Radiation biology in the context of changing patterns of radiotherapy

Metformin Radiosensitizing Effect on Hypoxic Oral Squamous Cell Carcinoma Cells by GAPDH and TAGLN2

OBJECTIVE

Tumor hypoxia is associated with a poorer prognosis in cancer patients and can diminish the efficacy of radiation therapy (RT). This study investigates the potential of metformin to enhance radiosensitivity in hypoxic cancer cells.

METHODS

Preliminary experiments were conducted to validate the impact of hypoxia on radiation response. Reactive oxygen species (ROS) levels, cell migration, and cell death were assessed in hypoxic, radiated cells treated with metformin. Proteomic and ontological analyses were employed to identify molecular targets associated with the radiosensitizing effect of metformin. Proteomic and ontological findings were validated through patient samples and in vitro studies.

RESULTS

Metformin amplified cell death, induced DNA fragmentation, decreased cell migration, and elevated ROS levels in hypoxic, radiated cells. Proteomic analyses revealed that GAPDH and TAGLN2 were identified as pivotal targets linked to the radiosensitizing effect of metformin. Oral cancer patients exhibited elevated levels of TAGLN2 and reduced levels of GAPDH. Metformin downregulated TAGLN2 and upregulated GAPDH in hypoxic, radiated cells. Additionally, metformin reduced levels of mutated p53.

CONCLUSIONS

This study suggests that metformin can enhance radiosensitivity in hypoxic cells, operating through modulation of GAPDH and TAGLN2. Furthermore, metformin effectively reduces mutated p53 levels in radiated cells under hypoxic conditions.

Combination of NKG2A and PD-1 Blockade Improves Radiotherapy Response in Radioresistant Tumors

Radiotherapy (RT) is commonly employed to treat solid tumors. Immune checkpoint blockade of programmed cell death protein 1 (PD-1) and CTLA-4 improves survival in RT patients, yet many fail to respond to combination therapy. Natural killer group 2 (NKG2) family receptors, particularly inhibitory NKG2A and activating NKG2D, have emerged as promising therapeutic targets to improve antitumor T cell responses; thus, we examined how these receptors and their ligands (Qa-1b and retinoic acid early inducible 1 [Rae-1], respectively) regulate the RT response in C57BL/6 mice bearing syngeneic B16F10 melanoma and MC38 colorectal adenocarcinoma tumors. RT (15 Gy) transiently reduced B16F10 tumor burden, whereas MC38 tumors exhibited durable response to RT. Intratumoral NK and CD8 T cells expressed NKG2A and NKG2D in both models, which was unaltered by RT. In vitro/in vivo RT increased tumor/stromal cell Qa-1b and Rae-1 expression in both models, especially B16F10 tumors, but IFN-γ stimulation induced both Qa-1b and Rae-1 only in B16F10 tumors. NKG2A/Qa-1b inhibition alone did not improve RT response in either model, but combined RT and NKG2A/PD-1 blockade improved survival in the B16F10 model. Depletion experiments indicate that the triple therapy efficacy is CD8 T cell-dependent with negligible NK cell contribution. RNA sequencing of CD8 T cells from triple therapy-treated B16F10 tumors showed increased proliferative capacity compared with RT and PD-1 blockade alone. Our work demonstrates that RT modulates NKG2A ligand expression, which inhibits RT-induced T cell responses in tumors that fail to respond to combined RT and PD-1 blockade. These results provide a rationale for combining NKG2A blockade with immune checkpoint blockade therapies and RT to improve clinical response.

Neuroprotective agents effective against radiation damage of central nervous system

Ionizing radiation caused by medical treatments, nuclear events or even space flights can irreversibly damage structure and function of brain cells. That can result in serious brain damage, with memory and behavior disorders, or even fatal oncologic or neurodegenerative illnesses. Currently used treatments and drugs are mostly targeting biochemical processes of cell apoptosis, radiation toxicity, neuroinflammation, and conditions such as cognitive-behavioral disturbances or others that result from the radiation insult. With most drugs, the side effects and potential toxicity are also to be considered. Therefore, many agents have not been approved for clinical use yet. In this review, we focus on the latest and most effective agents that have been used in animal and also in the human research, and clinical treatments. They could have the potential therapeutical use in cases of radiation damage of central nervous system, and also in prevention considering their radioprotecting effect of nervous tissue.

