p53-independent early and late apoptosis is mediated by ceramide after exposure of tumor cells to photon or carbon ion irradiation

A natural approach to breast cancer treatment: investigation of chemical features of aerial parts of endemic Onosma sintenisii Hausskn. ex Bornm and its antioxidant properties, in vitro cytotoxic and apoptosis induction on MCF-7 cells

Onosma sintenisii Hausskn. ex Bornm. (O. sintenisii) belongs to the Boraginaceae family and it is an endemic species from Irano-turanian phytogeographical region (central and eastern Anatolia) that distributes in steppe areas. This study aimed to investigate the chemical composition, antioxidant, in vitro cytotoxic and apoptosis induction of methanol extract of aerial parts of O. sintenisii. As a result of GC/MS analysis, 14 components were identified, and the major compounds of the extracts are retronecine (13.94%), α.-D-Glucopyranosiduronic acid (10.86%), melaniline (7.5%) and 1,2-Butanediol (4.02%), respectively. Antioxidant properties of O. sintenisii were determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, ferric reducing antioxidant power (FRAP) and superoxide radical scavenging activity methods. While the DPPH free radical scavenging activity results of O. sintenisii extract varied between 62.49% and 32.27%, reducing power activity and superoxide radical scavenging activity were found to be low. The result of the MTT assay revealed strong anticancer activity of O. sintenisii extract. The most significant cytotoxic effect was noted at a concentration of 1000 µg/mL after 48 hours. These findings together with flow cytometry analysis suggest that apoptosis can be the main mechanism underlying cell death after O. sintenisii extract treatment.

Differential Formation of Stress Granules in Radiosensitive and Radioresistant Head and Neck Squamous Cell Carcinoma Cells

PURPOSE

Stress granules (SGs) are cytoplasmic aggregates in which mRNAs and specific proteins are trapped in response to a variety of damaging agents. They participate in the cellular defense mechanisms. Currently, their mechanism of formation in response to ionizing radiation and their role in tumor-cell radiosensitivity remain elusive.

METHODS AND MATERIALS

The kinetics of SG formation was investigated after the delivery of photon irradiation at different doses to head and neck squamous cell carcinoma cell lines with different radiosensitivities and the HeLa cervical cancer cell line (used as reference). In parallel, the response to a canonical inducer of SGs, sodium arsenite, was also studied. Immunolabeling of SG-specific proteins and mRNA fluorescence in situ hybridization enabled SG detection and quantification. Furthermore, a ribopuromycylation assay was used to assess the cell translational status. To determine whether reactive oxygen species were involved in SG formation, their scavenging or production was induced by pharmacologic pretreatment in both SCC61 and SQ20B cells.

RESULTS

Photon irradiation at different doses led to the formation of cytoplasmic foci that were positive for different SG markers. The presence of SGs gradually increased from 30 minutes to 2 hours postexposure in HeLa, SCC61, and Cal60 radiosensitive cells. In turn, the SQ20B and FaDu radioresistant cells did not form SGs. These results indicated a correlation between sensitivity to photon irradiation and SG formation. Moreover, SG formation was significantly reduced by reactive oxygen species scavenging using dimethyl sulfoxide in SCC61 cells, which supported their role in SG formation. However, a reciprocal experiment in SQ20B cells that depleted glutathione using buthionine sulfoximide did not restore SG formation in these cells.

CONCLUSIONS

SGs are formed in response to irradiation in radiosensitive, but not in radioresistant, head and neck squamous cell carcinoma cells. Interestingly, compared with sodium arsenite-induced SGs, photon-induced SGs exhibited a different morphology and cellular localization. Moreover, photon-induced SGs were not associated with the inhibition of translation; rather, they depended on oxidative stress.

High-LET charged particles: radiobiology and application for new approaches in radiotherapy

The number of patients treated with charged-particle radiotherapy as well as the number of treatment centers is increasing worldwide, particularly regarding protons. However, high-linear energy transfer (LET) particles, mainly carbon ions, are of special interest for application in radiotherapy, as their special physical features result in high precision and hence lower toxicity, and at the same time in increased efficiency in cell inactivation in the target region, i.e., the tumor. The radiobiology of high-LET particles differs with respect to DNA damage repair, cytogenetic damage, and cell death type, and their increased LET can tackle cells' resistance to hypoxia. Recent developments and perspectives, e.g., the return of high-LET particle therapy to the US with a center planned at Mayo clinics, the application of carbon ion radiotherapy using cost-reducing cyclotrons and the application of helium is foreseen to increase the interest in this type of radiotherapy. However, further preclinical research is needed to better understand the differential radiobiological mechanisms as opposed to photon radiotherapy, which will help to guide future clinical studies for optimal exploitation of high-LET particle therapy, in particular related to new concepts and innovative approaches. Herein, we summarize the basics and recent progress in high-LET particle radiobiology with a focus on carbon ions and discuss the implications of current knowledge for charged-particle radiotherapy. We emphasize the potential of high-LET particles with respect to immunogenicity and especially their combination with immunotherapy.

Particle radiotherapy in the era of radioimmunotherapy

Radiotherapy (RT) is one of the key modalities for cancer treatment, and more than 70% of tumor patients will receive RT during the course of their disease. Particle radiotherapy, such as proton radiotherapy, carbon-ion radiotherapy (CIRT) and boron neutron capture therapy (BNCT), is currently available for the treatment of patients Immunotherapy combined with photon RT has been successfully used in the clinic. The effect of immunotherapy combined with particle RT is an area of interest. However, the molecular mechanisms underlying the effects of combined immunotherapy and particle RT remain largely unknown. In this review, we summarize the properties of different types of particle RT and the mechanisms underlying their radiobiological effects. Additionally, we compared the main molecular players in photon RT and particle RT and the mechanisms involved the RT-mediated immune response.

