Inhibition of cell division by interferons: Changes in the transport and intracellular metabolism of thymidine in human lymphoblastoid (Daudi) cells

Synergistic interaction between selective drugs in cell populations models

The design of selective drugs and combinatorial drug treatments are two of the main focuses in modern pharmacology. In this study we use a mathematical model of chimeric ligand-receptor interaction to show that the combination of selective drugs is synergistic in nature, providing a way to gain optimal selective potential at reduced doses compared to the same drugs when applied individually. We use a cell population model of proliferating cells expressing two different amounts of a target protein to show that both selectivity and synergism are robust against variability and heritability in the cell population. The reduction in the total drug administered due to the synergistic performance of the selective drugs can potentially result in reduced toxicity and off-target interactions, providing a mechanism to improve the treatment of cell-based diseases caused by aberrant gene overexpression, such as cancer and diabetes.

Role of growth factors in oncogenesis: growth factor-proto-oncogene pathways of mitogenesis

Cellular genes which encode proteins involved in the response of cells to stimulation by growth factors may be potential oncogenes. The factors involved in the signal transmission from growth factor-receptor interaction to DNA synthesis constitute a cascade system which we call the 'growth factor-proto-oncogene pathway(s) of mitogenesis'. For each growth factor, all the responsive cells, regardless of cell types and tissue source, have specific growth factor receptors which are similar, if not identical, in molecular weight and biological activity. Thus, we believe that the growth factor-proto-oncogene pathway(s) functions in the same manner in all responsive cells. Platelet-derived growth factor (PDGF), epidermal growth factor (EGF), and brain-derived growth factor (BDGF) are major growth factors for connective tissue cells and do not share a common pathway in mitogenesis in responsive cells. The gene product of c-myc may be involved in the cellular response of cells stimulated by PDGF or FGF, but not directly in the signal transmission which leads to DNA synthesis.

Determination of growth inhibitory action point of interferon gamma on WISH cells in cell cycle progression and the window of responsiveness of the cells to the interferon

We had earlier shown that human foetal epithelial cells (WISH), growth-inhibited by interferon gamma (IFNgamma), were reversibly detained at a point prior to DNA synthesis. In the present study, we determined the window of action of IFNgamma in the G1 phase duration and the exact point of detention of WISH cells in cell cycle progression with respect to the known points of detention by the inhibitors of DNA replication initiation (aphidicolin and carbonyl diphosphonate) and of activation of replication protein A (6-dimethylaminopurine), of which RPA activation being the earlier event compared to DNA replication initiation in cell cycle progression. WISH cells, which were released from IFNgamma-induced arrest, permeabilised and exposed independently to these inhibitors show that IFNgamma detains WISH cells prior to initiation of DNA synthesis. Further, exposure of IFNalpha-synchronized (at G0/G1) or mimosine-synchronized (at G1/S) WISH cells to IFNgamma, which was added at different time points post-release from the synchronizing agent, showed that the cells were promptly responsive to the growth inhibitory action of IFNgamma only during the first 11h in G1 phase. Taken together, these results suggest that IFNgamma inhibits growth of WISH cells by detaining them at a point prior to initiation of DNA synthesis and that the IFN acts within the first 11h in G1 phase of the cell cycle.

Biochemical modulation of 5-fluorouracil with interferon alpha/beta and gamma on murine renal cell carcinoma

BACKGROUND

Conventional therapy for renal cell carcinoma (RCC) using interferon (IFN) has shown limited antitumor action. The purpose of the present study was to investigate the synergistic antitumor effects of IFN and 5-fluorouracil (5-FU) and to elucidate the mechanism underlying antitumor effects.

METHODS

The antitumor effects and biochemical modulation of murine IFN and 5-FU were determined using murine renal cell carcinoma (RENCA). The activity of thymidylate synthase, thymidine kinase and the concentration of 5-FU incorporated into RNA was measured using cytosolic extracts of tumors.

RESULTS

Triple combination therapy (5-FU, IFN alpha/beta and IFN gamma) showed a synergistic antitumor effect on RENCA tumors, because triple combination therapy suppressed growth significantly compared to combination therapy (IFN alpha/beta and IFN gamma, P = 0.0258) and 5-FU (P < 0.0001). Total thymidylate synthase was decreased by triple combination therapy (5-FU, IFN alpha/beta and IFN gamma, P = 0.0019) and combination therapy (5-FU and IFN gamma, P = 0.0018) compared to 5-FU alone. Thymidine kinase activity was decreased by triple combination therapy (5-FU, IFN alpha/beta and IFN gamma, P < 0.0001) and combination therapy (5-FU and IFN alpha/beta, P < 0.0001) compared to 5-FU alone. The concentration of 5-FU incorporated into RENCA tumors was increased by triple combination therapy (P = 0.0132) and combination therapy (5-FU and IFN alpha/beta, P = 0.0124) compared to 5-FU alone.

CONCLUSIONS

Interferons alpha/beta and gamma showed different biochemical modulation for 5-FU. Therefore, combination therapy using 5-FU and IFN showed synergistic antitumor effects on murine RCC.

A phase II trial of etoposide, leucovorin, 5-FU, and interferon alpha 2b (ELFI) + G-CSF for patients with pancreatic adenocarcinoma: a Southwest Oncology Group study (SWOG 9413)

BACKGROUND

Chemotherapeutic treatments using combinations of etoposide, leucovorin and 5-FU (ELF) have shown activity in the treatment of gastrointestinal malignancies. Interferon alpha 2b is known to have antiproliferative effects on several cell lines and has well documented in vitro evidence of synergism with 5-FU. It was postulated that the combination of ELF and interferon alpha 2b would improve response rates and survival in patients with pancreas cancer.

METHODS

Fifty-five eligible patients with locally-advanced or metastatic pancreatic adenocarcinoma received a regimen consisting of: i.v. leucovorin at 300 mg/m2/day on Days 1-3 (of 28-day cycle), i.v. etoposide at 80 mg/m2/day on Days 1-3, i.v. 5-FU at 500 mg/m2/day on Days 1-3, subcutaneous interferon alpha 2b at 3 million units TIW, and subcutaneous G-CSF at 5 microg/kg/day on Days 4-14 (or until WBC exceeds 10,000/microl). Patients with no evidence of disease progression continued on treatment for a total of 6 cycles.

RESULTS

Complete response was demonstrated in 1 patient, partial response in 5 patients (11% confirmed response rate). The median survival was 5 months, and the six-month survival rate was 40%. Ten patients completed all 6 cycles of treatment. Toxicity-related dose delays and reductions were necessary for most patients.

CONCLUSIONS

Although the combination of ELF and interferon alpha 2b (ELFI) has modest activity in pancreatic cancer, it is a toxic and complex regimen that is not superior to other currently available approaches for the chemotherapeutic management of pancreatic cancer. ELFI cannot be recommended as a standard therapy.

