Estrogen therapy for osteoporosis in the modern era.

Menopause predisposes women to osteoporosis due to declining estrogen levels. This results in a decrease in bone mineral density (BMD) and an increase in fractures. Osteoporotic fractures lead to substantial morbidity and mortality, and are considered one of the largest public health priorities by the World Health Organization (WHO). It is therefore essential for menopausal women to receive appropriate guidance for the prevention and management of osteoporosis. The Women's Health Initiative (WHI) randomized controlled trial first proved hormonal therapy (HT) reduces the incidence of all osteoporosis-related fractures in postmenopausal women. However, the study concluded that the adverse effects outweighed the potential benefits on bone, leading to a significant decrease in HT use for menopausal symptoms. Additionally, HT was not used as first-line therapy for osteoporosis and fractures. Subsequent studies have challenged these initial conclusions and have shown significant efficacy of HT in various doses, durations, regimens, and routes of administration. These studies support that HT improves BMD and reduces fracture risk in women with and without osteoporosis. Furthermore, the studies suggest that low-dose and transdermal HT are less likely associated with the adverse effects of breast cancer, endometrial hyperplasia, coronary artery disease (CAD), and venous thromboembolism (VTE) previously observed in standard-dose oral HT regimens. Given the need for estrogen in menopausal women and evidence supporting the cost effectiveness, safety, and efficacy of HT, we propose that HT should be considered for the primary prevention and treatment of osteoporosis in appropriate candidates. HT should be individualized and the once "lowest dose for shortest period of time" concept should no longer be used. This review will focus on the prior and current studies for various HT formulations used for the prevention and treatment of osteoporosis, exploring the safety profile of low-dose and transdermal HT that have been shown to be safer than oral standard-dose HT.

Improvement in quality of oocytes in polycystic ovarian syndrome in programs of in vitro fertilization.

Inositol therapy is aimed at improving the quality of oocytes during preconception care in patients with polycystic ovarian syndrome (PCOS), a cause of infertility and reproductive dysfunction. The objectives of this observational comparative multicentre study were to evaluate the effectiveness of inositol in improving the quality of oocytes/embryos and IVF cycle outcome. Group 1 patients (N = 133) received inositol 1000 mg (Inofert or Nutrilinea) + folic acid 0.1 mg. Group 2 consisted of patients with preserved ovarian reserve without PCOS (N = 137), not administered inositol prior to pregnancy. Effectiveness criteria were numbers of mature oocytes and good quality embryos, pregnancy rates per ET, 'take home baby' index and miscarriage rates. Pregnancy rates per ET (87.0% vs. 87.4%), 'take home baby' index (79.6% vs. 89.4%) and miscarriage rates (14.3% vs. 10.6%) were comparable. Use of inositol in patients with PCOS during preconception care is an effective method allowing improvement of oocytes quality and positively affecting IVF cycle prognosis. High pregnancy rates per ET and 'take home baby' index after treatment are justifying inositol usage in patients with PCOS and infertility.

Overexpression of E2F-1 in glioma triggers apoptosis and suppresses tumor growth in vitro and in vivo.

The transfer of apoptosis genes to tumors is one of the most promising strategies for cancer gene therapy. We have shown that massive apoptosis occurs when wild-type p53 expression is induced in glioma cells carrying a p53 gene mutation. However, adenovirus-mediated p53 gene transfer is ineffective in causing apoptosis in glioma cells that retain a wild-type p53 genotype. We evaluated the effect of E2F-1 overexpression on the growth of gliomas in vitro and in vivo. In the in vitro study, the adenovirus-mediated transfer of exogenous E2F-1 protein precipitated generalized apoptosis in gliomas. The treatment with Ad5CMV-E2F-1 of nude mice carrying subcutaneous gliomas arrested tumor growth. Our results indicate that E2F-1 has anti-glioma activity in vitro and in vivo.

Two phase II trials of temozolomide with interferon-alpha2b (pegylated and non-pegylated) in patients with recurrent glioblastoma multiforme.