The 'stealth-bomber' paradigm for deciphering the tumour response to carbon-ion irradiation

Numerous studies have demonstrated the higher biological efficacy of carbon-ion irradiation (C-ions) and their ballistic precision compared with photons. At the nanometre scale, the reactive oxygen species (ROS) produced by radiation and responsible for the indirect effects are differentially distributed according to the type of radiation. Photon irradiation induces a homogeneous ROS distribution, whereas ROS remain condensed in clusters in the C-ions tracks. Based on this linear energy transfer-dependent differential nanometric ROS distribution, we propose that the higher biological efficacy and specificities of the molecular response to C-ions rely on a 'stealth-bomber' effect. When biological targets are on the trajectories of the particles, the clustered radicals in the tracks are responsible for a 'bomber' effect. Furthermore, the low proportion of ROS outside the tracks is not able to trigger the cellular mechanisms of defence and proliferation. The ability of C-ions to deceive the cellular defence of the cancer cells is then categorised as a 'stealth' effect. This review aims to classify the biological arguments supporting the paradigm of the 'stealth-bomber' as responsible for the biological superiority of C-ions compared with photons. It also explains how and why C-ions will always be more efficient for treating patients with radioresistant cancers than conventional radiotherapy.

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.

Functional imaging-guided carbon ion irradiation with simultaneous integrated boost for localized prostate cancer: study protocol for a phase II randomized controlled clinical trial

Background

Due to the physical dose distribution characteristic of “Bragg peak” and the biological effect as a kind of high linear energy transfer ray, heavy ion therapy has advantages over conventional photon therapy in both efficacy and safety. Based on the evidence that prostate cancer lesions before treatment are the most common sites of tumor residual or recurrence after treatment, simultaneous integrated boost radiation therapy for prostate cancer has been proven to have the advantage of improving efficacy without increasing toxicities.

Methods

This study is a prospective phase II randomized controlled clinical trial evaluating the efficacy and safety of functional imaging-guided carbon ion irradiation with simultaneous integrated boost for localized prostate cancer. One hundred and forty patients with localized prostate cancer will be randomized into carbon ion radiotherapy group and simultaneous integrated boost carbon ion radiotherapy group at a 1:1 ratio. The primary endpoint is to compare the incidence of treatment-related grade 2 and higher acute toxicities between the two groups according to National Cancer Institute Common Terminology Criteria for Adverse Events (NCI-CTCAE) version 4.03. Secondary endpoints are late toxicities, biochemical relapse-free survival, overall survival, progression-free survival, and quality of life.

Discussion

This study adopts functional imaging-guided simultaneous integrated boost of carbon ion radiotherapy for localized prostate cancer, aiming to evaluate the differences in the severity and incidence of acute toxicities in patients with localized prostate cancer treated with carbon ion radiotherapy and simultaneous integrated boost carbon ion radiotherapy, in order to optimize the carbon ion treatment strategy for localized prostate cancer.

Trial registration

ClinicalTrials.gov NCT05010343. Retrospectively registered on 18 August 2021

Comparison of the efficacy and toxicity of postoperative proton versus carbon ion radiotherapy for head and neck cancers

Background

To compare the efficacy and toxicity of adjuvant proton beam vs. carbon-ion beam radiotherapy for head and neck cancers after radical resection and to explore the value of particle beam radiotherapy (PBRT) in postoperative radiotherapy for head and neck cancers.

Methods

Data from 38 head and neck cancer patients who received adjuvant PBRT after complete surgical resection at the Shanghai Proton and Heavy Ion Center (SPHIC) between October 2015 and March 2019 were retrospectively analyzed. In total, 18 patients received adjuvant proton beam therapy (54-60 GyE/27-30 fractions) and 20 received adjuvant carbon-ion radiotherapy (CIRT) (54-60 GyE/18-20 fractions). Survival rates were calculated using Kaplan-Meier analysis. Toxicity was evaluated according to the Common Terminology Criteria for Adverse Effects (version 4.03).

Results

With a median follow-up time of 21 (range, 3-45) months, the 2-year overall survival (OS), progression-free survival (PFS), local-regional recurrence-free survival (LRRFS) and distant metastasis-free survival (DMFS) rates were 93.3%, 87.4%, 94.1%, and 90.7%, respectively, for the entire cohort. The rates after proton beam therapy vs. CIRT were 94.1% vs. 91.7% (P=0.96), 88.1% vs. 86.2% (P=0.96), 94.4% vs. 93.3% (P=0.97), and 88.1% vs. 92.9% (P=0.57), respectively. Furthermore, 16 of the 18 (88.9%) patients developed acute grade I/II dermatitis (13 grade I; 3 grade II) after proton beam therapy, and only 7 of the 20 (35%) patients developed acute grade I dermatitis after CIRT (P=0.001). The incidence of acute grade I/II mucositis and xerostomia in proton and carbon ion cases were 45% vs. 55% (P=0.75) and 56% vs. 50% (P=0.87) respectively.

Conclusions

Adjuvant proton beam therapy and CIRT after radical surgical resection for head and neck cancers provided satisfactory therapeutic effectiveness, but no significant difference was observed between the two radiotherapy technologies. However, adjuvant CIRT was associated with a more favorable acute toxicity profile as compared to proton beam therapy with significantly lower frequency and severity of acute dermatitis observed.

