Translational Research to Improve the Efficacy of Carbon Ion Radiotherapy: Experience of Gunma University

Killing two birds with one stone: Abscopal effect mechanism and its application prospect in radiotherapy

Abscopal effects are characterized by the emergence of neoplasms in regions unrelated to the primary radiation therapy site, displaying a gradual attenuation or regression throughout the progression of radiation therapy, which have been of interest to scientists since Mole's proposal in 1953. The incidence of abscopal effects in radiation therapy is intricately linked to the immune system, with both innate and adaptive immune responses playing crucial roles. Biological factors impacting abscopal effects ultimately exert their influence on the intricate workings of the immune system. Although abscopal effects are rarely observed in clinical cases, the underlying mechanism remains uncertain. This article examines the biological and physical factors influencing abscopal effects of radiotherapy. Through a review of preclinical and clinical studies, this article aims to offer a comprehensive understanding of abscopal effects and proposes new avenues for future research in this field. The findings presented in this article serve as a valuable reference for researchers seeking to explore this topic in greater depth.

The rationale for a carbon ion radiation therapy facility in Australia

Australia has taken a collaborative nationally networked approach to achieve particle therapy capability. This supports the under-construction proton therapy facility in Adelaide, other potential proton centres and an under-evaluation proposal for a hybrid carbon ion and proton centre in western Sydney. A wide-ranging overview is presented of the rationale for carbon ion radiation therapy, applying observations to the case for an Australian facility and to the clinical and research potential from such a national centre.

An international approach to estimating the indications and number of eligible patients for carbon ion radiation therapy (CIRT) in Australia

BACKGROUND AND PURPOSE

To establish the treatment indications and potential patient numbers for carbon ion radiation therapy (CIRT) at the proposed national carbon ion (and proton) therapy facility in the Westmead precinct, New South Wales (NSW), Australia.

METHODS

An expert panel was convened, including representatives of four operational and two proposed international carbon ion facilities, as well as NSW-based CIRT stakeholders. They met virtually to consider CIRT available evidence and experience. Information regarding Japanese CIRT was provided pre- and post- the virtual meeting. Published information for South Korea was included in discussions.

RESULTS

There was jurisdictional variation in the tumours treated by CIRT due to differing incidences of some tumours, referral patterns, differences in decisions regarding which tumours to prioritise, CIRT resources available and funding arrangements. The greatest level of consensus was reached that CIRT in Australia can be justified currently for patients with adenoid cystic carcinomas and mucosal melanomas of the head and neck, hepatocellular cancer and liver metastases, base of skull meningiomas, chordomas and chondrosarcomas. Almost 1400 Australian patients annually meet the consensus-derived indications now.

CONCLUSION

A conservative estimate is that 1% of cancer patients in Australia (or 2% of patients recommended for radiation therapy) may preferentially benefit from CIRT for initial therapy of radiation resistant tumours, or to boost persistently active disease after other therapies, or for re-irradiation of recurrent disease. On this basis, one national carbon ion facility with up to four treatment rooms is justified for Australian patients.

Dosimetric comparison between stereotactic body radiotherapy and carbon-ion radiation therapy for prostate cancer

Background

Prostate cancer rates have been steadily increasing in recent years. As high-precision radiation therapy methods, stereotactic body radiation therapy (SBRT) and carbon-ion radiation therapy (CIRT) have unique advantages. Analyzing the dosimetric differences between SBRT and CIRT in the treatment of localized prostate cancer can help provide patients with more accurate, individualized treatment plans.

Methods

We selected computed tomography positioning images and the contours of target volumes of 16 patients with localized prostate cancer who received radiotherapy. We delineated the organs at risk (OARs) on the CyberKnife (CK) treatment planning system (TPS) MultiPlan4.0, which were imported into the CIRT uniform scanning TPS HIMM-1 ci-Plan. Two treatment plans, SBRT and CIRT, were designed for the same patient, and we used SPSS 22.0 for the statistical analysis of data.

