Phase I/II study of intraventricular and intrathecal ACNU for leptomeningeal neoplasia

Intrathecal therapy for the management of leptomeningeal metastatic disease: a scoping review of the current literature and ongoing clinical trials

PURPOSE

Leptomeningeal metastatic disease (LMD) from advanced malignancies has poor prognoses and limited treatments. Intrathecal therapy (ITT) protocols are available, showing variable outcomes. We reviewed the therapeutic and toxicity profiles of ITT in LMD.

METHODS

PubMed, EMBASE, Web-of-Science, and Scopus were searched following the PRISMA-ScR guidelines to include studies reporting ITT for LMD.

CLINICALTRIAL

gov and Cochrane were searched to identify ongoing clinical trials.

RESULTS

We included 27 published studies encompassing 2161 patients and 4 ongoing trials. LMD originated from brain metastases (85.5%), lymphomas (5.4%), high-grade gliomas (4.6%), medulloblastomas (2.3%), and leukemias (2.1%). LMD was mostly diagnosed with the co-presence of neurological-related symptoms and positive imaging and/or cerebrospinal fluid cytology (60.8%). The most common ITT agents were methotrexate (35.9%), cytarabine (21.9%), and thiotepa (8.2%), standalone or combined. Patients received a median of 6.5 ITT cycles (range, 1.0-71.0) via intraventricular (58.8%) or lumbar intrathecal (41.2%) routes. The Ommaya reservoir was implanted in 38.5% cases. Concurrent systemic chemotherapy (45.2%) and/or radiotherapy (30.6%) were used. After 1-3 cycles, 44.7% patients had improved clinical status and 29.9% converted into negative cerebrospinal fluid cytology. The most common ITT-related severe adverse events were neutropenia (6.5%), meningitis (5.2%) and encephalopathy (4.5%). Median freedom from progression was 2.4 months (range, 0.1-59.5) and median overall survival 5.5 months (range, 0.1-148.0).

CONCLUSION

Current ITT protocols are variable but effective and well-tolerated in LMD. Ongoing trials are investigating dose-limiting toxicity profiles and long-term overall survival. Future studies should analyze the therapeutic and safety profiles of ITT compared to newer systemic therapies.

Leptomeningeal Spread in Glioblastoma: Diagnostic and Therapeutic Challenges

BACKGROUND

Glioblastoma (GBM) is the most common and aggressive primary malignant brain tumor. Leptomeningeal spread (LMS) is a severe complication of GBM, raising diagnostic and therapeutic challenges in clinical routine.

METHODS

We performed a review of the literature focused on LMS in GBM. MEDLINE and EMBASE databases were queried from 1989 to 2019 for articles describing diagnosis and therapeutic options in GBM LMS, as well as risk factors and pathogenic mechanisms.

RESULTS

We retrieved 155 articles, including retrospective series, case reports, and early phase clinical trials, as well as preclinical studies. These articles confirmed that LMS in GBM remains (a) a diagnostic challenge with cytological proof of LMS obtained in only 35% of cases and (b) a therapeutic challenge with a median overall survival below 2 months with best supportive care alone. For patients faced with suggestive clinical symptoms, whole neuroaxis magnetic resonance imaging and cerebrospinal fluid analysis are both recommended. Liquid biopsies are under investigation and may help prompt a reliable diagnosis. Based on the literature, a multimodal and personalized therapeutic approach of LMS, including surgery, radiotherapy, systemic cytotoxic chemotherapy, and intrathecal chemotherapies, may provide benefits to selected patients. Interestingly, molecular targeted therapies appear promising in case of actionable molecular target and should be considered.

CONCLUSION

As the prognosis of glioblastoma is improving over time, LMS becomes a more common complication. Our review highlights the need for translational studies and clinical trials dedicated to this challenging condition in order to improve diagnostic and therapeutic strategies.

IMPLICATIONS FOR PRACTICE

This review summarizes the diagnostic tools and applied treatments for leptomeningeal spread, a complication of glioblastoma, as well as their outcomes. The importance of exhaustive molecular testing for molecular targeted therapies is discussed. New diagnostic and therapeutic strategies are outlined, and the need for translational studies and clinical trials dedicated to this challenging condition is highlighted.