Immune Modulation Plus Tumor Ablation: Adjuvants and Antibodies to Prime and Boost Anti-Tumor Immunity In Situ

In situ tumor ablation techniques, like radiotherapy, cryo- and heat-based thermal ablation are successfully applied in oncology for local destruction of tumor masses. Although diverse in technology and mechanism of inducing cell death, ablative techniques share one key feature: they generate tumor debris which remains in situ. This tumor debris functions as an unbiased source of tumor antigens available to the immune system and has led to the concept of in situ cancer vaccination. Most studies, however, report generally modest tumor-directed immune responses following local tumor ablation as stand-alone treatment. Tumors have evolved mechanisms to create an immunosuppressive tumor microenvironment (TME), parts of which may admix with the antigen depot. Provision of immune stimuli, as well as approaches that counteract the immunosuppressive TME, have shown to be key to boost ablation-induced anti-tumor immunity. Recent advances in protein engineering have yielded novel multifunctional antibody formats. These multifunctional antibodies can provide a combination of distinct effector functions or allow for delivery of immunomodulators specifically to the relevant locations, thereby mitigating potential toxic side effects. This review provides an update on immune activation strategies that have been tested to act in concert with tumor debris to achieve in situ cancer vaccination. We further provide a rationale for multifunctional antibody formats to be applied together with in situ ablation to boost anti-tumor immunity for local and systemic tumor control.

Intrinsic Radiosensitivity Is Not the Determining Factor in Treatment Response Differences between HPV Negative and HPV Positive Head and Neck Cancers

Head and neck squamous cell carcinomas (HNSCC) resulting from human papillomavirus (HPV) are increasing in incidence but demonstrate significantly better treatment response than HNSCC from other causes such as tobacco and alcohol. This study sought to identify differences in HNSCC, intrinsic to HPV status, in their response to radiation dose. Previously unexamined changes in radio-responsiveness following fractionated X-ray irradiation were compared between HPV positive and negative statuses of HNSCC. Six HNSCC cell lines, 3 of each HPV status, were investigated for radiosensitivity by clonogenic assay and modelled by response as a function of dose. Generational cultures of each cell line were developed to follow changes in radiosensitivity after repeated irradiations simulating fractionated radiation therapy. As a group, the HPV positive cell lines were more radiosensitive, but with changes following repeated fractions of dose, and modelling of response as a function of dose, both statuses displayed large radiobiological heterogeneity. These findings challenge current radiobiological assumptions of head and neck cancers as early responding tissue to radiation and may go some way in explaining difficulties reaching consensus in stratification of treatment by HPV status. Consequently, results from this study do not support stratifying radiation therapy by HPV status.

The Molecular Effects of Ionizing Radiations on Brain Cells: Radiation Necrosis vs. Tumor Recurrence

The central nervous system (CNS) is generally resistant to the effects of radiation, but higher doses, such as those related to radiation therapy, can cause both acute and long-term brain damage. The most important results is a decline in cognitive function that follows, in most cases, cerebral radionecrosis. The essence of radio-induced brain damage is multifactorial, being linked to total administered dose, dose per fraction, tumor volume, duration of irradiation and dependent on complex interactions between multiple brain cell types. Cognitive impairment has been described following brain radiotherapy, but the mechanisms leading to this adverse event remain mostly unknown. In the event of a brain tumor, on follow-up radiological imaging often cannot clearly distinguish between recurrence and necrosis, while, especially in patients that underwent radiation therapy (RT) post-surgery, positron emission tomography (PET) functional imaging, is able to differentiate tumors from reactive phenomena. More recently, efforts have been done to combine both morphological and functional data in a single exam and acquisition thanks to the co-registration of PET/MRI. The future of PET imaging to differentiate between radionecrosis and tumor recurrence could be represented by a third-generation PET tracer already used to reveal the spatial extent of brain inflammation. The aim of the following review is to analyze the effect of ionizing radiations on CNS with specific regard to effect of radiotherapy, focusing the attention on the mechanism underling the radionecrosis and the brain damage, and show the role of nuclear medicine techniques to distinguish necrosis from recurrence and to early detect of cognitive decline after treatment.

