Histone Deacetylase Inhibitors and Mithramycin A Impact a Similar Neuroprotective Pathway at a Crossroad between Cancer and Neurodegeneration

Mithramycin A (MTM) and histone deacetylase inhibitors (HDACi) are effective therapeutic agents for cancer and neurodegenerative diseases. MTM is a FDA approved aureolic acid-type antibiotic that binds to GC-rich DNA sequences and interferes with Sp1 transcription factor binding to its target sites (GC box). HDACi, on the other hand, modulate the activity of class I and II histone deacetylases. They mediate their protective function, in part, by regulating the acetylation status of histones or transcription factors, including Sp1, and in turn chromatin accessibility to the transcriptional machinery. Because these two classes of structurally and functionally diverse compounds mediate similar therapeutic functions, we investigated whether they act on redundant or synergistic pathways to protect neurons from oxidative death. Non-protective doses of each of the drugs do not synergize to create resistance to oxidative death suggesting that these distinct agents act via a similar pathway. Accordingly, we found that protection by MTM and HDACi is associated with diminished expression of the oncogene, Myc and enhanced expression of a tumor suppressor, p21waf1/cip1. We also find that neuroprotection by MTM or Myc knockdown is associated with downregulation of class I HDAC levels. Our results support a model in which the established antitumor drug MTM or canonical HDACi act via distinct mechanisms to converge on the downregulation of HDAC levels or activity respectively. These findings support the conclusion that an imbalance in histone acetylase and HDAC activity in favor of HDACs is key not only for oncogenic transformation, but also neurodegeneration

Hypoxia-inducible factor prolyl hydroxylases as targets for neuroprotection by “antioxidant” metal chelators: From ferroptosis to stroke

AbstractNeurologic conditions including stroke, Alzheimer disease, Parkinson disease, and Huntington disease are leading causes of death and long-term disability in the United States, and efforts to develop novel therapeutics for these conditions have historically had poor success in translating from bench to bedside. Hypoxia-inducible factor (HIF)-1α mediates a broad, evolutionarily conserved, endogenous adaptive program to hypoxia, and manipulation of components of the HIF pathway is neuroprotective in a number of human neurological diseases and experimental models. In this review, we discuss molecular components of one aspect of hypoxic adaptation in detail and provide perspective on which targets within this pathway seem to be ripest for preventing and repairing neurodegeneration. Further, we highlight the role of HIF prolyl hydroxylases as emerging targets for the salutary effects of metal chelators on ferroptosis in vitro as well in animal models of neurological diseases

Hydroxamate-Based Histone Deacetylase Inhibitors Can Protect Neurons from Oxidative Stress via a Histone Deacetylase-Independent Catalase-Like Mechanism

Histone deacetylase (HDAC) inhibitors have shown enormous promise for treating various disease states, presumably due to their ability to modulate acetylation of histone and non-histone proteins. Many of these inhibitors contain functional groups capable of strongly chelating metal ions. We demonstrate that several members of one such class of compounds, the hydroxamate-based HDAC inhibitors, can protect neurons from oxidative stress via an HDAC-independent mechanism. This previously unappreciated antioxidant mechanism involves the in situ formation of hydroxamate-iron complexes that catalyze the decomposition of hydrogen peroxide in a manner reminiscent of catalase. We demonstrate that while many hydroxamate-containing HDAC inhibitors display a propensity for binding iron, only a subset form active catalase mimetics capable of protecting neurons from exogenous H2O2. In addition to their impact on stroke and neurodegenerative disease research, these results highlight the possibility that HDAC-independent factors might play a role in the therapeutic effects of hydroxamate-based HDAC inhibitors

Histone Deacetylase Inhibitors and Mithramycin A Impact a Similar Neuroprotective Pathway at a Crossroad between Cancer and Neurodegeneration

