Ionizing radiation as a response-enhancing agent for CD95-mediated apoptosis

Narrative Review of Synergistics Effects of Combining Immunotherapy and Stereotactic Radiation Therapy

Stereotactic radiotherapy (SRT) has become an attractive treatment modality in full bloom in recent years by presenting itself as a safe, noninvasive alternative to surgery to control primary or secondary malignancies. Although the focus has been on local tumor control as the therapeutic goal of stereotactic radiotherapy, rare but intriguing observations of abscopal (or out-of-field) effects have highlighted the exciting possibility of activating antitumor immunity using high-dose radiation. Furthermore, immunotherapy has revolutionized the treatment of several types of cancers in recent years. However, resistance to immunotherapy often develops. These observations have led researchers to combine immunotherapy with SRT in an attempt to improve outcomes. The benefits of this combination would come from the stimulation and suppression of various immune pathways. Thus, in this review, we will first discuss the immunomodulation induced by SRT with the promising results of preclinical studies on the changes in the immune balance observed after SRT. Then, we will discuss the opportunities and risks of the combination of SRT and immunotherapy with the preclinical and clinical data available in the literature. Furthermore, we will see that many perspectives are conceivable to potentiate the synergistic effects of this combination with the need for prospective studies to confirm the encouraging data.

The future potential of Annona muricata L. extract and its bioactive compounds as radiation sensitizing agent: proposed mechanisms based on a systematic review

Despite technological advances in cancer treatment, especially in radiotherapy, many efforts are being made in improving cancer cell radio-sensitivity to increase therapeutic ratio and overcome cancer cell radio-resistance. In the present review, we evaluated the anticancer mechanism of Annona muricata L. (AM) leaves extract and its bioactive compounds such as annonaceous acetogenins, annomuricin, annonacin, or curcumin; and further correlated them with the potential of the mechanism to increase or to reduce cancer cells radio-sensitivity based on literature investigation. We see that AM has a promising future potential as a radio-sensitizer agent.

FAS and FASL variations in outcomes of tobacco- and alcohol-related head and neck squamous cell carcinoma patients

Radiotherapy and cisplatin lead to cell killing in head and neck squamous cell carcinoma patients, but adverse events and response to treatment are not the same in patients with similar clinicopathological aspects. The aim of this prospective study was to evaluate the roles of TP53 c.215G > C, FAS c.-671A > G, FAS c.-1378G > A, FASL c.-844 C > T, CASP3 c.-1191A > G, and CASP3 c.-182-247G > T single nucleotide variants in toxicity, response rate, and survival of cisplatin chemoradiation-treated head and neck squamous cell carcinoma patients. Genomic DNA was analyzed by polymerase chain reaction for genotyping. Differences between groups of patients were analyzed by chi-square test or Fisher's exact test, multiple logistic regression analysis, and Cox hazards model. One hundred nine patients with head and neck squamous cell carcinoma were enrolled in study. All patients were smokers and/or alcoholics. Patients with FAS c.-671GG genotype, FAS c.-671AG or GG genotype, and FASL c.-844CC genotype had 5.52 (95% confidence interval (CI): 1.42-21.43), 4.03 (95% CI: 1.51-10.79), and 5.77 (95% CI: 1.23-27.04) more chances of presenting chemoradiation-related anemia of grades 2-4, lymphopenia of grade 3 or 4, and ototoxicity of all grades, respectively, than those with the remaining genotypes. FAS c.-671GG genotype was also seen as an independent predictor of shorter event-free survival (hazard ratio (HR): 2.05; P = 0.007) and overall survival (HR: 1.83; P = 0.02) in our head and neck squamous cell carcinoma patients. These findings present, for the first time, preliminary evidence that inherited abnormalities in apoptosis pathway, related to FAS c.-671A > G and FASL c.-844 C > T single nucleotide variants, can alter toxicity and survival of tobacco- and alcohol-related head and neck squamous cell carcinoma patients homogeneously treated with cisplatin chemoradiation.

