Irradiation With Carbon Ion Beams Induces Apoptosis, Autophagy, and Cellular Senescence in a Human Glioma-Derived Cell Line

A Practical Primer on Particle Therapy

PURPOSE

Particle therapy is a promising treatment technique that is becoming more commonly used. Although proton beam therapy remains the most commonly used particle therapy, multiple other heavier ions have been used in the preclinical and clinical settings, each with its own unique properties. This practical review aims to summarize the differences between the studied particles, discussing their radiobiological and physical properties with additional review of the available clinical data.

METHODS AND MATERIALS

A search was carried out on the PubMed databases with search terms related to each particle. Relevant radiobiology, physics, and clinical studies were included. The articles were summarized to provide a practical resource for practicing clinicians.

RESULTS

A total of 113 articles and texts were included in our narrative review. Currently, proton beam therapy has the most data and is the most widely used, followed by carbon, helium, and neutrons. Although oxygen, neon, silicon, and argon have been used clinically, their future use will likely remain limited as monotherapy.

CONCLUSIONS

This review summarizes the properties of each of the clinically relevant particles. Protons, helium, and carbon will likely remain the most commonly used, although multi-ion therapy is an emerging technique.

Review of Recent Improvements in Carbon Ion Radiation Therapy in the Treatment of Glioblastoma

Purpose

This article provides an overview of the physical and biologic properties of carbon ions, followed by an examination of the latest clinical outcomes in patients with glioma who have received carbon ion radiation therapy.

Methods and Materials

According to thee articles that have been reviewed, glioma represents the predominant form of neoplastic growth in the brain, accounting for approximately 51% of all malignancies affecting the nervous system. Currently, high-grade glioma, specifically glioblastoma, comprises 15% of cases and is associated with a high mortality rate. The development of novel drugs for the treatment of high-grade tumors has been impeded by various factors, such as the blood-brain barrier and tumor heterogeneity, despite numerous endeavors. According to the definition of tumor grade established by the World Health Organization, the conventional treatment involves surgical resection followed by adjuvant radiation and chemotherapy. Despite numerous attempts in photon radiation therapy to apply the highest possible dose to the tumor site while minimizing damage to healthy tissue, there has been no success in increasing patient survival. The primary cause of resistance to conventional radiation therapy methods, namely x-ray and gamma-ray, is attributed to the survival of radio-resistant glioma stem cells, which have the potential to trigger a recurrence of tumors. Particle beams, such as protons and carbon ions, can deposit the highest dose to a confined region, thus offering a more accurate dose distribution compared with photon beams.

Results

Carbon ions exhibit higher linear energy transfer and relative biologic effectiveness compared with photons, potentially enabling them to overcome radio-resistant tumor cells.

Conclusions

Therefore, it can be hypothesized that carbon ion radiation therapy may show superior efficacy in destroying neoplastic cells with reduced negative outcomes compared with x-ray radiation therapy.

Remodeling of Chromatin Accessibility Regulates the Radiological Responses of NSCLC A549 Cells to High-LET Carbon Ions

Carbon-ion radiation therapy (CIRT) may offer remarkable advantages in cancer treatment with its unique physical and biological characteristics. However, the underlying epigenetic regulatory mechanisms of cancer response to CIRT remain to be identified. In this study, we showed consistent but different degrees of biological effects induced in NSCLC A549 cells by carbon ions of different LET. The genome-wide chromatin accessibility and transcriptional profiles of carbon ion-treated A549 cells were performed using transposase-accessible chromatin sequencing (ATAC-seq) and RNA-seq, respectively, and further gene regulatory network analysis was performed by integrating the two sets of genomic data. Alterations in chromatin accessibility by carbon ions of different LET predominantly occurred in intron, distal intergenic and promoter regions of differential chromatin accessibility regions. The transcriptional changes were mainly regulated by proximal chromatin accessibility. Notably, CCCTC-binding factor (CTCF) was identified as a key transcription factor in the cellular response to carbon ions. The target genes regulated by CTCF in response to carbon ions were found to be closely associated with the LET of carbon ions, particularly in the regulation of gene transcription within the DNA replication- and metabolism-related signaling pathways. This study provides a regulatory profile of genes involved in key signaling pathways and highlighted key regulatory elements in NSCLC A549 cells during CIRT, which expands our understanding of the epigenetic mechanisms of carbon ion-induced biological effects and reveals an important role for LET in the regulation of changes in chromatin accessibility, although further research is needed.

Network pharmacology -based study on the mechanism of traditional Chinese medicine in the treatment of glioblastoma multiforme

BACKGROUND

Glioblastoma multiforme (GBM) is one of the most common primary malignant brain tumors. Yi Qi Qu Yu Jie Du Fang (YYQQJDF) is a traditional Chinese medicine (TCM) prescription for GBM. The present study aimed to use a network pharmacology method to analyze the underlying mechanism of YQQYJDF in treating GBM.

METHODS

GBM sample data, active ingredients and potential targets of YQQYJDF were obtained from databases. R language was used to screen differentially expressed genes (DEGs) between GBM tissues and normal tissues, and to perform enrichment analysis and weighted gene coexpression network analysis (WGCNA). The Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) database was used to perform a protein‒protein interaction (PPI) analysis. A Venn diagram was used to obtain the core target genes of YQQYJDF for GBM treatment. Molecular docking was used to verify the binding between the active ingredient molecules and the proteins corresponding to the core target genes. Cell proliferation assays and invasion assays were used to verify the effect of active ingredients on the proliferation and invasion of glioma cells.

RESULTS

A total of 73 potential targets of YQQYJDF in the treatment of GBM were obtained. Enrichment analyses showed that the biological processes and molecular functions involved in these target genes were related to the activation of the G protein-coupled receptor (GPCR) signaling pathway and the regulation of hypoxia. The neuroactive ligand‒receptor pathway, the cellular senescence pathway, the calcium signaling pathway, the cell cycle pathway and the p53 signaling pathway might play important roles. Combining the results of WGCNA and PPI analysis, five core target genes and their corresponding four core active ingredients were screened. Molecular docking indicated that the core active ingredient molecules and the proteins corresponding to the core target genes had strong binding affinities. Cell proliferation and invasion assays showed that the core active ingredients of YQQYJDF significantly inhibited the proliferation and invasion of glioma cells (P < 0.01).

CONCLUSIONS

The present study predicted the possible active ingredients and targets of YQQYJDF in treating GBM, and analyzed its possible mechanism. These results may provide a basis and ideas for further research.

Cellular senescence in glioma

INTRODUCTION

Glioma is the most common primary brain tumor and is often associated with treatment resistance and poor prognosis. Standard treatment typically involves radiotherapy and temozolomide-based chemotherapy, both of which induce cellular senescence-a tumor suppression mechanism.

