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S Parodi

Publications and source records attributed to S Parodi.

At least 73 records · Page 4Linked to original sources
PubMed1996

Nongenotoxic carcinogens: development of detection methods based on mechanisms: a European project.

While the accumulation of genetic changes in a somatic cell is considered essential for the genesis of a cancer, it has become clear that not all carcinogens are genotoxic, suggesting that some carcinogens indirectly participate in the generation of genetic changes during carcinogenesis. A European project funded by the European Community was thus conceived to study mechanisms of nongenotoxic aspects of carcinogenesis. Two main strategical approaches were adapted: (i) to study whether and how Syrian hamster embryo (SHE), Syrian hamster dermal (SHD) and BALB/c 3T3 cell transformation systems simulate in vivo carcinogenesis, and to examine whether they can detect nongenotoxic carcinogens; (ii) to study, refine and validate mechanisms-based end-points for detection of nongenotoxic carcinogens. For mechanisms-based research, the proposed end-points included gap junctional intercellular communication (GJIC) inhibition, altered expression of critical genes, immortalization and aberrant cell proliferation. We also selected model compounds commonly usable for various endpoints. Our major results can be summarized as follows: (1) SHE and BALB/c 3T3 transformation systems reflect both genotoxic and nongenotoxic carcinogenic events; they detect not only genotoxic but also many although not all, nongenotoxic carcinogens. This is further supported by the fact that both genotoxic and nongenotoxic carcinogens were able to immortalize SHD cells. (2) Many nongenotoxic carcinogens, although not all, inhibit GJIC in vitro as well as in vivo. Mechanistic studies suggest an important role of blocked GJIC in carcinogenesis and that different mechanisms are involved in inhibition of the communication by different agents used. However, inhibition of GJIC is not a prerequisite for the enhancement (or induction) of transformation of SHE or BALB/c 3T3 cells. (3) Among compounds examined, there was a good correlation between induction of micronuclei and cell transformation in SHE cells while no such correlation was found between the induction of cell transformation and ornithine decarboxylase activity. (4) Two transgenic mouse mutation assays (lacI and lacZ) were established and validated. The genotoxin dimethylnitrosamine was shown to be mutagenic to the liver in both assays. Ortho-anisidine, a bladder-specific carcinogen that was inactive in standard rodent genetic toxicity assays was uniquely mutagenic to the bladder of the transgenic mice. The peroxisome proliferator methyl clofenipate was established as nonmutagenic to the liver of both transgenic mice. That eliminated DNA damage as a cause of the liver tumours produced by this chemical and weakened the idea that induced cell division leads to mutation induction. (5) With an in vitro DNA replication model, it was found that DNA damage induced by genotoxic agents can be responsible for inhibition of DNA replication, while certain nongenotoxic agents such as phorbol esters increase DNA replication. (6) An attempt to use structure-activity relationship for subfamilies of nongenotoxic carcinogens, e.g., receptor-mediated carcinogens, has been initiated with some promising results. Our results support the idea that there are multiple nongenotoxic mechanisms in carcinogenesis, and that working hypothesis-oriented approaches are encouraged rather than simple screening of chemicals in developing test systems for the detection of nongenotoxic carcinogens.

3T3 Cells↗
PubMed1996

A computerized connectivity approach for analyzing the structural basis of mutagenicity in Salmonella and its relationship with rodent carcinogenicity.

