.01 respectively).

CONCLUSION

Gross tumour volume undergoes significant changes during SBRT. Early regression in tumour volume may be used as a predictor of poor LRFS and OS.

Targeting Phosphatidylinositide3-Kinase/Akt pathway by BKM120 for radiosensitization in hepatocellular carcinoma

Tumor control of hepatocellular carcinoma by radiotherapy remains unsatisfactory. The phosphatidylinositol 3-kinase (PI3K)/Akt pathway plays a critical role in inhibiting cancer cell death. Elevated PI3K/Akt activity is associated with increased cellular resistance to irradiation. Our aim was to determine whether the inhibition of PI3K/Akt activity by a PI3K inhibitor, BKM120, contributes to the increased sensitivity of liver cancer cells to irradiation. The hepatocellular carcinoma cell lines (Huh7 and BNL) were used to evaluate the in vitro synergism between BKM120 and irradiation. Balb/c mice bearing ectopic BNL xenografts were treated with BKM120 and/or radiotherapy to assess the in vivo response. BKM120 increased cell killing by radiation, increased the expression of apoptotic markers, and suppressed the repair of radiation-induced DNA double-strand breaks. BKM120 pretreatment inhibited radiation-induced Akt phosphorylation and enhanced the tumor-suppressive effect and radiation-induced tumor cell apoptosis in ectopic xenografts. Inhibition of mTOR phosphorylation by rapamycin enhanced the radiosensitivity of BKM120-treated hepatocellular carcinoma cells. The synergism between BKM120 and irradiation likely inhibits the activation of Akt by radiation, leading to increased cell apoptosis and suppression of DNA-double-strand breaks repair in hepatocellular carcinoma cells. These data suggest that the BKM120/radiation combination may be a strategy worthy of clinical trials.

The prognostic significance of tumor epidermal growth factor receptor (EGFR) expression change after neoadjuvant chemoradiation in patients with rectal adenocarcinoma

Aim of the study

The aim of this retrospective study was to determine the prognostic impact of epidermal growth factor receptor (EGFR) expression changes during neoadjuvant chemoradiotherapy in patients with locally advanced rectal cancer.

Material and methods

Fifty patients with locally advanced rectal cancer were evaluated. All the patients were administered the total dose of 44 Gy. Capecitabine has been concomitantly administered in the dose 825 mg/m² in two daily oral administrations. Surgery was indicated 4–8 weeks from the chemoradiotherapy completion. Epidermal growth factor receptor expression in the pretreatment biopsies and in the resected specimens was assessed with immunohistochemistry.

Results

All of 50 patients received radiotherapy without interruption up to the total planned dose. In 30 patients sphincter-saving surgery was performed, 20 patients underwent amputation of the rectum. Downstaging was described in 30 patients. Four patients have had complete pathologic remission. Twenty-six patients have had partial remission, the disease was stable in 15 patients. Progression was reported in 5 patients. The median disease-free survival was 64.9 months, median overall survival was 76.4 months. Increased EGFR expression was found in 12 patients (26.1%). A statistically significantly shorter overall survival (p < 0.0001) and disease-free survival (p < 0.0001) was found in patients with increased expression of EGFR compared with patients where no increase in the expression of EGFR during neoadjuvant chemoradiotherapy was observed.

Conclusions

The overexpression of EGFR during neoadjuvant chemoradiotherapy for locally advanced rectal adenokarcinoma associated with significant shorter overall survival and disease free survival.

Scientific impact of studies published in temporarily available radiation oncology journals: a citation analysis

The purpose of this study was to review all articles published in two temporarily available radiation oncology journals (Radiation Oncology Investigations, Journal of Radiosurgery) in order to evaluate their scientific impact. From several potential measures of impact and relevance of research, we selected article citation rate because landmark or practice-changing research is likely to be cited frequently. The citation database Scopus was used to analyse number of citations. During the time period 1996-1999 the journal Radiation Oncology Investigations published 205 articles, which achieved a median number of 6 citations (range 0-116). However, the most frequently cited article in the first 4 volumes achieved only 23 citations. The Journal of Radiosurgery published only 31 articles, all in the year 1999, which achieved a median number of 1 citation (range 0-11). No prospective randomized studies or phase I-II collaborative group trials were published in these journals. Apparently, the Journal of Radiosurgery acquired relatively few manuscripts that were interesting and important enough to impact clinical practice. Radiation Oncology Investigations’ citation pattern was better and closer related to that reported in several previous studies focusing on the field of radiation oncology. The vast majority of articles published in temporarily available radiation oncology journals had limited clinical impact and achieved few citations. Highly influential research was unlikely to be submitted during the initial phase of establishing new radiation oncology journals.