Results

Both SBRT and CIRT plans met the prescribed dose requirements. In terms of target volume exposure dose, D2 (P<0.001), D5 (P<0.001), D50 (P<0.001), D90 (P=0.029), D95 (P<0.001), D98 (P<0.001), and Dmean (P<0.001) under SBRT were significantly higher than those under CIRT; the conformity index (CI) under SBRT was significantly better than that under CIRT (P<0.001); the target volume coverage rate (V95%) and dose homogeneity index (HI) under CIRT were significantly better than those under SBRT (P<0.001). In terms of OAR exposure dosage, the Dmax of the bladder and rectum under SBRT was significantly lower than that under CIRT (P<0.001), but Dmean was in the other direction; the exposure dose of the intestinal tract under CIRT was significantly lower than that under SBRT (P<0.05); Dmax of the femoral head under CIRT was significantly lower than that under SBRT (P<0.05), and there was no statistical difference between them at other doses.

Conclusions

In this study, we found that when CIRT was used for treating localized prostate cancer, the dose distribution in target volume was more homogeneous and the coverage rate was higher; the average dose of OARs was lower. SBRT had a better CI and higher dose in target volume; the dose hotspot was lower in OARs. It is important to comprehensively consider the dose relationship between local tumor and surrounding tissues when selecting treatment plans.

Carbon ion radiation and clustered DNA double-strand breaks

A carbon ion categorized as a heavy ion particle has been used for cancer radiotherapy. High linear energy transfer (LET) carbon ion irradiation deposits energy at a high density along a particle track, generating multiple types of DNA damage. Complex DNA lesions, comprising DNA double-strand breaks (DSBs), single-strand breaks, and base damage within 1-2 helical turns (<3-4nm), are thought to be difficult to repair and critically influence cell viability. In addition to the effect of lesion complexity, the most recent studies have demonstrated another characteristic of high LET particle radiation-induced DNA damage, clustered DSBs. Clustered DSBs are defined as the formation of multiple DSBs in close proximity where the scale of clustering is approximately 1-2μm³, i.e., the scale of the event is estimated to be > ∼1Mbp. This chapter reviews the hallmarks of clustered DSBs and how such DNA damage influences genome instability and cell viability in the context of high LET carbon ion radiotherapy.

Flourish of Proton and Carbon Ion Radiotherapy in China

Proton and heavy ion therapy offer superior relative biological effectiveness (RBE) in the treatment of deep-seated tumors compared with conventional photon radiotherapy due to its Bragg-peak feature of energy deposition in organs. Many proton and carbon ion therapy centers are active all over the world. At present, five particle radiotherapy institutes have been built and are receiving patient in China, mainly including Wanjie Proton Therapy Center (WPTC), Shanghai Proton Heavy Ion Center (SPHIC), Heavy Ion Cancer Treatment Center (HIMM), Chang Gung Memorial Hospital (CGMH), and Ruijin Hospital affiliated with Jiao Tong University. Many cancer patients have benefited from ion therapy, showing unique advantages over surgery and chemotherapy. By the end of 2020, nearly 8,000 patients had been treated with proton, carbon ion or carbon ion combined with proton therapy. So far, there is no systemic review for proton and carbon ion therapy facility and clinical outcome in China. We reviewed the development of proton and heavy ion therapy, as well as providing the representative clinical data and future directions for particle therapy in China. It has important guiding significance for the design and construction of new particle therapy center and patients’ choice of treatment equipment.

64Cu-ATSM Predicts Efficacy of Carbon Ion Radiotherapy Associated with Cellular Antioxidant Capacity

Simple Summary

Carbon ion radiotherapy is an emerging cancer treatment modality that has a greater therapeutic window than conventional photon radiotherapy. To maximize the efficacy of this extremely scarce medical resource, it is important to identify predictive biomarkers of higher carbon ion relative biological effectiveness (RBE) over photons. Here we show that the carbon ion RBE in human cancer cells correlates with the cellular uptake of ⁶⁴Cu(II)-diacetyl-bis(N4-methylthiosemicarbazone) (⁶⁴Cu-ATSM), a potential radioligand that reflects an over-reduced intracellular environment. High RBE/⁶⁴Cu-ATSM cells show greater steady-state levels of antioxidant proteins and increased capacity to scavenge reactive oxygen species in response to X-rays than low RBE/⁶⁴Cu-ATSM counterparts. These data suggest that the cellular antioxidant activity is a possible determinant of carbon ion RBE predictable by ⁶⁴Cu-ATSM uptake.

