Neurotoxicity of vincristine after the osmotic opening of the blood-brain barrier

Modulating the Blood-Brain Barrier: A Comprehensive Review

The highly secure blood-brain barrier (BBB) restricts drug access to the brain, limiting the molecular toolkit for treating central nervous system (CNS) diseases to small, lipophilic drugs. Development of a safe and effective BBB modulator would revolutionise the treatment of CNS diseases and future drug development in the area. Naturally, the field has garnered a great deal of attention, leading to a vast and diverse range of BBB modulators. In this review, we summarise and compare the various classes of BBB modulators developed over the last five decades-their recent advancements, advantages and disadvantages, while providing some insight into their future as BBB modulators.

Mind the Gaps: Ontogeny of Human Brain P-gp and Its Impact on Drug Toxicity

Available data on human brain P-glycoprotein ontogeny during infancy and childhood are limited. This review discusses the current body of data relating to maturation of human brain P-glycoprotein including transporter expression levels in post-mortem human brain samples, in vivo transporter activity using probe substrates, surrogate marker endpoints, and extrapolations from animal models. Overall, the data tend to confirm that human brain P-glycoprotein activity keeps developing after birth, although with a developmental time frame that remains unclear. This knowledge gap is a concern given the critical role of brain P-glycoprotein in drug safety and efficacy, and the vulnerable nature of the pediatric population. Future research could include the measurement of brain P-glycoprotein activity across age groups using positron emission tomography or central pharmacodynamic responses. For now, caution is advised when extrapolating adult data to children aged younger than 2 years for drugs with P-glycoprotein-dependent central nervous system activity.

Chemotherapy-induced neurotoxicity in pediatric solid non-CNS tumor patients: An update on current state of research and recommended future directions

Neurocognitive sequelae are known to be induced by cranial radiotherapy and central-nervous-system-directed chemotherapy in childhood Acute Lymphoblastic Leukemia (ALL) and brain tumor patients. However, less evidence exists for solid non-CNS-tumor patients. To get a better understanding of the potential neurotoxic mechanisms of non-CNS-directed chemotherapy during childhood, we performed a comprehensive literature review of this topic. Here, we provide an overview of preclinical and clinical studies investigating neurotoxicity associated with chemotherapy in the treatment of pediatric solid non-CNS tumors. Research to date suggests that chemotherapy has deleterious biological and psychological effects, with animal studies demonstrating histological evidence for neurotoxic effects of specific agents and human studies demonstrating acute neurotoxicity. Although the existing literature suggests potential neurotoxicity throughout neurodevelopment, research into the long-term neurocognitive sequelae in survivors of non-CNS cancers remains limited. Therefore, we stress the critical need for neurodevelopmental focused research in children who are treated for solid non-CNS tumors, since they are at risk for potential neurocognitive impairment.

Boron neutron capture therapy for glioblastoma multiforme: enhanced drug delivery and antitumor effect following blood-brain barrier disruption induced by focused ultrasound

AIM

This study investigated whether the efficacy of boron neutron capture therapy was enhanced by means of intravenous administration of boronophenylalanine (BPA) with blood-brain barrier disruption induced by focused ultrasound (FUS).

MATERIALS & METHODS

BPA was administered, followed by pulsed FUS, and the boron concentration in the treated brains was quantified by inductively coupled plasma mass spectroscopy. Growth of the firefly luciferase-labeled glioma cells was monitored through noninvasive biophotonic imaging. Finally, the brain tissue was histologically examined after sacrifice.

RESULTS

Compared with the nonsonicated tumor group, animals treated with an injection of 500 mg/kg of BPA followed by FUS exhibited not only significantly increased accumulation of the drug at the sonicated tumor site, but also a significantly elevated tumor-to-normal brain drug ratio (p < 0.05).

DISCUSSION

The data demonstrated that FUS significantly enhances the tumor-to-normal brain drug ratio in the sonicated tumor and subsequently the efficacy of boron neutron capture therapy.

Pulsed high-intensity focused ultrasound enhances the relative permeability of the blood-tumor barrier in a glioma-bearing rat model

The use of pulsed high-intensity focused ultrasound (HIFU) with an ultrasound contrast agent (UCA) has been shown to disrupt the blood-brain barrier (BBB) noninvasively and reversibly in the targeted regions. This study evaluated the relative permeability of the blood-tumor barrier (BTB) after sonication by pulsed HIFU. Entry into the brain of chemotherapeutic agents is impeded by the BBB even though the permeability of this barrier may be partially reduced in the presence of a brain tumor. F98 glioma-bearing rats were injected intravenously with Evans blue (EB) with or without BTB disruption induced by pulsed HIFU. Sonication was applied at an ultrasound frequency of 1 MHz with a 5% duty cycle, and a repetition frequency of 1 Hz. The accumulation of EB in brain tumor and the tumor-to-contralateral brain ratio of EB were highest after pulsed HIFU exposure. Sonication followed by EB injection showed a tumor-to-contralateral brain ratio in the target tumors which was about 2 times that of the control tumors. This research demonstrates that pulsed HIFU enhances the relative permeability of the BTB in glioma- bearing rats. The results of this pilot study support the idea that further evaluation of other treatment strategies, such as HIFU exposure in addition to combined chemotherapy or repeated pulsed HIFU exposure to increase delivery of drugs into brain tumors, might be useful.

