Document xzqQoqvwzxOgKQv14nLgX0QxQ

i. o fin Environmental Health Pertpeetives Vol. 21. pp. IS, 1977 Recent Findings on the Carcinogenicity of Chlorinated Olefins by Cesare Maltoni* Data art pratnttd on factors affecting th carcinogenic effect* ofchlorinated olefin*, *nch a* molecular (tructure, concentration, length of treatment, route of administration and animal species, strain, sex, and age. The observation* are based upon carcinogenicity experimental bioassays of vinyl chloride and vinylidene chloride. Early results, which appear to show that some of these factors (particularly species, strain, and sex) act by affecting the metabolism of the tested compounds, are presented, and the need for metabolic charac terization of experimental animals in chemical carcinogenesis is stressed. A project of integrated research On the car cinogenicity of different haiogenated and related compounds has been going on at .the Bologna Insti tute of Oncology and Tumour Center since 1971, and additional programs in this area are under way or under study. Past and ongoing experiments deal with vinyl chloride (VO. vinylidene chloride (VDC). styrene, acrylonitrile, dichloroethane, chlorofluorocarbons, trichloroethylene, carbon tetrachloride, and vinyl idene fluoride. The experiments were performed by the same group in a very standard way, thus providing homogeneous and comparable information. One is now becoming increasingly more aware that a great deal of this information may help not only to learn the effects of the particular com pounds under study and their mechanism of action, but to better understand the basic factors involved in carcinogenesis in general. ministration, animal species, strain, sex, age, and their relevance will be illustrated with VC and VDC. Influence of the Molecular Structure By comparing the carcinogenic activity of VC with that of VDC it can immediately be seen that molecules of very similar structure, such as vinyl chloride and vinylidene chloride, may have very different biological effects (Table I). While VC has been shown to affect many organs of different animal species, i.e., to be a clear multi potential carcinogen, VDC, to the present, has produced oncogenic effects definitively only in one organ (kidney) of a single species (mouse) (1-4). Vinyl Chloride: ch, -- CHCI Factors Affecting Neoplastic Response The present report deals with the results obtained in our studies on the carcinogenicity of VC and VDC, pointing out the major factors affecting the neoplastic response. The factors considered are: molecular structure, concentration, length of treatment, route of ad- Insutute of Oncology and Tumour Center, Bologna, Italy. Vinylidene Chloride: CH, -- CCi, Influence of Concentration. The studies on VC have already confirmed the dose-response relationship effect (1-3). Further more, they show that different concentrations, though within a narrow range of dose, may greatly affect the relative proportion of different types of tumors caused by VC (Table 2). December 1977 1 WW' CMA. 050811 4 Table 1. Effect* of chemical rtructure: comparative oncogenic effect* of VC and VDC oa rodent*. Angiotar- Com- comas of pound Specie Kver vc VDC Ru Mouse Humier (Golden) Rat Mouse Hamster (Chinese) + + 4 Anposarcomat and angiomas of other sees 4 4 <+) Nephrobiasto- mas Adenocarananas of kidney Seba- ctoos Oici' nomas* 44 4 4 Tumors Other cuuneous Turnon Turnon (km of of Hepaturnon hmg team tomas 4 44 44 4 Mammiry arct* nomas 4 4 Forenomach Lymphopapikouas mas and and leukeacamomas mas 4 4 4 <+> `Including Zymbal gland carcinomas. Table 2. Effect* of concentration.* Concen tration of VC. Groups ppm No. ofanimals No. ofanimals with tumors (Sprague-Dawley Liver Nephro- rats) angiomas blastomas 1 200 II 150 111 100 IV None 120 120 120 120 12 3 57 1 10 0 .0 `Exposure by inhalation to VC in air. at 200. 150. 