Secondary analysis of Radiation Therapy Oncology Group study (RTOG) 9310: an intergroup phase II combined modality treatment of primary central nervous system lymphoma.

PURPOSE: To determine whether a lower dose of hyperfractionated whole brain radiation reduces central nervous system morbidity without compromising survival for primary CNS lymphoma (PCNSL) patients receiving combined modality treatment. MATERIALS AND METHODS: One hundred and two patients received a course of pre-radiation chemotherapy, followed by whole brain radiation, followed by cytosine-arabinoside. Initial radiation dose was 45 Gy/25 fractions (RT) then the study was amended to reduce this dose for complete responders to induction chemotherapy to 36 Gy/30 fractions/3 weeks (HFX). Eighty-two patients received radiotherapy and were evaluable for toxicity analysis (66 RT patients and 16 HFX patients). MMSE scores and survival for the 40 patients who received radiotherapy after complete response to chemotherapy (27 RT and 13 HFX) were compared. There were no notable differences in pre-treatment patient characteristics between the RT and HFX groups. RESULTS: Neurotoxicity: By 4 years, there were 8/82 (10%) grade 5 neurotoxicities which included 2/16 (13%) grade 5 encephalopathies and 0/27 in the RT group of complete responders to chemotherapy. Survival: There was no statistically significant difference in overall or progression-free survival (PFS) between the chemotherapy-complete responders who received RT and HFX. Cognitive function testing: MMSE scores improved at 8 months across both treatment groups. Analysis of the area under the MMSE curve at 8 months showed no statistically significant difference between RT and HFX groups (P=0.81). Leukoencephalopathy occurred later in the HFX group than in the RT patients. CONCLUSION: Although the HFX schedule represented a 25% reduction in biologically effective tumor dose in comparison, PFS and overall survival were not significantly affected. The HFX regimen delayed but did not eliminate severe neurotoxicity from chemoradiation in PCNSL patients.

Synergy between methionine stress and chemotherapy in the treatment of brain tumor xenografts in athymic mice.

This study describes a novel approach to the treatment of brain tumors with the combination of recombinant L-methionine-alpha-deamino-gamma-lyase and chemotherapeutic regimens that are currently used against such tumors. The growth of Daoy, SWB77, and D-54 xenografts in athymic mice was arrested after the depletion of mouse plasma methionine (MET) with a combination of a MET- and choline-free diet and recombinant L-methionine-alpha-deamino-gamma-lyase. The treated tumor-bearing mice were rescued from the toxic effects of MET withdrawal with daily i.p. homocystine. This regimen suppressed plasma MET to levels below 5 microM for several days, with no treatment-related deaths. MET depletion for 10-12 days induced mitotic and cell cycle arrest, apoptotic death, and widespread necrosis in tumors but did not prevent tumor regrowth after cessation of the regimen. However, when a single dose of 35 mg/m(2) of N,N'-bis(2-chloroethyl)-N-nitrosourea (BCNU), which was otherwise ineffective as a single therapy in any of the tumors tested, was given at the end of the MET depletion regimen, a more than 80-day growth delay was observed for Daoy and D-54, whereas the growth of SWB77 was delayed by 20 days. MET-depleting regimens also trebled the efficacy of temozolomide (TMZ) against SWB77 when TMZ was given to animals as a single dose of 180 mg/m(2) at the end of a 10-day period of MET depletion. The enhanced responses of both Daoy and SWB77 to DNA alkylating agents such as BCNU and TMZ could be attributed to the down-regulation of O(6)-methylguanine-DNA methyltransferase activity. However, the synergy of MET depletion and BCNU observed with D-54 tumors, which do not express measurable O(6)-methylguanine-DNA methyltransferase protein, is probably mediated by a different mechanism. MET depletion specifically sensitizes tumors to alkylating agents and does not significantly lower the toxicity of either BCNU or TMZ for the host. In this regard, the combination approach of MET depletion and genotoxic chemotherapy demonstrates significant promise for clinical evaluation.

Characterization of initiated cells in N-methylnitrosourea-induced carcinogenesis of the CNS in the adult rat.

