Prenatal ozone exposure abolishes stress activation of Fos and tyrosine hydroxylase in the nucleus tractus solitarius of adult rat

Ozone (O₃) is widely distributed in the environment, with high levels of air pollution. However, very few studies have documented the effects on postnatal development of O₃ during pregnancy. The long-term effects of prenatal O₃ exposure in rats (0.5 ppm 12 h/day from embryonic day E5 to E20) were evaluated in the adult nucleus tractus solitarius (NTS) regulating respiratory control. Neuronal response was assessed by Fos protein immunolabeling (Fos-IR), and catecholaminergic neuron involvement by tyrosine hydroxylase (TH) labeling (TH-IR). Adult offspring were analyzed at baseline and following immobilization stress (one hour, plus two hours’ recovery); immunolabeling was observed by confocal microscopy. Prenatal O₃ increased the baseline TH gray level per cell (p < 0.001). In contrast, the number of Fos-IR cells, Fos-IR/TH-IR colabeled cells and proportion of TH double-labeled with Fos remained unchanged. After stress, the TH gray level (p < 0.001), number of Fos-IR cells (p < 0.001) and of colabeled Fos-IR/TH-IR cells (p < 0.05) and percentage of colabeled Fos-IR/TH-IR neurons against TH-IR cells (p < 0.05) increased in the control group. In prenatal-O₃ rats, immobilization stress abolished these increases and reduced the TH gray level (p < 0.05), indicating that prenatal O₃ led to loss of adult NTS reactivity to stress. We conclude that long-lasting sequelae were detected in the offspring beyond the prenatal O₃ exposure. Prenatal O₃ left a print on the NTS, revealed by stress. Disruption of neuronal plasticity to new challenge might be suggested.     

p53 abnormalities in adenocarcinoma of the gastric cardia and antrum.

AIM: To compare the frequency and type of p53 alterations (gene mutation and/or protein overexpression) in a consecutive series of surgically resected adenocarcinomas arising in the gastric cardia and gastric antrum, and to evaluate associations with clinicopathological findings (age, sex, and tumour histology, grade, and stage). METHODS: The series comprised 50 patients with adenocarcinoma of the cardia and 20 patients with adenocarcinoma of the antrum. p53 gene mutations (exons 5-8) were detected by denaturing gradient gel analysis and DNA sequencing. Nuclear p53 overexpression was detected by immunohistochemistry with the DO7 antibody. RESULTS: p53 gene mutations were found in 21 of 50 and five of 20 adenocarcinomas of the cardia and the antrum, respectively. Base transitions occurring at CpG dinucleotides were frequent in both types of tumour. p53 protein overexpression was seen in 32 of 50 and seven of 20 adenocarcinomas of the cardia and of the antrum, respectively. p53 gene mutation and/or protein overexpression were significantly more frequent in adenocarcinomas of the cardia (37 of 50) than in adenocarcinomas of the antrum (seven of 20). There were no differences in the clinicopathological characteristics of the tumours between p53 positive and p53 negative cases in both types of cancer. CONCLUSIONS: This study shows that p53 alterations are more frequent in adenocarcinoma of the cardia than in adenocarcinoma of the antrum. This feature is consistent with the clinical and epidemiological characteristics of these cancers, which suggest that adenocarcinoma arising in the gastric cardia might be related to oesophageal adenocarcinoma, and unrelated to adenocarcinomas of the gastric body and antrum.     

MSI-L gastric carcinomas share the hMLH1 methylation status of MSI-H carcinomas but not their clinicopathological profile

