Characterization of a new cell line (ESKOL) resembling hairy-cell leukemia: a model for oncogene regulation and late B-cell differentiation

Molecular Action of Polyphenols in Leukaemia and Their Therapeutic Potential

Leukaemia is a malignant disease of the blood. Current treatments for leukaemia are associated with serious side-effects. Plant-derived polyphenols have been identified as potent anti-cancer agents and have been shown to work synergistically with standard chemotherapy agents in leukaemia cell lines. Polyphenols have multiple mechanisms of action and have been reported to decrease cell proliferation, arrest cell cycle and induce apoptosis via the activation of caspase (3, 8 and 9); the loss of mitochondrial membrane potential and the release of cytochrome c. Polyphenols have been shown to suppress activation of transcription factors, including NF-kB and STAT3. Furthermore, polyphenols have pro-oxidant properties, with increasing evidence that polyphenols inhibit the antioxidant activity of glutathione, causing oxidative DNA damage. Polyphenols also induce autophagy-driven cancer cell death and regulate multidrug resistance proteins, and thus may be able to reverse resistance to chemotherapy agents. This review examines the molecular mechanism of action of polyphenols and discusses their potential therapeutic targets. Here, we discuss the pharmacological properties of polyphenols, including their anti-inflammatory, antioxidant, anti-proliferative, and anti-tumour activities, and suggest that polyphenols are potent natural agents that can be useful therapeutically; and discuss why data on bioavailability, toxicity and metabolism are essential to evaluate their clinical use.

Hyperforin inhibits P-gp and BCRP activities in chronic lymphocytic leukaemia cells and myeloid cells

We showed previously that hyperforin (HF), a natural phloroglucinol, stimulated apoptosis in B cell chronic lymphocytic leukaemia cells (CLL) and displayed anti-angiogenic properties. In the present work, we investigated the effects of hyperforin on the activity of P-gp/MDR1, an ABC (ATP-binding cassette) transporter putatively involved in multidrug resistance (MDR). Ex vivo treatment of CLL cells with HF markedly impaired the activity of P-gp, as measured by the inhibition of the capacity of the treated cells to efflux the rhodamine 123 probe. In addition, most CLL cells expressed breast cancer resistance protein (BCRP), another ABC transporter. The activity of BCRP was also inhibited by HF, as assessed by the impaired capacity of HF-treated CLL cells to efflux the specific probe mitoxantrone. The capacity of HF to reverse P-gp and BCRP activity was confirmed in myeloid leukaemia cell lines, notably in HL-60/DNR cells selected for their resistance to daunorubicine and overexpressing P-gp. Our results therefore suggest that HF might be of interest in the therapy of CLL and other haematological malignancies through its potential capacity to revert MDR in addition to its pro-apoptotic properties.

Apoptotic effects on B-cell chronic lymphocytic leukemia (B-CLL) cells of heterocyclic compounds isolated from Guttiferaes

A series of 10 heterocyclic compounds purified from Allanblackia were tested on two B cell lines, ESKOL and EHEB, and on cells from B-CLL patients. Several molecules inhibited the proliferation of both cell lines and promoted apoptosis of B-CLL cells through different mechanisms, some of them elicited a dissipation of the mitochondrial transmembrane potential, other triggered caspase-3 activation and cleavage of the inducible nitric oxide synthase. Blood mononuclear cells and B-lymphocytes from healthy donors appeared less sensitive than B-CLL cells. These results indicate that these molecules may be of interest in the development of new therapies for B-CLL.

Flavopiridol-induced iNOS downregulation during apoptosis of chronic lymphocytic leukemia cells is caspase-dependent

We previously reported that flavopiridol-induced apoptosis of B cell chronic lymphocytic leukemia (CLL) patients' cells ex vivo is associated with downregulation of both the inducible nitric oxide (NO) synthase (iNOS) that produces the antiapoptotic molecule NO, and the CDK inhibitor p27kip1 that is thought to block the cell cycle of CLL cells. Here, we show that iNOS downregulation is caspase-dependent and thus can be considered as one of the effector mechanisms of apoptosis, but not a primary triggering event induced by flavopiridol. Furthermore, we also find that this flavone favors the entry into the S and G2 phases of the cell cycle of a subpopulation of the leukemic cells, confirming that flavopiridol might be useful for improving the efficacy of cell cycle-dependent cytostatic agents in the therapy of CLL.