Glial tumors may originate from the malignant transformation of multipotent glial progenitor cells, but tools to study malignant transformation leading to gliomas are limited by the lack of biological systems that represent early stages of this disease in adult animals. In order to characterize the initiated cells that give rise to gliomas, we have employed the N-methylnitrosourea (MNU) model for induction of brain tumors in adult rats (Rushing et al., 1998). Specifically, we have isolated and cultured transformed (premalignant) cells from normal-appearing brains of rats exposed to MNU for 10 weeks and from histologically abnormal brains of rats exposed to MNU for 15 weeks. We compared them with cells cultured from control animals under identical conditions. Cultured cells were classified according to their morphology, immunophenotype, karyotype, proliferation capacity, and tumorigenicity in athymic mice. Cultures from untreated normal rat brains grew as monolayers and had normal karyotypes (42 X,Y), epithelioid morphology, and slow proliferative capacity (doubling time > 120 h). In contrast, cultured cells from brains of MNU-exposed animals had karyotypes that ranged from normal to highly aneuploid. Aneuploid lines grew rapidly in multilayers (doubling time < 24 h), had differentiated astrocytic or oligodendroglial morphology and immunohistochemical staining profile, and yielded tumors in athymic mice. Initiated cells with minor chromosomal aberrations assumed mixed bipolar or tripolar morphologies in high density cultures, proliferated rapidly, but showed contact inhibition and failed to induce tumors when injected s.c. in athymic mice. In general, lines showing no evidence of chromosomal aberrations had the most epithelioid morphology, proliferated slowly (doubling time > 72 h), and retained strict contact growth inhibition. The presumed undifferentiated glial progenitor cells in culture from either control or MNU-treated rats variably expressed markers such as vimentin, nestin, and NG2 proteoglycan, and they weakly expressed the mature astrocytic or oligodendroglial markers glial fibrillary acidic protein or galactocerbroside, respectively. These cultures differentiated to bipolar-tripolar morphology with concomitant maturation to a GFAP+ or GalC+ phenotype upon exposure to secondary messengers such as dibutyryl-cyclic-AMP and/or growth factors such as basic fibrillary growth factor. Continuous stimulation with these messengers resulted in terminal differentiation and consequent death upon withdrawal of the stimulus. These results provide information that could lead to detailed characterization of initiated, premalignant cells in the adult brain and to a better understanding of glial carcinogenesis.

Thresholds of O6-alkylguanine-DNA alkyltransferase which confer significant resistance of human glial tumor xenografts to treatment with 1,3-bis(2-chloroethyl)-1-nitrosourea or temozolomide.

Bis-2-chloroethylnitrosourea (BCNU) or temozolomide (TMZ) were tested alone or in combination with the AGT inhibitors O6-benzyl-2'-deoxyguanosine (dBG) or O6-benzylguanine (BG) against human glial tumor xenografts growing s.c. in athymic mice. Four glioblastoma (SWB77, SWB40, SWB39, and D-54) and one anaplastic oligodendroglioma (SWB61) xenografts having O6-alkylguanine-DNA alkyltransferase (AGT) activities of 75, 45, 10, < 10, and 16 fmol/mg protein, respectively, were used. BCNU at 35 mg/m2 was ineffective against these tumors, although 70 mg/m2 (LD10, 75 mg/m2) produced a marked tumor growth delay (T-C) in D54 but had no effect against SWB40 or SWB77. Coadministration of BG or dBG and BCNU necessitated reduction of the BCNU dose to a maximum of 30 and 35 mg/m2, respectively, because of increased toxicity. Optimized treatment with dBG (250 mg/m2) and BCNU (35 mg/m2) resulted in T-Cs of 30, 29, 11, 16, and 14 days for SWB77, SWB40, SWB39, D-54 and SWB61, respectively. These delays were more pronounced than those induced with optimized, isotoxic treatments with BG (180 mg/m2) and BCNU (30 mg/m2). In comparison to BCNU, TMZ was less toxic, with an LD10 of 400 mg/m2. TMZ (300 mg/m2) was more effective than BCNU against SWB77, SWB40, and SWB61, inducing T-Cs of 23, 53, and 56 days, respectively. BG and dBG enhanced the toxicity of TMZ in athymic mice by decreasing the LD10 from 400 to 200 mg/m2. TMZ (180 mg/m2) with either BG (180 mg/m2) or dBG (250 mg/m2) resulted in T-Cs of 31 and 49 days in SWB77, respectively, as compared with 16 days for TMZ (180 mg/m2) alone. In SWB40, the combination of TMZ with dBG, but not with BG, was significantly more effective than the maximum tolerated dose of TMZ (300 mg/m2) alone. The combination of TMZ with AGT inactivators had no benefit, as compared with TMZ alone, against xenografts with marginal AGT activity. In conclusion, at equimolar doses dBG was less toxic than BG in athymic mice when combined with either BCNU or TMZ. In this regard, BCNU or TMZ can be used at higher doses in combination with dBG than with BG. This study further demonstrates that there is a significant benefit of depleting AGT with nonspecific AGT inhibitors prior to treatment with either BCNU or TMZ in tumors having AGT activity >45 fmol/mg protein.

