Analysis of the steady state binding, internalization, and degradation of human interferon-alpha2

Development of interferon alpha-2b microspheres with constant release

Interferon alpha-2b (IFNα-2b) is an important immune regulator used widely in clinic. However, frequent subcutaneous injection and substantial toxicity decrease patients' compliance. So, drug delivery with more precisely controlled drug release is urgent for IFNα-2b. Microsphere is a promising sustained drug delivery system, which has been studied widely for delivery of proteins. However, it was found difficult to keep proteins' activity and guarantee complete release. In this study, we solidified IFNα-2b as microparticles firstly by co-lyophilizing it with gelatin and ZnSO(4). Microspheres were then prepared. The preparing procedure and formulation were optimized with encapsulation efficiency and in vitro release as main parameters. Finally, the microspheres were prepared by S/O/W method with microparticle size about 5 μm and PEGT/PBT-PLGA (9:1, w/w) as matrix material. The diameter of microspheres was 28.94 μm, the encapsulation efficiency was 86.01%, the burst release was 16.69%, the cumulative release was 83.06% at 23th day, and IFNα-2b was released from microspheres with a zero-order profile. These microspheres also demonstrated sustained and steady release for about 13 days in rats. In conclusion, the procedure and formulation used in this study were supposed to be successful to keep IFNα-2b active and released constantly and completely.

Cell surface receptors for signal transduction and ligand transport: a design principles study

Receptors constitute the interface of cells to their external environment. These molecules bind specific ligands involved in multiple processes, such as signal transduction and nutrient transport. Although a variety of cell surface receptors undergo endocytosis, the systems-level design principles that govern the evolution of receptor trafficking dynamics are far from fully understood. We have constructed a generalized mathematical model of receptor–ligand binding and internalization to understand how receptor internalization dynamics encodes receptor function and regulation. A given signaling or transport receptor system represents a particular implementation of this module with a specific set of kinetic parameters. Parametric analysis of the response of receptor systems to ligand inputs reveals that receptor systems can be characterized as being: i) avidity-controlled where the response control depends primarily on the extracellular ligand capture efficiency, ii) consumption-controlled where the ability to internalize surface-bound ligand is the primary control parameter, and iii) dual-sensitivity where both the avidity and consumption parameters are important. We show that the transferrin and low-density lipoprotein receptors are avidity-controlled, the vitellogenin receptor is consumption-controlled, and the epidermal growth factor receptor is a dual-sensitivity receptor. Significantly, we show that ligand-induced endocytosis is a mechanism to enhance the accuracy of signaling receptors rather than merely serving to attenuate signaling. Our analysis reveals that the location of a receptor system in the avidity-consumption parameter space can be used to understand both its function and its regulation.

Cells interact with their environment using molecules on their surface known as receptors. Receptors bind specific companion molecules known as ligands, which either carry information about the outside environment or are critical cell nutrients. Signaling receptors bind the former ligand type and convert information about the outside environment to a cell response such as migration or growth. Transport receptors bind the latter class of ligand and deliver them to the cell interior. A variety of receptors are internalized into the cell through a process known as endocytosis. Receptors display a wide range of endocytosis patterns, but the functional motivation behind the observed differences is not well understood. We have constructed a generalized model to understand how receptor endocytosis and other receptor–ligand properties affect the function of receptor systems. We find that the efficiency and robustness of receptor systems are encoded by two fundamental parameters: i) the avidity which quantifies the ability of a receptor system to capture ligand, and ii) the consumption which quantifies the ability to internalize bound ligand. By examining a number of receptor systems, we demonstrate that the internalization dynamics of receptor systems can be explained by examining its effect on the avidity and consumption parameters.

Growth inhibitory effects of pegylated IFN alpha-2b on human liver cancer cells in vitro and in vivo

PURPOSE

We investigated the effects of pegylated IFN-alpha2b (PEG-IFN-alpha2b) on the growth of human liver cancer cells.

