Doxorubicin and irinotecan drug-eluting beads for treatment of glioma: a pilot study in a rat model

Nanoparticles for Drug and Gene Delivery in Pediatric Brain Tumors' Cancer Stem Cells: Current Knowledge and Future Perspectives

Primary malignant brain tumors are the most common solid neoplasm in childhood. Despite recent advances, many children affected by aggressive or metastatic brain tumors still present poor prognosis, therefore the development of more effective therapies is urgent. Cancer stem cells (CSCs) have been discovered and isolated in both pediatric and adult patients with brain tumors (e.g., medulloblastoma, gliomas and ependymoma). CSCs are a small clonal population of cancer cells responsible for brain tumor initiation, maintenance and progression, displaying resistance to conventional anticancer therapies. CSCs are characterized by a specific repertoire of surface markers and intracellular specific pathways. These unique features of CSCs biology offer the opportunity to build therapeutic approaches to specifically target these cells in the complex tumor bulk. Treatment of pediatric brain tumors with classical chemotherapeutic regimen poses challenges both for tumor location and for the presence of the blood-brain barrier (BBB). Lastly, the application of chemotherapy to a developing brain is followed by long-term sequelae, especially on cognitive abilities. Novel avenues are emerging in the therapeutic panorama taking advantage of nanomedicine. In this review we will summarize nanoparticle-based approaches and the efficacy that NPs have intrinsically demonstrated and how they are also decorated by biomolecules. Furthermore, we propose novel cargoes together with recent advances in nanoparticle design/synthesis with the final aim to specifically target the insidious CSCs population in the tumor bulk.

Nucleic acid-based therapy for brain cancer: Challenges and strategies

Nucleic acid-based therapy emerges as a powerful weapon for the treatment of tumors thanks to its direct, effective, and lasting therapeutic effect. Encouragingly, continuous nucleic acid-based drugs have been approved by the Food and Drug Administration (FDA) and the European Medicines Agency (EMA). Despite the tremendous progress, there are few nucleic acid-based drugs for brain tumors in clinic. The most challenging problems lie on the instability of nucleic acids, difficulty in traversing the biological barriers, and the off-target effect. Herein, nucleic acid-based therapy for brain tumor is summarized considering three aspects: (i) the therapeutic nucleic acids and their applications in clinical trials; (ii) the various administration routes for nucleic acid delivery and the respective advantages and drawbacks. (iii) the strategies and carriers for improving stability and targeting ability of nucleic acid drugs. This review provides thorough knowledge for the rational design of nucleic acid-based drugs against brain tumor.

Fine-Tuning the Linear Release Rate of Paclitaxel-Bearing Supramolecular Filament Hydrogels through Molecular Engineering

One key design feature in the development of any local drug delivery system is the controlled release of therapeutic agents over a certain period of time. In this context, we report the characteristic feature of a supramolecular filament hydrogel system that enables a linear and sustainable drug release over the period of several months. Through covalent linkage with a short peptide sequence, we are able to convert an anticancer drug, paclitaxel (PTX), to a class of prodrug hydrogelators with varying critical gelation concentrations. These self-assembling PTX prodrugs associate into filamentous nanostructures in aqueous conditions and consequently percolate into a supramolecular filament network in the presence of appropriate counterions. The intriguing linear drug release profile is rooted in the supramolecular nature of the self-assembling filaments which maintain a constant monomer concentration at the gelation conditions. We found that molecular engineering of the prodrug design, such as varying the number of oppositely charged amino acids or through the incorporation of hydrophobic segments, allows for the fine-tuning of the PTX linear release rate. In cell studies, these PTX prodrugs can exert effective cytotoxicity against glioblastoma cell lines and also primary brain cancer cells derived from patients and show enhanced tumor penetration in a cancer spheroid model. We believe this drug-bearing hydrogel platform offers an exciting opportunity for the local treatment of human diseases.

Natural product drug delivery: A special challenge?

Natural products have a long-standing and critical role in drug development and medical use. The structural and physicochemical properties of natural products, while derived evolutionarily to be effective in living systems, may create challenges in translation to a pharmaceutical product. Molecular complexity, low solubility, functional group reactivity and general instability are among the challenges that typically need to be overcome. This review looks at some of the ways that natural products have been formulated and delivered to enable the successful application of these vitally important medicines to patients.

