SIRT3 deficiency decreases oxidative metabolism capacity but increases lifespan in male mice under caloric restriction

Mitochondrial NAD⁺ -dependent protein deacetylase Sirtuin3 (SIRT3) has been proposed to mediate calorie restriction (CR)-dependent metabolic regulation and lifespan extension. Here, we investigated the role of SIRT3 in CR-mediated longevity, mitochondrial function, and aerobic fitness. We report that SIRT3 is required for whole-body aerobic capacity but is dispensable for CR-dependent lifespan extension. Under CR, loss of SIRT3 (Sirt3^-/- ) yielded a longer overall and maximum lifespan as compared to Sirt3^+/+ mice. This unexpected lifespan extension was associated with altered mitochondrial protein acetylation in oxidative metabolic pathways, reduced mitochondrial respiration, and reduced aerobic exercise capacity. Also, Sirt3^-/- CR mice exhibit lower spontaneous activity and a trend favoring fatty acid oxidation during the postprandial period. This study shows the uncoupling of lifespan and healthspan parameters (aerobic fitness and spontaneous activity) and provides new insights into SIRT3 function in CR adaptation, fuel utilization, and aging.

The Lung Elastin Matrix Undergoes Rapid Degradation Upon Adult Loss of Hox5 Function

Hox genes encode transcription factors that are critical for embryonic skeletal patterning and organogenesis. The Hoxa5, Hoxb5, and Hoxc5 paralogs are expressed in the lung mesenchyme and function redundantly during embryonic lung development. Conditional loss-of-function of these genes during postnatal stages leads to severe defects in alveologenesis, specifically in the generation of the elastin network, and animals display bronchopulmonary dysplasia (BPD) or BPD-like phenotype. Here we show the surprising results that mesenchyme-specific loss of Hox5 function at adult stages leads to rapid disruption of the mature elastin matrix, alveolar enlargement, and an emphysema-like phenotype. As the elastin matrix of the lung is considered highly stable, adult disruption of the matrix was not predicted. Just 2 weeks after deletion, adult Hox5 mutant animals show significant increases in alveolar space and changes in pulmonary function, including reduced elastance and increased compliance. Examination of the extracellular matrix (ECM) of adult Tbx4rtTA; TetOCre; Hox5a f a f bbcc lungs demonstrates a disruption of the elastin network although the underlying fibronectin, interstitial collagen and basement membrane appear unaffected. An influx of macrophages and increased matrix metalloproteinase 12 (MMP12) are observed in the distal lung 3 days after Hox5 deletion. In culture, fibroblasts from Hox5 mutant lungs exhibit reduced adhesion. These findings establish a novel role for Hox5 transcription factors as critical regulators of lung fibroblasts at adult homeostasis.

Resveratrol targeting of AKT and p53 in glioblastoma and glioblastoma stem-like cells to suppress growth and infiltration

OBJECTIVE Glioblastoma multiforme (GBM) is an aggressive brain cancer with median survival of less than 2 years with current treatment. Glioblastomas exhibit extensive intratumoral and interpatient heterogeneity, suggesting that successful therapies should produce broad anticancer activities. Therefore, the natural nontoxic pleiotropic agent, resveratrol, was studied for antitumorigenic effects against GBM. METHODS Resveratrol's effects on cell proliferation, sphere-forming ability, and invasion were tested using multiple patient-derived GBM stem-like cell (GSC) lines and established U87 glioma cells, and changes in oncogenic AKT and tumor suppressive p53 were analyzed. Resveratrol was also tested in vivo against U87 glioma flank xenografts in mice by using multiple delivery methods, including direct tumor injection. Finally, resveratrol was delivered directly to brain tissue to determine toxicity and achievable drug concentrations in the brain parenchyma. RESULTS Resveratrol significantly inhibited proliferation in U87 glioma and multiple patient-derived GSC lines, demonstrating similar inhibitory concentrations across these phenotypically heterogeneous lines. Resveratrol also inhibited the sphere-forming ability suggesting anti-stem cell effects. Additionally, resveratrol blocked U87 glioma and GSC invasion in an in vitro Matrigel Transwell assay at doses similar to those mediating antiproliferative effects. In U87 glioma cells and GSCs, resveratrol reduced AKT phosphorylation and induced p53 expression and activation that led to transcription of downstream p53 target genes. Resveratrol administration via oral gavage or ad libitum in the water supply significantly suppressed GBM xenograft growth; intratumoral or peritumoral resveratrol injection further suppressed growth and approximated tumor regression. Intracranial resveratrol injection resulted in 100-fold higher local drug concentration compared with intravenous delivery, and with no apparent toxicity. CONCLUSIONS Resveratrol potently inhibited GBM and GSC growth and infiltration, acting partially via AKT deactivation and p53 induction, and suppressed glioblastoma growth in vivo. The ability of resveratrol to modulate AKT and p53, as well as reportedly many other antitumorigenic pathways, is attractive for therapy against a genetically heterogeneous tumor such as GBM. Although resveratrol exhibits low bioavailability when administered orally or intravenously, novel delivery methods such as direct injection (i.e., convection-enhanced delivery) could potentially be used to achieve and maintain therapeutic doses in the brain. Resveratrol's nontoxic nature and broad anti-GBM effects make it a compelling candidate to supplement current GBM therapies.

