Development of an Interleukin-12 Fusion Protein That Is Activated by Cleavage with Matrix Metalloproteinase 9

Interleukin-12 (IL-12) is a pleiotropic cytokine that has profound effects on many aspects of cell-mediated responses and can enhance antitumor responses in experimental models. IL-12 has been tested clinically, however, side-effects have limited its use. We are developing an attenuated form of IL-12 whose biological activity could be restricted to sites of tumors by taking advantage of overexpressed tumor proteases that can activate the cytokine. We constructed a panel of fusion proteins (FPs) consisting of IL-12 joined to a specific inhibitor connected by a protease cleavage sequence (cs). We first identified a panel of single-chain Fragment variable (scFv) that bind to 3 independent epitopes on IL-12 and then incorporated them into separate IL-12 FPs containing either a matrix metalloproteinase (MMP) cs or a scrambled (scram) control cs. The intact IL-12 FPs showed attenuation in IL-12 activity compared to free IL-12 in 2 separate in vitro functional assays; proliferation of CTLL-2 and interferon-gamma (IFN-γ) induction by spleen cells. Furthermore, the FP containing the MMPcs showed an increase in biological activity of IL-12 in vitro when cleaved by MMP9. This FP strategy could be applied to other immunomodulators and potentially reduce unwanted side-effects observed with systemic delivery thus improving cytokine immunotherapy strategies.