Effect of celecoxib on inhibiting tumor repopulation during radiotherapy in human FaDu squamous cell carcinoma

Aim of the study

FaDu human squamous cell carcinoma (FaDu-hSCC) demonstrated accelerated tumor repopulation during fractionated irradiation with pathological validation in a xenograft model system. Previous studies showed that the selective cyclooxygenase (COX)-2 inhibitor celecoxib can enhance the tumor response to radiotherapy. So we aimed to explore the effect of celecoxib in inducing apoptosis and inhibiting repopulation of FaDu tumors in nude mice during fractionated radiotherapy.

Material and methods

FaDu-hSCC was transplanted into the right hind leg of BALB/C nude mice. Mice were treated with celecoxib and/or fractionated irradiation. Celecoxib (100 mg/kg/day) was administered by daily gavage. Irradiation was delivered with 12 to 18 fractions of 3.0 Gy daily or every second day based on Petersen's repopulation model. At different time points, tumors were excised for immunohistochemistry staining.

Results

Significant tumor repopulation occurred after about 18 days of radiotherapy. On average, Ki-67 and bromodeoxyuridine (BrdUrd) labeling indices (LI) decreased with daily irradiation (both p < 0.05) and increased with every-second-day irradiation (both p > 0.05), suggesting accelerated repopulation. Ki-67 LI decreased in celecoxib concurrent with radiotherapy for 12 fractions in 24 days and 18 fractions in 36 days compared with irradiated alone (p = 0.004 and 0.042, respectively). BrdUrd LI values were lower in the concurrent groups than irradiated alone (p = 0.001 and 0.006, respectively). Epithelial growth factor receptor (EGFR) expression score decreased in the concurrent groups than irradiated alone (p = 0.037 and 0.031, respectively). Caspase-3 expression scores were higher in the concurrent groups than irradiated alone (p = 0.05 and 0.006, respectively).

Conclusions

Celecoxib concurrent radiotherapy could inhibit tumor repopulation and increase tumor apoptosis during the treatment in FaDu squamous cell carcinoma.

Biphasic modulation of cancer stem cell-driven solid tumour dynamics in response to reactivated replicative senescence

OBJECTIVES

Cell senescence is a physiological programme of irreversible mitotic arrest that is triggered after a variety of intracellular and extracellular events. Its purpose is to protect tissue integrity by disabling mitosis in stressed or damaged cells. The senescence program serves as a tumour suppressor, and cancer cells are believed to bypass senescence to advance to malignancy. Recent studies have shown that senescence can be reactivated in cancer cells through a number of external perturbations, including oncogene activation, tumour suppressor gene withdrawal and irradiation.

MATERIALS AND METHODS

We have developed an agent-based model of solid tumour growth whose input population composition is based on the cancer stem-cell hypothesis. It is used to show how cancer stem cells can drive tumour progression, while non-stem cancer cells (CCs) interfere with this by impeding cancer stem-cell dynamics.

RESULTS

Here we show that intratumoural competition between the two cell types may arise to modulate tumour progression and ultimately cancer presentation risk. Model simulations reveal that reactivation of the replicative senescence programme in CCs initially increases total tumour burden, as attrition from cell death is partially averted, but evolves to provide tumour control in the long-term through increasing constraints on stem-cell compartment kinetics.

CONCLUSIONS

Reactivation of replicative senescence can prolong CC competition with cancer stem cells, thereby ultimately inhibiting malignant progression regardless of tumour size.

Repopulation of tumor cells during fractionated radiotherapy and detection methods (Review)

Repopulation of tumor cells during radiotherapy is believed to be a significant cause for treatment failure. The phenomenon of tumor repopulation during fractionated radiotherapy was found from clinical observations that identified that the local control rate decreased with a prolonged treatment time. A series of animal experiments with varied overall treatment time and fractionated doses were performed to demonstrate tumor cell repopulation during radiotherapy in various mouse xenograft models. However, conventional detection methods are challenging, as it is difficult to separate viable cells from those destined for apoptosis during fractionated radiotherapy. In essence, the mechanism of tumor repopulation involves the continuing proliferation of clonogenic tumor cells. In vivo imaging, tracking and targeting of the repopulation of these cells has been of clinical interest so as to administer a higher dose to the tumor repopulation regions. Currently, functional imaging methods, including 3'-deoxy-3'-¹⁸F-fluorothymidine positron emission tomography (¹⁸F-FLT PET), are showing promise in assessing the proliferation activity of tumors in vivo. This review mainly focuses on the phenomenon of tumor repopulation during radiotherapy and its conventional and novel detection methods, particularly on the feasibility of ¹⁸F-FLT PET for the detection of tumor-cell repopulation.

