Drug delivery embolization systems: a physician's perspective

Evaluation of the safety and efficacy of transarterial sevelamer embolization in a rabbit liver cancer model: A challenge on the size rule for vascular occlusion

As the most efficient method to treat hepatocellular carcinoma in the immediate or advanced stage, transarterial chemoembolization (TACE) is coming into the era of microsphere (MP). Drug-eluting beads have shown their huge potential as an embolic agent and drug carrier for chemoembolization, but their sizes are strictly limited to be above 40 μm, which was considered to occlude vessels in a safe mode. microsphere smaller than 40 µm is easy to be washed out and transported to the normal liver lobe or other organs, causing severe adverse events and failed embolization. To determine whether sevelamer ultrafine particle (0.2-0.5 µm) is qualified as a safe and efficient embolic agent, we investigated the safety and therapeutic efficiency of transarterial sevelamer embolization (TASE) in the VX2 rabbit liver cancer model, aiming to challenge the "40 µm" rule on the selection criteria of the MP. In a four-arm study, blank bead (Callisphere, 100-300 µm), luminescent polystyrene microsphere (10, 100 µm), and sevelamer particle were transarterially administered to evaluate the threshold size of the MP size for intrahepatic or extrahepatic permeability. Another four-arm study was designed to clarify the safety and efficiency of preclinical transarterial sevelamer embolizationTASE tests over other techniques. Sham (saline), TASE, C-TACE, and D-TACE (n = 6) were compared in terms of serum chemistry, histopathology, and tumor necrosis ratio. In the first trials, the "40 µm" rule was detectable on the VX2 cancer model, but the regulation has no application to the new embolic agent as sevelamer ultrafine particles have not been found to leak out from the VX2 lesions, only found in the embolized vessels. Pathology proves that less viable tumor residue was found 2 weeks after the procedure, evidencing a better therapeutic outcome. No adverse events were found except for a short stress response. These results indicate that sevelamer is a safe and efficient embolic as an alternative to the current MP-based embolization therapy techniques.

Visualization and Evaluation of Chemoembolization on a 3D Decellularized Organ Scaffold

Transarterial chemoembolization (TACE) has emerged as the mainstay treatment for patients suffering from unresectable intermediate hepatocellular carcinoma and also holds the potential to treat other types of hypervascular cancers such as renal cell carcinoma. However, an in vitro model for evaluating both embolic performance and drug-release kinetics of the TACE embolic agents is still lacking since the current models greatly simplified the in vivo vascular systems as well as the extracellular matrices (ECM) in the organs. Here, we developed a decellularized organ model with preserved ECM and vasculatures as well as a translucent appearance to investigate chemoembolization performances of a clinically widely used embolic agent, i.e., a doxorubicin-loaded ethiodised oil (EO)-based emulsion. We, for the first time, utilized an ex vivo model to evaluate the liquid-based embolic agent in two organs, i.e., liver and kidneys. We found that the EO-based emulsion with enhanced stability by incorporating an emulsifier, i.e., hydrogenated castor oil-40 (HCO), showed an enhanced occlusion level and presented sustained drug release in the ex vivo liver model, suggesting an advantageous therapeutic effect for TACE treatment of hepatocellular carcinoma. In contrast, we observed that drug-release burst happened when applying the same therapy in the kidney model even with the HCO emulsifier, which may be explained by the presence of the specific renal vasculature and calyceal systems, indicating an unfavorable effect in the renal tumor treatment. Such an ex vivo model presents a promising template for chemoembolization evaluation before in vivo experiments for the development of novel embolic agents.

Predicting pharmacokinetic behaviour of drug release from drug-eluting embolization beads using in vitro elution methods

Drug-eluting Embolic Bead - Transarterial Chemoembolisation (DEB-TACE) is a minimally invasive embolising treatment for liver tumours that allows local release of chemotherapeutic drugs via ion exchange, following delivery into hepatic arterial vasculature. Thus far, no single in vitro model has been able to accurately predict the complete kinetics of drug release from DEB, due to heterogeneity of rate-controlling mechanisms throughout the process of DEB delivery. In this study, we describe two in vitro models capable of distinguishing between early phase and late phase drug release by mimicking in vivo features of each phase. First, a vascular flow system (VFS) was used to simulate the early phase by delivering DEB into a silicon vascular cast under high pulsatile flow. This yielded a burst release profile of drugs from DEB which related to the dose adjusted C_max observed in pharmacokinetic plasma profiles from a preclinical swine model. Second, an open loop flow-through cell system was used to model late phase drug release by packing beads in a column with an ultra-low flow rate. DEB loaded with doxorubicin, irinotecan and vandetanib showed differential drug release rates due to their varying chemical properties and unique drug-bead interactions. Using more representative in vitro models to map discrete phases of DEB drug release will provide a better capability to predict the pharmacokinetics of developmental formulations, which has implications for treatment safety and efficacy.