Leptomeningeal metastasis

Leptomeningeal metastasis (LM) results from dissemination of cancer cells to both the leptomeninges (pia and arachnoid) and cerebrospinal fluid (CSF) compartment. Breast cancer, lung cancer, and melanoma are the most common solid tumors that cause LM. Recent approval of more active anticancer therapies has resulted in improvement in survival that is partly responsible for an increased incidence of LM. Neurologic deficits, once manifest, are mostly irreversible, and often have a significant impact on patient quality of life. LM-directed therapy is based on symptom palliation, circumscribed use of neurosurgery, limited field radiotherapy, intra-CSF and systemic therapies. Novel methods of detecting LM include detection of CSF circulating tumor cells and tumor cell-free DNA. A recent international guideline for a standardization of response assessment in LM may improve cross-trial comparisons as well as within-trial evaluation of treatment. An increasing number of retrospective studies suggest that molecular-targeted therapy, such as EGFR and ALK inhibitors in lung cancer, trastuzumab in HER2+ breast cancer, and BRAF inhibitors in melanoma, may be effective as part of the multidisciplinary management of LM. Prospective randomized trials with standardized response assessment are needed to further validate these preliminary findings.

Recent Advancements of Treatment for Leptomeningeal Carcinomatosis

Treatment of Leptomeningeal carcinomatosis (LMC) from solid cancers has not advanced noticeably since the introduction of intra-cerebrospinal fluid (CSF) chemotherapy in the 1970's. The marginal survival benefit and difficulty of intrathecal chemotherapy injection has hindered its wide spread use. Even after the introduction of intraventricular chemotherapy with Ommaya reservoir, frequent development of CSF flow disturbance, manifested as increased intracranial pressure (ICP), made injected drug to be distributed unevenly and thus, the therapy became ineffective. Systemic chemotherapy for LMC has been limited as effective CSF concentration can hardly be achieved except high dose methotrexate (MTX) intravenous administration. However, the introduction of small molecular weight target inhibitors for primary cancer treatment has changed the old concept of 'blood-brain barrier' as the ultimate barrier to systemically administered drugs. Conventional oral administration achieves an effective concentration at the nanomolar level. Furthermore, many studies report that a combined treatment of target inhibitor and intra-CSF chemotherapy significantly prolongs patient survival. Ventriculolumbar perfusion (VLP) chemotherapy has sought to increase drug delivery to the subarachnoid CSF space even in patients with disturbed CSF flow. Recently authors performed phase 1 and 2 clinical trial of VLP chemotherapy with MTX, and 3/4th of patients with increased ICP got controlled ICP and the survival was prolonged. Further trials are required with newly available drugs for CSF chemotherapy. Additionally, new LMC biologic/pharmacodynamic markers for early diagnosis and monitoring of the treatment response are to be identified with the help of advanced molecular biology techniques.

Carcinomatous meningitis: Leptomeningeal metastases in solid tumors

Leptomeningeal metastasis (LM) results from metastatic spread of cancer to the leptomeninges, giving rise to central nervous system dysfunction. Breast cancer, lung cancer, and melanoma are the most frequent causes of LM among solid tumors in adults. An early diagnosis of LM, before fixed neurologic deficits are manifest, permits earlier and potentially more effective treatment, thus leading to a better quality of life in patients so affected. Apart from a clinical suspicion of LM, diagnosis is dependent upon demonstration of cancer in cerebrospinal fluid (CSF) or radiographic manifestations as revealed by neuraxis imaging. Potentially of use, though not commonly employed, today are use of biomarkers and protein profiling in the CSF. Symptomatic treatment is directed at pain including headache, nausea, and vomiting, whereas more specific LM-directed therapies include intra-CSF chemotherapy, systemic chemotherapy, and site-specific radiotherapy. A special emphasis in the review discusses novel agents including targeted therapies, that may be promising in the future management of LM. These new therapies include anti-epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors erlotinib and gefitinib in nonsmall cell lung cancer, anti-HER2 monoclonal antibody trastuzumab in breast cancer, anti-CTLA4 ipilimumab and anti-BRAF tyrosine kinase inhibitors such as vermurafenib in melanoma, and the antivascular endothelial growth factor monoclonal antibody bevacizumab are currently under investigation in patients with LM. Challenges of managing patients with LM are manifold and include determining the appropriate patients for treatment as well as the optimal route of administration of intra-CSF drug therapy.

