Hyperplasia of alveolar neuroendocrine cells in rat lung carcinogenesis by silica with selective expression of proadrenomedullin-derived peptides and amidating enzymes

Pulmonary neuroendocrine (NE) cells are found as clusters called neuroepithelial bodies (NEBs) or as single cells scattered in the respiratory epithelium. They express a variety of bioactive peptides, and they are thought to be the origin of NE lung tumors. Proadrenomedullin N-terminal 20 peptide (PAMP) is a peptide derived from the same precursor as adrenomedullin (AM). AM and PAMP are C-terminally amidated during their processing by a well-characterized amidating enzyme, peptidylglycine alpha-amidating monooxygenase (PAM). We explored AM, PAMP, and PAM expression as markers for NE hyperplasia in three rodent species (Fischer 344 rats, Syrian golden hamsters, and A/J mice) after a single intratracheal instillation of crystalline silica (quartz), which was previously found to induce different reactions in the three species. Rats developed a marked silicosis, with alveolar and bronchiolar hyperplasia and formation of peripheral lung epithelial tumors. Mice developed a moderate degree of silicosis, but not epithelial hyperplasia or tumors. Hamsters showed dust-storage lesions, but not silicosis or tumors. NE cells were immunolabeled for calcitonin gene-related peptide (CGRP), AM, PAMP, and PAM in serial sections of each lung. The numbers of positive NEBs per lung area and positive cells per NEB were quantified. A marked hyperplastic reaction in the NEBs of silica treated rats occurred only in alveolar NEBs, but not in bronchiolar NEBs. From Month 11 onwards, there were marked differences in the number of alveolar NEBs per section and in the number of cells per alveolar NEB immunoreactive for CGRP. No hyperplastic NE cell reaction was observed in silica-treated mice and hamsters. Significant PAMP and PAM expression was seen only in rat hyperplastic alveolar and in bronchiolar NEBs from Month 11 onwards. In E18, rat fetal lung NEBs were found to be strongly positive for PAMP and PAM.

Relationship between surface properties and cellular responses to crystalline silica: studies with heat-treated cristobalite

A fibrogenic sample of cristobalite dust, CRIS (crystalline silica of mineral origin), was heated to 1300 degrees C (CRIS-1300) to relate induced physicochemical modifications to cytotoxicity. Heating did not affect dust micromorphology and crystallinity, except for limited sintering and decreased surface area of CRIS-1300. Thermal treatments deeply affected surface properties. Electron paramagnetic resonance showed surface radicals progressively annealed by heating, mostly disappearing at >/=800 degrees C. Surface hydrophilicity or hydrophobicity, evaluated with water vapor adsorption, still showed some hydrophilic patches in CRIS-800, but CRIS-1300 was fully hydrophobic. Heating modified the biological activity of cristobalite. Cytotoxicity, tested on proliferating cells of the mouse monocyte macrophage cell line J774, showed that CRIS was cytotoxic and CRIS-800 was still cytotoxic, but CRIS-1300 was substantially inert. Cytotoxicity of CRIS to the rat lung alveolar epithelial cell line, AE6, as measured by colony forming efficiency, was greatly reduced for CRIS-800 and eliminated for CRIS-1300. The rate of lactate dehydrogenase release by rat alveolar macrophages was lowered for CRIS-800, and release was completely inactivated for CRIS-1300. The absence of surface radicals and the onset of hydrophobicity may both account for the loss of cytotoxicity upon heating. Differences observed between CRIS-800 and CRIS-1300, both fully deprived of surface radicals, indicate that hydrophobicity is at least one of the surface properties determining the cytotoxic potential of a dust.

Respiratory tract carcinogenesis by mineral fibres and dusts: models and mechanisms

Experimental pathology studies in respiratory carcinogenesis by mineral fibres and dusts are reviewed. Animal models, analogous to the corresponding human pathology, were developed for carcinogenesis by polycyclic aromatic hydrocarbons carried on mineral particles, by N-nitroso compounds, by asbestos fibres and by crystalline silica (quartz). Species and organ susceptibility factors determine marked differences in the carcinogenic response to silica in different species and target organs, suggesting possible pathogenetic mechanisms, such as the role of surface oxygen radicals and the induction of related enzymes. Cellular models have been effectively used to study the induction of toxicity and neoplastic transformation by mineral fibres and dusts. Cell culture models have been developed for respiratory epithelial cells and for their transformation. These include not only models for the laryngotracheobronchial columnar epithelium, but also for the alveolar type II epithelium and its transformation by silica. Recent studies on simian virus (SV)40 carcinogenesis in animal and cellular models and on the detection of SV40-like sequences in the deoxyribonucleic acid of human tumours point to the need for much further research on the role of interactions of viral, chemical and physical factors in human respiratory carcinogenesis.

The association of cancers of the larynx with cancers of the lung

We report 77 cases of associated primary cancers of the larynx and lung that were managed at the Department of Otolaryngology, University of Padua, between 1980 and 1994. To our knowledge, this is the largest series reported in the literature to date. This association is not a chance finding, but presumably the result of common pathogenetic factors.

Transforming growth factor beta expression and transformation of rat lung epithelial cells by crystalline silica (quartz)

Crystalline silica (quartz) induces silicosis and associated peripheral lung carcinomas in rats. The role and pattern of expression of transforming growth factor (TGF)-beta1/beta2 mRNA transcripts were investigated in the fetal rat lung epithelial cell line FRLE, its neoplastic transformants and derived tumors in athymic nude mice. FRLE cells, treated with 100 microgram/cm2 of quartz in serum-free medium, gave rise to phenotypically altered, tumorigenic cells. Quartz-treated, transformed and tumorigenic cells, subcultured directly (QTT-C1) or after growth in soft agar (QTT-C2), formed tumors in athymic nude mice (QTT-T1). Cells subcultured from the tumors (QTT-T1C) were also tumorigenic in nude mice (QTT-T2). QTT-T1 and QTT-T2 tumors were poorly differentiated carcinomas with variable amounts of extracellular matrix-associated TGF-beta1 and desmoplasia. For comparison, a tumorigenic cell line derived from FRLE cells transformed with a mutated K-ras plasmid (RT-C1) and cells subcultured from a corresponding nude mouse tumor (RT-T1) and designated RT-T1C were used. Whereas TGF-beta1 and TGF-beta2 inhibited the growth of QTT-T1C and FRLE cells in a dose-dependent fashion, RT-T1C cells, containing an activated ras gene, were relatively unaffected. TGF-beta1 and TGF-beta2 mRNAs were expressed at higher levels in QTT-T1C cells than in FRLE and TR-T1C cells, and there was an increase in TGF-beta type II receptor (TGR-betaR) mRNA expression in QTT-T1C and RT-T1C cells compared to FRLE cells. Carcinomas in nude mice derived from QTT and RT cells and silicosis-associated lung carcinomas induced in rats by intra-tracheal quartz did not express either active or latent forms of TGF-beta1 protein on immunohistochemistry. The disparity between TGF-beta1 mRNA and TGF-beta1 protein expression in QTT tumors may be due to post-transcriptional regulation of TGF-beta1.