Immunomodulation therapy in colorectal carcinoma

There has been much progress in the understanding of the relationship between the immune system and colorectal cancer. This has led to the use of immunomodulatory therapy in the adjuvant and palliative treatment of the condition. Although attempts at the use of non-specific immunomodulation with agents such as levamisole, cimetidine, alpha interferon and Bacillus Calmette-Guerin (BCG) have not produced significant clinical benefits when tested in randomized trials in both the adjuvant setting and for metastatic disease, promising results are being obtained with more specific therapy. Edrecolomab [corrected], a murine monoclonal antibody targeting the 17-1A antigen on malignant colorectal cells has produced a reduction in relapse and mortality rates when used as adjuvant treatment following surgery for Dukes' C colon cancer. Active specific therapy with autologous tumour vaccine administered with BCG has produced similar benefits in Dukes' B cancer. Both 3H1 anti-idiotypic antibody against carcinoembryonic antigen and 105AD7 antibody to gp72 glycoprotein have demonstrated in-vitro and in-vivo immune activation against tumour. Non-randomized studies postulate prolongation of survival using these antibodies in advanced disease. These agents are all currently being tested in randomized studies powered to detect meaningful survival differences and clinical benefit. Immune therapy offers the potential of low toxicity therapy in colorectal cancer and may have a role as an adjunct to conventional chemotherapy.

Modulation of fluorouracil cytotoxicity by interferon-alpha and -gamma

Because interferons (IFN)-alpha and -gamma individually have increased fluorouracil (FUra) cytotoxicity in several in vitro models, we studied the effects of FUra combined with IFN-alpha + gamma in HT29 colon cancer cells. A 96-hr exposure to IFN-alpha (500 units/ml) plus IFN-gamma (10 units/ml) and a 72-hr exposure to 0. 25-1 microM FUra (hr 24-96) inhibited cell growth and colony formation in an additive or more-than-additive fashion. When cells were exposed to IFN-alpha + gamma and FUra, free FdUMP levels became detectable, whereas [3H]FUra-RNA incorporation decreased. Exposure to IFN-alpha + gamma, FUra, or the combination decreased dTTP pools to 58%, 43%, and 17% of control, respectively. A marked increase in the dATP to dTTP ratio was seen with FUra with or without IFN-alpha + gamma. Thymidylate synthase catalytic activity was reduced to 28% and 24% of control with FUra with or without IFN-alpha + gamma, suggesting that the enhanced dTTP depletion must be due to another mechanism. FUra-mediated thymidylate synthase inhibition was accompanied by a 124-fold increase in total deoxyuridylate immunoreactivity and a 31-fold increase in dUTP pools, but the addition of IFN-alpha + gamma attenuated the accumulation. Treatment with IFN-alpha + gamma and FUra individually interfered with nascent DNA chain elongation, whereas the three-drug combination produced the most striking effects. IFN-alpha + gamma plus FUra produced the greatest amount of single-strand breaks in nascent DNA and dramatically decreased net DNA synthesis. IFN-alpha + gamma with or without FUra produced double-strand breaks in parental DNA. These results suggest that dTTP depletion, dATP/dTTP imbalance, pronounced inhibition of DNA synthesis, and damage to nascent and parental DNA contribute to the enhanced cytotoxicity with the triple combination.

Biochemical modulation of 5-fluorouracil with murine interferon-alpha/beta against murine renal cell carcinoma

BACKGROUND

Conventional therapy for renal cell carcinoma using interferon (IFN) has shown limited antitumor action. The purpose of our study was to investigate synergistic antitumor effects of IFN and 5-fluorouracil (5-FU), and to elucidate the mechanisms of interaction between the 2 agents in mice.

METHODS

Antitumor effects and biochemical modulation of murine IFN-alpha/beta and 5-FU were determined against the murine renal cell carcinoma cell line, Renca, in vivo. The activity of thymidylate synthetase and thymidine kinase was measured using cytosolic extracts of the tumors.

RESULTS

Combination treatment with IFN-alpha/beta and 5-FU produced a significant enhancement of growth inhibition against Renca tumor. Treatment with 5-FU resulted in a 2.7-fold increase in the total amount of thymidylate synthetase and an 11.6-fold increase in the thymidylate synthetase inhibition rate, while the administration of IFN-alpha/beta did not significantly reduce the 5-FU-induced increase in thymidylate synthetase. The administration of IFN-alpha/beta decreased thymidine kinase activity to 65.5% maximally, compared with that in the control mice or the mice treated with 5-FU.

CONCLUSIONS

The reduction of thymidine kinase caused by treating the mice with IFN-alpha/beta changes the utilization of exogenous thymidine for DNA synthesis, and may represent the mechanism of the additive antitumor effect of the 2 agents, through the suppression of the salvage pathway for deoxythymidine monophosphate induction.

Human recombinant interferon alpha-2a plus 3'-azido-3'-deoxythymidine. Synergistic growth inhibition with evidence of impaired DNA repair in human colon adenocarcinoma cells

We reported that 3'-azidothymidine-3'-deoxythymidine (AZT) plus 5-fluorouracil or methotrexate produces additive cytotoxicity in HCT-8 cells: a reflection of increased AZT metabolism when de novo thymidylate (dTMP) synthesis was inhibited. We now report that AZT plus human recombinant interferon alpha-2a (rIFN-alpha 2a) produces synergistic growth inhibition in these cells. Evaluation of the effect of rIFN-alpha 2a on dTMP metabolism revealed that exposure to rIFN-alpha 2a (+/-AZT) did not affect dTMP synthase activity significantly but increased thymidine (dThd) kinase activity significantly. Consequently, AZT nucleotide production and incorporation into DNA were increased by coexposure to rIFN-alpha 2a. This alone, however, cannot explain the observed synergism. Therefore, the effect of these agents on DNA excision/repair processes was assessed. Isotope clearance studies demonstrated that rIFN-alpha 2a did not alter the rate of [3H]AZT excision from DNA. In contrast, filter-elution studies revealed that rIFN-alpha 2a (+/-AZT) produced more DNA damage and delayed repair compared with the effects produced by AZT alone. Since DNA polymerases alpha and beta are directly involved in gap-filling repair synthesis, experiments next assessed the effect of rIFN-alpha 2a and/or 3'- azido-3'-deoxythymidine-5'-triphosphate (AZTTP) on their activities. Polymerase alpha was inhibited slightly by AZTTP but not by rIFN-alpha 2a. Polymerase beta activity, however, was inhibited dramatically by rIFN-alpha 2a + AZTTP. Finally, western analysis revealed that a 24-hr exposure to 5000 IU/mL rIFN-alpha 2a (+/-20 microM AZT) significantly reduced wild-type p53 expression compared with AZT-exposed cells. We conclude that rIFN-alpha 2a enhances AZT-induced tumor cell growth inhibition by (i) increasing AZT metabolism, and (ii) inhibiting DNA repair and p53-mediated cell cycle control processes.

