Certification of Total Arsenic in Blood and Urine Standard Reference Materials by Radiochemical Neutron Activation Analysis and Inductively Coupled Plasma - Mass Spectrometry

A newly developed procedure for determination of arsenic by radiochemical neutron activation analysis (RNAA) was used to measure arsenic at four levels in SRM 955c Toxic Elements in Caprine Blood and at two levels in SRM 2668 Toxic Elements in Frozen Human Urine for the purpose of providing mass concentration values for certification. Samples were freeze-dried prior to analysis followed by neutron irradiation for 3 h at a fluence rate of 1×1014cm-2s-1. After sample dissolution in perchloric and nitric acids, arsenic was separated from the matrix by extraction into zinc diethyldithiocarbamate in chloroform, and 76As quantified by gamma-ray spectroscopy. Differences in chemical yield and counting geometry between samples and standards were monitored by measuring the count rate of a 77As tracer added before sample dissolution. RNAA results were combined with inductively coupled plasma - mass spectrometry (ICP-MS) values from NIST and collaborating laboratories to provide certified values of (10.81 ± 0.54) μg/kg and (213.1 ± 0.73) μg/kg for SRM 2668 Levels I and II, and certified values of (21.66 ± 0.73) μg/kg, (52.7 ± 1.1) μg/kg, and (78.8 ± 4.9) μg/kg for SRM 955c Levels 2, 3, and 4 respectively. Because of discrepancies between values obtained by different methods for SRM 955c Level 1, an information value of < 5 μg/kg was assigned for this material.

Effect of 6-aminonicotinamide and other protein synthesis inhibitors on formation of platinum-DNA adducts and cisplatin sensitivity

The present study was undertaken to examine the mechanistic basis for the recent observation that the pyridine nucleotide derivative 6-aminonicotinamide (6AN, NSC 21206) enhances the accumulation and resulting cytotoxicity of cisplatin in a variety of tumor cell lines. When A549 lung cancer cells or K562 leukemia cells were treated with 62.5 microM 6AN for 21 h and then pulse-labeled with [(35)S]methionine for 1 h, increased labeling of five polypeptides, one of which corresponded to a M(r) approximately 78,000 glucose-regulated protein (GRP78), was observed. Two subsequent observations, however, suggested that up-regulation of these polypeptides was unlikely to explain the interaction between 6AN and cisplatin: 1) the concentration of 6AN required to induce GRP78 was 4-fold higher than the dose required to sensitize cells to cisplatin; and 2) simultaneous treatment of cells with 6AN and cycloheximide prevented the increase in GRP78 but not the sensitizing effect of 6AN. On the contrary, treatment with the protein synthesis inhibitors cycloheximide, anisomycin, or puromycin as well as prolonged exposure to the RNA synthesis inhibitor actinomycin D mimicked the biochemical modulating effects of 6AN on cisplatin action. Conversely, 6AN inhibited protein synthesis, whereas 18 6AN analogs that failed to enhance Pt-DNA adducts and cisplatin cytotoxicity failed to inhibit protein synthesis. These observations are consistent with a model in which 6AN and other inhibitors of protein synthesis act as modulating agents by increasing cisplatin accumulation, thereby enhancing the formation of Pt-DNA adducts and subsequent cisplatin-induced cell death.

Characterization of an ovarian carcinoma cell line resistant to cisplatin and flavopiridol

Flavopiridol, the first inhibitor of cyclin-dependent kinases to enter clinical trials, has shown promising antineoplastic activity and is currently undergoing Phase II testing. Little is known about mechanisms of resistance to this agent. In the present study, we have characterized an ovarian carcinoma cell line [OV202 high passage (hp)] that spontaneously developed drug resistance upon prolonged passage in tissue culture. Standard cytogenetic analysis and spectral karyotyping revealed that OV202 hp and the parental low passage line OV202 shared several marker chromosomes, confirming the relatedness of these cell lines. Immunoblotting demonstrated that OV202 and OV202 hp contained similar levels of a variety of polypeptides involved in cell cycle regulation, including cyclin-dependent kinases 2 and 4; cyclins A, D1, and E; and proliferating cell nuclear antigen. Despite these similarities, OV202 hp was resistant to flavopiridol and cisplatin, with increases of 5- and 3-fold, respectively, in the mean drug concentrations required to inhibit colony formation by 90%. In contrast, OV202 hp and OV202 displayed indistinguishable sensitivities to oxaliplatin, paclitaxel, topotecan, 1,3-bis(2-chloroethyl)-1-nitrosourea, etoposide, doxorubicin, vincristine, and 5-fluorouracil, suggesting that the spontaneously acquired resistance was not attributable to altered P-glycoprotein levels or a general failure to engage the cell death machinery. After incubation with cisplatin, whole cell platinum and platinum-DNA adducts measured using mass spectrometry were lower in OV202 hp cells than OV202 cells. Similarly, after flavopiridol exposure, whole cell flavopiridol concentrations measured by a newly developed high performance liquid chromatography assay were lower in OV202 hp cells. These data are consistent with the hypothesis that acquisition of spontaneous resistance to flavopiridol and cisplatin in OV202 hp cells is due, at least in part, to reduced accumulation of the respective drugs. These observations not only provide the first characterization of a flavopiridol-resistant cell line but also raise the possibility that alterations in drug accumulation might be important in determining sensitivity to this agent.

