Endoscopic sellar floor reconstruction with concha bullosa bone autograft and nasal septal flap: technical case report.

INTRODUCTION: A novel method is introduced for sellar floor reconstruction after expanded endoscopic endonasal transsphenoidal surgery using concha bullosa bone autograft and vascularized, posteriorly based flaps of septal mucoperichondrium. CASE REPORT: A 62-year-old woman presented to her primary care physician with the insidious onset of enlarging hands and feet, coarsening of facial features, and bilateral carpal tunnel syndrome. Endocrine studies revealed elevated growth hormone (22 ng/mL) and somatomedian-C (810 ng/mL) levels. Brain magnetic resonance imaging displayed a 1.2-cm pituitary adenoma. The patient was diagnosed with acromegaly secondary to a pituitary adenoma and underwent expanded endoscopic endonasal transsphenoidal surgery for tumor resection. Preoperatively, the patient was noted to have abnormal right middle turbinate pneumatization (concha bullosa). Following adenoma resection, the sellar floor was reconstructed using concha bullosa bone autograft resected during the endonasal approach. Bilateral vascularized nasoseptal mucosal flaps were then placed over the sellar floor. CONCLUSION: In patients with concha bullosa, conchal bone provides a useful substrate for sellar reconstruction after endoscopic endonasal transsphenoidal surgery.

Intratumoral hemorrhage after remote subtotal microsurgical resection and gamma knife radiosurgery for vestibular schwannoma.

Our report describes the occurrence of intratumoral hemorrhage in a vestibular schwannoma, which was treated with microsurgical resection thirteen years and gamma knife surgery (GKS) more than two years prior to the event. Although rare, it is apparent that bleeding into a vestibular schwannoma remains a possibility, even after the tumor has responded favorably to GKS. Long-term followup of patients with vestibular schwannoma who have been treated with GKS is advisable to assess treatment response and to detect adverse events (e.g. hemorrhage) suspected on clinical grounds.

Focal enhancement of cranial nerve V after radiosurgery with the Leksell gamma knife: experience in 15 patients with medically refractory trigeminal neuralgia.

BACKGROUND AND PURPOSE: Gamma knife radiosurgery is an alternative for the treatment of medically refractory trigeminal neuralgia. Few reports of posttreatment MR imaging appearance of cranial nerve V exist. Our purpose was to define MR imaging characteristics in cranial nerve V after gamma knife radiosurgery. METHODS: We retrospectively reviewed MR images of 15 patients who underwent gamma knife radiosurgery for trigeminal neuralgia. Radiation doses were 35-45 Gy at the 50% isodose line. Thin-section T2-weighted images and contrast-enhanced and nonenhanced T1-weighted images were obtained the day of radiosurgery and within the next 5 mo. Images were scored for enhancement and hyperintensity on T2-weighted images. Time to follow-up imaging and radiation dose were recorded. RESULTS: Mean time to follow-up imaging was 61 +/- 29 d. Posttreatment T2-weighted images showed stable signal intensity in all cases, with radiosurgical target site enhancement in 10. All five patients whose images did not show treatment-related enhancement received radiation doses of 35 Gy. The data suggested a correlation between enhancement with radiation dose (P =.06). No correlation of enhancement with treatment response or time to follow-up existed (P >.05). CONCLUSION: The trigeminal nerve often enhances at the target site after radiosurgery. Lack of trigeminal nerve enhancement occurred only with lower doses (35 Gy at 50%). MR imaging may be useful to confirm the presence and location of the treatment site after gamma knife radiosurgery for trigeminal neuralgia.

2-[1-hexyloxyethyl]-2-devinyl pyropheophorbide-a (HPPH) in a nude rat glioma model: implications for photodynamic therapy.

