Does P-glycoprotein play a role in clinical resistance of malignant astrocytoma?

P-glycoprotein (P-gp) is a 170 kDa transmembrane glycoprotein which plays a significant role in modulating pleomorphic or multiple drug resistance (MDR) in a wide variety of human cancers like renal and colorectal carcinoma. However, its role in modulating drug resistance in other types of cancer is less well defined. The purpose of this review is to critically examine the evidence that P-gp plays an important role in producing drug resistance in astrocytic gliomas. Malignant astrocytoma is clinically resistant to most types of cytotoxic drugs, including those associated with the MDR phenotype and the cross-resistance patterns of short-term cultures derived from malignant glioma are consistent with this phenotype. Consequently, it might be expected that this tumor would express high levels of P-gp. However, immunohistochemical findings from a number of previous studies have provided conflicting data about the expression of P-gp in these tumors, although P-gp has been consistently detected in normal brain in the endothelial cells in cerebral blood vessels and is thought to contribute to the blood-brain barrier phenomena. In order to determine if P-gp contributes to drug resistance in malignant astrocytoma, we undertook a study of P-gp expression in a panel of short-term cultures derived from these tumors in which we determined the in vitro chemosensitivity. However, immunocytochemical studies with a panel of antibodies which recognize both internal and external epitopes of the P-gp molecule have consistently failed to show the characteristic membrane staining associated with MDR in any of the cultures, including those markedly cross-resistant to vincristine and doxorubicin. One antibody, JSB-1, showed heterogeneous granular cytoplasmic staining which was unrelated to a particular pattern of drug resistance. This is probably because this antibody cross-reacts with a widely distributed cytoplasmic antigen, pyruvate carboxylase, which is present in abundance in normal astrocytes. The unexpectedly poor specificities of many of the antibodies thought to be specific for P-gp is reviewed in the context of malignant astrocytoma. In conclusion, the role of P-gp in producing drug resistance in malignant astrocytoma is questionable and further studies might more profitably concentrate on the mechanisms of resistance to DNA-damaging agents like the nitrosoureas, methylating agents or platinum-based drugs.

Routes and doses of lignocaine hydrochloride for analgesia of the velvet antler of stags

AIM

To evaluate the effectiveness of various routes of administration and doses of local anaesthetic to provide analgesia of the velvet antler of young stags.

METHODS

In study 1, in which an electrical stimulus was used, 64 l-year-old male red and red X wapiti deer with velvet antler lo-30 cm long, were randomly allocated to one of ten treatments with four treatments/animal, and 23 or 24 antlers/treatment. Treatments delivered included three control groups, three local anaesthetic (2% lignocaine HCL) doses delivered by ring block (5, 10 or 15 ml per pedicle), and a high or low regional block with or without an auriculopalpebral nerve block (5 ml per site). An electrical stimulus was applied before and 1,2,4 and 8 minutes after local anaesthetic treatments and to controls, at an increasing voltage until a response was observed. The voltage and animal responses were recorded. In Study 2 the same seven local anaesthetic treatments (16-I 8 antlers/treatment) were evaluated using 58 of the stags from Study 1 when antlers were ready for removal, but a saw cut was used as the test stimulus. A test cut was applied to the antler I,2 and 4 minutes after application of local anaesthetic. If no response was observed, the antler was removed at that time.

RESULTS

In Study 1, major dose and treatment effects were significantly different (p < 0.05) with the outcome variable being whether or not the deer responded. No stags given the high dose ring block responded to electrical stimulation 1 minute after treatment, one responded at 2 minutes, and none responded at 4 or 8 minutes. At least one animal responded after all other treatments at all time intervals. More deer responded after the low regional block than the high regional block, and there was a lower response rate when the auriculopalpebral nerves were anaesthetised. In Study 2, no deer responded 2 minutes after the medium dose ring block treatment. Three of 18 stags receiving the high dose ring block still responded after 2 minutes, and one responded after 4 minutes. Responses occurred to all other treatments at each time, with some deer requiring further administration of local anaesthetic before antler removal, even with the four minute waiting period.