Quantifying Cellular Repair, Misrepair and Apoptosis Induced by Boron Ions, Gamma Rays and PRIMA-1 Using the RHR Formulation

The recent interaction cross-section-based formulation for radiation-induced direct cellular inactivation, mild and severe sublethal damage, DNA-repair and cell survival have been developed to accurately describe cellular repair, misrepair and apoptosis in TP53 wild-type and mutant cells. The principal idea of this new non-homologous repairable-homologous repairable (RHR) damage formulation is to separately describe the mild damage that can be rapidly handled by the most basic repair processes including the non-homologous end joining (NHEJ), and more complex damage requiring longer repair times and high-fidelity homologous recombination (HR) repair. Taking the interaction between these two key mammalian DNA repair processes more accurately into account has significantly improved the method as indicated in the original publication. Based on the principal mechanisms of 7 repair and 8 misrepair processes presently derived, it has been possible to quite accurately describe the probability that some of these repair processes when unsuccessful can induce cellular apoptosis with increasing doses of γrays, boron ions and PRIMA-1. Interestingly, for all LETs studied (≈0.3-160 eV/nm) the increase in apoptosis saturates when the cell survival reaches about 10% and the fraction of un-hit cells is well below the 1% level. It is shown that most of the early cell kill for low-to-medium LETs are due to apoptosis since the cell survival as well as the non-apoptotic cells agree very well at low doses and other death processes dominate beyond D > 1 Gy. The low-dose apoptosis is due to the fact that the full activation of the checkpoint kinases ATM and Chk2 requires >8 and >18 DSBs per cell to phosphorylate p53 at serine 15 and 20. Therefore, DNA repair is not fully activated until well after 1/2 Gy, and the cellular response may be apoptotic by default before the low-dose hyper sensitivity (LDHS) is replaced by an increased radiation tolerance as the DNA repair processes get maximal efficiency. In effect, simultaneously explaining the LDHS and inverse dose rate phenomena. The partial contributions by the eight newly derived misrepair processes was determined so they together accurately described the experimental apoptosis induction data for γ rays and boron ions. Through these partial misrepair contributions it was possible to predict the apoptotic response based solely on carefully analyzed cell survival data, demonstrating the usefulness of an accurate DNA repair-based cell survival approach. The peak relative biological effectiveness (RBE) of the boron ions was 3.5 at 160 eV/nm whereas the analogous peak relative apoptotic effectiveness (RAE) was 3.4 but at 40 eV/nm indicating the clinical value of the lower LET light ion (15 \le {\rm{LET}} \le 55{\rm{\ eV}}/{\rm{nm}},{\rm{\ }}2 \le Z \le 5) in therapeutic applications to maximize tumor apoptosis and senescence. The new survival expressions were also applied on mouse embryonic fibroblasts with key knocked-out repair genes, showing a good agreement between the principal non-homologous and homologous repair terms and also a reasonable prediction of the associated apoptotic induction. Finally, the formulation was used to estimate the increase in DNA repair and apoptotic response in combination with the mutant p53 reactivating compound PRIMA-1 and γ rays, indicating a 10-2 times increase in apoptosis with 5 μM of the compound reaching apoptosis levels not far from peak apoptosis boron ions in a TP53 mutant cell line. To utilize PRIMA-1 induced apoptosis and cellular sensitization for reactive oxygen species (ROS), concomitant biologically optimized radiation therapy is proposed to maximize the complication free tumor cure for the multitude of TP53 mutant tumors seen in the clinic. The experimental data also indicated the clinically very important high-absorbed dose ROS effect of PRIMA-1.

Role of Mitochondria in Radiation Responses: Epigenetic, Metabolic, and Signaling Impacts

Until recently, radiation effects have been considered to be mainly due to nuclear DNA damage and their management by repair mechanisms. However, molecular biology studies reveal that the outcomes of exposures to ionizing radiation (IR) highly depend on activation and regulation through other molecular components of organelles that determine cell survival and proliferation capacities. As typical epigenetic-regulated organelles and central power stations of cells, mitochondria play an important pivotal role in those responses. They direct cellular metabolism, energy supply and homeostasis as well as radiation-induced signaling, cell death, and immunological responses. This review is focused on how energy, dose and quality of IR affect mitochondria-dependent epigenetic and functional control at the cellular and tissue level. Low-dose radiation effects on mitochondria appear to be associated with epigenetic and non-targeted effects involved in genomic instability and adaptive responses, whereas high-dose radiation effects (>1 Gy) concern therapeutic effects of radiation and long-term outcomes involving mitochondria-mediated innate and adaptive immune responses. Both effects depend on radiation quality. For example, the increased efficacy of high linear energy transfer particle radiotherapy, e.g., C-ion radiotherapy, relies on the reduction of anastasis, enhanced mitochondria-mediated apoptosis and immunogenic (antitumor) responses.