Vanadium(IV)-mediated free radical generation and related 2'-deoxyguanosine hydroxylation and DNA damage

Free radical generation, 2'-deoxyguanosine (dG) hydroxylation and DNA damage by vanadium(IV) reactions were investigated. Vanadium(IV) caused molecular oxygen dependent dG hydroxylation to form 8-hydroxyl-2'-deoxyguanosine (8-OHdG). During a 15 min incubation of 1.0 mM dG and 1.0 mM VOSO4 in phosphate buffer solution (pH 7.4) at room temperature under ambient air, dG was converted to 8-OHdG with a yield of about 0.31%. Catalase and formate inhibited the 8-OHdG formation while superoxide dismutase enhanced it. Metal ion chelators, DTPA and deferoxamine, blocked the 8-OHdG formation. Incubation of vanadium(IV) with dG in argon did not generate any significant amount of 8-OHdG, indicating the role of molecular oxygen in the mechanism of vanadium(IV)-induced dG hydroxylation. Vanadium(IV) also caused molecular oxygen-dependent DNA strand breaks in a pattern similar to that observed for dG hydroxylation. ESR spin trapping measurements demonstrated that the reaction of vanadium(IV) with H2O2 generated OH radicals, which were inhibited by DTPA and deferoxamine. Incubation of vanadium(IV) with dG or with DNA in the presence of H2O2 resulted in an enhanced 8-OHdG formation and substantial DNA double strand breaks. Sodium formate inhibited 8-OHdG formation while DTPA had no significant effect. Deferoxamine enhanced the 8-OHdG generation by 2.5-fold. ESR and UV measurements provided evidence for the complex formation between vanadium(IV) and deferoxamine. UV-visible measurements indicate that dG, vanadium(IV) and deferoxamine are able to form a complex, thereby, facilitating site-specific 8-OHdG formation. Reaction of vanadium(IV) with t-butyl hydroperoxide generated hydroperoxide-derived free radicals, which caused 8-OHdG formation from dG and DNA strand breaks. DTPA and deferoxamine attenuated vanadium(IV)/t-butyl-OOH-induced DNA strand breaks.

Neoplastic transformation by quartz in the BALB/3T3/A31-1-1 cell line and the effects of associated minerals

Quartz, the most common form of crystalline silica, was tested quantitatively for neoplastic transformation in the mouse embryo cell line, BALB/3T3/A31-1-1. Five quartz dust samples of respirable size [Min-U-Sil 5 (MQZ); hydrofluoric-acid-etched MQZ (HFMQZ); Chinese standard quartz (CSQZ); DQ12; and F600] all induced significant levels of neoplastic transformation, showing dose-dependent increases in the frequency of morphologically transformed foci at lower tested doses and a plateau level of response at higher doses. The plateau levels reached by the five tested samples did not differ substantially (maximum transformation frequencies per 10(5) cells ranging from 53.2 for MQZ to 28.3 for HFMQZ). F600 had minimal cytotoxicity but transforming activity comparable to the other samples. Cells from all tested transformed foci, when injected s.c. in nude mice, grew as sarcomas. Cytogenetic analysis showed that all tested silica-transformed cell lines had acquired one to five additional marker chromosomes, of types not seen in untreated control lines, indicative of induced chromosomal translocations and amplification. Increased expression of one or more of five genes (p53, myc, H-ras, K-ras, and abl) was observed in several quartz-transformed cell lines. No transforming activity was found for hematite and anatase (both nontoxic), and for rutile (more toxic than MQZ). Combined exposure (1:1 w/w per unit culture area) of each of these dusts with MQZ showed that hematite and anatase inhibited MQZ toxicity as well as transformation, whereas rutile markedly enhanced MQZ toxicity but not MQZ-induced transformation.

DNA strand breakage, thymine glycol production, and hydroxyl radical generation induced by different samples of crystalline silica in vitro

Five preparations of alpha-quartz [Min-U-Sil 5 (MQZ), MQZ pretreated with hydrofluoric acid (HFMQZ), Chinese standard alpha-quartz (CSQZ), and two German samples, DQ-12 and F600] and two preparations of the crystalline silica polymorphs, cristobalite and tridymite, previously characterized for surface area and surface charge, were evaluated for their relative activities in the following assays: (i) in vitro assays of short duration (< or = 15 min) for oxygen consumption and for generation of hydroxyl radicals (measured by electron spin resonance spin trapping), and (ii) in vitro assays of longer duration for DNA strand breakage (measured using linear DNA as a detector molecule) and for production of the oxidized DNA base, thymine glycol (measured by gas chromatography-mass spectrometry). Marked differences among the samples were found for their levels of oxygen consumption and of hydroxyl radicals' generation. All samples caused increased formation of thymine glycol, with wide variations in activity among samples. When normalized for equal surface area, the samples produced different levels of DNA strand breakage. Addition of hydrogen peroxide strongly accelerated DNA damage--more for cristobalite than for the alpha-quartz samples. DNA damage by quartz was enhanced by ferric chloride and inhibited by iron chelators. The order of relative activity of the samples varied with different types of in vitro assays and was not directly correlated to surface area. Electrophoretic mobility, as measured by zeta potential, was not significantly different among samples. The results suggest that the ability of different crystalline silica samples to generate a rapid burst of oxygen free radicals is distinct from their ability to induce DNA damage and DNA base oxidation over longer time periods. The relative activities of the samples in cellular assays (hemolysis of human erythrocytes; cytotoxicity and neoplastic transformation of BALB/3T3/A31-1-1 cells) were in turn markedly different from those listed above, suggesting a more critical role for surface area. The mechanisms of carcinogenesis by crystalline silica need to be further investigated in relation to the underlying physicochemical characteristics.

Antioxidant activity of tetrandrine and its inhibition of quartz-induced lipid peroxidation

Tetrandrine is a benzylisoquinoline alkaloid that has been used in China as an antifibrotic drug to treat the lesions of silicosis. Its mechanism in the treatment of silicosis is unclear. Electron spin resonance (ESR) spin trapping was employed to investigate the antioxidant properties of tetrandrine. The spin trap used was 5,5-dimethyl-1-pyrroline N-oxide (DMPO). Tetrandine efficiently reacted with hydroxyl (.OH) radicals with a reaction rate of approximately 1.4 x 10(10) M-1 s-1. The .OH radicals were generated by the Fenton reaction [Fe(II) + H2O2) as well as by reaction of chromium(V) with H2O2. Similar results were obtained using .OH radicals generated by reaction of freshly fractured quartz particles with aqueous medium. Tetrandrine also scavenged superoxide (O2-) radicals produced from xanthine/xanthine oxidase. The effect of tetrandrine on lipid peroxidation induced by freshly fractured quartz particles was evaluated using linoleic acid as a model lipid. The results showed that tetrandrine caused a significant inhibition on freshly fractured quartz-induced lipid peroxidation.

