Sonnet BioTherapeutics Holdings, Inc. announced that the safety of SON-1010 dosing has been formally reviewed in both of the current Phase 1 clinical trials and the Company is now increasing the target dose of SON-1010 during dose escalation. SON-1010 is a proprietary version of recombinant human interleukin-12 (rhIL-12), configured using Sonnet's Fully Human Albumin Binding (FHAB®) platform, which extends the half-life and activity of the IL-12 component due to binding native albumin in the serum and targets the tumor microenvironment (TME) by strongly binding gp60 and Secreted Protein Acidic and Rich in Cysteine (SPARC). SB101 is a Phase 1 multiple-ascending dose (MAD) trial in adult patients with advanced solid tumors (NCT05352750) that commenced in Second Quarter 2022 and is currently enrolling the sixth dose cohort.

SB221 is a Phase 1b/2a dose-escalation and proof-of-concept study of the combination of SON-1010 with atezolizumab (in collaboration with Genentech, a member of the Roche Group), in a study focused on platinum-resistant ovarian cancer (PROC) (NCT05756907) that started in Fourth Quarter 2023, now enrolling the fourth dose cohort. In addition, SON-1010 was studied in SB102, which was a Phase 1 single-ascending dose (SAD) trial in healthy volunteers (NCT05408572) that started in Third Quarter 2022; the results were recently published (Kenney, et al, Frontiers in Immunology, 2024). Safety in both of the active cancer trials has been reviewed by their respective Safety Review Committees at each step during dose escalation.

Both trials use a ?desensitizing' first dose to take advantage of the known tachyphylaxis with rhIL-12, which minimizes toxicity and allows higher maintenance doses. No dose-limiting toxicities or related serious adverse events have occurred to date. The safety and toxicity profile that has developed is typical for a Phase 1 oncology trial, with the majority of adverse events (AEs) being reported as mild.

All have been transient, with no evidence of cytokine release syndrome. Of the 25 cancer patients dosed to date and evaluable for follow-up at this latest cutoff, 15 (60%) had stable disease at their first follow-up scan, 8 of whom were progressing at study entry. At four months follow-up, 8 of 23 evaluable patients remained stable at the second CT scan, suggesting clinical benefit of SON-1010 in 35% of the patients.One patient with progressive endometrial sarcoma receiving SON-1010 monotherapy in SB101 had stable disease (SD) for almost 2 years before progressing - her ascites had resolved and tumors had shrunk at one point but she never reached a partial response (PR) by Response Evaluation Criteria in Solid Tumors (RECIST) rules.

Cytokine analysis following each dose in that study revealed controlled and prolonged induction of interferon gamma (IFN?) that peaked at 24 to 48 hours and returned to baseline within 2 to 4 weeks. A small increase in IL-10 was observed with each dose as expected in response to IFN?. There was either a minimal or no signal for IL-1ß, IL-6, IL-8, and TNFa, and there was no indication of any potential for cytokine release syndrome (CRS) at these doses.

One patient in Part 1 of SB221 with uterine sarcomas received 8 cycles of the SON-1010/atezolizumab combination therapy every 3 weeks before progressing; another two have received 8 and 10 cycles, respectively, and are continuing on the study. The stable AE profiles despite dose escalation led us to reevaluate the target dose, so the Company has added groups in both studies to evaluate 1200 ng/kg SON-1010 as a maintenance dose (the molar equivalent of 800 ng/kg rhIL-12). Finally, Part 2 of the SB221 combination study has been trimmed to remove the monotherapy arm.