Enriching suicide gene bearing tumor cells for an increased bystander effect

The success of cancer gene therapies requiring in vivo gene transfer is severely hampered by the low efficacy of gene transfer, which has been difficult to improve. We therefore established a novel strategy to increase the share of transduced cells post gene transfer. We hypothesized that in vivo selection of tumor cells transduced with a suicide gene effectively enriches these cells within a tumor, thus allowing for an increased bystander effect after the prodrug is given, leading to enhanced eradication of tumor cells. We reasoned that in vivo enrichment should be achieved by exploiting the metabolism of the suicide gene product. For this 'enrichment-eradication' strategy we chose a fusion gene of cytosine deaminase and uracil phosphoribosyl transferase. Positive selection (enrichment) was to be achieved by concurrently giving N-(phosphonacetyl)-L-aspartate, an inhibitor of pyrimidine de novo synthesis, which leads to pyrimidine depletion-mediated death of non-transduced cells, and cytosine, to rescue fusion gene expressing cells via the pyrimidine salvage pathway. Negative selection (eradication) was to be induced by giving the prodrug 5-fluorocytosine. Indeed, murine NXS2 neuroblastoma cells transduced with the fusion gene were effectively enriched in vitro, leading to a near-complete bystander effect. In vivo enrichment-eradication of NXS2 cells led to decreased tumor growth. This proof-of-principle study shows that enrichment-eradication may compensate the effects of low in vivo gene transfer efficacy, a major obstacle in cancer gene therapy.

Inhibition of nitric-oxide-mediated apoptosis in Jurkat leukemia cells despite cytochrome c release

We have recently shown that nitric-oxide (NO)-induced apoptosis in Jurkat human leukemia cells requires degradation of mitochondria phospholipid cardiolipin, cytochrome c release, and activation of caspase-9 and caspase-3. Moreover, an inhibitor of lipid peroxidation, Trolox, suppressed apoptosis in Jurkat cells induced by NO donor glycerol trinitrate. Here we demonstrate that this antiapoptotic effect of Trolox occurred despite massive release of the mitochondrial protein cytochrome c into the cytosol and mitochondrial damage. Incubation with Trolox caused a profound reduction of intracellular ATP concentration in Jurkat cells treated by NO. Trolox prevented cardiolipin degradation and caused its accumulation in Jurkat cells. Furthermore, Trolox markedly downregulated the NO-mediated activation of caspase-9 and caspase-3. Caspase-9 is known to be activated by released cytochrome c and together with caspase-3 is considered the most proximal to mitochondria. Our results suggest that the targets of the antiapoptotic effect of Trolox are located downstream of the mitochondria and that caspase activation and subsequent apoptosis could be blocked even in the presence of cytochrome c released from the mitochondria.

Glutathione is a factor of resistance of Jurkat leukemia cells to nitric oxide-mediated apoptosis

We have previously reported that nitric oxide (NO) stimulates apoptosis in different human neoplastic lymphoid cell lines through mitochondrial damage (including degradation of cardiolipin, a major mitochondrial lipid) followed by activation of caspases. Here we demonstrate that Jurkat human leukemia cells which survive after 24 h treatment with NO form subpopulations with higher and lower cardiolipin content (designated as NAO(high) and NAO(low), respectively). Sorted NAO(high) cells were found to survive in culture whereas sorted NAO(low) cells died. Moreover, NAO(high) cells acquired an increased resistance to the exposure to NO donors which remained unchanged during long-term culture. These cells showed a similar cardiolipin content and expressed the same level of anti-apoptotic proteins Bcl-2 and Bcl-x(L) as APO-S unsorted cells but contained significantly higher concentration of the antioxidant glutathione. Depletion of glutathione in these cells with buthionine-sulfoximine (BSO) correlated with a significant stimulation of NO-mediated apoptosis whereas the exposure of NO-sensitive APO-S cells to the glutathione precursor N-acetylcysteine (NAC) resulted in a substantial suppression of this effect. Our data suggest a complex mechanism of the resistence to NO-induced apoptosis in Jurkat human leukemia cells in which glutathione plays an important role.

Mixed-lineage kinase 3 delivers CD3/CD28-derived signals into the IkappaB kinase complex

The phosphorylation of IkappaB by the multiprotein IkappaB kinase complex (IKC) precedes the activation of transcription factor NF-kappaB, a key regulator of the inflammatory response. Here we identified the mixed-lineage group kinase 3 (MLK3) as an activator of NF-kappaB. Expression of the wild-type form of this mitogen-activated protein kinase kinase kinase (MAPKKK) induced nuclear immigration, DNA binding, and transcriptional activity of NF-kappaB. MLK3 directly phosphorylated and thus activated IkappaB kinase alpha (IKKalpha) and IKKbeta, revealing its function as an IkappaB kinase kinase (IKKK). MLK3 cooperated with the other two IKKKs, MEKK1 and NF-kappaB-inducing kinase, in the induction of IKK activity. MLK3 bound to components of the IKC in vivo. This protein-protein interaction was dependent on the central leucine zipper region of MLK3. A kinase-deficient version of MLK3 strongly impaired NF-kappaB-dependent transcription induced by T-cell costimulation but not in response to tumor necrosis factor alpha or interleukin-1. Accordingly, endogenous MLK3 was phosphorylated and activated by T-cell costimulation but not by treatment of cells with tumor necrosis factor alpha or interleukin-1. A dominant negative version of MLK3 inhibited NF-kappaB- and CD28RE/AP-dependent transcription elicited by the Rho family GTPases Rac and Cdc42, thereby providing a novel link between these GTPases and the IKC.

