Cancer Letters, 67 (1992) 21 - 25 Elsevier Scientific Publishers Ireland Ltd.
21
Carcinogenesis induced by a single administration of 1,Sdiethylhydrazine in female rats of various ages Vladimir Laboratory
N. Anisimov of Experimental
Tumors,
N.N.
Petrou
Research
Institute
of Oncology, St. Petersburg
(Russia)
(Received 25 February 1992) (Revision received 4 August 1992) (Accepted 13 August 1992)
Summary
Keywords: 1,2_diethylhydrazine;carcinogenesis; aging; rats
Three- or fourteen-month-old female LlO rats were exposed to a single intravenous injection of 1 ,Zdiethylhydrazine (SDEH) at 150 mg/kg of body weight. At the 95th week after carcinogen treatment when the experiment was stopped, 30.7 % and 4.5% of rats from the younger and older groups survived, respectively. Tota! tumor incidences were 68.8% and 84.6 % , respectively, in rats treated with SDEH at the age of 3 or 14 months vs. 18.2% and 34.5% in corresponding young and old controls (P < 0.01). Leukemias, thyroia!adenomas, uterine tumors and mammary malignancies deueloped more frequently in animals exposed to carcinogens than in control groups. No age-related differences in tumor incidence or localization between rats exposed to SDEH at various ages were obserued, but tumors deoeloped earlier in older groups than in younger groups. The results supported the suggestion that the accumulation of initiated cells in some tissues during natural agi,ng is a cause of the agerelated increase in cancer incidence. Correspondence to: V.N. Anisimov, Chief, Laboratory of Experimental Tumors, N.N. Petrov Research Institute of Oncology, 68, Leningadskaya Str., Pesochny-2, St. Petersburg 189646, Russia. 0304-3835/92/$05.00 Printed and Published
0 1992 Elsevier Scientific Publishers in ‘Ireland
Introduction At present there is no consensus on the causes of the age-related increase of tumor incidence in either humans or animals. Some researchers believe that this phenomenon results from an accumulation of cell damage, induced by carcinogenic agents and/or the increase of the time of exposure to the latter, while susceptibility to carcinogens remain unchanged in time [16,22]. Others consider that it is the age-related alterations in the organism itself that promote tumor development [8,9]. The results of available epidemiological observations and numerous experiments, in which animals were exposed to various carcinogens, are rather controversial and do not provide conclusive support for any concepts on the cause of age-related increase in cancer incidence in either humans or animals [2,4,21]. Analysis of the possible background of these contradictions [2,4] suggests that, among many other causes, the problem of choosing both an adequate age for animals at the start of an experiment and adequate age-matched controls is sufficient. However, if tumor latency exceeds the survival time of animals exposed to carcinogens in old age, it could lead to the Ireland Ltd
22
wrong conclusion that older animals are less sensitive to carcinogens. The data on survival of animals subjected to carcinogens at old age, on the one hand and on spontaneous tumor incidence in the period of time preceding the beginning of treatment with the carcinogen, on the other hand, could be taken into consideration during analysis of the results. In our previous experiment the effect of age on selective colon carcinogenesis induced by 1,2_dimethylhydrazine (SDEH) has been evaluated [18]. In the present data on agerelated peculiarities of carcinogenesis induced by other alkyl derivatives of hydrazine, 1,2which has no specific dimethylhydrazine, organotropism [10,l l] are reported. Materials Animals Outbred Department Institute of were kept laboratory libitum.
and Methods
LlO female rats, from the Animal of the N.N. Petrov Research Oncology [7] were used. Animals 6-7 per cage, received standard chow and drank tap water ad
Chemicals
SDEH (chemical purity 99%) was synthesized at the Chemical Faculty of the St. Petersburg State University and stored at - 18OC. Experiment The details of the experiment are given in Fig. 1. SDEH was dissolved in a 0.9% solution of NaCl, neutralized by sodium bicarbonate (pH 7.0) and injected at a dose of 150 mg/kg of body weight under light ether anesthesia for 1 h into the tail vein of 26 rats aged 3 months and of 22 rats aged 14 months. Sixty-eight untreated rats 3 months of aie at the start of the experiment were intact and served as controls. At the 95th week after SDEH injection all carcinogen-treated rats were killed by ether vapor. The control animals were followed up to natural death and in some cases were sacrificed by ether vapor when moribund. The data on survival and tumor pathology for con-
S~EH
,____T-, SDEH a
Control ,____
200
0
I
1
1
J&r)0
600
800 I
1000 AW,
Fig.
