Comparison between radiation-induced cell cycle delay in lymphocytes and radiotherapy response in head and neck cancer

Dual effects of radiation bystander signaling in urothelial cancer: purinergic-activation of apoptosis attenuates survival of urothelial cancer and normal urothelial cells

Radiation therapy (RT) delivers tumour kill, directly and often via bystander mechanisms. Bladder toxicity is a dose limiting constraint in pelvic RT, manifested as radiation cystitis and urinary symptoms. We aimed to investigate the impact of radiation-induced bystander signaling on normal/cancer urothelial cells. Human urothelial cancer cells T24, HT1376 and normal urothelial cells HUC, SV-HUC were used. Cells were irradiated and studied directly, or conditioned medium from irradiated cells (CM) was transferred to naïve, cells. T24 or SV-HUC cells in the shielded half of irradiated flasks had increased numbers of DNA damage foci vs non-irradiated cells. A physical barrier blocked this response, indicating release of transmitters from irradiated cells. Clonogenic survival of shielded T24 or SV-HUC was also reduced; a physical barrier prevented this phenomenon. CM-transfer increased pro-apoptotic caspase-3 activity, increased cleaved caspase-3 and cleaved PARP expression and reduced survival protein XIAP expression. This effect was mimicked by ATP. ATP or CM evoked suramin-sensitive Ca²⁺-signals. Irradiation increased [ATP] in CM from T24. The CM-inhibitory effect on T24 clonogenic survival was blocked by apyrase, or mimicked by ATP. We conclude that radiation-induced bystander signaling enhances urothelial cancer cell killing via activation of purinergic pro-apoptotic pathways. This benefit is accompanied by normal urothelial damage indicating RT bladder toxicity is also bystander-mediated.

Downregulation of Annexin A1 is correlated with radioresistance in nasopharyngeal carcinoma

Radiotherapy is the primary treatment for nasopharyngeal carcinoma (NPC), but radioresistance often remains an obstacle to successful treatment. In our previous study, it was demonstrated that Annexin A1 (ANXA1) was involved in the p53-mediated radioresponse in NPC cells, which suggested that it may be associated with radioresistance in NPC; however, the role of ANXA1 in NPC radioresistance is unknown. In the present study, CNE2 cells were stably transfected with pLKO.1-ANXA1-small hairpin (sh)RNAs to investigate the effects of ANXA1 on the radiosensitivity of NPC. CNE2 cells transfected with pLKO.1 were used as the control. The radiosensitivities of the cells in vitro were analyzed using the clonogenic survival assay, cell growth analysis, flow cytometry and Hoechst 33258 staining. ANXA1 downregulation significantly enhanced clonogenic survival and cell growth following treatment of CNE2 cells with ionizing radiation (IR), increased the number of cells in the S phase and decreased IR-induced apoptosis. These results suggested that the radiosensitivity of CNE2 cells transfected with ANXA1-specific shRNA was significantly lower compared with the control cells. Therefore, ANXA1 downregulation may be involved in the radioresistance of NPC, and ANXA1 may be considered a novel biomarker for predicting NPC response to radiotherapy.

Let-7b overexpression leads to increased radiosensitivity of uveal melanoma cells

Uveal melanoma (UM) is an intraocular malignant tumor in adults that is characterized by rapid progression and recurrence. Irradiation has become the primary therapy for UM patients who are not candidates for surgery. However, after large-dose fraction irradiation treatment, some patients undergo subsequent enucleation because of radiotherapy-related complications. This situation has raised concerns on how to optimize the effectiveness of radiation treatment. Recent investigations of microRNAs are changing our understanding of UM tumor biology and are helping to identify novel targets for radiotherapy. The radioresistant UM cell lines OM431 and OCM1 were selected and exposed to irradiation, and let-7b was found to be downregulated after exposure. We then confirmed that let-7b mimics could inhibit UM growth both in vitro and in vivo. More specifically, transfection with let-7b mimics markedly resensitized OCM1 and OM431 cells to irradiation by reducing the population of S-phase cells. Cyclin D1 plays a vital role in cell cycle arrest, which is induced by let-7b overexpression. Cyclin D1 is also a target of let-7b and its expression is suppressed by upregulation of let-7b. Collectively, our results indicate that let-7b overexpression can in turn downregulate cyclin D1 expression and enhance the radiosensitivity of UM through cell cycle arrest. Let-7b could serve as a marker for radiosensitivity and could enhance the therapeutic benefit of UM cell irradiation.