DNA binding to crystalline silica characterized by Fourier-transform infrared spectroscopy

The interaction of DNA with crystalline silica in buffered aqueous solutions at physiologic pH has been investigated by Fourier-transform infrared spectroscopy (FT-IR). In aqueous buffer, significant changes occur in the spectra of DNA and silica upon coincubation, suggesting that a DNA-silica complex forms as silica interacts with DNA. As compared to the spectrum of silica alone, the changes in the FT-IR spectrum of silica in the DNA-silica complex are consistent with an Si-O bond perturbation on the surface of the silica crystal. DNA remains in a B-form conformation in the DNA-silica complex. The most prominent changes in the DNA spectrum occur in the 1225 to 1000 cm-1 region. Upon binding, the PO2- asymmetric stretch at 1225 cm-1 is increased in intensity and slightly shifted to lower frequencies; the PO2- symmetric stretch at 1086 cm-1 is markedly increased in intensity and the band at 1053 cm-1, representing either the phosphodiester or the C-O stretch of DNA backbone, is significantly reduced in intensity. In D2O buffer, the DNA spectrum reveals a marked increase in intensity of the peak at 1086 cm-1 and a progressive decrease in intensity of the peak at 1053 cm-1 when DNA is exposed to increasing concentrations of silica. The carbonyl band at 1688 cm-1 diminishes and shifts to slightly lower frequencies with increasing concentrations of silica. The present study demonstrates that crystalline silica binds to the phosphate-sugar backbone of DNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Silica radical-induced DNA damage and lipid peroxidation

In recent years, more attention has been given to the mechanism of disease induction caused by the surface properties of minerals. In this respect, specific research needs to be focused on the biologic interactions of oxygen radicals generated by mineral particles resulting in cell injury and DNA damage leading to fibrogenesis and carcinogenesis. In this investigation, we used electron spin resonance (ESR) and spin trapping to study oxygen radical generation from aqueous suspensions of freshly fractured crystalline silica. Hydroxyl radical (.OH), superoxide radical (O2.-) and singlet oxygen (1O2) were all detected. Superoxide dismutase (SOD) partially inhibited .OH yield, whereas catalase abolished .OH generation. H2O2 enhanced .OH generation while deferoxamine inhibited it, indicating that .OH is generated via a Haber-Weiss type reaction. These spin trapping measurements provide the first evidence that aqueous suspensions of silica particles generate O2.- and 1O2. Oxygen consumption measurements indicate that freshly fractured silica uses molecular oxygen to generate O2.- and 1O2. Electrophoretic assays of in vitro DNA strand breakages showed that freshly fractured silica induced DNA strand breakage, which was inhibited by catalase and enhanced by H2O2. In an argon atmosphere, DNA damage was suppressed, showing that molecular oxygen is required for the silica-induced DNA damage. Incubation of freshly fractured silica with linoleic acid generated linoleic acid-derived free radicals and caused dose-dependent lipid peroxidation as measured by ESR spin trapping and malondialdehyde formation. SOD, catalase, and sodium benzoate inhibited lipid peroxidation by 49, 52, and 75%, respectively, again showing the role of oxygen radicals in silica-induced lipid peroxidation.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of carcinogenesis by crystalline silica in relation to oxygen radicals

The carcinogenic effects of crystalline silica in rat lungs were extensively demonstrated by many experimental long-term studies, showing a marked predominance for adenocarcinomas originating from alveolar type II cells and associated with areas of pulmonary fibrosis (silicosis). In contrast with its effects in rats, silica did not induce alveolar type II hyperplasia and lung tumors in mice and hamsters, pointing to a critical role for host factors. Using these animal models, we are investigating the role of cytokines and other cellular mediators on the proliferation of alveolar type II cells. Immunohistochemical localization of TGF-beta 1 precursor in alveolar type II cells adjacent to silicotic granulomas was shown to occur in rats, but not in mice, and hamsters, suggesting a pathogenetic role for this regulatory growth factor. Recent investigations in our laboratory on the biologic mechanisms of crystalline silica included determination of anionic sites on crystalline silica surfaces by binding of the cationic dye Janus Green B; binding of crystalline silica to DNA, demonstrated by infrared spectrometry; production of oxygen radicals by crystalline silica in aqueous media; induction of DNA strand breakage and base oxidation in vitro and its potentiation by superoxide dismutase and by hydrogen peroxide; and induction by crystalline silica of neoplastic transformation and chromosomal damage in cells in culture. On the basis of these in vitro studies, we propose that DNA binding to crystalline silica surfaces may be important in silica carcinogenesis by anchoring DNA close to sites of oxygen radical production on the silica surface, so that the oxygen radicals are produced within a few A from their target DNA nucleotides.

Generation of thiyl and ascorbyl radicals in the reaction of peroxynitrite with thiols and ascorbate at physiological pH

Electron spin resonance (ESR) spin trapping was utilized to investigate the reaction of peroxynitrite with thiols and ascorbate at physiological pH. The spin trap used was 5,5-dimethyl-1-pyrroline N-oxide (DMPO). The reaction of peroxynitrite with DMPO generated 5,5-dimethylpyrrolidone-(2)-oxy-(1) (DMPOX). Formate enhanced the peroxynitrite decomposition but did not generate any detectable amount of formate-derived free radicals. Thus, the spin trapping measurements provided no evidence for hydroxyl (.OH) radical generation in peroxynitrite decomposition at physiological pH. Thiols (glutathione, cysteine, and penicillamine) and ascorbate reacted with peroxynitrite to generate the corresponding thiyl and ascorbyl radicals. The one-electron oxidation of thiols by peroxynitrite may be one of the important mechanisms for peroxynitrite-induced toxicity and ascorbate may provide a detoxification pathway.

Binding of the cationic dye, Janus green B, as a measure of the specific surface area of crystalline silica in aqueous suspension

Twelve preparations of crystalline silica, with a wide range of particle sizes, were assayed by a new method, which measures surface adsorption of the cationic dye Janus green B to crystalline silica samples in a buffered aqueous suspension. The same samples were also assayed for total surface area by the Brunauer-Emmett-Teller (BET) method of surface adsorption of nitrogen gas. A strong linear correlation was found between the two methods of measurement (r = 0.977). Reproducible specific surface area measurements by the Janus green B adsorption method were made on 2-mg samples using ordinary visible wave-length spectrophotometric equipment, whereas the BET method necessitated sample sizes in excess of 100 mg and more specialized instrumentation. Five size-fractionated preparations from the same Min-U-Sil alpha-quartz sample showed an increase in BET surface area and Janus green B binding per unit weight with decreasing particle size. Among four standard alpha-quartz samples tested, Min-U-Sil 5 and F600 had the lowest specific surface areas, whereas DQ-12 and Chinese standard alpha-quartz had much higher surface areas. The synthetic silica preparations cristobalite and tridymite had intermediate surface areas. Binding by the cationic dye Janus green B is consistent with a surface charge mechanism and provides a useful new technique for the assessment of surface characteristics of crystalline silica samples. Its linear relationship to surface area suggests that the ratio of aqueous surface charge to surface area is constant for different crystalline silica preparations. Comparison of surface areas for different preparations of crystalline silica is important in understanding the relative activities of these preparations in studies on mechanisms of silicosis and silica-induced lung cancer.

