Development of a large-scale chemogenomics database to improve drug candidate selection and to understand mechanisms of chemical toxicity and action

Successful drug discovery requires accurate decision making in order to advance the best candidates from initial lead identification to final approval. Chemogenomics, the use of genomic tools in pharmacology and toxicology, offers a promising enhancement to traditional methods of target identification/validation, lead identification, efficacy evaluation, and toxicity assessment. To realize the value of chemogenomics information, a contextual database is needed to relate the physiological outcomes induced by diverse compounds to the gene expression patterns measured in the same animals. Massively parallel gene expression characterization coupled with traditional assessments of drug candidates provides additional, important mechanistic information, and therefore a means to increase the accuracy of critical decisions. A large-scale chemogenomics database developed from in vivo treated rats provides the context and supporting data to enhance and accelerate accurate interpretation of mechanisms of toxicity and pharmacology of chemicals and drugs. To date, approximately 600 different compounds, including more than 400 FDA approved drugs, 60 drugs approved in Europe and Japan, 25 withdrawn drugs, and 100 toxicants, have been profiled in up to 7 different tissues of rats (representing over 3200 different drug-dose-time-tissue combinations). Accomplishing this task required evaluating and improving a number of in vivo and microarray protocols, including over 80 rigorous quality control steps. The utility of pairing clinical pathology assessments with gene expression data is illustrated using three anti-neoplastic drugs: carmustine, methotrexate, and thioguanine, which had similar effects on the blood compartment, but diverse effects on hepatotoxicity. We will demonstrate that gene expression events monitored in the liver can be used to predict pathological events occurring in that tissue as well as in hematopoietic tissues.

Prediction of BCNU pulmonary toxicity in patients with malignant gliomas: an assessment of risk factors

Symptomatic pulmonary disease occurred in 20 per cent of 93 patients with anaplastic gliomas being treated with carmustine (BCNU). An analysis of the variables has revealed a relation between the occurrence of pulmonary toxicity on the one hand, and the total cumulative dose of BCNU, the number of cycles over which the BCNU was administered, the history of lung disease, the patient's age, and the platelet-count nadir after the first course of BCNU on the other. An equation has been generated that allows prediction of pulmonary toxicity during the course of therapy with BCNU with 80 per cent accuracy. Pretreatment analysis of individual cases should allow safe use of BCNU and prevention of most of the serious pulmonary complications caused by this drug.

Inhibition by nitric oxide of the repair protein, O6-methylguanine-DNA-methyltransferase

Nitric oxide (NO) has been shown to be involved in a number of physiological processes. In the presence of oxygen, this reactive diatomic molecule is capable of generating reactive nitrogen oxide species (NOx) which possess both nitrosating and oxidizing ability for various substrates, including certain biological macromolecules. This report shows the inhibition of the DNA repair protein, O6-methylguanine-DNA-methyltransferase, by Et2N[N(O)NO]Na (DEA/NO), a compound which decomposes with concurrent release of NO. The inhibition of the purified transferase activity by NO was dose- and time-dependent and the extent of inhibition by DEA/NO corresponded to the total quantity of NO released. This inhibitory effect by NO was also demonstrated to be reversible over time. The reaction of the NO released from DEA/NO with cysteine under aerobic conditions resulted in the formation of an S-nitrosothiol adduct, suggesting that a similar adduct could be responsible for the inactivation.

Vitamin E protection against chemical-induced cell injury. I. Maintenance of cellular protein thiols as a cytoprotective mechanism

Vitamin E protection against chemical-induced toxicity to isolated hepatocytes was examined during an imbalance in the thiol redox system. Intracellular reduced glutathione (GSH) was depleted by two chemicals of distinct mechanisms of action: adriamycin, a cancer chemotherapeutic agent that undergoes redox cycling, producing reactive oxygen species that consume GSH, and ethacrynic acid, a direct depleter of GSH. The experimental system used both nonstressed vitamin E-adequate isolated rat hepatocytes and compromised hepatocytes subjected to physiologically induced stress, generated by incubation in calcium-free medium. At doses whereby intracellular GSH was near total depletion, cell injury induced by either chemical was found to follow the depletion of cellular alpha-tocopherol, regardless of the status of the GSH redox system. Changes in protein thiol contents of the cells closely paralleled the changes in alpha-tocopherol contents throughout the incubation period. Supplementation of the calcium-depleted hepatocytes with alpha-tocopheryl succinate (25 microM) markedly elevated their alpha-tocopherol content and prevented the toxicities of both drugs. The prevention of cell injury and the elevation in alpha-tocopherol contents were both associated with a prevention of the loss in cellular protein thiols in the near total absence of intracellular GSH. The mechanism of protection by vitamin E against chemical-induced toxicity to hepatocytes may therefore be an alpha-tocopherol-dependent maintenance of cellular protein thiols.