Ultrasound enhanced delivery of macromolecular agents in brain tumor rat model

The purpose of this study was to evaluate the permeability of the blood-brain barrier (BBB) after focused ultrasound (FUS) exposure and to investigate if such an approach increases the tumor-to-ipsilateral brain permeability ratio. Normal rats and F98 glioma-bearing rats were injected intravenously with Evans blue (EB); these treatments took place with or without BBB disruption induced by transcranial FUS of one hemisphere of the brain. Sonication was applied at an ultrasound frequency of 1 MHz with a 5% duty cycle, and a repetition frequency of 1 Hz. The permeability of the BBB was quantitatively assessed by means of the extravasation of EB. Contrast-enhanced MR images were used to monitor the gadolinium deposition path associated with transcranial FUS and the influence of size and location was also investigated. Furthermore, whole brain histological analysis was performed. The results were compared by two-tailed unpaired t test. The accumulation of EB in brains and the tumor-to-ipsilateral brain permeability ratio of EB were significantly increased after FUS exposure. EB injection followed by sonication showed an increase in the tumor-to-ipsilateral brain ratio of the target tumors of about two-fold compared with the control tumors on day 8 after tumor implantation. MR images showed that FUS locally enhances the permeability of the BBB in the glioma-bearing rats. The BBB can be locally disrupted with FUS in the presence of microbubbles. This technology may offer new opportunities that will allow enhanced synergistic effects with respect to other brain tumor treatment regimens.

Accidental intrathecal administration of vincristine

We describe a case of accidental intrathecal administration of vincristine in a 33-year-old man with clinical diagnosis of acute lymphocytic leukemia. The patient died 20 days after receiving the drug. Clinically, the patient developed acute ascending paralysis with motor and sensory dysfunctions, and respiratory failure. Neuropathological investigation revealed lesions in spinal cord, roots, and cerebellum characterized by rarefaction of the neuropil, axonal, and myelin degeneration, accompanied by macrophagic infiltration.

Locoregional opening of the rodent blood-brain barrier for paclitaxel using Nd:YAG laser-induced thermo therapy: a new concept of adjuvant glioma therapy?

BACKGROUND AND OBJECTIVES

Nd:YAG laser-induced thermo therapy (LITT) of rat brains is associated with blood-brain barrier (BBB) permeability changes. We address the question of whether LITT-induced locoregional disruption of the BBB could possibly allow a locoregional passage of chemotherapeutic agents into brain tissue to treat malignant glioma.

STUDY DESIGN/MATERIALS AND METHODS

CD Fischer rats were subject to LITT of the left forebrain. Disruption of the BBB was analyzed using Evans blue and immunohistochemistry (IH). Animals were perfused with paclitaxel, and high-pressure liquid chromatography (HPLC) was employed to analyze the content of paclitaxel in brain and plasma samples.

RESULTS

LITT induces an opening of the BBB as demonstrated by locoregional extravasation of Evans blue, C3C, fibrinogen, and IgM. HPLC proved the passage of paclitaxel across the disrupted BBB.

CONCLUSIONS

LITT induces a locoregional passage of chemotherapeutic agents into the brain tissue. This is of potential interest for the treatment of brain tumors.

Massive cell death of cerebellar granule neurons accompanied with caspase-3-like protease activation and subsequent motor discoordination after intracerebroventricular injection of vincristine in mice

Vincristine, a microtubule-depolymerizing agent, is known to induce neuronal cell damage. Biochemical, histological and behavioral alterations were investigated after intracerebroventricular injection of vincristine in mice. Intracerebroventricular injection of vincristine caused caspase-3-like protease activation followed by nucleosomal release in the cerebellum. Histological examinations showed that vincristine-induced damage was relatively specific to granule cells in the cerebellum, and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling-positive cells were observed among these cells. Chromatin condensation, one of the criteria for apoptosis, was seen on electron microscopy. Behavioral changes, namely head movements, pivoting and backward walking, were observed in parallel with the increase of caspase-3-like protease activity and nucleosomal release. Furthermore, motor function tests (bulb balance test and rotating rod test) showed deficits of motor coordination ability. These observations suggest that intracerebroventricular vincristine causes massive apoptosis of cerebellar granule cells accompanied with caspase-3-like protease activation, leading to motor dysfunction, in this model. These vincristine-treated mice should be a useful in vivo model for examination of neuronal apoptosis, which might be involved in a variety of neurodegenerative diseases.

Advances in osmotic opening of the blood-brain barrier to enhance CNS chemotherapy

The blood-brain barrier (BBB) to water-soluble drugs and macromolecules can be opened in vivo by infusing a hypertonic solution of arabinose or mannitol into the carotid artery for 30 sec. Opening involves widening of tight junctions between endothelial cells of the cerebrovasculature and is mediated by endothelial cell shrinkage, vascular dilatation associated with removal of water from brain, and modulation of the contractile state of the endothelial cytoskeleton and junctional proteins by increased intracellular calcium. A 10-fold increase in BBB permeability to intravascular substances, lasting about 10 min following osmotic exposure, reflects both increased diffusion and bulk fluid flow from blood into brain. Furthermore, recent evidence indicates that the duration of peak BBB opening can be extended beyond 30 min, by pre-treatment with a Na(+)/Ca(2+) channel blocker. In experimental animals, the osmotic method has been used to grant wide access to brain of water-soluble drugs, peptides, antibodies, boron compounds for neutron capture therapy, viral vectors for gene therapy and enzymes. Ongoing multi-centre clinical studies suggest that the method, when used with intra-arterially administered anticancer drugs, can prolong survival in patients with malignant brain tumours, with minimal morbidity. However, controlled clinical trials are critical to see if the osmotic procedure with intra-arterial drugs enhances survival in brain tumour patients compared with intra-arterial drug alone.

