Gold nanoparticles (AuNP) can increase the efficacy of radiation therapy by sensitising tumor cells to radiation damage. When used in combination with radiation, AuNPs enhance the rate of cell killing; hence, they may be of great value in radiotherapy. This study assessed the effects of radiation and AuNPs on mitochondrial reactive oxygen species (ROS) generation in cancer cells as an adjunct therapeutic target in addition to the DNA of the cell. Mitochondria are considered one of the primary sources of cellular ROS. High levels of ROS can result in an intracellular state of oxidative stress, leading to permanent cell damage. In this study, human melanoma and prostate cancer cell lines, with and without AuNPs, were irradiated with 6-Megavolt X-rays at doses of 0–8 Gy. Indicators of mitochondrial stress were quantified using two techniques, and were found to be significantly increased by the inclusion of AuNPs in both cell lines. Radiobiological damage to mitochondria was quantified via increased ROS activity. The ROS production by mitochondria in cells was enhanced by the inclusion of AuNPs, peaking at ~4 Gy and then decreasing at higher doses. This increased mitochondrial stress may lead to more effectively kill of AuNP-treated cells, further enhancing the applicability of functionally-guided nanoparticles.

Background: Gold nanoparticles (AuNPs) can modify cellular responses to ionizing radiation. We examined whether 1.9 nm AuNPs alter early apoptosis across a 0–8 Gy dose range in DU145 prostate and MM418-C1 melanoma cells. Methods: Cells were incubated with or without 0.5 mM AuNPs for 24 h, irradiated with 6 MV X-rays (0, 2, 4, 6, or 8 Gy), and analysed by Annexin V-FITC/PI flow cytometry 48 h later in three independent experiments. Only adherent cells were collected for analysis; cells detached into the culture supernatant were not included. A two-factor repeated-measures ANOVA tested radiation dose, AuNP exposure, and their interaction. Because sphericity could not be assessed reliably with n = 3, a conservative Geisser–Greenhouse lower-bound correction was also applied to effects involving dose. Results: The uncorrected analysis showed dose × AuNP interactions in DU145 [F(4,8) = 5.26, p = 0.0224, partial η² = 0.725] and MM418-C1 [F(4,8) = 50.13, p = 1.05 × 10⁻⁵, partial η² = 0.962]. After the conservative correction, the interaction remained significant in MM418-C1 (p = 0.0194) but not in DU145 (p = 0.149). In MM418-C1, AuNP exposure was associated with a higher early-apoptotic fraction at 2 Gy (+5.10 percentage points; Holm-adjusted p = 0.0019) but a lower fraction at 8 Gy (−17.03 percentage points; Holm-adjusted p = 0.0048). No DU145 dose-specific comparison remained significant after Holm correction. Conclusions: The AuNP-associated early-apoptotic response varied with radiation dose and cell line, most clearly in MM418-C1, while the DU145 interaction was less robust under the conservative correction. Given the small number of independent experiments and the 48 h endpoint, these findings should be interpreted as exploratory and not as a direct measure of total cytotoxicity or a specific cell-death mechanism.