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This article explores the concept of "Peto's paradox," which refers to the observation that cancer incidence in humans and mice does not correlate with body size and longevity. Recent studies have supported this paradox, showing that cancer incidence is independent of body size in various species and that humans accumulate fewer mutations than mice. However, the mechanisms that prevent tissues with high mutational burdens from developing cancer are not fully understood. The article challenges the traditional belief that multiple mutations are necessary for tumor development and suggests that promoting factors may play a significant role. It emphasizes the importance of combining epidemiological and mechanistic approaches to better understand and prevent cancer, and highlights ongoing research on tumor promotion mechanisms. [Extracted from the article]

Autophagy is a tightly controlled process comprising lysosomal degradation and recycling of cellular proteins and organelles. In cancer, its paradoxical dual role of cytoprotection and cytotoxicity is context-dependent and controversial. Autophagy primarily acts as a mechanism of tumour suppression, by maintenance of genomic integrity and prevention of proliferation and inflammation. This, combined with immune-surveillance capabilities and autophagy's implicated role in cell death, acts to prevent tumour initiation. However, established tumours exploit autophagy to survive cellular stresses in the hostile tumour microenvironment. This can lead to therapy resistance, one of the biggest challenges facing current anti-cancer approaches. Autophagy modulation is an exciting area of clinical development, attempting to harness this fundamental process as an anti-cancer strategy. Autophagy induction could potentially prevent tumour formation and enhance anti-cancer immune responses. In addition, drug-induced autophagy could be used to kill cancer cells, particularly those in which the apoptotic machinery is defective. Conversely, autophagy inhibition may help to sensitise resistant cancer cells to conventional chemotherapies and specifically target autophagy-addicted tumours. Currently, hydroxychloroquine is in phase I and II clinical trials in combination with several standard chemotherapies, whereas direct, deliberate autophagy induction remains to be tested clinically. More comprehensive understanding of the roles of autophagy throughout different stages of carcinogenesis has potential to guide development of novel therapeutic strategies to eradicate cancer cells. [ABSTRACT FROM AUTHOR]

Abstract: Programmed cell death 4 (Pdcd4), a tumour suppressor, is frequently down‐regulated in various types of cancer. Pdcd4 has been demonstrated to efficiently suppress tumour promotion, progression and proliferation. The biochemical function of Pdcd4 is a protein translation inhibitor. Although the fact that Pdcd4 inhibits protein translation has been known for more than a decade, the mechanism by which Pdcd4 controls tumorigenesis through translational regulation of its target genes is still not fully understood. Recent studies show that Pdcd4 inhibits translation of stress‐activated‐protein kinase interacting protein 1 to suppress tumour invasion, depicting a picture of how Pdcd4 inhibits tumorigenesis through translational inhibition. Thus, understanding the mechanism of how Pdcd4 attenuates tumorigenesis by translational control should provide a new strategy for combating cancer. [ABSTRACT FROM AUTHOR]

The role of myeloid-derived suppressor cells ( MDSCs) in cancer development has become clear over recent years, and MDSC targeting is an emerging opportunity for enhancing the effectiveness of current anticancer therapies. As MDSCs are not only able to limit anti-tumour T-cell responses, but also to promote tumour angiogenesis and invasion, their monitoring has prognostic and predictive value. Herein, we review the key features of MDSCs in cancer promotion. © 2017 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland. [ABSTRACT FROM AUTHOR]

Abstract: Microcystin-LR (MCLR) is a peptide produced by freshwater cyanobacteria that induces severe hepatotoxicity in humans and animals. MCLR is also a potent tumour promoter and it has been proposed that this activity is mediated by the inhibition of protein phosphatases PP1/PP2A, possibly through the activation of proto-oncogenes c-jun, c-fos and c-myc. However, the mechanisms underlying MCLR-induced tumour promotion are still largely unknown, particularly in non-liver cells. In previous studies we have demonstrated that micromolar concentrations of MCLR induce cytotoxic effects in the kidney Vero-E6 cell line. The purpose of the present work was to evaluate whether the exposure to subcytotoxic concentrations of MCLR was sufficient to induce the proliferation of Vero-E6 cells. Through BrdU incorporation assay we show that at nanomolar concentrations MCLR stimulates cell cycle progression in Vero-E6 kidney cell line. Moreover, the analysis of mitogen-activated protein kinases p38, JNK and ERK1/2 activity revealed that the proliferative effect of MCLR is associated with the activation of the pro-proliferative ERK1/2 pathway. These results emphasise the importance to confirm in vivo the impact of MCLR on tumour promotion at kidney level. [ABSTRACT FROM AUTHOR]