Cross-linking of DNA induced by chloroethylnitrosourea is presented by O6-methylguanine-DNA methyltransferase

The DNA repair enzyme O6-methylguanine-DNA methyltransferase has been used as a reagent to analyse the initial reaction sites of alkylating agents such as chloroethylnitrosourea that cross-link DNA. The transferase can be employed for this purpose because it removes substituted ethyl groups from DNA, as shown by its ability to act on O6-hydroxyethylguanine residues in DNA. The enzyme counteracts the formation of interstrand cross-links induced by bis-chloroethylnitrosourea, but not those induced by nitrogen mustard. Once formed, chloroethylnitrosourea-induced cross-links are not broken by the enzyme. In agreement with deductions from experiments with living cells, it is concluded that chloroethylnitrosourea act by forming reactive monoadducts at the O6 position of guanine and/or the O4 position of thymine, which subsequently generate -CH2CH2- bridges to the complementary DNA strand. A new method for quantitating interstrand cross-links in DNA has been employed.

Results of the vincristine, doxorubicin, and dexamethasone regimen in adults with standard- and high-risk acute lymphocytic leukemia

One hundred five untreated adult patients with acute lymphocytic leukemia (ALL) were entered on the vincristine, Adriamycin (doxorubicin; Adria Laboratories, Columbus, OH), and Decadron (dexamethasone; Merck Sharp and Dohme, West Point, PA) (VAD) regimen. Induction therapy with VAD and VAD plus cyclophosphamide (CVAD) was followed by a 2-year rotating maintenance program with multiple antileukemic combinations, and included early intensifications with Adriamycin and high-dose cytarabine (ara-C) and a late intensification with cyclophosphamide, carmustine (BCNU), and etoposide (VP-16) (CBV) followed by autologous bone marrow transplantation (BMT). Duration of therapy was 24 to 30 months. Eight-eight patients (84%) achieved complete remission (CR) with VAD-CVAD, and 94 (90%) ultimately had CR with continuation of the maintenance as planned. Induction mortality was 3%; only half of the patients required prolonged hospitalization of 1 week or longer, or intravenous antibiotics. Maintenance therapy was given to 79 patients, while nine with histocompatibility locus antigen (HLA)-matched related donors underwent allogeneic BMT. The median remission duration was 22 months, and the median survival was 19 months. Factors associated with significantly worse CR rates were older age, the presence of hypoalbuminemia or hyperbilirubinemia, L2 or L3 morphology, and myeloid markers on leukemic cells. Those associated with significantly worse remission durations were the presence of elevated leukocyte or absolute peripheral blast counts, Philadelphia chromosome (Ph)-positive or B-cell ALL, L2 morphology, and more than one course to achieve CR. Patients could be divided into standard-risk ALL (28% of patients) and high-risk ALL (72% of patients) with long-term remission rates of 70% versus less than 30%. The 26 patients who underwent CBV autologous BMT had similar long-term outcome compared with 21 patients who did not (older age, medical contraindications, or socioeconomic problems). The presence or absence of myeloid markers on leukemic cells did not affect long-term prognosis. We conclude that VAD therapy is a well-tolerated effective induction regimen. High-risk ALL patients require alternative maintenance investigational approaches.

Vitamin E reversal of the effect of extracellular calcium on chemically induced toxicity in hepatocytes

Isolated rat hepatocytes were incubated in the presence or absence of extracellular calcium and alpha-tocopherol succinate with three different toxic chemicals; namely, adriamycin in combination with 1,3-bis(2-chloroethyl)-1-nitrosourea, ethyl methanesulfonate, and the calcium ionophore A23187. In the absence of extracellular calcium these three compounds were far more toxic to the cells than in its presence. The addition of vitamin E to calcium-free medium, however, protected hepatocytes against toxic injury, whereas cells incubated in medium containing calcium were not protected. Hepatocyte viability during each toxic insult correlated well with the cellular alpha-tocopherol content but not with the presence or absence of extracellular calcium. These results suggest that cellular alpha-tocopherol maintains the viability of the cell during a toxic insult and that the presence or absence of vitamin E in the incubation medium probably explains the conflicting reports on the role of extracellular calcium in toxic cell death.