DISCUSSION

Gliomas employ various mechanisms to bypass or escape senescence and remain in a proliferative state. Importantly, senescent cells remain viable and secrete a large number of factors collectively known as the senescence-associated secretory phenotype (SASP) that, paradoxically, also have pro-tumorigenic effects. Furthermore, senescent cells may represent one form of tumor dormancy and play a role in glioma recurrence and progression.

CONCLUSION

In this article, we delineate an overview of senescence in the context of gliomas, including the mechanisms that lead to senescence induction, bypass, and escape. Furthermore, we examine the role of senescent cells in the tumor microenvironment and their role in tumor progression and recurrence. Additionally, we highlight potential therapeutic opportunities for targeting senescence in glioma.

Immune checkpoint inhibitors and Carbon iON radiotherapy In solid Cancers with stable disease (ICONIC)

ICONIC is a multicenter, open-label, nonrandomized phase II clinical trial aiming to assess the feasibility and clinical activity of the addition of carbon ion radiotherapy to immune checkpoint inhibitors in cancer patients who have obtained disease stability with pembrolizumab administered as per standard-of-care. The primary end point is objective response rate, and the secondary end points are safety, survival and disease control rate. Translational research is an exploratory aim. The planned sample size is 27 patients. The study combination will be considered worth investigating if at least four objective responses are observed. If the null hypothesis is rejected, ICONIC will be the first proof of concept of the feasibility and clinical activity of the addition of carbon ion radiotherapy to immune checkpoint inhibitors in oncology.

Are charged particles a good match for combination with immunotherapy? Current knowledge and perspectives

Charged particle radiotherapy, mainly using protons and carbon ions, provides physical characteristics allowing for a volume conformal irradiation and a reduction of the integral dose to normal tissue. Carbon ion therapy additionally features an increased biological effectiveness resulting in peculiar molecular effects. Immunotherapy, mostly performed with immune checkpoint inhibitors, is nowadays considered a pillar in cancer therapy. Based on the advantageous features of charged particle radiotherapy, we review pre-clinical evidence revealing a strong potential of its combination with immunotherapy. We argue that the combination therapy deserves further investigation with the aim of translation in clinics, where a few studies have been set up already.

Establishment of a cell senescence related prognostic model for predicting prognosis in glioblastoma

Background: Glioblastoma (GBM) is highly malignant and has a worse prognosis with age, and next-generation sequencing (NGS) provides us with a huge amount of information about GBM. Materials and Methods: Through the enrichment scores of cell senescence-related pathways, we constructed a consensus matrix and mined molecular subtypes and explored the differences in pathological, immune/pathway and prognostic. Also we identified key genes related to cell senescence characteristics using least absolute shrinkage and selection operator (Lasso) regression and univariate COX regression analysis models. The use of risk factor formats to construct clinical prognostic models also explored the differences in immunotherapy/chemotherapy within the senescence-related signatures score (SRS.score) subgroups. Decision trees built with machine learning to identify the main factors affecting prognosis have further improved the prognosis model and survival prediction. Results: We obtained seven prognostic-related pathways related to cell senescence. We constructed four different molecular subtypes and found patients with subtype C1 had the worst prognosis. C4 had the highest proportion of patients with IDH mutations. 1005 differentially expressed genes (DEGs) were analyzed, and finally 194 Risk genes and 38 Protective genes were obtained. Eight key genes responsible for cell senescence were finally identified. The clinical prognosis model was established based on SRS.score, and the prognosis of patients with high SRS.score was worse. SRS.score and age were the vital risk factors for GBM patients through decision tree model mining. Conclusion: We constructed a clinical prognosis model that could provide high prediction accuracy and survival prediction ability for adjuvant treatment of patients with GBM.

Recent advances in glioblastoma multiforme therapy: A focus on autophagy regulation

Despite conventional treatment options including chemoradiation, patients with the most aggressive primary brain tumor, glioblastoma multiforme (GBM), experience an average survival time of less than 15 months. Regarding the malignant nature of GBM, extensive research and discovery of novel treatments are urgently required to improve the patients' prognosis. Autophagy, a crucial physiological pathway for the degradation and recycling of cell components, is one of the exciting targets of GBM studies. Interventions aimed at autophagy activation or inhibition have been explored as potential GBM therapeutics. This review, which delves into therapeutic techniques to block or activate autophagy in preclinical and clinical research, aims to expand our understanding of available therapies battling GBM.

Key biological mechanisms involved in high-LET radiation therapies with a focus on DNA damage and repair

DNA damage and repair studies are at the core of the radiation biology field and represent also the fundamental principles informing radiation therapy (RT). DNA damage levels are a function of radiation dose, whereas the type of damage and biological effects such as DNA damage complexity, depend on radiation quality that is linear energy transfer (LET). Both levels and types of DNA damage determine cell fate, which can include necrosis, apoptosis, senescence or autophagy. Herein, we present an overview of current RT modalities in the light of DNA damage and repair with emphasis on medium to high-LET radiation. Proton radiation is discussed along with its new adaptation of FLASH RT. RT based on α-particles includes brachytherapy and nuclear-RT, that is proton-boron capture therapy (PBCT) and boron-neutron capture therapy (BNCT). We also discuss carbon ion therapy along with combinatorial immune-based therapies and high-LET RT. For each RT modality, we summarise relevant DNA damage studies. Finally, we provide an update of the role of DNA repair in high-LET RT and we explore the biological responses triggered by differential LET and dose.

Autophagy inhibition is the next step in the treatment of glioblastoma patients following the Stupp era

It has now been nearly 15 years since the last major advance in the treatment of patients with glioma. "The addition of temozolomide to radiotherapy for newly diagnosed glioblastoma resulted in a clinically meaningful and statistically significant survival benefit with minimal additional toxicity". Autophagy is primarily a survival pathway, literally self-eating, that is utilized in response to stress (such as radiation and chemotherapy), enabling clearance of effete protein aggregates and multimolecular assemblies. Promising results have been observed in patients with glioma for over a decade now when autophagy inhibition with chloroquine derivatives coupled with conventional therapy. The application of autophagy inhibitors, the role of immune cell-induced autophagy, and the potential role of novel cellular and gene therapies, should now be considered for development as part of this well-established regimen.

