Transcriptional Repression of SIRT3 Potentiates Mitochondrial Aconitase Activation to Drive Aggressive Prostate Cancer to the Bone.

Metabolic dysregulation is a known hallmark of cancer progression, yet the oncogenic signals that promote metabolic adaptations to drive metastatic cancer remain unclear. Here, we show that transcriptional repression of mitochondrial deacetylase sirtuin 3 (SIRT3) by androgen receptor (AR) and its coregulator steroid receptor coactivator-2 (SRC-2) enhances mitochondrial aconitase (ACO2) activity to favor aggressive prostate cancer. ACO2 promoted mitochondrial citrate synthesis to facilitate de novo lipogenesis, and genetic ablation of ACO2 reduced total lipid content and severely repressed in vivo prostate cancer progression. A single acetylation mark lysine258 on ACO2 functioned as a regulatory motif, and the acetylation-deficient Lys258Arg mutant was enzymatically inactive and failed to rescue growth of ACO2-deficient cells. Acetylation of ACO2 was reversibly regulated by SIRT3, which was predominantly repressed in many tumors including prostate cancer. Mechanistically, SRC-2-bound AR formed a repressive complex by recruiting histone deacetylase 2 to the SIRT3 promoter, and depletion of SRC-2 enhanced SIRT3 expression and simultaneously reduced acetylated ACO2. In human prostate tumors, ACO2 activity was significantly elevated, and increased expression of SRC-2 with concomitant reduction of SIRT3 was found to be a genetic hallmark enriched in prostate cancer metastatic lesions. In a mouse model of spontaneous bone metastasis, suppression of SRC-2 reactivated SIRT3 expression and was sufficient to abolish prostate cancer colonization in the bone microenvironment, implying this nuclear-mitochondrial regulatory axis is a determining factor for metastatic competence. SIGNIFICANCE: This study highlights the importance of mitochondrial aconitase activity in the development of advanced metastatic prostate cancer and suggests that blocking SRC-2 to enhance SIRT3 expression may be therapeutically valuable. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/1/50/F1.large.jpg.

Design, synthesis and QSAR study of novel isatin analogues inspired Michael acceptor as potential anticancer compounds.

Molecular hybridization is considered as an effective tactic to develop drugs for the treatment of cancer. A series of novel hybrid compounds of isatin and Michael acceptor were designed and synthesized on the basis of association principle. These hybrid compounds were tested for cytotoxic potential against human cancer cell lines namely, BGC-823, SGC-7901 and NCI-H460 by MTT assay. Most compounds showed good anti-growth activities in all tested human cancer cells. SAR and QSAR analysis may provide vital information for the future development of novel anti-cancer inhibitors. Notably, compound 6a showed potent growth inhibition on BGC-823, SGC-7901 and NCI-H460 with the IC50 values of 3.6 ±â€¯0.6, 5.7 ±â€¯1.2, 3.2 ±â€¯0.7 µM, respectively. Besides, colony formation assays, wound healing assays and flow cytometry analysis indicated 6a exhibited a potent anti-growth and anti-migration ability in a concentration-dependence manner through arrested cells in the G2/M phase of cell cycle. Moreover, 6a significantly repressed tumor growth in a NCI-H460 xenograft mouse model. Overall, our findings suggested isatin analogues inspired Michael acceptor may provide promising lead compounds for the development of cancer chemotherapeutics.

Intra-iliac Artery Injection for Efficient and Selective Modeling of Microscopic Bone Metastasis.

Intra-iliac artery (IIA) injection is an efficient approach to introduce metastatic lesions of various cancer cells in animals. Compared to the widely used intra-cardiac and intra-tibial injections, IIA injection brings several advantages. First, it can deliver a large quantity of cancer cells specifically to hind limb bones, thereby providing spatiotemporally synchronized early-stage colonization events and allowing robust quantification and swift detection of disseminated tumor cells. Second, it injects cancer cells into the circulation without damaging the local tissues, thereby avoiding inflammatory and wound-healing processes that confound the bone colonization process. Third, IIA injection causes very little metastatic growth in non-bone organs, thereby preventing animals from succumbing to other vital metastases, and allowing continuous monitoring of indolent bone lesions. These advantages are especially useful for the inspection of progression from single cancer cells to multi-cell micrometastases, which has largely been elusive in the past. When combined with cutting-edge approaches of biological imaging and bone histology, IIA injection can be applied to various research purposes related to bone metastases.

Devil's Wake: Early-stage bone colonization by breast cancer.