Evolving concepts in the pathogenesis of hairy-cell leukaemia

Hairy-cell leukaemia (HCL) has long been recognized as distinct from other chronic B-cell malignancies, but several questions remain unanswered. What is the HCL cell of origin? Why does HCL lack the hallmarks of most mature B-cell tumours (for example, chromosomal translocations and consistent lymph node involvement) and show unique features like 'hairy' morphology and bone-marrow fibrosis? Gene-expression profiling and other studies have recently provided new insights into HCL biology and have the potential to affect clinical practice.

RhoGTPases and p53 are involved in the morphological appearance and interferon-alpha response of hairy cells

Hairy cell leukemia is an uncommon B-cell lymphoproliferative disease of unknown etiology in which tumor cells display characteristic microfilamentous membrane projections. Another striking feature of the disease is its exquisite sensitivity to interferon (IFN)-alpha. So far, none of the known IFN-alpha regulatory properties have explained IFN-alpha responsiveness nor have they taken into account the morphological characteristics of hairy cells. IFN-alpha profoundly alters cytoskeletal organization of hairy cells and causes reversion of the hairy appearance into a rounded morphology. Because cytoskeletal rearrangements are controlled by the Rho family of GTPases, we investigated the GTPase activation status in hairy cells and their regulation by IFN-alpha. Using immunolocalization techniques and biochemical assays, we demonstrate that hairy cells display high levels of active Cdc42 and Rac1 and that IFN-alpha down-regulates these activities. In sharp contrast, RhoA activity was low in hairy cells but was increased by IFN-alpha treatment. Finally, IFN-alpha-mediated morphological changes also implicated a p53-induced response. These observations shed light on the mechanism of action of IFN-alpha in hairy cell leukemia and are of potential relevance for the therapeutical applications of this cytokine.

Flavones and polyphenols inhibit the NO pathway during apoptosis of leukemia B-cells

We recently reported that resveratrol, a grape-derived polyphenol, in vitro induces the apoptosis of leukemic B-cells and simultaneously inhibits the production of endogenous nitric oxide (NO) through inducible NO synthase (iNOS) down-regulation. The same results were observed in the present study with not only acetate derivatives of polyphenols, particularly the pentaacetate of -viniferin (resveratrol dimer), but also with a synthetic flavone (a diaminomethoxyflavone) in both leukemia B-cell lines and B-cell chronic lymphocytic leukemia (B-CLL) patients' cells. Moreover, flavopiridol, another flavone already known for its pro-apoptotic properties in B-CLL cells, was also found to down-regulate both iNOS expression and NO production. Thus, inhibition of the NO pathway during apoptosis of leukemia B-cells appears a common mechanism for several compounds belonging to two distinct families of phytoalexins, the flavones and grape-derived polyphenols.

Comparative antiproliferative and apoptotic effects of resveratrol, epsilon-viniferin and vine-shots derived polyphenols (vineatrols) on chronic B lymphocytic leukemia cells and normal human lymphocytes

