Involvement of angiogenesis in weight-loss in tumor-bearing and diet-restricted animals

The body's weight loss mechanism while in a tumor-bearing state is still unclear. In this study, we investigated expressions of angiogenic factors in the adipose tissue of tumor-bearing and diet-restricted rabbits evaluating the differences between the two groups. We postulated that low nutrition induced vasculogenesis to transport nutrition in the adipose tissues of diet-restricted rabbits, unlike in tumor-bearing rabbits, and that vascular endothelial growth factor (VEGF) and platelet-derived endothelial cell growth factor (PD-ECGF) were related to angiogenesis of the adipose tissues. Although we investigated the expressions of VEGF and PD-ECGF immunohistochemically in tumor-bearing and diet-restricted rabbits, there was no significant difference between the two groups. Whether angiogenesis of the adipose tissue in the diet-restricted animals may be observed during the nutritional recovery period should be investigated.

Senescent fibroblasts promote epithelial cell growth and tumorigenesis: a link between cancer and aging

Mammalian cells can respond to damage or stress by entering a state of arrested growth and altered function termed cellular senescence. Several lines of evidence suggest that the senescence response suppresses tumorigenesis. Cellular senescence is also thought to contribute to aging, but the mechanism is not well understood. We show that senescent human fibroblasts stimulate premalignant and malignant, but not normal, epithelial cells to proliferate in culture and form tumors in mice. In culture, the growth stimulation was evident when senescent cells comprised only 10% of the fibroblast population and was equally robust whether senescence was induced by replicative exhaustion, oncogenic RAS, p14(ARF), or hydrogen peroxide. Moreover, it was due at least in part to soluble and insoluble factors secreted by senescent cells. In mice, senescent, much more than presenescent, fibroblasts caused premalignant and malignant epithelial cells to form tumors. Our findings suggest that, although cellular senescence suppresses tumorigenesis early in life, it may promote cancer in aged organisms, suggesting it is an example of evolutionary antagonistic pleiotropy.

Simultaneous administration of glucose and hyperoxic gas achieves greater improvement in tumor oxygenation than hyperoxic gas alone

PURPOSE

To test the feasibility of hyperglycemic reduction of oxygen consumption combined with oxygen breathing (O(2)), to improve tumor oxygenation.

METHODS AND MATERIALS

Fischer-344 rats bearing 1 cm R3230Ac flank tumors were anesthetized with Nembutal. Mean arterial pressure, heart rate, tumor blood flow ([TBF], laser Doppler flowmetry), pH, and pO(2) were measured before, during, and after glucose (1 or 4 g/kg) and/or O(2).

RESULTS

Mean arterial pressure and heart rate were unaffected by treatment. Glucose at 1 g/kg yielded maximum blood glucose of 400 mg/dL, no change in TBF, reduced tumor pH (0.17 unit), and 3 mm Hg pO(2) rise. Glucose at 4 g/kg yielded maximum blood glucose of 900 mg/dL, pH drop of 0.6 unit, no pO(2) change, and reduced TBF (31%). Oxygen tension increased by 5 mm Hg with O(2). Glucose (1 g/Kg) + O(2) yielded the largest change in pO(2) (27 mm Hg); this is highly significant relative to baseline or either treatment alone. The effect was positively correlated with baseline pO(2), but 6 of 7 experiments with baseline pO(2) < 10 mm Hg rose above 10 mm Hg after combined treatment.

CONCLUSION

We demonstrated the feasibility of combining hyperglycemia with O(2) to improve tumor oxygenation. However, some cell lines are not susceptible to the Crabtree effect, and the magnitude is dependent on baseline pO(2). Additional or alternative manipulations may be necessary to achieve more uniform improvement in pO(2).

