Riluzole Enhancing anti-PD-1 Efficacy by Activating cGAS/STING Signaling

Colorectal cancer is the second leading cause of cancer mortality in the US. Although immune checkpoint blockade therapies such as anti-PD-1/PD-L1 have had successes in some patients, the response rate is still low. We have found that riluzole, a well-tolerated FDA-approved oral medicine for treating amyotrophic lateral sclerosis, increased intratumoral CD8+ T cells and suppressed tumor growth of colon cancer cells in syngeneic immune competent mice. Riluzole-mediated tumor suppression was dependent on the presence of CD8+ T cells. Riluzole activates the cytosolic DNA sensing cGAS/STING pathway and increases expression of interferon β (IFNβ) and IFNβ-regulated genes including CXCL10. Inhibition of ATM, but not ATR, results in a synergistic increase in IFNβ expression, suggesting that riluzole-dependent double strand breaks contribute to cGAS/STING activation. Knockout of cGAS or STING significantly attenuated expression of IFNβ and CXCL10 and nearly abolished suppression of tumor growth. Riluzole failed to increase intratumoral CD8+ T cells in STING knockout tumors. These results indicate that riluzole recruits CD8+ T cells into the tumor microenvironment through tumor cell intrinsic STING activation. When riluzole was combined with a PD-1 antibody, the treatment was more effective in suppressing tumor growth in vivo. Taken together, our studies indicate that riluzole inhibits tumor growth through the activation of cGAS/STING signaling and may increase the efficacy of anti-PD-1/PD-L1 therapies in colon cancer.