In situ evaluation of spatiotemporal distribution of doxorubicin from Drug-eluting Beads in a tissue mimicking phantom.

Understanding the intra-tumoral distribution of chemotherapeutic drugs is extremely important in predicting therapeutic outcome. Tissue mimicking gel phantoms are useful for studying drug distribution in vitro but quantifying distribution is laborious due to the need to section phantoms over the relevant time course and individually quantify drug elution. In this study we compare a bespoke version of the traditional phantom sectioning approach, with a novel confocal microscopy technique that enables dynamic in situ measurements of drug concentration. Release of doxorubicin from Drug-eluting Embolization Beads (DEBs) was measured in phantoms composed of alginate and agarose over comparable time intervals. Drug release from several different types of bead were measured. The non-radiopaque DC Bead™ generated a higher concentration at the boundary between the beads and the phantom and larger drug penetration distance within the release period, compared with the radiopaque DC Bead LUMI™. This is likely due to the difference of compositional and structural characteristics of the hydrogel beads interacting differently with the loaded drug. Comparison of in vitro results against historical in vivo data show good agreement in terms of drug penetration, when confounding factors such as geometry, elimination and bead chemistry were accounted for. Hence these methods have demonstrated potential for both bead and gel phantom validation, and provide opportunities for optimisation of bead design and embolization protocols through in vitro-in vivo comparison.

Safety and Tolerability of Topotecan-Eluting Radiopaque Microspheres for Hepatic Chemoembolization in a Rabbit Preclinical Model.

PURPOSE: Topotecan is a camptothecin analogue with potential advantages over irinotecan for transarterial chemoembolization (TACE) of hepatic colorectal metastases including greater anti-neoplastic activity without enzymatic activation. The purpose of this study was to assess safety and tolerability of topotecan-loaded radiopaque microspheres (ROMTOP) administered by TACE in a rabbit model and to compare the in vitro elution of topotecan from microspheres to irinotecan. MATERIALS AND METHODS: Topotecan was loaded into radiopaque microspheres (70-150 µm, DC Bead LUMI™, Biocompatibles UK Ltd-Boston Scientific Corporation) to the maximum capacity of 80 mg/mL of microspheres. Six healthy New Zealand White rabbits underwent hepatic TACE with ROMTOP under fluoroscopic guidance until angiographic stasis. Assessment of toxicities included regular liver function tests and complete blood counts until euthanasia 28 days post-TACE. In vitro topotecan elution from the microspheres was assessed using an open-loop flow-through system and compared to irinotecan. RESULTS: The mean bead volume and topotecan dose delivered were 0.086 mL (0.076-0.105 mL) and 1.99 mg/kg (1.51-2.55 mg/kg), respectively. Aspartate aminotransferase and alanine aminotransferase were elevated post-embolization but resolved within 2 weeks. One rabbit died two days after TACE with pyloric duodenal perforation observed at necropsy, potentially due to non-target embolization. In vitro elution of topotecan from ROMTOP was complete in 10 h compared to 3 h for irinotecan-loaded microspheres. CONCLUSION: Selective embolization with ROMTOP was tolerated at a dose of 2 mg/kg (24 mg/m2) in rabbits. In vitro topotecan elution from microspheres was more prolonged compared to irinotecan.

Handling and performance characteristics of a new small caliber radiopaque embolic microsphere.

