Shourong Wu

Improving Drug Potency and Efficacy by Nanocarrier-Mediated Subcellular Targeting

Polymeric micelles containing a chemotherapeutic drug carry it adjacent to the DNA target in tumor cells, enhancing the drug potency. Special Delivery to the Nucleus Micelles are useful in the washing machine, where they self-assemble from soaps, trap grease inside, and carry it away. These spheres, formed by linear molecules with hydrophobic tails that cluster in the core and hydrophilic heads sticking out, can carry cargo other than dirt. Micelles self-assembled in the presence of a chemotherapeutic drug can ensnare and carry it to tumors, where they are ingested by cells. By creating micelles that disperse in specific environment within the late endosome and lysosome, a region of the cell near the nucleus, Murakami et al. force these soapy spheres to release their deadly cargo—in this case a platinum-based drug called DACHPt [(1,2-diaminocyclohexane) platinum(II)]—right in the neighborhood of its target: DNA. This direct assault on the genome proves to be an effective antitumor strategy: Tumor cells growing in mice succumb more readily to a micelle-delivered derivative of platinum than they do to free drug. The authors’ micelle carriers are carefully assembled from block copolymers with properties suited to their task. A poly(ethylene glycol) polymer is linked to a string of glutamic acids, with a boron dipyrromethene at each end. By attaching fluorescent tags of different colors to the ends, the authors endowed their micelles with the ability to signal to an observer whether they are intact. When all the poly(glutamic acid) segments were clustered in the core, their red fluorescence was quenched and only the green surface dye on the poly(ethylene glycol) was visible. Once the micelle encountered specific conditions in the late endosome and lysosome, the core dispersed, releasing the drug and dequenching the red dye. By taking advantage of these visible markers of the micelle state, the authors showed by time-lapse confocal laser scanning microscopy that the micelles were taken up into tumor cells by endocytosis and that they traveled to the late endosomal/lysosomal compartment, where the micelles dispersed and the drug was released. This color-coded behavior was apparent both in cultured tumor cells and in tumor cells growing subcutaneously in mice, which the authors monitored in the animals, also by confocal laser scanning microscopy. But does the direct delivery of DACHPt to the nuclear area improve its effectiveness? A comparison of free DACHPt to the micelle-carried drug shows that it can help with one serious problem of cancer therapeutics—tumors that become drug-resistant. After repeated exposure to DACHPt, tumor cells develop defensive proteins, such as metallothionein and methionine synthase, in their cytoplasm that inactivate the drug, protecting the tumor cell DNA from damage. Tumors that have become resistant to DACHPt grow well in the presence of the drug, but the micelle-delivered version effectively inhibited the tumors’ growth, most likely by bypassing the cells’ cytoplasmic defenses. Therefore, with appropriate chemical modifications, micelles can be used to carry medicinal cargo right where it is needed. Nanocarrier-mediated drug targeting is an emerging strategy for cancer therapy and is being used, for example, with chemotherapeutic agents for ovarian cancer. Nanocarriers are selectively accumulated in tumors as a result of their enhanced permeability and retention of macromolecules, thereby enhancing the antitumor activity of the nanocarrier-associated drugs. We investigated the real-time subcellular fate of polymeric micelles incorporating (1,2-diaminocyclohexane) platinum(II) (DACHPt/m), the parent complex of oxaliplatin, in tumor tissues by fluorescence-based assessment of their kinetic stability. These observations revealed that DACHPt/m was extravasated from blood vessels to the tumor tissue and dissociated inside each cell. Furthermore, DACHPt/m selectively dissociated within late endosomes, enhancing drug delivery to the nearby nucleus relative to free oxaliplatin, likely by circumvention of the cytoplasmic detoxification systems such as metallothionein and methionine synthase. Thus, these drug-loaded micelles exhibited higher antitumor activity than did oxaliplatin alone, even against oxaliplatin-resistant tumors. These findings suggest that nanocarriers targeting subcellular compartments may have considerable benefits in clinical applications.

