7,12-DMBA-induced rat leukemia: a review with insights into future research

Bithiophene derivative induced apoptosis and suppression of Akt pathway in mouse leukemic model

BACKGROUND: Bithiophene derivatives show a promising anti-cancer potential. We previously showed that Bithienyl Fluorobenzamidine (BFB) has an anti-proliferative effect against several leukemia cell lines. Acute myeloid leukemia (AML) accounts for 18% of the total leukemia cases worldwide with heavier burden during the past 30 years. Therefore, the main aim remains the discovery of safe and effective medications. OBJECTIVE: The current research aims to investigate the anti-cancer efficacy of BFB and its effect on the apoptosis in the 7,12-Dimethylbenz[a]anthracene (DMBA) induced AML in mice. METHODS: AML was induced in mice by DMBA and then treated by 2 different doses of BFB. After BFB treatment, the hematological and histological pattern changes was examined. Furthermore, the molecular effect of BFB on apoptosis, cell cycle markers and Protein kinase B (Akt) pathway was examined using qPCR, Western blotting and ELISA. RESULTS: BFB treatment ameliorates leukemia histological and hematological markers significantly, despite non-significant changes in normal mice. This improvement exhibits cell cycle arrest and apoptosis induction, represented by elevation of tp53/p53, p21/p21, Caspase3 and downregulation of ckk1/Cdk1 in the bone marrow, as well as Akt pathway suppression. CONCLUSIONS: Our results establishes BFB as a promising therapeutic candidate against AML through cell cycle arrest, apoptosis induction and Akt pathway modulation.

N-(benzylidene)-2-((2-hydroxynaphthalen-1-yl)diazenyl)benzohydrazides (1-2) (NCHDH and NTHDH) attenuate DMBA-induced breast cancer via Nrf2/NF-κB/apoptosis signaling

The present study investigated the effect of the N-(benzylidene)-2-((2-hydroxynaphthalen-1-yl)diazenyl)benzohydrazides (1-2) (NCHDH and NTHDH) against breast cancer using in vitro and in vivo approaches. The NCHDH and NTHDH significantly inhibited the growth of the MCF-7 cells using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. The NCHDH and NTHDH treatment significantly inhibited the tumor size, tumor weight, and tumor volume, while it enhanced the survival and tumor free survival rate following 7,12-Dimethylbenz[a]anthracene (DMBA)-induced breast cancer. The NCHDH and NTHDH markedly attenuated the oxidative stress markers and induced the antioxidant level. The enzyme-linked immunosorbent assay (ELISA) showed significant reduction in the inflammatory cytokines production compared with the DMBA control. The NCHDH and NTHDH treatment significantly improved the histological features using hematoxylin and eosin (H and E) staining, Masson's trichrome, PAS (periodic acid Schiff), and Toluidine blue staining compared with the DMBA-induced group. The NCHDH and NTHDH treatment improved the hematological and serological parameters following DMBA-induced breast tumor compared with DMBA-induced group. Furthermore, the NCHDH and NTHDH treatment significantly enhanced the antioxidants signaling proteins such as nuclear factor erythroid 2-related factor 2 (Nrf2) and Heme oxygenase 1 (HO-1). The NCHDH and NTHDH enhanced the inhibitor of NF-κB (IκB) level, while it attenuated the NF-κB level. Similarly, the NCHDH and NTHDH showed marked increase in the apoptosis proteins such as Caspase-3, Caspase-9, and Bcl-2 Associated X-protein (Bax), while it inhibited the B-cell lymphoma 2 (Bcl-2) expression. In conclusion, the NCHDH and NTHDH significantly improved the DMBA-induced breast cancer via attenuating oxidative stress and inflammatory cytokines.