The in vitro and in vivo handling and performance characteristics of a small caliber radiopaque embolic microsphere, 40-90 µm DC Bead LUMI™ (LUMI40-90), were studied. Microsphere drug loading and elution and effects on size, suspension, and microcatheter delivery were evaluated using established in vitro methodologies. In vivo evaluations of vascular penetration (rabbit renal artery embolization), long-term biocompatibility and X-ray imaging properties, pharmacokinetics and local tissue effects of both doxorubicin (Dox) and irinotecan (Iri) loaded microspheres (swine hepatic artery embolization) were conducted. Compared to 70-150 µm DC Bead LUMI (LUMI70-150), LUMI40-90 averaged 70 µm versus 100 µm, which was unchanged upon drug loading. Handling, suspension, and microsphere delivery studies were successfully performed. Dox loading was faster (20 min) and Iri equivalent (<10 min) while drug elution rates were similar. Contrast suspension times were longer with no delivery complications. Vascular penetration was statistically greater (rabbit) with no unexpected adverse safety findings (swine). Microspheres ± drug were visible under X-ray imaging (CT) at 90 days. Peak plasma drug levels and area under the curve were greater for LUMI40-90 compared to LUMI70-150 but comparable to 70-150 µm DC BeadM1™ (DC70-150). Local tissue effects showed extensive hepatic necrosis for Dox, whereas Iri displayed lower toxicity with more pronounced lobar fibrosis. LUMI40-90 remains suspended for longer and have greater vessel penetration compared to the other DC Bead LUMI sizes and are similarly highly biocompatible with long-term visibility under X-ray imaging. Drug loading is equivalent or faster with pharmacokinetics similar to DC70-150 for both Dox and Iri.

Mapping Drug Dose Distribution on CT Images Following Transarterial Chemoembolization with Radiopaque Drug-Eluting Beads in a Rabbit Tumor Model.

Purpose To correlate bead location and attenuation on CT images with the quantity and distribution of drug delivered to the liver following transarterial chemoembolization (TACE) with radiopaque drug-eluting beads (DEB) in a rabbit tumor model. Materials and Methods All procedures were performed with a protocol approved by the Institutional Animal Care and Use Committee. TACE was performed in rabbits (n = 4) bearing VX2 liver tumors by using radiopaque DEB (70-150 µm) loaded with doxorubicin (DOX). Livers were resected 1 hour after embolization, immediately frozen, and cut by using liver-specific three-dimensional-printed molds for colocalization of liver specimens and CT imaging. DOX penetration into tissue surrounding beads was evaluated with fluorescence microscopy. DOX levels in liver specimens were predicted by using statistical models correlating DOX content measured in tissue with bead volume and attenuation measured on CT images. Model predictions were then compared with actual measured DOX concentrations to assess the models' predictive power. Results Eluted DOX remained in close proximity (<600 µm) to beads in the liver 1 hour after TACE. Bead volume and attenuation measured on CT images demonstrated positive linear correlations (0.950 and 0.965, respectively) with DOX content in liver specimens. DOX content model predictions based on CT images were accurate compared with actual liver DOX levels at 1 hour. Conclusion CT may be used to estimate drug dose delivery and distribution in the liver following transarterial chemoembolization (TACE) with doxorubicin-loaded radiopaque drug-eluting beads (DEB). Although speculative, this informational map might be helpful in planning and understanding the spatial effects of TACE with DEB. © RSNA, 2018.

Bench-to-clinic development of imageable drug-eluting embolization beads: finding the balance.

This review describes the historical development of an imageable spherical embolic agent and focuses on work performed in collaboration between Biocompatibles UK Ltd (a BTG International group company) and the NIH to demonstrate radiopaque bead utility and bring a commercial offering to market that meets a clinical need. Various chemistries have been investigated and multiple prototypes evaluated in search of an optimized product with the right balance of handling and imaging properties. Herein, we describe the steps taken in the development of DC Bead LUMI™, the first commercially available radiopaque drug-eluting bead, ultimately leading to the first human experience of this novel embolic agent in the treatment of liver tumors.

Comparison of microsphere penetration with LC Bead LUMI™ versus other commercial microspheres.

