National Cancer Institute, National Institutes of Health, Bethesda, MD, USA.
Cell Cycle. 2011 Sep 15;10(18):3119-28. doi: 10.4161/cc.10.18.17190.
Small cell lung cancer (SCLC) is an aggressive lung cancer subtype in need of better therapies. Histone deacetylase inhibitors (HDIs) promote increased lysine acetylation in nucleosomal histones and are thought to relax chromatin, thereby allowing increased access of transcription factors and DNA damaging agents alike to DNA. We studied whether two HDIs, belinostat and romidepsin, could be effectively combined with cisplatin or etoposide (VP-16) for SCLC cells. Analysis of cell survival and synergy was performed using CalcuSyn mathematical modeling to calculate a combination index. Immunostaining of γH2AX was performed to evaluate persistence of DNA damage following simultaneous or sequential exposure. Based on CalcuSyn modeling, HDIs synergized with DNA damaging agents only when added simultaneously. An additive-to-antagonistic effect was seen with HDI pretreatment for 24 h or with addition after cisplatin or etoposide. Furthermore, pretreatment with HDIs resulted in normalization of cell cycle and reduced PARP degradation as compared with simultaneous treatment. The increase in γH2AX phosphorylation confirmed that simultaneous but not sequential treatment enhanced double-stranded DNA breaks. These results suggest that DNA relaxation is not required for synergy of HDIs with DNA damaging agents, and that scheduling of drug administration will be critical for rational development of clinical protocols.
小细胞肺癌（SCLC）是一种侵袭性肺癌亚型，需要更好的治疗方法。组蛋白去乙酰化酶抑制剂（HDIs）可促进核小体组蛋白赖氨酸乙酰化增加，被认为能使染色质松弛，从而使转录因子和 DNA 损伤剂更易接近 DNA。我们研究了两种 HDIs，贝林司他和罗米地辛，是否能与顺铂或依托泊苷（VP-16）有效地联合用于 SCLC 细胞。使用 CalcuSyn 数学模型分析细胞存活和协同作用，以计算组合指数。通过同时或顺序暴露进行 γH2AX 免疫染色来评估 DNA 损伤的持续时间。根据 CalcuSyn 模型，只有同时添加 HDIs 与 DNA 损伤剂才具有协同作用。HDI 预处理 24 小时或在顺铂或依托泊苷添加后，会产生相加至拮抗的作用。此外，与同时处理相比，HDI 预处理可使细胞周期正常化并减少 PARP 降解。γH2AX 磷酸化的增加证实，同时而非顺序处理可增强双链 DNA 断裂。这些结果表明，DNA 松弛不是 HDIs 与 DNA 损伤剂协同作用所必需的，并且药物给药时间安排对于合理开发临床方案至关重要。
