Recombinant human interferon sensitizes resistant myeloid leukemic cells to induction of terminal differentiation

Characterization of the human zinc finger nfx‑1‑type containing 1 encoding ZNFX1 gene and its response to 12‑O‑tetradecanoyl‑13‑acetate in HL‑60 cells

Human promyelocytic HL‑60 cells can be differentiated into macrophage‑like cells by treatment with 12‑O‑tetra decanoylphorbol‑13‑acetate (TPA). Certain 5' upstream regions of the zinc finger protein (ZNF)‑encoding genes contain duplicated GGAA motifs, which are frequently found in the TPA‑responding gene promoter regions. To examine transcriptional responses to TPA, 5'flanking regions of human zinc finger CCCH‑type containing, antiviral, ZNF252, ZNF343, ZNF555, ZNF782 and zinc finger nfx‑1‑type containing 1 (ZNFX1) genes were isolated by polymerase chain reaction (PCR) and ligated into a multiple‑cloning site of the pGL4.10[luc2] vector. Transient transfection and a luciferase assay revealed that the ZNFX1 promoter most prominently responded to the TPA treatment. Deletion and point mutation experiments indicated that the duplicated GGAA motif in the 100‑bp region positively responded to TPA. In addition, reverse transcription‑quantitative PCR and western blotting showed that the mRNA and protein of ZNFX1 accumulate during the differentiation of HL‑60 cells. These results indicated that expression of the TPA‑inducible ZNFX1 gene, which belongs to the group of interferon‑responsive genes, is regulated by the cis‑action of the duplicated GGAA motif.

Interferon-α in acute myeloid leukemia: an old drug revisited

Interferon-α (IFN-α), a type I IFN, is a well-known antitumoral agent. The investigation of its clinical properties in acute myeloid leukemia (AML) has been prompted by its pleiotropic antiproliferative and immune effects. So far, integration of IFN-α in the therapeutic arsenal against AML has been modest in view of the divergent results of clinical trials. Recent insights into the key pharmacokinetic determinants of the clinical efficacy of IFN along with advances in its pharmaceutical formulation, have sparked renewed interest in its use. This paper reviews the possible applicability of IFN-α in the treatment of AML and provides a rational basis to re-explore its efficacy in clinical trials.

Functions of the cytoplasmic RNA sensors RIG-I and MDA-5: key regulators of innate immunity

The innate immune system responds within minutes of infection to produce type I interferons and pro-inflammatory cytokines. Interferons induce the synthesis of cell proteins with antiviral activity, and also shape the adaptive immune response by priming T cells. Despite the discovery of interferons over 50 years ago, only recently have we begun to understand how cells sense the presence of a virus infection. Two families of pattern recognition receptors have been shown to distinguish unique molecules present in pathogens, such as bacterial and fungal cell wall components, viral RNA and DNA, and lipoproteins. The first family includes the membrane-bound toll-like receptors (TLRs). Studies of the signaling pathways that lead from pattern recognition to cytokine induction have revealed extensive and overlapping cascades that involve protein-protein interactions and phosphorylation, and culminate in activation of transcription proteins that control the transcription of genes encoding interferons and other cytokines. A second family of pattern recognition receptors has recently been identified, which comprises the cytoplasmic sensors of viral nucleic acids, including MDA-5, RIG-I, and LGP2. In this review we summarize the discovery of these cytoplasmic sensors, how they recognize nucleic acids, the signaling pathways leading to cytokine synthesis, and viral countermeasures that have evolved to antagonize the functions of these proteins. We also consider the function of these cytoplasmic sensors in apoptosis, development and differentiation, and diabetes.

mda-5: An interferon-inducible putative RNA helicase with double-stranded RNA-dependent ATPase activity and melanoma growth-suppressive properties