Anti-IgM-mediated regulation of c-myc and its possible relationship to apoptosis

Anti-IgM treatment of Burkitt's lymphoma cells is followed by either growth arrest or induction of apoptosis. In this study we have explored the role of c-myc in these events. Our results in Ramos cells indicate the following. (a) The decline in c-myc mRNA occurs at about 4 h; inhibition of about 80% being observed. (b) The stability of c-myc message is involved since the half-life of c-myc mRNA is decreased from about 30 min in untreated cells to about 15 min following treatment with anti-IgM. In the presence of cycloheximide, a protein synthesis inhibitor, the half-life is increased to about 50 min and was unaltered by treatment with anti-IgM. (c) By contrast, nuclear run-on experiments indicated no change in transcription rates for c-myc message due to treatment with anti-IgM. (d) A decrease in c-myc causes apoptosis since specific repression of c-myc with antisense oligonucleotides decreases the levels of c-Myc, inhibits growth rate, decreases viability, and induces apoptosis. (e) Anti-CD40 inhibition of apoptosis occurs without alteration in anti-IgM-induced down-regulation of c-myc mRNA, suggesting that it acts distally to c-myc down-regulation. Other cell lines were also investigated. In Epstein-Barr virus (EBV)-positive cell lines (Daudi, Raji, and Namalwa), anti-IgM treatment for 24 h results in growth inhibition without induction of apoptosis. In EBV-negative cell lines (ST486 and CA46, as well as Ramos), a more heterogeneous pattern of responses to anti-IgM are observed. Ramos and ST486 cells both show growth inhibition and apoptosis upon anti-IgM treatment; CA46 cells shown only growth inhibition but not apoptosis. Anti-IgM causes a decline in c-myc mRNA levels in all of these lines, as well as in c-Myc protein level in the two lines investigated, Daudi and Ramos, regardless of apoptosis. Addition of antisense c-myc oligonucleotides to the cells reduced growth in both Daudi and Ramos cells lines, however it resulted in substantial apoptosis only in Ramos cells. These results suggest that anti-IgM destabilizes c-myc mRNA by a process that involves mRNA turnover, rather than transcription rates. However anti-IgM exerts differential effects in EBV-positive and EBV-negative cell lines. EBV-positive cells are uniformly resistant to apoptosis, while EBV-negative cell lines show a tendency to apoptosis but with exceptions. Growth inhibition can be uncoupled from apoptosis in EBV-positive cell lines, but not in those EBV-negative cell lines prone to apoptosis. Furthermore, down-regulation of c-myc message correlates with growth inhibition in these cells, but is an insufficient link to apoptosis. By contrast inhibition of apoptosis by anti-CD40 occurs even though c-myc mRNA is decreased.

Treatment of metastatic renal cell carcinoma with constant-rate floxuridine infusion plus recombinant alpha 2b-interferon

BACKGROUND

Floxuridine (FUDR) and alpha-interferon (IFN) are active agents in advanced renal cell carcinoma, with different dose-limiting toxic effects and antitumor synergism in experimental models. The main purpose of this phase II study was to assess the activity and toxic effects of a combination of FUDR and alpha 2b-IFN in metastatic renal cell carcinoma.

PATIENTS AND METHODS

Metastatic renal cell carcinoma patients with measurable disease entered the study. FUDR was administered as a constant-rate continuous infusion for 14 days every 28 days at a starting daily dose of 0.1 mg/kg and with dose escalations of 0.025 mg/kg/day at each subsequent cycle if WHO > or = 2 toxicity had not occurred. IFN-alpha 2b 10 x 10(6) I.U. was administered intramuscularly 3 times per week.

RESULTS

Forty-two patients entered the study and a total of 272 cycles of FUDR + alpha 2b-IFN were administered. In 41 evaluable patients WHO grade III-IV toxic effects included nausea and vomiting (22%), diarrhea (32%), stomatitis (12%), fatigue (27%) and anorexia (12%). It was possible to increase the initial FUDR does in 21 (50%) patients; the median FUDR dose intensity was 0.35 mg/kg/week (range 0.18-0.54). Among 39 evaluable patients, 3 (7.5%) complete and 10 (25.5%) partial responses were observed (response rate 33%, 95% confidence interval (CI) 19%-50%) which lasted a median of 13 months (5.5-40+). Responses also occurred in liver (2), in patients pretreated with systemic therapy (5) and in patients who had other unfavourable prognostic characteristics (7). Median progression-free and survival times were 9 and 16 months, respectively.

CONCLUSIONS

In this study FUDR + alpha 2b-IFN demonstrated interesting activity in metastatic renal cell carcinoma, showing promise also in patients with unfavourable prognostic characteristics. The antitumor activity of FUDR and alpha 2b-IFN seems to be cumulative, but cumulative toxicity is also observed. These results require confirmation in randomised trials.

The HLA-A,B,C genotype of the class I negative cell line Daudi reveals novel HLA-A and -B alleles

Daudi, a lymphoblastoid B cell line derived from an African Burkitt lymphoma does not express HLA-A,B,C antigens at the cell surface. Although HLA-A,B,C heavy chains are made normally they do not assemble into functional molecules because beta 2-microglobulin is absent. Previous serological analysis of somatic cell hybrids indicated that the HLA haplotypes of Daudi encoded HLA-A1, A10(A26), B17, and B16(38) antigens. Here we describe the application of molecular methods: ARMS-PCR, cDNA cloning and sequencing, immunoprecipitation and gel electrophoresis, to define the class I genotype of the Daudi cell line which is HLA-A*0102, A*6601, B*5801, B*5802, Cw*0302 and Cw*0602. With the exception of the B38 antigen, which is not a product of the alleles defined, the genotype is consistent with the serological description. Two previously undiscovered alleles emerged from this analysis: A*0102 and B*5802. The A*0102 allele differs from A*0101 by 5 nucleotide substitutions within exon 2 where it has a motif shared with A*30 alleles; the B*5802 allele differs from B*5801 by 3 substitutions in exon 3 where it has a motif shared with B*14 alleles. Subtyping HLA-A1 alleles showed A*0102 was well represented amongst individuals typed serologically as A1 in an African population but was absent from caucasoids. B*5802 has been found in a second individual. Thus the novel A and B alleles are not specific to the Daudi tumor. Overall, this analysis of a single East African cell illustrates the power of molecular methods to define new class I HLA alleles in non-caucasoid populations.

3'-Azido-3'-deoxythymidine cytotoxicity and metabolism in the human colon tumor cell line HCT-8