The role of autologous transplantation in patients with multiple myeloma aged 65 years and over

Autologous stem cell transplantation after high-dose melphalan for the treatment with multiple myeloma has resulted in prolonged progression-free survival and overall survival in patients under 65 years. We have examined the role of autologous transplantation in 17 patients with multiple myeloma over 65 years at our centre using a matched pair analysis with younger patients. The median age of this cohort of patients over 65 years was 67 years (65-74) and their outcome and transplant-related morbidity was compared with 17 younger pair mates with a median age of 55 years (31-64). Sixteen patients received high-dose melphalan, and one received busulphan with autologous stem cell rescue. The high-dose therapy was well tolerated in both elderly patients and the matched pairs, with comparable time to recover neutrophils and platelets. Treatment-related mortality also did not differ significantly in both the groups. Median overall survival of the elderly patients was 3.59 years similar to 3.01 years of the pair mates (P = 0.92). Autologous stem cell transplantation after high-dose melphalan conditioning was equally well tolerated in groups of patients above and below 65 years. There was no difference in relapse rate, OS and myelotoxicity in both the groups. These findings suggest that advanced age should not be an exclusion criterion from autologous transplant programmes. Bone Marrow Transplantation (2000) 25, 533-539.

Drug streaming during intra-arterial chemotherapy

Treatment of brain tumors by intra-arterial (IA) chemotherapy is occasionally complicated by sites of focal toxicity in the brain and retina. A possible cause of focal toxicity is non-uniform drug delivery due to intravascular drug streaming. To investigate this phenomenon in vivo, the authors examined the distribution of drug delivery after internal carotid artery (ICA) infusion in rhesus monkeys. Carbon-14 (14C)-labeled iodoantipyrine was delivered into the ICA of eight monkeys at slow infusion rates (1% to 2% of ICA flow) or at fast infusion rates (20% of ICA flow) combined with additional techniques to promote mixing with ICA blood. Two monkeys received intravenous (IV) 14C-antipyrine. Uniformity of delivery was assessed by comparing high-to-low ratios of isotope concentration in four brain regions evaluated by quantitative autoradiography. There was striking non-uniformity of drug delivery in the slow IA infusion group, with as much as 13-fold differences in drug concentration in anatomically contiguous areas. The values of high-to-low concentration ratios (mean +/- standard deviation) in individual autoradiographic planes were: 1) frontoparietal cortex: slow IA infusion 4.54 +/- 2.07, fast IA infusion 1.71 +/- 0.31, IV infusion 1.30 +/- 0.174; 2) frontoparietal white matter: slow IA infusion 2.94 +/- 1.45, fast IA infusion 1.59 +/- 0.41, IV infusion 1.34 +/- 0.21; 3) temporal cortex: slow IA infusion 5.43 +/- 3.57, fast IA infusion 1.69 +/- 0.24, IV infusion 1.67 +/- 0.25; 4) basal ganglia: slow IA infusion 3.6 +/- 2.9, fast IA infusion 1.18 +/- 0.10, IV infusion 1.09 +/- 0.04. Differences between concentration ratios after slow IA and fast IA infusion are significant (p less than 0.01); those between fast IA and IV infusion are not significant. Intra-arterial drug administration at infusion rates analogous to those currently used clinically results in drug streaming with markedly heterogeneous drug deposition in the perfused hemisphere. This may cause suboptimal drug levels in the tumor, and toxic levels at sites within the perfused hemisphere. This effect can be abrogated by techniques that eliminate drug streaming.

Intensive 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), NSC #4366650 and cryopreserved autologous marrow transplantation for refractory cancer. A phase I-II study

