Treatment of intracranial rat glioma model with implant of radiosensitizer and biomodulator drug combined with external beam radiotherapy

Implantable and transdermal polymeric drug delivery technologies for the treatment of central nervous system disorders

The complexity of the brain and the membranous blood-brain barrier (BBB) has proved to be a significant limitation to the systemic delivery of pharmaceuticals to the brain rendering them sub-therapeutic and ineffective in the treatment of neurological diseases. Apart from this, lack of innovation in product development to counteract the problem is also a major contributing factor to a poor therapeutic outcome. Various innovative strategies show potential in treating some of the neurological disorders; however, drug delivery remains the most popular. To attain therapeutic drug levels in the central nervous system, large, intolerable systemic doses are generally administered. The major factors responsible for the success maintenance therapy of neurological diseases included controlled and sustained release of neurotherapeutics, reduced frequency of administration, higher bioavailability, and patient compliances. Conventional oral or injectable formulations cannot satisfy all the requirements in many circumstances. This article reviews the therapeutic implantable polymeric and transdermal devices employed in an attempt to effectively achieve therapeutic quantities of drug across the BBB over a prolonged period, to improve patient disease prognosis.

DNA Distortion Caused by Uracil-Containing Intrastrand Cross-Links

Four uracil-containing intrastrand cross-links have been detected in human cells upon UV irradiation of 5-bromouracil-containing DNA, namely 5'-G[8-5]U-3', 5'-U[5-8]G-3', 5'-A[8-5]U-3', and 5'-A[2-5]U-3'. These lesions feature unique composition and connectivity compared with other intrastrand cross-links reported in the literature. For the first time, structural information obtained using molecular dynamics (MD) simulations reveal that all four lesions distort the DNA helix, which can involve an extrahelical location of the cross-link, changes in the helical interactions of the complementary nucleotides, or disruption of hydrogen bonding in the flanking base pairs up to two positions from the cross-linked site; however, the degree of distortion varies between the cross-links, being affected by the sequence, nucleobase-nucleobase connectivity, and the purine involved. Most importantly, the relative distortion of the damaged DNA provides the first structural explanation for the observed abundances of the four uracil-containing cross-links. Furthermore, the highly distorted conformations suggest that these lesions will likely have severe implications for DNA replication and repair processes in cells.

Glucose transporter and folic acid receptor-mediated Pluronic P105 polymeric micelles loaded with doxorubicin for brain tumor treating

In this study, glucose transporter and folic acid (FA) receptor-mediated Pluronic P105 polymeric micelles loaded with DOX (GF-DOX) were prepared for enhancing the blood-brain barrier (BBB) transportation and improving the drug accumulation in the glioma cells. The pH-triggered DOX release of GF-DOX indicating a comparatively fast drug release at weak acidic condition and stable state of the carrier at physiological environment. The transport of GF-DOX across the in vitro BBB model showed that GF-DOX exhibited higher BBB transportation ability with the transporting ratio of 21.47% in 4 h. The carrier was internalized into C6 glioma cells upon crossing the BBB model for the combined effect of the brain targeting by transportation of glucose transporter and active tumor cell targeting by FA receptor-mediated endocytosis. Moreover, minimized weight changes and high suppression ratio of tumor growth were observed after intravenous injection of GF-DOX. In conclusion, the glucose transporter and FA dual-targeting micelles would provide a safe and effective strategy for new modalities to treat brain tumor.

Targeted therapy for glioma using cyclic RGD-entrapped polyionic complex nanomicelles

BACKGROUND

The purpose of this study was to test the efficacy of cyclic Arg-Gly-Asp (RGD) peptide conjugated with polyionic complex nanomicelles as targeted therapy for glioma.

METHODS

A stable cyclic RGD polyionic complex nanostructure, ie, a c(RGDfC) polyionic complex micelle, was synthesized and its biocompatibility with cultured neurons was assessed using a cell viability assay. Targeted binding to cultured glioma cells was evaluated by the CdTe quantum dot marking technique and a cell viability assay. The inhibitory effect of the nanomicelles against glioma cells was also evaluated, and their targeted migration into rat brain glioma cells and apoptotic effects were traced by the CdTe quantum dot marking and immunohistochemical staining.