MDM2/X Inhibitors as Radiosensitizers for Glioblastoma Targeted Therapy

Inhibition of the MDM2/X-p53 interaction is recognized as a potential anti-cancer strategy, including the treatment of glioblastoma (GB). In response to cellular stressors, such as DNA damage, the tumor suppression protein p53 is activated and responds by mediating cellular damage through DNA repair, cell cycle arrest and apoptosis. Hence, p53 activation plays a central role in cell survival and the effectiveness of cancer therapies. Alterations and reduced activity of p53 occur in 25-30% of primary GB tumors, but this number increases drastically to 60-70% in secondary GB. As a result, reactivating p53 is suggested as a treatment strategy, either by using targeted molecules to convert the mutant p53 back to its wild type form or by using MDM2 and MDMX (also known as MDM4) inhibitors. MDM2 down regulates p53 activity via ubiquitin-dependent degradation and is amplified or overexpressed in 14% of GB cases. Thus, suppression of MDM2 offers an opportunity for urgently needed new therapeutic interventions for GB. Numerous small molecule MDM2 inhibitors are currently undergoing clinical evaluation, either as monotherapy or in combination with chemotherapy and/or other targeted agents. In addition, considering the major role of both p53 and MDM2 in the downstream signaling response to radiation-induced DNA damage, the combination of MDM2 inhibitors with radiation may offer a valuable therapeutic radiosensitizing approach for GB therapy. This review covers the role of MDM2/X in cancer and more specifically in GB, followed by the rationale for the potential radiosensitizing effect of MDM2 inhibition. Finally, the current status of MDM2/X inhibition and p53 activation for the treatment of GB is given.

Chemical and biological basis for development of novel radioprotective drugs for cancer therapy

Ionizing radiation (IR) causes chemical changes in biological systems through direct interaction with the macromolecules or by causing radiolysis of water. This property of IR is harnessed in the clinic for radiotherapy in almost 50% of cancers patients. Despite the advent of stereotactic radiotherapy instruments and other advancements in shielding techniques, the inadvertent deposition of radiation dose in the surrounding normal tissue can cause late effects of radiation injury in normal tissues. Radioprotectors, which are chemical or biological agents, can reduce or mitigate these toxic side-effects of radiotherapy in cancer patients and also during radiation accidents. The desired characteristics of an ideal radioprotector include low chemical toxicity, high risk to benefit ratio and specific protection of normal cells against the harmful effects of radiation without compromising the cytotoxic effects of IR on cancer cells. Since reactive oxygen species (ROS) are the major contributors of IR mediated toxicity, plethora of studies have highlighted the potential role of antioxidants to protect against IR induced damage. However, owing to the lack of any clinically approved radioprotector against whole body radiation, researchers have shifted the focus toward finding alternate targets that could be exploited for the development of novel agents. The present review provides a comprehensive insight in to the different strategies, encompassing prime molecular targets, which have been employed to develop radiation protectors/countermeasures. It is anticipated that understanding such factors will lead to the development of novel strategies for increasing the outcome of radiotherapy by minimizing normal tissue toxicity.

The anti-cancer effect of flaxseed lignan derivatives on different acute myeloid leukemia cancer cells

Flaxseeds have been known for their anti-cancerous effects due to the high abundance of lignans released upon ingestion. The most abundant lignan, secoisolariciresinol diglucoside (SDG), is ingested during the dietary intake of flax, and is then metabolized in the gut into two mammalian lignan derivatives, Enterodiol (END) and Enterolactone (ENL). These lignans were previously reported to possess anti-tumor effects against breast, colon, and lung cancer. This study aims to investigate the potential anti-cancerous effect of the flaxseed lignans SDG, END and ENL on acute myeloid leukemia cells (AML) in vitro and to decipher the underlying molecular mechanism. AML cell lines, (KG-1 and Monomac-1) and a normal lymphoblastic cell line were cultured and treated with the purified lignans. ENL was found to be the most promising lignan, as it exhibits a significant selective dose- and time-dependent cytotoxic effect in both AML cell lines, contrary to normal cells. The cytotoxic effects observed were attributed to apoptosis induction, as revealed by an increase in Annexin V staining of AML cells with increasing ENL concentrations. The increase in the percentage of cells in the pre-G phase, in addition to cell death ELISA analysis, validated cellular and DNA fragmentation respectively. Analysis of protein expression using western blots confirmed the activation of the intrinsic apoptotic pathway upon ENL treatment. This was also accompanied by an increase in ROS production intracellularly. In conclusion, this study demonstrates that ENL has promising anti-cancer effects in AML cell lines in vitro, by promoting DNA fragmentation and the intrinsic apoptotic pathway, highlighting the protective health benefits of flax seeds in leukemia.

Ceramide-Enriched Membrane Domains Contribute to Targeted and Nontargeted Effects of Radiation through Modulation of PI3K/AKT Signaling in HNSCC Cells

We investigated the potential involvement of ceramide-enriched membrane domains in radiation-induced targeted and nontargeted effects using head and neck squamous cell carcinoma with opposite radiosensitivities. In radiosensitive SCC61 cells, the proportion of targeted effects was 34% and nontargeted effects killed 32% of cells. In contrast, only targeted effects (30%) are involved in the overall death of radioresistant SQ20B cells. We then demonstrated in SCC61 cells that nontargeted cell response was driven by the formation of the radiation-induced ceramide-enriched domain. By contrast, the existence of these platforms in SQ20B cells confers a permissive region for phosphatidylinositol-3-kinase (PI3K)/AKT activation. The disruption of lipid raft results in strong inhibition of PI3K/AKT signaling, leading to radiosensitization and apparition of nontargeted effects. These results suggest that ceramide-enriched platforms play a significant role in targeted and nontargeted effects during radiotherapy and that drugs modulating cholesterol levels may be a good alternative for improving radiotherapy effectiveness.