Mesenchymal stem cells targeting PI3K/AKT pathway in leukemic model

Mesenchymal stem cells have therapeutic properties that are related to their potentials for trans-differentiation, immunomodulation, anti-inflammatory, inhibitory effect on tumor proliferation, and induction of apoptosis. This study was performed to analyze the role of mesenchymal stem cells as an alternative for cellular signaling growth factors involved in the pathogenesis of leukemogenesis in rats. Treatment of rats with 7,12-dimethyl benz [a] anthracene induced leukemogenesis appeared as a significant decrease in hematological parameters with concomitant significant increase in bone marrow oxidative and inflammatory indices (transforming growth factor beta and interleukin-6) in comparison with normal groups. On the contrary, Western immunoblotting showed a significant increase in the signaling growth factors: PI3K, AKT, mTOR proteins and a significant decrease in PTEN in 7,12-dimethyl benz [a] anthracene-treated group. In addition, a significant increase in the transcript levels of B cell lymphoma-2 protein gene in the 7,12-dimethyl benz [a] anthracene group, while that of C-X-C motif chemokine receptor-4 and B cell lymphoma-2 protein associated x-protein were significantly downregulated compared to controls. Meanwhile, therapeutic mesenchymal stem cells treatment predict a significant improvement versus 7,12-dimethyl benz [a] anthracene group through the modulation of growth factors that confront bone marrow dysplasia. In the same direction treatment of 7,12-dimethyl benz [a] anthracene group with mesenchymal stem cells, it induced apoptosis and increased the homing efficacy to bone marrow. In conclusion, mesenchymal stem cells improve hematopoiesis and alleviate inflammation, and modulated PI3K/AKT signaling pathway contributed to experimental leukemogenesis.

Tyrosine Kinase Inhibitor Imatinib Mesylate Alters DMBA-Induced Early Onco/Suppressor Gene Expression with Tissue-Specificity in Mice

Tyrosine kinases play crucial roles in cellular development and tumorigenesis. Tyrosine kinase inhibitors (TKIs) are effective and widely used drug molecules in targeted cancer therapies. Altered expressions of protooncogenes and tumor suppressor genes after DMBA (7,12-dimethylbenz[a]anthracene) treatment have been described as early markers of tumor induction; however their tissue-specific effects remain still unclear. Our study was aimed at examining the short-term possible antineoplastic and chemopreventive effects of a TKI compound (imatinib mesylate) on a DMBA-induced mouse tumor model. In addition, we also investigated the tissue-specific expressions of Hras, Kras, Myc, and Trp53 genes in the brain, bone marrow, spleen, liver, abdominal lymph nodes, thymus, lungs, and kidneys, respectively. 24 hours after the imatinib mesylate injection, we observed significant Kras downregulation in the bone marrow and lung of the DMBA-treated mice. Moreover, the mRNA expression of Myc was also found to be decreased significantly in the spleen. Interestingly, while Trp53 expression was significantly increased in the lung, it was decreased in the other tissues. However, there was also a tendency in the decreased Myc level in the bone marrow, brain, kidneys, lungs, and lymph nodes and in the decreased Hras level in the bone marrow, kidneys, and lungs, although no significant differences were observed. Our findings indicate rapid tissue-specific impact of imatinib mesylate on DMBA-induced gene expression in vivo, supporting the chemopreventive potential of imatinib mesylate in cancer.

Development of In Silico Protocols to Predict Structural Insights into the Metabolic Activation Pathways of Xenobiotics

To establish in silico model to predict the structural insight into the metabolic bioactivation pathway of xenobiotics, we considered two specific and one non-specific mammary procarcinogen [e.g., dibenzo[a,l]pyrene (DBP), 7,12-dimethylbenz[a]anthracene (DMBA), and benzo[a]pyrene (BP)]. The CYP1A1, 1B1, 2C9, 1A2 and 2B6 reported in wet-lab studies to actively metabolize DBP also showed strong binding energies (kcal/mol) of -11.50, -10.67, -10.37, -9.76 and -9.72, respectively, with inhibition constants ranging between 0.01 and 0.08 µM. The CYP3A4 depicted minimum binding energy (-9.51 kcal/mol) which is in agreement with the wet-lab reports. Further, relatively better affinity of CYP1A1 and CYP1B1 with the dibenzo[a,l]pyrene-11,12-diol (DBPD) might be indicative of their involvement in carcinogenicity of parent compound. Like DBP, BP (-10.13 kcal/mol, Ki: 0.04 µM) and BP-diols (BPD) (-9.01 kcal/mol, Ki: 0.25 µM) observed plausible binding with CYP1A1 supporting to the reported data that emphasize the major contribution of CYP1A1 in the activation of similar procarcinogens and mutagens. Likewise, in silico results further highlighted the CYP1A1 as key player in bioactivation of DMBA to its carcinogenic metabolites. In case of PhIP metabolism, strong binding interaction predicted with CYP1A1 (-9.63 kcal/mol) rather than CYP1A2 (-8.84 kcal/mol). Dissimilarity in the binding affinity of PhIP might be due to its basic scaffold. Further, molecular dynamics (MD) simulation of 10 ns has been revealed that docked complexes of CYP1A1 with DBP, DMBA and BP are comparatively more stable than the complex of PhIP. Moreover, the current findings might be valuable as reference model in prediction and elucidation of the approximate metabolic pathway of xenobiotics.