We have reported that 3'-azido-3'-deoxythymidine (AZT) possesses significant cytotoxicity in human tumor models when combined with agents that inhibit de novo thymidylate (dTMP) synthesis, such as 5-fluorouracil (FUra) and methotrexate (MTX). To aid in the further development of these and related cancer chemotherapeutic regimens, this study was undertaken to identify the biochemical processes relevant to the induction of AZT cytotoxicity in the model human colon tumor cell line HCT-8. The IC50 of AZT in this cell line after a 5-day exposure was 55 microM. In cells incubated for 5 days with various concentrations of [3H]AZT alone, both [3H]AZT nucleotide pools and [3H]AZT incorporation into DNA increased as the concentration of AZT in the medium increased. In addition, a 5-day exposure to AZT, at medium concentrations < or = 100 microM, resulted in a reduction in dTMP synthase (EC 2.1.1.45; methylene tetrahydrofolate:deoxyuridine-5'-monophosphate C methyltransferase) and dTHd kinase (EC 2.7.1.27; ATP: thymidine phosphotransferase) activities, compared with cells incubated without drug. The IC50 of AZT was unchanged when the medium concentration of dThd was increased from 0.1 to 50 microM. Increasing the concentration of dThd to 50 microM also did not affect intracellular pools of [3H]AZTDP and [3H]AZTTP or the degree to which [3H]AZT was incorporated into cellular DNA, but did reduce intracellular [3H]AZTMP by approximately 75%. The degree to which 3'-amino-3'-deoxythymidine (AMT) was generated from AZT and incorporated into DNA also was not affected by varying the medium concentration of dThd. However, the amount of [3H]-AMT detected in DNA, < or = 3 pmol/10(6) cells at medium concentrations of [3H]AZT < or = 100 microM, was below that associated with significant cytotoxicity in these cells. These data support the notion that, in this model, AZT cytotoxicity is determined by the relative size of AZTTP pools and its utilization in DNA synthesis. Studies to verify this relationship assessed the effect of alterations in the concentration of dTTP and [3H]AZTTP on [3H]AZT incorporation into newly synthesized DNA in vitro, using DNA polymerases isolated from HCT-8 cells. The results of these studies confirmed that alterations in the concentration of either dTTP or AZTTP to reduce the dTTP/AZTTP ratio resulted in an increase in AZT incorporation into DNA. These findings are discussed in light of their biochemical implications and relevance to ongoing clinical trials.

Alpha interferon, leucovorin, and 5-fluorouracil (ALF) in advanced cancer: results of a dose-finding study and evidence of activity in non-small cell lung cancer

In a phase I trial, 17 patients were treated with 5-fluorouracil (5-FU) 500 mg/m2 and leucovorin (LV) 500 mg/m2 intravenously weekly for 6 weeks followed by 2 weeks' rest and interferon alfa-2b 1, 3, 5, 8, or 10 million units (MU) subcutaneously tiw with no rest period. The most common toxicities were fatigue (12), diarrhea (10), nausea/vomiting (7), and fever (7). The maximum tolerated interferon dose was 8 MU tiw. Fatigue and increased incidence of other toxicities rather than a single dose-limiting toxicity occurred at the next highest interferon level. ECOG grade III/IV toxicity occurred in 5 patients and included transient supraventricular tachycardia and brief seizure episode (1), dyspnea (1), decreased performance status (1), anemia requiring transfusion (1), and deep vein thrombosis (1). No toxic deaths occurred. Two patients with non-small cell lung cancer (NSCLC) had partial responses lasting 5 and 4 months. Two other patients with NSCLC had either minor response or stable disease, and 1 patient with colon cancer had a significant decline in serum CEA. The recommended alpha interferon dose is 8 MU tiw when given with this schedule of 5-FU/LV.

Biologic agents as biochemical modulators: pharmacologic basis for the interaction of cytotoxic chemotherapeutic drugs and interferon

Biochemical modulation of cytotoxic cancer chemotherapeutic agents is one means of enhancing the activity and selectivity of antitumor drugs. Traditionally this approach has utilized detailed information regarding a particular enzymatic reaction or biochemical pathway to develop potential modulating agents. In contrast, the reported clinical therapeutic activity of IFN in combination with cytotoxic agents has prompted a reexamination of the biochemical actions of the cytokine. Interferon elicits a number of cellular actions that might contribute to its pharmacologic activity, including both direct antitumor effects and host-mediated actions. The best understood are those related to the cytotoxicity of the fluoropyrimidine antimetabolites and include enzymatic reactions involved in fluoropyrimidine metabolic activation, catabolism, and interaction with its target enzyme. However, even in this instance, a mechanistic association of a specific pharmacologic action with therapeutic activity remains to be determined. These studies demonstrate that cytokines and other biologic agents may exert specific biochemical modulations that augment (or potentially attenuate) the activity of the cytotoxic chemotherapeutic agents.

Alpha-2B-interferon plus floxuridine in metastatic renal cell carcinoma. A phase I-II study

BACKGROUND

Both alpha-interferon and floxuridine are active in metastatic renal cell carcinoma (MRCC); the two agents have demonstrated antitumor synergism and different clinical toxicities. The purpose of this study was to determine the maximum tolerable dose (MTD) of floxuridine (FUDR), administered as a constant continuous infusion for 14 days every 28 days, in combination with fixed doses of alpha-2B-interferon and to preliminarily evaluate the antitumor activity of this combination.

METHODS

Sixteen patients entered the study; six had previously received alpha-interferon. Alpha-2B-interferon was administered at the dose of 10 x 10(6) IU intramuscularly 3 times/week and floxuridine at the starting daily dose of 0.075 mg/kg. This dose was escalated at each subsequent cycle up to dose-limiting toxicity.

RESULTS

Most common toxicities included fever and flue-like symptoms, fatigue, anorexia, diarrhea, mucositis, and nausea, and 55% of patients experienced greater than or equal to Grade 2 toxicity, mostly diarrhea, for floxuridine doses greater than 0.125 mg/kg/d. Among 15 evaluable patients, 1 achieved a complete response and 4 achieved a partial one (33%; 95% confidence interval, 12-62%). Three partial responses were obtained in patients pretreated with alpha-interferon plus vinblastine.

CONCLUSIONS

The combination of alpha-2B-interferon and floxuridine is feasible, and in our regimen the recommended daily dose of floxuridine for Phase II studies was 0.125 mg/kg. This combination is active in metastatic renal carcinoma, but further studies are needed to determine whether alpha-2B-interferon has added anything to the FUDR infusion or vice versa.

Nonsurgical management of recurrent colorectal cancer

Most patients with colorectal carcinoma undergo attempts at curative surgery. However, some present with metastatic disease and many others ultimately relapse. Most recurrences of colorectal cancer are not resectable and require nonsurgical approaches such as chemotherapy and radiation therapy directed against local recurrences, hepatic metastases, and widely disseminated disease. Nonsurgical therapy for locoregional recurrence of rectal cancer can offer significant palliation. Intraarterial chemotherapy for liver metastases increases the likelihood of response compared to systemic treatments, but has little effect on survival. Extrahepatic progression and hepatic toxicity are important limitations to this regional therapy. 5-fluorouracil (5-FU) is the mainstay of systemic chemotherapy, and efforts to modulate biochemically the cytotoxic effects of 5-FU with folinic acid, phosphonacetyl-L-aspartate, interferon, and other agents have resulted in promising response rates. The different approaches to biochemical modulation are being studied in ongoing cooperative group trials. Novel approaches, including monoclonal antibody therapy, biologic modifier therapy, and gene therapy, are under investigation.

Inositol lipid-mediated intranuclear signalling: a comparative analysis of in vivo labelling in interferon alpha-sensitive and -resistant Daudi lymphoma cells

Changes in inositol lipid and diacylglycerol metabolism have been analysed in Daudi lymphoma cells treated up to 24 h with human DNA recombinant interferon alpha. Results showing a different response of nuclear phosphoinositides and diacylglycerol, compared to whole cells, suggest that the intranuclear signalling system activated by interferon in Daudi cells involves nuclear inositol lipid metabolism. A well-characterized clone of Daudi cells selected for resistance to the antiproliferative action of interferon provided controls for the specificity of results.