Osmotic opening of the blood-brain barrier: principles, mechanism, and therapeutic applications

1. Osmotic opening of the blood-brain barrier by intracarotid infusion of a hypertonic arabinose or mannitol solution is mediated by vasodilatation and shrinkage of cerebrovascular endothelial cells, with widening of the interendothelial tight junctions to an estimated radius of 200 A. The effect may be facilitated by calcium-mediated contraction of the endothelial cytoskeleton. 2. The marked increase in apparent blood-brain barrier permeability to intravascular substances (10-fold for small molecules) following the osmotic procedure is due to both increased diffusion and bulk fluid flow across the tight junctions. The permeability effect is largely reversed within 10 min. 3. In experimental animals, the osmotic method has been used to grant wide access to the brain of water-soluble drugs, peptides, antibodies, boron compounds for neutron capture therapy, and viral vectors for gene therapy. The method also has been used together with anticancer drugs to treat patients with metastatic or primary brain tumors, with some success and minimal morbidity.

Spatial learning deficits in rats after injection of vincristine into the dorsal hippocampus

In the present study, performance in the Morris water escape task after bilateral lesioning of the dorsal hippocampus induced by the microtubule poison vincristine is discussed as a cognitive deficit model in rats. As we are especially interested in spontaneous or pharmacologically induced recovery processes after experimentally induced cognitive dysfunctions, the model should fulfil a number of criteria. Firstly, a clear dose-effect relationship between the dose of vincristine and the amount of spatial learning impairments should be present. Secondly, lesions must remain within the target area. Thirdly, there should be an observable behavioural recovery or compensation of the induced deficit. Two experiments evaluated the influence of the application volume (experiment 1) and the concentration of vincristine (experiment 2) on lesion location and size, and on spatial learning. The results of both experiments demonstrated that the effect of vincristine on the performance in the Morris water escape task seems to be characterized by an "all-or-none" relationship. Concentrations above a "threshold" value induced severe damage in the hippocampus and adjacent brain structures, whereas concentrations below the "threshold" value had marginal or no effects. The non-selective and highly toxic properties of vincristine make this neurotoxin an unsuitable tool for the establishment of a learning and memory deficit model.

Choice of vincristine or 6-mercaptopurine on the basis of polyamine level in tumor-bearing regions of the brain

The effects of vincristine (VC) and 6-mercaptopurine (6-MP) on body weight, regional weights, and the contents of putrescine, spermidine, and spermine in six regions of the brain were examined in rats that had been given these drugs for 5 consecutive days. VC is recommended for management of tumors in the corpus striatum and/or hippocampus, and cortex although its efficacy is dependent on the doubling time of the tumor cells, whereas 6-MP is recommended for the management of tumors in the cortex, thalamus and/or hypothalamus, and diencephalon. VC and 6-MI are chosen for treatment of the brain tumors because they reduce polyamines which are associated with the reduction of drug-sensitive cells and an inhibition of tumor growth.

Chemotherapy in experimental brain tumor, part 2: pretreatment with leukotriene C4 prolongs survival

Previous work in our laboratory has shown a correspondence between the chemosensitivity of C6 rat glioma and that of human glioblastoma (GBM) to a panel of chemotherapeutic agents in vitro, as determined by the MTT [3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H tetrazolium bromide] colorimetric assay. In the present study, an in vivo model of intracerebral C6 glioma in Sprague-Dawley rats was used to determine if a correlation exists between in vitro chemosensitivity and in vivo survival of the animals, and post-mortem histopathological changes in the tumor. Cisplatin (CDDP) and methotrexate (MTX), agents previously shown to demonstrate high and low in vitro cytotoxicity, respectively, against C6, were administered by intra-carotid infusion over the course of two days. In a separate series of animals, LTC4 was administered prior to infusion of CDDP or MTX; LTC4 was used in view of its known, selective, vasogenic effect on the permeability of brain tumor capillaries. It was found that survival of animals treated with CDDP alone was increased, although this did not reach statistical significance; histopathologically, CDDP-treated animals showed significant tumor necrosis. However, in CDDP-treated animals, pre-treatment with LTC4 increased survival to a statistically significant degree. When administered alone, LTC4 (not followed by CDDP) had no effect on either survival or histology. The survival-enhancing effect of CDDP, when combined with LTC4, was probably not due to any cytotoxic effect of LTC4; this is based on our finding that, on the in vitro MTT colorimetric assay, LTC4 showed low cytotoxicity for C6 glioma cells. By contrast with CDDP, MTX -- with or without pretreatment with LTC4 -- affected neither survival nor tumor histology. With respect to the question of correspondence between the MTT colorimetric in vitro assay and in vivo effect, MTX showed a clear correlation: low cytotoxicity in vitro and poor in vivo response. In the case of CDDP, the correspondence was not clear-cut: there was a high level of in vitro chemosensitivity of the C6 cell line to CDDP as well as post-mortem tumor necrosis, but in vivo testing showed no significant prolongation of survival. However, pre-treatment with LTC4 did significantly extend survival in animals treated with CDDP.

Selective boron drug delivery to brain tumors for boron neutron capture therapy

Malignant glioma is one of the most deadly forms of cancer in humans and remains refractory to presently available treatments. Boron neutron capture therapy (BNCT) is a promising therapeutic modality for the treatment of malignant brain tumors. For successful BNCT, a sufficient quantity of boron atoms must be selectively delivered to individual brain tumor cells while at the same time the boron concentration in the normal brain tissue should be kept low to minimize the damage to normal brain tissue. However, the brain entry of drugs is restricted by the blood-brain barrier (BBB), even though the permeability of the pathological area of this barrier may be partially increased due to the present of brain tumors. Therefore, selective delivery of boron to tumor cells across the BBB is a major challenge to the BNCT of brain tumors. This review briefly discusses four main mechanisms responsible for drug transport across the BBB. Brain tumor-localizing boron compounds are described, such as borocaptate sodium, p-boronophenylalanine, boronated porphyrins and boronated nucleosides. Strategies employed to selectively deliver boron drug into brain tumors are reviewed including hyperosmotic BBB modification, biochemical opening of BBB, electropermeabilization and direct intracerebral delivery of boron drugs. Conjugation of boron drugs to macromolecules like monoclonal antibodies and epidermal growth factor are discussed for active tumor targeting. Boron delivery via microparticles such as liposomes, high density lipoproteins and nanoparticles is also covered for their potential utilization in BNCT of brain tumors.

