Blood-brain barrier integrity and host responses in experimental metastatic brain tumours

The role of tight junctions in cancer metastasis

Over the last decade, it has become apparent that the tight junction (TJ) is a key component in tumour progression and metastasis. In addition to its role in the control of paracellular diffusion of ions and certain molecules, the TJ has a vital role in maintaining cell to cell adhesion and tissue integrity. Changes in the expression and/or distribution of TJ proteins can result in loss in cohesion of the TJ structure, which in turn results in the ability of cancer cells to become invasive and then ultimately lead to the metastasis of cancer cells. This review will discuss recent insights into how TJ are involved in the process of tumour metastasis.

Comparison between symptomatic treatment and lomustine supplementation in 71 dogs with intracranial, space-occupying lesions

Brain neoplasia is diagnosed in an increasing number of dogs. Consequently, there is a higher need for an effective treatment. Chemotherapy is considered in cases where surgery or radiation is not optional. The objective of this retrospective study was to evaluate the difference in median survival time (MST) of dogs with intracranial masses, treated symptomatically with corticosteroids and anti-epileptic drugs, compared with the same symptomatic treatment supplemented with lomustine. The records of 71 dogs with intracranial masses were retrospectively evaluated. Fifteen dogs were treated symptomatically with corticosteroids and anti-epileptics, and 56 dogs received additional therapy with lomustine. There was no statistically significant difference in MST between both groups, being 60 and 93 days, respectively. Age, duration of symptoms, intracranial localization of the mass and intra- or extra-axial localization had no influence on survival time. However, female dogs survived significantly longer than male dogs.

Walker 256 tumour cells increase substance P immunoreactivity locally and modify the properties of the blood-brain barrier during extravasation and brain invasion

It is not yet known how tumour cells traverse the blood-brain barrier (BBB) to form brain metastases. Substance P (SP) release is a key component of neurogenic inflammation which has been recently shown to increase the permeability of the BBB following CNS insults, making it a possible candidate as a mediator of tumour cell extravasation into the brain. This study investigated the properties of the BBB in the early stages of tumour cell invasion into the brain, and the possible involvement of SP. Male Wistar rats were injected with Walker 256 breast carcinoma cells via the internal carotid artery and euthanised at 1, 3, 6 and 9 days post tumour inoculation. Culture medium-injected animals served as controls at 1 and 9 days. Evidence of tumour cell extravasation across the BBB was first observed at 3 days post-inoculation, which corresponded with significantly increased albumin (p < 0.05) and SP immunoreactivity (p < 0.01) and significantly reduced endothelial barrier antigen labelling of microvessels when compared to culture medium control animals (p < 0.001). By day 9 after tumour cell inoculation, 100 % of animals developed large intracranial neoplasms that had significantly increased albumin in the peri-tumoral area (p < 0.001). The increased SP immunoreactivity and altered BBB properties at 3 days post-inoculation that coincided with early tumour invasion may be indicative of a mechanism for tumour cell extravasation into the brain. Thus, extravasation of tumour cells into the brain to form cerebral metastases may be a SP-mediated process.

13N-NH3: a selective contrast-enhancing tracer for brain tumor

PURPOSE

The purpose of this study is to determine whether there is a qualitative and quantitative relationship between the breakdown of the blood-brain barrier, defined radiologically by the contrast enhancement of MRI, and the uptake of N-NH3 in brain tumors.

METHODS

The results of N-NH3 PET in 42 patients suspected of having brain tumors were compared with the findings of contrast-enhanced MRI. A histopathological diagnosis was carried out in 33 patients, and a clinical diagnosis was performed in the remaining patients. PET and MRI images were visually inspected, and the contrast index (CI) of MRI and the uptake index (UI) of N-NH3 were measured.