BACKGROUND: Because of the poor outcomes for patients with recurrent glioblastoma multiforme (GBM), and some laboratory and clinical evidence of efficacy using interferon in GBM, we assessed the toxicity and efficacy of temozolomide (TMZ) combined with either short-acting (IFN) or long-acting (pegylated) interferon alpha2b (PEG) in two single-arm phase II studies, and compared the results to 6-month progression-free survival (PFS-6) data from historical controls. METHODS: Two single-arm phase II studies were carried out in adults with GBM. Patients were treated with the standard regimen of TMZ (150-200 mg m(-2) per day x 5 days every month) combined with either 4 million units per m(2) subcutaneously (SQ) three times weekly of IFN or 0.5 microg kg(-1) SQ weekly of PEG. Physical exams and imaging evaluations were carried out every 8 weeks. RESULTS: On the IFN study, 34 adults (74% men) were enrolled, and 29 adults (55% men) on the PEG study; median Karnofsky performance status was 80 and 90 for the IFN and PEG studies, respectively. Grade 3 or 4 toxicities were common, leucopoenia and thrombocytopoenia occurring in 35-38% and 18-21% of patients, respectively. Grade 3 or 4 fatigue occurred in 18% of patients on both studies. Lymphopoenia was infrequent. PFS-6 was 31% for 29 evaluable patients in the IFN study and 38% for 26 evaluable patients in the PEG study. CONCLUSION: In recurrent GBM patients, both studies of standard dose TMZ with either IFN or PEG showed improved efficacy when compared to historical controls, or reports using TMZ alone. Even though the TMZ+PEG study met criteria for further study, the results of both of these studies must be considered in light of the standard of care (TMZ plus radiotherapy) for newly diagnosed GBM, which has evolved since the inception of these studies. Despite the results of the current studies being eclipsed by the new GBM standard of care, these results can still inform the development of newer approaches for GBM, either in an earlier, upfront setting, or by extrapolation of the results and consideration of the use of PEG or IFN in conjunction with other antiglioma strategies.

Cerebrospinal fluid production by the choroid plexus and brain.

The production of cerebrospinal fluid and the transport of (24)Na from the blood to the cerebrospinal fluid were studied simultaneously in normal and choroid plexectomized rhesus monkeys. Choroid plexectomy reduced the production of cerebrospinal fluid by an average of 33 to 40 percent and the rate of appearance of (24)Na in the cerebrospinal fluid and its final concentration were proportionately reduced. In both normal and plexectomized animals, (24)Na levels were found to be markedly greater in the gray matter surrounding the ventricles and in the gray matter bordering the subarachnoid space. That sodium exchanges in these two general areas of the brain may be linked to the formation of the cerebrospinal fluid is discussed here.

Regulation of ornithine decarboxylase during oncogenic transformation: mechanisms and therapeutic potential.

The activity of ornithine decarboxylase (ODC(1)), the first enzyme in polyamine biosynthesis, is induced during carcinogenesis by a variety of oncogenic stimuli. Intracellular levels of ODC and the polyamines are tightly controlled during normal cell growth, and regulation occurs at the levels of transcription, translation and protein degradation. Several known proto-oncogenic pathways appear to control ODC transcription and translation, and dysregulation of pathways downstream of ras and myc result in the constitutive elevation of ODC activity that occurs with oncogenesis. Inhibition of ODC activity reverts the transformation of cells in vitro and reduces tumor growth in several animal models, suggesting high levels of ODC are necessary for the maintenance of the transformed phenotype. The ODC irreversible inactivator DFMO has proven to be not only a valuable tool in the study of ODC in cancer, but also shows promise as a chemopreventive and chemotherapeutic agent in certain types of malignancies.

Dianhydrogalactitol (NSC-132313): pharmacokinetics in normal and tumor-bearing rat brain and antitumor activity against three intracerebral rodent tumors.