Human melanoma cells can be reprogrammed to terminally differentiate and irreversibly lose proliferative capacity by appropriate pharmacological manipulation. Subtraction hybridization identified melanoma differentiation-associated gene-5 (mda-5) as a gene induced during differentiation, cancer reversion, and programmed cell death (apoptosis). This gene contains both a caspase recruitment domain and putative DExH group RNA helicase domains. Atypical helicase motifs of MDA-5 deviate from consensus sequences but are well conserved in a potentially new group of cloned and hypothetical proteins. mda-5 is an early response gene inducible by IFN and tumor necrosis factor-alpha, responding predominantly to IFN-beta. Protein kinase C activation by mezerein further augments mda-5 expression induced by IFN-beta. Expression of mda-5 is controlled transcriptionally by IFN-beta, and the MDA-5 protein localizes in the cytoplasm. mda-5 displays RNA-dependent ATPase activity, and ectopic expression of mda-5 in human melanoma cells inhibits colony formation. In these contexts, mda-5 may function as a mediator of IFN-induced growth inhibition and/or apoptosis. MDA-5 is a double-stranded RNA-dependent ATPase that contains both a caspase recruitment domain and RNA helicase motifs, with a confirmed association with growth and differentiation in human melanoma cells.

Cytokine-induced restoration of differentiation and cell cycle arrest in v-Myc transformed U-937 monoblasts correlates with reduced Myc activity

Deregulated expression of the myc-family of oncogenes in hematopoietic and other cell types plays an important role in tumorigenesis, and results in increased proliferative potential and block of cellular differentiation. We have previously shown that IFN-gamma restores phorbol ester-induced differentiation and cell cycle arrest in v-myc transformed human U-937 monoblasts. To investigate whether other cytokine signals could also abrogate such a block, IL-1, IL-3, IL-4, IL-6, IL-7, IL-10, IL-11, LIF, oncostatin M, M-CSF, G-CSF and GM-CSF, and TGFbeta1, TNF-alpha, IFN-alpha were examined. We show that GM-CSF and IL-6, in combination with the phorbol ester 12-O-tetradecanoyl-phorbol acetate (TPA), restored differentiation and cell cycle arrest. In contrast, treatment by TGFbeta1 +/- TPA resulted in an efficient G1/G0 arrest, but did not appear to induce terminal differentiation. Restoration of differentiation and cell cycle arrest was accomplished despite maintained expression of the v-Myc protein. Our results show that the cytokine-induced signals reduced Myc-dependent transcription of an artificial target promoter/reporter gene construct, correlating in most, but not all, cases with decreased association of v- and c-Myc with its essential partner, Max. Thus, cytokine-induced signals may counteract the activity of deregulated Myc, and contribute to the normalization of differentiation, arrest in the G1/G0 phase of the cell cycle, or both.

Interferon gamma regulates a unique set of proteins in fresh human bladder transitional cell carcinomas

Poly(A) mRNA was isolated from human placental trophoblast cells stimulated with 100 U/mL of interleukin-2 and 5 microg/mL of phytohemagglutinin and reverse-transcribed. The cDNA coding for the mature interferon-gamma (IFN-gamma) protein was amplified using specific primers, cloned into the pGEX-4T2 vector, and expressed in Escherichia coli. Treatment of four fresh bladder transitional cell carcinoma (TCC) biopsies (TCCs 845-1, grade II, Ta; TCC 925-1, grade II, Ta; TCC 919-1, grade III, T1; TCC 950-1, grade III, T1) with the purified recombinant trophoblast IFN-gamma (50 U/mL, 20 h), followed by proteome analysis using two-dimensional gel electrophoresis, revealed several major proteins whose level of expression were affected by this cytokine. Of these, five (tryptophanyl-tRNA synthetase, the interferon gamma-inducible protein gamma3, mangase superoxide dismutase, and two unknown proteins of apparent molecular masses of 35.8 and 11.2 kDa, respectively) were upregulated in at least 75% of the tumors analyzed while one was downregulated (aldose reductase). Proteins were identified using a combination of techniques that included microsequencing, two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) immunoblotting and comparison with the transitional cell carcinoma isoelectric focusing (IEF) database (http://biobase.dk/cgi-bin/celis). Proteome profile analysis of primary cultures from a low-grade lesion (TCC 846-1, Grade II, Ta) labeled in the presence and absence of IFN-gamma showed that all of the proteins disregulated in vivo were also affected in the cultures. The cultured cells, on the other hand, exhibited additional changes that were not detected in vivo and that may reflect adaptation to the culturing conditions. Taken together, the results provide a first glance at the effect of IFN-gamma on the protein expression profiles of TCCs, and in due course may form the basis for more comprehensive studies aimed at evaluating the usefulness of this cytokine in bladder cancer management.

