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Pancreatic cancer DNMT1 expression and sensitivity to DNMT1 inhibitors
Ang Li1, Noriyuki Omura1, Seung-Mo Hong1
1Department of Pathology, The Johns Hopkins University School of Medicine.
Abstract:
DNA methyltransferase I (DNMT1) is the major methyltransferase responsible for methylating DNA and is overexpressed in many cancers. DNMT1 is also a therapeutic target for chemotherapy and chemoprevention. We hypothesized that loss of DNMT1 copy number could result in reduced DNMT1 levels and greater sensitivity to DNMT1 inhibitors. We examined DNMT1 expression in pancreatic cancers by immunohistochemistry and western blotting. We also examined DNMT1 copy number in 20 pancreatic cancer cell lines using Affymetrix SNP arrays and correlated copy number with DNMT1 expression. We tested 8 pancreatic cancer cell lines with DNMT1 inhibitors and measured growth inhibition. We identified overexpression of DNMT1 relative to normal pancreatic duct in 78.7% of pancreatic cancers (37/47) by immunohistochemistry and in 16/20 pancreatic cancer cell lines by western blot. Pancreatic cancer cell lines with loss of DNMT1 alleles tended to have lower DNMT1 expression (3 of 9 cell lines) compared to those without DNMT1 copy number loss (1 of 11). 5-aza-deoxycytidine (5-Aza-dC) treatment (1-10 uM) depleted DNMT1 in 7 of 8 pancreatic cancer cell lines. Three of four pancreatic cancers cell lines with low/normal DNMT1 expression were sensitive to growth inhibition by low dose 5-Aza-dC (1 uM), whereas only 1 of 4 cell lines with high DNMT1 expression had growth inhibition, and this occurred without evidence of DNMT1 depletion suggesting a different mechanism for growth inhibition in this cell line. Loss of DNMT1 alleles may reduce DNMT1 levels in some pancreatic cancers. Pancreatic cancers with low DNMT1 expression tend to be more sensitive to low-dose 5-azadeoxycytidine.
Insights
DNA methyltransferase I (DNMT1) is overexpressed in pancreatic cancers and is a therapeutic target. Loss of DNMT1 copy number may reduce its levels, potentially increasing sensitivity to DNMT1 inhibitors like 5-aza-deoxycytidine.
Area of Science:
- Oncology
- Molecular Biology
- Cancer Therapeutics
Background:
- DNA methyltransferase I (DNMT1) is crucial for DNA methylation and frequently overexpressed in various cancers.
- DNMT1 is a validated therapeutic target for chemotherapy and chemoprevention strategies.
- Understanding DNMT1 copy number alterations and their impact on drug sensitivity is vital for pancreatic cancer treatment.
Purpose of the Study:
- To investigate the correlation between DNMT1 copy number, DNMT1 expression levels, and sensitivity to DNMT1 inhibitors in pancreatic cancer.
- To determine if reduced DNMT1 copy number leads to decreased DNMT1 levels and enhanced sensitivity to DNMT1 inhibitors.
- To evaluate the efficacy of 5-aza-deoxycytidine (5-Aza-dC) in pancreatic cancer cell lines with varying DNMT1 expression and copy numbers.
Main Methods:
- Immunohistochemistry and western blotting were used to assess DNMT1 expression in pancreatic cancer tissues and cell lines.
- Affymetrix SNP arrays were employed to determine DNMT1 copy number in 20 pancreatic cancer cell lines.
- Pancreatic cancer cell lines were treated with DNMT1 inhibitors (5-Aza-dC) to measure growth inhibition and DNMT1 depletion.
Main Results:
- DNMT1 was overexpressed in 78.7% of pancreatic cancers and 16/20 cell lines.
- Pancreatic cancer cell lines with DNMT1 copy number loss showed a trend towards lower DNMT1 expression.
- Low/normal DNMT1 expression correlated with increased sensitivity to low-dose 5-Aza-dC, while high DNMT1 expression showed less sensitivity or different mechanisms of growth inhibition.
Conclusions:
- Loss of DNMT1 alleles can contribute to reduced DNMT1 levels in some pancreatic cancers.
- Pancreatic cancers with lower DNMT1 expression appear more sensitive to low-dose 5-azadeoxycytidine treatment.
- These findings suggest a potential role for DNMT1 copy number and expression in predicting response to DNMT1-targeted therapies.
