NTCU induced pre-malignant and malignant stages of lung squamous cell carcinoma in mice model

Mice have served as an excellent model to understand the etiology of lung cancer for years. However, data regarding dual-stage carcinogenesis of lung squamous cell carcinoma (SCC) remain elusive. Therefore, we aim to develop pre-malignant (PM) and malignant (M) lung SCC in vivo using N-nitroso-tris-chloroethylurea (NTCU). BALB/C mice were allotted into two main groups; PM and M groups which received treatment for 15 and 30 weeks, respectively. Then, the mice in each main group were allotted into three groups; control, vehicle, and cancer (n = 6), which received normal saline, 70% acetone, and 0.04 M NTCU by skin painting, respectively. Histopathologically, we discovered a mix of hyperplasia, metaplasia, and dysplasia lesions in the PM group and intracellular bridge; an SCC feature in the M group. The M group was positive for cytokeratin 5/6 protein which confirmed the lung SCC subtype. We also found significantly higher (P < 0.05) epithelium thickness in the cancer groups as compared to the vehicle and control groups at both the PM and M. Overall, this study discovered that NTCU is capable of developing PM and M lung SCC in mice model at appropriate weeks and the vehicle group was suggested to be adequate as control group for future research.

Role of deltaNp63(pos)CD44v(pos) cells in the development of N-nitroso-tris-chloroethylurea-induced peripheral-type mouse lung squamous cell carcinomas

The role of cells expressing stem cell markers deltaNp63 and CD44v has not yet been elucidated in peripheral-type lung squamous cell carcinoma (pLSCC) carcinogenesis. Female A/J mice were painted topically with N-nitroso-tris-chloroethylurea (NTCU) for induction of pLSCC, and the histopathological and molecular characteristics of NTCU-induced lung lesions were examined. Histopathologically, we found atypical bronchiolar hyperplasia, squamous metaplasia, squamous dysplasia, and pLSCCs in the treated mice. Furthermore, we identified deltaNp63(pos)CD44v(pos)CK5/6(pos)CC10(pos) clara cells as key constituents of early precancerous atypical bronchiolar hyperplasia. In addition, deltaNp63(pos)CD44v(pos) cells existed throughout the atypical bronchiolar hyperplasias, squamous metaplasias, squamous dysplasias, and pLSCCs. Overall, our findings suggest that NTCU induces pLSCC through an atypical bronchiolar hyperplasia-metaplasia-dysplasia-SCC sequence in mouse lung bronchioles. Notably, Ki67-positive deltaNp63(pos)CD44v(pos) cancer cells, cancer cells overexpressing phosphorylated epidermal growth factor receptor and signal transducer and activator of transcription 3, and tumor-associated macrophages were all present in far greater numbers in the peripheral area of the pLSCCs compared with the central area. These findings suggest that deltaNp63(pos)CD44v(pos) clara cells in mouse lung bronchioles might be the origin of the NTCU-induced pLSCCs. Our findings also suggest that tumor-associated macrophages may contribute to creating a tumor microenvironment in the peripheral area of pLSCCs that allows deltaNp63(pos)CD44v(pos) cancer cell expansion through activation of epidermal growth factor receptor signaling, and that exerts an immunosuppressive effect through activation of signal transducer and activator of transcription 3 signaling.

Tracheal dysplasia precedes bronchial dysplasia in mouse model of N-nitroso trischloroethylurea induced squamous cell lung cancer

Squamous cell lung cancer (SCC) is the second leading cause of lung cancer death in the US and has a 5-year survival rate of only 16%. Histological changes in the bronchial epithelium termed dysplasia are precursors to invasive SCC. However, the cellular mechanisms that cause dysplasia are unknown. To fill this knowledge gap, we used topical application of N-nitroso-tris chloroethylurea (NTCU) for 32 weeks to induce squamous dysplasia and SCC in mice. At 32 weeks the predominant cell type in the dysplastic airways was Keratin (K) 5 and K14 expressing basal cells. Notably, basal cells are extremely rare in the normal mouse bronchial epithelium but are abundant in the trachea. We therefore evaluated time-dependent changes in tracheal and bronchial histopathology after NTCU exposure (4, 8, 12, 16, 25 and 32 weeks). We show that tracheal dysplasia occurs significantly earlier than that of the bronchial epithelium (12 weeks vs. 25 weeks). This was associated with increased numbers of K5⁺/K14⁺ tracheal basal cells and a complete loss of secretory (Club cell secretory protein expressing CCSP⁺) and ciliated cells. TUNEL staining of NTCU treated tissues confirmed that the loss of CCSP⁺ and ciliated cells was not due to apoptosis. However, mitotic index (measured by bromodeoxyuridine incorporation) showed that NTCU treatment increased proliferation of K5⁺ basal cells in the trachea, and altered bronchial mitotic population from CCSP⁺ to K5⁺ basal cells. Thus, we demonstrate that NTCU-induced lung epithelial dysplasia starts in the tracheal epithelium, and is followed by basal cell metaplasia of the bronchial epithelium. This analysis extends our knowledge of the NTCU-SCC model by defining the early changes in epithelial cell phenotypes in distinct airway locations, and this may assist in identifying new targets for future chemoprevention studies.

Honokiol inhibits lung tumorigenesis through inhibition of mitochondrial function

Honokiol is an important bioactive compound found in the bark of Magnolia tree. It is a nonadipogenic PPARγ agonist and capable of inhibiting the growth of a variety of tumor types both in vitro and in xenograft models. However, to fully appreciate the potential chemopreventive activity of honokiol, a less artificial model system is required. To that end, this study examined the chemopreventive efficacy of honokiol in an initiation model of lung squamous cell carcinoma (SCC). This model system uses the carcinogen N-nitroso-trischloroethylurea (NTCU), which is applied topically, reliably triggering the development of SCC within 24 to 26 weeks. Administration of honokiol significantly reduced the percentage of bronchial that exhibit abnormal lung SCC histology from 24.4% bronchial in control to 11.0% bronchial in honokiol-treated group (P = 0.01) while protecting normal bronchial histology (present in 20.5% of bronchial in control group and 38.5% of bronchial in honokiol-treated group. P = 0.004). P63 staining at the SCC site confirmed the lung SCCs phenotype. In vitro studies revealed that honokiol inhibited lung SCC cells proliferation, arrested cells at the G1-S cell-cycle checkpoint, while also leading to increased apoptosis. Our study showed that interfering with mitochondrial respiration is a novel mechanism by which honokiol changed redox status in the mitochondria, triggered apoptosis, and finally leads to the inhibition of lung SCC. This novel mechanism of targeting mitochondrial suggests honokiol as a potential lung SCC chemopreventive agent.

SarCNU in recurrent or metastatic colorectal cancer: a phase II study of the National Cancer Institute of Canada Clinical Trials Group

PURPOSE

To evaluate the activity and toxicity of SarCNU, an oral chloroethylnitrosourea in patients with recurrent or metastatic colorectal cancer who have progressed after first-line chemotherapy.

PATIENTS AND METHODS

Eighteen patients with recurrent or metastatic colorectal cancer following first-line chemotherapy were treated with SarCNU 860 mg/m2 orally day 1, 5 and 9 every 6 weeks. The patient's median age was 64 and the ECOG performance status was 0 in six, 1 in eleven and 2 in one patients. All patients were evaluable for toxicity and 16 were evaluable for response.

RESULTS

There were no objective responses (0%). One patient had stable disease and 15 had progressive disease at their first follow-up assessment. Median survival was 7.36 months (3.75-7.49 95% C.I.). Neutropenia and thrombocytopenia were the most severe toxicities (grade 3-4 in six and nine patients respectively). Pulmonary toxicity was also seen in five patients who had a drop of DLCO grade from baseline and two patients who had a fall in FVC from baseline.

CONCLUSIONS

SarCNU is inactive in recurrent or metastatic colorectal patients who have progressed after first-line chemotherapy.

Phase II Trial of SarCNU in Malignant Glioma: Unexpected Pulmonary Toxicity with a Novel Nitrosourea

PURPOSE

A multi-centre phase II study of SarCNU-a novel chloroethylnitrosourea (CNU)-in patients with recurrent malignant glioma to assess response rate, survival and effects of treatment.

PATIENTS AND METHODS

Ten patients with histologically proven malignant glioma (seven with glioblastoma multiforme (GBM) and three with anaplastic astrocytoma) received SarCNU (860 mg/m(2)) orally on days 1, 5 and 9 on a 6 week schedule.