METHODS

The effect of PEG-IFN-alpha2b on the proliferation of 13 liver cancer cell lines was investigated in vitro. Chronological changes in growth and IFN-alpha receptor-2 (IFNAR-2) expression were monitored in hepatocellular carcinoma (HCC) cells (HAK-1B) cultured with PEG-IFN-alpha2b. After HAK-1B cells were transplanted into nude mice, various doses of PEG-IFN-alpha2b or IFN-alpha2b were administered, and tumor volume, weight, histology, and IFNAR-2 expression were examined.

RESULTS

PEG-IFN-alpha2b inhibited the growth of nine cell lines with apoptosis in a dose- and time-dependent manner. Continuous contact with PEG-IFN-alpha2b induced time-dependent growth inhibition and down-regulation of IFNAR-2 expression. PEG-IFN-alpha2b induced a dose-dependent decrease in tumor volume and weight, a significant increase of apoptotic cells, and a decrease in IFNAR-2 expression in the tumor. The clinical dose for chronic hepatitis C was also effective. The antitumor effect of PEG-IFN-alpha2b was significantly stronger than that of non-PEG-IFN-alpha2b in vivo.

CONCLUSIONS

Continuous contact with PEG-IFN-alpha2b induces strong antitumor effects and the down-regulation of IFNAR-2 in HCC cells. The data suggest potential clinical application of PEG-IFN-alpha2b for the prevention and treatment of HCC.

A flow cytometric method for determination of the interferon receptor IFNAR2 subunit in peripheral blood leukocyte subsets

INTRODUCTION

It is expected that expression levels in the peripheral blood mononuclear cells (PBMC) of IFNAR2, a subunit of the interferon (IFN) receptor, may be a marker for predicting IFN response. In the present study, we have established a rapid and convenient method for assaying IFNAR2, using flow cytometry.

METHODS

Fifty microliters of whole blood from healthy volunteers was treated with an anti-IFNAR2 antibody and stained with a Fluorescein isothiocyanate (FITC)-conjugated secondary antibody. In addition, the cells were stained with subset-specific antibodies conjugated with phycoerythrin (PE) and PE covalently linked to cyanin 5 at the same time. The mean FITC-fluorescence intensities were analyzed separately by gating on subset-specific regions.

RESULTS

IFNAR2 was detected in most lymphocytes, monocytes, and granulocytes, although IFNAR2 expression was higher in the monocytes and granulocytes than in the lymphocytes. The intra- and interdaily variations of IFNAR2 in lymphocytes, monocytes, and granulocytes were small. Among the lymphocyte subsets, IFNAR2 showed high expression in natural killer (NK) cells and low expression in T lymphocytes. The effect of IFN-alpha on IFNAR2 expression was examined in vitro. A down-regulation of IFNAR2 was observed by IFN-alpha above 100 IU/ml.

DISCUSSION

This assay may be useful for examining IFNAR2 in various leukocyte subsets, separately, as well as providing a rapid and easy method for monitoring expression of type I IFN receptors.

Prolonged STAT1 Activation Related to the Growth Arrest of Malignant Lymphoma Cells by Interferon-α

Multiple biologic effects of interferon-α (IFN-α), including cell growth inhibition and antiviral protection, are initiated by tyrosine phosphorylation of STAT proteins. Although this signal pathway has been intensively investigated, the relevance of STAT signal persistence has received scant attention. Using paired isogenic lymphoma cells (Daudi), which either are sensitive or resistant to growth inhibition by IFN-α, we found comparable initial tyrosine phosphorylation of multiple STAT proteins; however, the phosphorylation durations and associated DNA-binding activities diverged. Phosphorylation and DNA-binding capacity of STAT1 decreased after 4 to 8 hours in resistant cells, as compared with 24 to 32 hours in sensitive cells, whereas phosphorylation of STAT3 and STAT5b was briefer in both lines. Functional significance of the prolonged STAT1 signal, therefore, was explored by experimental interruption of tyrosine phosphorylation, either by premature withdrawal of the IFN-α or deferred addition of pharmacologically diverse antagonists: staurosporine (protein kinase inhibitor), phorbol 12-myristate 13-acetate (growth promoter), or aurintricarboxylic acid (ligand competitor). Results indicated that an approximately 18-hour period of continued STAT1 phosphorylation was associated with growth arrest, but that antiviral protection developed earlier. These differences provide novel evidence of a temporal dimension to IFN-α signal specificity and show that duration of STAT1 activation may be a critical variable in malignant cell responsiveness to antiproliferative therapy.