Nitric oxide-mediated apoptosis in human breast cancer cells requires changes in mitochondrial functions and is independent of CD95 (APO-1/Fas)

We have previously shown that nitric oxide (NO) induces apoptosis in different human neoplastic lymphoid cells through caspase activation. Here we studied the NO-mediated apoptosis in human breast cancer cell lines derived from primary tumor (BT-20) or from metastasis (MCF-7). NO donor glycerol trinitrate (GTN) induced apoptosis in both cell lines which was completely abrogated after pretreatment with the broad spectrum caspase inhibitor zVAD-fmk. NO triggered also a time-dependent activation of caspase-1, caspase-3, and caspase-6 in these cells. Moreover, NO caused a release of mitochondrial protein cytochrome c into the cytosol, an increase in the number of cells with low mitochondrial transmembrane potential and with high level of reactive oxygen species production. However, NO did not induce mRNA expression of CD95 (APO-1/Fas) ligand. FAS-associated phosphatase-1 (FAP-1) molecule was constitutively expressed at the mRNA level and did not show any changes upon NO treatment in both breast cancer cell lines. The expression of the pro-apoptotic protein Bax and of the anti-apoptotic protein Bcl-2 remained unchanged in MCF-7 and BT-20 cells upon GTN treatment. We suggest that the mechanism of NO-mediated activation of the caspase cascade and subsequent apoptosis in human breast cancer cells required mitochondrial damage (in particular, cytochrome c release, disruption of mitochondrial transmembrane potential and generation of reactive oxygen species) but not the activation of the CD95/CD95L pathway.

Differential reconstitution of mitochondrial respiratory chain activity and plasma redox state by cysteine and ornithine in a model of cancer cachexia

The mechanism of wasting, as it occurs in malignant diseases and various etiologically unrelated conditions, is still poorly understood. We have, therefore, studied putative cause/effect relationships in a murine model of cancer cachexia, C57BL/6 mice bearing the fibrosarcoma MCA-105. The plasma of these mice showed decreased albumin and increased glutamate levels, which are typically found in practically all catabolic conditions. Skeletal muscles from tumor-bearing mice were found to have an abnormally low mitochondrial respiratory chain activity (mito.RCA) and significantly decreased glutathione (GSH) levels. The decrease in mito.RCA was correlated with an increase in the i.m. GSH disulfide/GSH ratio, the plasma cystine/thiol ratio, and the GSH disulfide/GSH ratio in the bile. This is indicative of a generalized shift in the redox state extending through different body fluids. Treatment of tumor-bearing mice with ornithine, a precursor of the radical scavenger spermine, reversed both the decrease in mito.RCA and the change in the redox state, whereas treatment with cysteine, a GSH precursor, normalized only the redox state. Treatment of normal mice with difluoromethyl-ornithine, a specific inhibitor of ornithine decarboxylase and spermine biosynthesis, inhibited the mito.RCA in the skeletal muscle tissue, thus illustrating the importance of the putrescine/spermine pathway in the maintenance of mito.RCA. Ornithine, cysteine, and N-acetyl-cysteine (NAC) also reconstituted the abnormally low concentrations of the GSH precursor glutamate in the skeletal muscle tissue of tumor-bearing mice. Higher doses, however, enhanced tumor growth and increased the plasma glucose level in normal mice. In the latter, cysteine and NAC also decreased i.m. catalase and GSH peroxidase activities. Taken together, our studies on the effects of ornithine, cysteine, and NAC illuminate some of the mechanistic pathways involved in cachexia and suggest targets for therapeutic intervention.

Nitric-oxide-induced apoptosis in human leukemic lines requires mitochondrial lipid degradation and cytochrome C release

We have previously shown that nitric oxide (NO) stimulates apoptosis in different human neoplastic lymphoid cell lines through activation of caspases not only via CD95/CD95L interaction, but also independently of such death receptors. Here we investigated mitochondria-dependent mechanisms of NO-induced apoptosis in Jurkat leukemic cells. NO donor glycerol trinitrate (at the concentration, which induces apoptotic cell death) caused (1) a significant decrease in the concentration of cardiolipin, a major mitochondrial lipid; (2) a downregulation in respiratory chain complex activities; (3) a release of the mitochondrial protein cytochrome c into the cytosol; and (4) an activation of caspase-9 and caspase-3. These changes were accompanied by an increase in the number of cells with low mitochondrial transmembrane potential and with a high level of reactive oxygen species production. Higher resistance of the CD95-resistant Jurkat subclone (APO-R) cells to NO-mediated apoptosis correlated with the absence of cytochrome c release and with less alterations in other mitochondrial parameters. An inhibitor of lipid peroxidation, trolox, significantly suppressed NO-mediated apoptosis in APO-S Jurkat cells, whereas bongkrekic acid (BA), which blocks mitochondrial permeability transition, provided only a moderate antiapoptotic effect. Transfection of Jurkat cells with bcl-2 led to a complete block of apoptosis due to the prevention of changes in mitochondrial functions. We suggest that the mitochondrial damage (in particular, cardiolipin degradation and cytochrome c release) induced by NO in human leukemia cells plays a crucial role in the subsequent activation of caspase and apoptosis.