RESULTS

Contrast enhancement of MRIs was seen in 20 of 29 brain tumors (69%). Increased uptake of N-NH3 was seen in 24 of 29 brain tumors (83%). Nineteen of 20 contrast-enhancing brain tumors exhibited the increased uptake of N-NH3 (95%). Areas of the increased N-NH3 uptake corresponded to areas enhanced on MR images in the majority of cases. Five out of nine nonenhancing tumors exhibited increased uptake of N-NH3 (56%). The contrast enhancement of MRIs was seen in nine of 13 nonneoplastic lesions (69%). None of the nonneoplastic lesions showed increased uptake of N-NH3, yielding a specificity of 100% for brain tumors (0 of 13). CI for tumor tissue was 1.46+/-0.64. UI of N-NH3 for tumor tissue was 1.64+/-0.71. CI and UI for tumor tissue were significantly correlated (r=0.86, P<0.01). A statistically significant difference in uptake levels of N-NH3 between contrast-enhancing tumors and nonenhancing tumors (1.88+/-0.66, n=20 vs. 1.11+/-0.52, n=9, P<0.01) was observed. UI was higher in brain tumors compared with the nonneoplastic lesions (1.64+/-0.71 vs. 0.71+/-0.19, P<0.01).

CONCLUSION

N-NH3 is a potential selective contrast-enhanced tracer for brain tumor, and may prove especially useful for evaluating the contrast-enhancing lesions on MRI to distinguish brain tumors from nonneoplastic lesions.

Diagnosis and management of brain metastases

In the past 15 years, significant advancement has been made in the diagnosis and treatment of brain metastases. The distinction between the management of single and multiple brain metastases is an important one. Although radiotherapy remains a mainstay of treatment, especially in multiple brain metastases, surgical resection and stereotactic radiosurgery also have their place in the management of selected patients. Rarely, interstitial radiation or chemotherapy also may be used to treat brain metastases in the setting of relapse.

Enhanced brain tumor selectivity of cationic magnetic polysaccharide microspheres

A novel cationic delivery system composed of magnetic aminodextran microspheres (MADM) 1-2 microm in diameter was evaluated along with neutral magnetic dextran microspheres (MDM) for their ability to target intracerebral rat glioma-2 (RG-2) tumors in vivo. The tissue distribution of the microspheres was determined following intraarterial injection (25 mg/kg) over 2 min in male Fisher 344 rats bearing RG-2 tumors as well as normal animals with a magnetic field of 0 or 0.6 T applied to the brain for 30 min. Animals were sacrificed at 30 min or 6 h post-injection after which the microspheres were recovered from various tissues and analyzed for magnetite (Fe3O4) content by atomic absorption. Overall, administration of cationic MADM and neutral MDM particles in normal animals resulted in low brain tissue concentrations with the highest concentrations observed in lung and spleen tissue. In contrast, studies in brain tumor bearing animals resulted in cationic MADM particles concentrating in brain tumor at levels significantly higher than neutral MDM particles (p = 0.0111). Cationic particles were also retained in brain tissue over a longer period of time compared to neutral particles (p = 0.0161) with MADM tumor concentrations decreasing only 4% after 6h compared with a 32% decrease for MDM. Application of a magnetic field failed to produce any significant effect on tissue distribution due to high variability in these groups, but generally resulted in increased brain concentrations and decreased non-target tissue concentrations. TEM analysis of brain tissue sections in tumor animals also revealed differences in particle distribution with MADM particles observed in the interstitial space and MDM particles trapped in the vasculature. In summary, particle charge, state of the vascular endothelium and time significantly influenced particle distribution contributing to the ability of MADM to selectively target brain tumor and supports further investigation of magnetic cationic microspheres as a targeted drug delivery system for brain tumors.