A New Platinum-Based Prodrug Candidate for Chemotherapy and Its Synergistic Effect With Hadrontherapy: Novel Strategy to Treat Glioblastoma

Glioblastoma (GBM) is the most common tumor of the central nervous system. Current therapies, often associated with severe side effects, are inefficacious to contrast the GBM relapsing forms. In trying to overcome these drawbacks, (OC-6-44)-acetatodiamminedichlorido(2-(2-propynyl)octanoato)platinum(IV), also called Pt(IV)Ac-POA, has been recently synthesized. This new prodrug bearing as axial ligand (2-propynyl)octanoic acid (POA), a histone deacetylase inhibitor, has a higher activity due to (i) its high cellular accumulation by virtue of its high lipophilicity and (ii) the inhibition of histone deacetylase, which leads to the increased exposure of nuclear DNA, permitting higher platination and promoting cancer cell death. In the present study, we investigated the effects induced by Pt(IV)Ac-POA and its potential antitumor activity in human U251 glioblastoma cell line using a battery of complementary techniques, i.e., flow cytometry, immunocytochemistry, TEM, and Western blotting analyses. In addition, the synergistic effect of Pt(IV)Ac-POA associated with the innovative oncological hadrontherapy with carbon ions was investigated, with the aim to identify the most efficient anticancer treatment combination. Our in vitro data demonstrated that Pt(IV)Ac-POA is able to induce cell death, through different pathways, at concentrations lower than those tested for other platinum analogs. In particular, an enduring Pt(IV)Ac-POA antitumor effect, persisting in long-term treatment, was demonstrated. Interestingly, this effect was further amplified by the combined exposure to carbon ion radiation. In conclusion, Pt(IV)Ac-POA represents a promising prodrug to be incorporated into the treatment regimen for GBM. Moreover, the synergistic efficacy of the combined protocol using chemotherapeutic Pt(IV)Ac-POA followed by carbon ion radiation may represent a promising approach, which may overcome some typical limitations of conventional therapeutic protocols for GBM treatment.

Could Protons and Carbon Ions Be the Silver Bullets Against Pancreatic Cancer?

Pancreatic cancer is a very aggressive cancer type associated with one of the poorest prognostics. Despite several clinical trials to combine different types of therapies, none of them resulted in significant improvements for patient survival. Pancreatic cancers demonstrate a very broad panel of resistance mechanisms due to their biological properties but also their ability to remodel the tumour microenvironment. Radiotherapy is one of the most widely used treatments against cancer but, up to now, its impact remains limited in the context of pancreatic cancer. The modern era of radiotherapy proposes new approaches with increasing conformation but also more efficient effects on tumours in the case of charged particles. In this review, we highlight the interest in using charged particles in the context of pancreatic cancer therapy and the impact of this alternative to counteract resistance mechanisms.

The Unfolded Protein Response: Neutron-Induced Therapy Autophagy as a Promising Treatment Option for Osteosarcoma

Radiotherapy using high linear energy transfer (LET) radiation results in effectively killing tumor cells while minimizing dose (biological effective) to normal tissues to block toxicity. It is well known that high LET radiation leads to lower cell survival per absorbed dose than low LET radiation. High-linear energy transfer (LET) neutron treatment induces autophagy in tumor cells, but its precise mechanisms in osteosarcoma are unknown. Here, we investigated this mechanism and the underlying signaling pathways. Autophagy induction was examined in gamma-ray-treated KHOS/NP and MG63 osteosarcoma cells along with exposure to high-LET neutrons. The relationship between radiosensitivity and autophagy was assessed by plotting the cell surviving fractions against autophagy levels. Neutron treatment increased autophagy rates in irradiated KHOS/NP and MG63 cells; neutrons with high-LETs showed more effective inhibition than those with lower LET gamma-rays. To determine whether the unfolded protein response and Akt-mTOR pathways triggered autophagy, phosphorylated eIF2α and JNK levels, and phospho-Akt, phosphor-mTOR, and phospho-p70S6 levels were, respectively, investigated. High-LET neutron exposure inhibited Akt phosphorylation and increased Beclin 1 expression during the unfolded protein response, thereby enhancing autophagy. The therapeutic efficacy of high-LET neutron radiation was also assessed in vivo using an orthotopic mouse model. Neutron-irradiated mice showed reduced tumor growth without toxicity relative to gamma-ray-treated mice. The effect of high-LET neutron exposure on the expression of signaling proteins LC3, p-elF2a, and p-JNK was investigated by immunohistochemistry. Tumors in high-LET-neutron radiation-treated mice showed higher apoptosis rates, and neutron exposure significantly elevated LC3 expression, and increased p-elF2a and p-JNK expression levels. Overall, these results demonstrate that autophagy is important in radiosensitivity, cell survival, and cellular resistance against high-LET neutron radiation. This correlation between cellular radiosensitivity and autophagy may be used to predict radiosensitivity in osteosarcoma.

AMP-Activated Protein Kinase Mediates the Effect of Leptin on Avian Autophagy in a Tissue-Specific Manner

Autophagy, a highly conserved intracellular self-digestion process, plays an integral role in maintaining cellular homeostasis. Although emerging evidence indicate that the endocrine system regulates autophagy in mammals, there is still a scarcity of information on autophagy in avian (non-mammalian) species. Here, we show that intracerebroventricular administration of leptin reduces feed intake, modulates the expression of feeding-related hypothalamic neuropeptides, activates leptin receptor and signal transducer and activator of transcription (Ob-Rb/STAT) pathway, and significantly increases the expression of autophagy-related proteins (Atg3, Atg5, Atg7, beclin1, and LC3B) in chicken hypothalamus, liver, and muscle. Similarly, leptin treatment activates Ob-Rb/STAT pathway and increased the expression of autophagy-related markers in chicken hypothalamic organotypic cultures, muscle (QM7) and hepatocyte (Sim-CEL) cell cultures as well as in Chinese Hamster Ovary (CHO-K1) cells-overexpressing chicken Ob-Rb and STAT3. To define the downstream mediator(s) of leptin's effects on autophagy, we determined the role of the master energy sensor AMP-activated protein kinase (AMPK). Leptin treatment significantly increased the phosphorylated levels of AMPKα1/2 at Thr172 site in chicken hypothalamus and liver, but not in muscle. Likewise, AMPKα1/2 was activated by leptin in chicken hypothalamic organotypic culture and Sim-CEL, but not in QM7 cells. Blocking AMPK activity by compound C reverses the autophagy-inducing effect of leptin. Together, these findings indicate that AMPK mediates the effect of leptin on chicken autophagy in a tissue-specific manner.

Induction of autophagy and interleukin 6 secretion in bystander cells: metabolic cooperation for radiation-induced rescue effect?

We hypothesized that radiation-induced rescue effect (RIRE) shared similar mechanisms with 'metabolic cooperation', in which nutrient-deprived cancer cells prompted normal cells to provide nutrients. Our data demonstrated that X-ray irradiation induced autophagy in HeLa cells, which could last at least 18 h, and proved that the irradiated cells (IRCs) resorted to breaking down their own intracellular components to supply the molecules required for cell-repair enhancement (e.g. to activate the NF-κB pathway) in the absence of support from bystander unirradiated cells (UICs). Furthermore, autophagy accumulation in IRCs was significantly reduced when they were partnered with UICs, and more so with UICs with pre-induced autophagy before partnering (through starvation using Earle's Balanced Salt Solution), which showed that the autophagy induced in UICs supported the IRCs. Our results also showed that interleukin 6 (IL-6) was secreted by bystander UICs, particularly the UICs with pre-induced autophagy, when they were cultured in the medium having previously conditioned irradiated HeLa cells. It was established that autophagy could activate the signal transducer and activator of transcription 3 (STAT3) that was required for the IL-6 production in the autophagy process. Taken together, the metabolic cooperation of RIRE was likely initiated by the bystander factors released from IRCs, which induced autophagy and activated STAT3 to produce IL-6 in bystander UICs, and was finally manifested in the activation of the NF-κB pathway in IRCs by the IL-6 secreted by the UICs.

