Carcinogenicity of 2',3'-dideoxycytidine in mice

2',3'-dideoxycytidine (ddC) is a synthetic pyrimidine nucleoside analogue approved for treatment of HIV-positive patients. Previous studies indicated that ddC has the potential to cause thymic lymphoma in C57BL/6 x C3H F1 (hereafter called B6C3F1) mice. In this study, we evaluated the carcinogenic potential of ddC in two different mouse models. B6C3F1 hybrid mice carry ecotropic endogenous proviral sequences that may be activated to cause lymphoma, whereas NIH Swiss mice lack proviral sequences that can be expressed. The mice were treated with ddC by gavage at 500 and 1000 mg/kg/day for up to 6 months (human dose, 2.25 mg/day) and evaluated for toxicity, plasma levels of ddC, and pathological changes. Lymphocyte cell markers from the thymic lymphomas were assessed by immunophenotyping. Expression of p53 protein was evaluated using immunohistochemical staining. Treatment-related thymic lymphomas were present in both mouse models with a higher incidence in NIH Swiss than in B6C3F1 mice. The lymphomas were more prevalent in females than in males of both mouse models. Most mice with thymic lymphoma died during the course of the study. In addition to the thymus, lymphoma was often present in lymph nodes, spleen, and other organs. Lymphomas arose more frequently in mice that lack endogenous ecotropic retroviral sequences and thus were not due to activation of endogenous provirus. During the third month of the study, a few NIH Swiss mice that died had granulosa cell tumors of the ovary. Treatment-related but reversible thymic atrophy was observed in both mouse models. There was a very high correlation between the internal dose of ddC and the incidence of thymic lymphoma in both mouse models. Most of the lymphocytes from control thymuses and ddC-induced lymphomas were positive for Thy-1.2 (pan-T), heat stable antigen, and CD4 and CD8 markers, with no marked differences in the lymphocyte markers of the tumors between sexes or dose groups. p53 protein was detected in only 20% (23/115) of the ddC-induced lymphomas with mostly minimal expression in scattered cells. Because ddC induced lymphomas in two different mouse models, the potential carcinogenic risk should be considered in long-term treatment of HIV-positive patients, especially children and adolescent patients treated with ddC.

Activation of K-ras in aflatoxin B1-induced lung tumors from AC3F1 (A/J x C3H/HeJ) mice

In addition to being a potent hepatocarcinogen, aflatoxin B1 (AFB1) is a pulmonary carcinogen in experimental animals and epidemiological studies have shown an association between AFB1 exposure and lung cancer in humans. Since point mutations at codons 12, 13 and 61 of the K-ras protooncogene are often implicated in chemically induced mouse lung tumors and in human lung adenocarcinomas, we undertook an investigation of the role of K-ras activation in AFB1-induced pulmonary carcinogenesis. Female AC3F1 (A/J x C3H/HeJ) mice were treated with AFB1 (150 mg/kg i.p., divided into 24 doses over 8 weeks), and 6-14 months after the completion of dosing mice were killed and pulmonary adenomas and carcinomas removed. Of the 76 AFB1-induced lung tumors analyzed by single strand conformation polymorphism (SSCP) and direct sequencing, 75 possessed K-ras codon 12 mutations (46 GTT, 14 GAT, 13 TGT and 2 TTT; normal, GGT) and one had a GGC-->CGC mutation in codon 13. The observation that K-ras mutations occurred only at G:C base pairs is in agreement with N7-guanine being the primary site of AFB1-DNA adduct formation and with guanine residues being targets for AFB1-induced oxidative DNA damage via formation of 8-hydroxydeoxyguanosine (8-OHdG). The AFB1-specific nature of the observed K-ras mutation spectrum and the fact that 100% of the tumor samples examined contained K-ras mutations is consistent with K-ras activation being an early, critical event in AFB1-induced pulmonary carcinogenesis in AC3F1 mice. The parental origin of the observed K-ras mutations was determined by allele-specific PCR amplification of AFB1-induced lung tumor DNA followed by SSCP analysis. In the vast majority of tumors (73/76), the mutated K-ras allele was derived from the lung tumor susceptible A/J parent. This finding supports the existence of a link between K-ras and differences in mouse lung tumor susceptibility.