Dianhydrogalactitol (DAG; NSC-132313), a hexitol epoxide, was used to treat intracerebral rodent tumors. DAG was most active against the murine ependymoblastoma [treated/controls (T/C)greater than 440%], less active against murine glioma 26 (T/C approximately 112-150%), and least active against rat 9L gliosarcoma (T/C approximately 100%). Application of a two-compartment open model for plasma disappearance of 14C-DAG in rats gave a volume of distribution at steady state of approximately 872 ml, a clearance of approximately 9.4 ml/minute, and an elimination constant of 0.025/minute. Entry of 14C-DAG was more rapid into the 9L tumor than into the normal brain. When a two-compartment series model for brain and tumor entry was applied, the t1/2 (half-time) for compartmental equilibrium was approximately 22 and 105 minutes in the brain, and 4 and 56 minutes in the 9L tumor. The drug rapidly entered the brain and tumor intracellular compartments. Binding to RNA was linear with time, and the absolute amount of binding was approximately six times greater for RNA than for DNA.

Treatment of recurrent gliomas with eflornithine.

BACKGROUND: Oral eflornithine in combination with intravenous mitoguazone (methylbisguanylhydrazone) has shown activity against recurrent anaplastic gliomas. Eflornithine alone, however, has not been evaluated against recurrent gliomas. PURPOSE: This study compared the antitumor activity of oral eflornithine with that of oral eflornithine combined with intravenous mitoguazone in the treatment of patients with recurrent or progressive glioblastoma multiforme as well as nonglioblastoma anaplastic gliomas. METHODS: During the 1st year of therapy with eflornithine alone, the drug was given at a dose of 3.6 g/m2 on days 1-14, 22-35, and 43-56 every 8 hours; cycles were repeated every 63 days until progression. For the 2nd year, the drug was given on days 1-14, 29-42, and 57-70, with 84 days between cycles. For the 1st and 2nd years of eflornithine-mitoguazone therapy, eflornithine was given at 1.8 g/m2 on the same schedule. Mitoguazone was given intravenously at 200 mg/m2 on the final day of each 2-week sequence of eflornithine therapy. Response was determined by evaluating changes in the size of contrast-enhanced neuroimages. RESULTS: Because of two cases of lethal hepatic necrosis, the initial random allocation of patients to the eflornithine-mitoguazone arm was stopped after 23 patients had been accrued. Ninety-eight patients were entered in the eflornithine arm; 80 patients (36 glioblastoma multiforme patients and 44 anaplastic glioma patients) were assessable for response. Antitumor activity (partial response, minor response, and stable disease) was seen in 45% of the patients with anaplastic gliomas, for a median of 49 weeks, but in only 17% of patients with glioblastoma multiforme (median not attained). Twenty-one (20%) of the patients with anaplastic glioma and 33% of the patients with glioblastoma multiforme were removed from the study before completing the first 8-week course of therapy because of neurological deterioration and tumor progression by the 5th week of treatment. CONCLUSION: This study suggests that eflornithine alone is an effective palliative therapy for recurrent anaplastic gliomas. Additional studies are needed to confirm our finding.

Characterization of p53 and p21 functional interactions in glioma cells en route to apoptosis.

BACKGROUND: Alterations of the p53 (also called TP53) gene are one of the most common abnormalities in gliomas. We have previously reported that restoration of wild-type p53 protein function in glioma cells results in programmed cell death (apoptosis). Since p53 functions are mediated by genes that directly control the tumor suppressor effect of the p53 protein, understanding the relationship between p53 and p53-related genes in glioma cells will aid in the design of more rational treatment strategies for brain tumors. PURPOSE: We conducted this study to examine the timing of the p53-mediated events preceding apoptosis. More specifically, we undertook this work to characterize the genetic and cell cycle-related factors that may increase the resistance of glioma cells to p53-induced apoptosis. METHODS: Two human glioma cell lines (U-251 MG and U-373 MG) that express mutant p53 protein and two (U-87 MG and EFC-2) that express wild-type p53 protein were used. Replication-deficient adenovirus was utilized as an expression vector to transfer exogenous p53 and p21 complementary DNAs into the glioma cells; control cells were infected with the viral expression vector alone. To monitor gene transfer and the expression of exogenous genes (as well as the expression of endogenous genes), we used western blot analyses and immunohistochemistry analyses. Flow cytometry studies of cellular DNA content were performed to determine the cell cycle phenotype of the glioma cells before and after treatment. RESULTS: p53-mediated apoptosis was preceded by elevation in the levels of the p21 (cell cycle-related) and Bax (apoptosis-related) proteins. In addition, cell cycle analyses showed that glioma cells were arrested in the G2 phase before undergoing cell death. Transfer of p21 induced a G2 block but did not induce apoptosis. Moreover, coexpression of p21 and p53 prevented glioma cells from undergoing apoptosis. Expression of exogenous p53 in wild-type p53 cells did not induce elevation of Bax levels, arrest in G2 phase, or apoptosis. CONCLUSIONS AND IMPLICATIONS: Our data confirmed the ability of wild-type p53 to induce apoptosis in p53 mutant glioma cells. In addition, our results document that p21 plays a role in protecting cells from p53-mediated programmed cell death and suggest that p53-mediated apoptosis and p21 induction may represent, at least in certain cases, opposite signals. Finally, our data suggest that over expression of p21 in gliomas may be related to resistance to treatments that induce apoptosis.