Inhibition of both paracrine and autocrine VEGF/ VEGFR-2 signaling pathways is essential to induce long-term remission of xenotransplanted human leukemias

Antiangiogenic agents block the effects of tumor-derived angiogenic factors (paracrine factors), such as vascular endothelial growth factor (VEGF), on endothelial cells (EC), inhibiting the growth of solid tumors. However, whether inhibition of angiogenesis also may play a role in liquid tumors is not well established. We recently have shown that certain leukemias not only produce VEGF but also selectively express functional VEGF receptors (VEGFRs), such as VEGFR-2 (Flk-1, KDR) and VEGFR1 (Flt1), resulting in the generation of an autocrine loop. Here, we examined the relative contribution of paracrine (EC-dependent) and autocrine (EC-independent) VEGF/VEGFR signaling pathways, by using a human leukemia model, where autocrine and paracrine VEGF/VEGFR loops could be selectively inhibited by neutralizing mAbs specific for murine EC (paracrine pathway) or human tumor (autocrine) VEGFRs. Blocking either the paracrine or the autocrine VEGF/VEGFR-2 pathway delayed leukemic growth and engraftment in vivo, but failed to cure inoculated mice. Long-term remission with no evidence of disease was achieved only if mice were treated with mAbs against both murine and human VEGFR-2, whereas mAbs against human or murine VEGFR-1 had no effect on mice survival. Therefore, effective antiangiogenic therapies to treat VEGF-producing, VEGFR-expressing leukemias may require blocking both paracrine and autocrine VEGF/VEGFR-2 angiogenic loops to achieve remission and long-term cure.

Intravascular HBO(2) saturations, perfusion and hypoxia in spontaneous and transplanted tumor models

Clinical trials utilizing strategies to manipulate tumor oxygenation, blood flow and angiogenesis are under way, although limited quantitative information exists regarding basic tumor pathophysiology. The current study utilized murine KHT fibrosarcomas, spontaneous mammary carcinomas and first-generation spontaneous transplants to examine heterogeneity in vascular structure and function, to relate these changes to the distribution of tumor hypoxia and to determine whether fundamental relationships among the different pathophysiological parameters exist. Three methods were included: (i) immunohistochemical staining of anatomical and perfused blood vessels, (ii) cryospectrophotometric measurement of intravascular oxyhemoglobin saturations and (iii) fluorescent detection of the EF5 hypoxic marker. While a distinct pattern of decreasing oxygenation with increasing distance from the tumor surface was observed for KHT tumors, striking intertumor variability was found in both spontaneous and first-generation transplants, with a reduced dependence on tumor volume. EF5 hypoxic marker uptake was also much more heterogeneous among individual spontaneous and first-generation tumors compared to KHT. Although mammary carcinomas demonstrated fewer anatomical blood vessels than fibrosarcomas, the proportion of perfused vessels was substantially reduced in KHT tumors, especially at larger tumor volumes. Vascular morphology, tissue histological appearance and pathophysiological parameters differed substantially between KHT tumors and both spontaneous and first-generation tumors. Such differences in vascular structure and function are also likely to correlate with altered response to therapies targeted to the vascular system. Finally, spontaneous differentiation status, tumor morphology, vascular configuration and function were well preserved in first-generation transplanted tumors, suggesting a close relationship between vascular development and function in early-generation transplants and spontaneous tumor models.

Modulation of radioprotective effects of respiratory hypoxia by changing the duration of hypoxia before irradiation and by combining hypoxia and administration of hemopoiesis-stimulating agents

AIM

Analysis of radioprotective effect of respiratory hypoxia on hemopoietic tissue and enhancement of this effect by hemopoietic activation.

MATERIAL AND METHODS

In mice breathing hypoxic gas mixture during total body gamma irradiation the recovery of pluripotent and committed granulocyte-macrophage progenitor cells and animal lethality were determined.

