Low-Dose Fractionated Radiation Potentiates the Effects of Cisplatin Independent of the Hyper-Radiation Sensitivity in Human Lung Cancer Cells

Strategies for overcoming tumour resistance to immunotherapy: harnessing the power of radiation therapy

Immune checkpoint inhibitors (ICI) have revolutionized cancer treatment; yet their efficacy remains variable across patients. This review delves into the intricate interplay of tumour characteristics contributing to resistance against ICI therapy and suggests that combining with radiotherapy holds promise. Radiation, known for its ability to trigger immunogenic cell death and foster an in situ vaccination effect, may counteract these resistance mechanisms, enhancing ICI response and patient outcomes. However, particularly when delivered at high-dose, it may trigger immunosuppressive mechanism and consequent side-effects. Notably, low-dose radiotherapy (LDRT), with its capacity for tumour reprogramming and reduced side effects, offers the potential for widespread application. Preclinical and clinical studies have shown encouraging results in this regard.

Diallyl trisulfide induces pyroptosis and impairs lung CSC-like properties by activating the ROS/Caspase 1 signaling pathway

Lung cancer stem cells (CSCs) drive continuous cancer growth and metastatic dissemination; thus, there is an urgent requirement to acquire effective therapeutic strategies for targeting lung CSCs. Diallyl trisulfide (DATS), a garlic organosulfide, possesses suppressive potential in lung cancer; however, its underlying mechanism is still unclear. In this study, we identified DATS as a pyroptosis inducer in lung cancer cells. DATS-treated A549 and H460 cells exhibited pyroptotic cell death, with characteristic large bubbles appearing on their plasma membrane and LDH release. DATS induced cell death, arrested the cell cycle at the G2/M phase, and inhibited colony formation in lung cancer cells. Meanwhile, we found that DATS significantly suppressed the malignant features by impairing lung CSC-like properties, including sphere formation ability, CD133 positive cell number, and lung CSCs marker expression. Mechanistically, DATS induced cell pyroptosis via increasing the expression of NLRP3, ASC, Pro Caspase 1, Cleaved Caspase 1, GSDMD, GSDMD-N, and IL-1β. The verification experiments showed that the effects of DATS on pyroptosis and lung CSC-like properties were weakened after Caspase 1 inhibitor VX-765 treatment, indicating that DATS activated NLRP3 inflammasome-mediated pyroptosis by targeting Caspase 1 in lung cancer cells. Moreover, DATS increased ROS overproduction and mitochondrial dysfunction, which contributed to DATS-induced pyroptosis of lung cancer cells. NAC treatment reversed the effects of DATS on pyroptosis and CSC-like properties. In vivo experiment further confirmed that DATS restrained tumor growth. Together, our results suggest that DATS promotes pyroptosis and impairs lung CSC-like properties by activating ROS/Caspase 1 signaling pathway, thereby retarding lung cancer progression.

Exploring low-dose radiotherapy to overcome radio-immunotherapy resistance

Immune checkpoint inhibitors (ICIs) have revolutionized the current treatment landscape for cancer, yet the response rates of ICIs remain unmet. Synergistic with immunotherapy, low-dose radiotherapy (LDRT) has been demonstrated to activate anti-tumor immunity - a transition from traditional radiation therapy geared toward local radical treatment to a type of immunological adjuvant. As such, studies utilizing LDRT to enhance the efficacy of immunotherapy have been increasing preclinically and clinically. This paper reviews the recent strategies of using LDRT to overcome the resistance of ICIs, as well as providing potential opportunities in cancer treatment. Despite the potential of LDRT in immunotherapy is recognized, the mechanisms behind this form of treatment remain largely elusive. Thus, we reviewed history, mechanisms and challenges associated with this form of treatment, as well as different modes of its application, to provide relatively accurate practice standards for LDRT as a sensitizing treatment when combined with immunotherapy or radio-immunotherapy.

Opportunities and challenges of low-dose radiation to enable immunotherapy efficacy

Therapeutic monoclonal antibodies blocking different immune checkpoints, have demonstrated efficacy against a wide variety of solid tumors. The exclusion or absence of lymphocytes within the tumor microenvironment (TME) is one of the main resistance mechanisms to immune checkpoint inhibitor (ICI)-based therapies. Therefore, there is a growing interest in identifying novel approaches to promote T cell infiltration on immune-deserted (cold) and immune-excluded tumors to turn them into inflamed (hot) tumors. Here, we provide a comprehensive overview of the recently published studies showing the potential of low-dose radiation (LDRT) to reprogram the TME to allow and promote T-cell infiltration and thus, improve currently approved ICI-based therapies.

Natural Baicalein-Rich Fraction as Radiosensitizer in Combination with Bismuth Oxide Nanoparticles and Cisplatin for Clinical Radiotherapy

Purpose

Methods

Results

Conclusion

Clinical Studies on Ultrafractionated Chemoradiation: A Systematic Review

Aim

The efficacy of low-dose fractionated radiotherapy (LDFRT) and chemotherapy (CHT) combination has large preclinical but little clinical evidence. Therefore, the aim of this review was to collect and analyze the clinical results of LDRT plus concurrent CHT in patients with advanced cancers.

Methods

A systematic literature search was conducted on PubMed using the PRISMA methodology. Only studies based on the combination of LDFRT (< 1 Gy/fraction) and CHT were included. Endpoints of the analysis were tumor response, toxicity, and overall survival, with particular focus on any differences between LDFRT-CHT and CHT alone.

Results

Twelve studies (307 patients) fulfilled the selection criteria and were included in this review. Two studies were retrospective, one was a prospective pilot trial, six were phase II studies, two were phase I trials, and one was a phase I/II open label study. No randomized controlled trials were found. Seven out of eight studies comparing clinical response showed higher rates after LDFRT-CHT compared to CHT alone. Three out of four studies comparing survival reported improved results after combined treatment. Three studies compared toxicity of CHT and LDFRT plus CHT, and all of them reported similar adverse events rates. In most cases, toxicity was manageable with only three likely LDFRT-unrelated fatal events (1%), all recorded in the same series on LDFRT plus temozolomide in glioblastoma multiforme patients.

Conclusion

None of the analyzed studies provided level I evidence on the clinical impact of LDFRT plus CHT. However, it should be noted that, apart from two small series of breast cancers, all studies reported improved therapeutic outcomes and similar tolerability compared to CHT alone.

Systematic Review Registration

www.crd.york.ac.uk/prospero/, identifier CRD42020206639.

Variation of 4 MV X-ray dose rate in fractionated irradiation strongly impacts biological endothelial cell response in vitro

PURPOSE

Even though X-ray beams are widely used in medical diagnosis or radiotherapy, the comparisons of their dose rates are scarce. We have recently demonstrated in vitro (clonogenic assay, cell viability, cell cycle, senescence) and in vivo (weight follow-up of animals and bordering epithelium staining of lesion), that for a single dose of irradiation, the relative biological effectiveness (RBE) deviates from 1 (up to twofold greater severe damage at the highest dose rate depending on the assay) when increasing the dose rate of high energy X-ray beams.

MATERIAL AND METHODS

To further investigate the impact of the dose rate on RBE, in this study, we performed in vitro fractionated irradiations by using the same two dose rates (0.63 and 2.5 Gy.min^-1) of high-energy X-rays (both at 4 MV) on normal endothelial cells (HUVECs). We investigated the viability/mortality, characterized radiation-induced senescence by using flow cytometry and measured gene analysis deregulations on custom arrays.

RESULTS

The overall results enlighten that, in fractionated irradiations when varying the dose rate of high-energy X-rays, the RBE of photons deviates from 1 (up to 2.86 for viability/mortality experiments performed 21 days postirradiation).

CONCLUSION

These results strengthen the interest of multiparametric analysis approaches in providing an accurate evaluation of the outcomes of irradiated cells in support of clonogenic assays, especially when such assays are not feasible.

Targeting radiation-induced upstream stimulatory factor-1 by histone deacetylase inhibitors to reverse radioresistance in prostate cancer

BACKGROUND

Ionizing radiation (IR) is a standard modality for the management of solid tumors. Apart from its killing effects, IR can induce pro-survival factors leading to radioresistance of cancer. Mechanistic understanding of radiation resistance is warranted to overcome the pro-survival effects of IR.

AIM

The aim of this study was to investigate the role of upstream stimulatory factor-1 (USF-1) in the induction of radioresistance in prostate cancer and its targeting by histone deacetylase (HDAC) inhibitors to reverse resistance.