RESULTS

c(RGDfC) polyionic complex micelles did not affect the growth of neurons but bonded selectively to and inhibited proliferation of glioma cells in vitro. When tested in vivo, the micelles migrated into glioma cells, inducing apoptosis in the rat brain.

CONCLUSION

The c(RGDfC) polyionic complex micelle is an effective targeted therapy against glioma.

Formation mechanism and structure of a guanine-uracil DNA intrastrand cross-link

The formation and structure of the 5'-G[8-5]U-3' intrastrand cross-link are studied using density functional theory and molecular dynamics simulations due to the potential role of this lesion in the activity of 5-halouracils in antitumor therapies. Upon UV irradiation of 5-halouracil-containing DNA, a guanine radical cation reacts with the uracil radical to form the cross-link, which involves phosphorescence or an intersystem crossing and a rate-determining step of bond formation. Following ionizing radiation, guanine and the uracil radical react, with a rate-limiting step involving hydrogen atom removal. Although cross-link formation from UV radiation is favored, comparison of calculated reaction thermokinetics with that for related experimentally observed purine-pyrimidine cross-links suggests this lesion is also likely to form from ionizing radiation. For the first time, the structure of 5'-G[8-5]U-3' within DNA is identified by molecular dynamics simulations. Furthermore, three conformations of cross-linked DNA are revealed, which differ in the configuration of the complementary bases. Distortions, such as unwinding, are localized to the cross-linked dinucleotide and complementary nucleotides, with minimal changes to the flanking bases. Global changes to the helix, such as bending and groove alterations, parallel cisplatin-induced distortions, which indicate 5'-G[8-5]U-3', may contribute to the cytotoxicity of halouracils in tumor cell DNA using similar mechanisms.

DNA damage and interstrand cross-link formation upon irradiation of aryl iodide C-nucleotide analogues

The 5-halopyrimidine nucleotides damage DNA upon UV-irradiation or exposure to gamma-radiolysis via the formation of the 2'-deoxyuridin-5-yl sigma-radical. The bromo and iodo derivatives of these molecules are useful tools for probing DNA structure and as therapeutically useful radiosensitizing agents. A series of aryl iodide C-nucleotides were incorporated into synthetic oligonucleotides and exposed to UV-irradiation and gamma-radiolysis. The strand damage produced upon irradiation of DNA containing these molecules is consistent with the generation of highly reactive sigma-radicals. Direct stand breaks and alkali-labile lesions are formed at the nucleotide analogue and flanking nucleotides. The distribution of lesion type and location varies depending upon the position of the aryl ring that is iodinated. Unlike 5-halopyrimidine nucleotides, the aryl iodides produce interstrand cross-links in duplex regions of DNA when exposed to gamma-radiolysis or UV-irradiation. Quenching studies suggest that cross-links are produced by gamma-radiolysis via capture of a solvated electron, and subsequent fragmentation to the sigma-radical. These observations suggest that aryl iodide C-nucleotide analogues may be useful as probes for excess electron transfer and radiosensitizing agents.

Biological in situ dose painting for image-guided radiation therapy using drug-loaded implantable devices

PURPOSE

Implantable devices routinely used for increasing spatial accuracy in modern image-guided radiation treatments (IGRT), such as fiducials or brachytherapy spacers, encompass the potential for in situ release of biologically active drugs, providing an opportunity to enhance the therapeutic ratio. We model this new approach for two types of treatment.

METHODS AND MATERIALS

Radiopaque fiducials used in IGRT, or prostate brachytherapy spacers ("eluters"), were assumed to be loaded with radiosensitizer for in situ drug slow release. An analytic function describing the concentration of radiosensitizer versus distance from eluters, depending on diffusion-elimination properties of the drug in tissue, was developed. Tumor coverage by the drug was modeled for tumors typical of lung stereotactic body radiation therapy treatments for various eluter dimensions and drug properties. Six prostate (125)I brachytherapy cases were analyzed by assuming implantation of drug-loaded spacers. Radiosensitizer-induced subvolume boost was simulated from which biologically effective doses for typical radiosensitizers were calculated in one example.