The role of cyclin D1 in response to long-term exposure to ionizing radiation

The health-related hazards resulting from long-term exposure to radiation remain unknown. Thus, an appropriate molecular marker is needed to clarify these effects. Cyclin D1 regulates the cell cycle transition from the G 1 phase to the S phase. Cyclin D1 is degraded as a G1/S checkpoint after 10 Gy of single acute radiation exposure, whereas conversely, cyclin D1 is stabilized when human tumor cells are exposed to fractionated radiation (FR) with 0.5 Gy of x-rays for 31 d. In this article, we review new findings regarding cyclin D1 overexpression in response to long-term exposure to FR. Cyclin D1 overexpression is associated with induction of genomic instability in irradiated cells. Therefore, repression of cyclin D1 expression is likely to cancel the harmful effects of long-term exposure to FR. Thus cyclin D1 may be a marker of long-term exposure to radiation and is a putative molecular radioprotection target for radiation safety.

New paradigms and future challenges in radiation oncology: an update of biological targets and technology

Radiation oncology exploits the biological interaction of radiation within tissue to promote tumor death while minimizing damage to surrounding normal tissue. The clinical delivery of radiation relies on principles of radiation physics that define how radiation energy is deposited in the body, as well as technology that facilitates accurate tumor targeting. This review will summarize the current landscape of recent biological and technological advances in radiation oncology, describe the challenges that exist, and offer potential avenues for improvement.

Long-term recovery of irradiated prostate cancer increases cancer stem cells

BACKGROUND

Despite improvements in treatment, prostate cancer (PC) remains the second-leading cause of cancer death in men. Radiotherapy is among the first-line treatments for PC, but a significant number of patients relapse. Recent evidence supports the idea that PC is initiated by a subset of cells, termed cancer stem cells (CSCs). CSCs have also been implicated in radioresistance in various malignancies, but their role in PC has not yet been investigated.

METHODS

We compared the relative radiosensitivity of isolated CSCs to the total population of their corresponding cell lines, and examined the relative numbers of CSCs in irradiated cell lines following long-term recovery and in recurrent human PC.

RESULTS

Here, we show that while irradiation does not immediately favor increased survival of CSCs, irradiated PC cell lines showed an increase in CSC properties with long-term recovery. These data suggest that, although CSCs are initially damaged by radiation, they possess a greater capacity for recovery and regrowth.

CONCLUSIONS

The combination of radiotherapy with a CSC-targeted therapeutic strategy may prevent tumor recurrence.

Intracytoplasmic epidermal growth factor receptor shows poor response to the cetuximab antitumor effect in irradiated non-small cell lung cancer cell lines

PURPOSE

The purpose of this study was to evaluate the antitumor effect of a blocking antibody for EGFR in the cytoplasm of a lung cancer cell line.

METHODS & MATERIALS

The A549 and H1299 cell lines were employed to demonstrate differential responses to cetuximab in combination with radiotherapy. Localization of EGFR was detected using confocal microscopy, and radiosensitivity was measured.

RESULTS

Treatment with cetuximab inhibited colony formation in a dose-dependent manner in A549, but not H1299 cells. Confocal microscopy revealed EGFR localized in the cytosolic fraction, particularly around the golgi apparatus in H1299, in contrast to cell membrane localization in A549 cell line. After irradiation, nuclear EGFR was detected in the A549 cell line. However, EGFR did not translocate to the nucleus in H1299 cells. While EGFR expression was decreased in both A549 and H1299 cell lines upon treatment with a combination of cetuximab and radiation, radiosensitivity was increased solely in A549 cells.

CONCLUSIONS

Our findings suggest that localization of EGFR is related to the sensitivity/resistance of cells to a combination of cetuximab and radiotherapy.

Activation of the AKT/cyclin D1/Cdk4 survival signaling pathway in radioresistant cancer stem cells

Radioresistance, which is a major cause of failure of radiotherapy (RT), is proposed as one of the intrinsic characteristics of cancer stem cells (CSCs) whose unique DNA damage response (DDR), efficient DNA repair and resistance to apoptosis are thought to confer the phenotype. We have isolated surviving CSCs by exposure to long-term fractionated radiation for 82 days from HepG2 and A172 cells (82FR-31NR cells). 82FR-31NR cells exhibited CSC properties, such as high expression of CSC marker CD133 and the ABC transporters (MDR1 and BCRP1), and high tumorigenic potential after transplantation into nude mice. The advantage of our isolated CSCs is that they can proliferate in as the same growth medium as that of parental cells without loss of CSC properties. Therefore, we can analyze DDR of non-stem cells and CSCs without any influences caused by different culture conditions. 82FR-31NR cells showed efficient DNA repair of radiation-induced DNA damage and radioresistance with activation of the AKT/cyclin D1 survival signaling pathway. In contrast, DNA damage persisted for a long time after irradiation in parental cells compared with isolated CSCs. Persisted DNA damage induced apoptosis in parental cells without activation of the AKT/cyclin D1 pathway. Therefore, inhibition of the AKT/cyclin D1 pathway by an AKT inhibitor, API-2, or cyclin D1 siRNA resulted in a loss of efficient DNA repair and radiosensitization of 82FR-31NR cells. Furthermore, knockdown of Cdk4 by its siRNA or a Cdk4 inhibitor was sufficient to suppress radioresistance of CSCs. In this study, we present a newly discovered DDR regarding the AKT/cyclin D1/Cdk4 pathway in response to radiation in CSCs. Combination of fractionated RT and reagents targeting the AKT/cyclin D1/Cdk4 pathway to eradicate CSCs would be effective therapeutic modality.