METHODS AND RESULTS

This study reports here that USF-1 is a marker for radioresistance in PC-3 cells. Using protein-DNA array analysis, it was documented that DNA binding activity of USF-1 was elevated following IR in PC-3 cells. Novel HDAC inhibitors downregulated USF-1 binding either alone or in combination with IR. A 5 Gy dose of IR induced the expression of target genes of USF-1 (human telomerase reverse transcriptase [hTERT], IGF2R, CyclinB1, and Cdk1), however, HDAC inhibitors alone or in combination with IR reduced their expression as measured by real time RT PCR analysis. Furthermore, immunofluorescence analysis revealed that while USF-1 localized primarily in the nucleus following IR, it localized in the cytoplasm when treated with HDAC inhibitors/combination. Maximum effects of modulation of USF-1 expression (overexpression or suppression) were observed on hTERT activity as determined by dual-luciferase reporter assay. To further confirm the role of USF-1 in radioresistance, cell growth was analyzed using the real-time cell electronic sensing (RT-CES) system. This study found that USF-1-transfected cells proliferated faster than the vector-transfected cells with or without treatments with HDAC inhibitors/IR/combination. Colony forming assay also confirmed that USF-1 overexpression led to increased survival following IR. Importantly, colony-forming assay demonstrated that HDAC inhibitors reversed the radioresistance in both PC-3 and DU-145 cells.

CONCLUSION

These studies demonstrate that HDAC inhibitors reverse the radioresistance in prostate cancer through down-modulation of USF-1-mediated transactivation of target genes involved in cell proliferation and cell cycle.

DUOX2, a New Biomarker for Disseminated Gastric Cancer's Response to Low Dose Radiation in Mice

Treatment options are rather limited for gastrointestinal cancer patients whose disease has disseminated into the intra-abdominal cavity. Here, we designed pre-clinical studies to evaluate the potential application of chemopotentiation by Low Dose Fractionated Radiation Therapy (LDFRT) for disseminated gastric cancer and evaluate the role of a likely biomarker, Dual Oxidase 2 (DUOX2). Nude mice were injected orthotopically with human gastric cancer cells expressing endogenous or reduced levels of DUOX2 and randomly assigned to four treatment groups: 1; vehicle alone, 2; modified regimen of docetaxel, cisplatin and 5'-fluorouracil (mDCF) for three consecutive days, 3; Low Dose- Whole Abdomen Radiation Therapy (LD-WART) (5 fractions of 0.15 Gy in three days), 4; mDCF and LD-WART. The combined regimen increased the odds of preventing cancer dissemination (mDCF + LD-WART OR = 4.16; 80% CI = 1.0, 17.29) in the DUOX2 positive tumors, while tumors expressing lower DUOX2 levels were more responsive to mDCF alone with no added benefit from LD-WART. The molecular mechanisms underlying DUOX2 effects in response to the combined regimen include NF-κB upregulation. These data are particularly important since our study indicates that about 33% of human stomach adenocarcinoma do not express DUOX2. DUOX2 thus seems a likely biomarker for potential clinical application of chemopotentiation by LD-WART.

SMAC Mimetic/IAP Inhibitor Birinapant Enhances Radiosensitivity of Glioblastoma Multiforme

Birinapant is a novel SMAC peptidomimetic molecule in clinical development. It suppresses the inhibitor of apoptosis proteins (IAPs) and promotes cytochrome-C/Apaf-1/caspase-9 activation to induce effective apoptosis. Because IAP inhibition has been shown to enhance the sensitivity of cancer cells to radiation, we investigated the role of birinapant in radiosensitization of glioblastoma cells in vitro and in vivo. Two glioblastoma cell lines, U-251 and U-87, were used to analyze radiosensitization in vitro with 7-AAD cell death/apoptosis and clonogenic assays. Subcutaneous flank (U-251 and U-87) and intracranial orthotopic (U-251) xenografts in nude mice were used to evaluate radiosensitization in vivo. TNF-α levels in media and serum were measured using electrochemiluminescence. Radiosensitization in vitro was more prominent for U-251 cells than for U-87 cells. In vivo, in both tumor models, significant tumor growth delay was observed with combination treatment compared to radiation alone. There was a survival benefit with combination treatment in the orthotopic U-251 model. TNF-α levels in media correlated directly with radiation dose in vitro. These findings show that birinapant can enhance the radiosensitivity of glioblastoma cell lines in cell-based assays and tumor models via radiation-induced TNF-α. Further study into the use of birinapant with radiation therapy is warranted.

High-dose irradiation in combination with non-ablative low-dose radiation to treat metastatic disease after progression on immunotherapy: Results of a phase II trial

AIM

To report early findings from a phase II trial of high-dose radiotherapy (HD-RT) with or without low-dose RT (LD-RT) for metastatic cancer.

METHODS

Eligible patients had metastatic disease that progressed on immunotherapy within 6 months. Patients were given either HD-RT (20-70 Gy total; 3-12.5 Gy/f), or HD-RT + LD-RT (0.5-2 Gy/f up to 1-10 Gy total) to separate lesions, with continued immunotherapy. Radiographic response was assessed per RECIST 1.1 and Immune-Related Response Criteria (irRC). Primary endpoints: (1) 4-month disease control (DCR, complete/partial response [CR/PR] or stable disease [SD]) or an overall response (ORR, CR/PR) at any point in ≥10% of patients, per RECIST 1.1; (2) dose-limiting toxicity within 3 months not exceeding 30%. Secondary endpoint was lesion-specific response.

RESULTS

Seventy-four patients (NSCLC, n = 38; melanoma n = 21) were analyzed (39 HD-RT and 35 HD-RT + LD-RT). The median follow-up time was 13.6 months. The primary endpoint was met for 72 evaluable patients, with a 4-month DCR of 42% (47% [16/34] vs. 37% [14/38] in HD-RT + LD-RT vs. HD-RT, P = 0.38), and 19% ORR at any time (26% [9/34] vs. 13% [5/38] in HD-RT + LD-RT vs. HD-RT, P = 0.27). Three patients had toxicity ≥grade 3. LD-RT lesion response (53%) was improved compared to nonirradiated lesions in HD-RT + LD-RT (23%, P = 0.002) and HD-RT (11%, P < 0.001). T- and NK cell infiltration was enhanced in lesions treated with LD-RT.

CONCLUSIONS

HD-RT plus LD-RT safely improved lesion-specific response in patients with immune resistant solid tumors by promoting infiltration of effector immune cells into the tumor microenvironment.

The Role and Mechanism of ATM-Mediated Autophagy in the Transition From Hyper-Radiosensitivity to Induced Radioresistance in Lung Cancer Under Low-Dose Radiation

Objective: This study aimed to investigate the effect of ataxia telangiectasia mutated (ATM)–mediated autophagy on the radiosensitivity of lung cancer cells under low-dose radiation and to further investigate the role of ATM and its specific mechanism in the transition from hyper-radiosensitivity (HRS) to induced radioresistance (IRR).

Methods: The changes in the HRS/IRR phenomenon in A549 and H460 cells were verified by colony formation assay. Changes to ATM phosphorylation and cell autophagy in A549 and H460 cells under different low doses of radiation were examined by western blot, polymerase chain reaction (PCR), and electron microscopy. ATM expression was knocked down by short interfering RNA (siRNA) transfection, and ATM-regulated molecules related to autophagy pathways were screened by transcriptome sequencing analysis. The detection results were verified by PCR and western blot. The differential metabolites were screened by transcriptome sequencing and verified by colony formation assay and western blot. The nude mouse xenograft model was used to verify the results of the cell experiments.

Results: (1) A549 cells with high expression of ATM showed positive HRS/IRR, whereas H460 cells with low expression of ATM showed negative HRS/IRR. After the expression of ATM decreased, the HRS phenomenon in A549 cells increased, and the radiosensitivity of H460 cells also increased. This phenomenon was associated with the increase in the autophagy-related molecules phosphorylated c-Jun N-terminal kinase (p-JNK) and autophagy/Beclin 1 regulator 1 (AMBRA1). (2) DL-Norvaline, a product of carbon metabolism in cells, inhibited autophagy in A549 cells under low-dose radiation. DL-Norvaline increased the expression levels of ATM, JNK, and AMBRA1 in A549 cells. (3) Mouse experiments confirmed the regulatory role of ATM in autophagy and metabolism and its function in HRS/IRR.