Ionizing Radiation Increases the Activity of Exosomal Secretory Pathway in MCF-7 Human Breast Cancer Cells: A Possible Way to Communicate Resistance against Radiotherapy

Radiation therapy, which applies high-energy rays, to eradicate tumor cells, is considered an essential therapy for the patients with breast cancer. Most tumor cells secrete exosomes, which are involved in cell-to-cell communication in tumor tissue and contribute therapeutic resistance and promote tumor aggressiveness. Here, we investigated the effect of clinically applicable doses of X-ray irradiation (2, 4, 6, 8, 10 Gy) on the dynamics of the exosomes' activity in MCF-7 breast cancer cells. Survival and apoptosis rate of cells against X-ray doses was examined using MTT and flow cytometry assays, respectively. Whereas, the levels of reactive oxygen species (ROS) in the X-ray-treated cells were detected by fluorometric method. The mRNA levels of vital genes involved in exosome biogenesis and secretion including Alix, Rab11, Rab27a, Rab27b, TSPA8, and CD63 were measured by real-time PCR. The protein level of CD63 was examined by Western blotting. Additionally, exosomes were characterized by monitoring acetylcholinesterase activity, transmission electron microscopy, size determination, and zeta potential. The result showed that in comparison with control group cell survival and the percentage of apoptotic cells as well as amount of ROS dose-dependently decreased and increased in irradiated cells respectively (p < 0.05). The expression level of genes including Alix, Rab27a, Rab27b, TSPA8, and CD63 as well as the protein level of CD63 upraised according to an increase in X-ray dose (p < 0.05). We found that concurrent with an increasing dose of X-ray, the acetylcholinesterase activity, size, and zeta-potential values of exosomes from irradiated cells increased (p < 0.05). Data suggest X-ray could activate exosome biogenesis and secretion in MCF-7 cells in a dose-dependent way, suggesting the therapeutic response of cells via ROS and exosome activity.

Long-lasting complete response status of advanced stage IV gall bladder cancer and colon cancer after combined treatment including autologous formalin-fixed tumor vaccine: two case reports

BACKGROUND

The prognosis of advanced (stage IV) cancer of the digestive organs is very poor. We have previously reported a case of advanced breast cancer with bone metastasis that was successfully treated with combined treatments including autologous formalin-fixed tumor vaccine (AFTV). Herein, we report the success of this approach in advanced stage IV (heavily metastasized) cases of gall bladder cancer and colon cancer.

CASE PRESENTATION

Case 1: A 61-year-old woman with stage IV gall bladder cancer (liver metastasis and lymph node metastasis) underwent surgery in May 2011, including partial resection of the liver. She was treated with AFTV as the first-line adjuvant therapy, followed by conventional chemotherapy. This patient is still alive without any recurrence, as confirmed with computed tomography, for more than 5 years. Case 2: A 64-year-old man with stage IV colon cancer (multiple para-aortic lymph node metastases and direct abdominal wall invasion) underwent non-curative surgery in May 2006. Following conventional chemotherapy, two courses of AFTV and radiation therapy were administered sequentially. This patient has had no recurrence for more than 5 years.

CONCLUSION

We report the success of combination therapy including AFTV in cases of liver-metastasized gall bladder cancer and abdominal wall-metastasized colon cancer. Both patients experienced long-lasting, complete remission. Therefore, combination therapies including AFTV should be considered in patients with advanced cancer of the digestive organs.

The paradox role of caspase cascade in ionizing radiation therapy

Radiotherapy alone or in combination with chemotherapy/surgery is widely used for treatment of cancers. It reduces tumor growth and prevents metastasis. While ionizing radiation activates caspase cascade resulted in apoptosis in cancer cells, it also stimulates tumor cell re-population that leads to reduce the effectiveness of the radiation therapy. This review describes the mechanisms for paradox role of caspase cascade in cancer therapy and discusses the logical and practical strategies for improvement the therapeutic index of radiotherapy through enhancement of radiosensitivity and decreasing the rate of tumor recurrence.

