Effective Suppression of Pulmonary Metastasis in Combined Carbon Ion Radiation Therapy With Dendritic-Cell Immunotherapy in Murine Tumor Models

Photon- and Proton-Mediated Biological Effects: What Has Been Learned?

The current understanding of the effects of radiation is gradually becoming broader. However, it still remains unclear why some patients respond to radiation with a pronounced positive response, while in some cases the disease progresses. This is the motivation for studying the effects of radiation therapy not only on tumor cells, but also on the tumor microenvironment, as well as studying the systemic effects of radiation. In this framework, we review the biological effects of two types of radiotherapy: photon and proton irradiations. Photon therapy is a commonly used type of radiation therapy due to its wide availability and long-term history, with understandable and predictable outcomes. Proton therapy is an emerging technology, already regarded as the method of choice for many cancers in adults and children, both dosimetrically and biologically. This review, written after the analysis of more than 100 relevant literary sources, describes the local effects of photon and proton therapy and shows the mechanisms of tumor cell damage, interaction with tumor microenvironment cells and effects on angiogenesis. After systematic analysis of the literature, we can conclude that proton therapy has potentially favorable toxicological profiles compared to photon irradiation, explained mainly by physical but also biological properties of protons. Despite the fact that radiobiological effects of protons and photons are generally similar, protons inflict reduced damage to healthy tissues surrounding the tumor and hence promote fewer adverse events, not only local, but also systemic.

Photon versus carbon ion irradiation: immunomodulatory effects exerted on murine tumor cell lines

While for photon radiation hypofractionation has been reported to induce enhanced immunomodulatory effects, little is known about the immunomodulatory potential of carbon ion radiotherapy (CIRT). We thus compared the radio-immunogenic effects of photon and carbon ion irradiation on two murine cancer cell lines of different tumor entities. We first calculated the biological equivalent doses of carbon ions corresponding to photon doses of 1, 3, 5, and 10 Gy of the murine breast cancer cell line EO771 and the OVA-expressing pancreatic cancer cell line PDA30364/OVA by clonogenic survival assays. We compared the potential of photon and carbon ion radiation to induce cell cycle arrest, altered surface expression of immunomodulatory molecules and changes in the susceptibility of cancer cells to cytotoxic T cell (CTL) mediated killing. Irradiation induced a dose-dependent G2/M arrest in both cell lines irrespective from the irradiation source applied. Likewise, surface expression of the immunomodulatory molecules PD-L1, CD73, H2-Db and H2-Kb was increased in a dose-dependent manner. Both radiation modalities enhanced the susceptibility of tumor cells to CTL lysis, which was more pronounced in EO771/Luci/OVA cells than in PDA30364/OVA cells. Overall, compared to photon radiation, the effects of carbon ion radiation appeared to be enhanced at higher dose range for EO771 cells and extenuated at lower dose range for PDA30364/OVA cells. Our data show for the first time that equivalent doses of carbon ion and photon irradiation exert similar immunomodulating effects on the cell lines of both tumor entities, highlighted by an enhanced susceptibility to CTL mediated cytolysis in vitro.

Radiotherapy and immune response: the systemic effects of a local treatment

Technological developments have allowed improvements in radiotherapy delivery, with higher precision and better sparing of normal tissue. For many years, it has been well known that ionizing radiation has not only local action but also systemic effects by triggering many molecular signaling pathways. There is still a lack of knowledge of this issue. This review focuses on the current literature about the effects of ionizing radiation on the immune system, either suppressing or stimulating the host reactions against the tumor, and the factors that interact with these responses, such as the radiation dose and dose / fraction effects in the tumor microenvironment and vasculature. In addition, some implications of these effects in cancer treatment, mainly in combined strategies, are addressed from the perspective of their interactions with the more advanced technology currently available, such as heavy ion therapy and nanotechnology.

Evolution of Carbon Ion Radiotherapy at the National Institute of Radiological Sciences in Japan

Charged particles can achieve better dose distribution and higher biological effectiveness compared to photon radiotherapy. Carbon ions are considered an optimal candidate for cancer treatment using particles. The National Institute of Radiological Sciences (NIRS) in Chiba, Japan was the first radiotherapy hospital dedicated for carbon ion treatments in the world. Since its establishment in 1994, the NIRS has pioneered this therapy with more than 69 clinical trials so far, and hundreds of ancillary projects in physics and radiobiology. In this review, we will discuss the evolution of carbon ion radiotherapy at the NIRS and some of the current and future projects in the field.

Impact of Particle Irradiation on the Immune System: From the Clinic to Mars

Despite the generalized use of photon-based radiation (i.e., gamma rays and X-rays) to treat different cancer types, particle radiotherapy (i.e., protons and carbon ions) is becoming a popular, and more effective tool to treat specific tumors due to the improved physical properties and biological effectiveness. Current scientific evidence indicates that conventional radiation therapy affects the tumor immunological profile in a particular manner, which in turn, might induce beneficial effects both at local and systemic (i.e., abscopal effects) levels. The interaction between radiotherapy and the immune system is being explored to combine immune and radiation (including particles) treatments, which in many cases have a greater clinical effect than any of the therapies alone. Contrary to localized, clinical irradiation, astronauts are exposed to whole body, chronic cosmic radiation, where protons and heavy ions are an important component. The effects of this extreme environment during long periods of time, e.g., a potential mission to Mars, will have an impact on the immune system that could jeopardize the health of the astronauts, hence the success of the mission. To this background, the purpose of this mini review is to briefly present the current knowledge in local and systemic immune alterations triggered by particle irradiation and to propose new lines of future research. Immune effects induced by particle radiation relevant to clinical applications will be covered, together with examples of combined radiotherapy and immunotherapy. Then, the focus will move to outer space, where the immune system alterations induced by cosmic radiation during spaceflight will be discussed.

The Future of Combining Carbon-Ion Radiotherapy with Immunotherapy: Evidence and Progress in Mouse Models

After >60 years since the first treatment, particle radiation therapy (RT) is now used to treat various types of tumors worldwide. Particle RT results in favorable outcomes, especially in local control, because of its biological properties and excellent dose distribution. However, similar to other types of cancer treatment, metastasis control is a crucial issue. Notably, immunotherapy is used for cancer treatment with high risk for recurrence and/or metastasis. These 2 cancer therapies could be ideal, complementary partners for noninvasive cancer treatment. In this review, we will focus on preclinical studies combining particle RT, especially carbon ion RT, and immunotherapy.