Unexpected neurotoxicity of etoposide phosphate administered in combination with other chemotherapeutic agents after blood-brain barrier modification to enhance delivery, using propofol for general anesthesia, in a rat model.

OBJECTIVE: Osmotic blood-brain barrier disruption (BBBD) increases brain and brain tumor delivery of chemotherapeutic agents, which results in increased efficacy against brain tumors. We previously noted that the use of propofol anesthesia for BBBD increased the percentage of successful disruptions, resulting in delivery of increased amounts of chemotherapeutic drugs. This study evaluated the neurotoxicity of combination chemotherapeutic administration with this enhanced delivery system. METHODS: Osmotic BBBD was performed in Long-Evans rats with isoflurane (n = 11) or propofol (n = 90) anesthesia. Carboplatin and/or melphalan, methotrexate, or etoposide phosphate was administered intra-arterially (IA) after BBBD using propofol anesthesia. Animals were assessed for systemic and neurological toxicity. Animals were killed for neuropathological evaluation 30 days after treatment. RESULTS: With propofol or isoflurane anesthesia, BBBD alone produced no systemic or neurological toxicity. Single agents were relatively non-neurotoxic when administered IA with BBBD, as were the combinations of carboplatin or melphalan with methotrexate. Etoposide phosphate in combination with any other agent was observed to be highly neurotoxic if both agents were administered after BBBD. Administration of etoposide phosphate before BBBD completely eliminated neurotoxicity, although acute pulmonary toxicity occurred with any combination of etoposide phosphate and methotrexate, regardless of the timing of administration. CONCLUSION: Neurotoxicity was significantly increased for etoposide phosphate combination groups, particularly when both drugs were administered IA after BBBD. This increase in neurotoxicity may reflect on increase in drug delivery observed with propofol anesthesia. The neurotoxicity of IA administered etoposide phosphate with BBBD and propofol anesthesia could be minimized by administering etoposide phosphate IA before BBBD and administering carboplatin or melphalan IA after BBBD.

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.

Differential permeability of a human brain tumor xenograft in the nude rat: impact of tumor size and method of administration on optimizing delivery of biologically diverse agents.

To assess how to maximize drug delivery to intracerebral tumors and surrounding brain, this study examined the effects of route and method of administration and tumor size on the distribution of three agents in a nude rat intracerebral tumor xenograft model. Aminoisobutyric acid (M(r) 103), methotrexate (M(r) 454), and dextran 70 (M(r) 70,000) were administered i.v. or intra-arterially (i.a.) with or without osmotic blood-brain barrier disruption (BBBD) at 8, 12, or 16 days after tumor cell inoculation (n = 72). A 2.2- to 2.5-fold increase in delivery to tumor and surrounding brain was observed when i.a. was compared with i.v., and a 2.5- to 7.6-fold increase was observed when BBBD was compared with the saline control. The combined effect of i.a. administration and BBBD was to increase delivery 6.3-16.7-fold. The greatest benefit of BBBD was seen in animals with 8-day tumors, whereas BBBD had less benefit in improving delivery to intracerebral tumor and brain around tumor as the tumors grew larger. Regional delivery decreased as the molecular weight of the agent increased. Based on these results, we suggest that i.a. administration of antitumor agents may be adequate to obtain initial responses in large, very permeable, intracerebral tumors. However, in smaller, less permeable tumors or after an initial response to treatment, there may be a significant therapeutic advantage to i.a. agent administration and BBBD.

Long-term toxicity and neuropathology associated with the sequencing of cranial irradiation and enhanced chemotherapy delivery.

OBJECTIVE: The goal was to evaluate, at 1 year, 75 Long-Evans rats for survival rates and toxicity associated with the sequencing of cranial irradiation and enhanced chemotherapy delivery. METHODS: Seventy-five Long-Evans rats were randomized into four groups and evaluated at 1 year for survival rates and toxicity associated with the sequencing of cranial irradiation and enhanced chemotherapy delivery. Radiation (2,000 cGy) was administered as a single fraction, by using parallel opposed portals, 30 days before chemotherapy (Group 1), 24 hours before chemotherapy (Group 2), 30 days after chemotherapy (Group 3), or without chemotherapy or without radiation (control group, Group 4). Five subgroups within each treatment group included rats receiving intra-arterially administered methotrexate (1 g/m2) or intravenously administered etoposide (200 mg/m2) combined with intra-arterially administered carboplatin (200 mg/m2), administered with or without osmotic blood-rain barrier disruption, and a group receiving normal saline solution after blood-brain barrier disruption. RESULTS: There was a significant increase in total toxic effects when the three experimental groups were compared with the control group (P = 0.001, 0.006, and 0.013 for Groups 1, 2, and 3, respectively). All groups receiving radiation and chemotherapy (particularly carboplatin and etoposide) had an increased incidence of hind limb paralysis, resembling experimental allergic neuritis (P = 0.053). Statistical analysis showed a trend toward increased mortality rates in Group 1 (antecedent radiation), compared with the control group (P = 0.082), and an increased incidence of intracerebral calcification (P = 0.019). No differences in mortality rates were observed for Group 2 or 3, compared with the control group. CONCLUSION: Radiation before chemotherapy was a more toxic sequence and, surprisingly, carboplatin/etoposide administered in combination with radiotherapy was more detrimental than methotrexate. Additional studies are in progress to evaluate the toxicity and efficacy of sequences of cranial irradiation and enhanced chemotherapy in tumor-bearing rats.