Cellular Pathways in Response to Ionizing Radiation and Their Targetability for Tumor Radiosensitization

During the last few decades, improvements in the planning and application of radiotherapy in combination with surgery and chemotherapy resulted in increased survival rates of tumor patients. However, the success of radiotherapy is impaired by two reasons: firstly, the radioresistance of tumor cells and, secondly, the radiation-induced damage of normal tissue cells located in the field of ionizing radiation. These limitations demand the development of drugs for either radiosensitization of tumor cells or radioprotection of normal tissue cells. In order to identify potential targets, a detailed understanding of the cellular pathways involved in radiation response is an absolute requirement. This review describes the most important pathways of radioresponse and several key target proteins for radiosensitization.

Radiation for Awakening the Dormant Immune System, a Promising Challenge to be Explored

Recent advances that have been made in our understanding of cancer biology and immunology show that infiltrated immune cells and cytokines in the tumor microenvironment may play different functions that appear tightly related to clinical outcomes. Strategies aimed at interfering with the cross-talk between microenvironment tumor cells and their cellular partners have been considered for the development of new immunotherapies. These novel therapies target different cell components of the tumor microenvironment and importantly, they may be coupled and boosted with classical treatments, such as radiotherapy. In this work, we try to summarize recent data on the microenvironment impact of radiation therapy, from pre-clinical research to the clinic, while taking into account that this new knowledge will probably translate into indication and objective of radiation therapy changes in the next future.

Radiation for Awakening the Dormant Immune System, a Promising Challenge to be Explored

Recent advances that have been made in our understanding of cancer biology and immunology show that infiltrated immune cells and cytokines in the tumor microenvironment may play different functions that appear tightly related to clinical outcomes. Strategies aimed at interfering with the cross-talk between microenvironment tumor cells and their cellular partners have been considered for the development of new immunotherapies. These novel therapies target different cell components of the tumor microenvironment and importantly, they may be coupled and boosted with classical treatments, such as radiotherapy. In this work, we try to summarize recent data on the microenvironment impact of radiation therapy, from pre-clinical research to the clinic, while taking into account that this new knowledge will probably translate into indication and objective of radiation therapy changes in the next future.

Eradication of breast cancer with bone metastasis by autologous formalin-fixed tumor vaccine (AFTV) combined with palliative radiation therapy and adjuvant chemotherapy: a case report

Skeletal metastasis of breast carcinoma is refractory to intensive chemo-radiation therapy and therefore is assumed impossible to cure. Here, we report an advanced case of breast cancer with vertebra-Th7 metastasis that showed complete response to combined treatments with formalin-fixed autologous tumor vaccine (AFTV), palliative radiation therapy with 36 Gy, and adjuvant chemotherapy with standardized CEF (cyclophosphamide, epirubicin, and 5FU), zoledronic acid, and aromatase inhibitors following mastectomy for the breast tumor. The patient has been disease-free for more than 4 years after the mammary surgery and remains well with no evidence of metastasis or local recurrence. Thus, a combination of AFTV, palliative radiation therapy, and adjuvant chemotherapy may be an effective treatment for this devastating disease.

Crosstalk between Fas and JNK determines lymphocyte apoptosis after ionizing radiation

Radiation simultaneously activate Fas and JNK pathway in lymphocytes but their precise interaction is not clearly understood. Activation of Fas pathway is required for radiation induced apoptosis, however induction of JNK pathway may or may not contribute in apoptosis. Here we report that Fas, Fas associated death domain and total JNK are activated in a dose- and time-dependent radiation exposure. A biphasic pattern of phospho-JNK was found at lower doses (1 and 2 Gy), however at higher doses of radiation phospho-JNK was continuously activated. Interestingly, Fas ligand expression remained biphasic at all the doses of radiation. Our results suggest that the Fas pathway is the major player in radiation-induced apoptosis, with JNK playing a contributory role. We also observed that Fas ligand expression by radiation is dependent on JNK activation. We also propose that radiation activates JNK pathway, but sustained activation is required for maximal induction of apoptosis at later times. Our findings define a mechanism for crosstalk between JNK and Fas pathway in radiation-induced apoptosis, which may lead to the development of new therapeutic strategies.

