Standardized workflow enables reproducibility of drug synergism detection: Results from a multi-center in vitro ring test on complex drug combinations in pancreatic cancer models.

In the framework of REMEDi4ALL's mission to strengthen reproducibility in drug repurposing, we conducted a multicenter ring study to evaluate the reproducibility and translational value of combining histone deacetylase inhibitors (HDACi) with simvastatin (SIM) in pancreatic ductal adenocarcinoma (PDAC) cells. Initial inconsistencies due to misaligned protocols were resolved through harmonized SOPs across three European laboratories (INT-NA, ITMP, KI), enabling robust and comparable results. Under standardized procedures, valproic acid (VPA) and SIM emerged as the most synergistic combination, confirming our previous findings. The reproducible enhancement of antitumor activity when VPA/SIM was added to the standard chemotherapy (gemcitabine+nab-paclitaxel) further supports its translational relevance. Beyond validating this drug combination, the resulting open dataset enables systematic evaluation of technical confounders affecting drug sensitivity and provides a reference for data harmonization across heterogeneous assay platforms. All centers independently delivered high-quality data, demonstrating their readiness for future REMEDi4ALL repurposing efforts with enhanced rigor, robustness and interoperability.