Combination of S-1 and the oral ATR inhibitor ceralasertib is effective against pancreatic cancer cells

PurposeIn our previous study, we found that the Chk1 inhibitor prexasertib enhances the antitumour effect of the oral anticancer drug S-1 against pancreatic cancer cells. In this study, we investigated the effect of combining S-1 and ceralasertib, an oral inhibitor of ATR, which is located upstream of Chk1. Ceralasertib is currently being investigated in multiple clinical trials for various cancers.MethodsThe cell-proliferation inhibitory effect was measured by MTT assay, using the pancreatic cancer cell lines BxPC-3, SUIT-2, PANC-1, and MIA PaCa-2, while apoptosis was measured by flow cytometry using PI/Annexin staining. The mechanism underlying the combined effect was analysed using western blotting, and the antitumor effect was analysed using a mouse xenograft model.ResultsMTT assay revealed that the combination of S-1 and ceralasertib had a synergistic effect, leading to the suppression of cell proliferation. Measurement with PI/Annexin staining revealed that the combination of S-1 and ceralasertib induced apoptosis more efficiently than either drug alone. Western blotting results showed that ceralasertib inhibited S-1-induced activation of ATR and Chk1. The average estimated tumour volume after 3 weeks of administration was 601 mm3 in the S-1 group, 580 mm3 in the ceralasertib group, and 298 mm3 in the combination group.ConclusionThe combination of S-1 and ceralasertib demonstrated a high antiproliferative effect in inhibiting tumour growth in vitro.