The convergence of radiation and immunogenic cell death signaling pathways

Ionizing radiation (IR) triggers programmed cell death in tumor cells through a variety of highly regulated processes. Radiation-induced tumor cell death has been studied extensively in vitro and is widely attributed to multiple distinct mechanisms, including apoptosis, necrosis, mitotic catastrophe (MC), autophagy, and senescence, which may occur concurrently. When considering tumor cell death in the context of an organism, an emerging body of evidence suggests there is a reciprocal relationship in which radiation stimulates the immune system, which in turn contributes to tumor cell kill. As a result, traditional measurements of radiation-induced tumor cell death, in vitro, fail to represent the extent of clinically observed responses, including reductions in loco-regional failure rates and improvements in metastases free and overall survival. Hence, understanding the immunological responses to the type of radiation-induced cell death is critical. In this review, the mechanisms of radiation-induced tumor cell death are described, with particular focus on immunogenic cell death (ICD). Strategies combining radiotherapy with specific chemotherapies or immunotherapies capable of inducing a repertoire of cancer specific immunogens might potentiate tumor control not only by enhancing cell kill but also through the induction of a successful anti-tumor vaccination that improves patient survival.

The tipping point for combination therapy: cancer vaccines with radiation, chemotherapy, or targeted small molecule inhibitors

Therapeutic cancer vaccines are a unique treatment modality in that they initiate a dynamic process of activating the host immune system, which can then be exploited by concurrent or subsequent therapies. The addition of immunotherapy to standard-of-care cancer therapies has shown evidence of efficacy in preclinical models and in the clinical setting. This review examines the preclinical and clinical interactions between vaccine-mediated tumor-specific immune responses and local radiation, systemic chemotherapy, or select small molecule inhibitors, as well as the potential synergy between these modalities.

Dcr3 inhibit p53-dependent apoptosis in gamma-irradiated lung cancer cells

PURPOSE

To identify genes responsible for the radiosensitivity, we investigated the role of the differential gene expression profiles by comparing radioresistant H1299 with radiosensitive H460 lung cancer cell lines.

MATERIALS AND METHODS

mRNA profiles of lung cancer cell lines were assessed using microarray, and subsequent validation was performed with qRT-PCR (Quantitative real time-polymerase chain reaction). The expression levels of differentially expressed genes were determined by Western blot and the radioresistance of lung cancer cell lines was measured by clonogenic assay.

RESULTS

From the differentially expressed apoptosis-related genes between H1299 and H460, we found Dcr3 (Decoy receptor 3, also known as TNFRSF6B; Tumour necrosis factor receptor super family member 6B) expression was significantly (P = 4.38 x 10(-7)) higher in H1299 cells than H460 cells. Moreover, the Dcr3 mRNA expression level in the radioresistant cell lines (H1299, A549, DLD1, MB231, MB157) was increased in comparison to the radiosensitive cell lines (ME180, Caski, U87MG, MCF7, H460). Overexpression of Dcr3 increased the survival rate of radiosensitive H460, MCF7, and U87MG cells, and knockdown of Dcr3 abolished the radioresistance of A549 cells. The survival rate of p53 (Tumour protein 53)-deficient H1299 after gamma-irradiation was not affected by the suppression of Dcr3 expression. However, when we introduced p53 into H1299 cells, siDcr3 (siRNA of Dcr3) suppressed the radioresistance of H1299 cells by inducing p53-dependent Fas (Fas receptor, also known as TNFRSF6; Tumour necrosis factor receptor super family member 6)-mediated apoptosis pathway.

CONCLUSION

Characterisation of gene expression profiles in two lung cancer cell lines revealed that Dcr3 expression and p53-dependent apoptosis signalling pathway regulate cellular response to ionising radiation.