Induction of CYP1A1 and ALDH-3 in lymphoid tissues from Fisher 344 rats exposed to 2,3,7,8-tetrachlorodibenzodioxin (TCDD)

The immune system is a primary target for toxic insult by a number of drugs and environmental chemicals, many of which require activation to toxic metabolites by drug-metabolizing enzymes. We compared the induction of drug-metabolizing enzymes, including cytochrome P450 1A1 (CYP1A1) and aldehyde dehydrogenase (ALDH), in lymphoid tissues of F344 rats following treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). ALDH was induced in both the spleen and the thymus after TCDD treatment, with maximal expression at 9 and 15 days, respectively. Thymic microsomal preparations from TCDD-treated animals expressed elevated levels of inducible CYP1A1 as compared to microsomes from the spleens of treated animals or tissues from control rats. TCDD treatment also resulted in increased ethoxyresorufin-O-deethylase (EROD) activity in the thymus. There were no detectable mRNA transcripts for CYP1A1 in peripheral blood or splenic lymphocytes from treated animals; however, CYP1A1 transcripts were induced in isolated thymocytes, whole spleen, and whole thymus. In vitro exposure to TCDD did not result in induction of immunoreactive CYP1A1 in thymocytes unless simultaneously activated with the mitogen, phytohemagglutinin (PHA). Immunohistochemical localization of CYP1A1 in immune tissues indicated that cells other than the lymphoid populations are responsible for the increased CYP1A1 expression. The pattern of CYP1A1 induction was related to the expression of the Ah receptor (AhR) in immune tissues. Western blot analyses demonstrated less AhR present in peripheral blood lymphoid cells and spleen, as compared to whole tissues. These studies indicate that while drug-metabolizing enzymes are present in immune tissues, the induction of enzymes is selective in different lymphoid cells.

Hepatic and pulmonary carcinogenicity of methylene chloride in mice: a search for mechanisms

An inhalation study utilizing over 1400 female B6C3F1 mice was undertaken to study mechanistic factors associated with liver and lung tumor induction following exposure to 2000 ppm of methylene chloride. Mice were exposed to methylene chloride (treated) or chamber air (controls) 6 h per day, for varying durations up to 104 weeks. Several interim sacrifices and 'stop exposures' were included. Exposure to 2000 ppm methylene chloride caused an increase in liver and lung neoplasia in the absence of overt cytotoxicity. Measurement of replicative DNA synthesis done after 13, 26, 52 and 78 weeks of exposure showed a significant decrease in the hepatocyte labeling index at 13 weeks. Replicative DNA synthesis in pulmonary airways after 1, 2, 3, 4, 13 and 26 weeks of exposure to methylene chloride was significantly lower than in air-exposed controls. Likewise, the increase in tumor induction in treated mice was not associated with increased replicative DNA synthesis in liver foci or in alveolar parenchyma. The frequency and pattern of H-ras gene activation were similar in control and methylene chloride-induced liver neoplasms. Similarly, the frequency and pattern of K-ras activation in lung neoplasms were not altered by exposure to methylene chloride. Early exposure to methylene chloride for only 26 weeks was sufficient to cause an increase in lung tumors by 2 years, suggesting that methylene chloride may cause early and persistent loss of growth control in lung cells. This implies that risk management strategies should be aimed at minimizing or eliminating exposure to methylene chloride. Liver neoplasms continued to increase in incidence and multiplicity as exposure continued, suggesting that methylene chloride-induced hepatocarcinogenesis is facilitated by continuing exposure to methylene chloride. Since methylene chloride is a more potent inducer of lung than liver neoplasia, it is recommended that health risk assessment be based on the lung data. While no novel molecular lesions have been found to explain the induction of lung and liver neoplasia in mice, ongoing studies may identify other molecular changes that are important in the genesis of these neoplasms. Hence, it may be necessary to revise risk assessment and management strategies in light of future research findings.

High frequency of K-ras mutations in spontaneous and vinyl carbamate-induced lung tumors of relatively resistant B6CF1 (C57BL/6J x BALB/cJ) mice

The murine K-ras proto-oncogene is hypothesized to be a pulmonary adenoma susceptibility gene. This postulate is supported by the previous demonstration of a preference for mutation of the K-ras allele from the susceptible parent in lung tumors of A/J x C3H F1 mice. We have examined K-ras activation in control and vinyl carbamate (VC) (single dose 0.03 mumol/g i.p.) treated B6CF1 mice, the progeny of resistant C57BL/6J and intermediately sensitive BALB/cJ parents. Thirty-four of 37 tumors from VC-treated mice and 17 of 23 from controls contained activating K-ras mutations. The spectra of mutations in codons 12 and 61 of K-ras were similar for the two groups, except that 7 tumors from VC-treated mice had A-->T transversions in the second base of codon 61; none were observed in tumors from saline-treated animals. PCR-based genotyping of first exon K-ras mutations revealed that the vast majority (15 of 18) of the mutations were in the BALB/cJ allele. Furthermore, the three tumors with mutated C57BL/6J K-ras were among the smallest tumors analyzed. These results are consistent with previous findings in other mouse hybrids showing parental bias for K-ras mutations and suggest that mutation of the allele of the susceptible parent may provide a growth advantage to the tumor.