Conclusion: ATM may influence autophagy through p-JNK and AMBRA1 to participate in the regulation of the HRS/IRR phenomenon. Autophagy interacts with the cellular carbon metabolite DL-Norvaline to participate in regulating the low-dose radiosensitivity of cells.

Effect of Piperine in Combination with Gamma Radiation on A549 Cells

Background Lung cancer is a major constrain that increases mortality globally. Radiotherapy is one of the treatment modalities against lung cancer. A high dose of targeted radiation is required to achieve the treatment efficacy of cell killing. After radiotherapy, eventual tumor progression and therapy resistance are still a consequence of patient who undertakes nonsurgical radiation therapy. Piperine, a plant alkaloid, has been known to enhance the action of the anticancer drugs in various drug-resistant cancer cells. The aim of the current in vitro study was to study the effect of piperine on radiosensitizing property against A549 cells.

Methods In vitro radiosensitizing activity of piperine was elucidated on A549 cells using MTT (3-(4, 5-dimethylthiazol-2-yl)-25-diphenyltetrazolium bromide) assay. CompuSyn analysis was used to compute the combination index values to analyze the combinatory effect of piperine and radiation

Results and Conclusion We observed that piperine increased tumor cell killing in combination with the γ-radiation in vitro. However, further studies are warranted to understand the molecular mechanism of the radiosensitizing action of piperine.

Chemopotentiating effects of low-dose fractionated radiation on cisplatin and paclitaxel in cervix cancer cell lines and normal fibroblasts from patients with cervix cancer

The aim of the present study was to compare the effects (assessed by clonogenic survival and γH2AX foci assays) of low-dose fractionated radiation LDFR (4 × 0.125 Gy, 4 × 0.25 Gy and 4 × 0.5 Gy) versus single radiation doses (0.5 Gy, 1 Gy and 2 Gy) on cisplatin and paclitaxel in HRS-negative cervix cancer cell lines SiHa and CaSki to see if the effects of LDFR can emerge in cells that not present low-dose hyper-radiosensitivity (HRS) phenomenon. Additionally, we report the effects in normal fibroblasts (HRS-negative and HRS-positive) from two patients with cervix cancer to see if the chemopotentiating effects of LDFR also apply to normal cells. LDFR (4 × 0.125 Gy, 4 × 0.25 Gy and 4 × 0.5 Gy) as well as single doses (0.5 Gy, 1 Gy and 2 Gy) enhanced cytotoxicity of cisplatin and paclitaxel in all the cell lines. Cisplatin-potentiating effects were maximum with LDFR 4 × 0.5 Gy, and were two-fold greater than those with a single dose of 2 Gy in SiHa, CaSki and HFIB2 cells. Paclitaxel-enhancing effects were also maximum with LDFR 4 × 0.5 Gy, however only in HRS-positive HFIB2 fibroblasts were significantly greater than those with a single dose of 2 Gy. The results demonstrate that LDFR may enhance the effects of cisplatin and paclitaxel in SiHa and CaSki cells, although they lack HRS phenomenon, and show that the magnitude of the potentiating effects of LDFR depends on cytostatic type and the size of low doses. In normal fibroblasts the chemopotentiating effects of LDFR seem to depend on HRS status. In conclusion, the unique enhancing effects of LDFR on cisplatin in cervical cancer cell lines, even when HRS negative, suggest that all patients with cervical cancer may benefit from the addition of LDFR to adjuvant cisplatin-based chemotherapy.

Radiation and immunotherapy: emerging mechanisms of synergy

Immunotherapy (IO) has become a standard treatment in patients with metastatic and locally advanced non-small cell lung cancer (NSCLC), and is now being tested in patients with early stage disease. IO agents currently in use for lung cancer target PD-1, PD-L1, and CTLA-4. While survival and tumor control have improved with IO, many patients have limited or short responses to IO. Therefore, methods to improve the systemic response to IO are needed. Radiation therapy (RT) is an integral component of lung cancer treatment, and may improve systemic response to IO by increasing antigen presentation, increasing co-stimulatory signaling, increasing T-cells recruitment, upregulating PD-L1, increasing tumor stromal lymphocyte infiltration, and altering the microenvironment. IO after definitive chemoradiation is now standard treatment in unresectable stage III NSCLC following publication of the PACIFIC clinical trial. For early stage NSCLC, IO is being investigated in conjunction with stereotactic body radiotherapy (SBRT). The benefit of adding RT to IO in patients with metastatic disease may be especially pronounced in patients with low baseline PD-L1 expression, potentially when delivered as a short course of SBRT, as supported by the PEMBRO-RT clinical trial. Current and ongoing clinical trials are evaluating the optimal radiation dose, timing, and sequencing of RT with IO.

Synergetic Influence of Bismuth Oxide Nanoparticles, Cisplatin and Baicalein-Rich Fraction on Reactive Oxygen Species Generation and Radiosensitization Effects for Clinical Radiotherapy Beams

Purpose

This study aimed to quantify synergetic effects induced by bismuth oxide nanoparticles (BiONPs), cisplatin (Cis) and baicalein-rich fraction (BRF) natural-based agent on the reactive oxygen species (ROS) generation and radiosensitization effects under irradiation of clinical radiotherapy beams of photon, electron and HDR-brachytherapy. The combined therapeutic responses of each compound and clinical radiotherapy beam were evaluated on breast cancer and normal fibroblast cell line.

Methods

In this study, individual BiONPs, Cis, and BRF, as well as combinations of BiONPs-Cis (BC), BiONPs-BRF (BB) and BiONPs-Cis-BRF (BCB) were treated to the cells before irradiation using HDR brachytherapy with 0.38 MeV iridium-192 source, 6 MV photon beam and 6 MeV electron beam. The individual or synergetic effects from the application of the treatment components during the radiotherapy were elucidated by quantifying the ROS generation and radiosensitization effects on MCF-7 and MDA-MB-231 breast cancer cell lines as well as NIH/3T3 normal cell line.

Results

The ROS generated in the presence of Cis stimulated the most substantial amount of ROS compared to the BiONPs and BRF. Meanwhile, the combination of the components had induced the higher ROS levels for photon beam than the brachytherapy and electron beam. The highest ROS enhancement relative to the control is attributable to the presence of BC combination in MDA-MB-231 cells, in comparison to the BB and BCB combinations. The radiosensitization effects which were quantified using the sensitization enhancement ratio (SER) indicate the highest value by BC in MCF-7 cells, followed by BCB and BB treatment. The radiosensitization effects are found to be more prominent for brachytherapy in comparison to photon and electron beam.

Conclusion

The BiONPs, Cis and BRF are the potential radiosensitizers that could improve the efficiency of radiotherapy to eradicate the cancer cells. The combination of these potent radiosensitizers might produce multiple effects when applied in radiotherapy. The BC combination is found to have the highest SER, followed by the BCB combination. This study is also the first to investigate the effect of BRF in combination with BiONPs (BB) and BC (BCB) treatments.

Low-dose fractionated radiation with induction docetaxel and cisplatin followed by concurrent cisplatin and radiation therapy in locally advanced nasopharyngeal cancer: A randomized phase II-III trial

OBJECTIVE/BACKGROUND

To evaluate the efficacy and outcome of adding low-dose fractionated radiotherapy (LDFRT) to induction chemotherapy plus concurrent chemoradiation in locally advanced nasopharyngeal carcinoma (LANPC).

METHODS

A single-institute, phase II-III, prospectively controlled randomized clinical trial was performed at King Faisal Specialist Hospital and Research Centre. Patients aged 18-70 years with WHO type II and III, stage III-IVB nasopharyngeal carcinoma, Eastern Cooperative Oncology Group performance score of 0-2, with adequate hematological, renal, and hepatic function were eligible. In total, 108 patients were enrolled in this trial. All patients received two cycles of induction docetaxel and cisplatin (75 mg/m² each) chemotherapy on Days 1 and 22, followed by concurrent chemoradiation therapy. Radiation therapy consisted of 70 Gy in 33 fractions, with concurrent cisplatin 25 mg/m² for 4 days on Days 43 and 64. Patients were randomly assigned to either adding LDFRT (0.5 Gy twice daily 6 hours apart for 2 days) to induction chemotherapy in the experimental arm (54 patients) or induction chemotherapy alone in the control arm (54 patients).

RESULTS

There was no significant difference in the post-induction response rates (RRs) or in toxicity between the two treatment arms. The 3-year overall survival (OS), locoregional control (LRC), and distant metastases-free survival (DMFS) rates for experimental arm and control arm were 94% versus 93% (p = .8), 84.8% versus 87.5% (p = .58), and 84.1% versus 91.6% (p = .25), respectively.