A Phase II study of paclitaxel in patients with recurrent malignant glioma using different doses depending upon the concomitant use of anticonvulsants: a North American Brain Tumor Consortium report.

BACKGROUND: The primary objective of the current study was to determine the response rate of paclitaxel in patients with recurrent malignant glioma by using different doses dependent on the concomitant use of anticonvulsants. Secondary objectives were to determine the time period to treatment failure, to evaluate toxicities, and to obtain pharmacokinetic data. METHODS: Adult patients who had recurrent malignant glioma were treated with paclitaxel. Patients were treated at different doses depending on the concomitant use of anticonvulsants known to induce the p450 hepatic enzyme system. Patients on such agents were treated at a dose of 330 mg/m2, whereas those not on these anticonvulsants were treated at a dose of 210 mg/m2. Tumor response was assessed at 6-week intervals. Treatment was continued until documented tumor progression or unacceptable toxicity occurred, or a total of 12 paclitaxel infusions was completed. RESULTS: From January 1997 to June 1997, 23 patients were treated with paclitaxel. Four patients were ineligible for the current study. Of the 19 eligible patients, there were no responses seen. Four (21%) had stabilization of disease. Median time to treatment failure was 1 month (95% confidence interval [CI], 1-2 mos) and median survival was 7 months (95% CI, 6-10 mos). Three patients were removed from the current study because they had toxicity. Pharmacokinetic studies demonstrated that drug levels and clearance values were consistent with previously reported findings. CONCLUSION: Even though higher doses were administered to patients who had recurrent malignant glioma and who were on concomitant anticonvulsants, there were no objective responses to paclitaxel. Time to tumor progression was 1 month. Further testing of paclitaxel at this dose schedule does not appear to be warranted in this patient population.

Potentiation of BCNU antitumor efficacy by 9-substituted O6-benzylguanines. Effect of metabolism.

PURPOSE: O6-Benzylguanine (BG), an O6-methylguanine-DNA methyltransferase (MGMT) inactivator, potentiates the efficacy of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and of other DNA chloroethylating and methylating anticancer drugs and is currently undergoing clinical trials. O6-Benzyl-2'-deoxyguanosine (dBG), a less effective MGMT inactivator than BG in vitro, is at least as effective as BG in combination with BCNU against tumor xenografts in athymic mice. In order to identify the mechanism of dBG activation in in vivo systems we tested the metabolism, ability to inactivate MGMT, and efficacy to potentiate BCNU in vivo of two additional 9-substituted derivatives of BG, namely O6-benzyl-9-cyanomethylguanine (CMBG) and O6-benzylguanosine (BGS). METHODS: Metabolism and disposition of these drugs was examined in athymic mice and Sprague-Dawley rats. MGMT suppression was determined in human medulloblastoma (Daoy) tumor xenografts in athymic mice following treatment with BGS, dBG, and CMBG and was compared with the loss of resistance to BCNU as determined by tumor growth delays. RESULTS: Growth delays at 25 mg/m2 BCNU and 133 mg/m2 BG or equimolar doses of CMBG, BGS or dBG were 23.0, 2.5, 21.3 days. and 30.4 days, respectively. The above differences did not correlate with the ED50S of 0.2, 13, 11 microM, and 2 microM determined for the above compounds, respectively, in cell free extracts. Differences in the efficacies of the 9-substituted compounds did correlate, however, with the extent of their metabolic conversion to BG. The maximum concentrations of BG in blood achieved after the administration of equimolar (250 micromol/kg) doses of CMBG, BGS and dBG were 10, 30 microM, and 55 microM, respectively. Although such levels were lower than those achieved in circulation by administration of an equimolar amount of BG, BG levels persisted longer following treatments with BGS or dBG than after treatment with BG itself. Formation of BG was required for continuous and prolonged (> 16 h) suppression of MGMT activity to non-detectable levels (< 5 fmol/mg protein). CONCLUSION: Metabolism of BGS and dBG to BG explains the unexpected high efficacy of these compounds in potentiating the antitumor activity of BCNU in the athymic mouse model. The faster and more effective suppression of tumor MGMT by dBG and its greater efficacy, as compared with BGS, also correlates with a more rapid accumulation of BG in blood after dBG than after BGS administration, which results in faster and complete suppression of MGMT in Daov xenografts. Thus, metabolism of dBG and BGS to BG appears to be the determining factor for continuous and prolonged suppression of MGMT activity, and that near complete suppression of such activity during and following BCNU administration is required for the higher efficacy of treatments. Similarly, the failure of CMBG to suppress tumor MGMT to the same extent as BGS, in spite of their similar ED50 values, could be attributed to the metabolism of this compound mainly by pathways other than conversion to BG.