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.

Increased radioresistance via G12S K-Ras by compensatory upregulation of MAPK and PI3K pathways in epithelial cancer

BACKGROUND

Irradiation-induced signaling via the 2 pathways, Raf-MEK-ERK and PI3K-Akt, is known to be closely associated with a limited response to radiotherapy. In the present study we analyzed the relevance of constitutively active K-Ras for postradiogenic pathway stimulation and the option of coordinated inhibition to overcome these rescue mechanisms.

METHODS

We used 2 epithelial tumor cell lines as a model system, one of them harboring a G12S K-Ras mutation. Cells were irradiated and the effect of combined treatment with ionizing radiation and inhibitors on the expression of pERK and pAkt was determined by Western blotting. Additionally, clonogenic assays were performed to functionally analyze survival of the cell lines.

RESULTS

Compared with the nonmutated cells we observed the G12S cell line showing a clearly reduced response to inhibitor treatment under irradiation. In the case of pharmacologic inhibition of 1 of the pathways a compensatory upregulation of the second cascade leading to increased clonogenic survival seems feasible. However, there was a good functional response of this cell line to double inhibition with both compounds represented by minimized colony forming ability. The activation of ERK and Akt after irradiation was confirmed in xenotransplants showing elevated postradiogenic protein levels.

CONCLUSION

With our data we confirmed our hypothesis of postradiogenic constitutive activation of the 2 pathways both required for Ras-mediated radioresistance in epithelial cells. If this effect should prove itself as a general mechanism in Ras-mutated tumors, application of specific inhibitors to block both cascades in parallel could contribute to enhance radiosensitivity in these types of cancer.

DNA double-strand break - induced pro-survival signaling

Radiation and other types of DNA damaging agents induce a plethora of signaling events simultaneously originating from the nucleus, cytoplasm, and plasma membrane. As a result, this presents a dilemma when seeking to determine causal relationships and better insight into the intricacies of stress signaling. ATM plays critical roles in both nuclear and cytoplasmic signaling, of which, the DNA damage response (DDR) is the best characterized. We have recently created experimental conditions where the DNA damage signal alone can be studied while minimizing the influence from the extranuclear compartment. We have been able to document pro-survival and growth promoting signaling (via ATM-AKT-ERK) resulting from low levels of DSBs (equivalent to ≤2 Gy). More extensive DSBs (>2 Gy eq.) result in phosphatase-mediated ERK dephosphorylation, and thus shutdown of ERK signaling. In contrast, radiation does not result in such dephosphorylation even at very high doses. We propose that phosphatases are inactivated perhaps as a result of reactive oxygen species, which does not occur in response to 'pure' DNA damage. Our findings suggest that clinically relevant radiation doses, which are intended to halt tumor growth and induce cell death, are unable to inhibit tumor pro-survival signaling via ERK dephosphorylation.

Growth of breast cancer recurrences assessed by consecutive MRI

Background

Women with a personal history of breast cancer have a high risk of developing an ipsi- or contralateral recurrence. We aimed to compare the growth rate of primary breast cancer and recurrences in women who had undergone prior breast magnetic resonance imaging (MRI).

Methods

Three hundred and sixty-two women were diagnosed with breast cancer and had undergone breast MRI at the time of diagnosis in our institution (2005 - 2009). Among them, 37 had at least one prior breast MRI with the lesion being visible but not diagnosed as cancer. A linear regression of tumour volume measured on MRI scans and time data was performed using a generalized logistic model to calculate growth rates. The primary objective was to compare the tumour growth rate of patients with either primary breast cancer (no history of breast cancer) or ipsi- or contralateral recurrences of breast cancer.

Results

Twenty women had no history of breast cancer and 17 patients were diagnosed as recurrences (7 and 10 were ipsi- and contralateral, respectively). The tumour growth rate was higher in contralateral recurrences than in ipsilateral recurrences (growth rate [10^-3 days^-1] 3.56 vs 1.38, p < .001) or primary cancer (3.56 vs 2.09, p = 0.01). Differences in tumour growth were not significant for other patient-, tumour- or treatment-related characteristics.

Conclusions

These findings suggest that contralateral breast cancer presents accelerated growth compared to ipsilateral recurrences or primary breast events.

