Evaluation of Anti-Cancer Properties of Selective Histone Deacetylase 6 Inhibitors in Uveal Melanoma

Abstract

Purpose : Approximately 50% of patients diagnosed with uveal melanoma (UM) develop metastatic disease, with a median overall survival of 4 to 15 months. Current treatment options display limited benefit, hence, the need to identify novel drugs to treat primary and metastatic UM. Histone deacetylase 6 inhibitors (HDAC6i) show promise as anti-cancer agents and are under clinical trial investigation for several cancers. The goal of this study is to: 1) uncover the ability of select HDAC6i to prevent primary and metastatic UM cell growth in vitro and 2) to understand how HDAC6i prevent UM cancer hallmarks.

Methods : Correlation between HDAC6 expression and patient survival was determined in UM patient samples from The Cancer Genome Atlas (TCGA) database (n = 80). Survival of UM cells derived from primary (Mel285 and Mel270) and metastatic (OMM2.5) tumours was evaluated following selective inhibition of HDAC6, using clonogenic cell survival assays. Cells were treated with 10, 20 or 50 µM of three selective HDAC6i (Tubastatin A, ACY-1215 and Tubacin; N = 3) for 96 hours and cultured for an additional 10 days. Apoptotic populations were detected in ACY-1215 treated OMM2.5 cells (24 or 96 hours) by YOPRO-1/propidium iodide staining using flow cytometry. To uncover the mechanism of action of HDAC6i, mass spectrometry analysis was performed on whole proteome of OMM2.5 cells treated with 20 µM ACY-1215 for 24 hours (N = 4).

Results : HDAC6 expression in UM patient samples from TCGA database revealed that low levels of HDAC6 expression correlated to a statistically significant reduction in overall survival (p = 0.0033) and progression free survival (p = 0.024) probabilities. A dose dependent reduction in cell survival was observed across all three UM cell lines treated with HDAC6i. OMM2.5 cells treated with 50 µM ACY-1215 for 96 hours resulted in extensive apoptosis with <2% of cell populations surviving compared to vehicle controls (>90% survival). Whole proteome profiling of ACY-1215 treated OMM2.5 cells identified 4423 proteins with 352 significantly altered compared to vehicle control treated cells.

Conclusions : Our findings suggest that HDAC6i are efficacious as anti-UM agents. Further investigations will utilise in vivo zebrafish xenograft models and validation of mechanism of action.

This is a 2021 ARVO Annual Meeting abstract.