Abstract

Carbon ion radiotherapy is an emerging cancer treatment modality that has a greater therapeutic window than conventional photon radiotherapy. To maximize the efficacy of this extremely scarce medical resource, it is important to identify predictive biomarkers of higher carbon ion relative biological effectiveness (RBE) over photons. We addressed this issue by focusing on cellular antioxidant capacity and investigated ⁶⁴Cu(II)-diacetyl-bis(N4-methylthiosemicarbazone) (⁶⁴Cu-ATSM), a potential radioligand that reflects an over-reduced intracellular environment. We found that the carbon ion RBE correlated with ⁶⁴Cu-ATSM uptake both in vitro and in vivo. High RBE/⁶⁴Cu-ATSM cells showed greater steady-state levels of antioxidant proteins and increased capacity to scavenge reactive oxygen species in response to X-rays than low RBE/⁶⁴Cu-ATSM counterparts; this upregulation of antioxidant systems was associated with downregulation of TCA cycle intermediates. Furthermore, inhibition of nuclear factor erythroid 2-related factor 2 (Nrf2) sensitized high RBE/⁶⁴Cu-ATSM cells to X-rays, thereby reducing RBE values to levels comparable to those in low RBE/⁶⁴Cu-ATSM cells. These data suggest that the cellular activity of Nrf2-driven antioxidant systems is a possible determinant of carbon ion RBE predictable by ⁶⁴Cu-ATSM uptake. These new findings highlight the potential clinical utility of ⁶⁴Cu-ATSM imaging to identify high RBE tumors that will benefit from carbon ion radiotherapy.

High linear energy transfer carbon-ion irradiation upregulates PD-L1 expression more significantly than X-rays in human osteosarcoma U2OS cells

Programmed death ligand 1 (PD-L1) expression on the surface of cancer cells affects the efficacy of anti-PD-1/PD-L1 immune checkpoint therapy. However, the mechanism underlying PD-L1 expression in cancer cells is not fully understood, particularly after ionizing radiation (IR). Here, we examined the impact of high linear energy transfer (LET) carbon-ion irradiation on the expression of PD-L1 in human osteosarcoma U2OS cells. We found that the upregulation of PD-L1 expression after high LET carbon-ion irradiation was greater than that induced by X-rays at the same physical and relative biological effectiveness (RBE) dose, and that the upregulation of PD-L1 induced by high LET carbon-ion irradiation was predominantly dependent on ataxia telangiectasia and Rad3-related (ATR) kinase activity. Moreover, we showed that the downstream signaling, e.g. STAT1 phosphorylation and IRF1 expression, was upregulated to a greater extent after high LET carbon-ion irradiation than X-rays, and that IRF1 upregulation was also ATR dependent. Finally, to visualize PD-L1 molecules on the cell surface in 3D, we applied immunofluorescence-based super-resolution imaging. The three-dimensional structured illumination microscopy (3D-SIM) analyses revealed substantial increases in the number of presented PD-L1 molecules on the cell surface after high LET carbon-ion irradiation compared with X-ray irradiation.

Brain Tumor Causes, Symptoms, Diagnosis and Radiotherapy Treatment

The strategy used for the treatment of given brain cancer is critical in determining the post effects and survival. An oncological diagnosis of tumor evaluates a range of parameters such as shape, size, volume, location and neurological complexity that define the symptomatic severity. The evaluation determines a suitable treatment approach chosen from a range of options such as surgery, chemotherapy, hormone therapy, radiation therapy and other targeted therapies. Often, a combination of such therapies is applied to achieve superior results. Radiotherapy serves as a better treatment strategy because of a higher survival rate. It offers the flexibility of synergy with other treatment strategies and fewer side effects on organs at risk. This review presents a radiobiological perspective in the treatment of brain tumor. The cause, symptoms, diagnosis, treatment, post-treatment effects and the framework involved in its elimination are summarized.