RESULTS

A total of ten patients were treated on protocol before accrual was suspended for a high rate of pulmonary toxicity. Of eight evaluable patients, five demonstrated at least one grade deterioration in DLCO from baseline. This necessitated premature closure of the trial. Stable disease was seen in five of seven evaluable patients (median duration 4.8 months; range 0.8-9.2) with progressive disease in the remainder.

CONCLUSION

Despite promising preclinical data, SarCNU caused pulmonary toxicity in patients with recurrent malignant glioma and we plan no further studies in this indication.

SarCNU-induced G2/M arrest in hepatoma cells is mediated by a p53-independent phosphorylation of cdc-2 at Tyr15

Hepatocellular carcinoma (HCC) is a major health problem in the Asia-Pacific region, with high incidence and mortality rate. There is currently no effective treatment for inoperable cases that represent the vast majority of patients. In the present study, we report that in vitro treatment of primary hepatoma, HepG2 (wild-type p53), PLC/PRF/5 (p53-mutant), and Hep3B (p53-deleted) cells with 2-chloroethyl-3-sarcosinamide-1-nitrosourea (SarCNU) resulted in upregulation of p53, p21(Cip1/Waf1), phosphorylated cdc-2 at Tyr15 in wild-type p53 cells and phosphorylation of cdc-2 at Tyr15 in p53-mutant or p53-deleted hepatoma cells. This was accompanied by the reduction in cdc-2 kinase activity and G(2)/M cell cycle arrest. These findings indicate that SarCNU-induced G(2)/M growth arrest in hepatoma cells by a p53-independent phosphorylation of cdc-2. Our data suggest the potential use of SarCNU in treatment of HCC.

2-Chloroethyl-3-sarcosinamide-1-nitrosourea (SarCNU) exhibits p53-dependent and -independent antiproliferative activity in human nasopharyngeal carcinoma cells in vitro and in vivo

2-Chloroethyl-3-sarcosinamide-1-nitrosourea (SarCNU) has been used to treat patients with advanced solid tumours. However, the molecular mechanisms are not well understood. In the present study, we report that SarCNU inhibited proliferation of human HK-1 and CNE-2 nasopharyngeal carcinoma (NPC) in vivo and in vitro. In vitro study showed that wild-type p53 HK-1 cells were 3-fold more sensitive to SarCNU than p53 mutant CNE-2 cells. G2/M arrest, reduction in p21(Cip1/Waf1) and inactivation of cellular cdc-2 activity were seen in both SarCNU-treated HK-1 and CNE-2 cells. Upregulation of p53, phosphorylated p53 at Ser15 and biochemical markers for apoptosis, such as cleaved caspase-3, cleaved caspase-7 and cleaved PARP, were observed in SarCNU-treated HK-1 but not CNE-2 cells. The levels of cyclin B1, Wee1 and phosphorylated cdc-2 but not total cdc-2 in HK-1 cells were significantly reduced by SarCNU treatment. In contrast to HK-1 cells, decrease in total cdc-2 but increase in phosphorylated cdc-2 at Tyr15, cyclin B1 and Wee1 was observed in CNE-2 cells treated with SarCNU. Introduction of mutant p53 into HK-1 cells resulted in growth enhancement in vivo and increased resistance to SarCNU-induced apoptosis in vitro. Furthermore, CNE-2 cells transfected with wild-type p53 became susceptible to SarCNU-induced apoptosis in vitro but not their growth rate in vivo. The data indicate that in NPC cells SarCNU-induced apoptosis was p53-dependent while SarCNU-induced G2/M arrest was mediated by altering the levels of cyclin B1-cdc-2 complex and phosphorylation of cdc-2 at Tyr15 resulting in inactivation of cellular cdc-2 activity. Our data suggest a potential use of SarCNU in the treatment of NPC.

2-Chloroethyl-3-sarcosinamide-1-nitrosourea (SarCNU) inhibits prostate carcinoma cell growth via p53-dependent and p53-independent pathways

BACKGROUND

Prostate carcinoma is the most commonly occurring malignancy in men. Although 2-chloroethyl-3-sarcosinamide-1-nitrosourea (SarCNU), an analog of the chloroethylnitrosoureas, has been used in the treatment of advanced solid tumors, the molecular mechanisms underlying the antineoplastic activity of this agent are not well understood. In the current study, the authors sought to investigate the effects of SarCNU on prostate carcinoma cell growth in vivo and in vitro.

METHODS

Male SCID mice underwent subcutaneous implantation (on both flanks) of human CWR-22 and CWR-22R prostate carcinoma xenografts. Mice were treated with either vehicle or 60 or 80 mg SarCNU per kg body weight for 5 days, with tumor growth being assessed every 3 days. Animals were sacrificed 21 days after the final injection, and tumors subsequently were collected, weighed, and processed for analysis. Immunohistochemical analyses were performed to obtain data on the localization of p53 and p21Cip1/Waf1. Cell counting, terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL) assays, cell cycle analyses, Western blotting, and in vitro kinase assays were performed to determine the effects of SarCNU on growth, apoptosis, cell cycle arrest, cell cycle-regulated protein levels, and Cdc-2 activity, respectively.

RESULTS

SarCNU reduced tumor incidence and inhibited the growth of CWR-22 and CWR-22R xenografts. In addition, treatment with this agent led to increases in p21Cip1/Waf1 levels and p53 phosphorylation at Ser15. In vitro administration of SarCNU to cells with wild-type p53 (LNCaP and primary CWR-22 cells) and cells with mutant p53 (PC-3 cells) resulted in G2/M arrest and the reduction of cellular Cdc-2 activity. Up-regulation of p53 levels, p53 phosphorylation at Ser15, and p21Cip1/Waf1 levels in primary CWR-22 and LNCaP cells, as well as up-regulation of Cdc-2 phosphorylation at Tyr15 in PC-3 cells, was detected.

CONCLUSIONS

SarCNU induced G2/M arrest in prostate carcinoma cells via p53-dependent up-regulation of p21Cip1/Waf1 and p53-independent phosphorylation of Cdc-2 at Tyr15. These findings suggest a potential role for SarCNU in the treatment of prostate malignancies.

In vitro evaluation of dimethane sulfonate analogues with potential alkylating activity and selective renal cell carcinoma cytotoxicity

We identified five structurally related dimethane sulfonates with putative selective cytotoxicity in renal cancer cell lines. These compounds have a hydrophobic moiety linked to a predicted alkylating group. A COMPARE analysis with the National Cancer Institute Anticancer Drug Screen standard agent database found significant correlations between the IC50 of the test compounds and the IC50 of alkylating agents (e.g., r = 0.68, P < 0.00001 for chlorambucil). In this report, we examined whether these compounds had activities similar to those of conventional alkylating agents. In cytotoxicity studies, chlorambucil-resistant Walker rat carcinoma cells were 4- to 11-fold cross-resistant to the test compounds compared with 14-fold resistant to chlorambucil. To determine effects on cell cycle progression, renal cell carcinoma (RCC) line 109 was labeled with bromodeoxyuridine prior to drug treatment. Complete cell cycle arrest occurred in cells treated with an IC90 dose of NSC 268965. p53 protein levels increased as much as 5.7-fold in RCC line 109 and as much as 20.4-fold in breast cancer line MCF-7 following an 18-hour drug exposure. Finally, DNA-protein cross-links were found following a 6-hour pretreatment with all compounds. Thus, the dimethane sulfonate analogues have properties expected of some alkylating agents but, unlike conventional alkylating agents, appear to possess activity against RCC.

SarCNU mediates selection of P140K methylguanine-DNA-methyltransferase transduced human CD34(+) cells in vitro

The therapeutic combination O(6)-benzylguanine (BG) and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) can be used to select for P140K methylguanine-DNA-methyltransferase (P140K MGMT) transduced hematopoietic progenitors both in vitro and in vivo. SarCNU is a new alkylating agent which has advantages over BCNU. We tested the ability of P140K MGMT transduced human CD34(+) cells to resist SarCNU treatment and be selected for in vitro. BG/SarCNU exposure led to an increase in the proportion of transduced cells from 13 to 27%. The IC(90) was increased sixfold by P140K MGMT transduction. These results suggest that SarCNU may be a suitable agent for in vivo selection strategies.

SarCNU, a nitrosourea analog on a day 1, 5, and 9 oral schedule: a phase I and pharmacokinetic study in patients with advanced solid tumors

PURPOSE

2-Chloroethyl-3-sarcosinamide-1-nitrosourea (SarCNU) is a novel chloroethylnitrosourea that demonstrates selective cytotoxicity in athymic mice bearing human glioma. SarCNU demonstrates selective cytotoxicity in vitro against human glioma at least in part because of the selective SarCNU uptake by the extraneuronal monoamine transporter. The purpose of this phase I study was to determine the maximum-tolerated dose (MTD), the toxicity profile, the pharmacokinetics profile, and recommended phase II dose.

