On March 19, 2025 Sonnet BioTherapeutics Holdings, Inc. (the "Company" or "Sonnet") (NASDAQ: SONN), a clinical-stage company developing targeted immunotherapeutic drugs, reported that the United States Patent and Trademark Office (USPTO) has issued a Notice of Allowance to the Company for a second patent in the IL-18 variant protein field which discloses the amino acid sequence of its variant human IL-18BPR protein (Press release, Sonnet BioTherapeutics, MAR 19, 2025, View Source [SID1234651261]). The allowed patent claims cover variant human IL-18 (hIL-18) proteins, including but not limited to hIL-18 proteins having amino acid substitutions at the following positions: Y1W, Y1K, M51Y, M51S, M60W, S105E, and D110Y, relative to human wildtype IL-18. Additionally, the Company announced the release of a Virtual Investor "What This Means" segment to discuss the allowed patent, which is now available here.

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"I believe that Sonnet has become of one of the few companies that hold proprietary rights to IL-18BPR which could be a highly valuable cytokine for cancer patients. This patent covers the composition of matter of the amino acid sequence of our human IL-18BPR variant protein which bolsters our intellectual property position and provides further validation to our approach that when IL-18BPR is synergistically combined with IL-12, we believe we will have the potential to develop an important therapeutic asset for oncology and cell-based therapy. Additionally, we feel that this patent enables us to explore opportunities for IL-18BPR to be licensed independent of our FHAB platform. We continue to believe that novel bifunctional molecules such as SON-1411, when combined with our proprietary FHAB platform, have the potential to demonstrate improved tumor targeting, extended half-life and an enhanced therapeutic window," said Pankaj Mohan, Ph.D., Sonnet Founder and Chief Executive Officer.

Sonnet previously reported the generation of two novel drug candidates, SON-1411 (IL18BPR-FHAB-IL12) and SON-1400 (IL18BPR-FHAB), each containing a variant 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 while 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).

"SON-1411 (IL18BPR-FHAB-IL12) is a bifunctional combination of IL-12 and the FHAB domain with a human variant of human interleukin-18 ("IL-18BPR"), which was modified to resist an inhibitory interaction with IL-18 binding protein (IL-18BP). IL-18 is involved in activating both innate and adaptive immune responses; however, IL-18 clinical therapies have been hampered by a lack of efficacy due to the inhibitory activity of the IL-18BP," 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.