First report on extended distance between tumor lesion and adjacent organs at risk using interventionally applied balloon catheters: a simple procedure to optimize clinical target volume covering effective isodose in interstitial high-dose-rate brachytherapy of liver malignomas

Purpose

Organs at risk (OARs), which are very close to a clinical target volume (CTV), can compromise effective tumor irradiation. The present study investigated the feasibility and safety of a novel approach, in particular, the extent of the dosimetric effect of distancing CTV from adjacent OARs by means of interventionally applied balloon catheters.

Material and methods

Patients with peripheral hepatic malignancies, in whom the critical proximity of an OAR to the CTV in the assessment by contrast-enhanced magnetic resonance imaging (MRI) scans and the preplanning process were included. Additionally, patients underwent placement of an interventional balloon catheter during computed tomography (CT)-guided application of interstitial brachytherapy (iBT) catheters inserted into the tissue between hepatic capsule and adjacent OAR. The virtual position of an OAR without balloon catheter was anticipated and contoured in addition to contouring of CTV and OAR. The calculated dose values for CTV as well as 1 cc of the relevant OAR (D_1cc) with and without balloon were recorded. The D_1cc of the realized irradiation plan was statistically compared to the D_1cc of the virtually contoured OARs.

Results

In 31 cases, at least one balloon catheter was administered. The mean D_1cc of the OAR in the group with balloon(s) was 12.6 Gy compared with 16 Gy in the virtual cohort without the device, therefore significantly lower (p < 0.001). Overall, there were no acute complications. Severe (> 2 CTCAEv4.03) late complications observed in 3/31 (9.6%) patients during follow-up period after brachytherapy were most certainly not due to the balloon application. Side effects were probably associated with pre-existing serious diseases and potentially additional local late effects of the irradiation in general rather than with the balloon catheters.

Conclusions

The distancing of the adjacent OARs allows a higher D₁₀₀ value of CTV, therefore allowing for more efficient local control.

Radiobiological dose calculation parameters for cervix cancer brachytherapy: A systematic review

The GEC-ESTRO recommendation in cervical cancer treatment planning, including external beam radiotherapy and brachytherapy boosts, is to use radiobiological dose calculations. Such calculations utilize the linear-quadratic model to estimate the effect of multiple cellular response factors and dose delivery parameters. The radiobiological parameters utilized in these calculations are literature values estimated based on clinical and experimental results. However, the impact of the uncertainties associated with these parameters is often not fully appreciated. This review includes a summary of the radiobiological dose calculation (for both high-dose-rate and pulsed-dose-rate brachytherapy boost treatments) for cervical cancer and a compilation of the reported values of the associated parameters. As discrepancies exist between conventionally recommended and published values, equivalencies between current brachytherapy boosts may be imprecise and could create underappreciated uncertainties in the radiobiological dose calculations. This review highlights these uncertainties by calculating the radiobiological dose delivered by the brachytherapy boost when assuming different radiobiological parameter values (within the range reported by previous research). Furthermore, conventional treatment planning does not consider the effects of proliferation of the tumor over the treatment time, which can significantly decrease its radiobiological dose and can introduce an additional variance of over 7 Gy₁₀. Further investigation of uncertainties in parameter values and modifications of current dose models could improve the accuracy of radiobiological dose calculation.

Radiation therapy-induced metastasis: radiobiology and clinical implications

Radiation therapy is an effective means of achieving local control in a wide range of primary tumours, with the reduction in the size of the tumour(s) thought to mediate the observed reductions in metastatic spread in clinical trials. However, there is evidence to suggest that the complex changes induced by radiation in the tumour environment can also present metastatic risks that may counteract the long-term efficacy of the treatment. More than 25 years ago, several largely theoretical mechanisms by which radiation exposure might increase metastatic risk were postulated. These include the direct release of tumour cells into the circulation, systemic effects of tumour and normal tissue irradiation and radiation-induced changes in tumour cell phenotype. Here, we review the data that has since emerged to either support or refute these putative mechanisms focusing on how the unique radiobiology underlying modern radiotherapy modalities might alter these risks.

Structural and functional damages of whole body ionizing radiation on rat brain homogenate membranes and protective effect of amifostine

PURPOSE

To investigate the effects of whole body ionizing radiation at a sublethal dose on rat brain homogenate membranes and the protective effects of amifostine on these systems at molecular level.