Sporadic gastric carcinomas (SGC) with microsatellite instability (MSI) exhibit mutations in target genes and display a particular clinicopathological profile. In SGC the MSI phenotype has been associated with hMLH1 promoter hypermethylation. Fifty-seven SGC, classified as high-frequency MSI (MSI-H), low-frequency MSI (MSI-L), and microsatellite stable (MSS), were analyzed for hMLH1 promoter methylation status and clinicopathological features. hMLH1 mutations and hMLH1 expression, as well as target gene mutations, were also evaluated. Our aims were to characterize the molecular and clinicopathological features of SGC, with and without hMLH1 promoter hypermethylation, and to compare the molecular and clinicopathological features of MSI-L, MSI-H, and MSS tumors in an attempt to clarify the place of MSI-L tumors in the mismatch repair (MMR) pathway. Hypermethylation of hMLH1 promoter occurred in 27 of 57 SGC (47.3%) and was significantly associated with MSI status, target gene mutations, and expansive pattern of growth of the tumors. Seventy-five percent of the MSI-H and 50% of MSI-L carcinomas showed hypermethylation (Met+) of hMLH1 in contrast to 0% in MSS carcinomas. No hMLH1 expression was observed in MSI-L/Met+ and MSI-H/Met+ cases. MSS and MSI-L tumors share the same clinicopathological profile regardless of the methylation status of the latter and are distinct from MSI-H tumors. We conclude that mutations in target genes, more than hypermethylation or absence of expression of hMLH1, are the link between MSI status and most of the clinicopathological features of SGC.     

Comparative analysis of mutation frequency of coding and non coding short mononucleotide repeats in mismatch repair deficient colorectal cancers

Coding repeats are usually short mononucleotide tracts (SMT) of 10 or less base pairs in size. A number of such sequences contained in genes suspected to play a role in human carcinogenesis have been found to be mutated in mismatch repair deficient tumors (MSI-H cancers). Because of the high background of instability characterizing these cancers and in the absence of functional criteria, the significance of most frameshift gene alterations is unclear. In the present work, we analysed a series of 22 transcribed but non-coding SMT that are thus unlikely to play a tumorigenic role. Their frequency of size alteration in germline DNA and in DNA from MSI-H and microsatellite stable (MSS) tumors were compared to those previously reported in a series of 25 coding SMT of similar size. Non-coding SMT were either monomorphic or polymorphic in germline DNA whereas coding SMT were all monomorphic. In MSI-H tumors, non-coding SMT showed infrequent alterations (0-44%), as opposed to coding SMT which were altered at extremely variable frequencies (0 to 92%). Seven of the 22 non-coding SMT were monomorphic in MSS tumors but presented size alterations in MSI-H tumors with variable frequencies (3-28%). They were thus selected for further comparative statistical analyses for instability in coding SMT in MSI-H colorectal cancers. Only seven out of 25 of the coding SMT showed a significantly higher mutation frequency in these tumors. In the absence of functional criteria, we propose this as a novel and comprehensive approach for distinguishing real target genes amongst the numerous proposed gene mutations. It should allow identification of those that are genuinely selected for during MSI-H tumoral progression from others that play a less important role, if any, in MSI-H carcinogenesis.     

Target gene mutation profile differs between gastrointestinal and endometrial tumors with mismatch repair deficiency

Mutation frequencies at 25 genes containing coding repeats were compared in colorectal, gastric, and endometrial mismatch repair-deficient (MSI-H) tumors. The overall number of mutations was significantly lower in endometrial than in gastrointestinal MSI-H cancers. Using a likelihood statistical method, target genes were divided in each tumor location into two groups likely to represent gene mutations that do or do not provide selective pressures during tumoral progression. Mutation profiles were quite similar in gastric and colorectal MSI-H cancers but were different in endometrial MSI-H tumors. Deletions in Bat-25 and Bat-26 noncoding repeats were also significantly less important in endometrial as compared with gastrointestinal MSI-H tumors. Our results show that the profile of target gene mutations in MSI-H tumors is tissue specific, with both qualitative and quantitative differences between gastrointestinal and endometrial MSI-H cancers.     

Complementary antineoplastic activity of the cytosine nucleoside analogues troxacitabine (Troxatyl) and cytarabine in human leukemia cells

