Abstract 2546: Impact of CDK4/6 inhibition on tumor immune microenvironment and immunomodulatory effects PD-L1 blockade in a physiologically relevant 3D-tumoroid model of fresh patient tumor tissue ex vivo
Authors: Page Melba Marie , Varela Melanie Mediavilla , Agrawal Vijayendra , Kreahling Jenny , Altiok Soner 
Published: August 2019

Abstract
Introduction: In mammalian cells, exposure to growth factors triggers de novo synthesis of D-type cyclins, which then associate with their catalytic partners, cyclin dependent kinase CDK4 or CDK6 to regulate the cell cycle. Recent studies implied the role of CK4/6 inhibitors such as Abemaciclib in modulating tumor immune microenvironment and response to PD1/PD-L1 inhibitors. However, the mechanisms by which CD4/6 inhibitors affect the tumor microenvironment is not well understood. Here we investigated the effect of CDK4/6 inhibition by Abemaciclib on the tumor immune microenvironment and response to PD1/PD-L1 inhibitors using Nilogen’s 3D-EX ex vivo drug screening platform utilizing un-propagated 3D tumoroids of fresh patient tumor tissue with an intact tumor microenvironment.
Materials and Methods: All non-small cell lung carcinoma tumor samples were obtained with patient consent and relevant IRB approval. For the ex vivo assays 3D tumoroids measuring 100-150 micron in size were treated with Abemaciclib, pembrolizumab (Keytruda) alone or in combination. Treatment-mediated changes in tumor immune cell composition including CD4 and CD8 T-cells, Tregs, NK cells, macrophages and cell surface expression of checkpoint proteins as well as T-cell activation were evaluated by multiplex flow cytometry. Multiplex cytokine assays were performed to assess drug-induced changes in cytokine release. High-content confocal analysis was used to quantify tumor cell killing.
Results: We showed that drug treatments had significant impact on immune cell compositions, specifically on M1/M2 macrophage polarization as well as on CD4 and CD8 lymphocyte populations in selected tumors, which was accompanied by significant changes in pro-inflammatory cytokine release. We further characterized pharmacological interaction between Abemaciclib and pembrolizumab and correlated with tumor cell killing in quantitative imaging studies.
Conclusion: In this comprehensive study we documented the pharmacological effect of CDK4/6 inhibition on tumor immune microenvironment in a physiologically relevant 3D tumoroid model of ex vivo drug testing. We further characterized the pharmacological interaction between Abemaciclib and pembrolizumab to better understand the mechanisms by which CDK4/6 inhibition may enhance therapeutic response to PD1 blockade in patient tumors.
Citation Format: Melba Marie Page, Melanie Mediavilla Varela, Vijayendra Agrawal, Jenny Kreahling, Soner Altiok. Impact of CDK4/6 inhibition on tumor immune microenvironment and immunomodulatory effects PD-L1 blockade in a physiologically relevant 3D-tumoroid model of fresh patient tumor tissue ex vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2546.