LAUSR

Biological therapies for the treatment of cancer are utilized for the same ultimate purpose as chemically derived cancer drugs, to induce tumor cell death. However, the differing mechanisms of action often make the evaluation of biologic drug efficacy more complex, requiring the support and/or recapitulation of functional immune components. Biologics also have different limitations that can govern their efficacy such as their large size potentially impeding sufficient penetration to target sites and in the case of live biotherapeutic products, the need to maintain sustained function, or persistence, by resisting immunosuppression by the tumor microenvironment. Preclinical testing of biologics is often confined to cell lines which lack an immune system and mouse models which are expensive, time consuming, and poor proxies for the human immune system. To address these issues, we have developed ex vivo 3D spheroid platforms to measure the efficacy of three types of biologics: antibody-drug conjugates (ADCs), bispecific antibodies, and chimeric antigen receptor (CAR) T-cells. Primary cells from cancer patients or from patient-derived xenografts were evaluated for the expression of the biologic target molecule then cultured to form 3D spheroids. Spheroid models were validated for the evaluation of antibody-based therapies by determining sufficient diffusion of antibodies to target sites. For ADC testing, cell death was measured in a plate-based read-out following treatment with the ADC trastuzumab deruxtecan, and the cytotoxic efficacy of the ADC was compared to trastuzumab alone or free exatecan. Differences in killing kinetics and the maximum efficacy of the ADC were determined compared to the other tested agents. HER2 inhibition was evaluated through changes in constitutive downstream signaling. Two biologics with the same molecular target, a bispecific antibody targeting carcinoembryonic antigen (CEA) on tumor cells and CD3 on T-cells, as well as a CAR T-cell product targeting CEA were also evaluated. Following treatment with the bispecific, tumor cell viability was detected using flow cytometry and changes in T-cell activation were measured via cytokine secretion using primary colorectal cancer models. Importantly, bispecific antibody efficacy was dependent upon the presence of T-cells. Finally, CAR T-cell mediated tumor cell killing was detected using a fluorescent image-based approach. Collectively, this work establishes a model for testing multiple classes of drugs in a 3D ex vivo model that can be used to advance preclinical drug development and evaluate mechanisms of action of diverse drug classes in a physiologically relevant model. Citation Format: Katy A. Lassahn, Ashley K. Elrod, Aaron L. Carlson, Natalie A. Dance, Melissa Millard, Michael J. Wick, Teresa M. DesRochers, Kathryn M. Appleton. Preclinical testing of therapeutic biologics using patient-derived 3D spheroids [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2275.