One hundred forty-three patients with refractory cancer were treated with intensive BCNU (600-2850 mg/m2) and autologous marrow transplantation to determine the maximum tolerated dose and antitumor effects of this regimen. Recovery from severe pancytopenia in less than 4 weeks after transplantation occurred in 92.8% of evaluable patients, suggesting the efficacy of the autologous marrow in limiting the prolonged myelosuppression anticipated with intensive BCNU. Serious extramedullary toxicity was encountered at BCNU 1200 mg/m2, where a 9.5% incidence of fatal interstitial pneumonitis and a 3.0% incidence of fatal hepatic necrosis was observed. Higher BCNU doses, 1500 to 2850 mg/m2, were associated with a 35.3% incidence of fatal hepatotoxicity. Fatal encephalomyelopathy was encountered in two patients given BCNU 2250 and 2850 mg/m2. One patient who received the highest cumulative dose of BCNU (3450 mg/m2 in 2 courses) died of cardiac necrosis. Other serious extramedullary toxicities were not encountered, even in the 14 patients who survived from 1 to nearly 5 years after BCNU therapy. Antitumor responses occurred in 40.0% of evaluable patients; a dose effect could not be evaluated due to patient heterogeneity. The BCNU doses associated with acceptable toxicity, 600 to 1200 mg/m2, produced a 37.5% total and an 11.3% complete response (CR) rate, including five patients with prolonged CRs of 1 to nearly 5 years. Notable among the CRs was the 25.0% CR rate in previously untreated metastatic melanoma, and the production of CRs in malignant disease in the central nervous system (CNS) including melanoma, lung cancer, adenocarcinoma of unknown primary, acute leukemia and glioblastoma multiforme. It is concluded that augmented doses of BCNU can be given when autologous marrow transplantation is used to limit myelosuppression. Lung and liver toxicity prevent the use of BCNU doses greater than 1200 mg/m2; neurotoxicity, and perhaps cardiotoxicity, are manifestations of the highest doses used in this study. The antitumor activity of BCNU 600 to 1200 mg/m2 remains to be determined for most neoplasms; these results suggest improved results in melanoma and CNS malignancy compared to conventional-dose BCNU therapy.

Increasing DNA repair methyltransferase levels via bone marrow stem cell transduction rescues mice from the toxic effects of 1,3-bis(2-chloroethyl)-1-nitrosourea, a chemotherapeutic alkylating agent

The chloroethylnitrosourea (CNU) alkylating agents are commonly used for cancer chemotherapy, but their usefulness is limited by severe bone marrow toxicity that causes the cumulative depletion of all hematopoietic lineages (pancytopenia). Bone marrow CNU sensitivity is probably due to the inefficient repair of CNU-induced DNA damage; relative to other tissues, bone marrow cells express extremely low levels of the O6-methylguanine DNA methyltransferase (MGMT) protein that repairs cytotoxic O6-chloroethylguanine DNA lesions. Using a simplified recombinant retroviral vector expressing the human MGMT gene under control of the phosphoglycerate kinase promoter (PGK-MGMT) we increased the capacity of murine bone marrow-derived cells to repair CNU-induced DNA damage. Stable reconstitution of mouse bone marrow with genetically modified, MGMT-expressing hematopoietic stem cells conferred considerable resistance to the cytotoxic effects of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), a CNU commonly used for chemotherapy. Bone marrow harvested from mice transplanted with PGK-MGMT-transduced cells showed extensive in vitro BCNU resistance. Moreover, MGMT expression in mouse bone marrow conferred in vivo resistance to BCNU-induced pancytopenia and significantly reduced BCNU-induced mortality due to bone marrow hypoplasia. These data demonstrate that increased DNA alkylation repair in primitive hematopoietic stem cells confers multilineage protection from the myelosuppressive effects of BCNU and suggest a possible approach to protecting cancer patients from CNU chemotherapy-related toxicity.

Effects of hypoxia on drug resistance phenotype and genotype in human glioma cell lines

Recurrent gliomas are most often treated by chemotherapy. However, these tumors typically acquire resistance to most drugs administered, and patients will usually die of recurrent tumor. Factors which may play a role include overexpression of putative multidrug resistance genes, such as the multidrug resistance gene 1 (MDR1), multidrug resistance associated protein gene (MRP), 06-alkylguanine, DNA alkyltransferase gene (06MT) and excision repair cross complementing gene 1 (ERCC1). Tumor hypoxia has also been shown to be associated with drug resistance in other soft tissue tumors. Since gliomas have regions of diminished oxygenation, and have clinical resistance to chemotherapy, the relationship between phenotypic resistance to chemotherapy after hypoxic exposure and expression of drug resistance genes was investigated in glioma cell lines (U373 MG, PFAT-MT). After a 24 hour exposure to hypoxia, drugs 1, 3-bis, 2-chloroethyl-1-nitrosurea (BCNU) and cis-diammine, dichloroplatinum II (CDDP) were administered, and cell survival was determined. Hypoxic exposure was associated with increased survival of the cell lines after administration of BCNU and CDDP, with resistance to BCNU 15 to 30-fold when compared to cells which did not undergo hypoxic exposure. Both tumor cell lines also showed some degree of resistance to CDDP, although not to the extent of BCNU (2 to 3-fold increased resistance). The expression of the drug resistance genes was found to be unchanged when comparing cells which had undergone hypoxic exposure and those which had not. Thus, hypoxic exposure is associated with substantial drug resistance in brain tumor cell lines. The lack of correlation between the induced phenotype and known drug resistance genes suggests other mechanisms may be acting in these tumors in hypoxic conditions.