Tretinoin. A review of its pharmacodynamic and pharmacokinetic properties and use in the management of acute promyelocytic leukaemia

Tretinoin (all-trans retinoic acid), a vitamin A derivative, induces cellular differentiation in several haematological precursor cell lines and cells from patients with acute promyelocytic leukaemia. Drug treatment with tretinoin is associated with morphological and functional maturation of leukaemic promyelocytes and a progressive reduction in the occurrence of the characteristic t(15;17) chromosomal translocation. Recent therapeutic trials indicate that tretinoin induces remission in 64 to 100% of patients with acute promyelocytic leukaemia. In newly diagnosed patients, remission induction treatment with tretinoin followed by intensive chemotherapy resulted in a significant reduction in relapse rate and prolongation of event-free and overall survival compared with chemotherapy alone in 1 comparative trial. Tretinoin alone does not totally eradicate the leukaemic clone and consolidation chemotherapy is recommended as follow-up. The use of reverse transcription polymerase chain reaction (RT-PCR) provides a sensitive and specific technique to assist in prediction and monitoring of a patient's response to treatment and to help detect the presence of residual or recurrent disease. The use of tretinoin is potentially limited by the rapid and almost universal development of drug resistance and occurrence of the often severe retinoic acid syndrome. Useful strategies have been described to manage these effects but current and future efforts must be directed at elucidating the mechanisms involved and determining the optimum therapeutic management. In summary, results to date indicate that the combination of tretinoin and intensive chemotherapy is more effective than chemotherapy alone and appears to improve the prognosis of newly diagnosed patients with acute promyelocytic leukaemia. Further information on the relative efficacy of various induction and post-remission strategies in subsets of patients will help determine optimum use of this promising agent in the management of acute promyelocytic leukaemia.

Potentiation of tumor necrosis factor-mediated cytotoxicity on human myeloid cell lines: effects of interferons versus dimethylsulphoxide

After prolonged incubation times of 72 h IFN alpha 2a and IFN beta 1 significantly reduced cell growth in the myelomonocytic U937 and THP1 cell lines. IFN gamma showed only slight growth inhibitory activities. IFN activities were potentiated by the highly polar differentiation inducer dimethylsulphoxide, which is similar to our previous study on tumor necrosis factor (TNF). However, in contrast with TNF, none of the interferon types induced cell cytotoxicity or DNA fragmentation. Like DMSO, all interferons potentiated TNF-induced cytotoxicity, IFN beta 1 and IFN gamma being the most potent in this respect. When applied together, DMSO and IFN gamma enhanced TNF-mediated cell lysis in either an additive (in the case of U937, THP1, HL60 cells) or a synergistic (in the case of KG1) manner, suggesting that the mechanisms of the potentiating activity of DMSO and IFN gamma are different. The potential role of the simultaneous use of DMSO-related molecules, and TNF and/or IFN in leukemic cancer chemotherapy is discussed.

Retinoic acid and interferon combination studies in human cancer

Retinoic acid and interferon-alpha have limited single-agent activity in advanced cancer. Cell culture data indicate that in combination these agents have enhanced activity (modulating growth and differentiation) in a number of malignant cell types. Recent clinical work in advanced squamous cell carcinoma reports major activity with this regimen. This paper reviews the preclinical and clinical data testing retinoic acid in combination with interferons and presents recent work integrating these agents with radiotherapy in locally advanced cervical cancer.

Retinoids and interferon: a new promising combination?