RBE and related modeling in carbon-ion therapy

Carbon ion therapy is a promising evolving modality in radiotherapy to treat tumors that are radioresistant against photon treatments. As carbon ions are more effective in normal and tumor tissue, the relative biological effectiveness (RBE) has to be calculated by bio-mathematical models and has to be considered in the dose prescription. This review (i) introduces the concept of the RBE and its most important determinants, (ii) describes the physical and biological causes of the increased RBE for carbon ions, (iii) summarizes available RBE measurements in vitro and in vivo, and (iv) describes the concepts of the clinically applied RBE models (mixed beam model, local effect model, and microdosimetric-kinetic model), and (v) the way they are introduced into clinical application as well as (vi) their status of experimental and clinical validation, and finally (vii) summarizes the current status of the use of the RBE concept in carbon ion therapy and points out clinically relevant conclusions as well as open questions. The RBE concept has proven to be a valuable concept for dose prescription in carbon ion radiotherapy, however, different centers use different RBE models and therefore care has to be taken when transferring results from one center to another. Experimental studies significantly improve the understanding of the dependencies and limitations of RBE models in clinical application. For the future, further studies investigating quantitatively the differential effects between normal tissues and tumors are needed accompanied by clinical studies on effectiveness and toxicity.

Carbon ions of different linear energy transfer (LET) values induce apoptosis & G2 cell cycle arrest in radio-resistant melanoma cells

Background & objectives:

The main goal when treating malignancies with radiation is to deprive tumour cells of their reproductive potential. One approach is to induce tumour cell apoptosis. This study was conducted to evaluate the ability of carbon ions (¹²C) to induce apoptosis and cell cycle arrest in human HTB140 melanoma cells.

Methods:

In this in vitro study, human melanoma HTB140 cells were irradiated with the 62 MeV/n carbon (¹²C) ion beam, having two different linear energy transfer (LET) values: 197 and 382 keV/μm. The dose range was 2 to 16 Gy. Cell viability was estimated by the sulforhodamine B assay seven days after irradiation. The cell cycle and apoptosis were evaluated 48 h after irradiation using flow cytometry. At the same time point, protein and gene expression of apoptotic regulators were estimated using the Western blot and q-PCR methods, respectively.

Results:

Cell viability experiments indicated strong anti-tumour effects of ¹²C ions. The analysis of cell cycle showed that ¹²C ions blocked HTB140 cells in G2 phase and induced the dose dependent increase of apoptosis. The maximum value of 21.8 per cent was attained after irradiation with LET of 197 keV/μm at the dose level of 16 Gy. Pro-apoptotic effects of ¹²C ions were confirmed by changes of key apoptotic molecules: the p53, Bax, Bcl-2, poly ADP ribose polymerase (PARP) as well as nuclear factor kappa B (NFκB). At the level of protein expression, the results indicated significant increases of p53, NFκB and Bax/Bcl-2 ratio and PARP cleavage. The Bax/Bcl-2 mRNA ratio was also increased, while no change was detected in the level of NFκB mRNA.

Interpretation & conclusions:

The present results indicated that anti-tumour effects of ¹²C ions in human melanoma HTB140 cells were accomplished through induction of the mitochondrial apoptotic pathway as well as G2 arrest.

Tumor Dormancy and Relapse: From a Natural Byproduct of Evolution to a Disease State

Species evolve by mutations and epigenetic changes acting on individuals in a population; tumors evolve by similar mechanisms at a cellular level in a tissue. This article reviews growing evidence about tumor dormancy and suggests that (i) cellular malignancy is a natural byproduct of evolutionary mechanisms, such as gene mutations and epigenetic modifications, which is manifested in the form of tumor dormancy in healthy individuals as well as in cancer survivors; (ii) cancer metastasis could be an early dissemination event that could occur during malignant dormancy even before primary cancer is clinically detectable; and (iii) chronic inflammation is a key factor in awakening dormant malignant cells at the primary site, leading to primary cancer development, and at distant sites, leading to advanced stage diseases. On the basis of this evidence, it is reasonable to propose that we are all cancer survivors rather than cancer-free individuals because of harboring dormant malignant cells in our organs. A better understanding of local and metastatic tumor dormancy could lead to novel cancer therapeutics for the prevention of cancer. Cancer Res; 77(10); 2564-9. ©2017 AACR.

Sequential histological findings and clinical response after carbon ion radiotherapy for unresectable sarcoma

Background and purpose

The efficacy of carbon ion radiotherapy (CIRT) for bone and soft tissue sarcoma has been reported recently. Although histological assessment after CIRT requires skilled interpretation, little information is presently available. In this study, we report sequential histological findings after treatment with CIRT, and evaluate the association between these findings and clinical response.

Material and methods

Seven patients with unresectable sarcoma underwent needle biopsy 12 times at an average of 14.3 months after CIRT and were included in this study.

Results

One patient underwent two biopsies after CIRT for chordoma. Although a few suspected residual chordoma cells were observed at 19 and 30 months after CIRT, the tumor continued to shrink at 75 months. Immunohistochemical analysis of post-CIRT specimens revealed CK AE1/3, EMA, and S100 expression, as in the pre-CIRT specimen. In total, viable tumor cells were found in 9 of 12 specimens; however, only 2 patients showed recurrent masses on radiological examination. The other 5 patients had stable disease.

Conclusions

Viable tumor cells after CIRT did not always cause recurrence. This may be due to observation of dying cells or radiation-induced deformed cells. Histological evaluation after CIRT should be done carefully.

Telomere-Mitochondrion Links Contribute to Induction of Senescence in MCF-7 Cells after Carbon-Ion Irradiation

The effects of carbon-ion irradiation on cancer cell telomere function have not been comprehensively studied. In our previous report cancer cells with telomere dysfunction were more sensitive to carbon-ion irradiation, but the underlying mechanisms remained unclear. Here we found that telomerase activity was suppressed by carbon-ion irradiation via hTERT down-regulation. Inhibition of telomere activity by MST-312 further increased cancer cell radiosensitivity to carbon-ion radiation. hTERT suppression caused by either carbon-ion irradiation or MST-312 impaired mitochondrial function, as indicated by decreased membrane potential, mtDNA copy number, mitochondrial mass, total ATP levels and elevated reactive oxygen species (ROS). PGC-1α expression was repressed after carbion-ion irradiation, and hTERT inhibition by MST-312 could further exacerbate this effect. Lowering the mitochondrial ROS level by MitoTEMPO could partially counteract the induction of cellular senescence induced by carbon-ion radiation and MST-312 incubation. Taken together, the current data suggest that telomere-mitochondrion links play a role in the induction of senescence in MCF-7 cells after carbon-ion irradiation.