CONCLUSION

The results showed no benefit from adding LDFRT to induction chemotherapy in terms of RR, OS, LRC, and DMFS.

Pulsed low dose-rate irradiation response in isogenic HNSCC cell lines with different radiosensitivity

Background

Management of locoregionally recurrent head and neck squamous cell carcinomas (HNSCC) is challenging due to potential radioresistance. Pulsed low-dose rate (PLDR) irradiation exploits phenomena of increased radiosensitivity, low-dose hyperradiosensitivity (LDHRS), and inverse dose-rate effect. The purpose of this study was to evaluate LDHRS and the effect of PLDR irradiation in isogenic HNSCC cells with different radiosensitivity.

Materials and methods

Cell survival after different irradiation regimens in isogenic parental FaDu and radioresistant FaDu-RR cells was determined by clonogenic assay; post irradiation cell cycle distribution was studied by flow cytometry; the expression of DNA damage signalling genes was assesed by reverse transcription-quantitative PCR.

Results

Radioresistant Fadu-RR cells displayed LDHRS and were more sensitive to PLDR irradiation than parental FaDu cells. In both cell lines, cell cycle was arrested in G₂/M phase 5 hours after irradiation. It was restored 24 hours after irradiation in parental, but not in the radioresistant cells, which were arrested in G₁-phase. DNA damage signalling genes were under-expressed in radioresistant compared to parental cells. Irradiation increased DNA damage signalling gene expression in radioresistant cells, while in parental cells only few genes were under-expressed.

Conclusions

We demonstrated LDHRS in isogenic radioresistant cells, but not in the parental cells. Survival of LDHRS-positive radioresistant cells after PLDR was significantly reduced. This reduction in cell survival is associated with variations in DNA damage signalling gene expression observed in response to PLDR most likely through different regulation of cell cycle checkpoints.

Risk stratification of pulmonary toxicities in the combination of whole lung irradiation and high-dose chemotherapy for Ewing sarcoma patients with lung metastases: a review

BACKGROUND

Whole lung irradiation (WLI) represents an important part of multimodal therapy in Ewing sarcoma (EwS) patients diagnosed with pulmonary metastases. This review discusses pulmonary toxicity in EwS patients with pulmonary metastases treated with WLI, who received different modes of high-dose chemotheray (HD-Cth).

METHODS

Literature was compiled using the Cochrane Library, PubMed database, and the National Institute of Health (NIH) clinical trials register. Relevant patient information, including nature of HD-Cth, acute and late lung toxicities, and pulmonary function disorders, was selected from the above databases.

RESULTS

Nine reports with a total of 227 patients, including 57 patients from a single randomized trial were included in this review. No acute or chronic symptomatic pulmonary toxicities were observed in patients that received WLI after HD busulfan-melphalan (HD-Bu/Mel), but 8% of these patients were diagnosed with asymptomatic restrictive lung disease. Grade 1 or 2 acute or chronic lung adverse effects were observed in up to 30% of patients that received WLI after HD treosulfan/Mel (HD-Treo/Mel) or HD etoposide (E)/Mel. Interstitial pneumonitis was present in 9% of patients treated concurrently with E/Mel and total body irradiation (TBI) with 8 Gy. Radiation doses as well as time between HD-Cth and WLI were both identified as significant risk factors for pulmonary function disorders.

CONCLUSION

The risk of adverse lung effects after WLI depends on several factors, including cumulative radiation dose and dose per fraction, HD-Cth regimen, and time interval between HD-Cth and WLI. A cumulative radiation dose of up to 15 Gy and a time interval of at least 60 days can potentially lead to a reduced risk of pulmonary toxicities. No evident adverse lung effects were registered in patients that received simultaneous therapy with HD-Cth and TBI. However, pulmonary function testing and lung toxicity reports were lacking for most of these patients.

Radiosensitization Effects by Bismuth Oxide Nanoparticles in Combination with Cisplatin for High Dose Rate Brachytherapy

Purpose

The aim of this study was to investigate the potential of the synergetic triple therapeutic combination encompassing bismuth oxide nanoparticles (BiONPs), cisplatin (Cis), and high dose rate (HDR) brachytherapy with Ir-192 source in breast cancer and normal fibroblast cell line.

Methods

In vitro models of breast cancer cell lines (MCF-7, MDA-MB-231) and normal fibroblast cell line (NIH/3T3) were employed. Cellular localization and cytotoxicity studies were conducted prior to inspection on the radiosensitization effects and generation of reactive oxygen species (ROS) on three proposed radiosensitizers: BiONPs, Cis, and BiONPs-Cis combination (BC). The optimal, non-cytotoxic concentration of BiONPs (0.5 mM) and the 25% inhibitory concentration of Cis (1.30 µM) were applied. The radiosensitization effects were evaluated by using a 0.38 MeV Iridium-192 HDR brachytherapy source over a prescribed dose range of 0 Gy to 4 Gy.

Results

The cellular localization of BiONPs was visualized by light microscopy and accumulation of the BiONPs within the vicinity of the nuclear membrane was observed. Quantification of the sensitization enhancement ratio extrapolated from the survival curves indicates radiosensitization effects for MCF-7 and MDA-MB-231 when treated with BiONPs, Cis, and BC. However, NIH/3T3 cells exhibited contradictive behavior as it only reacted towards the BC combination. Nonetheless, the MCF-7 cell line loaded with BC shows the highest SER of 4.29. ROS production analysis, on the other hand, shows that Cis and BC radiosensitizers generated the highest free radicals in comparison to BiONPs alone.

Conclusion

A BiONPs-Cis combination was unveiled as a novel approach that offers promising radiosensitization enhancement that will increase the efficiency of tumor control while preserving the normal tissue at a reduced dose. This data is the first precedent to prove the synergetic implication of BiONPs, Cis, and HDR brachytherapy that will be beneficial for future chemoradiotherapy strategies in cancer care.

Metformin enhances the radiosensitizing effect of cisplatin in non-small cell lung cancer cell lines with different cisplatin sensitivities

Cisplatin is an extensively used chemotherapeutic drug for lung cancer, but the development of resistance decreases its effectiveness in the treatments of non-small cell lung cancer (NSCLC). In this study, we examined the effects of metformin, a widely used antidiabetic drug, on cisplatin radiosensitization in NSCLC cell lines. Human NSCLC cell lines, A549 (cisplatin-resistant) and H460 (cisplatin-sensitive), were treated with metformin, cisplatin or a combination of both drugs before ionizing radiation. Cell proliferation, clonogenic assays, western blotting, cisplatin-DNA adduct formation and immunocytochemistry were used to characterize the treatments effects. Metformin increased the radiosensitivity of NSCLC cells. Metformin showed additive and over-additive effects in combination with cisplatin and the radiation response in the clonogenic assay in H460 and A549 cell lines (p = 0.018 for the interaction effect between cisplatin and metformin), respectively. At the molecular level, metformin led to a significant increase in cisplatin-DNA adduct formation compared with cisplatin alone (p < 0.01, ANOVA-F test). This was accompanied by a decreased expression of the excision repair cross-complementation 1 expression (ERCC1), a key enzyme in nucleotide excision repair pathway. Furthermore, compared with each treatment alone metformin in combination with cisplatin yielded the lowest level of radiation-induced Rad51 foci, an essential protein of homologous recombination repair. Ionizing radiation-induced γ-H2AX and 53BP1 foci persisted longer in both cell lines in the presence of metformin. Pharmacological inhibition of AMP-activated protein kinase (AMPK) demonstrated that metformin enhances the radiosensitizing effect of cisplatin through an AMPK-dependent pathway only in H460 but not in A549 cells. Our results suggest that metformin can enhance the effect of combined cisplatin and radiotherapy in NSCLC and can sensitize these cells to radiation that are not sensitized by cisplatin alone.

Radiation and hypoxia-induced non-targeted effects in normoxic and hypoxic conditions in human lung cancer cells

PURPOSE

Many cell lines with anaerobic metabolism do not show cytotoxic abscopal effect (AE) following irradiation. Further, there is no existing data on the radiation- and hypoxia (H)-induced AE. The purpose of this study was to investigate and compare the status of radiation-induced abscopal effect (RIAE) in normoxic and hypoxic conditions.

