An intracellular kinase signal-responsive gene carrier for disordered cell-specific gene therapy

Nanomediator-Effector Cascade Systems for Amplified Protein Kinase Activity Imaging and Phosphorylation-Induced Drug Release In Vivo

Protein kinases constitute a rich pool of biomarkers and therapeutic targets of tremendous diseases including cancer. However, sensing kinase activity in vivo while implementing treatments according to kinase hyperactivation remains challenging. Herein, we present a nanomediator-effector cascade system that can in situ magnify the subtle events of kinase-catalyzed phosphorylation via DNA amplification machinery to achieve kinase activity imaging and kinase-responsive drug release in vivo. In this cascade, the phosphorylation-mediated disassembly of DNA/peptide complex on the nanomediators initiated the detachment of fluorescent hairpin DNAs from the nanoeffectors via hybridization chain reaction (HCR), leading to fluorescence recovery and therapeutic cargo release. We demonstrated that this nanosystem simultaneously enabled trace protein kinase A (PKA) activity imaging and on-demand drug delivery for inhibition of tumor cell growth both in vitro and in vivo, affording a kinase-specific sense-and-treat paradigm for cancer theranostics.

Protein Kinase C α-Responsive Gene Carrier for Cancer-Specific Transgene Expression and Cancer Therapy

The presence of intracellular signal transduction and its abnormal activities in many cancers has potential for medical and pharmaceutical applications. We recently developed a protein kinase C α (PKCα)-responsive gene carrier for cancer-specific gene delivery. Here, we demonstrate an in-depth analysis of cellular signal-responsive gene carrier and the impact of its selective transgene expression in response to malfunctioning intracellular signaling in cancer cells. We prepared a novel gene carrier consisting of a linear polyethylenimine (LPEI) main chain grafted to a cationic PKCα-specific substrate (FKKQGSFAKKK-NH₂). The LPEI-peptide conjugate formed a nanosized polyplex with pDNA and mediated efficient cellular uptake and endosomal escape. This polyplex also led to successful transgene expression which responded to the target PKCα in various cancer cells and exhibited a 10-100-fold higher efficiency compared to the control group. In xenograft tumor models, the LPEI-peptide conjugate promoted transgene expression showing a clear-cut response to PKCα. Furthermore, when a plasmid containing a therapeutic gene, human caspase-8 (pcDNA-hcasp8), was used, the LPEI-peptide conjugate had significant cancer-suppressive effects and extended animal survival. Collectively, these results reveal that our method has great potential for cancer-specific gene delivery and therapy.

Cell division responsive peptides for optimized plasmid DNA delivery: the mitotic window of opportunity?

The delivery of plasmid DNA remains hard to achieve, especially due to the presence of the nuclear membrane barrier. During cell division, however, the nuclear membrane is temporarily disassembled. We evaluated two different strategies to optimize plasmid DNA delivery in dividing cells: 1) phosphorylation responsive peptides that release plasmid DNA preferentially during mitosis and 2) chromatin targeting peptides to anchor plasmid DNA in newly formed nuclei upon cell division. Peptide/DNA particles alone were not efficient in penetrating cells. Upon co-delivery with lipid-based carriers, however, transfection efficiency drastically improved when compared to controls. For the phosphorylation responsive peptides, the presence of the phosphorylation sequence slightly increased transfection efficiency. For the chromatin targeting peptides, however, the chromatin targeting sequence did not seem to be the main reason for the improvement of transfection efficiency when applied in living cells. In conclusion, the pre-condensation of plasmid DNA with peptides improves lipid based delivery, but the nature of the peptides (cell responsive or not) does not seem to be the main reason for the improvement. It seems that the nuclear entry of foreign plasmid DNA is still under tight control, even during the mitotic window of opportunity.

CANCER-SPECIFIC GENE CARRIERS RESPONDING TO CANCER MICROENVIRONMENT: ACIDOSIS AND HYPER-ACTIVATED PROTEIN KINASES

Protein kinase (PK)-responsive gene carriers modified with polyethylene glycol (PEG) chains using an acid-labile linker were developed. These carriers were obtained by modifying the PEG chains and substrate peptides for the PKs (PKA or PKCα) on the branched polyethyleneimine main chain. Polyplexes formed from these carriers and plasmid DNA (pDNA) were stably dispersed under neutral pH medium. The polyplexes were also taken up by cells on the release of the PEG chains under the slightly acidic extracellular pH associated with cancer cells. The polyplexes taken up by cells resulted in gene expression when the substrate peptides were phosphorylated by the intracellular PKs to release pDNA from the polyplexes. These novel gene carriers are expected to be promising for cancer-specific gene therapy via intravenous administration.

A review of RGD-functionalized nonviral gene delivery vectors for cancer therapy

The development of effective treatments that enable many patients suffering from cancer to be successfully cured is highly demanded. Angiogenesis, which is a process for the formation of new capillary blood vessels, has a crucial role in solid tumor progression and the development of metastasis. Antiangiogenic therapy designed to prevent tumor angiogenesis, thereby arresting the growth or spread of tumors, has emerged as a non-invasive and safe option for cancer treatment. Due to the fact that integrin receptors are overexpressed on the surface of angiogenic endothelial cells, various strategies have been made to develop targeted delivery systems for cancer gene therapy utilizing integrin-targeting peptides with an exposed arginine-glycine-aspartate (RGD) sequence. The aim of this review is to summarize the progress and prospect of RGD-functionalized nonviral vectors toward targeted delivery of genetic materials in order to achieve an efficient therapeutic outcome for cancer gene therapy, including antiangiogenic therapy.