CircZNF208 enhances the sensitivity to X-rays instead of carbon-ions through the miR-7-5p /SNCA signal axis in non-small-cell lung cancer cells

BACKGROUND

Mounting evidence suggests that circular RNAs (circRNAs) are closely related to the regulation of gene expression during tumour development. However, the role of circRNAs in modulating the radiosensitivity of non-small cell lung cancer (NSCLC) cells has not been explored.

METHODS

Transcriptome sequencing was used to explore the expression profiles of circRNAs in NSCLC. The expression level of circRNAs was changed by inducing instantaneous knockdown or overexpression. Changes in proliferation and radiosensitivity of NSCLC cells were investigated using CCK-8, EDU, and clonal survivals.

RESULTS

By analysing the circRNA expression profile of NSCLC cells, we found that circRNA ZNF208 (circZNF208) was significantly upregulated in a radioresistant NSCLC cell line (A549-R11), which was acquired from the parental NSCLC cell line A549. Knockout experiments indicated that circZNF208 enhanced the radiosensitivity of A549 and A549-R11 cells to X-rays. Mechanistically, circZNF208 upregulated SNCA expression by acting as a sponge of miR-7-5p and subsequently promoted the resistance of NSCLC cells to low linear energy transfer (LET) X-rays. However, this effect was not observed in NSCLC cells exposed to high-LET carbon ions.

CONCLUSIONS

Knockdown of circZNF208 altered the radiosensitivity of patients with NSCLC to X-rays but did not significantly change the sensitivity to carbon ions. Therefore, circZNF208 might serve as a potential biomarker and therapeutic target for NSCLC treatment with radiotherapy of different modalities.

Immunomodulatory Effects of Radiotherapy

Radiation therapy (RT), an integral component of curative treatment for many malignancies, can be administered via an increasing array of techniques. In this review, we summarize the properties and application of different types of RT, specifically, conventional therapy with x-rays, stereotactic body RT, and proton and carbon particle therapies. We highlight how low-linear energy transfer (LET) radiation induces simple DNA lesions that are efficiently repaired by cells, whereas high-LET radiation causes complex DNA lesions that are difficult to repair and that ultimately enhance cancer cell killing. Additionally, we discuss the immunogenicity of radiation-induced tumor death, elucidate the molecular mechanisms by which radiation mounts innate and adaptive immune responses and explore strategies by which we can increase the efficacy of these mechanisms. Understanding the mechanisms by which RT modulates immune signaling and the key players involved in modulating the RT-mediated immune response will help to improve therapeutic efficacy and to identify novel immunomodulatory drugs that will benefit cancer patients undergoing targeted RT.

Different Mechanisms Underlie the Metabolic Response of GBM Stem-Like Cells to Ionizing Radiation: Biological and MRS Studies on Effects of Photons and Carbon Ions

Glioblastoma multiforme (GBM) is a malignant primary brain tumor with very poor prognosis, high recurrence rate, and failure of chemo-radiotherapy, mainly due to a small fraction of cells with stem-like properties (GSCs). To study the mechanisms of GSCs resistance to radiation, two GSC lines, named line #1 and line #83, with different metabolic patterns and clinical outcome, were irradiated with photon beams and carbon ions and assessed by ¹H Magnetic Resonance Spectroscopy (MRS). Both irradiation modalities induced early cytotoxic effects in line #1 with small effects on cell cycle, whereas a proliferative G2/M cytostatic block was observed in line #83. MR spectroscopy signals from mobile lipids (ML) increased in spectra of line #1 after photon and C-ion irradiation with effects on lipid unsaturation level, whereas no effects were detected in line #83 spectra. Gamma-Aminobutyric Acid (GABA), glutamic acid (glu) and Phosphocreatine (pCr) signals showed a significant variation only for line #1 after carbon ion irradiation. Glucose (glc) level and lactate (Lac) extrusion behaved differently in the two lines. Our findings suggest that the differences in irradiation response of GSCs #1 and #83 lines are likely attributable to their different metabolic fingerprint rather than to the different radiation types.

