Interstitial Drug Therapy for Brain Tumors: A Case Study

Rationally designed drug delivery systems for the local treatment of resected glioblastoma

Glioblastoma (GBM) is a particularly aggressive brain cancer associated with high recurrence and poor prognosis. The standard of care, surgical resection followed by concomitant radio- and chemotherapy, leads to low survival rates. The local delivery of active agents within the tumor resection cavity has emerged as an attractive means to initiate oncological treatment immediately post-surgery. This complementary approach bypasses the blood-brain barrier, increases the local concentration at the tumor site while reducing or avoiding systemic side effects. This review will provide a global overview on the local treatment for GBM with an emphasis on the lessons learned from past clinical trials. The main parameters to be considered to rationally design fit-of-purpose biomaterials and develop drug delivery systems for local administration in the GBM resection cavity to prevent the tumor recurrence will be described. The intracavitary local treatment of GBM should i) use materials that facilitate translation to the clinic; ii) be characterized by easy GMP effective scaling up and easy-handling application by the neurosurgeons; iii) be adaptable to fill the tumor-resected niche, mold to the resection cavity or adhere to the exposed brain parenchyma; iv) be biocompatible and possess mechanical properties compatible with the brain; v) deliver a therapeutic dose of rationally-designed or repurposed drug compound(s) into the GBM infiltrative margin. Proof of concept with high translational potential will be provided. Finally, future perspectives to facilitate the clinical translation of the local perisurgical treatment of GBM will be discussed.

Nanoplatforms for Targeted Stimuli-Responsive Drug Delivery: A Review of Platform Materials and Stimuli-Responsive Release and Targeting Mechanisms

To achieve the promise of stimuli-responsive drug delivery systems for the treatment of cancer, they should (1) avoid premature clearance; (2) accumulate in tumors and undergo endocytosis by cancer cells; and (3) exhibit appropriate stimuli-responsive release of the payload. It is challenging to address all of these requirements simultaneously. However, the numerous proof-of-concept studies addressing one or more of these requirements reported every year have dramatically expanded the toolbox available for the design of drug delivery systems. This review highlights recent advances in the targeting and stimuli-responsiveness of drug delivery systems. It begins with a discussion of nanocarrier types and an overview of the factors influencing nanocarrier biodistribution. On-demand release strategies and their application to each type of nanocarrier are reviewed, including both endogenous and exogenous stimuli. Recent developments in stimuli-responsive targeting strategies are also discussed. The remaining challenges and prospective solutions in the field are discussed throughout the review, which is intended to assist researchers in overcoming interdisciplinary knowledge barriers and increase the speed of development. This review presents a nanocarrier-based drug delivery systems toolbox that enables the application of techniques across platforms and inspires researchers with interdisciplinary information to boost the development of multifunctional therapeutic nanoplatforms for cancer therapy.

Recent research and development in synthetic polymer-based drug delivery systems

In recent years, there has been increasing recognition that a number of synthetic polymers which have excellent biodegradability and biocompatibility are materials of pharmaceutical importance in the area of drug delivery technology. The aim of this review is to take a closer look at a few synthetic polymer-based drug delivery systems, specially the aliphatic polyesters, polyamides, polyethers, polyorthoesters, polyanhydrides, polyurethanes, hydrogels and dendritic polymers.

The development of polyanhydrides for drug delivery applications

This paper reviews the development of the polyanhydrides as bioerodible polymers for drug delivery applications. The topics include design and synthesis of the polymer, physical properties, techniques to fabricate the polymer into drug delivery devices, evaluation of biocompatibility, and example applications of the polyanhydrides. Discussion of the interrelationship between the physical-chemical properties of the polyanhydrides, fabrication methods, and drug release rates is included. One section is devoted to a case study to provide a historical perspective of the development a polyanhydride-based drug delivery treatment from the conception of the idea to the final stages of human clinical trials. This section includes an outline of the extensive in vitro and in vivo testing that is necessary for development of a new material for biomedical applications.