PATIENTS AND METHODS

Forty-three eligible patients with advanced solid tumors were enrolled. SarCNU was administered orally on days 1,5, and 9 every 28 days. The dose ranged from 30 to 1,075 mg/m2. Pharmacokinetic evaluation was done on the first cycle (one dose was given intravenously on day 1 or 5 of the first cycle to determine bioavailability).

RESULTS

Delayed myelosuppression (thrombocytopenia and neutropenia occurring 4 to 6 weeks after administration) was the dose-limiting toxicity (DLT). Anemia occurred but was mild. Nonhematologic toxicity was generally mild, but one patient died with pulmonary toxicity that was probably secondary to SarCNU. There were no partial or complete responses, but eight patients had stable disease for 19 to 46 weeks. The oral bioavailability of SarCNU was 80% +/- 37%. The terminal phase half-life was similar after intravenous (58.4 +/- 23.5 minutes) or oral (64.0 +/- 34.8 minutes) administration. The total plasma clearance was 20.4 +/- 8.8 L/h/m2, and the apparent volume of distribution was 29.9 +/- 17.6 L/m2. The area under the plasma concentration-time profile increased proportionally with the dose, and the pharmacokinetics seemed to be independent of the route of administration and the number of doses.

CONCLUSION

SarCNU was well tolerated and the MTD was 1,075 mg/m2. The recommended starting dose for phase II trials is 860 mg/m2 orally on days 1, 5, and 9 every 6 weeks.

Stabilization and preformulation of anticancer drug--SarCNU

The stability of SarCNU (NSC364432), 1-(2-chloroethyl)-3-sarcosinamide-1-nitrosourea in several pharmaceutically acceptable solvents was investigated by high pressure liquid chromatography (HPLC). The influences of light, ionic strength, pH, buffer concentration, and the following excipients: benzyl alcohol, ascorbic acid, sodium bisulfite, and disodium EDTA were studied at room temperature. The stability of the drug was also determined in water, EtOH, PG, Capmul PG, DMSO, and in different combinations of these cosolvents at four different temperatures. The degradation of the drug, which is catalyzed not only by general but also by specific acid and base, follows first order kinetics. Antioxidants, EDTA, and light have no effect on the degradation rate, suggesting oxidation is not a major degradation pathway. The t(90) in pure cosolvent is 25-50 times higher than that in water or semi-aqueous vehicles. Neat EtOH can be used to store the drug in a nonaqueous concentrate that is diluted with aqueous solvent prior to injection.

Antitumor efficacy of SarCNU in a human glioma xenograft model expressing both MGMT and extraneuronal monoamine transporter

Treatment of malignant brain tumors with chloroethylnitrosoureas (CENUs) in addition to surgical resection and radiotherapy remains the foundation of glioma therapy. However, the clinical response to CENUs is at best modest. A novel analogue of nitrosoureas, 2-chloroethyl-3-sarcosinamide-1-nitrosourea (SarCNU), as compared to the standard CENU, 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), has been demonstrated to have increased anticancer effects both in vitro and in vivo. Unfortunately, many human tumors have been known to be resistant to CENUs since they express DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT). In order to assess whether SarCNU has an effect on MGMT positive tumors, we evaluated its antitumor efficacy using an MGMT positive human glioma (SF-767) nude mouse xenograft model. Since SF-767 has high MGMT levels, BCNU treatment (20 mg/kg, Q4D x 3 i.p.) alone did not result in a satisfactory anticancer effect (p > 0.05). As expected, O6-benzylguanine (O6-BG) (100 mg/kg), which was given prior to BCNU treatment, by depleting MGMT activity, significantly enhanced BCNU antitumor efficacy (p < 0.001). Moreover, SarCNU treatment (167 mg/kg, Q4D x 3 i.p.) alone had a better antitumor effect than O6-BG plus BCNU treatment (F = 51.7, p = 0.0004). However, in this xenograft model, O6-BG did not significantly enhance the anticancer efficacy of SarCNU (F = 0.8, p = 0.411). The SF-767 human glioma xenograft is positive for extraneuronal monoamine transporter EMT (EMT) as determined by reverse-transcription polymerase chain reaction (RT-PCR). Our present results suggest that SarCNU is also effective for MGMT positive tumor if they exhibit EMT.

Use of pure t-butanol as a solvent for freeze-drying: a case study

1-(2-Chloroethyl)-3-sarcosinamide-1-nitrosourea, (SarCNU) (NSC-364432) is a new antitumor drug that is of interest to the National Cancer Institute. It is intended for use as an intravenous injection. Although SarCNU is sufficiently soluble in water to obtain the desired dosage, it is highly unstable. Its T(90) in aqueous solution at room temperature is less than 6 h. Neat tertiary butyl alcohol (TBA), a low toxicity, high vapor pressure and low melting solvent, was determined to be an excellent freeze-drying medium. Lyophilization of SarCNU from pure TBA produces a uniform cake composed of needle-shaped crystals. Thermal analysis and gas chromatography indicate that the cake contains less than 0.001% residual solvent. The SarCNU cake can be readily reconstituted with either water or an aqueous solution of 40% propylene glycol and 10% ethanol. The reconstituted solutions are stable for 4 and 13 h, respectively.

Plasma pharmacokinetics and bioavailability of 1-(2-chloroethyl)-3-sarcosinamide-1-nitrosourea after intravenous and oral administration to mice and dogs

PURPOSE

Chloroethylnitrosoureas are among the most widely used chemotherapeutic agents for the treatment of brain tumors. SarCNU (1-(2-chloroethyl)3-sarcosinamide-1-nitrosourea) is an investigational nitrosourea analogue that has shown greater antitumor activity and a more favorable toxicity profile than 1,3-bis(2-chloroethyl)-1-nitrosourea in preclinical studies. The purpose of the present study was to characterize the plasma pharmacokinetics and oral bioavailability of SarCNU in mice and dogs treated by intravenous infusion and gastric intubation.

METHODS

SarCNU was administered to mice by i.v. injection or orally at doses ranging from 10 to 100 mg/kg. Plasma samples were obtained from groups of five animals at each time-point at intervals ranging from 3 min to 2.5 h after dosing. A group of three male beagle dogs were treated with Sar CNU 10 mg/kg given both by i.v. infusion and orally in a crossover design. The concentration of SarCNU in plasma was measured by high-performance liquid chromatography.

RESULTS

During the initial 90 min after i.v. injection to mice, SarCNU was eliminated from plasma in a monoexponential manner with a mean half-life of 9.8 +/- 0.8 min. The total plasma clearance was 47.3 +/- 8.7 ml/min per kg and the apparent volume of distribution was 0.7 +/- 0.1 l/kg. SarCNU exhibited linear pharmacokinetic behavior following both i.v. and oral administration of doses ranging from approximately 10 to 100 mg/kg. Peak plasma levels provided by a dose of 100 mg/kg given by the i.v. and oral routes were 142.4 microg/ml (0.5 min) and 27.8 microg/ml (9.8 min), respectively. The mean oral bioavailability of the drug was 57.3 +/- 12.6% in mice. In comparison, the disposition of SarCNU in dogs after rapid i.v. injection was biexponential, with half-lives of 5.4 +/- 8.4 min and 40.8 +/- 9.0 min for the initial and terminal disposition phases, respectively. Mean values of the total plasma clearance and apparent volume of distribution were 17.8 +/- 1.8 ml/min per kg and 1.1 +/- 0.3 l/kg, respectively. The Cmax was 18.5 +/- 6.5 microg/ml after i.v. injection and 8.5 0.4 microg/ml after oral administration of a 10 mg/kg dose. Oral bioavailability of the drug in dogs (71.7 +/- 21.2%) was greater than that observed in mice.

CONCLUSIONS

SarCNU exhibited linear and consistent pharmacokinetics in mice and dogs with very good oral bioavailability in both species. These findings support the rationale for evaluating SarCNU given by the oral route of administration in phase I clinical trials.

[Expression of extraneuronal monoamine transporter gene and DNA repair gene vis-à-vis with antitumor efficacy of SarCNU in human tumor xenografts]

OBJECTIVE

To clarify if there are any correlations between extraneuronal monoamine transmitters (EMT), DNA repair gene expressions and SarCNU antitumor efficacy.