Intratumoral dendritic cells and chemoradiation for the treatment of murine squamous cell carcinoma

Dendritic cells are potent antigen-presenting cells that have been shown to have significant antitumor effects in vitro and in vivo. However, the therapeutic efficacy of dendritic cells as an immunotherapeutic treatment has been limited by both immunologic tolerance and active immunosuppression in the tumor microenvironment. To address this problem, we examined the ability of concurrent systemic chemotherapy and local, fractionated radiation to augment intratumoral dendritic cell injections in a mouse model of squamous cell carcinoma. Intratumoral injections of dendritic cells alone did not have a significant antitumor effect in mice with squamous cell carcinoma flank tumors, but the addition of chemoradiation resulted in significant tumor regression. Concurrent chemoradiation alone resulted in slower tumor growth, but no complete tumor regressions. The combination of chemoradiation and intratumoral dendritic cell injections resulted in improved survival and complete tumor regression in 30% mice. Mice with complete tumor regression were partially resistant to the repeat challenge with relevant tumor 60 days after treatment. These findings were partially dependent on the presence of CD4 T cells, CD8 T cells, and natural killer cells. Chemoradiation may augment intratumoral dendritic cell injections through increased intratumoral apoptosis and decreased intratumoral regulatory T cells. This work suggests a possible role for the use of intratumoral dendritic cell therapy with more traditional chemoradiation strategies.

Multiple factors conferring high radioresistance in insect Sf9 cells

Sf9, a lepidopteran cell line isolated from the fall armyworm, Spodoptera frugiperda, was shown to be significantly more resistant to growth inhibition and apoptosis induction effects of x-ray irradiation than several human cell lines of different origins. The single-cell electrophoresis technique revealed that Sf9 cells showed lower x-ray irradiation-induced DNA damage as well as better efficiency at repairing these damages. In addition, Sf9 cells were lower in both background and x-ray irradiation-induced intracellular oxidative stress, in which the higher intracellular level of reduced glutathione seemed to play a major role. The significance of oxidative stress in determining the radioresistance of Sf9 cells was confirmed by their being more resistant to hydrogen peroxide while equally susceptible to other non-reactive oxygen species of N-nitroso alkylating agents when compared with a human cell line. Although the Sf9 and human cell lines were equally susceptible to the lethal effects of N-nitroso alkylating agents, the components of DNA damage-induced and the repair enzymes involved significantly differ. This phenomenon is also discussed in this report.

Enhanced CD95-mediated apoptosis contributes to radiation hypersensitivity of NBS lymphoblasts

The molecular causes for enhanced radiosensitivity of Nijmegen Breakage Syndrome cells are unclear, especially as repair of DNA damage is hardly impeded in these cells. We clearly demonstrate that radiation hypersensitivity is accompanied by enhanced gamma-radiation-induced apoptosis in NBS1 deficient lymphoblastoid cell lines. Differences in the apoptotic behavior of NBS1 (-/-) and NBS1 (+/-) cells are not due to an altered p53 stabilization or phosphorylation in NBS1 (-/-) cells. gamma-radiation-induced caspase-8 activity is increased and visualization of CD95 clustering by laser scanning microscopy shows a significant higher activation of the death receptor in NBS1 (-/-) cells. Further investigation of the molecular mechanisms reveals a role for reactive oxygen species-triggered activation of CD95. These results demonstrate that NBS1 suppresses the CD95 death receptor-dependent apoptotic pathway after gamma-irradiation and evidence is given that this is achieved by regulation of the PI3-K/AKT survival pathway.

CD154 induces p73 to overcome the resistance to apoptosis of chronic lymphocytic leukemia cells lacking functional p53