Distribution of small magnetic particles in brain tumor-bearing rats

Small (10-20 nm) uncharged magnetic particles (SMP) were evaluated for their ability to target intracerebral rat glioma-2 (RG-2) tumors in vivo. In an effort to determine the influence of particle size on blood-tumor barrier uptake, the tissue distribution of the injected particles was evaluated following intraarterial injection (4 mg/kg SMP) in male Fisher 344 rats bearing RG-2 tumors with a magnetic field of 0 G or 6000 G applied to the brain for 30 min. Animals were sacrificed at 30 min or 6 h post-injection after which tissues were collected and analyzed for magnetite content. In the presence of a magnetic field, SMP localized in brain tumor tissue at levels of 41-48% dose/g tissue after 30 min and 6 h respectively, significantly greater than non-target tissues. In the absence of a magnetic field only 31-23% dose/g tissue was achieved for the same time points. Tumor targeting of the SMP for brain tumor was demonstrated by large target selectivity indexes (ts) of 2-21 for normal brain tissue, indicating a 2-21 fold increase in concentrations compared to normal brain. In comparison with larger (1 micron) diameter magnetic particles, SMP concentrated in brain tumor at significantly higher levels than magnetic neutral dextran (p = 0.0003) and cationic aminodextran (p = 0.0496) microspheres previously studied. TEM analysis of brain tissue revealed SMP in the interstitial space of tumors, but only in the vasculature of normal brain tissue. These results suggest that changes in the vascular endothelium of tumor tissue promote the selective uptake of SMP and provide a basis for the design of new small drug-loaded particles as targeted drug delivery systems for brain tumors.

Differences in rates of incorporation of intravenously injected radiolabeled fatty acids into phospholipids of intracerebrally implanted tumor and brain in awake rats

This study investigates the incorporation of three intravenously administered radiolabeled fatty acids, [9,10-3H]palmitate (3H-PAM), [1-14C]arachidonate (14C-ACH) and [1-14C]docosahexaenoate (14C-DHA), into lipids of intracerebrally implanted tumor and contralateral brain cortex in awake rats. A suspension of Walker 256 carcinosarcoma cells (1 x 10(6) cells) was implanted into the right cerebral hemisphere of an 8- to 9-week-old Fischer-344 rat. Seven days later, the awake rat was infused intravenously for 5 min with 3H-PAM (6.4 mCi/kg), 14C-ACH (170 microCi/kg) or 14C-DHA (100 microCi/kg). Twenty min after the start of infusion, the rat was killed and intracranial tumor mass and brain cortex were removed for lipids analysis. Each radiolabel was incorporated more into tumor than into brain cortex. Ratios of net incorporation rate coefficients (k*) into tumor as compared with brain were 4.5, 3.4 and 1.7 for 3H-PAM, 14C-ACH and 14C-DHA, respectively. Lipid radioactivity comprised more than 80% of total tumor or brain radioactivity for each probe. Phospholipids contained 58%, 89% and 68% of tumor lipid radioactivity, and 58%, 82% and 74% of brain lipid radioactivity, for 3H-PAM, 14C-ACH and 14C-DHA, respectively. Incorporation coefficients (k*i) for a phospholipid class (i)--choline phosphoglycerides (PC), inositol monophosphoglycerides (PI), ethanolamine phosphoglycerides (PE), serine phosphoglycerides (PS), and sphingomyelin (SM)--were greater in tumor than in brain for each fatty acid probe, except that values for k*PE and k*PS using 14C-DHA were equivalent. Differences in k*i between tumor and brain were largest for SM and PC and the change in k*PC accounted for 65-90% of the increase in the net phospholipid incorporation rate for each probe. Differences in k*PI, k*PE and k*PS were smaller than those in were smaller than those in k*PC and k*SM, and varied with the probe. Differences in k*i were related to differences in tumor and brain phospholipid composition and metabolism. The results indicate that suitably radiolabeled fatty acids may be used to image and characterize metabolism of lipid compartments of a brain tumor in vivo using positron emission tomography.

Targeting anticancer drugs to the brain: II. Physiological pharmacokinetic model of oxantrazole following intraarterial administration to rat glioma-2 (RG-2) bearing rats

The disposition of the anticancer drug oxantrazole (OX) was characterized in rats bearing the rat glioma-2 (RG-2) brain tumor. Following intraarterial administration of 3 mg/kg of OX, serial sacrifices were completed from 5 min to 5 hr after administration. Blood and tissue samples collected at the time of sacrifice were processed and measured for OX concentrations by HPLC. The kidney had the greatest affinity for OX with the Cmax being 40.6 micrograms/ml at 15 min after administration. OX concentrations in brain tumor were higher than in normal right and left brain hemispheres, and consistent with enhanced drug blood-tumor barrier (BTB) permeability seen in experimental models for brain tumors. Observed heart, liver, lung, and spleen OX concentrations were similar, ranging from approximately 2 micrograms/ml to 20 micrograms/ml. A unique technique was used to develop a global physiological pharmacokinetic model for OX. A hybrid or forcing function method was used to estimate individual tissue compartment biochemical parameters (i.e., partition and mass transfer coefficients). A log likelihood optimization scheme was used to determine the best model structure and parameter sets for each tissue. Most tissues required a 3-subcompartment structure to adequately describe the observed data. The global model was then reconstructed with an arterial blood and rest of body compartments that provided predicted OX concentrations in agreement with the data. The model development strategy provides a systematic approach to physiological pharmacokinetic model development.

