Ciclopirox (CPX) is contained in a number of FDA-approved topical antifungal drug products as the free acid and olamine salt. CPX possesses anticancer activity in a number of in vitro and in vivo preclinical models. Its clinical utility is limited as an oral anticancer agent, however. The oral bioavailability of CPX is quite low due to extensive first pass effect. The poor water solubility of CPX and its olamine salt prevent formulation as an injectable drug product. Thirdly, dose-limiting gastrointestinal toxicities were observed following four times daily oral dosing of CPX in patients with advanced hematologic malignancies. Ciclopirox Prodrug (CPX-POM), in contrast, has demonstrated excellent bioavailability via injectable routes of administration. Here we describe the preclinical characterization of CPX-POM, a novel anticancer agent being developed for the treatment of non-muscle invasive (NMIBC) and muscle invasive (MIBC) bladder cancer. Following IV, SQ and IP administration to mice, CPX-POM is rapidly and completely metabolized to CPX in blood via circulating phosphatases. CPX and its major, inactive glucuronide metabolite are extensively eliminated in urine. At well-tolerated doses, steady-state urine concentrations of CPX exceed in vitro IC50 values in mice by 15-30 fold. CPX inhibited cell proliferation, colony formation, and bladdosphere formation in vitro in T24 (NMIBC) and 253JBV (MIBC) human cell lines in both concentration- and time-dependent manners with IC50 values of 2-4 µM. CPX exposure increased the percentage of NMIBC and MIBC cells arrested at the S and G0/G1 phases, and induced cell death. CPX exposure significantly reduced expression of genes at the mRNA level involved in cancer stem cell signaling pathways including Notch, Wnt, and Hedgehog. CPX was shown to inhibit bladder cancer cell growth in vitro by inhibiting the Notch 1 signaling pathway. The validated N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) chemical carcinogen mouse model of bladder cancer was employed to establish in vivo preclinical proof of principle for CPX-POM. Over the once-daily IP dose range of 25-200 mg/kg, CPX-POM treatment resulted in significant decreases in bladder weight, a clear migration to lower stage tumors, dose-dependent reduction in Ki67 and PCNA staining, as well as a reduction in PCNA-expressing cells. All CPX-POM doses were well tolerated with no evidence of toxicity to the urinary tract based on blinded pathologic evaluation. There were also dose-dependent decreases in Notch 1, Presenilin 1, and Hey 1 in bladder cancer tissues obtained from CPX-POM treated animals. Tumor response was similar, in vivo, following once-daily and three-times weekly CPX-POM administration. CPX-POM has received FDA clearance to proceed to Phase I, and is currently being evaluated in a first-in-human trial in patients with advanced solid tumors.
Citation Format: Scott J. Weir, Partha Ranjarajan, Robyn Wood, Karl Schorno, Prabhu Ramamoorthy, Lian Rajweski, Kathy Heppert, Michael J. McKenna, William McCulloch, Greg A. Reed, Amanda Brinker, Michael J. Baltezor, Roy A. Jensen, John A. Taylor, Shrikant Anant. Bench-to-bedside translation of ciclopirox prodrug for the treatment of non-muscle invasive and muscle-invasive bladder cancer [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 5882.