RESULTS

In mice forced to breathe 10% O2 and 8% O2 during irradiation, the oxygen tension in the spleen decreased to 40% and 20%, respectively, of control values. Hypoxia mitigated the lethal effect of gamma-rays and improved the recovery of hemopoiesis in compartments of pluripotent and committed progenitor cells. Enhancement of the proliferative activity in hemopoietic tissue by a cytokine (rmGM-CSF) or an immunomodulator (dextran sulfate) increased the effect of hypoxic radioprotection, while elimination of proliferative cells by hydroxyurea decreased the radioprotective effect. Adaptation of experimental animals to hypoxic conditions was found to reduce the radioprotective effect without influencing tissue partial oxygen pressure lowered by hypoxic conditions.

CONCLUSION

The data presented confirm the radioprotective effect of 10% and 8% O2 respiratory hypoxia on hemopoiesis. These findings may represent a way out for further experimental and clinical research aimed at considering differential protection of various tissues by hypoxia.

Intratumoral spread and increased efficacy of a p53-VP22 fusion protein expressed by a recombinant adenovirus

In vitro experiments have demonstrated intercellular trafficking of the VP22 tegument protein of herpes simplex virus type 1 from infected cells to neighboring cells, which internalize VP22 and transport it to the nucleus. VP22 also can mediate intercellular transport of fusion proteins, providing a strategy for increasing the distribution of therapeutic proteins in gene therapy. Intercellular trafficking of the p53 tumor suppressor protein was demonstrated in vitro using a plasmid expressing full-length p53 fused in-frame to full-length VP22. The p53-VP22 chimeric protein induced apoptosis both in transfected tumor cells and in neighboring cells, resulting in a widespread cytotoxic effect. To evaluate the anti-tumor activity of p53-VP22 in vivo, we constructed recombinant adenoviruses expressing either wild-type p53 (FTCB) or a p53-VP22 fusion protein (FVCB) and compared their effects in p53-resistant tumor cells. In vitro, treatment of tumor cells with FVCB resulted in enhanced p53-specific apoptosis compared to treatment with equivalent doses of FTCB. However, in normal cells there was no difference in the dose-related cytotoxicity of FVCB compared to that of FTCB. In vivo, treatment of established tumors with FVCB was more effective than equivalent doses of FTCB. The dose-response curve to FVCB was flatter than that to FTCB; maximal antitumor responses could be achieved using FVCB at doses 1 log lower than those obtained with FTCB. Increased antitumor efficacy was correlated with increased distribution of p53 protein in FVCB-treated tumors. This study is the first demonstration that VP22 can enhance the in vivo distribution of therapeutic proteins and improve efficacy in gene therapy.

Expression of apoptosis regulatory proteins in the skeletal muscle of tumor-bearing rabbits compared with diet-restricted rabbits

The mechanism of body weight loss in the tumor-bearing state is still unclear. In this study, we investigated expressions of apoptosis regulatory proteins in the skeletal muscle of tumor-bearing and diet-restricted rabbits, and tried to evaluate the differences between the two groups. The apoptotic index (AI) in the tumor-bearing group was 28.1+/-2.84 on day 10. By day 20, many more apoptotic cells were found (AI: 40.5+/-3.20), but then after day 20 their numbers gradually decreased (AI: 9.67+/-2.22 on day 30 and 0.93+/-0.96 on day 40). By contrast, no apoptotic cells were detected in the diet-restricted group at any of the times examined. Bcl-2 immunoreactivity was either not detected at all or only weakly observed in both groups. By contrast, Bax expression increased gradually after implantation in the tumor-bearing group. Bax expression in skeletal muscle cell was graded (moderate) 10 days after tumor implantation, and (high) by day 20, in 2 of the 5 tumor-bearing rabbits. After day 20, however, Bax immunoreactivity decreased continuously in the tumor-bearing group. By contrast, hardly any Bax-immuno-positive cells were detected in the diet-restricted group. These results suggest that loss of body weight in the tumor-bearing group is different from that in the diet-restricted group, and is related to apoptosis of skeletal muscles.