Selected inflammatory conditions increase the risk of cancer. An inflammatory component is present also in the micro-environment of tumours epidemiologically unrelated to inflammation. An intrinsic (driven by genetic events that cause neoplasia) and an extrinsic (driven by inflammatory conditions which predispose to cancer) pathway link inflammation and cancer. Smouldering inflammation in the tumour microenvironment contributes to proliferation and survival of malignant cells, angiogenesis, metastasis, subversion of adaptive immunity, response to hormones, and chemotherapeutic agents. Emerging evidence also suggests that cancer-related inflammation promotes genetic instability. Thus, cancer-related inflammation represents a target for innovative diagnostic and therapeutic strategies. [ABSTRACT FROM AUTHOR]

Abstract: Aim: β-Carotene has shown cancer-preventive effects in preclinical studies while increasing lung cancer mortality in clinical trials. We have shown that β-carotene stimulates cAMP signalling in vitro. Here, we have tested the hypothesis that β-carotene promotes the development of pulmonary adenocarcinoma (PAC) in vivo via cAMP signalling. Methods: PAC was induced in hamsters with the carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), followed by β-carotene for 1.5 years. Incidence, multiplicity and size of lung tumours were recorded, and phosphorylated CREB and ERK1/2 in tumour cells were determined by Western blots. Cyclic AMP in blood cells was analysed by immunoassays, retinoids in serum and lungs by HPLC. Results: β-Carotene increased lung tumour multiplicity, lung tumour size, blood cell cAMP, serum and lung levels of retinoids and induced p-CREB and p-ERK1/2 in lung tumours. Conclusions: Our data suggest that β-carotene promotes the development of PAC via increased cAMP signalling. [Copyright &y& Elsevier]

Abietic acid (AA) and dehydroabietic acid (DHA) have been detected in virgin paper products and recycled paper products used for food packaging. In order to evaluate the cell transformation activities of AA and DHA, the Bhas 42 cell-transformation assay for initiation and promotion was carried out. Tested in the initiation stage, AA and DHA did not significantly increase transformation frequencies. On the other hand, both chemicals induced transformed foci dose dependently at the promotion stage. The highest transformed foci density induced by AA was about 13 foci/well at 60 nmol ml-1, and that of DHA was about 16 foci/well at 40 nmol ml-1 (solvent control = 2.3 ± 1.4 foci/well). The present results suggest that AA and DHA may have tumour-promoting potential. [ABSTRACT FROM AUTHOR]

Aims: To investigate the production of the tumour promoter 1,2- sn-diacylglycerol (DAG) by a human gut isolate of Bifidobacterium longum biovar infantis. Methods and Results: Bifidobacterium longum biovar infantis was grown in vitro using anaerobic static batch cultures in the presence of phosphatidylcholine (PC) and trans-galactooligosaccharides (TOS). Production of DAG was found to be dependent upon the presence of PC, while TOS had a reducing effect. Considerable differences in morphology, growth and metabolic end products from the micro-organism were observed under the different culture conditions. Conclusions: Our results have provided evidence that B. longum biovar infantis can produce DAG in vitro and that a prebiotic exerted a reducing effect upon this production. Significance and Impact of the Study: The results presented in this study demonstrate an ability of ostensibly beneficial member of the colonic environment to produce unwanted compounds under certain conditions. Therefore, it may be important that a combination of substrates and other factors are assessed when studying the behaviour of any bacterial group or species, especially when designing the dietary interventions. [ABSTRACT FROM AUTHOR]

