Ontak® is a FDA-approved diphtheria toxin-based recombinant fusion toxin for treatment of human CD25+ cutaneous T cell lymphoma (CTCL). However, it has been discontinued clinically due to the production issue related to the bacterial expression system with difficult purification. Recently we have developed monovalent and bivalent human IL-2 fusion toxins targeting human CD25+ cells using advanced unique diphtheria toxin resistant yeast Pichia Pastoris expression system. In vitro efficacy characterization using human CD25+ HUT102/6TG cells demonstrated that both monovalent and bivalent isoforms are potent and the bivalent isoform is approximately two logs more potent than the monovalent isoform. In this study, we further assessed the in vivo efficacy of the human IL-2 fusion toxins using human CD25+ HUT102/6TG tumor-bearing NSG mouse model. The data demonstrated that both monovalent and bivalent human IL-2 fusion toxins significantly prolonged the survival of the human CD25+ tumor-bearing NSG mice in a dose-dependent manner. Then we further assessed the residual tumor cells from the HUT102/6TG tumor-bearing NSG mice using the residual tumor cell bearing NSG mouse model. The results demonstrated that the residual tumor cells were still sensitive to the continual treatment with the human IL-2 fusion toxin. This yeast-expressed human IL-2 fusion toxin will be a promising candidate to replace the clinically discontinued Ontak®.
Keywords: CD25; CTCL; Diphtheria toxin; IL-2 fusion toxin; Ontak; Pichia Pastoris.
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