Pharmacokinetics of the recombinant ovine interferon-tau in lambs.

In the current study, twenty lambs, aged 4 months, half male and half female, were classified into four groups, with five in each group. The experimental three groups of lambs were given intravenous (IV), intramuscular (IM) and subcutaneous (SC) administrations of recombinant ovine interferon-τ (roIFN-τ). The fourth group (normal control) of lambs was given normal saline injections in the same way. After administrations, blood samples were collected from the tested animals at different time points post injection, and the serum titers of roIFN-τ were measured using cytopathic effect (CPE) inhibition bioassay. The results of calculating pharmacokinetic (PK) parameters using DAS software showed that the PK characteristics of roIFN-τ through IV injection conformed to the two-compartment open model, whose half-life of distribution phases (T1/2α) was 0.33±0.034 h and the elimination half-life(T1/2ß) was 5.01±0.24 h. However, the PK features of IM injection and SC injection of roIFN-τ conformed to the one compartment open model, whose Tmax were 3.11±0.26 h and 4.83±0.43 h, respectively, together with an elimination half life(T1/2ß) of 9.11±0.76 h and 7. 43±0.58 h, and an absorption half-life (T1/2k(a)) of 1.13±0.31 h and 1.85±0.40 h, respectively. The bioavailability of roIFN-τ after IM administration reaches 73.57%, which is greater than that of SC administration (53.43%). These results indicate that the drug administration effect can be preferably obtained following a single dose IM administration of the roIFN-τ aqueous preparation. This study will facilitate the clinical application of roIFN-τ as a potential antiviral agent in future work.

Type I interferon receptor is a primary regulator of target-mediated drug disposition of interferon-beta in mice.

The purpose of this study is to evaluate the primary mechanism through which interferon (IFN)-beta exhibits target-mediated drug disposition (TMDD) and whether the theoretical assumptions of TMDD models are consistent with experimental pharmacokinetic (PK) data. Recombinant murine IFN-beta was administered as an intravenous injection at two dose levels (0.5 and 1 million IU/kg) to male wild-type (WT) and type-I IFN-alpha/beta receptor subunit (IFNAR-1) knockout (KO) mice (A129S7/SvEvBrd strain). Sampling was conducted at various times (n = 3/time point), and plasma was analyzed for IFN-beta concentrations using a validated enzyme-linked immunosorbent assay. The pharmacodynamic (PD) biomarker was IP-10 mRNA that was isolated from the distal femur bone and quantified using reverse transcription-polymerase chain reaction. An integrated model that includes rapid-binding TMDD and an indirect mechanism of drug action was used to characterize the PK/PD profiles. For an experimental control, PK profiles of recombinant murine erythropoietin (muEPO), another drug that exhibits TMDD, were determined after a single intravenous dose (0.5 microg/kg) in WT and KO animals. The concentration-time profiles for IFN-beta differed substantially at initial times for the WT and KO mice at the same dose levels. These differences are characteristic of ligands exhibiting receptor-mediated disposition and were well described by a rapid-binding TMDD model. No differences in muEPO PK were observed in the control study. In summary, the intact IFNAR receptor is a primary regulator of in vivo IFN-beta exposure. An integrated PK/PD model was successfully used to assess the receptor-mediated disposition and dynamics of IFN-beta.

Interspecies scaling of receptor-mediated pharmacokinetics and pharmacodynamics of type I interferons.

PURPOSE: To develop an integrated mechanism-based modeling approach for the interspecies scaling of pharmacokinetic (PK) and pharmacodynamic (PD) properties of type I interferons (IFNs) that exhibit target-mediated drug disposition (TMDD). METHODS: PK and PD profiles of human IFN-beta1a, IFN-beta1b, and IFN-alpha2a in humans, monkeys, rats, and mice from nine studies were extracted from the literature by digitization. Concentration-time profiles from different species were fitted simultaneously using various allometric relationships to scale model-specific parameters. RESULTS: PK/PD profiles of IFN-beta1a in humans and monkeys were successfully characterized by utilizing the same rate constant parameters and scaling the volume of the central compartment to body weight using an allometric exponent of 1. Concentration and effect profiles of other IFNs were also well described by changing only the affinity of the drug to its receptor. PK profiles in rodents were simulated using an allometric exponent of -0.25 for the first-order elimination rate constant, and no receptor-binding was included given the lack of cross-reactivity. CONCLUSIONS: An integrated TMDD PK/PD model was successfully combined with classic allometric scaling techniques and showed good predictive performance. Several parameters obtained from one IFN can be effectively shared to predict the kinetic behavior of other IFN subtypes.