Trans-resveratrol, its dimer epsilon-viniferin and two preparations of vineatrol (a grape-derived polyphenol fraction isolated from vine-shots extracts) were compared for their effects on the proliferation and survival of normal and leukemic human lymphocytes. The two different batches of vineatrol (vineatrol 10 and 25%) was obtained by HPLC fractionation and contained 10 and 25% trans-resveratrol, respectively. The different polyphenols were added to cultures of leukemic cells from chronic B cell malignancies (B-cell chronic lymphocytic leukemia, B-CLL or hairy cell leukemia, HCL) or normal peripheral blood-derived mononuclear cells (PBMC) as a control. The different polyphenols displayed anti-proliferative effect on the leukemic cells, as estimated by the observed inhibition of tritiated thymidine uptake and the reduction of cell recovery. Vineatrol 10% was the most potent whereas vineatrol 25% and resveratrol displayed comparable activity, epsilon-viniferin only exhibiting slight effets. The same order of potency was observed for their capacity to induce apoptosis in leukemic B cells. In contrast, the survival of normal peripheral blood mononuclear cells (PBMC) was little affected in the presence of these polyphenolic compounds and higher concentrations were required in order to elicit cell death. Polyphenol-driven apoptosis in chronic leukemic B cells was shown to correlate with an activation of caspase 3, a drop in the mitochondrial transmembrane potential, a reduction in the expression of the anti-apoptotic protein bcl-2, as well as a reduction in the expression of the inducible nitric oxide synthase (iNOS). Our data therefore indicate that vine-shoots may be a convenient and natural source of material for the purification of resveratrol and other polyphenolic compounds of putative therapeutic interest.

Analysis of resveratrol-induced apoptosis in human B-cell chronic leukaemia

Trans-resveratrol was analysed for its apoptotic and growth inhibitory activity in human B-cell lines derived from chronic B-cell malignancies (WSU-CLL and ESKOL), and in leukaemic lymphocytes from patients with B-cell chronic lymphocytic leukaemia (B-CLL). Resveratrol displayed antiproliferative activity on both B-cell lines, as estimated by the decrease in cell recovery and inhibition of thymidine uptake. Furthermore, resveratrol induced apoptosis in the two cell lines as well as in B-CLL patients' cells, as evidenced by the increase in annexin V binding, caspase activation, DNA fragmentation and decrease of the mitochondrial transmembrane potential DeltaPsim. We previously reported that nitric oxide (NO), endogenously released by an iNO synthase (iNOS) spontaneously expressed in these leukaemic cells, contributed to their resistance towards apoptosis. We show here that resveratrol inhibited both iNOS protein expression and in situ NO release in WSU-CLL, ESKOL and B-CLL patients'cells. In addition, Bcl-2 expression was also inhibited by resveratrol. Thus, downregulation of the two anti-apoptotic proteins iNOS and Bcl-2 can contribute to the apoptotic effects of resveratrol in leukaemic B cells from chronic leukaemia. Our data suggest that this drug is of potential interest for the therapy of B-CLL.

Interferon-alpha 2b and vesnarinone influence levels of tumor necrosis factor-alpha, apoptosis, or interleukin 6 in ESKOL, a hairy cell leukemic cell line. A potential cytokine and oncogene relationship regulating apoptosis is suggested

The in vitro effects of interferon-alpha (IFN) on levels of secreted interleukin 6 (IL-6), tumor necrosis factor-alpha (TNF alpha), and nuclear matrix proteins (NMP) were examined in ESKOL, a B-lymphoblastoid cell line resembling hairy cell leukemia (HCL). IFN enhances differentiation in ESKOL, decreases TNF alpha levels, decreases apoptosis, increases IL-6 levels, and down regulates the expression of several oncogenes. Vesnarinone (Ves), a TNF alpha repressor, lowers TNF-alpha and decreases apoptosis in the same cell line. ESKOL exhibits enhanced apoptosis and reduced B-cell lymphomas (Bcl-2) levels over WIL-2. IL-6 and TNFalpha have been shown to decrease and increase apoptosis in B-cells respectively; however, treatment of ESKOL with these cytokines had no significant effect on apoptosis. We suggest that IFN decreases apoptosis by mechanisms involving enhanced IL-6 and Bcl-2 levels, decreased TNF alpha and the down regulation of apoptotic oncogenes, including c-myc.