Role of protein kinase C in induction of gene expression and inhibition of cell proliferation by interferon alpha

Recent studies have suggested that protein kinase C (PKC) may be involved in the mechanism of signal transduction by which members of the interferon (IFN) family regulate gene expression and cell phenotype. We have investigated the role of PKC in the control of cell growth and gene expression by IFN alpha in Daudi cells. Treatment of these cells with two analogues of staurosporine, which are potent inhibitors of PKC, completely blocked the induction by IFN alpha of the mRNA for 2',5'-oligoadenylate synthetase and the 6-16 gene. These compounds also inhibited cell proliferation and thymidine incorporation in this system. In contrast, the protein kinase inhibitor 1-(5-isoquinolinylsulphonyl)-2-methylpiperazine (H7) did not significantly inhibit the induction of these genes by IFN alpha and had no effect on Daudi cell growth or thymidine incorporation in the presence or absence of IFN alpha. No effect of IFN alpha on total PKC activity could be observed, and there were no significant changes in the overall levels of individual PKC isoforms or their mRNA following IFN alpha treatment. In contrast, treatment of Daudi cells with the phorbol ester 12-O-tetradecanoylphorbol 13-acetate, which also inhibits cell proliferation, strongly down-regulated PKC. These data suggest that the activity of a PKC species, or a closely related enzyme, may be required both for continued cell proliferation and the response to IFN alpha in Daudi cells, but that IFN-induced growth inhibition does not involve overall down-regulation or change in activity of PKC.

A phase II trial of interferon alpha-2A plus fluorouracil in advanced renal cell carcinoma. A Hoosier Oncology Group study

In vitro studies have documented the synergistic activity of interferon (IFN) and fluorouracil (5-FU) in human cancer cell lines, and recent clinical trials have demonstrated the efficacy of this combination in metastatic colon cancer. The current study was undertaken to evaluate the combination of IFN alpha-2a plus 5-FU in previously untreated patients with metastatic renal cell carcinoma. From May 1990 through August 1990, 14 patients with metastatic renal cell carcinoma were treated with 5-FU 750 mg/m2/day continuous infusion IV days 1-5, followed by weekly IV infusions of 5-FU 750 mg/m2 beginning on day 12. Patients concurrently received IFN alpha-2a 9 x 10(6) IU subcutaneously 3 times per week beginning on day 1. The median age of patients treated was 57 (range 38-80) with a median Karnofsky performance status of 90 (range 60-100). Sites of metastases included lung only in 6 patients, liver only in 1 patient, 1 patient had bilateral disease at presentation, and the remaining patients had multiple sites of metastases. The median duration of therapy was 2 months. The predominant toxicities seen were stomatitis, nausea, flu-like symptoms and neurotoxicity. The only grade IV toxicity observed was severe vomiting in 1 patient, though 5 patients discontinued therapy within 2 months because of poor subjective response. With a minimum follow-up of 13 months no objective responses were seen. Thirteen of the 14 patients have had progressive disease and 11 have died. The median time to progression was 2 months (range 0.5-6 months) and the median survival was 5 months (range 2-14.5 + months).(ABSTRACT TRUNCATED AT 250 WORDS)

alpha-Interferon inhibits spontaneous and induced DNA synthesis in hairy cell leukemia

The effect of alpha-interferon (alpha-IFN) on spontaneous or induced proliferation of isolated peripheral blood mononuclear cells from 5 hairy cell leukemia patients was studied. alpha-IFN inhibited the low spontaneous proliferation of B-ly7 positive hairy cells (HCs) and also the proliferation induced by tumour necrosis factor (TNF). Interleukin-2 did not affect HCs, but induced CD4 positive T cells to proliferate, an effect which alpha-IFN antagonized. The stimulatory effect of TNF on the growth of HCs proved to be reversible and was partially blocked with either anti-TNF receptor or anti-lymphotoxin antibodies. Cellular or secreted thymidine kinase levels reflected the proliferative state of HCs in response to different in vitro treatments, as confirmed by thymidine incorporation and cell cycle studies.

A phase I trial of 5-fluorouracil, folinic acid, and alpha-2a-interferon in patients with metastatic colorectal carcinoma

The mechanisms of biochemical modulation of 5-fluorouracil (5-FU) cytotoxicity by folinic acid (FA) have been elucidated, and the clinical use of this combination has improved response rates and survival in patients with metastatic colorectal cancer. Recently, Phase II trials also showed potential synergism between alpha-2a-interferon (rHuIFN-alpha 2a) and 5-FU. Therefore, a Phase I trial of these three agents 5-FU, FA, and rHuIFN-alpha 2a was conducted in patients with metastatic colorectal cancer. The drugs were given over 5 days, with dose escalation of either rHuIFN-alpha 2a or 5-FU. Fifty-five eligible patients were treated at eight dosing levels. The maximal tolerated dose (MTD) was as follows: 5-FU 430 mg/m2/d intravenously (IV) on days 1 to 5, FA 200 mg/m2 IV on days 1 to 5, and rHuIFN-alpha 2a 4.0 x 10(6) U/m2/d subcutaneously on days 1 to 5. The dose-limiting toxicities were mucositis and neutropenia. Objective responses were seen at most dosing levels, and overall 15 of 55 patients (27%; 95% confidence interval, 16% to 41%) responded (median duration, 6.5 months). A Phase II trial using the MTD is ongoing.

DNA synthesis in nuclei isolated from Daudi B cells: a model to study the antiproliferative mechanisms of interferon-alpha

To study the antiproliferative response of B cells to interferon-alpha (IFN-alpha) at the molecular level, we developed a cell-free system to assess DNA synthesis in nuclei isolated from IFN-sensitive Daudi B lymphoblastoid cells. [3H]dTTP incorporation in isolated nuclei was shown to be representative of replicative DNA synthesis by evidence that (i) incorporation was dependent on ATP and all four nucleoside precursors, (ii) incorporation was inhibited greater than 97% by aphidicolin, a specific inhibitor of DNA polymerase alpha and delta, and (iii) the DNase I-sensitive product banded in neutral CsCl at a density indicative of replicative DNA. This cell-free model was used in conjunction with flow cytometric cell cycle analysis to determine the effect of IFN-alpha on DNA synthesis in Daudi cells. The addition of IFN-alpha to an IFN-growth sensitive Daudi subclone in G0/early G1 inhibited the initiation of DNA synthesis, assessed in isolated nuclei, and prevented the progression of cells into S phase. IFN-alpha failed to inhibit DNA synthesis or cell cycle progression when added to IFN-sensitive Daudi cells in late G1/early S phase or to an IFN-resistant Daudi subclone. These studies suggest that IFN-alpha inhibits DNA replication and cellular proliferation in Daudi B cells by interfering with G1 cell cycle events.