Intracarotid infusion of RMP-7, a bradykinin analog, and transport of gallium-68 ethylenediamine tetraacetic acid into human gliomas

The bradykinin analog, RMP-7, was investigated for its ability to increase selectively the transport of 68Ga ethylenediamine tetraacetic acid (EDTA) into recurrent malignant gliomas in nine patients. For each patient, two position emission tomography (PET) studies (one with and one without RMP-7) were performed. For studies with RMP-7, 10 to 300 ng/kg of the compound was infused into the supraophthalmic carotid artery over 15 minutes. In each PET study, a sequence of PET scans was initiated simultaneously with an intravenous bolus of 68Ga EDTA (5-10 mCi). Arterial samples were taken to provide the input function. All PET scans were coregistered to the magnetic resonance (MR) images of the patient. Regions of interest were defined for tumor and normal tissue regions on MR images and were copied to the coregistered PET dynamic images to provide brain tissue-time activity curves. The constant (Ki) for the transport of gallium-68 from plasma to brain tissue was determined using a simple compartmental model. Intracarotid infusion of RMP-7 significantly increased transport into tumor regions with an average increase of 46 +/- 42% (mean +/- standard deviation, p < 0.05). Permeability in normal tissue regions was not significantly increased. Tumors in three of six patients treated with 300 ng/kg RMP-7 and carboplatin had at least a 50% reduction in tumor volume as measured by MR imaging. Intracarotid infusion of RMP-7 is a novel technique for selective delivery of antitumor compounds into brain tumors.

Intralesionally implanted cisplatin cures primary brain tumor in rats

BACKGROUND AND OBJECTIVES

Chemotherapy has added little to the overall survival of the patients with primary malignant brain tumors, primarily due to its difficulty penetrating the blood-brain barrier. Use of polymers, releasing high doses of chemotherapy locally over time, is a promising new treatment strategy. Three experiments were conducted to test the effect of cisplatin, released from biodegradable polymer, on rats with 1 week established brain tumor.

METHODS

9L gliosarcoma cells and drug-free or cisplatin-loaded polymer were administered through a right frontal lobe cannula in male Fischer 344 rats. Tumor cells were infused on day 0 and polymer on day 7. Animals were monitored for 60 days.

RESULTS

In experiment one, 0.5 mg/m2 of cisplatin loaded in polymer resulted in a mean survival time (MST) of 51 +/- 14 days with 63% (10/16) rats surviving to day 60. MST for the control group was 24 +/- 4 days (p = 2.5 x 10(-9)). Evidence of clinical or histologic brain toxicity was minimal. In a second experiment, using drug-free polymer (n = 7), MST was 24 +/- 3 days. This was compared against an MST of 24 +/- 4 days in the tumor control group (n = 7) and 49 +/- 7 days in a cisplatin-polymer treated group (n = 6). In a third experiment, two doses of drug-free polymer and three doses of cisplatin-loaded polymer were tested in normal nontumor-bearing rats and found to be well tolerated.

CONCLUSIONS

Intralesional sustained release of cisplatin from biodegradable polymer is safe and effective for the treatment of brain 9L gliosarcoma in rats.

Enhanced tumor uptake of carboplatin and survival in glioma-bearing rats by intracarotid infusion of bradykinin analog, RMP-7

OBJECTIVE

Intracarotid infusion of the bradykinin analog, RMP-7, can increase permeability in brain tumor capillaries. This study sought to determine the following: 1) the unidirectional transport, Ki, of radiolabeled [14C]carboplatin into brain tumors with either intravenous or intracarotid RMP-7 infusions; 2) the duration and extent of increased permeability in tumor capillaries during continuous RMP-7 infusions; and 3) the effect on survival of carboplatin combined with RMP-7 treatment in rats with gliomas.

METHODS

Wistar rats with RG2 gliomas were used, and a unidirectional transfer constant, Ki, was determined using quantitative autoradiography. In the survival study, the rats were treated with intra-arterial carboplatin and RMP-7 at Days 5 and 7 after tumor implantation.

RESULTS

Intracarotid infusion of RMP-7 for 15 minutes increased the transport of [14C]carboplatin to tumors by 2.7-fold, as compared with saline infusion alone (P < 0.001). The transports of [14C]dextran and [14C]carboplatin into tumors were significantly higher with 15 minutes of intracarotid infusion of RMP-7 (0.1 microgram/kg/min), compared to those with 10-, 30-, or 60-minute infusions (P < 0.01). Rats treated at Days 5 and 7 after tumor implantation with carboplatin alone (10 mg/kg) exhibited a modest increase in survival at 31 days (37%, compared to < 10% of controls), while those given the combination of carboplatin with RMP-7 exhibited a significantly higher survival rate (74%).

CONCLUSION

Intracarotid infusion of RMP-7 can selectively increase transport of carboplatin into brain tumors and results in higher survival in rats with gliomas. These findings support the use of intracarotid infusion of RMP-7 to enhance the delivery of carboplatin to patients with malignant brain tumors.

