PARP Inhibitors in Clinical Use Induce Genomic Instability in Normal Human Cells

Poly(ADP-ribose) polymerases (PARPs) are the first proteins involved in cellular DNA repair pathways to be targeted by specific inhibitors for clinical benefit. Tumors harboring genetic defects in homologous recombination (HR), a DNA double-strand break (DSB) repair pathway, are hypersensitive to PARP inhibitors (PARPi). Early phase clinical trials with PARPi have been promising in patients with advanced BRCA1 or BRCA2-associated breast, ovary and prostate cancer and have led to limited approval for treatment of BRCA-deficient ovary cancer. Unlike HR-defective cells, HR-proficient cells manifest very low cytotoxicity when exposed to PARPi, although they mount a DNA damage response. However, the genotoxic effects on normal human cells when agents including PARPi disturb proficient cellular repair processes have not been substantially investigated. We quantified cytogenetic alterations of human cells, including primary lymphoid cells and non-tumorigenic and tumorigenic epithelial cell lines, exposed to PARPi at clinically relevant doses by both sister chromatid exchange (SCE) assays and chromosome spreading. As expected, both olaparib and veliparib effectively inhibited poly-ADP-ribosylation (PAR), and caused marked hypersensitivity in HR-deficient cells. Significant dose-dependent increases in SCEs were observed in normal and non-tumorigenic cells with minimal residual PAR activity. Clinically relevant doses of the FDA-approved olaparib led to a marked increase of SCEs (5-10-fold) and chromatid aberrations (2-6-fold). Furthermore, olaparib potentiated SCE induction by cisplatin in normal human cells. Our data have important implications for therapies with regard to sustained genotoxicity to normal cells. Genomic instability arising from PARPi warrants consideration, especially if these agents will be used in people with early stage cancers, in prevention strategies or for non-oncologic indications.聚腺苷二磷酸核糖聚合酶（Poly(ADP-ribose) polymerases, PARPs）是首个被靶向特异性抑制剂以获取临床益处的、参与细胞DNA修复通路的蛋白质。携带同源重组（homologous recombination, HR）——一种DNA双链断裂（DNA double-strand break, DSB）修复通路——遗传缺陷的肿瘤，对PARP抑制剂（PARP inhibitors, PARPi）具有高度敏感性。早期PARPi临床试验在晚期BRCA1或BRCA2相关乳腺癌、卵巢癌及前列腺癌患者中展现出良好前景，并已有限获批用于BRCA缺陷型卵巢癌的治疗。与同源重组缺陷细胞不同，同源重组功能正常的细胞在暴露于PARPi时虽会启动DNA损伤应答，但仅表现出极弱的细胞毒性。然而，当包括PARPi在内的药物干扰正常细胞的修复过程时，其对正常人体细胞的遗传毒性效应尚未得到充分研究。本研究通过姐妹染色单体交换（sister chromatid exchange, SCE）实验及染色体铺展技术，对临床相关剂量下暴露于PARPi的人体细胞——包括原代淋巴样细胞、非致瘤性及致瘤性上皮细胞系——的细胞遗传学改变进行了定量分析。正如预期，奥拉帕利（olaparib）与维利帕尼（veliparib）均能有效抑制多聚腺苷二磷酸核糖基化（poly-ADP-ribosylation, PAR），并在同源重组缺陷细胞中引发显著的超敏反应。在残留PAR活性极低的正常及非致瘤性细胞中，观察到SCE水平呈现显著的剂量依赖性升高。临床相关剂量的美国食品药品监督管理局（FDA）批准的奥拉帕利，可使SCE水平显著升高5~10倍，染色单体畸变水平升高2~6倍。此外，奥拉帕利可增强顺铂（cisplatin）在正常人体细胞中诱导SCE的效应。本研究数据为PARPi疗法对正常细胞的持续遗传毒性带来了重要启示。由PARPi引发的基因组不稳定值得关注，尤其是当此类药物用于早期癌症患者、预防策略或非肿瘤学适应症时。