We recently discovered that bone micrometastases of breast cancer predominantly reside in the microenvironment termed the "osteogenic niche". The heterotypic adherens junctions between cancer cells and osteogenic cells promote early-stage bone colonization by activating the mTOR pathway in cancer cells. Here, we discuss a few questions raised by these findings.

Retrieval of Disseminated Tumor Cells Colonizing the Bone in Murine Breast Cancer Metastasis Models.

In breast cancer, the most frequent site of metastasis is bone. Disseminated tumor cells (DTCs) can be detected in the bone marrow of patients by their expression of epithelial oroncogenic markers [1], and the presence and frequency of these DTCs are associated with poor prognosis. However, many of the details behind this process remain elusive, including the biological properties and fates of these apparently indolent cancer cells. To provide pre-clinical models of DTCs, we have developed a procedure that allows for controlled and enhanced delivery of tumor cells to the bone in animal experiments via injection into the iliac artery of the hind limb [2]. To our surprise, we found that most cancer cells became integrated into the solid bone matrix shortly after arriving in the bone, and only a minority can be flushed out with the bone marrow.Here we describe a method that helps to retrieve DTCs homing to the bone in which we achieve an improved recovery of those tumor cells closely associated with the bone microenvironment. In our view it is especially important to analyze these tumor cell subpopulations, as they may take full advantage of growth-, survival- and immune-protective signals provided by neighbor cells. We also show a pilot study on how this approach may be applied to the analysis of cancer dormancy. Our study suggests that the detection and retrieval of DTCs in clinical studies are incomplete because they are conducted exclusively with bone marrow aspirates.

The osteogenic niche promotes early-stage bone colonization of disseminated breast cancer cells.

Breast cancer bone micrometastases can remain asymptomatic for years before progressing into overt lesions. The biology of this process, including the microenvironment niche and supporting pathways, is unclear. We find that bone micrometastases predominantly reside in a niche that exhibits features of osteogenesis. Niche interactions are mediated by heterotypic adherens junctions (hAJs) involving cancer-derived E-cadherin and osteogenic N-cadherin, the disruption of which abolishes niche-conferred advantages. We elucidate that hAJ activates the mTOR pathway in cancer cells, which drives the progression from single cells to micrometastases. Human data set analyses support the roles of AJ and the mTOR pathway in bone colonization. Our study illuminates the initiation of bone colonization, and provides potential therapeutic targets to block progression toward osteolytic metastases.

Inhibiting heat-shock protein 90 reverses sensory hypoalgesia in diabetic mice.

Increasing the expression of Hsp70 (heat-shock protein 70) can inhibit sensory neuron degeneration after axotomy. Since the onset of DPN (diabetic peripheral neuropathy) is associated with the gradual decline of sensory neuron function, we evaluated whether increasing Hsp70 was sufficient to improve several indices of neuronal function. Hsp90 is the master regulator of the heat-shock response and its inhibition can up-regulate Hsp70. KU-32 (N-{7-[(2R,3R,4S,5R)-3,4-dihydroxy-5-methoxy-6,6-dimethyl-tetrahydro-2H-pyran-2-yloxy]-8-methyl-2-oxo-2H-chromen-3-yl}acetamide) was developed as a novel, novobiocin-based, C-terminal inhibitor of Hsp90 whose ability to increase Hsp70 expression is linked to the presence of an acetamide substitution of the prenylated benzamide moiety of novobiocin. KU-32 protected against glucose-induced death of embryonic DRG (dorsal root ganglia) neurons cultured for 3 days in vitro. Similarly, KU-32 significantly decreased neuregulin 1-induced degeneration of myelinated Schwann cell DRG neuron co-cultures prepared from WT (wild-type) mice. This protection was lost if the co-cultures were prepared from Hsp70.1 and Hsp70.3 KO (knockout) mice. KU-32 is readily bioavailable and was administered once a week for 6 weeks at a dose of 20 mg/kg to WT and Hsp70 KO mice that had been rendered diabetic with streptozotocin for 12 weeks. After 12 weeks of diabetes, both WT and Hsp70 KO mice developed deficits in NCV (nerve conduction velocity) and a sensory hypoalgesia. Although KU-32 did not improve glucose levels, HbA1c (glycated haemoglobin) or insulin levels, it reversed the NCV and sensory deficits in WT but not Hsp70 KO mice. These studies provide the first evidence that targeting molecular chaperones reverses the sensory hypoalgesia associated with DPN.

Hyperglycemia alters the schwann cell mitochondrial proteome and decreases coupled respiration in the absence of superoxide production.