Introduction of stearoyl moieties into a biocompatible cationic polyaspartamide derivative, PAsp(DET), with endosomal escaping function for enhanced siRNA-mediated gene knockdown

Applications of siRNA for cancer therapy have been spotlighted in recent years, but the rational design of efficient siRNA delivery carriers is still controversial, especially because of possible toxicity of the carrier components. Previously, a cationic polyaspartamide derivative, poly{N-[N-(2-aminoethyl)-2-aminoethyl]aspartamide} (PAsp(DET)), was reported to exert high transfection efficacy for plasmid DNA with negligible cytotoxicity. However, its direct application for siRNA delivery was fairly limited due to the unstable polymer/siRNA complex formation. In this study, to overcome such instability, stearic acid as a hydrophobic moiety was conjugated to the side chain of PAsp(DET) with various substitution degrees. The stearoyl introduction contributed not only to siRNA complex formation with higher association numbers but also to complex stabilization. The obtained stearoyl PAsp(DET)/siRNA complex significantly accomplished more efficient endogenous gene (BCL-2 and VEGF) knockdown in vitro against the human pancreatic adenocarcinoma (Panc-1) cells than did the unmodified PAsp(DET) complex and commercially available reagents, probably due to the facilitated cellular internalization. This finding suggests that the hydrophobic PAsp(DET)-mediated siRNA delivery is a promising platform for in vivo siRNA delivery.

Enhancement of angiogenesis through stabilization of hypoxia-inducible factor-1 by silencing prolyl hydroxylase domain-2 gene

Hypoxia-inducible factor-1 (HIF-1) plays a central role in cellular response to hypoxia by activating vascular endothelial growth factor (VEGF) and other angiogenic factors. Prolyl hydroxylase domain-2 (PHD2) protein induces the degradation of HIF-1 by hydroxylating specific prolyl residues. Therefore gene silencing of PHD2 by RNA interference (RNAi) might increase the expression of angiogenic growth factors and, consequently, neoangiogenesis through the stabilization of HIF-1alpha. In this study we have shown that the specific silencing of PHD2 is sufficient for stabilizing HIF-1alpha and increasing its transcriptional activity, resulting in the increased expression of angiogenic factors including VEGF and fibroblast growth factor-2 (FGF2). Moreover, when PHD2-siRNA vector was used, the increase in VEGF secretion was observed for as long as 18 days after transfection. In vitro treatment of human umbilical vein endothelical cells with conditioned medium from PHD2-siRNA vector-transfected NIH3T3 cells was shown to increase cell proliferation. Also, in vivo angiogenesis was observed in mice implanted with Matrigel plugs mixed with NIH3T3 cells transfected with PHD2-siRNA vector. These results indicate that PHD2 silencing induces expressions of multiple angiogenic growth factors by stabilizing HIF-1alpha, and that the implantation of cells transfected with PHD2-siRNA vector is sufficient to enhance angiogenesis in vivo. In the light of these findings, PHD2 silencing by RNAi might offer a potential tool for angiogenic therapy.

Transcription Factor YY1 Contributes to Tumor Growth by Stabilizing Hypoxia Factor HIF-1α in a p53-Independent Manner

In response to hypoxic stress, hypoxia-inducible factor (HIF)-1α is a critical transcription factor regulating fundamental cellular processes, and its elevated expression level and activity are associated with poor outcomes in most malignancies. The transcription factor Yin Yang 1 (YY1) is an important negative regulator of the tumor suppressor factor p53. However, the role of YY1 under tumor hypoxic condition is poorly understood. Herein, we show that inhibition of YY1 reduced the accumulation of HIF-1α and its activity under hypoxic condition, and consequently downregulated the expression of HIF-1α target genes. Interestingly, our results revealed that the downregulation of HIF-1α by inhibiting YY1 is p53-independent. Functionally, the in vivo experiments revealed that inhibition of YY1 significantly suppressed growth of metastatic cancer cells and lung colonization and also attenuated angiogenesis in a p53-null tumor. Collectively, our findings unraveled a novel mechanism by which YY1 inhibition disrupts hypoxia-stimulated HIF-1α stabilization in a p53-independent manner. Therefore, YY1 inhibition could be considered as a potential tumor therapeutic strategy to give consistent clinical outcomes independent of p53 status.