A randomized, crossover evaluation of methylphenidate in cancer patients receiving strong narcotics

Sedation may be a dose-limiting side-effect of opioid therapy in some cancer patients. This study was designed to evaluate further the use of the psychostimulant, methylphenidate, an agent that has been reported to counter-act opioid-induced sedation, in patients with cancer-related pain. Patients receiving a stable dose of an opioid for cancer-related pain were recruited for this randomized, double-blind, crossover clinical trial. In addition to their regular dose of narcotics, they received 5 days of methylphenidate followed by 5 days of placebo, or vice versa. Our data did not definitively demonstrate any statistically significant benefit for methylphenidate, but did suggest that this drug could mildly decrease narcotic-induced drowsiness and could increase night-time sleep. These data, in conjunction with other published data, suggest that methylphenidate can counteract narcotic-induced daytime sedation to a limited degree.

Allelotype analysis of mouse lung carcinomas reveals frequent allelic losses on chromosome 4 and an association between allelic imbalances on chromosome 6 and K-ras activation

We generated allelotypes of 38 methylene chloride-induced lung carcinomas from female C57BL/6J x C3H/6J F1 (hereafter called B6C3F1) mice. Two or more polymorphic markers per autosome, most of them microsatellites, were examined for loss of heterozygosity. Allelic losses throughout the genome were generally infrequent except for markers on chromosome 4, which were lost in approximately one-half of the carcinomas. Analysis of lung adenomas indicated that chromosome 4 loss was associated with malignant conversion. In addition, chromosome 4 loss were specific for lung carcinomas based on comparison to methylene chloride-induced liver tumors and additional studies of lung tumors from a variety of treatment protocols and different mouse strains. Preferential loss of the maternal chromosome 4 was observed in B6C3F1 carcinomas. Analyses of additional tumors induced in mice from two reciprocal crosses, A/J x C3H/HeJ F1 (hereafter called AC3F1) and C3H/HeJ x A/J F1 (hereafter called C3AF1), provided evidence for the inactivation of one allele of the putative chromosome 4 tumor suppressor gene by parental imprinting. Most B6C3F1 tumors lost all chromosome 4 markers examined, suggesting nondisjunction events. In contrast, several C3AF1 and AC3F1 tumors appeared to have interstitial deletions that defined the smallest region of overlap as a 9-cM interval between Ifa-2 and D4Nds2. The homologous region on human chromosome 9p21-22 is frequently lost in a variety of tumors including lung cancers. A candidate tumor suppressor gene, MTS1, is located in this region, which is homozygously deleted or mutated in cell lines derived from a variety of human tumors. Finally, an association between K-ras gene activation and allelic imbalances on chromosome 6 was observed for B6C3F1 lung tumors.

Assignment of a locus for mouse lung tumor susceptibility to proximal chromosome 19

Previous studies have hypothesized that at least three genetic loci contribute to differences in pulmonary adenoma susceptibility between mouse strains A/J and C57BL/6J. One gene that may confer susceptibility to lung tumorigenesis is the Kras protooncogene. To identify other relevant loci involved in this polygenic trait, we determined tumor multiplicity in 56 randomly chosen N-ethyl-N-nitrosourea-treated (A/J x C57BL/6J) N1 x C57BL/6 backcross (AB6N2) progeny and correlated it with genotypes at 77 microsatellite markers spanning the genome. A correlation of lung tumor multiplicity phenotypes with genotypes of microsatellite markers on distal Chromosome (Chr) 6 in the Kras region (Pas1) was confirmed, and a new region on Chr 19 (designated Pas3) was identified that also contributes to susceptibility. Linkage analysis on Chr 19 with 270 AB6N2 mice localized the region flanked by D19Mit42 and D19Mit19 that is most closely associated with lung tumor susceptibility. The Pas3 locus may be an enhancer of the susceptibility locus on Chr 6.

ras proto-oncogene activation in dichloroacetic acid-, trichloroethylene- and tetrachloroethylene-induced liver tumors in B6C3F1 mice

The frequency and mutation spectra of proto-oncogene activation in hepatocellular neoplasms induced by tetrachloroethylene, trichloroethylene and dichloroacetic acid were examined to help define the molecular basis for their carcinogenicity. H-ras codon 61 activation was not significantly different among dichloroacetic acid- and trichloroethylene-induced and combined historical and concurrent control hepatocellular tumors (62%, 51% and 69% respectively). The mutation spectra of H-ras codon 61 mutations showed a significant decrease in AAA and increase in CTA mutations for dichloroacetic acid- and trichloroethylene-induced tumors when compared to combined controls. The H-ras codon 61 mutation frequency for tetrachloroethylene-induced tumors was significantly lower (24%) than that of combined controls and also that of the two other chemicals. Mutations at codons 13 and 117 plus a second exon insert contributed 4% to the total H-ras frequencies for trichloroethylene and tetrachloroethylene. There was also a higher incidence of K-ras activation (13%) in tetrachloroethylene-induced tumors than in the other chemically induced or control tumors. Four liver tumors were found to contain insertions of additional bases within the second exon of K- or H-ras. These findings suggest that exposure to dichloroacetic acid, trichloroethylene and tetrachloroethylene provides a selective growth advantage to spontaneously occurring mutations in codon 61 of H-ras and, at the same time, is responsible for a small number of unique molecular lesions suggestive of either a random genotoxic mode of action or a non-specific result of secondary DNA damage. However, the absence of ras activation in many of the liver neoplasms suggests that alternative mechanisms are also important in B6C3F1 mouse hepatocarcinogenesis.