A phase I trial of 1,3-bis(2-chloroethyl)-1-nitrosourea plus temozolomide: a North American Brain Tumor Consortium study.

The North American Brain Tumor Consortium conducted a phase I trial of the combination 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and temozolomide. Eligibility included a patient with a cancer type that was considered refractory to standard therapy. Prior nitrosourea treatments were not permitted. There were parallel dose escalations in two treatment schedules. Forty-five patients were enrolled during an 18-month period. The maximum tolerated doses (MTDs) when temozolomide followed BCNU (Arm A) were temozolomide at 550 mg/m2/p.o. and BCNU at 150 mg/m2/i.v.), whereas the MTD when temozolomide preceded BCNU (Arm B) was temozolomide at 400 mg/m2/p.o. and BCNU at 100 mg/m2/i.v. Toxicity was predominantly hematologic, although there were three instances of pulmonary toxicity, which in one case could have represented potentiation of nitrosourea-induced pulmonary fibrosis. The half-life of temozolomide was 1.86 (+/-0.31) h. There was a moderate relationship between dose and peak concentration and a strong relationship between dose and plasma concentration time curve. Pharmacokinetic parameters of temozolomide were unaffected by the treatment schedule, so the difference in MTD between the schedules is likely due to a biologic rather than a pharmacokinetic sequence interaction. There were 9 partial responses among 43 patients evaluable for response, including 5 of 25 with a histologic diagnosis of glioblastoma. The recommended dose and schedule for phase II trials of this regimen are BCNU 150 mg/m2/i.v. followed in 2 h by temozolomide 550 mg/m2/p.o. repeated every 6 weeks. We are also recommending screening and periodic pulmonary function testing during treatment to assess the possible potentiation of nitrosourea-induced pulmonary fibrosis.

Eradication of human medulloblastoma tumor xenografts with a combination of O6-benzyl-2'-deoxyguanosine and 1,3-bis(2-chloroethyl)1-nitrosourea.

O6-Benzyl-2'-deoxyguanosine (dBG), a water-soluble inhibitor of O6-methylguanine-DNA methyltransferase (MGMT), potentiates the efficacy of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) against MGMT-positive, BCNU-resistant Daoy human medulloblastoma tumor xenografts in athymic mice (S. C. Schold et al., Cancer Res., 56: 2076-2081, 1996). Such potentiation was comparable to that observed for O6-benzylguanine, the prototype MGMT inhibitor that is currently undergoing clinical trials. In this study, we optimized the therapeutic effect of the dBG and BCNU combination against brain tumor xenografts without inducing substantial toxicity in the host by adjusting the doses of both compounds. dBG was escalated from 133 mg/m2 to 200 and 300 mg/m2, whereas corresponding doses of BCNU were reduced from 25 mg/m2 to 17 and 11 mg/m2, respectively. The growth delays of 30.2, 38.4, and 22.3 days, respectively, observed for the above regimens suggest that the optimal drug combination is not achieved with maximum doses of dBG. In fact, the highest doses of dBG (300 mg/m2) contributed to more frequent BCNU-related toxicities, despite the reduced BCNU dosage, and a reduction of the therapeutic effect. Toxicity was related to the depletion of MGMT activity in the gut of host mice and was manifested by edema, inflammation, and hemorrhage in the bowel wall by subsequent BCNU administration. With additional dosage adjustments, we found that tumor suppression of >90 days without toxicity was observed at 200 mg/m2 dBG and 23 mg/m2 BCNU. At these doses, tumors were eradicated (regressed to an undetectable size for >90 days) in 8 of 12 animals. Thus, dBG is the first of the MGMT inhibitors to show a curative effect in combination with BCNU against a human central nervous system tumor xenograft in athymic mice.