Macrophage-Mediated Bystander Effects after Different Irradiations through a p53-dependent Pathway

The goal of this work was to elucidate the mechanisms of bystander effects outside the localized irradiation field and their potential hematological toxicity. In this study, an in vitro multicellular co-culture system was used to investigate the intercellular commutation and related signaling pathways between either irradiated A549 cells or Beas-2B cells and bystander lymphoblast TK6 cells with or without macrophage U937 cells as an intermediator. Results showed that the proliferation ability of bystander TK6 cells was inhibited after co-culture with A549 cells irradiated with γ rays rather than carbon ions. When macrophages were contained in the co-culture system, the cell viability damage to the bystander TK6 cells were further enhanced. However, the proliferation inhibition of bystander TK6 cells after co-culture with irradiated Beas-2B cells was observed only when intermediator macrophages existed in the cell co-culture system. More serious cell injury was detected after carbon-ion irradiation compared with γ-ray irradiation. The p53-relevant apoptosis pathway was activated in both irradiated A549 and Beas-2B cells, each to a different extent. When the p53 pathway of irradiated cells was inhibited by PFT-α, PFTµ or p53 siRNA, the bystander damage to TK6 cells were clearly alleviated. In conclusion, the bystander lymphoblast damage was induced in different cells using different LET radiations. An amplified bystander response was modulated by the intermediator macrophage. The underlying molecular mechanisms of these bystander effects were dependent on the activation of p53 and its relevant apoptosis pathway in the irradiated cells. These results suggest that the bystander and macrophage-mediated bystander effects contribute to the common acute side effect of lymphocytopenia after local irradiation.

Carbon ion radiotherapy boost in the treatment of glioblastoma: a randomized phase I/III clinical trial

Background

Glioblastoma (GBM) is a highly virulent tumor of the central nervous system, with a median survival < 15 months. Clearly, an improvement in treatment outcomes is needed. However, the emergence of these malignancies within the delicate brain parenchyma and their infiltrative growth pattern severely limit the use of aggressive local therapies. The particle therapy represents a new promising therapeutic approach to circumvent these prohibitive conditions with improved treatment efficacy.

Methods and design

Patients with newly diagnosed malignant gliomas will have their tumor tissue samples submitted for the analysis of the status of O-6-methylguanine-DNA methyltransferase (MGMT) promoter methylation. In Phase I, the patients will undergo an induction carbon ion radiotherapy (CIRT) boost followed by 60 GyE of proton irradiation with concurrent temozolomide (TMZ) at 75 mg/m². To determine the maximal dose of safe induction boost, the tolerance, and acute toxicity rates in a dose-escalation manner from 9 to 18 GyE in three fractions will be used. In Phase III, GBM-only patients will be randomized to receive either 60 GyE (2 GyE per fraction) of proton irradiation with concurrent TMZ (control arm) or a CIRT boost (dose determined in Phase I of this trial) followed by 60 GyE of proton irradiation with concurrent TMZ. The primary endpoints are overall survival (OS) and toxicity rates (acute and long-term). Secondary endpoints are progression-free survival (PFS), and tumor response (based upon assessment with C-methionine/fluoro-ethyl-tyrosine positron emission tomography [MET/FET PET] or magnetic resonance imaging [MRI] and detection of serologic immune markers). We hypothesize that the induction CIRT boost will result in a greater initial tumor-killing ability and prime the tumor microenvironment for enhanced immunologic tumor clearance, resulting in an expected 33% improvement in OS rates.

Discussion

The prognosis of GBM remains grim. The mechanism underpinning the poor prognosis of this malignancy is its chronic state of tumor hypoxia, which promotes both immunosuppression/immunologic evasion and radio-resistance. The unique physical and biological properties of CIRT are expected to overcome these microenvironmental limitations to confer an improved tumor-killing ability and anti-tumor immune response, which could result in an improvement in OS with minimal toxicity.

Trial registration number This trial has been registered with the China Clinical Trials Registry, and was allocated the number ChiCTR-OID-17013702.

Ceramide-Graphene Oxide Nanoparticles Enhance Cytotoxicity and Decrease HCC Xenograft Development: A Novel Approach for Targeted Cancer Therapy

Despite substantial efforts to develop novel therapeutic strategies for treating hepatocellular carcinoma (HCC), the effectiveness and specificity of available drugs still require further improvement. Previous work has shown that exogenous ceramide can play a key role in inducing the apoptotic death of cancer cells, however, the poor water-solubility of this compound has hampered its use for cancer treatment. In the present study, we used polyethylene glycol (PEG) and polyethylenimine (PEI) co-conjugated ultra-small nano-GO (NGO-PEG-PEI) loaded with C6-ceramide (NGO-PEG-PEI/Cer) as a strategy for HCC treatment. We assessed the biological role of NGO-PEG-PEI/Cer, and we assessed its antitumor efficacy against HCC both in vitro and in vivo in combination with the chemotherapeutic drug sorafenib. We found that NGO-PEG-PEI significantly enhanced the cellular uptake of C6-ceramide. By investigating the mechanism of cellular delivery, we determined that the internalization of NGO-PEG-PEI/Cer progressed primarily via a clathrin-mediated mechanism. The combination of NGO-PEG-PEI/Cer and sorafenib exhibited synergy between these two drugs. Further work revealed that NGO-PEG-PEI/Cer may play a role in subverting multidrug resistance (MDR) in HCC cells by inactivating MDR and Akt signaling. NGO-PEG-PEI/Cer also significantly inhibited tumor growth and improved survival times in vivo, and the synergetic effect of NGO-PEG-PEI/Cer combined with sorafenib was also observed in drug-resistant HCC xenografts. In conclusion, our NGO-PEG-PEI nanocomposite is an effective nano-platform for loading C6-ceramide for therapeutic use in treating HCC, exhibiting high cancer cell killing potency in this tumor model. The NGO-PEG-PEI/Cer/sorafenib combination additionally represents a promising potential therapeutic strategy for the treatment of drug-resistant HCC.

