Identification of Cooperative Interactions of Pharmacologic Pembrolizumab Combinations Using In Vitro Human Tumor Microenvironment Model Systems Neethan A Lobo1, Sharlene Velichko1, Alexandra E. Folias1, Evan Callihan1, Jennifer I. Drake1, Dat Nguyen1, Jennifer Melrose1, Ellen L. Berg1, Alison O'Mahony1,* 1Eurofins DiscoverX, South San Francisco, CA 94080 *Corresponding Author
The goal of a combination strategy is to achieve better clinical outcomes by either enhancing efficacy, reducing adverse effects, or both. Currently, there is a need for innovative in vitro and in vivo preclinical models to guide combination strategies by addressing two fundamental challenges: firstly, how to determine if a combination would be more effective than its respective individual agents and secondly, to understand combination mechanisms. We utilized a phenotypic profiling approach to study drug combination mechanisms, differentiating these from their respective monotherapies using in vitro models of the host tissue/immune/cancer cell tumor microenvironment (TME). Human primary tissue cells (stromal fibroblasts or vascular endothelial cells) and PMBCs pooled from healthy donors were co-cultured with the HT29 colorectal (CRC) cell line and these systems were exposed to a concentration matrix and individual agents. We identified differential impacts of individual drugs and combinations on a panel of translational biomarkers to determine additive, antagonistic and potential novel effects. We evaluated the combination of pembrolizumab with either gemcitabine or paclitaxel in two CRC TME model systems. In both studies, pembrolizumab increased cytokine levels consistent with its ability to restore immune function relevant for immune oncology (IO). Tested individually, both gemcitabine and paclitaxel had broad impacts beyond modulation of immune cytokines including effects on inflammation and matrix related biomarkers relevant for modulation of the TME. The combination of pembrolizumab with paclitaxel not only preserved the IO activities of pembrolizumab and the broader TME effects of paclitaxel but also enhanced the expression of select cytokines. Interestingly, the combination of pembrolizumab with gemcitabine at select concentrations led to novel effects (e.g. increased IL-17) that were not observed with either monotherapy at equivalent concentrations alone. Overall, both combination pairs were determined to be significantly different from their respective monotherapies exhibiting novel and enhanced effects on sentinel IO response biomarkers (e.g. IL-6). We propose that orthogonal approaches to expensive clinical studies, such as in vitro phenotypic profiling, can inform on the mechanisms of drug combinations. Identifying effects on clinically relevant translational biomarkers can help guide the design of combination strategies with the goal of understanding how to achieve higher response rates and more durable remissions.