MR of carcinoma-specific monoclonal antibody conjugated to monocrystalline iron oxide nanoparticles: the potential for noninvasive diagnosis.

PURPOSE: To determine if tumor-specific monoclonal antibodies conjugated to superparamagnetic monocrystalline iron oxide nanoparticles can be used to yield specific diagnoses with the use of MR imaging. METHODS: Monoclonal antibodies conjugated to monocrystalline iron oxide nanoparticles were given to nude rats with intracranial tumors either by intravenous injection, intraarterial injection with osmotic blood-brain barrier disruption, or direct intratumoral inoculation. Either L6, a tumor-specific antibody, or P-1.17, a control isotype-matched antibody, was used. Coronal T1-weighted, T2-weighted, and spoiled gradient-recalled acquisition in the steady state images were obtained before, 30 minutes after, 6 hours after, and 24 hours after injection. RESULTS: Intravenous injection of greater than 2 mg of the tumor-specific antibody showed a specific pattern of enhancement of the tumors with the largest concentration of antibody in the area with the greatest density of tumor cells. The control antibody showed nonspecific changes. After intraarterial injection with barrier disruption to increase delivery globally or direct inoculation to increase delivery focally, no specific enhancement pattern was seen. CONCLUSION: Monoclonal antibodies conjugated with monocrystalline iron oxide particles may provide a method to obtain specific diagnoses with the use of MR imaging.

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.

Decreased delivery and acute toxicity of cranial irradiation and chemotherapy given with osmotic blood-brain barrier disruption in a rodent model: the issue of sequence.

The sequence of chemotherapy administered prior to cranial irradiation rather than the more traditional order of radiation followed by chemotherapy is currently being evaluated. This rodent study was designed to assess the sequencing of radiation therapy and chemotherapy administered with osmotic blood-brain barrier disruption (BBBD). Drug delivery and acute toxicity were evaluated. Two clinically relevant chemotherapy regimens were given with BBBD: intraarterial methotrexate (MTX, 1 g/m2), or a combination of intraarterial carboplatin (200 mg/m2) and i.v. etoposide (200 mg/m2). In a randomized protocol, the standard rodent model of 2000 cGy as a single fraction using parallel opposed portals was administered 30 days prior to, concurrent with (24 h prior), or 30 days after these two chemotherapeutic regimens. A total of 72 animals was evaluated in this study. The administration of external beam radiation therapy either prior to or concurrent with the administration of a high molecular weight marker 14C-labeled dextran 70 (Mr 70,000), or a low molecular weight marker 3H-labeled MTX (Mr 456) resulted in a statistically significant (P < 0.01) decrease in drug delivery when compared to animals not receiving cranial irradiation. Seizures were observed in 26% of the animals that received radiation prior to the administration of intraarterial MTX after BBBD. It did not matter whether the radiotherapy was administered 30 days prior to or concurrent with MTX. Seizures were not seen in any other group. The mortality in animals receiving radiotherapy 30 days prior to chemotherapy was significantly (P = 0.03) higher than the mortality in control animals receiving chemotherapy after osmotic BBBD, but no radiation. Drug delivery was significantly decreased when the animals received prior radiotherapy; the administration of radiation prior to MTX with BBBD resulted in an increased incidence of seizures, and there was a significant increase in mortality when cranial irradiation was given 30 days prior to chemotherapy administered with BBBD. With regard to delivery and toxicity, chemotherapy with BBBD administered prior to radiotherapy may have advantages over the other sequences utilizing chemotherapy and cranial irradiation.

Differential permeability and quantitative MR imaging of a human lung carcinoma brain xenograft in the nude rat.