The purpose of this study was to evaluate LC Bead LUMI™ (40-90µm and 70-150µm) in order to determine if their increased resistance to compression influences microsphere penetration and distribution compared to more compressible commercial microspheres. LC Bead LUMI™ 40-90µm and 70-150µm, LC BeadM1® 70-150µm, Embozene™ 40µm and Embozene™ 100µm size and distributions were measured using optical microscopy. Penetration in vitro was evaluated using an established 'plate model', consisting of a calibrated tapered gap between a glass plate and plastic housing to allow visual observation of microsphere penetration depth. Behaviour in vivo was assessed using a rabbit renal embolization model with histopathologic confirmation of vessel penetration depth. Penetration behaviour in vitro was reproducible and commensurate with the measured microsphere size, the smaller the microsphere the deeper the penetration. Comparison of the microsphere diameter measured on the 2D plate model versus the corresponding average microsphere size measured by histopathology in the kidney showed no significant differences (p = > 0.05 Mann-Whitney, demonstrating good in vitro - in vivo predictive capabilities of the plate model) confirming predictable performance for LC Bead LUMI™ (40-90µm and 70-150µm) based on microsphere size, their increased rigidity having no bearing on their depth of penetration and distribution. An assessment of a LC Bead LUMI™ (40-90µm and 70-150µm) has shown that despite having greater resistance to compression, these microspheres behave in a predictable manner within in vitro and in vivo models comparable with more compressible microspheres of similar sizes.

Characterization of a novel intrinsically radiopaque Drug-eluting Bead for image-guided therapy: DC Bead LUMI™.

We have developed a straightforward and efficient method of introducing radiopacity into Polyvinyl alcohol (PVA)-2-Acrylamido-2-methylpropane sulfonic acid (AMPS) hydrogel beads (DC Bead™) that are currently used in the clinic to treat liver malignancies. Coupling of 2,3,5-triiodobenzaldehyde to the PVA backbone of pre-formed beads yields a uniformly distributed level of iodine attached throughout the bead structure (~150mg/mL) which is sufficient to be imaged under standard fluoroscopy and computed tomography (CT) imaging modalities used in treatment procedures (DC Bead LUMI™). Despite the chemical modification increasing the density of the beads to ~1.3g/cm3 and the compressive modulus by two orders of magnitude, they remain easily suspended, handled and administered through standard microcatheters. As the core chemistry of DC Bead LUMI™ is the same as DC Bead™, it interacts with drugs using ion-exchange between sulfonic acid groups on the polymer and the positively charged amine groups of the drugs. Both doxorubicin (Dox) and irinotecan (Iri) elution kinetics for all bead sizes evaluated were within the parameters already investigated within the clinic for DC Bead™. Drug loading did not affect the radiopacity and there was a direct relationship between bead attenuation and Dox concentration. The ability (Dox)-loaded DC Bead LUMI™ to be visualized in vivo was demonstrated by the administration of into hepatic arteries of a VX2 tumor-bearing rabbit under fluoroscopy, followed by subsequent CT imaging.

Long-term biocompatibility, imaging appearance and tissue effects associated with delivery of a novel radiopaque embolization bead for image-guided therapy.

The objective of this study was to undertake a comprehensive long-term biocompatibility and imaging assessment of a new intrinsically radiopaque bead (LC Bead LUMI™) for use in transarterial embolization. The sterilized device and its extracts were subjected to the raft of ISO10993 biocompatibility tests that demonstrated safety with respect to cytotoxicity, mutagenicity, blood contact, irritation, sensitization, systemic toxicity and tissue reaction. Intra-arterial administration was performed in a swine model of hepatic arterial embolization in which 0.22-1 mL of sedimented bead volume was administered to the targeted lobe(s) of the liver. The beads could be visualized during the embolization procedure with fluoroscopy, DSA and single X-ray snapshot imaging modalities. CT imaging was performed before and 1 h after embolization and then again at 7, 14, 30 and 90 days. LC Bead LUMI™ could be clearly visualized in the hepatic arteries with or without administration of IV contrast and appeared more dense than soluble contrast agent. The CT density of the beads did not deteriorate during the 90 day evaluation period. The beads embolized predictably and effectively, resulting in areas devoid of contrast enhancement on CT imaging suggesting ischaemia-induced necrosis nearby the sites of occlusion. Instances of off target embolization were easily detected on imaging and confirmed pathologically. Histopathology revealed a classic foreign body response at 14 days, which resolved over time leading to fibrosis and eventual integration of the beads into the tissue, demonstrating excellent long-term tissue compatibility.

