Conjunctival melanoma & histone deacetylase inhibitors

Abstract

Abstract Purpose: Conjunctival melanoma is a rare disease with a poor prognosis. Malignant conjunctival melanoma or primary acquired melanosis (PAM) with atypia are usually treated by surgical excision and cryotherapy. Topical mitomycin C (MMC) is also increasingly used for treating PAM with atypia. Histone deacetylase (HDAC) inhibitors can modify tumour growth and induce tumour cell death, and may be useful adjuvants for treating conjunctival melanoma. We examined the effects of HDAC inhibitors (sodium butyrate ‐ SB , Trichostatin A ‐ TSA) and MMC on the growth and survival of human conjunctival melanoma cells. Methods: Two conjunctival melanoma cell lines (CRMM‐1 & CRMM‐2), and primary human melanocytes and fibroblasts, were treated with SB (0‐8mM), TSA (0‐1uM), and MMC (0‐20ug/ml) for up to 72 hrs. Viability was assessed using MTT assays and cell counts. Inverted and fluorescence microscopy was used to assess morphology and cell death (DNA stains). Results: HDACs and MMC significantly decreased cell growth and viability in a concentration and time dependent manner for both conjunctival melanoma cell lines. Low concentration HDACs (<2mM SB; <0.1uM TSA) reduced melanoma cell growth, associated with morphological differentiation, particularly in CRMM‐1 cells. Melanocytes and fibroblasts remained viable with HDACs, although at maximal doses used (SB 8mM, TSA 1uM), some cell death was seen. At 48 hrs, MMC >5ug/ml killed >80% of CRMM‐1 & CRMM‐2 cells. Conclusions: These observations suggest that HDACs do not affect melanocyte and fibroblast viability at doses which can inhibit growth and survival of conjunctival melanoma cells. As such, these compounds may be useful for controlling conjunctival melanoma growth, alone or combined with topical agents such as MMC.