Aberrant expression and localization of the cytoskeleton-binding pp52 (LSP1) protein in hairy cell leukemia

Non-retractable cell surface projections and cytoskeleton-mediated functional defects are distinguishing features of both hairy cell leukemia (HCL) and neutrophil actin dysfunction (NAD). These defects in NAD neutrophils are attributed to moderate over-expression of pp52 (LSP1), the F-actin-binding, leukocyte-specific phosphoprotein. Here we report that pp52 is similarly elevated in HCL patient PBMCs. Established HCL cell lines exhibited characteristic morphological features like those of fresh HCL cells and showed elevated pp52 levels. The excess pp52 in these HCL cell lines was selectively associated with the F-actin-rich cytoskeletal arrays in surface projections. Treatments producing radical changes in HCL cell shape also altered pp52 expression and intracellular distribution. Alpha interferon (IFNalpha, used to treat HCL) reduced pp52 levels, normalized intracellular pp52 distribution and reverted HCL cells to rounded B cell morphology. Phorbol ester stimulation rapidly generated hyper-phosphorylated pp52 isoforms which translocated from the cytoskeleton to the cytosol prior to the further elongation of surface spikes. This indicates a direct role for phosphorylation in controlling pp52 interactions with the cytoskeleton. Overall, these findings strongly suggest that elevated pp52 expression and/or selective cytoskeletal association contributes to the distinctive morphology of HCL cells.

Expression of a functional inducible nitric oxide synthase in hairy cell leukaemia and ESKOL cell line

The expression of nitric oxide synthase (NOS) isoforms was investigated in the established ESKOL hairy cell line and in leukemic cells of patients with hairy cell leukemia (HCL). By reverse transcription-polymerase chain reaction (RT-PCR), these cells were found to spontaneously express inducible NOS (iNOS)-specific mRNA, but not endothelial constitutive NOS (ecNOS) mRNA. The iNOS protein was detected by immunofluorescence in the cytoplasm of permeabilized leukemic cells and ESKOL cells, using different anti-iNOS monoclonal antibodies. A protein of 135 kDa was identified by Western blotting in ESKOL and HCL lysates, confirming the presence of an iNOS in these cells. Cytosolic homogenates displayed NOS catalytic activity, as measured by the conversion of 14C-labelled L-arginine into 14C L-citrulline and by detection in situ using the DAF-2DA (diaminofluorescein diacetate) NO-sensitive fluorescent probe. Ligation of CD23 (low affinity IgE receptor) was found to increase iNOS expression in ESKOL and conversely to decrease the percentage of cells undergoing apoptosis, as measured by the percentage of cells expressing annexin V. These results indicate that, as in chronic B cell lymphocytic leukemia cells (B-CLL) a functional iNOS is expressed constitutively in hairy cells that contributes to protecting these tumoral cells from apoptosis.

Switch in the protein tyrosine phosphatase associated with human CD100 semaphorin at terminal B-cell differentiation stage

Human CD100, the first semaphorin identified in the immune system, is a transmembrane protein involved in T-cell activation. In the present study, we showed that activation of peripheral blood or tonsillar B lymphocytes induced the expression of CD100 in CD38+CD138− cell populations, including in CD148+ subpopulations, thus expressing a memory B-cell–like phenotype. Using an in vitro enzymatic assay, we found that protein tyrosine phosphatase (PTP) activities were immunoprecipitated with CD100 in these cell populations, which were isolated by cell sorting, as well as in most B-cell lines representing various stages of B-cell differentiation. Immunodepletion and Western blotting experiments demonstrated that CD45 was the PTP associated with CD100 in cell lines displaying pre-B, activated B, and pre-plasma cell phenotypes. CD45 also accounted for PTP activity immunoprecipitated with CD100 in CD38+CD138− cells sorted after activation of peripheral blood or tonsillar B lymphocytes. In contrast, no CD100-CD45 association was observed in plasma cell lines corresponding to the terminal B-cell differentiation stage. CD148, the other transmembrane PTP known to be implicated in lymphocyte signaling pathways, was either only partly involved in the CD100-associated PTP activity or not expressed in plasma cell lines, indicating the association of CD100 with another main PTP. Our data show that CD100 is differentially expressed and can functionally associate with distinct PTPs in B cells depending on their activation and maturation state. They also provide evidence for a switch in the CD100-associated PTP at terminal stage of B-cell differentiation.

