Enhancing the cytotoxicity of chemoradiation with radiation-guided delivery of anti-MGMT morpholino oligonucleotides in non-methylated solid tumors.

The DNA repair enzyme O6-methylguanine DNA methyltransferase (MGMT) is epigenetically silenced in some tumors by MGMT gene promoter methylation. MGMT-hypermethylated solid tumors have enhanced susceptibility to the cytotoxic effects of alkylating chemotherapy such as temozolomide, compared with non-methylated tumors. In glioblastoma, subjects with MGMT hypermethylation have significantly longer survival rates after chemoradiotherapy. We report the first successful use of a non-ablative dose of ionizing radiation to prime human cancer cells to enhance the uptake of unmodified anti-MGMT morpholino oligonucleotide (AMON) sequences. We demonstrate >40% reduction in the in vitro proliferation index and cell viability in radiation-primed MGMT-expressing human solid tumor cells treated with a single dose of AMONs and temozolomide. We further demonstrate the feasibility of using a non-ablative dose of radiation in vivo to guide and enhance the delivery of intravenously administered AMONs to achieve 50% MGMT knockdown only at radiation-primed tumor sites in a subcutaneous tumor model. Local upregulation of physiological endocytosis after radiation may have a role in radiation-guided uptake of AMONs. This approach holds direct translational significance in glioblastoma and brain metastases where radiation is part of the standard of care; our approach to silence MGMT could overcome the significant problem of MGMT-mediated chemoresistance.

Therapeutic efficacy of aortic administration of N-acetylcysteine as a chemoprotectant against bone marrow toxicity after intracarotid administration of alkylators, with or without glutathione depletion in a rat model.

Modulation of thiol levels may alter both the efficacy and toxicity of chemotherapeutic agents. We investigated cytoenhancement, using L-buthionine-[S,R]-sulfoximine (BSO) to reduce cellular glutathione levels prior to intracarotid alkylator administration. We also evaluated chemoprotection against chemotherapy-induced systemic toxicity when the thiol agents N-acetylcysteine (NAC) and sodium thiosulfate were administered into the descending aorta to limit brain delivery. BSO treatment reduced rat brain and intracerebral tumor glutathione levels by 50-65%, equivalent to the reduction in liver and s.c. tumor. BSO treatment significantly enhanced the toxicity of chemotherapy with carboplatin, melphalan, and etoposide phosphate against granulocytes, total white cells, and platelets. Intracarotid administration of NAC resulted in high delivery to the brain, whereas infusion via the descending aorta minimized brain delivery. When NAC, with or without sodium thiosulfate, was administered via aortic infusion prior to chemotherapy, the magnitude of the bone marrow toxicity nadir was minimized, even with BSO-enhanced myelosuppression. Thus, BSO depleted brain and brain tumor glutathione but thereby increased chemotherapy-induced myelosuppression. Surprisingly, although NAC was found to readily cross the blood-brain barrier when given into the carotid artery, aortic infusion of NAC resulted in minimal exposure to the central nervous system (CNS) vasculature because of rapid clearance. As a result, aortic infusion of NAC to perfuse bone marrow and minimize myelosuppression and toxicity to visceral organs could be performed without interfering with the CNS cytotoxicity of intracarotid alkylators, even after BSO depletion of CNS glutathione.

Delayed administration of sodium thiosulfate in animal models reduces platinum ototoxicity without reduction of antitumor activity.