Inducing a Transient Increase in Blood-Brain Barrier Permeability for Improved Liposomal Drug Therapy of Glioblastoma Multiforme

The blood-brain barrier (BBB) selectively controls the passage of endogenous and exogenous molecules between systemic circulation and the brain parenchyma. Nanocarrier-based drugs such as liposomes and nanoparticles are an attractive prospect for cancer therapy since they can carry a drug payload and be modified to improve targeting and retention at the desired site. However, the BBB prevents most therapeutic drugs from entering the brain, including physically restricting the passage of liposomes and nanoparticles. In this paper, we show that a low dose of systemically injected recombinant human vascular endothelial growth factor induces a short period of increased BBB permeability. We have shown increased delivery of a range of nanomedicines to the brain including contrast agents for imaging, varying sizes of nanoparticles, small molecule chemotherapeutics, tracer dyes, and liposomal chemotherapeutics. However, this effect was not uniform across all brain regions, and permeability varied depending on the drug or molecule measured. We have found that this window of BBB permeability effect is transient, with normal BBB integrity restored within 4 h. This strategy, combined with liposomal doxorubicin, was able to significantly extend survival in a mouse model of human glioblastoma. We have found no evidence of systemic toxicity, and the technique was replicated in pigs, demonstrating that this technique could be scaled up and potentially be translated to the clinic, thus allowing the use of nanocarrier-based therapies for brain disorders.

Intracranial rat glioma model for tumor resection and local treatment

BACKGROUND

Although tumor resection is among the most important prognostic factors, high grade gliomas regrow in most cases. Also, resection of glial tumors in eloquent brain regions is not or only partially possible. Despite these severe restraints, however, only a few in-vivo models have been established to investigate tumor recurrence and local treatment. Here we characterize the intracranial BT4Ca rat glioma as a model for these aspects.

NEW METHOD

BT4Ca cells were stereotaxically implanted into the frontal cortex of BDIX rats. Rats were than allocated to (1) a control group, which received no further treatment; (2) a catheter group, where a catheter was implanted for repeated microinjection of vehicle every 3rd day as catheter-control; (3) a resection group, where the tumor was microsurgically removed eight days after cell injection. Postoperatively, survival time, weight and general health condition were scored and the tumor size was histologically assessed.

RESULTS

Injection of BT4Ca cells induced fast-growing tumors with a mean survival time of 16 days in the control and catheter groups. Resection significantly prolonged survival time whereby the tumor regrew in all rats. Tumor size was similar between all groups.

COMPARISON WITH EXISTING METHOD(S)

We here present a robust and reliable intracranial rat glioma model, which is suitable to simulate tumor recurrence after surgical resection and local treatment. Importantly, this model does not require advanced imaging or elaborate surgical techniques.

CONCLUSIONS

The intracranial BT4Ca glioma model appears to be a feasible tool to investigate tumor recurrence after resection and to test local treatment.

Low Dose of Doxorubicin Potentiates the Effect of Temozolomide in Glioblastoma Cells

Glioblastoma (GBM) is an aggressive brain tumor with temozolomide (TMZ)-based chemotherapy as the main therapeutic strategy. Doxorubicin (DOX) is not used in gliomas due to its low bioavailability in the brain; however, new delivery strategies and low doses may be effective in the long term, especially as part of a drug cocktail. Our aim was to evaluate the chronic effects of low doses of DOX and TMZ in GBM. Human U87-ATCC cells and a primary GBM culture were chronically treated with TMZ (5 μM) and DOX (1 and 10 nM) alone or combined. DOX resulted in a reduction in the number of cells over a period of 35 days and delayed the cell regrowth. In addition, DOX induced cell senescence and reduced tumor sphere formation and the proportion of NANOG- and OCT4-positive cells after 7 days. Low doses of TMZ potentiated the effects of DOX on senescence and sphere formation. This combined response using low doses of DOX may pave the way for its use in glioma therapy, with new technologies to overcome its low blood-brain barrier permeability.

Vandetanib-eluting Radiopaque Beads: In vivo Pharmacokinetics, Safety and Toxicity Evaluation following Swine Liver Embolization

PURPOSE: To evaluate the plasma and tissue pharmacokinetics, safety and toxicity following intra-arterial hepatic artery administration of Vandetanib (VTB)-eluting Radiopaque Beads (VERB) in healthy swine.

