Adaphostin-Induced Oxidative Stress in Oesophageal Neuroendocrine Carcinoma: A Potential Therapeutic Strategy

Advanced oesophageal neuroendocrine carcinoma (ENEC) is a highly aggressive and rare malignancy with poor prognosis. Due to the rarity of this cancer there are currently no standardised treatment regimens for ENEC, and models to study this disease are difficult to obtain. To address this, we screened our established circulating tumour cell line from a patient with metastatic ENEC, termed UWG01CTC, using the LOPAC® ¹²⁸⁰ drug repurposing library. The redox modulatory agent adaphostin was identified as a potent cytotoxin against UWG01CTC but not non-ENEC cell lines. Secondary adaphostin cell viability screens returned IC ₅₀ values of 0.201 ± 0.024 µM confirming the high sensitivity of this ENEC CTC line to the drug. Inclusion of the antioxidant N-acetyl cysteine significantly protected the UWG01CTCs against the cytotoxic effects of adaphostin (IC ₅₀  = 0.928 ± 0.425 µM) corroborating a mechanism mediated through the generation of reactive oxygen species (ROS). The expression of DNA damage marker γH2AX and apoptotic marker cleaved-PARP1 were both elevated in cells treated with adaphostin, suggesting that the increased intracellular ROS levels induced by the drug causes downstream DNA damage and ultimately apoptosis. Thus, adaphostin shows promise as a potential new and selective treatment for ENEC.