Platinum-based chemotherapeutic agents, such as carboplatin and cisplatin, are effective against many human tumors, but their use may be limited by a high incidence of ototoxicity. Delayed administration of the chemoprotective agent sodium thiosulfate (STS) reduces the ototoxicity of carboplatin in a guinea-pig model, when given up to 8 h after the chemotherapy, and also reduces hearing loss in patients given carboplatin with osmotic blood-brain barrier opening for treatment of brain tumors. We tested whether STS, given at times that achieved otoprotection, could impact the chemotherapeutic efficacy of carboplatin. The impact of STS was evaluated by measuring the onset of growth of LX-1 human small cell lung carcinoma s.c. xenografts in the nude rat. When STS was administered as two boluses, 2 and 6 h after treatment with carboplatin and etoposide, there was a decrease in the time to tumor progression. In contrast, when STS administration was delayed until 8 h after carboplatin/etoposide, there was no reduction in the antitumor cytotoxicity of the chemotherapy. STS infusion did not significantly affect ultrafilterable platinum pharmacokinetics in the guinea pig. To explore the potential wider applicability of STS, in a pilot study we tested its efficacy against cisplatin ototoxicity. Delayed administration of STS, 2 h after cisplatin, was protective against cisplatin-induced ototoxicity in the guinea pig model, as determined by electrophysiological measures. On the basis of these data, we suggest that delayed administration of STS may provide a mechanism to reduce the ototoxicity caused by administration of carboplatin or cisplatin for both central nervous system and systemic cancer chemotherapy.

The influence of anesthetic choice, PaCO2, and other factors on osmotic blood-brain barrier disruption in rats with brain tumor xenografts.

UNLABELLED: Increasing the delivery of therapeutic drugs to the brain improves outcome for patients with brain tumors. Osmotic opening of the blood-brain barrier (BBB) can markedly increase drug delivery, but achieving consistent, good quality BBB disruption (BBBD) is essential. We evaluated four experiments compared with our standard isoflurane/O2 protocol to improve the quality and consistency of BBBD and drug delivery to brain tumor and normal brain in a rat model. Success of BBBD was assessed qualitatively with the large molecular weight marker Evans blue albumin and quantitatively by measuring delivery of the low molecular weight marker [3H]-methotrexate. With isoflurane/O2 anesthesia, the effects of two BBBD drugs of different osmolalities were evaluated at two different infusion rates and infusion durations. Arabinose was superior to saline (P = 0.006) in obtaining consistent Evans blue staining in 16 of 24 animals, and it significantly increased [3H]-methotrexate delivery compared with saline in the tumor (0.388 +/- 0.03 vs 0.135 +/-0.04; P = 0.0001), brain around the tumor (0.269 +/- 0.03 vs 0.035 +/- 0.03; P = 0.0001), brain distant to the tumor (0.445 +/- 0.05 vs 0.034 +/- 0.07; P = 0.001), and opposite hemisphere (0.024 +/- 0.00 vs 0.016 +/- 0.00; P = 0.0452). Forty seconds was better than 30 s (P = 0.0372) for drug delivery to the tumor. Under isoflurane/O2 anesthesia (n = 30), maintaining hypocarbia was better than hypercarbia (P = 0.025) for attaining good BBBD. A propofol/ N2O regimen was compared with the isoflurane/O2 regimen, altering blood pressure, heart rate, and PaCO2 as covariates (n = 48). Propofol/N2O was superior to isoflurane/O2 by both qualitative and quantitative measures (P < 0.0001). Neurotoxicity and neuropathology with the propofol/N2O regimen was evaluated, and none was found. These data support the use of propofol/N2O along with maintaining hypocarbia to optimize BBBD in animals with tumors. IMPLICATIONS: Propofol/N2O anesthesia may be better than isoflurane/O2 for optimizing osmotic blood-brain barrier disruption for delivery of chemotherapeutic drugs to brain tumor and normal brain.

A physiological barrier distal to the anatomic blood-brain barrier in a model of transvascular delivery.