BACKGROUND AND OBJECTIVE: In this study, we evaluated 2-[1-hexyloxyethyl]-2-devinyl pyropheophorbide-alpha (HPPH or Photochlor) as a photosensitizer for the treatment of malignant gliomas by photodynamic therapy (PDT). STUDY DESIGN/MATERIALS AND METHODS: We performed in vivo reflection spectroscopy in athymic rats to measure the attenuation of light in normal brain tissue. We also studied HPPH pharmacokinetics and PDT effects in nude rats with brain tumors derived from stereotactically implanted U87 human glioma cells. Rats implanted with tumors were sacrificed at designated time points to determine the pharmacokinetics of HPPH in serum, tumor, normal brain, and brain adjacent to tumor (BAT). HPPH concentrations in normal brain, BAT and tumor were determined using fluorescence spectroscopy. Twenty-four hours after intravenous injection of HPPH, we administered interstitial PDT treatment at a wavelength of 665 nm. Light was given in doses of 3.5, 7.5 or 15 J/cm at the tumor site and at a rate of 50 mW/cm. RESULTS: In vivo spectroscopy of normal brain tissue showed that the attenuation depth of 665 nm light is approximately 30% greater than that of 630 nm light used to activate Photofrin, which is currently being evaluated for PDT as an adjuvant to surgery for malignant gliomas. The t1/2 of disappearance of drug from serum and tumor was 25 and 30 hours, respectively. CONCLUSION: Twenty-four hours after injection of 0.5 mg/kg HPPH, tumor-to-brain drug ratios ranged from 5:1 to 15:1. Enhanced survival was observed in each of the HPPH/PDT-treated animal groups. These data suggest that HPPH may be a useful adjuvant for the treatment of malignant gliomas.

Evaluation of systemically administered radiolabeled epidermal growth factor as a brain tumor targeting agent.

We have previously reported a method for labeling epidermal growth factor (EGF) with technetium-99m and have shown that 99mTc-EGF localized in EGF receptor (R) positive intracerebral C6EGFR rat gliomas following intratumoral (i.t.) injection of the radioligand. In the present study, we have evaluated the potential use of 99mTc-EGF as a tumor targeting agent after systemic administration to Fischer rats bearing intracerebral implants of C6EGFRgliomas. Radiolocalization was determined following intravenous (i.v.) or intracarotid (i.c.) injection with or without hyperosmotic mannitol induced disruption of the blood-brain barrier (BBB-D). As determined by gamma-scintillation counting, 4 h after i.c. injection of 99mTc-EGF, 0.34% of the injected dose per gram (% ID/g) was localized in C6EGFR tumors. which expressed 10(5)-10(6) EGFR sites per cell, compared to 0.07% ID/g in animals bearing C6 wildtype gliomas, which do not express EGFR. The corresponding tumor to brain ratios were 5.6 and 1.6, respectively. Tumors could be visualized by external gamma-scintigraphy in rats bearing C6EGFR but not C6 wildtype gliomas, thereby establishing that radiolocalization was dependent upon receptor expression. Intracarotid administration of 99mTc-EGF significantly increased tumor uptake compared to i.v. injection (0.34 vs 0.14% ID/g, p < 0.04). BBB-D disruption, followed by i.c. injection of 99mTc-EGF, however, did not significantly enhance tumor uptake compared to i.c. injection without BBB-D (0.45% vs 0.34% ID/g, p > 0.1). The uptake of 99mTc-EGF was approximately 4-9% ID/g in the liver and 12-20% ID/g in the kidneys after i.c. or i.v. administration. External gamma-scintigraphy of regions of interest over the liver and kidneys revealed that approximately 70-80% of the whole body radioactivity accumulated in these organs, and only 0.47-0.83% in the tumor following i.v. or i.c. administration of 99m9Tc-EGF. Our study has demonstrated that EGF can be used as a specific targeting agent for EGFR (+) rat brain tumors. However, it is unlikely that systemic injection of EGF-based bioconjugates can deliver sufficient amounts of the ligand to brain tumors for therapeutic purposes and direct delivery by means of either intratumoral injection or a variant of it such as convection enhanced delivery will be required.

The impact of age and sex on the incidence of glial tumors in New York state from 1976 to 1995.

OBJECT: In this study the authors describe secular trends in the incidence of three glial tumors--glioblastoma multiforme (GBM), astrocytoma not otherwise specified (ANOS), and anaplastic astrocytoma (AA)--in New York state from 1976 through 1995. They also describe the effect of age and sex on the relative risk (RR) for these tumors, specifically GBM. METHODS: Crude, age-, and sex-specific incidence rates were calculated for each tumor type from 1976 to 1995 by using data from the New York State Cancer Registry. Age-adjusted incidence rates were calculated by the direct standardization procedure, in which the 1970 United States Census Population Standard Million is used. The RR of GBM for the female population was calculated and plotted. Statistical comparisons were made using Pearson's correlation coefficient and regression analysis with the coefficient of variation. CONCLUSIONS: The age-adjusted incidence of these three glial tumors increased during the study period. Increases in age-specific incidence of GBM were primarily limited to patients 60 years of age or older. The reasons for these increases cannot be fully explained with the data. Those in the female population had a lower risk of developing these tumors than those in the male. For GBM, the protective effect of sex was first evident at the approximate age of menarche, was greatest at the approximate age of menopause, and decreased in postmenopausal age strata. The overall protective effect of female sex and the described trend in RR for GBM in the female population suggests that sex hormones and/or genetic differences between males and females may play a role in the pathogenesis of this tumor.

