Histone deacetylase 6 (HDAC6) regulates many physiological processes that are involved in cancer development and progression such as cell proliferation, apoptosis, motility, epithelial to mesenchymal transition, by deacetylation of multiple substrates and association with interacting proteins. Due to its the ability to remove misfolded proteins, induce autophagy, and regulate unfolded protein response, HDAC6 plays a protective role in responses to stress and enables tumor cells survival. HDAC6 is often overexpressed in tumors, including colorectal cancer (CRC) and is correlated with poor disease prognosis. However, it has been shown in animal models that HDAC6 is not essential for normal mammalian development. Therefore, it represents a good target for the development of novel cancer therapeutics. Selective inhibition of HDAC6 impairs growth and progression of many tumors without inducing major adverse events in experimental animals. In CRC, HDAC6 inhibitors have shown potential to reduce tumor progression and to enhance the therapeutic effect of other drugs. As HDAC6 is involved in regulation of immune responses, HDAC6 inhibitors have shown potential to improve antitumor immunity by increasing immunogenicity of tumor cells, augmenting immune cell activity and alleviating immunosuppression in tumor microenvironment. Therefore, HDAC6 inhibitors may represent promising candidates to improve the effect and to overcome resistance to immunotherapy.

Neurodegenerative diseases are universally marked by the accumulation of misfolded protein. Neurons respond to these proteostatic disturbances by sequestering, and thus inactivating, toxic misfolded proteins into a perinuclear organelle called the aggresome. The aggresome can be subsequently degraded in bulk by autophagy, a process termed aggrephagy. The formation of protein aggregates has historically been considered a spontaneous and unregulated process, but emerging research has instead discovered a diverse cohort of regulatory proteins that mediate protein aggregation. Chaperones are the first proteins to respond to misfolded proteins, and do so by recognizing the aberrant exposure of hydrophobic domains. When chaperones are unable to correctly refold proteins, their substrates are transferred to ubiquitin ligating machinery to catalyze polyubiquitination. Although ubiquitin chains typically direct proteins towards proteasomes, severe proteotoxic stress can overwhelm, or even directly inhibit, proteasomes. As an alternative to proteasomal degradation, misfolded proteins are redirected towards the mitotic organizing center (MTOC) and, following retrograde transport by dynein, are packaged and sequestered within an intermediate filament (IF) cage to form the aggresome. The biogenesis of the aggresome is thus a highly regulated event, and a better understanding of the mechanisms facilitating this process will provide critical insight into neurodegenerative disease.

Inappropriate expression of histone deacetylase (HDAC6) and deregulation of the phosphatidylinositol 3-kinase (PI3K) signaling pathway are common aberrations observed in cancers. LASSBio-2208, was previously described as a dual inhibitor in the nanomolar range of HDAC6 and PI3Kα, being three times more potent in inhibiting HDAC-6. In this paper we described the cytotoxic and antiproliferative potency of LASSBio-2208 on different tumour cell lines, its possible synergism effect in association with PI3K and HDAC-6 inhibitors, and its DMPK in vitro profile. Our studies have demonstrated that LASSBio-2208 has moderate cytotoxic potency on MCF-7 (IC50 = 23 µM), CCRF-CEM (IC50 = 8.54 µM) and MOLT-4 (IC50 = 7.15 µM), with no cytotoxic effect on hPBMC. In addition, it has a good antiproliferative effect on MCF-7 cells (IC50 = 5.44 µM), low absorption by PAMPA-GIT and low permeation through the blood-brain barrier by PAMPA-BBB, exhibiting high metabolic stability in rat plasma. Moreover, LASSBio-2208 exhibited synergism when combined with getadolisib and tubastatin A, using the concentration corresponding to their CC50 values on MOLT-4 and CCRF-CEM cells.

Zika virus (ZIKV) infection and pathogenesis are linked to the disruption of neurogenesis, congenital Zika syndrome and microcephaly by affecting neural progenitor cells. Nonstructural protein 5 (NS5) is the largest product encoded by ZIKV-RNA and is important for replication and immune evasion. Here, we studied the potential effects of NS5 on microtubules (MTs) and autophagy flux, together with the interplay of NS5 with histone deacetylase 6 (HDAC6). Fluorescence microscopy, biochemical cell-fractionation combined with the use of HDAC6 mutants, chemical inhibitors and RNA interference indicated that NS5 accumulates in nuclear structures and strongly promotes the acetylation of MTs that aberrantly reorganize in nested-like structures. Similarly, NS5 accumulates the p62 protein, an autophagic-flux marker. Therefore, NS5 alters events that are under the control of the autophagic tubulin-deacetylase HDAC6. HDAC6 appears to degrade NS5 by autophagy in a deacetylase- and BUZ domain-dependent manner and to control the cytoplasmic expression of NS5. Moreover, NS5 inhibits RNA-mediated RIG-I interferon (IFN) production, resulting in greater activity when autophagy is inhibited (i.e., effect correlated with NS5 stability). Therefore, it is conceivable that NS5 contributes to cell toxicity and pathogenesis, evading the IFN-immune response by overcoming HDAC6 functions. HDAC6 has emerged as an anti-ZIKV factor by targeting NS5.