Targeting sideroflexin 4, a mitochondrial inner membrane protein involved iniron sulfur cluster biogenesis, to enhance the efficacy of DNA-damaging drugs inovarian cancer

摘要 今天被诊断患有卵巢癌的女性长期存活的机会只有很小的改善。 与40年前确诊的女性相比。两个不同但相关的观察结果可能会提供 有机会改善卵巢癌患者的前景。两者都涉及DNA损伤和修复。1) 最有效和最广泛使用的药物，铂化合物(顺铂和卡铂)，失去了 随时间推移的有效性--产生抗药性。耐药的一个重要(但不是唯一)原因 是卵巢癌修复顺铂DNA加合物造成的损伤的后天能力。2)不同的 导致DNA损伤的一类药物，PARP抑制剂，最近已被FDA批准用于 有DNA修复缺陷的患者，例如种系或BRACA1/2的获得性突变。不幸的是， DNA修复基因缺陷的患者只占卵巢癌患者的一小部分。 我们认为，以线粒体蛋白铁弹性蛋白4(SFXN4)为靶点可能提供了一条解决 这两个问题。我们发现，降低SFXN4水平扰乱了Fe-S团簇的形成 卵巢癌细胞的线粒体和胞浆。我们认为，Fe-S团簇的损失将对 影响卵巢癌的细胞后果。首先，铁-S蛋白的减少会增加氧化应激 以及通过细胞铁的获取和重新分配而造成的DNA损伤。第二，因为关键酶 参与核苷酸切除修复(NER)和同源重组修复(HRR)需要Fe-S簇 为了它们的功能和稳定性，靶向SFXN4会降低DNA这些修复途径的活性。vt.给出 SFXN4的减少既可能导致DNA损伤，又可能抑制DNA修复，我们进一步 假设SFXN4的破坏可能会增强铂基化合物的疗效并扩大 PARP抑制剂对无DNA修复缺陷的卵巢癌的有效性：即使这些 癌症对铂类药物和PARP抑制剂非常敏感，就像BRCA突变细胞一样。在试行中 实验中，我们确实观察到抑制SFXN4)抑制DNA修复蛋白；2)增强 对顺铂的敏感性；3)增敏的卵巢癌细胞对PARP抑制剂。 我们提出了三个特定的目标来研究SFXN4在卵巢癌中的作用。在目标1中，我们探索如何 以及SFXN4的减少在多大程度上增加了氧化应激，限制了DNA修复和增强了DNA 损坏。在目标2中，我们研究了靶向SFXN4在增强铂-2的有效性方面的作用。 细胞培养和小鼠模型中的基于化合物和PARP抑制剂。在目标3中，我们确定了 SFXN4在Fe-S团簇生物发生中的分子位置和作用机制，并直接与之联系 对NER和HRR途径中DNA修复蛋白减少的影响。 影响：以SFXN4为靶点可能是增强铂类药物疗效的机会 将PARP抑制剂的使用扩大到大多数DNA修复功能正常的卵巢癌患者。

ABSTRACT A woman diagnosed today with an ovarian cancer has only a minimally improved chance of long term survival compared to a woman diagnosed 40 years ago. Two different yet related observations may provide an opportunity to improve the outlook of ovarian cancer patients. Both involve DNA damage and repair. 1) The most effective and widely used drugs, the platinum compounds (cisplatin and carboplatin), lose their effectiveness over time – drug resistance develops. An important (but not the only) reason for drug resistance is an acquired ability of ovarian cancers to repair the damage caused by cisplatin DNA adducts. 2) A different class of drugs that induce DNA damage, the PARP inhibitors, has recently been approved by the FDA for patients with DNA repair defects, such as germline or acquired mutations in BRACA1/2. Unfortunately, patients with defects in DNA repair genes represent only a small fraction of ovarian cancer patients. We propose that targeting the mitochondrial protein sideroflexin 4 (SFXN4) may provide a path to addressing both these problems. We discovered that reducing the levels of SFXN4 disrupted Fe-S cluster formation in the mitochondria and cytosol of ovarian cancer cells. We propose that the loss of Fe-S clusters will have major cellular consequences affecting ovarian cancer. First, reduction of Fe-S proteins will increase oxidative stress and DNA damage via the acquisition and redistribution of cellular iron. Second, because critical enzymes involved in NER (nucleotide excision repair) and HRR (homologous recombination repair) require Fe-S clusters for their function and stability, targeting SFXN4 will reduce the activity of DNA these repair pathways. Given the possibility that reduction of SFXN4 could both induce DNA damage and inhibit DNA repair, we further hypothesize that disruption of SFXN4 might enhance the efficacy of platinum-based compounds and expand the effectiveness of PARP inhibitors to ovarian cancers without defects in DNA repair: i.e., render these cancers exquisitely sensitive, like BRCA-mutant cells, to platinum-based drugs and PARP inhibitors. In pilot experiments, we indeed observed that inhibiting SFXN4 1) inhibited DNA repair proteins; 2) enhanced sensitivity to cisplatin; 3) sensitized ovarian cancer cells to PARP inhibitors. We propose three Specific Aims to study the effects of SFXN4 in ovarian cancer. In Aim 1, we explore how and to what extent reduction of SFXN4 increases oxidative stress, limits DNA repair and enhances DNA damage. In Aim 2, we examine the role of targeting SFXN4 in enhancing the effectiveness of both platinum- based compounds and PARP inhibitors in cell cultures and mouse models. In Aim 3 we determine the precise molecular site and mechanism by which SFXN4 functions in Fe-S cluster biogenesis, and directly link this effect to the reduction of DNA repair proteins in NER and HRR pathways. Impact: targeting SFXN4 may represent an opportunity to enhance the efficacy of platinum-based drugs and extend the use of PARP inhibitors to the majority of ovarian cancer patients with normal DNA repair function.