1.
The scheme
1290 days
of the experiment.
trol groups were calculated as two sets: lst, ‘young’ control rats, from the age of 3 months to the time of sacrifice of ‘young’ rats exposed to SDEH group, and 2nd, ‘old’ control rats, from the age of 14 months to natural death (Fig. 1). Pathohistological examination All animals that died or were killed were autopsied and their liver, kidney, spleen and all macroscopically abnormal organs were fixed in 10% neutral formalin. Routine histological treatment of 5 - 7-pm sections was followed by staining with haematoxylin and eosin and subsequent microscopic examinations. The tumors were classified according to the IARC classification [23]. Statistics Student’s t-test and Fischer’s exact test were used as appropriate [12]. An IBM PC/AT computer (USA) was employed for statistical processing of data. Results and Discussion Exposure of female rats at the age of 3 or 14 months to a single i.v. administration of SDEH resulted in a significant increase of tumor incidence in comparison to age-matched controls (P < 0.01; Table I). Leukemias, thyroid
23 Table
1. Tumor incidence and localition
in femaie rats exposed to SDEH at various ages. -
Parameters
Age of rats at SDEH exposure: 3 months
Number of rats at start Effective number of rats Number of tumor-bearing rats Total number of tumors Number of malignant tumors Tumor
SDEH
Control”
SDEH
Control
26 16 11(69%) 20 7
68 55 lO(lS%) 11 3
22 13 11(85%)’ 21 7
55 55 19(35%) 25 4
l
site and type:
Pituitary Thyroid Adrenal cortex Ovary
Uterus Mammary gland
Haematopoietic system Lung Liver
14 months
adenoma adenocarcinoma adenoma adenoma fibroma granulesa cell tumor androblastoma adenocarcinoma endometrial polyp sarcoma fibroadenoma adenocarcinoma sarcoma leukemia lymphosarcoma adenoma reticulosarcoma hemangioma
2 4 1 4 2 1 1 -
5 1 1 -
4 1
-
3 3 1 2 3 1 2 1 4 1 -
11 1 1 1 1 7 1 2 -
“The data presented for young control group at the end of the experiment (95th week after treatment with SDEH)_ *The difference with age-matched control is significant, P < 0.01.
adenomas, uterine tumors and malignancies of mammary glands developed more frequently in animals exposed to the carcinogen than in controls. The majority of tumors were localized in endocrine glands and organs of the reproductive system both in younger and older groups. In rats exposed to SDEH at the age of 3 months these turnors were discovered earlier than those in the age-matched control group. Total tumor incidence as well as the incidence of tumors of any tocalization were similar in both age groups exposed to SDEH, however, the latency of tumors in older groups was
shorter than that in younger ones (Fig. 2). SDEH administration inhibited spontaneous tumor development during the 10 months after injection (Fig. 2). Both significant carcinogenic effects in target tissues and the therapeutic effects on spontaneous benign tumors in female rats exposed to a single i.v. administration of N-nitrosomethylurea at the age of 3 or 15 months have been shown elsewhere [3]. Weekly subcutaneous injections of SDEH at doses of 25, 50 or 150 mg/kg for 30 weeks to BD rats resulted in the development of brain,
24
0
100
200
300
400
500
600
700
2. Tumor yield curves in female rats exposed to a single administration of SDEH at the age of 3 or 14 months. Ordinate, number of tumor-bearing rats in percentages; abscissa, time after SDEH injection in days. (1) SDEH at 3 months; (2) control, from the age of 3 months; (3) SDEH at 14 months; (4) control, from the age 14 months.