Randomized trial of cyclophosphamide, methotrexate, and 5-fluorouracil with or without estrogenic recruitment in women with metastatic breast cancer

BACKGROUND

The fraction of breast cancer cells undergoing DNA synthesis at any one time is relatively low, which is problematic because most chemotherapeutic agents are most effective against dividing cells. Estrogens administered in vitro and in vivo can increase breast cancer cell proliferation. A randomized clinical trial was performed to determine if estrogenic recruitment could increase the effectiveness of combination chemotherapy.

METHODS

One hundred sixty-five women were randomized, with two excluded from these analyses, to either an intravenous cyclophosphamide, methotrexate, and 5-fluorouracil (CMF) regimen alone (cyclophosphamide, 600 mg/m2; methotrexate, 40 mg/m2; 5-fluorouracil, 600 mg/m2) or CMF preceded by 3 days of diethylstilbestrol (DES) at a dose of 1 mg orally per day. The planned cycle length was 3 weeks.

RESULTS

Objective responses were seen in 20 of 80 patients (25%) treated with CMF and 32 of 83 patients (39%) treated with DES-CMF, and this difference almost achieved statistical significance (chi-square, two-sided P = 0.06). However, duration of response, time to disease progression, and survival time were similar for the two regimens.

CONCLUSIONS

Estrogenic recruitment with DES as used in this study does not substantially increase the efficacy of a CMF regimen administered intravenously every 3 weeks.

Evaluation of external-beam radiation therapy plus 5-fluorouracil (5-FU) versus external-beam radiation therapy plus hycanthone (HYC) in confined, unresectable pancreatic cancer

From March 1981 to November 1987, 87 patients with histologically confirmed pancreatic adenocarcinoma, unresectable but confined to the pancreatic region, were randomized to two treatments. The standard treatment was 40-50 Gy external-beam radiation therapy (RT) to gross tumor plus potential microscopic tumor with a 5 Gy boost to gross tumor plus a 1.5-2.0 cm margin, using multiple fields and 5-fluorouracil (5-FU) 500 mg/m2/d intravenously by rapid infusion. The 5-FU was given each of the initial 3 days of each of three 20 Gy radiation courses. The experimental treatment used identical radiation fields, but the two Gy daily radiation fractions were administered in a continuous course to a total dose of 50 Gy. Hycanthone was administered 60 mg/m2 intravenously within 2 to 4 hr during each day of the 5-day course of infusions during the first and fifth weeks of radiation therapy. There was no statistically significant difference between treatment arms in survival (p = 0.82) or disease-free survival (p = 0.27). Seven percent of hycanthone-treated patients demonstrated hepatic toxicity which was usually mild in nature. There was, however, one death due to hepatic toxicity.

Detecting proliferating cell nuclear antigen in archival rodent tissues

The detection of proliferating cell nuclear antigen (PCNA), an endogenous cell replication marker, has lacked sensitivity in paraffin-embedded archival tissues fixed in formalin. An enhanced immunohistochemical procedure to detect PCNA has been successfully applied to rat and mouse tissues. Tissue sections are heated in a microwave oven in the presence of an antigen-retrieval solution of heavy-metal salts. Positive immunostaining of S-phase cells, an indication of DNA replicative activity, has been consistently obtained in tissues fixed for more than 24 months in formalin and in paraffin blocks stored for up to 19 months. Use of this technique will allow retrospective staining of rodent tissues from previously conducted toxicity and carcinogenicity studies.

Effect of methylene chloride inhalation on replicative DNA synthesis in the lungs of female B6C3F1 mice

In the National Toxicology Program 2-year inhalation study of dichloromethane (DCM), there was a significant increase in pulmonary neoplasms in female B6C3F1 mice exposed to 2000 ppm (overall rates of 30/48 versus 5/50 in control). Replicative DNA synthesis was examined to evaluate the potential role of treatment-induced lung cell proliferation on pulmonary carcinogenicity. Tritiated thymidine incorporation was assessed in methacrylate plastic sections after 1, 2, 3, or 4 weeks of inhalation exposure to 2000 ppm or 8000 ppm DCM. Similar measurements of labeling indexes were made after 13 and 26 weeks of exposure to 2000 ppm DCM using bromodeoxyuridine as the labeling agent. In all cases the labeling agent was delivered over a 6-day period using osmotic minipumps. The labeling index (LI) of bronchiolar epithelium (two branches proximal to the terminal bronchiole) of mice exposed to 2000 ppm DCM for 2-26 weeks decreased to 40-60% of the control. Terminal bronchioles showed a similar decrease in LI. Mice exposed to 8000 ppm DCM had a less dramatic decrease in LI. No pathological change was found in the exposed lungs. It is concluded that inhalation exposure to DCM for up to 26 weeks reduces cell turnover of bronchiolar cells in female B6C3F1 mice.

