Preparation of Radiopaque Drug-Eluting Beads for Transcatheter Chemoembolization

Bench-to-bedside development of multifunctional flexible embolic agents

Transarterial chemoembolization (TACE) has been demonstrated to provide a survival benefit for patients with unresectable hepatocellular carcinoma (HCC). However, conventional TACE still faces limitations associated with complications, side effects, unsatisfactory tumor responses, repeated treatment, and narrow indications. For further improvement of TACE, additional beneficial functions such as degradability, drug-loading and releasing properties, detectability, targetability, and multiple therapeutic modalities were introduced. The purpose here is to provide a comprehensive overview of current and emerging particulate embolization technology with respect to materials. Therefore, this review systematically identified and described typical features, various functions, and practical applications of recently emerging micro/nano materials as particulate embolic agents for TACE. Besides, new insights into the liquid metals-based multifunctional and flexible embolic agents were highlighted. The current development routes and future outlooks of these micro/nano embolic materials were also presented to promote advancement in the field.

Magnetic liquid metal loaded nano-in-micro spheres as fully flexible theranostic agents for SMART embolization

Transcatheter arterial chemoembolization (TACE) has become one of the preferred choices for advanced liver cancer patients. Current clinically used microsphere embolic agents, such as PVA, gelatin, and alginate microspheres, have limited therapeutic efficacy and lack the function of real-time imaging. In this work, we fabricated magnetic liquid metal nanoparticle (Fe@EGaIn NP) loaded calcium alginate (CA) microspheres (denoted as Fe@EGaIn/CA microspheres), which integrate CT/MR dual-modality imaging and photothermal/photodynamic functions of the Fe@EGaIn NP core, as well as embolization and drug-loading functions of CA microspheres. Namely, such nano-in-micro spheres can be used as fully flexible theranostic agents to achieve smart-chemoembolization. It has been confirmed by in vitro and in vivo experiments that Fe@EGaIn/CA microspheres have advantageous morphology, favorable biocompatibility, splendid versatility, and advanced embolic efficacy. Benefiting from these properties, excellent therapeutic efficiency was achieved with a tumor growth-inhibiting value of 100% in tumor-bearing rabbits. As a novel microsphere embolic agent with promising therapeutic efficacy and diagnostic capability, Fe@EGaIn/CA microspheres have shown potential applications in clinical transcatheter arterial chemoembolization. And the preparation strategy presented here provides a generalized paradigm for achieving multifunctional and fully flexible theranostics.

Comparison of the efficacy and safety of conventional transarterial chemoembolization with and without drug-eluting beads embolization for the treatment of unresectable large hepatocellular carcinoma

AIM

Hepatocellular carcinoma (HCC) has a poor prognosis. Moreover, large HCCs have been commonly observed. We aimed to evaluate the efficacy and safety of drug-eluting beads transarterial chemoembolization (DEB-TACE) combined with conventional TACE (cTACE) for the treatment of patients with unresectable large HCCs (main tumor ≥5 cm in diameter) compared with cTACE alone.

METHODS

A retrospective matched cohort study was performed on consecutive patients with unresectable large HCCs who underwent TACE as the initial treatment at the Fujian Medical University Cancer Hospital from May 2017 and March 2019. Fifty-five patients who underwent DEB-TACE combined with cTACE were compared with a case-matched control group of 110 patients who received cTACE alone. We compared the tumor response at 1 and 3 months after TACE, time to progression (TTP), and adverse events between the groups.

RESULTS

The objective response rate was higher for the DEB-TACE combined with cTACE group than for the cTACE alone group at 1 (39 of 55 [70.9%] vs. 57 of 110 [51.8%], p = 0.019) and 3 months (27 of 43 [62.8%] vs. 31 of 71 [43.7%], p = 0.048) post-treatment. The DEB-TACE combined with cTACE group also had a significantly longer median TTP than that of the cTACE group (7.2 vs. 5.3 months, p = 0.039). Compared with the cTACE group, occurrences of abdominal pain, nausea/vomiting, and constipation were significantly more frequent in the DEB-TACE combined with cTACE group (p < 0.05).

CONCLUSION

Compared with cTACE alone, DEB-TACE combined with cTACE significantly increased the objective response rate at 1 and 3 months after the treatment of unresectable large HCCs, and had a longer TTP, without any significant increase in the number of severe complications.

Drug-eluting embolic microspheres: State-of-the-art and emerging clinical applications

INTRODUCTION

Drug-eluting embolic (DEE) microspheres, or drug-eluting beads (DEB), delivered by transarterial chemoembolization (TACE) serve as a therapeutic embolic to stop blood flow to tumors and a drug delivery vehicle. New combinations of drugs and DEE microspheres may exploit the potential synergy between mechanisms of drug activity and local tissue responses generated by TACE to enhance the efficacy of this mainstay therapy.