Upregulation of CD38 gene expression in leukemic B cells by interferon types I and II

The activation antigen CD38, which has NAD+ glycohydrolase activity in its extracellular domain, is expressed by a large variety of cell types. Few investigations into the regulation of CD38 expression by physiologic stimuli have been reported. As the CD38 promoter contains potential binding sites for interferon (IFN) regulatory factor-1 (IRF-1), we investigated the influence of IFN type I (alpha and beta) and type II (gamma) on CD38 gene expression of leukemic B cells. Using the IFN-responsive B cell line Eskol, we found by RT-PCR analysis a rapid time-dependent induction in CD38 mRNA (starting at 6 h) with each type of IFN. This induction was independent of protein synthesis, suggesting that CD38 gene activation does not require IRF-1 but is merely under direct transcriptional regulation by latent IFN-inducible factors. mRNA stimulation was followed within 24 h by induction of membrane CD38, which coincided with rises of CD38-specific ectoenzymatic activities, that is, NAD+ glycohydrolase, (A/G)DP-ribosyl cyclase, and cyclic ADP ribose hydrolase activities. IFN failed to induce or upregulate the other CD38-related ectoenzymes analyzed, that is, CD39, CD73, CD157, and PC-1. Similarly, treatment of leukemic cells of patients with B chronic lymphocytic leukemia (B-CLL) with IFN resulted in an increase in CD38 mRNA mirrored by plasma membrane upregulation of CD38 and NAD+ glycohydrolase activity. Further investigation in relation to CD38 gene activation and B-CLL behavior remains to be defined.

The hairy cell leukemia cell line Eskol spontaneously synthesizes tumor necrosis factor-alpha and nitric oxide

Tumor necrosis factor-alpha (TNF-alpha) and nitric oxide (NO) exert a wide array of immunoregulatory, partly related effects. We examined the production of these two mediators by the human hairy cell leukemia cell line Eskol. Combined cell lysate and supernatant of Eskol cells (0.5 x 10(6) cells ml(-1)) incubated for 18 h, contained a mean of 1.5 ng ml(-1) TNF-alpha. This spontaneous TNF-alpha synthesis was enhanced by phorbol ester (PMA) and phytohemagglutinin (PHA) and decreased by dexamethasone. Nitrite, the stable product of NO, accumulated in the supernatant of Eskol cells after prolonged incubation. Maximal nitrite concentrations (range: 0.8-3.5 microM at 2 x 10(6) cells ml(-1)) were detected after 7 days of incubation. NO production was augmented by PHA and reduced by PMA. The inhibitors of NO synthase N(G)-monomethyl-L-arginine (L-NMMA) and aminoguanidine decreased NO synthesis. Simultaneous activation with the proinflammatory cytokines, interferon-gamma, interleukin-1beta and TNF-alpha, increased NO synthesis. These results suggest that NO production in Eskol cells results from inducible NO synthase activity. This is the first direct demonstration of NO formation in human lymphoid cells. The cell line, Eskol, may serve as a model to study regulation of TNF-alpha and NO synthesis in human B-cell leukemia.

Establishment of a new cell line from a patient with hairy cell leukemia-Japanese variant

A cell line, JHC-2, was established from the peripheral blood of a patient with hairy cell leukemia (HCL)-Japanese variant. The JHC-2 cells have cytologic features similar to those of the original tumor cells. They displayed hairy cytoplasmic projections by phase contrast and scanning electron microscopy. The tartrate-resistant acid phosphatase reaction was weakly positive. The immunophenotype of the JHC-2 cells was CD5-, CD10-, CD11c+/-, CD19+, CD21+, CD23+, CD24-, CD25+/-, CD38- and FMC-7+. The expression of surface immunoglobulin (IgG, kappa) and the configuration of Ig gene rearrangements in the JHC-2 cells were identical to those in the original leukemic cells, and the JHC-2 cells displayed trisomy 9 on cytogenetic examination. Southern blot analysis for the Epstein-Barr virus (EBV) genome showed that the JHC-2 cells contained the EBV genome, although the freshly isolated leukemic cells did not. These results indicate that the JHC-2 cell line is an EBV spontaneously transformed B cell line originating from HCL cells.