CONCLUSION

Ring blocks produced more consistent analgesia of the velvet antler than regional nerve blocks. The high dose ring block produced analgesia faster and more effectively than lower doses, and the regional nerve blocks were more effective when the auriculopalpebral nerve was blocked.

Unilateral pallidotomy for Parkinson's disease: results after more than 1 year

OBJECTIVE

To examine follow up results of unilateral ventral medial pallidotomy in 22 patients with advanced Parkinson's disease more than 1 year after the operation in comparison with their results (previously reported) at 3 months.

METHODS

Twenty patients who had undergone unilateral pallidotomy were assessed with the core assessment programme for intracerebral transplantation (CAPIT) protocol preoperatively, at 3 months postoperatively, and again after a median postoperative follow up of 14 months. Two further patients had only one evaluation 3 months postoperatively.

RESULTS

The reduction of contralateral dyskinesias (median 67%) at 3 months was slightly attenuated after 1 year to 55% (both p<0.001 compared with baseline). A less pronounced effect on ipsilateral and axial dyskinesias decreased from 39% to 33% (p<0.005 and p<0.01), and from 50% to 12.5% (p<0.001 and p<0.01), respectively. However, there was no significant change between the 3 month and the follow up assessment. The modest improvement of the contralateral unified Parkinson's disease rating scale (UPDRS) motor score in the "off" state remained improved compared with preoperative levels, but less significantly (26%, p<0.001, and 18%, p<0.01). The activities of daily living (ADL) subscore of the UPDRS in the off state remained improved with median changes of 23% and 22% at follow up (both p<0. 005). There was no significant improvement of "on" state or ipsilateral off state motor scores. Median modified Hoehn and Yahr scores in off and on state were unchanged, as was the time spent off. Speech in off had significantly deteriorated by 1 year after the operation.

CONCLUSIONS

The beneficial effects of unilateral pallidotomy persist for at least 12 months and, dyskinesias are most responsive to this procedure.

Structural changes induced by mupirocin in Staphylococcus aureus cells

Cells of mupirocin-sensitive, moderately-resistant and highly-resistant cultures of Staphylococcus aureus (mupirocin MICs 0.13, 16 and > 512 mg/l, respectively) were exposed to various concentrations of the antibiotic and examined by transmission electron microscopy. The most severe damage occurred in mupirocin-sensitive cells. Cells from moderately-resistant cultures trained in vitro to high-level mupirocin resistance were more hydrophobic than the parent cells. The antibiotic was slowly lethal to the mupirocin-sensitive strain and sub-inhibitory concentrations prevented or reduced growth of the other strains over a 6 h incubation period, irrespective of whether the drug was added at zero time or in the exponential growth phase.

Accuracy of true frameless stereotaxy: in vivo measurement and laboratory phantom studies. Technical note

The authors present the results of accuracy measurements, obtained in both laboratory phantom studies and an in vivo assessment, for a technique of frameless stereotaxy. An instrument holder was developed to facilitate stereotactic guidance and enable introduction of frameless methods to traditional frame-based procedures. The accuracy of frameless stereotaxy was assessed for images acquired using 0.5-tesla or 1.5-tesla magnetic resonance (MR) imaging or 2-mm axial, 3-mm axial, or 3-mm helical computerized tomography (CT) scanning. A clinical series is reported in which biopsy samples were obtained using a frameless stereotactic procedure, and the accuracy of these procedures was assessed using postoperative MR images and image fusion. The overall mean error of phantom frameless stereotaxy was found to be 1.3 mm (standard deviation [SD] 0.6 mm). The mean error for CT-directed frameless stereotaxy was 1.1 mm (SD 0.5 mm) and that for MR image-directed procedures was 1.4 mm (SD 0.7 mm). The CT-guided frameless stereotaxy was significantly more accurate than MR image-directed stereotaxy (p = 0.0001). In addition, 2-mm axial CT-guided stereotaxy was significantly more accurate than 3-mm axial CT-guided stereotaxy (p = 0.025). In the clinical series of 21 frameless stereotactically obtained biopsies, all specimens yielded the appropriate diagnosis and no complications ensued. Early postoperative MR images were obtained in 16 of these cases and displacement of the biopsy site from the intraoperative target was determined by fusion of pre- and postoperative image data sets. The mean in vivo linear error of frameless stereotactic biopsy sampling was 2.3 mm (SD 1.9 mm). The mean in vivo Euclidean error was 4.8 mm (SD 2 mm). The implications of these accuracy measurements and of error in stereotaxy are discussed.

