Pantoprazole and riluzole target H⁺/K⁺-ATPases and pH-sensitive K⁺ channels in pancreatic cancer cells

Pancreatic ductal adenocarcinoma (PDAC) remains the most lethal cancer type. PDAC is characterized by fibrotic, hypoxic, and presumably acidic tumor microenvironment (TME). Acidic TME is an important player in tumor development, progression, aggressiveness, and chemoresistance. The dysregulation of ductal ion transporters/channels might contribute to extracellular pH (pH_e) acidification and PDAC progression. Our aim was to test whether H⁺/K⁺-ATPases and pH-sensitive K⁺ channels contribute to these processes and could be targeted by clinically approved drugs. We used human pancreatic cancer cells adapted to various pH_e conditions and grown in monolayers and spheroids. First, we created cells expressing pHoran4 at the outer plasma membrane and showed that pantoprazole, the H⁺/K⁺-ATPase inhibitor, alkalinized pH_e. Second, we used FluoVolt to monitor the membrane voltage (V_m) and showed that riluzole hyperpolarized V_m, most likely by opening of pH-sensitive K⁺ channels such as TREK-1. Third, we show that pantoprazole and riluzole inhibited cell proliferation and viability of monolayers and spheroids of cancer cells adapted to various pH_e conditions. Most importantly, combination of the two drugs had significantly larger inhibitory effects on PDAC cell survival. We propose that co-targeting H⁺/K⁺-ATPases and pH-sensitive K⁺ channels by re-purposing of pantoprazole and riluzole could provide novel acidosis-targeted therapies of PDAC.