Abstract
Propranolol suppresses tumor growth in a variety of preclinical solid tumor models, with a number of proposed cell signaling and immunological mechanisms. We want to confirm the potential mechanisms, including reduced phosphorylation of AKT/MAPK pathways, as well as enhanced CD8+ T-cell-mediated antitumor immune response. To clarify the mechanism of propranolol activity in colorectal cancer, the therapeutic activity of propranolol was then assessed in CT26WT tumors engrafted in BALB/C mice. Then the effect of propranolol treatment was also examined by randomizing patients undergoing surgical resection of a previously untreated colorectal cancer to propranolol or placebo group and treated for 1 week prior to surgery. CT26WT tumor size was smaller after propranolol than vehicle control. Propranolol downregulated the expression of p-AKT/p-ERK/p-MEK in tumor tissue. The frequency of tumor CD8+ T cells was significantly elevated in propranolol-treated mice. The expression of GzmB/IFN-γ/T-bet in the CD8+ T-cell population was significantly increased in propranolol treated mice tumor tissue. In propranolol-treated surgical specimens, the expression of p-ERK was decreased and the frequency of CD8+ was significantly elevated. The expression of GzmB in the CD8+ T-cell population was significantly increased in propranolol-treated subjects. Together, these data show propranolol simultaneously activating autologous CD8+ T cells and decreasing the expression of p-AKT/p-ERK/p-MEK in mouse tumor models, while inhibiting the expression of p-ERK in clinical colorectal cancer. Effort is now needed to further dissect whether both pathways are required for antitumor effect, as the activity of this old drug is moved forward.