Interaction of a synthetic peptide of the interferon alpha-2 C-terminal part with human blood leukocytes. Binding to peripheral blood mononuclear cells

A biologically active synthetic peptide, 2438, representing the 124-138 amino acid sequence of the human interferon alpha-2 (IFN alpha-2) molecule, which is known to possess IFN-like antiproliferative activity, specifically binds to human blood leukocytes. Scatchard plots reveal two different Kd values, for the 'low' and 'high' affinity binding. The interaction of the 125I-labelled peptide 2438 with the cells is not impaired by human IFN alpha-2 or cholera toxin.

Kinetic analysis of receptor-mediated endocytosis of epidermal growth factor by isolated rat hepatocytes

The interaction of epidermal growth factor (EGF) with cell surface receptors and their subsequent endocytosis in isolated rat hepatocytes were analyzed by measuring changes in the concentrations of cell surface-bound, internalized, and degraded EGF. The kinetic model proposed by Wiley and Cunningham (Cell 25: 433-440, 1981) and Gex-Fabry and Delisi [Am. J. Physiol. 247 (Regulatory Integrative Comp. Physiol. 16): R768-R779, 1984] was basically utilized for the model analysis. The following kinetic parameters were obtained: association and dissociation rate constants for EGF-receptor interaction, internalization rate constant for EGF-receptor complex (kappa e), internalization rate constant for free receptor (kappa t), sequestration rate constant (kappa s) of the complex from shallow (exchangeable) to deep (nonexchangeable) membraneous compartment, intracellular degradation rate constant and initial cell-surface receptor density. The kappa s value, which was obtained by analyzing the time profiles of EGF association with cells, was approximately 5-10 times larger than the kappa e value determined by directly measuring internalized EGF with the acid-washing technique. This suggests the necessary presence of deep (nonexchanging) compartment of the complex in the plasma membrane. The calculated kappa e value is at least several times larger than the kappa t value, yielding the kinetic basis for the occurrence of receptor downregulation induced by excess EGF. We conclude that, in the overall receptor-mediated processing of EGF after bound to the cell surface receptors, the dissociation process is rapid [half-time (t1/2) less than 1 min], the degradation process is much slower (t1/2 approximately equal to 3 h), and the receptor internalization process is intermediate (t1/2 approximately equal to 6-7 min). In addition, two pools for EGF-receptor complex in the plasma membrane seem to be present, although their identification cannot be made.

The cellular receptor of the alpha-beta interferons

This is a selective review of recent trends in research on the cellular receptor for the alpha-beta interferons. It deals mainly with work published in the last three years (1985-88), and therefore mainly with receptors for the human interferons. The binding characteristics of several human alpha interferons are examined, and the importance of in vitro experimental models for establishing the relationship between receptor binding and the cellular response is emphasized.

The inhibitory effect of human interferon alpha on the generation of lymphokine-activated killer activity

The generation of lymphokine-activated killer (LAK) activity and the proliferative response to human recombinant interleukin-2 (IL-2) were significantly reduced by the presence of human recombinant leukocyte interferon (IFN alpha) in cultures of human peripheral blood mononuclear cells (PBMC). Mature natural killer (NK) cells can be depleted from PBMC with the toxic lysosomotropic agent L-leucine methyl ester. The generation of cytotoxic cells from lymphocytes depleted in leucine methyl ester was also inhibited by indicating that the IFN-alpha effect is not limited to mature cytotoxic NK cells. Depletion of adherent cells from PBMC did not affect the suppression of LAK induction by IFN-alpha. Surface marker analyses of Tac antigen and transferrin receptor (TfR) showed that the presence of IFN alpha throughout the culture period significantly suppressed the typical increase in IL-2-induced Tac- and TfR-positive cells. In contrast, IFN alpha treatment before and after IL-2 culture enhanced LAK cytotoxic activity. Therefore, combinations of these biological response modifiers for clinical use should take into account the dual effect of IFN alpha on key features of the IL-2 response.