Immunohistochemical localization of transforming growth factor-beta 1 in rats with experimental silicosis, alveolar type II hyperplasia, and lung cancer

Immunohistochemical localization of transforming growth factor-beta 1 (TGF-beta 1) was studied in the lungs of rats given crystalline silica or ferric oxide by single intratracheal instillation. Ferric oxide elicited no progressive granulomatous reaction, no epithelial hyperplasia, and no lung tumors; no demonstrable reactivity to TGF-beta 1 was observed. Silica induced a granulomatous reaction with progressive fibrosis, adjacent alveolar type II hyperplasia, and alveolar carcinomas. Rabbit polyclonal antibodies to synthetic peptides corresponding to the first 30 amino acids of mature TGF-beta 1, anti-LC (1-30), and anti-CC (1-30) were used for the localization of intracellular and extracellular TGF-beta 1. An antibody to a peptide corresponding to amino acids 266-278 of the TGF-beta 1 precursor sequence, anti-Pre (266-278), was used to detect the TGF-beta precursor and the latency-associated peptide. Intracellular mature TGF-beta (anti-LC) was demonstrated in fibroblasts and macrophages located at the periphery of silicotic granulomas and in fibroblasts adjacent to hyperplastic type II cells. Extracellular mature TGF-beta 1 was localized in the connective tissue matrix of the granulomas and in the stroma of both hyperplastic type II cells and well-differentiated adenocarcinomas. Immunoreactivity to anti-Pre was localized, intracellularly, in hyperplastic alveolar type II cells and their proliferative lesions adjacent to granulomas, in adenomas, but not in adenocarcinomas. The hyperplastic type II cells appear to be the sites of production and secretion of TGF-beta 1, which may regulate their own growth and differentiation and mediate the production of extracellular TGF-beta 1-associated matrix. The lack of reactivity to TGF-beta 1 precursor in the adenocarcinomas is consistent with the loss of normal cellular differentiation and function. TGF-beta 1 appears to have a pathogenetic role in silica-induced mesenchymal and epithelial lesions. The role of TGF-beta 1 and other cytokines in silica-induced carcinogenesis requires further investigation.

Oxidative DNA damage by crystalline silica

Using a simple DNA strand breakage assay, we detected the production of oxidant species, probably hydroxyl free radicals, in buffered suspensions of crystalline silica at pH 7.4. DNA damage was affected by the presence of oxygen and was accelerated by superoxide dismutase and by hydrogen peroxide. Deferoxamine blocked damage by hydrogen peroxide and silica but accelerated DNA damage by silica alone and by superoxide dismutase and silica. DNA damage was blocked by catalase and by the scavenging agents dimethyl sulfoxide and sodium benzoate. Chemical etching of crystalline silica to remove impurities by treatment of the surface with hydrofluoric acid resulted in markedly diminished DNA damaging ability. Even preparations of crystalline silica previously characterized as highly pure contained trace iron impurities in amounts significant enough to produce oxygen free radicals in aqueous suspension. Both superoxide and Fenton reaction oxidants were produced. We conclude that silica is able to mediate DNA strand breakage in vitro and that this DNA damage may be an important factor in silica toxicity.

Registry of Experimental Cancers of the National Cancer Institute. A database resource for cancer research

The National Cancer Institute established the Registry of Experimental Cancers in March 1970. This registry consists of a permanent collection of pathological materials on spontaneous and induced lesions in laboratory animals that includes histological slides, paraffin blocks, autopsy findings, pathological diagnoses, photographs, and experimental records. The material presently is composed of approximately 60,000 consecutive records and is a valuable resource for researchers interested in tumors and other lesions arising spontaneously or from specific induction protocols in experimental animals. The entire registry database was transferred to an object-oriented database that permits registry staff to write programs for the different data field objects, thus customizing searches and other database functions. Twenty-seven animal species are represented and a total of 6,496 diagnostic entities and 1,106 treatment and control protocols are listed. Archival material may be retrieved for analysis of molecular markers.

Angiofollicular lymphoid hyperplasia (Castleman's disease) in two mice treated with polyoma virus or urethane

Localized angiofollicular hyperplasia, otherwise known as Castleman's disease, is described in the lymph nodes of 2 mice of different strains, one inoculated with polyoma virus at birth and the other given urethane within 24 hr of birth. A plasma cell component in the lesion, suggestive of bone marrow stem cell involvement, was present in the mouse treated with polyoma virus but absent in the mouse given intraperitoneal urethane. Dysregulated interleukin 6 has recently been reported to produce the systemic variety of angiofollicular hyperplasia in mice, but the role of this cytokine in the localized variety described in this report is not known. This lesion appears to be rare in mice, but when present it could easily be missed or overlooked because the typical layering of follicle cells and the relatively large germinal centers seen in humans do not appear prominent in mice. Although there is, obviously, no proof of a causal relationship between the lesion and polyoma virus or urethane, it is suggested that this lesion be searched for in order to estimate its frequency and possible etiologic associations.

Detection and cellular localization of lead by electron probe analysis in the diagnosis of suspected lead poisoning in rhesus monkeys

Lead poisoning of unknown source was diagnosed histologically in 2 rhesus monkeys (Macaca mulatta) by finding acid-fast intranuclear inclusion bodies in the epithelial cells of renal cortical tubules. The presence of lead in the inclusions was determined by scanning electron microscopy/energy dispersive x-ray analysis using sections from paraffin embedded tissues. This observation indicates the usefulness of this technique for the detection and cellular localization of lead in tissues, even from archival material.

Neoplastic transformation of BALB/3T3 cells by metals and the quest for induction of a metastatic phenotype

In the mouse embryo cell line BALB/3T3 Clone A31-1-1, dose-dependent morphologic neoplastic transformation was obtained with NaAsO2, Na2HAsO4, CdCl2, and K2CrO4. Cellular uptake was four fold higher for As3+ than for As5+, and As5- was metabolized to As3+ in cytosol. Cytotoxicity and transformation rates were four fold higher for As3+ than As5+, but when correlated to cellular As burden they were equivalent. As3+ appears responsible for the transforming activity. The foci transformed by metals (or by other carcinogens) gave rise to tumorigenic cell lines (sc sarcomas in nude mice), none of which, however, induced metastases when tested by sc or by iv injection in nude mice. Thus carcinogens change this aneuploid cell line from a preneoplastic stage to the expression of malignant growth but not of metastatic activity. Metastatic and type IV collagenolytic activities can be induced by transfection of the c-Ha-ras oncogene and inhibited by the Ad2-E1a gene (so far shown in other cell types). It remains to be seen whether metal or other carcinogens can induce the nonmetastatic phenotype to become metastatic. The molecular mechanisms of metal carcinogenesis, studied in cell culture systems, in combination with other factors or oncogenes, may reveal the effect of individual metal carcinogens on discrete steps of the complex process of carcinogenesis.