BACKGROUND AND PURPOSE: Osmotic disruption of the blood-brain barrier (BBB) provides a method for transvascular delivery of therapeutic agents to the brain. The apparent global delivery of viral-sized iron oxide particles to the rat brain after BBB opening as seen on MR images was compared with the cellular and subcellular location and distribution of the particles. METHODS: Two dextran-coated superparamagnetic monocrystalline iron oxide nanoparticle contrast agents, MION and Feridex, were administered intraarterially in rats at 10 mg Fe/kg immediately after osmotic opening of the BBB with hyperosmolar mannitol. After 2 to 24 hours, iron distribution in the brain was evaluated first with MR imaging then by histochemical analysis and electron microscopy to assess perivascular and intracellular distribution. RESULTS: After BBB opening, MR images showed enhancement throughout the disrupted hemisphere for both Feridex and MION. Feridex histochemical staining was found in capillaries of the disrupted hemisphere. Electron microscopy showed that the Feridex particles passed the capillary endothelial cells but did not cross beyond the basement membrane. In contrast, after MION delivery, iron histochemistry was detected within cell bodies in the disrupted hemisphere, and the electron-dense MION core was detected intracellularly and extracellularly in the neuropil. CONCLUSION: MR images showing homogeneous delivery to the brain at the macroscopic level did not indicate delivery at the microscopic level. These data support the presence of a physiological barrier at the basal lamina, analogous to the podocyte in the kidney, distal to the anatomic (tight junction) BBB, which may limit the distribution of some proteins and viral particles after transvascular delivery to the brain.

Improving drug delivery to intracerebral tumor and surrounding brain in a rodent model: a comparison of osmotic versus bradykinin modification of the blood-brain and/or blood-tumor barriers.

OBJECTIVE: To compare transient blood-brain barrier disruption (BBBD) by hypertonic mannitol with pharmacological modification of the blood-tumor barrier by the vasoactive peptide bradykinin for delivery of small and large agents to nude rat intracerebral xenografts. METHODS: Female nude rats (n = 104) with 6-day intracerebral human small cell lung carcinoma tumors were treated using BBBD (n = 24), intracarotid bradykinin (n = 38), or saline (controls, n = 32) administered intra-arterially. During or immediately after infusion, the rats were given radiolabeled agent (methotrexate or dextran 70; Dupont NEN, Boston, MA). The rats were killed 10 minutes later, and samples of tumor and brain regions were obtained for scintillation counting. Twenty-two additional rats were examined using magnetic resonance imaging after administering one of two contrast agents (gadoteridol or iron oxide nanoparticles) or saline (controls) in conjunction with BBBD or bradykinin. RESULTS: After BBBD, the delivery of both small (methotrexate) and large (dextran 70) radiolabeled tracers was increased 2- to 6-fold in the tumor and 3- to 20-fold in surrounding brain, as compared with saline controls. After bradykinin treatment, there was minimal change in delivery of methotrexate or dextran 70 to tumor and brain around tumor, with the greatest increase less than 60% over controls. Magnetic resonance imaging demonstrated increased delivery of both small and large contrast agents to the treated hemisphere after BBBD. In comparison, no increased tumor enhancement could be detected after bradykinin treatment. CONCLUSION: BBBD resulted in global delivery of a variety of agents in a wide range of sizes. In this human brain tumor xenograft model, bradykinin was not effective at increasing delivery to the tumor of any agent tested.

First evidence of otoprotection against carboplatin-induced hearing loss with a two-compartment system in patients with central nervous system malignancy using sodium thiosulfate.

Sodium thiosulfate (STS) provides protection against carboplatin-induced ototoxicity in an animal model. The purpose of this study was to determine the STS dose required for otoprotection, in patients with malignant brain tumors treated with carboplatin in conjunction with osmotic blood-brain barrier disruption. Twenty-nine patients received STS intravenously 2 hr after carboplatin. Doses were escalated from 4 g/m2 to 8, 12, 16 and 20 g/m2 on consecutive months. Audiologic assessment was performed at baseline and monthly. The audiograms were compared with those of 19 similarly treated historical control patients who did not receive STS. The incidence of ototoxicity in the historical control group of patients was 79% (15/19). This group had an average loss of 20.8 +/- 5.9 dB (n = 19) at 8 kHz after one treatment with carboplatin, whereas the STS treatment group lost only 3.7 +/- 2 dB (n = 15) after one treatment. This difference was statistically significant as assessed by Student's t test (P < .05). Furthermore, patients in the STS treatment group with excellent base-line hearing showed little change in hearing thresholds at 8 kHz after the second treatment (8.0 +/- 8.3 dB) (n = 5) compared with the historical control patients with excellent base-line hearing, (40.5 +/- 8.6 dB) (n = 11). Our data support that doses of 16 or 20 g/m2 of STS decrease carboplatin-induced hearing loss without central nervous system entry. Clinical demonstration of an otoprotective effect with a two-compartment system to prevent drug-induced hearing loss, while preserving central nervous system cytotoxicity, has not been reported previously.