MATERIALS AND METHODS: In a first phase, healthy swine were treated with hepatic intra-arterial administration of VERB at target dose loading strengths of 36 mg/mL (VERB36), 72 mg/mL (VERB72) and 120 mg/mL (VERB120). Blood and tissue samples were taken and analysed for VTB and metabolites to determine pharmacokinetic parameters for the different dose forms over 30 days. In a second phase, animals were treated with unloaded radiopaque beads or high dose VTB loaded beads (VERB100, 100 mg/mL). Tissue samples from embolized and non-embolized areas of the liver were evaluated at necropsy (30 and 90 days) for determination of VTB and metabolite levels and tissue pathology. Imaging was performed prior to sacrifice using multi-detector computed tomography (MDCT) and imaging findings correlated with pathological changes in the tissue and location of the radiopaque beads.

RESULTS: The peak plasma levels of VTB (C_max) released from the various doses of VERB ranged between 6.19-17.3 ng/mL indicating a low systemic burst release. The plasma profile of VTB was consistent with a distribution phase up to 6 h after administration followed by elimination with a half-life of 20-23 h. The AUC of VTB and its major metabolite N-desmethyl vandetanib (NDM VTB) was approximately linear with the dose strength of VERB. VTB plasma levels were at or below limits of detection two weeks after administration. In liver samples, VTB and NDM VTB were present in treated sections at 30 days after administration at levels above the in vitro IC₅₀ for biological effectiveness. At 90 days both analytes were still present in treated liver but were near or below the limit of quantification in untreated liver sections, demonstrating sustained release from the VERB. Comparison of the reduction of the liver lobe size and associated tissue changes suggested a more effective embolization with VERB compared to the beads without drug.

CONCLUSIONS: Hepatic intra-arterial administration of VERB results in a low systemic exposure and enables sustained delivery of VTB to target tissues following embolization. Changes in the liver tissue are consistent with an effective embolization and this study has demonstrated that VERB100 is well tolerated with no obvious systemic toxicity.

Nanotherapeutic systems for local treatment of brain tumors

Malignant brain tumor, including the most common type glioblastoma, are histologically heterogeneous and invasive tumors known as the most devastating neoplasms with high morbidity and mortality. Despite multimodal treatment including surgery, radiotherapy, chemotherapy, and immunotherapy, the disease inevitably recurs and is fatal. This lack of curative options has motivated researchers to explore new treatment strategies and to develop new drug delivery systems (DDSs); however, the unique anatomical, physiological, and pathological features of brain tumors greatly limit the effectiveness of conventional chemotherapy. In this context, we review the recent progress in the development of nanoparticle-based DDSs aiming to address the key challenges in transporting sufficient amount of therapeutic agents into the brain tumor areas while minimizing the potential side effects. We first provide an overview of the standard treatments currently used in the clinic for the management of brain cancers, discussing the effectiveness and limitations of each therapy. We then provide an in-depth review of nanotherapeutic systems that are intended to bypass the blood-brain barrier, overcome multidrug resistance, infiltrate larger tumorous tissue areas, and/or release therapeutic agents in a controlled manner. WIREs Nanomed Nanobiotechnol 2018, 10:e1479. doi: 10.1002/wnan.1479 This article is categorized under: Implantable Materials and Surgical Technologies > Nanomaterials and Implants Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

SW43-DOX ± loading onto drug-eluting bead, a potential new targeted drug delivery platform for systemic and locoregional cancer treatment - An in vitro evaluation

Treatment of unresectable primary cancer and their distant metastases, with the liver representing one of the most frequent location, is still plagued by insufficient treatment success and poor survival rates. The Sigma-2 receptor is preferentially expressed on many tumor cells making it an appealing target for therapy. Thus, we developed a potential targeted drug conjugate consisting of the Sigma-2 receptor ligand SW43 and Doxorubicin (SW43-DOX) for systemic cancer therapy and for locoregional treatment of primary and secondary liver malignancies when loaded onto drug-eluting bead (DEB) which was compared in vitro to the treatment with Doxorubicin alone. SW43-DOX binds specifically to the Sigma-2 receptor expressed on hepatocellular (Hep G2, Hep 3B), pancreatic (Panc-1) and colorectal (HT-29) carcinoma cell lines with high affinity and subsequent early specific internalization. Free SW43-DOX showed superior concentration and time depended cancer toxicity than treatment with Doxorubicin alone. Action mechanisms analysis revealed an apoptotic cell death with increased caspase 3/7 activation and reactive oxygen species (ROS) production. Only ROS scavenging with α-Tocopherol, but not the caspase inhibition (Z-VAD-FMK), partly reverted the effect. SW43-DOX could successfully be loaded onto DEB and showed prolonged eluting kinetics compared to Doxorubicin. SW43-DOX loaded DEB vs. Doxorubicin loaded DEB showed a significantly greater time dependent toxicity in all cell lines. In conclusion, the novel conjugate SW43-DOX ± loading onto DEB is a promising drug delivery platform for targeted systemic and locoregional cancer therapy.

