Forlong Biotechnology, a clinical-stage biotech company developing transformative cytokine therapies for patients with severe unmet needs, today announced that the first patient has been dosed in a Phase 1 study of subcutaneous (SC) FL115 in patients with advanced solid tumors in Australia.

FL115 is an engineered IL-15/IL-15Rα-Fbody® fusion protein designed to stimulate natural killer (NK) cells and T cells, key components of the immune system responsible for antitumor activity. In prior clinical studies in patients with advanced solid tumors, intravenous (IV) administration of FL115 as a monotherapy has shown a favorable safety profile, robust NK- and T-cell expansion and preliminary clinical efficacy. Notably, three patients achieved stable disease or confirmed partial responses lasting more than 12 months, highlighting the potential of FL115 to deliver durable clinical benefit as a monotherapy. Furthermore, at low doses, it potently stimulates IFN-γ with minimal induction of IL-6 systemically.

The advancement of FL115 into subcutaneous clinical development is supported by a differentiated pharmacokinetic profile observed in preclinical studies. Compared with IV administration, SC injection reduced peak plasma concentration (Cmax) by more than 20-fold while prolonging meaningful systemic exposure. Preclinical studies also demonstrated systemic bioavailability of 60% or greater, without significant gross skin irritation. These findings support further clinical evaluation of SC administration as a potential approach to optimize immune-cell stimulation, improve tolerability, and expand the therapeutic window of FL115.

“Dosing the first patient in the Phase I study of subcutaneous FL115 marks an important milestone in advancing this promising IL-15 superagonist,” said Dong Wei, Ph.D., Chief Executive Officer of Forlong Biotechnology. “Building on the encouraging clinical profile observed with intravenous administration, the subcutaneous formulation has the potential to further optimize FL115’s therapeutic window and broaden its clinical applicability. Following the recent completion of our pre-Series B financing, we are accelerating the development of FL115 across multiple therapeutic approaches, including preparing for advancing intravesical FL115 into Phase III for patients with BCG-unresponsive papillary non-muscle-invasive bladder cancer (NMIBC), and developing subcutaneous FL115 for other solid tumors and diseases. Through these complementary development strategies, we aim to establish FL115 as a potential best-in-class IL-15 superagonist and bring new treatment options to patients with significant unmet medical needs.”

About Forlong Biotechnology

Forlong Biotechnology is a clinical-stage biotech company focused on developing transformative cytokine therapies for cancer patients with severe unmet needs. The company has established four proprietary synthetic immunology platforms: the Fbody® Long-acting Technology Platform, the Fc Engineering Platform, the Syntokine® Synthetic Cytokine Platform, and an AI-driven Intelligent Biomolecular Discovery Platform.

Forlong’s lead candidate, FL115, is an interleukin-15 (IL-15) superagonist with best-in-class potential, currently being tested as IV infusion in combination with an anti-PD-1 antibody in a Phase 1 study for patients with solid tumors, as intravesical delivery in combination with BCG in a Phase 2 study for patients with NMIBC and as subcutaneous injection in a Phase 1 study for patients with solid tumors. The company’s second candidate, FL116, is a PD-1 antibody fused with an interleukin-18 (IL-18) mutein engineered to bind the IL-18 receptor without binding IL-18BP (a decoy receptor), and has demonstrated potent tumor-killing efficacy across multiple in vivo tumor models resistant to immune checkpoint inhibitors and significant safety margin in IND-enabling studies.

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