This study characterized agent differential permeability, three-dimensional tumor volume, and survival in an LX-1 human small cell lung carcinoma intracerebral xenograft model in the nude rat. The percent accessible tissue space (distribution volume) and the permeability x capillary surface product for aminoisobutyric acid (M(r) 103), methotrexate (M(r) 454), dextran 10 (M(r) 10,000), and dextran 70 (M(r) 70,000) were measured between 8 and 16 days after inoculation of tumor. Magnetic resonance imaging and histology were used to quantitate intracerebral tumor volume (mm3). Accessible tissue space (ml/g) and permeability x capillary surface product in intracranial tumor, surrounding brain, and subcutaneous tumor decreased with increasing molecular weight of the agent, regardless of the number of days after inoculation. Accessible tissue space in intracranial tumor increased between 8 and 16 days for all agents except dextran 70. There was little change in the subcutaneous tumor or other tissues with time. Tumor volume calculations from imaging studies correlated with volumetric measurements from histological sections (r2 = 98.5%) and illustrated natural tumor progression (9 to 225 mm3). These results provide a basis for therapeutic design based on differential permeability of specific agents and the ability to quantitatively measure brain tumor volume for accessing tumor response.

Effect of blood-brain barrier disruption on intact and fragmented monoclonal antibody localization in intracerebral lung carcinoma xenografts.

UNLABELLED: These studies highlight several factors that affect monoclonal antibody (Mab) localization to a tumor in the brain, including tumor permeability, nonspecific and specific binding, plasma half-life, radiolabeled antibody stability and the blood-brain barrier. METHODS: A pancarcinoma Mab [L6 IgG, F(ab')2 and Fab] and an irrelevant isotype-matched antibody [P1.17 IgG and F(ab')2] were given with and without osmotic blood-brain barrier disruption in a LX-1 human small-cell lung carcinoma intracerebral xenograft model. RESULTS: Intracerebral tumor size and permeability to antibody increased with the selection of 10, 14 or 17 days postinoculation when antibody was administered. Barrier disruption increased the delivery, particularly at earlier time points, which was dependent on antibody-specific and nonspecific binding and tumor permeability. Dehalogenation and/or antibody binding stability also appeared to affect the percent delivery. CONCLUSION: These studies demonstrate important variables that should be considered when clinical trials are designed or Mab delivery and localization in intracerebral tumor models are evaluated.

Effects of Gd-DTPA after osmotic BBB disruption in a rodent model: toxicity and MR findings.

OBJECTIVE: This experiment was done to evaluate the gross neurotoxicity of intravenous Gd-DTPA administered in conjunction with osmotic blood-brain barrier (BBB) disruption and to image a human small cell lung carcinoma intracerebral tumor xenograft before and after osmotic BBB disruption. MATERIALS AND METHODS: Neurotoxicity studies were performed in normal Sprague-Dawley rats following osmotic BBB disruption by the injection of 25% mannitol in the right internal carotid artery and intravenous administration of Gd-DTPA (n = 10). Animals were observed for major neurologic changes such as seizure or substantial motor defects, and after death neuropathologic examination was performed. Human small cell lung carcinoma cells were implanted intracerebrally in athymic nude rats (n = 4). Gadopentetate dimeglumine was injected intravenously and serial T1-weighted images were obtained. Blood-brain barrier disruption was produced in each animal, followed by a second dose of intravenous Gd-DTPA, and imaging studies were repeated. RESULTS: No gross neurologic toxicity was observed. Tumors showed dense enhancement in a small area, and BBB disruption resulted in marked enhancement in most of the gray matter of the right cerebral hemisphere. CONCLUSION: Gadopentetate dimeglumine appears to be safe in doses up to 21 mmol/m2 in conjunction with barrier disruption in rats. A human small cell lung carcinoma intracerebral xenograft provides a useful method to study brain tumors.

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.

Dexamethasone decreases the delivery of tumor-specific monoclonal antibody to both intracerebral and subcutaneous tumor xenografts.