Fig.
olfactory bulbs, mammary and liver tumors in 96% of cases [lo]. Outbred rats exposed for 6 months to weekly oral gavage of SDEH at a dose of 30 mg/kg developed hepatomas and liver cavernous hemangioma [19]. Single i.v. injections of 50 and 150 mg/kg SDEH were administered to pregnant BD rats on the 15th day of gestation followed by a high incidence of brain, spinal cord or peripheral nervous system tumors in offspring [ll]. Exposure of female LlO rats to a single i.v. administration of SDEH at the age of 3 or 14 months failed to induce tumors of the nervous system, but was followed by a high incidence of neoplasia in organs of endocrine, reproductive and hematopoietic systems, which is in accordance with data on organ distribution of the radioactivity of tritium-labeled SDEH in rats [6,17]. The differences in organotropism of the carcinogenic effect of SDEH administered by
various routes could depend on differences in pharmacodynamics and pharmacokinetics due to the route and schedule of administration of the carcinogen [ 17,191. Available data do not suggest mechanisms for the carcinogenic effect of SDEH, because there is no direct evidence of the alkylating potential of SDEH. Azoethane and azoxyethane, the possible metabolites of SDEH, have been shown to be carcinogenic [ZO], but the mechanism of their carcinogenic effects needs clarification. In our experiments an agerelated decrease in susceptibility to carcinogenesis induced by alkylating agents, including 1,2-dimethylhydrazine, in target organs has been observed [1,3,14,18]. It was correlated with age-related changes in the activity of carcinogen-metabolizing enzymes, DNA synthesis, proliferation rate and, in some cases, with activity of 06-alkylguanine-DNA alkyltransferase in target tissues [ 14,15,18]. At the same time, in 14 - 18-month-old rats exposed to the carcinogen in comparison to 3month-old rats the decrease of the latency of tumors induced by these agents at the target localization was shown [ 1,3,18]. The results of the present experiment are in agreement with these data. The data on the decrease of tumor latency (at the same tumor incidence rate) in older groups exposed to a carcinogen, as compared to those exposed to the same dose of carcinogen at a young age, could be interpreted in the framework of a multistate model of carcinogenesis as a support for the suggestion that the accumulation of initiated cells in some tissues during natural aging is a cause of the age-related increase in cancer incidence [2 - 5,131. References Anisimov, V.N.
(1981)
Carcinogenesis and aging: I. Modi-
fying effect of aging on N-methyl-N-nitrosourea-induced carcinogenesis in female rats. Exp. Pathol., Anisimov, V.N.
and 2. CRC Press, Inc., Boca Raton, Anisimov,
19, 81-
90.
(1987) Carcinogenesis and Aging, Vols. 1
V.N.
(1988)
FL.
Effect of age on dose-response
relationship in carcinogenesis induced by single administration of N-nitosomethylurea Clin. Oncol.,
114, 628-635.
in female rats. J. Cancer Res.
25
4
5
6
7
8
9
10
11
12
13
14
Anisimov, V.N. (1989) Age-related mechanisms of susceptibility to carcinogenesis. Semin. Oncol., 19, lo- 19. Anisimov. V.N. (1991) Effect of factors prolonging life span on carcinogenesis. Ann. N.Y. Acad. Sci., 621, 373-384. Anisimov, V.N., Azarova, M.A., Dmitrievskaya, A.Yu., Likhachev, A.J., Petrov, A.S. and Shaposhnikov, J.D. (1976) Distribution of carcinogenic 3H-dialkylhydrazines in the neuroendocrine system and their antigonadotropic effect in rats. Bull. Exp. Biol. Med., 83, 1473- 1475. Anisimov, V.N., Pliss, G.B., logannsen, M.G., Popovich, I.G., Romanov, K.P., Monakhov, AS. and Averyanova, T.K. (1989) Spontaneous tumors in outbred LlO