High-dose immunosuppressive therapy with PBPC support in the treatment of poor risk multiple sclerosis

High-dose immunoablative chemotherapy with autologous haematopoietic cell support might be beneficial in the treatment of intractable forms of MS. We mobilised PBPC in 11 patients with secondary progressive MS and finally eight patients were grafted after high-dose BEAM chemotherapy with either in vitro or in vivo T cell depletion. Median EDSS and SNRS scores at the time of inclusion were 6.5 (6.5-7.5) and 56 (44-65), respectively. PBPC mobilisation was safe with no serious adverse effects, and without significant aggravation of disability. One patient improved significantly (by 1.0 point on EDSS) after the mobilisation. Two mobilisation failures were observed. No life-threatening events occurred during the transplantation. All grafted patients, except one, at least stabilised their disability status. One patient improved significantly (by 1.5 points on EDSS), two patients improved slightly (by 0.5 points on EDSS), one patient worsened by 1.0 point on the EDSS in 10 months. Improvement occurred with a delay of 2-4 months. Median EDSS and SNRS of grafted patients at the last follow up were 6.5 (5.5-8.5) and 64 (39-73), respectively with median follow-up of 8.5 months. Further follow-up is needed to determine the disease course after complete immune reconstitution. Bone Marrow Transplantation (2000) 25, 525-531.

Glutathione monoethyl ester can selectively protect liver from high dose BCNU or cyclophosphamide

Normal Swiss Webster mice were treated with monocrotaline or high doses of three antitumor alkylating agents (BCNU, cyclophosphamide, or mitomycin C), all of which have been connected with hepatic veno-occlusive disease at our clinic. Prior administration of WR-2721 did not improve the survival of monocrotaline-treated animals. Glutathione (GSH) improved the survival of these animals to a small degree. Glutathione monoethyl ester (GSHet) almost completely protected animals from the toxicity of monocrotaline. Pretreatment with WR-2721 produced moderate increases in survival at the highest doses of BCNU, and at the lower BCNU doses none of the animals pretreated with WR-2721 died before they were killed on day 150. Pretreatment with GSHet gave good protection from BCNU toxicity at the highest dose of the drug, and there were no deaths in the groups of animals treated with GSHet 1 hour before BCNU. On a multiple dose schedule, GSH provided some protection from cyclophosphamide toxicity; GSHet gave a very good level of protection from cyclophosphamide. In none of these treatment groups were lesions suggestive of hepatic or pulmonary venoocclusive disease identified. In all three experimental protocols (monocrotaline, BCNU, and cyclophosphamide), there was a consistent decrease in hepatic toxicity after GSHet pretreatment; this was not observed in GSH- or WR-2721-pretreated animals. There was no evidence of protection of the FSaIIC fibrosarcoma growing in C3H mice as assayed by tumor growth delay or tumor cell survival in groups treated with two different doses of GSHet 1 hour before each drug injection compared to those treated with the BCNU or cyclophosphamide alone, or BCNU with cyclophosphamide. Pretreatment with GSHet did not alter the toxicity of these drugs to bone marrow. GSHet appears to be an effective protector of critical normal tissue and does not appear to protect tumor.