Natural products induce a G protein-mediated calcium pathway activating p53 in cancer cells

Paclitaxel, etoposide, vincristine and doxorubicin are examples of natural products being used as chemotherapeutics but with adverse side effects that limit their therapeutic window. Natural products derived from plants and having low toxicity, such as quercetin, resveratrol, epigallocatechin gallate and piceatannol, have been shown to inhibit tumor cell growth both in vitro and in pre-clinical models of cancer, but their mechanisms of action have not been fully elucidated, thus restricting their use as prototypes for developing synthetic analogs with improved anti-cancer properties. We and others have demonstrated that one of the earliest and consistent events upon exposure of tumor cells to these less toxic natural products is a rise in cytoplasmic calcium, activating several pro-apoptotic pathways. We describe here a G protein/inositol 1,4,5-trisphosphate pathway (InsP3) in MDA-MB-231 human breast cancer cells that mediates between these less toxic natural products and the release of calcium from the endoplasmic reticulum. Further, we demonstrate that this elevation of intracellular calcium modulates p53 activity and the subsequent transcription of several pro-apoptotic genes encoding PIG8, CD95, PIDD, TP53INP, RRM2B, Noxa, p21 and PUMA. We conclude from our findings that less toxic natural products likely bind to a G protein coupled receptor that activates a G protein-mediated and calcium-dependent pathway resulting selectively in tumor cell death.

Resveratrol: challenges in translation to the clinic--a critical discussion

Low cancer survival rates and the serious side effects often associated with current chemotherapeutics highlight the need for new and effective nontoxic anticancer agents. Since 1997 when Jang and colleagues first described resveratrol's ability to inhibit carcinogenesis, it has consistently proven effective at tumor inhibition in diverse human cancer models. This finding has raised the hope that resveratrol would pioneer a novel class of nontoxic chemotherapeutics. As a consequence of initial basic and preclinical studies, resveratrol is now being extensively promoted in the unregulated nutraceutical sector. However, some fundamental aspects of resveratrol's action need to be understood before it can be developed into a clinically viable anticancer drug. These areas pertain to the key mechanism(s) by which resveratrol potentiates its antitumor effects. Current research suggests that these mechanisms might be through novel pathways, requiring an understanding of cellular uptake, sentinel targets, and in vivo biological networks. The metabolism of resveratrol and its bioavailability also warrant further consideration in light of recent in vitro and in vivo studies. Finally, we need to appreciate the sorts of information about resveratrol that may translate between different disease entities. We present a critical discussion of these issues and suggest important experiments that could pave the way to the successful translation of resveratrol to the clinic.

Resveratrol inhibits uveal melanoma tumor growth via early mitochondrial dysfunction

PURPOSE

To test the efficacy of resveratrol, a nontoxic plant product, in the treatment of uveal melanoma.

METHODS

The effect of oral administration and peritumor injection of resveratrol was tested on tumor growth in two animal models of uveal melanoma. The mechanism of resveratrol action on uveal melanoma cells was studied in vitro in a cell-viability assay: with JC-1 dye, to measure mitochondrial membrane potential; by Western blot analysis, to analyze the cellular redistribution of cytochrome c and Smac/diablo; and in a fluorescence assay with specific substrates, to measure activation of different caspases.

RESULTS

Resveratrol treatment inhibited tumor growth in animal models of uveal melanoma. Since oral administration resulted in relatively low bioavailability of resveratrol, the effect of increased local levels was tested by peritumor injection of the drug. This method resulted in tumor cell death and tumor regression. In vitro experiments with multiple uveal melanoma cell lines demonstrate that resveratrol causes a decrease in cell viability, resulting at least in part from an increase in apoptosis through a mitochondrial pathway. An early event in drug action is the direct targeting of mitochondria by resveratrol, which leads to a decrease in mitochondrial membrane potential and the eventual activation of caspase-3.