We have applied a new software program, based on graph theory and developed by our group, to predict mutagenicity in Salmonella. The software analyzes, as information in input, the structural formula and the biological activities of a relatively large database of chemicals to generate any possible molecular fragment with size ranging from two to ten nonhydrogen atoms, and detects (as predictors of biological activity) those fragments statistically associated with the biological property investigated. Our previous work used the program to predict carcinogenicity in small rodents. In the current work we applied a modified version of the program, which bases its predictions solely on the most important fragment present in a given molecule, considering as practically negligible the effects of additional less important fragments. For Salmonella mutagenicity we used a database of 551 compounds, and the program achieved a level of predictivity (73.9%) comparable to that obtained by other authors using the Computer Automated Structure Evaluation (CASE) program. We evaluated the relative contributions of biophores and biophobes to overall predictivity: biophores tended to be more important than biophobes, and chemicals containing both biophores and biophobes were more difficult to predict. Many of the molecular fragments identified by the program as being strongly associated with mutagenic activity were similar to the structural alerts identified by the human experts Ashby and Tennant. Our results tend to confirm that structural alerts useful to predict Salmonella mutagenicity are generally not very strong predictors of rodent carcinogenicity. Although the predictivity level achieved for oncogenic activity improved when the program was directly trained with carcinogenicity data, carcinogenicity as a biological endpoint was still more difficult to predict than Salmonella mutagenicity.

Animals↗
PubMed1996

Tumour necrosis factor enhances the therapeutic effect of mitoxantrone in human ovarian cancer xenograft.

The combination of Tumour Necrosis Factor (TNF) and mitoxantrone was evaluated for potential chemotherapeutic effect against a human ovarian cancer cell line A2774 hetero-transplanted in female nude mice. Both antitumour efficacy (relative survival and reduction of ascites) and toxicity (weight loss and liver toxicity) of TNF alone, mitoxantrone alone or TNF + mitoxantrone were evaluated. A significant difference (P < 0.002) was observed only among animals bearing tumours treated with mitoxantrone (0.012 mg/Kg) + TNF (5 x 10(5) U/Kg) and controls. No cytotoxic effects were observed for this combination. These observations provide a rationale for further evaluation of TNF + mitoxantrone based regimes for the treatment of recurrent ovarian cancer.

Animals↗
PubMed1996

Interactions between taxol and camptothecin.

Taxol is an antitumor drug which, as its mechanism of action, promotes microtubule assembly in vitro. Camptothecin (CPT) is an anticancer agent with the peculiar mechanism of poisoning eukaryotic DNA topoisomerase I. Both drugs are in clinical trials and their chemotherapeutic efficacy seems promising in refractory human ovarian cancer. We studied the molecular and cellular pharmacology of the two drugs when administered simultaneously toward human ovarian cancer cell line A2780. Taxol inhibits CPT-induced single-strand breaks as well as CPT-induced cytotoxicity. Taken together, our experiments indicate that the two drugs might interact with the same class of nuclear enzyme, i.e. DNA topoisomerase I.

Antineoplastic Agents, Phytogenic↗
PubMed1996

Endogenous tumor necrosis factor enhances topoisomerase II inhibitors activity in human ovarian cancer cell lines.

In this study, we demonstrated that tumor necrosis factor (TNF), secreted endogenously by four human ovarian cancer cell lines (A2774, IGROV-1, OVCAR-8, SW626), is biologically active against L929 cells and its activity is specifically inhibited by anti-TNF antibodies. Its endogenous production is increased by treatment for 24 h with phorbol myristate acetate (PMA)/ Ionomycin (Iono). All cell lines express TNF high-affinity receptors and release only 60-kdalton soluble TNF receptor, both spontaneously and after stimulation with PMA/Iono. TNF endogenously secreted by human ovarian cancer cell lines is very efficient in potentiating the activity of DNA topoisomerase II inhibitors (doxorubicin, mitoxantrone, VP16). The activity of vinblastine and bleomycin is not potentiated and, more interestingly, cisplatin's activity is inhibited. In 24-h PMA/Iono-stimulated A2774 cells, mitoxantrone specifically generated more cleavable complexes than in unstimulated cells. This result could provide an important tool in the therapy of human ovarian cancer secreting TNF protein, previously considered as a negative prognostic factor.

Antineoplastic Agents↗
PubMed1996

(32)P-postlabeling detection of DNA adducts in peripheral white blood cells of greenhouse floriculturists from western Liguria, Italy.