Internalization and degradation of human recombinant interferon-gamma in the human histiocytic lymphoma cell line, U937: relationship to Fc receptor enhancement and antiproliferation

This report describes the association between the intracellular fate of human recombinant interferon-gamma (rIFN-gamma) and the induction of enhanced numbers of Fc receptors and an antiproliferative effect in the human monocyte-like cell line, U937. Full receptor occupancy of Bolton-Hunter labeled 125I-rIFN-gamma occurred within 10 min at 37 degrees C. However, only 50% of those molecules bound were internalized within 30 min. Residency of rIFN-gamma within the cell was 60-120 min. Eventually, 60-70% of those molecules initially bound to the cell were completely degraded within monensin-sensitive compartments of the cell as measured by the presence of trichloroacetic acid-soluble radioactivity in the medium. Exposure of rIFN-gamma to cell extracts resulted in a shift in its pI from 8 to 6, presumably due to proteolytic cleavage of carboxy-terminal basic amino acids. A single brief exposure (5-15 min) of U937 cells to rIFN-gamma resulted in enhanced numbers of receptors for the Fc portion of 125I-IgG1 as measured 24 hr later. Eighty percent of a maximal Fc receptor response occurred at only 30% receptor occupancy (50 U/ml). In contrast, repeated daily exposure of U937 cells to moderate concentrations of rIFN-gamma (125-250 U/ml) was necessary to induce an antiproliferative effect. These data suggest that a given response of the cell to rIFN-gamma may require different intensities of the signal. This may reflect the overall complexity of the response generated.

Binding, internalization, and degradation of 125I-multipotential colony-stimulating factor (interleukin-3) by FDCP-1 cells

The kinetic parameters involved in determining the steady-state interaction of Multi-CSF with FDCP-1 cells at 37 degrees C have been determined by kinetic analysis under steady-state conditions and by curve-fitting the rate of approach to steady-state conditions. The two methods are in substantial agreement and yield values of Vr = 28 receptors/cell/min for the rate of appearance of receptors at the cell surface, ke and kt = 0.061 min-1 and 0.0044 min-1 for the rate constants of internalization of occupied and unoccupied receptors, respectively, kh = 0.008 min-1 for the rate constant of degradation of internalized ligand, ka = 2.9 X 10(8) M-1 min-1 for the rate constant of association and kd = 0.11 min-1 for the rate constant of dissociation of ligand with receptor. Analysis of steady-state conditions indicated that Multi-CSF caused substantial down-regulation of surface receptors and that considerably more Multi-CSF was inside the cell than at the cell surface. The implications of these results for utilization rates of Multi-CSF by FDCP-1 cells and the relationship of receptor occupancy to biological activity are discussed.

Cellular processing of murine colony-stimulating factor (Multi-CSF, GM-CSF, G-CSF) receptors by normal hemopoietic cells and cell lines

The binding, internalization and degradation rates of three different murine colony-stimulating factors (Multi-CSF or interleukin-3, GM-CSF and G-CSF) and their receptor turnover rates were determined for normal bone marrow cells and a number of different cell lines at 37 degrees C. The kinetic parameters were extracted from a curve-fitting analysis of the approach to steady-state of surface-bound and internalized CSFs by methods described by Myers et al. (1987). The primary binding kinetic constants (association and dissociation) for each CSF on different cell types were similar, suggesting a single type of receptor for each CSF. In all cases, CSF binding induced a faster rate of internalization of occupied receptors than unoccupied receptors and resulted in significant accumulation of CSF inside the cell under steady-state conditions. The steady-state constant, determining the relationship between CSF concentration and receptor occupancy, indicated that, in all cases, more receptors were occupied at a given CSF concentration under steady-state conditions than would be under equilibrium conditions. Nevertheless, the data predicted that maximal biological effects of the CSFs were exerted at concentrations that did not result in full receptor occupancy. Comparison of the kinetic constants derived for the same CSF interacting with different types of cells or different CSFs interacting with the same cell type indicated that CSF and receptor processing resulted from a dynamic interplay of receptor-determined and cell-determined events. This resulted in a flexibility of the kinetic parameters that matched the variety of biological responses elicited by CSFs in different cell types.