Pharmacokinetic properties of a 40 kDa branched polyethylene glycol-modified form of consensus interferon-alpha (PEG-CIFN) in rhesus monkeys.

The pharmacokinetic properties of a branched 40 kDa polyethylene glycol (PEG) conjugate formulation of consensus interferon-alpha (CIFN) was evaluated in rhesus monkeys following subcutaneous administration. Four groups of rhesus monkeys (n=6 per group) received 1250, 300 and 150 microg/kg of PEG-CIFN and 150 microg/kg CIFN, respectively. Serum concentrations of the interferons were measured with an antiviral activity assay at various time points after administration. The PK profiles of the pooled data were described by a noncompartmental method. Peak concentration of PEG-CIFN was observed at 27-31 h, followed by a prolonged decay in comparison with the unmodified CIFN, the PEG-CIFN had a 4-5-fold longer terminal half-life. The apparent clearance (dose(sc)/AUC) decreased from 150 mL/h/kg for CIFN to 19.0-45.5 mL/h/kg for PEG-CIFNs. The AUC was lower for PEG-CIFN than that for CIFN at the 150 microg/kg.

Bioequivalence of two subcutaneous pharmaceutical products of interferon beta la.

Blastoferon, in the following referred to as the test product, is a pharmaceutical product of interferon beta la (CAS 220581-49-7) currently marketed as a biosimilar to the innovator Interferon beta la product (referred to as the reference product). Pharmacokinetics and pharmacodynamIcs assays are critically relevant to demonstrate similarity between biopharmaceuticals. The aims of the present study were to investigate the bioavailability (BA) of the test product (either absolute or relative to the innovator product) and to compare the extent of increase of neopterin concentration following administration of either product. Two studies were performed: initially, an absolute BA assay with i.v. and s.c. injection of test product to 12 healthy subjects. Second, a formal relative BA study with s.c. injections of 88 microg of both products to 24 healthy volunteers. Blood samples for pharmacokinetic and pharmacodynamic profiling were drawn at different intervals after injection. Interferon beta (IFNB) concentrations were determined by ELISA. In the absolute BA study, a single s.c. dose of 44 microg of the test product resulted in a median bioavailable fraction of 29%, a median T(max) of 4 h (4-6) and a C(max) of 3.69 (3.27-4.41) IU x ml(-1). In the relative BA study, values for the test product were: median T(max) of 3 h (2-18), C(max) of 5.39 (4.99-6.31) IU x ml(-1), AUC (0-72) of 142.86 (134.16-190.15) IU x h x ml(-1) and AUC(0-infinity) of 190.95 (174.23-303.13) IU x h x ml(-1). The corresponding values for the innovator product were: T(max) of 3 h (1-24), C(max) of 4.44 (4.12-5.40) IU x ml(-1), AUC(0-72) of 128.77 (121.18-170.92) IU x h x ml(-1) and AUC(0-affinity) of 192.61 (183.04-286.46) IU x h x ml(-1). The AUC(0-72) ratio was 111% (CI 90%: 106-116), the AUC(0-affinity) was 99% (CI 90%: 92-107) and the C(max) ratio was 121% (CI 90%: 112-131). IFNB1a increased neopterin levels in both studies. Both products induced side-effects commonly reported for IFN with no serious adverse events. This study presents pharmacokinetics parameters of the test product and demonstrates similar bioavailability of IFNB1a for both pharmaceutical products.

A recombinant human enzyme for enhanced interstitial transport of therapeutics.

Subcutaneously injected therapeutics must pass through the interstitial matrix of the skin in order to reach their intended targets. This complex, three-dimensional structure limits the type and quantity of drugs that can be administered by local injection. Here we found that depolymerization of the viscoelastic component of the interstitial matrix in animal models with a highly purified recombinant human hyaluronidase enzyme (rHuPH20) increased the dispersion of locally injected drugs, across a broad range of molecular weights without tissue distortion. rHuPH20 increased infusion rates and the pattern and extent of appearance of locally injected drugs in systemic blood. In particular, rHuPH20 changed the pharmacokinetic profiles and significantly augmented the absolute bioavailability of locally injected large protein therapeutics. Importantly, within 24 h of injection, the interstitial viscoelastic barriers were restored without histologic alterations or signs of inflammation. rHuPH20 may function as an interstitial delivery enhancing agent capable of increasing the dispersion and bioavailability of coinjected drugs that may enable subcutaneous administration of therapeutics and replace intravenous delivery.