Deletion and tandem duplication of exons 2 - 7 in the epidermal growth factor receptor gene of a human malignant glioma.

The epidermal growth factor receptor (EGFR) gene is frequently amplified and rearranged in malignant gliomas with expression of oncogenic deletion mutants (DM). The most common mutant EGFRvIII, which contains a deletion of exons 2 - 7, is constitutively autophosphorylated and inefficiently downregulated. Other less common EGFR mRNA species in gliomas contain tandem duplication of exons, which encode the tyrosine kinase (TK) and calcium mediated receptor internalization (CAIN) domains of the molecule. We examined a panel of human malignant gliomas and found one tumor that expressed four related EGFR proteins, including 125-, 140-, 170-, and 180-kDa species. This tumor also contained four EGFR-related mRNA species, including both wild type EGFR and EGFRvIII transcripts. A third transcript contained a deletion of exons 2 - 7 and 12 - 13 corresponding to the 125-kDa protein. A fourth transcript contained an in-frame, tandem duplication of exons 2 - 7 (EGFR.TDM/2 - 7). The 180-kDa, tandem duplication mutant (TDM) exhibited enhanced basal phosphorylation and impaired downregulation. In contrast to the 140-kDa EGFRvIII; however, phosphorylation of the 180-kDa EGFR.TDM/2 - 7 was strongly induced by ligand. Expression of both deletion and tandem duplication mutants in the same tumor suggests that the mechanisms responsible for DM and TDM formation might be closely related. Oncogene (2000) 19, 4542 - 4548.

Oncogenic epidermal growth factor receptor mutants with tandem duplication: gene structure and effects on receptor function.

A number of epidermal growth factor receptor (EGFR) deletion mutants have been identified in gliomas, in which the EGFR gene is frequently amplified and rearranged. We have previously characterized the structure of a gene in A-172 human glioma cells that encodes a 190-kDa EGFR mutant with tandem duplication of the tyrosine kinase (TK) and calcium-mediated internalization (CAIN) domains. Here we describe a 185-kDa tandem duplication mutant (TDM) that is expressed in KE and A-1235 glioma cells, along with certain functional characteristics of the mutants. The corresponding transcripts in KE and A-1235 cells contain 1053 additional nucleotides representing an in-frame duplication of exons 18 through 25 which encode the entire TK region and a portion of the CAIN domain. As with duplication of the entire TK/CAIN region (exons 18-26) in A-172 cells, duplication of exons 18-25 is associated with a specific genomic rearrangement between flanking introns. Involved introns contain homology to recombination signal sequence (RSS) heptamers present in the V(D)J region of the T lymphocyte receptor gene. In defined medium, both oncogenic TDM are constitutively autophosphorylated and inefficiently downregulated. High-affinity binding is reduced in EGFR.TDM/18-26, although the t1/2 of receptor internalization is not prolonged.

Synergistic cytotoxicity, apoptosis and protein-linked DNA breakage by etoposide and camptothecin in human U87 glioma cells: dependence on tyrosine phosphorylation.

In this study, simultaneous administration of certain inhibitors of topoisomerase I and topoisomerase II produced synergistic cytotoxicity in a series of human glioma cell lines. Camptothecin (CPT) and etoposide (VP-16) produced combination indices (CI) <1.0 in all glioma cell lines tested, including those that were relatively resistant to the two topoisomerase inhibitors individually. In contrast, CPT and VP-16 produced additive cytotoxicity in HT-29 and SW-620 colon carcinoma cell lines. To explore the molecular basis for synergy in glioma cells, we focused on one glioma cell line (U87) in which even sub-cytotoxic doses of CPT potentiated the action of VP-16. Except for genistein (a topo II agent with tyrosine kinase inhibitory function), all topo II inhibitors tested (doxorubicin, ellipticine, and m-AMSA) were synergistic with CPT. While CPT and VP-16 produced cytotoxicity and protein-linked DNA breaks (PLDB) that were supra-additive in U87 glioma cells, CPT and genistein produced additive results. Pretreatment of U87 cells with the tyrosine kinase inhibitor tyrphostin-A23 or the tyrosine phosphatase activator O-phospho-L-tyrosine (OPLT) reduced combination PLDB from synergistic to additive levels, but had no effect on the formation of PLDB induced by either CPT or VP-16 alone. CPT and VP-16 also produced a synergistic accumulation of sub-G0 (apoptotic) cells which was blocked by tyrphostin-A23. No significant increase in topoisomerase protein levels could be detected in response to combination treatment. Thus, synergistic effects between topoisomerase I and topoisomerase II inhibitors in U87 glioma cells may depend upon phosphorylation of cellular proteins other than the topoisomerases themselves.