Sex differences and pathology status correlated to the toxicity of some common carcinogens in experimental skin carcinoma

The increased susceptibility of men as compared to women to develop different types of cancer, including skin cancer, is well known; however, the mechanisms involved in this process are still a matter of debate. This study aimed to obtain animal models of photo-chemically-induced skin carcinogenesis by exposure to ultraviolet radiation B (UVB) coupled with topical applications of a tumor initiator (7,12-dimethylbenz(a)anthracene, DMBA) and a tumor promoter (12-O-tetradecanoylphorbol-13-acetate, TPA) in order to characterize the gender disparities regarding the skin lesions developed by the female and male SKH-1 hairless mice included in this study. Histopathological analysis confirmed the presence of malignant lesions in both cases, in female and male mice, following chronic exposure (24 weeks) to the noxious effects of the carcinogens applied, whereas the tumors in male mice had a more severe histological grade. In addition, tumor incidence, size and multiplicity were higher in male mice than in female mice.

Lymphoid metastasis of rat My2/De leukemia

By grafting spontaneous leukemia tumor cells, the myeloid My2/De leukemia rat model was established. Death was caused by impaired functions of heavily infiltrated organs. In vitro culturing of tumor cells, blood and bone marrow counts and cytochemic reactions indicated the leukemic the origin resembling human myeoloblastic leukemia. Metastatic spread was followed after i.v. and i.p. injection, and by implantation of leukemia cells under the renal capsule of rats. Primary tumor and metastasis formation was visualized by (18)FDG or (11)C-methionine administration and MiniPET. The accumulation of radiotracers was measured in different organs and expressed as Differential Absorption Ratios (DARs). Subrenal implantation of My2/De cells resulted in their appearance in other abdominal organs and in parathymic lymph nodes. The release of tumor cells from the primary kidney to the peritoneum was mimicked by the i.p. administration of ink particles. Ink particles deposited in the abdominal organs and in the thoracal lymph nodes, preferentially in parathymic lymph nodes, confirming the notion of lymphatic spread of metastasis.

Incomplete chromatin condensation in enlarged rat myelocytic leukemia cells

The distinguishable morphologic features of nuclei of acute myelogenous leukemia cells with enlarged size and finely distributed nuclear chromatin indicate incomplete chromosome condensation that can be related to elevated gene expression. To confirm this, interphase chromosome structures were studied in exponentially growing rat myelomonocytic leukemia 1 cells isolated at the University of Debrecen (My1/De cells). This cell line was established from primary rat leukemia chemically induced by 7,12-dimethylbenz[a]anthracene treatment. The enlarged nuclei of My1/De cells allowed improved fluorescent visualization of chromosomal structures. Increased resolution revealed major interphase intermediates consisting of (1) veil-like chromatin, (2) chromatin ribbon, (3) chromatin funnel, (4) chromatin bodies, (5) elongated prechromosomes, (6) seal-ring, spiral shaped, and circular chromosomal subunits, (7) elongated, bent, u- and v-shaped prechromosomes, and (8) metaphase chromosomes. Results confirmed the existence of the chromatin funnel, the first visible interphase chromosome generated by the supercoiling of the chromatin ribbon. Other intermediates not seen previously included the spiral subunits that are involved in the chromonemic folding of metaphase chromosomes. The existence of spiral subunits favors the helical coil model of chromosome condensation. Incomplete chromatin condensation in leukemia cells throughout the cell cycle is an indication of euchromatization contributing to enhanced gene expression and is regarded as a leukemic factor.