Pesticides are widely used in agriculture to enhance crop yields and to control disease vectors. Floriculturists work frequently in greenhouses and may be exposed to high levels of pesticides, which may result in adverse health effects. To evaluate the relationship between exposure to pesticides and DNA adduct formation in peripheral WBCs of Italian floriculturists, the nuclease P1 modification of a (32)P-postlabeling assay was used to analyze WBC DNA from floriculturists (n = 26) and matched controls (n = 22). DNA adduct-positive samples were more frequent in floriculturists (11/26; 42%) than in matched controls (2/22; 9%) (P < 0.01). Slightly higher frequencies of DNA adduct-positive samples were observed in floriculturists > or = 44 years of age (53%) and in female floriculturists (57%). Floricultural practice was found to be associated with a significantly higher DNA adduct-positive rate in WBCs (rate ratio, 5.12; 95% confidence interval, 1.1-23.7) after allowing for the effects of age and gender. These two latter covariates were not significantly associated with DNA adduct-positive rates. The quantitative levels of DNA adducts were significantly higher in floriculturists than in matched controls according to the Mann-Whitney nonparametric statistic (P = 0.0052). The median adduct level for positive samples among floriculturists was 1.5/10(8) bases. A specific, well-visible spot, named alpha adduct, was detected in 7 out of the 11 DNA adduct-positive samples from floriculturists but in none of the (22 + 20) referent samples (P = 0.0004). The presence of pesticide-related DNA adducts was confirmed clearly using the butanol extraction procedure. Six of 8 floriculturists and 0 of 10 referents were found positive with this method. The median adduct level for positive samples was 6.0/10(8) bases. Two strong spots close to the origin could be identified in all six positive floriculturists, using the butanol extraction procedure. No association between DNA adducts and use of specific pesticides was observed.

Adult↗
PubMed1995

Molecular fragments associated with non-genotoxic carcinogens, as detected using a software program based on graph theory: their usefulness to predict carcinogenicity.

We assembled 390 chemicals with a structure non-alerting to DNA-reactivity (145 carcinogens and 245 non-carcinogens) for which rodent carcinogenicity data were available. These non-alerting chemicals were defined by the absence in their molecules of DNA-reactive (directly or after metabolic activation) alerting structures, as described by Ashby and coworkers (Mutat. Res., 204 (1988) 17-115; Mutat. Res., 223 (1989) 73-103; Mutat. Res., 257 (1991) 209-227; Mutat. Res., 286 (1993) 3-74). Using our software program based on graph theory we analyzed the compounds in order to estimate the program's ability to predict nonalerting carcinogens. Our software fragmented the structural formula of the chemicals into all possible fragments of contiguous atoms with size between 2 and 8 (non-hydrogen) atoms and learned about statistically significant fragments from a training set of chemicals. These fragments were used to predict carcinogenicity or lack thereof in a verification set of compounds. For 390 runs of the software program we used (n - 1) of the chemicals as a training set, to predict the excluded chemical at each run (as a test set). Using two different probability thresholds to select significant fragments (P = 0.05 and P = 0.125 1-tailed according to binomial distribution), we performed two analyses: in the better one (P = 0.05) 19% of the molecules tested lacked significant fragments, for the remaining 81% the observed level of accuracy of the prediction was 66.0% against an expected level of accuracy of 51.7%. The difference was highly significant (P < 0.0001). We also examined the more significant activating fragments (biophores) and discussed at length both their biological plausibility and the working hypothesis that additional alerting structures for carcinogenicity (not only those related to genotoxicity) can be detected using this type of SAR approach. This new class of alerting structures could identify subfamilies of congeneric analogs active through mechanisms of receptor mediated carcinogenesis.

Carcinogens↗
PubMed1995

Genotoxic and non-genotoxic activities of 2,4- and 2,6-diaminotoluene, as evaluated in Fischer-344 rat liver.