Intratumoral infusion of topotecan prolongs survival in the nude rat intracranial U87 human glioma model.

Topotecan is a topoisomerase (topo) I inhibitor with promising activity in preclinical studies. We hypothesized that low-dose intratumoral delivery of topotecan would be highly effective for gliomas. Human glioma cell lines (U87, U138 and U373) displayed different sensitivities to topotecan (IC50 range: 0.037 microM to 0.280 microM) in cell culture. The most resistant of the glioma cell lines (U87) was implanted stereotactically into the brains of nude rats. Twelve days later, at which time tumor diameter measured 2 to 2.5 mm, animals were randomized to three groups: group I, intratumoral topotecan infused via osmotic pump (n = 12); group II, intratumoral saline infusion (n = 7); and group III, no treatment (n = 10). Animals were sacrificed when signs of deterioration developed, or at 60 days. Animals in group I had a mean survival time (MST) of > 55 days (range = 40-60); whereas, those in groups II and III had MST of 26.1 (range = 21-31) and 26.5 (range = 20-30) days, respectively. The differences in survival between group I and each of the other groups were statistically significant (p < 0.0001; Logrank Mantel-Cox). None of the animals that survived 60 days had histological evidence of residual tumor at sacrifice. Measurement of topotecan levels in normal brain revealed cytotoxic concentrations up to 4.5 mm from the site of infusion. This study demonstrates that intratumoral topotecan delivered via an osmotic pump prolongs survival in the U87 human glioma model.

Neurosarcoidosis presenting as a large suprasellar mass. Magnetic resonance imaging findings.

We present unusual magnetic resonance imaging (MRI) findings in a case of neurosarcoidosis. MRI revealed a large solitary suprasellar mass which resembled a neoplasm. The lesion was isointense and hyperintense on T1-weighted images, hypointense on T2-weighted images, and intensely homogeneously enhancing. Biopsy revealed a polymorphous inflammatory lesion with giant cells, which extended from the hypothalamus, consistent with neurosarcoidosis. The diagnosis of neurosarcoidosis should be considered in patients presenting with large midline tumor-like suprasellar mass lesions.

Correlation of intraluminal thrombosis in brain tumor vessels with postoperative thrombotic complications: a preliminary report.

OBJECT: Thrombotic complications (deep vein thrombosis and/or pulmonary embolization [DVT/PE]) occur in 18 to 50% of patients harboring brain tumors who undergo neurosurgical procedures. Such patients are at risk for DVT/PE because of immobility, paresis, hypovolemia, and lengthy surgery. The present study was undertaken to see whether tumor patients at highest risk for DVT/PE could be identified so that augmentation of prophylactic measures might be used to reduce the incidence of thrombotic complications. METHODS: The authors conducted a retrospective analysis of 488 patients enrolled in their brain tumor registries between 1988 and 1995, identifying 57 patients (12%) with recorded symptomatic DVT, PE, or both postoperatively. In 24 of these 57 cases histological specimens were retrievable for review, allowing an in-depth analysis. Forty-five patients were lost to follow-up review, and the remaining 386 patients had no record of systemic thrombosis. Slides of pathological specimens were retrievable in 50 cases in which there was no DVT/PE. From these 50 cases, 25 were selected at random to represent the control group by a blinded observer. Seventeen (71%) of the 24 brain tumor specimens obtained in patients with DVT/PE stained positively for intraluminal thrombosis (ILT) after hematoxylin and eosin had been applied. The odds ratio associated with the presence of ILT was 17.8, with a confidence interval ranging from 4 to 79.3. No evidence of ILT was found in 22 patients (88%) within the control group (p < 0.0001, Fisher's exact test). Other factors that may predispose patients with brain tumors to DVT/PE-limb paresis, extent of tumor removal, and duration of the surgery-were also analyzed and found not to be statistically significant. Therefore, these factors were not the basis for differences seen between the study and control groups. CONCLUSIONS: These preliminary observations suggest that the presence of ILT within malignant glioma or glioblastoma tumor vessels may represent a marker of tumor-induced hypercoagulability.