Selective inactivation of p53 facilitates mouse epithelial tumor progression without chromosomal instability

We examined the selective pressure for, and the impact of, p53 inactivation during epithelial tumor evolution in a transgenic brain tumor model. In TgT(121) mice, cell-specific inactivation of the pRb pathway in brain choroid plexus epithelium initiates tumorigenesis and induces p53-dependent apoptosis. We previously showed that p53 deficiency accelerates tumor growth due to diminished apoptosis. Here we show that in a p53(+/-) background, slow-growing dysplastic tissue undergoes clonal progression to solid angiogenic tumors in all animals. p53 is inactivated in all progressed tumors, with loss of the wild-type allele occurring in 90% of tumors. Moreover, similar progression occurs in 38% of TgT(121)p53(+/+) mice, also with loss of at least one p53 allele and inactivation of p53. Thus, the selective pressure for p53 inactivation, likely based on its apoptotic function, is high. Yet, in all cases, p53 inactivation correlates with progression beyond apoptosis reduction, from dysplasia to solid vascularized tumors. Hence, p53 suppresses tumor progression in this tissue by multiple mechanisms. Previous studies of fibroblasts and hematopoietic cells show that p53 deficiency can be associated with chromosomal instability, a mechanism that may drive tumor progression. To determine whether genomic gains or losses are present in tumors that progress in the absence of p53, we performed comparative genomic hybridization analysis. Surprisingly, the only detectable chromosomal imbalance was partial or complete loss of chromosome 11, which harbors the p53 gene and is thus the selected event. Flow cytometry confirmed that the majority of tumor cells were diploid. These studies indicate that loss of p53 function is frequent under natural selective pressures and furthermore that p53 loss can facilitate epithelial tumor progression by a mechanism in addition to apoptosis reduction and distinct from chromosomal instability.

Experimental animal models in pancreatic carcinogenesis: lessons for human pancreatic cancer

The silent course of pancreatic cancer and its explosive fatal outcome have hindered studies of tumor histogenesis and the identification of early biochemical and genetic alterations that could help to diagnose the disease at a curable stage and develop therapeutic strategies. Experimental animal models provide important tools to assess risk factors, as well as preventive and therapeutic possibilities. Although several pancreatic cancer models presently exist, only models that closely resemble human tumors in morphological, clinical, and biological aspects present useful media for preclinical studies. Because an estimated 70% of human tumors are induced by carcinogens and because a significant association has been found between cigarette smoking and pancreatic cancer, chemically induced models are of particular value. Moreover, in such models the etiology, modifying factors, effects of diets, and naturally occurring products can be studied and early diagnostic, preventive, and therapeutic possibilities sought out. Many of the existing models are described in this review, and the advantages and shortcomings of each model and their clinical implications are discussed.

Journey of the iodide transporter NIS: from its molecular identification to its clinical role in cancer

The Na+/I- symporter (NIS) is an intrinsic plasma membrane protein that mediates the active transport of I- in the thyroid, lactating mammary gland, stomach and salivary glands. The presence of NIS in the thyroid is exploited in diagnostic scintigraphic imaging and radioiodide therapy in thyroid cancer. The continued rapid progress in NIS research (aimed at the elucidation of the Na+-dependent I- transport mechanism, the analysis of NIS structure-function relations and the study of the tissue-specific regulation of NIS at all levels), holds potentially far-reaching medical applications beyond thyroid disease, in breast cancer and malignancies in other tissues.

Seasonal rhythms of 6-sulphatoxymelatonin (aMT6s) excretion in female rats are abolished by growth of malignant tumors

The effect of development and growth of malignant tumors on pineal melatonin production was studied in two different hormone-dependent tumor systems in female rats. Urinary excretion of 6-sulphatoxymelatonin (aMT6s), the metabolic end product of melatonin, which parallels its production, was determined by radioimmunoassay at fortnightly or monthly intervals over the period of 1 year in female F344 Fischer rats bearing chemically-induced mammary carcinomas and in BDII/Han rats with spontaneous endometrial carcinomas. Untreated Fischer rats and BDII/Han rats in which tumor growth was suppressed by treatment with a progestin served as controls. Based on the cosinor analysis, animals without tumors showed significant seasonal rhythms of aMT6s excretion, with peaks in August (Fischer rats) and in May (BDII/Han rats). In contrast, such rhythms were absent in animals with developing and manifest tumors. It is concluded that animals kept under constant environmental conditions still show seasonal rhythms of pineal activity. Tumor development and growth affect pineal activity leading to disturbance of these rhythms.