Carbon Ion-Irradiated Hepatoma Cells Exhibit Coupling Interplay between Apoptotic Signaling and Morphological and Mechanical Remodeling

A apoptotic model was established based on the results of five hepatocellular carcinoma cell (HCC) lines irradiated with carbon ions to investigate the coupling interplay between apoptotic signaling and morphological and mechanical cellular remodeling. The expression levels of key apoptotic proteins and the changes in morphological characteristics and mechanical properties were systematically examined in the irradiated HCC lines. We observed that caspase-3 was activated and that the Bax/Bcl-2 ratio was significantly increased over time. Cellular morphology and mechanics analyses indicated monotonic decreases in spatial sizes, an increase in surface roughness, a considerable reduction in stiffness, and disassembly of the cytoskeletal architecture. A theoretical model of apoptosis revealed that mechanical changes in cells induce the characteristic cellular budding of apoptotic bodies. Statistical analysis indicated that the projected area, stiffness, and cytoskeletal density of the irradiated cells were positively correlated, whereas stiffness and caspase-3 expression were negatively correlated, suggesting a tight coupling interplay between the cellular structures, mechanical properties, and apoptotic protein levels. These results help to clarify a novel arbitration mechanism of cellular demise induced by carbon ions. This biomechanics strategy for evaluating apoptosis contributes to our understanding of cancer-killing mechanisms in the context of carbon ion radiotherapy.

Autophagic flux in glioblastoma cells

To establish metabolic context for radiation sensitivity by measuring autophagic flux in two different glioblastoma (GBM) cell lines. Clonogenic survival curve analysis of U87 or U251 cells exposed to γ radiation, fast neutrons, a mixed energy neutron beam (METNB) or Auger electrons from a gadolinium neutron capture (GdNC) reaction suggested other factors, beyond a defective DNA damage response, contribute to cell death of U251 cells. Altered tumor metabolism (autophagy) was hypothesized as a factor in U251 cells' clonogenic response. Each of the four different radiation modalities induced an increase in the number of autophagosomes in both U87 and U251 cells. Changes in the number of autophagosomes can be explained by either induction of autophagy or alterations in autophagic flux so autophagic flux was assayed by p62 immunoblotting or in engineered GBM cells that stably express an autophagy marker protein, LC3B-eGFP-mCherry. Perturbations in later stages of autophagy in U251 cells corresponded with radiation sensitivity of U251 cells irradiated with 10 Gy γ rays. Establishment of altered autophagic flux is a useful biomarker for metabolic stress and provided metabolic context for radiation sensitization to 10 Gy γ rays. These results provide strong evidence for the usefulness of managing tumor cell metabolism as a tool for the enhancement of radiation therapy.

Therapeutic interactions of autophagy with radiation and temozolomide in glioblastoma: evidence and issues to resolve

Glioblastoma is a unique model of non-metastasising disease that kills the vast majority of patients through local growth, despite surgery and local irradiation. Glioblastoma cells are resistant to apoptotic stimuli, and their death occurs through autophagy. This review aims to critically present our knowledge regarding the autophagic response of glioblastoma cells to radiation and temozolomide (TMZ) and to delineate eventual research directions to follow, in the quest of improving the curability of this incurable, as yet, disease. Radiation and TMZ interfere with the autophagic machinery, but whether cell response is driven to autophagy flux acceleration or blockage is disputable and may depend on both cell individuality and radiotherapy fractionation or TMZ schedules. Potent agents that block autophagy at an early phase of initiation or at a late phase of autolysosomal fusion are available aside to agents that induce functional autophagy, or even demethylating agents that may unblock the function of autophagy-initiating genes in a subset of tumours. All these create a maze, which if properly investigated can open new insights for the application of novel radio- and chemosensitising policies, exploiting the autophagic pathways that glioblastomas use to escape death.

Encorafenib (LGX818), a potent BRAF inhibitor, induces senescence accompanied by autophagy in BRAFV600E melanoma cells

Encorafenib (LGX818) is a new-generation BRAF inhibitor that is under evaluation in clinical trials. However, the underlying mechanism remains to be elucidated. Here we show that LGX818 potently decreased ERK phosphorylation and inhibited proliferation in BRAFV600E melanoma cell lines. Moreover, LGX818 downregulated CyclinD1 in a glycogen synthase kinase 3β-independent manner and induced cell cycle arrest in the G1 phase, Surprisingly, LGX818 triggered cellular senescence in BRAFV600E melanoma cells, as evidenced by increased β-galactosidase staining, while no appreciable induction of apoptosis was detected, as determined by Annexin V and propidium iodide staining and immunoblot analysis of caspase-3 processing and poly (ADP-ribose) polymerase cleavage. Increased p27KIP1 expression and retinoblastoma protein activation were detected during LGX818-induced senescence. Additionally, inhibition of dual-specificity tyrosine phosphorylation-regulated kinase 1B by AZ191 reversed LGX818-induced CyclinD1 turnover and senescence. Interestingly, autophagy is triggered through inhibition of the mTOR/70S6K pathway during LGX818-induced senescence. Moreover, autophagy inhibition by pharmacological and genetic regulation attenuates LGX818-induced senescence. Notably, combining LGX818 with autophagy modulators has anti-proliferative effect in LGX818-resistant BRAF mutant melanoma cells. Altogether, we uncovered a mechanism by which LGX818 exerts its anti-tumor activity in BRAFV600E melanoma cells.

Carbon ion beam triggers both caspase-dependent and caspase-independent pathway of apoptosis in HeLa and status of PARP-1 controls intensity of apoptosis

High linear energy transfer (LET) carbon ion beam (CIB) is becoming very promising tool for various cancer treatments and is more efficient than conventional low LET gamma or X-rays to kill malignant or radio-resistant cells, although detailed mechanism of cell death is still unknown. Poly (ADP-ribose) polymerase-1 (PARP-1) is a key player in DNA repair and its inhibitors are well-known as radio-sensitizer for low LET radiation. The objective of our study was to find mechanism(s) of induction of apoptosis by CIB and role of PARP-1 in CIB-induced apoptosis. We observed overall higher apoptosis in PARP-1 knocked down HeLa cells (HsiI) compared with negative control H-vector cells after irradiation with CIB (0-4 Gy). CIB activated both intrinsic and extrinsic pathways of apoptosis via caspase-9 and caspase-8 activation respectively, followed by caspase-3 activation, apoptotic body, nucleosomal ladder formation and sub-G1 accumulation. Apoptosis inducing factor translocation into nucleus in H-vector but not in HsiI cells after CIB irradiation contributed caspase-independent apoptosis. Higher p53 expression was observed in HsiI cells compared with H-vector after exposure with CIB. Notably, we observed about 37 % fall of mitochondrial membrane potential, activation of caspase-9 and caspase-3 and mild activation of caspase-8 without any detectable apoptotic body formation in un-irradiated HsiI cells. We conclude that reduction of PARP-1 expression activates apoptotic signals via intrinsic and extrinsic pathways in un-irradiated cells. CIB irradiation further intensified both intrinsic and extrinsic pathways of apoptosis synergistically along with up-regulation of p53 in HsiI cells resulting overall higher apoptosis in HsiI than H-vector.