Enhancement of the stability of BCNU using self-emulsifying drug delivery systems (SEDDS) and in vitro antitumor activity of self-emulsified BCNU-loaded PLGA wafer

The main purpose of this study was to develop self-emulsifying drug delivery systems (SEDDS) for the improvement of the stability of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) after released from poly (D,L-lactide-co-glycolide) (PLGA) wafer and to evaluate its in vitro antitumor activity against 9L gliosarcoma cells. The in vitro stability test of BCNU was characterized by the BCNU amount in phosphate buffered saline (PBS, pH 7.4) at 37 degrees C. SEDDS increased in vitro half-life of BCNU up to 130 min compared to 45 min of intact BCNU. Self-emulsified (SE) BCNU was fabricated into wafers with flat and smooth surface by compression molding. In vitro release of BCNU from SE BCNU-loaded PLGA wafer was prolonged up to 7 days followed first order release kinetics. Beside, the cytotoxicity of SE BCNU-loaded PLGA wafer against 9L gliosarcoma cells was higher than intact BCNU-loaded PLGA wafer which is more susceptible to hydrolysis. SE BCNU degraded much more slowly than the intact BCNU in PLGA matrix at 25 degrees C. These results strongly suggest that the self-emulsion system increased the stability of BCNU after released from PLGA wafer. From these results, it could be expected that the penetration depth of BCNU could be improved in brain tissue using self-emulsion system.

Evaluation of in vitro and in vivo antitumor activity of BCNU-loaded PLGA wafer against 9L gliosarcoma

The purpose of the present study was to develop implantable BCNU-loaded poly(D,L-lactide-co-glycolide) (PLGA) wafer for the controlled release of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and to evaluate its in vitro and in vivo antitumor activity. The release rate of BCNU from PLGA wafer increased with the increase of BCNU amount loaded and the release was continued until 7 days. In vitro and in vivo antitumor activity of BCNU-loaded PLGA wafer was investigated using in vitro cytotoxicity against 9L gliosarcoma cells and a subcutaneous (s.c.) solid tumor model of 9L gliosarcoma, respectively. The wafers containing BCNU showed more effective cytotoxicity than BCNU powder due to its short half-life and inhibited the proliferation of 9L gliosarcoma cells. BCNU-loaded PLGA wafer delayed the growth of the tumors significantly and increasing the dose of BCNU in the wafer resulted in a substantial regression of the tumor. These results of antitumor activity of BCNU-loaded PLGA wafer demonstrate the feasibility of the wafers for clinical application.

Role of polyanhydrides as localized drug carriers

Many drugs that are administered in an unmodified form by conventional systemic routes fail to reach target organs in an effective concentration, or are not effective over a length of time due to a facile metabolism. Various types of targeting delivery systems and devices have been tried over a long period of time to overcome these problems. Targeted delivery or localized drug delivery offers an advantage of reduced body burden and systemic toxicity of the drugs, especially useful for highly toxic drugs like anticancer agents. Local drug delivery via polymer is a simple approach and hypothesized to avoid the above stated problems. Polyanhydrides are a unique class of polymer for drug delivery because some of them demonstrate a near zero order drug release and relatively rapid biodegradation in vivo. Further, the release rate of polyanhydride fabricated device can be altered over a thousand fold by simple changes in the polymer backbone. Hence, these are one of the best-suited polymers for drug delivery, with biodegradability and biocompatibility. The review focuses on the advantages of polyanhydride carriers in localized drug delivery along with their degradability behavior, toxicological profile and role in various disease conditions.

BCNU-loaded poly(D, L-lactide-co-glycolide) wafer and antitumor activity against XF-498 human CNS tumor cells in vitro

Implantable polymeric device that can release chemotherapeutic agent directly into central nervous system (CNS) has had an impact on malignant glioma therapy. The purpose of our study was to develop an implantable polymeric device, which can release intact 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) for long-term period over 1 month, and to evaluate its cytotoxicity against XF 498 human CNS tumor cells in vitro. BCNU was incorporated into biodegradable poly(D,L-lactide-co-glycolide) (PLGA), by using spray-drying method. BCNU-loaded PLGA microparticles were characterized by scanning electron microscopy (SEM), powder X-ray diffraction, and differential scanning calorimetry. SEM observation of the microparticles showed that the microparticles were spherical, i.e. microspheres. Homogeneous distribution of BCNU in PLGA microsphere was confirmed by significant reduction of crystallinity of BCNU. Microspheres were fabricated into wafers with flat and smooth surface by direct compression method. In vitro release of BCNU in pH 7.4 phosphate buffered saline was prolonged up to 8 weeks after short initial burst period. Antitumor activity of BCNU-loaded PLGA wafer against XF 498 human CNS tumor cells continued over 1 month and, PLGA only did not affect the growth of the cells. Meanwhile, the cytotoxic activity of BCNU powder disappeared within 12 h. These results strongly suggest that the BCNU/PLGA formulations increase release period of carmustine in vivo and also be useful in the development of implantable polymeric device for malignant glioma.