Transformation of human neonatal prostate epithelial cells by strontium phosphate transfection with a plasmid containing SV40 early region genes

Neonatal human prostatic epithelial cells (NP-2s) were transfected by strontium phosphate coprecipitation with a plasmid (pRSV-T) containing the SV40 early region genes. The cells transfected with pRSV-T, but not the sham-transfected controls, formed rapidly growing, multilayered colonies within 2 weeks at a frequency of 1 x 10(-4) in a serum-free medium (P4-8F). In all, 28 colonies of transformed cells were isolated. Three of these have been cultured for a sufficient length of time to show that their growth potentials are well beyond that of the normal progenitor cells (NP-2s). There is also little or no indication of the culture "crisis" commonly seen in SV40-transformed cells in these transfected lines. All contain cytokeratins and SV40 T-antigen as revealed by immunofluorescence, have ultrastructural features of epithelial cells, and are pseudodiploid. None have produced tumors within 1 year after s.c. injection into nude mice. The transformed as well as the parental NP-2s cells require bovine pituitary extract for growth in serum-free medium and are stimulated by transforming growth factor beta 1 (TGF-beta 1) and epidermal growth factor in clonal growth assays. In contrast, a prostatic carcinoma cell line (PC-3) is inhibited by TGF-beta 1. This serum-free system and immortalized transfected clones will be useful for studying the action of putative prostatic carcinogens and tumor-promoting agents.

Morphological and cytokinetic responses of hamster airways to intralaryngeal or intratracheal cannulation with instillation of saline or ferric oxide particles in saline

The morphological and proliferative effects of intratracheal cannulation (ITC) or intralaryngeal cannulation (ILC), with or without the instillation of saline or Fe2O3 particles in saline, were studied in Syrian golden hamsters. Instillation of Fe2O3 in saline at either airway level resulted in a similar distribution of Fe2O3 particles in all lung lobes. ILC produced laryngeal mucosal wounds. ITC produced laryngeal and tracheal mucosal wounds. The cannula-induced wounds were associated with proliferative epithelial lesions. ITC, but not ILC, resulted in significant increases in the mitotic rates (MR, 6-h colchicine blockade) of tracheal epithelial cells at 24 and 32 h postcannulation. Instillation of saline by ITC produced slight increases in intrapulmonary bronchial and bronchiolar MR, but saline given by ILC did not increase MR at any airway level. Instillation of Fe2O3 particles in saline by ITC produced increases in tracheal, intrapulmonary bronchial, and bronchiolar MR. Instillation of Fe2O3 particles in saline by ILC had little effect on tracheal MR, but increased intrapulmonary bronchial and bronchiolar MR. Foci of Fe2O3 particle-laden macrophages were associated with mild bronchiolar-alveolar hyperplasia at the junctions of the terminal bronchioles and the alveolar ducts. The cytokinetic and morphological changes in the intrapulmonary airways were associated with the influx of inflammatory cells in response to Fe2O3 particle deposition. The marked increases in tracheal MR and the localized hyperplastic tracheal epithelial lesions were clearly associated with mechanical wounding from the cannula during ITC. Comparative studies using ILC or ITC instillation techniques allowed further investigations of the important role of tracheal mucosal wounding in the induction of respiratory carcinogenesis, as described in a companion paper (Keenan et al., Cancer Res., 49: 1528-1540, 1989).

Multifactorial hamster respiratory carcinogenesis with interdependent effects of cannula-induced mucosal wounding, saline, ferric oxide, benzo[a]pyrene and N-methyl-N-nitrosourea

The carcinogenic response induced in the respiratory tract of Syrian golden hamsters by repeated intratracheal instillations of benzo[a]pyrene (BP) adsorbed to ferric oxide (Fe2O3) particles suspended in saline, is shown to result from the interactions of these factors and cannula-induced tracheal wounding. Previous acute studies of intratracheal cannulation (ITC) versus intralaryngeal cannulation (ILC) showed that tracheal cell proliferation increased significantly in ITC-induced mucosal wounds. Only mild increases in intrapulmonary cell proliferation were produced by Fe2O3-saline given by ILC or ITC (Keenan et al., Cancer Res., 49: 1521-1527, 1989). The present chronic studies included the following variables: a single instillation by ILC of N-methyl-N-nitrosourea (MNU) at 5 weeks of age; 15 weekly treatments (beginning at 7 weeks of age) by ILC or ITC alone, or with instillations of saline, or Fe2O3-saline, or BP-Fe2O3-saline; and appropriate controls. Repeated ITC-induced tracheal wounds caused persistent tracheal epithelial hyperplasia, metaplasia and/or atrophy and submucosal fibroplasia during the observation period of 22 to 78 weeks of age (the time of terminal sacrifice). Tracheal cancers (in situ or invasive carcinomas) were seen only in those hamsters which had received repeated ITC and one or both carcinogens. The cancer latency was shortest and the incidence of tracheal (50%) and main-stem bronchial (21%) cancers highest in hamsters given MNU and repeated ITC with BP-Fe2O3-saline. Hamsters given carcinogens by ILC (which induced laryngeal but not tracheal wounds) developed proliferative lesions and cancers of the larynx but no tracheobronchial cancers. These data show the singular importance of repeated ITC-induced intratracheal wounding as an enhancing factor in this respiratory carcinogenesis model. The findings suggest that the mechanism of tumor enhancement involves not only changes in target epithelial cell proliferation, but also alterations in normal epithelial-mesenchymal interactions during tracheal regeneration from repeated chronic submucosal inflammation and mesenchymal repair. In the present experimental model, a single dose of MNU at 5 weeks of age, repeated instilled doses of BP, and tracheal mucosal wounding were each found to be important determinants of the carcinogenic response. Additional effects were observed for instilled Fe2O3 particles, and possibly saline. Interplay of all these factors, as well as of genetic, nutritional, and infectious factors, are considered in relation to risk assessment and prevention.

Spontaneous establishment and characterization of mouse keratinocyte cell lines in serum-free medium

Mouse keratinocytes cultures readily develop into established cell lines without undergoing a "crisis" in a newly-developed serum-free medium, LEP/MK2. LEP/MK2 consists of calcium-free MEM with non-essential amino acids supplemented with 8 factors. Two lines, MK1 and MKDC4, have been isolated and have now doubled more than 400 and 200 times respectively. In MK1 cells, Giemsa banding has revealed significant karyotypic changes as early as the 4th passage, leading to a near-tetraploid karyotype with random loss and gain of individual chromosomes. Minute chromosomes, but no stable markers have been observed. After these initial changes, examination of cultures at several passage levels has shown that the karyotype has remained essentially stable. The MKDC4 line, also sub-tetraploid at the 7th passage, had 4 marker chromosomes by the 47th passage. The rapid increase in chromosome number may have contributed to the "immortalization" of these lines. The response of these established keratinocyte lines to growth factors and serum-derived inhibitors changed with increasing passage level. Most notable of these changes were a reduction in the requirement for bovine pituitary extract (an absolute requirement for growth of secondary MK1 cells) and a decreased sensitivity to serum and serum-derived inhibitors, e.g., transforming growth factor-beta. The established lines, like primary and secondary keratinocytes, remain responsive to calcium-induced terminal differentiation and are non-tumorigenic in athymic, nude mice. This serum-free system is suitable for transformation studies with oncogenes and chemical carcinogens.