Astrocytes reverted to a neural progenitor-like state with transforming growth factor alpha are sensitized to cancerous transformation

Gliomas, the most frequent primitive central nervous system tumors, have been suggested to originate from astrocytes or from neural progenitors/stem cells. However, the precise identity of the cells at the origin of gliomas remains a matter of debate because no pre-neoplastic state has been yet identified. Transforming growth factor (TGF)-alpha, an epidermal growth factor family member, is frequently overexpressed in the early stages of glioma progression. We previously demonstrated that prolonged exposure of astrocytes to TGF-alpha is sufficient to trigger their reversion to a neural progenitor-like state. To determine whether TGF-alpha dedifferentiating effects are associated with cancerous transforming effects, we grafted intracerebrally dedifferentiated astrocytes. We show that these cells had the same cytogenomic profile as astrocytes, survived in vivo, and did not give birth to tumors. When astrocytes dedifferentiated with TGF-alpha were submitted to oncogenic stress using gamma irradiation, they acquired cancerous properties: they were immortalized, showed cytogenomic abnormalities, and formed high-grade glioma-like tumors after brain grafting. In contrast, irradiation did not modify the lifespan of astrocytes cultivated in serum-free medium. Addition of TGF-alpha after irradiation did not promote their transformation but decreased their lifespan. These results demonstrate that reversion of mature astrocytes to an embryonic state without genomic manipulation is sufficient to sensitize them to oncogenic stress.

[Relation between epidermal growth factor receptor (EGFR) and p53 expression and radiocurability of laryngeal squamous cell cancer]

Radiotherapy and surgery are the most important treatment modalities for the majority of laryngeal cancers. Because of high efficacy and better organ preservation radiotherapy is generally preferred for early and intermediate stage of the disease. Some of patients with more locally advanced cancers can still be cured by means of radiotherapy, but we have not got reliable prognostics factors for predicting radiocurability. THE AIM OF MY STUDY: was to investigate the value of p53 and EGFR expression for predicting clinical outcomes of laryngeal cancer patients treated with radiotherapy.

METHODS AND MATERIALS

The study included 50 patients with laryngeal cancer treated in Department of Radiotherapy of Silesian Oncology Center between the years 1998 and 2003. Paraffin sections from archival material were studied immunohistochemically for detection p53 and EGFR and correlated with clinical parameters and local tumor control and patient survival.

RESULTS

Accumulation of p53 and EGFR were detected in 65% and 50% of tumor respectively. No relationship was observed between immunostaining for investigated proteins and clinicopathologic factors. The TNM tumor stage was the most significant prognostic factor for local control and overall survival. p53 was favorable prognostic factor with 5-years disease free survival rate 82% for patients p53-positive and 75% for p53-negative patients (p = 0.04).

CONCLUSION

The TNM tumor stage is the most important prognostic factor for laryngeal cancer. Tumors accumulating p53 have better prognosis what indicates possibly role for p53 immunohistochemical analysis for predicting outcomes of radiotherapy in patients with laryngeal cancer.

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.

Concurrent chemotherapy and re-irradiation for locoregionally recurrent head and neck cancer

Recurrent and second primary tumors arising within a previously radiated head and neck volume represent a difficult clinical scenario to manage. For patients who have resectable disease, surgery is the standard treatment. Chemotherapy is the standard for patients with unresectable or metastatic disease but offers no chance for cure. Re-irradiation (RRT) with concurrent chemotherapy is a potentially curative treatment option. In this article, we will review the basis for current chemoradiotherapy (CRT) regimens used in previously radiated patients, focusing on outcome and toxicity. Additionally, we will review radiotherapy techniques used in this setting and highlight the differences between definitive radiotherapy and RRT. Controversies, such as the utility of chemotherapy and RRT following surgical salvage, will be addressed. Finally, we will review investigations seeking to improve the therapeutic outcomes of patients treated with chemotherapy and RRT.

Alteration of apoptotic signaling molecules as a function of time after radiation in human neuroblastoma cells

Ascertaining the time-dependent regulation of induced apoptosis and radioresistance is important to understand the relationship between the level of spontaneous apoptosis in cells and their radiosensitivity. Accordingly, we investigated the time-dependent expression of apoptosis related genes and radioresistance in neuroblastoma cells. Serum-starved human SK-N-MC cells were exposed to low linear energy transfer (LET) radiation (2 Gy) and incubated for 15, 30, 45 min, and 48 h. Radioresistance was investigated by examining the NF kappa B DNA-binding activity, cellular toxicity, DNA fragmentation, and expression of apoptotic signal transduction molecules. NF kappa B DNA binding activity was analyzed using electrophoretic mobility shift assay (EMSA). Cellular toxicity was measured using MTT assay. DNA fragmentation was quantified by labeling with fluorescein-conjugated deoxynucleotides. Microarray analysis was performed using cDNA microarray and relative gene expression was measured as % GAPDH and, subsequently validated using Q-PCR. Induction of NF kappa B analyzed using EMSA showed an increased DNA-binding activity at all time points investigated. Induced DNA fragmentation was observed after 15, 30, and 45 min post-radiation. Relatively, induced fragmentation was reduced after 48 h. Compared to the untreated controls cellular toxicity was induced with low LET radiation after 15, 30, and 45 min. Conversely, cytotoxicity was relatively less at 48 h after low LET radiation. Microarray analysis after low LET radiation revealed time-dependent modulation of apoptosis-related genes that are involved in radio-adaptation, spontaneous apoptosis-related early-responsive genes and late response genes. These results suggest that the time-dependent regulation of apoptotic response may determine the relationship between the level of spontaneous apoptosis in cells and their radiosensitivity.