Increasing volume of distribution to the brain with interstitial infusion: dose, rather than convection, might be the most important factor.

The volume of distribution in tissue (Vt) that can be achieved by direct interstitial infusion of therapeutic agents into brain is limited. The maintenance of a pressure gradient during interstitial infusion to establish fluid convection has been shown to increase the Vt of small, medium, and large molecules. We have used monocrystalline iron oxide nanocompounds, superparamagnetic particles of sizes the same order of magnitude as virions, to investigate the effect of dose, the volume of infusate, and the time of infusion on the distribution of large molecules in rodent brain. Our initial study in rats (n = 6) replicated the results of a previously described report of convection-enhanced delivery in cats. At a constant rate and concentration, the Vt increased in a linear fashion, proportional to the increases in time, volume, and dose. When using a constant rate and a constant concentration, however, it is unclear which variable or variables (dose, volume, infusion time) have the greatest influence on this effect. Therefore, we assessed each variable independently (n = 12). When the iron dose was increased from 5.3 to 26.5 micrograms, there was a three- to fivefold increase in the Vt, depending on the volume and time of infusion (2 Microliters/20 min, 24 microliters/20 min, or 24 microliters/120 min) (P < 0.001). When the volume of infusate was increased from 2 to 24 microliters, at an infusion time of 20 minutes and a dose of either 5.3 or 26.5 micrograms, there was a 43 or 52% decline in the Vt, respectively (P = 0.018). When the time for the infusion of 24 microliters was increased from 20 to 120 minutes, there was a 79% increase in the Vt at a dose of 26.5 micrograms but no change in the Vt at a dose of 5.3 micrograms. The effect associated with infusion time was not significant (P = 0.113). Magnetic resonance imaging was performed to document the distribution of monocrystalline iron oxide nanocompounds in vivo, and histochemical staining for iron was used to document the distribution of monocrystalline iron oxide nanocompounds in tissue sections. The Vt for both methods was calculated by computer image analysis, and the correlation between magnetic resonance and histological volumes was determined (r2 = 0.93). On the basis of this model, we suggest that dose, rather than convection, might be the most important variable in maximizing the Vt and improved distribution might be achieved by administering an increased concentration of agent.

In vitro and animal studies of sodium thiosulfate as a potential chemoprotectant against carboplatin-induced ototoxicity.

When carboplatin (cis-diammine-1,1-cyclobutane-dicarboxylato-platinum) delivery to brain tumors is optimized with osmotic blood-brain barrier disruption (BBBD), high frequency hearing loss can result. Treatment with sodium thiosulfate (STS) blocked carboplatin cytotoxicity against the LX-1 human small cell lung carcinoma cell line in vitro. STS decreased carboplatin-induced ototoxicity in a guinea pig model, as determined by electrophysiological measurements and analysis of inner ear outer hair cell numbers. Protection was found when STS was administered up to 8 h subsequent to carboplatin but not 24 h after carboplatin. In a rat model of osmotic BBBD, STS was neurotoxic when given immediately after BBBD but not when given 60 min after BBBD, when the barrier is reestablished. Thus, delayed administration of STS may provide a mechanism to reduce the cochlear toxicity caused by BBBD-enhanced carboplatin delivery to the brain.