Germline p53 gene mutations in subsets of glioma patients.

BACKGROUND: Heritable germline mutations of the p53 gene have been described in patients with Li-Fraumeni syndrome, occasionally in nonfamilial malignancies such as multifocal osteosarcoma, in a small subgroup of young patients with two or more primary malignancies, and in patients with sporadic breast carcinoma. We recently reported that multifocal gliomas are frequently associated with other primary malignancies, and we hypothesized that genetic alterations may account for this phenomenon. PURPOSE: We examined the frequency of germline p53 gene mutations in patients with glioma and either multifocality of lesions, history of an additional primary (different) malignancy, or a family history of cancer. METHODS: Lymphocytes from 51 glioma patients were analyzed for germline p53 gene mutations using RNA-polymerase chain reaction analysis, single-strand conformation polymorphism, and gene sequencing techniques. RESULTS: Germline p53 gene mutations were detected in six of 19 patients with multifocal glioma, including two with family history of cancer, one with another primary malignancy, and two with all three risk factors; one of four patients with unifocal glioma, another primary malignancy, and a family history of cancer; and two of 15 patients with unifocal glioma and a family history of cancer but no second malignancies. No mutations were detected in the patient with unifocal glioma and another malignancy or in the 12 control patients with unifocal glioma and no second malignancies or family history of cancer. Patients having mutations were younger than other patients in the same group. CONCLUSIONS: Germline p53 mutations are frequent in patients with multifocal glioma, glioma and another primary malignancy, and glioma associated with a family history of cancer, particularly if these factors are combined. IMPLICATIONS: Relatives at high risk can be identified for genetic counseling, early cancer detection, and possible enrollment in chemoprevention trials.

Gamma-radiation sensitivity and risk of glioma.

BACKGROUND: About 9% of human cancers are brain tumors, of which 90% are gliomas. gamma-Radiation has been identified as a risk factor for brain tumors. In a previous pilot study, we found that lymphocytes from patients with glioma were more sensitive to gamma-radiation than were lymphocytes from matched control subjects. In this larger case-control study, we compared the gamma-radiation sensitivity of lymphocytes from glioma patients with those from control subjects and investigated the association between mutagen sensitivity and the risk for developing glioma. METHODS: We used a mutagen sensitivity assay (an indirect measure of DNA repair activity) to assess chromosomal damage. We gamma-irradiated (1.5 Gy) short-term lymphocyte cultures from 219 case patients with glioma and from 238 healthy control subjects frequency matched by age and sex. After irradiation, cells were cultured for 4 hours, and then Colcemid was added for 1 hour to arrest cells in mitosis. Fifty metaphases were randomly selected for each sample and scored for chromatid breaks. All statistical tests were two-sided. RESULTS: We observed a statistically significantly higher frequency of chromatid breaks per cell from case patients with glioma (mean = 0.55; 95% confidence interval [CI] = 0.50 to 0.59) than from control subjects (mean = 0.44; 95% CI = 0.41 to 0.48) (P<.001). Using 0.40 (the median number of chromatid breaks per cell in control subjects) as the cut point for defining mutagen sensitivity and adjusting for age, sex, and smoking status, we found that mutagen sensitivity was statistically significantly associated with an increased risk for glioma (odds ratio = 2.09; 95% CI = 1.43 to 3.06). When the data were divided into tertiles, the relative risk for glioma increased from the lowest tertile to the highest tertile (trend test, P<.001). CONCLUSION: gamma-Radiation-induced mutagen sensitivity of lymphocytes may be associated with an increased risk for glioma, a result that supports our earlier preliminary findings.