Preparation of Radiopaque Drug-Eluting Beads for Transcatheter Chemoembolization.

PURPOSE: To develop a simple method to produce radiopaque drug-eluting microspheres (drug-eluting beads [DEBs]) that could be incorporated into the current clinical transcatheter arterial chemoembolization workflow and evaluate their performance in vitro and in vivo. MATERIALS AND METHODS: An ethiodized oil (Lipiodol; Guerbet, Villepinte, France) and ethanol solution was added to a lyophilized 100-300 µm bead before loading with doxorubicin. These radiopaque drug-eluting beads (DEBs; Biocompatibles UK Ltd, Farnham, United Kingdom) were evaluated in vitro for x-ray attenuation, composition, size, drug loading and elution, and correlation between attenuation and doxorubicin concentration. In vivo conspicuity was evaluated in a VX2 tumor model. RESULTS: Lipiodol was loaded into lyophilized beads using two glass syringes and a three-way stopcock. Maximum bead attenuation was achieved within 30 minutes. X-ray attenuation of radiopaque beads increased linearly (21-867 HU) with the amount of beads (0.4-12.5 vol%; R(2) = 0.9989). Doxorubicin loading efficiency and total amount eluted were similar to DC Bead (Biocompatibles UK Ltd); however, the elution rate was slower for radiopaque DEBs (P < .05). Doxorubicin concentration linearly correlated with x-ray attenuation of radiopaque DEBs (R(2) = 0. 99). Radiopaque DEBs were seen in tumor feeding arteries after administration by fluoroscopy, computed tomography, and micro-computed tomography, and their location was confirmed by histology. CONCLUSIONS: A simple, rapid method to produce radiopaque DEBs was developed. These radiopaque DEBs provided sufficient conspicuity to be visualized with x-ray imaging techniques.

Radiopaque drug-eluting beads for transcatheter embolotherapy: experimental study of drug penetration and coverage in swine.

PURPOSE: To determine local doxorubicin levels surrounding radiopaque drug-eluting beads (DEBs) in normal swine liver and kidney following transcatheter arterial chemoembolization. The influence of bead size (70-150 µm or 100-300 µm) was compared with regard to tissue penetration and spatial distribution of the bead, as well as eventual drug coverage (ie, amount of tissue exposed to drug). MATERIALS AND METHODS: Radiopaque DEBs were synthesized by suspension polymerization followed by incorporation of iodized oil and doxorubicin. Chemoembolization of swine liver and kidney was performed under fluoroscopic guidance. Three-dimensional tissue penetration of "imageable" DEBs was investigated ex vivo with micro-computed tomography (microCT). Drug penetration from the bead surface and drug coverage was evaluated with epifluorescence microscopy, and cellular localization of doxorubicin was evaluated with confocal microscopy. Necrosis was evaluated with hematoxylin and eosin staining. RESULTS: MicroCT demonstrated that 70-150-µm DEBs were present in more distal arteries and located in a more frequent and homogeneous spatial distribution. Tissue penetration of doxorubicin from the bead appeared similar (∼300 µm) for both DEBs, with a maximum tissue drug concentration at 1 hour coinciding with nuclear localization of doxorubicin. The greater spatial frequency of the 70-150-µm DEBs resulted in approximately twofold improved drug coverage in kidney. Cellular death is predominantly observed around the DEBs beginning at 8 hours, but increased at 24 and 168 hours. CONCLUSIONS: Smaller DEBs penetrated further into targeted tissue (ie, macroscopic) with a higher spatial density, resulting in greater and more uniform drug coverage (ie, microscopic) in swine.

Development of "imageable" beads for transcatheter embolotherapy.