The retinoids: all-transretinoic acid (tretinoin), 13-cis retinoic acid (isotretinoin) and the aromatic retinoids etretinate and acitretin have a preventive and therapeutic effect on chemically-induced tumours. Clinically, retinoids have shown variable effectiveness in therapy and/or prevention of oncological diseases of skin, head and neck, lung, bladder, vulva and bone marrow. With a few exceptions, monotherapy with retinoids has not been satisfactory. Similarly, monotherapy with interferon alpha has been used successfully only for some specific indications. Retinoids have a marked differentiation-inducing effect which may contribute to their therapeutic effect. Experiments were carried out in transformed cell lines to test the combination of retinoids with interferon alpha and other cytokines on differentiation. In HL-60 cells, an acute promyelocytic leukaemia cell line, induction of differentiation was determined by induction of an oxidative burst potential. Retinoids showed the following order of activity: tretinoin greater than isotretinoin greater than acitretin. Cytokines had no differentiation-inducing effect by themselves. However, the addition of the following cytokines to retinoids potentiated the retinoid-induced differentiation: IFN alpha, IFN beta, IFN gamma, TNF alpha, G-CSF, IL-1 alpha and IL-4. In experiments with HL-60 or other cell lines, the pattern of differentiation-induction was always dependent on the particular retinoid/cytokine combination. IFN alpha provoked a marked potentiation of retinoid-induced differentiation. The combination of the antiproliferative and differentiation-inducing effect of the retinoids together with the antiproliferative, immunostimulatory and differentiation-potentiating effects of IFN alpha suggests that this combination might be a particularly promising treatment for neoplastic diseases.

Interleukin-6 and 12-O-tetradecanoyl phorbol-13-acetate act synergistically in inducing cell-cell separation and migration of human breast carcinoma cells

Interleukin-6 (IL-6) causes an epithelial to fibroblastoid conversion and an increase in the motility of human ductal breast carcinoma cell lines ZR-75-1 and T-47D. Although IL-6 decreases DNA synthetic activity in these cell lines, the IL-6-induced alterations in cell shape and motility occur independently of inhibition of DNA synthesis per se. Whereas tumor necrosis factor alpha (TNF-alpha) inhibits DNA synthesis in T-47D cells, it does not cause an epithelial-fibroblastoid conversion or other major morphological changes and does not increase cell motility; TNF-alpha rapidly lyses a majority of ZR-75-1 cells. Furthermore, the DNA synthesis inhibitors 5-fluoro-2'-deoxyuridine (FUDR) and methotrexate (MTX) also do not cause effects mimicking the action of IL-6 on cell structure and motility. Transforming growth factors alpha and beta 1, acidic and basic fibroblast growth factors, epidermal growth factor, and insulin-like growth factor-1 (TGF-alpha, TGF-beta 1, aFGF, bFGF, EGF, and IGF-1) have little or no effect on breast cancer cell morphology, which serves to exclude the possibility that the IL-6-induced changes are a consequence of induction of these growth factors by IL-6. 12-O-tetradecanoyl phorbol-13-acetate (TPA) but not 8-bromoadenosine 3',5'-cyclic monophosphate (Br-cAMP) induces changes in the morphology and associative behavior of ZR-75-1 cells that are similar but not identical to those caused by IL-6. The TPA-induced alterations are not blocked by anti-IL-6 neutralizing antibodies; staurosporine inhibits the TPA-induced cell alterations but not those induced by IL-6. IL-6 and TPA used together have a phenotypic effect that greatly exceeds that of either agent alone and results in extensive cell scattering in less than 1 day. These findings are consistent with the hypothesis that IL-6 and TPA induce similar morphological changes and cell scattering via independent pathways.

Effects of cytokines from virus-induced human lymphoblasts on the growth and viability of the promyelocytic leukemia cell line HL-60

Cells of the human B-cell lymphoblastic leukemia line, BALL-1, were stimulated with Sendai virus. It is shown that the crude culture supernatants contain not only interferon-alpha (IFN-alpha) and tumor necrosis factor-alpha (TNF-alpha) but also other cytokines, here collectively termed 'X' cytokines. The latter did not affect the cytostatic or differentiation-inducing effect of IFN-alpha but synergistically increased the cytotoxicity of TNF-alpha.

