Dual benefit of supplementary oral 5‐aminolevulinic acid to pelvic radiotherapy in a syngenic prostate cancer model

Abstract

Background Normal tissue damage caused by radiotherapy remains the largest dose‐limiting factor in radiotherapy for cancer. Therefore, the aim of this study was to investigate the supplementary oral 5‐aminolevulinic acid (ALA) to standard radiation therapy as a novel radioprotective approach that would not compromise the antitumor effect of radiation in normal rectal and bladder mucosa in a syngenic prostate cancer (PCa) model. Methods To evaluate the radiosensitizing effect of ALA in vitro, clonogenic survival assays were performed in DU145, PC3, and MyC‐CaP cell lines. To evaluate the effect of ALA in vivo a single dose (25 Gy) of radiation with or without ALA was given to healthy mice. Next, a syngenic PCa model of MyC‐CaP cells in FVB mice was created, and multiple doses (12 Gy total) of radiation were administered to the mouse pelvic area with or without ALA administration. Resected tumors, recta, and urinary bladders were immunostained with antibodies against Ki‐67, γ‐H2AX, CD204, and uroplakin‐III. Total RNA levels in recta and urinary bladders were analyzed via RT2 Profiler polymerase chain reaction (PCR) arrays related to “Stress & Toxicity PathwayFinder,” “Mitochondria,” and “Inflammasomes.” Results The addition of in vitro single or in vivo repeated administration of exogenous ALA acted as a radiosensitizer for PCa cells. Rectal toxicity was characterized by histological changes including loss of surface epithelium, fibrosis, severe DNA damage, and the aggregation of M2 macrophages. Urinary bladder toxicity was characterized by bladder wall thickening and urothelium denuding. The higher dose (300 mg/kg/day) of ALA exerted a better radioprotective profile than the lower dose (30 mg/kg/day) in normal recta and urinary bladders. Out of the 252 genes tested, 35 (13.4%) were detected as relevant genes which may be involved in the radioprotective role of ALA administration. These included interleukin‐1a (IL‐1a), IL‐1b, IL‐12, chemokine (C‐X‐C motif) ligand 1 (CXCL1), CXCL3, and NLRP3. Conclusions Our study provides novel and comprehensive insights into the dual benefits including radiosensitizing PCa tumor tissues and radioprotection of normal pelvic organs from radiation therapy. Knowledge of the underlying mechanism will facilitate the search for optimal treatment parameters for supplemental oral ALA during radiotherapy for PCa.

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

“…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].…”

A New Treatment Opportunity for DIPG and Diffuse Midline Gliomas: 5-ALA Augmented Irradiation, the 5aai Regimen

“…Malignant cell radiosensitization by selective 5-ALA uptake was also seen in preclinical models of cancers other than glioma, for example, colon, melanoma, and prostate [22,24,26]. This radiosensitization is thought to occur through mitochondrial damage mediated by PpIX, a metabolic product of 5-ALA that captures light or keV or MeV photons and transfers the energy to O 2 to then generate singlet oxygen.…”

“…Interestingly, 5-ALA with subsequent intracellular PpIX accumulation also increases keV or MeV irradiation cytotoxicity in a variety of contexts [22][23][24][25][26][27][28][29][30][31][32][33]. A robust, detailed physics-based explanation for this is currently lacking, but ample preclinical data attest to the basic mechanism of PpIX interacting with keV photons to generate cytotoxicity greater than the same irradiation given without 5-ALA where 5-ALA serves as a radiosensitizer.…”

“…A robust, detailed physics-based explanation for this is currently lacking, but ample preclinical data attest to the basic mechanism of PpIX interacting with keV photons to generate cytotoxicity greater than the same irradiation given without 5-ALA where 5-ALA serves as a radiosensitizer. These twelve recent studies drive the imperative to study 5-ALA during the irradiation of DIPG [22][23][24][25][26][27][28][29][30][31][32][33].…”