The biologic activity and molecular characterization of a novel synthetic interferon-alpha species, consensus interferon

Consensus interferon (Infergen) is a wholly synthetic type I interferon (IFN), developed by scanning several interferon-alpha nonallelic subtypes and assigning the most frequently observed amino acid in each position, resulting in a consensus sequence. The antiviral, antiproliferative, NK cell activation activity, cytokine induction, and interferon-stimulated gene-induction activity of consensus interferon has been compared with naturally occurring type I interferons. In all of these comparisons, consensus interferon had a higher activity when compared, on a mass basis, with IFN-alpha 2a and IFN-alpha 2b, although the activity was the same for all of these parameters on an antiviral unit basis. That a synthetic type I interferon could have higher activities than naturally occurring molecules is surprising and may be a result of the higher affinity for the array of type I interferon receptors demonstrated for consensus interferon when compared with IFN-alpha. In contrast, consensus interferon was shown to be an inferior inducer of IL-1 beta when compared with IFN-alpha. These results may reflect differential binding to multiple accessory proteins interacting with a type I interferon receptor. These unique biologic properties may lead to a favorable clinical benefit for consensus interferon when compared with the naturally occurring recombinant molecules. Ongoing clinical trials will ascertain whether consensus interferon can be used in a wide array of disease situations, such as chronic viral infections and certain malignancies.

Interferon-alpha-2b downregulation of oncogenes H-ras, c-raf-2, c-kit, c-myc, c-myb and c-fos in ESKOL, a hairy cell leukemic line, results in temporal perturbation of signal transduction cascade

ESKOL, a B-lymphoblastoid cell line consisting of late differentiated cells, resembles hairy cell leukemia (HCL). It is pseudodiploid with a deleted 7q and an unbalanced translocation between chromosomes 4 and 6. It was screened by Northern hybridization for oncogenes, including H-ras, c-raf-2 (c-raf1p1), c-kit, c-myc, c-myb, c-fos, Fim-1, c-jun, ski, and c-mos, which are believed to contribute to B-cell differentiation and maturation. Interferon-alpha-2b (IFN) downregulates the expression of H-ras, c-raf-2, c-kit, c-myc, c-myb, c-fos, as determined by Northern hybridization of RNA isolated from cells harvested at time points during a 30 h time course. Downregulation of oncogenes H-ras, c-raf-2, c-kit, whose proteins are associated with cell surfaces or are cytosolar transducers, occurs before those oncogenes c-myc, c-myb, and c-fos, whose products are DNA binding proteins. This suggests a temporal perturbation of signal transduction by IFN. No change in oncogene expression occurred in non-treated cells nor were these oncogenes expressed in the non-transformed B-lymphoblast cell line, Wil-2, under the same treatment regimen. The basis for the IFN perturbation is not understood; yet the role of these oncogenes as signal transducers in differentiation and proliferation of human hematopoietic progenitors is unfolding, and ESKOL is an excellent system in which to study this phenomenon.

An interferon resistant variant of the hairy-cell leukemic cell line, Eskol: biochemical and immunological characterization

The B-lymphoblastoid cell line Eskol, which is composed of differentiated cells resembling hairy-cell leukemia, has been used to study the effects of type I interferon in vitro. In order to study the mechanism of delayed interferon therapy resistance, a hairy-cell leukemia-like clonal cell line (IREs-4) was isolated from Eskol after 4 months of exposure to r-metIFN-con1. When compared to Eskol cells, the IREs-4 cells were resistant to the antiproliferative effect of type I interferons as well as interferon induced protection against LAK cells. Treatment of IREs-4 with type I interferon did not induce MHC antigens, although both MHC class I and II antigens were induced in Eskol. Binding studies indicated the presence of equal numbers of high affinity binding sites with similar affinities on both cell lines. The resistant phenotype appears to result from an intracellular event which is essential to interferon signal transduction. It is hypothesized that this variant may reflect heterogeneity in the normal population of hairy-cell leukemia cells, and may explain the partial resistance of HCL patients to IFN therapy.

