Autophagy induction by SIRT6 is involved in oxidative stress-induced neuronal damage.

SIRT6 is a NAD(+)-dependent histone deacetylase and has been implicated in the regulation of genomic stability, DNA repair, metabolic homeostasis and several diseases. The effect of SIRT6 in cerebral ischemia and oxygen/glucose deprivation (OGD) has been reported, however the role of SIRT6 in oxidative stress damage remains unclear. Here we used SH-SY5Y neuronal cells and found that overexpression of SIRT6 led to decreased cell viability and increased necrotic cell death and reactive oxygen species (ROS) production under oxidative stress. Mechanistic study revealed that SIRT6 induced autophagy via attenuation of AKT signaling and treatment with autophagy inhibitor 3-MA or knockdown of autophagy-related protein Atg5 rescued H2O2-induced neuronal injury. Conversely, SIRT6 inhibition suppressed autophagy and reduced oxidative stress-induced neuronal damage. These results suggest that SIRT6 might be a potential therapeutic target for neuroprotection.

Regulation of SIRT2 levels for human non-small cell lung cancer therapy.

Seven Sirtuin family members (SIRT1-7), comprising a family of NAD+-dependent protein deacetylases and ADP-ribosyltransferases, are key proteins that regulate multiple physiological processes. SIRT2 was recently reported to play an important role in carcinogenesis. However, its role in non-small cell lung cancer (NSCLC) has not yet been investigated. In this study, we analyzed the expression pattern of SIRT2 in NSCLC tissues from clinical patients and in cell lines, and found that SIRT2 was significantly down-regulated at both the mRNA and protein levels in tumor than non-tumor tissues or cells, which were corroborated by the NSCLC tissue microarray results. Overexpression of SIRT2 in A549 and H1299 cells caused cell proliferation inhibition, cell apoptosis induction and cell cycle arrest. Further analysis showed that SIRT2 overexpression increased the ROS (reactive oxygen species) production and p27 levels. Moreover, up-regulation of SIRT2 in NSCLC cells increased the sensitivity to Cisplatin treatment. Taken together, our results implied that down-regulation of SIRT2 was associated with NSCLC, and regulation of SIRT2 might be an important target for NSCLC therapy.

Inhibition of SIRT6 in prostate cancer reduces cell viability and increases sensitivity to chemotherapeutics.

SIRT6 is an important histone modifying protein that regulates DNA repair, telomere maintenance, energy metabolism, and target gene expression. Recently SIRT6 has been identified as a tumor suppressor and is down-regulated in certain cancer types, but not in other cancers. From deposited gene profiling studies we found that SIRT6 was overexpressed in prostate tumors, compared with normal or paratumor prostate tissues. Tissue micro-array studies confirmed the higher levels of SIRT6 in both prostate tumor tissues and prostate cancer cells than in their normal counterparts. Knockdown of SIRT6 in human prostate cancer cells led to sub-G1 phase arrest of cell cycle, increased apoptosis, elevated DNA damage level and decrease in BCL2 gene expression. Moreover, SIRT6-deficiency reduced cell viability and enhanced chemotherapeutics sensitivity. Taken together, this study provides the first evidence of SIRT6 overexpression in human prostate cancer, and SIRT6 regulation could be exploited for prostate cancer therapy.

Adjudin attenuates lipopolysaccharide (LPS)- and ischemia-induced microglial activation.

Neuroinflammation caused by microglial activation plays a key role in ischemia, neurodegeneration and many other CNS diseases. In this study, we found that Adjudin, a potential non-hormonal male contraceptive, exhibits additional function to reduce the production of proinflammatory mediators. Adjudin significantly inhibited LPS-induced IL-6 release and IL-6, IL-1ß, TNF-α expression in BV2 microglial cells. Furthermore, Adjudin exhibited anti-inflammatory properties by suppression of NF-κB p65 nuclear translocation and DNA binding activity as well as ERK MAPK phosphorylation. To determine the in vivo effect of Adjudin, we used a permanent middle cerebral artery occlusion (pMCAO) mouse model and found that Adjudin could reduce ischemia-induced CD11b expression, a marker of microglial activation. Furthermore, Adjudin treatment attenuated brain edema and neurological deficits after ischemia but did not reduce infarct volume. Thus, our data suggest that Adjudin may be useful for mitigating neuroinflammation.