Dose response for TCDD promotion of hepatocarcinogenesis in rats initiated with DEN: histologic, biochemical, and cell proliferation endpoints

The present study examines the dose-response relationship for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) promotion of histologic and biochemical parameters by using a two-stage model for hepatocarcinogenesis in female Sprague-Dawley rats initiated with a single intraperitoneal dose of 175 mg of diethylnitrosamine (DEN)/kg body weight at 70 days of age. Starting 2 weeks after initiation, treatment groups of 8-10 rats were given TCDD by gavage in corn oil once every 2 weeks for 30 weeks. Doses were 3.5, 10.7, 35.7, and 125 ng TCDD/kg body weight/day. A significant body weight reduction was present in the noninitiated group that received 125 ng TCDD. Relative liver weight was statistically increased in initiated rats treated with > or = 10.7 ng TCDD and in noninitiated rats treated with > or = 35.7 ng TCDD. Histopathologic evidence of cytotoxicity was dose-related in all TCDD-treated groups. There was a statistically significant dose response in the bromodeoxyuridine (BrdU) S-phase labeling index (LI) in the DEN-initiated rats (p < 0.01) and a marginally significant trend in the saline-treated rats (p = 0.10), but proliferating cell nuclear antigen S-phase LI and growth fraction within altered hepatic foci showed no increase. Among the DEN-initiated groups there was a significant increase in glutathione S-transferase altered hepatic foci stereological parameters in the 125 ng TCDD group. This study demonstrates that dose-response relationships for TCDD's effects on cell proliferation growth of altered hepatic foci are different from previously reported effects on P450 gene expression, indicating that different biological or biochemical responses may exhibit different dose-response relationships.(ABSTRACT TRUNCATED AT 250 WORDS)

A randomized phase II trial of amonafide or trimetrexate in patients with advanced non-small cell lung cancer. A trial of the North Central Cancer Treatment Group

BACKGROUND

In an effort to identify new active chemotherapeutic agents against non-small cell lung cancer (NSCLC), the authors conducted a randomized Phase II trial to evaluate the efficacy of amonafide or trimetrexate in patients with Stage IV disease.

METHODS

This was a multicenter Cooperative Oncology Group trial. All patients had advanced NSCLC and were previously untreated with chemotherapy. Patients were randomized to treatment after enrollment. Amonafide was administered as a 24-hour continuous infusion (1600 mg/m2) every 21 days. Trimetrexate (150 mg/m2) was administered intravenously over 30 minutes every 2 weeks. The primary endpoints of the study were clinical response and toxic effects. All patients were observed for survival.

RESULTS

Thirty-five patients received amonafide and were assessable. There were no complete responses and two partial responses (6%). Thirty-seven patients were treated with trimetrexate. There were no complete responses and five (14%) partial responses. Myelosuppression was the primary toxic effect observed with amonafide treatment. Trimetrexate was associated infrequently with clinically significant side effects.

CONCLUSIONS

Amonafide is inactive against NSCLC, and no additional studies with this agent are planned. Trimetrexate has some activity against NSCLC, but its role in the future therapy of this disease is questionable.

Characterization of p53 mutations in methylene chloride-induced lung tumors from B6C3F1 mice

Mutations of the p53 tumor suppressor gene are the most common defined genetic alterations seen in a wide variety of human cancers. In contrast, little is known about the importance of the p53 gene in chemically induced tumors of rodents, which are widely used as models for the evaluation of human health risks. In this study we examined 54 methylene chloride-induced and seven spontaneously arising lung tumors from female B6C3F1 mice for losses of heterozygosity (LOH) at markers near the p53 gene on chromosome 11. LOH was detected in seven methylene chloride-induced lung carcinomas by Southern analysis of a restriction fragment length polymorphism and PCR analysis of five simple sequence length polymorphisms. In each case allele loss was observed at all six markers; thus, these chromosomal alterations were likely to have resulted from mitotic nondisjunction. In contrast, LOH was not detected in 20 liver tumors from methylene chloride-treated mice at the Acrb locus, which is tightly linked to the p53 gene on chromosome 11. In addition single strand conformation polymorphism analysis was performed to screen for mutations in the most conserved regions of the p53 gene (exons 5 to 8). Consequently, potential mutations identified by direct sequencing, were only detected in four of the seven tumor samples with LOH, but not in any of the remaining lung tumors. Overexpression of the p53 protein by immunohistochemical staining was detected only in the four tumors that contained p53 point mutations and in a focal area of another tumor. Finally, using a simple sequence length polymorphism within the retinoblastoma tumor suppressor gene, LOH on mouse chromosome 14 was also detected in three lung carcinomas and one liver tumor. Inactivation of p53 and possibly the retinoblastoma tumor suppressor gene appear to be infrequent events in lung and liver tumors from methylene chloride treated mice.