Phase II study of phenylacetate in patients with recurrent malignant glioma: a North American Brain Tumor Consortium report.

PURPOSE: To determine the response rate, time to treatment failure, and toxicity of phenylacetate in patients with recurrent malignant glioma and to identify plasma concentrations achieved during repeated continuous infusion of this agent. PATIENTS AND METHODS: Adult patients with recurrent malignant glioma were treated with phenylacetate. The schedule consisted of a 2-week continuous, intravenous infusion followed by a 2-week rest period (14 days on, 14 days off). A starting dose of 400 mg/kg total body weight per day of phenylacetate was initially used and subsequently changed to 400 mg/kg/d based on ideal body weight. Intrapatient dose escalations were allowed to a maximum of 450 mg/kg ideal body weight/d. Tumor response was assessed every 8 weeks. The National Cancer Institute common toxicity criteria were used to assess toxicity. Plasma concentrations achieved during the patients' first two 14-day infusions were assessed. RESULTS: Forty-three patients were enrolled between December 1994 and December 1996. Of these, 40 patients were assessable for toxicity and response to therapy. Reversible symptoms of fatigue and somnolence were the primary toxicities, with only mild hematologic toxicity. Thirty (75%) of the 40 patients failed treatment within 2 months, seven (17.5%) had stable disease, and three (7.5%) had a response defined as more than 50% reduction in the tumor. Median time to treatment failure was 2 months. Thirty-five patients have died, with a median survival of 8 months. Pharmacokinetic data for this dose schedule showed no difference in the mean plasma concentrations of phenylacetate between weeks 1 and 2 or between weeks 5 and 6. CONCLUSION: Phenylacetate has little activity at this dose schedule in patients with recurrent malignant glioma. Further studies with this drug would necessitate an evaluation of a different dose schedule.

Phase I trial of O6-benzylguanine for patients undergoing surgery for malignant glioma.

PURPOSE: The major mechanism of resistance to alkylnitrosourea therapy is the DNA repair protein O6-alkylguanine-DNA alkyltransferase (AGT), which removes chlorethylation or methylation damage from the O6-position of guanine. O6-benzylguanine (O6-BG) is an AGT substrate that inhibits AGT by suicide inactivation. We conducted a phase I trial to define the presurgical dose required for depletion of tumor AGT activity in patients with malignant glioma. MATERIALS AND METHODS: Patients were to be treated 18 hours before craniotomy with intravenous doses that ranged between 40 and 100 mg/m2 given over 1 hour. Resected tumor was snap-frozen in liquid nitrogen and AGT activity analyzed by high-pressure liquid chromatography (HPLC). Up to 13 patients were treated at a specific dose of O6-BG, with a target end point of > or = 11 of 13 patients with undetectable tumor AGT levels (< 10 fmol/mg protein). RESULTS: Thirty patients with malignant gliomas were enrolled, with 11 of 11 patients treated at 100 mg/m2 O6-BG demonstrating tumor AGT levels less than 10 fmol/mg protein. No toxicity was noted in any patient treated. CONCLUSION: These results indicate that 100 mg/m2 of O6-BG can maintain tumor AGT levels less than 10 fmol/mg protein for at least 18 hours after treatment, a time interval in which bis(2-chloroethyl)nitrosourea (BCNU)-induced chloroethyl adducts are fully converted into interstrand cross-links. A 100-mg/m2 dose of O6-BG will be used in combination with BCNU in another phase I trial designed to determine the maximal-tolerated dose of BCNU.

Glial tumors in the MNU rat model: induction of pure and mixed gliomas that do not require typical missense mutations of p53.