Safety pharmacology, toxicology and pharmacokinetic assessment of recombinant human omega-interferon produced from CHO-SS cells.

Human omega-interferon (IFN-omega) has been shown to be well-tolerated in man and to induce reductions of hepatitis C virus RNA levels in a series of human clinical trials. Here we provide an overview of our preclinical safety evaluation of the fully-glycosylated human IFN-omega produced from CHO-SS cells that is currently being evaluated clinically. IFN-omega was not associated with any biologically-relevant adverse effects in a series of 10 safety pharmacology experiments, in the Ames mutagenicity test, in the micronucleus test, or in intraarterial, intravenous, paravenous or subcutaneous local tolerance studies. Acute, subacute, subchronic and reproductive toxicity studies performed in cynomolgus monkeys and rats showed a toxicity profile similar to that of human alpha interferon (IFN-alpha). Except for the acute (single-dose) toxicology study, all of the other toxicity studies showed evidence for the formation of anti-IFN-omega antibodies over time in the animals. These antibodies were found to neutralize IFN-omega antiviral activity in vitro in a dose-dependent manner. The average pharmacokinetic parameters following a single subcutaneous dose of IFN-omega in rabbits, rats and monkeys were determined and found to be similar to that of human IFN-alpha. These findings demonstrate that IFN-omega has a safety profile consistent with that required for its use in man. IFN-omega might be beneficial for the treatment of patients infected with hepatitis C virus who fail to respond to IFN-alpha or as a first-line treatment option.

Pegylated interferon alpha-2a (40 kDa) in the treatment of chronic hepatitis B.

Chronic hepatitis B virus (HBV) is a serious and life-threatening disease afflicting 350 million of the world's population. So far, current monotherapy with conventional interferon-alpha, lamivudine, and adefovir dipivoxil remains unsatisfactory. In addition, the use of conventional interferon-alpha needs to be administered subcutaneously daily or thrice weekly and is associated with frequent adverse events. Although nucleoside-nucleotide analogs such as lamivudine and adefovir dipivoxil are well tolerated and can normalize serum alanine aminotransaminase rapidly, 1-year therapy with either lamivudine or adefovir dipivoxil results in low hepatitis B e antigen (HBeAg) seroconversion rates. In HBeAg negative patients, most of the patients would relapse after lamivudine has been discontinued. Pegylated interferon alpha-2a, an immunomodulatory agent, is a new drug that has just completed phase III clinical trials for the treatment of both HBeAg positive and HBeAg negative chronic HBV infection. The advantage of pegylated interferon alpha-2a in achieving sustained virological response over nucleoside-nucleotide analogs is particularly obvious in the HBeAg negative group. In both of these phase III studies, sustained off-treatment response is superior to the use of lamivudine. These recent data put pegylated interferon alpha-2a as the first choice of anti-HBV therapy, especially in young and motivated patients with chronic HBV infection.

Interferon alfacon1 is an inhibitor of SARS-corona virus in cell-based models.

Preliminary data examining interferon alfacon1 treatment of SARS-CoV (severe acute respiratory syndrome-corona virus)-infected patients suggests this therapy is well tolerated and of therapeutic benefit. We report herein that interferon alfacon1, has potent in vitro antiviral activity against SARS-CoV. In a cytopathic effect protection (CPE) assay, interferon alfacon1 inhibited the generation of CPE in a dose-dependent manner with an IC50 of 0.001 microg/ml, a clinically achievable level. Furthermore, interferon alfacon1 also demonstrated significant antiviral activity in yield reduction and plaque reduction assays. The in vitro antiviral activity of interferon alfacon1 against SARS-CoV suggests continued evaluation of interferon alfacon1 as a therapeutic treatment for patients infected with SARS-CoV.

Formation of human IFN-beta complex with the soluble type I interferon receptor IFNAR-2 leads to enhanced IFN stability, pharmacokinetics, and antitumor activity in xenografted SCID mice.