100 ppm. 4 hr/day. f days/week, for 52 weeks. (Results after 143 weeks * end of the experiments.) Influence of the Length of Treatment The schedule of treatment and especially the length of administration, may also greatly affect the neoplastic response in VC carcinogenesis (Table 3). Influence of the Route of Administration The route of administration of VC may signifi cantly vary the type of neoplastic response (Table 4), probably by affecting the distribution of the com pound and its metabolites in the body. Influence of Animal Species The animal species is a very important factor in carcinogenesis. Studies on VC carcinogenesis have shown that the range of VC-dependent tumors greatly varies from species to species, though some, such as liver angiosarcomas, are observed in all species tested (/-J). Recent result with VDC iff) have pointed out that Table 3. EITMt of length of treatment." Croups Concentration of VC. ppm Length of treatment, weeks No. of animals (Sprague-Dawley rats) Animals with liver angiosarcomas No. 1 10.000 II 6.000 III 10.000 IV 6.000 V 10.000 VI 6.000 VII None 52 52 17 17 5 5 -- 60 9 15 60 13 22 60 0 -- 60 1 ' 0.6 120 0 120 0 -- 500 0 -- `Exposure by inhalation to VC in air at 10.000 and 6.000 ppm. 4 hr/day. 5 days/week, for 52. 17, and 5 weeks. (Results after 155 weeks end of the experiments.) Table 4. Effects of route of administration." Groups VC treatment Concentration Route No. of animals (Sprague-Dawley) rats) No. of animals with tumors Liver angiosarcomas Nephroblas- Zymbal gland tomas carcinomas 1 10.000 ppm Inhalation 60 II 6.000 ppm Inhalation 60 111 50 mg/kg Ingestion 80 IV 16.65 mg/kg Ingestion 80 9 5 16 13 4 7 16 2 1 93 2 `Exposure to VC by inhalation in air at different concentrations. 4 hr/day. 5 days/week, for 52 weeks (Group I and H), and by stomach tube in olive oil, at different concentrations. 4-5 days/week (Groups 111 and IV). (Results after 136 weeks ; end of the experiments.) Environmental Health Perspectives uCMA. 050812 b *v- the only type of tumor known at present as defini tively VDC-dependent, the renal adenocarcinoma, is observed in mice but not in the other two tested species, i.e., rats and Chinese hamsters, though rats have been treated with higher doses (Table 5). Influence of Strain Differences have been observed among strain in VC carcinogenesis. As an example, the onset of Zymbal gland car cinomas, following the treatment with this monomer, varies greatly in Sprague-Dawley and Wistar rats, though the spontaneous onset is excep tionally rare even in the most sensitive strain (Table 6). Influence of Sex If VDC had been tested only on female Swiss mice, probably the knowledge of its capacity to produce kidney adenocarcinomas would not have come to light (Table 7). Influence of Age Hepatocarcinogenesis by VC is a striking exam ple of the influence of age in neoplastic response (Table 8). Table 5. Effects of tpedes.* Croups Concentration of VDC, ppm Animafs Species and strain No. Animals with kidney adenocarcinomas No. % 1 200-130 Rats 120 0 -- Sprague-Dawley 11 100 Rats 60 0 -- Sprague-Dawley III 30 Rats 60 0 -- Sprague-Dawely IV 23 Rats 60 0 -- Sprague-Dawley V None Rats 200 0 -- Sprague-Dawley VI 23 Mice 300 23 8.3 Swiss vu None Mice 200 0 -- Swiss 'Exposure by inhalation to VDC in air at different concentrations, 4 hr/day, 4-3 days/week, for 32 weeks. (Results after 98 weeks - ongoing experiments.) Table 6. Effects of strain.* Groups Concentration of VC. ppm Strain Animals (male rats) No. Animals with Zymbal gland carcinomas SD W 1 II III IV V VI Vll VIII IX X Total 10.000 10.000 6,000 6,000 2.500 2,500 300 500 None None Sprague-Dawley Wistar Sprague-Dawley Wistar Sprague-Dawley Wistar Sprague-Dawley Wistar Sprague-Dawley Wistar 30 10 30 30 3 30 30 1 30 30 3 30 30 0 30 17 1 0 0 0 0 1 'Exposure by inhalation to VC in air at different concentrations, 4 hr/day. 4-3 days/week, for 32 weeks. (Results after 143 weeks end of the experiments.) December 1977 3 CMA 050813 ,1 Tabic 7. EITccti of sex.