Modification of uptake and antiproliferative effect of methylglyoxal bis(guanylhydrazone) by treatment with alpha-difluoromethylornithine in rodent cell lines with different sensitivities to methylglyoxal bis(guanylhydrazone).

Uptake characteristics and growth-inhibitory effects of methylglyoxal bis(guanylhydrazone) (MGBG), a competitive inhibitor of S-adenosylmethionine decarboxylase, were investigated in 9L rat brain tumor cells and in V79 hamster lung cells. Proliferation of 9L cells was only slightly inhibited by treatment with 40 microM MGBG alone, but when used in combination with 0.5 mM alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, proliferation was much more effectively inhibited. The intracellular concentration of MGBG was approximately 2-fold higher 4 days after cells were treated with both DFMO and MGBG, either simultaneously or when MGBG was added after a 48-hr DFMO pretreatment, than that in cells treated with MGBG alone. Polyamine levels in DFMO- and MGBG-treated cells correlated with the antiproliferative effects of the drugs. Used either alone or in combination with 1 mM DFMO, 0.5 microM MGBG inhibited the growth of and eventually killed V79 cells. Simultaneous or sequential treatment with DFMO and MGBG increased intracellular concentrations of MGBG at 4 days by 2- and 3-fold, respectively, compared to treatment with MGBG alone. Intracellular polyamine levels did not correlate with the antiproliferative effect of the two drugs in V79 cells. In both cell lines, polyamines and MGBG share a common transport system. The net transport of polyamines and MGBG was more temperature dependent and up to 10-fold more active in V79 cells than in 9L cells. The Km and Vmax values for spermidine and MGBG measured 10 sec after addition (initial permeation) were not affected by DFMO pretreatment in either cell line. However, 1 hr after administration, the Vmax values for spermidine and MGBG uptake were doubled in V79 cells pretreated for 48 hr with DFMO; no significant change occurred in 9L cells. Mitochondrial function, assessed by pyruvate oxidation, was substantially impaired by MGBG in V79 cells but not in 9L cells when the intracellular concentrations of MGBG were equal in each cell line. Pretreatment with DFMO did not increase MGBG-induced inhibition of pyruvate oxidation in V79 cells. These results show that, compared with V79 cells, the decreased sensitivity of 9L cells to MGBG may be related to decreased intracellular MGBG accumulation but not to cellular permeation such as carrier transport. Results of measurements of both polyamine levels and mitochondrial function indicate that V79 cells may be more susceptible to nonpolyamine-dependent effects of MGBG than are 9L cells.

Comparative pharmacokinetics of 1-(2-chloroethyl)-3-(2,6-dioxo-1-piperidyl)-1-nitrosourea in rats and patients and extrapolation to clinical trials.

The plasma pharmacokinetics of 1-(2-chloroethyl)-3-(2,6-dioxo-1-piperidyl)1-nitrosourea (PCNU) were determined in ambulatory rats and in patients receiving PCNU chemotherapy in Phase 1 and II studies. After derivativization to the methyl carbamate, both rat and human PCNU plasma levels were measured by gas chromatography-mass spectrometry. Comparison of the tolerated dose levels and pharmacokinetics of PCNU to the values determined for 1,3-bis(2-chloroethyl)-1-nitrosourea in humans indicated that PCNU has a lower plasma drug area under the curve at equitoxic doses. We conclude that PCNU may show less clinical efficacy than 1,3-bis(2-chloroethyl)-1-nitrosourea in the treatment of solid tumors.

Potential antiglioma activity of 9-hydroxy-2-N-methylellipticine as determined by pharmacological and human tumor clonogenic cell studies.