Abstract: In this study the potential impact of food chain-based biotransformation and physico-chemical weathering of toxaphene on its tumour promoting potential was investigated in vitro and in vivo. Human exposure to toxaphene is mainly through consumption of contaminated fish, therefore fish-borne residues of toxaphene (cod liver extract, CLE) were prepared by exposing cod to technical toxaphene (TT) for 63 days. UV-irradiated toxaphene (uvT) was included to represent a physico-chemical weathered toxaphene mixture. In vitro, TT, uvT and CLE all showed a dose- and time-dependent inhibition of gap junctional intercellular communication (GJIC) with a relative potency of CLE>TT=uvT. Tumour promoting potency was further studied in vivo in a medium term two-stage initiation/promotion bioassay in female Sprague–Dawley rats, using an increase in altered hepatic foci positive for glutathione-S-transferase-P (AHF-GST-P) as read out. No increase in AHF-GST-P occurred following exposure to either TT, uvT, or CLE, except for the positive control group (2,3,7,8-TCDD). Based on this study the no observed adverse effect level (NOAEL) for tumour promoting potency is at least 12.5mg/kg/week, or higher for CLE. Considering current human exposure levels in Europe it is doubtful that consumption of fish at current levels of toxaphene contamination give rise to human health risk. [Copyright &y& Elsevier]

Abstract: The ability of tumour promoters to alter DNA stability within regions that contain tandemly repeated sequences (TRSs), was studied in a cell culture model of multi-stage carcinogenesis. Non-cytotoxic concentrations of TPA (12-O-tetradecanoyl-phorbol-13-acetate) and xanthine oxidase with xanthine substrate, sufficient to promote morphological transformation in C3H/10T1/2 cultures, were tested for their effects on mutation frequencies in TRSs by a DNA fingerprinting approach. Specifically, restriction digests of genomic DNA samples from randomly selected, non-transformed clones, isolated from cultures after several days exposure to promoters, were visualized by Southern hybridizations with the multi-locus pentamer repeat sequence probe, Ms6-Hm (Pc-1). Basal and promoter-induced frequencies of sub-clone TRS fingerprint polymorphisms were estimated in five cell populations: an uncloned stock culture, three populations established from normal-appearing sub-clones, and one clonal population established from a 3-methylcholanthrene (MCA)-transformed focus. Basal variant fingerprint frequencies spanned a range from 0.0 to 0.43% mutants/band among cells from the four untransformed populations. Both TPA and xanthine oxidase treatments significantly increased recorded mutation frequencies, 2.3- and 2.7-fold, respectively, using combined data from the progenitor population and three untransformed clones. The untreated MCA-transformed clonal population appeared to contain a single, pre-existing mutant restriction fragment, but additional mutations were induced thereafter, in response to the promoting treatments. Taken together, the measured increases in mutations were highly significant and suggest that promoters of cell transformation in the C3H/10T1/2 cell line might induce a genome-wide instability targeted to regions containing Ms6-Hm sequence motifs. [Copyright &y& Elsevier]

Mouse models of human cancer have played an important role in formulating modern concepts of multistage carcinogenesis, and are providing us with a new armoury of tools for the testing of novel therapeutic approaches to cancer treatment. The development of inducible and conditional technologies provide us with greater opportunity to generate mouse models which faithfully recapitulate human tumorigenesis, in terms of both the biology and the genetics of this disease. It is now feasible to control, in time and space, the development of tumours in almost any mouse tissue, such that we now have available mouse models of all major human cancers. Moreover, novel non-invasive approaches to tumour imaging will enable us to follow tumour development and metastasis in vivo, as well as the effects of candidate therapeutic drugs. Such new generation tumour models, which accurately emulate the disease state in situ, should provide a useful platform with which to experimentally test drugs targeted to specific gene products, or combinations of genes that control rate-limiting steps of tumour development. [Copyright &y& Elsevier]

Growth of Acanthamoeba castellanii was inhibited by chitosanoligosaccharide (up to 20 mg ml-1) from the shells of crabs but was reversed by the polyamines, putrescine or spermidine, at 0.8 mM. Chitosanoligosaccharide strongly inhibited the induction of ornithine decarboxylase by 12-O-tetradecanoylphorbol-13-acetate, a key enzyme of polyamine biosynthesis, which is enhanced in tumour promotion. [ABSTRACT FROM AUTHOR]