Carbon ions induce autophagy effectively through stimulating the unfolded protein response and subsequent inhibiting Akt phosphorylation in tumor cells

Heavy ion beams have advantages over conventional radiation in radiotherapy due to their superb biological effectiveness and dose conformity. However, little information is currently available concerning the cellular and molecular basis for heavy ion radiation-induced autophagy. In this study, human glioblastoma SHG44 and cervical cancer HeLa cells were irradiated with carbon ions of different linear energy transfers (LETs) and X-rays. Our results revealed increased LC3-II and decreased p62 levels in SHG44 and HeLa cells post-irradiation, indicating marked induction of autophagy. The autophagic level of tumor cells after irradiation increased in a LET-dependent manner and was inversely correlated with the sensitivity to radiations of various qualities. Furthermore, we demonstrated that high-LET carbon ions stimulated the unfolded protein response (UPR) and mediated autophagy via the UPR-eIF2α-CHOP-Akt signaling axis. High-LET carbon ions more severely inhibited Akt-mTOR through UPR to effectively induce autophagy. Thus, the present data could serve as an important radiobiological basis to further understand the molecular mechanisms by which high-LET radiation induces cell death.

Radiosensitizing effect of carboplatin and paclitaxel to carbon-ion beam irradiation in the non-small-cell lung cancer cell line H460

The present study investigated the ability of carboplatin and paclitaxel to sensitize human non-small-cell lung cancer (NSCLC) cells to carbon-ion beam irradiation. NSCLC H460 cells treated with carboplatin or paclitaxel were irradiated with X-rays or carbon-ion beams, and radiosensitivity was evaluated by clonogenic survival assay. Cell proliferation was determined by counting the number of viable cells using Trypan blue. Apoptosis and senescence were evaluated by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining and senescence-associated β-galactosidase (SA-β-gal) staining, respectively. The expression of cleaved caspase-3, Bax, p53 and p21 was analyzed by western blotting. Clonogenic survival assays demonstrated a synergistic radiosensitizing effect of carboplatin and paclitaxel with carbon-ion beams; the sensitizer enhancement ratios (SERs) at the dose giving a 10% survival fraction (D10) were 1.21 and 1.22, respectively. Similarly, carboplatin and paclitaxel showed a radiosensitizing effect with X-rays; the SERs were 1.41 and 1.29, respectively. Cell proliferation assays validated the radiosensitizing effect of carboplatin and paclitaxel with both carbon-ion beam and X-ray irradiation. Carboplatin and paclitaxel treatment combined with carbon-ion beams increased TUNEL-positive cells and the expression of cleaved caspase-3 and Bax, indicating the enhancement of apoptosis. The combined treatment also increased SA-β-gal-positive cells and the expression of p53 and p21, indicating the enhancement of senescence. In summary, carboplatin and paclitaxel radiosensitized H460 cells to carbon-ion beam irradiation by enhancing irradiation-induced apoptosis and senescence.

Emerging issues in radiogenic cataracts and cardiovascular disease

In 2011, the International Commission on Radiological Protection issued a statement on tissue reactions (formerly termed non-stochastic or deterministic effects) to recommend lowering the threshold for cataracts and the occupational equivalent dose limit for the crystalline lens of the eye. Furthermore, this statement was the first to list circulatory disease (cardiovascular and cerebrovascular disease) as a health hazard of radiation exposure and to assign its threshold for the heart and brain. These changes have stimulated various discussions and may have impacts on some radiation workers, such as those in the medical sector. This paper considers emerging issues associated with cataracts and cardiovascular disease. For cataracts, topics dealt with herein include (i) the progressive nature, stochastic nature, target cells and trigger events of lens opacification, (ii) roles of lens protein denaturation, oxidative stress, calcium ions, tumor suppressors and DNA repair factors in cataractogenesis, (iii) dose rate effect, radiation weighting factor, and classification systems for cataracts, and (iv) estimation of the lens dose in clinical settings. Topics for cardiovascular disease include experimental animal models, relevant surrogate markers, latency period, target tissues, and roles of inflammation and cellular senescence. Future research needs are also discussed.

Role of autophagy in high linear energy transfer radiation-induced cytotoxicity to tumor cells

Heavy-ion radiotherapy has a potential advantage over conventional radiotherapy due to improved dose distribution and a higher biological effectiveness in cancer therapy. However, there is a little information currently available on the cellular and molecular basis for heavy-ion irradiation-induced cell death. Autophagy, as a novel important target to improve anticancer therapy, has recently attracted considerable attention. In this study, the effect of autophagy induced by high linear energy transfer (LET) carbon ions was examined in various tumor cell lines. To our knowledge, our study is the first to reveal that high-LET carbon ions could induce autophagy in various tumor cells effectively, and the autophagic level in the irradiated cells increased in a dose- and LET-dependent manner. The ability of carbon ions to inhibit the activation of the PI3K/Akt pathway rose with increasing their LET. Moreover, modulation of autophagy in tumor cells could modify their sensitivity to high-LET radiation, and inhibiting autophagy accelerated apoptotic cell death, resulting in an increase in radiosensitivity. Our data imply that targeting autophagy might enhance the effectiveness of heavy-ion radiotherapy.