The antiglioma activity of elliptinium (HME) was investigated in a human glioma clonogenic cell assay. Early passage cells of three human glioma cell lines (SF126, SF375, and SF407) were exposed to HME at the clinically achievable dose of 3 microM for 3 h. At this HME concentration, clonogenic cell survival was reduced by more than 3 logs in SF126 and SF375, and by 0.8 logs in SF407. A study of the kinetics of cell kill showed that whereas at moderate (less than or equal to 1.5 microM) HME doses cell kill increased with treatment time up to a maximum at approximately 3 h, cytotoxicity was more dose than time dependent at higher doses. Flash treatment of SF375 cells with 3 microM HME resulted in more than 2 logs clonogenic cell kill. Using high-pressure liquid chromatography, we investigated the in vitro decay kinetics of HME under our in vitro drug treatment conditions and observed a very rapid, protein nondependent 40% drop in HME concentration which was dose dependent and was probably due to HME adsorption on the surface of tissue culture plasticware. Subsequent decay of the drug was very slow, with a decay rate constant of 0.022/h and a half-life of 298 h. In order to determine whether HME crosses the blood-brain barrier, we measured the rat brain capillary permeability coefficient, P, of [3H]HME and [14C]HME. The mean P value of 2.2 X 10(-6) cm/s +/- 16% (SD) suggests that HME crosses the blood-brain barrier (t 1/2 = 46 min) consistent with its molecular size and octanol-water partition coefficient.

The relationship of polyamines in cerebrospinal fluid to the presence of central nervous system tumors.

Cerebrospinal fluid (CSF) polyamine concentrations were assayed in patients with and without central nervous system tumors, using a high-pressure liquid chromatographic technique. Definite elevations were found in the CFS polyamine concentrations of patients with untreated malignant central nervous system tumors when compared with those concentrations observed in the CSF of patients without neoplasia. Patients undergoing successful tumor therapy for malignant central nervous system tumors showed CSF polyamine concentrations that closely approximated the concentrations found in the CSF of patients without tumor.

Cerebrospinal fluid polyamines in patients with Glioblastoma multiforme and anaplastic astrocytoma.

Eighteen cerebrospinal fluid polyamine determinations in 12 patients with glioblastoma multiforme and 76 determinations in 37 patients with anaplastic astrocytoma were evaluated. Cerebrospinal fluid polyamine levels showed no significant relationship to the degree of malignancy or to enhanced tumor volume or volume of tumor central low density as determined by contrast-enhanced computerized tomography. A significant correlation was found between polyamine levels and the proximity of the tumor to the cerebral ventricles. Polyamine levels were correlated with clinical status as determined by neurological examination, radionuclide scan, and computerized tomography. Compared with those of stable patients, cerebrospinal fluid polyamine levels were significantly elevated in patients with recurrent tumors; however, elevation of polyamine levels did not appear to precede tumor recurrence. A large fraction of the results were false-positive or false-negative results. In contrast to our findings in patients with medulloblastoma, it appears that cerebrospinal fluid polyamine levels determinations may be of little use for monitoring tumor progression in patients with glioblastoma multiforme and anaplastic astrocytoma.

Protein-tyrosine kinase activity and pp60v-src expression in whole cells measured by flow cytometry.

The expression and phosphotyrosine activity of pp60v-src were measured in the B31 avian sarcoma virus-transformed rat cell line by flow cytometry using monoclonal antibodies against pp60v-src (EB7) and phosphotyrosine (1G2). Although the immunocytochemical staining was markedly heterogeneous, binding of both antibodies was significantly greater to B31 cells than to untransformed Rat 1 cells. Binding of 1G2 to phosphotyrosine residues was specific; it was entirely inhibited by adding excess phenylphosphate but was not affected by phosphoserine or phosphothreonine. The relationship between the amount of phosphorylated tyrosine measured by our FCM technique and total cellular phosphotyrosine measured by phosphoamino acid analysis was linear in vanadate-treated BALB/c 3T3 cells. Treatment of B31 cells for 48 h with herbimycin A, a benzenoid ansamycin antibiotic, to decrease the expression and tyrosine kinase activity of pp60v-src caused reductions of 42% in anti-pp60v-src and 58% in anti-phosphotyrosine antibody immunofluorescence. DNA staining with the fluorescent dye propidium iodide showed no cell cycle specificity in the binding of either antibody. Herbimycin A also caused the transformed cell line to revert to the morphology, actin configuration, and growth behavior of untransformed cells; these changes were reversed within 12 h after removal of the drug. Flow cytometric evaluation of tyrosine kinase expression and activity was fast and easy, and the results correlated well with other measures of cell phenotype. This technique can be used to quantitate the effects of drugs on oncogenic proteins such as pp60v-src and their associated tyrosine kinase activity.

