Functional impact of high extracellular K+ on human T-cells

Abstract

T-cell immunology has become a central focus for research in the fight against cancer. To mount an effective antitumor activity, T-cells migrate to and infiltrate into the tumor, proliferate, secrete cytokines and differentiate into specialized T-helper (Th) subsets. However, the tumor microenvironment (TME) presents a major challenge to tumor-infiltrating T-cells. Dying necrotic cancer cells release potassium (K+), the main intracellular cation, leading to a 10-fold increase in the extracellular K+ concentration ([K+]e) within the local microenvironment. This results in an accumulation of intracellular K+ ions ([K+]i) in T-cells, causing them to be immunosuppressed. The implications of exposure to a K+-rich microenvironment on T-cell effector function remain poorly understood. The goal of this interdisciplinary thesis was to investigate functional impact of high-[K+]e on T-cells and develop a strategy that could rescue T-cells from high-[K+]e-mediated immunosuppression. In aim 1, we characterized the effect of high-[K+]e on T-cell motility. Findings revealed that exposure to high- [K+]e inhibited T-cell motility and chemotaxis by impairing the LFA-1-mediated signal transduction pathway, interfering with cytoskeletal regulators and downregulating the chemokine receptor, CXCR4. In aim 2, we investigated whether and how high-[K+]e affects T-cell effector function. Findings showed that exposure to high-[K+]e perturbed T-cell proliferation and cytokine production by dysregulating T-cell receptor/co-receptor signaling pathways and metabolism that ultimately skewed T-cell differentiation towards Th2 and regulatory T-cell (Treg) subsets that favor tumor growth while restricting antitumor Th1 and Th17 subsets. Biopsies from patient-derived HCC/CRC tumors showed similar phenotypes. In aim 3, we designed, synthesized and biologically evaluated a panel of novel thiazoloquinolin-2-amine derivatives as KCa3.1 channel activators. We identified SKA-346 as a KCa3.1-selective activator with an in vitro EC50 of 1.9 μM and an in vivo circulating half-life (t1/2) of 2.8 h. Overall, the current thesis significantly broadens the understanding of the immunosuppressive TME. Results presented here have implications for future therapeutic advancements and underscore the potential of SKA-346 in augmenting the antitumor immune response.