CD40 and B chronic lymphocytic leukemia cell response to fludarabine: the influence of NF-kappaB/Rel transcription factors on chemotherapy-induced apoptosis

WITHDRAWN: Evidence for the critical roles of NF-κB p65 and specificity proteins in the apoptosis-inducing activity of proteasome inhibitors in leukemia cells

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The NF-κB subunit Rel A is associated with in vitro survival and clinical disease progression in chronic lymphocytic leukemia and represents a promising therapeutic target

In this study, we characterized nuclear factor κB (NF-κB) subunit DNA binding in chronic lymphocytic leukemia (CLL) samples and demonstrated heterogeneity in basal and inducible NF-κB. However, all cases showed higher basal NF-κB than normal B cells. Subunit analysis revealed DNA binding of p50, Rel A, and c-Rel in primary CLL cells, and Rel A DNA binding was associated with in vitro survival (P = .01) with high white cell count (P = .01) and shorter lymphocyte doubling time (P = .01). NF-κB induction after in vitro stimulation with anti-IgM was associated with increased in vitro survival (P < .001) and expression of the signaling molecule ZAP-70 (P = .003). Prompted by these data, we evaluated the novel parthenolide analog, LC-1, in 54 CLL patient samples. LC-1 induced apoptosis in all the samples tested with a mean LD50 of 2.8 μM after 24 hours; normal B and T cells were significantly more resistant to its apoptotic effects (P < .001). Apoptosis was preceded by a marked loss of NF-κB DNA binding and sensitivity to LC-1 correlated with basal Rel A DNA binding (P = .03, r2 = 0.15). Furthermore, Rel A DNA binding was inversely correlated with sensitivity to fludarabine (P = .001, r2 = 0.3), implicating Rel A in fludarabine resistance. Taken together, these data indicate that Rel A represents an excellent therapeutic target for this incurable disease.

Proteasome inhibition as novel treatment strategy in leukaemia

Following its success in multiple myeloma (MM), proteasome inhibition has become a topic of interest as novel treatment strategy of cancer. By simultaneously affecting multiple pathways in the cancer cell, such as deregulation of the programmed degradation of many cellular proteins, proteasome inhibition causes rapid apoptosis of these cells. Both in rapidly proliferating leukaemic cell lines and in primary leukaemic cells isolated from patients, proteasome inhibition results in antileukaemic activity. The normal counterparts of these cells are much more resistant to proteasome inhibitors (PI), thereby resulting in a favourable therapeutic index. Importantly, while leukaemic stem cells are sensitive to proteasome inhibition, normal haematopoietic stem cells are still viable after drug exposure. Nowadays, many PIs are being identified; bortezomib is the most well known since obtaining Food and Drug Administration approval for clinical use in MM. This review summarises the biological and clinical aspects of proteasome inhibition and discusses the potential role of these inhibitors in the treatment of leukaemia.

NF-kappaB modulation and ionizing radiation: mechanisms and future directions for cancer treatment

NF-kappaB transcription factor regulates important cellular processes ranging from establishment of the immune and inflammatory responses to regulation of cell proliferation or apoptosis, through the induction of a large array of target genes. NF-kappaB is now considered as an important actor in the tumorigenic process mainly because it exerts strong anti-apoptotic functions in cancer cells. NF-kappaB is triggered by chimio- and radio-therapeutic strategies that are intended to eliminate cancerous cells through induction of apoptosis. Numerous studies have demonstrated that inhibition of NF-kappaB by different means increased sensitivity of cancer cells to the apoptotic action of diverses effectors such as TNFalpha or chemo- or radio-therapies. From these studies as emerged the concept that NF-kappaB blockade could be associated to conventional therapies in order to increase their efficiency. This review focuses on the current knowledge on NF-kappaB regulation and discusses the therapeutic potential of targeting NF-kappaB in cancer in particular during radiotherapy.