Combining Heavy-Ion Therapy with Immunotherapy: An Update on Recent Developments

Clinical trials and case reports of cancer therapies combining radiation therapy with immunotherapy have at times demonstrated total reduction or elimination of metastatic disease. While virtually all trials focus on the use of immunotherapy combined with conventional photon irradiation, the dose-distributive benefits of particles, in particular the distinct biological effects of heavy ions, have unknown potential vis-a-vis systemic disease response. Here, we review recent developments and evidence with a focus on the potential for heavy-ion combination therapy.

Inhibition of PI3K signalling increases the efficiency of radiotherapy in glioblastoma cells

Glioblastoma, the most common primary brain tumour, is also considered one of the most lethal cancers per se. It is highly refractory to therapeutic intervention, as highlighted by the mean patient survival of only 15 months, despite an aggressive treatment approach, consisting of maximal safe surgical resection, followed by radio- and chemotherapy. Radiotherapy, in particular, can have effects on the surviving fractions of tumour cells, which are considered adverse to the desired clinical outcome: It can induce increased cellular proliferation, as well as enhanced invasion. In this study, we established that differentiated glioblastoma cells alter their DNA repair response following repeated exposure to radiation and, therefore, high single-dose irradiation (SD-IR) is not a good surrogate marker for fractionated dose irradiation (FD-IR), as used in clinical practice. Integrating irradiation into a combination therapy approach, we then investigated whether the pharmacological inhibition of PI3K signalling, the most abundantly activated survival cascade in glioblastoma, enhances the efficacy of radiotherapy. Of note, treatment with GDC-0941, which blocks PI3K-mediated signalling, did not enhance cell death upon irradiation, but both treatment modalities functioned synergistically to reduce the total cell number. Furthermore, GDC-0941 not only prevented the radiation-induced increase in the motility of the differentiated cells, but further reduced their speed below that of untreated cells. Therefore, combining radiotherapy with the pharmacological inhibition of PI3K signalling is a potentially promising approach for the treatment of glioblastoma, as it can reduce the unwanted effects on the surviving fraction of tumour cells.

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.

The Immunoregulatory Potential of Particle Radiation in Cancer Therapy

Cancer treatment, today, consists of surgery, chemotherapy, radiation, and most recently immunotherapy. Combination immunotherapy-radiotherapy (CIR) has experienced a surge in public attention due to numerous clinical publications outlining the reduction or elimination of metastatic disease, following treatment with specifically ipilimumab and radiotherapy. The mechanism behind CIR, however, remains unclear, though it is hypothesized that radiation transforms the tumor into an in situ vaccine which immunotherapy modulates into a larger immune response. To date, the majority of attention has focused on rotating out immunotherapeutics with conventional radiation; however, the unique biological and physical benefits of particle irradiation may prove superior in generation of systemic effect. Here, we review recent advances in CIR, with a particular focus on the usage of charged particles to induce or enhance response to cancerous disease.

Sphingolipids and mitochondrial apoptosis

The sphingolipid family of lipids modulate several cellular processes, including proliferation, cell cycle regulation, inflammatory signaling pathways, and cell death. Several members of the sphingolipid pathway have opposing functions and thus imbalances in sphingolipid metabolism result in deregulated cellular processes, which cause or contribute to diseases and disorders in humans. A key cellular process regulated by sphingolipids is apoptosis, or programmed cell death. Sphingolipids play an important role in both extrinsic and intrinsic apoptotic pathways depending on the stimuli, cell type and cellular response to the stress. During mitochondrial-mediated apoptosis, multiple pathways converge on mitochondria and induce mitochondrial outer membrane permeabilization (MOMP). MOMP results in the release of intermembrane space proteins such as cytochrome c and Apaf1 into the cytosol where they activate the caspases and DNases that execute cell death. The precise molecular components of the pore(s) responsible for MOMP are unknown, but sphingolipids are thought to play a role. Here, we review evidence for a role of sphingolipids in the induction of mitochondrial-mediated apoptosis with a focus on potential underlying molecular mechanisms by which altered sphingolipid metabolism indirectly or directly induce MOMP. Data available on these mechanisms is reviewed, and the focus and limitations of previous and current studies are discussed to present important unanswered questions and potential future directions.

Melanoma: Last call for radiotherapy

Melanoma is traditionally considered to be a radioresistant tumor. However, radiotherapy and immunotherapy latest developments might upset this radiobiological dogma. Stereotactic radiotherapy allows high dose per fraction delivery, with high dose rate. More DNA lethal damages, less sublethal damages reparation, endothelial cell apoptosis, and finally clonogenic cell dysfunction are produced, resulting in improved local control. Radiotherapy can also enhance immune responses, inducing neoantigens formation, tumor antigen presentation, and cytokines release. A synergic effect of radiotherapy with immunotherapy is expected, and might lead to abscopal effects. If hadrontherapy biological properties seem able to suppress hypoxia-induced radioresistance and increase biological efficacy, ballistic advantages over photon radiations might also improve radiotherapy outcomes on usually poor prognosis locations. The present review addresses biological and clinical effects of high fraction dose, bystander effect, abscopal effect, and hadrontherapy features in melanoma. Clinical trials results are warranted to establish indications of innovative radiotherapy in melanoma.