PI3K/Akt/mTOR pathway inhibitors enhance radiosensitivity in radioresistant prostate cancer cells through inducing apoptosis, reducing autophagy, suppressing NHEJ and HR repair pathways

The PI3K/Akt/mTOR pathway has a central role in cancer metastasis and radiotherapy. To develop effective therapeutics to improve radiosensitivity, understanding the possible pathways of radioresistance involved and the effects of a combination of the PI3K/Akt/mTOR inhibitors with radiotherapy on prostate cancer (CaP) radioresistant cells is needed. We found that compared with parent CaP cells, CaP-radioresistant cells demonstrated G0/G1 and S phase arrest, activation of cell cycle check point, autophagy and DNA repair pathway proteins, and inactivation of apoptotic proteins. We also demonstrated that compared with combination of single PI3K or mTOR inhibitors (BKM120 or Rapamycin) and radiation, low-dose of dual PI3K/mTOR inhibitors (BEZ235 or PI103) combined with radiation greatly improved treatment efficacy by repressing colony formation, inducing more apoptosis, leading to the arrest of the G2/M phase, increased double-strand break levels and less inactivation of cell cycle check point, autophagy and non-homologous end joining (NHEJ)/homologous recombination (HR) repair pathway proteins in CaP-radioresistant cells. This study describes the possible pathways associated with CaP radioresistance and demonstrates the putative mechanisms of the radiosensitization effect in CaP-resistant cells in the combination treatment. The findings from this study suggest that the combination of dual PI3K/Akt/mTOR inhibitors (BEZ235 or PI103) with radiotherapy is a promising modality for the treatment of CaP to overcome radioresistance.

MicroRNA-449a enhances radiosensitivity in CL1-0 lung adenocarcinoma cells

Lung cancer is the leading cause of cancer-related mortality worldwide. Radiotherapy is often applied for treating lung cancer, but it often fails because of the relative non-susceptibility of lung cancer cells to radiation. MicroRNAs (miRNAs) have been reported to modulate the radiosensitivity of lung cancer cells and have the potential to improve the efficacy of radiotherapy. The purpose of this study was to identify a miRNA that can adjust radiosensitivity in lung adenocarcinoma cells. Two lung adenocarcinoma cell lines (CL1-0 and CL1-5) with different metastatic ability and radiosensitivity were used. In order to understand the regulatory mechanisms of differential radiosensitivity in these isogenic tumor cells, both CL1-0 and CL1-5 were treated with 10 Gy radiation, and were harvested respectively at 0, 1, 4, and 24 h after radiation exposure. The changes in expression of miRNA upon irradiation were examined using Illumina Human microRNA BeadChips. Twenty-six miRNAs were identified as having differential expression post-irradiation in CL1-0 or CL1-5 cells. Among these miRNAs, miR-449a, which was down-regulated in CL1-0 cells at 24 h after irradiation, was chosen for further investigation. Overexpression of miR-449a in CL1-0 cells effectively increased irradiation-induced DNA damage and apoptosis, altered the cell cycle distribution and eventually led to sensitization of CL1-0 to irradiation.

The NEDD8 conjugation pathway regulates p53 transcriptional activity and head and neck cancer cell sensitivity to ionizing radiation

Human papillomavirus (HPV)-related oropharyngeal cancer represents a distinct head and neck squamous cell carcinoma (HNSCC) subpopulation, with improved disease-free and overall survival. In general, HPV-positive HNSCCs express wild-type TP53, which could explain its increased radiosensitivity. However, the molecular mechanisms underlying this higher sensitivity remain elusive. We have previously shown that HPV-related oropharyngeal carcinomas express decreased levels of the NEDD8-activating enzyme 1/amyloid β precursor protein-binding protein 1 (NAE1/APP-BP1) gene. NAE1/APP-BP1 function is required for the NEDDylation of target proteins, and has been shown to be a negative regulator of p53 transcriptional activity. In this study, we addressed the hypothesis that NAE1/APP-BP1 expression levels regulate p53 activity and cell survival upon ionizing irradiation. We used the radiosensitive and naturally HPV16-infected UPCI:SCC90 cell line and the radioresistant and HPV-negative SQ20B cell line as the control. NAE1/APP-BP1 expression levels were modulated with expression constructs and siRNAs. Radiosensitivity was evaluated with clonogenic survival assays. p53 transcriptional activity was measured with a luciferase assay. The overexpression of NAE1/APP-BP1 in UPCI:SCC90 cells resulted in the increased NEDDylation of p53, inhibition of p53 activity and increased cell resistance to ionizing radiation. Conversely, the inhibition of NAE1/APP-BP1 expression in SQ20B cells induced p53-dependent cell death after treatment with X-rays. Taken together, these results indicate that NAE1/APP-BP1 and NEDDylation are invovled in modulating p53 activity and regulating its role in the response of cells to ionizing radiation. Our findings bring new insights in the molecular mechanisms underlying the increased radiosensitivity of HPV-related oropharyngeal tumors. This is of importance, as no reliable and robust predictive biomarkers for tumor response to radiotherapy are currently available. These results also have potential clinical significance, as drugs targeting NAE1/APP-BP1 have recently emerged as a novel therapeutic modality in cancer treatment.