Leukotriene E4 selectively increase the delivery of methotrexate to the C6 gliomas in rats

Leukotriene E4 (LTE4) infused into the carotid artery ipsilateral to an experimental glial tumor will selectively increase the blood-tumor permeability within the tumor. In this study the effects of intracarotid infusion of LTE4 on blood-tumor barrier (BTB) permeability for intravenously administered 14C-aminoisobutyric acid, 14C-5-fluorouracil (5-FU) 14C-sucrose and 3H-methotrexate (MTX) were examined in C6 gliomas of rats. The intracarotic administration of LTE4 selectively opened the BTB, without affecting permeability of normal brain tissue, to all of the above tracers. Intracarotid infusion of LTE4 had the tendency to increase the uptake of intravenously administered 5-FU within the tumor, but this effect was not statistically significant. The intracarotid infusion of LTE4, however, increased the uptake of intravenously injected MTX about twofolds within the tumor (Ki = 19.48 +/- 1.06 vs 10.12 +/- 1.19, p < 0.01) without increasing the uptake in the normal brain tissue.

Intracarotid infusion of RMP-7, a bradykinin analog: a method for selective drug delivery to brain tumors

The bradykinin analog, RMP-7, was investigated for its ability to selectively increase uptake of molecular tracers in RG2 glial tumors. When infused in low doses (0.1 microgram/kg/min) through the intracarotid artery ipsilateral to RG2 gliomas in rats, RMP-7 significantly increased the permeability of tumor capillaries to methotrexate and to four other tracers of varying molecular weights, compared to intracarotid infusion of vehicle alone. Tracers used to examine permeability included radiolabeled alpha-aminoisobutyric acid (M(r) 103 D), sucrose (M(r) 342 D), methotrexate (M(r) 454.5 D), inulin (M(r) 5000 D), and dextran (M(r) 70,000 D). Permeability was expressed as the unidirectional transfer constant, Ki (microliters/gm/min). The permeability (Ki) of tumors in the RMP-7 group compared to the vehicle control group was as follows: alpha-aminoisobutyric acid, 35.3 +/- 9.11 versus 12.7 +/- 4.56 (p < 0.001); sucrose, 16.5 +/- 3.83 versus 9.28 +/- 3.12 (p < 0.05); methotrexate, 26.3 +/- 10.3 versus 8.98 +/- 6.78 (p < 0.005); inulin, 13.5 +/- 3.23 versus 6.55 +/- 4.32 (p < 0.005); dextran, 15.2 +/- 3.42 versus 1.47 +/- 1.24 (p < 0.001). The permeability of RG2 gliomas to high-molecular-weight dextran (70,000 D) was 10.3-fold higher in the RMP-7 group than in the vehicle control group. Intracarotid infusion of RMP-7 did not significantly increase the blood volume in tumor or brain tissue. The permeability of normal brain capillaries was unaffected by intracarotid infusion of 0.1 microgram/kg/min RMP-7 relative to that achieved in tumor. These data support the idea that intracarotid infusion of RMP-7 will be a useful technique for selective delivery of antitumor compounds to brain tumors.

Intracarotid infusion of bradykinin selectively increases blood-tumor permeability in 9L and C6 brain tumors

This study investigated the effects of bradykinin on blood-tumor barrier (BTB) permeability in transplanted 9L gliosarcomas (9L) and C6 gliomas (C6) in rats. Permeability, expressed as the unidirectional transfer constant, Ki (microliter/g/min), was measured by quantitative autoradiography. Tracers used to examined permeability included radiolabeled alpha-aminoisobutyric acid ([14C]AIB), sucrose ([14C]sucrose) and dextran ([14C]dextran). Intracarotid infusion of bradykinin (10 mg/kg/min) significantly increased the BTB permeability in both 9L and C6 tumors to [14C]AIB and [14C]sucrose, but did not increase permeability to [14C]dextran. Blood-brain barrier (BBB) permeability in normal (non-tumor) brain was not significantly increased to any of the tracers by intracarotid bradykinin infusion. Ki values for [14C]AIB, [14C]sucrose and [14C]dextran of 9L tumors in the bradykinin group versus control group were 41.6 +/- 12.6 vs. 24.8 +/- 6.30 (P < 0.02), 17.5 +/- 9.34 vs. 9.05 +/- 4.36 (P < 0.05), and 3.90 +/- 2.59 vs. 2.42 +/- 1.76, respectively (mean +/- S.D.). Ki values to [14C]AIB, [14C]sucrose and [14C]dextran of C6 tumors in the bradykinin group versus control group were 41.4 +/- 19.0 vs. 19.5 +/- 11.4 (P < 0.01), 18.0 +/- 8.88 vs. 7.06 +/- 3.05 (P < 0.01), and 4.07 +/- 1.45 vs. 2.27 +/- 1.26, respectively (mean +/- S.D.). Intracarotid infusion of bradykinin did not significantly increase the blood volume in tumor or brain tissue despite its known vasodilative effect. Intracarotid infusion of bradykinin may be a useful technique for selective delivery of compounds to brain tumors.

