P300/CBP inhibition sensitizes mantle cell lymphoma to PI3Kδ inhibitor idelalisib.

Mantle cell lymphoma (MCL) is a lymphoproliferative disorder lacking reliable therapies. PI3K pathway contributes to the pathogenesis of MCL, serving as a potential target. However, idelalisib, an FDA-approved drug targeting PI3Kδ, has shown intrinsic resistance in MCL treatment. Here we report that a p300/CBP inhibitor, A-485, could overcome resistance to idelalisib in MCL cells in vitro and in vivo. A-485 was discovered in a combinational drug screening from an epigenetic compound library containing 45 small molecule modulators. We found that A-485, the highly selective catalytic inhibitor of p300 and CBP, was the most potent compound that enhanced the sensitivity of MCL cell line Z-138 to idelalisib. Combination of A-485 and idelalisib remarkably decreased the viability of three MCL cell lines tested. Co-treatment with A-485 and idelalisib in Maver-1 and Z-138 MCL cell xenograft mice for 3 weeks dramatically suppressed the tumor growth by reversing the unsustained inhibition in PI3K downstream signaling. We further demonstrated that p300/CBP inhibition decreased histone acetylation at RTKs gene promoters and reduced transcriptional upregulation of RTKs, thereby inhibiting the downstream persistent activation of MAPK/ERK signaling, which also contributed to the pathogenesis of MCL. Therefore, additional inhibition of p300/CBP blocked MAPK/ERK signaling, which rendered maintaining activation to PI3K-mTOR downstream signals p-S6 and p-4E-BP1, thus leading to suppression of cell growth and tumor progression and eliminating the intrinsic resistance to idelalisib ultimately. Our results provide a promising combination therapy for MCL and highlight the potential use of epigenetic inhibitors targeting p300/CBP to reverse drug resistance in tumor.

Natural product 1,2,3,4,6-penta-O-galloyl-ß-D-glucopyranose is a reversible inhibitor of glyceraldehyde 3-phosphate dehydrogenase.

Aerobic glycolysis, also known as the Warburg effect, is a hallmark of cancer cell glucose metabolism and plays a crucial role in the activation of various types of immune cells. Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) catalyzes the conversion of D-glyceraldehyde 3-phosphate to D-glycerate 1,3-bisphosphate in the 6th critical step in glycolysis. GAPDH exerts metabolic flux control during aerobic glycolysis and therefore is an attractive therapeutic target for cancer and autoimmune diseases. Recently, GAPDH inhibitors were reported to function through common suicide inactivation by covalent binding to the cysteine catalytic residue of GAPDH. Herein, by developing a high-throughput enzymatic screening assay, we discovered that the natural product 1,2,3,4,6-penta-O-galloyl-ß-D-glucopyranose (PGG) is an inhibitor of GAPDH with Ki = 0.5 µM. PGG blocks GAPDH activity by a reversible and NAD+ and Pi competitive mechanism, suggesting that it represents a novel class of GAPDH inhibitors. In-depth hydrogen deuterium exchange mass spectrometry (HDX-MS) analysis revealed that PGG binds to a region that disrupts NAD+ and inorganic phosphate binding, resulting in a distal conformational change at the GAPDH tetramer interface. In addition, structural modeling analysis indicated that PGG probably reversibly binds to the center pocket of GAPDH. Moreover, PGG inhibits LPS-stimulated macrophage activation by specific downregulation of GAPDH-dependent glucose consumption and lactate production. In summary, PGG represents a novel class of GAPDH inhibitors that probably reversibly binds to the center pocket of GAPDH. Our study sheds new light on factors for designing a more potent and specific inhibitor of GAPDH for future therapeutic applications.

Histone deacetylase inhibitor givinostat attenuates nonalcoholic steatohepatitis and liver fibrosis.

Nonalcoholic steatohepatitis (NASH) is a common chronic liver disease that is increasingly prevalent worldwide. Liver inflammation is an important contributor to disease progression from nonalcoholic fatty liver (NAFL) to NASH, but there is a lack of efficient therapies. In the current study we evaluated the therapeutic potential of givinostat, a histone deacetylase (HDAC) inhibitor, in the treatment of NASH in vivo and in vitro. Liver inflammation was induced in mice by feeding a methionine- and choline-deficient diet (MCD) or a fructose, palmitate, cholesterol diet (FPC). The mice were treated with givoinostat (10 mg·kg-1·d-1, ip) for 8 or 10 weeks. At the end of the experiment, the livers were harvested for analysis. We showed that givoinostat administration significantly alleviated inflammation and attenuated hepatic fibrosis in MCD-induced NASH mice. RNA-seq analysis of liver tissues form MCD-fed mice revealed that givinostat potently blocked expression of inflammation-related genes and regulated a broad set of lipid metabolism-related genes. In human hepatocellular carcinoma cell line HepG2 and human derived fetal hepatocyte cell line L02, givinostat significantly decreased palmitic acid-induced intracellular lipid accumulation. The benefit of givinostat was further confirmed in FPC-induced NASH mice. Givinostat administration significantly attenuated hepatic steatosis, inflammation as well as liver injury in this mouse model. In conclusion, givinostat is efficacious in reversing diet-induced NASH, and may serve as a therapeutic agent for the treatment of human NASH.

Histone deacetylase inhibitor givinostat alleviates liver fibrosis by regulating hepatic stellate cell activation.

Hepatic fibrosis, a common pathological manifestation of chronic liver injury, is generally considered to be the end result of an increase in extracellular matrix produced by activated hepatic stellate cells (HSCs). The aim of the present study was to target the mechanisms underlying HSC activation in order to provide a powerful therapeutic strategy for the prevention and treatment of liver fibrosis. In the present study, a high­throughput screening assay was established, and the histone deacetylase inhibitor givinostat was identified as a potent inhibitor of HSC activation in vitro. Givinostat significantly inhibited HSC activation in vivo, ameliorated carbon tetrachloride­induced mouse liver fibrosis and lowered plasma aminotransferases. Transcriptomic analysis revealed the most significantly regulated genes in the givinostat treatment group in comparison with those in the solvent group, among which, dermokine (Dmkn), mesothelin (Msln) and uroplakin­3b (Upk3b) were identified as potential regulators of HSC activation. Givinostat significantly reduced the mRNA expression of Dmkn, Msln and Upk3b in both a mouse liver fibrosis model and in HSC­LX2 cells. Knockdown of any of the aforementioned genes inhibited the TGF­ß1­induced expression of α­smooth muscle actin and collagen type I, indicating that they are crucial for HSC activation. In summary, using a novel strategy targeting HSC activation, the present study identified a potential epigenetic drug for the treatment of hepatic fibrosis and revealed novel regulators of HSC activation.