Intravenous infusion of autologous chronic lymphocytic leukemia (CLL) cells transduced with an adenovirus encoding CD40-ligand (CD154) caused rapid reductions in leukemia-cell counts and lymphnode size. We hypothesized that CD40-ligation via CD154 sensitized CLL cells to death-receptor-mediated apoptosis. We found that CD154-expressing cells induced expression of CD95 and the BH3-interacting-domain death agonist (Bid) in CLL, regardless of whether the leukemia cells had functional p53. Such treatment also induced p73, a p53-related transcription factor regulated by c-Abl kinase, and enhanced the sensitivity to fludarabine (F-ara-A) of CLL cells lacking functional p53. Transduction of CLL cells with an adenovirus encoding p73 also induced Bid and CD95 and enhanced the sensitivity to F-ara-A of p53-deficient CLL cells. However, inhibition of c-Abl with imatinib suppressed CD154-induced expression of p73, p73-induced expression of Bid and CD95, and blocked the sensitization of p53-deficient CLL cells to CD95-mediated or F-ara-A-induced apoptosis. Conversely, CLL cells transduced with an imatinib-resistant c-Abl mutant could be induced by CD154 to express p73 and Bid even when treated with imatinib. These results indicate that CD154 can sensitize leukemia cells to apoptosis via the c-Abl-dependent activation of p73 and mitigate the resistance of p53-deficient CLL cells to anticancer drug therapy.

Combining radiotherapy and immunotherapy: a revived partnership

Ionizing radiation therapy (RT) is an important local modality for the treatment of cancer. The current rationale for its use is based largely on the ability of RT to kill the cancer cells by a direct cytotoxic effect. Nevertheless, considerable evidence indicates that RT effects extend beyond the mere elimination of the more radiosensitive fraction of cancer cells present within a tumor at the time of radiation exposure. For instance, a large body of evidence is accumulating on the ability of RT to modify the tumor microenvironment and generate inflammation. This might have far-reaching consequences regarding the response of a patient to treatment, especially if radiation-induced tumor cell kill were to translate into the generation of effective antitumor immunity. Although much remains to be learned about how radiation can impact tumor immunogenicity, data from preclinical studies provide the proof of principle that different immunotherapeutic strategies can be combined with RT to enhance antitumor effects. Conversely, RT could be a useful tool to combine with immunotherapy. This article will briefly summarize what is known about the impact of RT on tumor immunity, including tumor-associated antigens, antigen-presenting cells, and effector mechanisms. In addition, the experimental evidence supporting the contention that RT can be used as a tool to induce antitumor immunity is discussed, and a new approach to radioimmunotherapy of cancer is proposed.

Involvement of p53 and Fas/CD95 in murine neural progenitor cell response to ionizing irradiation

We investigated the role of tumor suppressor p53 and Fas (CD95/APO-1), a member of the tumor necrosis factor receptor family, in neural progenitors response to gamma-irradiation exposure. Telencephalic cells were obtained from wild-type C57Bl/6, or p53-/- or fas-/-, 15-day-old mouse embryos. They were cultured in conditions allowing neural progenitors to form proliferating clusters (neurospheres). A 2 Gy gamma-irradiation induced a G1 cell cycle arrest and triggered apoptosis in wild-type neural progenitor cultures in correlation with an enhanced expression of p53 and of its downstream target p21(WAF1), both of them acquiring a nuclear localization. These effects did not occur in p53-/- neural progenitors demonstrating the central role played by p53 in their response to ionizing radiation. Furthermore, the monoclonal antibody Jo2 directed against Fas induced apoptosis of wild type but not of fas-/- neural progenitors, indicating the existence of a functional Fas signaling pathway in neural progenitors. Ionizing radiation induced an increase of Fas membrane expression related to a p53-dependent increase of fas mRNA expression in wild-type neural progenitors. Moreover, fas-/- neural progenitors exhibited delayed radiation-induced apoptosis compared to wild-type cells. Therefore, these findings establish a role for Fas/CD95 related to p53 in the response of neural progenitors to gamma-radiation exposure. Similar mechanisms could be triggered in neural progenitors in case of different stresses during brain development or in the course of various diseases affecting the adult brain.

X-irradiation to human malignant glioma cells enhances the cytotoxicity of autologous killer lymphocytes under specific conditions

PURPOSE

To clarify the effect of combining x-irradiation and human killer lymphocytes against autologous malignant glioma cells, we analyzed not only the alteration of surface antigen expression in irradiated tumor cells, but also the cytotoxic effects of human killer lymphocytes on the autologous tumor cells with and without x-irradiation.

