Do cell culturing influence the radiosensitizing effect of gold nanoparticles: a Monte Carlo study

Abstract

Background: Cell culture can be categorized into two major types: adherent and suspension. Both are used in a range of diverse research applications, exhibiting Pros and Cons, depending on what is being studied. In the field of Internal Emitters (IE), different morphological features such as nuclei size, cytoplasm ratio, and shape could influence its non-uniformity deposition and thus impact on the biological outcome. In this work we tested the hypothesis that cellular morphology differences, offered by adherent and suspension cultures, influence the radiosensitizing effect of gold nanoparticles (AuNPs).

Methods: Using two PC3 cellular models, taken using confocal microscopy, we conducted Monte Carlo simulations to investigate the effects of different irradiation conditions on cellular Survival Fractions (SF). Our simulations focused on cells exposed to two distinct irradiation sources: ⁶⁰Co and 14 MeV protons, along both the longer and shorter axes of the cells to assess directional influences on cell survival. Additionally, we compared the SF of cells adherent to the culture flask with those in suspension, reflecting different experimental and potentially clinical scenarios.

Results: In the absence of AuNPs, neither cell type nor irradiation direction significantly affected SF for the radiation types tested. However, with AuNPs present, SF demonstrated a strong dependence on irradiation direction and cell morphology.

Conclusions: Our results indicate that the direction of irradiation plays a crucial role in determining the effectiveness of AuNPs in reducing SF. Furthermore, the results suggest that using cells in suspension will reduce the dependence of cell survival on the beam direction during irradiation, regardless of the radiation quality used.

Keywords: Cell culturing; Cell survival fraction; Direction of irradiation; Gold nanoparticles; Monte Carlo simulation; Radiosensitizers; Realistic cell model.

Fig. 1

Left: The inside of Precisa-22. Right: Irradiation setup implemented on TOPAS: Two sources: grey bars represent the stainless-steel cylinders, yellow cylinders represent the ⁶⁰Co sources, and green represents the 96-well plate

Fig. 2

Realistic cell geometry modeling. Top images show (a) the 2D confocal microscopy image and (b) the reconstructed cell phantom defined in TOPAS for the adherent cell culture (voxel dimensions of 0.21 × 0.21 × 0.47 ). Bottom images show (c) the 2D confocal microscopy image and (d) the reconstructed cell phantom defined in TOPAS for the suspension cell culture (voxel dimensions of 0.21 × 0.21 × 0.60 ). In both reconstructed cell phantoms in yellow are illustrated the nucleus and in red the cytoplasm. The images are not at scale

Fig. 3

Comparison of the experimental survival fraction (black) with the one obtained by MC simulation, in the absence of AuNPs, for the (A) suspension and (B) adherent cell culture for all the simulated irradiations, 2 sources (blue), along the z-axis (orange) and x-axis (green). The region of statistical uncertainty of the LQM fit is illustrated (shaded area) as well

Fig. 4

- Comparison of the SF obtained by MC simulation for a 2 Gy ⁶⁰Co radiation, in the presence of AuNPs, for the suspension (green) and adherent (orange) cell cultures. (A) Represents the results with 2 sources, (B) along the z-axis and (C) along the x-axis of irradiation. The solid bars represent the SF obtained using the LEM and the patterned bars illustrate the SF obtained by the mean dose approach

Fig. 5

–Energy spectra of the secondary electrons produced from the interaction of (A)⁶⁰Co γ-rays and (B) 14 MeV protons with the AuNPs

Fig. 6

- Comparison of the survival fraction enhancement factor for a 2 Gy ⁶⁰Co source irradiation, for the 2 sources (blue), along the z-axis (green) and x-axis (orange) irradiation, for the (A) suspension and (B) adherent cell culture

Fig. 7

Comparison of the results obtained by MC simulation, in the absence of AuNPs, for the (A) suspension and (B) adherent cell culture for proton irradiation along the z-axis (orange) and x-axis (green)

Fig. 8

- Comparison of the survival fraction obtained by MC simulation for a 0.5 Gy proton along the (A) z-axis and (B) x-axis irradiation, in the presence of AuNPs (4326 NPs), for the suspension (green) and adherent (orange) cell culture. The solid bars represent the SF obtained using the LEM and the patterned bars illustrate the SF obtained by the mean dose approach

Fig. 9

- Comparison of the survival fraction enhancement factor for a 0.5 Gy proton source irradiation along the z-axis (green) and x-axis (orange), for the (A) suspension and (B) adherent cell models