Ras proto-oncogene activation in liver and lung tumors from B6C3F1 mice exposed chronically to methylene chloride

Methylene chloride has been the subject of recent toxicological and carcinogenesis studies because of significant human exposure and widespread use in industrial processing, food preparation and agriculture. In this study, liver and lung tumors, induced in female B6C3F1 mice by inhalation of 2000 p.p.m. methylene chloride (6 h/day, 5 days/week continuous exposure), were examined for the presence of activated ras proto-oncogenes. DNA was isolated from 49 spontaneous and 50 methylene chloride-induced liver tumors and screened by oligonucleotide hybridization of PCR amplified H-ras gene fragments for codon 61 mutations. In the chemically induced tumors, 38 mutations were detected, 16 C to A transversions in base 1, 16 A to G transitions in base 2 and 6 A to T transversions in base 2. This mutation profile was similar to that identified for the H-ras gene in the spontaneous liver tumors and suggests that methylene chloride acts in liver by promoting cells with spontaneous lesions. Tumors in which H-ras codon 61 mutations were not detected were examined for the presence of transforming genes by the nude mouse tumorigenicity assay. Except for activated K-ras genes detected in DNA from two methylene chloride induced tumors and one spontaneous tumor, no other transforming genes were identified. DNA from 54 lung tumors was screened by direct sequencing of PCR amplified DNA fragments of the K-ras gene for first and second exon mutations, and 12 mutations were identified, 5 in exon one and 7 in exon 2. The low number of spontaneous tumors available in this study limits the interpretation of the data, and thus the frequency and spectrum of K-ras activation in the methylene chloride induced tumors was not significantly different from that in the seven spontaneous tumors analyzed. Since K-ras activation was not detected in 80% of the tumors, the nude mouse tumorigenicity assay was used to examine the lung tumors for the presence of other transforming genes. At present no transforming genes other than ras genes were identified in either liver or lung tumors.

Effect of varying exposure regimens on methylene chloride-induced lung and liver tumors in female B6C3F1 mice

Methylene chloride is a high production chemical used in a variety of applications resulting in estimated occupational and consumer exposures of at least one million people per day. Results of previously reported chronic evaluations of inhaled methylene chloride indicated that it caused mammary tumors in Fischer 344 rats and neoplasia in the lungs and liver of B6C3F1 mice. Mechanism(s) for methylene chloride-induced carcinogenesis have not been adequately elucidated. In this paper we describe the histologic evaluation of animals at a number of intermittent times for the purposes of assessing the progressive development of liver and lung neoplasia. Additionally, a series of stop-exposure treatments was conducted to evaluate the role of different methylene chloride exposure durations on the induction of hepatic and pulmonary neoplasia in female mice. Inhalation exposure to 2000 p.p.m. methylene chloride for 6 h per day, 5 days per week, for 104 weeks resulted in an 8-fold increase in the incidence of exposed animals having a lung adenoma or carcinoma (63 versus 7.5%; P < 0.01) and a 13-fold increase in the total number of pulmonary adenomas and carcinomas per animal at risk (0.97 versus 0.075; P < 0.01). This exposure also caused a 2.5-fold increase in the incidence of mice having liver tumors (69 versus 27%; P < 0.01) and a 3-fold increase in the total number of hepatic adenomas and carcinomas per animal at risk (1.34 versus 0.46; P < 0.01). Methylene chloride exposure hastened the first appearance of lung tumors (by 1 year) compared to that observed in control animals; chemical-induced and spontaneous liver tumors first occurred simultaneously. A shorter exposure duration was sufficient to attain maximal numbers of lung tumors than that needed for a maximal liver tumor burden. Lung tumor multiplicity was substantially increased by having additional time after cessation of the chemical treatment. This contrasts with the findings in liver, where additional post-exposure latency time did not effect tumor multiplicity compared to that of mice evaluated immediately after cessation of exposure. The incidence of lung alveolar hyperplasia in methylene chloride exposed animals was very low, even in tumor-bearing animals and the hyperplasias were not seen until at least 13 weeks after appearance of adenomas and carcinomas. Thus, the genesis of methylene chloride induced lung tumors in B6C3F1 mice is not preceded by overt cytotoxicity, enhanced cell proliferation nor observed hyperplasia.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhalation exposure to a hepatocarcinogenic concentration of methylene chloride does not induce sustained replicative DNA synthesis in hepatocytes of female B6C3F1 mice