Measurement of changes in opioid receptor binding in vivo during trigeminal neuralgic pain using [11C] diprenorphine and positron emission tomography

The binding of [11C]diprenorphine to mu, kappa, and delta subsites in cortical and subcortical structures was measured by positron emission tomography in vivo in six patients before and after surgical relief of trigeminal neuralgia pain. The volume of distribution of [11C]diprenorphine binding was significantly increased after thermocoagulation of the relevant trigeminal division in the following areas: prefrontal, insular, perigenual, mid-cingulate and inferior parietal cortices, basal ganglia, and thalamus bilaterally. In addition to the pain relief associated with the surgical procedure, there also was an improvement in anxiety and depression scores. In the context of other studies, these changes in binding most likely resulted from the change in the pain state. The results suggest an increased occupancy by endogenous opioid peptides during trigeminal pain but cannot exclude coexistent down-regulation of binding sites.

Radiotherapy in the treatment of benign meningioma of the skull base

OBJECT

This study was undertaken to assess the long-term efficacy and toxicity of conventional fractionated external-beam radiation in the treatment of benign skull base meningioma.

METHODS

This is a retrospective study of 82 patients with histologically verified benign skull base meningioma treated by surgery followed by fractionated external-beam radiation at the Royal Marsden Hospital between 1962 and 1992. The 5- and 10-year progression-free survival (PFS) rates were 92% and 83%, respectively, with the site of disease being the only independent prognostic factor for tumor control according to multivariate analysis. The 10-year PFS rate for patients with sphenoid ridge meningiomas was 69% compared with 90% for those with tumors in the parasellar region. The overall 10-year survival rate was 71%, with performance status and patient age found to be significant independent prognostic factors. Six patients had worsening vision, which was due to cataract in five cases and retinopathy in one. There were no recorded cases of cranial nerve neuropathy.

CONCLUSIONS

The excellent long-term tumor control and length of survival with minimal toxicity associated with conventional external-beam radiation should serve as a baseline for evaluation of new treatment strategies such as radiosurgery and skull base surgery.

MRI-guided stereotactic brain biopsy: a review of 33 cases

MRI is being increasingly used for the detection of intracranial lesions. MRI-guided stereotactic brain biopsy is infrequently performed. We audited our recent experience of this procedure, and demonstrated that it is feasible and comparable to CT-guided biopsy in terms of diagnostic accuracy with a low procedural morbidity. We critically analyse its future role in the presence of more recent developments.

Mupirocin resistance in staphylococci: development and transfer of isoleucyl-tRNA synthetase-mediated resistance in vitro

Mupirocin resistance could be transferred from highly resistant clinical isolates of Staphylococcus aureus to highly sensitive recipients of Staph. aureus, Staph. epidermidis and Staph. haemolyticus. Transconjugants of the latter two organisms could transfer this resistance into mupirocin-sensitive Staph. aureus. Moderately resistant strains did not transfer this resistance to sensitive recipients, nor did strains with high-level mupirocin resistance developed by serial transfer or habituation. The inhibitory effects of mupirocin on crude isoleucyl-tRNA synthetases (IRS) isolated from mupirocin-sensitive and -resistant strains of Staph. aureus have been determined. Drug concentrations needed to produce 50% inhibition, I50 values, were very low against IRS from a highly sensitive strain, somewhat higher against IRS from moderately resistant strains, much higher against enzyme from strains trained in vitro to high-level resistance, and considerably higher still against IRS extracted from clinical isolates possessing high-level mupirocin resistance and from the transconjugates of such strains resulting from crosses with mupirocin-sensitive strains. It is concluded that high-level resistance in clinical isolates is plasmid-mediated involving a second, mupirocin-resistant IRS whereas in moderately resistant strains, and in strains trained in vitro to high-level resistance, chromosomal mutations are likely to be responsible for decreasing IRS sensitivity.