Bradykinin selectively opens blood-tumor barrier in experimental brain tumors

Bradykinin, infused in low doses (10 micrograms/kg/min) through the carotid artery ipsilateral to RG2 glioma in rats, significantly increased the permeability in tumor capillaries to six different tracers of varying molecular weights compared with intracarotid infusion of saline alone. Permeability in normal brain capillaries was not significantly increased by intracarotid bradykinin infusion. Tracers used to examined permeability included radiolabeled alpha-aminoisobutyric acid (AIB; MW 103), sucrose (MW 342.3), inulin (MW 5000), and dextran (MW 70,000), horseradish peroxidase (HRP) and Evans blue (EB). Permeability was expressed as the unidirectional transfer constant K(i) (microliter/g/min). The permeabilities (K(i)) of tumors in the bradykinin group versus the control saline group for AIB, sucrose, inulin, and dextran were 25.91 +/- 6.78 vs. 13.95 +/- 4.29 (p < 0.01), 17.90 +/- 2.65 vs. 10.75 +/- 4.55 (p < 0.01), 23.92 +/- 6.99 vs. 6.20 +/- 4.37 (p < 0.01), and 17.84 +/- 1.00 vs. 1.47 +/- 1.24 (p < 0.001), respectively (mean +/- SD). Permeability of RG2 gliomas to high molecular weight dextran (70,000) was 12-fold higher in the bradykinin group than in the saline infusion group. Intracarotid infusion of bradykinin did not significantly increase the blood volume in tumor or brain tissue despite its known vasodilative effect. The permeability of normal brain capillaries was unaffected by intracarotid bradykinin infusion. The increased permeability was reversed 20 min after stopping the intracarotid infusion. Electron microscopic and gross qualitative analysis was performed using HRP and EB. Intracarotid bradykinin infusion increased HRP and EB within tumor tissue but not normal tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain uptake and anticancer activities of vincristine and vinblastine are restricted by their low cerebrovascular permeability and binding to plasma constituents in rat

Unidirectional blood-brain barrier transfer of the lipophilic anticancer agents vincristine and vinblastine was studied in anesthetized rats, using an isolated, in situ brain perfusion technique. Drug binding to plasma constituents was also measured. Despite the high lipophilicity of these agents (the log octanol/physiological saline partition coefficient equalled 2.14 and 1.68, respectively), the cerebrovascular permeability-surface area product, PA, of vincristine in plasma was only 0.49 x 10(-4) ml s-1 g-1 for parietal cerebral cortex, whereas that of vinblastine was too low for determination. These values are similar to those of water-soluble, poorly diffusible nonelectrolytes. The PAs were significantly higher in the absence of plasma protein, being 1.24 x 10(-4) and 5.36 x 10(-4) ml s-1 g-1, respectively. Even these values, determined by brain perfusion of protein-free buffer, were lower than would be expected from the lipophilicity of the agents. The results suggest that additional factors, such as steric hindrance and molecular charge distribution, related to the chemical and geometric structure and the large size of vincristine and vinblastine (molecular weight, 825 and 814 daltons, respectively) restrict their passage across the blood-brain barrier. As a consequence of their paradoxically low permeability at the blood-brain barrier and restrictive binding to plasma and blood constituents, doses of both agents that cause significant inhibition of extracerebral Walker 256 carcinosarcoma tumor implants in rat have no effect on tumor located in the brain.

Selective opening of the blood-tumor barrier by intracarotid infusion of leukotriene C4

Intracarotid infusions of leukotriene C4 (LTC4) were used to selectively open the blood-tumor barrier in rats with RG-2 gliomas. Blood-brain and blood-tumor permeability was determined by quantitative autoradiography using 14C aminoisobutyric acid. Leukotriene C4 (4 micrograms total dose) infused into the carotid artery ipsilateral to the tumor increased twofold the unidirectional transfer constant for permeability within the tumor while no effect on permeability was seen in normal brain. No gamma glutamyl transpeptidase (gamma-GTP) activity was seen in tumor capillaries in contrast to high gamma-GTP in normal brain capillaries. These findings suggest that normal brain capillaries may resist the vasogenic effects of LTC4, while LTC4 will increase permeability in tumor capillaries. This could relate to the ability of gamma-GTP to act as an enzymatic barrier and inactivate leukotrienes in normal brain capillaries. Intracarotid LTC4 infusion may be a useful tool to selectively open the blood-tumor barrier for delivery of antineoplastic compounds.

Selective opening of the blood-tumour barrier by intracarotid infusion of leukotriene C4

Intracarotid infusions of leukotriene C4 (LTC4) were used to selectively open the blood-tumour barrier in rats with RG-2 gliomas. Blood-brain and blood-tumour barrier permeability was determined by quantitative autoradiography using 14C aminoisobutyric acid. LTC4 (4 micrograms total dose) infused into the carotid artery ipsilateral to the tumour increased the unidirectional transfer constant for permeability, Ki, two-fold within the tumour while no effect on permeability was seen in the normal brain. No gamma glutamyl transpeptidase (gamma-GTP) activity was seen in tumour capillaries in contrast to high gamma-GTP in normal brain capillaries. These findings suggest that normal brain capillaries may resist the vasogenic effects of LTC4 while LTC4 will increase permeability in tumour capillaries. This could relate to the ability of gamma-GTP to act as an enzymatic barrier and inactivate leukotrienes in normal brain capillaries. Intracarotid LTC4 infusion may be a useful tool to selectively open the blood-tumour barrier for delivery of antineoplastic compounds.

Vincristine-induced changes in the retina of the isolated arterially-perfused cat eye

We have attempted to determine in this study whether the arterial administration of vincristine produces in cat the functional defects associated with hereditary and vincristine-induced night blindness in man. Using the isolated perfused cat eye, it has been possible to mimic some of the essential features of human night blindness, namely, retention of normal rhodopsin chemistry and normal photoreceptor activity, with marked suppression of the ERG b-wave. In addition, we find that vincristine produces an early, rapid fall in the c-wave, a potential that arises largely in the pigment epithelium. Ultrastructurally, it appears that many classes of retinal neuron are affected by the drug, but the principal changes in cytoarchitecture are seen in the photoreceptors. Except for the outer segments, paracrystalline deposits were found in all parts of the visual cell. The disruption of the normal microtubular organization of these cells suggests that the drug interferes with the functional integrity of the transport system by which synaptic activity is maintained. By reducing the efficacy of communication between visual cells and their second-order neurons, the electrical responses of post-synaptic elements is degraded. The route by which vinca alkaloids reach the neural retina is still uncertain, but our preliminary studies using HRP indicate that the relatively high concentration of vincristine used in this study may be responsible for compromising the blood-retinal barrier.

