Real Tech Fund Invests in CastBio, a Company Aiming to Treat Refractory Solid Tumors with a Proprietary ADC

Real Tech Fund*, operated by UntroD Capital Japan Inc. (Location: Minato-ku, Tokyo; Representative: Akihiko Nagata), has invested in CastBio Inc. (Head Office: Chuo-ku, Tokyo; CEO: Masaaki Fujiwara, hereafter "CastBio"), a company developing next-generation Antibody-Drug Conjugates (ADCs) based on its proprietary VLK linker technology. With this investment, CastBio will advance its non-clinical development and organizational structure, aiming to create innovative treatments for refractory solid tumors. Company Overview: CastBio is a drug discovery startup established through a company split from Rinsho K.K., a venture originating from the National Cancer Center. Refractory solid tumors such as glioblastoma (GBM), pancreatic cancer, and scirrhous gastric cancer have extremely low 5-year survival rates and represent significant unmet medical needs. One reason for their refractory nature is believed to be the cancer stroma in tumor tissue, which hinders drug penetration. CastBio is tackling this challenge with a new therapeutic approach. They have developed an anti-IF-ADC that combines an antibody that specifically binds to insoluble fibrin (IF) present in the cancer stroma with a VLK linker technology that is cleaved by plasmin, which is abundant in the stroma. This achieves efficient drug delivery to the tumor tissue. Purpose and Use of Funds: The funds raised by CastBio will be used to build the R&D structure for the anti-IF-ADC, advance its non-clinical development, and strengthen and protect its intellectual property. Comments from the Person in Charge: There is a strong demand for the development of innovative treatments for refractory solid tumors, which have an extremely poor prognosis with a 5-year survival rate below 10%. The cancer stroma, a factor in their refractory nature, is formed as cancer cells proliferate while incorporating blood vessels, repeating a process of bleeding, hemostasis, and the subsequent breakdown of fibrin clots by plasmin. The anti-IF-ADC is designed to target the cancer stroma using an anti-IF antibody that targets the insoluble fibrin accumulated in this process. By using a VLK linker that is cleaved by plasmin, the payload can diffuse throughout the stroma to attack cancer cells. As this developmental drug utilizes properties common to the cancer stroma of refractory solid tumors, it can be applied across different cancer types without depending on specific biomarkers, potentially bringing hope to patients for whom standard treatments are not sufficiently effective. Real Tech Fund will support CastBio's efforts to tackle the serious societal challenge of refractory solid tumors. (Tatsuhiko Fujimoto, Growth Manager, UntroD Capital Japan Inc.) *Official Name: "Real Tech Fund IV, L.P." About CastBio Inc.: Established: March 2026; Location: 2F Success Ginza Higashi Bldg., 1-13-10 Tsukiji, Chuo-ku, Tokyo; Representative: Masaaki Fujiwara; Capital: 10 million yen; Business: R&D of pharmaceuticals including ADCs; Investment Timing: April 2026. About UntroD Capital Japan Inc. and Real Tech Fund: UntroD Capital Japan Inc. established the "Real Tech Fund" in 2015 to promote the social implementation of deep-tech startups with innovative R&D technologies that contribute to solving global and human challenges. It has been providing lead investment and hands-on support to seed and early-stage startups. To date, it has managed Real Tech Fund I-IV (Japan funds), Real Tech Global Fund I & II (global funds), Real Tech Growth Fund I (Japan fund), and a Crossover Impact Fund (Japan fund), with total assets under management exceeding 40 billion yen. To further embody its will to be the first to venture into unexplored domains where capital is scarce despite societal need, and to create a sustainable system where capital and talent continue to flow by proving its economic viability, the company relaunched in June 2024 under the name "UntroD," meaning "untrodden." HP: https://untrod.inc; Contact: UntroD Capital Japan Inc. PR: Narita https://untrod.inc/contact