Gold nanoparticles as a radio-sensitizer of colon cancer cells at high megavoltage energies: An In-Vitro study

Introduction: In the point of physical view, there are no significant differences between tumor and normal tissues during radiation therapy. Radio-sensitizers have a key role to address the issue. Exploiting high atomic number, gold nanoparticles (GNPs) have been introduced as novel radio-sensitizers and have shown promising result in the field. Owing to high mass attenuation coefficient of gold at kV energies compared to soft tissue, many studies have been done at the energy range. But for deep located tumors like colon, it is necessary to utilize high energy photons to spare surrounding normal tissues. Therefore, the aim of this work was to investigate the effect of GNPs on radio-sensitivity of a colon cancer cell line (HT- 29) at 18 MV energy. Materials and Methods: The GNPs were synthesized by seeding-growth method. To determine the morphology and size distribution of the synthesized GNPs, transmission electron microscopy (TEM) was used. The cytotoxicity of GNPs on HT-29 cells was assessed by MTT method in various concentration of GNPs. Moreover, the uptake extent of the nanoparticles into the cells was measured by graphite furnace atomic absorption spectroscopy (GF-AAS). After treatment of the cell with GNPs, they were irradiated by 18 MV photons and colony formation assay was done to calculate sensitization enhancement ratio (SER). Results: The mean size of synthesized GNPs was 24.75 nm and standard deviation 3.6 nm. TEM images showed spherical like shape for the GNPs. The cytotoxicity of GNPs on Ht-29 cells showed a time-dependent manner so that it was lower for incubation time 48 h than 24 h. Additionally, by increase in GNPs concentration the viability rate of the cells was reduced. The uptake results also exhibited a time dependent pattern and it reached to the maximum after 12 h of incubation time. The colony survival test revealed that the differences between only irradiated and GNPs + irradiated groups was significant for 4, 6 and 8 Gy doses (P<0.05). For HT-29 cells at 18 MV energy, the SER was calculated as 1.25. Conclusion: It seems the GNPs have great potential to use as radio-sensitizer for colon cancer cells at high megavoltage energies. However, it is recommended to study the effect on animal models.