Protective Effects of Nigranoic Acid on Cerebral Ischemia–Reperfusion Injury and its Mechanism Involving Apoptotic Signaling Pathway

Synthesis of nigranoic acid and manwuweizic acid derivatives as HDAC inhibitors and anti-inflammatory agents

As a successful anti-tumor drug target, the family of histone deacetylases (HDACs) is also a critical player in immune response, making the research of anti-inflammatory HDAC inhibitors an attractive new focus. In this report, triterpenoids nigranoic acid (NA) and manwuweizic acid (MA) were identified as HDAC inhibitors through docking-based virtual screening and enzymatic activity assay. A series of derivatives of NA and MA were synthesized and assessed for their biological effects. As a result, hydroxamic acid derivatives of NA and MA showed moderately increased activity for HDAC1/2/4/6 inhibition (the lowest IC₅₀ against HDAC1 is 1.14 μM), with no activity against HDAC8. In J774A.1 macrophage, compound 1-3, 13 and 17-19 demonstrated inhibitory activity against lactate dehydrogenase (LDH) and IL-1β production, without affecting cell viability. Compound 19 increased the histone acetylation level in J774A.1 cells, as well as inhibited IL-1β maturation and caspase-1 cleavage. These results indicated that compound 19 blocks the activation of NLRP3 inflammasome, probably related to HDAC inhibition. This work provided a natural scaffold for developing low-cytotoxic and anti-inflammatory HDAC inhibitors, as well as a class of tool molecules for studying the relationship between HDACs and NLRP3 activation.

Targeting ubiquitin conjugating enzyme UbcH5b by a triterpenoid PC3-15 from Schisandra plants sensitizes triple-negative breast cancer cells to lapatinib

Increasing evidence suggested that a number of ubiquitin enzymes, including ubiquitin-activating enzymes, ubiquitin-conjugating enzymes, E3 ubiquitin ligases and deubiquitination enzymes contribute to therapeutic resistance in triple-negative breast cancer (TNBC) cells. Inhibition of these enzymes with small molecule inhibitors may restore therapeutic sensitivity. Here, we demonstrated ubiquitin conjugating enzyme UbcH5b strongly supports HECTD3 auto-ubiquitination in vitro. Based on this, we developed a Fluorescence Resonance Energy Transfer (FRET) assay and identified three Schisandraceae triterpenoids, including PC3-15, to block HECTD3/UbcH5b auto-ubiquitination. Furthermore, we revealed that PC3-15 directly binds to UbcH5b and also inhibits UbcH5b-mediated p62 ubiquitination. We found that the UbcH5b-p62 axis confers TNBC cells resistance to lapatinib by promoting autophagy. Consistently, PC3-15 inhibits lapatinib-induced autophagy and increases lapatinib sensitivity in TNBC in vitro and in mouse xenografts. These findings suggest that the UbcH5b-p62 axis provides potential therapeutic targets and that Schisandraceae triterpenoids may be used for TNBC treatment in combination with lapatinib.