TNF-α-mediated apoptosis in normal human prostate epithelial cells and tumor cell lines

In this study we compared the role of TNF-alpha in the regulation of growth and apoptosis in normal human prostate epithelial cells (NP) and prostate tumor cell lines PC3 and LNCap. The NP and PC3 cells were resistant whereas the LNCap cell line was highly sensitive to TNF-alpha induced growth arrest and apoptosis. The resistance of NP and PC3 cells was mediated via an NF-kB survival pathway as treatment of resistant cells with TNF-alpha was accompanied by phosphorylation of I-kBalpha and translocation of NF-kB to the nucleus. TNF-alpha did not induce phosphorylation of I-kB in the sensitive LNCap cells. The sensitivity of LNCap cells involved a cysteine protease cascade as Z-VAD-CH2 F reversed the sensitivity of LNCap cells and induced resistance to TNF-alpha. The differences in susceptibilities to TNF-alpha induced apoptosis of NP and certain prostate tumor cells offer intriguing possibilities for the treatment of prostate cancer without affecting the normal prostate tissue.

NF- kappa B2/p100 induces Bcl-2 expression

The NF-kappaB2/p100 and bcl-3 genes are involved in chromosomal translocations described in chronic lymphocytic leukemias (CLL) and non-Hodgkin's lymphomas, and nuclear factor kappaB (NF-kappaB) protects cancer cells against apoptosis. Therefore, we investigated whether this transcription factor could modulate the expression of the Bcl-2 antiapoptotic protein. Bcl-2 promoter analysis showed multiple putative NF-kappaB binding sites. Transfection assays of bcl-2 promoter constructs in HCT116 cells showed that NF-kappaB can indeed transactivate bcl-2. We identified a kappaB site located at position -180 that can only be bound and transactivated by p50 or p52 homodimers. As p50 and p52 homodimers are devoid of any transactivating domains, we showed that they can transactivate the bcl-2 promoter through association with Bcl-3. We also observed that stable overexpression of p100 and its processed product p52 can induce endogenous Bcl-2 expression in MCF7AZ breast cancer cells. Finally, we demonstrated that, in breast cancer and leukemic cells (CLL), high NF-kappaB2/p100 expression was associated with high Bcl-2 expression. Our data suggest that Bcl-2 could be an in vivo target gene for NF-kappaB2/p100.

Enhancement of cytosine arabinoside-induced apoptosis in human myeloblastic leukemia cells by NF-kappa B/Rel- specific decoy oligodeoxynucleotides

The activity of NF-kappa B/Rel nuclear factors is known to inhibit apoptosis in various cell types. We investigated whether the subtraction of NF-kappa B/Rel activity influenced the response of 11 AML (M1, M2 and M4) patients' cells to AraC. To this end we used a phosphorothioate double-stranded decoy oligodeoxynucleotide (ODN) carrying the NF-kappa B/Rel- consensus sequence. Cell incubation with this ODN, but not its mutated (scrambled) form used as a control, resulted in abating the NF-kappa B/Rel nuclear levels in these cells, as verified by electrophoretic mobility shift assay (EMSA) of cells' nuclear extracts. We incubated the leukemic cells with AraC (32 or 1 microM), in either the absence or presence of the decoy or the scrambled ODN, and analyzed cell apoptosis. The spontaneous cell apoptosis detectable in the absence of AraC (<25%) was not modulated by the oligonucleotide presence in cell cultures. On the other hand, in 10 of the 11 samples tested, the decoy kappa B, but not the scrambled ODN significantly (P < 0.01 in a Student's t test) enhanced cell apoptotic response to AraC. Such an effect was particularly remarkable at low AraC doses (1 microM). These findings indicate that NF-kappa B/Rel activity influences response to AraC in human primary myeloblastic cells, and suggests that the inhibition of NF-kappa B/Rel factors can improve the effect of chemotherapy in AML. Gene Therapy (2000) 7, 1234-1237.