Extravascular use of drug-eluting beads: A promising approach in compartment-based tumor therapy

Intraperitoneal carcinomatosis (PC) may occur with several tumor entities. The prognosis of patients suffering from PC is usually poor. Present treatment depends on the cancer entity and includes systemic chemotherapy, radiation therapy, hormonal therapy and surgical resection. Only few patients may also benefit from hyperthermic intraperitoneal chemotherapy with a complete tumor remission. These therapies are often accompanied by severe systemic side-effects. One approach to reduce side effects is to target chemotherapeutic agents to the tumor with carrier devices. Promising experimental results have been achieved using drug-eluting beads (DEBs). A series of in vitro and in vitro experiments has been conducted to determine the suitability of their extravascular use. These encapsulation devices were able to harbor CYP2B1 producing cells and to shield them from the hosts immune system when injected intratumorally. In this way ifosfamide - which is transformed into its active metabolites by CYP2B1 - could be successfully targeted into pancreatic tumor growths. Furthermore DEBs can be used to target chemotherapeutics into the abdominal cavity for treatment of PC. If CYP2B1 producing cells are proven to be save for usage in man and if local toxic effects of chemotherapeutics can be controlled, DEBs will become promising tools in compartment-based anticancer treatment.

Investigation of the mechanisms governing doxorubicin and irinotecan release from drug-eluting beads: mathematical modeling and experimental verification

Drug-eluting beads (DEBs) are embolising devices in clinical use for the treatment of liver cancer by transarterial chemoembolisation. In this study, release kinetics of doxorubicin (DOX) and irinotecan (IRI) were investigated by experimental evaluations and mathematical modeling, based on Langmuir isotherm and two phenomenological models (Boyd/Bhaskar) developed to determine the actual mechanisms controlling drug release rate. The model was validated through release studies, in particular by assessing how drug loading, ionic strength of the release medium and device swelling during release influence drug release kinetics. Results demonstrated that IRI is released much faster than DOX, and that DEB volume strongly depends upon drug loading and fractional release. This effect was properly taken into account in developing the mathematical model. Experimental results were well fit by numerical simulations, and two different rate-controlling mechanisms were found to govern DOX and IRI delivery.

Current status of local therapy in malignant gliomas--a clinical review of three selected approaches

Malignant gliomas are the most frequently occurring, devastating primary brain tumors, and are coupled with a poor survival rate. Despite the fact that complete neurosurgical resection of these tumors is impossible in consideration of their infiltrating nature, surgical resection followed by adjuvant therapeutics, including radiation therapy and chemotherapy, is still the current standard therapy. Systemic chemotherapy is restricted by the blood-brain barrier, while methods of local delivery, such as with drug-impregnated wafers, convection-enhanced drug delivery, or direct perilesional injections, present attractive ways to circumvent these barriers. These methods are promising ways for direct delivery of either standard chemotherapeutic or new anti-cancer agents. Several clinical trials showed controversial results relating to the influence of a local delivery of chemotherapy on the survival of patients with both recurrent and newly diagnosed malignant gliomas. Our article will review the development of the drug-impregnated release, as well as convection-enhanced delivery and the direct injection into brain tissue, which has been used predominantly in gene-therapy trials. Further, it will focus on the use of convection-enhanced delivery in the treatment of patients with malignant gliomas, placing special emphasis on potential shortcomings in past clinical trials. Although there is a strong need for new or additional therapeutic strategies in the treatment of malignant gliomas, and although local delivery of chemotherapy in those tumors might be a powerful tool, local therapy is used only sporadically nowadays. Thus, we have to learn from our mistakes in the past and we strongly encourage future developments in this field.

