Abstract LB059: Multimeric linker-exatecan-based ADC targeting guanylyl cyclase C (GCC) as novel therapeutic modality for treatment of colorectal cancer

Abstract Background: The approval of sacituzumabgovitecan (Trodelvy) and trastuzumab deruxtecan (Enhertu) demonstrated the potential of topoisomerase I inhibitors in cancer therapy. Both ADCs rely on payload conjugation to interchain cysteines of an unmodified wildtype antibody coming along with unfavorable properties like instability in circulation, premature payload release and unspecific uptake via Fc gamma receptors. Heidelberg Pharma uses a proprietary, site-specific conjugation to engineered cysteines andFcγR silencing mutations (LALA) to obtain a homogeneous and stable ADC void of Fc-mediated uptake. To achieve a DAR of 4, a multimeric linker comprisingexatecan and a solubility enhanceris used to obtain more than one payload per conjugation site. In the current study, in vitro and in vivo data of an ADC targeting GCC (guanylyl cyclase C) for the treatment of colorectal cancer with favorable potency and tolerability are presented. Material and methods: Cell lines: GCC+cell line: HEK293-GUCY2C mono2; GCC-cell line: HEK293 ADC: The cysteine-reactive multimeric linker-exatecan construct was synthesized at Heidelberg Pharma and conjugated site-specifically to engineered cysteine residues of a proprietary anti-GCC antibody yielding ADCs with a DAR of 4. 0. Animal models: Female NOD SCID mice were subcutaneously inoculated with GCC-overexpressing HEK293-GUCY2C mono2 tumor cells. Animals were treated with anti GCC ADC at single or multiple doses. Tolerability was assessed in female NODSCID mice. Results: The anti-GCC ADC with multimeric linker-exatecan payload showed favorable in vitro cytotoxicity with nanomolar activity on the GCC+ cell line and no cytotoxic activity on target-negative cells. In mouse xenograft models, the anti-GCCADC caused dose-dependent tumor regression in HEK293-GUCY2C mono2 s. c. xenografts. Multiple dosing improved this anti-tumor efficacy even further without negative impact on toxicity. The MTD of the ADC in mice was determined to be ≥200 mg/kg. Conclusions: Targeted cytotoxic drug delivery to GCC positive cell lines was achieved by using an anti-GCC ADCwith multimeric linker-exatecan payload. The use of solubility enhancers within the structure of the multimeric linker facilitated site-specific coupling to cysteines resulting in a stable, potent, and well tolerated ADC. The use of anti-GCC ADCs with multimeric linker-exatecan payloads in the therapy of GCC positive colorectal cancer, represents a promising approach in cancer therapy. Citation Format: Sarah-Jane Neuberth, Christian Orlik, Aniko Palfi, Christoph Mueller, Hendrik Gruss, Torsten Hechler. Multimeric linker-exatecan-based ADC targeting guanylyl cyclase C (GCC) as novel therapeutic modality for treatment of colorectal cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (7Suppl): Abstract nr LB059.