Systemic Delivery Of KDR-Targeted Magnetic Nanoparticles In Rhesus Macaques: A Novel Approach For Non-Invasive Imaging Of Endometriosis

Ov D. Slayden¹, Addie Luo¹, Prem Singh², Olena Taratula², Oleh Taratula²

1. Division of Reproductive & Developmental Sciences, Oregon National Primate Research Center, Beaverton,USA

2. Department of Pharmaceutical Sciences, Oregon State University, Portland, USA

Abstract Text:

Endometriosis is the infiltration of endometrium-like tissue at sites outside the uterus.  The heterotopic endometrium creates a painful disorder that impacts >190 million women worldwide. Recent reports support the use of magnetic resonance imaging (MRI) in the diagnosis of endometriotic cysts and deep infiltrating endometriosis, and potentially for the early detection of superficial endometriotic lesions.  Magnetic hyperthermia is an emerging cancer therapy based on the concept that magnetic particles delivered to tumors can generate cytotoxic intra-tumoral temperatures when exposed to a strong alternating magnetic field (AMF).  Previously, we created nanoparticle reagents that, when administered intravenously, enter the endometriotic lesions both passively, and actively by binding to vascular endothelial growth factor receptor 2 (KDR), which is highly expressed in endometriotic tissues. The KDR-targeted particles can carry various payloads for imaging and treatment of the lesions, and we further showed that KDR-targeted, cobalt-doped, hexagonal iron oxide magnetic nanoparticles with a high heating efficiency could be injected systemically into SCID mice bearing human (or) macaque endometriotic grafts.  MRI imaging of the treated mice revealed strong negative MRI contrast in the endometriotic xenografts. Exposure of the mice bearing the grafts to a strong external AMF 24 hours after treatment resulted in elevated intra-graft temperature and thermal ablation of the grafted tissues.  A concern was raised, however, that the grafting surgery might have confounding effects on passive particle uptake or that the grafted tissues could accumulate KDR-targeted particles as part of the healing process. To address the concern, in this study, we evaluated KDR-targeted magnetic nanoparticle uptake in macaques with advanced spontaneous endometriosis.  Six rhesus monkeys with advanced endometriosis were identified based on symptoms including heavy/prolonged menstruation, chronic pain during menses, loss of weight, and appetite.  Endometriotic masses were identified in each animal by pelvic ultrasound and/or abdominal palpation. We treated the monkeys with single intravenous injection of KDR-targeted cobalt-doped iron oxide magnetic particles (3 mg Fe/kg). The animals underwent T1 and T2 weighted MRI 24 hours before nanoparticle treatment to map potential endometriotic sites, and then again 24 hours after nanoparticle injection.  After MRI, the endometriotic and control samples were collected for histological analysis and ex vivo exposure to an AMF.  The optical density of the MRI images was evaluated and compared to skeletal muscle with Image J. The KDR-targeted magnetic particles preferentially accumulated in the monkey endometriotic lesions and provided high-resolution negative contrast images during T2-weighed MRI. Image J analysis revealed a significant increase in image density by approximately 3-fold (P < 0.05).   Minor (not significant) accumulation was observed in the eutopic endometrium and myometrium. Prussian Blue staining of the lesions revealed a strong accumulation of iron.  Iron staining was only lightly detectable in liver and undetectable in other organs (colon, bladder, kidney).  Ex vivo treatment of lesion tissues with an AMF resulted in a potentially cell-lethal temperature ( >42 C) within 8 minutes of AMF exposure, whereas temperature profiles for the control tissues did not rise above 37 C.  We conclude that KDR-directed magnetic particles accumulate in spontaneous endometriotic lesions to produce an endometriosis-specific, negative MRI signal and may provide an approach to removing endometriotic tissues. Supported by R01 HD108148 and P51 OD011092.