Introduction: To increase therapeutic ratio, using radio-sensitizers is recommended and nowadays some types of them are utilized clinically. In recent years, Gold nanoparticles (GNPs) were considered as radio-sensitizers in many studies due to high atomic number. Although theoretical works showed that GNPs have an insignificant effect at MV energies, some In-vitro and In-vivo studies have proven promising result for using GNPs at the energy range. The work aims to investigate the effect of GNPs on apoptosis induction and double strand breaks (DSBs) incidence for colon cancer cell line (HT-۲۹) at ۱۸ 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-۲۹ 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). The cells irradiation was done by ۱۸ MV photons after incubation with GNPs. For apoptosis test, ۲۴ h after irradiation, the cells were prepared and read by flowcytometer. As a well-known biomarker of DSBs in cells, γ-H۲Ax foci formation were investigated by flowcytometer. Results: The mean size of synthesized GNPs was ۲۴.۷۵ nm and standard deviation ۳.۶ nm. TEM images showed spherical like shape for the GNPs. The cytotoxicity of GNPs on Ht-۲۹ cells showed a time-dependent manner so that it was lower for incubation time ۴۸ h than ۲۴ 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 ۱۲ h of incubation time.
Apoptosis test showed that the GNPs treated group has significantly more apoptotic cells than other group (P<۰.۰۵). Moreover, GNPs caused to forming more γ-H۲Ax foci in ۱۸ MV irradiated HT-۲۹ cells. Conclusion: Considering result of apoptosis and γ-H۲Ax foci formation tests, it seems the GNPs have a great potential to utilize as radio-sensitizer for colon cancer cells at ۱۸ MV energy. However, it needs to study the effect under various conditions as well on animal models.