Distinct histone modifications denote early stress-induced drug tolerance in cancer

Area of Science:

• Cancer Biology
• Epigenetics
• Drug Resistance

Background:

• Acquired drug resistance in cancer is a complex challenge.
• Epigenetic reprogramming, beyond mutations or drug efflux, is a key mechanism.
• Induced drug-tolerant cells (IDTCs) represent an early-stage, stress-induced state of multi-drug tolerance.

Purpose of the Study:

• To investigate the epigenetic alterations associated with induced drug-tolerant cells (IDTCs).
• To identify common epigenetic changes across different cancer types during the development of multi-drug tolerance.
• To explore the role of histone methylation patterns and specific histone methyltransferases in IDTC formation and drug tolerance.

Main Methods:

• Generation of IDTCs from melanoma, lung, breast, and colon cancer cell lines.
• Analysis of histone modifications (H3K4me3, H3K27me3, H3K9me3) using genome-wide studies.
• Gene expression analysis (microarray, qRT-PCR) and protein expression studies.
• Assessment of DNA methylation patterns.
• Functional studies involving silencing of histone methyltransferases (SETDB1/2).

Main Results:

• A common epigenetic signature in IDTCs across cancer types: loss of H3K4me3 and H3K27me3, and gain of H3K9me3.
• These histone mark alterations were reversible upon removal of the drug or stressor.
• Up-regulation of histone methyltransferases SETDB1 and SETDB2 was observed, correlating with H3K9me3 accumulation.
• Transcriptional repression of genes was linked to the loss of H3K4me3 and regional increase of H3K9me3.
• No common changes in genome-wide CpG site-specific DNA methylation were found in IDTCs.
• Silencing of SETDB1/2 reversed multi-drug tolerance.

Conclusions:

• Distinct histone methylation patterns, particularly the interplay of H3K9me3, H3K4me3, and H3K27me3, drive the transition to multi-drug tolerance.
• Histone modifications, rather than DNA methylation, are the primary epigenetic drivers of this early drug tolerance state.
• The observed epigenetic alterations represent a generic response to stress and drug exposure, not specific to cancer type.
• Targeting histone methyltransferases like SETDB1/2 offers a potential therapeutic strategy to overcome acquired drug resistance.