Structural changes in the rat brain after carotid infusions of hyperosmolar solutions: a light microscopic and immunohistochemical study

A solution of mannitol or urea was infused into the carotid artery of rats to open the blood-brain barrier (BBB) and to find out if such a procedure results in brain injury. Paraformaldehyde-fixed, paraffin-embedded material was available to determine the localization and extent of albumin extravasation by immunochemistry. Other light microscopic and immunocytochemical techniques were applied on consecutive sections to find out if structural damage had occurred. The cerebral cortex, the hippocampus and the basal ganglia of the infused brain hemisphere contained within regions of albumin extravasation scattered, collapsed, acidophilic neurons. In addition, there were multifocal lesions with marked sponginess of the neuropil which contained numerous shrunken, acidophilic neurons and a perifocal astrocytic gliosis. A moderate macrophage infiltration was present in rats with 72 h survival. In conclusion, infusion of hypertonic mannitol or urea into the carotid artery of the rat may result in structural brain damage within regions showing BBB injury. The presence of acidophilic neurons and the macrophage response indicate that some of the brain changes are irreversible.

The effect of hyperosmotic blood-brain barrier disruption on blood-to-tissue transport in ENU-induced gliomas

Hyperosmotic blood-brain barrier disruption transiently increases the rate of blood-to-tissue transport of water-soluble compounds to normal brain and has been used in brain tumor patients to increase the delivery of chemotherapeutic drugs. This method remains controversial; debate concerns the extent to which it increases drug delivery to brain tumors. Ethylnitrosourea (ENU)-induced gliomas in rats have the lowest rate of blood-to-tissue transfer of the water-soluble compound alpha-aminoisobutyric acid of all experimental brain tumors studied to date. To gain further understanding about the effects of hyperosmotic blood-brain barrier disruption in brain tumors, we measured the unidirectional blood-to-tissue transfer constant of alpha-aminoisobutyric acid in ENU-induced brain tumors in rats after hyperosmotic disruption. Hyperosmotic blood-brain barrier disruption with 1.6 osmolar mannitol resulted in an averaged whole-tumor transfer constant of 0.013 +/- 0.003 (standard error) mL/(g/min), compared to a transfer constant of 0.007 +/- 0.002 mL/(g/min) for ENU-induced gliomas in the contralateral undisrupted hemisphere, a difference that was not significant. In contrast, hyperosmotic blood-brain barrier disruption produced a large and significant increase in the transfer constant of alpha-aminoisobutyric acid in tumor-free cortex (from 0.002 +/- 0.001 to 0.05 +/- 0.011 mL/[g/min]) and in tumor-free corpus callosum (from 0.001 +/- 0.003 to 0.017 +/- 0.005 mL/[g/min]). Hyperosmotic blood-brain barrier disruption does not appear to be an efficient method with which to increase the rate of delivery of water-soluble drugs to brain tumors but does result in a significant increase in the delivery rate of these drugs to normal brain tissue.

Effects of intracarotid hyperosmolar mannitol in triethyl tin (TET)-induced rat brain edema--preservation of blood-brain barrier (BBB) in TET edema

The effect of intracarotid hyperosmolar mannitol on the blood-brain barrier (BBB) in triethyl tin (TET)-induced rat brain edema was examined by using intravenous Evans blue (EB, MW 68,000) and Adriamycin (ADM, MW 580) as tracers. Three ml of 1.4 M mannitol solution were administered through the right carotid artery during 45 s for BBB opening. The barrier was opened for 60-120 minutes and then re-established. The reversibility was preserved in TET-treated rats and controls. In fact, the intravenous injection of EB stained both TET-treated and non-treated cerebral hemispheres with mannitol-induced transient BBB disruption, but not without BBB disruption. BBB was resistant to both high and low molecular weight substances in TET-induced edema. The importance of this hyperosmotic studies provides the evidence for normal BBB function in TET-induced brain edema.

Neurotoxicity of adriamycin passed through the transiently disrupted blood-brain barrier by mannitol in the rat brain

Neurotoxicity of adriamycin (ADM) was investigated following the transient disruption of the blood-brain barrier (BBB) in rats. The BBB disruption by the hyperosmotic agent (1.4 M mannitol) was confirmed by the leakage of ADM and Evans blue administered intravenously. Neuropathological changes due to the toxicity of ADM were found as early as day 4. The neurons in the cerebral cortex and nucleus caudatus-putamen showed focal clearing of the nuclear chromatin, increased dense bodies in the cytoplasm and dilatation of the cisternae of the rough endoplasmic reticulum (r-ER) and Golgi apparatus. By day 7, nucleolar segregation and irregular membranous structures appeared in the nuclei with the progression of cytoplasmic changes. By day 10, the cytoplasm of many neurons was vacuolated. Electron-microscopically, the cisternae of the r-ER and Golgi apparatus were prominently dilated in these neurons. Neuronal microtubules were increased in number, in particular in the perinuclear region. Numerous whorl-like membranous structures and separation of nuclear membrane were also observed. Some astrocytic processes surrounding the blood vessels revealed loss of organelles and a few pericytes showed an increased number of lysosomes on days 7 and 10. This experiment clearly demonstrates that ADM has strong neurotoxic effects in the central nervous system when the BBB is disrupted, and provides the warning for the possibilities of neurotoxic side effects when ADM is administered, in combination with a hyperosmotic agent, for the treatment of human malignant tumors, including brain tumors.