We have used methylene chloride as a model to study cellular and molecular processes responsible for liver tumor induction by chlorinated hydrocarbons. Because of current interest in the role of enhanced cell proliferation in tumor induction, measurement of S-phase hepatocytes was incorporated into recently conducted toxicity and carcinogenicity studies. In prechronic studies, female B6C3F1 mice were exposed to 0, 1000, 2000 or 8000 p.p.m. methylene chloride by inhalation, 5 days per week, for up to 4 weeks followed by a 1 and 2 week recovery period. Mice exposed to concentrations of 2000, 4000 or 8000 p.p.m. methylene chloride had sustained increased liver weight commencing after 1 week of exposure and returning to normal after the 1 or 2 week recovery period. The increased liver weight was attributed to hepatocellular hypertrophy secondary to intracellular glycogen accumulation. Tritiated thymidine was administered by osmotic minipumps to label S-phase hepatocytes over a 6 day period. At most intervals examined there was decreased hepatocyte labeling in mice exposed to methylene chloride. However, there was a transitory increased number of S-phase hepatocytes observed at the 2 week interval in the 1000, 4000 and 8000 p.p.m. methylene chloride groups. In a chronic study, female mice were exposed to 2000 p.p.m. methylene chloride for up to two years. Following labeling with BRDU using 6 day minipumps, a statistically significant decrease in S-phase hepatocytes was observed after 13 weeks of methylene chloride exposure. A minor increased labeling index (LI) observed at 52 weeks was not considered to be a methylene chloride treatment-related effect. Retrospective immunohistochemical staining for proliferating cell nuclear antigen (PCNA) in liver sections containing foci of cellular alteration allowed demonstration of S-phase hepatocytes in these clonally expanded preneoplastic lesions. While foci frequently had higher LI's than surrounding normal hepatocytes, there was no difference in the mean LI of foci from methylene chloride-treated mice versus foci occurring spontaneously in control mice. The absence of a sustained increase in S-phase hepatocytes in female B6C3F1 mice suggests that enhanced cell proliferation is not a major mechanistic factor associated with the observed hepatocarcinogenicity of methylene chloride.

Comparison of pulmonary O6-methylguanine DNA adduct levels and Ki-ras activation in lung tumors from resistant and susceptible mouse strains

The role of O6-methylguanine (O6MG) DNA adduct formation and persistence in the formation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumors from resistant C57BL/6 and susceptible A/J mice was investigated. In addition, the frequencies of pulmonary tumor formation and Ki-ras activation were defined in C57BL/6 mice treated with NNK or vinyl carbamate (VC), and the role of the p53 gene in pulmonary carcinogenesis in these resistant mice was examined. One day after treatment with 100 mg/kg NNK, O6MG adduct concentrations were twofold to eightfold higher in Clara cells and type II cells than in small cells or whole lungs from both mouse strains. The concentrations of O6MG in isolated cells decreased at a similar rate in the two strains of mice. Lung tumors were detected by 27 mo of age in 18% of the C57BL/6 mice after a single 100 mg/kg dose of NNK and in 46% of these mice after a single 60 mg/kg dose of VC. In contrast, the tumor incidence in untreated C57BL/6 mice was 4%. Only one of 22 lung tumors from C57BL/6 mice treated with NNK contained an activated Ki-ras gene that was associated with an O6MG DNA adduct, whereas previous studies detected activated Ki-ras oncogenes in most of the NNK-induced lung tumors analyzed from susceptible A/J and resistant C3H mice. The small differences in formation and persistence of the O6MG adduct in whole lung or isolated lung cells from A/J and C57BL/6 strains do not account for the differences in either susceptibility for tumor formation or activation of the Ki-ras gene between these strains. In contrast to the low number of NNK-induced tumors with Ki-ras mutations in the resistant mice, 11 of 20 lung tumors from VC-treated mice contained activated Ki-ras genes. Neither p53 tumor suppressor gene mutations nor overexpression of the p53 protein were detected in spontaneous or chemically induced lung tumors in C57BL/6 mice. Thus, although Ki-ras activation was detected in some tumors, pathways independent of ras activation and p53 inactivation also appear to be involved in lung tumorigenesis in this resistant mouse strain.

A phase III trial of mitomycin C alone versus mitomycin C, vinblastine, and cisplatin for metastatic squamous cell lung carcinoma

BACKGROUND

In an effort to confirm the efficacy of mitomycin C against metastatic squamous cell lung carcinoma and to compare the efficacy of single-agent therapy with a combination containing cisplatin, the authors conducted a randomized Phase III trial of mitomycin C alone versus mitomycin C, vinblastine, and cisplatin (MVP).