Intravenously injected radiolabelled fatty acids image brain tumour phospholipids in vivo: differential uptakes of palmitate, arachidonate and docosahexaenoate

This paper investigates the incorporation of intravenously (i.v.) administered radiolabelled fatty acids--[9,10(3)-H]palmitate (3H-PA), [1-14C]arachidonate (14C-AA) and [1-14C]docosahexaenoate (14C-DHA)--into intracerebrally implanted tumours in awake Fischer-344 rats. A suspension of Walker 256 carcinosarcoma tumour cells (1 x 10(6) cells) was implanted into the right cerebral hemisphere of 8- to 9-week-old rats. Seven days after implantation, the awake rat was infused i.v. for 5 min with 3H-PA (6.4 mCi/kg), 14C-AA (170 microCi/kg) or 14C-DHA (100 microCi/kg). Twenty minutes after the start of infusion, the rat was killed and coronal brain sections were obtained for quantitative autoradiography and histology. Each fatty acid showed well-demarcated incorporation into tumour tissue. Areas of necrosis or haemorrhage showed no or small levels of incorporation. The ratios of incorporation into the tumour to incorporation into contralateral brain regions were 2.8-5.5 for 3H-PA, 2.1-3.3 for 14C-AA and 1.5-2.2 for 14C-DHA. The mean ratios differed significantly between the fatty acids (P < 0.01). 3H-PA was not incorporated into necrotic tumours despite the presence of an open blood-tumour barrier, indicated by extravasated horseradish peroxidase. The incorporation rate constant of 3H-PA was similar for small intracerebral and large extracerebral tumours. The results show that 3H-PA, 14C-AA and 14C-DHA are incorporated more readily into tumour tissue than into brain, and that the increase is primarily due to increased utilization of fatty acids by tumour cells and not due to a high blood-tumour permeability. The relative increases in rates of incorporation for the different fatty acids may be related to lipid composition of the tumour and to the requirement of and specific role of these fatty acids in tumour cell growth and division.

Intra-arterial mannitol infusion in the chemotherapy for malignant brain tumors

To assess whether therapeutic efficacy is related to the intra-arterial (IA) mannitol infusion prior to ACNU and cisplatin (CDDP) for malignant brain tumors, the survival time of patients with and without mannitol infusion was compared. Ninety-eight patients were randomly assigned to either a mannitol infusion group (group A) or a non-mannitol infusion group (group B); 34 with malignant gliomas (18 in group A and 16 in group B) and 64 with brain metastases (36 in group A and 28 in group B). During radiotherapy, ACNU and CDDP at a dose of 100 mg/body were given through the common carotid artery at a rate of 20 mg/min. In group A, 50 ml of 20% mannitol was injected intra-arterially at a rate of 50 ml/min immediately prior to the injection of chemotherapeutic agents. Of the patients with malignant gliomas, the median survival time (MST) was 52 weeks for all 34 cases, 68 weeks for group A, and 47 weeks for group B. Survival analysis showed no significant differences between the two treatment groups. Of the patients with brain metastases, the MST was 40 weeks for all 64 cases, 47 weeks for group A, and 24 weeks for group B; the survival time was significantly longer in group A as compared to group B (p < 0.05). This study has demonstrated that, for the patients with brain metastases, IA mannitol infusion provided a survival benefit in the IA chemotherapy employing ACNU and CDDP. In contrast, IA mannitol infusion offered no survival benefit to the patients with malignant gliomas.