Purpose Troxacitabine (BCH-4556, l-(–)-OddC, Troxatyl) is a novel -l-nucleoside analogue with potent antineoplastic activity both in vitro and in several tumor models in vivo, and is presently in phase II clinical trials. The combination of the cytosine analogues troxacitabine and araC (1--d-arabinofuranosylcytosine, cytarabine) has shown promising activity in patients with acute myelogenous leukemia. To further examine the interactions between these two analogues, we investigated the in vitro and in vivo effects of their combination against a human leukemia cell line, CCRF-CEM.Methods The in vitro cytotoxic effect of the combination of troxacitabine and araC on the survival of CCRF-CEM cells was measured using a standard MTT assay and combination indices were generated with the CalcuSyn software. For in vivo studies, we evaluated the effect of both drugs, alone and in combination, on survival of CCRF-CEM tumor-bearing animals. Mechanistic studies addressed recovery of DNA synthesis, intracellular levels of araC metabolites, feedback inhibition by triphosphate species and pharmacokinetics of both drugs.Results The combination of troxacitabine and araC in vitro was synergistic with combination indices between 0.1 and 0.7. This appeared to be related to the impact of the combination on DNA synthesis recovery, which was significantly delayed following exposure to the combination of troxacitabine and araC compared to either agent alone. Analysis of the effect of troxacitabine on the intracellular metabolites of araC revealed that troxacitabine did not inhibit araC deamination and caused a slight decrease in the overall intracellular accumulation of araCTP. The lower accumulation of araCTP could not be attributed to feedback inhibition caused by troxacitabine triphosphate on dCK. Furthermore, our in vivo experiments demonstrated that the combination of araC and troxacitabine was better at slowing down the progression of leukemia in SCID mice than either agent used alone without additive toxicities. Injections of 10 mg/kg troxacitabine i.p. daily for 5 days in combination with araC at 10 mg/kg led to an increase in median survival time of 58 days compared to 49.5 and 53.5 days for araC and troxacitabine, respectively, given as single agents. This represents an increase in life span of 17%, respectively when compared to araC alone. A pharmacokinetic study revealed that troxacitabine did not influence the disposition of araC when coadministered.Conclusions Overall, our results show that the antileukemic activity of troxacitabine and araC is complementary when the two nucleoside analogues are combined in vivo. These effects appear to be related to their interaction at the level of DNA repair rather than to pharmacokinetic interactions. These results encourage the use of troxacitabine and araC in combination in patients with acute leukemia.Abbreviations AML Acute myelogenous leukemia - araC 1--d-Arabinofuranosylcytosine, cytarabine - araCMP Cytarabine-5-monophosphate - araCTP Cytarabine-5-triphosphate - araU 1--d-Arabinofuranosyluracil - dCyd Deoxycytidine - CDA Cytidine deaminase - CI Combination index - dCK Deoxycytidine kinase - dCTP Deoxycytidine-5-triphosphate - dFdC Gemcitabine, 2,2-difluorodeoxycytidine - troxacitabineTP Troxacitabine 5-triphosphate     

BRAF mutations characterize colon but not gastric cancer with mismatch repair deficiency

Genes from the RAF family are Ras-regulated kinases involved in growth cellular responses. Recently, a V599E hotspot mutation within the BRAF gene was reported in a high percentage of colorectal tumors and significantly associated to defective mismatch repair (MMR). Additionally, BRAF mutations were described only in K-Ras-negative colon carcinomas, suggesting that BRAF/K-Ras activating mutations might be alternative genetic events in colon cancer. We have addressed to what extent the tumorigenic-positive selection exerted by BRAF mutations seen in colorectal MMR-deficient tumors was also involved in the tumorigenesis of gastric cancer. Accordingly, BRAF mutations were detected in 34% (25/74) of colorectal MMR-deficient tumors and in 5% (7/142) of MMR-proficient colorectal cases (P=0.0001). All mutations found in the MSI cases corresponded to the previously reported hotspot V599E. Two D593K and a K600E additional mutations were also detected in three MSS cases. However, only one mutation of BRAF was found within 124 MSS gastric tumors and none in 37 MSI gastric tumors, clearly suggesting that BRAF mutations are not involved in gastric tumorigenesis. Nonetheless, a high incidence of mutations of K-Ras was found within the MSI gastric group of tumors (P=0.0005), suggesting that the activation of K-Ras-dependent pathways contributes to the tumorigenesis of gastric cancers with MMR deficiency. Accordingly, our results show evidences that BRAF mutations characterize colon but not gastric tumors with MMR deficiency and are not involved in the tumorigenesis of gastric cancer of the mutator phenotype pathway.