Selective and Bioavailable HDAC6 2‑(Difluoromethyl)-1,3,4-oxadiazole Substrate Inhibitors and Modeling of Their Bioactivation Mechanism

Histone deacetylase 6 (HDAC6) is a unique member of the
HDAC family
mainly targeting cytosolic non­histone substrates, such as α-tubulin,
cortactin, and heat shock protein 90 to regulate cell proliferation,
metastasis, invasion, and mitosis in tumors. We describe the identification
and characterization of a series of 2-(difluoromethyl)-1,3,4-oxadiazoles
(DFMOs) as selective nonhydroxamic acid HDAC6 inhibitors. By comparing
structure–activity relationships and performing quantum mechanical
calculations of the HDAC6 catalytic mechanism, we show that potent
oxadiazoles are electrophilic substrates of HDAC6 and propose a mechanism
for the bioactivation. We also observe that the inherent electrophilicity
of the oxadiazoles makes them prone to degradation in water solution
and the generation of potentially toxic products cannot be ruled out,
limiting the developability for chronic diseases. However, the oxadiazoles
demonstrate high oral bioavailability and low in vivo clearance and
are excellent tools for studying the role of HDAC6 in vitro and in
vivo in rats and mice.

组蛋白去乙酰化酶6（Histone deacetylase 6，HDAC6）是HDAC家族的独特成员，其主要靶向胞浆内非组蛋白底物，如α-微管蛋白、肌动蛋白皮质蛋白（cortactin）、热休克蛋白90，以调控肿瘤细胞的增殖、转移、侵袭及有丝分裂过程。本研究对一系列2-(二氟甲基)-1,3,4-噁二唑（2-(difluoromethyl)-1,3,4-oxadiazoles，DFMOs）类选择性非异羟肟酸型HDAC6抑制剂开展了鉴定与表征工作。通过对比构效关系并进行HDAC6催化机制的量子力学计算，本研究证实活性优异的噁二唑类化合物为HDAC6的亲电子底物，并提出了其生物活化机制。同时本研究发现，噁二唑类化合物固有的亲电性使其在水溶液中易发生降解，且无法排除其生成潜在毒性产物的可能性，这限制了其用于慢性疾病的开发潜力。尽管如此，该类噁二唑化合物仍展现出较高的口服生物利用度与较低的体内清除率，是在大小鼠体内外研究HDAC6功能的优良工具化合物。