Difference in effects of interferon-alpha and interferon-gamma on the induction of differentiation of retinoic acid-treated acute myeloid leukemia cells in primary culture

We studied differentiation inducing effects of retinoic acid (RA), 1 alpha, 25-dihydroxyvitamin D3 (D3) and interferons (IFNs), alone and in combination, on fresh myeloid leukemic cells from 8 patients. RA not only induced the differentiation of leukemic cells in 5/8 cases, but potentiated differentiation by IFNs either in granulocytic or monocytic pathways. In particular, interferon-alpha enhanced granulocytic differentiation and interferon-gamma induced mono-macrophage differentiation of promyelocytic leukemic cells in the presence of RA. Differentiation induced by D3, alone or in combination with IFNs, was limited in all cases. RA plus IFNs might be an effective combination for differentiation therapy for some types of myeloid leukemia.

Enhancement of interferon-induced 2-5 oligoadenylate synthetase activity by retinoic acid in human histiocytic lymphoma U937 cells and WISH cells

The effect of retinoic acid (RA) on the level of interferon (IFN)-induced 2-5 oligoadenylate (2-5A) synthetase activity was examined in human histiocytic lymphoma U937 cells and WISH cells** in order to ascertain the role of this polymerase in interaction between IFNs and RA. Cultures containing both IFNs (1-100 U/ml) and RA (0.1-10 microM) consistently had higher levels of enzyme activity than corresponding cells treated with IFN alone and this was true for all three types of IFNs in both cell lines. The potentiating effect of RA was dose- and time-dependent and under optimal conditions, the induction of the synthetase was synergistic between IFN-beta (10-100 U/ml) and RA (0.1-10 microM). Furthermore, pretreatment (but not posttreatment) with RA followed by subsequent treatment with IFNs preferentially induced higher levels of enzyme activity in U937 cells but not in WISH cells. In addition, our results indicated that the modulating effect of RA on IFNs did not involve interaction at the receptor level and the level of enhancement of 2-5A synthetase activity was not in parallel with either cell-growth arrest or promotion of differentiation. Lastly, the present study raises the possibility that interactions between IFNs and RA, in either a synergistic or antagonistic manner, may be mediated through amplification of the 2-5A system.

The role of polyamines in interferon and retinoic acid mediated synergistic antiproliferative action

Retinoic acid alone has no effect on the human breast cancer cell line BT-20 but can amplify the antiproliferative action of interferon-gamma (IFN-gamma). In our system ornithine decarboxylase (ODC) activity correlates well with growth rate; it was investigated whether the antiproliferative effects of IFN-gamma and IFN-gamma plus retinoic acid could be attributed to suppression of ODC activity. The ODC inhibitor difluoromethylornithine (DFMO), which is active as a single agent did not enhance growth inhibition induced by the biological response modifiers. The substitution of the BT-20 cells with putrescine, the product of the enzymatic reaction mediated by ODC, reversed DFMO induced antiproliferative action. On the other hand putrescine did not affect the proliferation of BT-20 cells treated with interferon alone or in combination with retinoic acid.

Effects of retinoic acid, 1,25-dihydroxyvitamin D3, cytosine arabinoside and alpha-interferon on bone marrow cells from patients with myelodysplastic syndromes

Bone marrow cells from 15 patients with myelodysplastic syndromes and 2 with acute myeloid leukemia were incubated in vitro with all-trans-retinoic acid (RA), 1,25-dihydroxy vitamin D3 (D3), cytosine arabinoside (ara-C) and alpha-interferon (IFN). 3H-thymidine incorporation (3H-TdR), differentiation and clonal growth were studied. D3 was found to be the most effective inducer of differentiation and differentiation was correlated with a decreased 3H-TdR. Differentiation with one of the inducers was significantly correlated to differentiation with any of the other inducers. Patterns of differentiation and spontaneous and D3-induced 3H-TdR were used to divide the patients into 3 different groups. In the first group, 5 patients with extremely low spontaneous 3H-TdR and differentiation in combination with a slightly increased 3H-TdR after induction differed from all other patients by a higher percentage of bone marrow blast and a more pronounced pancytopenia. The two other groups had a high spontaneous 3H-TdR but differed with respect to the D3-induced differentiation which was absent in one group (n = 6) and present in the other (n = 5). The two groups showed no difference in the clinical features.