Clustered DNA double-strand break formation and the repair pathway following heavy-ion irradiation

Photons, such as X- or γ-rays, induce DNA damage (distributed throughout the nucleus) as a result of low-density energy deposition. In contrast, particle irradiation with high linear energy transfer (LET) deposits high-density energy along the particle track. High-LET heavy-ion irradiation generates a greater number and more complex critical chromosomal aberrations, such as dicentrics and translocations, compared with X-ray or γ irradiation. In addition, the formation of >1000 bp deletions, which is rarely observed after X-ray irradiation, has been identified following high-LET heavy-ion irradiation. Previously, these chromosomal aberrations have been thought to be the result of misrepair of complex DNA lesions, defined as DNA damage through DNA double-strand breaks (DSBs) and single-strand breaks as well as base damage within 1-2 helical turns (<3-4 nm). However, because the scale of complex DNA lesions is less than a few nanometers, the large-scale chromosomal aberrations at a micrometer level cannot be simply explained by complex DNA lesions. Recently, we have demonstrated the existence of clustered DSBs along the particle track through the use of super-resolution microscopy. Furthermore, we have visualized high-level and frequent formation of DSBs at the chromosomal boundary following high-LET heavy-ion irradiation. In this review, we summarize the latest findings regarding the hallmarks of DNA damage structure and the repair pathway following heavy-ion irradiation. Furthermore, we discuss the mechanism through which high-LET heavy-ion irradiation may induce dicentrics, translocations and large deletions.

Targeted and Off-Target (Bystander and Abscopal) Effects of Radiation Therapy: Redox Mechanisms and Risk/Benefit Analysis

SIGNIFICANCE

Radiation therapy (from external beams to unsealed and sealed radionuclide sources) takes advantage of the detrimental effects of the clustered production of radicals and reactive oxygen species (ROS). Research has mainly focused on the interaction of radiation with water, which is the major constituent of living beings, and with nuclear DNA, which contains the genetic information. This led to the so-called target theory according to which cells have to be hit by ionizing particles to elicit an important biological response, including cell death. In cancer therapy, the Poisson law and linear quadratic mathematical models have been used to describe the probability of hits per cell as a function of the radiation dose. Recent Advances: However, in the last 20 years, many studies have shown that radiation generates "danger" signals that propagate from irradiated to nonirradiated cells, leading to bystander and other off-target effects.

CRITICAL ISSUES

Like for targeted effects, redox mechanisms play a key role also in off-target effects through transmission of ROS and reactive nitrogen species (RNS), and also of cytokines, ATP, and extracellular DNA. Particularly, nuclear factor kappa B is essential for triggering self-sustained production of ROS and RNS, thus making the bystander response similar to inflammation. In some therapeutic cases, this phenomenon is associated with recruitment of immune cells that are involved in distant irradiation effects (called "away-from-target" i.e., abscopal effects).

FUTURE DIRECTIONS

Determining the contribution of targeted and off-target effects in the clinic is still challenging. This has important consequences not only in radiotherapy but also possibly in diagnostic procedures and in radiation protection.

Clinical trials involving carbon-ion radiation therapy and the path forward

To describe the international landscape of clinical trials in carbon-ion radiotherapy (CIRT), the authors reviewed the current status of 63 ongoing clinical trials (median, 47 participants) involving CIRT identified from the US clinicaltrials.gov trial registry and the World Health Organization International Clinical Trials Platform Registry. The objectives were to evaluate the potential for these trials to define the role of this modality in the treatment of specific cancer types and identify the major challenges and opportunities to advance this technology. A significant body of literature suggested the potential for advantageous dose distributions and, in preclinical biologic studies, the enhanced effectiveness for CIRT compared with photons and protons. In addition, clinical evidence from phase I/II trials, although limited, indicated the potential for CIRT to improve cancer outcomes. However, current high-level phase III randomized clinical trial evidence does not exist. Although there has been an increase in the number of trials investigating CIRT since 2010, and the number of countries and sites offering CIRT is slowly growing, this progress has excluded other countries. Several recommendations are proposed to study this modality to accelerate progress in the field, including: 1) increasing the number of multinational randomized clinical trials, 2) leveraging the existing CIRT facilities to launch larger multinational trials directed at common cancers combined with high-level quality assurance; and 3) developing more compact and less expensive next-generation treatment systems integrated with radiobiologic research and preclinical testing.