Locoregional drug delivery using image-guided intra-arterial drug eluting bead therapy

Lipiodol-based transarterial chemoembolization (TACE) has been performed for over 3 decades for the treatment of solid tumors and describes the infusion of chemotherapeutic agents followed by embolization with particles. TACE is an effective treatment for inoperable hepatic tumors, especially hypervascular tumors such as hepatocellular carcinoma. Recently, drug eluting beads (DEBs), in which a uniform embolic material is loaded with a drug and delivered in a single image-guided step, have been developed to reduce the variability in a TACE procedure. DEB-TACE results in localization of drug to targeted tumors while minimizing systemic exposure to chemotherapeutics. Once localized in the tissue, drug is eluted from the DEB in a controlled manner and penetrates hundreds of microns of tissue from the DEB surface. Necrosis is evident surrounding a DEB in tissue days to months after therapy; however, the contribution of drug and ischemia is currently unknown. Future advances in DEB technology may include image-ability, DEB size tailored to tumor anatomy and drug combinations.

Development of a combination drug-eluting bead: towards enhanced efficacy for locoregional tumour therapies

Drug-eluting beads (DEBs) are becoming a mainstay locoregional therapy for hepatic malignancies but are currently loaded with single drugs alone. Here, we wished to prepare DEB containing different drug combinations, to screen their efficacy using an in-vitro cell culture assay and to include any promising combinations that demonstrate additive efficacy in an in-vivo model of locoregional tumour treatment. A modified in-vitro assay was used based upon the use of 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt (MTS) with either HepG2 liver cancer or PSN1 pancreatic cancer cell lines. The comparative cytotoxicity of DEB combinations prepared containing doxorubicin, irinotecan, topotecan and rapamycin was evaluated. Those combinations that demonstrated an additive cytotoxicity effect were investigated in vivo using a nude mouse xenograft model of pancreatic cancer. Although many of the DEB combinations showed either no effect or a slight antagonistic effect, the combination of doxorubicin and rapamycin DEBs demonstrated synergistic activity. On the basis of these findings, a method was developed to prepare a doxorubicin/rapamycin dual-loaded DEB, which was shown to possess the same drug-loading capacities, drug elution properties and HepG2 cell cytotoxicity synergy as the single drug-loaded DEB combination. Evaluation of this dual-loaded combination DEB versus the respective single drug-loaded DEBs in a mouse xenograft model of pancreatic cancer showed an equivalent tumour volume reduction as the doxorubicin DEB, but with less toxicity than the rapamycin DEB. The doxorubicin/rapamycin combination DEB offers great potential for enhanced efficacy in the locoregional treatment of malignant tumours.

Evaluation of biocompatibility and anti-glioma efficacy of doxorubicin and irinotecan drug-eluting bead suspensions in alginate

INTRODUCTION

Chemotherapeutic drug-eluting beads (DEBs) are microspheres that are in clinical use for intraarterial chemoembolisation of liver cancer. Here we report on the biocompatibility and anti-tumour efficacy of DEBs after intratumoral application in a rat BT4Ca glioma model.

METHODS AND RESULTS

Doxorubicin and irinotecan-eluting DEBs were suspended in a Ca(2+)-free aqueous alginate solution that provides a sol-gel transition when injected into the Ca(2+) rich brain tissue. In this way the DEBs are immobilised at the implantation site. Forced elution studies in vitro using a USP-4 flow-through apparatus demonstrated that the alginate excipient helped to reduce the burst effect and rate the elution from the beads. From the in vivo evaluation, doxorubicin DEBs demonstrated a significant local toxicity, while irinotecan-loaded DEBs showed good local tissue compatibility. Doxorubicin at higher concentrations and irinotecan-loaded DEBs were found to decrease tumour volume, increase survival time and decrease the Ki67 proliferation index of the tumour. Doxorubicin was shown by fluorescent microscopy to diffuse into the peritumoral tissue, but also penetrates along white matter tracts, to more distant areas.

DISCUSSION

We conclude that the alginate suspension of irinotecan DEBs can be considered safe and effective in a clinical setting.

