Background Interleukin-18 (IL-18) is a proinflammatory cytokine that modulates both innate and adaptive immune responses and induces high levels of interferon-γ.¹ Although recombinant IL-18 has demonstrated efficacy in mouse tumor models,² recombinant human IL-18 has not been efficacious in clinical studies,³ likely due to upregulation of IL-18 binding protein (IL-18BP), a negative regulator of the IL-18 signaling axis. IL-18BP is induced 10 – 100-fold after IL-18 administration, binds to IL-18 with high affinity, and prevents IL-18 binding to the IL-18 receptor.⁴ Inhibition of IL-18/IL-18BP binding, and especially the ability to release IL-18 from pre-formed complex, may therefore release IL-18 in situ, leading to IL-18-mediated proinflammatory effects and enhanced anti-tumor immunity.

Methods Here we analyze IL-18 and IL-18BP expression in tumors and describe the discovery of a high affinity monoclonal antibody that recognizes IL-18BP. Using in vitro and in vivo assays we analyze the ability of the antibody to disrupt IL-18/IL-18BP complex and activate IL-18-mediated responses.

Results Analysis of expression data from the TCGA database and archived patient samples from select indications reveals that both IL-18 and IL-18BP are co-expressed in multiple tumor types, suggesting there is a preexisting pool of IL-18/IL-18BP complex at the site of the tumor in some patients. Although the interaction of IL-18 with IL-18BP is a high affinity interaction (K_D 700 pM), we have been able to identify very high affinity antibodies with K_D values more than ten-fold lower for both human and mouse IL-18BP. These antibodies can both inhibit complex formation and importantly, disrupt existing IL-18/IL-18BP complexes, liberating endogenous IL-18 at the tumor site. These antibodies are active in cell-based functional assays, resulting in potent stimulation of interferon-γ production from both NK and T cells, including when IL-18/IL-18BP is present as a preexisting complex. In vivo, we observe efficacy in a syngeneic tumor model using an anti-mouse IL-18BP antibody and demonstrate that interferon-γ is upregulated at the tumor site but not in the serum. Combination therapy with anti-PD1 leads to significantly increased efficacy compared to anti PD-1 alone and results in complete responses in more than half of the animals. RNA and protein analysis demonstrates expression of both IL-18BP and IL-18 within the tumors. Additionally, we observe an increase in NK cells and granzyme B expression in response to combination therapy.

Conclusions These data suggest that inhibition of IL-18/IL-18BP binding may prove efficacious in the treatment of cancers where IL-18BP prevents an IL-18-mediated proinflammatory response.

References

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2. Fabbi M, Carbotti G, Ferrini S. Context-dependent role of IL-18 in cancer biology and counter-regulation by IL-18BP. J Leukoc Biol. 2015;97:665–75.

3. Tarhini AA, Millward M, Mainwaring P, Kefford R, Logan T, Pavlick A, Kathman SJ, Laubscher KH, Dar MM, Kirkwood JM. A phase 2, randomized study of SB-485232, rhIL-18, in patients with previously untreated metastatic melanoma. Cancer. 2009;115:859–68.

4. Dinarello CA, Novick D, Kim S, Kaplanski G. Interleukin-18 and IL-18 binding protein. Front Immunol. 2013;4:289.