RESULTS

Drug distributions from three-dimensional arrangements of drug eluters versus eluter size and drug properties were tabulated. Four radiosensitizer-loaded fiducials provide adequate radiosensitization for approximately 4-cm-diameter lung tumors, thus potentially boosting biologically equivalent doses in centrally located stereotactic body treated lesions. Similarly, multiple drug-loaded spacers provide prostate brachytherapy with flexible shaping of "biologically equivalent doses" to fit requirements difficult to meet by using radiation alone, e.g., boosting a high-risk region juxtaposed to the urethra while respecting normal tissue tolerance of both the urethra and the rectum.

CONCLUSIONS

Drug loading of implantable devices routinely used in IGRT provides new opportunities for therapy modulation via biological in situ dose painting.

188Re-loaded lipid nanocapsules as a promising radiopharmaceutical carrier for internal radiotherapy of malignant gliomas

PURPOSE

Lipid nanocapsules (LNC) entrapping lipophilic complexes of (188)Re ((188)Re(S(3)CPh)(2)(S(2)CPh) [(188)Re-SSS]) were investigated as a novel radiopharmaceutical carrier for internal radiation therapy of malignant gliomas. The present study was designed to evaluate the efficacy of intra-cerebral administration of (188)Re-SSS LNC by means of convection-enhanced delivery (CED) on a 9L rat brain tumour model.

METHODS

Female Fischer rats with 9L glioma were treated with a single injection of (188)Re-SSS LNC by CED 6 days after cell implantation. Rats were put into random groups according to the dose infused: 12, 10, 8 and 3 Gy in comparison with blank LNC, perrhenate solution (4 Gy) and non-treated animals. The radionuclide brain retention level was evaluated by measuring (188)Re elimination in faeces and urine over 72 h after the CED injection. The therapeutic effect of (188)Re-SSS LNC was assessed based on animal survival.

RESULTS

CED of (188)Re perrhenate solution resulted in rapid drug clearance with a brain T (1/2) of 7h. In contrast, when administered in LNC, (188)Re tissue retention was greatly prolonged, with only 10% of the injected dose being eliminated at 72 h. Rat median survival was significantly improved for the group treated with 8 Gy (188)Re-SSS LNC compared to the control group and blank LNC-treated animals. The increase in the median survival time was about 80% compared to the control group; 33% of the animals were long-term survivors. The dose of 8 Gy proved to be a very effective dose, between toxic (10-12 Gy) and ineffective (3-4 Gy) doses.

CONCLUSIONS

These findings show that CED of (188)Re-loaded LNC is a safe and potent anti-tumour system for treating malignant gliomas. Our data are the first to show the in vivo efficacy of (188)Re internal radiotherapy for the treatment of brain malignancy.

Carmustine wafers: localized delivery of chemotherapeutic agents in CNS malignancies

High-grade glioma is a devastating disease that leaves the majority of its victims dead within 2 years. To meaningfully increase survival, a trimodality approach of surgery, radiation, and chemotherapy is needed. Carmustine (1,3-bis (2-chloroethyl)-1-nitrosourea) is a nitrosourea alkylating agent that exerts its antitumor effect by akylating DNA and RNA. Systemic administration of nitrosoureas as a single agent or as part of procarbazine/3-cyclohexyl-1-nitroso-urea/vincristine has demonstrated little efficacy in the treatment of high-grade glioma. The development of carmustine wafers (Gliadel((R)) Wafer) as a method for controlled released delivery of carmustine from biodegradable polymer wafers enhances the therapeutic ratio by fully containing the drug within the confines of the brain tumor environment while minimizing systemic toxicities. Preclinical and clinical studies have proven the safety and efficacy of Gliadel in the management of glioblastoma. From these results, Gliadel is currently approved for use in patients with recurrent glioblastoma as an adjunct to surgery and in newly diagnosed patients with high-grade glioma as an adjunct to surgery and radiation. Other promising advances in the use of locally delivered chemotherapy for CNS malignancies, including Gliadel for brain metastases and combination therapies with systemic or biologic agents, are discussed.