AREAS COVERED

This review provides an overview of key drug delivery concepts related to DEE microspheres with a focus on recent technological developments and promising emerging clinical applications as well as speculation into the future.

EXPERT OPINION

TACE has been performed for nearly four decades by injecting chemotherapy drugs into the arterial supply of tumors while simultaneously cutting off their blood supply, trying to starve and kill cancer cells, with varying degrees of success. The practice has evolved over the decades but has yet to fulfill the promise of truly personalized therapies envisioned through rational selection of drugs and real-time multi-parametric image guidance to target tumor clonality or heterogeneity. Recent technologic and pharmacologic developments have opened the door for potentially groundbreaking advances in how TACE with DEE microspheres is performed with the goal of achieving advancements that benefit patients.

Synthesis, characterization, and imaging of radiopaque bismuth beads for image-guided transarterial embolization

Current therapy for hypervascular cancers, e.g., hepatocellular carcinoma, includes occlusion of the tumor blood supply by arterial infusion of embolic microspheres (beads) suspended in iodine-based contrast under fluoroscopic guidance. Available radiopaque, imageable beads use iodine as the radiopacifier and cannot be differentiated from contrast. This study aimed to synthesize and characterize imageable beads using bismuth as the radiopacifier that could be distinguished from iodine contrast based upon the difference in the binding energy of k-shell electrons (k-edge). Radiodense bismuth beads were successfully synthesized some with uniform bismuth distribution across the beads. The beads were spherical and could be infused through clinical microcatheters. The bismuth beads could be imaged with clinical dual-energy computed tomography (CT), where iodine-based contrast could be distinguished from the microspheres. The ability to separate iodine from bismuth may enhance the diagnostic information acquired on follow-up CT, identifying the distribution of the embolic beads separately from the contrast. Furthermore, with sequential use of iodine- and bismuth-based beads, the two radiopaque beads could be spatially distinguished on imaging, which may enable the development of dual drug delivery and dual tracking.

Evaluation of novel formulations for transarterial chemoembolization: combining elements of Lipiodol emulsions with Drug-eluting Beads

There are currently two methods widely used in clinical practice to perform transarterial chemoembolization (TACE). One is based on mixing an aqueous drug with an iodized oil (Lipiodol) and creating an emulsion that is delivered intraarterially, followed by embolization with a particulate agent. The other is based on a one-step TACE using Drug-eluting Beads (DEBs) loaded with drug. It is not recommended to mix Lipiodol with DEBs due to incompatibility. For the first time, novel DEB: Lipiodol: doxorubicin (Dox) emulsions are identified using lyophilized polyvinyl alcohol (PVA) hydrogels (non-iodinated or iodinated) DEBs.

Methods: 15 DEB emulsions (50mg Dox) were assessed for stability and deliverability in vitro and in vivo in a swine model. Dox release from selected formulations was measured in vitro using a vascular flow model and in vivo in a VX2 rabbit tumor model.

Results: Both DEB formats were shown to be able to form emulsions, however only Iodinated DEBs consistently met defined handling criteria. Those based on the non-iodinated DEB achieved >99%+ Dox loading in <5 minutes but were generally less stable. Those prepared using iodinated DEBs, which are more hydrophobic, were able to form stable Pickering-like emulsions (separation time ≥ 20 minutes) and demonstrated handling, administration and imaging observations more akin to Lipiodol™ TACE emulsions in both embolization models. Controlled Dox release and hence beneficial in vivo pharmacokinetics associated with DEB-TACE were maintained.

Conclusions: This study demonstrates that it is possible to formulate novel DEB emulsions suitable for TACE that combine positive elements of both Lipiodol™ based and DEB-TACE procedures.

The opacity of mineral ion-loaded bead (DC beads®) on low-keV monochromatic images from dual energy CT and T1-weighted gradient-echo MRI

PURPOSE

To evaluate the opacity of DC beads^® (DCB) loaded with mineral ions on low-keV monochromatic images from dual energy computed tomography (DECT) and T1-weighted gradient-echo (T1-GRE) MRI.

MATERIALS AND METHODS

Fe²⁺ or Ca²⁺-loaded DCBs were prepared by mixing DCBs in 100 mM FeSO₄ or CaSO₄ solution and scanned by DECT from 10 min to 27 h after mixing. The Hounsfield units (HUs) of sedimented DCBs on 40-keV monochromatic images were measured. Next, we mixed DCBs in 100, 10, 5 and 1 mM FeSO₄ solutions, and scanned these solutions from 15 to 120 min after mixing using a 3 T MR scanner. The signal-noise ratios (SNRs) of sedimented DCBs on T1-GRE were measured. Venous blood was scanned to compare with DCBs.

