Pre-clinical toxicity of Il-4: A model for studying protein therapeutics

Abstract

The purpose of this presentation was to review issues and findings in the pre-clinical development and evaluation of recombinant human protein therapeutics. Since human cytokines and lymphokines are endogenous proteins, their pre-clinical development and evaluation would seem straightforward and theor toxicities minimal. Unfortunately, the pre-clinical development of this class of agents has been problematic and confounding. Some of the clinical toxicities and pharmacodynamics have been predicted by the pre-clinical evaluation and others have not. Some molecules are species specific which limits species selection for pre-clinical evaluation. Other confounding issues include: route of exposure, synergy of toxicity with other lymphokines, length of study design, immunogenicity, predictiveness of pre-clinical evaluation and iatrogenic toxicities. An approach used by SWPRD in the evaluation of this class of molecules was discussed. Insight gained during the pre-clinical and clinical development of these molecules should simplify the further development of protein therapeutics that follow. Specific studies with recombinant human interleukin-4 (rhuIL-4) were reviewed in detail as part of a pre-clinical safety evaluation. Native IL-4 has properties that exemplify many of the immune recognition-induced lymphokines and is produced principally by activated T-lymphocytes CD4 +. It is a co-factor in B-cell proliferation and enhances ex vivo B-cell expansion and is believed to be a candidate for the treatment of refractory cancer based on this immune enhancement ability. rhyIL-4 is a 15,400 molecular weight cytokine produced in a yeast expression system. The unique species specificity of this lymphokine led to its ultimate evaluation in a non-human primate species. rhuIL-4 was administered subcutaneously (B.I.D.) at doses of 0, 1, 5 or 25 μg/kg/day for 28 days with a 14 day recovery to cynomolgus monkeys. Clinical pathology changes related to treatment were evidence of consumptive coagulopathy, lymphocytosis and lymphocyte morphologic changes indicative of marked antigenic or mitogenic stimulation, mild eosinophilia and neutrophilia, hypoalbuminemia, hypocholesterolemia, and hypertryglyceridemia. Histomorphologic evaluation revealed proliferation and inflammatory vascular lesions with eosinophil infiltration which principally affected the arterial tree, granulocytic hyperplasia, seminiferous tubular atrophy and splenic congestion. After 2 weeks of recovery, granulocytic hyperplasia was not observed and the vascular lesions occured with an overall lower incidence. The arteritis may be a direct pharmacodynamic effect of rhuIL-4 on vascular smooth endothelial cells possibly related to enhanced adhesion molecule expression. The antigenicity of this molecule for cynomolgus monkeys was also demonstrated and appeared to alter the pharmacokinetics of the protein drug substance at the end of the exposure period. The pre-clinical safety evaluation of rhuIL-4 has proven an interesting molecule to illustrate several of the confounding issues associated with the pre-clinical development of lymphokines.