Department of Medicine, University of California San Diego, La Jolla, CA, 92093, USA.
Sci Rep. 2020 Feb 26;10(1):3478. doi: 10.1038/s41598-020-60469-6.
Heterochromatin is essential for regulating global gene transcription and protecting genome stability, and may play a role in tumor suppression. Drugs promoting heterochromatin are potential cancer therapeutics but very few are known. In order to identify drugs that can promote heterochromatin, we used a cell-based method and screened NCI drug libraries consisting of oncology drugs and natural compounds. Since heterochromatin is originally defined as intensely stained chromatin in the nucleus, we estimated heterochromatin contents of cells treated with different drugs by quantifying the fluorescence intensity of nuclei stained with Hoechst DNA dye. We used HeLa cells and screened 231 FDA-approved oncology and natural substance drugs included in two NCI drug libraries representing a variety of chemical structures. Among these drugs, streptonigrin most prominently caused an increase in Hoechst-stained nuclear fluorescence intensity. We further show that streptonigrin treated cells exhibit compacted DNA foci in the nucleus that co-localize with Heterochromatin Protein 1 alpha (HP1α), and exhibit an increase in total levels of the heterochromatin mark, H3K9me3. Interestingly, we found that streptonigrin promotes heterochromatin at a concentration as low as one nanomolar, and at this concentration there were no detectable effects on cell proliferation or viability. Finally, in line with a previous report, we found that streptonigrin inhibits STAT3 phosphorylation, raising the possibility that non-canonical STAT function may contribute to the effects of streptonigrin on heterochromatin. These results suggest that, at low concentrations, streptonigrin may primarily enhance heterochromatin formation with little toxic effects on cells, and therefore might be a good candidate for epigenetic cancer therapy.
异染色质对于调节全局基因转录和保护基因组稳定性至关重要，并且可能在肿瘤抑制中发挥作用。促进异染色质的药物是潜在的癌症治疗药物，但已知的很少。为了鉴定能够促进异染色质的药物，我们使用基于细胞的方法筛选了包含肿瘤药物和天然化合物的 NCI 药物库。由于异染色质最初被定义为细胞核中染色强烈的染色质，因此我们通过定量用 Hoechst DNA 染料染色的细胞核的荧光强度来估计用不同药物处理的细胞中的异染色质含量。我们使用 HeLa 细胞筛选了两种 NCI 药物库中包含的 231 种 FDA 批准的肿瘤和天然物质药物，这些药物库代表了各种化学结构。在这些药物中，streptonigrin 最显著地导致 Hoechst 染色核荧光强度增加。我们进一步表明，streptonigrin 处理的细胞在细胞核中显示出与 Heterochromatin Protein 1 alpha (HP1α) 共定位的紧凑型 DNA 焦点，并表现出异染色质标记 H3K9me3 的总水平增加。有趣的是，我们发现 streptonigrin 在低至一纳摩尔的浓度下即可促进异染色质，并且在该浓度下对细胞增殖或活力没有可检测的影响。最后，与之前的报告一致，我们发现 streptonigrin 抑制 STAT3 磷酸化，这表明非典型 STAT 功能可能有助于 streptonigrin 对异染色质的作用。这些结果表明，在低浓度下，streptonigrin 可能主要增强异染色质形成，对细胞几乎没有毒性作用，因此可能是一种很好的表观遗传癌症治疗候选药物。