PURPOSE: To develop and characterize radiopaque embolization microspheres capable of in vivo detection with intraprocedural fluoroscopy and computed tomography (CT) imaging and to evaluate their spatial distribution inside target tissues during and after transcatheter embolization. MATERIALS AND METHODS: Polyvinyl alcohol hydrogel microspheres were loaded with Lipiodol and examined for iodine content, stability of loading, and conspicuity with fluoroscopy and CT in vitro. Transcatheter embolization of swine liver and kidney was performed with the radiopaque microspheres and spatial distribution was evaluated with intraprocedural fluoroscopy and CT. Ex vivo evaluation was performed with light microscopy and micro-CT. RESULTS: In vitro analyses demonstrated that radiopaque microspheres could be loaded with sufficient iodine content to be detected with routine fluoroscopy and CT imaging and that such loading was relatively stable. Radiopaque microspheres were visible in vivo with fluoroscopy and CT during transcatheter embolization. CT imaging during embolization procedures demonstrated a dose-dependent relationship in the number and size of visualized embolized arteries. Imaging features of radiopaque microsphere distribution inside target tissues correlated well with ex vivo light microscopic and micro-CT evaluation of microsphere distribution. CONCLUSIONS: Radiopaque embolization microspheres are visualized during transcatheter embolization with routine intraprocedural fluoroscopy and CT. These radiopaque microspheres provided the three-dimensional spatial distribution of embolic material inside target organs during the procedure, and therefore can provide real-time intraprocedural feedback for the interventional radiologist. These microspheres may be useful for demonstrating the influence of material and technical variability in transcatheter embolization in addition to providing intraprocedural identification of tissue at risk of undertreatment.

Pharmacokinetic and safety study of doxorubicin-eluting beads in a porcine model of hepatic arterial embolization.

PURPOSE: To present the pathologic and pharmacokinetic findings from hepatic embolization in a porcine model comparing doxorubicin-eluting beads with bland embolization and to correlate these findings with in vitro release kinetics. MATERIALS AND METHODS: Drug-eluting beads (DEB; 100-300 microm and 700-900 microm) loaded with 37.5 mg doxorubicin per milliliter hydrated beads were used to embolize the hepatic artery feeding the left lobe of the liver in young adult Yucatan pigs (n = 5 per group). Control animals underwent embolization with bland beads (100-300 microm; n = 5). Systemic plasma levels of doxorubicin were measured and correlated to in vitro drug release. Blood sampling and histopathologic examination were performed during the 90-day follow-up. RESULTS: All animals underwent successful embolization, and the treatment was well tolerated. Mean volumes of beads administered were 2.0-3.4 mL, with mean doses of 127.5 mg and 78.7 mg of doxorubicin for the 100- to 300-microm and 700- to 900-microm DEB groups, respectively. Gross pathologic examination revealed no effects on organs other than the liver. There was a transient increase in liver enzyme levels, particularly in the groups of animals who underwent embolization with 100- to 300-microm DEB. Histopathologic study showed mostly nonnecrotic changes with bland beads, whereas the effects of DEB were more severe, with large areas of pannecrosis evident with the 100- to 300-microm DEB. Maximum plasma concentrations were 651 ng/mL and 42.8 ng/mL for the 100- to 300-microm and 700- to 900-microm DEB groups, respectively, observed at 1 minute for both groups. Correlation with in vitro data showed a strong linear relationship. CONCLUSIONS: Hepatic arterial embolization with DEB was shown to be safe and well tolerated. The locoregional delivery of doxorubicin from DEB caused targeted tissue damage with minimal systemic impact and could be a promising new approach to transarterial chemoembolization of solid tumors.

DC bead: in vitro characterization of a drug-delivery device for transarterial chemoembolization.

