Exposure to a histone deacetylase inhibitor has detrimental effects on human lymphocyte viability and function

Area of Science:

• Immunology
• Oncology
• Pharmacology

Background:

• Histone deacetylase inhibitors (HDACi) enhance tumor antigen expression and show promise as adjuvants for melanoma immunotherapy in preclinical models.
• Panobinostat (LBH589) is a pan-HDAC inhibitor investigated for its effects on human immune cells and melanoma.

Purpose of the Study:

• To evaluate the effects of panobinostat on human lymphocytes and melanoma cell lines.
• To determine the therapeutic window of panobinostat for potential use in melanoma treatment.

Main Methods:

• Assessed cell viability, cell cycle, apoptosis, and DNA damage in peripheral blood mononuclear cells (PBMC) and melanoma cell lines using panobinostat.
• Analyzed intracellular signaling pathways in lymphocytes via phospho-flow cytometry.
• Determined IC50 values and measured phospho-histone variant H2A.X (pH2A.X) levels.

Main Results:

• Panobinostat exhibited significantly higher cytotoxicity in PBMCs (IC50 <20 nmol/L) compared to melanoma cell lines (>600 nmol/L).
• Apoptotic cell death was greater in PBMCs (>40%) than in melanoma cells (<10%) at equivalent concentrations.
• Panobinostat induced DNA damage (pH2A.X increase) at lower concentrations in healthy PBMCs than in melanoma cells, but showed inhibition in patient PBMCs and melanoma cells.
• Signaling pathway analysis revealed inhibition in healthy lymphocytes but activation in melanoma patient samples.

Conclusions:

• Panobinostat demonstrates a narrow therapeutic window due to its potent cytotoxicity towards human lymphocytes at concentrations lower than those effective against melanoma.
• The differential effects on immune cells versus tumor cells suggest potential challenges for its use as an adjuvant in melanoma immunotherapy.
• Further research is needed to optimize HDACi strategies for melanoma treatment, considering immune system modulation.