METHODS

Lung cancer cells (A549, H460) were exposed either to hypoxia or normoxia and then irradiated (2 or 10 Gy). After 24 h, unirradiated hypoxic (H-CM) or normoxic (N-CM) conditioned media (CM) and irradiated hypoxic (H-RCM) or normoxic (N-RCM) CM was collected. Hypoxia-resistant clones (HR: A549/HR, H460/HR) were generated by continuous exposure of the cells to hypoxia. Unirradiated parental cells or HR were exposed to H-CM, N-CM, H-RCM or N-RCM. In some groups, 24 h after exposure to CM, cells were directly irradiated with 2 Gy. Cell growth was monitored using real-time cell electronic sensing system. Further, levels of hypoxia and HIF1α regulated angiogenesis related growth factors, basic fibroblast growth factor (bFGF), placental growth factor (PlGF), soluble fms-like tyrosine kinase (sFlt-1) and vascular endothelial growth factor (VEGF) were assessed in CM.

RESULTS

In the radio-resistant A549 cells, H-RCM was much more effective in inducing growth delay compared to N-RCM. In the radio-sensitive H460 cells, both N-RCM and H-RCM induced growth delay. Interestingly, effects of N-RCM were completely reversed in HR cells. Exposure of cells to direct irradiation (2 Gy) 24 h after incubation with CM resulted in 50-60% reduction in cell proliferation in A549/HR cells and a very significant induction of death (>95%) in H460/HR cells. Direct irradiation of parental or HR clones of A549 and H460 cells exposed to H-CM 24 h with 2 Gy induced significant reduction in cell proliferation (from 40% to >95%) in all the cells. Further, levels of sFlt-1 correlated with growth delay in all the cells.

CONCLUSIONS

These results for the first time demonstrate that irradiation of hypoxic cells and exposing the cells to acute hypoxia lead to significant AE.

Impact of time interval and dose rate on cell survival following low-dose fractionated exposures

Enhanced cell lethality, also known as hyper-radiosensitivity, has been reported at low doses of radiation (≤0.5 Gy) in various cell lines, and is expected to be an effective cancer therapy. We conducted this study to examine the impact of time interval and dose rate of low-dose fractionated exposures with a short time interval. We evaluated the cell-survival rates of V79 and A549 cells using clonogenic assays. We performed fractionated exposures in unit doses of 0.25, 0.5, 1.0 and 2.0 Gy. We exposed the cells to 2 Gy of X-rays (i) at dose-rates of 1.0, 1.5 and 2.0 Gy/min at 1-min intervals and (ii) at a dose-rate of 2.0 Gy/min at 10-s, 1-min and 3-min intervals by fractionated exposures. Apoptosis and cell cycle analyses were also evaluated in the fractionated exposures (unit dose 0.25 Gy) and compared with single exposures by using flow cytometry. Both cell-type survival rates with fractionated exposures (unit dose 0.25 Gy) with short time intervals were markedly lower than those for single exposures delivering the same dose. When the dose rates were lower, the cytotoxic effect decreased compared with exposure to a dose-rate of 2.0 Gy/min. On the other hand, levels of apoptosis and cell cycle distribution were not significantly different between low-dose fractionated exposures and single exposures in either cell line. These results indicate that a stronger cytotoxic effect was induced with low-dose fractionated exposures with a short time interval for a given dose due to the hyper-radiosensitivity phenomenon, suggesting that dose rates are important for effective low-dose fractionated exposures.

Autophagy influences the low-dose hyper-radiosensitivity of human lung adenocarcinoma cells by regulating MLH1

PURPOSE

To investigate the impact of autophagy on the low-dose hyper-radiosensitivity (HRS) of human lung adenocarcinoma cells via MLH1 regulation.

MATERIALS AND METHODS

Immunofluorescent staining, Western blotting, and electron microscopy were utilized to detect autophagy in A549 and H460 cells. shRNA was used to silence MLH1 expression. The levels of MLH1, mTOR, p-mTOR, BNIP3, and Beclin-1 were measured by real-time polymerase chain reaction (PCR) and Western blotting.

RESULTS

A549 cells, which have low levels of MLH1 expression, displayed HRS/induced radioresistance (IRR). Conversely, the radiosensitivity of H460 cells, which express high levels of MLH1, conformed to the linear-quadratic (LQ) model. After down-regulating MLH1 expression, A549 cells showed increased HRS and inhibition of autophagy, whereas H460 cells exhibited HRS/IRR. The levels of mTOR, p-mTOR, and BNIP3 were reduced in cells harboring MLH1 shRNA, and the changes in the mTOR/p-mTOR ratio mirrored those in MLH1 expression.

CONCLUSIONS

Low MLH1-expressing A549 cells may exhibit HRS. Both the mTOR/p-mTOR and BNIP3/Beclin-1 signaling pathways were found to be related to HRS, but only mTOR/p-mTOR is involved in the regulation of HRS via MLH1 and autophagy.

The predictive value of 18F-FDG PET-CT for assessing the clinical outcomes in locally advanced NSCLC patients after a new induction treatment: low-dose fractionated radiotherapy with concurrent chemotherapy

Background

Patients with locally advanced non-small-cell lung cancer (LA-NSCLC) have poor prognosis despite several multimodal approaches. Recently, low-dose fractionated radiotherapy concurrent to the induction chemotherapy (IC-LDRT) has been proposed to further improve the effects of chemotherapy and prognosis. Until now, the predictive value of metabolic response after IC-LDRT has not yet been investigated. Aim: to evaluate whether the early metabolic response, assessed by ¹⁸F-fluoro-deoxyglucose positron emission-computed tomography (¹⁸F-FDG PET-CT), could predict the prognosis in LA-NSCLC patients treated with a multimodal approach, including IC-LDRT.

Methods

Forty-four consecutive patients (35males, mean age: 66 ± 7.8 years) with stage IIIA/IIIB NSCLC were retrospectively evaluated. Forty-four patients underwent IC-LDRT (2 cycles of chemotherapy, 40 cGy twice daily), 26/44 neo-adjuvant chemo-radiotherapy (CCRT: 50.4Gy), and 20/44 surgery. ¹⁸F-FDG PET-CT was performed before (baseline), after IC-LDRT (early) and after CCRT (final), applying PET response criteria in solid tumours (PERCIST). Patients with complete/partial metabolic response were classified as responders; patients with stable/progressive disease as non-responders. Progression free survival (PFS) and overall survival (OS) were assessed using Kaplan-Meyer analysis; the relationship between clinical factors and survivals were assessed using uni-multivariate regression analysis.

Results

Forty-four out of 44, 42/44 and 23/42 patients underwent baseline, early and final PET-CT, respectively. SUL_peak of primary tumour and lymph-node significantly (p = 0.004, p = 0.0002, respectively) decreased after IC-LDRT with a further reduction after CCRT (p = 0.0006, p = 0.02, respectively). At early PET-CT, 20/42 (47.6%) patients were classified as responders, 22/42 (52.3%) as non-responders. At final PET-CT, 19/23 patients were classified as responders (12 responders and 7 non-responders at early PET-CT), and 4/23 as non-responders (all non-responders at early PET-CT). Early responders had better PFS and OS than early non-responders (p ≤ 0.01). Early metabolic response was predictive factor for loco-regional, distant and global PFS (p = 0.02, p = 0.01, p = 0.005, respectively); surgery for loco-regional and global PFS (p = 0.03, p = 0.009, respectively).

Conclusions

In LA-NSCLC patients, ¹⁸F-FDG metabolic response assessed after only two cycles of IC-LDRT predicts the prognosis. The early evaluation of metabolic changes could allow to personalize therapy. This multimodality approach, including both low-dose radiotherapy that increases the effects of induction chemotherapy, and surgery that removes the disease, improved clinical outcomes. Further prospective investigation of this new induction approach is warranted.

Radiotherapy combination opportunities leveraging immunity for the next oncology practice

Approximately one-half of patients with newly diagnosed cancer and many patients with persistent or recurrent tumors receive radiotherapy (RT), with the explicit goal of eliminating tumors through direct killing. The current RT dose and schedule regimens have been empirically developed. Although early clinical studies revealed that RT could provoke important responses not only at the site of treatment but also on remote, nonirradiated tumor deposits-the so-called "abscopal effect"- the underlying mechanisms were poorly understood and were not therapeutically exploited. Recent work has elucidated the immune mechanisms underlying these effects and has paved the way for developing combinations of RT with immune therapy. In the wake of recent therapeutic breakthroughs in the field of immunotherapy, rational combinations of immunotherapy with RT could profoundly change the standard of care for many tumor types in the next decade. Thus, a deep understanding of the immunologic effects of RT is urgently needed to design the next generation of therapeutic combinations. Here, the authors review the immune mechanisms of tumor radiation and summarize the preclinical and clinical evidence on immunotherapy-RT combinations. Furthermore, a framework is provided for the practicing clinician and the clinician investigator to guide the development of novel combinations to more rapidly advance this important field. CA Cancer J Clin 2017;67:65-85. © 2016 American Cancer Society.