CONCLUSION

These data suggest that resveratrol can inhibit tumor growth and can induce apoptosis via the intrinsic mitochondrial pathway and that by further increasing bioavailability of resveratrol the potency of the drug can be increased, leading to tumor regression. The nontoxic nature of the drug at levels needed for therapy make resveratrol an attractive candidate for the treatment of uveal melanoma.

Resveratrol Inhibits Tumor Growth of Human Neuroblastoma and Mediates Apoptosis by Directly Targeting Mitochondria

PURPOSE

Neuroblastoma is an aggressive childhood disease of the sympathetic nervous system. Treatments are often ineffective and have serious side effects. Because resveratrol, a natural plant product, has been reported to have limited toxicity at chemotherapeutic levels, we investigated its efficacy in the treatment of neuroblastoma as well as its underlying mechanism of action.

EXPERIMENTAL DESIGN

Resveratrol was tested in mouse xenograft models of human neuroblastoma and in vitro using human cell lines.

RESULTS

Resveratrol inhibited the outgrowth of tumors by as much as 80%. The bioavailability of the drug in serum was in the low micromolar range (2-10 micromol/L) and no accumulation was observed in tumor tissue. When resveratrol levels were increased by peritumor injection, rapid tumor regression occurred. Resveratrol decreased tumor cell viability in vitro by 75% to 90%, resulting from an inhibition of cell proliferation and an induction of apoptosis. Loss of mitochondrial membrane potential was an early response to resveratrol. In addition, resveratrol treatment of isolated mitochondria also led to depolarization, suggesting that the drug may target mitochondria directly. Following depolarization, resveratrol caused the release of cytochrome c and Smac/Diablo from the mitochondria and subsequently the activation of caspase-9 (4- to 8-fold) and caspase-3 (4- to 6-fold).

CONCLUSIONS

These studies indicate that, despite low bioavailability, resveratrol is effective at inhibiting tumor growth. Elevated levels of resveratrol enhance its antitumor potency leading to tumor regression, associated with widespread tumor cell death, the underlying mechanism of which involves the direct activation of the mitochondrial intrinsic apoptotic pathway.

1 alpha-Hydroxyvitamin D2 inhibits growth of human neuroblastoma

Neuroblastoma is the most common extracranial solid tumor in childhood. The poor outcomes of patients with high-risk neuroblastoma have encouraged the search for new therapies. In the current study, the effect of the vitamin D analog 1alpha-hydroxyvitamin D2 (1alpha-OH-D2, doxercalciferol) was assessed in a mouse xenograft model of human neuroblastoma. Vitamin D receptor (VDR) expression levels in seven neuroblastoma cell lines were compared using real-time PCR. SK-N-AS cells, which express relatively high levels of VDR, were injected into the flanks of 60 mice. The mice were treated daily via oral gavage for 5 weeks with vehicle (control), 0.15 microg, or 0.3 microg of 1alpha-OH-D2. The animals were then euthanized, and tumors, sera, and kidneys were collected and analyzed. End tumor volumes were significantly smaller in both the 0.15 microg group (712.07 mm3, P = 0.0121) and 0.3 microg group (772.97 mm3, P = 0.0209) when compared to controls (1,681.75 mm3). In terms of toxicity, serum calcium levels were increased but mortality was minimal in both treatment groups. These results were similar to those previously described in the transgenic (LHbeta-Tag) and human xenograft (Y-79) models of retinoblastoma, a related tumor. In vitro cell viability studies of SK-N-AS and NGP cells, which represent two major human neuroblastoma subtypes that differ in their genetic abnormalities as well as their VDR expression levels, show that both are sensitive to calcitriol, the active metabolite of vitamin D3. In conclusion, the present study shows that 1alpha-OH-D2 can inhibit human neuroblastoma growth in vivo with relatively low toxicity. The safety of 1alpha-OH-D2 has been extensively studied; the drug is FDA-approved for the treatment of adult kidney patients, and Phase I/II trials have been conducted in adult oncology patients. There should not be major obstacles to starting Phase I and II clinical trials with this drug in pediatric patients with high-risk neuroblastoma.

Mitochondria as the primary target of resveratrol-induced apoptosis in human retinoblastoma cells

PURPOSE

To determine the molecular mechanisms by which resveratrol induces retinoblastoma tumor cell death.