Cellular uptake and metabolic reduction of pentavalent to trivalent arsenic as determinants of cytotoxicity and morphological transformation

Cytotoxicity, morphological neoplastic transformation, cellular uptake and metabolic reduction were determined in BALB/3T3 Cl A31-1-1 cells for trivalent arsenic (sodium arsenite, As3+) and for pentavalent arsenic (sodium arsenate, As5+). The levels of cellular uptake of 73As-labelled sodium arsenite and arsenate were dose-dependent and highest in the first hour. At equimolar concentration (3 X 10(-6) M), cellular uptake was 4-fold higher for As3+ than for As5+. Cytotoxicity was higher for As3+ than for As5+, but when correlated to total As cell burden it showed no significant difference for the two forms. Morphological transformation focus assays showed transforming activity for both As3+ and As5+, with relative transformation frequencies also of approximately 4:1. Recovery from the cytosol after exposure for 1-24 h was greater than 90% for either form of absorbed As. Exposure to As3+ yielded 100% as As3+ in cytosol, but exposure to As5+ yielded greater than 70% as As3+, showing a high rate of intracellular metabolic reduction. No methylated metabolites were detected by ion-exchange chromatography. After 24-h incubation in cell-free medium, oxidation of As3+ to As5+ occurred up to 30% of the dose, but incubation in the presence of cells lowered the oxidation level to 4%. As5+ was recovered unchanged from cell-free medium (24-h incubation), but in the presence of the cells it yielded up to 5% as As3+ within 24 h and the cumulative release of As3+ by cells exposed to As5+ was dose-dependent. Glutathione depletion by diethylmaleate inhibited reduction of As5+ to As3+ by these cells up to 25% of controls, showing that As5+ reduction is partly dependent on glutathione. These results suggest that As3+ is the form responsible for the cytotoxic and transforming effects, independently of the valence state of the inorganic arsenic in the culture medium.

Secretion of type IV collagenolytic protease and metastatic phenotype: induction by transfection with c-Ha-ras but not c-Ha-ras plus Ad2-E1a

Activated ras oncogene transfection into suitable recipient cells has been shown to induce the metastatic phenotype (Thorgeirsson, et al., Mol. Cell. Biol., 5: 259-262, 1985). We have used this model system to study the correlation of basement membrane collagenolysis with metastatic propensity. The c-Ha-ras oncogene alone, or combined with v-myc, transfected into early passage rat embryo fibroblasts, induce these cells to secrete high levels of type IV collagenolytic metalloproteinase and to concomitantly exhibit a high incidence of spontaneous metastases in nude mice. Cotransfection of c-Ha-ras plus the adenovirus type 2 E1a gene yields cells which are highly tumorigenic but nonmetastatic and fail to produce type IV collagenase. This effect is due to a suppression of collagenase elaboration, not increased production of a collagenase inhibitor, and not decreased production of a collagenase activator. The characteristics of the collagenase are identical to tumor type IV collagenase described previously. The nonmetastatic cells which failed to produce type IV collagenase retain the ability to secrete high levels of plasminogen activator. Transfection with the protooncogenic forms of Ha-ras or mos, or spontaneous transformation of NIH 3T3 cells or chemical transformation of BALB 3T3 cells yields cells which fail to produce collagenase, are tumorigenic, but totally nonmetastatic. These data support a biochemical linkage of type IV collagenase expression with the metastatic phenotype in this rodent system.

Characterization and chromosomal localization of a cDNA encoding brain amyloid of Alzheimer's disease

Four clones were isolated from an adult human brain complementary DNA library with an oligonucleotide probe corresponding to the first 20 amino acids of the beta peptide of brain amyloid from Alzheimer's disease. The open reading frame of the sequenced clone coded for 97 amino acids, including the known amino acid sequence of this polypeptide. The 3.5-kilobase messenger RNA was detected in mammalian brains and human thymus. The gene is highly conserved in evolution and has been mapped to human chromosome 21.

Induction kinetics of mutations at two genetic loci, DNA damage and repair in CHO cells after different exposure times to N-ethyl-N-nitrosourea

Ouabain resistance (ouar) and 6-thioguanine resistance (6-TGr) mutation frequencies were measured in Chinese hamster ovary cells after treatment with N-ethyl-N-nitrosourea (ENU) for varying periods of time. Maximal mutation frequency at the Na+/K+ ATPase gene locus (ouar mutations) was attained within 5 min of exposure, whereas the mutation frequency at the hypoxanthine guanine phosphoribosyltransferase locus (6-TGr mutations) continued to increase up to 60 min, following the theoretical curve for exponential decay of ENU with time. Detection of DNA single strand breaks (ssb) by alkaline elution showed that maximal levels were attained within 5 min of treatment with ENU. Fast repair of DNA ssb occurred early after exposure (greater than 50% repair within 10 min). Analysis of DNA ethylation products by h.p.l.c. showed initially rapid removal of O2-ethylcytosine (25% in the first hour), slow removal of 7-ethylguanine, 3-ethyladenine and 3-ethylguanine and no removal at all of O6-ethylguanine, O4-ethylthymine and ethylphosphotriesters. These time-course studies reveal different target gene responses in the fixation of DNA damage into mutations.

Clonal proliferation of rat tracheal epithelial cells in serum-free medium and their responses to hormones, growth factors and carcinogens

A serum- and feeder cell-free medium has been developed for the proliferation of rat tracheal epithelial (RTE) cells at clonal density. In this medium, RTE cells continue to proliferate for several weeks after cells in serum containing medium on feeder cells have begun to differentiate. The responsiveness of RTE cells to selected hormones and growth factors was determined using a clonal growth assay. The colony-forming efficiency (CFE) of RTE cells was reduced greater than 85% when bovine pituitary extract or bovine serum albumin were deleted from the medium and 45-70% reductions in CFE were observed when insulin, hydrocortisone, epidermal growth factor or cholera toxin were deleted. RTE cells also require high concentrations of Ca2+ (0.8 mM) for maximal clonal proliferation in this medium. The induction by carcinogens of preneoplastic RTE cell variants resistant to serum-mediated squamous differentiation was compared in serum-free medium and in serum-containing medium on feeder cells. N-methyl-N'-nitro-N-nitrosoguanidine was considerably more cytotoxic and effective as a transforming agent on an equivalent dose basis for RTE cells in serum-free medium. In contrast, (+/-)-7B,8-dihydroxy-9,10-epoxy-7,8,9, 10-tetrahydrobenzo[a]pyrene was equally cytotoxic and transforming under both culture conditions. This serum-free culture system for primary RTE cells will be useful in studies on the control of normal epithelial cell proliferation and differentiation by defined growth factors and in studies on the cellular changes involved in carcinogenesis.

Effects of serum and serum-derived factors on growth and differentiation of mouse keratinocytes

Mouse epidermal keratinocytes (MK cells) were grown as replicating subcultures at clonal density, in a serum-free, low calcium basal medium supplemented with seven different growth factors (Bertolero et al., Exp. Cell. Res. 155:64-80, 1984). This serum-free system was used to investigate the activity of fetal bovine serum (FBS) and of serum-derived factors on the growth and differentiation of MK cells. Unfractionated, whole FBS inhibited growth and induced terminal differentiation of normal MK cells. The growth inhibitory activity was considerably reduced by passing whole FBS over a resin (Chelex) to remove Ca2+ and other di- and trivalent cations. It is not known whether this treatment removed other factors. Addition of individual serum components either stimulated or inhibited cell-growth and differentiation. Fetuin, a major alpha-globulin of FBS, and high density lipoprotein strongly inhibited the colony forming efficiency (CFE) of MK cells, whereas bovine serum albumin increased the CFE 4.5-fold and stimulated the growth rate as well. The addition of impure commercial preparations of platelet-derived growth factor inhibited the CFE and induced the morphological features of squamous terminally-differentiating keratinocytes. As reported in other systems, transforming growth factor beta (TGF-beta) inhibited the growth of secondary keratinocytes in a dose-dependent manner. Thus, at least three factors present in FBS inhibited growth whereas others were stimulatory. These observations explain the difficulties in obtaining replicating subcultures of mouse keratinocytes in serum-supplemented media and emphasize the importance of a serum-free system for studies on growth control and carcinogenesis in keratinocytes.