PURPOSE: The purpose of this investigation is to present the in vitro characterization and detailed drug-loading procedure for DC Bead, a microsphere product that can be loaded with chemotherapeutic agents for embolization. MATERIALS AND METHODS: DC Bead is an embolic microsphere product that is capable of being loaded with anthracycline drugs such as doxorubicin just before administration in a transarterial chemoembolization (TACE) procedure. Beads can be loaded from solutions prepared from doxorubicin powder or the doxorubicin HCl formulation. In this evaluation, bead sizes were measured by optical microscopy with video imaging. Gravimetric analysis demonstrated the effect of drug loading on bead water content, and its consequent impact on bead compressibility was determined. The subsequent deliverability of the beads was assessed by mixing the beads with contrast medium and saline solution and passing the beads through an appropriately sized microcatheter. A T-cell apparatus was used to monitor the in vitro elution of the drug from the beads over a period of 24 hours in various elution media. RESULTS: DC Bead spheres could be easily loaded with doxorubicin to a recommended level of 25 mg/mL of hydrated beads by immersion of the beads in the drug solution for 10-120 minutes depending on microsphere size. Other commercial embolic microspheres were shown not to load doxorubicin to the same extent or release it in the same fashion and were considered unsuitable for local drug delivery. Maximum theoretic capacity for DC Bead was approximately 45 mg/mL. Increase in doxorubicin loading resulted in a concomitant decrease in water content and consequential increase in bead resistance to compression force. Drug loading also resulted in a decrease in the average size of the beads, which was dependent on bead size and drug dose. This did not impact bead delivery at any drug loading level to a maximum of 37.5 mg/mL. Beads 100-700 microm in size could be delivered through 2.7-F microcatheters, whereas the 700-900-microm range required 3-F catheters. Modeling of the kinetics of drug elution from the beads in vitro at a loading dose of 25 mg/mL yielded calculated half-lives of 150 hours for the 100-300-microm range to a maximum of 1,730 hours for the 700-900-microm size range, which was dependent on the ionic strength of the elution medium. For comparison, there was a rapid loss of drug from an unstable Lipiodol emulsion with a half-life of approximately 1 hour. CONCLUSIONS: DC Bead can be loaded with doxorubicin to provide an accurate dosage of drug per unit volume of beads. Drug elution is dependent on ion exchange with the surrounding environment and is controlled and sustained, unlike the rapid separation of the drug from Lipiodol. Drug loading has no impact on the handling and deliverability of the beads, making them suitable for superselective TACE.

Drug loading and elution from a phosphorylcholine polymer-coated coronary stent does not affect long-term stability of the coating in vivo.

A drug eluting coronary stent was developed for use in preclinical and clinical trial evaluation. The stent was coated with a phosphorylcholine (PC)-based polymer coating containing the cell migration inhibitor batimastat. A pharmacokinetic study was conducted in a rabbit iliac model using (14)C-radiolabeled version of the drug; this showed the drug release to be first order with 94% of it being released within 28 days. Unloaded and drug-loaded stents were implanted in a porcine coronary artery model; a number were explanted at 5 days and scanning electron microscopy was used to show that the presence of the drug did not affect the rate of stent endothelialization. The remainder of the stents were removed after 6 months and the stents carefully removed from the arterial tissue. Fourier-transform infrared (FT-IR) spectroscopy (both attenuated total reflectance and microscopic imaging) was used to show the presence of the PC coating on control unloaded, drug-loaded and explanted stents, providing evidence that the coating was still present. This was further confirmed by use of atomic force microscopy (AFM) amplitude-phase, distance (a-p,d) curves which generated the characteristic traces of the PC coating. Further AFM depth-profiling techniques found that the thicknesses of the PC coatings on an control unloaded stent was 252+/-19 nm, on an control batimastat-loaded stent 906+/-224 nm and on an explanted stent 405+/-224 nm. The increase in thickness after the drug-loading process was a consequence of drug incorporation in the film, and the return to the unloaded dimensions for the explanted sample indicative of elution of the drug from the coating. The drug delivery PC coating was therefore found to be stable following elution of the drug and after 6 months implantation in vivo.