METHODS

After resveratrol treatment, Y79 tumor cell viability was measured using a fluorescence-based assay, and proapoptotic and antiproliferative effects were characterized by Hoechst stain and flow cytometry, respectively. Mitochondrial transmembrane potential (DeltaPsim) was measured as a function of drug treatment using 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethyl-benzamidazolocarbocyanin iodide (JC-1), whereas the release of cytochrome c from mitochondria was assayed by immunoblotting and caspase activities were determined by monitoring the cleavage of fluorogenic peptide substrates.

RESULTS

Resveratrol induced a dose- and time-dependent decrease in Y79 tumor cell viability and inhibited proliferation by inducing S-phase growth arrest and apoptotic cell death. Preceding cell death, resveratrol evoked a rapid dissipation of DeltaPsim. This was followed by the release of cytochrome c into the cytoplasm and a substantial increase in the activities of caspase-9 and caspase-3. Additionally, in a cell-free system, resveratrol directly induced the depolarization of isolated mitochondria.

CONCLUSIONS

These results demonstrate that resveratrol, a nontoxic natural plant compound, inhibits Y79 cell proliferation and stimulates apoptosis through activation of the mitochondrial (intrinsic) apoptotic pathway and may warrant further exploration as an adjuvant to conventional anticancer therapies for retinoblastoma.

Ca2+ binding to EF hands 1 and 3 is essential for the interaction of apoptosis-linked gene-2 with Alix/AIP1 in ocular melanoma

Apoptosis-linked gene-2 (ALG-2) encodes a 22 kDa Ca(2+)-binding protein of the penta EF-hand family that is required for programmed cell death in response to various apoptotic agents. Here, we demonstrate that ALG-2 mRNA and protein are down-regulated in human uveal melanoma cells compared to their progenitor cells, normal melanocytes. The down regulation of ALG-2 may provide melanoma cells with a selective advantage. ALG-2 and its putative target molecule, Alix/AIP1, are localized primarily in the cytoplasm of melanocytes and melanoma cells independent of the intracellular Ca(2+) concentration or the activation of apoptosis. Cross-linking and analytical centrifugation studies support a single-species dimer conformation of ALG-2, also independent of Ca(2+) concentration. However, binding of Ca(2+) to both EF-1 and EF-3 is necessary for ALG-2 interaction with Alix/AIP1 as demonstrated using surface plasmon resonance spectroscopy. Mutations in EF-5 result in reduced target interaction without alteration in Ca(2+) affinity. The addition of N-terminal ALG-2 peptides, residues 1-22 or residues 7-17, does not alter the interaction of ALG-2 or an N-terminal deletion mutant of ALG-2 with Alix/AIP1, as might be expected from a model derived from the crystal structure of ALG-2. Fluorescence studies of ALG-2 demonstrate that an increase in surface hydrophobicity is primarily due to Ca(2+) binding to EF-3, while Ca(2+) binding to EF-1 has little effect on surface exposure of hydrophobic residues. Together, these data indicate that gross surface hydrophobicity changes are insufficient for target recognition.

Expression of the receptor tyrosine kinase Axl promotes ocular melanoma cell survival

Metastatic tumor cells originating from cancers of a variety of tissues such as breast, skin, and prostate may remain dormant for long periods of time. In the case of uveal melanoma, the principal malignancy of the eye, complete removal of the primary tumor by enucleation can nonetheless be followed by metastatic tumor growth in distant organs months, years, or even decades later. This suggests that tumor cells have already spread to secondary sites at the time of treatment and remain dormant as micrometastases. Identifying factors that govern long-lived survival of metastatic tumor cells is therefore key to decreasing mortality associated with this and other diseases. While investigating factors differentially expressed in melanoma cells and normal melanocytes, we identified the receptor tyrosine kinase Axl and found up-regulation of Axl in uveal melanomas and melanoma cell lines by RNase protection, Western analysis, and immunohistochemistry. Axl has been shown to mediate cell growth and survival through its ligand Gas6 in non-transformed cells. To test whether stimulation of Axl can enhance survival of uveal melanoma cells, we assessed the degree of mitogenesis and cell survival by bromodeoxyuridine incorporation and trypan blue exclusion, respectively, upon stimulation of Mel 290 uveal melanoma cells with Gas6 in vitro. We show that Gas6 mediates mitogenesis and cell survival in Mel 290 cells. We further demonstrate that these effects occur specifically through the Axl receptor by modulating the expression of Axl with an antisense construct. cDNA microarray analysis of 12,687 genes then revealed that Gas6 stimulation of Axl in Mel 290 cells results primarily in the down-regulation of Cyr61, a member of the CCN protein family involved in tumor progression. These data show that the Axl pathway mediates increased survival of uveal melanoma cells, potentially advantageous during cancer dormancy, and that Axl may function in part through regulation of Cyr61.