The use of reverse diffusion to validate the performance of diffusive samplers.

A number of different protocols have been put forth for measuring reverse diffusion from diffusive samplers. The basic concept is that reverse diffusion tests, depending as they do on basic laws of mass transfer, are not independent of one another, but may give general information about the limits to the possible change that can occur if the conditions to measure reverse diffusion are changed. Laboratory measurements of the reverse diffusion of vinyl chloride, using 3M and SKC diffusive samplers, following both the National Institute for Occupational Safety and Health (NIOSH) and the European Union test protocols, support the mathematical analysis developed in this article. An important conclusion is that if in following the NIOSH protocol a diffusive sampler loses 10% of its analyte over a period of 4 hours, then the maximum loss expected from a sampler allowed to back-diffuse for 8 hours is 19%.

Expression of antisense RNA to aldehyde dehydrogenase class-1 sensitizes tumor cells to 4-hydroperoxycyclophosphamide in vitro.

Previous studies in this laboratory showed that the overexpression of human aldehyde dehydrogenase class-1 (ALDH-1) with a retroviral vector resulted in increased resistance to 4-hydroperoxycyclophosphamide (4-HC), an active metabolite of cyclophosphamide. The present study examined the effect of ALDH-1 antisense RNA expression on ALDH-1 activity and sensitivity to 4-HC toxicity. Three different ALDH-1 cDNAs were synthesized that are either missing the N terminus (N), C terminus (C), or both (NC) and subcloned into the BamHI cloning site of pLXSN retroviral vector in the antisense (AS) orientation (AS-N, AS-C, and AS-NC, respectively). It was demonstrated that the overexpression of each of the AS constructs in K562 leukemic cells and A549 lung cancer cells results in suppression of ALDH-1 mRNA and enzymatic activity. Furthermore, the AS-N and AS-NC were generally more effective than AS-C in reducing the ALDH-1 activity. Both K562 and A549 cells expressing the ALDH-1 AS became significantly more sensitive to 4-HC toxicity as demonstrated by clonogenic and liquid culture assays. The increase in 4-HC sensitivity was in correlation with the degree of suppression of ALDH-1 activity. Moreover, such increase in 4-HC sensitivity, especially with AS-N and AS-NC, was to a similar degree seen with the use of diethylaminobenzaldehyde, a specific inhibitor of ALDH-1. These results indicate that ALDH-1 expression and activity can be specifically and effectively suppressed by AS RNA and lead to increased sensitivity to 4-HC.

In vitro selection for K562 cells with higher retrovirally mediated copy number of aldehyde dehydrogenase class-1 and higher resistance to 4-hydroperoxycyclophosphamide.

Previously, we have reported the successful expression of human aldehyde dehydrogenase class-1 (ALDH-1) in K562 leukemia cells using a retroviral vector and demonstrated low expression that resulted in up to three-fold increase in resistance to 4-hydroperoxycyclophosphamide (4-HC), an active derivative to cyclophosphamide. The purpose of this study was to investigate whether in vitro treatment with 4-HC will allow selection of K562 cells expressing higher levels of ALDH-1, and whether these selected cells are more resistant to 4-HC. Stably transfected or transduced K562 cells with retroviral pLXSN vector containing ALDH-1 cDNA (ALDH-1 cells) were treated repeatedly with 4-HC and then allowed to grow to confluence in liquid culture. Subsequently, the resistance to 4-HC of ALDH-1 cells treated once (ALDH-1+) or twice (ALDH-1++) with 4-HC was compared to ALDH-1 cells or wild-type K562 cells (WT cells). The results show significant increase in 4-HC resistance of ALDH-1+ (2- to 16-fold, p < 0.005) over ALDH-1 or WT cells. No difference was detected between ALDH-1+ and ALDH-1++. In addition, higher ALDH-1 mRNA and enzyme activity were found in ALDH-1+ compared to ALDH-1 cells. Southern analysis of DNA extracted from the different experimental groups demonstrated an eight-fold increase in ALDH-1 cDNA in ALDH-1+ versus the ALDH-1 cells. This was confirmed by sequential FISH analysis using biotin labeled pLXSN/ALDH-1 vector. Positive signals consistently localized to the centromeric region of chromosome 9 and the long arm of chromosome 17 were demonstrated only in the ALDH-1+ cells and represented a fusion product of multiple copies of the pLXSN/ALDH-1 vector. In summary, we have demonstrated that in vitro treatment with 4-HC results in the selection of K562 cells with multiple copies of ALDH-1 gene that are clustered in two main integration sites. These cells demonstrate significantly higher resistance to 4-HC when compared to previously untreated cells. Such successful in vitro selection could have significant implications for future cancer gene therapy protocols.