Using low-dose radiation to potentiate the effect of induction chemotherapy in head and neck cancer: Results of a prospective phase 2 trial

Purpose

Low-dose fractionated radiation therapy (LDFRT) induces effective cell killing through hyperradiation sensitivity and potentiates effects of chemotherapy. We report our second investigation of LDFRT as a potentiator of the chemotherapeutic effect of induction carboplatin and paclitaxel in locally advanced squamous cell cancer of the head and neck (SCCHN).

Experimental design

Two cycles of induction therapy were given every 21 days: paclitaxel (75 mg/m²) on days 1, 8, and 15; carboplatin (area under the curve 6) day 1; and LDFRT 50 cGy fractions (2 each on days 1, 2, 8, and 15). Objectives included primary site complete response rate; secondary included overall survival, progression-free survival (PFS), disease-specific survival, and toxicity.

Results

A total of 24 evaluable patients were enrolled. Primary sites included oropharynx (62.5%), larynx (20.8%), oral cavity (8.3%), and hypopharynx (8.3%). Grade 3/4 toxicities included neutropenia (20%), leukopenia (32%), dehydration/hypotension (8%), anemia (4%), infection (4%), pulmonary/allergic rhinitis (4%), and diarrhea (4%). Primary site response rate was 23/24 (95.8%): 15/24 (62.5%) complete response, 8/24 (33.3%) partial response, and 1/24 (4.2%) stable disease. With median follow-up of 7.75 years, 9-year rates for overall survival were 49.4% (95% confidence interval [CI], 30.5-79.9), PFS was 72.2% (CI, 55.3-94.3), and disease-specific survival was 65.4% (44.3-96.4).

Conclusion

Chemopotentiating LDFRT combined with paclitaxel and carboplatin is effective in SCCHN and provided an excellent median overall survival of 107.2 months, with median PFS not yet reached in this locally advanced SCCHN cohort. This compares favorably to prior investigations and caused fewer grade 3 and 4 toxicities than more intensive, 3-drug induction regimens. This trial demonstrates the innovative use of LDFRT as a potentiator of chemotherapy.

Low-dose radiotherapy and concurrent FOLFIRI-bevacizumab: a Phase II study

Aims: Low-dose radiation therapy (LDRT) can increase biological efficacy of chemotherapy. This Phase II trial evaluates LDRT plus FOLFIRI-bevacizumab (FOLFIRI-B) in metastatic colorectal cancer. Materials & methods: Primary objective: raising the clinical complete response rate from 5 to 25%. Secondary objectives: toxicity, progression-free survival. Patients underwent 12 FOLFIRI-B cycles plus two daily LDRT fractions (20 cGy/6 h interval) on each cycle. Statistical analysis was planned on 18 patients. Results: Results on 18 patients are reported. Specifically considering irradiated sites: 15/18 patients had a partial (11/18) or complete (4/18) response. Among 11 partial responders, three became a pathological CR after surgery. Grade 3–4 toxicity was recorded in two patients (11.1%). At median follow-up of 30 months (range: 8-50), 7/18 patients progressed in irradiated sites. Conclusion: Seven out of 18 patients (38.9%) had clinical or pathological CR in lesions treated with LDRT. Further studies on this newer treatment modality seem justified.

p16INK4a Status and Response to Induction Low-Dose Fractionated Radiation in Advanced Head and Neck Cancer

OBJECTIVE

To evaluate the impact of p16INK4a (p16) expression on clinical efficacy of induction low-dose fractionated radiation therapy (LDFRT) with concurrent chemotherapy in patients with locally advanced squamous cell carcinoma of the head and neck (SCCHN).

STUDY DESIGN

Historical cohort study.

SETTING

Tertiary medical center.

METHODS

A total of 66 Patients with locally advanced SCCHN were enrolled in 2 clinical trials using paclitaxel, carboplatin, and concurrent LDFRT induction therapy. Patients were evaluated for response to induction by a multidisciplinary team and then were given definitive treatment. Adequate tissue samples from the pretreatment biopsies of 42 individuals were identified and analyzed for p16 expression. Expression was correlated with clinical outcomes.

RESULTS

Of 42 tumors, 15 (35.7%) were positive for p16. Patients with p16-positive tumors had improved response to induction, but this was not statistically significant (P = .06). Five-year overall survival was 80% in p16-positive patients and 58% in p16-negative patients (P = .025).

CONCLUSIONS

p16 Expression affects treatment response in patients treated with induction LDFRT with concurrent chemotherapy. This is similar to results reported for standard induction chemotherapy.

Contribution of Dual Oxidase 2 (DUOX2) to Hyper-Radiosensitivity in Human Gastric Cancer Cells

Whole-abdominal radiotherapy (WART) is a primary method for managing gastrointestinal cancers that have disseminated into intra-abdominal tissues. While effective, this approach is limited because of the increased toxicity to normal tissue associated with combined WART and full-dose chemotherapy regimens. Recent studies have demonstrated a survival advantage in a novel treatment paradigm that allows for the safe use of full-dose systemic chemotherapy in combination with low-dose fractionated radiotherapy (LDFRT). Traditionally, radiation doses greater than 120 cGy have been used in radiotherapy because lower doses were thought to be ineffective for tumor therapy. However, we now know that LDFRT can produce hyper-radiosensitivity (HRS), a phenomenon where cells undergo apoptosis at radiation doses as low as 15 cGy, in a number of proliferating cells. The objectives of our current study were to determine whether LDFRT can induce HRS in gastrointestinal cancer cells and to identify biomarkers of chemopotentiation by LDFRT. Our data indicate that three consecutive daily fractions of 15 cGy produced HRS in gastric cancer cells and potentiated a modified regimen of docetaxel, cisplatin and 5'-fluorouracil (mDCF). Colony survival assays indicated that 15 cGy was sufficient to kill 90% of the cells when LDFRT was combined with mDCF whereas a dose almost 10 times higher (135 cGy) was needed to achieve the same rate when using conventional radiotherapy alone. RT(2) PCR Profiler™ array analysis indicated that this combined regimen upregulated dual oxidase 2 (DUOX2), an enzyme functioning in the production of hydrogen peroxide, without upregulating genes involved in DNA repair. Moreover, downregulation of DUOX2 increased radioresistance at every radiation dose tested. In addition, our data indicate that reactive oxygen species (ROS) increase up to 3.5-fold in cells exposed to LDFRT and mDCF. Furthermore, inhibition of NADPH oxidase abrogated the killing efficiency of this combined regimen. Taken together these data suggest that chemopotentiation by LDFRT in gastric cancer cells may be due, at least in part, to increased ROS production (DUOX2) without upregulation of the DNA repair machinery. These data thus provide a rationale for further explorations of potential clinical applications of LDFRT, such as in WART, as a chemopotentiator for advanced and metastatic gastric cancers.

CDK1-Mediated SIRT3 Activation Enhances Mitochondrial Function and Tumor Radioresistance

Tumor adaptive resistance to therapeutic radiation remains a barrier for further improvement of local cancer control. SIRT3, a member of the sirtuin family of NAD(+)-dependent protein deacetylases in mitochondria, promotes metabolic homeostasis through regulation of mitochondrial protein deacetylation and plays a key role in prevention of cell aging. Here, we demonstrate that SIRT3 expression is induced in an array of radiation-treated human tumor cells and their corresponding xenograft tumors, including colon cancer HCT-116, glioblastoma U87, and breast cancer MDA-MB231 cells. SIRT3 transcriptional activation is due to SIRT3 promoter activation controlled by the stress transcription factor NF-κB. Posttranscriptionally, SIRT3 enzymatic activity is further enhanced via Thr150/Ser159 phosphorylation by cyclin B1-CDK1, which is also induced by radiation and relocated to mitochondria together with SIRT3. Cells expressing Thr150Ala/Ser159Ala-mutant SIRT3 show a reduction in mitochondrial protein lysine deacetylation, Δψm, MnSOD activity, and mitochondrial ATP generation. The clonogenicity of Thr150Ala/Ser159Ala-mutant transfectants is lower and significantly decreased under radiation. Tumors harboring Thr150Ala/Ser159Ala-mutant SIRT3 show inhibited growth and increased sensitivity to in vivo local irradiation. These results demonstrate that enhanced SIRT3 transcription and posttranslational modifications in mitochondria contribute to adaptive radioresistance in tumor cells. CDK1-mediated SIRT3 phosphorylation is a potential effective target to sensitize tumor cells to radiotherapy.