Gliomas were induced in adult male Sprague-Dawley rats by continuous exposure to 100 ppm of N-nitrosmethylurea (MNU) in drinking water. Latency periods for such tumors were 20 and 50 weeks following completion of exposure intervals of 20, 15, and 10 weeks, respectively. Based on histomorphology and the pattern of GFAP immunoreactivity, a large percentage of MNU-induced tumors (>40%) were anaplastic mixed gliomas, having both neoplastic astrocytic and oligodendroglial components. Typical oligodendrogliomas and astrocytomas also occurred less frequently. Unlike the majority of tumors induced by ethylnitrosourea (ENU), MNU yielded glial tumors that did not express synaptophysin. Anaplastic mixed gliomas and glioblastoma multiforme (GBMs) had no missense p53 mutations in the commonly mutated exons 4 through 8 and did not overexpress wild-type p53, suggesting that MNU-induced oncogenesis in rat brain tumors may not require inactivation/alteration of the p53 tumor suppressor gene. The K-ras gene was also analyzed and found to have no activating mutations in brain tumors. This model is suitable for studying genetic events leading to the majority of gliomas that apparently express functional p53.

Correlation of tumor O6 methylguanine-DNA methyltransferase levels with survival of malignant astrocytoma patients treated with bis-chloroethylnitrosourea: a Southwest Oncology Group study.

PURPOSE: Prior studies show that increased levels of the DNA repair protein O6 methylguanine-DNA methyltransferase (MGMT), also referred to as O6-alkylguanine-DNA alkyltransferase (AGT) correlate with the resistance of glioma cell lines to nitrosoureas. The observed nitrosourea sensitivity of MGMT-deficient lines (methyl excision repair negative [MER-]) and those repair-proficient lines pretreated with MGMT-specific inhibitors (eg, O6 benzylguanine) has raised the possibility that tumor MGMT levels may be an important predictor of survival in patients with gliomas. PATIENTS AND METHODS: We correlated the MGMT level in malignant astrocytoma tissues, obtained from patients treated with radiotherapy and bis-chloroethylnitrosourea (BCNU) on a prior prospective trial (Southwest Oncology Group [SWOG] 8737), with overall and failure-free survival. RESULTS: Of 64 assessable patients with malignant astrocytoma (63% glioblastoma, 37% anaplastic astrocytoma), 64% had high (> 60,000 molecules/nucleus) MGMT levels. The overall median survival for patients with high versus low MGMT levels was 8 and 29 months, respectively (P=.0002), and median failure-free survival 3 and 6 months, respectively (P=.008). Subset analysis by histology (high v low MGMT levels) for anaplastic astrocytoma was 14 versus 62 months (n=24) and for glioblastoma was 7 versus 12 months (n=40). The overall hazards ratio (risk for death) for high versus low MGMT levels was 3.41; in young patients, the hazards ratio was higher (age 18 to 40 years, 4.19; age 41 to 60 years, 3.08) but became equal by MGMT level at age older than 60 years (1.11). Multivariate analysis showed that MGMT was independent of other known prognostic factors (age, performance status, histology). CONCLUSION: The MGMT level in tumor tissue specimens may be a predictive marker of survival in patients with malignant astrocytoma that is independent of other previously described prognostic variables.

Phase I study of paclitaxel in patients with recurrent malignant glioma: a North American Brain Tumor Consortium report.

PURPOSE: To determine the maximum-tolerated dose (MTD) of paclitaxel administered as a 3-hour infusion in patients with recurrent malignant glioma. PATIENTS AND METHODS: Patients were stratified by starting dose of paclitaxel and concurrent anticonvulsant (AC) use and were treated in cohorts of three patients. The starting dose was 240 mg/m2 administered intravenously with escalations of 30 mg/m2 until the MTD was established. Pharmacokinetic data were obtained for each patient for the first infusion. Tumor response was assessed at 6-week intervals and treatment was continued until documented tumor progression, unacceptable toxicity, or a total of 12 paclitaxel infusions. RESULTS: From April 1995 to December 1996, 34 patients were treated; 27 patients in the AC group and seven patients in the non-AC group. The MTD for patients who received ACs was established at 360 mg/m2 and the dose-limiting toxicity (DLT) was central neurotoxicity, characterized as transient encephalopathy and seizures. In contrast, the MTD for patients who did not receive ACs was 240 mg/m2, and myelosuppression, gastrointestinal toxicity, and fatigue were the DLTs. Pharmacokinetic data confirmed that the plasma drug levels and clearance rates were similar for patients in both groups at the respective dose levels that produced DLTs. CONCLUSION: The pharmacokinetics of paclitaxel are altered by ACs, and significantly larger doses of the drug can be administered to patients with brain tumors on AC therapy. The toxicity profile is different for patients on AC therapy treated at these higher doses. A phase II study has been initiated that uses a dose of 330 mg/m2 for patients on AC therapy and 210 mg/m2 for patients not on AC therapy.