Antitumor efficacy and local distribution of doxorubicin via intratumoral delivery from polymer millirods

The purpose of this study was to evaluate the antitumor efficacy and local drug distribution from doxorubicin-containing poly(D,L-lactide-co-glycolide) (PLGA) implants for intratumoral treatment of liver cancer in a rabbit model. Cylindrical polymer millirods (length 8 mm, diameter 1.5 mm) were produced using 65% PLGA, 21.5% NaCl, and 13.5% doxorubicin. These implants were placed in the center of VX2 liver tumors (n = 16, 8 mm in diameter) in rabbits. Tumors were removed 4 and 8 days after millirod implantation, and antitumor efficacy was assessed using tumor size measurements, tumor histology, and fluorescent measurement of drug distribution. The treated tumors were smaller than the untreated controls on both day 4 (0.17 +/- 0.06 vs. 0.31 +/- 0.08 cm(2), p = 0.048) and day 8 (0.14 +/- 0.04 vs. 1.8 +/- 0.8 cm(2), p = 0.025). Drug distribution profiles demonstrated high doxorubicin concentrations (>1000 microg/g) at the tumor core at both time points and drug penetration distances of 2.8 and 1.3 mm on day 4 and 8, respectively. Histological examination confirmed necrosis throughout the tumor tissue. Biodegradable polymer millirods successfully treated the primary tumor mass by providing high doxorubicin concentrations to the tumor tissue over an eight day period.

Detailed characterization of the mouse glioma 261 tumor model for experimental glioblastoma therapy

Mouse glioma 261 (Gl261) cells are used frequently in experimental glioblastoma therapy; however, no detailed description of the Gl261 tumor model is available. Here we present that Gl261 cells carry point mutations in the K-ras and p53 genes. Basal major histocompatibility complex (MHC)I, but not MHCII, expression was detected in Gl261 cells. The introduction of interferon-gamma-encoding genes increased expression of both MHCI and MHCII. A low amount of B7-1 and B7-2 RNA was detected in wild-type cells, but cytokine production did not change expression levels. Gl261 cells were transduced efficiently by adenoviral vectors; the infectivity of retroviral vectors was limited. Low numbers of transplanted Gl261 cells formed both subcutaneous and intracranial tumors in C57BL/6 mice. The cells were moderately immunogenic: prevaccination of mice with irradiated tumor cells 7 days before intracranial tumor challenge prevented tumor formation in approximately 90% of mice. When vaccination was carried out on the day or 3 days after tumor challenge, no surviving animals could be found. In vitro-growing cells were radiosensitive: less than 2 Gy was required to achieve 50% cell mortality. Local tumor irradiation with 4 Gy X-rays in brain tumor-bearing mice slowed down tumor progression, but none of the mice were cured off the tumor. In conclusion, the Gl261 brain tumor model might be efficiently used to study the antitumor effects of various therapeutic modalities, but the moderate immunogenicity of the cells should be considered.

Barriers to carrier mediated drug and gene delivery to brain tumors

Brain tumor patients face a poor prognosis despite significant advances in tumor imaging, neurosurgery and radiation therapy. Potent chemotherapeutic drugs fail when used to treat brain tumors because biochemical and physiological barriers limit drug delivery into the brain. In the past decade a number of strategies have been introduced to increase drug delivery into the brain parenchyma. In particular, direct drug administration into the brain tumor has shown promising results in both animal models and clinical trials. This technique is well suited for the delivery of liposome and polymer drug carriers, which have the potential to provide a sustained level of drug and to reach cellular targets with improved specificity. We will discuss the current approaches that have been used to increase drug delivery into the brain parenchyma in the context of fluid and solute transport into, through and from the brain, with a focus on liposome and polymer drug carriers.

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.