Diesters of glycosylglycerols active in cancer chemoprevention

Enzymatic transesterification, mediated by Pseudomonas cepacia lipase (lipase PS), led to the pure 1,6'-diacylderivatives of 2-O-beta-D-glucosyl-sn-glycerol and 2-O-beta-D-galactosyl-sn-glycerol, the acyl chains being derived from short-medium length fatty acids. A study of the in vitro inhibitory effects of these diacylderivatives on Epstein-Barr virus early antigen activation induced by the tumour promoter 12-O-tetradecanoylphorbol-13-acetate revealed that maximum activity was reached for the hexanoyl chain and that the introduction of a second acyl chain did not significantly modify the inhibitory potential referring to the corresponding 1- or 6'-monoesters.

Vitamin D and cancer: effects of 1,25(OH)2D3 and its analogs on growth control and tumorigenesis

Today, it is well established that besides playing a crucial role in the establishment and maintenance of the calcium homeostasis in the body, the active form of vitamin D, 1,25(OH)2D3, also acts an effective regulator of cell growth and differentiation in a number of different cell types, including cancer cells. This has led to an increased interest in using 1,25(OH)2D3 in the treatment or prevention of cancer patients and to a substantial number of studies investigating the effect of 1,25(OH)2D3 on cancer cells. The results are encouraging, but clearly demonstrate that the therapeutic window of 1,25(OH)2D3 is extremely narrow due to the calcemic adverse effects of this compound. Much effort has consequently been directed into identifying vitamin D analogs with potent cell regulatory effects but with weaker effects on the calcium metabolism than those of 1,25(OH)2D3. In an attempt to clarify the mechanisms implicated in the cell regulatory effects of 1,25(OH)2D3 and eventually facilitate the process of developing new specific vitamin D analogs, numerous investigations have been carried out with 1,25(OH)2D3 and its analogs. The present review will focus on the results obtained in these studies and describe some of the synthetic analogs, which have shown to be of particular interest in relation to cancer.

In vivo molecular target assessment of matrix metalloproteinase inhibition

A number of different matrix metalloproteinase (MMP) inhibitors have been developed as cytostatic and anti-angiogenic agents and are currently in clinical testing. One major hurdle in assessing the efficacy of such drugs has been the inability to sense or image anti-proteinase activity directly and non-invasively in vivo. We show here that novel, biocompatible near-infrared fluorogenic MMP substrates can be used as activatable reporter probes to sense MMP activity in intact tumors in nude mice. Moreover, we show for the first time that the effect of MMP inhibition can be directly imaged using this approach within hours after initiation of treatment using the potent MMP inhibitor, prinomastat (AG3340). The developed probes, together with novel near-infrared fluorescence imaging technology will enable the detailed analysis of a number of proteinases critical for advancing the therapeutic use of clinical proteinase inhibitors.

Selenium and signal transduction: roads to cell death and anti-tumour activity

Accumulated evidence from prospective studies, intervention trials and studies on animal models of cancer have suggested a strong inverse correlation between selenium intake and cancer incidence. Several putative mechanisms have been suggested to mediate the chemopreventive activities of selenium: of these, the inhibition of cellular proliferation and the induction of apoptosis are particularly attractive. The mitogen activated protein kinase (MAPK) pathways are known to be important regulators of cell death and our recent work has focused on the involvement of these pathways in selenium-induced apoptosis in primary cultures of oral cancers and corresponding normal mucosa derived from biopsy material. Using this system, the oral carcinoma cells were found to have enhanced sensitivity to apoptosis when treated with certain selenium compounds compared to normal oral mucosa. Induction of Fas ligand was associated with selenium-induced apoptosis. Signal transduction studies suggests that selenium induces several changes in the MAPK signalling pathways but functional intervention/inhibitor studies indicate that activation of the JNK pathway seems to be most important.