rats. J. Exp. Clin. Cancer Res., 8, 254-262. Burnet, F.M. (1976) Immunology, Aging and Cancer. Medical Aspects of Mutation and Selection. Freeman & Co, San Francisco. Dilman, V.M. (1985) Ageing and cancer in the light of the ontogenetic ‘model of medicine’. In: Age-Related Factors in Carcinogenesis, pp 21- 34. Editors: A. Likhachev. V. Anisimov and R. Montesano. (IARC Sci. Publ. No. 58), IARC, Lyon. Druckrey, H., Ivankovic, S., Presussmann, R., Landschutz, C.. Stekar, J., Brunner, U. and Schagen, B. (1968) Transplacentar induction of neurogenic malignomas by 1,2-diethyl-hydrazine, azo- and azoxyethane in rats. Experientia, 24, 561- 566. Druckrey, H., Preussmann, R., Matzkies. F. and Ivankovich, S. (1966) Carcinogene Wirkung von 1,2Diathylhydrazin an Ratten. Naturwissenschaften, 53, 557 - 558. Gubler, E.V. (1978) Calculating Methods of Analysis and Recognition of Pathological Processes. Meditsina, Leningrad. Kraupp-Grasl, B., Hubert, W.. Taper, H. and SchulteHermann, R. (1991) Increased susceptibility of aged rats to hepatocarcinogenesis by the peroxisome proliferator nafenopin and the possible involvement of altered liver foci occurring spontaneously. Cancer Res., 51, 666 - 67 1. Likhachev, A.J., Ohshima, H.. Anisimov, V.N., Ovsyannikov, A.I., Revskoy S.Yu., Keefer, L. and Reist, E.J. (1983) Carcinogenesis and aging. II. Modifying effect of
15
16
17
18
19
20
21
22
aging on metabolism of methyl(acetoxymethyl)nitrosamine and its interactions with DNA of various tissues in rats. Carcinogenesis, 4, 967 - 973. Likhachev, A., Zhukovskaya, N., Anisimov, V., Hall, J. and Napalkov, N. (1991) Activity of 06-alkylguanineDNA alkyl transferase in the liver, kidney and white blood cells of rats of different ages. In: Relevance to Human Cancer of N-Nitroso Compounds, Tobacco Smoke and Micotoxins. pp. 407-411. Editors: I.K. O’Neill, J. Chen and H. Bartsch. (IARC Sci. Publ. No. 105). IARC, Lyon Peto, R., Parish, S.E. and Gray, R.G. (1985) There is no such thing as aging and cancer is not related to it. In: AgeRelated Factors in Carcinogenesis, pp. 43 - 53. Editors: A. Likhachev, V. Anisimov and R. Montesano. (IARC Sci. Publ. No. 58), IARC, Lyon. Pozharisski, K.M., Kapustin, Yu.M., Likhachev, A. J. and Shaposhnikov, J.D. (1975) The mechanism of carcinogenic action of 1,2-dimethylhydrazine (SDMH) in rats. Int. J. Cancer, 15, 673-683. Pozharisski, K.M., Prvanova, L.G., Anisimov, V.N. and Klimashevski, V.F. (1982) Effect of aging on colon carcinogenesis in rats. Exp. Onkol. 2, 20-22 Pozharisski, K.M., Shaposhnikov, J.D., Petrov, AS. and Likhachev, A.J. (1976) Distribution and carcinogenic action of 1,2-dimethylhydrazine (SDMH) in rats. Z. Krebsforsch., 87, 67 - 80. Preussmann, R., Druckrey, H., Ivankovic, S. and von Hodenberg, A. (1969) Chemical structure and carcinogenicity of aliphatic hydrazo, azo and azoxy compounds and triazenes, potential in vivo alkylating agents. Ann. N.Y. Acad. Sci., 163, 679-716. Richie, J.P. and Williams, G.M. (1991). Aging and cancer. In: The Potential for Nutritional Modulation of Aging Processes, pp. 51-66. Editors: D.K. Ingram, G.T. Baker and N.W. Shock. Food & Nutriton Press, Inc., Trumbull. Stenback, F., Peto, R. and Shubik, P. (1981) Initiation and promotion
at different ages and doses in 2200
Linear extrapolation
low-dose risk. Br. J. Cancer,
23
Turusov, VS.
mice: Ill.
from high doses may underestimate 44, 24-34.
and Mohr U. (1990)
Pathology of Tumours
in Laboratory Animals, 2nd edn., Vol. 1, Tumours of the Rat. (IARC Sci. Publ. No. 99).
IARC,
Lyon.
21
Carcinogenesis induced by a single administration of 1,Sdiethylhydrazine in female rats of various ages Vladimir Laboratory
N. Anisimov of Experimental
Tumors,
N.N.
