Gold silver alloy nanoparticles (GSAN): an imaging probe for breast cancer screening with dual-energy mammography or computed tomography

Abstract

Earlier detection of breast cancer reduces mortality from this disease. As a result, the development of better screening techniques is a topic of intense interest. Contrast-enhanced dual-energy mammography (DEM) is a novel technique that has improved sensitivity for cancer detection. However, the development of contrast agents for this technique is in its infancy. We herein report gold-silver alloy nanoparticles (GSAN) that have potent DEM contrast properties and improved biocompatibility. GSAN formulations containing a range of gold : silver ratios and capped with m-PEG were synthesized and characterized using various analytical methods. DEM and computed tomography (CT) phantom imaging showed that GSAN produced robust contrast that was comparable to silver alone. Cell viability, reactive oxygen species generation and DNA damage results revealed that the formulations with 30% or higher gold content are cytocompatible to Hep G2 and J774A.1 cells. In vivo imaging was performed in mice with and without breast tumors. The results showed that GSAN produce strong DEM and CT contrast and accumulated in tumors. Furthermore, both in vivo imaging and ex vivo analysis indicated the excretion of GSAN via both urine and feces. In summary, GSAN produce strong DEM and CT contrast, and has potential for both blood pool imaging and for breast cancer screening.

Figure 1

A) Schematic depiction of GSAN synthesis. B) A photo of GSAN formulations. C) UV-visible spectra of GSAN formulations. D) TEM images of GSAN formulations (scale is the same in all panels).

Figure 2

Energy dispersive x-ray spectra of GSAN formulations. The graphs are normalized to the height of the silver peak.

Figure 3

Schematics showing (A) leaching of silver ions from the silver nanoparticles and (B) GSAN not leaching silver ions. Silver ion release from different formulations (C) in DI water and (D) in simulated lysosomal fluid. Cell viability of (E) J774A.1 and (F) Hep G2 cells, when incubated with GSAN.

Figure 4

Reactive oxygen species generation in (A) J774A.1 and (B) Hep G2 cells, when incubated with GSAN. Evaluation of DNA damage effects of GSAN with J774A.1 (C) and Hep G2 (D) cells.

Figure 5

Phantom imaging with DEM and CT. A) HE, LE and DE images of a step phantom containing GSAN scanned with a DEM system. B) DE subtraction images of step phantom containing GSAN formulations and controls. The silver concentration was kept constant i.e. 16 mg Ag/ml for all GSAN formulation. C) Quantification of DEM phantom data. (n.s. = non-significant). D) CT phantom images of silver nitrate, iopamidol, and GSAN (Ag-80) scanned at 120 kV (in the case of GSAN, the concentration is given as the mass of silver and gold); E) CT attenuation rates of different agents.

Figure 6

In vivo DEM imaging with GSAN and iodine. A) DEM images of a mouse (without a tumor) injected with GSAN. DEM images aquired at 5 minutes post-injection. Red and yellow arrows indicates DEM contrast in the heart and blood vessels respectively. B) DEM images of representative tumor-bearing mice pre-injection and at 30 minutes post-injection with GSAN or iopamidol. The yellow circles indicate tumors. C) SNR in the tumors at different time points. Error bars are standard deviations. * indicates statistically significant between pre- and post-injection scan (p < 0.05); ** indicates statistically significant between GSAN and iopamidol (p < 0.05).

Figure 7

In vivo CT imaging with GSAN. A) 3D volume rendered CT images of a mouse (without a tumor) injected with GSAN. Green arrowheads indicate blood vessels and green circles indicate the bladder. Hearts, kidneys, intestines and bladders are labeled H, K, I and B, respectively. B) 2D CT images of a tumor-bearing mouse showing accumulation of GSAN in the tumors at different time points. Yellow circles indicate tumors. C) Quantification of CT attenuation in different organs of mice injected with GSAN at different time points. Error bars are standard error of mean.

Figure 8

Biodistribution of GSAN (Ag-60) in different organs at 2 hours post-injection.