Pharmacokinetics of the carmustine implant

Controlled release delivery of carmustine from biodegradable polymer wafers was approved as an adjunct to surgical resection in the treatment of recurrent glioblastoma multiforme after it was shown in clinical trials to be well tolerated and effective. Given the localised nature of the drug in the brain tissue, no direct pharmacokinetic measurements have been made in humans after implantation of a carmustine wafer. However, drug distribution and clearance have been extensively studied in both rodent and non-human primate brains at various times after implantation. In addition, studies to characterise the degradation of the polymer matrix, the release kinetics of carmustine and the metabolic fate of the drug and polymer degradation products have been conducted both in vitro and in vivo. GLIADEL wafers have been shown to release carmustine in vivo over a period of approximately 5 days; when in continuous contact with interstitial fluid, wafers should degrade completely over a period of 6 to 8 weeks. Metabolic elimination studies of the polymer degradation products have demonstrated that sebacic acid monomers are excreted from the body in the form of expired CO(2), whereas 1,3-bis-(p-carboxyphenoxy)propane monomers are excreted primarily through the urine. Carmustine degradation products are also excreted primarily through the urine. Pharmacokinetic studies in animals and associated modelling have demonstrated the capability of this modality to produce high dose-delivery (millimolar concentrations) within millimetres of the polymer implant, with a limited penetration distance of carmustine from the site of delivery. The limited spread of drug is presumably due to the high transcapillary permeability of this lipophilic molecule. However, the presence of significant convective flows due to postsurgical oedema may augment the diffusive transport of drug in the hours immediately after wafer implantation, leading to a larger short-term spread of drug. Additionally, in non-human primates, the presence of significant doses in more distant regions of the brain (centimetres away from the implant) has been shown to persist over the course of a week. The drug in this region was presumed to be transported from the implant site by either cerebral blood flow or cerebrospinal fluid flow, suggesting that although drug is able to penetrate the blood-brain barrier at the site of delivery, it may re-enter within the confines of the brain tissue.

FTIR-ATR spectroscopy for monitoring polyanhydride/anhydride-amine reactions

The reactivity of 1,3-bis(p-carboxyphenoxy) propane:sebacic acid anhydride copolymer (CPPSA1:6), myristic and benzoic anhydrides with amine nucleophiles were investigated in non-polar solvents. FTIR-ATR (attenuated total reflectance) spectroscopy was used to monitor the polyanhydride/anhydride reaction rates in dichloromethane, dichloroethane, chloroform, and 1,4-dioxane solutions at room temperature. The reaction kinetics was determined by measuring the anhydride peak loss with time. Aminolysis resulted from nucleophilic attack of the added amine on the carbonyl group of the anhydride moiety. Primary and secondary amines reacted to form amides and the reaction followed second-order kinetics. Second-order rate constants and reaction half-life (t(1/2)) were calculated from the semilog plots of [anhydride]/[amine] in 1,4-dioxane at room temperature. The aminolysis rate decreased with pK(a) of the amine reactant, and half-life (t(1/2)) decreased with increasing amine concentration, as expected. With trifluoroethylamine (pK(a) 5.8), myristic anhydride reacted about 6-fold faster than benzoic anhydride. The lower reaction rate of benzoic anhydride was due to the higher stability of the aromatic anhydride compared to aliphatic. The overall CPPSA1:6 copolymer reactivity was the sum of aliphatic-aliphatic (SA-SA), aliphatic-aromatic (SA-CPP), and aromatic-aromatic (CPP-CPP) anhydride linkage reactivities. Based on the monomer ratio, the probability of SA-SA, SA-CPP, and CPP-CPP dyads were calculated to be 0.74, 0.24, and 0.02, respectively. This indicated that CPPSA1:6 reactivity will mainly result from SA-SA and SA-CPP linkages. The second-order rate constants and t(1/2) obtained for CPPSA1:6 with TFEA were closer to those for myristic anhydride than benzoic anhydride with TFEA.