DNA-dependent protein kinase catalytic subunit inhibitor reverses acquired radioresistance in lung adenocarcinoma by suppressing DNA repair

The mechanisms underlying lung cancer radioresistance remain to be fully elucidated. The DNA repair pathway is a predominant target of radiotherapy, which is considered to be involved in the acquired radioresistance of cancer cells. The present study aimed to establish a radioresistant cell model using the A549 human lung cancer cell line, and to further investigate the potential mechanisms underlying the radioresistance. The A549R radioresistant lung cancer cell variant was established by exposing the parental A549 cells to repeated γ-ray irradiation at a total dose of 60 Gy. Colony formation assays were then used to determine cell survival following γ-ray exposure. The established radioresistant cells were subsequently treated with or without the NU7026 DNA-PKcs inhibitor. The levels of DNA damage were determined by counting the number of fluorescent γ-H2AX foci in the cells. The cellular capacity for DNA repair was assessed using antibodies for the detection of various DNA repair pathway proteins. The radioresistant sub-clones exhibited significantly decreased survival following NU7026 treatment, compared with the parental cells, as determined by colony formation assays (P<0.05), and this finding was found to be dose-dependent. Treatment with the DNA-dependent protein kinase (DNA-PK) inhibitor significantly reduced γ-H2AX foci formation (P<0.05) following acute radiation exposure in the radioresistant sub-clones, compared with the parental control cells. The decreased levels of γ-H2AX were accompanied by an increase in the percentage of apoptotic cells in the radioresistant cell line following post-radiation treatment with the DNA-PKcs inhibitor. The expression levels of proteins associated with the DNA repair pathway were altered markedly in the cells treated with NU7026. The results of the present study suggested that radioresistance may be associated with enhanced DNA repair following exposure to radiation, resulting in reduced apoptosis. Therefore, the quantity of γ-H2AX determines the radioresistance of cells. The DNA repair pathway is important in mediating radioresistance, and treatment with the DNA-PKcs inhibitor, NU7026 restored the acquired radiation resistance.

The effect of radiation exposure on multidrug resistance: in vitro and in vivo studies using non-small lung cancer cells

Background

Technetium-99m methoxyisobutylisonitrile (Tc MIBI) is a substrate with the same uptake kinetics as doxorubicin. Multidrug resistance (MDR) is a mechanism that impedes chemotherapy of non-small cell lung cancer (NSCLC). We examined the effect of radiation exposure on MDR in NSCLC and the synergy between an MDR modulator, GG918, and radiation, using ^99mTc MIBI in vitro and doxorubicin in vivo.

Methods

In vitro NSCLC cells (H1299) were exposed to radiation (3-, 6-, and 9-Gy-irradiated groups) alongside a not-irradiated (0 Gy) group. Technetium-99 metastable methoxyisobutylisonitrile (^99mTc MIBI) was administered to cell suspensions at 48 h after irradiation. Cell radioactivity was measured, and C_in/C_out ratios were calculated and compared. NSCLC cells were also subcutaneously transplanted into the left thigh of nude mice, which were subsequently raised for 2 weeks. Two groups of mice were used: mice exposed to irradiation (9-Gy-irradiated) and those that were not (not-irradiated). Doxorubicin was administered through the caudal vein at 48 h after the irradiation. Using an in vivo imaging system, intratumoural photon counts were measured. To determine the synergy between the MDR modulator and 3- or 6-Gy irradiation, the final GG918 concentration was determined: 0.1 μM (N-H, 3-H, and 6-H groups), 0.001 μM (N-L, 3-L, and 6-L groups), and 0 μM (N-0, 3-0, and 6-0 groups). C_in/C_out ratios were calculated and compared among the groups.

Results

C_in/C_out after 6- or 9-Gy irradiation was significantly higher than that of the not-irradiated group (0 Gy). In vivo, fluorescence photon counts were significantly higher in the tumours of 9-Gy-irradiated mice, up to 270 min after administration of doxorubicin, as compared to the not-irradiated mice. The C_in/C_out ratio in the N-H, 3-H, and 6-H groups was significantly higher than that in the N-0, 3-0, and 6-0 groups. There was no significant difference between C_in/C_out in the N-L group and that of the N-0 group. However, the C_in/C_out ratio in the 3-L and 6-L groups was significantly higher than that in the 3-0 and 6-0 groups.

Conclusions

Irradiation decreased MDR in NSCLC cells. In combination with a low-dose MDR modulator, GG918, MDR transport function was synergistically reduced 48 h post-irradiation.

Exploiting sensitization windows of opportunity in hyper and hypo-fractionated radiation therapy

In contrast to the conventional radiotherapy/chemoradiotherapy paradigms used in the treatment of majority of cancer types, this review will describe two areas of radiobiology, hyperfractionated and hypofractionated radiation therapy, for cancer treatment focusing on application of novel concepts underlying these treatment modalities. The initial part of the review discusses the phenomenon of hyper-radiation sensitivity (HRS) at lower doses (0.1 to 0.6 Gy), describing the underlying mechanisms and how this could enhance the effects of chemotherapy, particularly, in hyperfractionated settings. The second part examines the radiobiological/physiological mechanisms underlying the effects of high-dose hypofractionated radiation therapy that can be exploited for tumor cure. These include abscopal/bystander effects, activation of immune system, endothelial cell death and effect of hypoxia with re-oxygenation. These biological properties along with targeted dose delivery and distribution to reduce normal tissue toxicity may make high-dose hypofractionation more effective than conventional radiation therapy for treatment of advanced cancers. The novel radiation physics based methods that take into consideration the tumor volume to be irradiated and normal tissue avoidance/tolerance can further improve treatment outcome and post-treatment quality of life. In conclusion, there is enough evidence to further explore novel avenues to exploit biological mechanisms from hyper-fractionation by enhancing the efficacy of chemotherapy and hypo-fractionated radiation therapy that could enhance tumor control and use imaging and technological advances to reduce toxicity.

C646, a selective small molecule inhibitor of histone acetyltransferase p300, radiosensitizes lung cancer cells by enhancing mitotic catastrophe

BACKGROUND AND PURPOSE

Chromatin remodeling through histone modifications, including acetylation, plays an important role in the appropriate response to DNA damage induced by ionizing radiation (IR). Here we investigated the radiosensitizing effect of C646, a selective small molecule inhibitor of p300 histone acetyltransferase, and explored the underlying mechanisms.

MATERIALS AND METHODS

A549, H157 and H460 human non-small cell lung carcinoma (NSCLC) cells, and HFL-III human lung fibroblasts were assessed by clonogenic survival assay. Apoptosis and necrosis were assessed by annexin V staining. Senescence was assessed by Senescence-associated β-galactosidase staining. Mitotic catastrophe was assessed by evaluating nuclear morphology with DAPI staining. Cell cycle profiles were analyzed by flow cytometry. Protein expression was analyzed by immunoblotting.

RESULTS

C646 sensitized A549, H460 and H157 cells to IR with a dose enhancement ratio at 10% surviving fraction of 1.4, 1.2 and 1.2, respectively. C646 did not radiosensitize HFL-III cells. In A549 cells, but not in HFL-III cells, C646 (i) enhanced mitotic catastrophe but not apoptosis, necrosis, or senescence after IR; (ii) increased the hyperploid cell population after IR; and (iii) suppressed the phosphorylation of CHK1 after IR.

CONCLUSIONS

C646 radiosensitizes NSCLC cells by enhancing mitotic catastrophe through the abrogation of G2 checkpoint maintenance.

FOLFIRI-bevacizumab and concurrent low-dose radiotherapy in metastatic colorectal cancer: preliminary results of a phase I-II study

BACKGROUND

To evaluate the effectiveness of low-dose radiation therapy (LDRT) and FOLFIRI-bevacizumab (FOLFIRI-B) combination in metastatic colorectal cancer.

METHODS

The primary objective of the study is to raise the clinical complete response (CR) rate from 5% to 25%. Secondary objectives include toxicity and progression-free survival. Patients underwent 12 FOLFIRI-B cycles plus two daily LDRT (20 cGy/6-hour interval) on the first and second days of each cycle.

