| dc.description.abstract | Cisplatin, a DNA damaging agent, is the common chemotherapy drug for various kind
of cancer which has been shown its limitation in providing side effects and developing
resistance. Combining drugs with less toxicity to normal cells may enhance the efficacy of
cisplatin chemotherapy. Selenocystine is proven to have anticancer effect and selective
mechanism by targeting cancer cells but not non-cancerous cell lines. The current study is
aimed to investigate whether a combination treatment between Cisplatin (cDDP) and
Selenocystine (SeC) may improve the therapeutic effect against liver cancer cells. We found
out that pretreatment SeC followed by cDDP exhibited more inhibition than HepG2 or Hep3B
cells with the treatment of single drug exposure, while there was only little effect shown in L02 normal liver cells. This significant decrease was correlated with DNA damage response as
both cDDP and SeC have been proven their ability to elicit DNA damage. In the genotoxicity
level, pretreatment 10 µM SeC for 1 hour, followed by 5 µM cDDP for 24 hours, generated
significant DNA damage in alkaline and neutral comet assay, indicating single- and doublestrand breaks occurrence. Subsequent phosphorylation of H2AX, DNA Double Strand Break
(DSB) of biomarker, resulted in activation of DNA repair pathways. To determine the
response of DSBs, we investigated the implication of Homologous Recombination (HR) and
Non-Homologous End-Joining (NHEJ) repair pathways. We observed that significant
increase of RAD51 level treated by cDDP can be suppressed by pretreatment of SeC.
Moreover, combination treatment exhibited the most significant blocking of HR repair
activity in HepG2 cells compared to each single drug exposure. Another DSB repair pathway,
Non-Homologous End-Joining (NHEJ) showed that expression level of Ku-70 and Ku-80
showed no considerable effect, but downstream proteins involved in NHEJ such as Artemis,
XRCC4, and DNA Ligase IV resulted in a significant decrease by combination treatment.
These results suggested that combination treatment of SeC and cDDP can block DNA DSBs
repair pathways via HR and NHEJ. Taken together, our study demonstrated that
Selenocystine can selectively enhance Cisplatin sensitivity to promote cell death through
induction of DNA damage and inhibition of DNA repair pathways. | en_US |