The effect of dexamethasone on the delivery of monoclonal antibody L6 IgG to intracerebral and subcutaneous LX-1 small cell lung carcinoma xenografts was evaluated in nude rats (n = 157). Dexamethasone (0, 8, or 24 mg/m2) was given 18 hours before infusion of L6 IgG, with or without osmotic disruption of the blood-brain barrier. Compared with controls, the 8 mg/m2 dose decreased delivery of L6 IgG (12-37%) to all tissues, but the only significant decrease (P < 0.001) was in the subcutaneous tumor (37%). In the 24 mg/m2 group, L6 IgG delivery was significantly (P < 0.001) decreased to all tissues (37-60%). Dexamethasone had no effect on plasma levels. Barrier disruption significantly (P < 0.0001) increased L6 IgG delivery to intracranial tumor and surrounding brain, but not to subcutaneous tumor or plasma. The percentage of decremental effect of dexamethasone on L6 IgG delivery was the same with and without barrier disruption and was not associated with the time the animals were killed (P > 0.05). Compared with controls, the ratio of intracranial tumor to normal brain showed no change with dexamethasone, but the ratios of both intracranial and subcutaneous tumors to plasma significantly (P < 0.002) decreased with both doses. The in vitro cell binding capacity of L6 IgG to LX-1 cells remained unchanged after incubation of cells with dexamethasone over a 3-log concentration for 4 days, demonstrating no effect on antigen expression. This study suggests that dexamethasone has a clinically relevant generalized (i.e., central nervous system and systemic) vascular effect on permeability to L6 IgG monoclonal antibody.

Effects of gadopentetate dimeglumine administration after osmotic blood-brain barrier disruption: toxicity and MR imaging findings.

Osmotic blood-brain barrier disruption with intraarterial chemotherapy has been shown to be beneficial in the treatment of malignant brain tumors. Imaging blood-brain barrier disruption is necessary to document the extent and degree of disruption and to correlate disruption with drug delivery. The present study evaluated blood-brain barrier disruption with gadopentetate dimeglumine-enhanced MR imaging and the associated toxicity of gadopentetate dimeglumine administration. Blood-brain barrier disruption was performed in seven dogs for imaging analysis and 17 dogs for toxicity evaluation. In the absence of gadopentetate dimeglumine administration, blood-brain barrier disruption could not be imaged. Enhanced MR imaging with a gadopentetate dimeglumine dose of 0.1 mmol/kg provided good images of disruption at an imaging time of 3 hr after disruption. However, when gadopentetate dimeglumine was given intravenously in conjunction with osmotic blood-brain barrier disruption, there was a statistically significant (p = .02) dose-dependent increase in the frequency of seizures, with 50% of the animals who received 0.1 mmol/kg and 75% who received 0.2 mmol/kg developing delayed seizures. Our findings show that, as with ionized iodinated CT contrast agents, gadopentetate dimeglumine is associated with toxicity when used in conjunction with osmotic blood-brain barrier disruption in dogs. Such toxicity may be a contraindication to the use of gadopentetate dimeglumine for monitoring patients with osmotically induced disruption of the blood-brain barrier.

Delivery of melanoma-associated immunoglobulin monoclonal antibody and Fab fragments to normal brain utilizing osmotic blood-brain barrier disruption.

Iodinated monoclonal antibodies (IgG 96.5 and two monomeric Fab fragments 96.5 and 48.7) to melanoma-associated antigens were administered after osmotic blood-brain barrier (BBB) opening in normal rats. Osmotic BBB disruption significantly (P less than 0.0001) increased monoclonal antibody delivery to the brain. Following BBB opening and intracarotid administration, there was no difference in the disrupted brain concentration integral area under the curve between Fab and IgG over the 72-h experimental period. However, Fab concentration in the disrupted brain was initially higher than IgG, and the clearance was more rapid (P less than 0.0001), decreasing 50% by approximately 4.5 h compared to 25.5 h for IgG. Plasma clearance was also more rapid for the Fab than IgG. The levels decreased 50% by 1.5 h for Fab and 15 h for IgG. The route and timing of antibody infusion had a significant effect on delivery to the disrupted brain with the Fab fragments but not with the intact IgG. Antibody recovered from disrupted brain retained its immunological reactivity as measured by a cell binding assay for at least 24 h. IgG and Fab delivery to the ipsilateral brain after BBB disruption increased (P less than 0.001) with increasing dose over a more than 3-log dose range. These data provide information applicable to the therapeutic use of monoclonal antibodies in brain tumor treatment.

Osmotic blood-brain barrier opening to IgM monoclonal antibody in the rat.