Among aminoaromatics, 2,4-diaminotoluene (2,4-DAT) and 2,6-diaminotoluene (2,6-DAT) represent a conflicting couple of isomers; despite showing the same structural alert to DNA reactivity (and thus potential genotoxicity), they are different in terms of carcinogenicity. Of the two, 2,4-DAT alone is a potent rodent carcinogen, the liver being its major target. According to the literature, assays using various short-term genotoxicity tests have not discriminated satisfactorily between the carcinogenic and non-carcinogenic isomer, both chemicals producing overall positive results. To investigate their mechanism of action, we assayed both 2,4-DAT and 2,6-DAT in F-344 rat liver for their ability to induce DNA adducts, as detected by the 32P-postlabelling technique, and to enhance the induction of preneoplastic foci, as detected by GGT-staining in diethylnitrosamine (DENA)-initiated hepatocytes. Our expectation was that, using the correct target/metabolism, a classic genotoxicity assay and an assay detecting non-genotoxic activities could, together, reflect the different carcinogenic behaviour of the two isomers. The results indicate that, at the single equimolar dose of 250 mg/kg i.p., 2,4-DAT was able to induce approximately 6500 times more DNA adducts than 2,6-DAT; the estimated RAL values for the two isomers were 18.6 x 10(-6) and 0.29 x 10(-8), respectively. Moreover, of the two, only 2,4-DAT was able to significantly enhance the growth of DENA-initiated hepatocytes. Indeed, liver sections from rats treated with 2,4-DAT (30 daily doses of 25 mg/kg, i.g.) exhibited an average total number and area of foci of 10.53/cm2 and 1.22 mm2/cm2 vs. 4.46/cm2 and 0.33 mm2/cm2, for their respective controls. By contrast, no effect on the growth of GGT-positive foci was observed when liver sections from rats treated with 2,6-DAT (30 daily doses of 50 mg/kg, i.g.) were scored (5.54 foci per cm2 and total area of 0.42 mm2/cm2). The results indicate that in spite of the structural alert common to the two isomers, 2,4-DAT and 2,6-DAT, only the former appears to significantly affect the carcinogenic process in the liver.

Animals↗
PubMed1995

Role of H1 in chromatin folding. A thermodynamic study of chromatin reconstitution by differential scanning calorimetry.

In a series of related papers, we have recently presented the results of a thermodynamic approach to the conformational transitions of bulk chromatin induced in vitro by different structure-perturbing agents, such as the intercalating dye ethidium bromide or the ionic strength. In all these studies, we took advantage of the capability of differential scanning calorimetry to detect the changes in the melting behavior of the structural domains of chromatin (the linker and the core particle) associated with the order-disorder transitions. This technique also revealed that the higher-order structure undergoes a catastrophic decondensation process in the course of the transformation of rat hepatocytes as well as of cultured cells. Therefore, several questions arose concerning the biological function (if any) of the changes in the degree of condensation of bulk chromatin, as well as the mechanism of transition and the nature of the modulating agents. In this paper, we report a thermodynamic analysis of the reconstitution of H1-depleted calf thymus chromatin with the purpose of establishing (1) the binding mode of H1 and (2) the energetics and cooperativity of the transition from the unfolded to the condensed state. When H1 is progressively extracted from calf thymus nuclei by high-salt treatment, the endotherm at 107 degrees C, characteristic of the core particles interacting within condensed domains, converts into the thermal transition at 90 degrees C, resulting from the denaturation of noninteracting core particles. Binding of H1 fully restores the thermal profile of native chromatin. Analysis of H1 association shows that binding occurs at independent sites with KA = (3.67 +/- 0.60) x 10(4) M-1 and each site comprising 180 +/- 10 bp. The experimental dependence of the fraction of condensed chromatin on R, the moles of bound H1 per nucleosome mole, was compared with a simple thermodynamic model for the conformational change. This analysis yields a value of -5 kcal per nucleosome mole for the interaction free energy of nucleosomes within the ordered state. The process of condensation, is not, however, a highly cooperative (all-or-none) one, as expected from a consideration of the solenoidal model for the 30 nm fiber. Rather, nucleation of the helical state involves the face-to-face interaction between consecutive core particles, and the growth is largely determined by the mergence and rearrangement of neighboring clusters of helically arrayed nucleosomes.

