KY102, a novel Glypican 3-targeting nanobody drug conjugate bearing a topoisomerase 1 inhibitor payload demonstrates compelling preclinical activity in hepatocellular carcinoma models

Background: Glypican-3(GPC3), a cell-surface oncofetal glycoprotein highly expressed in hepatocellular carcinoma (HCC) with minimal presence in normal adult tissues. KY102 is a nanobody-drug conjugate (NDC)targeting human GPC3, composed of a monovalent nanobody covalently conjugated to a topoisomerase 1 inhibitor, DXD. via a maleimide anchor and a glycyl glycyl phenylalanyl glycine (GGFG)- aminomethyl (AM) cleavable linker at a drug to nanobody ratio (DAR) of 3. Materials and Methods: Extensive functional characterization was performed to assess the mechanism of action and therapeutic potential of the KY102 (NDC) at DARs of 3. 1.Nanobody binding to human,cynomolgus monkey rat and mouse GPC3 was assessed by biolayer interferometry (BLI) and flow cytometry(FACs). 2.Am assessment of off-target binding, and target specificity was conducted using 177-Lu labeled Nanobody in normal and cell line derived animalmodel. 3.KY102 nanobody internalization in GPC3-expressing tumor cell lines was assessed by flow cytometry. 4.In vitro KY102 (NDC) cytotoxicity against tumor monolayers was assessed in a panel of HCC cell lines. 5.Tumor cell co-culture assays were also performed to assess bystander-mediated cell killing by KY102. 6.Anti-tumor activity of KY102 was investigated in a panel of cell line-derived xenograft (CDX) and patient-derived xenograft (PDX) mouse models representing a range of GPC3 expression. 7.The tolerability of KY102 was assessed in a single dose and repeat-dose (4 doses; once every weeks) non-GLP toxicology study in a cell line-derived xenograft (CDX) in mice. Results: 1.The KY102 nanobody backbone demonstrated pico-molar binding affinity to both human, cynomolgus monkey, rat and mouse GPC3, and strong binding to target-expressing cancer cell lines. 2.Rapid internalization of KY102 nanobody was observed in GPC3-expressing HCC cell lines. 3.KY102 exhibited potent and target-specific cytotoxicity in a panel of HCC cells cultured either in monolayer. 4.KY102 showed effective bystander-mediated killing of GPC3 negative cancer cells when in co-culture with GPC3 positive cancer cells. 5.A single administration of KY102 ( 2.5mg/kg and 5.0 mg/kg) resulted in robust tumor growth inhibition of a panel of CDX and PDX models representing a range of GPC3-expression. 6.A single dose and a repeat-dose mouse toxicology study of KY102 showed encouraging tolerability at 30, and 60 mg/kg dose levels. 7.A dose-dependent nanobody pharmacokinetics at 2.5 mg/kg, and 5 mg/kg dose levels, without the maximum tolerated dose (MTD) determined. Conclusions: Overall, these results support the potential of KY102 as a novel therapeutic agent against GPC3-bearing cancers including HCC. An IND application is anticipated in 2026. No conflict of interest