Contrasting effect of IFN-gamma and IFN-alpha/beta on differentiation of some clones of mouse myeloid leukemic cells

Mouse myeloid leukemic M1 cells are induced to differentiate into macrophage-like cells by a differentiation-inducing factor (D-factor) and various agents. IFN-gamma alone did not induce differentiation of clone T22-3 of M1 cells but inhibited their differentiation by D-factor. That is, IFN-gamma at 4 U/ml inhibited 50% of phagocytic activity of T22-3 cells induced by 7 x 10(-11) M D-factor. In addition, it inhibited the induction of lysozyme activity and morphological differentiation of these cells by D-factor. IFN-gamma also inhibited dexamethasone-induced differentiation of T22-3 cells. Previously interferon-alpha/beta was shown not to induce differentiation of M1 cells itself, but to enhance induction of their differentiation by D-factor. The present study showed that IFN-alpha/beta and IFN-gamma had opposite effects on induction of differentiation of T22-3 cells by D-factor. The effect of IFN-gamma on the differentiation of M1 cells varied with the clone of M1 cells used: IFN-gamma inhibited D-factor-induced differentiation of cells of clones T22-3 and S2, but induced differentiation of cells of clones B24 and S1.

Retinoic acid regulates IgG Fc receptor expression in human myelomonocytic leukemia cells and normal peripheral monocytes

The regulation of IgG Fc receptor (Fc gamma R) expression by retinoic acid (RA) in human myelomonocytic cells at different stages of maturation was studied. RA suppressed IgG-coated erythrocyte (EA) rosette formation of myelomonocytic cells blocked at relatively late stages of differentiation such as ML-1, U-937, THP-1-T, normal monocytes, and fresh cells of patients with acute myelomonocytic leukemia. However, RA increased the percentage of EA rosetting promyelocytes of HL-60 and of patients with acute promyelocytic leukemia and a part of myeloblasts isolated from acute myelogenous leukemia patients. Other myeloblasts including KG-1a, KG-1, and fresh cells from patients with acute myelogenous leukemia were not affected. A kinetic study using HL-60 and THP-1-T demonstrated that an increase required at least a 48-h exposure and that the maximum decrease required approximately 6 h. The RA effect on both cell lines was dose-dependent. The number of Fc gamma R of HL-60 and THP-1-T treated with RA became very close, although untreated THP-1 had almost 10 times as many as HL-60. Kd for IgG in both THP-1-T and HL-60, either untreated or treated with RA, remained unchanged. These observations indicate that one of the important roles of RA is regulation of Fc gamma R expression in myeloid cells.

Therapeutic effects of low-dose cytosine arabinoside, alpha-interferon, 1 alpha-hydroxyvitamin D3 and retinoic acid in acute leukemia and myelodysplastic syndromes

62 evaluable patients with myelodysplastic syndromes (MDS) or acute leukemia were treated with different combinations of low dose ara-C, alpha-interferon (IFN), 1 alpha-hydroxyvitamin D3 (vit D3) and retinoic acid. The aim was to study the efficacy and toxicity of each combination. The overall rate was 44%. Of these, 50% responded favorably to the combination of IFN, vit D3 and retinoic acid (IDR), which was comparable to the response rate of 43% for low-dose ara-C. The results of the IDR treatment may be explained by additive or synergistic effects between the separate drugs in the combination. Ara-C and IDR treatment was generally well-tolerated but interferon gave more side effects than any other drug used in the study. Evaluation of the full combination of ara-C, IFN, vit D3 and retinoic acid was not possible because of toxicity. Marrow hypoplasia was infrequent (5/27 patients) in cases responding favorably to treatment. Complete remissions were not longer than partial remissions or significant responses.