Retroviral transduction of a mutant methylguanine DNA methyltransferase gene into human CD34 cells confers resistance to O6-benzylguanine plus 1,3-bis(2-chloroethyl)-1-nitrosourea

Human CD34 cells express low levels of the DNA repair protein O6-alkylguanine-DNA alkyltransferase (AGT) and are sensitive to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). Gene transfer of the AGT gene, methylguanine DNA methyltransferase (MGMT), results in only modest BCNU resistance. Recently, an AGT inhibitor, O6-benzylguanine (BG), entered clinical trials. In preclinical studies, BG potentiated the cytotoxic effect of BCNU in tumors but increased toxicity to normal CD34 cells. We transferred a mutant MGMT containing a glycine-to-alanine mutation at position 156, resulting in marked resistance to BG, into Chinese hamster cells; the K562 cell line and human CD34 cells used the retroviral backbone MFG. In each instance, cells expressed increased AGT and were much more resistant to the combination of BG and BCNU than the parental cells or cells transduced with wild-type MGMT. Furthermore, the transduction efficiency in human CD34 cells was in excess of 70%, and the proportion of CD34 transduced cells resistant to the combination was > 30%. Thus, retroviral-mediated transduction of a mutant MGMT into CD34 cells appears to be an effective way to induce selective resistance to a drug combination designed to overcome a significant resistance mechanism to nitrosoureas in tumors.

Primary and immortalized (BEAS 2B) human bronchial epithelial cells have significant antioxidative capacity in vitro

Antioxidant enzymes located in the bronchial epithelium can be expected to be important in protecting these cells against both endogenous and exogenous oxidants. In this study, human bronchial epithelial cells were isolated and cultured from specimens obtained from donors for lung transplantation. The levels and relative importance of different antioxidant enzymes were also assessed using an immortalized human bronchial epithelial cell line (BEAS 2B cells). Immunocytochemical studies showed a similar pattern of intracellular localization with the moderate degrees of labeling for Mn superoxide dismutase (SOD), CuZn SOD, and catalase in freshly isolated bronchial epithelial cells, bronchial epithelial cells in primary culture, and BEAS 2B cells. CuZn SOD and catalase decreased in labeling density whereas Mn SOD was unchanged when bronchial epithelial cells were placed in primary cultures. In contrast, Mn SOD and catalase were decreased in BEAS 2B cells compared with primary cultures. Although Mn SOD was low in BEAS 2B cells, it could be significantly induced by tumor necrosis factor treatment. Biochemical analysis showed remarkably similar catalase and glutathione reductase activities in primary cultured epithelial cells and BEAS 2B cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary toxicity following carmustine-based preparative regimens and autologous peripheral blood progenitor cell transplantation in hematological malignancies

Sixty-five patients with hematological malignancies (25 multiple myeloma, 18 Hodgkin's disease, 22 non-Hodgkin's lymphomas) who received a carmustine-based regimen followed by autologous PBPC transplantation, were studied retrospectively to evaluate the incidence of post-transplant non-infective pulmonary complications (NIPCs), risk factors predictive of NIPCs, and response to steroids. Carmustine (BCNU) given i.v. at a dose of 600 mg/m2 was combined with etoposide and cyclophosphamide in 40 patients (BCV regimen) and with etoposide and melphalan in 25 patients (BEM regimen). Seventeen of 65 patients (26%) had one episode of NIPCs. The median time to NIPCs was 90 days (52-289). Factors that increased the risk of developing NIPCs on multivariate analysis were female sex (P < 0. 001) and BCV regimen (P < 0.05). All patients with NIPCs received prednisone at a dose of 1 mg/kg body weight for 10 days then tapered by 5 mg every two days; complete response to steroids was achieved in 15 of 17 patients; one unresponsive patient died of interstitial pneumonia. BCNU given at the dose of 600 mg/m2 is well tolerated when associated with melphalan and etoposide. In females and in patients receiving BCNU with cyclophosphamide, a BCNU dose reduction may be advisable. Bone Marrow Transplantation (2000) 25, 309-313.

Mechanism of chemical-induced toxicity. I. Use of a rapid centrifugation technique for the separation of viable and nonviable hepatocytes

