A54
The role of Histone Deacetylase 4 (HDAC4) and its involvements in cisplatin resistant ovarian cancer
Albanderi Alfraidi, Nona Rama, Roberto Dina, Charles Gourley, Caroline Michie, Antonello Mai, Robert Brown, Hani Gabra, Euan Stronach
Imperial College London, London, UK
Background
Development of resistance to chemotherapy is a major obstacle in the treatment of ovarian cancer. Expression profiling of isogenically paired ovarian cancer cell-lines (derived from patients before and after acquired cisplatin resistance) identified overexpression of HDAC4 in the resistant cells.
Method
Using siRNA coupled to caspase 3/7 based apoptosis assays we assessed the effect of HDAC4 knockdown on platinum sensitivity. Small molecule HDAC inhibitors were used to corroborate this evidence. We assessed the involvement of other HDACs in our systems and considered their interactions by immunoprecipitation. Downstream consequences of HDAC modulation were assessed by western blots. HDAC4 levels were assessed by immunohistochemistry in a series of 16 paired FFPE tumour blocks representing pre and post acquired platinum resistance.
Results
SiRNA knockdown of HDAC4 in resistant cells enhanced platinum induced apoptosis, suggesting a functional role for HDAC4 in resistance. Treatment using an aroyl-pyrrolyl-hydroxy-amide (APHA) derived HDAC inhibitor resulted in loss of HDAC4 and potent enhancement of cisplatin-mediated apoptosis. Analysis of the expression of Class I, II and IV HDACs across our isogenic cell lines revealed similar patterns for HDAC4, HDAC1 and HDAC3. SiRNA knockdown of HDAC1, and less-so HDAC3, also enhanced platinum sensitivity. Binding of HDAC4:HDAC1 and HDAC4:HDAC3 was identified by immunoprecipitation. We assessed the effect of HDAC4 on modulation of p21 as upregulation has been reported following HDACi treatment. In our cisplatin-sensitive cell lines p21 was upregulated following HDAC4 knockdown however p21 expression decreased in the cisplatin-resistant paired counterparts, indicating fundamentally altered regulation of p21 by HDAC4 in acquired platinum-resistance. Assessment of HDAC4 expression in paired pre and post resistance FFPE blocks revealed significant HDAC4 upregulation in the resistant ovarian tumours (Wilcoxon signed-rank test, p=0.0413).
Conclusion
These studies indicate a role for HDAC4 as a mediator of platinum resistance in ovarian cancer and suggest HDAC4 as a potential biomarker and/or therapeutic target for reversal of acquired platinum resistance in ovarian cancer.
