Synergism between clofarabine and decitabine through p53R2: A pharmacodynamic drug-drug interaction modeling. Leuk Res. 2012;36:1410-1416. [PMID: 22884950 DOI: 10.1016/j.leukres.2012.07.015]

Genetic and epigenetic variants contributing to clofarabine cytotoxicity

2-chloro-2-fluoro-deoxy-9-D-arabinofuranosyladenine (Clofarabine), a purine nucleoside analog, is used in the treatment of hematologic malignancies and as induction therapy for stem cell transplantation. The discovery of pharmacogenomic markers associated with chemotherapeutic efficacy and toxicity would greatly benefit the utility of this drug. Our objective was to identify genetic and epigenetic variants associated with clofarabine toxicity using an unbiased, whole genome approach. To this end, we employed International HapMap lymphoblastoid cell lines (190 LCLs) of European (CEU) or African (YRI) ancestry with known genetic information to evaluate cellular sensitivity to clofarabine. We measured modified cytosine levels to ascertain the contribution of genetic and epigenetic factors influencing clofarabine-mediated cytotoxicity. Association studies revealed 182 single nucleotide polymorphisms (SNPs) and 143 modified cytosines associated with cytotoxicity in both populations at the threshold P ≤ 0.0001. Correlation between cytotoxicity and baseline gene expression revealed 234 genes at P ≤ 3.98 × 10(-6). Six genes were implicated as: (i) their expression was directly correlated to cytotoxicity, (ii) they had a targeting SNP associated with cytotoxicity, and (iii) they had local modified cytosines associated with gene expression and cytotoxicity. We identified a set of three SNPs and three CpG sites targeting these six genes explaining 43.1% of the observed variation in phenotype. siRNA knockdown of the top three genes (SETBP1, BAG3, KLHL6) in LCLs revealed altered susceptibility to clofarabine, confirming relevance. As clofarabine's toxicity profile includes acute kidney injury, we examined the effect of siRNA knockdown in HEK293 cells. siSETBP1 led to a significant change in HEK293 cell susceptibility to clofarabine.

Synergistic effect of 5-aza-2′-deoxycytidine and 5-fluorouracil in human gastric cancer cells

AIM: To examine the impact of DNA methyltransferase inhibitor 5-aza-2′-deoxycytidine (5-Aza-CdR) on gastric cancer cells and to unveile the interaction between 5-Aza-CdR and conventional chemotherapeutic agent 5-fluorouracil (5-Fu).

METHODS: Gastric cell lines expressing either wild-type P53 (AGS) or mutant-type P53 (BGC-823) were treated with 2.5 µmol/L of 5-Aza-CdR and/or 5-Fu for 0-96 h. Cell viability and proliferation were determined by 3-(4,5)-dimethylthiahiazo(-z-y1)-3,5-di-phenytetrazoliumromide (MTT) assay. Cell apoptosis was detected by annexin V staining. The activity of caspases was determined, and expression of downstream molecules was detected by Western blot.

RESULTS: Compared to untreated AGS and BGC-823 cells, treatment with 5-Aza-CdR significantly suppressed cell proliferation and viability in both cell lines in a time-dependent manner (both P < 0.01). In addition, 5-Aza-CdR induced marked apoptosis of AGS and BGC-823 cells in a time-dependent manner. However, the stimulation of distinct apoptotic pathways was largely dependent on P53 status. In AGS cells, 5-Aza-CdR-induced apoptosis was mediated by intrinsic apoptotic pathway which was modified dramatically by caspase 9. In BGC-823 cells expressing mutant P53, 5-Aza-CdR-induced apoptosis was dependent on caspase-independent apoptotic signaling due to the fact that we failed to observe elevated caspase activity or expression. 5-Aza-CdR in combination with 5-FU showed significant synergistic effects in both AGS and BGC-823 cells, implying that 5-Aza-CdR could efficaciously sensitize the responses of both cell lines to 5-Fu.

CONCLUSION: Our findings strongly demonstrate that 5-Aza-CdR is a potential anti-gastric cancer candidate. 5-Aza-CdR and 5-Fu have significant synergistic effects in human gastric cancer cells.