Petrou
Research
Institute
of Oncology, St. Petersburg
(Russia)
(Received 25 February 1992) (Revision received 4 August 1992) (Accepted 13 August 1992)
Summary
Keywords: 1,2_diethylhydrazine;carcinogenesis; aging; rats
Three- or fourteen-month-old female LlO rats were exposed to a single intravenous injection of 1 ,Zdiethylhydrazine (SDEH) at 150 mg/kg of body weight. At the 95th week after carcinogen treatment when the experiment was stopped, 30.7 % and 4.5% of rats from the younger and older groups survived, respectively. Tota! tumor incidences were 68.8% and 84.6 % , respectively, in rats treated with SDEH at the age of 3 or 14 months vs. 18.2% and 34.5% in corresponding young and old controls (P < 0.01). Leukemias, thyroia!adenomas, uterine tumors and mammary malignancies deueloped more frequently in animals exposed to carcinogens than in control groups. No age-related differences in tumor incidence or localization between rats exposed to SDEH at various ages were obserued, but tumors deoeloped earlier in older groups than in younger groups. The results supported the suggestion that the accumulation of initiated cells in some tissues during natural agi,ng is a cause of the agerelated increase in cancer incidence. Correspondence to: V.N. Anisimov, Chief, Laboratory of Experimental Tumors, N.N. Petrov Research Institute of Oncology, 68, Leningadskaya Str., Pesochny-2, St. Petersburg 189646, Russia. 0304-3835/92/$05.00 Printed and Published
0 1992 Elsevier Scientific Publishers in ‘Ireland
Introduction At present there is no consensus on the causes of the age-related increase of tumor incidence in either humans or animals. Some researchers believe that this phenomenon results from an accumulation of cell damage, induced by carcinogenic agents and/or the increase of the time of exposure to the latter, while susceptibility to carcinogens remain unchanged in time [16,22]. Others consider that it is the age-related alterations in the organism itself that promote tumor development [8,9]. The results of available epidemiological observations and numerous experiments, in which animals were exposed to various carcinogens, are rather controversial and do not provide conclusive support for any concepts on the cause of age-related increase in cancer incidence in either humans or animals [2,4,21]. Analysis of the possible background of these contradictions [2,4] suggests that, among many other causes, the problem of choosing both an adequate age for animals at the start of an experiment and adequate age-matched controls is sufficient. However, if tumor latency exceeds the survival time of animals exposed to carcinogens in old age, it could lead to the Ireland Ltd
22
wrong conclusion that older animals are less sensitive to carcinogens. The data on survival of animals subjected to carcinogens at old age, on the one hand and on spontaneous tumor incidence in the period of time preceding the beginning of treatment with the carcinogen, on the other hand, could be taken into consideration during analysis of the results. In our previous experiment the effect of age on selective colon carcinogenesis induced by 1,2_dimethylhydrazine (SDEH) has been evaluated [18]. In the present data on agerelated peculiarities of carcinogenesis induced by other alkyl derivatives of hydrazine, 1,2which has no specific dimethylhydrazine, organotropism [10,l l] are reported. Materials Animals Outbred Department Institute of were kept laboratory libitum.
and Methods
LlO female rats, from the Animal of the N.N. Petrov Research Oncology [7] were used. Animals 6-7 per cage, received standard chow and drank tap water ad
Chemicals
SDEH (chemical purity 99%) was synthesized at the Chemical Faculty of the St. Petersburg State University and stored at - 18OC. Experiment The details of the experiment are given in Fig. 1. SDEH was dissolved in a 0.9% solution of NaCl, neutralized by sodium bicarbonate (pH 7.0) and injected at a dose of 150 mg/kg of body weight under light ether anesthesia for 1 h into the tail vein of 26 rats aged 3 months and of 22 rats aged 14 months. Sixty-eight untreated rats 3 months of aie at the start of the experiment were intact and served as controls. At the 95th week after SDEH injection all carcinogen-treated rats were killed by ether vapor. The control animals were followed up to natural death and in some cases were sacrificed by ether vapor when moribund. The data on survival and tumor pathology for con-
S~EH
,____T-, SDEH a
Control ,____
200
0
I
1
1
J&r)0
600
800 I
1000 AW,
Fig.
1.