METHODS

EMT, DNA repair gene O6-methylguanine-DNA methyltransferase (MGMT) and excision repair cross-complementing rodent repair deficiency gene (ERCC1-6) expressions in 9 human xenograft tumor models were determined by RT-PCR. The results were compared with the antitumor effects of SarCNU on these tumor xenografts.

RESULTS

Multiple regression analysis revealed significant correlations of SarCNU antitumor activity with different combinations of gene expression. The most significant correlation was observed with all of the 4 genes expressed.

CONCLUSION

The results suggest that expression of both EMT and DNA repair genes, specifically, MGMT, ERCC2 and ERCC4, are important determinants of SarCNU activity against human tumors. While DNA repair decreases SarCNU's activity by repairing damaged DNA, EMT appears to enhance its antitumor efficacy.

Both extraneuronal monoamine transporter and O(6)-methylguanine-DNA methyltransferase expression influence the antitumor efficacy of 2-chloroethyl-3-sarcosinamide- 1-nitrosourea in human tumor xenografts

We previously have found that 2-chloroethyl-3-sarcosinamide-1-nitrosourea (SarCNU) is a selective cytotoxin that enters cells via the extraneuronal transporter for monoamine transmitters (EMT). Both in vitro and in vivo studies demonstrated that SarCNU was more effective than BCNU against human gliomas. To clarify whether EMT expression correlates with antitumor efficacy of SarCNU, we determined human EMT (EMTh) and O(6)-methylguanine-DNA methyltransferase (MGMT) expression in nine human xenograft models using semiquantitative reverse-transcription polymerase chain reaction. These results were compared with the antitumor effects of SarCNU and the standard chloroethylnitrosourea antitumor agent 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). There was no significant correlation between EMTh expression and antitumor efficacy of SarCNU or BCNU. Also, there was no significant correlation between MGMT expression and SarCNU efficacy. However, a significant correlation was found between MGMT expression and BCNU antitumor efficacy. Interestingly, multiple regression analysis demonstrated a significant correlation between SarCNU efficacy and EMTh plus MGMT expression, whereas there was no correlation between BCNU efficacy and MGMT plus EMTh expression. Thus, the absence of a linear correlation between SarCNU efficacy and EMTh expression appears to be due, at least in part, to the presence of DNA repair, specifically, MGMT, in these xenograft models. These studies suggest that MGMT expression alone correlates with BCNU activity, whereas both EMTh and MGMT expression are important determinants of SarCNU activity against human tumor xenograft models. SarCNU is in clinical trials and these results may have important clinical implications.

Extraneuronal monoamine transporter expression and DNA repair vis-à-vis 2-chloroethyl-3-sarcosinamide-1-nitrosourea cytotoxicity in human tumor cell lines

We previously found that 2-chloroethyl-3-sarcosin-amide-1-nitrosourea (SarCNU), a new chloroethylnitrosourea analogue presently in phase I clinical trials, is a selective cytotoxin that enters cells via the extraneuronal transporter for monoamine transmitters (EMT). In this study, we assessed whether EMT expression correlates with SarCNU cytotoxicity by determining EMT expression in 23 human tumor cell lines with reverse-transcription PCR. Western blot analysis was used to measure protein levels of the DNA repair genes, O6-methylguanine-DNA methyltransferase (MGMT), and excision repair cross-complementing rodent repair deficiency gene 2 (ERCC2). SarCNU cytotoxicity was determined by the sulforhodamine B colorimetric anti-cancer-drug screening assay and correlated with gene expression. Almost all of the cell lines screened were positive for EMT expression. However, seven cell lines (MGR-1, MGR-2, T98-G, SKI-1, SKNSH, 297, and GBM) expressed low levels of EMT. Although there was no linear correlation between SarCNU cytotoxicity and EMT expression, SarCNU cytotoxicity significantly correlated with ERCC2 protein levels, and MGMT-rich (Mer+) cell lines (MGMT protein level >0.1) were more resistant to SarCNU than MGMT-poor (Mer-) cell lines (MGMT protein level <0.1). Moreover, multiple regression analysis indicated that the best correlation with SarCNU cytotoxicity was attainable with EMT plus MGMT and ERCC2 expression. This study suggests that in human tumor cell lines both EMT and DNA repair factors, specifically, MGMT and ERCC2, are important determinants of SarCNU activity. Because EMT is expressed in a wide variety of human tumors, SarCNU should be a more widely effective alternative chemotherapeutic agent.

Enhanced antitumor activity of sarCNU in comparison to BCNU in an extraneuronal monoamine transporter positive human glioma xenograft model

A novel analogue of nitrosoureas, 2-chloroethyl-3-sarcosinamide-1-nitrosourea (SarCNU), has demonstrated increased anticancer effects in vitro and in vivo. Our previous work suggested that SarCNU enters cells via the extraneuronal monoamine transporter (EMT), that contributes to its enhanced cytotoxicity. In the present study, comparative activities of SarCNU and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) were evaluated in an EMT positive human glioma xenograft model. Athymic nude mice implanted subcutaneously or intracranially with human glioma SHG-44, a cell line that has been confirmed EMT positive by using reverse-transcription polymerase chain reaction (RT-PCR) assay, were treated with SarCNU at an optimal dose of 167 mg/kg, or BCNU at 20 mg/kg or 30 mg/kg, q4d x 3 intraperitoneally (i.p.). In 17 animals with subcutaneous tumor grafts treated with SarCNU, 9 animals became tumor free and 8 demonstrated tumor regression. While in the BCNU treated group, there were only 2 out of 10 mice in the 20 mg/kg group and 2 out of 7 in the 30 mg/kg group, which demonstrated some tumor regression. There were 4 drug related deaths in the BCNU (30 mg/kg) group, while there were no drug related deaths in the SarCNU group. In the intracranially implanted mice, the median survival time in the SarCNU group was more than 130 days, while in the BCNU treated group it was only 22 days which was similar to the control group (18 days). This is the first demonstration that SarCNU, in comparison to BCNU, has enhanced anticancer activity in an EMT positive human glioma xenograft model.

Relationship between drug delivery and the intra-arterial infusion rate of SarCNU in C6 rat brain tumor model

The influences of the flow rate on the concentration and distribution of drug in the rat brains and brain tumors after intra-arterial (intra-carotid) administration of [3H]SarCNU (sarcosinamide chloroethyl-1-nitrosourea) were examined. Results obtained at three flow rates via intra-carotid route were compared to those obtained with intravenous administrations. Adult female Wistar rats bearing C6 brain tumor were randomized into four-groups. Groups 1 (G.1) to 3 (G.3) received intra-arterial injection and Group 4 (G.4) received intravenous administration of [3H]SarCNU. G.1 (slow infusion rate) was administered 1 ml of [3H]SarCNU solution over 60 min (0.017 ml/min), Group 2 (G.2; medium infusion rate): 0.2 ml over 5 min (0.04 ml/min), G.3 (fast infusion rate): 1 ml over 5 min (0.2 ml/min), and G.4 (intravenous infusion): 1 ml intravenously over 5 min. Quantitative autoradiographic method was used to measure the concentration and the distribution of [3H]SarCNU in the brain and the brain tumors. The tissue uptake constant of SarCNU in both viable (tumor tissue excluding necrosis) and peak regions (the area of tumor containing top 20% of the tracer concentration) of the intra-arterial injection groups were significantly higher (p < 0.0001) than those in the intravenous group. The mean concentrations of the viable tumor in the intra-arterial groups were 2.92 (G.1), 16.06 (G.2), and 20.8 (G.3) times higher than those of intravenous group. Between the intra-arterial groups, the mean concentration in the viable tumors of G.1 (slow flow rate) was significantly (p < 0.0001) lower than in G.2 and G.3. However, there was no significant difference between G.2 and G.3. In three intra-arterial groups the mean concentration delivery ratios of the brain tumors were high and ranged from 3.07 (G.3) to 3.87 (G.2), but there was no significant difference between them. Only G.4, intravenous group, showed significantly (p < 0.005) lower concentration delivery ratio, 1.26. These results suggest that higher infusion rate in the intra-arterial chemotherapy could have an effect not only on the streaming phenomenon which results in the brain toxicities, but also on the increase in the concentration and the sufficient distribution of a drug in tumors. By finding chemotherapeutic agents to which tumors show high sensitivity and using intra-arterial administration of these agents at more effective flow rate, better clinical results could be achieved in the treatment of patients with malignant brain tumors.