Hyperglycemia-induced mitochondrial dysfunction contributes to sensory neuron pathology in diabetic neuropathy. Although Schwann cells (SCs) also undergo substantial degeneration in diabetic neuropathy, the effect of hyperglycemia on the SC mitochondrial proteome and mitochondrial function has not been examined. Stable isotope labeling with amino acids in cell culture (SILAC) was used to quantify the temporal effect of hyperglycemia on the mitochondrial proteome of primary SCs isolated from neonatal rats. Of 317 mitochondrial proteins identified, about 78% were quantified and detected at multiple time points. Pathway analysis indicated that proteins associated with mitochondrial dysfunction, oxidative phosphorylation, the TCA cycle, and detoxification were significantly increased in expression and over-represented. Assessing mitochondrial respiration in intact SCs indicated that hyperglycemia increased the overall rate of oxygen consumption but decreased the efficiency of coupled respiration. Although a glucose-dependent increase in superoxide production occurs in embryonic sensory neurons, hyperglycemia did not induce a substantial change in superoxide levels in SCs. This correlated with a 1.9-fold increase in Mn superoxide dismutase expression, which was confirmed by immunoblot and enzymatic activity assays. These data support that hyperglycemia alters mitochondrial respiration and can cause remodeling of the SC mitochondrial proteome independent of significant contributions from glucose-induced superoxide production.

HER2-targeting recombinant protein with truncated pseudomonas exotoxin A translocation domain efficiently kills breast cancer cells.

The second domain of Pseudomonas exotoxin A (PEAII, residues 253-364) has been shown to facilitate translocation of extracellular and vesicular contents into the cytoplasm, and can transport heterologous molecules into target cells. Because full length PEAII may elicit a host immune response, we tried to identify the minimal PEAII translocation motif and use this fragment in combination with an antibody and constitutively active granzyme B (ImmunoGrB) to kill HER2-positive tumor cells. We constructed four ImmunoGrB fusion proteins containing different PEAII deletions and tested their abilities to kill HER2-positive cells. Our data showed that while a complete deletion of PEAII in ImmunoGrB resulted in an inability to kill cancer cells, ImmunoGrBs containing either PEAII (253-358aa) or PEAII (275-358aa) could efficiently kill HER2-positive SK-BR-3 cells. Most interestingly, the construct which contains only a furin cleavage site, named PEAII (275-280aa), could still induce SK-BR-3 apoptosis, although less efficiently. Moreover, delivery of the recombinant proteins by intramuscular plasmid injection led to an apparent tumor regression and prolonged animal survival in a nude mouse xenograft SK-BR-3 tumor model, indicating in vivo antitumor activity of the different PEAII containing ImmunoGrBs. Our results may help in understanding PEAII translocation and may lead to the development of useful tools or alternative therapy.

Hyperglycemia and downregulation of caveolin-1 enhance neuregulin-induced demyelination.

Neuregulins (NRGs) are growth factors which bind to Erb receptor tyrosine kinases that localize to Schwann cells (SCs). Although NRGs can promote cell survival, mitogenesis, and myelination in undifferentiated SCs, they also induce demyelination of myelinated co-cultures of SCs and dorsal root ganglion (DRG) neurons. We have shown previously that Erb B2 activity increased in premyelinating SCs in response to hyperglycemia, and that this correlated with the downregulation of the protein caveolin-1 (Cav-1). As myelinated SCs undergo substantial degeneration in diabetic neuropathy, we used myelinated SC/DRG neuron co-cultures to determine if hyperglycemia and changes in Cav-1 expression could enhance NRG-induced demyelination. In basal glucose, NRG1 caused a 2.4-fold increase in the number of damaged myelin segments. This damage reached 3.8-fold under hyperglycemic conditions, and was also associated with a robust decrease in the expression of Cav-1 and compact myelin proteins. The loss of Cav-1 and compact myelin proteins following hyperglycemia and NRG treatment was not due to neuronal loss, since the axons remained intact and there was no loss of PGP 9.5, an axonal marker protein. To examine if changes in Cav-1 were sufficient to alter the extent of NRG-induced demyelination, SC/DRG neurons co-cultures were infected with antisense or dominant-negative Cav-1(P132L) adenoviruses. Either antisense-mediated downregulation or mis-localization of endogenous Cav-1 by Cav-1(P132L) resulted in a 1.5- to 2.4-fold increase in NRG-induced degeneration compared to that present in control cultures. These data support that hyperglycemia and changes in Cav-1 are sufficient to sensitize myelinated SC/DRG co-cultures to NRG-induced demyelination.