Sustained-release butorphanol microparticles

Various butorphanol-loaded microparticles have been prepared with a biodegradable copolymer P(FAD-SA) of erucic acid dimer (FAD) and sebacic acid (SA) and a copolymer P(CPP-SA) of carboxyphenoxypropane (CPP) and SA using a melt compounding and milling method. Drug release was measured in vitro following incubation of drug-loaded microparticles in water for injection at 37 degrees C. It was found that butorphanol was released in a sustained manner, yielding a cumulative drug release of about 100% over a period of 48 hr. Also, drug release was affected by drug loading and the size of the microparticles; however, it was not significantly influenced by the copolymer composition. Scanning electron microscopic (SEM) results showed that most of the particles were irregular in shape with uneven surfaces. The molecular weights of the copolymers were not changed after this fabrication process. In addition, 20% butorphanol-encapsulated microspheres were prepared with copolymer P(FAD-SA) by spray-drying. The SEM micrograph shows that the particle sizes of the microspheres ranged from 2 to 10 microns, and the external surfaces appear smooth. Moreover, rapid drug release was observed for these microspheres, with more than 92% of the encapsulated drug released within the first 2 hr.

Biodegradable cisplatin microspheres for direct brain injection: preparation and characterization

The objectives of the present study were to prepare cisplatin loaded-PLGA microspheres that are suitable for direct brain injection and to characterize them in terms of their physicochemical properties, in vitro drug release, and self-removal mechanism. The microspheres were prepared by emulsification/solvent evaporation method using PLGA (50:50) as the biodegradable matrix forming polymer. The physicochemical characterization encompassed the following: surface morphology, particle size, entrapment efficiency, surface area, and density. The in vitro release and in vitro degradation studies were performed in phosphate buffer and in 10% rat brain preparation. SEM micrographs revealed that the microspheres have a rough porous surface and a smooth interior. Particle size typically ranged from 180 to 250 microns with an average of 230 T microns. Entrapment efficiency was approximately 70% and was found to be dependent on the particle size. Surface area and density ranged from 0.038 to 0.025 m2/g and from 1.44 to 1.39 g/cm3, respectively. Both were also dependent on particle size. In the in vitro release study in phosphate buffer, approximately 80% of cisplatin was released over 30 days, after which the release rate plateaued. The release profile in 10% rat brain preparation was comparable in shape to that obtained in phosphate buffer. However, the release rate was lower and the total amount released by the end of the study was only 55% of the total cisplatin content. The degradation of PLGA microspheres in phosphate buffer and in rat brain homogenate correlated well with the respective release profiles. Based on the evidence of self-removal and the sustained release of cisplatin for over a month, cisplatin-loaded PLGA microspheres may be useful for local delivery to brain tumors.

Controlled release of macromolecules from a degradable polyanhydride matrix

Polymeric matrices that slowly release macromolecules may be useful for the controlled delivery of proteins or polymer-drug conjugates for targeted drug delivery. Solid particles of fluorescein and fluorescently-labeled, size-fractionated dextran (4000-150,000 number average molecular weight) were dispersed in degradable polyanhydride matrices composed of a 1:1 copolymer of fatty acid dimers and sebacic acid. The release of macromolecules from the polymer matrix into buffered saline was measured; changes in the polymer during immersion were monitored by infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy. Although significant hydrolysis of the polymer occurred within the first day, the matrices remained intact and water-soluble tracers were slowly released for several days. During polymer hydrolysis and erosion, micron-sized pores developed throughout the 2 mm thick polymer matrix, permitting water penetration into the matrix and tracer diffusion out of the matrix. The rate of tracer release from the matrix depended on tracer particle size; rates of fluorescein isothiocyanate dextran release were controlled by adjusting the size of particles dispersed in the matrix.

In vivo versus in vitro degradation of controlled release polymers for intracranial surgical therapy

Intracranial studies to analyze the degradation kinetics of the bioerodible polymer poly[bis(p-carboxyphenoxy)propane-sebacic acid] [p(CPP-SA) 20:80] copolymer wafers were conducted in a rat model. Rats were separated into four groups: those receiving 1) polymer, 2) polymer loaded with the chemotherapeutic agent BCNU, 3) drug-loaded polymer with previous tumor implantation, and 4) polymer and an absorbable hemostatic material. A polymer wafer was surgically implanted into the brain of each animal. Residual polymer was harvested at varying times for chromatographic analysis. In vitro effects of pH, mixing, and water availability on degradation were also studied. The results of in vitro and in vivo studies were compared to understand the behavior of polymers in a clinical setting. We found that degradation of p(CPP-SA) initially occurred more slowly in vivo than in vitro. The presence of BCNU, tumor, and absorbable hemostatic material did not affect the ultimate time of polymer degradation in vivo, and the intrinsic polymer degradation time of 1 mm thick p(CPP-SA) 20:80 disks in vivo was 6-8 weeks.