Pharmacological aspects of clinical stage I/II trials with human beta interferon in children

Pharmacology and side-effects of interferons

The distribution, catabolic sites and turnover of interferons are reviewed in order firstly to improve their utilization, secondly to reduce toxicity and thirdly to evaluate alternative routes of administration. In fact catabolic pathways are now seen as a salutary system capable in most cases to reduce toxicity to an acceptable level.

Distribution of mouse interferon-beta in normal and brain tumour-bearing mice

The distribution of 125I-labelled recombinant mouse interferon-beta (rMuIFN-beta) in normal and glioma (203 glioma) bearing mice was studied by radioassay and macro-autoradiography at 15 and 30 min after a single intravenous injection. The level of rMuIFN-beta in the spleen was about 20-fold higher than in serum. Concentrations higher than the serum level was detected in the lung, liver and kidney. The concentration of rMuIFN-beta in the brain was 8% of the serum level and the concentration in the glioma 30 min after administration was about 10-fold higher than in normal mouse brain. Macro-autoradiographic study demonstrated a wide distribution range and selective uptake in glioma tissue. Furthermore, we found that mouse gliomas were sensitive to mouse IFN-beta. Our findings demonstrate that in the mouse glioma model, intravenously administered interferon reaches the tumour.

The lymphatic route--III. Pharmacokinetics of human natural interferon-beta injected with albumin as a retarder in rabbits

The aim of the present investigation was to define whether multisite, subcutaneous (s.c.) administration in unanesthetized, unrestrained rabbits of human natural interferon-beta (nat. IFN-beta) either in saline, or in a human albumin (ALB) solution (10 and 13% final concentrations) modified the pharmacokinetic parameters calculated from the IFN plasma levels. Plasma disappearance rates of nat. INF-beta were measured in two rabbits after intravenous (i.v.) administration and the kinetic was adequately represented by a bi-exponential curve. The highest ALB concentration (13%) caused a significant reduction of the plasma IFN Cmax, a longer half-life, a three-fold increase of the area under curve (AUC value) and a marked decrease of the plasma clearance. Interestingly, the bio-availability of IFN was increased almost four-fold. The data suggest that, when nat. IFN-beta is injected subcutaneously, the presence of a high concentration of ALB may prevent its inactivation and may favour its absorption via lymphatics rather than blood capillaries. It is remarkable that by using this approach, low but constant IFN levels are maintained for as long as two days, a fact that may well increase the therapeutic index of IFN in patients.

Evaluation of routes of administration of interferon in cancer: a review and a proposal

Interferons are endowed with antiviral and antitumoral activities; the latter particularly has attracted attention, even though it remains uncertain whether it is preferentially due to a direct antiproliferative effect or to enhancement of host-mediated immune responses. Unfortunately, interferons administered in pharmacological doses produce considerable toxicity that is dose-related and that may require cessation of therapy. The administration of interferon has been carried out mostly by intravenous and intramuscular routes. High serum interferon titers have been expected to correlate with therapeutic efficacy. However, there is no such correlation, and certainly interferon levels in the interstitial fluid of target or effector cells would be more critical and informative. Moreover, because they are rapidly filtered by the kidneys, high serum titers are accompanied by considerable renal loss. Thus, several factors, one of which may be the unsuitability of administration routes, may explain the modest therapeutic efficacy of interferon so far observed in cancer. It must be emphasized that interferons and other biological response modifiers are pharmacodynamically unique substances able to elicit unpredictable responses; effects of these drugs depend on the nutritional and metabolic status and immune responsiveness of the host rather than simply on their plasma levels. After reviewing possible routes of administration, a new one, the lymphatic route, appears of interest. The basic strategy is to shift most of the interferon into the lymph pool minimizing direct absorption into the blood. In this way, the lymph/plasma ratio of interferon concentration will resemble that observed during the physiological response and will be greater than 1. Most of the injected interferon will then interact with the lymphoid system, even though eventually it will slowly drain into the blood pool. If the therapeutic index can be shown to be improved in patients, facilitated lymphatic absorption could become a preferential route for the administration of biological response modifiers.