Parental smoking and childhood leukemia

Childhood leukemia is the most common cancer among children, representing 31% of all cancer cases occurring in children younger than the age of 15 years in the USA. There are only few known risk factors of childhood leukemia (sex, age, race, exposure to ionizing radiation, and certain congenital diseases, such as Down syndrome and neurofibromatosis), which account for only 10% of the childhood leukemia cases. Several lines of evidence suggest that childhood leukemia may be more due to environmental rather than genetic factors, although genes may play modifying roles. Human and animal studies showed that the development of childhood leukemia is a two-step process that requires a prenatal initiating event(s) plus a postnatal promoting event(s). Despite a substantial public health effort to reduce cigarette smoking, a large proportion of the US and world population still smoke. Tobacco smoke contains at least 60 known human or animal carcinogens, with the major chemical classes being volatile hydrocarbons, aldehydes, aromatic amines, polycyclic aromatic hydrocarbons, and nitrosamines; among these chemicals, only benzene is an established leukemogen, although other chemicals in the tobacco could interact with one another in a complex way to jointly attain a significant carcinogenic effect on the development of leukemia. Although tobacco smoke is an established risk factor for adult myeloid leukemia, the studies of association between parental smoking and childhood leukemia have produced inconsistent results. The majority of the studies on maternal smoking and childhood leukemia did not find a significant positive association and some even reported an inverse association. In contrast to studies of maternal smoking, studies of paternal smoking and childhood leukemia reported more positive associations but only by less than half of the studies. Future directions to be considered for improving the study of parental smoking and childhood leukemia are: 1) consider all sources of benzene exposure in addition to smoking, including occupational exposure and traffic exhausts; 2) childhood leukemia is a heterogeneous disease and epidemiologic studies of childhood leukemia can be greatly improved by grouping childhood leukemia into more homogeneous groups by molecular techniques (e.g., structural and numerical chromosomal changes); and 3) assess gene-environment interaction. It is hoped that through the continual effort, more will be uncovered regarding the causes of childhood leukemia. In the meantime, more effort should be spent on educating the parents to quit smoking, because parental smoking is known to affect many childhood diseases (e.g., asthma, respiratory tract infection, and otitis media) that are much more prevalent than childhood leukemia.

p53 and ATM/ATR regulate 7,12-dimethylbenz[a]anthracene-induced immunosuppression

The tumor suppressor protein p53 is a transcription factor that regulates apoptotic responses produced by genotoxic agents. Previous studies have reported that 7,12-dimethylbenz[a]anthracene (DMBA)-induced bone marrow toxicity is p53-dependent in vivo. Our laboratory has shown that DMBA-induced splenic immunosuppression is CYP1B1- and microsomal epoxide hydrolase (mEH)-dependent, demonstrating that the DMBA-3,4-dihydrodiol-1,2-epoxide metabolite (DMBA-DE) is probably responsible for DMBA-induced immunosuppression. DMBA-DE is known to bind to DNA leading to strand breaks. Therefore, we postulated that a p53 pathway is required for DBMA-induced immunosuppression. In the present studies, our data show that activated p53 accumulated in the nuclei of spleen cells in WT and AhR-null mice after DMBA treatment, but not in CYP1B1-null or mEH-null mice. These results suggest that DMBA activates p53 in a CYP1B1- and mEH-dependent manner in vivo but is not AhR-dependent. Ataxia telangiectasia mutated (ATM) and ATM and Rad3-related protein (ATR) are sensors for DNA damage that signal p53 activation. Increased ATM, phospho-ATM (Ser(1987)), and ATR levels were observed after DMBA treatment in WT, p53-null, and AhR-null mice but not in CYP1B1-null or mEH-null mice. Therefore, ATM and ATR seem to act upstream of p53 as sensors of DNA damage. Ex vivo immune function studies demonstrated that DMBA-induced splenic immunosuppression is p53-dependent at doses of DMBA that produce immunosuppression in the absence of cytotoxicity. High-dose DMBA cytotoxicity may be associated with p53-independent pathways. This study provides new insights into the requirement of genotoxicity for DMBA-induced immunosuppression in vivo and highlights the roles of ATM/ATR in signaling p53.

Harnessing preclinical mouse models to inform human clinical cancer trials

The urgent need for better cancer treatments has stimulated interest in employing small-animal models to evaluate potential drug therapies. Robust mouse models of many human cancers have been generated using sophisticated technologies for engineering germ-line mutations. As we enter into an age of targeted therapeutics, these strains provide novel platforms for validating new anticancer drugs, assessing therapeutic index, identifying surrogate markers of tumor progression, and defining epigenetic and environmental influences on tumorigenesis.