* Groups VDC treatment ppm Animals Animals with kidney (Swiss mice) adenocarcinomas Sex No. No. % 1 25 11 25 111 None IV None male female male female 150 150 190 190 24 16 1 0.7 0-- 0-- Exposure by inhalation to VDC in air at 2J ppm, 4 hr/day, 4-5 days/week, for 52 weeks. (Results after 98 weeks " ongoing expenments.) However it becomes more and more evident that experimental and biological factors affecting the neoplastic response in chemical carcinogenesis as well as other possible toxic effects may act by de termining the metabolic pathway of the tested com pounds. Recent research has shown that VC and VDC do not act per se, but through products of metabolic transformation, probably epoxy-derivatives. Experiments performed in our laboratories ap pear to indicate that species, strain and sex greatly Table 8. Effect* of age.* Groups 1 II 111 IV V VC treatment, ppm 10.000 6,000 None 10.000 6,000 Age 13 weeks 13 weeks 13 weeks 1 day 1 day No. of animals Total Survivors 120 16 120 15 249 55 46 8 43 5 No. of liver tumors Angiosarcomas Hepatomas --1 ---- ---- 10 15 10 13 incidence of hepatic tumors (angiosarcomas and hepatomas) among Spiague-Dawley rats, exposed to. VC in air at 10,000 and 6,000 ppm, 4 hr/day, 5 days/week, for 5 weeks, at ages 13 weeks or I day. (Results after 135 weeks _ end of the experiments). Explanation of Role of Factors How-the experimental and biological factors which have been considered and other possible ones determine the neoplastic response, is a matter of hypothesis and inference, more or less based upon experimental evidence. To explain the influence of some biological parameters (such as species and strain), one has first to consider the genetic basis of responsive ness of different tissues and organs in various types of animals, often expressing itself in the onset of spontaneous neoplasia in the same tissue and organ. affect the production of active metabolites, which in turn are responsible for toxic effects of VDC (Table 9) (5). The major regressive and necrotic changes pro duced by intoxication are found in liver and kid neys. In the case of Sprague-Dawley rats and Swiss mice there is a clear cut parallelism between toxic and carcinogenic effects of VDC (in relation to species and sex). ' As far as Balb/c, C3H, and C57BL mice are con cerned, we are now undertaking long-term studies to assess if there is the same parallelism (in relation to strain). Table 9. Comparative acute toxic effect* of vinylidene chloride (VDC), at 200 ppm In air, 4 hr/day for 2 days. Species Rats Mice Strain SpragueDawley Swiss Balb/c C3H C57BL Sex No. . No. of survivors/day Performance 1 2 3 4 5 6 7 8 9 Weight* status1 M 60 60 60 60 60 59 59 59 59 59 F 60 60 60 60 60 60 60 60 60 60 M 60 31 26 24 20 16 11 10 10 9 t- 60 60 60 60 60 60 60 60 60 60 M 30 25 12 6 6 6 6 6 6 6 H 30 30 30 30 30 30 30 30 30 30 M 30 30 25 17 17 15 14 14 14 13 F 30 22 19 19 19 19 19 19 19 19 M 30 28 25 23 23 23 23 23 23 23 F 30 30 30 30 30 30 30 30 30 30 <+) f -- - (+) + + -<+) +-K+) -- ++ +(+) +<+) Code'. -, decrease; _. no change; +, enhancement (on 5th day). Code: no effect; +, slight effect; + + , moderate effect; + + + , marked effect; + + + + , profound effect. Recovery has been observed on nearly ah the survivors on the 5th day. 4 Environmental Health Perspectives i i CMA. 050814 V it be confirmed, we do believe that there new routes for establishing priorities for erm carcinogenicity bioassays, for choosing oest experimental animal models and for the iderstanding of mechanism of action of many or ganic carcinogens. REFERENCES I. Maltoni. C.. and Lefemine. G. Le potenzialita dei saggi spcrimentali nella prediziont dei rischt oncogtm ambienlali. Un esempio; it clorum di vinile. Atti Aecad. Nazi. Lined, Rend. [SJ56: (1974). 2 Maltoni, C.. and Lefemine. G. Carcinogenicity bioastays of vinyl chloride: current remits. In: Toxicity of Vinyl Chloride-Polyvinyl Chloride. I. J. Selikoff and E. C. Ham monds, Eds., New York Academy of Sciences, I97S. pp. 195-218. 3. Maltoni. C., et a). La cancerogenesi ambientale e profes sional: nuove prospettive alia luce della cancerogenesi da cloruro di vinile. Ospedali Viu I (3-6): 4 (1974), 4. Maltoni, C.. et al. Carcinogenicity bioassays of vinylidene chloride. Research plan and eariy results. Med. Lavoro. in press. 3. Maltoni. C.. Maioli, P,. and Patella, V. The effect of animal species, strain and sex on acute toxicity of vinylidene chloride. Med. Lavoro in press. December 1977 CHA 050815