Transthyretin Promotes Axon Growth via Regulation of Microtubule Dynamics and Tubulin Acetylation

Transthyretin (TTR), a plasma and cerebrospinal fluid protein, increases axon growth and organelle transport in sensory neurons. While neurons extend their axons, the microtubule (MT) cytoskeleton is crucial for the segregation of functional compartments and axonal outgrowth. Herein, we investigated whether TTR promotes axon elongation by modulating MT dynamics. We found that TTR KO mice have an intrinsic increase in dynamic MTs and reduced levels of acetylated α-tubulin in peripheral axons. In addition, they failed to modulate MT dynamics in response to sciatic nerve injury, leading to decreased regenerative capacity. Importantly, restoring acetylated α-tubulin levels of TTR KO dorsal root ganglia (DRG) neurons using an HDAC6 inhibitor is sufficient to completely revert defective MT dynamics and neurite outgrowth. In summary, our results reveal a new role for TTR in the modulation of MT dynamics by regulating α-tubulin acetylation via modulation of the acetylase ATAT1, and suggest that this activity underlies TTR neuritogenic function.

The immunomodulatory properties of the HDAC6 inhibitor ACY241 supports robust anti-tumor response in NSCLC when coupled with the chemotherapy drug Oxaliplatin

Background: Durable treatments that benefit a wide pool of patients remain elusive for Non-small cell lung cancer (NSCLC). The success of immunotherapy in a subset of NSCLC patients highlights the potential contribution of immune response to anti-tumor immunity while underscoring a need for broadly applicable therapeutic strategies. HDAC inhibitors are a promising class of drugs whose immunomodulatory properties are now being appreciated. In the present study, we evaluated the effects of the HDAC6 inhibitor, ACY241 on lung tumor immune compartment with the goal of understanding the scope of its immunomodulatory properties and its therapeutic potential in combination with Oxaliplatin. Methods: Lung adenocarcinoma-bearing mice were treated with ACY241 or vehicle after which the proportions and phenotype of tumor-associated T cells and macrophages were evaluated by comprehensive flow cytometric analysis. Bulk RNA-sequencing was also conducted on both cellular subsets to interrogate the transcriptomic changes associated with ACY241 treatment relative to vehicle controls. In vivo drug efficacy study was performed by administration of ACY241 and/or Oxaliplatin and assessing tumor growth and survival of tumor-bearing mice. Ex vivo functional studies was performed to assess tumor-associated T cell effector function as it correlates with measured outcomes. Results: We demonstrate that ACY241 promotes increased presence of T and NK cells in the lung tumors of treated mice. The tumor-associated T cells under ACY241 treatment displayed enhanced activation, proliferation, and effector profile. In addition, tumor-associated macrophages exhibited increased expression of MHC and co-stimulatory molecules while expression of inhibitory ligands were reduced. RNA-sequencing of both tumor-associated T cells and macrophages revealed significant genomic changes in both subsets that is consistent with ACY241-mediated enhancement of immune priming. These broad immunomodulatory properties of ACY241 were associated with significantly enhanced tumor-associated T cell effector functionality, robust anti-tumor response, and significantly prolonged survival of NSCLC-bearing mice when combined with the chemotherapy drug Oxaliplatin. Conclusion: Collectively, our studies highlight the broad immunomodulatory effect of ACY241 as a promising HDAC6 inhibitor which coupled with Oxaliplatin promotes robust therapeutic outcomes in a pre-clinical model of NSCLC, providing compelling rationale for the clinical testing of this novel combinatorial regimen in NSCLC.