Split-dose exposure to N-methyl-N'-nitro-N-nitrosoguanidine in BALB/3T3 C1 a31-1-1 cells: evidence of DNA repair by alkaline elution without changes in cell survival, mutation and transformation rates

Dose fractionation of a direct-acting chemical carcinogen, the alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), was studied for its concurrent effects on survival, DNA damage and repair, ouabain resistance (Ouar) mutations and neoplastic transformation, in the mouse embryo cell line BALB/3T3 C1A31-1-1. MNNG doses of 0.5, 1 and 2 micrograms/ml were added to the cells either as a single exposure or in two equal fractions separated by 1, 3 or 5 h intervals. No significant difference in cytotoxicity was found when single and split-dose treatments were compared. No recovery from sublethal damage was therefore found in this cell line by split-dose administration of MNNG, although such an effect was found when the same cell line was treated with single and split doses of X-rays. Repair of DNA damage as measured by alkaline elution was studied up to 24 h after a single MNNG exposure (0.5 micrograms/ml). DNA repair was rapid during the first 5 h after treatment and slow thereafter. DNA damage detected after split doses of MNNG at 1 and 5 h intervals was significantly lower than after a corresponding single dose. With both single and split doses, rejoining of single-strand breaks (ssb) was nearly complete after 24 h of repair time. Ouar mutation and neoplastic transformation frequencies were determined for single and split doses of MNNG with the second treatment being given during (1 h) or after (5 h) the period of rapid DNA repair. No significant differences in either effect were detected for dose splitting at any tested dose.

Mouse epidermal keratinocytes. Clonal proliferation and response to hormones and growth factors in serum-free medium

A serum-free medium (LEP-1) has been developed for mouse epidermal keratinocytes. LEP-1 consists of "Ca2+-free" Eagle's MEM with non-essential amino acids and seven added supplements (transferrin, 5 micrograms/ml; epidermal growth factor (EGF), 5 ng/ml; hydrocortisone, 0.5 microM; insulin, 5 micrograms/ml; phosphoethanolamine and ethanolamine, each 50 microM; bovine pituitary extract, 180 micrograms of protein/ml). Although serum-free the culture system was dependent for growth on bovine pituitary extract as the only still undefined supplement. LEP-1 supports sustained multiplication of mouse keratinocytes for 25 or more population doublings. A clonal growth assay was developed to investigate the action of growth factors, hormones and other supplements on keratinocytes. Cells grown in LEP-1 (calcium concentration was 0.03 mM) maintained a high proliferative rate and presented the typical morphology of basal epidermal cells. When the calcium concentration of the medium was raised to 1.0 mM, the cells were triggered to differentiate terminally. The epithelial nature of the cells was demonstrated both by electron microscopy and by immunostaining with anti-keratin antibody. The maturation stage of the keratinocytes was defined by several morphological features during the proliferative phase and in terminally differentiating cultures. This serum-free system supported a useful number of cell divisions while keratinocytes retained the capacity to undergo terminal differentiation when given the appropriate stimulus. It provides, therefore, provides a useful model for investigations on growth, differentiation and malignant transformation of epidermal cells in culture.

Studies on chemically induced neoplastic transformation and mutation in the BALB/3T3 Cl A31-1-1 cell line in relation to the quantitative evaluation of carcinogens

Mutagenesis and neoplastic transformation assays on mammalian cells in culture have been extensively used for quantitative estimates of the activity of carcinogens, in spite of the limitations that such in vitro systems have when compared with in vivo systems for tumor induction. In order to assess the validity of these correlations, a series of studies was undertaken in our laboratory with the BALB/3T3 Cl A31-1-1 mouse embryo cell line. Different carcinogens were found to induce dose-dependent frequencies of transformation, including the direct-acting alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and carcinogens that were metabolically activated by these cells through different pathways (benzo[a]pyrene, 3-methylcholanthrene, aflatoxin B1, and benzidine). Their respective level of activity on a molar basis was different from that obtained in standard Salmonella + S9 mutagenesis tests. Studies currently underway indicate the possibility of lowering the serum content in the medium considerably, thereby reducing a major variable in the assay. Methods were established for the induction of ouabain-resistant (ouar) mutants in these cells. Studies were conducted by applying 30-min MNNG exposures to cells that were synchronized by serum deprivation followed by serum-induced release from growth block. While maximal induction of mutants occurred in the S phase, the transformation frequency remained constant for treatments in G1 and early or late S.(ABSTRACT TRUNCATED AT 250 WORDS)

Temporal dissociation in the exposure times required for maximal induction of cytotoxicity, mutation, and transformation by N-methyl-N'-nitro-N-nitrosoguanidine in the BALB/3T3 ClA31-1-1 cell line

Cytotoxicity, alkali-labile DNA lesions, ouabain resistance mutations, and neoplastic transformation were analyzed concurrently in the BALB/3T3 ClA31 -1-1 cell line treated with the alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) for different exposure times (15, 30, 60, 90, 120, and 240 min; 24, 48, and 72 hr). The half-life of MNNG in complete medium was approximately 70 min, both without cells and with cell numbers as used in the assays for cytotoxicity (2 X 10(2) cells/60-mm dish), transformation (1 X 10(4) cells/dish), and mutation (1 X 10(5) cells/dish). The cytotoxic effect of MNNG (0.5 or 2 micrograms/ml) appeared to be completed after an exposure time between 100 and 200 min. Maximal frequency of ouabain resistance mutations, however, was reached after a much shorter treatment time (30 to 60 min). Detection of DNA damage by alkaline elution analysis showed maximal increase in single-strand breaks already after treatment for 30 min. Exposures for 30 min followed by posttreatment incubation for 30 or 90 min showed active repair of single-strand breaks during these periods, indicative of an even balance between the additional MNNG-induced damage and its repair. Morphological transformation assays, at the same treatment times and concentrations used in the mutation assays, yielded frequency curves that reached their maxima 1 to 3 hr later than did the mutation frequencies. The ratio of transformation to ouabain resistance mutation frequencies was 3.7 for short treatment times (30 to 60 min), while it increased to more than 20 for exposure times of 240 min or longer. The temporal dissociation in the exposure times for maximal induction of mutation and transformation, observed with MNNG in this cell line, supports the hypothesis that a single gene mutational event is not sufficient to account for the full expression of neoplastic transformation.