Comparison of intracerebral inoculation and osmotic blood-brain barrier disruption for delivery of adenovirus, herpesvirus, and iron oxide particles to normal rat brain.

Delivery of adenovirus, herpes simplex virus (HSV), and paramagnetic monocrystalline iron oxide nanoparticles (MION) to rat brain (n = 64) was assessed after intracerebral inoculation or osmotic disruption of the blood-brain barrier (BBB). After intracerebral inoculation, the area of distribution was 7.93 +/- 0.43 mm2 (n = 9) for MION and 9.17 +/- 1.27 mm2 (n = 9) for replication-defective adenovirus. The replication-compromised HSV RH105 spread to 14.00 +/- 0.87 mm2 (n = 8), but also had a large necrotic center (3.54 +/- 0.47 mm2). No infection was detected when virus was administered intra-arterially without hyperosmotic mannitol. After osmotic BBB disruption, delivery of the viruses and MIONs was detected throughout the disrupted cerebral cortex. Positive staining was found in 4 to 845 cells/100 microns thick coronal brain section (n = 7) after adenovirus administration, and in 13 to 197 cells/section (n = 8) after HSV administration. Cells of glial morphology were more frequently stained after administration of adenovirus, whereas neuronal cells were preferentially stained after delivery of both HSV vectors and MION. In a preliminary test of vector delivery in the feline, MION was detected throughout the white matter tracts after inoculation into normal cat brain. Thus MION may be a tool for use in vivo, to monitor the delivery of virus to the central nervous system. Additionally, BBB disruption may be an effective method to globally deliver recombinant viruses to the CNS.

Delivery of herpesvirus and adenovirus to nude rat intracerebral tumors after osmotic blood-brain barrier disruption.

The delivery of viral vectors to the brain for treatment of intracerebral tumors is most commonly accomplished by stereotaxic inoculation directly into the tumor. However, the small volume of distribution by inoculation may limit the efficacy of viral therapy of large or disseminated tumors. We have investigated mechanisms to increase vector delivery to intracerebral xenografts of human LX-1 small-cell lung carcinoma tumors in the nude rat. The distribution of Escherichia coli lacZ transgene expression from primary viral infection was assessed after delivery of recombinant virus by intratumor inoculation or intracarotid infusion with or without osmotic disruption of the blood-brain barrier (BBB). These studies used replication-compromised herpes simplex virus type 1 (HSV; vector RH105) and replication-defective adenovirus (AdRSVlacZ), which represent two of the most commonly proposed viral vectors for tumor therapy. Transvascular delivery of both viruses to intracerebral tumor was demonstrated when administered intraarterially (i.a.) after osmotic BBB disruption (n = 9 for adenovirus; n = 7 for HSV), while no virus infection was apparent after i.a. administration without BBB modification (n = 8 for adenovirus; n = 4 for HSV). The thymidine kinase-negative HSV vector infected clumps of tumor cells as a result of its ability to replicate selectively in dividing cells. Osmotic BBB disruption in combination with i.a. administration of viral vectors may offer a method of global delivery to treat disseminated brain tumors.

White matter changes associated with feline GM2 gangliosidosis (Sandhoff disease): correlation of MR findings with pathologic and ultrastructural abnormalities.

PURPOSE: To establish changes on MR of the brain in a feline model of Sandhoff disease in order to develop standards by which this model may be used in future noninvasive studies. METHODS: Five affected felines and six age-matched, littermate controls were evaluated. T1- and T2-weighted images were obtained once or twice for each of four affected and five control animals at 4 1/2 to 12 weeks of age, for a total of 15 MR examinations. Images were evaluated qualitatively for the pattern of myelination and the size of the ventricular system. After the animals were killed, pathologic specimens of the brain were examined with light and electron microscopy, and pathologic changes were correlated with MR. RESULTS: Compared with control animals, affected animals showed MR evidence of delayed myelination, manifested by white matter signal hypointensity on T1-weighted images and signal hyperintensity on T2-weighted images. This finding was corroborated by histopathologic findings of decreased myelin in the subcortical and internal capsule regions. White matter abnormalities were not detected ultrastructurally in the animals examined. CONCLUSION: Although GM2 gangliosidosis is primarily a neuronal disease, MR imaging can show changes in myelination of white matter tracts that may be secondary to the neuronal damage. This provides a noninvasive method of in vivo monitoring as therapeutic strategies are developed in this animal model.