Sensitivity of short-term cultures derived from human malignant glioma to the anti-cancer drug temozolomide

The activity of temozolomide, which has shown clinical activity against malignant glioma, has been assessed in vitro against short-term cultures derived from these tumors using an intermediate duration microtitration assay with MTT reduction as the end-point This assay has previously been shown to correlate closely with a monolayer clonogenic assay. Sensitivity was assessed in 15 short-term cultures (passage levels 3-9) derived from WHO grade III and IV astrocytomas. These cultures had a median ID50 value of 258 microM for temozolomide and 16.13 microM for CCNU. Maximum serum concentrations of temozolomide are of the order of 75 microM but only three of 15 (20%) cultures had ID50s below this value. Fourteen of 15 (93%) cultures displayed cross-resistance between temozolomide and CCNU, although one line which was extremely resistant to CCNU retained sensitivity to temozolomide. Comparative studies of published clonogenic survival curves indicate that the short-term glioma cell lines used in this study have similar sensitivities to established glioma cell lines, whilst colon carcinoma cell lines and bladder carcinoma are often more resistant to these drugs. Cell lines from testicular teratoma cell lines may show exquisite sensitivity to temozolomide and this level of sensitivity is seen only occasionally in short-term cultures derived from malignant glioma.

Accuracy of true frameless stereotaxy: in vivo measurement and laboratory phantom studies. Technical note

The authors present the results of accuracy measurements, obtained in both laboratory phantom studies and an in vivo assessment, for a technique of frameless stereotaxy. An instrument holder was developed to facilitate stereotactic guidance and enable introduction of frameless methods to traditional frame-based procedures. The accuracy of frameless stereotaxy was assessed for images acquired using 0.5-tesla or 1.5-tesla magnetic resonance (MR) imaging or 2-mm axial, 3-mm axial, or 3-mm helical computerized tomography (CT) scanning. A clinical series is reported in which biopsy samples were obtained using a frameless stereotactic procedure, and the accuracy of these procedures was assessed using postoperative MR images and image fusion. The overall mean error of phantom frameless stereotaxy was found to be 1.3 mm (standard deviation [SD] 0.6 mm). The mean error for CT-directed frameless stereotaxy was 1.1 mm (SD 0.5 mm) and that for MR image-directed procedures was 1.4 mm (SD 0.7 mm). The CT-guided frameless stereotaxy was significantly more accurate than MR image-directed stereotaxy (p = 0.0001). In addition, 2-mm axial CT-guided stereotaxy was significantly more accurate than 3-mm axial CT-guided stereotaxy (p = 0.025). In the clinical series of 21 frameless stereotactically obtained biopsies, all specimens yielded the appropriate diagnosis and no complications ensued. Early postoperative MR images were obtained in 16 of these cases and displacement of the biopsy site from the intraoperative target was determined by fusion of pre- and postoperative image data sets. The mean in vivo linear error of frameless stereotactic biopsy sampling was 2.3 mm (SD 1.9 mm). The mean in vivo Euclidean error was 4.8 mm (SD 2 mm). The implications of these accuracy measurements and of error in stereotaxy are discussed.