Radioprotection and radiosensitization by curcumin

This chapter gives an overview of the radioprotective and radiosensitizing effect of curcumin. Ionizing radiations interact with biological molecules inducing radiolytic products like e(aq), *OH, *H, -OH, +H, O2, and peroxides. These free radicals damage important biomolecules and subsequently inflict deleterious effects in the organism. Whole-body exposure to ionizing radiations results in central nervous system, gastrointestinal tract, and bone marrow syndromes, whereas chronic irradiation causes cancer, birth anomalies, erythema, and dysfunctions to almost all organ of the body depending on the total dose and site of irradiation. Curcumin (diferuloyl methane), a yellow pigment present in the rhizomes of turmeric, has been used in Southeast Asia to give yellow color and flavor to curries. Turmeric has been used to treat various ailments in the Ayurvedic system of medicine in India. Recently, it has been evaluated for its radioprotective and radiosensitizing activities. Curcumin has been found to exert a dual mode of action after irradiation depending on its dose. It has been reported to protect various study systems against the deleterious effects induced by ionizing radiation and to enhance the effect of radiation. Therefore, curcumin can be very useful during radiotherapy of cancer. Administration of curcumin in patients will be able to kill the tumor cells effectively by enhancing the effect of radiation and, at the same time, protect normal cells against the harmful effects of radiation. The available information on curcumin suggests that the radioprotective effect might be mainly due to its ability to reduce oxidative stress and inhibit transcription of genes related to oxidative stress and inflammatory responses, whereas the radiosensitive activity might be due the upregulation of genes responsible for cell death.

EGFR-targeted anti-cancer drugs in radiotherapy: preclinical evaluation of mechanisms

Preclinical and clinical results indicate that the EGFR can mediate radioresistance in different solid human tumours. Combination of radiotherapy and EGFR inhibitors can improve local tumour control compared to irradiation alone and has been introduced into clinical radiotherapy practice. So far several mechanisms have been identified in preclinical studies to contribute to improved local tumour control after radiation combined with EGFR inhibitors. These include direct kill of cancer stem cells by EGFR inhibitors, cellular radiosensitization through modified signal transduction, inhibition of repair of DNA damage, reduced repopulation and improved reoxygenation during fractionated radiotherapy. Effects and mechanisms may differ for different classes of EGFR inhibitors, for different tumours and for normal tissues. The mechanisms underlying this heterogeneity are currently poorly understood, and predictive assays are not available yet. Importantly, mechanisms and predictors for the combined effects of radiation with EGFR inhibitors appear to be considerably different to those for application of EGFR inhibitors alone or in combination with chemotherapy. Therefore to further evaluate the efficacy and mechanisms of EGFR-inhibition in combined treatments, radiotherapy-specific preclinical research strategies, which include in vivo experiments using local tumour control as an endpoint, as well as animal studies on normal tissue toxicity are needed.

Nuclear factor-kappaB and manganese superoxide dismutase mediate adaptive radioresistance in low-dose irradiated mouse skin epithelial cells

Mechanisms governing inducible resistance to ionizing radiation in untransformed epithelial cells pre-exposed to low-dose ionizing radiation (LDIR; </=10 cGy) are not well understood. The present study provides evidence that pre-exposure to 10 cGy X-rays increases clonogenic survival of mouse skin JB6P+ epithelial cells subsequently exposed to 2 Gy doses of gamma-rays. To elucidate the molecular pathways of LDIR-induced adaptive radioresistance, the transcription factor nuclear factor-kappaB (NF-kappaB) and a group of NF-kappaB-related proteins [i.e., p65, manganese superoxide dismutase (MnSOD), phosphorylated extracellular signal-regulated kinase, cyclin B1, and 14-3-3zeta] were identified to be activated as early as 15 min after LDIR. Further analysis revealed that a substantial amount of both 14-3-3zeta and cyclin B1 accumulated in the cytoplasm at 4 to 8 h when cell survival was enhanced. The nuclear 14-3-3zeta and cyclin B1 were reduced and increased at 4 and 24 h, respectively, after LDIR. Using YFP-fusion gene expression vectors, interaction between 14-3-3zeta and cyclin B1 was visualized in living cells, and LDIR enhanced the nuclear translocation of the 14-3-3zeta/cyclin B1 complex. Treatment of JB6P+ cells with the NF-kappaB inhibitor IMD-0354 suppressed LDIR-induced expression of MnSOD, 14-3-3zeta, and cyclin B1 and diminished the adaptive radioresistance. In addition, treatment with small interfering RNA against mouse MnSOD was shown to inhibit the development of LDIR-induced radioresistance. Together, these results show that NF-kappaB, MnSOD, 14-3-3zeta, and cyclin B1 contribute to LDIR-induced adaptive radioresistance in mouse skin epithelial cells.