Male contraceptive Adjudin is a potential anti-cancer drug.

Adjudin, also known as AF-2364 and an analog of lonidamine (LND), is a male contraceptive acting through the induction of premature sperm depletion from the seminiferous epithelium when orally administered to adult rats, rabbits or dogs. It is also known that LND can target mitochondria and block energy metabolism in tumor cells. However, whether Adjudin exhibits any anti-cancer activity remains to be elucidated. Herein we described the anti-proliferative activity of Adjudin on cancer cells in vitro and on lung and prostate tumors inoculated in nude mice. We found that Adjudin induced apoptosis in cancer cells through a Caspase-3-dependent pathway. Further experiments revealed that Adjudin could trigger mitochondrial dysfunction in cancer cells, apparently affecting the mitochondrial mass, inducing the loss of mitochondrial membrane potential and reducing cellular ATP levels. Intraperitoneal administration of Adjudin to tumor-bearing athymic nude mice also significantly suppressed the lung and prostate tumor growth. When used in combination with cisplatin, Adjudin enhances the sensitivity to cisplatin-induced cancer cell cytotoxicity. Taken together, these findings have demonstrated that Adjudin may be a potential drug for cancer therapy.

Delivering hydrophilic and hydrophobic chemotherapeutics simultaneously by magnetic mesoporous silica nanoparticles to inhibit cancer cells.

Using nanoparticles to deliver chemotherapeutics offers new opportunities for cancer therapy, but challenges still remain when they are used for the delivery of multiple drugs, especially for the synchronous delivery of hydrophilic and hydrophobic drugs in combination therapies. In this paper, we developed an approach to deliver hydrophilic-hydrophobic anticancer drug pairs by employing magnetic mesoporous silica nanoparticles (MMSNs). We prepared 50 nm-sized MMSNs with uniform pore size and evaluated their capability for the loading of two combinations of chemotherapeutics, namely doxorubicin-paclitaxel and doxorubicin-rapamycin, by means of sequential adsorption from the aqueous solution of doxorubicin and nonaqueous solutions of paclitaxel or rapamycin. Experimental results showed that the present strategy successfully realized the co-loading of hydrophilic and hydrophobic drugs with high-loading content and widely tunable ratio range. We elaborate on the theory behind the molecular interaction between the silica hydroxyl groups and drug molecules, which underlie the controllable loading, and the subsequent release of the drug pairs. Then we demonstrate that the multidrug-loaded MMSNs could be easily internalized by A549 human pulmonary adenocarcinoma cells, and produce enhanced tumor cell apoptosis and growth inhibition as compared to single-drug loaded MMSNs. Our study thus realized simultaneous and dose-tunable delivery of hydrophilic and hydrophobic drugs, which were endowed with improved anticancer efficacy. This strategy could be readily extended to other chemotherapeutic combinations and might have clinically translatable significance.

The packaging of siRNA within the mesoporous structure of silica nanoparticles.

Mesoporous silica nanoparticle (MSN) is a promising material for biomedical applications, such as delivering drugs or biological molecules (siRNA or DNA), to the target cells or tissues. With positive-charge functionalization on their surface, MSNs have already been used as vectors for siRNA delivery. Nevertheless, such siRNA packaging strategy avoids utilizing the mesopores and consequently hinders further modifications on the delivery vehicle surface. To solve these problems, we have successfully packaged siRNA into the mesopores of magnetic mesoporous silica nanoparticles (M-MSNs) under a strongly dehydrated solution condition. The siRNA-loaded M-MSNs were mixed with polyethyleneimine (PEI) to form a polymer layer on their external surface. The obtained aggregates were further treated by ultrasonication in acidic solution to prepare well dispersed siRNA delivery vehicles (M-MSN_siRNA@PEI). Such delivery vehicles, with effective siRNA protective effect and negligible cytotoxicity, could be internalized into cancer cells and release siRNA in the cytoplasm. In gene silencing experiments, these delivery vehicles mediated, with high efficiency, knockdown of both exogenous enhanced green fluorescent protein (EGFP) gene and endogenous B-cell lymphoma 2 (Bcl-2) gene. In summary, our siRNA packaging strategy extends the application potential of M-MSNs and the resulting siRNA delivery vehicles can be further tested for in vivo experiments.