METHODS AND MATERIALS

Six malignant glioma cell-lines (MG 1-6) established from each patient with a malignant glioma in our institute, and U87MG, were used as materials. They were irradiated by 0-50 Gy of X-rays, and the alternations of their human histocompatability leukocyte antigen (HLA), HLA-ABC, HLA-DR, -DP, -DQ, and FAS expressions were examined. Then, three sets of autologous natural killer (NK) cells, and autologous tumor-specific T lymphocytes (ATTL) were induced from the peripheral blood mononuclear cells (PBMCs) of three patients, and in vitro cytotoxic effects of these killer cells on the irradiated autologous tumor cells were analyzed.

RESULTS

Irradiation-enhanced HLA-DR, -DP, -DQ, and FAS expression in glioma cell lines with low p53 expression. However, there was no correlation between HLA-ABC expression and X-ray dose. After irradiation of the tumor cells, cytotoxicity was enhanced in four of six effectors; in particular, it was significantly elevated in two killer lymphocytes. It was speculated that the enhancing effect was influenced not only by the p53 status of the tumor, but also by the types of killer lymphocytes; the alteration of cytotoxicity in NK cells on irradiated tumor cells may be compensatory for alteration in ATTLs.

CONCLUSION

It was indicated that irradiation of malignant tumor cells enhanced killer cell-mediated cytotoxicity in autologous models under specific conditions. These basic data should contribute to clinical trials using local radiotherapy and systemic adoptive immunotherapy with killer lymphocytes.

Perillyl alcohol as a radio-/chemosensitizer in malignant glioma

The prognosis for patients with malignant glioma has not significantly changed in two decades, despite advances in surgery, radiation, and chemotherapy, emphasizing the growing need for novel approaches to glioma therapy. Perillyl alcohol (POH) is a naturally occurring monoterpene that has been shown to possess chemotherapeutic as well as chemopreventive activity in animal tumor models and is currently in Phase I and Phase II clinical trials. In the present study, we have demonstrated that POH is an effective radiosensitizer at clinically relevant doses of radiation using established glioma cell lines. POH caused a transient arrest in the G2/M phase of the cell cycle and induced apoptosis in glioma cells. POH treatment sensitized glioma cells to Fas-mediated apoptosis, which was further augmented in the presence of ionizing radiation and abrogated in the presence of antagonistic antibody. POH-induced radiosensitization was partially inhibited in glioma cells expressing dominant negative Fas-associated death domain and completely inhibited in glioma cells overexpressing the cytokine response modifier A. In addition, POH treatment resulted in a dose-dependent sensitization to cisplatin and doxorubicin induced cytotoxicity in glioma cells, highlighting its usefulness as a potent radio/chemosensitizer in the treatment of malignant glioma.

Transcriptional response of lymphoblastoid cells to ionizing radiation

The effects of ionizing radiation (IR) on the temporal transcriptional response of lymphoblastoid cells were investigated in this study. We used oligonucleotide microarrays to assess mRNA levels of genes in lymphoblastoid cells at various time points within 24 h following gamma-irradiation. We identified 319 and 816 IR-responsive genes following 3 Gy and 10 Gy of IR exposure, respectively, with 126 genes in common between the two doses. A high percentage of IR-responsive genes are involved in the control of cell cycle, cell death, DNA repair, DNA metabolism, and RNA processing. We determined the temporal expression profiles of the IR-responsive genes and assessed effects of IR dose on this temporal pattern of expression. By combining dose-response data with temporal profiles of expression, we have identified sets of coordinately responding genes. Through a genomic approach, we characterized a set of genes that are implicated in cellular adaptation to IR stress. These findings will allow a better understanding of complex processes such as radiation-induced carcinogenesis and the development of biomarkers for radiation exposure.