Effects of interferons and other cytokines on tumors in animals: a review

The term cytokine describes a group of protein cell regulators involved in the control of cell growth and differentiation in embryogenesis, immunity and inflammation. They are of low molecular weight, are produced locally, and act in an autocrine or paracrine manner. In the past decade their use as cancer therapy has become a reality. Thirty years ago mice were treated with the antiviral protein interferon (IFN) which not only produced a reduction in the incidence of virus-induced tumors but also slowed the development of transplantable tumors. This was one of the first indications that cytokines can be negative regulators of cell growth. Here we outline current knowledge of the actions of IFNs and other cytokines in animal models, and draw parallels with clinical trials to illustrate the invaluable nature of this preclinical and mechanistic work.

Fluorouracil and recombinant interferon alfa-2a in advanced gastrointestinal neoplasms

Based on preclinical studies which demonstrated synergy between recombinant interferon alfa-2a (rIFN alpha-2a) and 5-fluorouracil (5FU), clinical studies have been initiated to investigate this combination. The initial study conducted by investigators from the Albert Einstein Cancer Center reported a response rate of 76% with 13/17 patients with advanced colorectal carcinoma responding. To further evaluate this regimen, two clinical trials have been conducted in previously untreated advanced colorectal carcinoma patients with measurable disease. The regimen consisted of 5FU administered as a continuous infusion, 750 mg/m2/d for 5 consecutive days. Intravenous bolus administration of 5FU 750 mg/m2 was given weekly for 7 weeks starting 1 week after completion of the continuous infusion. rIFN alpha-2a, 9 MU, was administered subcutaneously three times weekly. In The University of Texas M.D. Anderson Cancer Center trial, 15/45 evaluable patients experienced partial response, and one patient achieved a complete response for an overall response rate of 35%. Another trial of this regimen conducted by Memorial Sloan-Kettering has reported a 26% response rate with 9/34 evaluable patients experiencing a partial response. Current randomized trials comparing this schedule of 5FU with rIFN alpha-2a to 5FU plus folinic acid or single-agent 5FU may clarify its role in the treatment of advanced colorectal carcinomas.

Phorbol ester-induced inhibition of proliferation of Daudi Burkitt's lymphoma cells by impairment of cytokinesis

The phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) exerts a dose-dependent effect on Daudi cell proliferation. A low concentration has a slight mitogenic effect but higher concentrations inhibit proliferation. The inhibitory effect is associated with increases in cell size, macromolecular content, and incorporation of precursors into RNA and protein. Cell cycle analysis indicates that TPA at 1-10 nM leads to an apparent accumulation of cells in G2/M phase. However, within this population a significant proportion of cells undergo nuclear division but fail to carry out cytokinesis, giving rise to cells with two or more nuclei. Consistent with this, DNA synthesis continues in cells which cease to divide in the presence of TPA. The ability of the phorbol ester to inhibit proliferation can thus be attributed mainly to an inhibition of cytokinesis rather than DNA replication.

Human small-cell lung-cancer cells are cytokine-resistant but NK/LAK-sensitive

We have studied the effects of 8 cytokines and their combinations on the in vitro growth of 10 human small-cell cancer lines (SCLC). Interferon-alpha and gamma (IFN-alpha and gamma) caused significant but slight growth inhibition over a 7-day incubation period. However, none of the other 6 cytokines, tumor necrosis factor (TNF), lymphotoxin (LT), interleukin-1 beta (IL-1 beta) interleukin-2 (IL-2), transforming growth factor-beta 1 (TGF-beta 1), or granulocyte colony-stimulating factor (G-CSF), modified SCLC cell proliferation. In contrast, all 10 lines were sensitive to lysis by natural killer (NK) and lymphokine-activated killer (LAK) cells. Sensitivity to LAK cells could be increased by pretreatment of SCLC cells with IFN-gamma. As resistance to the cytostatic/cytotoxic activity of some cytokines has been associated with autocrine production of cytokines, we screened the SCLC lines for cytokine mRNAs. Within the limits of detection of the assay we found no expression of TNF, TGF-beta 1, IL-1 beta or IL-6 mRNA in the 10 SCLC lines.

5-Fluorouracil and recombinant alpha interferon-2a in the treatment of advanced colorectal carcinoma: a dose optimization study

A dose optimization study was carried out with the aim of identifying the maximally tolerated dose of recombinant alpha interferon-2a (raIFN-2a) in combination with 5-fluorouracil (5FU). 5FU was given at the dose of 750 mg/m2 over a 4-hour infusion on day 1- - greater than 5 followed by 750 mg/m2 weekly i.v. bolus. Recombinant aIFN-2a was started at 3 x 10(6) IU subcutaneously three times/week. 12 patients with advanced colorectal carcinoma were included in the study. 10 patients had previously received chemotherapy for advanced disease. Severe fatigue, most likely attributable to rIFN, was the dose-limiting toxicity. The dosage of raIFN-2a could not be further escalated above 12 x 10(6) IU. At this dose level all patients required dose reduction due to fatigue, fever, myalgia and severe reduction of performance status.

Characterization of interleukin 5 receptors on eosinophilic sublines from human promyelocytic leukemia (HL-60) cells

The T cell product interleukin 5 (IL-5) has been shown to be a key factor in the development and the maturation of the eosinophilic cell lineage. We report here on the detection of human IL-5 receptors on eosinophilic sublines of the promyelocytic leukemia HL-60. Sodium butyrate, which initiates differentiation to mature eosinophils, also induces the appearance of high affinity (Kd 1-5 X 10(-11) M) IL-5 binding sites on these cells. The receptors are specific for IL-5, since binding of radiolabeled ligand can only be inhibited with homologous or murine IL-5 and not by other cytokines. We further show that the receptors are functional, since IL-5 can stimulate the proliferation of these cells. Affinity crosslinking of surface-bound 125I human IL-5 or 35S mouse IL-5 identified two membrane polypeptides of approximately 60 and approximately 130 kD to which IL-5 is closely associated. The presence of granulocyte/macrophage-colony-stimulating factor or tumor necrosis factor during butyrate induction decreased the expression of IL-5 binding sites compared with control cultures. The identification and characterization of human IL-5 receptors on HL-60 sublines should provide new insight into the role of this cytokine in eosinophil differentiation.

Nucleoside metabolism in herpes simplex virus-infected cells following treatment with interferon and acyclovir, a possible mechanism of synergistic antiviral activity

Alpha interferon (IFN-alpha) and nucleoside analogs have been shown to have synergistic antiherpesvirus activity in cultured cells. The mechanisms responsible for this synergistic activity are not known, but we hypothesize that IFN-alpha-induced alterations of nucleoside metabolism in virus-infected cells may play an important role. Infection of cells with herpes simplex virus type 1 (HSV-1) led to an increase in uptake of thymidine into cells. Treatment of infected cells with recombinant IFN-alpha for 24 h prior to infection resulted in a significant reduction in the uptake of exogenous thymidine but did not reduce the apparent incorporation of exogenous thymidine into DNA. The amount of exogenous thymidine phosphorylated relative to the amount taken up was the same in IFN-alpha-treated and control cultures. IFN-alpha treatment of HSV-1-infected cells also resulted in a reduction in the pool sizes of endogenous deoxyribonucleoside-5'-triphosphates relative to those of untreated HSV-1-infected cultures. Although IFN-alpha affected the metabolism of natural nucleosides in HSV-1-infected cells, it did not significantly reduce the uptake of the antiviral guanosine analog acyclovir into HSV-1-infected cells or the amount of acyclovir-5'-triphosphate accumulated. Therefore, in IFN-alpha-treated cells the concentration of a natural nucleoside, thymidine, was reduced, as were the pools of all deoxyribonucleoside-5'-triphosphates. No decrease in acyclovir or acyclovir-5'-triphosphate concentration was observed, however, when acyclovir-treated cells were exposed to IFN-alpha. These data suggest that IFN-alpha-induced alterations in nucleoside metabolism may be one mechanism whereby IFN-alpha and acyclovir express synergistic antiherpes-virus activity.