Tandem duplication of the epidermal growth factor receptor tyrosine kinase and calcium internalization domains in A-172 glioma cells.

Amplification and rearrangement of the epidermal growth factor receptor (EGFR) gene occur frequently in malignant gliomas. Rearrangement may also lead to the expression of potentially oncogenic EGFR deletion mutants. Data presented here indicate the existence of a 190 kDa mutant form of the EGFR in A-172 glioma cells that is substantially different from the deletion mutants characterized previously. The EGFR-like protein is expressed along with the 170 kDa wild type EGFR. It is detectable with antibodies to both extracellular and intracellular regions of the EGFR, but is not crossreactive with other HER-family members. The wild type and mutant receptors undergo phosphorylation in response to treatment with TGFalpha and are associated with expression of both 10.5 kb and 11.5 kb EGFR-related transcripts. Combined reverse transcription-polymerase chain reaction (RT-PCR) identifies a unique transcript in A-172 cells that encodes an in-frame, tandem duplication of both tyrosine kinase and calcium internalization (TK/CAIN) domains (exons 18 through 26). The duplication of these domains is associated with a specific genomic rearrangement between potential v-myb and c-myb consensus binding sites within introns 26 and 17 of the EGFR gene resulting in the formation of a chimeric intron.

Loop III region of platelet-derived growth factor (PDGF) B-chain mediates binding to PDGF receptors and heparin.

Site-directed mutagenesis of the platelet-derived growth factor (PDGF) B-chain was conducted to determine the importance of cationic amino acid residues (Arg160-Lys161-Lys162; RKK) located within the loop III region in mediating the biological and cell-association properties of the molecule. Binding to both PDGF alpha-and beta-receptors was inhibited by the conversion of all three cationic residues into anionic glutamates (RKK-->EEE), whereas an RKK-->SSS mutant also exhibited a modest loss in affinity for beta-receptors. Replacements with serine at either Arg160 (RKK-->SKK) or at all three positions (RKK-->SSS) had little effect on binding to alpha-receptors. Replacements with either glutamic or serine residues at any of the three positions also resulted in significant inhibition of heparin-binding activity. Furthermore, the RKK-->EEE mutant exhibited decreased association with the cell surface and accumulated in the culture medium as 29-32 kDa forms. Stable transfection of U87 astrocytoma cells with RKK-->EEE mutants of either the A-chain or the B-chain inhibited malignant growth in athymic nude mice. Despite altered receptor-binding activities, each of the loop III mutants retained full mitogenic activity when applied to cultured Swiss 3T3 cells. CD spectrophotometric analysis of the RKK-->EEE mutant revealed a secondary structure indistinguishable from the wild type, with a high degree of beta-sheet structure and random coil content (50% and 43% respectively). These findings indicate an important role of the Arg160-Lys161-Lys162 sequence in mediating the biological and cell-associative activities of the PDGF-BB homodimer, and reveal that the mitogenic activity of PDGF-BB is insufficient to mediate its full oncogenic properties.

Radiolabeling of epidermal growth factor with 99mTc and in vivo localization following intracerebral injection into normal and glioma-bearing rats.

High grade gliomas may have amplified expression of the epidermal growth factor receptor (EGFR) gene c-erb-B, which often is associated with increased expression of transmembrane EGFR. The purpose of the present study was to develop a method for labeling EGF with 99mTc and to determine whether the resulting radioligand would localize, following intracerebral injection, in rats bearing EGFR-positive gliomas. EGF has a relatively low molecular mass (approximately 6 kDa) compared to monoclonal antibodies, and this has allowed smaller bioconjugates, which should diffuse more rapidly within the brain and more effectively target disseminated glioma cells, to be constructed. In the present study, EGF has been labeled with either 131I or 99mTc, and in vitro uptake of the resulting radioligand has been investigated using C6EGFR rat glioma cells, which had been transfected with the EGFR gene. Cellular uptake of 131I radioactivity peaked after approximately 30 min of incubation with [131I]EGF, following which time it declined, while 99mTc radioactivity continued to increase over a 6 h incubation with [99mTc]-EGF. To determine if radiolabeled EGF had in vivo tumor-localizing properties, C6EGFR glioma cells were implanted stereotactically into the brains of Fischer rats. Four weeks later, either 99mTc- or 131I-labeled EGF was injected intracerebrally into normal or glioma-bearing animals using the same stereotactic coordinates. External gamma scintigraphy revealed that 131I radioactivity disappeared rapidly from the brain regions of tumor-bearing animals compared to 99mTc, approximately 50% of which remained in the tumor for up to 12 h. In contrast, only approximately 20% remained in the brains of non-tumor-bearing animals after 6 h. These studies are the first to describe a method for radiolabeling EGF with 99mTc and to detect it by external scintigraphy in the brains of tumor-bearing animals.

