by H. Lee Moffitt Cancer Center & Research Institute

HDAC8 increases the establishment of melanoma brain metastases. a–c HDAC8 and EV expressing WM164 cells were introduced into NOD.CB17-Prkdcscid/J mice by intracardiac injection. a Tumors were allowed to establish for indicated time points with numbers of metastases measured in H&E sections of the liver and lung. Number of metastases present in the (b) liver and (c) lungs were calculated using Imagescope. Significance in (b) and (c) was determined by a one-way ANOVA followed by a 2-tailed post hoc t test with *=p < 0.05, and #=p > 0.05. In (b), day 5 p = .0213. Data are presented as mean values of 5 mice ±SD. d–f HDAC8 and EV expressing WM164, SK-MEL-28 and 1205Lu cells were introduced into NOD.CB17-Prkdcscid/J mice by intracardiac injection and allowed to incubate for 14 days. d Number of mice with brain tumors were counted for each condition using Imagescope software. Significance in (d) was determined by a 2-sided chi-squared test on an n of 20 mice in WM164 cells and an n of 10 mice in SK-MEL-28 cells with **=p < 0.01. (WM164: p = 0.0035 and SK-MEL-28: p = 0.0098). e Number of brain metastases per mouse brain under each condition were counted using Imagescope software. Significance was determined by a one-way ANOVA followed by a 2-tailed t test on an n of 20 mice in WM164 cells, an n of 10 mice in SK-MEL-28 cells and an n of 3 mice in 1205Lu cells with *=p < 0.05 (WM164 p = 0.0109, SK-MEL-28 p = 0.0291, 1205Lu p = 0.0463). f Embedded brain sections were stained with H&E and an IHC for PMEL (gp100) to determine tumor formation. Scale bars in 1x images = 4 mm. Scale bars in 10x images = 300 µm. g Patient-derived scRNA-Seq data (#’s=melanoma cutaneous samples, LMD melanoma leptomeningeal metastasis samples, MB melanoma brain metastases samples) were interrogated for expression of NCSC genes. (Left: sample level data for melanoma cells. Right: Expression of the NCSC gene signature in the melanoma cells). h A Spearman correlation analysis was run to determine the relationship of HDAC8 expression and the NCSC gene expression signature from the human scRNA-Seq data. A p value p < 0.05 corresponds to a significant correlation. Source data are provided as a Source Data file. Credit: Nature Communications (2023). DOI: 10.1038/s41467-023-43519-1

Melanoma is the deadliest form of skin cancer because of its ability to quickly grow and spread throughout the body. More than half of those with advanced melanoma will see the disease spread to the brain, where it rapidly progresses, often leading to death in only three to four months. Researchers in Moffitt Cancer Center's Donald A. Adam Melanoma and Skin Cancer Center of Excellence have been working to better understand what drives melanoma brain metastasis.

In a new study published in Nature Communications, they report on the identification of a cell signaling pathway that regulates the metastatic spread of melanoma cells to the brain.

Melanoma tumors comprise subgroups of cells with different gene expression patterns with varied abilities to invade surrounding tissues and survive anticancer treatments. It is unclear how these different melanoma subgroups contribute to tumor development and progression.

In previous studies, Moffitt researchers determined that the protein HDAC8 regulated resistance to BRAF and MEK inhibitors commonly used to treat melanoma. HDAC8 removes chemical modifications called acetyl groups from other proteins, leading to alterations in gene expression patterns. The Moffitt team hypothesized that HDAC8 may also be involved in regulating gene expression patterns of melanoma cell subgroups.

The researchers performed laboratory experiments demonstrating that HDAC8 activity increased melanoma cell survival under stress conditions, including low oxygen, UV radiation, and BRAF/MEK inhibitor treatment. HDAC8 activity also changed the gene expression pattern of melanoma cells and caused the cells to develop characteristics associated with cell subgroups that could migrate into and invade surrounding sites.

Their pre-clinical experiments found that increased HDAC8 expression and activity enhanced the ability of melanoma cells to metastasize to the brain, while no significant impact was observed in the number of metastatic tumors to other organs, such as the liver or lung. The researchers further investigated the molecular pathways of HDAC8-mediated brain metastasis and discovered that HDAC8 chemically modified the protein EP300, which subsequently caused cells to develop invasive characteristics.

The researchers confirmed the importance of EP300 to melanoma brain metastases by showing that increased expression of EP300 decreased cell invasion and caused melanoma cells to be more sensitive to cell death.

"These data show the importance of HDAC8 and EP300 activity to melanoma cell invasion to the brain and suggest that agents that target these pathways may inhibit brain metastasis," said Keiran Smalley, Ph.D., lead study author and director of Moffitt's Melanoma and Skin Cancer Center of Excellence. "Our work provides the first evidence that stress-induced HDAC8 is a regulator of an invasive melanoma cell state that leads to increased brain metastasis."

More information: Michael F. Emmons et al, HDAC8-mediated inhibition of EP300 drives a transcriptional state that increases melanoma brain metastasis, Nature Communications (2023). DOI: 10.1038/s41467-023-43519-1

Journal information: Nature Communications 

Provided by H. Lee Moffitt Cancer Center & Research Institute