RESULTS

The CT values of DCBs in FeSO₄ and CaCl₂ solutions gradually increased, and were 113.3 and 43.1 HU at 27 h, respectively; that of blood was 17.8 HU. The SNR of DCB in 1 mM FeSO₄ solution increased and achieved equilibrium at 120 min, and was 120.5 and higher than in the other FeSO₄ solutions. The SNR of blood was 49.7.

CONCLUSION

Optimally Fe²⁺-loaded DCBs can be discriminated from venous blood on 40-keV monochromatic images from DECT and T1-GRE.

Reversed Lipid-Based Nanoparticles Dispersed in Iodized Oil for Transarterial Chemoembolization

Transarterial chemoembolization (TACE) is a promising treatment for patients suffering from unresectable liver malignancy. A coarse emulsion of doxorubicin solution and iodized oil is widely used in clinical practice. However, this coarse emulsion lacks sufficient physical stability and can split into water and oil very quickly. Furthermore, most chemotherapeutics are quickly released into systematic circulation, causing serious adverse effects. In this study, we aimed to prepare reversed lipid-based nanoparticles (RLBNs) dispersed in iodized oil as nanocarriers for the delivery of hydrophilic chemotherapeutics. Unlike a simple mixture of drug solution and oil, RLBN is a homogenous system and possesses a hydrophobic nanostructure that has high dispersibility in oils. Hydrophilic chemotherapeutics were entrapped in the polar core juxtaposed by highly biocompatible lipid materials, such as egg phospholipids. A sustained drug-release profile was observed in both in vitro and in vivo pharmacokinetics studies. The results of computed tomography showed that RLBN-doxorubicin-iodized oil could remain in the tumor region for more than 14 days and that the growth of tumors was effectively suppressed. Thus, the current results suggest that RLBN is a promising drug delivery system and is compatible with TACE treatment.

Radiopaque and uniform alginate microspheres loaded with tantalum nanoparticles for real-time imaging during transcatheter arterial embolization

One restriction to the development and application of transcatheter arterial chemoembolization (TACE) therapy is the lack of an inherently radiopaque embolic whose location and distribution can be precisely visualized in real time and be used for non-invasive examination after surgery. Methods: A one-step electrospray method was developed to fabricate calcium alginate microspheres loaded with tantalum nanoparticles (Ta@CaAlg). The parameters of electrospraying were assessed. The in vivo X-ray imaging capability and embolic effect of Ta@CaAlg microspheres were evaluated in the renal arteries of normal rabbits by digital radiography and computed tomography. Doxorubicin hydrochloride (Dox) was chosen as a model drug, and the drug loading capacity and release behavior of these microspheres was valuated in vitro.Results: Spherical Ta@CaAlg microspheres with monodisperse sizes ranging from 150 to 1200 μm were fabricated by electrospraying. The results of an in vivo study showed that Ta@CaAlg microspheres possessed the qualities of both embolic agents and contrast media. They could not only feed back the real-time location and distribution of the embolic microspheres but also maintained clear X-ray imaging of embolized sites for up to 4 weeks as assessed by digital radiography and computed tomography. Digital subtraction angiography showed that they had an excellent embolic effect. Ta@CaAlg microspheres could be loaded with Dox to form "3-in-1" embolic microspheres. The maximum Dox loading was 97.3 mg Dox per mL beads and loaded microspheres exhibited pH-dependent release profiles. Conclusion: The X-ray opacity and drug-loading capability of Ta@CaAlg microspheres offers great promise in direct, real-time, in vivo investigation for TACE and long-term non-invasive re-examination.

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.

Radiopaque nano and polymeric materials for atherosclerosis imaging, embolization and other catheterization procedures

A review of radiopaque nano and polymeric materials for atherosclerosis imaging and catheterization procedures is presented in this paper. Cardiovascular diseases (CVDs) are the leading cause of death in the US with atherosclerosis as a significant contributor for mortality and morbidity. In this review paper, we discussed the physics of radiopacity and X-ray/CT, clinically used contrast agents, and the recent progress in the development of radiopaque imaging agents and devices for the diagnosis and treatment of CVDs. We focused on radiopaque imaging agents for atherosclerosis, radiopaque embolic agents and drug eluting beads, and other radiopaque medical devices related to catheterization procedures to treat CVDs. Common strategies of introducing radiopacity in the polymers, together with examples of their applications in imaging and medical devices, are also presented.

Drug-eluting embolic microspheres for local drug delivery - State of the art

Embolic microspheres or beads used in transarterial chemoembolization are an established treatment method for hepatocellular carcinoma patients. The occlusion of the tumor-feeding vessels by intra-arterial injection of the beads results in tumor necrosis and shrinkage. In this short review, we describe the utility of using these beads as devices for local drug delivery. We review the latest advances in the development of non-biodegradable and biodegradable drug-eluting beads for transarterial chemoembolization. Their capability to load different drugs, such as chemotherapeutics and anti-angiogenic compounds with different physicochemical properties, like charge and hydrophilicity/hydrophobicity, are discussed. We specifically address controlled and sustained drug release from the microspheres, and the resulting in vivo pharmacokinetics in the plasma vs. drug distribution in the targeted tissue.