Phase II study of Didemnin B in central nervous system tumors: a Southwest Oncology Group study.

Didemnin B 6.3 mg/m2 was administered intravenously to 48 patients with recurrent or progressive central nervous system tumors. One patient of 39 (2.9%, 95% confidence limits 0.1 to 13.5) eligible patients had a confirmed partial response utilizing standard solid tumor criteria which lasted 14 months. Toxicity was significant. Nausea and vomiting and lethargy were the most frequent toxicities, but multiple severe toxicities were seen. Further investigation of Didemnin B at this dose is not warranted in patients with central nervous system malignancies.

Methylator resistance mediated by mismatch repair deficiency in a glioblastoma multiforme xenograft.

A methylator-resistant human glioblastoma multiforme xenograft, D-245 MG (PR), in athymic nude mice was established by serially treating the parent xenograft D-245 MG with procarbazine. D-245 MG xenografts were sensitive to procarbazine, temozolomide, N-methyl-N-nitrosourea, 1,3-bis(2-chloroethyl)-1-nitrosourea, 9-aminocamptothecin, topotecan, CPT-11, cyclophosphamide, and busulfan. D-245 MG (PR) xenografts were resistant to procarbazine, temozolomide, N-methyl-N-nitrosourea, and busulfan, but they were sensitive to the other agents. Both D-245 MG and D-245 MG (PR) xenografts displayed no O6-alkylguanine-DNA alkyltransferase activity, and their levels of glutathione and glutathione-S-transferase were similar. D-245 MG xenografts expressed the human mismatch repair proteins hMSH2 and hMLH1, whereas D-245 MG (PR) expressed hMLH1 but not hMSH2.

Telomerase activity in ordinary meningiomas predicts poor outcome.

Telomerase, the enzyme that stabilizes telomere length, is reactivated with almost all cancer types, and it may be necessary for unlimited cell proliferation. Assessment of malignancy in ordinary meningiomas is inconclusive because no clear-cut correlation exists between aggressive clinical behavior and histological features or karyotypic abnormalities. We analyzed telomerase activity in 52 cases of meningioma by using the highly sensitive telomeric repeat amplification protocol and then compared clinical behavior in telomerase-positive and -negative ordinary meningiomas. Twenty-six of the 52 tumors (50%) had detectable telomerase activity. Twenty-one of the 22 neoplasms classified as malignant or atypical (95%) had detectable telomerase activity, and these tumors generally had a poor outcome. Interestingly, 5 of 30 ordinary (morphologically benign) meningiomas (17%) also showed detectable telomerase activity. Of the 5 patients with telomerase-positive ordinary meningiomas, 3 had rapid regrowth of the tumor despite gross total resection. The remaining 2 patients also had other primary malignancies. We observed a highly significant correlation in ordinary meningiomas between the presence of telomerase activity and a poor prognosis for the patient (P = .0002). Telomerase activity in benign meningiomas is clinically relevant because the presence of the enzyme suggests that these benign-appearing tumors may contain a population of immortal cells. The detection of telomerase activity may help to identify benign meningiomas that would be more likely to continue to grow and to recur clinically if surgical resection were incomplete.

Effect of long-term depletion of plasma methionine on the growth and survival of human brain tumor xenografts in athymic mice.