Interferon-beta (IFN-beta) is biologically unstable under physiologic conditions in vitro and is cleared rapidly from the bloodstream on administration in vivo. In the present study, we demonstrate that a soluble recombinant form of the type I IFN receptor subunit, sIFNAR-2, can neutralize the bioactivity of type I IFNs at high concentrations and, at lower concentrations, causes an enhancement of IFN-beta-mediated antiviral activity. The in vitro enhancement is due to the specific interaction of IFN-beta with sIFNAR-2, followed by dissociation of IFN-beta from the complex over time in culture. In vivo, the serum half-life of IFN-beta is extended from minutes to hours when administered intravenously in mice as a sIFNAR-2-associated complex. Moreover, the antitumor effect of IFN-beta is increased by between 9-fold and 27-fold when injected as an sIFNAR-2-associated complex, as demonstrated by an increase in the mean survival time of immunodeficient mice challenged with human Burkitt lymphoma cell (Daudi) xenografts (sIFNAR-2-complexed vs. free IFN-beta treatment). These results show that on association with sIFNAR-2, IFN-beta is more stable in vitro and exhibits increased efficacy when administered in vivo. Administration as a complex with sIFNAR-2 may, therefore, provide a method of enhancing the delivery and effectiveness of type I IFNs.

An IFN-beta-albumin fusion protein that displays improved pharmacokinetic and pharmacodynamic properties in nonhuman primates.

The long half-life and stability of human serum albumin (HSA) make it an attractive candidate for fusion to short-lived therapeutic proteins. Albuferon (Human Genome Sciences [HGS], Inc., Rockville, MD) beta is a novel recombinant protein derived from a gene fusion of interferon-beta (IFN-beta ) and HSA. In vitro, Albuferon beta displays antiviral and antiproliferative activities and triggers the IFN-stimulated response element (ISRE) signal transduction pathway. Array analysis of 5694 independent genes in Daudi-treated cells revealed that Albuferon beta and IFN-beta induce the expression of an identical set of 30 genes, including 9 previously not identified. In rhesus monkeys administered a dose of 50 microg/kg intravenously (i.v.) or subcutaneously (s.c.) or 300 microg/kg s.c., Albuferon beta demonstrated favorable pharmacokinetic properties. Subcutaneous bioavailability was 87%, plasma clearance at 4.7-5.7 ml/h/kg was approximately 140-fold lower than that of IFN-beta, and the terminal half-life was 36-40 h compared with 8 h for IFN-beta. Importantly, Albuferon beta induced sustained increases in serum neopterin levels and 2',5' mRNA expression. At a molar dose equivalent to one-half the dose of IFN-beta, Albuferon beta elicited comparable neopterin responses and significantly higher 2',5'-OAS mRNA levels in rhesus monkeys. The enhanced in vivo pharmacologic properties of IFN-beta when fused to serum albumin suggest a clinical opportunity for improved IFN-beta therapy.

Interferon alfacon-1: a review of its pharmacology and therapeutic efficacy in the treatment of chronic hepatitis C.