Site-directed mutagenesis of the N-linked glycosylation site in platelet-derived growth factor B-chain results in diminished intracellular retention.

Pulse-chase analysis of human platelet-derived growth factor (PDGF) B-chain was conducted in stably transfected Chinese hamster ovary cells to determine precisely the kinetics of processing, intracellular trafficking and secretion. Newly synthesized 31 kDa monomers of the B-chain (p31) dimerized rapidly via disulfide bonds to a p54 species (t1/2 < 30 min). The p54 dimer was processed to a group of intracellular, cell surface (suramin-releasable) and secreted forms whose rates of appearance and disappearance from the cell were measured over a 48 h period. The newly synthesized p31 species was quantitatively converted to p27 by treatment with endoglycosidase H, consistent with efficient N-glycosylation at a site in the N-terminal propeptide region (Asn63-Met64-Thr65). Interruption of B-chain glycosylation by oligodeoxynucleotide-directed mutagenesis resulted in a significant increase in suramin-releasable forms at the cell surface (p34-38) and a concomitant decrease in accumulation of an intracellular p24 species. The glycosylation-defective mutant exhibited slight increases in receptor binding and mitogenic activity. Our results suggest that N-linked glycosylation of the B-chain is not important for formation of mitogenically active protein, but that it plays a role in early intracellular sorting and proteolytic processing events.

Boronated epidermal growth factor as a potential targeting agent for boron neutron capture therapy of brain tumors.

In order for boron neutron capture therapy (BNCT) to be successful, a large number (approximately 10(9)) of 10B atoms must be delivered to each cancer cell in order to sustain a lethal 10B(n, alpha)7Li reaction. The majority of high grade gliomas express an amplified epidermal growth factor receptor (EGFR) gene, and increased numbers of EGFR are found on the cell surface. If a sufficiently large number of 10B atoms could be attached to EGF, the resulting bioconjugates might be useful for targeting brain tumors. In order to accomplish this, we have boronated a fourth-generation starburst dendrimer (SD) using an isocyanato polyhedral borane, Na(CH3)3NB10H8NCO. For conjugation, reactive thiol groups were introduced into the boronated SD using N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP), and EGF was derivatized with m-maleimidobenzoyl-N-hydroxysulfosuccinimide ester (sMBS). Subsequent reaction of thiol groups of derivatized BSD with maleimide groups of derivatized EGF produced stable BSD-EGF bioconjugates containing approximately 960 atoms of boron per molecule of EGF. As determined by electron spectroscopic imaging, the BSD-EGF initially was bound to the cell surface membrane and then was endocytosed, which resulted in accumulation of boron in lysosomes. The favorable in vitro properties of these bioconjugates suggest that they may be useful for the in vivo targeting of EGFR positive brain tumors.

The effect of epidermal growth factor receptor (EGFR) expression on in vivo growth of rat C6 glioma cells.

The discovery of EGFR gene amplification in glioblastoma multiforme has prompted interest in experimental therapies to target the receptor on brain tumor cells. To develop an animal model for in vivo study of such strategies, we transfected C6 glioma cells with a plasmid containing the neomycin resistance gene and the human EGFR gene under the control of the glucocorticoid-inducible MMTV promoter. Following selection with G418, individual clones that expressed EGFR at high levels were selected. Kinetics of EGF binding fit a dual site model indicating the presence of both high (KA = 2.5 x 10(9) M-1) and low (KA = 3.3 x 10(7) M-1) affinity receptors. To assess growth in vivo, graded numbers of either wild-type or transfected cells were implanted into the brains of CD Fischer 344 rats. No differences in survival were observed between groups of animals injected with either wild-type or transfected cells at inocula of 10(3) or 10(4) respectively. In addition, one-third of animals (7/21) challenged with 10(5) or 10(6) transfected cells survived > 50 days compared to 0% of animals (0/12) challenged with 10(5) or 10(6) wild-type cells. Such an effect suggests greater immunogenicity of transfected cells, but only at the larger inocula. Since C6 glioma cells will grow in both outbred and inbred strains, our model should have a number of applications including the in vivo study of EGFR targeting for glioma therapy.