Mutational analysis of uterine cervical cancer that survived multiple rounds of radiotherapy

Radiotherapy is an essential component of cancer therapy. Despite advances in cancer genomics, the mutation signatures of radioresistant tumors have not yet been fully elucidated. To address this issue, we analyzed a unique set of clinical specimens from a uterine cervical cancer that repeatedly locally recurred after multiple rounds of radiotherapy. Exon sequencing of 409 cancer-related genes in the treatment-naïve tumor and the tumors that recurred after initial and secondary radiotherapy identified (i) activating mutations in PIK3CA and KRAS, and putative inactivating mutations in SMAD4, as trunk mutation signatures that persisted over the clinical course; and (ii) mutations in KMT2A, TET1, and NLRP1 as acquired mutation signatures observed only in recurrent tumors after radiotherapy. Comprehensive mining of published in vitro genomics data pertaining to radiosensitivity revealed that simultaneous mutations in KRAS and SMAD4, which have not been described previously in uterine cervical cancer, are associated with cancer cell radioresistance. The association between this mutation signature and radioresistance was validated by isogenic cell-based experiments. These results provide proof-of-principle for the analytical pipeline employed in this study, which explores clinically relevant mutation signatures for radioresistance, and demonstrate that this approach is worth pursuing with larger cohorts in the future.

3D-structured illumination microscopy reveals clustered DNA double-strand break formation in widespread γH2AX foci after high LET heavy-ion particle radiation

DNA double-strand breaks (DSBs) induced by ionising radiation are considered the major cause of genotoxic mutations and cell death. While DSBs are dispersed throughout chromatin after X-rays or γ-irradiation, multiple types of DNA damage including DSBs, single-strand breaks and base damage can be generated within 1–2 helical DNA turns, defined as a complex DNA lesion, after high Linear Energy Transfer (LET) particle irradiation. In addition to the formation of complex DNA lesions, recent evidence suggests that multiple DSBs can be closely generated along the tracks of high LET particle irradiation. Herein, by using three dimensional (3D)-structured illumination microscopy, we identified the formation of 3D widespread γH2AX foci after high LET carbon-ion irradiation. The large γH2AX foci in G₂-phase cells encompassed multiple foci of replication protein A (RPA), a marker of DSBs undergoing resection during homologous recombination. Furthermore, we demonstrated by 3D analysis that the distance between two individual RPA foci within γH2AX foci was approximately 700 nm. Together, our findings suggest that high LET heavy-ion particles induce clustered DSB formation on a scale of approximately 1 μm³. These closely localised DSBs are considered to be a risk for the formation of chromosomal rearrangement after heavy-ion irradiation.

Repurposing DNA repair factors to eradicate tumor cells upon radiotherapy

Cancer is the leading cause of death worldwide. Almost 50% of all cancer patients undergo radiation therapy (RT) during treatment, with varying success. The main goal of RT is to kill tumor cells by damaging their DNA irreversibly while sparing the surrounding normal tissue. The outcome of RT is often determined by how tumors recognize and repair their damaged DNA. A growing body of evidence suggests that tumors often show abnormal expression of DNA double-strand break (DSB) repair genes that are absent from normal cells. Defects in a specific DNA repair pathway make tumor cells overly dependent on alternative or backup pathways to repair their damaged DNA. These tumor cell-specific abnormalities in the DNA damage response (DDR) machinery can potentially be used as biomarkers for treatment outcomes or as targets for sensitization to ionizing radiation (IR). An improved understanding of genetic or epigenetic alterations in the DNA repair pathways specific to cancer cells has paved the way for new treatments that combine pharmacological exploitation of tumor-specific molecular vulnerabilities with IR. Inhibiting DNA repair pathways has the potential to greatly enhance the therapeutic ratio of RT. In this review, we will discuss DNA repair pathways in active cells and how these pathways are deregulated in tumors. We will also describe the impact of targeting cancer-specific aberrations in the DDR as a treatment strategy to improve the efficacy of RT. Finally, we will address the current roadblocks and future prospects of these approaches.