Abstract 2865: Ciclopirox olamine: A common antifungal agent that inhibits growth of esophageal tumor cells in vitro and in vivo

Esophageal carcinoma continues to carry a poor prognosis due presentation at advanced stages. Current chemotherapeutics often only prolong survival for months to a few years. Drug repositioning is an important pharmacologic strategy that involves investigation and implementation of known drugs for treatment of new diseases. This method significantly reduces the costs required for establishing the safety of a drug and is associated with higher rates of drug approval. Ciclopirox olamine (CPX) is an antifungal agent that has been on the market since the 1970s. The mechanism of action is believed to include disruptions of DNA repair and cell division signals. Recently, however, this drug has been studied for its antitumor properties demonstrated in human rhabdomyosarcoma, breast carcinoma, colon adenocarcinoma, bladder carcinoma, and hematologic malignancies. To date, there are no studies related to the effect of CPX on esophageal cancer. Here, we show that ciclopirox olamine causes growth inhibition of four esophageal cell lines: TE-10, SKGT4, FLO1 and ESO1. This growth inhibition is demonstrated by hexosaminidase assay performed after incubation with the drug for 24-72 h. The IC50 values range between 5-20µM depending on the cell line used. Cell death was also demonstrated by immunofluorescent staining with Hoschst and propidium iodide, which shows a decrease in the number of viable cells with increasing concentrations of CPX. Clonogenicity assay was also performed with each cell line and demonstrates a decrease in the ability of cells to form colonies after 24 and 48 hour treatment with CPX and subsequent incubation in standard media for 5-7 days. Cell cycle analysis demonstrates G0/G1 arrest in cells treated with CPX. The effects of CPX on the cell cycle are further supported by Western blot analysis showing a decrease in in CDK4 and CDK6, which are necessary for cell cycle progression from the G0/G1 phase. We have also found that treatment with CPX results in a decrease in β-catenin in TE10 cells, suggesting that the drug is affecting this pathway to cause growth inhibition of tumor cells. Finally, we used our ESO1 mouse esophageal squamous cell carcinoma cell line for a xenograft study in which tumor cells were injected into the flanks of mice. Mice treated with intraperitoneal injections of 300 mg/m2 of CPX had smaller tumor volumes compared to untreated controls. In summary, we have shown that CPX inhibits growth of esophageal tumor cells both in vitro and in vivo. Our data suggest that CPX induces cell cycle arrest of tumor cells. The mechanism of tumor cell inhibition may be related to downregulation of the WNT/β-catenin signaling pathway. In future studies, we plan to analyze the effects of CPX on other components in the WNT family from in vitro cells as well as tumor xenografts. Citation Format: Randi J. Ryan, Prabhu Ramamoorthy, Dharmalingam Subramaniam, Shrikant Anant, Scott Weir. Ciclopirox olamine: A common antifungal agent that inhibits growth of esophageal tumor cells in vitro and in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2865.