Abstract 5447: Development and preclinical evaluation of JK06, a biparatopic ADC against 5T4

Abstract Trophoblast glycoprotein, also known as 5T4, is an oncofetal antigen that is upregulated on a variety of solid tumors including breast, lung, and genitourinary cancers. 5T4 expression levels correlate with stage of cancer progression and are associated with poor clinical outcomes. Herein, we describe the pre-clinical design and validation of JK06, a humanized, quadrivalent, biparatopic antibody-drug conjugate (ADC) that targets 5T4, allowing for efficient and selective delivery of a cytotoxic payload, monomethyl auristatin E (MMAE), to tumor cells. JK06 is engineered from 2 monoclonal antibodies (mAbs) that bind to distinct epitopes of 5T4. The first mAb clone was converted to a single-chain fragment variable (ScFv) format and fused to the C-terminal Fc end of a second mAb. This yields a hybrid molecule with four 5T4 binding sites, targeting two distinct epitopes of the 5T4 antigen. This design increases 5T4 avidity, an important feature given the generally low expression of 5T4 on tumor cells and enhances internalization of the drug. JK06 binds to recombinant 5T4 protein with low picomolar affinity measured by surface plasmon resonance, an approximately 10-fold increase in comparison to the two parental mAbs. JK06 induces internalization into 5T4 expressing tumor cells more rapidly and to a greater extent in vitro, than the parental mAbs. The tubulin inhibitor MMAE was conjugated to the Fc backbone of JK06 in a site-specific manner with a cleavable linker at a drug:antibody ratio (DAR) of two. In vivo CDX studies utilizing the MDA-MB-461 breast cancer and H1975 lung cancer cell lines in nude mice demonstrated that JK06 induces robust control of tumor growth in vivo. A repeat-dose GLP toxicology study, with a once every 3-week (Q3W) dosing schedule, demonstrated that JK06 was well tolerated, and without any observed adverse effects at the tested doses. Toxicokinetic evaluation showed a half-life which projects sustained exposure in humans with a Q3W dosing regimen. JK06 is currently being evaluated in an open-label, dose-escalation and expansion Phase I study to assess the safety, pharmacokinetics, and preliminary efficacy in a basket of solid tumors known to express 5T4. Citation Format: Jonathan McNally, Binyam Bezabeh, Jijun Dong, Samuel Murphy. Development and preclinical evaluation of JK06, a biparatopic ADC against 5T4 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5447.