Abstract LB-A20: Strategies to Improve the Safety and Efficacy of Biparatopic Antibody Drug Conjugates

Abstract

Abstract Antibody drug conjugates (ADC’s) define an emerging class of targeted therapies for cancer, with over 60 ADC’s currently in clinical development. Although antibodies can exhibit exquisite target specificity, expression of the tumor target in normal tissue can limit the tolerated dose that one can achieve with an ADC. We designed two different affinity variant biparatopic antibodies that recognize distinct epitopes on EGFR and promote receptor clustering that leads to enhanced lysosomal trafficking. These ADC’s comprise two different strategies to target EGFR expressing tumors: a high affinity, potency driven approach and a lowered affinity, threshold driven approach. We show that both ADC’s bind to tumor cells, are rapidly internalized, and traffic to the lysosome, where the warhead is efficiently released by lysosomal hydrolases. In vitro, the high affinity ADC exhibited potent killing of cancer cell lines, with IC50’s in the double digit picomolar range in cells with relative EGFR densities as low as 25,000, while the low affinity ADC was most effective when the EGFR density was greater than 500,000. The high affinity ADC was active in patient derived xenograft (PDX) models derived from colorectal and lung cancer patients harboring clinically relevant oncogenic drivers, such as KRAS and BRAF mutations or EGFR aberrations. This ADC induced tumor stasis or regression, with minimally efficacious doses between 1 and 3 mg/kg, in multiple tumor models across a broad range of EGFR expression (IHC scores ranging from 1 to 3). In a cynomolgus monkey safety study, this ADC showed a manageable safety profile at 2 mg/kg, with skin effects as the dose limiting toxicity. The potency of the high affinity ADC may provide meaningful activity across a range of EGFR expression levels, at doses that are tolerable in the clinic. The lowered affinity ADC exhibited an improved safety profile compared to the high affinity ADC, with a highest non-severely toxic dose (HNSTD) of 6 mg/kg, presumably driven by a reduction in binding to normal tissues that express comparably lower EGFR levels relative to the tumor. This lowered affinity ADC showed a more restricted anti-tumor activity, causing regressions at a minimally efficacious dose between 3 and 5 mg/kg, in PDX models that expressed high levels of EGFR, as judged by IHC scores of 3. The lowered affinity ADC required higher EGFR expression for activity, but the improved tolerability may provide a selectivity threshold that discriminates tumor from normal tissue in patients whose tumors overexpress EGFR. Our findings support the concept that modulating antibody affinity can yield distinct ADC’s that represent different strategies for balancing safety and efficacy. The work presented here provides a conceptual framework for designing unique ADC candidates tailored to the particular expression profile and safety considerations around specific tumor associated targets. Citation Format: Frank I. Comer, Xinzhong Wang, Andy Q. Yuan, Vanessa Muniz-Medina, Agnieszka Sadowska, Lan Xu, Samuel Perry, Pamela Thompson, Ralph Minter, Robert Woods, Mary Jane Hinrichs, Molly Reed, Shameen Affif-Rider, Marlon Rebelatto, Charles Brown, Hui Feng, Rakesh Dixit, Steven Coats, Jane Osbourn. Strategies to Improve the Safety and Efficacy of Biparatopic Antibody Drug Conjugates [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr LB-A20.