An in vitro bioassay for quantitation of human interferons by measurements of antiproliferative activity on a continuous human lymphoma cell line

Interferons have, in addition to their antiviral effects, been shown to possess several non-antiviral activities. In this study, an in vitro bioassay for interferon alpha (IFN-alpha) preparations based on their antiproliferative effect in cultured Daudi cells has been developed. Briefly, about 10(5) cells per ml treated with different concentrations of IFN were incubated under standard culture conditions for 3 days. Two different end points, i.e. incorporation of [3H]thymidine and final cell density, were used and responses were evaluated according to established pharmacopoeial principles for quantification of biomolecules. Both methods gave similar results. However, measurement of final cell density yielded the most precise results. The proposed assay, with an effective assay range of 1-10 IU/ml (approximately 0.2-2 x 10(-12)M, had a high sensitivity and precision as well as a good reproducibility. Compared with antiviral assays, it is less resource demanding. In conclusion, the in vitro bioassay described is well suited for potency determinations of IFN-alpha and probably also IFN-beta preparations.

Constitutive expression of a 2',5'-oligoadenylate synthetase cDNA results in increased antiviral activity and growth suppression

The interferon (IFN)-induced enzyme 2',5'-oligoadenylate (2-5A) synthetase has been implicated in the development of antiviral activity in human and animal cells. However, its role in IFN-mediated growth inhibition remains unclear. To elucidate the function of 2-5A synthetase, we have stably introduced a human 2-5A synthetase cDNA into a human glioblastoma cell line (T98G). Constitutive expression of the cDNA in these cells is associated with increased levels of resistance to infection by encephalomyocarditis virus. One transfected subclone, which expresses elevated levels of 2-5A synthetase enzyme activity, also shows a reduced rate of cellular proliferation.

Interferon effects upon fluorouracil metabolism by HL-60 cells

In order to better understand the synergistic antiproliferative effects of interferon in combination with fluorouracil (FUra), we studied effects of alpha 2-interferon upon FUra induced inhibition of thymidylate synthase of HL-60 cells. The 50% inhibitory dose for FUra decreased from approximately 75 microM to 10 microM following interferon treatment, as measured by whole cell activity assays. Enhanced FUra inhibition of cytosolic [3H] - FdUMP binding of interferon treated cells was also noted. FdUMP accumulation following FUra treatment increased over 10 fold in interferon treated cells, but dUMP did not increase. These results suggest that interferon can sensitize cells to FUra inhibition of thymidylate synthase by enhancing accumulation of FdUMP.

Relationship of cellular oncogene expression to inhibition of growth and induction of differentiation of Daudi cells by interferons or TPA

Human alpha or beta interferons inhibit the proliferation of Daudi Burkitt lymphoma cells and induce the differentiation of these cells towards a mature plasma cell phenotype. Similar responses are seen when Daudi cells are treated with the phorbol ester, TPA. Both interferons and TPA down-regulate expression of the c-myc oncogene in these cells. Although TPA can mimic the effect of interferon on cell differentiation, it does not induce 2'5' oligoadenylate synthetase or the interferon-sensitive mRNAs, 6-16 or 9-27. Thus chronic stimulation of protein kinase C by TPA cannot mimic all of the effects of interferon treatment on gene expression. Inhibition of ADP-ribosyl transferase activity by 3-methoxybenzamide impairs interferon- or TPA-induced differentiation of Daudi cells. This agent induces a higher level of c-myc mRNA in the cells and stimulates the incorporation of [3H]thymidine into DNA; although these effects are partially counteracted by interferon or TPA treatment, the elevated expression of the c-myc gene may be sufficient to prevent terminal differentiation and allow cell proliferation to continue.

Differential activity of the 30-kD and the 100-kD forms of 2'-5'An synthetase induced by recombinant human interferon-alpha and interferon-gamma

Two molecular weight variants of the interferon (IFN)-induced intracellular enzyme 2',5'-oligoadenylate (2-5A) synthetase have been described recently; a 100-kD (cytoplasmic) and a 30-kD (intranuclear) form of the enzyme. The 30-kD form has been located primarily in the nucleus, while the 100-kD enzyme was found mainly in the cytoplasm. We examined 2-5A synthetase activity in extracts of human melanoma (Hs294t) cells treated with either recombinant (r) IFN-alpha A or rIFN-gamma to determine the differential regulation of these enzyme subtypes by treatment with the two types of IFN. Cells were treated (continuous exposure) with doses of rIFN-alpha A (1,000 U/ml) or rIFN-gamma (5,000 U/ml), each of which reduced the number of viable cells to 50% of control values (ED50) by day 3 of treatment. At equieffective doses, the maximal increase in 2-5A synthetase occurred at 48 h for both rIFN-alpha A and rIFN-gamma continuous exposure. The maximal 2-5A intracellular activities at 48 h were 800 +/- 40 and 160 +/- 15 nmoles/mg protein for rIFN-alpha A and rIFN-gamma treatment, respectively. High-performance gel permeation chromatography of cell lysates resolved the 2-5A activity into both 100-kD and 30-kD fractions. At 48 h after treatment with rIFN-alpha A, the activity of the 30-kD synthetase was approximately twofold greater than that of the 100-kD enzyme. In contrast, the activity of both 30- and 100-kD enzymes were equivalent 48 h after treatment with rIFN-gamma.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of recombinant cytokines on the proliferative potential and phenotype of cells of the human myelomonocytic leukaemia line, RC-2A

Cells of the human myelomonocytic line RC-2A can be induced to differentiate towards mature monocytes by culture in the presence of phytohaemagglutinin-treated lymphocyte conditioned medium (Lyons and Ashman, Leukemia Res. 11, 797, 1987). We have now examined the effect on RC-2A cells of some (recombinant) cytokines which might be present in conditioned medium. Gamma interferon most closely mimicked the effect of conditioned medium in inducing clonogenic suppression and the induction of monocytic maturation over 7 days of culture. Granulocyte colony stimulating factor induced enhancement of proliferation followed by clonogenic suppression, while granulocyte-macrophage colony stimulating factor had a purely stimulatory effect on proliferation over a 7-day period. Tumour necrosis factor alpha failed to affect cell proliferation or to induce characteristic monocytic differentiation, but did increase the expression of C3bi receptors. We conclude that RC-2A cells have receptors for all four cytokines studied, and that gamma interferon is a major differentiation-inducing stimulus for these cells.