MATERIALS AND METHODS

Sprague-Dawley rats, in the absence and presence of amifostine, were whole-body irradiated at a single dose of 8 Gy and decapitated after 24 h. The brain homogenate membranes of these rats were analyzed using Fourier Transform Infrared (FTIR) spectroscopy.

RESULTS

Ionizing radiation caused a significant increase in the lipid to protein ratio and significant decreases in the ratios of olefinic = CH/lipid, CH₂/lipid, carbonyl ester/lipid and CH₃/lipid suggesting, respectively, a more excessive decrease in the protein content and the degradation of lipids as a result of lipid peroxidation. In addition, radiation changed the secondary structure of proteins and the status of packing of membrane lipid head groups. Furthermore, it caused a decrease in lipid order and an increase in membrane fluidity. The administration of amifostine before ionizing radiation inhibited all the radiation-induced alterations in brain homogenate membranes.

CONCLUSIONS

The results revealed that whole body ionizing radiation at a sublethal dose causes significant alterations in the structure, composition and dynamics of brain homogenate membranes and amifostine has a protective effect on these membranes.

Potential strategies to ameliorate risk of radiotherapy-induced second malignant neoplasms

This review is aimed at the issue of radiation-induced second malignant neoplasms (SMN), which has become an important problem with the increasing success of modern cancer radiotherapy (RT). It is imperative to avoid compromising the therapeutic ratio while addressing the challenge of SMN. The dilemma is illustrated by the role of reactive oxygen species in both the mechanisms of tumor cell kill and of radiation-induced carcinogenesis. We explore the literature focusing on three potential routes of amelioration to address this challenge. An obvious approach to avoiding compromise of the tumor response is the use of radioprotectors or mitigators that are selective for normal tissues. We also explore the opportunities to avoid protection of the tumor by topical/regional radioprotection of normal tissues, although this strategy limits the scope of protection. Finally, we explore the role of the bystander/abscopal phenomenon in radiation carcinogenesis, in association with the inflammatory response. Targeted and non-targeted effects of radiation are both linked to SMN through induction of DNA damage, genome instability and mutagenesis, but differences in the mechanisms and kinetics between targeted and non-targeted effects may provide opportunities to lessen SMN. The agents that could be employed to pursue each of these strategies are briefly reviewed. In many cases, the same agent has potential utility for more than one strategy. Although the parallel problem of chemotherapy-induced SMN shares common features, this review focuses on RT associated SMN. Also, we avoid the burgeoning literature on the endeavor to suppress cancer incidence by use of antioxidants and vitamins either as dietary strategies or supplementation.

Cancer-associated fibroblasts from lung tumors maintain their immunosuppressive abilities after high-dose irradiation

Accumulating evidence supports the notion that high-dose (>5 Gy) radiotherapy (RT) regimens are triggering stronger pro-immunogenic effects than standard low-dose (2 Gy) regimens. However, the effects of RT on certain immunoregulatory elements in tumors remain unexplored. In this study, we have investigated the effects of high-dose radiotherapy (HD-RT) on the immunomodulating functions of cancer-associated fibroblasts (CAFs). Primary CAF cultures were established from lung cancer specimens derived from patients diagnosed for non-small cell lung cancer. Irradiated and non-irradiated CAFs were examined for immunomodulation in experiments with peripheral blood mononuclear cells from random, healthy donors. Regulation of lymphocytes behavior was checked by lymphocyte proliferation assays, lymphocyte migration assays, and T-cell cytokine production. Additionally, CAF-secreted immunoregulatory factors were studied by multiplex protein arrays, ELISAs, and by LC-MS/MS proteomics. In all functional assays, we observed a powerful immunosuppressive effect exerted by CAF-conditioned medium on activated T-cells (p > 0.001), and this effect was sustained after a single radiation dose of 18 Gy. Relevant immunosuppressive molecules such as prostaglandin E2, interleukin-6, and -10, or transforming growth factor-β were found in CAF-conditioned medium, but their secretion was unchanged after irradiation. Finally, immunogenic cell death responses in CAFs were studied by exploring the release of high motility group box-1 and ATP. Both alarmins remained undetectable before and after irradiation. In conclusion, CAFs play a powerful immunosuppressive effect over activated T-cells, and this effect remains unchanged after HD-RT. Importantly, CAFs do not switch on immunogenic cell death responses after exposure to HD-RT.