Sonnet BioTherapeutics Holdings, Inc. announced the generation and in vitro characterization of two novel drug candidates, SON-1411 (IL18BPR-FHAB-IL12) and SON-1400 (IL18BPR-FHAB), each containing a modified version of recombinant human interleukin-18 (IL-18BPR). SON-1411 is a proprietary bifunctional fusion protein consisting of IL-18BPR combined with single-chain wild-type IL-12, linked to Sonnet's Fully Human Albumin Binding (FHAB®) platform, which will replace SON-1410 as a development target. SON-1400 is a monofunctional fusion protein comprising the same IL-18BPR domain linked to the FHAB.

FHAB extends the half-life and biological activity of linked molecules by binding native albumin in the serum and targets the tumor microenvironment (TME) through high affinity binding to glycoprotein 60 (gp60) and the Secreted Protein Acidic and Rich in Cysteine (SPARC). IL-18 can regulate both innate and adaptive immune responses through its effects on natural killer (NK) cells, monocytes, dendritic cells, T cells, and B cells. IL-18 acts synergistically with other pro-inflammatory cytokines to promote interferon-?

(IFN-?) production by NK cells and T cells. Systemic administration of IL-18 has been shown to have anti-tumor activity in several animal models. Moreover, tumor-infiltrating lymphocytes (TILs) express more IL-18 receptors than other T cells.

However, IL-18 clinical trials have shown that, although it is well tolerated, IL-18 has poor efficacy in the treatment of cancers, most likely due in large part to the high co-expression of IL-18 binding protein (IL-18BP) in the TME. In particular, IL-18BP serves as a ?decoy receptor? that binds to IL-18 with higher affinity, compared with the IL-18Rc complex, thereby causing a negative feedback loop with IL-18 and inhibiting IL-18-mediated TIL activation.

Thus, there exists a potential for the discovery of IL-18 variant compositions that could harness the therapeutic potential of IL-18 for the treatment of cancers. Sonnet?s strategy for amino acid modifications to rIL-18 was based on a compilation of literature review, 3D X-ray crystallography structures, and computer modeling analysis. Subsequently, certain IL-18 variant sequences were synthesized, engineered into expression constructs and manufactured at small scale in either CHO cell culture or E. coli.

Highly purified milligram quantities of SON-1411 or SON-1400 were analyzed in vitro for IL-18Rc or IL-18BP binding activities, respectively, using the HEK-Blue? and Bright-Glo Luciferase IL-18Rc reporter assays. In vitro results for at least one variant of IL-18 showed equivalent binding to the IL-18 Rc, compared to the wild-type IL-18 reference molecule, concomitant with no or reduced binding to IL-18BP.