Immune systems, geographic information systems (GIS), environment and health impacts

Exposure to dioxins, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs) has been related to alterations in cellular and humoral immune responses in both adaptive and innate immune systems of most animal species. These compounds share a common signaling mechanism to exert their effects on cells of the immune system, which includes the aryl-hydrocarbon receptor (AhR) and the AhR nuclear translocator (ARN). Recently, the interference of AhR-ARNT with the nuclear factor (NF)-kappaB signaling pathway has been proposed as a critical event in the adverse effects on the immune system. Studies on the effects of these AhR-ARNT-related toxicants on the immune system of higher and lower phylum animals and knowledge of intracellular mechanisms of toxicity may contribute to development of biomarkers of ecotoxicant exposure and effects. Biomarkers of this kind allow sampling over extended geographic areas, in several sentinel species, including wildlife animals, and facilitate the building of risk models and risk maps of environmentally induced diseases. On the basis of location, biomarker sampled data obtained through evaluation of ecotoxicant exposure and effects on the immune system in sentinel species can be further integrated and analyzed together with other sources of environmental geographic information, or human population health data, by means of geographic information systems (GIS). The spatial analysis capability of GIS can help to evaluate the complex relationships of overlaid information and to identify areas with high risk indices or "hot spots." This integrative approach can be useful in studies contributing to support environmental and health-related policies and regulations.

The rat Ruby ( R) locus is Rab38: identical mutations in Fawn-hooded and Tester-Moriyama rats derived from an ancestral Long Evans rat sub-strain

Hermansky-Pudlak syndrome (HPS) is a group of rare, recessive disorders in which oculocutaneous albinism, progressive pulmonary fibrosis, bleeding diathesis, and other abnormalities result from defective biogenesis of multiple cytoplasmic organelles. Seven different HPS genes are known in humans; in mouse, at least 16 loci are associated with HPS-like mutant phenotypes. In the rat, only two HPS models are known, Fawn-hooded (FH) and Tester Moriyama (TM), non-complementing strains in which HPS-like hypopigmentation and platelet storage pool deficiency result from a mutation of the Ruby (red eyed dilution; R) locus on Chromosome (Chr) 1. We have identified the R locus as the Rab38 gene, establishing that rat R is homologous to mouse chocolate ( cht). Further, we show that FH and TM rats have identical Rab38 Met1Ile mutations, occurring on an identical Chr 1 marker allele haplotype, indicating that these two strains derive from a common ancestor. This ancestor appears to have been a sub-strain of the outbred Long Evans (LE) strain, and several modern LE sub-strains carry the Rab38 Met1Ile R mutation on the same Chr 1 marker haplotype. These findings have significant implications for the many past and ongoing studies that involve the FH and LE-derivative rat strains. Hermansky-Pudlak syndrome (HPS; MIM 203300) is a group of autosomal recessive diseases in which oculocutaneous albinism (OCA), progressive and fatal pulmonary fibrosis, and bleeding diathesis due to platelet storage pool deficiency result from defects in the biogenesis of specific cytoplasmic organelles and granules: melanosomes, lysosomes, and platelet dense granules. In humans, seven different HPS genes are known. In the mouse, at least 16 loci associated with HPS-like mutant phenotypes are known, seven of which are homologous to the human HPS loci.

[Chromosomal abnormalities in secondary myelodysplastic syndromes and leukemias]

Secondary leukemias group essentially together myelodysplastic syndromes and acute leukemias, therapy-related (chemo- or radio-), or consecutive to environmental factors. It's now proven that some recurrent abnormalities are associated with effects of therapeutic agents, as -5/del(5q), -7/del(7q) linked to alkylating agents, or 11q23 and 21q22 abnormalities linked to inhibitors of Topoisomerase II. Even if important differences between secondary and "de novo" forms exist, the discrimination between these 2 categories is not always obvious: many common chromosomal abnormalities, "de novo" leukemias in older patients having characteristics close to those of postalkylating leukemias, neonatal forms possibly secondary to maternal affect. Recent studies identified some others chromosomal abnormalities in the secondary leukemias and confirmed the poor prognosis of these hemopathies. This review sums up criterions, circumstances and cytogenetic abnormalities.