Regulation of cell growth by interferon

Interferons can regulate growth and differentiation in a wide range of cell types. These mechanisms are currently being examined. Interferons inhibit the growth of tumour cells and are thus potential anti-cancer agents. They can also inhibit normal cell growth in vitro, and stimulate tumour cell growth in vitro. They may also be involved in some autoimmune diseases. This review examines the effect of interferons on cell proliferation, function, and growth, focusing primarily on in vitro cell systems.

Interferon alpha-2 for hairy cell leukemia: evidence for induction of RNA synthesis in hairy cells and failure to correlate enhancement of natural killer cells with elimination of hairy cells

The effect of human recombinant interferon alpha 2 (IFN alpha 2) on hairy cells obtained from 16 patients was evaluated. All patients promptly responded to induction of remission with 2 X 10(6) U/m2 interferon alpha 2 b, three times a week, sc. In order to achieve a more detailed insight into the mode of action of interferon in this disease, we determined the influence of IFN alpha 2 on the incorporation of radiolabeled thymidine and uridine into hairy cells. While both 3H-thymidine and 3H-uridine incorporation were unaffected by IFN alpha 2 in a 3-hour incubation period, a significant increase in uridine incorporation into hairy cells, but not CLL cells, was observed after 24 h. Cell surface marker analysis performed with monoclonal antibodies did not reveal a quantitative alteration of the immunophenotype of hairy cells in vitro. In addition, natural killer cells, assessed by monoclonal antibodies and a cytotoxicity assay against K 562 cells, were found to be decreased in 9 out of 10 patients prior to therapy. Although IFN alpha 2 could stimulate natural killer cells in vivo, we did not find a consistent correlation between the activation of these cells and the response to therapy. We conclude, therefore, that NK cells play no major role in the regression of hairy cells. Furthermore, IFN alpha 2 does not alter antigenic determinants in vitro, but leads to an enhanced incorporation of 3H-uridine into hairy cells in vitro, thus indicating a possible role for the induction of RNA synthesis in vivo.

Induction of B-cell differentiation antigens in interferon- or phorbol ester-treated Daudi cells is impaired by inhibitors of ADP-ribosyltransferase

Treatment of the Daudi Burkitt lymphoma-derived cell line with human interferon alpha, which inhibits cell proliferation in this system, induces differentiation of these B-lymphoid cells into cells with a plasmacytoid phenotype. This differentiation, quantified by the appearance of surface antigens characteristic of mature plasma cells, is impaired by addition to the culture medium of the ADP-ribosyltransferase (ADPRT; EC 2.4.2.30) inhibitors 3-methoxybenzamide or 3-aminobenzamide. These agents also protect the cells against the inhibition of proliferation induced by low doses of interferon alpha. In contrast, the large inhibition of thymidine incorporation into DNA caused by interferon treatment is not affected by the ADPRT inhibitors. The phorbol ester phorbol 12-tetradecanoate 13-acetate induces the same plasma cell surface antigens that are induced by interferon treatment, and this effect is also impaired by the ADPRT inhibitors. These results suggest that interferons and phorbol esters share a mechanism of action that requires ADPRT activity. Protection of the cells against the antiproliferative effect of interferons by the ADPRT inhibitors suggests that growth inhibition may be a consequence of cell differentiation. In contrast, the inhibition of thymidine incorporation alone is not sufficient for the cessation of cell proliferation and is not a true reflection of the rate of DNA synthesis.

Anti-proliferative effects of interferons on Daudi Burkitt lymphoma cells: induction of cell differentiation and loss of response to autocrine growth factors

Treatment of Daudi B-lymphoblastoid cells with low concentrations of either natural or recombinant human alpha-interferons inhibits cell proliferation and modulates the expression of a number of cell-surface antigens. Using a panel of monoclonal antibodies (MAbs) identifying determinants expressed at the surface of normal plasma cells, and polyclonal antibodies against surface and cytoplasmic immunoglobulin, we have found that growth inhibition is accompanied by plasmacytoid differentiation. Assays of growth stimulation of heterologous cells indicate that the culture medium from interferon-treated Daudi cells contains substantially more B-cell growth factor activity than that from control cells. However, the interferon-treated cells exhibit an impaired ability to respond to both these autocrine factors and exogenous factors produced by another Burkitt lymphoma line. These findings show that, in the case of Daudi cells, growth inhibition by interferons is closely associated with both terminal differentiation and a refractoriness to growth factors. In this system IFN-alpha may therefore be considered to be a B-cell differentiation factor, suggesting a possible basis for the anti-proliferative effects observed with certain human B-cell malignancies.

Interferon inhibits preferentially the synthesis of proteins associated with growth stimulation of Swiss 3T3 mouse fibroblasts

The putative role of inhibition of protein synthesis within the antiproliferative effect of interferon was analyzed in serum-stimulated Swiss 3T3 mouse fibroblasts. We observed an apparent coupling between protein-synthesis inhibition during G1 and a delayed entry into the S-phase. To reveal any specificity in the protein-synthesis inhibition, we measured the amounts of synthesis of 56 major individual proteins, by using isotope double-labelling and two-dimensional gel electrophoresis. Interferon inhibited preferentially the synthesis of proteins which were increased after serum stimulation, whereas proteins synthesized in constant or decreased amounts after serum stimulation were significantly more resistant. The effects of interferon were also compared to those of 5,6-dichloro-1-beta-ribofuranosylbenzimidazole (DRB), an inhibitor of transcription. All interferon-sensitive proteins studied were inhibited by DRB treatment, but in addition DRB also inhibited several proteins which were completely resistant to interferon. We conclude that interferon primarily inhibits protein synthesis originating from a subset of newly transcribed messenger RNAs. The mechanism(s) for inhibition of protein synthesis and the possible relationship to the antiproliferative and antiviral effects of interferon are discussed.

Modification of ribonucleotide and deoxyribonucleotide metabolism in interferon-treated human B-lymphoblastoid cells

The effect of recombinant interferon-alpha 2 (IFN-alpha 2) (50 U/ml) on the cell cycle, nucleotide metabolism, and protein and nucleic acid synthesis was studied in human B-lymphoblastoid (Daudi) cells. Cell cycle analysis showed that IFN treatment resulted in G0/G1 arrest (69%) as compared to control cells (42% at G0/G1). IFN inhibited the incorporation of radioactive thymidine and uridine into DNA and RNA, respectively, but had only slight effect on incorporation of radioactive threonine, leucine, or valine into proteins. IFN inhibited ribonucleotide biosynthesis by de novo and salvage pathways and decreased level of the P-ribose-PP. Both pathways of deoxyribonucleotide biosynthesis, ribonucleotide reduction and deoxyribonucleoside salvage, were also markedly inhibited by IFN., In contrast, ribonucleotide catabolism was significantly increased in the presence of IFN. No changes in ribonucleotide interconversion were found. Intracellular concentrations of both ribonucleotides and deoxyribonucleotides were markedly diminished by IFN. These results suggest that inhibition of both ribonucleotide and deoxyribonucleotide biosynthesis, together with increased rate of nucleotide catabolism, may significantly decrease intracellular nucleotide availability. Decrease of the supply of nucleic acid precursors, as well as limitation of nucleotides for energy metabolism and other processes, may result in the inhibition of cell multiplications.