The EASI project--improving the effectiveness and quality of image-guided surgery

In recent years, advances in computer technology and a significant increase in the accuracy of medical imaging have made it possible to develop systems that can assist the clinician in diagnosis, planning, and treatment. This paper deals with an area that is generally referred to as computer-assisted surgery, image-directed surgery, or image-guided surgery. We report the research, development, and clinical validation performed since January 1996 in the European Applications in Surgical Interventions (EASI) project, which is funded by the European Commission in their "4th Framework Telematics Applications for Health" program. The goal of this project is the improvement of the effectiveness and quality of image-guided neurosurgery of the brain and image-guided vascular surgery of abdominal aortic aneurysms, while at the same time reducing patient risks and overall cost. We have developed advanced prototype systems for preoperative surgical planning and intraoperative surgical navigation, and we have extensively clinically validated these systems. The prototype systems and the clinical validation results are described in this paper.

Neuronavigation--impact on operating time

It is uncertain whether the use of image-guided surgery has an influence on operating time. We prospectively studied the time requirements which have to be invested for using image-guided surgery and performed a comparison of operating room times from 125 matched pairs of image-guided and conventional operations. Our study revealed that neuronavigation has to be regarded as time neutral in general neurosurgery, whereas in stereotactic surgery, namely biopsy retrival, a significant reduction of anaesthetic time can be achieved through the complete separation of imaging and operation in the frameless approach.

Malignant meningioma of the oculomotor nerve without dural attachment. Case report and review of the literature

Meningiomas, thought to arise from arachnoid cap cells, are usually attached to the dura. Malignancy is present in approximately 1% of these tumors. The authors report the case of a patient with a malignant meningioma arising from the oculomotor nerve with no dural attachment. The patient presented with a 7-month history of left-sided ptosis and diplopia. Magnetic resonance imaging demonstrated an extrinsic mass compressing the root of the oculomotor nerve at its exit from the midbrain. During surgery, a left-sided subtemporal approach revealed the tumor to be arising from the oculomotor nerve. Histological investigation showed a malignant spindle cell lesion with an immunohistochemical profile that was consistent with malignant meningioma. To the authors' knowledge, this is the first documented case of a malignant meningioma arising from the oculomotor nerve.

Postimaging brain distortion: magnitude, correlates, and impact on neuronavigation

OBJECT

This prospective study was conducted to quantify brain shifts during open cranial surgery, to determine correlations between these shifts and image characteristics, and to assess the impact of postimaging brain distortion on neuronavigation.

METHODS

During 48 operations, movements of the cortex on opening, the deep tumor margin, and the cortex at completion were measured relative to the preoperative image position with the aid of an image-guidance system. Bone surface offset was used to assess system accuracy and correct for registration errors. Preoperative images were examined for the presence of edema and to determine tumor volume, midline shift, and depth of the lesion below the skin surface. Results were analyzed for all cases together and separately for four tumor groups: 13 meningiomas, 18 gliomas, 11 nonglial intraaxial lesions, and six skull base lesions. For all 48 cases the mean shift of the cortex after dural opening was 4.6 mm, shift of the deep tumor margin was 5.1 mm, and shift of the cortex at completion was 6.7 mm. Each tumor group displayed unique patterns of shift, with significantly greater shift at depth in meningiomas than gliomas (p = 0.007) and significantly less shift in skull base cases than other groups (p = 0.003). Whereas the preoperative image characteristics correlating with shift of the cortex on opening were the presence of edema and depth of the tumor below skin surface, predictors of shift at depth were the presence of edema, the lesion volume, midline shift, and magnitude of shift of the cortex on opening.

CONCLUSIONS

This study quantified intraoperative brain distortion, determined the different behavior of tumors in four pathological groups, and identified preoperative predictors of shift with which the reliability of neuronavigation may be estimated.