Human A1, a Bcl-2-related gene, is induced in leukemic cells by cytokines as well as differentiating factors.

Based on previously published observations regarding the protective effects of interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha) against gamma radiation, alkylating agents and ultraviolet radiation, we hypothesized that the protection against such DNA damaging treatments can be the result of a 'stress'-like response induced by these cytokines and mediated by early response cellular gene(s). By applying the mRNA differential display to RNA obtained from A549 lung carcinoma cell line that was incubated with 50 ng/ml IL-1 for 0, 1, 2, and 6 h, we identified several cDNA fragments that correspond to genes regulated by IL-1. The full length cDNA for one fragment was obtained using 5'RACE, cloned, sequenced, and found to be homologous to human A1, a Bcl-2-related gene. In this study, we report that the expression of human A1 is either absent or present at low levels in leukemic cells, while it is expressed in human bone marrow cells and abundant in peripheral blood progenitors. It is induced by IL-1 and TNF alpha in A549 lung carcinoma, bone marrow, and certain leukemic cells. A1 is also induced in leukemic cells during granulocytic or macrophage but not erythroid differentiation. In conclusion, this is the first demonstration that A1 is inducible by cytokines in human bone marrow and certain tumor cells as well as myeloid differentiation in leukemic cells.

Overexpression of the human aldehyde dehydrogenase class I results in increased resistance to 4-hydroperoxycyclophosphamide.

A correlation between overexpression of aldehyde dehydrogenase and resistance to oxazaphosphorines, widely used anticancer agents, has been shown. To investigate the direct role of the human aldehyde dehydrogenase class 1 (ALDH-1) in the resistance to one of these agents, 4-hydroperoxycyclophosphamide (4-HC), an active metabolite of cyclophosphamide, neomycin-selectable plasmid or retroviral constructs harboring the wild-type ALDH-1 complementary DNA in the sense orientation were transfected into K562 leukemic cell lines. Polymerase chain reaction (PCR) analysis confirmed the presence of vector DNA in the stably transfected K562 cells. Reverse transcriptase PCR and Northern and Western blot analysis showed expression of ALDH-1 mRNA and protein in the cells transfected with ALDH-1 in the sense orientation but not in cells transfected with vector alone. The activity of the expressed ALDH-1 was demonstrated using spectrophotometric assay. Stably transfected K562 cells were subjected to various doses of 4-HC, and cell viability was assayed using clonogenic cell culture in semisolid medium. Results demonstrate that K562 cells transfected with ALDH-1 in the sense orientation display increased resistance to 4-HC compared with wild-type or vector-transfected K562 cells. Furthermore, the addition of diethylaminobenzaldehyde, a specific inhibitor for ALDH-1, restored the sensitivity of the ALDH-1-expressing K562 cells to 4-HC. Thus, the data pinpoint the direct role of ALDH-1 in the protection against 4-HC cytotoxicity.

Interleukin-1 and tumor necrosis factor alpha induce class 1 aldehyde dehydrogenase mRNA and protein in bone marrow cells.

Interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha) protect normal human hematopoietic progenitors from the toxicity of 4-hydroperoxycyclophosphamide (4-HC). Aldehyde dehydrogenase Class 1 (ALDH-1) is the enzyme that inactivates 4-HC. Diethylaminobenzaldehyde (DEAB), a competitive inhibitor of ALDH-1, was shown to prevent the protective effects of IL-1 and TNF alpha. In this study, we examined the effect of IL-1 and TNF alpha on the expression of ALDH-1 in normal bone marrow as well as malignant cells. ALDH-1 mRNA and protein were quantified using Northern and Western blotting, respectively. In addition, the ALDH-1 enzyme activity in untreated as well as IL-1 and TNF alpha treated bone marrow cells was determined spectrophotometrically. The role of glutathione (GSH) in the protection against 4-HC toxicity was also studied. The results show that pretreatment with IL-1 and TNF alpha for 6 h or 20 h increase the expression of ALDH-1 mRNA and protein, respectively, in human bone marrow cells. In contrast, IL-1 and TNF alpha treatment did not affect the ALDH-1 expression in several leukemic and solid tumor cell lines, regardless of whether or not ALDH-1 is expressed constitutively. Furthermore, the ALDH-1 enzyme activity was significantly induced in bone marrow cells after 20 h pre-treatment with IL-1 and TNF alpha. Finally, the depletion of or inactivation of GSH did not affect the protection against 4-HC toxicity. In conclusion, inhibition of the protection from 4-HC toxicity by DEAB, together with the increase in ALDH-1 expression and activity, provide strong evidence that IL-1 and TNF alpha mediate their protective action, at least partially, through ALDH-1.