RESULTS

CR and toxicity of 10 patients are reported. Considering irradiated sites, 10/10 patients had clinical partial response (PR) (7/10) or CR (3/10). Three clinical PR patients subsequently underwent surgery and reported a pathological CR in the irradiated sites. Grade 3-4 toxicities rate was 30%. With a median follow-up of 29 months (range: 12-49 months), 2/10 progression of disease in irradiated sites and 3/5 in non-irradiated sites were observed.

CONCLUSIONS

The very high response rate requires urgent verification in a larger patient series.

Protective effect of acetyl-l-carnitine against cisplatin ototoxicity: role of apoptosis-related genes and pro-inflammatory cytokines

OBJECTIVES

Cisplatin is an anti-neoplastic agent treatment with which causes many side effects including ototoxicity. The aim of this study was to investigate whether acetyl-L-carnitine would have protective effects on cisplatin-induced ototoxicity in vitro, and if present, to reveal roles of apoptotic gene expressions and pro-inflammatory cytokines.

MATERIALS AND METHODS

House Ear Institute-Organ of Corti 1 cell line was used for this study. Apoptotic genes were evaluated with an apoptosis PCR array and pro-inflammatory cytokine levels were measured using ELISA.

RESULTS

Apoptotic cell death reduced by around 22% with acetyl-L-carnitine-cisplatin treatment compared to cisplatin alone. Genes displaying increase in expression of apoptosis, related to cisplatin treatment, were Casp8, Bcl10, Bcl2, Bcl2l1, Bcl2l2, Bid, Naip1, Bnip3l, Card6, Pak7, Cd40, Trp 53inp1, Cideb and Cd70. The acetyl-L-carnitine-cisplatin combination caused reduced expression of genes Casp8, Fas, Casp1, Tnfrsf11b, Tnfrsf10b induced by cisplatin. Acetyl-L-carnitine-cisplatin also caused reduced levels of IL-6, IL-1β and TNF-α, pro-inflammatory cytokines, induced by cisplatin.

CONCLUSION

Protective mechanisms of aceytl-L-carnitine against cisplatin induced apoptosis, mainly due to activation of anti-apoptotic Bcl family members' genes, and in an Akt-related gene expression dependent manner. This is the first study to indicate that acetyl-L-carnitine can be an effective agent against cisplatin ototoxicity in auditory cells, with induction of anti-apoptotic gene expression and attenuating levels of pro-inflammatory cytokines.

A Logarithmic Formula to Describe the Relationship between the Increased Radiosensitivity at Low Doses and the Survival at 2 Gray

OBJECTIVES

Intrinsic radiosensitivity at doses used in radiotherapy is linked to hypersensitivity (HRS) and increased radio resistance (IRR) at low doses. The aim of this study was to explore this relationship.

METHODS

Survival curves for 18 human tumour cell lines were analysed, using two models to fit the data points in order to extract the necessary parameters relevant for this study.

RESULTS

The IRR ratio αs/αr versus the survival at 2 gray (Gy) can be described by a logarithmic relation which leads to a series of straight lines.

CONCLUSION

The relationship obtained implies that there is a direct link between HRS/IRR and survival at clinically relevant doses of 2 Gy.

Towards predicting the response of a solid tumour to chemotherapy and radiotherapy treatments: clinical insights from a computational model

In this paper we use a hybrid multiscale mathematical model that incorporates both individual cell behaviour through the cell-cycle and the effects of the changing microenvironment through oxygen dynamics to study the multiple effects of radiation therapy. The oxygenation status of the cells is considered as one of the important prognostic markers for determining radiation therapy, as hypoxic cells are less radiosensitive. Another factor that critically affects radiation sensitivity is cell-cycle regulation. The effects of radiation therapy are included in the model using a modified linear quadratic model for the radiation damage, incorporating the effects of hypoxia and cell-cycle in determining the cell-cycle phase-specific radiosensitivity. Furthermore, after irradiation, an individual cell's cell-cycle dynamics are intrinsically modified through the activation of pathways responsible for repair mechanisms, often resulting in a delay/arrest in the cell-cycle. The model is then used to study various combinations of multiple doses of cell-cycle dependent chemotherapies and radiation therapy, as radiation may work better by the partial synchronisation of cells in the most radiosensitive phase of the cell-cycle. Moreover, using this multi-scale model, we investigate the optimum sequencing and scheduling of these multi-modality treatments, and the impact of internal and external heterogeneity on the spatio-temporal patterning of the distribution of tumour cells and their response to different treatment schedules.

Anti-cancer treatments such as radiotherapy and chemotherapy have evolved through clinical trial-and-error over decades, and although they cure some cases and are partially effective in many, the majority of such cancers ultimately recur. Doctors turn to new, expensive drugs as they emerge, but perhaps fail to study and learn how to use the therapies they already have most effectively. This is partly because clinical trials are expensive to conduct, both in terms of time and money. The cancer cell is complicated, but many mechanisms that control its response to treatment are now understood. We show here how a mathematical model accurately reproduces the results of previous biological experiments of cancer treatment, opening up the possibility of using it to predict which combinations of drugs and radiotherapy would be best for patients.

Exposure to low dose ionising radiation: molecular and clinical consequences

This review article provides a comprehensive overview of the experimental data detailing the incidence, mechanism and significance of low dose hyper-radiosensitivity (HRS). Important discoveries gained from past and present studies are mapped and highlighted to illustrate the pathway to our current understanding of HRS and the impact of HRS on the cellular response to radiation in mammalian cells. Particular attention is paid to the balance of evidence suggesting a role for DNA repair processes in the response, evidence suggesting a role for the cell cycle checkpoint processes, and evidence investigating the clinical implications/relevance of the effect.

A liquid crystal-related compound induces cell cycle arrest at the G2/M phase and apoptosis in the A549 human non-small cell lung cancer cell line

Liquid crystals are the state of matter existing between liquid and crystalline phases, and recently there has been increasing interest in their biological effects. Following our recently reported work, we investigated the cell suppressive effects of liquid crystal-related compounds (LCRCs), which are precursors of liquid crystals, in the human non-small lung cancer cell line A549. We found that 2-(4-butoxyphenyl)-5-(4-hydroxyphenyl)pyrimidine (LCRC-1) dramatically suppressed cell growth. Treatment with 12 µM LCRC-1 for 12 h induced cell cycle arrest at the G2/M phase. Furthermore, LCRC-1 increased the sub-G1 fraction and Annexin V-positive cells and activated caspase-3 in A549 cells, which showed that it can induce apoptosis in these cells. Furthermore, because the induction of apoptosis by LCRC-1 was partly inhibited by treatment with pan-caspase inhibitor, it appeared that LCRC-1 induced apoptosis by a caspase-dependent pathway. The ability of LCRC-1 to cause DNA damage was assessed, but LCRC-1 did not induce expression of γ-H2AX, which is a marker of DNA damage. Treatment with LCRC-1 did not inhibit the proliferation of WI-38 normal fibroblast cells, which makes the tumor-specific suppressive effect of LCRC-1 attractive for its application as a new antitumor drug.

8-Aminoadenosine enhances radiation-induced cell death in human lung carcinoma A549 cells

The combination of a chemotherapeutic agent and radiation is widely applied to enhance cell death in solid tumor cells in cancer treatment. The purine analogue 8-aminoadenosine (8-NH(2)-Ado) is known to be a transcription inhibitor that has proved very effective in multiple myeloma cell lines and primary indolent leukemia cells. In this report, to examine whether 8-NH(2)-Ado had the ability to enhance the radiation-induced cell killing in solid tumor cells, human lung adenocarcinoma A549 cells were irradiated in the presence and absence of 8-NH(2)-Ado. 8-NH(2)-Ado significantly increased reproductive cell death and apoptosis in A549 cells exposed to X-rays. When peptide inhibitors against caspase-3, -8, and -9 were utilized to evaluate the involvement of caspases, all inhibitors suppressed the enhancement of radiation-induced apoptosis, suggesting that not only mitochondria-mediated apoptotic signal transduction pathways but also death receptor-mediated pathways were involved in this enhancement of apoptosis. In addition, in the cells exposed to the treatment combining X-irradiation and 8-NH(2)-Ado, reduction of the intracellular ATP concentration was essential for survival, and down-regulation of the expression of antiapoptotic proteins such as survivin and XIAP was observed. These results indicate that 8-NH(2)-Ado has potential not only as an anti-tumor drug for leukemia and lymphoma but also as a radiosensitizing agent for solid tumors.