Hyperosmotic blood-brain barrier disruption in brains of rats with an intracerebrally transplanted RG-C6 tumor

To test the results of blood-brain barrier (BBB) disruption in the treatment of brain tumor, RG-C6 glioma was transplanted into the brains of rats. Intracarotid infusions of normal saline and hyperosmotic mannitol were then made, followed by intravenous injection of Evans blue dye plus albumin (EB, MW 68,000), horseradish peroxidase (HRP, MW 40,000), and 5-fluorouracil (5-FU, MW 130). Uptake of the drug and the consistency of drug levels in the normal brain and tumor varied widely among these three agents. Both EB and HRP penetrated the brain tumors but did not stain the normal brain tissues. After BBB opening, penetration of EB and HRP into the normal brain was drastically increased; however, the uptake of EB and HRP in the tumor was not increased. The concentration of 5-FU in the tumor was higher than that in the serum and, although it increased 1.5-fold after BBB opening, the increase was not statistically significant. Conversely, there was a progressive increase in concentrations of 5-FU in the tumor-free brain regions (p less than 0.05). These observations suggest that an intracarotid infusion of hyperosmotic mannitol may increase neurotoxicity because it allows greater delivery of anticancer drugs into the normal brain tissue than into the tumor tissues.

Morphometric effects of vincristine on nerve regeneration in the rat

Administration of vincristine (200, 100 or 50 micrograms/kg/week) for 6 months during regeneration of the sciatic nerve after crush injury caused a dose-dependent reduction in nerve fibre size and failure of removal of myelin debris. Successfully regenerating neurites showed an unusual amount of shape distortion. The ratio of myelin sheath thickness to axon circumference was reduced, but the ratio of myelin sheath thickness to axon area was normal. Microtubule concentration was diminished in axons, but neurofilament density was unaffected. Unmyelinated axons were reduced in number but their axon diameter distribution was not affected. Fibres on the non-crushed side appeared normal. The toxicity of vincristine to regenerating nerves is probably related to increased blood-nerve permeability occurring both at the site of crush and along the degenerating nerve.

Comparative neurotoxicity of tubulin-binding drugs: inhibition of goldfish optic nerve regeneration

Intraperitoneal or intraocular (io) injection of tubulin-binding drugs in goldfish, Carassius auratus L., inhibited axonal regeneration or restoration of functional synapses in optic axons following optic nerve crush. One eye was used to detect effects on regeneration and the other was kept intact to detect effects on maintenance of established optic circuits. Regeneration was assessed by measuring the time to reappearance of a visually evoked branchial suppression response. Three drugs, vincristine, vinblastine, and podophyllotoxin, administered semiweekly by ip injection, each inhibited regeneration at doses that did not impair maintenance of response. Similar results were previously reported for ip colchicine. Vincristine was several times more potent than podophyllotoxin or colchicine and 25 times more potent than vinblastine. Picropodophyllotoxin, an isomer of podophyllotoxin which has low affinity for tubulin, did not inhibit regeneration. The io experiments showed that maintenance of vision was reversibly inhibited by a single injection of 0.05 micrograms/g of colchicine but unaffected by 0.01 microgram/g, and that administration of the lower dose immediately following optic nerve crush inhibited regeneration. Intraocular lumicolchicine, a colchicine photoisomer which has low affinity for tubulin, did not inhibit maintenance or regeneration. In contrast, an io dose of vincristine sufficient to inhibit visual recovery also blocked maintenance of vision. Thus regeneration and maintenance effects could not be dissociated for io vincristine suggesting its mechanism of action on retinal cells is different. A conditioning lesion was shown to decrease the time to reappearance of the visually evoked branchial response following optic nerve crush, which indicates that it is a sensitive index of the rate of axonal outgrowth to the optic tectum.

Especial considerations for neurotoxicological research

In recent years, there has been much impetus toward a definition of behavior in terms of underlying biological events. Such correlations have been attempted in several areas ranging from learning and memory to neurological disease. Increased information concerning the relation between behavior and neurobiological mechanisms is especially important in the area of neurotoxicology. It is often abnormal behavior that is a first sign of exposure to a neurotoxic agent and such changes may give clues as to the anatomical or chemical sites of attack on the nervous system. These clues might also lead to the development of a therapeutic treatment as to the development of tests designed to reveal exposure to a toxic agent at levels below those causing gross behavioral change. Unfortunately, there is a relatively small amount of literature reporting on both behavioral and biological disturbances caused by a toxic agent in the same experimental animal. However, a variety of methodological advances combined with a growing interest in neurotoxicology is gradually changing this. Increased information concerning the role of defined nerve pathways and the means of action of their chemical constituents offers an opportunity to bring about a deepening understanding of neurotoxic events. This review will suggest how new pharmacological findings can be applied to neurotoxicology. Examples of human and animal exposure to toxic materials will be used and current problems will be shown to be major determinants of future research directions.

Syndrome of inappropriate secretion of antidiuretic hormone caused by vincristine therapy: a case report of the neuropathology

The syndrome of inappropriate secretion of antidiuretic hormone is a rare but well-recognized neurotoxic side effect of vincristine therapy. The first neuropathological report of a case is presented. A 6-month-old boy with skin leukemia developed inappropriate secretion of antidiuretic hormone caused by vincristine. Postmortem examination revealed axonal spheroids in the ansa lenticularis and the area surrounded by the substantia innominata, amygdala and supraoptic nucleus. The lesion was confined to that area and the neurosecretory neurons were intact with well preserved neurophysin. The pathological findings suggest that these fibers play a role in the development of inappropriate secretion of antidiuretic hormone caused by vincristine therapy.