Challenges in drug delivery to tumors of the central nervous system: an overview of pharmacological and surgical considerations

The majority of newly diagnosed brain tumors are treated with surgery, radiation, and the chemotherapeutic temozolomide. Development of additional therapeutics to improve treatment outcomes is complicated by the blood-brain barrier (BBB), which acts to protect healthy tissue from chemical insults. The high pressure found within brain tumors adds a challenge to local delivery of therapy by limiting the distribution of bolus injections. Here we discuss various drug delivery strategies, including convection-enhanced delivery, intranasal delivery, and intrathecal delivery, as well as pharmacological strategies for improving therapeutic efficacy, such as blood-brain barrier disruption.

Medulloblastoma in childhood: revisiting intrathecal therapy in infants and children

INTRODUCTION

Intrathecal chemotherapy is being explored in medulloblastoma in pre-school children as part of brain-sparing strategies and as an alternative to unacceptably neurotoxic cranio-spinal radiotherapy. The range of drugs suitable for this route of administration is restricted by the lack of research evidence of pharmacological suitability and efficacy of other drugs in medulloblastoma.

METHODS

Ideal clinical, biological, physicochemical and pharmaceutical properties for intrathecal administration were defined through literature review of pharmaceutical texts, Medline, Embase and consulting the manufacturers. A total of 126 chemotherapy agents were assessed against these criteria by searching the academic domain of pharmaceutical texts, computer databases and consultation with manufacturers.

RESULTS

Of the 126 candidate drugs, 99 were rejected because of documentation of their irritant nature, neurotoxicity and requirement for hepatic activation in standard pharmaceutical texts. Fifty were rejected for a single identifiable reason including, neurotoxicity (n = 24), irritant (n = 15), needs enzyme activation (n = 5), clinical evidence of intrathecal neurotoxicity (n = 4) and no evidence of tumour-specific efficacy (n = 2). Where two reasons were cited the justifications were: neurotoxic and irritant (n = 3) and needs activation and systemic administration results in equivalent concentration (n = 1). Twenty-seven drugs remained of which 12 were selected as eligible for further clinical investigation, and 15 were selected for further pre-clinical investigation.

CONCLUSIONS

The pre-determined criteria were not applicable, in their entirety, in the majority of drugs, due to lack of information in the academic domain, emphasising the importance of a more open approach for sharing basic drug information. The prioritised list of 12 candidate drugs for clinical trial and 15 for pre-clinical investigation justify that a concerted research effort in this area of practice is made.

Leptomeningeal metastases from solid malignancy: a review

Leptomeningeal metastases (LMM) consist of diffuse involvement of the leptomeninges by infiltrating cancer cells. In solid tumors, the most frequent primary sites are lung and breast cancers, two tumors where the incidence of LMM is apparently increasing. Careful neurological examination is required to demonstrate multifocal involvement of the central nervous system (CNS), cranial nerves, and spinal roots, which constitute the clinical hallmark of the disease. Cerebro-spinal fluid (CSF) analysis is almost always abnormal but only a positive cytology or demonstration of intrathecal synthesis of tumor markers is diagnostic. T1-weighted gadolinium-enhanced sequence of the entire neuraxis (brain and spine) plays an important role in supporting the diagnosis, demonstrating the involved sites and guiding treatment. Radionuclide CSF flow studies detect CSF compartmentalization and are useful for treatment planning. Standard therapy relies mainly on focal irradiation and intrathecal or systemic chemotherapy. Studies using other therapeutic approaches such as new biological or cytotoxic compounds are ongoing. The overall prognosis remains grim and quality of life should remain the priority when deciding which treatment option to apply. However, a sub-group of patients, tentatively defined here, may benefit from an aggressive treatment.