Gene expression from recombinant viral vectors in the central nervous system after blood-brain barrier disruption.

Direct intracerebral injection of recombinant adenoviral vectors within the brain parenchyma or the ventricular system results in a limited volume of distribution of virus, as demonstrated by transgene expression. Global delivery to the central nervous system may increase the use of these vectors but only if the viral vectors can cross the blood-brain barrier and result in transduction of the underlying cells. This short-term study examines whether osmotic disruption with mannitol can result in sufficient opening of the vascular endothelium to allow for passage of replication-defective adenovirus containing the Escherichia coli beta-galactosidase gene (lacZ). Virus was injected into the carotid artery of rats after blood-brain barrier disruption with intracarotid hypertonic mannitol, and the animals were killed and analyzed after 4 days. Histochemical analysis and electron microscopy confirmed expression of the E. coli lacZ gene in the pericapillary astrocytes of the ipsilateral cerebral cortex and deep grey matter. Furthermore, the extent of gene transfer and expression correlated with the degree of barrier opening, as measured by Evans blue staining. Transgene expression was not seen in control animals that received intracarotid saline before recombinant virus injection. These data demonstrate, for the first time, that blood-brain barrier disruption can allow for the delivery of functional viral vectors to the central nervous system.

Differential permeability of the blood-tumour barrier in intracerebral tumour-bearing rats: antidrug antibody to achieve systemic drug rescue.

The feasibility of utilizing the differential permeability of the blood-tumour barrier to low- vs. high-molecular-weight compounds is demonstrated in a brain tumour model. Nude rats (n = 27) with or without intracerebral tumours received intravenous [3H]methotrexate (M(r) 454), followed 60 min later by antimethotrexate antibody (M(r) 150,000) or nonspecific mouse antibody. Antimethotrexate antibody resulted in 93% binding of serum methotrexate. In contrast, the percentage of antibody-bound methotrexate in brain and intracerebral tumour was only slightly greater than preantibody protein binding. Methotrexate delivery to tumour was significantly greater than to brain adjacent to tumour and normal brain. The percentage delivery of [3H]methotrexate to all areas of brain was similar between animals receiving antimethotrexate antibody and nonspecific antibody. These findings support the theory that a drug rescue method may be developed that may permit the safe administration of increased dosages of chemotherapeutic drugs for the treatment of intracerebral tumours.

Characterization of the molecular defect in a feline model for type II GM2-gangliosidosis (Sandhoff disease).

The Korat cat provides an animal model for type II GM2-gangliosidosis (Sandhoff disease) that may be suitable for tests of gene replacement therapy with the HEXB gene encoding the beta subunit of the beta-hexosaminidases. In the present report, we examined the brain and liver pathology of a typical Sandhoff-affected cat. We characterized the feline HEXB complementary DNA (cDNA) and determined the molecular defect in this feline model. cDNA libraries were produced from one normal and one affected animal, and cDNA clones homologous to human HEXB were sequenced. In the affected cDNA clone, the deletion of a cytosine residue at position +39 of the putative coding region results in a frame shift and a stop codon at base +191. This disease-related deletion was consistently detected by sequencing of cloned polymerase chain reaction amplified reverse transcribed messenger RNA from one more normal Korat and two additional affected animals. The defect was further demonstrated using single-strand conformational polymorphism analysis of the polymerase chain reaction products. In addition, alternative splicing of both normal and affected messenger RNAs was demonstrated. These results should facilitate the use of this animal model to assess gene therapy.

Delivery of virus-sized iron oxide particles to rodent CNS neurons.