Influence of Dose Rate on the Cellular Response to Low- and High-LET Radiations

Nowadays, head and neck squamous cell carcinoma (HNSCC) treatment failure is mostly explained by locoregional progression or intrinsic radioresistance. Radiotherapy (RT) has recently evolved with the emergence of heavy ion radiations or new fractionation schemes of photon therapy, which modify the dose rate of treatment delivery. The aim of the present study was then to evaluate the in vitro influence of a dose rate variation during conventional RT or carbon ion hadrontherapy treatment in order to improve the therapeutic care of patient. In this regard, two HNSCC cell lines were irradiated with photons or 72 MeV/n carbon ions at a dose rate of 0.5, 2, or 10 Gy/min. For both radiosensitive and radioresistant cells, the change in dose rate significantly affected cell survival in response to photon exposure. This variation of radiosensitivity was associated with the number of initial and residual DNA double-strand breaks (DSBs). By contrast, the dose rate change did not affect neither cell survival nor the residual DNA DSBs after carbon ion irradiation. As a result, the relative biological efficiency at 10% survival increased when the dose rate decreased. In conclusion, in the RT treatment of HNSCC, it is advised to remain very careful when modifying the classical schemes toward altered fractionation. At the opposite, as the dose rate does not seem to have any effects after carbon ion exposure, there is less need to adapt hadrontherapy treatment planning during active system irradiation.

Carbon-ion beams effectively induce growth inhibition and apoptosis in human neural stem cells compared with glioblastoma A172 cells

Carbon-ion radiotherapy (CIRT) holds promise in the treatment of glioblastoma, an aggressive X-ray-resistant brain tumor. However, since glioblastoma cells show a highly invasive nature, carbon-ion (C-ion) irradiation of normal tissues surrounding the tumor is inevitable. Recent studies have revealed the existence of neural stem cells in the adult brain. Therefore, the damaging effect of C-ion beams on the neural stem cells has to be carefully considered in the treatment planning of CIRT. Here, we investigated the growth and death mode of human neural stem cells (hNSCs) and glioblastoma A172 cells after X-ray or C-ion beam irradiation. The X-ray dose resulting in a 50% growth rate (D(50)) was 0.8 Gy in hNSCs and 3.0 Gy in A172 cells, while the D(50) for C-ion beams was 0.4 Gy in hNSCs and 1.6 Gy in A172 cells; the relative biological effectiveness value of C-ion beams was 2.0 in hNSCs and 1.9 in A172 cells. Importantly, both X-rays and C-ion beams preferentially induced apoptosis, not necrosis, in hNSCs; however, radiation-induced apoptosis was less evident in A172 cells. The apoptosis-susceptible nature of the irradiated hNSCs was associated with prolonged upregulation of phosphorylated p53, whereas the apoptosis-resistant nature of A172 cells was associated with a high basal level of nuclear factor kappa B expression. Taken together, these data indicate that apoptosis is the major cell death pathway in hNSCs after irradiation. The high sensitivity of hNSCs to C-ion beams underscores the importance of careful target volume delineation in the treatment planning of CIRT for glioblastoma.

DNA promoter hypermethylation contributes to down-regulation of galactocerebrosidase gene in lung and head and neck cancers

Galactocerebrosidase (GALC) is a lysosomal enzyme responsible for glycosphingolipids degradation byproducts of which are important for synthesis of apoptosis mediator ceramide. Reduced expression of GALC has been identified in human malignancies; however, molecular mechanisms underlying down-regulation of GALC expression in cancer remain unknown. We performed methylation and expression analysis on GALC gene in a panel of head and neck cancer (HNC) and lung cancer cell lines, attempting to understand the regulation of GALC in human cancer. QRT-PCR and western blot analysis were performed to detect the expression of GALC in HNC. Bisulfite DNA sequencing and real-time qMSP were used to detect the methylation of GALC in HNC and lung cancer cell lines. 5aza-dC treatment assay was used to analysis the functional effect of GALC methylation on GALC expression in HNC. Reduction or complete absence of GALC expression was observed in more than a half of the tested HNC cell lines (8/14). 7 out of 8 cell lines with down-regulated expression harbored heavy CpG island methylation, while all cell lines with abundant expression of the gene contained no methylation. Hypermethylation was also found in primary HNC tumor tissues and lung cancer cell lines whereas absent in normal oral mucosa tissues. Demethylating treatment demonstrated that 5aza-dC significantly restored GALC expression in cell lines with methylated promoter while showed no effect on cell lines without promoter hypermethylation. Our findings for the first time demonstrated that promoter hypermethylation contributed to down-regulation of GALC Gene, implicating epigenetic inactivation of GALC may play a role in tumorigenesis of cancer.

Cellular and molecular portrait of eleven human glioblastoma cell lines under photon and carbon ion irradiation

This study aimed to examine the cellular and molecular long-term responses of glioblastomas to radiotherapy and hadrontherapy in order to better understand the biological effects of carbon beams in cancer treatment. Eleven human glioblastoma cell lines, displaying gradual radiosensitivity, were irradiated with photons or carbon ions. Independently of p53 or O(6)-methylguanine-DNA methyltransferase(1) status, all cell lines responded to irradiation by a G2/M phase arrest followed by the appearance of mitotic catastrophe, which was concluded by a ceramide-dependent-apoptotic cell death. Statistical analysis demonstrated that: (i) the SF2(2) and the D10(3) values for photon are correlated with that obtained in response to carbon ions; (ii) regardless of the p53, MGMT status, and radiosensitivity, the release of ceramide is associated with the induction of late apoptosis; and (iii) the appearance of polyploid cells after photon irradiation could predict the Relative Biological Efficiency(4) to carbon ions. This large collection of data should increase our knowledge in glioblastoma radiobiology in order to better understand, and to later individualize, appropriate radiotherapy treatment for patients who are good candidates.