Interactive image-guided neuroendoscopy: development and early clinical experience

Technical advances and pioneering surgeons have established neuroendoscopy as an accepted diagnostic and therapeutic tool. The clinical indications for endoscopy, variety of operative techniques and number of endoscopic surgeons continue to increase steadily. However, there are fundamental limits to the scope of freehand endoscopy principally governed by the need for direct vision of anatomical and pathological structures. In addition, whilst the expert neuroendoscopist is only occasionally disorientated by complex distorted anatomy, the rising number of novices are likely to be mislead relatively often. We report the integration of neuroendoscopy with an optical neuronavigation system to provide interactive image-guided neuroendoscopy. This combination both removes the constraining requirement for direct vision and provides accurate localisation to guide the surgeon during surgery. We describe the clinical application of this method to two cases where image-guided endoscopy was essential to the safe completion of the procedure.

A study of medial pallidotomy for Parkinson's disease: clinical outcome, MRI location and complications

We have studied the effects of unilateral ventral medial pallidotomy in 26 patients with medically intractable Parkinson's disease with marked drug-induced dyskinesias. Preoperatively, all patients were assessed during one 5-day admission according to the Core Assessment Programme for Intracerebral Transplantation (CAPIT) protocol, including rating in the 'practically defined off' and 'best on' states before and during a single-dose levodopa challenge. Motor performance was assessed with subset categories of the Unified Parkinson's Disease Rating Scale (UPDRS), timed motor tests and a standard dyskinesia rating scale. Pallidotomy was performed under stereotaxic CT guidance with intra-operative extracellular microelectrode recording made from the basal ganglia. All patients were re-assessed 3 months postoperatively and a subgroup (n = 9) have so far also been re-assessed after 1 year. Pre- and postoperative performance scores were compared in order to determine which categories of performance improved postoperatively. Significance was accepted at P < 0.005 in order to take into account the multiple number of comparisons performed. Patient medication was compared pre- and postoperatively and the morbidity associated with surgery was also recorded. The most significant improvement postoperatively was the diminution of 'on' dyskinesias contralaterally (67%, P = 0.0001); however, ipsilateral (45%, P = 0.0006) and axial (50%, P = 0.0008) dyskinesias also improved. Contralateral to pallidotomy, the median 'off' motor UPDRS score improved by 27% (P = 0.001) and a significant improvement was also observed in contralateral rigidity by 25% (P = 0.001). There were trends towards improvement in contralateral tremor (33%, P = 0.016) and bradykinesia (24%, P = 0.013) scores. Ipsilateral rigidity improved by 22% (P = 0.005), but other ipsilateral motor scores did not alter significantly. The 'off' gait/postural instability score and 'off' walking time showed marginally significant improvements by 7% (P = 0.007) and 29% (P = 0.014), respectively. On medication, no significant postoperative improvements in parkinsonism were detected. Anti-parkinsonian medication increased by 11% postoperatively. In the subgroup who were available for assessment 1 year postoperatively, responses were generally maintained. Two (7.7%) of the 26 patients had fatal complications (one cerebral haemorrhage and one haemorrhagic infarct) directly related to surgery. Among the remaining 24 patients, four (15.4% of the total 26) had major complications (two persisting and two transient). Ten patients (38.5%) had minor complications. The majority of the complications (major and minor) occurred in the earlier operated patients and the complication rate subsequently declined with increasing operative experience. The remaining 10 patients (38.5%) had no significant side-effects. One of these 10 patients died from an incidental malignant glioma 6 months postoperatively. These findings confirm that levodopa-induced dyskinesias are dramatically reduced following ventral medial pallidotomy and constitute the principal indication for pallidotomy. Improvements in underlying parkinsonism were of smaller magnitude. Pallidotomy may also offer some patients an opportunity to increase antiparkinsonian medication. Patient selection for medial pallidotomy should, therefore, be based largely on anticipated improvements in levodopa-induced dyskinesias, but this must be balanced against the associated morbidity and mortality.