Pharmacokinetic parameters of iodinated monoclonal antibody (MAb) delivery to normal rat brain were examined. The mean cerebrovascular permeability-surface area (PA; permeability X capillary surface area) to immunoglobulin M (IgM) MAb (mol wt 1,000,000) 10 min after infusion was 0.40 X 10(-6) S-1. When osmotic blood-brain barrier (BBB) disruption is utilized, the PA increased to 8.36 X 10(-6) S-1. Neither intravenous nor intracarotid MAb administration significantly affected delivery to brain. However, osmotic BBB opening significantly (P less than 0.0005) increased MAb uptake independent of the route of administration. After BBB opening and intracarotid MAb the maximum concentration in brain at 1 h was 0.72% per gram of the total administered dose. For 6 h postdisruption, ipsilateral brain levels were 25- to 100-fold greater than in the contralateral hemisphere or nonbarrier-disrupted controls. MAb concentration in brain slightly decreased over 72 h (P less than 0.05). Antibody recovered from disrupted brain retained 90% of its immunological reactivity for at least 24 h. MAb delivery to ipsilateral brain after BBB disruption was linear over a dose of 0.5-5.0 micrograms IgM, whereas the percentage of the total administered dose remained unchanged. After osmotic treatment, barrier opening was maximal to MAb delivery for 1 min with delivery declining rapidly thereafter. The type of anesthesia used and the administration of a thyroid-blocking agent were found to affect brain MAb levels after BBB disruption.

Osmotic blood-brain barrier modification: monoclonal antibody, albumin, and methotrexate delivery to cerebrospinal fluid and brain.

In the dog, osmotic opening of the blood-brain barrier (BBB) in the posterior circulation via the vertebral artery and in the anterior circulation via the internal carotid artery was utilized to increase the delivery of three substances of varying molecular weight to the central nervous system. The cerebrospinal fluid (CSF) concentration of all three agents dramatically increased after BBB opening. In contrast to methotrexate, Evans blue-albumin and monoclonal antibody (MAb) concentrations in CSF were 6-fold greater when given after posterior rather than anterior circulation BBB opening. Conversely, MAb delivery to brain parenchyma was optimized after osmotic BBB modification via the carotid artery. This suggests that, with higher molecular weight substances, osmotic barrier opening has a differential effect on the blood-brain vs. blood-CSF barriers.

Growth of human lung tumor in the brain of the nude rat as a model to evaluate antitumor agent delivery across the blood-brain barrier.

We have developed a brain tumor model in the nude rat utilizing NCI-N417D human small cell carcinoma of the lung grown both intracerebrally and s.c. The median latency period from the time of intracerebral tumor inoculation to the onset of neurological symptoms is 13 days with an intracerebral tumor take rate of 91% (29 of 32). The median survival is 13 days, and all animals were dead by Day 26. The tumor is discrete, well circumscribed, with occasional leptomeningeal spread and with minimal evidence of surrounding cerebral edema. Intracerebrally, this tumor is usually impermeable to Evan's blue:albumin (Mr 68,500) but not fluorescein (Mr 376). Although variable, the intracerebral tumor is less permeable to methotrexate than is the same tumor grown s.c. in the same animal (P less than 0.005). The intraarterial and i.v. routes of methotrexate administration in the presence and absence of blood-brain barrier opening were evaluated. Drug delivery to the intracerebral tumor and ipsilateral brain was significantly (P less than 0.025) greater when the methotrexate was given intraarterially and was significantly (P less than 0.0025) increased after osmotic blood-brain barrier opening. After barrier opening, methotrexate concentration was enhanced 3- to 4-fold in tumor and 10- to 20-fold in brain around tumor. Thus, the nude rat provides a model to investigate the biology and therapeutic responsiveness of human small cell carcinoma of the lung grown intracerebrally where it develops a blood-tumor barrier similar to that seen in humans. This model further provides the unique opportunity to investigate the role of osmotic blood-brain barrier opening in the treatment of a tumor which is sensitive to chemotherapeutic agents and for which tumor-specific monoclonal antibodies are available.

Immunosuppression by phenytoin: implication for altered immune competence in brain-tumor patients.

This investigation was conducted to examine the immunosuppressive potential of phenytoin in vivo and to document a correlation between phenytoin therapy and depressed lymphocyte responsiveness to mitogens. It was thought that phenytoin, the most widely used anticonvulsant agent, may play some role in the immunosuppression seen in brain-tumor patients. The effect of phenytoin on mitogen-stimulated lymphocyte function was evaluated by tritiated (3H)-thymidine incorporation and lymphocyte nuclear size distribution. Lymphocytes from either phenytoin-treated or normal rabbits were incubated for 90 hours in culture medium in the presence of three mitogens: phytohemagglutinin (PHA), concanavalin A (Con A), and pokeweed mitogen (PWM). Significant suppression of mitogen-induced activation of the lymphocytes from treated animals was demonstrated. The present studies suggest a possible connection between phenytoin therapy and altered immune competence in brain-tumor patients.