Pharmacokinetics Following Intraventricular Administration of Chemotherapy in Patients with Neoplastic Meningitis

Intraventricular administration of chemotherapy is one approach to overcoming the limited distribution of anticancer drugs and their active metabolites into the CNS. This form of regional chemotherapy has led to effective treatment of occult and overt meningeal leukaemia in humans. In contrast, the efficacy of this therapy is extremely limited in the treatment of leptomeningeal dissemination of various solid tumours. Pharmacokinetic studies of the commonly intraventricularly applied anticancer agents in humans have demonstrated that, using low drug doses, very high drug concentrations can be achieved in the cerebrospinal fluid (CSF) and relatively high concentrations in the leptomeninges but not in the brain tissue and the plasma. Therefore, this approach is not an effective treatment for bulky disease of brain tissue, and results in minimal systemic toxicity. In comparison with intralumbar administration, lower interpatient variability of CSF drug concentrations and improved clinical efficacy were observed. 'Concentration x time' schedules, i.e. frequent small drug doses over a short period, enable long-term CSF exposure to cytotoxic drug concentrations while avoiding excessively high and potentially neurotoxic drug concentrations. The technique of ventriculolumbar cerebrospinal perfusion delivers continuously high drug concentrations throughout the CSF for several hours, but its widespread use is limited by the technical complexities of this approach. In this article, the dosages, schedules and pharmacokinetic data of routinely used intraventricular agents in humans, e.g. methotrexate, cytarabine, glucocorticoids and thiotepa, are outlined in detail. In addition, pharmacokinetic data of investigational agents for intraventricular administration (diaziquone, DTC 101, mercaptopurine, mafosfamide, etoposide, topotecan, nimustine [ACNU] and bleomycin) are presented. Better understanding of the CSF pharmacology of these drugs is an essential prerequisite for safe, effective administration of these drugs. Investigational efforts are underway to verify the feasibility and efficacy of different dosages, schedules and combination therapies of these new intra-CSF agents. Current and future clinical research should also focus on methods allowing the delivery of tumoricidal drug concentrations for extended periods into the CSF and the brain tissue while minimising neurotoxicity and systemic toxicity (e.g. liposomal drug preparations, monoclonal antibodies, immunotoxins and gene therapy).

Survival of patients with high grade glioma treated with intrathecal thiotriethylenephosphoramide for ependymal or leptomeningeal gliomatosis

BACKGROUND

The diagnosis of leptomeningeal dissemination of malignant glioma (meningeal gliomatosis) is associated with poor survival. Intrathecal (IT) chemotherapeutic agents used to achieve tumor control and improve survival include methotrexate, cytosine arabinoside (ara-C), thiotriethylenephosphoramide (thio-TEPA), neocarzinostatin, and 3-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-1-(2-chloroethyl)-1-nitros ourea hydrochloride (ACNU). Little information exists about survival following administration of IT chemotherapy. The authors report survival data from a series of patients with supratentorial anaplastic astrocytoma (AA) or glioblastoma multiforme (GBM) treated for ependymal or leptomeningeal gliomatosis with IT thio-TEPA.

METHODS

The authors reviewed the records of 14 patients treated between 1991 and 1997 (GBM: n = 9; AA: n = 5). All patients were diagnosed with ependymal (n = 8) or leptomeningeal (n = 6) dissemination of tumor on the basis of clinical signs and symptoms, ependymal or leptomeningeal contrast enhancement on magnetic resonance imaging (MRI), and/or cerebrospinal fluid analysis. All 14 patients underwent placement of a ventricular reservoir system and subsequent instillation of IT thio-TEPA on a weekly basis for 6-12 weeks. Response to treatment was evaluated clinically and by MRI at intervals of 1-3 months and 3-6 months from the initiation of IT thio-TEPA. Data on survival from the time of diagnosis of dissemination was assessed.