Depletion of plasma methionine is expected to inhibit or reverse growth of methionine-dependent tumors; however, modulation of methionine and other sulfur amino acids is not a trivial task in experimental animals. L-Methioninase from Pseudomonas putida at 1,000 U/kg causes acute reduction of plasma methionine by 80% in mice, but recovery occurs within 14 hours. Restriction of dietary choline and replacement of dietary methionine with homocystine results in 50% chronic reduction of plasma methionine. A > 70% reduction can be accomplished with a diet deficient in methionine, homocystine, and choline, but ultimately this diet is lethal. Plasma methionine can be lowered to a steady state of < 5 microM in mice with a combination of dietary restriction of methionine, homocysteine, and choline and synchronous treatments with intraperitoneal injections of 1,000 U/kg L-methioninase and 25-50 mg/kg homocystine, each administered at 12-hour intervals. Modulation of plasma methionine by this means causes no weight loss or pathologies in liver or pancreas, and it does not markedly alter levels of cysteine, homocysteine, or glutathione in plasma or in hepatic tissue. When this procedure is applied to athymic mice bearing human medulloblastoma (Daoy) tumors subcutaneously, tumor growth is inhibited. Methionine deprivation arrests mitosis by blocking the cell cycle in G2 and induces apoptosis. Tumor stasis was achieved in 100% of treated animals within 4 days of treatment, and regression was seen in one-third of animals after a 10-day period. These data strongly support the use of methionine-depleting regimens for tumor treatments.

Regulation of O6-methylguanine-DNA methyltransferase by methionine in human tumour cells.

Methionine (MET)-dependent cell lines require MET to proliferate, and homocysteine (HCY) does not act as a substitute for this requirement. From six O6-methylguanine-DNA methyltransferase (MGMT)-efficient (mer+) cell lines tested, two medulloblastomas (Daoy and D-341) and a lung non-small-cell adenocarcinoma with metastatic potential (H-1623) were most sensitive to MET deprivation, while two glioblastomas (U-138, D-263) and a small-cell lung carcinoma H-1944 were moderately to weakly dependent. Regardless of the degree of MET dependence, all of these lines down-regulated their MGMT activity within 48-72 h of transfer from MET+HCY- to MET-HCY+ media, long before the eradication of the culture. Reduction of MGMT activity was due to a decline of both MGMT mRNA and protein levels. However, the reduction was not related to the methylation status of the MGMT promoter at the SmaI site or the HpaII sites in the body of the gene; such sites have been shown to be associated in MGMT regulation and in defining the mer phenotype. MET-dependent, mer+ tumour cells cultured in MET-HCY+ were more sensitive to BCNU (IC50 = 5-10 microM) than those cultured in MET+HCY-(IC50 = 45-90 microM), while MET-independent or mer- cell lines were unaffected. This indicates that reduction of MGMT, imposed by the absence of MET, renders mer+ tumour cells more susceptible to alkylating agents. The relatively selective suppression of MGMT activity in mer+ MET-dependent tumour cells, in combination with the inability of such cells to proliferate in the absence of MET, may lead to the development of more effective treatment strategies for mer+ MET-dependent tumours.

Phase II study of paclitaxel in patients with recurrent malignant glioma.

PURPOSE: To assess the efficacy and toxicity of paclitaxel administered as a 3-hour infusion to patients with recurrent malignant glioma. PATIENTS AND METHODS: Adult patients with recurrent malignant glioma following radiation therapy, who had received no more than one prior chemotherapy regimen and who had a Karnofsky performance status (KPS) > or = 60, were treated with a 3-hour infusion of paclitaxel every 3 weeks. The initial dose was 210 mg/m2; dose escalation to 240 mg/m2 was allowed. Tumor response was assessed at 6-week intervals using radiographic and clinical criteria. Treatment was continued until documented tumor progression or a total of 12 paclitaxel infusions. RESULTS: Of 41 eligible patients, all were assessable for treatment toxicity and 40 (98%) were assessable for response. The response rate (disease stabilization or better) was 35%. Twenty-nine patients (71%) underwent dose escalation to 240 mg/m2 without the use of growth factors. Toxicities included alopecia (98%), nausea (22%), arthralgias (32%), CNS toxicity (24%), peripheral neuropathy (15%), cardiac toxicity (7%), and myelosuppression (10% grade 3 or 4 hematologic toxicity). No patient developed febrile neutropenia. There was one allergic reaction (2%). CONCLUSION: Paclitaxel is well tolerated at this dose schedule in patients with recurrent malignant glioma, and affords a modest response rate. Because minimal myelotoxicity was encountered in our patients, a dose-escalating phase I/II study of paclitaxel is planned to determine the maximal-tolerated dose (MTD).