CNDAC (2'-C-cyano-2'-deoxy-1-β-d-arabino-pentofuranosyl-cytosine, DFP10917) and its orally bioavailable
prodrug,
sapacitabine, are undergoing clinical trials for
hematologic malignancies and solid
tumors. The unique action mechanism of inducing
DNA strand breaks distinguishes
CNDAC from other
deoxycytidine analogs. To optimize the clinical potentials of
CNDAC, we explored multiple strategies combining
CNDAC with chemotherapeutic agents targeting distinct DNA damage repair pathways that are currently in clinical use. The ability of each agent to decrease proliferative potential, determined by clonogenic assays, was determined in paired cell lines proficient and deficient in certain DNA repair
proteins. Subsequently, each agent was used in combination with
CNDAC at fixed concentration ratios. The clonogenicity was quantitated by median effect analysis, and a combination index was calculated. The c-Abl
kinase inhibitor
imatinib had synergy with
CNDAC in HCT116 cells, regardless of p53 status. Inhibitors of PARP1 that interfere with homologous recombination (HR) repair or base excision repair (BER) and agents such as
temozolomide that cause DNA damage repaired by the BER pathway were also synergistic with
CNDAC. The toxicity of the
nitrogen mustards
bendamustine and
cytoxan, or of
platinum compounds, which generate
DNA adducts repaired by nucleotide excision repair and HR, was additive with
CNDAC. An additive cell killing was also achieved by the combination of
CNDAC with
taxane mitotic inhibitors (
paclitaxel and
docetaxel). At concentrations that allow survival of the majority of wild-type cells, the synergistic or additive combination effects were selective in HR-deficient cells. This study provides mechanistic rationales for combining
CNDAC with other active drugs. Mol
Cancer Ther; 15(10); 2302-13. ©2016 AACR.