Targeting anticancer drugs to the brain. I: Enhanced brain delivery of oxantrazole following administration in magnetic cationic microspheres

A magnetic cationic microsphere delivery system, prepared from the polysaccharide chitosan and containing oxantrazole (OX), was examined for its ability to enhance brain delivery of OX compared to administration of OX in solution (OX-S). Magnetic chitosan microspheres containing OX (MCM-OX) and OX-S were administered intraarterially to male Fischer 344 rats at OX doses of 0.1 mg/kg and 0.5 mg/kg with a magnetic field of 6000 G applied to the brain for 30 min. Animals were sacrificed at 30 min and 120 min after MCM-OX and OX-S treatments, and multiple tissues were collected and analyzed for OX by HPLC. A statistical analysis of the effects of treatment, OX dose, and time on total OX in each sampled tissue was made. MCM-OX significantly increased OX brain concentrations compared to those achieved with OX-S treatments, concentrations after MCM-OX being a minimum of 100-fold greater. Within the MCM-OX treatment groups, ipsilateral OX concentrations were much greater, indicating target organ selectivity. A most interesting finding was that OX brain concentrations were similar at 120 min and 30 min after MCM-OX treatment. Thus, even in the absence of the magnetic field, MCM-OX were retained in the brain, possibly through cationic-anionic interactions with the blood-brain barrier.

In vivo incorporation of [9,10(-3)H]-palmitate into a rat metastatic brain-tumor model

Lipid metabolism of an intracerebrally implanted brain tumor and normal brain was investigated in awake Fischer 344 rats using intravenously injected [9,10(-3)H]-palmitate as a probe. A suspension of Walker 256 carcinosarcoma cells (250 cells in 5 microliters medium), with or without 1% low-melting-point agar, was implanted into the caudate nucleus of rats 8 to 9 weeks old. Control animals received an intracerebral injection without tumor cells. Seven days after implantation, awake rats were infused intravenously for 5 minutes with [9,10(-3)H]-palmitate (6.4 mCi/kg). The rats were killed 20 minutes after initiation of the infusion and coronal brain slices were obtained for quantitative autoradiography and light histological study. Tumor cell masses were histologically well demarcated from the surrounding brain tissue. Tumor tissue incorporation of [9,10(-3)H]-palmitate was heterogeneous, ranging on average from 3.1- to 6.1-fold greater than in the corresponding contralateral brain. In addition, incorporation corresponded to regional tumor cell density. The incorporation rate constant of [9,10(-3)H]-palmitate in tumor was significantly increased compared to control brain and was independent of tumor size. Necrotic areas within tumors showed no incorporation of radiolabeled palmitate. Brain surrounding the tumors and control injection sites showed reactive gliosis, and possessed 30% greater incorporation of [9,10(-3)H]-palmitate than contralateral normal brain. These results suggest that [9,10(-3)H]-palmitate can be used to image brain tumors in vivo, measuring turnover and/or synthesis of tumor and brain lipid.

Brain tumor imaging in rats using the positron emitting fatty acid dl-erythro-9,10-[18F]difluoropalmitate

Positron emitting dl-erythro-9,10[18F]difluoropalmitate, [18F]DFPA, was synthesized for the in vivo imaging of brain tumors in rats. Male Fischer 344 rats were intracerebrally implanted with Walker 256 carcinosarcoma tumor cells (1 x 10(6) in 5 microliters tissue culture media) and 7 days later were infused with [18F]DFPA (500-1000 mCi/mmol) i.v. for 5 min. Rats were killed after 20 min. Brains were removed and either prepared for autoradiography, or brain and tumor were separated and their radioactivity quantified by gamma spectroscopy. Brain tumors were well demarcated from surrounding and normal brain in autoradiographs, and closely paralleled tumor growth in histological sections. The mean optical density of tumor was significantly greater, by 318 +/- 68 per cent (P less than 0.025, n = 3), than normal brain in autoradiographs, and that of edematous brain surrounding a large tumor was intermediately increased. [18F]DFPA proved of value to image and circumscribe intracerebral tumors in awake rats, and studies are continuing to facilitate its clinical application in brain tumor patients.

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.