Review of the Development of Methods for Characterization of Microspheres for Use in Embolotherapy: Translating Bench to Cathlab

Therapeutic embolotherapy is the deliberate occlusion of a blood vessel within the body, which can be for the prevention of internal bleeding, stemming of flow through an arteriovenous malformation, or occlusion of blood vessels feeding a tumor. This is achieved using a wide selection of embolic devices such as balloons, coils, gels, glues, and particles. Particulate embolization is often favored for blocking smaller vessels, particularly within hypervascularized tumors, as they are available in calibrated sizes and can be delivered distally via microcatheters for precise occlusion with associated locoregional drug delivery. Embolic performance has been traditionally evaluated using animal models, but with increasing interest in the 3R's (replacement, reduction, refinement), manufacturers, regulators, and clinicians have shown interest in the development of more sophisticated in vitro methods for evaluation and prediction of in vivo performance. Herein the current progress in developing bespoke techniques incorporating physical handling, fluid dynamics, occlusive behavior, and sustained drug elution kinetics within vascular systems is reviewed. While it is necessary to continue to validate the safety of such devices in vivo, great strides have been made in the development of bench tests that better predict the behavior of these products aligned with the principles of the 3R's.

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.

First Human Experience with Directly Image-able Iodinated Embolization Microbeads

PURPOSE

To describe first clinical experience with a directly image-able, inherently radio-opaque microspherical embolic agent for transarterial embolization of liver tumors.

METHODOLOGY

LC Bead LUMI™ is a new product based upon sulfonate-modified polyvinyl alcohol hydrogel microbeads with covalently bound iodine (~260 mg I/ml). 70-150 μ LC Bead LUMI™ iodinated microbeads were injected selectively via a 2.8 Fr microcatheter to near complete flow stasis into hepatic arteries in three patients with hepatocellular carcinoma, carcinoid, or neuroendocrine tumor. A custom imaging platform tuned for LC LUMI™ microbead conspicuity using a cone beam CT (CBCT)/angiographic C-arm system (Allura Clarity FD20, Philips) was used along with CBCT embolization treatment planning software (EmboGuide, Philips).

RESULTS

LC Bead LUMI™ image-able microbeads were easily delivered and monitored during the procedure using fluoroscopy, single-shot radiography (SSD), digital subtraction angiography (DSA), dual-phase enhanced and unenhanced CBCT, and unenhanced conventional CT obtained 48 h after the procedure. Intra-procedural imaging demonstrated tumor at risk for potential under-treatment, defined as paucity of image-able microbeads within a portion of the tumor which was confirmed at 48 h CT imaging. Fusion of pre- and post-embolization CBCT identified vessels without beads that corresponded to enhancing tumor tissue in the same location on follow-up imaging (48 h post).

CONCLUSION

LC Bead LUMI™ image-able microbeads provide real-time feedback and geographic localization of treatment in real time during treatment. The distribution and density of image-able beads within a tumor need further evaluation as an additional endpoint for embolization.

DC BeadM1™: towards an optimal transcatheter hepatic tumour therapy

Clinical use of DC Bead™ loaded with doxorubicin (DEBDOX™) or irinotecan (DEBIRI™), for the treatment of primary and secondary tumours of the liver respectively, is showing great promise. Recently there has been a tendency to select smaller bead size ranges to treat tumours in an effort to allow more drug dose to be administered, improve tumoural penetration and resultant drug delivery and tumour coverage. Herein we describe the development and performance characterisation of a new DC Bead size range (DC BeadM1 (TM), 70-150 μm) capable of an increased bead delivery in the distal vasculature, corresponding to greater tumour coverage and drug dose delivered. Both unloaded and drug loaded DC BeadM1 were shown to have a greater density of distal volume of penetration although the ultimate distal level of penetration was the same as that of the 100-300 µm beads in an in vitro penetration model. Elution of doxorubicin was slower than irinotecan elution, but it was similar when comparing the same drug elution from 70 to 150 µm compared to 100-300 µm beads. Radiopaque versions of 70-150 and 100-300 µm beads were prepared in order to evaluate distribution ex vivo using µ-CT and doxorubicin distribution using epifluorescent microscopy. Liver distribution of the radiopaque versions of the beads was shown to be more distal and efficient at filling smaller vessels with the DC BeadM1 and correspondingly more beads were found per vessel histologically with a larger area of drug coverage with the smaller size range. This study indicates that the smaller (70-150 μm) beads should permit an increased dose of drug to be administered to both hypervascular and hypovascular tumours as compared to 100-300 µm beads.