Preliminary Assessment Of Nanoparticle-Lipiodol Formulation For Image Guided Thermal Therapy In Animal Models Of Liver Cancer

Magnetic nanoparticle (NP) hyperthermia after intratumoral NP injection and heating with alternating magnetic fields (AMF) offers potential therapeutic options for intractable cancer. To obtain consistent NP distribution within the tumor we explore the development of a NP-ethiodized oil emulsion (NLE). We present in vitro characterization and preliminary in vivo data of the NLE properties. NLE comprises lipiodol (50% w/v), polysorbate 20 (0.2% w/v) and biocompatible Fe3O4 nanoparticles (BNF, 49.8% w/v). Photon correlation spectroscopy (PCS) and transmission electron microscopy (TEM) were performed to characterize particle size of NP alone and in NLE. MR imaging of the NLE was performed with a 3T clinical scanner, using a 12-well plate with graded concentrations of NLE, NP, and lipiodol, suspended in agarose gel. T1-weighted (W), T2-W and T2*-W imaging sequences were acquired for MR relaxation time measurements. MRI data were compared with NP iron concentration to correlate MRI signal intensity with iron content in samples. TEM imaging was performed in HepG2 cell cultures at 18 hours after NLE infusion. In vivo experiments included intratumoral injections of a) NLE (n = 20), b) BNF (n = 12), c) PBS (n = 14) in Foxnu1 mice bearing flank xenograft HepG2 tumors with and without AMF hyperthermia exposure (15-min, 300-700 Gauss, 150 kHz, 18 hours post-injection). Core and intratumoral temperature measurements were acquired at 1-s intervals. Animals were either euthanized at 1-7 days or observed for tumor growth delay. Pathologic analysis included semiquantitative evaluation of tumor necrosis and iron distribution. In vitro MR reverse relaxation time measurements showed a linear increase along the iron gradient for NLE and NP (r = 0.94 and 0.98, respectively). Measured specific heating rate of NLE was higher than NP, 0.08°C/(s × mg Fe), compared with 0.06°C/(s × mg Fe). Mean particle diameter measured with PCS was 120 nm for NP alone and 276 nm for the NLE. Average maximum temperature increase measured at the tumor surface for NLE group (n = 8) was 7.4 ± 0.5°C while the NP alone group (n = 5) was 5.4 ± 0.3°C. At 24 days, there was a 4-fold difference in tumor growth delay between PBS and NLE-AMF heated tumors. Increased tumor necrosis was observed at 7 days in the NLE group. Semi-quantitative intratumoral iron distribution of NLE samples showed a characteristic distribution of NLE along the vascular tumor pathways at the tumor rim. Histological analysis confirmed intratumoral iron deposition and cellular damage consistent with cytotoxic thermal exposure. Intratumor iron distribution for NLE suggests that lipiodol influences NP distribution. Initial results are encouraging and motivate further in vivo evaluation.