RESULTS

The median survival, from the time of diagnosis of ependymal or leptomeningeal dissemination, of patients who received IT thio-TEPA was 10 months (AA = 19 months; GBM = 10 months). Five of 14 patients had a radiographic response to treatment within 6 months. The median survival of patients with a radiographic response was 15.5 months, compared with 10 months for nonresponders. No significant neurotoxicity or myelopathy was observed.

CONCLUSIONS

Early treatment with IT thio-TEPA may result in improved survival with minimal morbidity. Radiographic response may predict prolonged survival.

Intraventricular immunotoxin therapy for leptomeningeal neoplasia

OBJECTIVE

The goals of this clinical trial of intraventricular 454A12-rRA therapy were to identify dose-limiting toxicities, to evaluate the pharmacokinetics of single-dose intraventricular 454A12-rRA, and to detect antitumor activity.

METHODS

We performed a pilot study of intraventricular therapy with the immunotoxin 454A12-rRA in eight patients with leptomeningeal spread of systemic neoplasia. The immunotoxin 454A12-rRA is a conjugate of a monoclonal antibody against the human transferrin receptor and recombinant ricin A chain, the enzymatically active subunit of the protein toxin ricin. Patients were treated with single doses of 454A12-rRA ranging from 1.2 to 1200 micrograms.

RESULTS

The early phase half-life of 454A12-rRA in ventricular cerebrospinal fluid (CSF) averaged 44 +/- 21 minutes, and the late phase half-life averaged 237 +/- 86 minutes. The clearance of the immunotoxin was faster than the clearance of coinjected technetium-99m-diethylenetriamine penta-acetic acid, averaging approximately 2.4-fold greater. No 454A12-rRA degradation was detected by Western blot analysis of ventricular CSF for a period of 24 hours, and bioactivity was retained in CSF paralleling the concentration of immunotoxin. No acute or chronic drug toxicity was identified in patients who received less than or equal to 38 micrograms of 454A12-rRA by intraventricular injection. Doses more than or equal to 120 micrograms caused a CSF inflammatory response that was associated with transient headache, vomiting, and altered mental status. This acute syndrome was responsive to steroids and CSF drainage. No systemic toxicity was detected. In four of the eight patients, a greater than 50% reduction of tumor cell counts in the lumbar CSF occurred within 5 to 7 days after the intraventricular dose of 454A12-rRA; however, no patient had their CSF cleared of tumor, and clinical or magnetic resonance imaging evidence of tumor progression was demonstrated in seven of the eight patients after treatment.

CONCLUSION

Tumoricidal concentrations of the immunotoxin 454A12-rRA can be attained safely in the CSF of patients with leptomeningeal tumor spread.

Carcinomatous meningitis in solid tumours

Carcinomatous meningitis (CM) is an uncommon but devastating complication of malignancy. The management is controversial and clear recommendations cannot be made because: 1) Most series include patients with CM that has arisen from different primary malignancies which are associated with different median survival intervals. 2) There have been no prospective randomised investigations of treatment modalities in patients with CM from a particular tumour type. 3) The definition of response varies from one report to another so that some response rates refer to cytological changes in the CSF while others take clinical, cytological and biochemical parameters into account. 4) Reports include patients with and without parenchymal metastases and the natural history of carcinomatous meningitis in the two situations may differ. The median survival of solid tumour carcinomatous meningitis (excluding leukaemia and lymphoma) is approximately 2-3 months and patients with breast cancer have the longest survival (median 3 months). Currently patients are treated with radiotherapy to part or all of the neuraxis with either intrathecal or intravenous chemotherapy but the relative contribution of these modalities to survival or quality of life remains unknown. Approximately 50% of patients with carcinomatous meningitis die from other causes, including systemic disease. The two most important endpoints for the patient, neurological improvement and overall survival, are seldom used in isolation in the literature. Many reports have focused on surrogate markers of response, namely biochemical and cytological data points but the correlation between clinical status and these parameters is poor because of differences between lumbar and ventricular CSF and disturbances of CSF flow in CM. The current literature does not provide clear guidelines for the treatment of this condition. Multicentre, prospective, randomised trials should be conducted that address questions of most relevance to the patient, namely neurological status and overall survival.