Murine pharmacokinetics of 6-aminonicotinamide (NSC 21206), a novel biochemical modulating agent

The pyridine nucleotide 6-aminonicotinamide (6AN) was shown recently to sensitize a number of human tumor cell lines to cisplatin in vitro. The present studies were undertaken to compare the drug concentrations and length of exposure required for this sensitization in vitro with the drug exposure that could be achieved in mice in vivo. Human K562 leukemia cells and A549 lung cancer cells were incubated with 6AN for various lengths of time, exposed to cisplatin for 1-2 hr, and assayed for Pt-DNA adducts as well as the ability to form colonies. K562 cells displayed progressive increases in Pt-DNA adducts and cisplatin sensitivity during the first 10 hr of 6AN exposure. An 18-hr 6AN exposure was likewise more effective than a 6-hr 6AN exposure in sensitizing A549 cells to cisplatin. HPLC analysis of 6AN and its metabolite, 6-amino-NAD+, permitted assessment of exposures achieved in vivo after i.v. administration of 10 mg/kg of 6AN to CD2F1 mice. 6AN reached peak serum concentrations of 80-90 microM and was cleared rapidly, with T1/2alpha and T1/2beta values of 7.4 and 31.3 min, respectively. Bioavailability was 80-100% with identical plasma pharmacokinetics after i.p. administration. At least 25% of the 6AN was excreted unchanged in the urine. The metabolite 6-amino-NAD+ was detected in perchloric acid extracts of brain, liver, kidney, and spleen, but not in serum. Efforts to prolong systemic 6AN exposure by administering multiple i.p. doses or using osmotic pumps resulted in lethal toxicity. These results demonstrated that 6AN exposures required to sensitize tumor cells to cisplatin in vitro are difficult to achieve in vivo.

6-Aminonicotinamide sensitizes human tumor cell lines to cisplatin

The nicotinamide analogue 6-aminonicotinamide (6AN) is presently undergoing evaluation as a potential modulator of the action of various antineoplastic treatments. Most previous studies of this agent have focused on a three-drug regimen of chemical modulators that includes 6AN. In the present study, the effect of single-agent 6AN on the efficacy of selected antineoplastic drugs was assessed in vitro. Colony-forming assays using human tumor cell lines demonstrated that pretreatment with 30-250 microM 6AN for 18 h resulted in increased sensitivity to the DNA cross-linking agent cisplatin, with 6-, 11-, and 17-fold decreases in the cisplatin dose that diminishes colony formation by 90% being observed in K562 leukemia cells, A549 non-small cell lung cancer cells, and T98G glioblastoma cells, respectively. Morphological examination revealed increased numbers of apoptotic cells after treatment with 6AN and cisplatin compared to cisplatin alone. 6AN also sensitized cells to melphalan and nitrogen mustard but not to chlorambucil, 4-hydroperoxycyclophosphamide, etoposide, or daunorubicin. In additional studies undertaken to elucidate the mechanism underlying the sensitization to cisplatin, atomic absorption spectroscopy revealed that 6AN had no effect on the rate of removal of platinum (Pt) adducts from DNA. Instead, 6AN treatment was accompanied by an increase in Pt-DNA adducts that paralleled the degree of sensitization. This effect was not attributable to 6AN-induced decreases in glutathione or NAD+, because other agents that depleted these detoxification cofactors (buthionine sulfoximine and 3-acetylpyridine, respectively) did not increase Pt-DNA adducts. On the contrary, 6AN treatment increased cellular accumulation of cisplatin. Further experiments revealed that 6AN was metabolized to 6-aminonicotinamide adenine dinucleotide (6ANAD+). Concurrent administration of nicotinamide and 6AN had minimal effect on cellular 6AN accumulation but abolished the formation of 6ANAD+, the increase in Pt-DNA adducts, and the sensitizing effect of 6AN in clonogenic assays. These observations identify 6AN as a potential modulator of cisplatin sensitivity and suggest that the 6AN metabolite 6ANAD+ exerts this effect by increasing cisplatin accumulation and subsequent formation of Pt-DNA adducts.