Synthesis of Small Molecule Adjuvants to Combat Antibiotic Resistance Mechanisms

According to the Centers for Disease Control and Prevention (CDC), the U.S. lost a lot of the progress made towards combating the antibiotic resistance crisis back in 2020 due to the effects of the COVID-19 pandemic. They state that during the first year of the pandemic, more than 29,400 people died from a bacterial infection, with 40% of those infections being acquired during a hospital stay. Although determination of the full extent of the national burden of deaths from antimicrobial infections may be hindered from the statistical gaps caused by the pandemic, the 2019 CDC estimate of 2.8 million infections/year resulting in approximately 35,000 deaths, remains some of the strongest data obtained to date. These statistics, the loss of progress made, and the dearth of new antibiotics in the drug pipeline highlight the urgent need for novel ways to treat such infections.
The work presented in this document describes multiple projects focusing on the development of antibiotic adjuvants to combat this issue. In-depth discussions detail initial hits found for each project, followed by a structure activity relationship (SAR) study to reveal lead adjuvants. The first two projects focus on utilizing adjuvants to sensitize gram-negative pathogens to gram-positive selective antibiotics. Gram-negative bacteria are more resistant to many antibiotics than gram-positive bacteria, since they possess an outer membrane that acts as a first line of defense to many antibiotics by preventing their entry into the cell.
We identified a class of dimeric 2-aminoimidazole (2-AI) adjuvants that dramatically enhance the sensitivity of Acinetobacter baumannii to the macrolide antibiotic clarithromycin, with reductions of minimum inhibitory concentrations (MICs) as high as =512-fold. Activity for these adjuvants was seen across a variety of A. baumannii clinical isolates and among other gram-negative pathogens including: Klebsiella pneumoniae (KP2146), Pseudomonas aeruginosa PAO1, and Escherichia coli (EC25922). Furthermore, the dimeric 2-AI analogs exhibited highly reduced mammalian cell toxicity compared to earlier adjuvants, with IC50 values >200 µg/mL against HepG2 cells, which corresponds to therapeutic indices (TIs) >200. Another project identifies preliminary trends for a second-generation set of 2-AI dimer adjuvants for clarithromycin potentiation against A. baumannii. Lastly, this document describes the efforts made toward synthesizing a set of quinuclidine based natural products for the potentiation of oxacillin against Staphylococcus aureus.

据美国疾病控制与预防中心（Centers for Disease Control and Prevention, CDC）的数据，受新冠疫情影响，美国在对抗抗生素耐药性危机方面所取得的诸多进展在2020年付诸东流。该机构指出，在疫情首年，超过29400人死于细菌感染，其中40%为医院获得性感染。尽管疫情引发的统计数据缺口可能阻碍我们全面掌握全国抗菌药物感染相关死亡的实际规模，但CDC在2019年给出的估算数据——每年约280万例感染、造成约35000例死亡——仍是目前可得的最权威数据之一。这些统计数据、此前进展的付之东流，以及药物研发管线中新型抗生素的匮乏，都凸显出开发新型疗法治疗此类感染的迫切需求。
本文件所呈现的研究工作围绕抗生素佐剂的开发展开，旨在解决上述问题，共包含多个研究项目。报告将深入探讨各项目的初筛活性化合物，并通过构效关系（structure activity relationship, SAR）研究筛选得到先导佐剂。前两个项目聚焦于利用佐剂使革兰氏阴性病原体对革兰氏阳性选择性抗生素产生敏感性。革兰氏阴性菌对多数抗生素的耐药性强于革兰氏阳性菌，这是因为其拥有外膜，可作为第一道防线阻止多数抗生素进入菌体细胞。
本研究发现一类二聚体2-氨基咪唑（2-aminoimidazole, 2-AI）佐剂，可显著提升鲍曼不动杆菌对大环内酯类抗生素克拉霉素的敏感性，最低抑菌浓度（minimum inhibitory concentrations, MICs）降幅最高可达512倍。此类佐剂的活性在多种鲍曼不动杆菌临床分离株以及其他革兰氏阴性病原体中均得到验证，包括肺炎克雷伯菌（KP2146）、铜绿假单胞菌PAO1以及大肠埃希菌（EC25922）。此外，与早期佐剂相比，这类二聚体2-AI类似物对哺乳动物细胞的毒性大幅降低，针对HepG2细胞的半数抑制浓度（IC50）大于200 µg/mL，对应的治疗指数（therapeutic indices, TIs）大于200。另一项研究则明确了第二代2-AI二聚体佐剂用于增强克拉霉素对抗鲍曼不动杆菌活性的初步构效趋势。最后，本文件还介绍了一系列基于奎宁环的天然产物的合成工作，旨在增强苯唑西林对抗金黄色葡萄球菌的活性。