Animals↗
PubMed1995

"Atypical" multidrug resistance in human ovarian cancer cell line A2780 selected for resistance to doxorubicin (A2780 DX3).

Human ovarian cancer cells A2780, selected for resistance to doxorubicin (A2780-DX3), are cross-resistant to various other topoisomerase-II-targeted drugs but not to vinblastine. The parental cell line was very sensitive to doxorubicin-, mitoxantrone- or etoposide(VP16)-induced DNA single-strand breaks, under deproteinizing conditions. In contrast, little or no DNA strand breakage was seen in resistant A2780-DX3 cells, even at very high concentrations, indicating a good correlation, with cytotoxicity. No significant alterations in cellular drug uptake were observed in DX3 cells. Further studies showed that the nuclei isolated from resistant cells were also resistant to mitoxantrone- or VP16-induced single-strand breaks, indicating that nuclear modifications in resistant cells are responsible for this resistance. Catalytic activity in crude nuclear extracts from wild-type and DX3 cells was almost equal. However, an assay that specifically measures generation of 5'-protein-linked breaks in 32P-labeled 3 DNA revealed that, DNA cleavage activity in nuclear extract from the DX3 cell line is profoundly resistant to a stimulation by VP16. These data indicate that stimulation of topoisomerase-II-mediated DNA cleavage is responsible for topoisomerase-II-targeted drug-cytotoxicity rather than loss of normal topoisomerase catalytic function. These data support the hypothesis that A2780-DX3 cells display an "atypical" multidrug resistance.

Antineoplastic Agents↗
PubMed1995

Interferon-alpha or beta potentiate platinum analogous in human glioblastoma cell lines.

The effect of interferon-alpha or beta on platinum analogues [cisplatin (CDDP) and carboplatin] cytotoxicity was studied in four glioblastoma cell lines (U373MG, T98G, A172 and U118Mg). All cell lines were strongly resistant to the cytotoxic effect of CDDP or carboplatin. Although both interferons were not cytotoxic in all cell lines, they were able to significantly increase the cell platinum-sensitivity. Specifically interferon-alpha increased the magnitude of CDDP-induced DNA interstrand crosslinks. Our findings suggest that interferons are able to induce a very strong potentiation of platinum analogues cytotoxicity in drug-resistant human glioma cell lines.

Antineoplastic Agents↗
PubMed1995

Lack of significant promoting activity by benzene in the rat liver model of carcinogenesis.

The promoting activity of benzene on rat liver carcinogenesis was investigated. The chemical was tested for its ability to enhance the growth of preneoplastic foci, as detected by gamma-glutamyl transpeptidase (GGT) staining in diethylnitrosamine (DENA) initiated hepatocytes. Two weeks after receiving a single ip dose of 200 mg/kg DENA, F344 rats were given daily oral doses of 400 mg/kg benzene (5 d/wk) for 6 wk. At wk 3 after the experiment began, all animals underwent partial hepatectomy, and at wk 8 were sacrificed. Following benzene treatment, no variation in the liver/body weight ratio was observed. After scoring of foci in liver slides, no significant difference in foci number and area could be observed between rats treated with DENA plus benzene and rats treated with DENA alone. Practically no foci were observed in the liver of rats treated only with benzene. The lack of benzene promoting activity in the liver model is discussed.