[The effect of melatonin on the indices of biological age, on longevity and on the development of spontaneous tumors in mice]

Fifty female CBA mice were given melatonin with drinking water (20 mg/l) for 5 consecutive days monthly, beginning from the age of 6 months, until natural death. Another 50 intact mice were used as controls. Melatonin failed to significantly influence body weight or food consumption. Age-related switching-off of estrus function was delayed, body temperature decreased. Somewhat decreased motor activity did not affect physical one or endurance. Increase in life span led to higher spontaneous tumor incidence. Another experiment using 20 animals of the same line showed melatonin to inhibit free-radical processes. A conclusion was drawn that caution should be exercised before melatonin is recommended for long-term administration as a geroprotector.

Exercise and the immune system: regulation, integration, and adaptation

Stress-induced immunological reactions to exercise have stimulated much research into stress immunology and neuroimmunology. It is suggested that exercise can be employed as a model of temporary immunosuppression that occurs after severe physical stress. The exercise-stress model can be easily manipulated experimentally and allows for the study of interactions between the nervous, the endocrine, and the immune systems. This review focuses on mechanisms underlying exercise-induced immune changes such as neuroendocrinological factors including catecholamines, growth hormone, cortisol, beta-endorphin, and sex steroids. The contribution of a metabolic link between skeletal muscles and the lymphoid system is also reviewed. The mechanisms of exercise-associated muscle damage and the initiation of the inflammatory cytokine cascade are discussed. Given that exercise modulates the immune system in healthy individuals, considerations of the clinical ramifications of exercise in the prevention of diseases for which the immune system has a role is of importance. Accordingly, drawing on the experimental, clinical, and epidemiological literature, we address the interactions between exercise and infectious diseases as well as exercise and neoplasia within the context of both aging and nutrition.

Tumor-specific, replication-competent adenovirus vectors overexpressing the adenovirus death protein

We have constructed two novel adenovirus (Ad) replication-competent vectors, named KD1 and KD3, that may have use in anticancer therapy. The vectors have two key features. First, they markedly overexpress the Ad death protein (ADP), an Ad nuclear membrane glycoprotein required at late stages of infection for efficient cell lysis and release of Ad from cells. Overexpression of ADP was achieved by deleting the E3 region and reinserting the adp gene. Because ADP is overexpressed, KD1 and KD3 are expected to spread more rapidly and effectively through tumors. Second, KD1 and KD3 have two E1A mutations (from the mutant dl1101/1107) that prevent efficient replication in nondividing cells but allow replication in dividing cancer cells. These E1A mutations preclude binding of E1A proteins to p300 and pRB. As a result, the virus should not be able to drive cells from G(0) to S phase and therefore should not be able to replicate in normal tissues. We show that KD1 and KD3 do not replicate well in quiescent HEL-299 cells or in primary human bronchial epithelial cells, small airway epithelial cells, or endothelial cells; however, they replicate well in proliferating HEL-299 cells and human A549 lung carcinoma cells. In cultured A549 cells, KD1 and KD3 lyse cells and spread from cell to cell more rapidly than their control virus, dl1101/1107, or wild-type Ad. They are also more efficient than dl1101/1107 or wild-type Ad in complementing the spread from cell to cell of an E1(-) E3(-) replication-defective vector expressing beta-galactosidase. A549 cells form rapidly growing solid tumors when injected into the hind flanks of immunodeficient nude mice; however, when A549 cells were infected with 10(-4) PFU of KD3/cell prior to injection into mice, tumor formation was nearly completely suppressed. When established A549 tumors in nude mice were examined, tumors injected with buffer grew 13.3-fold over 5 weeks, tumors injected with dl1101/1107 grew 8-fold, and tumors injected with KD1 or KD3 grew 2.6-fold. Hep 3B tumors injected with buffer grew 12-fold over 3.5 weeks, whereas tumors injected with KD1 or KD3 grew 4-fold. We conclude that KD1 and KD3 show promise as anticancer therapeutics.