Potassium bromate (KBrO[sub 3]) is a potent nephrotoxic agent. In this paper, we report the chemopreventive effect of Nigella sativa (black cumin) on KBrO[sub 3]-mediated renal oxidative stress, toxicity and tumor promotion response in rats. KBrO[sub 3] (125 mg/kg body weight, intraperitoneally) enhances lipid peroxidation, γ-glutamyl transpeptidase, hydrogen peroxide and xanthine oxidase with reduction in the activities of renal antioxidant enzymes and renal glutathione content. A marked increase in blood urea nitrogen and serum creatinine has also been observed. KBrO[sub 3] treatment also enhances ornithine decarboxylase (ODC) activity and [[sup 3]H] thymidine incorporation into renal DNA. Prophylaxis of rats orally with Nigella sativa extract (50 mg/kg body weight and 100 mg/kg body weight) resulted in a significant decrease in renal micro-somal lipid peroxidation (P < 0.001), γ-glutamyl trans-peptidase (P < 0.001), H[sub 2]O[sub 2] (P < 0.001) and xanthine oxidase (P < 0.05). There was significant recovery of renal glutathione content (P < 0.01) and antioxidant enzymes (P < 0.001). There was also reversal in the enhancement of blood urea nitrogen, serum creatinine, renal ODC activity and DNA synthesis (P < 0.001). Data suggest that Nigella sativa is a potent chemopreventive agent and may suppress KBrO[sub 3]-mediated renal oxidative stress, toxicity and tumour promotion response in rats. [ABSTRACT FROM AUTHOR]

Dioxin and certain structurally related compounds increase the incidence of liver neoplasms in rodents upon chronic bioassay. Short-term studies indicate the lack of direct DNA-damaging effects including covalent binding to DNA; however, secondary mechanisms may be important in the observed carcinogenicity as these chemicals affect a number of pathways necessary for maintenance of normal growth control and differentiation status. Studies with TCDD in the mouse skin support a lack of initiating activity but an ability to promote the growth of previously initiated lesions indicative of a promoting agent. Mouse skin tumour promotion studies indicate that Ah receptor activation may be involved in promotion by TCDD and selected structurally related compounds. While the mechanism of carcinogenicity induced by TCDD is unknown, the processes involved have a no-effect level, which in the rat liver is at an exposure level below 10 ng TCDD/kg/ day. At least for the rodent liver, the relative effective dose for cytochrome P450 induction is not a good indicator of promotion potency. Studies on liver tumour promotion in the female rat liver support a nongenotoxic mechanism for the induction of neoplasms by TCDD. The ability of TCDD to enhance proliferation and inhibit apoptotic processes in focal hepatic lesions further supports an indirect mechanism of carcinogenicity. [ABSTRACT FROM AUTHOR]

To investigate effects that distinguish AAF from incomplete carcinogens, the rate of cell death (apoptosis) and cell proliferation was studied at early stages of AAF induced rat liver carcinogenesis. Male Wistar rats were fed 0.04% AAF in the diet for 2, 6 and 16 weeks and immunohistochemical markers were measured in the liver. The formation of initiated cells and preneoplastic foci was followed by staining for GST-P (glutathione-S-transferase). GST-P-positive foci were present from 6 weeks on. Apoptosis was increased in the periportal area and in preneoplastic foci at all time points. Cell proliferation was enhanced in the periportal area in oval cells and in bile duct-like cells particularly at 2 and 6 weeks and mainly in GST-P positive foci at 16 weeks. Notably, more cells always proliferated than were eliminated. Other apoptosis-related markers like p53 and FAS/Apo-1 could not be demonstrated in either normal hepatocytes, preneoplastic foci or in hepatocytes from treated animals. Scattered bcl-2 positive cells were present in livers at 16 weeks of treatment. The two cell growth and differentiation related proto-oncogenes c-FOS and c-JUN were increased in all treated animals at early stages. If feeding was stopped after 6 weeks, livers did not recover significantly within the following 10 weeks. The results support the complex effects of AAF in rat liver carcinogenesis. Chronic toxicity locally impairs the balance between cell proliferation and cell death and induces morphological alterations that promote the growth of initiated cells. [ABSTRACT FROM AUTHOR]