Interaction between lipid bilayers and a new class of antineoplastic agents derived from arylchloroethylurea: a 2H solid-state NMR study

We have investigated the interaction between a new class of antineoplastic agents derived from arylchloroethylurea (CEU) and model membrane of dimyristoylphosphatidylcholine by deuterium nuclear magnetic resonance spectroscopy. The results indicate that the drug incorporates in the bilayer and causes an increase of the lipid acyl chain order, this effect being greater close to the interfacial region of the lipid bilayer. The increase in ordering is dependent on the nature (degree of ramification, length of the alkyl chain, and presence of a sulfur atom) as well as on the position of the R substituent and is correlated with the cytotoxicity of the drugs. More specifically, the more cytotoxic drugs, such as 4-sec-butyl CEU, are those having a bulky ramified substituent and those for which the ordering effect on the lipid bilayer is the smallest. On the other hand, the ordering effect is greater and seen all along the lipid acyl chains for the long-chain CEUs, such as n-hexadecyl CEU, which have been shown to have very weak cytotoxic activity. Finally, the results obtained as a function of the drug concentration indicate that the ordering effect is seen for lipid to drug molar ratios as low as 20:1.

Genotoxic effect of 4-aroyl-1-(2-chloroethyl)-1nitrosohydrazinecarboxamides on Saccharomyces cerevisiae cells

The study of some 4-aroyl-1-(2-chloroethyl)-1-nitrosohydrazinecarboxamides with a Saccharomyces cerevisiae mutagenicity test of increased sensitivity defined two of them, 4-(4-bromobenzoyl)-1-(2-chloroethyl)-1-nitrosohydrazinecarboxam ide and 4-(4-fluorophenyl)-1-(2-chloroethyl)-1-nitrosohydrazine carboxamide as typical cytostatic agents. At concentrations of 2-5 microg/ml the substances kill up to 60%-70% of cells without having any detectable recombinogenic and mutagenic effects. At the same concentrations, lomustine, well known as a cytostatic reference, demonstrated recombinogenic and mutagenic activity on yeast cells. The advantage of the newly synthesized substances is that, in a certain concentration range, their biological activity is mainly cytotoxic without induction of recombinogenic and mutagenic events in surviving cells.

Excision repair cross-complementing rodent repair deficiency gene 2 expression and chloroethylnitrosourea resistance in human glioma cell lines

OBJECTIVE

Nitrosoureas are the standard chemotherapeutic agents for malignant brain tumors. However, their anticancer effects are limited because many tumors are resistant to these agents. Nucleotide excision repair can repair bulky deoxyribonucleic acid adducts, including deoxyribonucleic acid damage induced by ultraviolet light and some chemotherapeutic agents, and may be implicated in nitrosoureas resistance. In this study, we compared excision repair cross-complementing rodent repair deficiency Gene 2 (ERCC2), an important component of the nucleotide excision repair system, with 1 ,3-bis-(2-chloroethyl)-1-nitrosourea or (2-chloroethyl)-3-sarcosinamide-1-nitrosourea resistance in human glioma cell lines.

METHODS

ERCC2 expression was evaluated by using established quantitative reverse-transcription polymerase chain reaction. 1,3-Bis-(2-chloroethyl)-1-nitrosourea and (2-chloroethyl)-3-sarcosinamide-1-nitrosourea cytotoxicity were determined by a modification of the sulforhodamine B colorimetric anticancer drug screening assay.

RESULTS

A significant correlation between ERCC2 expression and 1 ,3-bis-(2-chloroethyl)-1-nitrosourea or (2-chloroethyl)-3-sarcosinamide-1-nitrosourea cytotoxicity was determined (r=0.737, P=0.0226 and r=0.789, P=0.0113, respectively).

CONCLUSION

Our results suggest that nucleotide excision repair, specifically ERCC2, may play an important role in nitrosoureas drug resistance in human gliomas.

2-Chloroethyl-3-sarcosinamide-1-nitrosourea, a novel chloroethylnitrosourea analogue with enhanced antitumor activity against human glioma xenografts

Nitrosoureas are among the most widely used agents used in the treatment of malignant gliomas. Here, the activity of 2-chloroethyl-3-sarcosinamide-1-nitrosourea (SarCNU) was compared with that of 1,3-bis-(2-chloroethyl)-1-nitrosourea (BCNU), in vivo against s.c. implanted SF-295 and U-251 central nervous system (CNS) tumor xenografts. When given i.v., q4d for 3 doses, to athymic mice bearing s.c. SF-295 tumors, SarCNU, at an optimum of 167 mg/kg/dose, produced 9 tumor-free animals of 10 total animals, 1 regression, and no evidence of overt toxicity (> or =20% body weight loss). With a similar dosing schedule, BCNU produced no tumor-free animals, six regressions, and one drug-related death at its optimum of 30 mg/kg/dose. Furthermore, SarCNU retained high antitumor activity at two lower dose levels, 66 and 45% of the optimal dose, whereas BCNU demonstrated a progressive loss of antitumor activity at lower doses. Following p.o. administration, SarCNU similarly demonstrated antitumor activity that was superior to that of BCNU. In the U-251 CNS tumor model, SarCNU yielded six of six tumor-free animals at 80 mg/kg/dose with i.p. administration q.d. for 5 days, starting on day 14, whereas BCNU, at 9 mg/kg/dose, yielded three of six tumor-free mice and one drug-related death. Again, SarCNU resulted in tumor-free animals at 66 and 45% of its optimal dose and was relatively nontoxic, in contrast to BCNU. Results of testing to date indicate that SarCNU is clearly more effective than BCNU against the human CNS tumors SF-295 and U-251 in vivo. These results encourage the initiation of clinical trials for SarCNU, in an effort to improve therapeutic approaches to glioma, but clinical trials must determine whether superiority of SarCNU in preclinical models can be extrapolated to patients.

Characterization of the catecholamine extraneuronal uptake2 carrier in human glioma cell lines SK-MG-1 and SKI-1 in relation to (2-chloroethyl)-3-sarcosinamide-1-nitrosourea (SarCNU) selective cytotoxicity

Transport of (2-chloroethyl)-3-sarcosinamide-1-nitrosourea (SarCNU) and (-)-norepinephrine was investigated in SarCNU-sensitive SK-MG-1 and -resistant SKI-1 human glioma cell lines. [3H]SarCNU influx was inhibited by SarCNU, sarcosinamide, and (+/-)-epinephrine in SK-MG-1 cells with competitive inhibition observed by (+/-)-epinephrine (Ki = 140 +/- 12 microM) and (+/-)-norepinephrine (Ki = 255 +/- 41 microM). No effect on influx was detected in SKI-1 cells. [3H](-)-Norepinephrine influx was linear to 15 sec in both cell lines and temperature dependent only in SK-MG-1 cells. Influx of [3H](-)-norepinephrine was found to be saturable in SK-MG-1 (K(m) = 148 +/- 28 microM, Vmax = 1.23 +/- 0.18 pmol/microL intracellular water/sec) but not in SKI-1 cells. In SK-MG-1 cells, [3H](-)-norepinephrine influx was found to be inhibited competitively by (-)-epinephrine (Ki = 111 +/- 7 microM) and SarCNU (Ki = 1.48 +/- 0.22 mM). Ouabain and KCl were able to inhibit the [3H](-)-norepinephrine influx in SK-MG-1 cells, consistent with influx being driven by membrane potential. Several catecholamine uptake2 inhibitors were able to reduce significantly the influx of [3H](-)-norepinephrine and [3H]SarCNU with no inhibition by a catecholamine uptake1 inhibitor. These findings suggest that increased sensitivity of SK-MG-1 to SarCNU is secondary to enhanced accumulation of SarCNU mediated via the catecholamine extraneuronal uptake2 transporter, which is not detectable in SKI-1 cells. The introduction of SarCNU into clinical trials will confirm if increased uptake via the catecholamine extraneuronal uptake2 transporter will result in increased antitumor activity.

Correlation of chloroethylnitrosourea resistance with ERCC-2 expression in human tumor cell lines as determined by quantitative competitive polymerase chain reaction

We have developed a method to quantitate ERCC-2 gene expression in tumor cell lines. A mutant ERCC-2 DNA fragment (1-bp mutation) is used as a competitive DNA template in a coamplification PCR reaction with cDNA obtained by reverse transcribing DNase-free total RNA from six human tumor cell lines. The PCR products are separated on agarose gel by virtue of their differential banding pattern upon restriction enzyme digestion. Densitometric readings of the PCR products from a negative film of the gel are used to establish a linear regression curve, which in turn is used to quantitate ERCC-2 levels. Beta-actin expression is similarly quantitated. Normalized ERCC-2 gene expression (either to beta-actin or to total RNA) correlates with cytotoxicity of 1,3-bis-(2-chloroethyl)-1-nitrosourea or (2-chloroethyl)-3-sarcosinamide-1-nitrosourea, suggesting that ERCC-2 may play an important role in drug resistance in these cell lines. This method is reliable and can be used to quantitate gene expression in clinical tumor specimens.