Ventriculolumbar perfusion of 3-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-1-(2-chloroethyl)-1-nitrosou rea hydrochloride

We report on the toxicity, intrathecal pharmacokinetics, and therapeutic effect of the ventriculolumbar perfusion of 3-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-1-(2-chloroethyl)-1-nitros our ea hydrochloride (ACNU) against the subarachnoid dissemination of primary central nervous system tumors. Fifteen patients received ventriculolumbar perfusion of ACNU. One was treated with ventriculolumbar perfusion of ACNU alone, and the others underwent concomitant systemic chemotherapy; three of these patients received irradiation as well. ACNU was administered at an initial dose of 0.5 and was increased to 1.5 to 10.0 mg in six patients. Because of a lack of Level 2 or greater toxicity, the subsequent seven patients received 8.7 to 10.0 mg of ACNU dissolved in artificial cerebrospinal fluid (CSF) at a concentration of 0.1 mg/ml, from the start of the treatment. During ACNU administration, the lumbar CSF was drained at approximately the same rate as that of the infusion. Twelve patients received from 3 to 42 courses (average, 14 courses). The cumulative dose of ACNU ranged from 5 to 330.4 mg (average, 82.9 mg). One patient had a convulsion; two patients experienced transient headache, nausea, and vomiting; two others reported transient headache, nausea, vomiting, and fecal incontinence; and one experienced transient nausea, vomiting, and fecal incontinence. No side effects were noted in the other nine patients. When 9.0 to 9.5 mg of ACNU, dissolved in 90 to 95 ml of artificial CSF, was administered for 37 to 52 min, the maximum concentration of ACNU in the lumbar CSF was 9.86 to 12.79 micrograms/ml and the area under the drug concentration-time curve was 260.8 to 502.5 micrograms.min/ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of intrathecally administered ACNU in mongrel dogs: pharmacokinetics and quantitative autoradiographic study

The pharmacokinetics of 1-(4-amino-2-methyl-5-pyrimidinyl) methyl-3-(2-chloroethyl)-3-nitrosourea (ACNU) in the cerebrospinal fluid (CSF), were determined in dogs after ventriculolumbar perfusion (VLP, n = 6), and bolus injection into the ventricle (VB, n = 2), cisterna magna (MB, n = 5), and lumbar cistern (LB, n = 3), by high-performance liquid chromatography. The VLP method introduced effective amounts of ACNU into the lumbar cistern for cell kill in vitro. That is, the areas under the time concentration curve (AUC) of ACNU in the lumbar CSF for those receiving a 1.5 mg perfusion of ACNU were 481, 791, and 520 micrograms.min/ml and those receiving a 5 mg perfusion were 1,081, 2,048, and 1,215 micrograms.min/ml, respectively. These values were superior to 3-log cell kill condition of 9L gliosarcoma and 1.5-log cell kill of HU-126 human glioma cell line. Among the groups to which 5 mg of ACNU was administered, the VLP method attained significantly higher AUC values in the lumbar CSF than MB method. Quantitative autoradiography using an imaging plate system was performed in the VLP group (n = 2), VB group (n = 1), MB group (n = 2), and LB group (n = 2) using a 10 microCi/kg [ethylene-14C] ACNU dose which is thought to be related to the alkylating activity of ACNU. The VLP method attained a stable and abundant distribution of ACNU in the neural axis from the ventricular cavity to the lumbar cistern, but the cerebral convexity surface was devoid of a significant level of ACNU. When the MB method was used, the pharmacokinetic data varied in the cisterna magna and lumbar region, and again no significant level of ACNU was detected in the ventricular cavity. With the LB method, although a rich distribution was detected in the spinal cord, the concentration decreased abruptly at the upper cervical level. The VB method was unsatisfactory for obtaining an effective amount of ACNU in the lumbar region. The research and testing to date indicate that the VLP method is the procedure of choice in the treatment of meningeal dissemination.