Effects of retinoids and interferon-gamma on cultured breast cancer cells in comparison with tumor necrosis factor alpha

The combination of retinoic acid or tumor necrosis factor alpha (TNF-alpha) with interferon gamma (IFN-gamma) resulted in a synergistic amplification of the anti-proliferative effect of IFN-gamma on cultured breast cancer cells. Retinoic acid could be replaced by other biologically active retinoids. This synergism was also observed for the induction of 2'-5'-oligoadenylate-synthetase, an enzyme which is not expressed constitutively on BT-20 human breast cancer cells and not inducible by retinoic acid or TNF-alpha alone. However, both substances augmented the IFN-gamma-mediated expression. On the other hand, only TNF-alpha and not retinoic acid was able to increase the IFN-gamma induced expression of HLA-DR on the cell surface. Both cytokines antagonized the IFN-gamma effect on detachability of cultured BT-20 cells. The combinations of retinoic acid with IFN-gamma increased the down-regulation of specific binding sites for 125I-IFN-gamma. On the other hand, IFN-gamma exerted no effect on the concentration of the cytoplasmic binding protein for retinoic acid. Data obtained in this study demonstrate a different pattern of action between retinoic acid and TNF-alpha regarding their synergism in combination with IFN-gamma.

Stimulation by interferon of the differentiation of human promyelocytic leukemia (HL-60) cells produced by retinoic acid and actinomycin D

Interferons (IFNs) have been shown to enhance or induce differentiation in several model systems, either alone or in combination with differentiating agents. To further study these phenomena, the effects of the recombinant interferons rIFN-alpha A, rIFN-alpha D, rIFN-alpha A/D (Bgl II), rIFN-beta, and rIFN-gamma on the differentiation-producing capacities of the anticancer agents aclacinomycin A and actinomycin D, and the differentiating agent retinoic acid, were examined in the HL-60 promyelocytic leukemia cell line. The addition of IFNs to aclacinomycin A did not produce any enhancement of differentiating capacity. The differentiating capacity of actinomycin D was enhanced only by rIFN-alpha A/D (Bgl II). The differentiating capacity of retinoic acid was enhanced by all the IFNs-alpha tested, and by rIFN-beta, but not rIFN-gamma.

Interferon-alpha A/D blocks an increase in Fc receptors of a human promyelocytic leukemia cell line (HL-60) induced by other recombinant interferons

The effect of recombinant hybrid interferon (IFN)-alpha A/D either alone or in combination with retinoic acid (RA) on induction of differentiation of the human promyelocytic leukemia cell line HL-60 was studied. The combination of 10 nM RA and IFN-alpha A/D at concentrations of 120 units/ml and higher induces differentiation into cells having many monocytic characteristics such as monocyte-like morphology, ability of superoxide anion production, antibody-dependent cellular cytotoxicity, and nonspecific esterase activity. However, this combination does not induce an increase in IgG Fc receptors (Fc gamma R) and immunoerythrophagocytosis. IFN-alpha A/D alone shows essentially no effect on these parameters. Pretreatment of HL-60 with IFN-alpha A/D blocks the Fc gamma R-increasing activity of IFN-alpha A, IFN-alpha D, and IFN-gamma. This block is complete after a 2-h pretreatment for IFN-alpha A and IFN-alpha D and after a 6-h pretreatment for IFN-gamma. Furthermore, an increase in Fc gamma R-mediated phagocytosis is also suppressed by the pretreatment. However, IFN-alpha A/D does not suppress superoxide anion production. These results indicate that the block of an Fc gamma R-increase by IFN-alpha A/D has not resulted in the competitive inhibition at IFN receptors, but may occur in intracellular events such as postreceptor transduction for the expression of Fc gamma R.