Delivery of viral particles to the brain is limited by the volume of distribution that can be obtained. Additionally, there is currently no way to non-invasively monitor the distribution of virus following delivery to the central nervous system (CNS). To examine the delivery of virus-sized particles across the blood-brain barrier (BBB), dextran coated, superparamagnetic monocrystalline iron oxide particles, with a hydrodynamic diameter of 20 +/- 4 nm, were delivered to rat brain by direct intracerebral inoculation or by osmotic BBB disruption with hypertonic mannitol. Delivery of these particles was documented by magnetic resonance (MR) imaging and, unexpectedly, neuronal uptake was demonstrated by histochemical staining. Electron microscopy (EM) confirmed iron particle delivery across the capillary basement membrane and localization within CNS parenchymal cells following administration with BBB disruption. This is the first histologic and ultrastructural documentation of the delivery of particles the size of virions across the blood-brain barrier. Additionally, these dextran-coated, iron oxide particles may be useful, in and of themselves, as vectors for diagnostic and/or therapeutic interventions directed at the CNS.

Further refinement of the Escherichia coli brain abscess model in rat.

The rat brain abscess model provides a substrate for the modeling of delivery of therapeutic agents to intracerebral mass lesions. We now report refinement of the Escherichia coli brain abscess model in rat. A K1 surface antigen-negative E. coli isolated from human blood culture was stereotaxically inoculated into deep brain sites. Histopathologic analyses and quantitative cultures demonstrated the consistent production of lesions. No animal in this consecutive series developed meningitis, ventriculitis or sepsis. By contrast, prior experience with E. coli abscess production resulted in 25% failure rate of abscess production or death from sepsis. This improvement in the model may be attributable to specific characteristics of the bacteria used, modification of the inoculation method or the intracerebral placement technique. The present work suggests a reliable and consistent brain abscess model, which may be further used to study brain suppuration.

Delivery of ultraviolet-inactivated 35S-herpesvirus across an osmotically modified blood-brain barrier.

The present studies were undertaken to determine if viral particles can be delivered across the rat blood-brain barrier (BBB). Osmotic BBB modification with intracarotid mannitol (25%) was immediately followed by bolus intracarotid administration of 0.5 ml purified, ultraviolet-inactivated, herpes simplex virus type 1 endogenously labeled with 35S-labeled methionine (2.0 x 10(6) cpm, approximately 5 x 10(8) plaque-forming units/ml). After 60 minutes, intravascular virus was cleared by saline perfusion and the animals were sacrificed. A marked increase (fourfold, p less than or equal to 0.02) in radioactivity was observed in the ipsilateral brain hemisphere when compared to control animals without barrier modification. Administration of intravenous virus immediately after BBB modification displayed no difference in delivery when compared to intracarotid saline-infused controls (without BBB modification) suggesting the importance of a first-pass phenomenon. There were no significant differences in serum concentrations among intracarotid or intravenous groups. These preliminary studies suggest the possibility of delivering viral particles across the BBB with osmotic disruption, which may permit delivery of genetic material in replication-defective viral vectors in the feline model of GM2-gangliosidosis.

The effect of steroids on gentamicin delivery to brain after blood-brain barrier disruption.

Osmotic modification of the blood-brain barrier (BBB) provides an experimental model of vasogenic edema, is totally reversible, and does not cause any structural damage. In the present communication, the effect of corticosteroids on drug delivery to normal rat brain was evaluated in this model. Intraperitoneal dexamethasone was administered at doses ranging from 12 to 48 mg/sq m for 3 days; gentamicin delivery to the brain was then evaluated after either intravenous or intracarotid administration in both control and BBB-modified animals. Only animals receiving the highest dose of dexamethasone and in which the gentamicin was given intravenously demonstrated a statistically significant decrease in drug delivery. The effect of dexamethasone over a wide range of dosages, therefore, exhibited only modest effects on drug delivery to normal brain after osmotic BBB disruption.