A safety and toxicity assessment of the administration of multiple intracerebral injections of irinotecan or doxorubicin drug-eluting beads

OBJECTIVE Previous research in a rat glioma model has shown that the local intratumoral application of polymerbased drug-eluting beads (DEBs) loaded with doxorubicin or irinotecan suppress tumour growth and prolong survival. For translation into a clinical setting, the present experiment investigates in the healthy cat brain the local and systemic toxicity of a multiple injection shot technique. METHODS Three injection shots were placed, each at a 1 cm distance in the frontal lobe. The DEBs were suspended in an aqueous alginate excipient solution, which becomes subject to a sol-gel transition when injected into the Ca(2+)- rich brain tissue environment. Systemic and local side effects were monitored over a period of two weeks. Injection sites were histologically investigated. RESULTS Gelling of the alginate results in the permanent immobilisation of the microspheres at the implantation site. A distinct local cytotoxic effect of doxorubicin was found with intracerebral and intraventricular haemorrhages, and signs of brain tissue necrosis. In cats injected with irinotecan DEBs, such local adverse side effects did not occur. No signs of systemic toxicity were found with both chemotherapeutics. DISCUSSION We conclude that the multiple injection shot technique with irinotecan DEBs meets feasibility criteria and safety requirements for a clinical application.

DC Bead embolic drug-eluting bead: clinical application in the locoregional treatment of tumours

INTRODUCTION

DC Bead is an embolic drug-eluting bead designed to be loaded with chemotherapeutic agents (such as doxorubicin and irinotecan), delivered intra-arterially into tumor blood vessels to block nutrient flow and then to deliver the drug locally in a sustained fashion. This product is finding increasing use in the treatment of patients with both primary and secondary liver cancers.

AREAS COVERED

This review positions DC Bead in the field of targeted embolic drug delivery and with respect to other competitive technologies in the treatment of liver cancer. An overview of the studies that demonstrate the product's performance, safety and efficacy is presented. The clinical application of the doxorubicin loaded DC Bead is firstly reviewed, in the context of treatment of patients with various stages of hepatocellular carcinoma. Its combination with other therapies is also discussed, together with consideration of the treatment of other liver tumors. Secondly, the use of irinotecan loaded DC Bead, primarily for the treatment of colorectal cancer metastases to the liver, but also some additional rare metastases, is summarized.

EXPERT OPINION

An opinion is proffered as to how this technology and its application is evolving, illustrating a move towards synergistic combination therapies and into other cancer indications.

Comparison of DC Bead-irinotecan and DC Bead-topotecan drug eluting beads for use in locoregional drug delivery to treat pancreatic cancer

DC Bead is a drug delivery embolisation system that can be loaded with doxorubicin or irinotecan for the treatment of a variety of liver cancers. In this study we demonstrate that the topoisomerase I inhibitor topotecan hydrochloride can be successfully loaded into the DC Bead sulfonate-modified polyvinyl alcohol hydrogel matrix, resulting in a sustained-release drug eluting bead (DEBTOP) useful for therapeutic purposes. The in vitro drug loading capacity, elution characteristics and the effects on mechanical properties of the beads are described with reference to our previous work with irinotecan hydrochloride (DEBIRI). Results showed that drug loading was faster when the solution was agitated compared to static loading and a maximum loading of ca. 40-45 mg topotecan in 1 ml hydrated beads was achievable. Loading the drug into the beads altered the size, compressibility moduli and colour of the bead. Elution was shown to be reliant on the presence of ions to perform the necessary exchange with the electrostatically bound topotecan molecules. Topotecan was shown by MTS assay to have an IC(50) for human pancreatic adenocarcinoma cells (PSN-1) of 0.22 and 0.27 microM compared to 28.1 and 19.2 microM for irinotecan at 48 and 72 h, respectively. The cytotoxic efficacy of DEBTOP on PSN-1 was compared to DEBIRI. DEPTOP loaded at 6 & 30 mg ml(-1), like its free drug form, was shown to be more potent than DEBIRI of comparable doses at 24, 48 & 72 h using a slightly modified MTS assay. Using a PSN-1 mouse xenograft model, DEBIRI doses of 3.3-6.6 mg were shown to be well-tolerated (even with repeat administration) and effective in reducing the tumour size. DEBTOP however, was lethal after 6 days at doses of 0.83-1.2 mg but demonstrated reasonable efficacy and tolerability (again with repeat injection possible) at 0.2-0.4 mg doses. Care must therefore be taken when selecting the dose of topotecan to be loaded into DC Bead given its greater potency and potential toxicity.