Effects of interferon and retinoic acid on the growth and differentiation of clonogenic leukemic cells from acute myelogenous leukemia patients treated with recombinant leukocyte-alpha A interferon

Studies with human myeloid leukemia cell lines indicate that combined interferon (INF) and retinoic acid (RA) have greater effects in inhibiting cell growth and in inducing terminal differentiation than either agent alone. Consequently, we studied the effects of these agents, singly and in combination, on fresh leukemic blast cells obtained from 13 acute myelogenous leukemia (AML) patients, most of whom were subsequently treated with recombinant leukocyte-alpha A interferon (rINF-alpha A). The in-vitro response to rINF-alpha A and RA was assessed in an established myeloid leukemic blast cell clonogenic assay containing conditioned medium from phytohemagglutinin-stimulated lymphocytes. Strong inhibition of colony cell growth (greater than or equal to 50%) was observed in 4/10 cases treated with rINF-alpha A alone, but only at high concentration (greater than or equal to 2500 U/ml) and in 4/10 cases treated with RA alone (5 X 10(-8) M or 5 X 10(-7) M). Combined rINF-alpha A and RA augmented the inhibition of primary or secondary colony cell growth in 5/8 evaluable cases. Stimulation of leukemic cell differentiation was observed in 1/8 cases by rINF-alpha A alone and in 4/7 cases by RA alone. Combined rINF-alpha A and RA enhanced cell differentiation in 4/7 cases. In addition, increased inhibition of clonal cell growth and/or differentiation by RA alone was observed in 2/5 cases following in-vivo rINF-alpha A treatment. These results suggest that treatment with combined rINF-alpha A and RA may be rewarding in some cases of AML.

Effects of interferon on differentiation of normal and tumor cells

As described in this review, both partially purified and recombinant interferons are potent modulators of differentiation in diverse cell culture systems (Table 2). Depending on the target cell, interferon exerts either an inhibitory or an inductive effect on cell differentiation. In certain myeloid leukemic cells, such as HL-60, interferon by itself is growth suppressive but does not induce cell maturation, whereas in combination with inducers of differentiation, such as DMSO, TPA or retinoic acid, interferon potentiates their ability to stimulate differentiation in both sensitive and resistant cell populations (Grant et al., 1982, 1983; Tomida et al., 1982). Interferon also interacts synergistically with phorbol ester tumor promoters in inhibiting melanogenesis in murine B-16 cells (Fisher et al., 1981a, 1984a) and adipocyte formation in 3T3 cells (Cioe et al., 1980), whereas the combination is synergistic in inducing differentiation in human melanoma cells (Fisher et al., 1984b,c). In contrast, interferon and TPA display antagonistic effects on differentiation in human skeletal muscle cultures, i.e. interferon induces and TPA inhibits myogenesis (Fisher et al., 1982, 1983). Recent studies have demonstrated the presence of high affinity saturable cell membrane receptors for mouse and human interferons (Aguet, 1980; Branca and Baglioni, 1981, 1982; Mogensen et al., 1981; Branca et al., 1982; Anderson et al., 1982; Joshi et al., 1982; Faltynek et al., 1983; Yonehara et al., 1983; Langer and Pestka, in preparation). Similarly, specific membrane receptors have been identified for phorbol esters and mezerein (Driedger and Blumberg, 1980; Shoyab and Todaro, 1980; Horowitz et al., 1981; Fisher et al., 1981b). These findings suggest that the plasma membrane may be a primary target for mediating the biochemical effects induced by both interferon and phorbol esters. Although the mechanism by which interferon and phorbol esters transmit the necessary membrane signal(s) required for altering differentiation are not known, a possible component of this transmembrane signaling process may involve changes in the physical dynamics of the plasma membrane. It is therefore of interest that both interferon and TPA induce early changes in the fluidity of the plasma membrane (Fisher et al., 1979, 1981b, 1984d; Castagna et al., 1979; Kuhry et al., 1983).(ABSTRACT TRUNCATED AT 400 WORDS)