METHODS

All patients had advanced squamous cell lung carcinoma, and survival was the primary end point. There were 133 eligible patients who received either mitomycin C alone (n = 64) or MVP (n = 69). The two groups were similar with respect to performance score, disease status, age, sex, and stage.

RESULTS

The major objective response rates were 30% (95% confidence interval [CI], 18-41%) and 43% (95% CI, 32-55%) for mitomycin C alone and MVP, respectively (P = 0.1). The median time to progression was 83 days for mitomycin C alone, compared with 119 days for MVP (P = 0.026). The median survival time was 114 days for mitomycin C and 163 days for MVP (P = 0.09). The 1-year survival rates were equivalent. Myelosuppression was the major toxicity, and there were significantly greater leukocyte nadirs with MVP therapy (P < 0.001).

CONCLUSION

Mitomycin C has antitumor activity against squamous cell lung carcinoma when used alone or in combination with MVP. The regimen containing cisplatin had marginally increased activity that did not translate into a clinically significant survival advantage.

Role of the alveolar type II cell in the development and progression of pulmonary tumors induced by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in the A/J mouse

The role of the type II cell in the development of pulmonary tumors induced in the adult A/J mouse (6 weeks of age) by treatment with a single dose (100 mg/kg, i.p.) of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) was investigated. Twenty-four h following treatment with NNK, the concentration of O6-methylguanine was similar in Clara and type II cells. However, hyperplasias were detected only along the alveolar septa in lungs 14 weeks after carcinogen treatment. Examination of the ultrastructure of several hyperplasias revealed that the proliferating cells resembled type II pneumocytes. The proliferating cells were cuboidal in shape, with centrally localized ovoid nuclei characterized by minor indentations. Lamellar bodies, one of the major hallmarks of the type II cell, were present in the cytoplasm. The progression of pulmonary lesions was followed by sacrificing mice at 4-week intervals from 14 to 54 weeks after treatment with NNK. From 34 to 42 weeks after treatment, progression to neoplasia was demonstrated by a decline in the frequency of hyperplasias and an increase in the frequency of adenomas. Approximately 50% of the adenomas were observed arising within hyperplasias. Carcinomas appeared to increase in frequency 34 weeks after carcinogen treatment and comprised greater than 50% of the pulmonary lesions by 54 weeks. Approximately 30% of the carcinomas were observed arising within adenomas. The growth pattern of carcinomas began to change from solid to mixed (solid and papillary) 42 weeks after NNK. Moreover, electron micrographic analysis demonstrated that, within a hyperplasia, proliferating type II cells could change from cuboidal to columnar in shape and could also exhibit nuclear indentations, both characteristics displayed by the Clara cell. Thus, this divergence of the type II cell from its well characterized morphological features indicates that the selective growth advantage which these initiated cells possess can result in changes to the normal ultrastructure of this cell as it progresses toward malignancy. DNA was isolated from 20 hyperplasias and screened for the presence of an activated K-ras gene. This gene was activated in 17 of 20 lesions, with 85% of the mutations involving a GC to AT transition within codon 12 (GGT to GAT), a mutation consistent with base mispairing produced by the formation of the O6-methylguanine adduct. This specificity for activation of the K-ras gene was identical to that observed previously in adenocarcinomas induced by NNK.(ABSTRACT TRUNCATED AT 400 WORDS)

Phase II evaluation of menogaril in patients with advanced cervical carcinoma. A collaborative trial of the North Central Cancer Treatment Group and Mayo Clinic

Fourteen patients with advanced/recurrent squamous cell carcinoma of the uterine cervix received menogaril, 200 mg/m2 by one hour intravenous infusion at four-week intervals. No objective regressions were observed. Median time to progression was less than two months and median survival was seven months. All patients experienced neutropenia. Platelet toxicity was negligible. Venous irritation and phlebitis occurred at the infusion site in 43% of patients. Menogaril as administered in this protocol is ineffective in treating previously irradiated advanced/recurrent squamous cell carcinoma of the uterine cervix and warrants no further investigation in this disease at the dosage and administration schedule used in this protocol.

An enhancement method for immunohistochemical staining of proliferating cell nuclear antigen in archival rodent tissues

An enhanced immunohistochemical procedure to detect proliferating cell nuclear antigen (PCNA), an endogenous cell replication marker, has been successfully applied to formalin-fixed, paraffin-embedded archival rat and mouse tissues. The procedure involves microwave oven heating of tissue sections in a commercially available antigen retrieval solution of heavy metal salts. Successful immunohistochemical staining of PCNA can be consistently obtained in tissues fixed for over 24 months in formalin and in sections made from paraffin blocks stored in our tissue archives for up to 19 months. Use of this technique will allow retrospective staining of rodent tissues for identification of S phase cells as an indication of DNA replicative activity in previously conducted toxicity and carcinogenicity studies.