Shalmali Dharmadhikari MS, Presenter: Nothing to Disclose

Mi-Ran Choi PhD, Abstract Co-Author: Nothing to Disclose

Navin Bansal PhD, Abstract Co-Author: Nothing to Disclose

Susan Clare MD, PhD, Abstract Co-Author: Nothing to Disclose

Naomi Halas PhD, DSc, Abstract Co-Author: Nothing to Disclose

The overall goal of this study is to develop MR-guided near-infrared photothermal therapy( PTT) of hypoxic tumors using bifunctional superparamagnetic nanoparticles. Superparamagnetic nanoparticles allow the use of MRI to detect infiltration of the particles in the tumor. In this study, we demonstrate the feasibility of imaging such nanoparticles in vivo using 1H MRI.

Bifunctional nanoparticles (Fe3O4-Au-NP) of 185-190 nm diameter, consisting of a silica core, a gold shell, a single layer coating of Fe3O4 and an outer coating of silica and having 815 nm plasmon wavelength were used for the study. The Fe3O4-Au-NP were incorporated into monocytes which served as a cellular “Trojan Horse” for selective delivery to the tumor. The Fe3O4-Au-NP-laden monocytes were injected into the tail vein of nu/nu mice implanted with MCF-7/IL1α human breast cancer cell line. Gradient echo 1H MR images were acquired on a 9.4-T, 31 cm diameter horizontal bore MR scanner with TR=50 ms and TE=6 ms before, and 4 and 24 h after the injection. Relaxivity of Fe3O4-Au-NP was measured using spherical phantoms containing known concentrations of Fe3O4-Au-NP in gel.

As the concentration Fe3O4-Au-NP in the phantoms increased, the T2* and the mean signal intensity of the MR image decreased. In the animal experiments, although the mean signal intensity decreased after 4 h, it did not change 24 h after the injection, suggesting the superparamagnetic particles infiltrate the tumor within duration of 4 h with a dwell time greater than 24 h. A plot of transverse relaxation rate as a function of the known nanoparticle concentration in phantoms showed a linear trend indicating that the relaxivity of Fe3O4-Au-NP is 1.08×10-8 mL/(nanoparticle × s).

Feasibility of 1H MRI to detect the presence of Fe3O4-Au-NP, both in phantoms and animals was demonstrated. The detection of nanoparticles in the tumor established the uptake of Fe3O4-Au-NP-laden macrophages by the tumor.

Localized photothermal therapy holds a tremendous potential for cancer treatment. Detection of bifunctional nanoparticles using MRI is a critical step towards the advancement of photothermal therapy.

Dharmadhikari, S, Choi, M, Bansal, N, Clare, S, Halas, N, MR Imaging Detection of Bifunctional Super-Paramagnetic Nanoparticles for Photothermal Therapy of Hypoxic Tumors.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9012544.html