Ionizing irradiation not only inactivates clonogenic potential in primary normal human diploid lens epithelial cells but also stimulates cell proliferation in a subset of this population

Over the past century, ionizing radiation has been known to induce cataracts in the crystalline lens of the eye, but its mechanistic underpinnings remain incompletely understood. This study is the first to report the clonogenic survival of irradiated primary normal human lens epithelial cells and stimulation of its proliferation. Here we used two primary normal human cell strains: HLEC1 lens epithelial cells and WI-38 lung fibroblasts. Both strains were diploid, and a replicative lifespan was shorter in HLEC1 cells. The colony formation assay demonstrated that the clonogenic survival of both strains decreases similarly with increasing doses of X-rays. A difference in the survival between two strains was actually insignificant, although HLEC1 cells had the lower plating efficiency. This indicates that the same dose inactivates the same fraction of clonogenic cells in both strains. Intriguingly, irradiation enlarged the size of clonogenic colonies arising from HLEC1 cells in marked contrast to those from WI-38 cells. Such enhanced proliferation of clonogenic HLEC1 cells was significant at ≥2 Gy, and manifested as increments of ≤2.6 population doublings besides sham-irradiated controls. These results suggest that irradiation of HLEC1 cells not only inactivates clonogenic potential but also stimulates proliferation of surviving uniactivated clonogenic cells. Given that the lens is a closed system, the stimulated proliferation of lens epithelial cells may not be a homeostatic mechanism to compensate for their cell loss, but rather should be regarded as abnormal. This is because these findings are consistent with the early in vivo evidence documenting that irradiation induces excessive proliferation of rabbit lens epithelial cells and that suppression of lens epithelial cell divisions inhibits radiation cataractogenesis in frogs and rats. Thus, our in vitro model will be useful to evaluate the excessive proliferation of primary normal human lens epithelial cells that may underlie radiation cataractogenesis, warranting further investigations.

Hyperdiploid tumor cells increase phenotypic heterogeneity within Glioblastoma tumors

Here we report the identification of a proliferative, viable, and hyperdiploid tumor cell subpopulation present within Glioblastoma (GB) patient tumors. Using xenograft tumor models, we demonstrate that hyperdiploid cell populations are maintained in xenograft tumors and that clonally expanded hyperdiploid cells support tumor formation and progression in vivo. In some patient tumorsphere lines, hyperdiploidy is maintained during long-term culture and in vivo within xenograft tumor models, suggesting that hyperdiploidy can be a stable cell state. In other patient lines hyperdiploid cells display genetic drift in vitro and in vivo, suggesting that in these patients hyperdiploidy is a transient cell state that generates novel phenotypes, potentially facilitating rapid tumor evolution. We show that the hyperdiploid cells are resistant to conventional therapy, in part due to infrequent cell division due to a delay in the G₀/G₁ phase of the cell cycle. Hyperdiploid tumor cells are significantly larger and more metabolically active than euploid cancer cells, and this correlates to an increased sensitivity to the effects of glycolysis inhibition. Together these data identify GB hyperdiploid tumor cells as a potentially important subpopulation of cells that are well positioned to contribute to tumor evolution and disease recurrence in adult brain cancer patients, and suggest tumor metabolism as a promising point of therapeutic intervention against this subpopulation.

For the next trick: new discoveries in radiobiology applied to glioblastoma

Glioblastoma (GBM) is the most common malignant brain tumor. Radiotherapy post surgical resection remained the mainstay of the management of GBM for decades until the addition of temozolomide was shown to prolong the median overall survival (OS) by 2.5 months to 14.6 months in 2005. Infiltrative growth to surrounding normal brain tissue and cooption of vascular niches, peripheral microvasuclar hyperplasia, and central hypoxic regions with pseudopalisading necrosis are characteristics of GBM and are causally linked to their exceptional radio- and chemo-resistant phenotype. An intratumoral hierarchy is postulated consisting of tumor stem cells in the apex with high DNA-repair proficiency resisting radiotherapy. It is conceivable that the stem cell property is more dynamic than originally anticipated. Niche effects such as exposure to hypoxia and intercellular communication in proximities to endothelial or bone marrow-derived cells (BMDC), for example, may activate such "stem cell" programs. GBM are exceptionally stroma-rich tumors and may consist of more than 70% stroma components, such as microglia and BMDC. It becomes increasingly apparent that treatment of GBM needs to integrate therapies targeting all above-mentioned distinct pathophysiological features. Accordingly, recent approaches in GBM therapy include inhibition of invasion (e.g., integrin, EGFR, CD95, and mTOR inhibition), antiangiogenesis and stroma modulators (TGFbeta, VEGF, angiopoetin, cMET inhibitors) and activation of immune response (vaccination and blockage of negative co-stimulatory signals). In addition, high LET-radiotherapy, for example with carbon ions, is postulated to ablate tumor stem cell and hypoxic cells more efficiently as compared with conventional low-LET photon irradiation. We discuss current key concepts, their limitations, and potentials to improve the outcome in this rapidly progressive and devastating disease.

What are the intracellular targets and intratissue target cells for radiation effects?

Exactly a century after Röntgen's discovery of X rays, I entered a university to major in radiological sciences. At that time, I felt that, despite extensive use and indispensable roles of ionizing radiation in medicine and industry, many fascinating questions have yet to be answered concerning its biological mechanisms of action, and thus I decided to get into the field of radiation research. Fifteen years have passed since I started radiobiological studies in 1998, during which time various basic tenets I initially learned in my late teens and early twenties have been challenged by recent observations. Of these, this brief overview particularly focuses on the following five different albeit non mutually exclusive questions: (i) "Is nuclear DNA the only intracellular target for radiation effects?"; (ii) "What is the significance of delayed cell death in clonogenic survival?"; (iii) "Does an irradiated cell become a cancer cell?"; (iv) "Are cataracts tissue reactions?"; and (v) "Why is high-LET radiation biologically effective?".

The autophagy-senescence connection in chemotherapy: must tumor cells (self) eat before they sleep?

Exposure of MCF-7 breast tumor cells or HCT-116 colon carcinoma cells to clinically relevant concentrations of doxorubicin (Adriamycin; Farmitalia Research Laboratories, Milan, Italy) or camptothecin results in both autophagy and senescence. To determine whether autophagy is required for chemotherapy-induced senescence, reactive oxygen generation induced by Adriamycin was suppressed by N-acetyl cysteine and glutathione, and the induction of ataxia telangiectasia mutated, p53, and p21 was modulated pharmacologically and/or genetically. In all cases, autophagy and senescence were collaterally suppressed. The close association between autophagy and senescence indicated by these experiments reflects their collateral regulation via common signaling pathways. The potential relationship between autophagy and senescence was further examined through pharmacologic inhibition of autophagy with chloroquine and 3-methyl-adenine and genetic ablation of the autophagy-related genes ATG5 and ATG7. However, inhibition of autophagy by pharmacological and genetic approaches could not entirely abrogate the senescence response, which was only reduced and/or delayed. Taken together, our findings suggest that autophagy and senescence tend to occur in parallel, and furthermore that autophagy accelerates the development of the senescent phenotype. However, these responses are not inexorably linked or interdependent, as senescence can occur when autophagy is abrogated.