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.

Targeting PEPT1: a novel strategy to improve the antitumor efficacy of doxorubicin in human hepatocellular carcinoma therapy

Proton coupled oligopeptide transporter 1 (PEPT1) is a member of the peptide transporter superfamily and plays important role in the absorption of oligopeptide and peptidomimetic drugs. Our previous research verified that PEPT1 expressed specifically in human Hepatocellular carcinoma (HCC) tissue and cell lines and showed potential transport activity to be a new candidate of the tumor therapeutic target. In this study, we aim to explore the feasibility of a novel tumor target therapeutic strategy: Targeting PEPT1 to improve the antitumor efficacy of Doxorubicin in human HCC therapy. First, Doxorubicin was conjugated with Glycylglycylglycine (Gly-Gly-Gly) − a tripeptide which was known as the substrate of PEPT1 and characterized by HPLC and MS successfully. Doxorubicin-tripeptide conjugate was then observed to clarify the target delivery by PEPT1 and the antitumor effect on human hepatocarcinoma in vivo and in vitro. Furthermore, the improvement of the toxic and side effect of Doxorubicin after conjugation was also evaluated by some biochemical tests. Our results reveal that targeting PEPT1 may contribute to the efficient delivery of Doxorubicin to hepatocarcinoma cells and the reduction of drug toxicity. PEPT1 has the prospect to be a novel target of HCC therapy.

Substitution of Percutaneous Ethanol Injection with a Low Molecular Weight Peptide Gel Mimicking Chemoembolization for Cancer Therapy

In order to avoid the instability and quick separation between emulsifier and drug in the interventional chemoembolization, an injectable low molecular weight peptide gel (LMWG) was prepared to localize ethanol and chemotherapeutic for in situ synergistic therapy. The formation mechanism, rheological property and morphology of the LMWG were investigated by NMR, UV-vis, MS and SEM. The interaction between gelator and anticancer drug doxorubicin hydrochloride (DOX) was evaluated by fluorescence spectroscopy and its contribution on drug loading properties was demonstrated. The gel was non-toxic to both 3T3 fibroblasts and 4T1 breast cancer cells. DOX as well as ethanol were encapsulated in the gel and injected in breast cancer bearing mice with low drug dose (2.5 mg/kg body weight). The LMWG surrounded tumors act as a depot for ethanol release and release DOX to induce the apoptosis of cancer cells. With the combination of percutaneous ethanol injection (PEI) and chemotherapy, the DOX loaded LMWG exhibited great significance in necrosis of tumor tissue and exciting tumor inhibition efficiency.

Towards Hypoxia-responsive Drug-eluting Embolization Beads

Drug release from chemoembolization microspheres stimulated by the presence of a chemically reducing environment may provide benefits for targeting drug resistant and metastatic hypoxic tumours. A water-soluble disulfide-based bifunctional cross-linker bis(acryloyl)-(l)-cystine (BALC) was synthesised, characterised and incorporated into a modified poly(vinyl) alcohol (PVA) hydrogel beads at varying concentrations using reverse suspension polymerisation. The beads were characterised to confirm the amount of cross-linker within each formulation and its effects on the bead properties. Elemental and UV/visible spectroscopic analysis confirmed the incorporation of BALC within the beads and sizing studies showed that in the presence of a reducing agent, all bead formulations increased in mean diameter. The BALC beads could be loaded with doxorubicin hydrochloride and amounts in excess of 300mg of drug per mL of hydrated beads could be achieved but required conversion of the carboxylic acid groups of the BALC to their sodium carboxylate salt forms. Elution of doxorubicin from the beads demonstrated a controlled release via ionic exchange. Some formulations exhibited an increase in size and release of drug in the presence of a reducing agent, and therefore demonstrated the ability to respond to an in vitro reducing environment.

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.

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.