A major obstacle in defining the mechanism of chemical-induced toxicity has been the inability to distinguish between events that cause cell death and those that result from cell death. This problem results from measuring biochemical parameters in tissues or cell pellets containing both viable and nonviable cells. In the present study, we described a method for the rapid separation of viable hepatocytes from nonviable cells and medium prior to biochemical analysis. Separation of viable hepatocytes was accomplished in a microcentrifuge tube by layering a sample of isolated hepatocyte suspension over a dibutyl phthalate oil layer and centrifuging for several seconds. As a result, greater than 90% of the hepatocytes centrifuged through dibutyl phthalate were viable while greater than 90% of the cells recovered above the oil layer were nonviable. The separation of viable hepatocytes by the dibutyl phthalate method was not affected by the presence of the hepatotoxins, adriamycin (ADR) in combination with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) or ethyl methanesulfonate (EMS), though the ratio of viable to nonviable cells in the suspension was drastically reduced. The metabolic and morphological integrity of hepatocytes centrifuged through dibutyl phthalate was altered after cell suspensions were treated with the ADR-BCNU or EMS. These chemically treated viable hepatocytes showed degenerative ultrastructural changes and a greater than 80% reduction in intracellular K+ and glutathione concentrations. Because centrifugation through dibutyl phthalate does not significantly alter the concentration of intracellular constituents nor the ultrastructure of control hepatocytes, the signs of reversible injury observed in hepatocytes centrifuged through oil resulted from the chemical treatment. These data indicate that the dibutyl phthalate separation technique offers the advantage of monitoring only viable hepatocytes for changes in membrane integrity or metabolic performance during a toxic chemical insult.

Cardiac toxicity following high-dose cyclophosphamide, cisplatin, and BCNU (STAMP-I) for breast cancer

We retrospectively evaluated 443 breast cancer patients treated with high-dose cyclophosphamide, cisplatin, and BCNU (STAMP-I) with autologous stem cell support to characterize the cardiac toxicity of this regimen. Patients had stage II-III (n = 243) or stage IV (n = 200) breast cancer. We observed an overall 5.1% incidence of cardiac complications, both clinical and subclinical, in the whole group: 4.9% in stage II-III and 5.5% in stage IV patients. Clinical cardiomyopathy (CMP) was observed in 1.6% of stage II-III patients (1 case of fatal grade 5 toxicity and 3 cases of grade 3 CMP) and in 3.5% of patients with stage IV disease (1 case of grade 4 and 6 cases of grade 3). The incidence of cardiac toxicity did not differ significantly between the groups. Prior radiation therapy to the mediastinum or left chest wall (P = .001) and advanced age (P = .01) were independent predictors of an increased risk of the appearance of this complication. No pharmacodynamic correlation was observed between any of the 3 drugs and cardiac toxicity.

Effect of O6-benzylguanine on the sensitivity of human colon tumor xenografts to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU)

A number of trials were conducted to determine the effect of O6-benzylguanine pretreatment on the sensitivity of human colon tumor xenografts to the antitumor effects of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). O6-Benzylguanine has been shown to inactivate the DNA repair protein, O6-alkylguanine-DNA alkyltransferase (AGT), which is primarily responsible for resistance to alkylnitrosoureas including BCNU. Colon tumor xenografts carried in nude mice were analyzed for their AGT content, and tumors with low, intermediate and high levels were chosen for further study. The AGT activity of HC-1, GC-3, VRC-5 and CX-1 human colon tumor xenografts was 16, 113, 180 and 367 fmol/mg protein, respectively. Treatment of mice consisted of vehicle alone, 6.25 to 50 mg/kg BCNU administered alone or BCNU (6.25 to 25 mg/kg) 1 hr after 120 mg/kg O6-benzylguanine on days 7 and 14 post-inoculation. Toxicity studies revealed that pretreatment with O6-benzylguanine increased the toxicity of BCNU, requiring administration of about 4-fold less drug. The growth of the VRC-5 tumor at day 42 post-inoculation was inhibited by 39% following treatment with 12.5 mg/kg BCNU alone and 92% when BCNU was combined with O6-benzylguanine pretreatment. The combination of O6-benzylguanine and BCNU (12.5 mg/kg) at day 42 resulted in an inhibition of HC-1 and CX-1 tumor growth by 84 and 72%, whereas BCNU alone inhibited growth by 54 and 14%, respectively. Therefore, the degree to which the antitumor effect of BCNU was increased by O6-benzylguanine pretreatment was dependent on the AGT activity, with a greater effect in tumors of intermediate or high activity. These data suggest that there is a role for O6-benzylguanine combined with BCNU in the treatment of human colon tumors.

Screening of cytotoxic drugs for residual bone marrow damage

Several cytotoxic drugs were tested for their ability to produce permanent residual damage to the bone marrow. A short course of the drug was given to BALB/c female mice, and the numbers of various types of bone marrow cells were determined at least two months later. Evidence of residual damage was found after administration of busulfan and 1,3-bis(chloroethyl)-1-nitrosourea, but not after administration of cyclophosphamide, 5-fluorouracil, 6-mercaptopurine, methotrexate, or vinblastine.

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.