The concurrent chemoradiation paradigm—general principles

During the past 20 years, the advent of neoadjuvant, primary, and adjuvant concurrent chemoradiotherapy has improved cancer care dramatically. Significant contributions have been made by technological improvements in radiotherapy, as well as by the introduction of novel chemotherapy agents and dosing schedules. This article will review the rationale for the use of concurrent chemoradiotherapy for treating malignancies. The molecular basis and mechanisms of action of combining classic cytotoxic agents (e.g. platinum-containing drugs, taxanes, etc.) and novel agents (e.g. tirapazamine, EGFR inhibitors and other targeted agents) with radiotherapy will be examined. This article is part one of two articles. In the subsequent article, the general principles outlined here will be applied to head and neck cancer, in which the impact of concurrent chemoradiotherapy is particularly evident.

Les thérapeutiques ciblées en association avec la radiothérapie dans le cancer bronchique

Targeted therapies are now more often used in lung cancer. Inhibitors of EGFR and of angiogenesis have demonstrated a certain activity in this disease. Some experimental in vitro or in vivo studies are in favour of combined targeted therapies and radiation. For example, additive or supra-additive effects have been shown when inhibitors of the EGFR tyrosine kinase were given with radiation. In advanced lung cancer, the combination of bevacizumab with chemotherapy was demonstrated to produce better survival outcomes. But a high rate of fatal hemoptysis was reported with this drug, particularly for central and squamous tumors. This could be a limitation for its use in combination with radiation. Drugs with multiple targets are becoming available; their association with radiation seems to be promising.

Enhancement of radiosensitivity by dual inhibition of the HER family with ZD1839 ("Iressa") and trastuzumab ("Herceptin")

PURPOSE

The aims of this study were twofold: (1) to examine the effects of dual inhibition of 2 members of the HER family, the epidermoid growth factor receptor (EGFR) and HER2/neu, by gefitinib (ZD1839) and trastuzumab on radiosensitivity; and (2) to explore the molecular mechanism of radiosensitization especially focusing on the survival signal transduction pathways by using A431 human vulvar squamous carcinoma cells expressing EGFR and HER2/neu.

METHODS AND MATERIALS

The effects of inhibitors on the radiation-induced activation of EGFR and/or HER2/neu, and the intracellular proteins that are involved in their downstream signaling, were quantified by the Western blot. Radiosensitizing effects by the blockage of EGFR and/or HER2/neu were determined by a clonogenic assay.

RESULTS

Radiation-induced activation of the EGFR and HER2/neu was inhibited with ZD1839 and/or trastuzumab. ZD1839 also inhibited the radiation-induced phosphorylation of HER2/neu. Radiation in combination with the HER family inhibitors inhibited the activation of Akt and MEK1/2, the downstream survival signaling of the HER family. ZD1839 enhanced radiosensitivity with a dose-modifying factor (DMF) (SF3) of 1.45 and trastuzumab did so with a DMF (SF3) of 1.11. Simultaneous blockade of EGFR and HER2/neu induced a synergistic radiosensitizing effect with a DMF (SF3) of 2.29.

CONCLUSIONS

The present data suggest that a dual EGFR and HER2/neu targeting may have potential for radiosensitization in tumors in which both of these pathways are active.

A phase II trial of accelerated radiotherapy using weekly stereotactic conformal boost for supratentorial glioblastoma multiforme: RTOG 0023

PURPOSE

This phase II trial was performed to assess the feasibility, toxicity, and efficacy of dose-intense accelerated radiation therapy using weekly fractionated stereotactic radiotherapy (FSRT) boost for patients with glioblastoma multiforme (GBM).

METHODS AND MATERIALS

Patients with histologically confirmed GBM with postoperative enhancing tumor plus tumor cavity diameter <60 mm were enrolled. A 50-Gy dose of standard radiation therapy (RT) was given in daily 2-Gy fractions. In addition, patients received four FSRT treatments, once weekly, during Weeks 3 to 6. FSRT dosing of either 5 Gy or 7 Gy per fraction was given for a cumulative dose of 70 or 78 Gy in 29 (25 standard RT + 4 FSRT) treatments over 6 weeks. After the RT course, carmustine (BCNU) at 80 mg/m(2) was given for 3 days, every 8 weeks, for 6 cycles.

