FF-10502, an Antimetabolite with Novel Activity on Dormant Cells, Is Superior to Gemcitabine for Targeting Pancreatic Cancer Cells.

In this paper, we report that 1-(2-deoxy-2-fluoro-4-thio-ß-d-arabinofuranosyl) cytosine (FF-10502), a pyrimidine nucleoside antimetabolite with a chemical structure similar to gemcitabine, shows beneficial anticancer activity via a novel mechanism of action on dormant cells. The growth inhibition of pancreatic cancer cell lines by FF-10502 (IC50, 60-330 nM) was moderately weaker than that by gemcitabine in vitro. In contrast, an in vivo orthotopic implantation model in mice with established human pancreatic cancer cell line, SUIT-2, revealed no mortality with FF-10502 intravenous treatment, which was related to regression of implanted tumor and little metastasis, whereas 75% of the mice treated with gemcitabine died by day 128. Two in vivo patient-derived xenograft models with gemcitabine-resistant pancreatic cancer cells also demonstrated complete tumor growth suppression with FF-10502, but only partial inhibition with gemcitabine. We also investigated the mechanism of action of FF-10502 by using dormant cancer cells, which are reportedly involved in the development of resistance to chemotherapy. In vitro serum starvation-induced dormant SUIT-2 cells developed resistance to gemcitabine even in combination with DNA damage inducers (DDIs; H2O2, cisplatin, and temozolomide). Interestingly, FF-10502 in combination with DDIs significantly induced concentration-dependent cell death in accordance with enhanced DNA damage. FF-10502 was far more potent than gemcitabine in inhibiting DNA polymerase ß, which may explain the difference in dormant cell injury, although further investigations for direct evidences are necessary. In conclusion, our study demonstrated the beneficial antitumor effects of FF-10502 in clinically relevant in vivo models, and suggests the importance of preventing DNA repair unlike gemcitabine.

Molecular targeting of inosine-5'-monophosphate dehydrogenase by FF-10501 promotes erythropoiesis via ROS/MAPK pathway.

One of the major symptoms of myelodysplastic syndromes (MDS) is severe cytopenia. Despite cytokine therapies, such as erythropoiesis-stimulating agents, many patients still require blood transfusions, and the development of new therapeutic approaches is needed. In this work, we studied the effects of the inosine-5'-monophosphate (IMP) dehydrogenase (IMPDH) inhibitor FF-10501 on erythropoiesis of human hematopoietic cells. Differentiation of K562 chronic myeloid leukemia cells to an erythroid lineage was promoted by FF-10501 in a dose-dependent manner. Interestingly, we found that metabolic conversion of IMP to hypoxanthine leads to elevation of reactive oxygen species (ROS). The differentiative effects of FF-10501 were abolished by the ROS scavenger dimethylthiourea or the p38 MAPK inhibitor SB203580. Furthermore, FF-10501 promoted erythropoiesis from CD34+ hematopoietic stem/progenitor cells, accompanied with ROS accumulation, while high-dose FF-10501 mainly showed cytotoxic effects. These findings denote the potential of IMPDH inhibition therapy with FF-10501 in amelioration of anemia in MDS patients.