Frank Nijsen

Targeting of liver tumour in rats by selective delivery of holmium-166 loaded microspheres: a biodistribution study

Abstract. Intra-arterial administration of beta-emitting particles that become trapped in the vascular bed of a tumour and remain there while delivering high doses, represents a unique approach in the treatment of both primary and metastatic liver tumours. Studies on selective internal radiation therapy of colorectal liver metastases using yttrium-90 glass microspheres have shown encouraging results. This study describes the biodistribution of 40-µm poly lactic acid microspheres loaded with radioactive holmium-166, after intra-arterial administration into the hepatic artery of rats with implanted liver tumours. Radioactivity measurements showed >95% retention of injected activity in the liver and its resident tumour. The average activity detected in other tissues was ≤0.1%ID/g, with incidental exceptions in the lungs and stomach. Very little 166Ho activity was detected in kidneys (<0.1%ID/g), thereby indicating the stability of the microspheres in vivo. Tumour targeting was very effective, with a mean tumour to liver ratio of 6.1±2.9 for rats with tumour (n=15) versus 0.7±0.5 for control rats (n=6; P<0.001). These ratios were not significantly affected by the use of adrenaline. Histological analysis showed that five times as many large (>10) and medium-sized (4–9) clusters of microspheres were present within tumour and peritumoural tissue, compared with normal liver. Single microspheres were equally dispersed throughout the tumour, as well as normal liver parenchyma.

Alginate Microspheres Containing Temperature Sensitive Liposomes (TSL) for MR-Guided Embolization and Triggered Release of Doxorubicin

Objective The objective of this study was to develop and characterize alginate microspheres suitable for embolization with on-demand triggered doxorubicin (DOX) release and whereby the microspheres as well as the drug releasing process can be visualized in vivo using MRI. Methods and Findings For this purpose, barium crosslinked alginate microspheres were loaded with temperature sensitive liposomes (TSL/TSL-Ba-ms), which release their payload upon mild hyperthermia. These TSL contained DOX and [Gd(HPDO3A)(H2O)], a T1 MRI contrast agent, for real time visualization of the release. Empty alginate microspheres crosslinked with holmium ions (T2* MRI contrast agent, Ho-ms) were mixed with TSL-Ba-ms to allow microsphere visualization. TSL-Ba-ms and Ho-ms were prepared with a homemade spray device and sized by sieving. Encapsulation of TSL in barium crosslinked microspheres changed the triggered release properties only slightly: 95% of the loaded DOX was released from free TSL vs. 86% release for TSL-Ba-ms within 30 seconds in 50% FBS at 42°C. TSL-Ba-ms (76 ± 41 μm) and Ho-ms (64 ± 29 μm) had a comparable size, which most likely will result in a similar in vivo tissue distribution after an i.v. co-injection and therefore Ho-ms can be used as tracer for the TSL-Ba-ms. MR imaging of a TSL-Ba-ms and Ho-ms mixture (ratio 95:5) before and after hyperthermia allowed in vitro and in vivo visualization of microsphere deposition (T2*-weighted images) as well as temperature-triggered release (T1-weighted images). The [Gd(HPDO3A)(H2O)] release and clusters of microspheres containing holmium ions were visualized in a VX2 tumor model in a rabbit using MRI. Conclusions In conclusion, these TSL-Ba-ms and Ho-ms are promising systems for real-time, MR-guided embolization and triggered release of drugs in vivo.

Microspheres for radioembolization of liver malignancies.

Microsphere radioembolization (RE) is applied increasingly in the management of patients with unresectable liver tumors. This type of internal radiation therapy deploys microspheres, loaded with the high-energy b-emitting radioisotope yttrium-90 (Y, E max = 2.280 MeV [I = 100.0%]), which are injected into the hepatic artery. The normal liver parenchyma is relatively sensitive to ionizing radiation [1]. However, intra-arterial instillation via a catheter results in a preferential accumulation in the tumorous tissue because liver tumors are exclusively supplied by the hepatic artery, by contrast to normal liver tissue that receives its blood supply predominantly from the portal vein [2]. If the radioactive microspheres are of the appropriate size, they will lodge in the tumors’ microvasculature and will subsequently deliver a high-radiation dose to the tumors. Two types of Y-microspheres are currently in clinical use: TheraSphere microspheres (MDS Nordion Inc., Kanata, Ontario, Canada), which have a glass matrix with a diameter of 25 ± 10 μm (mean ± SD), and the SIR-Spheres (SIRTeX Medical Ltd., Sydney, New South Wales, Australia), which are resinbased microspheres and have a diameter of 32 ± 10 μm (mean ± SD). The glass microspheres (Y 2 O 3 –Al 2 O 3 –SiO 2 ) are produced by forming a mixture of yttrium oxide, aluminum oxide and silicon oxide, which is melted at a temperature close to 1500°C. After cooling down, the glass is crushed into particles of a specific size. These particles are then melted again through a flame sprayer. The glass microspheres are obtained by surface tension. Subsequently, the Y glass microspheres are made radioactive by thermal neutron activation in a nuclear reactor [3]. The resin microspheres are produced by tagging Y to preformed Aminex resin (sulfonated divinyl benzene-styrene copolymer) microspheres (Bio-Rad Laboratories, Richmond, CA, USA) through ion exchange reaction. The Y is then precipitated inside the resin by washing with phosphate solutions, yielding insoluble Y-phosphate [4]. Meanwhile, worldwide, over 15,000 Y-RE treatments have been performed using either the resin or the glass microspheres. In the USA, the glass microspheres are approved by the US FDA as a humanitarian device for radiation treatment of unresectable hepatocellular carcinoma (HCC) or as a bridge to surgery or liver transplantation. SIR-Spheres are FDA-approved for the treatment of colorectal cancer metastatic to the liver. In Europe, both microsphere products have a CE marking for the treatment of patients with either primary or metastatic liver cancer. Maarten AD Vente

A novel approach to identify non-palpable breast lesions combining fluorescent liposomes and magnetic resonance-guided high intensity focused ultrasound-triggered release.

The combination of fluorescein-containing liposomes (FCL) and magnetic resonance-guided high intensity focused ultrasound (MR-HIFU)-triggered release is a promising approach for lesion demarcation and more efficient removal of non-palpable breast lesions. Exposure of FCL to ablation temperatures (60 °C) using MR-HIFU would result in palpable, stained tumors, which are more easy to identify during surgical resection. In this study, proof-of-concept concerning fluorescent FCL for MR-HIFU-triggered release and tumor demarcation of non-palpable breast lesions is presented. Ex vivo experiments in human blood and porcine muscle tissue showed increased label release from the liposomes, clear fluorescence enhancement and diffusion of the released compound after heating to 60 °C. Next, fluorescein release of FCL was observed after MR-HIFU-mediated mild hyperthermia (42 °C) and ablation temperature (60 °C) for a short period (30s), which is in line with the clinically relevant MR-HIFU treatment parameters. These results indicate the potential of the FCL as a tool to improve tumor demarcation in patients by MR-HIFU-triggered release. Therefore, this method may offer a new tool for efficient surgical resection of non-palpable breast tumor lesions by enabling proper discrimination between tumor tissue and adjacent healthy tissue.