Determination of the role of DDX3 a factor involved in mammalian RNAi pathway using an shRNA-expression library.

RNA interference (RNAi) is an endogenous RNA-destruction phenomenon induced by certain double-stranded RNAs (dsRNAs). In RNAi, dsRNAs are processed into small interfering RNAs (siRNAs) which in turn trigger the cleavage of the target mRNA. Here, using a short hairpin RNA-expression library, we identified a DEAD-box helicase 3, DDX3, as an essential factor involved in RNAi pathway and revealed that DDX3 is colocalized with Ago2, an essential factor in RNAi pathway that cleaves target mRNA. Results of experiments with a dominant negative mutant of DDX3 further confirmed that this factor affects the RNAi activity. Together, DDX3 functions to assure mammalian RNAi pathway. Together, our results indicate that DDX3 is a new key molecule to understand the molecular mechanism underlying RNAi pathway in mammals.

Inhibition of PHD3 by salidroside promotes neovascularization through cell–cell communications mediated by muscle-secreted angiogenic factors

Therapeutic angiogenesis has been considered as a potential strategy for treating peripheral artery diseases including hind-limb ischemia (HLI); however, no effective drug-based treatment is currently available. Here we showed that intramuscular administration of salidroside, an active compound of Chinese herb Rhodiola, could robustly enhance blood perfusion recovery by promoting neovascularization in HLI mice. We revealed that salidroside promoted skeletal muscle cell migration and paracrine function through inhibiting the transcriptional level of prolyl-hydroxylase domain 3 (PHD3) without affecting PHD1 and PHD2. Paracrine signals from salidroside-treated skeletal muscle cells enhanced endothelial and smooth muscle cells migration, while inhibition of FGF2/FGF2R and PDGF-BB/PDGFR-β pathways abolished this effect, as well as neovascularization in HLI mice. Furthermore, we elucidated that salidroside inhibition on PHD3 might occur through estrogen receptor alpha (ERα). Together, our findings highlights the potential application of salidroside as a novel pharmalogical inhibitor of ERα/PHD3 axis for therapeutic angiogenesis in HLI diseases.

Transcription factor Yin Yang 2 is a novel regulator of the p53/p21 axis

Yin Yang 2 (YY2) is a multifunctional zinc-finger transcription factor that belongs to YY family. Unlike the well-characterized YY1, our understanding regarding the biological functions of YY2 is still very limited. Here we found for the first time that in contrast to YY1, which had been reported to be oncogenic, the expression level of YY2 in tumor cells and/or tissues was downregulated compared with its expression level in the normal ones. We also demonstrated that YY2 exerts biological function contrary to YY1 in cell proliferation. We elucidated that YY2 positively enhances p21 expression, and concomitantly, its silencing promotes cells to enter G2/M phase and enhances cell proliferation. Furthermore, we found that YY2 regulation on p21 occurs p53-dependently. Finally, we identified a novel YY2 binding site in the promoter region of tumor suppressor p53. We found that YY2 binds to the p53 promoter and activates its transcriptional activity, and subsequently, regulates cell cycle progression via p53/p21 axis. Taken together, our study not only identifies YY2 as a novel tumor suppressor gene that plays a pivotal role in cell cycle regulation, but also provides new insights regarding the regulatory mechanism of the conventional p53/p21 axis.Yin Yang 2 (YY2) is a multifunctional zinc-finger transcription factor that belongs to YY family. Unlike the well-characterized YY1, our understanding regarding the biological functions of YY2 is still very limited. Here we found for the first time that in contrast to YY1, which had been reported to be oncogenic, the expression level of YY2 in tumor cells and/or tissues was downregulated compared with its expression level in the normal ones. We also demonstrated that YY2 exerts biological function contrary to YY1 in cell proliferation. We elucidated that YY2 positively enhances p21 expression, and concomitantly, its silencing promotes cells to enter G2/M phase and enhances cell proliferation. Furthermore, we found that YY2 regulation on p21 occurs p53-dependently. Finally, we identified a novel YY2 binding site in the promoter region of tumor suppressor p53. We found that YY2 binds to the p53 promoter and activates its transcriptional activity, and subsequently, regulates cell cycle progression via p53/p21 axis. Taken together, our study not only identifies YY2 as a novel tumor suppressor gene that plays a pivotal role in cell cycle regulation, but also provides new insights regarding the regulatory mechanism of the conventional p53/p21 axis.