RESULTS

A total of 76 patients were analyzed. Toxicity included: 3 Grade 4 chemotherapy, 3 acute Grade 4 radiotherapy, and 1 Grade 3 late. The median survival time was 12.5 months. No survival difference is seen when compared with the RTOG historical database. Patients with gross total resection (41%) had a median survival time of 16.6 months vs. 12.0 months for historic controls with gross total resection (p = 0.14).

CONCLUSION

This first, multi-institutional FSRT boost trial for GBM was feasible and well tolerated. There is no significant survival benefit using this dose-intense RT regimen. Subset analysis revealed a trend toward improved outcome for GTR patients suggesting that patients with minimal disease burden may benefit from this form of accelerated RT.

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.

ErbB receptor tyrosine kinase network inhibition radiosensitizes carcinoma cells

PURPOSE

The expression of epidermal growth factor receptor (EGFR)-CD533, a truncation mutant of the wild-type EGFR, radiosensitizes carcinoma and malignant glioma cell lines. This deletion mutant disrupts EGFR activation and downstream signaling through the formation of inhibitory dimerizations. In this study, the effects of EGFR-CD533 on other ErbB receptor tyrosine kinase (RTK) family members were quantified to better understand the mechanism of EGFR-CD533-mediated radiosensitization.

METHODS AND MATERIALS

Breast carcinoma cell lines with different ErbB RTK expression profiles were transduced with EGFR or ErbB2 deletion mutants (EGFR-CD533 and ErbB2-CD572) using an adenoviral vector. ErbB RTK activation, mitogen activated protein kinase (MAPK) and phosphatidylinositol-3-kinase (PI3K)/p70S6K signaling, and clonogenic survival were determined for expression of each deletion mutant.

RESULTS

EGFR-CD533 radiosensitizes carcinoma cells with either high EGFR expression (MDA-MB231) or low EGFR expression (T47D) through significant blockade of the ErbB RTK network. Analysis of clonogenic survival demonstrate significant enhancement of the alpha/beta ratios, as determined by the linear-quadratic model. Split-dose survival experiments confirm that EGFR-CD533 reduces the repair of cellular damage after ionizing radiation.

CONCLUSION

Expression of EGFR-CD533 inhibits the ErbB RTK network and radiosensitizes carcinoma cells irrespective of the ErbB RTK expression patterns, and ErbB2-CD572 does not radiosensitize cells with low EGFR expression. These studies demonstrate that the mechanism of action for EGFR-CD533-mediated radiosensitization is inhibition of the ErbB RTK network, and is an advantage for radiosensitizing multiple malignant cell types.

Kinetics of EGFR expression during fractionated irradiation varies between different human squamous cell carcinoma lines in nude mice

BACKGROUND AND PURPOSE

Preclinical and clinical data indicate that high pretherapeutic EGFR expression is associated with poor local tumour control, possibly caused by a high repopulation rate of clonogenic cells during radiotherapy in these tumours. Previous data reported from our laboratory showed a correlation between EGFR expression and acceleration of repopulation in poorly differentiated FaDu human squamous cell carcinoma (SCC) during fractionated irradiation. To test whether this is a general phenomenon, two further SCC were investigated in the present study.

PATIENTS AND METHODS

GL and UT-SCC-14, two moderately well differentiated and keratinising hSCC, were grown as xenografts in nude mice. Functional data on the repopulation kinetics during fractionated irradiation for these tumour models have been previously determined. The expression of EGFR during fractionation was analysed by immunohistochemistry. Endpoints were the membrane-staining score and the proportion of EGFR-positive cells (EGFR labelling index).

RESULTS

Different kinetics of EGFR expression during fractionated RT were found. In UT-SCC-14, EGFR staining score and labelling index increased significantly during radiotherapy. In GL SCC, the EGFR expression was unchanged. Both tumours are characterized by a small but significant repopulation rate during radiotherapy.

CONCLUSIONS

The expression of EGFR may change significantly during fractionated irradiation. No clear correlation between EGFR expression and the repopulation kinetics of clonogenic tumour cells during fractionated irradiation was found. The changes in EGFR expression during irradiation warrant further investigation on their prognostic implications and on their importance for therapeutic interventions.

Repopulation of cancer cells during therapy: an important cause of treatment failure

Radiotherapy and chemotherapy are given in multiple doses, which are spaced out to allow the recovery of normal tissues between treatments. However, surviving cancer cells also proliferate during the intervals between treatments and this process of repopulation is an important cause of treatment failure. Strategies developed to overcome repopulation have improved clinical outcomes, and now new strategies to inhibit repopulation are emerging in parallel with advances in the understanding of underlying biological mechanisms.