Specific high-performance liquid chromatographic assay with ultraviolet detection for the determination of 1-(2-chloroethyl)-3-sarcosinamide-1-nitrosourea in plasma

A facile, sensitive and highly specific HPLC method for assaying 1-(2-chloroethyl)-3-sarcosinamide-1-nitrosourea (SarCNU) in plasma has been developed. The drug was efficiently isolated from plasma by extraction with tert.-butyl methyl ether. A structurally related compound with similar physicochemical properties served as the internal standard (I.S.). Following evaporation of the organic solvent, the extract was reconstituted with 0.05 M ammonium acetate buffer, pH 5.0, and loaded onto a 4 micron Nova-Pak C18 column (15 cm x 3.9 mm), which was preceded by a 7 micron Brownlee RP-18 precolumn (1.5 cm x 3.2 mm). Chromatography was performed at ambient temperature using a mobile phase of methanol-0.1 M ammonium formate buffer, pH 3.7 (25:75, v/v). UV absorbance of the effluent was monitored at 240 nm. A flow-rate of 1.0 ml/ min was used for analyzing mouse and dog plasma extracts. Under these conditions, the drug eluted at 4.0 min and was followed by the I.S. at 6.1 min. An automatic switching valve was employed to allow the precolumn to be flushed 1.5 min into the run, without interrupting the flow of the mobile phase to the analytical column, thereby preventing the apparent build-up of extractable, strongly retained, UV-absorbing components present in mouse and dog plasma. Operating in this manner, more than 100 samples could be analyzed during a day using a refrigerated autosampler for overnight injection. The method was readily adapted to the determination of SarCNU in human plasma by simply decreasing the eluent flow-rate to 0.6 ml/min, whereby SarCNU and the I.S. eluted at approximately 5.8 and 9.1 min, respectively. Furthermore, the switching valve was not necessary for the analysis of human plasma samples. With a 50-microliter sample volume, the lowest concentration of SarCNU included in the plasma standard curves, 0.10 micrograms/ml, was quantified with a 7.8% R.S.D. (n = 27) over a 2 month period. Plasma standards, with concentrations of 0.26 to 5.1 micrograms/ml, exhibited R.S.D. values ranging from 1.3 to 4.7%. Thermospray-ionization MS detection was used to definitively establish the specificity of the method. The sensitivity of the assay was shown by application to be more than adequate for characterizing the plasma pharmacokinetics of SarCNU in mice.

Altered cytotoxicity of (2-chloroethyl)-3-sarcosinamide-1-nitrosourea in human glioma cell lines SK-MG-1 and SKI-1 correlates with differential transport kinetics

Resistance to (2-chloroethyl)-3-sarcosinamide-1-nitrosourea (SarCNU), an experimental anticancer compound, was investigated in the chloroethylnitrosourea-sensitive Mer- SK-MG-1 and -resistant Mer- SKI-1 human glioma cell lines. The transport of [3H]SarCNU was examined in suspension. The uptake of [3H]SarCNU was found to be temperature dependent in SK-MG-1 and SKI-1, but less so in SKI-1. At 37 degrees C, uptake of 50 microM [3H]SarCNU was linear up to 4 s in both cell lines, with uptake being significantly faster in SK-MG-1 than in SKI-1 under initial rate conditions. There was no significant difference in the rate of influx at 22 degrees C between both cell lines. Equilibrium was approached after 1 min at 22 and 37 degrees C. At 37 degrees C, steady state accumulation of SarCNU at 30 min was reduced significantly (35%) in SKI-1 cells compared with SK-MG-1 cells, although accumulation was similar at 22 degrees C. In SK-MG-1 cells, uptake of [3H]SarCNU at 37 degrees C was found to be saturable, but uptake in SKI-1 cells was not saturable over a 1000-fold range of concentrations. Analysis of efflux in cells preloaded with 50 microM [3H]SarCNU revealed that the rate of efflux was equivalent in both cell lines but that the efflux rate was more rapid at 37 degrees C compared with 22 degrees C. Metabolism of SarCNU at 37 degrees C was not different in either cell line after a 60-min incubation, as determined by thin layer chromatography. SKI-1 cells, compared with SK-MG-1 cells, were 3-fold more resistant to SarCNU at 37 degrees C but only 2-fold more resistant at 22 degrees C, a temperature at which SarCNU accumulation was similar in both cell lines. The 2-fold resistance at 22 degrees C was similar to that of 1,3-bis(2-chloroethyl)-1-nitrosourea at 37 and 22 degrees C. These findings indicate that increased cytotoxicity in SK-MG-1 cells is associated with a greater accumulation of SarCNU via an epinephrine-sensitive carrier that is not detectable in SKI-1 cells. However, part of the chloroethylnitrosourea resistance in SKI-1 cells is not secondary to decreased accumulation.

Transport of (2-chloroethyl)-3-sarcosinamide-1-nitrosourea in the human glioma cell line SK-MG-1 is mediated by an epinephrine-sensitive carrier system

The transport of (2-chloroethyl)-3-sarcosinamide-1-nitrosourea (SarCNU), an experimental anticancer compound, was investigated in the human glioma cell line SK-MG-1. The transport of [3H]SarCNU was examined in suspension. The uptake of [3H] SarCNU was found to be temperature dependent, with influx being linear to 4 sec at 37 degrees. Equilibrium was reached after 1 min at 22 degrees and 37 degrees, with accumulation slightly above unity. SarCNU was not significantly metabolized in the cells after a 60-min incubation at 37 degrees, as shown by thin layer chromatography. At 37 degrees, uptake of [3H]SarCNU was found to be saturable, sodium independent, and energy independent. Previous work demonstrated that SarCNU was able to inhibit the uptake of sarcosinamide, which is transported by the catecholamine uptake 2 system. This catecholamine system mediates the physiological transport of epinephrine. Epinephrine was able to significantly inhibit the uptake of [3H]SarCNU, at a concentration of 50 microM, by 40%. Additionally, several amino acids were unable to inhibit the uptake of SarCNU. The initial rate of SarCNU influx is mediated by both facilitated and nonfacilitated diffusion. The nonfacilitated diffusion rate could be estimated from the linear concentration dependence of the residual influx rate for SarCNU, which was not inhibited by the presence of excess co-permeant (epinephrine). Dixon plot analysis, corrected for nonfacilitated diffusion of SarCNU, revealed that epinephrine inhibited the uptake of SarCNU competitively, with a Ki of 163 +/- 15 microM, a value similar to the Km value for epinephrine influx in SK-MG-1 cells. Additionally, after appropriate corrections for nonfacilitated diffusion in the influx rates observed for SarCNU, it was revealed that SarCNU influx obeyed Michaelis-Menten kinetics over a 200-fold range of concentrations, with a Km of 2.39 +/- 0.37 mM and a Vmax of 236 +/- 53 pmol/microliters of intracellular water/sec. Metabolic poisons (2,4-dinitrophenol, iodoacetate, NaCN, NaF, or ouabain) were unable to inhibit the influx of SarCNU, suggesting that the carrier-mediated uptake of SarCNU is energy independent and mediated by facilitated diffusion. These findings indicate that SarCNU uptake in SK-MG-1 cells is mediated both by nonfacilitated diffusion and by facilitated diffusion via the catecholamine uptake 2 carrier system. SarCNU is the first chloroethylnitrosourea that has been demonstrated to have carrier-mediated uptake. Moreover, this carrier-mediated uptake may play a role in the increased cytotoxicity of SarCNU against gliomas, compared with that of 1,3-bis(2,-chloroethyl)-1-nitrosourea, which enters cells primarily by passive diffusion.