Mithramycin A (MTM) and histone deacetylase inhibitors (HDACi) are effective therapeutic agents for cancer and neurodegenerative diseases. MTM is a FDA approved aureolic acid-type antibiotic that binds to GC-rich DNA sequences and interferes with Sp1 transcription factor binding to its target sites (GC box). HDACi, on the other hand, modulate the activity of class I and II histone deacetylases. They mediate their protective function, in part, by regulating the acetylation status of histones or transcription factors, including Sp1, and in turn chromatin accessibility to the transcriptional machinery. Because these two classes of structurally and functionally diverse compounds mediate similar therapeutic functions, we investigated whether they act on redundant or synergistic pathways to protect neurons from oxidative death. Non-protective doses of each of the drugs do not synergize to create resistance to oxidative death suggesting that these distinct agents act via a similar pathway. Accordingly, we found that protection by MTM and HDACi is associated with diminished expression of the oncogene, Myc and enhanced expression of a tumor suppressor, p21waf1/cip1. We also find that neuroprotection by MTM or Myc knockdown is associated with downregulation of class I HDAC levels. Our results support a model in which the established antitumor drug MTM or canonical HDACi act via distinct mechanisms to converge on the downregulation of HDAC levels or activity respectively. These findings support the conclusion that an imbalance in histone acetylase and HDAC activity in favor of HDACs is key not only for oncogenic transformation, but also neurodegeneration

Hydroxamic Acid-Based Histone Deacetylase (HDAC) Inhibitors Can Mediate Neuroprotection Independent of HDAC Inhibition

Histone deacetylase (HDAC) inhibition improves function and extends survival in rodent models of a host of neurological conditions, including stroke, and neurodegenerative diseases. Our understanding, however, of the contribution of individual HDAC isoforms to neuronal death is limited. In this study, we used selective chemical probes to assess the individual roles of the Class I HDAC isoforms in protecting Mus musculus primary cortical neurons from oxidative death. We demonstrated that the selective HDAC8 inhibitor PCI-34051 is a potent neuroprotective agent; and by taking advantage of both pharmacological and genetic tools, we established that HDAC8 is not critically involved in PCI-34051's mechanism of action. We used BRD3811, an inactive ortholog of PCI-34051, and showed that, despite its inability to inhibit HDAC8, it exhibits robust neuroprotective properties. Furthermore, molecular deletion of HDAC8 proved insufficient to protect neurons from oxidative death, whereas both PCI-34051 and BRD3811 were able to protect neurons derived from HDAC8 knock-out mice. Finally, we designed and synthesized two new, orthogonal negative control compounds, BRD9715 and BRD8461, which lack the hydroxamic acid motif and showed that they stably penetrate cell membranes but are not neuroprotective. These results indicate that the protective effects of these hydroxamic acid-containing small molecules are likely unrelated to direct epigenetic regulation via HDAC inhibition, but rather due to their ability to bind metals. Our results suggest that hydroxamic acid-based HDAC inhibitors may mediate neuroprotection via HDAC-independent mechanisms and affirm the need for careful structure–activity relationship studies when using pharmacological approaches

Hydroxamic Acid-Based Histone Deacetylase (HDAC) Inhibitors Can Mediate Neuroprotection Independent of HDAC Inhibition

Histone deacetylase (HDAC) inhibition improves function and extends survival in rodent models of a host of neurological conditions, including stroke, and neurodegenerative diseases. Our understanding, however, of the contribution of individual HDAC isoforms to neuronal death is limited. In this study, we used selective chemical probes to assess the individual roles of the Class I HDAC isoforms in protecting Mus musculus primary cortical neurons from oxidative death. We demonstrated that the selective HDAC8 inhibitor PCI-34051 is a potent neuroprotective agent; and by taking advantage of both pharmacological and genetic tools, we established that HDAC8 is not critically involved in PCI-34051's mechanism of action. We used BRD3811, an inactive ortholog of PCI-34051, and showed that, despite its inability to inhibit HDAC8, it exhibits robust neuroprotective properties. Furthermore, molecular deletion of HDAC8 proved insufficient to protect neurons from oxidative death, whereas both PCI-34051 and BRD3811 were able to protect neurons derived from HDAC8 knock-out mice. Finally, we designed and synthesized two new, orthogonal negative control compounds, BRD9715 and BRD8461, which lack the hydroxamic acid motif and showed that they stably penetrate cell membranes but are not neuroprotective. These results indicate that the protective effects of these hydroxamic acid-containing small molecules are likely unrelated to direct epigenetic regulation via HDAC inhibition, but rather due to their ability to bind metals. Our results suggest that hydroxamic acid-based HDAC inhibitors may mediate neuroprotection via HDAC-independent mechanisms and affirm the need for careful structure-activity relationship studies when using pharmacological approaches