The scheme
1290 days
of the experiment.
trol groups were calculated as two sets: lst, ‘young’ control rats, from the age of 3 months to the time of sacrifice of ‘young’ rats exposed to SDEH group, and 2nd, ‘old’ control rats, from the age of 14 months to natural death (Fig. 1). Pathohistological examination All animals that died or were killed were autopsied and their liver, kidney, spleen and all macroscopically abnormal organs were fixed in 10% neutral formalin. Routine histological treatment of 5 - 7-pm sections was followed by staining with haematoxylin and eosin and subsequent microscopic examinations. The tumors were classified according to the IARC classification [23]. Statistics Student’s t-test and Fischer’s exact test were used as appropriate [12]. An IBM PC/AT computer (USA) was employed for statistical processing of data. Results and Discussion Exposure of female rats at the age of 3 or 14 months to a single i.v. administration of SDEH resulted in a significant increase of tumor incidence in comparison to age-matched controls (P < 0.01; Table I). Leukemias, thyroid
23 Table
1. Tumor incidence and localition
in femaie rats exposed to SDEH at various ages. -
Parameters
Age of rats at SDEH exposure: 3 months
Number of rats at start Effective number of rats Number of tumor-bearing rats Total number of tumors Number of malignant tumors Tumor
SDEH
Control”
SDEH
Control
26 16 11(69%) 20 7
68 55 lO(lS%) 11 3
22 13 11(85%)’ 21 7
55 55 19(35%) 25 4
l
site and type:
Pituitary Thyroid Adrenal cortex Ovary
Uterus Mammary gland
Haematopoietic system Lung Liver
14 months
adenoma adenocarcinoma adenoma adenoma fibroma granulesa cell tumor androblastoma adenocarcinoma endometrial polyp sarcoma fibroadenoma adenocarcinoma sarcoma leukemia lymphosarcoma adenoma reticulosarcoma hemangioma
2 4 1 4 2 1 1 -
5 1 1 -
4 1
-
3 3 1 2 3 1 2 1 4 1 -
11 1 1 1 1 7 1 2 -
“The data presented for young control group at the end of the experiment (95th week after treatment with SDEH)_ *The difference with age-matched control is significant, P < 0.01.
adenomas, uterine tumors and malignancies of mammary glands developed more frequently in animals exposed to the carcinogen than in controls. The majority of tumors were localized in endocrine glands and organs of the reproductive system both in younger and older groups. In rats exposed to SDEH at the age of 3 months these turnors were discovered earlier than those in the age-matched control group. Total tumor incidence as well as the incidence of tumors of any tocalization were similar in both age groups exposed to SDEH, however, the latency of tumors in older groups was
shorter than that in younger ones (Fig. 2). SDEH administration inhibited spontaneous tumor development during the 10 months after injection (Fig. 2). Both significant carcinogenic effects in target tissues and the therapeutic effects on spontaneous benign tumors in female rats exposed to a single i.v. administration of N-nitrosomethylurea at the age of 3 or 15 months have been shown elsewhere [3]. Weekly subcutaneous injections of SDEH at doses of 25, 50 or 150 mg/kg for 30 weeks to BD rats resulted in the development of brain,
24
0
100
200
300
400
500
600
700
2. Tumor yield curves in female rats exposed to a single administration of SDEH at the age of 3 or 14 months. Ordinate, number of tumor-bearing rats in percentages; abscissa, time after SDEH injection in days. (1) SDEH at 3 months; (2) control, from the age of 3 months; (3) SDEH at 14 months; (4) control, from the age 14 months.
Fig.
olfactory bulbs, mammary and liver tumors in 96% of cases [lo]. Outbred rats exposed for 6 months to weekly oral gavage of SDEH at a dose of 30 mg/kg developed hepatomas and liver cavernous hemangioma [19]. Single i.v. injections of 50 and 150 mg/kg SDEH were administered to pregnant BD rats on the 15th day of gestation followed by a high incidence of brain, spinal cord or peripheral nervous system tumors in offspring [ll]. Exposure of female LlO rats to a single i.v. administration of SDEH at the age of 3 or 14 months failed to induce tumors of the nervous system, but was followed by a high incidence of neoplasia in organs of endocrine, reproductive and hematopoietic systems, which is in accordance with data on organ distribution of the radioactivity of tritium-labeled SDEH in rats [6,17]. The differences in organotropism of the carcinogenic effect of SDEH administered by
various routes could depend on differences in pharmacodynamics and pharmacokinetics due to the route and schedule of administration of the carcinogen [ 17,191. Available data do not suggest mechanisms for the carcinogenic effect of SDEH, because there is no direct evidence of the alkylating potential of SDEH. Azoethane and azoxyethane, the possible metabolites of SDEH, have been shown to be carcinogenic [ZO], but the mechanism of their carcinogenic effects needs clarification. In our experiments an agerelated decrease in susceptibility to carcinogenesis induced by alkylating agents, including 1,2-dimethylhydrazine, in target organs has been observed [1,3,14,18]. It was correlated with age-related changes in the activity of carcinogen-metabolizing enzymes, DNA synthesis, proliferation rate and, in some cases, with activity of 06-alkylguanine-DNA alkyltransferase in target tissues [ 14,15,18]. At the same time, in 14 - 18-month-old rats exposed to the carcinogen in comparison to 3month-old rats the decrease of the latency of tumors induced by these agents at the target localization was shown [ 1,3,18]. The results of the present experiment are in agreement with these data. The data on the decrease of tumor latency (at the same tumor incidence rate) in older groups exposed to a carcinogen, as compared to those exposed to the same dose of carcinogen at a young age, could be interpreted in the framework of a multistate model of carcinogenesis as a support for the suggestion that the accumulation of initiated cells in some tissues during natural aging is a cause of the age-related increase in cancer incidence [2 - 5,131. References Anisimov, V.N.