Model for drug uptake by brain tumors: effects of osmotic treatment and of diffusion in brain

A mathematical model describing drug uptake into brain tumors, directly from blood and indirectly from neighboring tissue, is presented. The model quantitatively describes uptake into tumor, brain surrounding tumor (BST), and normal brain and uptake following reversible osmotic blood-brain barrier (BBB) and blood-tumor barrier disruption. It employs published data on the time course for reclosure of the BBB following osmotic treatment and on the brain and tumor uptake of [14C]alpha-aminoisobutyric acid by Walker 256 carcinomas and C6 gliomas implanted into the rat brain. Constant infusion and bolus injection infusion schedules are considered. In untreated brain, the BST acts as a sink, reducing the integrated exposure of the adjacent tumor to the drug, whereas following osmotic treatment, tumor exposure to drug is enhanced, not only by increased delivery from blood but also by diffusion (and bulk flow) from neighboring brain. The model provides a quantitative framework for examining the efficacy of osmotic treatment to enhance chemotherapy of brain tumors.

Brain and plasma pharmacokinetics and anticancer activities of cyclophosphamide and phosphoramide mustard in the rat

By a sensitive and quantitative fluorometric assay, brain and plasma time-dependent concentration profiles were generated for phosphoramide mustard (PM) and active alkylating metabolites derived from cyclophosphamide (CPA) administration to rats. Whereas PM rapidly disappeared from plasma, with a monophasic half-life of 15.1 min, equimolar administration of CPA generated active metabolites in plasma that disappeared monoexponentially, with a composite half-life of 63 min. As a consequence, the time-dependent concentration integral of active alkylating metabolites derived from CPA administration, calculated between 5 min and infinity, was 3-fold that of PM. Pharmacokinetic parameters were calculated for each compound. The brain/plasma concentration-integral ratios of PM and active alkylating metabolites derived from CPA were 0.18 and 0.20, respectively. The cerebrovascular permeability-surface area product of PM was 7.5 x 10(-5) s-1, which is similar to that of other water-soluble anticancer agents that are restricted from entering the brain. The activities of a range of daily doses of PM and CPA were assessed against subcutaneous and intracerebral implants of Walker 256 carcinosarcoma tumor in rats. Inhibition of subcutaneous tumor growth by 50% was caused by CPA and PM doses of 6.6 and 12.0 mg/kg (daily for 5 consecutive days, starting 36 h after tumor implantation), respectively. However, administration of daily doses of up to 40 mg/kg did not significantly increase the survival of animals with intracerebral tumor implants. These studies indicate that active metabolites of CPA are restricted from entering the brain and that only subtherapeutic concentrations are achieved in brain tissue after systemic administration of CPA or PM.

Alteration of blood-brain-CSF barrier in experimental meningeal carcinomatosis. A morphologic and adriamycin-penetration study

An experimental model of meningeal carcinomatosis has been produced by subarachnoid inoculation of B16 melanoma cells into C57BL mice. Injection of 10(3) viable cells was sufficient to cause 100% tumor incidence and death within a median survival time of 17 days. The tumor infiltrated diffusely the meninges of the brain and spinal cord and filled the ventricular system. Electron microscopic study of the leptomeningeal tumor revealed newly formed microvessels with fenestrated endothelium. The integrity of the blood-brain barrier was studied by the extravasation of the Evans blue and the Horseradish peroxidase tracers. Barrier disruption became evident from the seventh day on, using Evans blue. Electron microscopy study showed peroxidase activity in the luminal and abluminal sides of the meningeal microvessels, and within the tight junctions. Similar findings were noted in cortical capillaries adjacent to the meningeal tumor. Brain concentrations of Adriamycin (ADR) following administration of an intravenous dose of either 10 mg/kg or 50 mg/kg were measured on days 0 to 14 after tumor inoculation. A significant increase in mean +/- SEM content of whole brain ADR was observed only with the 50 mg/kg dose in days 7 to 14 (0.69 +/- 0.02 micrograms/g wet tissue weight) as compared to tumor-free controls (0.43 +/- 0.01, p less than 0.05). Our study suggests that barrier alteration in meningeal carcinomatosis allows extravasation of tracer solutes. Still, in order to achieve a significant increase in a water soluble drug penetration through the disrupted barrier, a high-dose drug regimen is required.

