Verification of 5-Aminolevurinic Radiodynamic Therapy Using a Murine Melanoma Brain Metastasis Model

Abstract

Melanoma is a highly aggressive cancer with a propensity for brain metastases. These can be treated by radiotherapy, but the radiation-resistant nature of melanoma makes the prognosis for melanoma patients with brain metastases poor. Previously, we demonstrated that treatment of mice with subcutaneous melanoma with 5-aminolevurinic acid (5-ALA) and X-rays in combination, (“radiodynamic therapy (RDT)”), instead of with 5-ALA and laser beams (“photodynamic therapy”), improved tumor suppression in vivo. Here, using the B16-Luc melanoma brain metastasis model, we demonstrate that 5-ALA RDT effectively treats brain metastasis. We also studied how 5-ALA RDT damages cells in vitro using a B16 melanoma culture. Cell culture preincubated with 5-ALA alone increased intracellular photosensitizer protoporphyrin IX. On X-ray irradiation, the cells enhanced their ∙OH radical generation, which subsequently induced γH2AX, a marker of DNA double-strand breaks in their nuclei, but decreased mitochondrial membrane potential. After two days, the cell cycle was arrested. When 5-ALA RDT was applied to the brain melanoma metastasis model in vivo, suppression of tumor growth was indicated. Therapeutic efficacy in melanoma treatment has recently been improved by molecular targeted drugs and immune checkpoint inhibitors. Treatment with these drugs is now expected to be combined with 5-ALA RDT to further improve therapeutic efficacy.

DNA Strand Break Properties of Protoporphyrin IX by X-ray Irradiation against Melanoma

“…For these reasons, 5-ALA, and not PpIX, is considered a radiosensitizer and is used in clinical practice and has been evaluated as a precursor in radiosensitized animal models. In this in vitro study, DSBs in melanoma cell nuclei were confirmed by γH2AX by X-ray irradiation and further enhanced by PpIX, as well as 5-ALA treatment in a previous study [8]. Further, the DSBs were accompanied by a decrease in cell surviving fraction, indicating that DNA damage enhanced by PpIX is one of the causes of anticancer activity.…”

“…A series of studies on the combination treatment of 5-ALA and ionizing radiation has been conducted by some research groups, and 5-ALA with subsequent intracellular PpIX accumulation has been found to increase kilo electron volt (KeV) or mega electron volt (MeV) irradiation cytotoxicity in a variety of contexts using mouse models of melanoma, glioma, colon cancer, etc. [5][6][7][8][9][10][11][12][13][14][15]. PpIX expression enhances ROS generation, which increases cellular DNA damage.…”

“…The total clinical radiation dose is limited to a threshold value to avoid causing any damage to normal cells [3,4]. To overcome this issue, a series of studies on the combination treatment of 5-aminolevulinic acid (5-ALA) and ionizing radiation have been conducted by some research groups using mouse models of melanoma, glioma, and colon cancer [5][6][7][8][9][10][11][12][13][14][15]. It is known that 5-ALA administration specifically results in the accumulation of protoporphyrin IX (PpIX) in cancer cells by inhibiting the conversion PpIX to heme [16,17].…”

Mechanisms for Tuning Engineered Nanomaterials to Enhance Radiation Therapy of Cancer

“…[39] It is worth mentioning that some of the published literature uses the term radiodynamic therapy (RDT) referring to the situation where ionizing radiation (X-ray) is used to excite a sensitizing agent. [40][41][42] This term tends to be used when the sensitizing agent is a molecule. Here, we will use the term X-PDT referring to the use of X-rays to excite sensitizing agents regardless of their molecular or NP character (see Section 7 for more clarifications of terminology used in this field).…”

Pyrene Excimer-Based Fluorescent Labeling of Cysteines Brought into Close Proximity by Protein Dynamics: ASEM-Induced Thiol-Ene Click Reaction for High Spatial Resolution CLEM

“…This novel fluorescent labeling has the potential to be widely applied in various studies, e.g., in super-resolution microscopy, in basic biology, and in X-ray radiotherapy of cancer cells [ 60 , 61 ], by exploiting the X-ray induced radicals, and also to radiotherapy using electrons, electron beam lithography for fine processing technologies and nanomaterials constructions, and to achieve the precise post modification of materials. In the future, this labeling might be further developed as an important research and clinical probe for the diagnoses of diseases due to high spatial resolution fluorescence labeling.…”