The role of polypeptide growth factors in human carcinomas: new targets for a novel pharmacological approach

The processes of cellular proliferation and progressive acquisition of a specialized phenotype show a high degree of coordination. In particular, these complex signaling networks mediating cell growth, differentiation, migration, and apoptosis are regulated in part by polypeptide growth factors that can act, by autocrine and/or paracrine mechanisms of action, as positive or negative modulators. Because these growth factors are unable to cross the hydrophobic cell membrane, they exert their effects via binding to cell surface receptors, most of which possess intrinsic tyrosine kinase activity. Owing to the interaction of polypeptide growth factors with their specific transmembrane receptors, a cascade of intracellular biochemical signals, resulting in the activation and repression of various subsets of genes, is triggered. One of the major incentives for studying factors that regulate processes of proliferation and differentiation is the recognition of their involvement in tumorigenesis. Genetic aberrations in growth factors signaling pathways are, in fact, inextricably linked to cancer. Malignant cells arise as a result of a stepwise progression of genetic events characterized by the unregulated expression of growth factors or components of their signaling networks. The main aim of this review is to examine the current understanding of the crucial contribution that several growth factors may have on transformation, tumorigenesis, and progression in several human tumors among the most widespread in western countries. For this purpose, we will analyze the chemistry and the molecular organization of the most important growth factors and their specific receptors. In addition, we will focus on the mechanisms of signal transduction, the complex cascade of biochemical events ensued from the growth factor/receptor binding. The present knowledge of the role of growth factor biochemical signaling networks in cancer leads to improvements not only in diagnosis and prognosis for this disease, but also for new and more targeted therapeutic intervention. The second part of this review will focus on the novel pharmacological approaches for cancer therapy that have been developed already or are being developed with the aim to specifically interfere at various steps of the growth factors signaling pathways.

Organ-dependent modifying effects of oltipraz on N-nitrosobis(2-oxopropyl)amine (BOP)-initiation of tumorigenesis in hamsters

5-(2-Pyrazinyl)-4-methyl-1,2-dithiole-thione (oltipraz), a substituted 1,2-dithiole-3-thione, is known to inhibit tumorigenesis induced by variety of carcinogens in several animal model systems. In the present experiment, the modifying effects of dietary oltipraz, given during N-nitrosobis(2-oxopropyl)amine (BOP) initiation of carcinogenesis, were investigated in Syrian hamsters. A total of 120 six-week-old females were divided into six groups. Groups 1-3 (30 animals each) were thrice given subcutaneous injections of BOP (10 mg/kg, body weight) at 1 week intervals and fed diets supplemented with 400 or 200 ppm of oltipraz or basal diet alone, starting 1 week prior and finishing 1 week after the carcinogen exposure. Groups 4-6 (10 animals each) were similarly treated without application of BOP. At the end of the 52nd experimental week, all surviving animals were autopsied and examined histopathologically for proliferative lesions of the major target organs for BOP tumorigenicity, including pancreas, liver, kidney, and lung. The incidences and multiplicity of adenocarcinomas of the pancreas were higher in groups 1 and 2 than in group 3 although without statistical significance. The incidence of pancreatic duct dysplasias was significantly (P<0.05) increased in group 2 (62.0%) but not in group 1 (50.0%) as compared with group 3 (46.6%). While the incidences of alveolar adenomas and carcinomas were significantly (P<0.05) decreased by the high dose, the multiplicities of hepatocellular adenomas, cholagiocellular carcinomas and gall bladder adenomas were elevated in the BOP/oltipraz groups (P<0.05). The results of the present study suggest that oltipraz exerts organ-dependent modifying effects on BOP-induced carcinogenesis in hamsters when given in the initiation stage.