Valproic acid (VPA), a class I and II histone deacetylase (HDAC) inhibitor and conjunctival melanoma

• Published in: Acta ophthalmologica (Oxford, England) England), 2012-09, Vol.90 (s249), p.0-0
• Main Authors: MADIGAN, MC, MUNOZ‐ERAZO, L, CONWAY, RM
• Format: Article
• Language: English
• Subjects: Cell cycle; Cellular biology; Ophthalmology; Proteins
• ISSN: 1755-375X; 1755-3768
• DOI: 10.1111/j.1755-3768.2012.3682.x

Purpose To investigate the expression of histone deacetylases (HDACs) in human conjunctival melanoma (CM) cell lines and primary melanocytes, and assess the effects of VPA, a broad Class I and II HDAC inhibitor, on cell viability and growth. Methods CM cell lines (CRMM1 & 2; CM2005.1) and primary melanocytes were immunolabelled with antibodies to HDACs: Class I (HDAC1, 2 and 3), Class IIA and IIB (HDAC4 and HDAC6), and Class III (SIRT2). Antibody localisation was visualised with immunofluorescence and confocal microscopy. Dose‐response and proliferative potential following treatment with VPA was assessed for up to 72hrs using MTT and colony assays, respectively Cell cycle dynamics were also assessed. Results Differential HDAC expression was observed in CM cells and melanocytes, for both immunolocalisation (nuclear vs cytoplasmic) and cell type. CM2005.1 cells displayed lower level expression of HDACs compared to CRMM1 and 2 cells. VPA IC50 (72hrs) was 3.75mM, 5.42mM and 8.33mM for CRMM1, 2 and CM2005.1 cells, respectively. Colony assays showed similar patterns of response, with surviving fractions 0.2 and 0.5 for CRMM1 (VPA 0.3125mM) and CRMM2 (VPA 2.5mM) respectively. Cell cycle analysis showed dose‐related G1 block for CRMM1 and G2 block for CRMM2 cells at 24hrs (0mM to 1.25mM VPA). Conclusion Overall, CM2005.1 cells are more resistant to VPA compared to CRMM1 and 2 cells. VPA inhibition of CM cell growth and proliferation may be related to the observed differential expression of HDACs between cell lines. Combination therapies using VPA and other HDAC inhibitors may be potentially useful in managing the growth of primary CM. Supported by Sydney Foundation for Medical Research.