Mitotic DNA damages induced by carbon-ion radiation incur additional chromosomal breaks in polyploidy

Compared with low linear energy transfer (LET) radiation, carbon-ion radiation has been proved to induce high frequency of more complex DNA damages, including DNA double strands (DSBs) and non-DSB clustered DNA lesions. Chemotherapeutic drug doxorubicin has been reported to elicit additional H2AX phosphorylation in polyploidy. Here, we investigated whether mitotic DNA damage induced by high-LET carbon-ion radiation could play the same role. We demonstrate that impairment of post-mitotic G1 and S arrest and abrogation of post-mitotic G2-M checkpoint failed to prevent mis-replication of damaged DNA and mis-separation of chromosomes. Meanwhile, mitotic slippage only nocodazole-related, cytokinesis failure and cell fusion collectively contributed to the formation of binucleated cells. Chk1 and Cdh1 activation was inhibited when polyploidy emerged in force, both of which are critical components for mitotic exit and cytokinesis. Carbon-ion radiation irrelevant of nocodazole incurred additional DNA breaks in polyploidy, manifesting as structural and numerical karyotype changes. The proliferation of cells given pre-synchronization and radiation was completely inhibited and cells were intensely apoptotic. Since increased chromosomal damage resulted in extensive H2AX phosphorylation during polyploidy, we propose that the additional γ-H2AX during polyploidy incurred by carbon-ion radiation provides a final opportunity for these dangerous and chromosomally unstable cells to be eliminated.

Ceramide targets xIAP and cIAP1 to sensitize metastatic colon and breast cancer cells to apoptosis induction to suppress tumor progression

Background

Ceramide is a bioeffector that mediates various cellular processes, including apoptosis. However, the mechanism underlying ceramide function in apoptosis is apparently cell type-dependent and is not well-understood. We aimed at identifying molecular targets of ceramide in metastatic human colon and breast cancer cells, and determining the efficacy of ceramide analog in suppression of colon and breast cancer metastasis.

Methods

The activity of and mechanism underlying ceramide as a cytotoxic agent, and as a sensitizer for Fas-mediated apoptosis was analyzed in human cell lines established from primary or metastatic colon and breast cancers. The efficacy of ceramide analog LCL85 in suppression of metastasis was examined in preclinical mouse tumor models.

Results

Exposure of human colon carcinoma cells to ceramide analog LCL85 results in apoptosis in a dose-dependent manner. Interestingly, a sublethal dose of LCL85 increased C16 ceramide content and overcame tumor cell resistance to Fas-mediated apoptosis. Subsequently, treatment of tumor cells with exogenous C16 ceramide resulted in increased tumor cell sensitivity to Fas-mediated apoptosis. LCL85 resembles Smac mimetic BV6 in sensitization of colon carcinoma cells to Fas-mediated apoptosis by inducing proteasomal degradation of cIAP1 and xIAP proteins. LCL85 also decreased xIAP1 and cIAP1 protein levels and sensitized metastatic human breast cancer cells to Fas-mediated apoptosis. Silencing xIAP and cIAP1 with specific siRNAs significantly increased the metastatic human colon carcinoma cell sensitivity to Fas-mediated apoptosis, suggesting that IAP proteins mediate apoptosis resistance in metastatic human colon carcinoma cells and ceramide induces IAP protein degradation to sensitize the tumor cells to apoptosis induction. Consistent with its apoptosis sensitization activity, subtoxic doses of LCL85 suppressed colon carcinoma cell metastatic potential in an experimental lung metastasis mouse model, as well as breast cancer growth and spontaneous lung metastasis in an orthotopic breast cancer mouse model.

Conclusion

We have identified xIAP and cIAP1 as molecular targets of ceramide and determined that ceramide analog LCL85 is an effective sensitizer in overcoming resistance of human cell lines established from metastatic colon and breast cancers to apoptosis induction to suppress metastasis in vivo.

Radiation-induced acid ceramidase confers prostate cancer resistance and tumor relapse

Escape of prostate cancer (PCa) cells from ionizing radiation-induced (IR-induced) killing leads to disease progression and cancer relapse. The influence of sphingolipids, such as ceramide and its metabolite sphingosine 1-phosphate, on signal transduction pathways under cell stress is important to survival adaptation responses. In this study, we demonstrate that ceramide-deacylating enzyme acid ceramidase (AC) was preferentially upregulated in irradiated PCa cells. Radiation-induced AC gene transactivation by activator protein 1 (AP-1) binding on the proximal promoter was sensitive to inhibition of de novo ceramide biosynthesis, as demonstrated by promoter reporter and ChIP-qPCR analyses. Our data indicate that a protective feedback mechanism mitigates the apoptotic effect of IR-induced ceramide generation. We found that deregulation of c-Jun induced marked radiosensitization in vivo and in vitro, which was rescued by ectopic AC overexpression. AC overexpression in PCa clonogens that survived a fractionated 80-Gy IR course was associated with increased radioresistance and proliferation, suggesting a role for AC in radiotherapy failure and relapse. Immunohistochemical analysis of human PCa tissues revealed higher levels of AC after radiotherapy failure than those in therapy-naive PCa, prostatic intraepithelial neoplasia, or benign tissues. Addition of an AC inhibitor to an animal model of xenograft irradiation produced radiosensitization and prevention of relapse. These data indicate that AC is a potentially tractable target for adjuvant radiotherapy.