Mouse bronchiolar cell carcinogenesis. Histologic characterization and expression of Clara cell antigen in lesions induced by N-nitrosobis-(2-chloroethyl) ureas

Female Swiss mice (Cr:NIH(S)) developed bronchiolar cell hyperplasia, dysplasia, metaplasia, and various morphologic types of bronchiolar cell tumors after topical (skin) application of N-nitroso-methyl-bis-chloroethylurea (NMBCU) or N-nitroso-tris-chloroethylurea (NTCU). These compounds are the first found to induce systemically bronchiolar cell tumors in mice in high incidence. Twice a week, with a 3-day interval, a 25-microliter drop of 0.04 mol/l (molar) NMBCU or NTCU in acetone was applied to the shaved interscapular integument for a maximum of 35 to 40 weeks. The earliest lung neoplasms were seen in mice that died after 23 weeks of treatment and affected 11 of 19 with NMBCU and 14 of 19 with NTCU treatment. Tumor growth pattern was nodular or the neoplastic tissue was frequently disseminated throughout the parenchyma, starting from multicentric peribronchiolar foci. The most common tumor types were squamous cell carcinomas and adenosquamous carcinomas, followed by adenocarcinomas with or without secretory cells, and a single ciliated-cell tumor. Histochemical and immunohistochemical studies were carried out on paraffin-embedded lungs using the avidin-biotin immunoperoxidase complex procedure and antisera against keratin, Clara cell antigen, surfactant apoprotein, neuron-specific enolase, bombesin, and chromogranin A. In several mice from both groups, hyperplasias and tumors were composed of cells expressing Clara cell antigen. No tumor cells were found expressing alveolar type II or neuroendocrine cell markers. It appeared that bronchiolar cells, in particular Clara cells, had migrated from terminal bronchioles or invaded bronchiolar walls to extend into the alveolar parenchyma. Squamous cell metaplasia with keratin expression was seen within airways or associated with glandular tumors, especially at the periphery. A unique cell type, with large eosinophilic globules and associated eosinophilic crystals, was seen lining airways or forming hyperplastic and neoplastic lesions. N-nitroso-methyl-bis-chloroethylurea- and NTCU-induced mouse bronchiolar cell alterations could be an interesting new model to study mechanisms of bronchiolar cell differentiation and tumor formation.

Pharmacokinetics of 11C-labelled BCNU and SarCNU in gliomas studied by PET

This paper describes the study of the pharmacodynamics of two 11C-labelled nitrosoureas, 1,3-bis-(2-chloroethyl) nitrosourea (BNCU) and sarcosinamide chloroethylnitrosourea (SarCNU), both labelled in the carbonyl position. Distribution of the radioactivity as measured by positron emission tomography was compared to the distribution of radioactivity observed after injection of 68Ga-EDTA, this being used as an indicator of the blood-brain barrier integrity around the brain tumor. Data suggest that the new nitrosourea, SarCNU, most likely enters brain tissue by different mechanism(s) than BCNU, which enters by diffusion. Data also indicate that use of SarCNU may result in a better tumor to brain ratio than BCNU.

Statin expression in the untreated and SarCNU-exposed human glioma cell line, SK-MG-1

Cytokinetic analyses of gliomas and other neoplasms rely exclusively on the use of proliferation-dependent markers such as [3H]-thymidine and BuDR incorporation and the detection of growth-dependent proteins such as proliferating cell nuclear antigen (PCNA) and Ki-67. In normal tissues, the monoclonal antibody S-44 recognizes statin, a nuclear protein expressed only in nonproliferating cells. In the present study, indirect immunofluorescence microscopy using S-44 identified nuclear statin in 5.9% of a population of untreated human SK-MG-1 glioma cells in vitro. Incremental doses of the alkylating agent sarcosinamide chloroethylnitrosourea (SarCNU) induced a linear increase in the fraction of statin-positive SK-MG-1 cells. Labeling of nuclear statin with the monoclonal antibody S-44 may be a potentially useful marker of the cytotoxic effects of anticancer drugs in gliomas and other neoplastic tissues.

Transport of amino acid amide sarcosinamide and sarcosinamide chloroethylnitrosourea in human glioma SK-MG-1 cells

The transport of the amino acid amide N-[3H]sarcosinamide (methyl glycinamide) was investigated in human glioma SK-MG-1 cells. Sarcosinamide uptake was found to be temperature dependent, sodium independent, and linear up to 1 min at 22 degrees C. Equilibrium was reached after 10 min at 22 degrees C with accumulation slightly above unity. Sarcosinamide was not metabolized in the cells as shown by thin layer chromatography. The uptake of sarcosinamide was significantly decreased when the extracellular pH was lowered from 7.5 to 6.0 and significantly enhanced at pH values above 7.5. The latter effect may be due mainly to increased cell permeability at high pH. The uptake of the labeled sarcosinamide was trans-stimulated by excess cold sarcosinamide. Sarcosinamide uptake over a 200-fold range of concentrations followed Michaelis-Menten kinetics with a Km of 0.284 +/- 0.041 mM and a Vmax of 0.154 +/- 0.024 nmol/10(6) cells/min. The uptake of sarcosinamide was significantly reduced by iodoacetate but not by the metabolic poisons NaF, ouabain, or dinitrophenyl, suggesting that the uptake is not dependent on energy, rather it proceeds by facilitated diffusion. Several naturally occurring substrates were unable to inhibit the uptake of sarcosinamide. Leucine significantly reduced the uptake of sarcosinamide, while sarcosinamide was a weak inhibitor of leucine transport. 2-Aminobicyclo[2,2,1]heptane-2-carboxylic acid a specific substrate for the sodium-independent, 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid-sensitive amino acid system L failed to inhibit the uptake of sarcosinamide. Epinephrine reduced the uptake of sarcosinamide and sarcosinamide was equally potent as an inhibitor of epinephrine transport. Dixon plot analysis demonstrated that epinephrine (Km = 0.270 mM) inhibits the uptake of sarcosinamide competitively (Ki = 0.260 mM). These results indicate that sarcosinamide is a substrate for the catecholamine transporter. The alkylating agent, sarcosinamide chloroethylnitrosourea, was tested for its ability to inhibit the uptake of sarcosinamide. The results of Dixon plot analysis were consistent with competitive inhibition of sarcosinamide uptake and the inhibition constant Ki for SarCNU was found to be 3.26 +/- 0.57 mM. The steady-state intracellular concentration of SarCNU was found to be significantly higher (cell:medium ratio of 1.03 +/- 0.01) than that of BCNU cell:medium ratio of 0.52 +/- 0.12). These findings indicate that SarCNU and sarcosinamide share the same carrier for uptake in SK-MG-1 cells. This transport mechanism may be responsible for the increased accumulation of SarCNU as compared to BCNU, a nitrosourea which enters cells by passive diffusion.

The cytotoxicity of a 2-chloroethylnitrosourea analog of sarcosinamide in the SK-MG-1 human glioma cell line as a possible indicator for transport

The cytotoxicities of a new sarcosinamide analog of chloroethylnitrosourea (SarCNU) and of BCNU were examined in the glioma cell line SK-MG-1 in the presence or absence of excess concentrations of amino acids and sarcosinamide. The cytotoxicity of SarCNU, but not of BCNU, was significantly reduced in the presence of excess sarcosinamide. The stability of SarCNU was not significantly altered by increasing concentrations of sarcosinamide. In order to investigate the possibility that sarcosinamide inhibits the uptake of SarCNU the transport of tritiated sarcosinamide was examined in SK-MG-1 cells. The uptake of 3H-sarcosinamide was inhibited by excess, unlabelled sarcosinamide and SarCNU but not by BCNU, glycine or sarcosine. These results suggest the existence of a carrier-mediated transport for sarcosinamide which can accomodate SarCNU in SK-MG-1 cells.

Synthesis of "no-carrier-added" carbon-11 SarCNU: the sarcosinamide analog of the chemotherapeutic agent BCNU

Carbon-11-labeled SarCNU [N-(2-chloroethyl)-N-nitroso-N'-(carboxamidomethylene)-N'-(methyl) - [11C]-urea], a potential chemotherapeutic agent, has been prepared by the nitrosation of the corresponding urea, N-(2-chloroethyl)-N'-(carboxamidomethylene)-N'-(methyl) [11C]urea (SarCU). SarCU was prepared by reacting sarcosinamide with [11C]-2-chloroethylisocyanate, which was itself prepared by reacting [11C]-phosgene with 2-chloroethylamine hydrochloride suspended in dioxane. The synthesis yielded [11C]SarCNU with an average radiochemical purity of 95% in an average overall radiochemical yield of 18% relative to the activity measured at the end of [11C]phosgene introduction.