1alpha,25-dihydroxyvitamin D(3) (calcitriol) and its analogue, 19-nor-1alpha,25(OH)(2)D(2), potentiate the effects of ionising radiation on human prostate cancer cells

Radiotherapy with external beam radiation or brachytherapy is an established therapeutic modality for prostate cancer. Approximately 30% of patients with localised prostate cancer relapse at the irradiated site. Secondary effects of ionising radiation (IR), for example, bowel and bladder complications, are common. Thus, the search for biological response modifiers that could potentiate the therapeutic effects of radiation and limit the occurrence of serious side effects is an important task in prostate cancer therapy. 1alpha,25-Dihydroxyvitamin D(3) (calcitriol), the active metabolite of vitamin D, and its analogues are under investigation for the treatment of several malignancies including prostate cancer. Here, we report that 1alpha,25-dihydroxyvitamin D(3) and its less calcaemic analogue 19-nor-1alpha,25-(OH)(2)D(2) (Zemplar) act synergistically with IR to inhibit the growth of the human prostate cancer cells in vitro. 1alpha,25-dihydroxyvitamin D(3) potentiated IR-induced apoptosis of LNCaP cells, and nanomolar doses of 1alpha,25-dihydroxyvitamin D(3) and 19-nor-1alpha,25-(OH)(2)D(2) showed synergistic inhibition of growth of LNCaP cells at radiobiologically relevant doses of IR (1-2 Gy). At higher doses of IR, the combination of 1alpha,25-dihydroxyvitamin D(3) and IR or 19-nor-1alpha,25-(OH)(2)D(2) and IR resulted in moderate antagonism. The synergistic effect at radiobiologically relevant doses of radiation suggests that a combination of 1alpha,25-dihydroxyvitamin D(3) or 19-nor-1alpha,25-(OH)(2)D(2) with IR could permit a reduction in the dose of radiation given clinically and thus potentially reduce treatment-related morbidity.

Irradiation of tumor cells up-regulates Fas and enhances CTL lytic activity and CTL adoptive immunotherapy

CD8(+) CTL play important roles against malignancy in both active and passive immunotherapy. Nonetheless, the success of antitumor CTL responses may be improved by additional therapeutic modalities. Radiotherapy, which has a long-standing use in treating neoplastic disease, has been found to induce unique biologic alterations in cancer cells affecting Fas gene expression, which, consequently, may influence the overall lytic efficiency of CTL. Here, in a mouse adenocarcinoma cell model, we examined whether exposure of these tumor cells to sublethal doses of irradiation 1) enhances Fas expression, leading to more efficient CTL killing via Fas-dependent mechanisms in vitro; and 2) improves antitumor activity in vivo by adoptive transfer of these Ag-specific CTL. Treatment of carcinoembryonic Ag-expressing MC38 adenocarcinoma cells with irradiation (20 Gy) in vitro enhanced Fas expression at molecular, phenotypic, and functional levels. Furthermore, irradiation sensitized these targets to Ag-specific CTL killing via the Fas/Fas ligand pathway. We examined the effect of localized irradiation of s.c. growing tumors on the efficiency of CTL adoptive immunotherapy. Irradiation caused up-regulation of Fas by these tumor cells in situ, based on immunohistochemistry. Moreover, localized irradiation of the tumor significantly potentiated tumor rejection by these carcinoembryonic Ag-specific CTL. Overall, these results showed for the first time that 1) regulation of the Fas pathway in tumor cells by irradiation plays an important role in their sensitization to Ag-specific CTL; and 2) a combination regimen of tumor-targeted irradiation and CTL promotes more effective antitumor responses in vivo, which may have implications for the combination of immunotherapy and radiation therapy.

The role of p53 in determining sensitivity to radiotherapy

Ionizing radiation (IR) has proven to be a powerful medical treatment in the fight against cancer. Rational and effective use of its killing power depends on understanding IR-mediated responses at the molecular, cellular and tissue levels. Tumour cells frequently acquire defects in the molecular regulatory mechanisms of the response to IR, which sensitizes them to radiation therapy. One of the key molecules involved in a cell's response to IR is p53. Understanding these mechanisms indicates new rational approaches to improving cancer treatment by IR.