The synthetic pyrethroids cypermethrin, deltamethrin, fenvalerate, permethrin, and the fenvalerate metabolite p-chlorophenylisovaleric acid were investigated for inhibition of gap-junctional intercellular communication in vitro in the Chinese hamster lung fibroblast (V79) metabolic cooperation assay. Fenvalerate was furthermore studied for enhancement of gamma-glutamyl transpeptidase-positive enzyme altered foci incidence in partially hepatectomized, nitrosodiethylamine-initiated male Sprague Dawley rats. The in vitro studies showed that fenvalerate and p-chlorophenylisovaleric acid were inhibitors of intercellular communication at non-cytotoxic concentrations while cypermethrin, deltamethrin, and permethrin were inactive. In the in vivo study in rat liver, fenvalerate administered p.o. (75 mg/kg/day) 5 days a week for 10 weeks induced significantly more foci per cm and a larger percentage of liver tissue occupied by foci tissue compared to a vehicle control group. Analysis of size distributions of foci in fenvalerate- and vehicle-treated rats showed elevated foci incidences in fenvalerate-treated rats at all foci sizes. Fenvalerate induced no hepatotoxic effects as judged by plasma transaminase activities and histopathology. The results of this study suggest fenvalerate to be a potential tumour promoter. [ABSTRACT FROM AUTHOR]

Simple Summary: Cytokines are a group of small proteins in the body that play an important part in boosting the immune system. Thymic stromal lymphopoietin (TSLP) is a cytokine that plays an important role in the maturation of T cells. Two variants of TSLP, long-form (lfTSLP) and short-form (sfTSLP), have been found, however their roles in cancers are not known. In this study, we discovered that sfTSLP, but not lfTSLP, is predominantly expressed in ovarian and endometrial cancers. The switch that turns the sfTSLP gene on or off is controlled by external modifications of DNA. Our results also found that sfTSLP promotes tumour growth through activating several signal pathways in cancer cells. Thymic stromal lymphopoietin (TSLP) is an epithelial cell derived cytokine belonging to the IL-7 family and a key initiator of allergic inflammation. Two main isoforms of TSLP, classified as long- (lfTSLP) and short-form (sfTSLP), have been reported in human, but their expression patterns and role(s) in cancers are not yet clear. mRNA expression was examined by isoform-specific RT-PCR and RNA in situ hybridisation. Epigenetic regulation was investigated by chromatin immunoprecipitation-PCR and bisulfite sequencing. Tumour progression was investigated by gene overexpression, cell viability assay, cancer organoid culture and transwell invasion. Signals were investigated by proteome profiler protein array and RNA-sequencing. With the use of isoform-specific primers and probes, we uncovered that only sfTSLP was expressed in the cell lines and tumour tissues of human ovarian and endometrial cancers. We also showed the epigenetic regulation of sfTSLP: sfTSLP transcription was regulated by histone acetylation at promoters in ovarian cancer cells, whereas silencing of the sfTSLP transcripts was regulated by promoter DNA methylation in endometrial cancer cells. In vitro study showed that ectopically overexpressing sfTSLP promoted tumour growth but not invasion. Human phosphokinase array application demonstrated that the sfTSLP overexpression activated phosphorylation of multiple intracellular kinases (including GSK3α/β, AMPKα1, p53, AKT1/2, ERK1/2 and Src) in ovarian cancer cells in a context-dependent manner. We further investigated the impact of sfTSLP overexpression on transcriptome by RNA-sequencing and found that EFNB2 and PBX1 were downregulated in ovarian and endometrial cancer cells, suggesting their role in sfTSLP-mediated tumour growth. In conclusion, sfTSLP is predominantly expressed in ovarian and endometrial cancers and promotes tumour growth. [ABSTRACT FROM AUTHOR]