Intrathecal chemotherapy with ACNU for meningeal gliomatosis

ACNU [1-(4-amino-2-methyl-5-pyrimidinyl) methyl-3-(2-chloroethyl)-3-nitrosourea hydrochloride], one of the chloroethylnitrosoureas (CENUs), is believed to be effective against malignant glioma when intravenously or intrathecally administered. A rat model with meningeal gliomatosis (MG) induced by an intracisternal inoculation of rat C6 or 9L glioma cells was intrathecally and intravenously treated with ACNU in order to test the feasibility of intrathecal chemotherapy with ACNU in the treatment of meningeal gliomatosis. The median survival time (MST) of the animals was significantly prolonged when ACNU was intrathecally administered at dosages of 0.5 to 1.5 mg kg-1 in the early stages of MG, i.e. within 3 days after the tumour inoculation, whereas intravenous therapy with ACNU at a dose of 15 mg kg-1 did not exhibit any efficacy in the rats inoculated with C6 glioma cells (C6-MG). Intrathecal ACNU, however, at dosages of up to 1.5 mg kg-1 failed to demonstrate any therapeutic effect in the late stage of MG, i.e. 5 days after the tumour inoculation, except in the rats inoculated with 9L brain tumour cells (9L-MG). Intravenous chemotherapy with ACNU at a dose of 15 mg kg-1 extended the MST of the 9L-MG rats more significantly in the late stage of MG than in its early stage. This points to the feasibility of intrathecal ACNU in the treatment of meningeal gliomatosis in its early stages, but not in its late stages in which intravenous ACNU might be more effective than intrathecal treatment against MG of which the parenchyma has already been deeply invaded by the tumour.

Intrathecal chemotherapy with ACNU in a meningeal gliomatosis rat model

Intrathecal administration of ACNU ((1-4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-chloroethyl)-3-nitroso urea hydrochloride) had a remarkable chemotherapeutic effect in a rat model of meningeal gliomatosis. This effect was evaluated in rats with meningeal gliomatosis induced by an intracisternal inoculation of rat C6 glioma cells. The median survival time of the rats treated with a single dose of intrathecal ACNU (1 mg/kg) on Day 1 or Day 3 after tumor inoculation was significantly prolonged by 35.7% to 42.9% or 25.0% to 28.6%, respectively, as compared with that of the control animals. Meningeal gliomatosis rat models treated intrathecally with ACNU (1 mg/kg) 5 days after tumor inoculation or intravenously with ACNU (15 mg/kg) both failed to prolong the survival time of the animals. These findings suggest that intrathecal chemotherapy with a low dose of ACNU is effective in the early stages of meningeal gliomatosis, whereas intravenous chemotherapy with a high dose of ACNU is always ineffective.

Isolation and preliminary characterization of ACNU-resistant sublines of rat brain tumors in vivo

Two variant cells lines resistant to the nitrosourea derivative ACNU ((1-4-amino-2-methyl-5-pyrimidinyl)-methyl-3-(2-chloroethyl)-3-nitrosourea hydrochloride), namely C6/ACNU and 9L/ACNU, were selected in vivo from rat brain tumors. Stable resistance to ACNU proved to be a characteristic of these cell lines, whether they were grown in vivo or in vitro. These cell lines exhibited a different pattern of cross-resistance to a wide range of chemotherapeutic agents with dissimilar chemical structures and mechanisms of action as compared with that of other ACNU-resistant cell lines established in vitro. Distinct cross-resistance was observed in both the C6/ACNU and 9L/ACNU cell lines to chloroethyl-nitrosoureas such as BCNU (carmustine), CCNU (lomustine), and methyl CCNU and, additionally, to vincristine, vinblastine, Adriamycin (doxorubicin), and arabinosylcytosine, but not to bleomycin, methotrexate, cis-platinum, and 5-fluorouracil. This might point to a multifactorial mechanism of drug resistance in ACNU-resistant cell lines derived from rat C6 and 9L brain tumor cells.