UNLABELLED: Interferon alfacon-1 (consensus interferon) is a non-naturally occurring, synthetic, type 1 interferon (IFN)alpha that is used for the treatment of patients with chronic hepatitis C. The efficacy of subcutaneously administered interferon alfacon-1 has been demonstrated in clinical trials during the treatment of LFN-naive patients (interferon alfacon-1 9microg 3 times a week for 24 weeks) and retreatment of nonresponders and relapsers to previous interferon therapy (interferon alfacon1 15 microg 3 times a week for up to 48 weeks). Higher and more frequent interferon alfacon-1 dosages have also been investigated. Results from a pivotal double-blind randomised trial in 704 patients with chronic hepatitis C showed that interferon alfacon-19 microg 3 times a week achieved virological and biochemical response rates of 34.9 and 42.2%, respectively, at treatment end-point (week 24). Sustained virological and biochemical responses (week 48) were reported in 12.1 and 20.3% of the patients, respectively. In general, response rates in recipients of interferon alfacon-1 9 microg 3 times a week were similar to those achieved with IFN-alpha2b 3 MIU 3 times a week. However, interferon alfacon-1 was more effective in the subgroup of patients infected with hepatitis C virus (HCV) genotype 1 at end-point (virological response, 24 vs 15%; p < 0.05) and post-treatment observation period (8 vs 4%) although the difference between treatment groups was statistically significant only at treatment end-point. The sustained virological response rate achieved in patients with high baseline levels of serum HCV RNA receiving interferon alfacon-1 was statistically superior to that exhibited in the IFN-alpha2b treatment group (7 vs 0%; p < Interferon alfacon-1 also showed efficacy during the retreatment of non-responders and relapsers to previous IFN therapy in a large nonblind multicentre trial. Sustained virological response (week 72) was observed among 13 and 58% of nonresponders and relapsers, respectively, after 48 weeks of treatment with interferon alfacon-1 15 microg 3 times a week. Interferon alfacon-1 has been generally well tolerated in clinical trials. As with other IFNs, adverse events were reported frequently but were usually considered of mild to moderate severity, decreased with time and caused a small percentage of patients to withdraw from the treatment. Fever, fatigue, arthralgia, myalgia, headache and rigors were the most frequently reported adverse events. Psychiatric adverse events appeared to be dose-related and caused the majority of treatment withdrawals. CONCLUSION: Interferon alfacon-1 is generally well tolerated and is an effective agent in the treatment of patients with chronic hepatitis C. Comparative data from a pivotal randomised trial indicate that the drug has at least equivalent efficacy to IFNalpha-2b, and a statistically significant advantage was demonstrated at treatment end-point in patients infected with HCV genotype 1. A number of ongoing trials with interferon alfacon-1 are evaluating issues such as the optimal dosage regimen and duration of therapy in an effort to improve sustained virological response to therapy, a goal for IFNs in general.

Intraperitoneal radioimmunochemotherapy of ovarian cancer: a phase I study.

A phase I trial was designed to examine the feasibility of combining interferon and Taxol with intraperitoneal radioimmunotherapy (177Lu-CC49). Patients with recurrent or persistent ovarian cancer confined to the abdominal cavity after first line therapy, Karnofsky performance status > 60, adequate liver, renal and hematologic function, and tumor that reacted with CC49 antibody were enrolled. Human recombinant alpha interferon (IFN) was administered as 4 subcutaneous injections of 3 x 10(6) U on alternate days beginning 5 days before RIT to increase the expression of the tumor-associated antigen, TAG-72. The addition of IFN increased hematologic toxicity such that the maximum tolerated dose (MTD) of the combination was 40 mCi/m2 compared to 177Lu-CC49 alone (45 mCi/m2). Taxol, which has radiosensitizing effects as well as antitumor activity against ovarian cancer, was given intraperitoneally (i.p.) 48 hrs before RIT. It was initiated at 25 mg/m2 and escalated at 25 mg/m2 increments to 100 mg/m2. Subsequent groups of patients were treated with IFN + 100 mg/m2 Taxol + escalating doses of 177Lu-CC49. Three or more patients were treated in each dose group and 34 patients were treated with the 3-agent combination. Therapy was well tolerated with the expected reversible hematologic toxicity. The MTD for 177Lu-CC49 was 40 mCi/m2 when given with IFN + 100 mg/m2 Taxol. Interferon increased the effective whole body half-time of radioactivity and the whole body radiation dose. Taxol did not have a significant effect on pharmacokinetic or dosimetry parameters. Four of 17 patients with CT measurable disease had a partial response (PR) and 4 of 27 patients with non-measurable disease have progression-free intervals of 18+, 21+, 21+, and 37+ months. The combination of intraperitoneal Taxol chemotherapy (100 mg/m2) with RIT using 177Lu-CC49 and interferon was well tolerated, with bone marrow suppression as the dose-limiting toxicity.

N-terminal amino acids of bovine alpha interferons are relevant for the neutralization of their antiviral activity

