A ferrocene-containing nucleoside analogue targets DNA replication in pancreatic cancer cells

Abstract

Pancreatic ductal adenocarcinoma ( PDAC ) is a disease that remains refractory to existing treatments including the nucleoside ana- logue gemcitabine. In the current study we demonstrate that an organometallic nucleoside analogue, the ferronucleoside 1- ( S ,R p ) , is cytotoxic in a panel of PDAC cell lines including gemcitabine-resistant MIAPaCa2, with IC 50 values comparable to cisplatin. Biochemical studies show that the mechanism of action is inhibition of DNA replication, S-phase cell cycle arrest and stalling of DNA-replication forks, which were directly observed at single molecule resolution by DNA-fibre fluorography. In agreement with this, transcriptional changes following treatment with 1- ( S ,R p ) include activation of three of the four genes ( HUS1 , RAD1 , RAD17 ) of the 9-1-1 check point complex clamp and two of the three genes ( MRE11 , NBN ) that form the MRN complex as well as activation of multiple downstream targets. Furthermore, there was evidence of phosphorylation of checkpoint kinases 1 and 2 as well as RPA1 and gamma H2AX, all of which are considered biochemical markers of replication stress. Studies in p53-deficient cell lines showed activation of CDKN1A ( p21 ) and GADD45A by 1- ( S ,R p ) was at least partially independent of p53. In conclusion, because of its potency and activity in gemcitabine- resistant cells, 1- ( S ,R p ) is a promising candidate molecule for development of new treatments for PDAC.