Active targeting theranostic iron oxide nanoparticles for MRI and magnetic resonance-guided focused ultrasound ablation of lung cancer

Abstract

Despite its great promise in non-invasive treatment of cancers, magnetic resonance-guided focused ultrasound surgery (MRgFUS) is currently limited by the insensitivity of magnetic resonance imaging (MRI) for visualization of small tumors, low efficiency of in vivo ultrasonic energy deposition, and damage to surrounding tissues. We hereby report the development of an active targeting nano-sized theranostic superparamagnetic iron oxide (SPIO) platform for significantly increasing the imaging sensitivity and energy deposition efficiency using a clinical MRgFUS system. The surfaces of these PEGylated SPIO nanoparticles (NPs) were decorated with anti-EGFR (epidermal growth factor receptor) monoclonal antibodies (mAb) for targeted delivery to lung cancer with EGFR overexpression. The potential of these targeted nano-theranostic agents for MRI and MRgFUS ablation was evaluated in vitro and in vivo in a rat xenograft model of human lung cancer (H460). Compared with nontargeting PEGylated SPIO NPs, the anti-EGFR mAb targeted PEGylated SPIO NPs demonstrated better targeting capability to H460 tumor cells and greatly improved the MRI contrast at the tumor site. Meanwhile, this study showed that the targeting NPs, as synergistic agents, could significantly enhance the efficiency for in vivo ultrasonic energy deposition in MRgFUS. Moreover, we demonstrated that a series of MR methods including T2-weighted image (T2WI), T1-weighted image (T1WI), diffusion-weighted imaging (DWI) and contrast-enhanced T1WI imaging, could be utilized to noninvasively and conveniently monitor the therapeutic efficacy in rat models by MRgFUS.

Introduction

Magnetic resonance-guided focused ultrasound surgery (MRgFUS), as a promising non-invasive ultrasound thermal treatment for soft tissue lesions, has been utilized in the treatment of prostate, kidney, and liver cancer [1], [2], [3]. In particular, there is precise control of beam direction and ongoing feedback is provided to detail temperature changes at and around the treated tissue in MRgFUS. The main advantages of MRgFUS are that it is non-invasive, able to provide real-time, three-dimensional imaging, and closed-loop MR feedback. Magnetic resonance imaging (MRI) is a clinically useful diagnostic and tumor detection technique and can provide real-time temperature monitoring in MRgFUS. MRgFUS ablation usually involves the use of gradient-echo MR imaging for real-time temperature monitoring, based on spin-lattice (T₁) relaxation time and temperature sensitivity of the proton resonance frequency [4]. The tumor ablation efficiency of MRgFUS highly depends on its capacity to deposit energy in tissue. However, when shifting from an in vitro environment to in vivo tissue, there is considerable attenuation of ultrasonic energy emitted by the MR-guided ultrasound transducer [5]. High ultrasound power must be employed to improve the therapeutic efficiency and guidance of conventional MRgFUS in order to achieve reduction effects on a deeper lesion. This high ultrasound power could cause severe side effects, such as skin burns, edema, perforation of intestines, and injury of peripheral nerve surrounding the tumor [6]. Furthermore, the set current is not sensitive enough to visualize small lesions using conventional MRgFUS settings [6], [7], [8], [9].

Due to their excellent biocompatibility and magnetic properties, superparamagnetic iron oxide (SPIO) NPs have been used extensively for drug delivery, MRI probes, and tumor thermotherapy [7], [8], [9], [10], [11], [12], [13], [14]. Previous studies have shown that dipole relaxation induced by an alternating magnetic field can contribute to magnetic hyperthermia of SPIO NPs. During irradiations of near-infrared (NIR) laser light and high intensity focused ultrasound (HIFU) treatment, SPIO NPs were used to induce the thermal therapy effect in tumor tissue [6], [15], [16], [17], [18], [19]. Recently, superparamagnetic iron oxide-polymer composite microcapsules (mean diameter, 587 nm & 885.6 nm) have been proposed for MRgFUS [5], [17]. These microcapsules were demonstrated with the ability to enhance ultrasonic wave absorption and energy deposition in the targeted tissue, thereby enhancing the tumor-ablative effects of MRgFUS [17].

In the present study, we propose to develop an active targeting, nanosized theranostic SPIO nanoplatform to improve the MRI sensitivity and tumor-ablative efficacy of a clinical MRgFUS system. These SPIO nanoparticles were coated with a layer of polyethylene glycol (PEG) to improve their biocompatibility [14], [20]. Epidermal growth factor receptor (EGFR) is a tyrosine kinase cellular transmembrane receptor and is linked to aberrant survival and poor prognosis. It is overexpressed in various epithelial tumors, such as non-small cell lung, kidney, breast, and head-and-neck squamous cell carcinoma [21], [22]. In this study, the surface of these PEGylated SPIO nanoparticles was further decorated with high affinity anti-EGFR monoclonal antibody (Cetuximab) to form a nanocomposite (anti-EGFR-PEG-SPIO) for targeted delivery to EGFR overexpressing H460 lung cancer. The anti-EGFR-PEG-SPIO was physicochemically characterized. Their targeting capability, MRI contrast enhancement and cytotoxicity were studied in H460 lung cancer cells as well as in nude rat models bearing H460 lung cancer xenografts. The capability of anti-EGFR-PEG-SPIO for synergistic MRgFUS treatment of cancer and the applications of a series of MRI approaches for non-invasive monitoring treatment response were demonstrated using nude rat lung tumor models (Scheme shown in Fig. 1a). To the best of our knowledge, this study represents the first evaluation of an active targeting and nano-sized SPIO platform for the enhancement of imaging sensitivity and tumor-ablative efficacy in MRgFUS.