Development of isoform-selective histone deacetylase (HDAC) inhibitors is important in elucidating the function of individual HDAC enzymes and their potential as therapeutic agents. Among the eleven zinc-dependent HDACs in humans, HDAC6 is structurally and functionally unique. Here, we show that a hydroxamic acid-based small-molecule N-hydroxy-4-(2-[(2-hydroxyethyl)(phenyl)amino]-2-oxoethyl)benzamide (HPOB) selectively inhibits HDAC6 catalytic activity in vivo and in vitro. HPOB causes growth inhibition of normal and transformed cells but does not induce cell death. HPOB enhances the effectiveness of DNA-damaging anticancer drugs in transformed cells but not normal cells. HPOB does not block the ubiquitin-binding activity of HDAC6. The HDAC6-selective inhibitor HPOB has therapeutic potential in combination therapy to enhance the potency of anticancer drugs.anticancer agents | epigenetics-based chemotherapy | drug discovery H istone deacetylase 6 (HDAC6) is unique among the eleven zinc-dependent HDACs in humans. HDAC6 is located in the cytoplasm, and it has two catalytic domains and an ubiquitinbinding domain at the C-terminal region (1-3). This study focused on the development of a HDAC6-selective inhibitor and its biological effects. The substrates of HDAC6 include nonhistone proteins such as α-tubulin, peroxiredoxin (PRX), cortactin, and heat shock protein 90 (Hsp90) but not histones (4-7). HDAC6 plays a key role in the regulation of microtubule dynamics including cell migration and cell-cell interactions. The reversible acetylation of Hsp90, a substrate of HDAC6, modulates its chaperone activity and, accordingly, the stability of survival and antiapoptotic factors, including epidermal growth factor receptor (EGFR), protein kinase AKT, proto-oncogene C-RAF, survivin, and other factors. HDAC6, through its ubiquitin-binding activity and interaction with other partner proteins, plays a role in the degradation of misfolded proteins by binding polyubiquitinated proteins and delivering them to the dynein and motor proteins for transport into aggresomes which are degraded by lysosomes (8-10). Thus, HDAC6 has multiple biological functions through deacetylasedependent and -independent mechanisms modulating many cellular pathways relevant to normal and tumor cell growth, migration, and death. HDAC6 is an attractive target for potential cancer treatment.There are several previous reports on the development of HDAC6-selective inhibitors (11)(12)(13)(14)(15). The most extensively studied is tubacin (16,17). Tubacin has non-drug-like qualities, high lipophilicity, and difficult synthesis and has proved to be more useful as a research tool rather than as a potential drug (18). We and others (12)(13)(14)(15)19) have developed HDAC6-selective inhibitors whose pharmacokinetics, toxicity, and efficacy make them potentially more useful than tubacin as therapeutic agents. ACY-1215, 2-(Diphenylamino)-N-(7-(hydroxyamino)-7-oxoheptyl)pyrimidine-5-carboxamide, a HDAC6-selective inhibitor, is currently being evaluated in clinical trial...

Glaucoma is the leading cause of blindness in individuals of African descent (AD). While open angle glaucoma (OAG) disproportionately affects individuals of AD compared to persons of European descent (ED); the physiological mechanisms behind this disparity are largely unknown. The more rapid progression and greater severity of the disease in persons of AD further raises the concern for identifying these underlying differences in disease pathophysiology between AD and ED glaucoma patients. Ocular structural differences between AD and ED patients, including larger optic disc area, cup:disc ratio and thinner corneas have been found. AD individuals are also disproportionately affected by systemic vascular diseases including: hypertension, cardiovascular disease, stroke and diabetes mellitus. Abnormal ocular blood flow has been implicated as a risk factor for glaucoma, and pilot research is beginning to identify localized ocular vascular differences between AD and ED OAG patients. Given the known systemic vascular deficits and the relationship between glaucoma and ocular blood flow, exploring these concepts in terms of glaucoma risk factors may have a significant impact in elucidating the mechanisms behind the disease disparity in the AD population.

Toxoplasma gondii, the causative agent of toxoplasmosis, is an obligate intracellular protozoan pathogen. The parasite invades and replicates within virtually any warm blooded vertebrate cell type. During parasite invasion of a host cell, the parasite creates a parasitophorous vacuole (PV) that originates from the host cell membrane independent of phagocytosis within which the parasite replicates. While IFN-dependentinnate and cell mediated immunity is important for eventual control of infection, innate immune cells, including neutrophils, monocytes and dendritic cells, can also serve as vehicles for systemic dissemination of the parasite early in infection. An approach is described that utilizes the host innate immune response, in this case macrophages, in a forward genetic screen to identify parasite mutants with a fitness defect in infected macrophages following activation but normal invasion and replication in naïve macrophages. Thus, the screen isolates parasite mutants that have a specific defect in their ability to resist the effects of macrophage activation. The paper describes two broad phenotypes of mutant parasites following activation of infected macrophages: parasite stasis versus parasite degradation, often in amorphous vacuoles. The parasite mutants are then analyzed to identify the responsible parasite genes specifically important for resistance to induced mediators of cell autonomous immunity. The paper presents a general approach for the forward genetics screen that, in theory, can be modified to target parasite genes important for resistance to specific antimicrobial mediators. It also describes an approach to evaluate the specific macrophage antimicrobial mediators to which the parasite mutant is susceptible. Activation of infected macrophages can also promote parasite differentiation from the tachyzoite to bradyzoite stage that maintains chronic infection. Therefore, methodology is presented to evaluate the importance of the identified parasite gene to establishment of chronic infection.

Toxoplasma gondii is an obligate intracellular protozoan parasite that causes the disease toxoplasmosis. Chronic infection is established through the formation of tissue cysts predominantly in cardiac and neurologic tissues. A defining characteristic of T. gondii is its ability to evade the host’s immune defenses; specifically, T. gondii can invade and persist within host phagocytes, using them to disseminate to the brain and central nervous system where cysts are then formed. This protocol is used to evaluate the ability of Toxoplasma gondii to survive and replicate within naive and activated murine bone marrow-derived macrophages at the level of single infected cells. In the following protocol macrophages are naive or activated with IFN-γ and LPS but different activation stimuli can be utilized as well as different host cell populations and diverse inhibitors. Parasite replication is determined by evaluating the number of parasites per vacuole over time using immunofluorescence staining for parasties and microscopic analysis. Kinetic determination of parasite number per vacuole accurately reflects parasite replication over time as vacuoles-containing parasites do not fuse with one another. Isolation of murine bone marrow-derived macrophages, preparation of conditioned L929 cells for collection of macrophage colony-stimulating factor, and staining for fluorescence microscopy included in the protocol has broad applicability. This protocol works well for pathogens like Toxoplasma gondii that reside in vacuoles that do not fuse with one another and that can be visualized by microscopy.

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