Consensus interferon induces peak mRNA accumulation at lower concentrations than interferon-alpha 2a

The biological activity of a novel recombinant interferon, r-metIFN-con1, which represents a consensus sequence of the most commonly appearing amino acids at each locus of 14 naturally occurring IFN-alpha s, was assessed and compared to that of IFN-alpha 2a. The increase in cellular mRNA levels for three IFN-inducible genes served as a quantitative measure of the effectiveness of the stimulation by each of the IFNs. Three cell lines were treated with equimolar amounts of two IFNs encompassing a 5 log range and mRNA was extracted at five different times after treatment. In all cases, r-metIFN-con1 produced mRNA increases at lower concentrations than IFN-alpha 2a. HLA-DR alpha mRNA, which is not affected by IFN-alpha in ME180 or Daudi cells, was also not affected by r-metIFN-con1. However, in Eskol cells, both IFNs effected an increase in HLA-DR alpha mRNA to similar levels. The r-metIFN-con1 was effective at approximately 10-fold lower molar concentrations. At effective concentrations (10-fold lower molar dose of r-metIFN-con1), both IFNs produced similar kinetics of accumulation of all three mRNAs tested. r-metIFN-con1 is therefore more effective than IFN-alpha 2a at the level of mRNA regulation as well as the antiviral and antiproliferative activities that have been reported previously.

A comparison of interferon-Con1 with natural recombinant interferons-alpha: antiviral, antiproliferative, and natural killer-inducing activities

The antiviral, antiproliferative, and natural killer (NK) cell activation by recombinant human interferon-consensus (IFN-Con1) has been compared with that of two other type I IFNs: IFN-alpha 2a (Roferon) and IFN-alpha 2b (Intron A). The specific activity (antiviral units/mg) of IFN-Con1 was 10-fold higher than that of the other two IFNs in the vesicular stomatitis virus (VSV)-HeLa antiviral assay. The antiproliferative activity on a molar basis of IFN-Con1 on Daudi cells and Eskol (a human leukemic hairy cell-like cell line) was significantly greater than that of IFN-alpha 2a and IFN-alpha 2b. IFN-Con1 also enhanced or induced NK cell killing of target cells to a greater extent than that of IFN-alpha 2a and IFN-alpha 2b. However, on antiviral unit basis, the activities were similar. These results would suggest that IFN-Con1 may be more effective at lower protein concentrations in clinical applications than other available IFNs.

A dual anti-tumor effect of a combination of interferon-α or interleukin-2 and 5-fluorouracil on natural killer (NK) cell-mediated cytotoxicity

Previous in vitro and in vivo studies have shown a synergism between interferon (IFN) and 5-fluorouracil (5-FU) against different tumor cell lines. In the present study we report that the combination of IFN-alpha and 5-FU has a significant effect not only on the inhibition of tumor cell growth but also on the regulation of natural killer cell-mediated cytotoxicity (NK-CMC). The addition of 5-FU to effector cell population neither affects NK cell activity nor activation of NK cells by IFN or by interleukin (IL)-2. However, pretreatment of target cells with 5-FU increased their susceptibility to NK activity and abolished the protective effect induced by IFN against NK-CMC. This dual effect of IFN-alpha and 5-FU was found to be applicable to target cells of different origins including a cervical carcinoma cell line (ME-180), a hairy cell leukemia-like cell line (Eskol), a CML cell line (K-562) and a primary culture of AIDS-related Kaposi's sarcoma cells. Similar results were found with IL-2 treatment of Eskol cells but not other cells. Combination of IL-2 with 5-FU resulted in enhancement of the sensitivity of the cells to NK activity and abolished the protection against NK-CMC. Based on these results we propose that the combination of IFN-alpha and 5-FU not only has a direct growth inhibitory effect on tumor cells but also has a regulatory role on the immunological arm of the NK-CMC. Moreover, since the combination gave the same pattern of response in different tumor cells, both NK-sensitive and NK-resistant, this combination treatment may be a candidate for clinical trials in various types of tumors.