Factors influencing the survival of rat brain tumor cells after in vitro treatment with 1,3-bis(2-chloroethyl)-1-nitrosourea.

The shape of dose-response curves obtained for asynchronous, exponentially growing 9L rat brain tumor cells treated in vitro with 1,3-bis(2-chloroethyl)-1-nitrosourea changed as a function of the drug exposure time. For short treatment times (less than 1 hr), the dose-response curves had shoulders, indicating that the cells may accumulate sublethal damage; however, after longer treatments (greater than 1 hr), little if any shoulder was apparent. The slope of the exponential portion of the dose-response curve increased progressively with treatment periods from 15 min to 2 hr. Longer exposure times (up to 24 hr) produced no further changes in the cell-kill kinetics. Cell survival was directly related to the BCNU exposure dose [o integral t Co(t)dt] and to the amount of bound BCNU per cell. Extrapolation of the curves for these two variables indicated that some BCNU damage accumulates before death occurs. The amount of serum and cell products available in the medium to bind BCNU affected the level of survival; however, there was no evidence that extracellular spontaneous breakdown products or chemical transformation products were involved in the cell-killing mechanism.

Central nervous system toxicity and cerebrospinal fluid pharmacokinetics of intraventricular 3-[(4-amino-2-methyl-5-pyrimidinyl)ethyl]-1-(2-chloroethyl)-1-nitro soureas and other nitrosoureas in beagles.

The central nervous system toxicity and cerebrospinal fluid (CSF) pharmacokinetics of 3-[(4-amino-2-methyl-5-pyrimidinyl)ethyl]-1-(2-chloroethyl)-1- nitrosoureas, a (ACNU) were determined in beagles and compared to those for three other nitrosoureas, 1-(2-chloroethyl)-3-(2,6-dioxo-3-piperidyl)-1-nitrosourea, 1,3-bis(2-chloroethyl)-1-nitrosourea, and chlorozotocin. Of the four drugs, ACNU was tolerated best and at doses of 0.2 to 0.8 mg/week for 8 consecutive weeks. We found that the average half-time for CSF elimination of ACNU was 18 min (range, 12 to 38 min). This value exceeded the known rate of ACNU decomposition in aqueous solution (28 to 29 min), implying that the disappearance of ACNU from CSF was due to hydrolytic decomposition and cellular entry and/or transcapillary loss across central nervous system capillaries. The drug exposure integral (C X t) of ACNU in the CSF after a "toxic dose low" of 0.8 mg in the dogs would achieve the equivalent of in vitro cell kills in excess of 3 logs for rat 9L and human glioma 126 cells. As a potential therapeutic agent for meningeal neoplasia, the major limiting factor may be that the CSF elimination of ACNU is rapid compared to its equilibration time from ventricle to spinal- and cerebral convexity-subarachnoid space. Based on these results, we have instituted clinical Phase I trials of intra-CSF ACNU.

Potentiation of the antitumor therapeutic effects of 1,3-bis(2-chloroethyl)-1-nitrosourea by alpha-difluoromethylornithine, an ornithine decarboxylase inhibitor.

alpha-Difluoromethylornithine (DFMO), an enzyme-activated irreversible inhibitor of ornithine decarboxylase, was used alone and in combination with various single doses of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) to treat animals bearing murine glioma 26 and rat 9L gliosarcoma intracerebral tumors. Used as a single agent, DFMO has little or no effect against these tumors. However, in both intracerebral tumor models, pretreatment with DFMO p.o. before i.p. administration of BCNU potentiates the effect of BCNU without increasing toxicity. The effects of DFMO administered p.o. after BCNU or before and after various doses of BCNU indicate that DFMO may also effectively slow the repopulation of these tumors after BCNU therapy.