Animals↗
PubMed1994

Sister-chromatid exchanges, chromosomal aberrations and cytotoxicity produced by topoisomerase II-targeted drugs in sensitive (A2780) and resistant (A2780-DX3) human ovarian cancer cells: correlations with the formation of DNA double-strand breaks.

Doxorubicin, ellipticine and etoposide are antineoplastic drugs with topoisomerase II inhibitory activity. The relationship between drug-induced sister-chromatid exchanges (SCEs) or chromosomal aberrations (CAs) and cytotoxicity, or drug-induced DNA double-strand breaks (DSBs) and cytotoxicity, or drug-induced SCEs and DSBs was investigated in human ovarian cancer cells sensitive (A2780) and resistant (A2780-DX3) to topoisomerase II inhibitors. 30-min drug treatments produced SCEs, CAs and DSBs in sensitive cells, doxorubicin being more potent than etoposide at equimolar concentrations. The same treatments of resistant (A2780-DX3) cells did not produce chromosomal damage (SCEs, CAs, DSBs) and no cytotoxicity was observed. A plot of cytotoxicity versus SCEs indicated a good correlation between these two parameters for topoisomerase II inhibitors and not for mytomicin C. The plot of DSBs versus SCEs also showed a very good correlation.

Antineoplastic Agents↗
PubMed1994

Induction of DNA double-strand breaks by 8-methoxycaffeine: cell cycle dependence and comparison with topoisomerase II inhibitors.

We have studied the ability of 8-methoxycaffeine (8-MOC)--one of the most effective caffeine derivatives in inducing chromosomal aberrations--to induce DNA double strand breaks (DSB) in purified human T lymphocytes during the cell cycle. Etoposide- or ellipticine-mediated DNA break frequency was used as a parameter of topoisomerase II activity. DNA-DSB induced by either 8-MOC or VP16 or ellipticine rose co-ordinately with the level of DNA topoisomerase II and with the onset of DNA replication. At concentrations between 10 and 50 microM 8-MOC was approximately 75% as active in terms of DSB as VP16 and ellipticine. By contrast with VP16 and ellipticine, 8-MOC was not cytotoxic. In conclusion, our data suggest that 8-MOC is an agent that efficiently induces DNA-DSB at non-toxic concentrations, and without direct inhibition of topoisomerase II.

Caffeine↗
PubMed1994

Circumvention of atypical multidrug resistance with tumor necrosis factor.

Some "multidrug-resistant" (MDR) cell lines are not associated with a defect in drug accumulation or with the overexpression of P-glycoprotein. These cell lines are defined as "atypical MDR" (at-MDR) and they often express altered or mutated topoisomerase II. We investigated the ability of tumor necrosis factor to reverse at-MDR (in the human ovarian cancer cell line A2780 DX3) on the basis of its efficacy in potentiating in vitro topoisomerase II-targeted drugs, and because there is convincing evidence that the synergy is due to an increased number of topoisomerase-associated strand-breaks as well as to an increased level of extractable topoisomerase.

DNA Damage↗
PubMed1994

Factors affecting plasma retinol decline during long-term administration of the synthetic retinoid fenretinide in breast cancer patients.

Administration of the synthetic retinoid Fenretinide lowers circulating retinol and may thus affect night vision. We have recently shown that plasma retinol levels below 100 ng/ml are associated with moderate alterations of the dark adaptometry test. To identify which patients are more likely to experience a decrease of plasma retinol under this threshold, we measured plasma levels of retinol, Fenretinide, and its metabolite 4-MPR in a cohort of 28 women receiving Fenretinide at the daily dose of 200 mg and studied their relationship with clinical characteristics such as age, menstrual status, body mass index, and time on treatment. Our results show that patients aged over 55 years with a higher percentage of adipose tissue had higher plasma concentrations of 4-MPR, which turned out to be the major determinant of the retinol decrease. This subgroup may thus deserve careful ophthalmological surveillance.

Adipose Tissue↗