On June 13, 2024 Sonnet BioTherapeutics Holdings, Inc. (NASDAQ:SONN) (the "Company" or "Sonnet"), a clinical-stage company developing targeted immunotherapeutic drugs, reported 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 (Press release, Sonnet BioTherapeutics, JUN 13, 2024, View Source [SID1234644307]). 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).
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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-γ (IFN-γ) 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.
"The development of a modified IL-18 has been a challenging scientific achievement. IL-18 is a key cytokine that, when combined synergistically with IL-12, has the potential to be an important therapeutic asset for oncology and cell-based therapy. We believe that these novel molecules combined with our proprietary FHAB platform are expected to demonstrate tumor targeting and longer half-lives, which in turn are expected to allow a therapeutic window for commercialization of these important oncology candidates", said Pankaj Mohan, Ph.D., Sonnet Founder and Chief Executive Officer.
"The known MOA of IL-18 inhibition by IL-18BP is reviving the importance of clinical applications of IL-18. IL-18BP has been shown to be elevated in cancer patients, thus negating the clinical use of IL-18. Sonnet is excited about the development of a novel bifunctional cytokine molecule, IL18BPR-FHAB-IL12, which contains a unique IL18 domain that does not bind the inhibitor IL-18BP but still maintains full IL-18 and IL-12 bioactivity. The clinical application of this bifunctional fusion protein could potentially expand immunotherapy applications for cancer patients" commented John Cini, Ph.D., Sonnet Chief Scientific Officer.
About SON-1411
SON-1411 is a candidate immunotherapeutic recombinant drug that is closely related to and will replace SON-1410, which links an unmodified single-chain human IL18 and an unmodified IL-12 with the albumin-binding domain of the single-chain antibody fragment A10m3. The only difference between SON-1410 and SON-1411 is that in the latter, the IL-18 domain has been modified via mutagenesis to retain wildtype binding to the IL-18 receptor (IL-18 Rc) while inhibiting or abolishing binding to the IL-18 binding protein (IL-18 BP). The A10m3 scFv was selected to bind both at normal pH, as well as at the acidic pH that is typically found in the TME. The FHAB technology targets tumor and lymphatic tissue, providing a mechanism for dose sparing and an opportunity to improve the safety and efficacy profile of IL-18 and IL-12, as well as a variety of potent immunomodulators that can be added using the platform. Interleukin-12 can orchestrate a robust immune response to many cancers and pathogens. Given the types of proteins induced in the TME, such as SPARC and gp60, several types of cancer such as non-small cell lung cancer, melanoma, head and neck cancer, sarcoma, and some gynecological cancers are particularly relevant for this approach. SON-1411 is designed to deliver IL-18BPR and IL-12 to local tumor tissue, turning ‘cold’ tumors ‘hot’ by stimulating IFNγ, which activates innate and adaptive immune cell responses and increases the production of Programed Death Ligand 1 (PD-L1) on tumor cells.