The structure-function relationship of interferons (IFNs) has been studied by epitope mapping. Epitopes of bovine IFNs, however, are practically unknown, despite their importance in virus infections and in the maternal recognition of pregnancy. It has been shown that recombinant bovine (rBo)IFN-alphaC and rBoIFN-alpha1 differ only in 12 amino acids and that the F12 monoclonal antibody (mAb) binds to a linear sequence of residues 10 to 34. We show here that the antiviral activities of these two IFNs were neutralized by the F12 mAb to different extents using two tests. In residual activity tests the antiviral activity dropped by more than 99 percent with rBoIFN-alphaC and by 84 percent with rBoIFN-alpha1. In checkerboard antibody titrations, the F12 mAb titer was 12,000 with rBoIFN-alphaC and only 600 with rBoIFN-alpha1. Since these IFNs differ in their amino acid sequence at positions 11, 16 and 19 of the amino terminus, only these amino acids could account for the different neutralization titers, and they should participate in antibody binding. According to the three-dimensional structure described for human and murine IFNs, these amino acids are located in the alpha helix A; amino acids 16 and 19 of the bovine IFNs would be expected to be exposed and could bind to the antibody directly. The amino acid at position 11 forms a hydrogen bond in human IFNs-alpha and it is possible that, in bovine IFNs-alpha, the F12 mAb, binding near position 11, would disturb this hydrogen bond, resulting in the difference in the extent of neutralization observed

N-terminal amino acids of bovine alpha interferons are relevant for the neutralization of their antiviral activity.

The structure-function relationship of interferons (IFNs) has been studied by epitope mapping. Epitopes of bovine IFNs, however, are practically unknown, despite their importance in virus infections and in the maternal recognition of pregnancy. It has been shown that recombinant bovine (rBo)IFN-alphaC and rBoIFN-alpha1 differ only in 12 amino acids and that the F12 monoclonal antibody (mAb) binds to a linear sequence of residues 10 to 34. We show here that the antiviral activities of these two IFNs were neutralized by the F12 mAb to different extents using two tests. In residual activity tests the antiviral activity dropped by more than 99% with rBoIFN-alphaC and by 84% with rBoIFN-alpha1. In checkerboard antibody titrations, the F12 mAb titer was 12,000 with rBoIFN-alphaC and only 600 with rBoIFN-alpha1. Since these IFNs differ in their amino acid sequence at positions 11, 16 and 19 of the amino terminus, only these amino acids could account for the different neutralization titers, and they should participate in antibody binding. According to the three-dimensional structure described for human and murine IFNs, these amino acids are located in the alpha helix A; amino acids 16 and 19 of the bovine IFNs would be expected to be exposed and could bind to the antibody directly. The amino acid at position 11 forms a hydrogen bond in human IFNs-alpha and it is possible that, in bovine IFNs-alpha, the F12 mAb, binding near position 11, would disturb this hydrogen bond, resulting in the difference in the extent of neutralization observed.

Pharmacokinetics and pharmacodynamics of IFN-beta 1a in healthy volunteers.

The pharmacokinetics of recombinant human interferon-beta1a (IFN-beta1a) (Rebif, Ares-Serono, Geneva, Switzerland) were investigated in healthy volunteers following intravenous (i.v.) administration of increasing single doses of the drug (22 microg/6 million international units [MIU], 44 microg/12 MIU, and 66 microg/18 MIU); i.v., intramuscular (i.m.), and subcutaneous (s.c.) administration of a 66-microg dose; and repeated s.c. administration of four 66-microg doses at 48-h intervals. The disposition of IFN-beta1a followed triexponential decay after i.v. administration (half-lives 3 min, 42 min, and 22 h, respectively). After s.c. and i. m. administration, absorption was the rate-limiting factor in the terminal phase. The median absolute bioavailabilities were 30% and 27%, respectively. The accumulation ratio after repeated s.c. injections was 2.4, and a terminal half-life of 66 h was observed. Intracellular 2-5A synthetase activity and serum neopterin and beta2-microglobulin concentrations increased after all IFN-beta1a injections and remained elevated following every-other-day administration. The local tolerance was good, and the systemic tolerance was satisfactory.

Simple mixing of IFN with a polysaccharide having high liver affinity enables IFN to target to the liver.

Interferon (IFN) therapy is only one method that is clinically effective in controlling disease activity in patients with chronic hepatitis. A chelating residue (diethylenetriamine pentaacetic acid, DTPA) was introduced to pullulan, which is a polysaccharide with high liver affinity. This DTPA-pullulan could conjugate with IFN through Zn2+ coordination on mixing these three components. Intravenous injection of the IFN-DTPA-pullulan conjugate with Zn2+ coordination induced activity in the liver of an antiviral enzyme. 2',5'-oligoadenylate synthetase at IFN doses lower than those used for free IFN injection. In addition, synthetase induction by the conjugate continued for a longer time than did induction by free IFN. Liver targeting of IFN by this conjugation technique based on Zn2+ coordination opens a new method of IFN therapy.