Purpose: The most important challenges in photodynamic therapy (PDT) are related to the limited penetration of light and the low uptake of photosensitizers. In radiotherapy, they are correlated to radiation damage of normal tissues. Therefore, a targeted radio and photosensitizer can reduce the limitations of the mentioned methods. In this study, photosensitizing and radio-sensitizing effects of 5-aminolevulinic acid (5ALA)-conjugated GNPs were investigated.
Materials and methods: First, cell toxicities of 5ALA, GNPs and a conjugate were assessed on Mel-Rm cell line. Then, the radio sensitizing effect of every agent was studied. Different experiments were designed in four separate groups, each group containing six subgroups receiving different radiation doses by using a superficial X-ray tube. Furthermore, the photosensitizing efficacy of the agents was evaluated after cells were irradiated by a He-Ne laser at four light doses in separate groups.
Results: With regards to radio sensitivity assessments, there was no significant difference between different irradiation doses. The investigation on photosensitivity of 5ALA and a conjugate showed significant differences between the control (without illumination) and groups that received PDT in the presence of 5ALA and conjugate, wherein ED50 were estimated at 136.2 J/cm2 and 56.2 J/cm2, respectively. With regards to PDT experiments, the conjugate induces cell death more than twice in comparison with 5ALA.
Conclusion: The conjugate does not cause any enhancement of radiation efficiency on MeL-Rm cell line. With regards to PDT, we found that the conjugate induced cell death at twice the rate when compared with 5ALA alone. Therefore, the conjugate can be an appropriate delivery agent for 5ALA and may also enhance the destruction of tumor cells. Finally, comparing the two types of treatment shows that PDT is a more efficient treatment for this cell line.
Keywords: 5-Aminolevulinic acid; Mel-Rm cell line; gold nanoparticle; photodynamic therapy; protoporphyrin IX; radiosensitizer.