[From the carbon track to therapeutic efficiency of hadrontherapy]

Carbon ions, thanks to their relative biological effectiveness much higher than that of photons and protons and their ballistic characteristics similar to those of protons, can effectively treat radioresistant tumours. The reasons for this increased efficiency are found in the microdosimetric and radiobiological features of ions. The energy deposit or linear energy transfer increases along the range and reaches a very high level at the end producing the Bragg peak, where the linear energy transfer is about hundred times higher than that of photons. These massive energy deposits create multiple DNA lesions that are difficult to repair. DNA repair is associated with longer blockage of the cell cycle and more frequent chromosomal aberrations that are lethal to cells. The types of cell death are identical to those triggered in response to photon irradiation, but the response is earlier and more important at equivalent physical dose. Radiobiological differences between carbon ions and photons have been studied for some years and many aspects remain to be explored. In general, these phenomena tend to reduce the differences of radiosensitivity among different tissues. It is therefore in situation where tumours are relatively radioresistant compared to healthy tissue, that carbon ions must be used and not in the opposite situations where the fractionation of low linear energy transfer radiation is sufficient to provide the necessary differential effect to cure the tumour.

Targeting autophagy enhances BO-1051-induced apoptosis in human malignant glioma cells

PURPOSE

BO-1051 is an N-mustard derivative that is conjugated with DNA-affinic 9-anilinoacridine. Since BO-1051 was reported to have strong anticancer activity, we investigated the effect and underlying mechanism of BO-1051 in human glioma cell lines.

METHODS

Human glioma cell lines U251MG and U87MG were studied with BO-1051 or the combination of BO-1051 and autophagic inhibitors. Growth inhibition was assessed by MTT assay. Apoptosis was measured by annexin V staining followed by flow cytometry and immunoblotting for apoptosis-related molecules. Induction of autophagy was detected by acridine orange labeling, electron microscopy, LC3 localization and its conversion. Transfection of shRNA was used to determine the involvement of Beclin1 in apoptotic cell death.

RESULTS

MTT assay showed that BO-1051 suppressed the viability of four glioma cell lines (U251MG, U87MG, GBM-3 and DBTRG-05MG) in a dose-dependent manner. The IC(50) values of BO-1051 for the glioma cells were significantly lower than the values for primary neurons cultures and normal fibroblast cells. Moreover, BO-1051 not only induced apoptotic cell death, but also enhanced autophagic flux via inhibition of Akt/mTOR and activation of Erk1/2. Importantly, suppression of autophagy by 3-methyladenine or bafilomycin A1 significantly increased BO-1051-induced apoptotic cell death in U251MG and U87MG cells. In addition, the proportion of apoptotic cells after BO-1051 treatment was enhanced by co-treatment with shRNA against Beclin1.

CONCLUSIONS

BO-1051 induced both apoptosis and autophagy, and inhibition of autophagy significantly augmented the cytotoxic effect of BO-1051. Thus, a combination of BO-1051 and autophagic inhibitors offers a potentially new therapeutic modality for the treatment of malignant glioma.

Response of human HTB140 melanoma cells to conventional radiation and hadrons

Conventional radiotherapy with X- and gamma-rays is one of the common and effective treatments of cancer. High energy hadrons, i.e., charged particles like protons and (12)C ions, due to their specific physics and radiobiological advantages are increasingly used. In this study, effectiveness of different radiation types is evaluated on the radio-resistant human HTB140 melanoma cells. The cells were irradiated with gamma-rays, the 62 MeV protons at the Bragg peak and in the middle of the spread-out Bragg peak (SOBP), as well as with the 62 MeV/u (12)C ions. The doses ranged from 2 to 24 Gy. Cell survival and proliferation were assessed 7 days after irradiation, whereas apoptosis was evaluated after 48 h. The acquired results confirmed the high radio-resistance of cells, showing better effectiveness of protons than gamma-rays. The best efficiency was obtained with (12)C ions due to higher linear energy transfer. All analyzed radiation qualities reduced cell proliferation. The highest proliferation was detected for (12)C ions because of their large killing capacity followed by small induction of reparable lesions. This enabled unharmed cells to preserve proliferative activity. Irradiations with protons and (12)C ions revealed similar moderate pro-apoptotic ability that is in agreement with the level of cellular radio-resistance.

Low-grade recurrence of a congenital high-grade supratentorial tumor with astrocytic features in the absence of adjuvant therapy

The biological behavior of pediatric gliomas and embryonal tumors can be highly variable. A few case reports have described differentiation of primitive neuroectodermal tumors (PNETs) and medulloblastomas, presumably induced by adjuvant chemotherapy and/or radiation. Herein we describe a case of a congenital supratentorial high-grade tumor with astrocytic features that, after near-total surgical resection, was not treated with adjuvant therapies. Thirteen years later the patient presented with recurrent tumor at the original surgical site. The recurrent tumor had completely different morphology compared to the original, with evidence of ganglion cell differentiation and changes more reminiscent of a low-grade pleomorphic xanthoastrocytoma. To the authors' knowledge, this is the first documented case of an untreated high-grade pediatric tumor that spontaneously differentiated into a low grade tumor. The clinical and biological implications of this are briefly discussed.

Heavy ion irradiation induces autophagy in irradiated C2C12 myoblasts and their bystander cells

Autophagy is one of the major processes involved in the degradation of intracellular materials. Here, we examined the potential impact of heavy ion irradiation on the induction of autophagy in irradiated C2C12 mouse myoblasts and their non-targeted bystander cells. In irradiated cells, ultrastructural analysis revealed the accumulation of autophagic structures at various stages of autophagy (i.e. phagophores, autophagosomes and autolysosomes) within 20 min after irradiation. Multivesicular bodies (MVBs) and autolysosomes containing MVBs (amphisomes) were also observed. Heavy ion irradiation increased the staining of microtubule-associated protein 1 light chain 3 and LysoTracker Red (LTR). Such enhanced staining was suppressed by an autophagy inhibitor 3-methyladenine. In addition to irradiated cells, bystander cells were also positive with LTR staining. Altogether, these results suggest that heavy ion irradiation induces autophagy not only in irradiated myoblasts but also in their bystander cells.

Recent advances in the biology of heavy-ion cancer therapy

Superb biological effectiveness and dose conformity represent a rationale for heavy-ion therapy, which has thus far achieved good cancer controllability while sparing critical normal organs. Immediately after irradiation, heavy ions produce dense ionization along their trajectories, cause irreparable clustered DNA damage, and alter cellular ultrastructure. These ions, as a consequence, inactivate cells more effectively with less cell-cycle and oxygen dependence than conventional photons. The modes of heavy ion-induced cell death/inactivation include apoptosis, necrosis, autophagy, premature senescence, accelerated differentiation, delayed reproductive death of progeny cells, and bystander cell death. This paper briefly reviews the current knowledge of the biological aspects of heavy-ion therapy, with emphasis on the authors' recent findings. The topics include (i) repair mechanisms of heavy ion-induced DNA damage, (ii) superior effects of heavy ions on radioresistant tumor cells (intratumor quiescent cell population, TP53-mutated and BCL2-overexpressing tumors), (iii) novel capacity of heavy ions in suppressing cancer metastasis and neoangiogenesis, and (iv) potential of heavy ions to induce secondary (especially breast) cancer.