Propranolol suppresses bladder cancer by manipulating intracellular pH via NHE1.

Background: In recent years, a large number of clinical and epidemiological studies have revealed the anti-cancer activity of propranolol in solid tumors, though the underline mechanism is yet to be clarified. Methods: The proliferation of bladder cancer cells treated with propranolol was detected by MTS assays. In vivo tumor xenograft experiments were used to observe the effect of propranolol on bladder cancer growth in mice. The expression levels of Na+/H+ exchanger (NHE1) was measured by western blot. The frequency of CD8+ T cells and CD4+ T cells were detected via flow cytometry. Results: In this study, propranolol inhibited the expression of NHE1 and sequentially led to a decrease of intracellular pH to 5.88 in MB49 cells and 6.85 in 5637 cells, thereafter, inhibited cell viability and induced apoptosis. Furthermore, propranolol inhibited the growth of bladder cancer in mice xenograft model. Flow cytometry found that the frequency of CD8+ T cells (34.58±2.11 vs. 32.34±0.6, P=0.35) and CD4+ T cells (57.80±2.45 vs. 51.44±0.79, P=0.06) in the spleen did not change compared with the control group, while the expression of IFN-γ, GZMB and T-bet secreted by CD8+ T cells increased respectively (IFN-γ 7.3±0.17 vs. 3.37±0.58, P=0.0017; GZMB 16.66±2.13 vs. 4.53±0.62, P=0.0034; T-bet 3.62±0.35 vs. 1.74±0.26, P=0.0027). Meantime, the expression of FoxP3 on CD4+ T cells decreased both in spleen and tumor tissue (1.53±0.11 vs. 0.91±0.1, P=0.004; 4.52±0.48 vs. 1.76±0.40, P=0.003). Conclusions: These results suggested that propranolol exerted anti-proliferation and pro-apoptosis effects in bladder cancer cell by inhibiting Na+/H+ exchange and activated systemic anti-tumor immune response in vivo.

PARPi treatment enhances radiotherapy-induced ferroptosis and antitumor immune responses via the cGAS signaling pathway in colorectal cancer.

In cancer cells, poly (ADP-ribose) polymerase (PARP)-1 and PARP2 initiate and regulate DNA repair pathways to protect against DNA damage and cell death caused by radiotherapy or chemotherapy. Radiotherapy and PARP inhibitors (PARPis) have been combined in clinical trials, but their action mechanisms remain unclear. Here, we show that activated by ionizing radiation (IR) generated dsDNA, cyclic GMP-AMP synthase (cGAS) signaling promoted regulated cell death, specifically ferroptosis, via the activating transcription factor 3 (ATF3)-solute carrier family 7 member 11 axis and the antitumor immune response via the interferon-ß-CD8+ T cell pathway. Niraparib, a widely used PARPi, augmented cGAS-mediated ferroptosis and immune activation. In colorectal cancer models, cGAS knockdown (KD) compromised IR-induced ferroptosis via downregulation of ATF3 (key ferroptosis regulator) expression. cGAS depletion reversed IR-induced infiltration of CD8+ T or CD8+GZMB+ T cells in the cGAS KD group. Survival analysis of paired tumor samples before and after standard radiotherapy revealed that high expression levels of cGAS, ATF3, and PTGS2 and high density of CD8+ T cells resulted in a significantly high disease-free survival rate in patients with rectal cancer. Therefore, PARPi treatment increases the cytoplasmic accumulation of dsDNA caused by IR, triggering the cGAS signaling-mediated tumor control in cancer cell lines and mouse xenograft models.

Dissecting the role of cell signaling versus CD8+ T cell modulation in propranolol antitumor activity.

Preclinical and early clinical mechanistic studies of antitumor activity from the beta-adrenergic receptor (ß-AR) blocker propranolol have revealed both cell signaling and immune function pathway effects. Intertumoral studies were performed using propranolol, a ß1-AR selective agent (atenolol), and a ß2-AR selective agent (ICI 118,551) in a preclinical in vivo model, as a step to dissect the contribution of cell signaling and CD8+ immunological effects on anticancer activity. We found that repression of ß2-AR but not ß1-AR signaling selectively suppressed cell viability and inhibited xenograft growth in vivo. Moreover, western blot analysis indicated that the phosphorylation levels of AKT/MEK/ERK were significantly decreased following the inhibition of ß2-AR. Furthermore, propranolol was found to activate the tumor microenvironment by inducing an increased intratumoral frequency of CD8+ T cells, whereas neither selective ß1 nor ß2-AR blockers had a significant effect on the tumor immune microenvironment. Thus, the results of this mechanistic dissection support a predominant role of tumor cell signaling, rather than the accumulation of CD8+ T cells, as the basis for propranolol antitumor activity. KEY MESSAGES : Molecular signaling of AKT/MAPK pathway contributes to propranolol caused cancer control. CD8+ T cells in tumor microenvironment were activated upon propranolol exposure. The basis for propranolol antitumor activity was predominantly dependent on cell signaling, rather than the activation of CD8+ T cells.