Bortezomib augments lymphocyte stimulatory cytokine signaling in the tumor microenvironment to sustain CD8+T cell antitumor function

// Samuel T. Pellom Jr. 1, 2, 3 , Duafalia F. Dudimah 1 , Menaka C. Thounaojam 1 , Roman V. Uzhachenko 1 , Ashutosh Singhal 1 , Ann Richmond 4, 5, 6, 7, 8, 9 , Anil Shanker 1, 3, 7, 8, 9 1 Department of Biochemistry and Cancer Biology, School of Medicine, Meharry Medical College, Nashville, Tennessee, USA 2 Department of Microbiology and Immunology, School of Medicine, Meharry Medical College, Nashville, Tennessee, USA 3 School of Graduate Studies and Research, Meharry Medical College, Nashville, Tennessee, USA 4 Tennessee Valley Healthcare System, Nashville, Tennessee, USA 5 Department of Veterans Affairs, Nashville, Tennessee, USA 6 Department of Cancer Biology, Vanderbilt University Medical Center, Nashville, Tennessee, USA 7 Host-Tumor Interactions Research Program, Vanderbilt-Ingram Comprehensive Cancer Center, Vanderbilt University, Nashville, Tennessee, USA 8 Vanderbilt Center for Immunobiology, Vanderbilt University, Nashville, Tennessee, USA 9 Vanderbilt Center for Translational and Clinical Immunology, Vanderbilt University, Nashville, Tennessee, USA Correspondence to: Anil Shanker, email: ashanker@mmc.edu Keywords: proteasome inhibition, CD8 + T cells, immunosuppression, cancer immunotherapy, adoptive cell therapy Received: November 07, 2016 Accepted: December 07, 2016 Published: December 29, 2016 ABSTRACT Tumor-induced immune tolerance poses a major challenge for therapeutic interventions aimed to manage cancer. We explored approaches to overcome T-cell suppression in murine breast and kidney adenocarcinomas, and lung fibrosarcoma expressing immunogenic antigens. We observed that treatment with a reversible proteasome inhibitor bortezomib (1 mg/kg body weight) in tumor-bearing mice significantly enhanced the expression of lymphocyte-stimulatory cytokines IL-2, IL-12, and IL-15. Notably, bortezomib administration reduced pulmonary nodules of mammary adenocarcinoma 4T1.2 expressing hemagglutinin (HA) model antigen (4T1HA) in mice. Neutralization of IL-12 and IL-15 cytokines with a regimen of blocking antibodies pre- and post-adoptive transfer of low-avidity HA 518-526 -specific CD8 + T-cells following intravenous injection of 4T1HA cells increased the number of pulmonary tumor nodules. This neutralization effect was counteracted by the tumor metastasis-suppressing action of bortezomib treatments. In bortezomib-treated 4T1HA tumor-bearing mice, CD4 + T-cells showed increased IL-2 production, CD11c + dendritic cells showed increased IL-12 and IL-15 production, and HA-specific activated CD8 + T-cells showed enhanced expression of IFNγ, granzyme-B and transcription factor eomesodermin. We also noted a trend of increased expression of IL-2, IL-12 and IL-15 receptors as well as increased phosphorylation of STAT5 in tumor-infiltrating CD8 + T-cells following bortezomib treatment. Furthermore, bortezomib-treated CD8 + T-cells showed increased phosphorylation of mitogen-activated protein kinase p38, and Akt, which was abrogated by phosphatidylinositide 3-kinase (PI3K) inhibitor. These data support the therapeutic potential of bortezomib in conjunction with other immunotherapies to augment the strength of convergent signals from CD8 + T-cell signaling molecules including TCR, cytokine receptors and downstream PI3K/Akt/STAT5 pathways to sustain CD8 + T-cell effector function in the tumor microenvironment.