(1981)
Carcinogenesis and aging: I. Modi-
fying effect of aging on N-methyl-N-nitrosourea-induced carcinogenesis in female rats. Exp. Pathol., Anisimov, V.N.
and 2. CRC Press, Inc., Boca Raton, Anisimov,
19, 81-
90.
(1987) Carcinogenesis and Aging, Vols. 1
V.N.
(1988)
FL.
Effect of age on dose-response
relationship in carcinogenesis induced by single administration of N-nitosomethylurea Clin. Oncol.,
114, 628-635.
in female rats. J. Cancer Res.
25
4
5
6
7
8
9
10
11
12
13
14
Anisimov, V.N. (1989) Age-related mechanisms of susceptibility to carcinogenesis. Semin. Oncol., 19, lo- 19. Anisimov. V.N. (1991) Effect of factors prolonging life span on carcinogenesis. Ann. N.Y. Acad. Sci., 621, 373-384. Anisimov, V.N., Azarova, M.A., Dmitrievskaya, A.Yu., Likhachev, A.J., Petrov, A.S. and Shaposhnikov, J.D. (1976) Distribution of carcinogenic 3H-dialkylhydrazines in the neuroendocrine system and their antigonadotropic effect in rats. Bull. Exp. Biol. Med., 83, 1473- 1475. Anisimov, V.N., Pliss, G.B., logannsen, M.G., Popovich, I.G., Romanov, K.P., Monakhov, AS. and Averyanova, T.K. (1989) Spontaneous tumors in outbred LlO rats. J. Exp. Clin. Cancer Res., 8, 254-262. Burnet, F.M. (1976) Immunology, Aging and Cancer. Medical Aspects of Mutation and Selection. Freeman & Co, San Francisco. Dilman, V.M. (1985) Ageing and cancer in the light of the ontogenetic ‘model of medicine’. In: Age-Related Factors in Carcinogenesis, pp 21- 34. Editors: A. Likhachev. V. Anisimov and R. Montesano. (IARC Sci. Publ. No. 58), IARC, Lyon. Druckrey, H., Ivankovic, S., Presussmann, R., Landschutz, C.. Stekar, J., Brunner, U. and Schagen, B. (1968) Transplacentar induction of neurogenic malignomas by 1,2-diethyl-hydrazine, azo- and azoxyethane in rats. Experientia, 24, 561- 566. Druckrey, H., Preussmann, R., Matzkies. F. and Ivankovich, S. (1966) Carcinogene Wirkung von 1,2Diathylhydrazin an Ratten. Naturwissenschaften, 53, 557 - 558. Gubler, E.V. (1978) Calculating Methods of Analysis and Recognition of Pathological Processes. Meditsina, Leningrad. Kraupp-Grasl, B., Hubert, W.. Taper, H. and SchulteHermann, R. (1991) Increased susceptibility of aged rats to hepatocarcinogenesis by the peroxisome proliferator nafenopin and the possible involvement of altered liver foci occurring spontaneously. Cancer Res., 51, 666 - 67 1. Likhachev, A.J., Ohshima, H.. Anisimov, V.N., Ovsyannikov, A.I., Revskoy S.Yu., Keefer, L. and Reist, E.J. (1983) Carcinogenesis and aging. II. Modifying effect of
15
16
17
18
19
20
21
22
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