Prolyl Hydroxylase Domain-2 Silencing Induced by Hydrodynamic Limb Vein Injection Enhances Vascular Regeneration in Critical Limb Ischemia Mice through Activation of Multiple Genes

Therapeutic revascularization had been considered as the most potential strategy for treating ischemic diseases. Reconstruction of mature blood vessels, which is the key for functional revascularization, is a complex process involving multiple angiogenesis factors. Attempts had been made to promote functional revascularization by delivering vectors or other macromolecules that could positively regulate angiogenesis; however, the delivery method of these therapeutic angiogenesis factors had been mostly limited to direct intramuscular injection. In this study, we showed that compared to intramuscular injection, the hydrodynamic limb vein (HLV) injection of naked short-hairpin RNA expression plasmid targeting PHD2 (shPHD2) into critical himblimb ischemia mice could increase not only the expressions of HIF-dependent and HIF-independent angiogenic factors, but also tissue protective factors involved in various endogenous pathways more efficiently. We also found that PHD2-silencing enhanced innate endogenous recovery mechanism, as the expression levels of these factors had been slightly upregulated merely by the ischemic condition. Finally, we showed that HLV injection of shPHD2 promoted the formation of mature and functional vessels, and thus, enhances the recovery of ischemic hindlimbs more efficiently. These results suggest that HLV delivery of shPHD2 might become a promising treatment strategy to promote vascular regeneration in critical limb ischemia disease via enhancing innate endogenous pathways.

Elevating VEGF-A and PDGF-BB secretion by salidroside enhances neoangiogenesis in diabetic hind-limb ischemia

Hind-limb ischemia (HLI) is one of the major complication of diabetic patients. Angiogenesis potential in diabetic patients is severely disrupted, and the mechanism underlying it has not been fully elucidated, making it an obstacle for developing an efficient therapeutic angiogenesis strategy. Skeletal muscle cells, through their paracrine function, had been known to be critical for neoangiogenesis. Here we found that hyperglycemia upregulates the expression of skeletal muscle cells prolyl hydroxylase domain 3 (PHD3), which resulted in the decrease of the secretion of angiogenic factors, especially VEGF-A and PDGF-BB. We showed that treatment with salidroside, a small molecule drug, significantly suppresses PHD3 expression and increases VEGF-A and PDGF-BB secretion from skeletal muscle cells, which in turn enhances the proliferation and migration potentials of endothelial and smooth muscle cells. Finally, we demonstrated that intramuscular injection of salidroside into the ischemic hind limbs of diabetic HLI model mice could efficiently induce neoangiogenesis and blood perfusion recovery. Thus, our novel findings not only reveal the effects of hyperglycemia on the angiogenesis potential of skeletal muscle cells and the mechanism underlying it, but also provides a novel finding suggesting that salidroside might be a potential small molecule drug for diabetic HLI.