The cytotoxicity of sarcosinamide chloroethylnitrosourea (SarCNU) and BCNU in primary gliomas and glioma cell lines: analysis of data in reference to theoretical peak plasma concentrations in man

The cytotoxicity of a new compound, sarcosinamide chloroethylnitrosourea (SarCNU), was compared with that of the clinically available bis-chloroethylnitrosourea (BCNU) in 13 primary human gliomas and in 3 human glioma cell lines using the Human Tumor Cloning Assay (HTCA). At concentrations less than or equal to 16 micrograms/ml, SarCNU reduced the growth to less than or equal to 30% of control in 11 of 13 primary gliomas. At similar concentrations, BCNU produced a comparable cytotoxic effect in 6 out of 13 specimens. At concentrations less than or equal to 16 micrograms/ml, BCNU reduced colony growth to less than or equal to 30% of control in all three glioma cell lines and SarCNU produced the same effect in only one glioma cell line. A recently described statistical model, which employs the LD50 dose of new agents in mice, was used to estimate the achievable peak plasma concentration (PPC) of SarCNU. The calculated PPC for SarCNU was found to be 14.8 micrograms/ml compared with 2 micrograms#ml for BCNU. A reevaluation of the cytotoxic activities of SarCNU and BCNU at concentrations approximating their respective PPCs revealed that SarCNU reduced the growth to less than or equal to 30% of control in one cell line at a concentration below its PPC. In contrast, BCNU exhibited similar toxicity in each cell line only at concentrations exceeding its PPC of 2 micrograms/ml. In the case of the primary gliomas, SarCNU was active (less than or equal to 30% of control) in ten tumors at concentrations less than or equal to 14.8 micrograms/ml, whereas BCNU was active in only one glioma at a concentration less than or equal to 2 micrograms/ml. The results suggest that SarCNU should be more active than BCNU against human gliomas, provided that the statistical model used has correctly estimated the PPC of SarCNU.

Utilization of the HTSCA and CFU-C assay to identify two new 2-chloroethylnitrosourea congeners of amino acid amides with increased in vitro activity against human glioma compared with BCNU

AspCNU and SarCNU are two amino acid amide congeners (L-asparaginamide and sarcosinamide congeners) of chloroethylnitrosoureas. The in vitro myelotoxicity of these agents compared with BCNU at 1-8 micrograms/ml was determined in bone marrow cells from normal volunteers in the CFU-C assay. AspCNU and SarCNU were significantly (P less than 0.05) less myelotoxic than BCNU at equivalent microgram concentrations. SarCNU or AspCNU at 3 micrograms/ml demonstrate equivalent in vitro myelotoxicity to BCNU 1 microgram/ml. We used the human tumor stem cell assay (HTSCA) to investigate in vitro antitumor activity. We obtained four specimens of malignant glioma and one specimen of meningioma from patients not previously treated with chemotherapy. AspCNU and SarCNU were significantly (P less than 0.05) more active than BCNU at 1-3 micrograms/ml concentrations in the HTSCA in all four malignant glioma specimens. In the one meningioma specimen, BCNU was significantly (P less than 0.05) more active than either AspCNU or SarCNU at all concentrations studied. These results suggest that AspCNU or SarCNU at doses that should produce less myelotoxicity than BCNU may be more active than BCNU against gliomas.

Chemotherapeutic activity of new 2-chloroethylnitrosoureas in rat L5222 leukemia: comparison of bifunctional and water-soluble derivatives with 1,3-bis(2-chloroethyl)-1-nitrosourea

The chemotherapeutic activity of eight nitrosourea derivatives was compared with that of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) in transplantable rat leukemia L5222 cells. Bifunctional 1,1'-polymethylenebis-3-(2-chloroethyl)-3-nitrosoureas effected cure rates between 30 and 75% in single equitoxic doses in the therapy of advanced ip implanted L5222 [staging of L5222 leukemia development (hr before median day of death in controls): early = greater than 120; advanced = 120--61; late = 60--25; and preterminal = 24--0]. Of three water-soluble monofunctional alkylating 1-(omega-hydroxyalkyl)-3-nitrosoureas, 1-(2-hydroxyethyl)-3-(2-chloroethyl)-3-nitrosourea yielded more cures (90%) than did BCNU (cure rate, 70%) and was also superior to the other substances. Against preterminal ip implanted and late intracerebrally implanted L5222, the hydroxyethyl compound was significantly superior to BCNU.

Mechanism of uptake of nitrosoureas by L5178Y lymphoblasts in vitro

The mechanism of uptake of nitrosoureas by L5178Y cells in vitro was investigated. A time course of the uptake of radioactivity on incubation of L5178Y lymphoblast with [14C]-1,3-bis(2-chloroethyl)-1-nitrosourea was linear for 30 min and then entered a plateau phase; it was markedly temperature dependent. A similar time course for cells incubated with [14C]ethylene-labeled 1-(2-chlorethyl)-3-cyclohexyl-1-nitrosourea reached equilibrium rapidly, was temperature independent, and resulted in a relatively low level of uptake of radioactivity. However, cells treated with 3-[cyclohexyl-14C]-1-(2-chlorethyl)-1-nitrosourea had a time course that was linear for 30 min, resulted in much higher levels of uptake of radioactivity, and was strongly temperature dependent. These findings, at least for 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea, suggest that some drug decomposition precedes uptake. The percentage of radioactivity found in the cell sap fraction was at least 85% of total cell activity when cells were incubated with any of the three 14C-labeled nitrosoureas. Furthermore, thin-layer chromatography of the cell sap fraction revealed the presence of free intact drug. These findings indicate that intracellular uptake of intact nitrosoureas occurred. A time course of uptake of intact 1,3-bis(2-chloroethyl)-1-nitrosourea reached equilibrium rapidly with cell/medium distribution ratios of 0.2 to 0.6 and was temperature independent. The addition of excess unlabeled 1,3-bis(2-chlorethyl)-1-nitrosourea or 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea had no effect on uptake of [14C]-1,3-bis(2-chloroethyl)-1-nitrosourea, These findings suggest that uptake of intact 1,3-bis(2-chloroethyl)-1-nitrosourea was by passive diffusion. A time course of the uptake of intact 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea with either [14C]ethylene- or ring-labeled drug rapidly reached equilibrium, was temperature independent, and attained a cell/medium ratio greater than unity. Uptake of 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea was sodium independent and was unaffected by the metabolic inhibitors (sodium fluoride, sodium cyanide, or 2,4-dinitrophenol) or by urea, a potential physiological competitor. Furthermore, addition of unlabeled 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea or 1,3-bis(2-chlorethyl)-1-nitrosourea had no effect on uptake of labeled 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea. These findings suggest that uptake of 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea also occurs by passive diffusion.

Genetic effects of some new bifunctional and water-soluble analogs of the anti-cancer agent 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) in Saccharomyces cerevisiae

A series of 1,1'-polymethylenebis-3-(2-chloroethyl)-3-nitrosoureas, 1-(omega-hydroxyalkyl)-3-(2-chloroethyl)-3-nitrosoureas, 1,1'(4-methyl-m-phenylenebis)-3-(2-chloroethyl)-3-nitrosourea, 2-[3-(2-chloroethyl)]-3-nitrosoureido-2-deoxy-D-glycopyranose (chlorozotocin and 1-(2-methanesulfonyloxyethyl)-3-(2-chloroethyl)-3-nitrosurea were examined for their genetic activities. BCNU was simultaneously tested as an established, clinically used reference compound. A diploid strain of Saccharomyces cerevisiae, heteroallelic at the gene loci ade2 and trp5, was used as a test system for the induction of mitotic gene conversion (intragenic recombination). All compounds showed strong genetic effects. In the series of aliphatic bifunctional nitrosoureas, 1,1'-ethylenebis-3-(2-chloroethyl)-3-nitrosourea (1) was the most active compound. The water-soluble derivatives, including chlorozotocin, displayed all genetic effects of the same order of magnitude. There was no correlation between genetic activity and chemotherapeutic potential of the test compounds.

Some new congeners of the anticancer agent 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). Synthesis of bifunctional analogs and water soluble derivatives and preliminary evaluation of their chemotherapeutic potential

The synthesis of new analogs of the anticancer agent BCNU is described. It involves the preparation of N-(2-chloroethyl)-N-nitrosocarbamoylazide and its reaction with aliphatic diamines and aminoalcohols to yield 1,1'-polymethylenebis 3-(2-chloroethyl)-3-nitrosoureas and 1-(omega-hydroxyalkyl)-3-(2-chloroethyl-3-nitrosoureas. Screening for chemotherapeutic activities of the newly synthesized nitrosoureas against rat leukemia L 5222 and s.c. Walker carcinosarcoma 256 revealed remarkable differences between individual compounds. The water soluble 1-(2-hydroxyethyl)-3-(2-chloroethyl)-3-nitrousourea was the most active compound of this series, effecting 90% cures in i.p. inoculated L5222 leukemia.