A novel orally active HDAC6 inhibitor T-518 shows a therapeutic potential for Alzheimer’s disease and tauopathy in mice

Accumulation of tau protein is a key pathology of age-related neurodegenerative diseases such as Alzheimer's disease and progressive supranuclear palsy. Those diseases are collectively termed tauopathies. Tau pathology is associated with axonal degeneration because tau binds to microtubules (MTs), a component of axon and regulates their stability. The acetylation state of MTs contributes to stability and histone deacetylase 6 (HDAC6) is a major regulator of MT acetylation status, suggesting that pharmacological HDAC6 inhibition could improve axonal function and may slow the progression of tauopathy. Here we characterize N-[(1R,2R)-2-{3-[5-(difluoromethyl)-1,3,4-oxadiazol-2-yl]-5-oxo-5H,6H,7H-pyrrolo[3,4-b]pyridin-6-yl}cyclohexyl]-2,2,3,3,3-pentafluoropropanamide (T-518), a novel, potent, highly selective HDAC6 inhibitor with clinically favorable pharmacodynamics. T-518 shows potent inhibitory activity against HDAC6 and superior selectivity over other HDACs compared with the known HDAC6 inhibitors in the enzyme and cellular assays. T-518 showed brain penetration in an oral dose and blocked HDAC6-dependent tubulin deacetylation at Lys40 in mouse hippocampus. A 2-week treatment restored impaired axonal transport and novel object recognition in the P301S tau Tg mouse, tauopathy model, while a 3-month treatment also decreased RIPA-insoluble tau accumulation. Pharmaceutical inhibition of HDAC6 is a potential therapeutic strategy for tauopathy, and T-518 is a particularly promising drug candidate.

HDAC6 inhibitor WT161 performs antitumor effect on osteosarcoma and synergistically interacts with 5-FU

An imbalance between protein aggregation and protein degradation may induce “stress” in the functionality of the endoplasmic reticulum. There are quality control mechanisms to minimize misfolding and to eliminate misfolded proteins before aggregation becomes lethal for the cell. Proper protein folding and maturation is one of the crucial functions of the endoplasmic reticulum. Chaperones of the endoplasmic reticulum and folding enzymes guarantee correct conformational maturation of emerging secretory proteins. HDAC6 is a masterpiece coordinating the cell response to protein aggregate formation. The balance between HDAC6 and its partner Valosin-containing protein/p97 determines the fate of polyubiquitinated misfolded proteins. WT161 is a terrific, selective, and bioavailable HDAC6 inhibitor. WT161 selectively inhibits HDAC6 and adequately increases levels of acetylated α-tubulin. This compound induces accumulation of acetylated tubulin and cytotoxicity in multiple myeloma (MM) cells. In this Journal, Dr. Sun et al. identified that WT161 suppresses the cell growth of osteosarcoma cells. This discovery opens the door to future chemotherapeutic regimens of this bone neoplasm.

Inhibition of histone deacetylase 6 suppresses inflammatory responses and invasiveness of fibroblast-like-synoviocytes in inflammatory arthritis

Background To investigate the effects of inhibiting histone deacetylase (HDAC) 6 on inflammatory responses and tissue-destructive functions of fibroblast-like synoviocytes (FLS) in rheumatoid arthritis (RA). Methods FLS from RA patients were activated with interleukin (IL)-1β in the presence of increasing concentrations of M808, a novel specific HDAC6 inhibitor. Production of ILs, chemokines, and metalloproteinases (MMPs) was measured in ELISAs. Acetylation of tubulin and expression of ICAM-1 and VCAM-1 were assessed by Western blotting. Wound healing and adhesion assays were performed. Cytoskeletal organization was visualized by immunofluorescence. Finally, the impact of HDAC6 inhibition on the severity of arthritis and joint histology was examined in a murine model of adjuvant-induced arthritis (AIA). Results HDAC6 was selectively inhibited by M808. The HDAC6 inhibitor suppressed the production of MMP-1, MMP-3, IL-6, CCL2, CXCL8, and CXCL10 by RA-FLS in response to IL-1β. Increased acetylation of tubulin was associated with decreased migration of RA-FLS. Inhibiting HDAC6 induced cytoskeletal reorganization in RA-FLS by suppressing the formation of invadopodia following activation with IL-1β. In addition, M808 tended to decrease the expression of ICAM-1 and VCAM-1. In the AIA arthritis model, M808 improved the clinical arthritis score in a dose-dependent manner. Also, HDAC6 inhibition was associated with less severe synovial inflammation and joint destruction. Conclusion Inhibiting HDAC6 dampens the inflammatory and destructive activity of RA-FLS and reduces the severity of arthritis. Thus, targeting HDAC6 has therapeutic potential.