[Blood-brain barrier and the penetration of cytostatic drugs]

The penetration of 12 commonly used anticancer agents through the blood-brain barrier (BBB) was measured in a rat model using a single-injection tissue-sampling technique. Two of the tested drugs penetrated the barrier, but only to a limited extent. Entry of the drugs into the brain tissue critically depends on molecular weight and lipophilia of the respective test compound. For drugs with a molecular weight of less than 500, BBB simply behaves like an oil/water interphase, whereas drugs with a molecular weight greater than 500 are practically excluded from transport through the BBB even if they show a favourable oil/water partition coefficient. However, permeability of cytostatics was strongly increased if short chain alkylglycerols, up to final concentrations of about 0.3 mol/l were added to the injected solution. Under these conditions the Brain-Uptake-Index (BUI) reached values up to about 50% (cyclophosphamide), depending on lipid solubility and molecular dimension of the respective test compound and the alkyl chain length of the glycerol derivative.

Microvascular permeability in induced astrocytomas and peritumor neuropil of rat brain. A high-voltage electron microscope-protein tracer study

Brain tumors, benign and malignant, are characteristically more permeable to various types of tracer molecules than the neuropil in which they are embedded. Impermeability of brain neuropil capillaries is imparted by the blood-brain barrier, the anatomic basis of which is the network of interendothelial zonulae occludentes that seal capillary endothelial cells. To explore both the vascular elements of brain neoplasms and the route of tracer extravasation from them, as well as the possible effects of brain tumors on the permeability of peritumoral neuropil capillaries, brain tumors were induced in newborn Wistar rats by intracerebral (i.c.) injection of C-6 astrocytoma cells. The protein tracer horseradish peroxidase (HRP) was injected systemically into both normal and tumor-bearing rats to mark the pathway along which it flowed into the tumor parenchyma tissue spaces, and to signal any concomitant tracer loss from the tumor extracellular compartment or peritumoral brain capillaries, into the neuropil extracellular milieu. Electron-microscopic examination of thin plastic sections of tumor and peritumoral neuropil revealed massive extravasation of tracer into the tumor tissue spaces, but none was seen outside of the capillaries in the surrounding brain neuropil. Zonulae occludentes of both tumor capillary endothelium and brain capillary endothelium were devoid of tracer and judged tight (sealed). Tracer was seen in pinocytotic vesicles in the highly attenuated endothelium of tumor capillaries and also in cytoplasmic vesicles within the tumor cells. The peritumoral and contralateral neuropil capillary endothelium exhibited reaction product-filled pinocytotic vesicles and vesiculo-tubular conduits. Often, one end of a HRP-filled vesiculo-tubular channel appeared continuous with either the luminal or abluminal plasmalemma. High-voltage electron microscopy of these conduits often showed them to be continuous with both luminal and abluminal surfaces of the endothelium, thus forming a continuum across the capillary wall. In addition, these transendothelial channels, clearly constituted as chains of fused vesicles, were often seen in close proximity to, or fused with, dense bodies in the endothelial cytoplasm. In spite of the presence of HRP-filled structures in the peritumoral neuropil capillary endothelium of tumor-bearing rats, no evidence of tracer extravasation from these vessels was apparent. These results suggest that although peritumoral and contralateral neuropil capillaries possess the machinery for extravasation of tracer, likely as a response to the presence of the neoplasm, tracer is not lost but, instead, is degraded by endothelial enzymes.(ABSTRACT TRUNCATED AT 400 WORDS)

Short communication: Metrazol enhances brain penetration and therapeutic efficacy of some anticancer agents: implications for brain metastases

The concurrent administration of Metrazol (60 mg/kg, i.v.) to anaesthetized rats enhances the cerebral penetration of the anticancer agent razoxane. Such an enhancement leads to an increase in the therapeutic efficacy of razoxane against intracerebrally sequestered L1210 leukaemia cells in mice. The combination of Metrazol and melphalan was also examined to see if the concentration of other anticancer agents in CSF could be enhanced.