Evaluation of mixed exposure to carcinogens and correlations of in vivo and in vitro systems

The biological evaluation of air pollutants is an example of the difficulties of evaluating the effects of mixed concurrent exposures to multiple agents, such as combinations of carcinogens with other carcinogens of the same or different chemical class, with incomplete carcinogens and cocarcinogens, with particulate materials and other factors that modify tissue distribution and retention, and with modifiers of metabolic pathways of activation and detoxication. A research approach is outlined to investigate such interactions in a series of biological systems of increasing complexity but closely related to each other in a step-by-step sequence, e.g., bacterial mutagenesis; mammalian cell mutagenesis, toxicity and neoplastic transformation, including embryo cells, fibroblasts and epithelial cells; organ cultures of target epithelia; in vivo animal systems for short-term and long-term studies, including animal models closely comparable to human pathology; observational studies of human pathology and histopathogenesis; experimental studies of corresponding human target tissues using organ and cell culture methods for metabolism, toxicity, mutagenicity and possibly neoplastic cell transformation. Respiratory carcinogenesis models were successfully used for studies of mixed exposures to different carcinogens and cofactors. The role of particulates has been found to be important but needs to be further characterized. Quantitative variations in the response to carcinogens and cofactors among different biological test systems and among different individuals in the human population make quantitative risk estimation very difficult, but studies in a sequence of related biological systems including human tissues indicate the importance of qualitative risk evaluation.

Mutagenesis and morphological transformation by N-methyl-N'-nitro-N-nitrosoguanidine in the BALB/3T3 clone A31-1-1 cell line

Concomitant induction of ouabain resistant mutations and morphological transformation in the BALB/3T3 ClA31-1-1-c mouse embryo cell line were obtained after a 30 min treatment with the direct alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Parameters affecting mutation frequencies were determined. The optimal expression time (48 h) for ouabain resistance was independent from the dose of the carcinogen. A linear dose-response relationship for mutation induction was found after treatment with increasing doses of MNNG. The ratio of malignant transformation to mutation frequencies induced by the short treatment with MNNG was found to be within the same order of magnitude over a four-fold dose range. The development of a mutational assay for ouabain resistance in the BALB/3T3 ClA31-1-1-c cell line makes quantitative comparisons possible between mutation and neoplastic transformation frequencies induced by chemical carcinogens in this single cellular system.

Dose-response studies on neoplastic transformation of BALB/3T3 clone A31-1-1 cells by aflatoxin B1, benzidine, benzo[a]pyrene, 3-methylcholanthrene, and N-methyl-N'-nitro-N-nitrosoguanidine

The BALB/3T3 clone A31-1-1 mouse embryo cell line at passages 7 to 13 was selected for morphologic studies of neoplastic transformation by carcinogens of different chemical classes, in the absence of any added extracellular metabolic activation. Dose-related transforming activity was demonstrated for the carcinogens aflatoxin B1 (AFB) and benzidine (BZ) not previously reported in this system, and was confirmed for benzo[a]pyrene (BP), 3-methylcholanthrene (MCA), and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Spontaneous transformation per cells at risk was low (0.14 type III foci x 10(-4), while chemically induced transformation was 2 to 3 orders of magnitude higher with all compounds. The molar concentration of carcinogens in complete medium, required to induce a transformation frequency of 1.0 type III foci x 10(-3) showed the highest level of activity for BP (0.04 microns), an intermediate level for AFB (0.2 to 1.4 microns), MCA (1.1 micron), and MNNG (2.3 microns), and the lowest level of activity for BZ (30.0 microns). The dose-related induction of morphological transformation in this clone by carcinogens of different classes indicates the potential value of this biological system in quantitative studies of carcinogen combinations, especially at low dose levels.

Identification and definition of chemical carcinogens: review of criteria and research needs

Advances in carcinogenesis research have greatly improved the methods for detection, investigation, and definition of occupational carcinogens. A basis of scientific criteria has been developed for carcinogen identification and evaluation. Research, legislative, and regulatory initiatives in the United States are reviewed. The 1979 Report of the Working Group on Occupational Carcinogenesis, Occupational Cancer Task Force, National Cancer Institute, is added as an appendix. A detailed discussion is given of the 1979 report of the Interagency Regulatory Liaison Group entitled "Scientific bases for identification of potential carcinogens and estimation of risks." Two separate approaches are considered, i.e., the qualitative determination that a substance poses a carcinogenic hazard and the quantitative estimation of risk. The qualitative criteria are reviewed in the present paper. The need for critical data evaluation and the judgmental nature of the process are emphasized. Research needs arising from the analysis of these criteria are discussed. Laboratory research contributions to the identification and characterization of carcinogens are summarized, including development and study of organ target models for carcinogenesis in animals; studies of human target tissues and cells in culture; studies of transformation, initiation, and promotion of epidermal cells in culture; studies of transplacental carcinogenesis; and studies of molecular mechanisms.

The problem of extrapolating from observed carcinogenic effects to estimates of risk for exposed populations

A review is presented of the complex problems involved in the quantitative estimation of cancer risk for populations exposed to carcinogens on the basis of evidence provided either by epidemiologic studies or by experimental data. Strain and species differences among experimental animals and wide interindividual differences among human subjects are discussed. Examples from quantitative laboratory studies on carcinogenic risk factors are discussed to illustrate research approaches in this field, especially in measurements of carcinogen interactions with animal and human target tissues, in human tissue-mediated mutagenesis of mammalian cells, and in studies of combined effects of different carcinogens. The scientific criteria for the quantitative estimation of carcinogenic risk, developed by the Interagency Regulatory Liaison Group, are reviewed, and related research needs are indicated. The implications for regulatory policy, as outlined by the U.S. Regulatory Council, are discussed. Precise and reliable quantitative estimates of cancer risk often appear not to be obtainable and, in such cases, nonquantitative risk assessments have been recognized as appropriate.

Experimental identification of chemical carcinogens, risk evaluation, and animal-to-animal correlations

Experimental methods for the identification of chemical carcinogens have been extensively developed, including animal bioassay methods, animal models for cancer induction at major organ sites, models for the study of the effects of carcinogens in cells and tissues in culture and methods for the study of molecular events (metabolic activation, binding and detoxification of carcinogens; DNA damage and repair; mutagenicity). Current sources of documentation on carcinogenicity data are reviewed. The number of "known carcinogens" will vary considerably, depending on the criteria adopted for accepting evidence of carcinogenicity. CRITERIA FOR THE EVALUATION OF RISKS, BENEFITS, AND TECHNOLOGICAL ALTERNATIVES FOR PUBLIC POLICY ON ENVIRONMENTAL CARCINOGENS ARE REVIEWED AND THE FOLLOWING STEPS DISCUSSED: registration of environmental chemical carcinogens and their uses; risk evaluation (considering sources, adequacy, quality and limits of the evidence; quantitative dose-response extrapolation within the same biological system; and species and model conversion factors); benefits evaluation; analysis of technological alternatives; comparative judgment and decision; open public documentation. The problem of animal-to-human correlations is considered, particularly for respiratory carcinogenesis. A laboratory approach is reviewed which includes: development and study of whole animal models for carcinogenesis, analysis of animal tissue responses to carcinogens in vivo and through in vitro culture methods for morphological and biochemical studies, and development of in vitro culture methods for human target tissues. This approach is aimed at providing an experimentally controlled and quantifiable method for the correlation of animal and human observations in carcinogenesis.