HDAC Inhibitors Inspired by Natural Products

描述（由申请人提供）：消化器官（如胃、结肠和肾脏）的癌症普遍存在，并且可能非常难以治疗，因此为寻求靶向这些类型的恶性肿瘤的新药提供了令人信服的理由。组蛋白去乙酰化酶（HDAC）是一种参与染色质重塑和表观遗传事件的酶家族，已引起相当大的兴趣。在这一领域已经有相当多的工作，主要集中在异羟肟酸类，其中第一个已获得批准用于治疗皮肤T细胞淋巴瘤。HDAC同工酶之间的选择性差被认为是与当前HDAC抑制剂的临床使用相关的大部分毒性的基础。具有上级活性的新HDAC抑制剂可以显著影响该靶标在癌症中的功效。我们有兴趣开发一种全新的HDAC抑制剂，具有更高的选择性。这些新的抑制剂是基于天然产物的化学型，环庚三烯酚酮系统。几个世纪以来，台湾扁柏和日本扁柏的木材和提取物在日本和中国都很珍贵。树的提取物（扁柏油）具有抗菌和抗增殖活性，目前用于许多局部制剂和化妆品。这些提取物的组成在20世纪40年代初进行了研究，导致鉴定出一种不寻常的tropolectin，称为扁柏酚（也称为thujaplicin），被证明是负责大部分生物活性。天然存在的环庚三烯酚酮（tropolones）如崖柏素（thujaplicin）已被认为具有通过螯合1-羟基酮与金属离子相互作用的能力，并且可以形成用于发现特异性靶向结合的金属离子（如金属酶中的那些）的试剂的通用平台。事实上，我们已经证明了托酚酮类似物能够抑制HDAC-2。在这个R21应用中，我们的目标是研究这种非苯型芳香族化合物作为发现HDAC新抑制剂的良好先导化合物的潜力。我们的初步分析表明，该类的独特结构特征提供了将高水平的效力和选择性结合起来的机会。我们的目标是使用R21机制来建立开发基于托酚酮的铅系列作为HDAC抑制剂的可行性。第一个具体目的将描述各种差异取代的环庚三烯酚酮的合成，总共约40种，其将在第二个目的中使用酶和基于细胞的测定进行评价。还将对前五种抑制剂进行初步代谢稳定性研究。在第三个目标中，将尝试使HDAC与铅抑制剂复合结晶。这些研究将最终支持基于结构的药物设计工作，因为我们将继续进行铅优化。实现R21应用中概述的目标将使我们能够高度控制对进一步开发化合物至关重要的关键合成，结构和生化方面。 公共卫生相关性：胃癌、结肠癌和肾癌是需要现代治疗的常见恶性肿瘤。组蛋白脱乙酰酶抑制剂已被证明是有效的抗增殖剂，但仍需要进一步开发选择性HDAC抑制剂。在这个提议中，我们的目标是评估天然产物托酚酮支架形成一类新的HDAC抑制剂的潜力。使用天然产物作为主导平台，我们将设计，合成和评估类似物对消化道癌细胞系的选择性和效力。

DESCRIPTION (provided by applicant): Cancers of the digestive organs such as the stomach, colon and the kidney are prevalent and can be very difficult to treat, thus providing a compelling rationale for the pursuit of new agents that target these types of malignancies. Emerging targets that have generated considerable interest are histone deacetylases (HDACs), a family of enzymes that is involved in chromatin remodeling and epigenetic events. There has already been considerable work in this area, largely focusing on the hydroxamate class, the first of which has gained approval for the treatment of cutaneous T-cell lymphoma. Poor selectivity between HDAC isozymes is believed to underlie much of the toxicity associated with the clinical use of current HDAC inhibitors. New HDAC inhibitors with superior activities could significantly impact the efficacy of this target in cancer. We are interested in developing a completely novel class of HDAC inhibitors with enhanced levels of selectivity. These new inhibitors are based on a natural product chemotype, the tropolone system. For centuries, the wood and extracts from taiwanhinoki (Chamaecyparis taiwanesis) and Japanese hinoki (Chamaecyparis obtuse) have been prized in Japan and China. The extracts of the tree (hinoki oil) have been valued for antibacterial and antiproliferative activity and are currently used in numerous topical agents and cosmetics. The composition of these extracts was studied in the early 1940s, leading to the identification of an unusual tropolonoid termed hinokitiol (also known as thujaplicin) that was shown to be responsible for much of the biological activity. Naturally occurring tropolones such as thujaplicin have been recognized for their ability to interact with metal ions through chelation of the 1-hydroxy ketone and could form a versatile platform for the discovery of agents that specifically target bound metal ions such as those in metalloenzymes. In fact, we have already demonstrated that tropolone analogs are capable of inhibiting HDAC-2. In this R21 application, we aim to investigate the potential of this non-benzenoid aromatic to serve as a good lead compound for the discovery of new inhibitors of HDAC. Our preliminary analysis suggests that the unique structural features of this class offer opportunities to incorporate high levels of potency and selectivity. It is our aim to use the R21 mechanism to establish the feasibility of developing a tropolone-based lead series as HDAC inhibitors. The first specific aim will describe the synthesis of a variety of differentially substituted tropolones, approximately 40 in total, which will be evaluated in the second aim using enzymatic and cell- based assays. Preliminary metabolic stability studies will also be conducted on the top five inhibitors. In the third aim, attempts will be made to crystallize HDAC in complex with a lead inhibitor. These studies will ultimately support a structure-based drug design effort as we move forward with lead optimization. Realization of the goals outlined in this R21 application would position us with high levels of control over the key synthetic, structural and biochemical facets critical for further compound development. PUBLIC HEALTH RELEVANCE: Stomach, colon and kidney cancers are common malignancies needing modern therapeutics. Inhibitors of histone deacetylase enzymes have been shown to function as effective antiproliferative agents but further development of selective HDAC inhibitors is still needed. In this proposal we aim to evaluate the potential of a natural product tropolone scaffold to form a novel class of HDAC inhibitors. Using the natural product as a lead platform, we will design, synthesize and evaluate analogs for selectivity and potency against digestive cancer cell lines.