Cellular Response to Ionizing Radiation: A MicroRNA Story

MicroRNAs (miRNAs) represent a class of small non-coding RNA molecules that regulate gene expression at the post-transcriptional level. They play a crucial role in diverse cellular pathways. Ionizing radiation (IR) is one of the most important treatment protocols for patients that suffer from cancer and affects directly or indirectly cellular integration. Recently it has been discovered that microRNA-mediated gene regulation interferes with radio-related pathways in ionizing radiation. Here, we review the recent discoveries about miRNAs in cellular response to IR. Thoroughly understanding the mechanism of miRNAs in radiation response, it will be possible to design new strategies for improving radiotherapy efficiency and ultimately cancer treatment.

Avaliação semanal dos efeitos da radioterapia externa convencional pela contagem dos leucócitos e plaquetas de pacientes portadores de câncer nas áreas de cabeça e pescoço, tórax e pelve

OBJETIVO: Avaliar a necessidade de monitoração semanal, pela contagem de leucócitos e plaquetas, dos pacientes portadores de câncer das áreas de cabeça e pescoço, tórax e pelve submetidos a radioterapia externa convencional. MATERIAIS E MÉTODOS: Cento e um adultos, portadores de câncer das áreas de cabeça e pescoço (11 pacientes), tórax (35 pacientes) e pelve (55 pacientes), submetidos a radioterapia, avaliados semanalmente com leucograma e contagem de plaquetas, comparando-se as contagens das células antes do início do tratamento com as obtidas nas semanas ao longo do tratamento, área tratada, sexo e faixa etária. RESULTADOS: A maior queda dos leucócitos e plaquetas ocorreu na quarta semana, quando linfócitos, leucócitos totais, neutrófilos, monócitos e plaquetas apresentaram diminuição de 53,5%, 26,8%, 19,4%, 22,2% e 14,6%, respectivamente, ao serem comparados aos valores do início do tratamento. Durante o tratamento, as médias geométricas da pelve foram estatisticamente menores do que as de tórax e cabeça e pescoço. Os linfócitos foram os mais sensíveis à irradiação. Não houve alteração da contagem de leucócitos e plaquetas relacionadas ao sexo ou à faixa etária. CONCLUSÃO: A partir dos resultados obtidos não parece ser necessária a contagem semanal de leucócitos e plaquetas para pacientes submetidos a radioterapia externa convencional em campos localizados.

Can 8-oxo-dG be used as a predictor for individual radiosensitivity?

PURPOSE

To develop predictive tests for individual radiosensitivity of tumor patients.

METHODS AND MATERIALS

Acute skin reactions were clinically scored among 40 women after 46 Gy, given with 2 Gy fractions to breast and regional lymph nodes, adjuvant after surgery. The acute skin reactions were compared to the excretion of 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxo-dG) in urine, determined by high-performance liquid chromatography (HPLC) with electrochemical detector. Specimens of urine were collected before and during postoperative radiation treatment at given intervals. We compared a group of 9 patients with the most pronounced skin reactions with another group of 8 patients with almost no skin reactions at 46 Gy.

RESULTS

The level of 8-oxo-dG excreted in urine during 8 h was measured. After normalizing the excretion to irradiated volumes, dose per volume and excretion before irradiation, the 8-oxo-dG level in urine was significantly (p < 0.001) lower for the patients with pronounced skin reactions as compared to patients with minor skin reactions, at an accumulated dose of 12 Gy. In addition, the background level of 8-oxo-dG excreted before treatment started, was significantly (p = 0.043) lower for patients with minor skin reactions as compared to patients with pronounced skin reactions. The background level of 8-oxo-dG was corrected for body weight and normalized to BMI.

CONCLUSION

We suggest that the excretion of 8-oxo-dG into urine of breast cancer patients is a possible marker for acute radiosensitivity.