Max_r: an optimal method for the selection of subsets of foods for the measurement of specific nutrient exposures

Max_r, a new method of food subset selection for the measurement of specific nutrient exposures, is programmed. Frequently, epidemiologic questionnaires are designed to measure several individual level exposures, including exposure to one or more nutrients. Although most nutrients are contained in a large number of foods, constraints on questionnaire size allow inclusion of only a subset of these. When nutrient exposure as measured in a subset of foods will be used to estimate the effect of the nutrient on disease risk with a logistic regression model, max_r is the optimal method of choosing the subset. Various aspects of the program are illustrated with a numerical example measuring dietary protein intake. The executable version of this Fortran program for IBM compatible PCs requires 3Mb of memory. It is available (along with complete documentation, test data and output) via e-mail from thomasd@epndce.nci.nih.gov or upon submission of a diskette formatted for MS-DOS.

Pretreatment prediction of the chemotherapeutic response of human glioma cell cultures using nuclear magnetic resonance spectroscopy and artificial neural networks

Both tumor metabolism and its response to cytotoxic drugs are intrinsic properties of tumor cells. It is therefore likely that there is a relationship between the two properties, however subtle and complex, wherein the metabolic characteristics of tumor cells can reflect the inherent response (resistance or sensitivity) of these cells to cytotoxic drugs. We used artificial neural network analysis to show that it is possible to distinguish, prior to treatment, between drug-resistant and drug-sensitive human glioma cell cultures from their metabolic profiles, as given by high-resolution proton nuclear magnetic resonance spectra of the cell extracts, and to predict their cellular response to the chemotherapeutic drug 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea in vitro. The results suggest that neural network analysis of tumor nuclear magnetic resonance spectra has potential as a prognostic tool for determining treatment of gliomas, ultimately noninvasively, and may be used to provide information about the metabolic pathways involved in drug response that may be helpful in developing novel treatments for these tumors.

Heterogeneity of chemosensitivity in six clonal cell lines derived from a spontaneous murine astrocytoma and its relationship to genotypic and phenotypic characteristics

Heterogeneity in drug sensitivity must, in part, account for the relative lack of success with single agent chemotherapy for glioblastoma multiforme (GBM). In order to develop in vitro model systems to investigate this, clones derived from the VM spontaneous murine astrocytoma have been characterised with regard to drug sensitivity. Six clonal cell lines have been tested for sensitivity to a panel of cytotoxic drugs using an intermediate duration 35S-methionine uptake assay. These lines have previously been extensively characterised with regard to morphological, antigenic, kinetic, tumourigenic potential in syngeneic animals and chromosomal properties and display considerable heterogeneity. The present study indicates that heterogeneity extends to sensitivity to all classes of cytotoxic drugs. The greatest difference in sensitivity between the clones was seen in response to cell cycle-specific drugs like the Vinca alkaloids (14-fold and 20-fold for vincristine (VCR) and vindesine (VIND) respectively), while the nitrosoureas, CCNU and BCNU displayed a smaller fold difference in sensitivity (4.3 and 3.6-fold difference respectively). All the clones were considerably more resistant to the adriamycin (ADM), cis-platinum (C-PLAT) and the Vinca alkaloids than the parental cell line although the difference in sensitivity between the clones and parental cell line were less marked for the nitrosoureas and procarbazine (PCB). It has also been possible to examine the relationship between drug sensitivity and the phenotypic and genotypic properties of these clonal cell lines. There is a relationship between chromosome number and sensitivity of a wide variety of cytotoxic drugs including the nitrosoureas, Vinca alkaloids, PCB, C-PLAT, BLEO but not ADR or 5-FU. Clones with small numbers of chromosomes were more resistant than clones with gross polyploidy. Similarly, sensitivity to Vinca alkaloids and ADM, but not other classes of drugs, was greatest in cells with numerous cytoplasmic processes and which did not express large amounts of cell surface fibronectin. Preliminary experiments have been conducted on reconstituting clonal mixtures of cells with different sensitivity to Vinca alkaloids and results from these studies indicate that the drug resistance phenotype is dominant, with clonal mixtures of sensitive and resistant cell adopting the sensitivity of the more resistant partner. These cell lines should prove to be useful models for examining the cell biological basis of drug resistance in glioma and may lead to the identification and exploitation of novel cellular targets in new therapies for GBM.