Improvement in the colloidal stability of protein kinase-responsive polyplexes by PEG modification

We have reported a disease-cell specific gene expression system that is responsive to intracellular signaling proteins (e.g., protein kinases and proteases) hyperactivated in diseased cells. For this system, cationic peptide-grafted polymers were synthesized for polyplex formation with genes. Here, we modified poly(ethylene glycol) (PEG) to a protein kinase A (PKA)-responsive polymer to improve polyplex stability. PEG modification neutralized the surface charge of the polyplex and successfully increased polyplex stability at physiological conditions. However, PEG modification (PEG contents, 0.6 and 3.3 mol %) showed almost negligible effects on the reactivity of grafted peptides to PKA and the promotion of gene expression responding to PKA activity. Excessive modification of PEG (PEG contents, 6.8 mol %) inhibited polyplex formation. These results indicate that moderate modification of PEG to the enzyme-responsive polymer improves polyplex stability without inhibiting the reaction with enzymes.

Intracellular partitioning of cell organelles and extraneous nanoparticles during mitosis

The nucleocytoplasmic partitioning of nanoparticles as a result of cell division is highly relevant to the field of nonviral gene delivery. We reviewed the literature on the intracellular distribution of cell organelles (the endosomal vesicles, Golgi apparatus, endoplasmic reticulum and nucleus), foreign macromolecules (dextrans and plasmid DNA) and inorganic nanoparticles (gold, quantum dot and iron oxide) during mitosis. For nonviral gene delivery particles (lipid- or polymer-based), indirect proof of nuclear entry during mitosis is provided. We also describe how retroviruses and latent DNA viruses take advantage of mitosis to transfer their viral genome and segregate their episomes into the host daughter nuclei. Based on this knowledge, we propose strategies to improve nonviral gene delivery in dividing cells with the ultimate goal of designing nonviral gene delivery systems that are as efficient as their viral counterparts but non-immunogenic, non-oncogenic and easy and inexpensive to prepare.

Effect of recombinant plasmid pEGFP-AFP-hTNF on liver cancer cells (HepG2 Cells) in vitro when delivered by PEG-PEI/Fe₃O₄ nanomagnetic fluid

BACKGROUND/PURPOSE

Gene delivery into liver cancer cells has been a problem. This study aimed to understand the effect of using PEGI/Fe₃O₄ nanomagnetic fluid as a gene vector for liver cancer gene therapy. An AFP enhancer aids in the expression of tumor-specific foreign genes in AFP-producing cancer cells like HepG2 cells, and was utilized in the delivery method in this study.

METHODS

We constructed recombinant plasmid PEGFP-AFP-hTNFα, which was transfected into AFP positive HepG2 cells and AFP negative Hela cells by PEG-PEI/Fe₃O₄ nanomagnetic fluid. Fluorescence microscopy was used to evaluate the transfection rate of the hTNFα gene in the HepG2 cells 12 hours after transfection. Reverse transcription polymerase chain reaction (RT-PCR) and western blot were used to detect expression of hTNFα gene in the HepG2 cells 48 hours after transfection. Methyl thiazolyl tetrazolium (MTT) assay was used to evaluate the inhibitory effect of hTNFα on the proliferation of HepG2 cells. Flow cytometry was used to analyze the apoptosis of HepG2 cells.

RESULTS

Plasmid PEGFP-AFP-hTNFα delivered by PEG-PEI/Fe₃O₄ nanomagnetic fluid was successfully transfected into HepG2 cells and expressed in the HepG2 cells. The transfection efficacy of hTNFα gene delivered by PEG-PEI/Fe₃O₄ nanomagnetic fluid was superior to that of hTNFα gene delivered by lipofectamine in HepG2 cells. RT-PCR and western blot demonstrated that hTNFα gene was expressed in HepG2 cells that were transfected with complexes of nanomagnetic fluid/PEGFP-AFP-hTNFα. MTT and flow cytometry showed that the hTNFα gene markedly exerted a cell killing effect.

CONCLUSION

PEG-PEI/Fe₃O₄ nanomagnetic fluid successfully transfected PEGFP-AFP-hTNFα into HepG2 cells and induced expression of hTNFα gene in the HepG2 cells, thus showing promise as a gene vector for liver cancer gene therapy. Furthermore, an AFP enhancer can specifically increase the expression of target genes in cells positive for AFP.

Effect of introduction of chondroitin sulfate into polymer-peptide conjugate responding to intracellular signals

We recently developed a novel tumor-targeted gene delivery system responding to hyperactivated intracellular signals. Polymeric carrier for gene delivery consists of hydrophilic neutral polymer as main chains and cationic peptide substrate for target enzyme as side chains, and was named polymer-peptide conjugate (PPC). Introduction of chondroitin sulfate (CS), which induces receptor-medicated endocytosis, into polymers mainly with a high cationic charge density such as polyethylenimine can increase tumor-targeted gene delivery. In the present study, we examined whether introduction of CS into PPC containing five cationic amino acids can increase gene expression in tumor cells. Size and zeta potential of plasmid DNA (pDNA)/PPC/CS complex were <200 nm and between -10 and -15 mV, respectively. In tumor cell experiments, pDNA/PPC/CS complex showed lower stability and gene regulation, compared with that of pDNA/PPC. Moreover, no difference in gene expression was identified between positive and negative polymer. These results were caused by fast disintegration of pDNA/PPC/CS complexes in the presence of serum. Thus, we suggest that introduction of negatively charged CS into polymers with a low charge density may lead to low stability and gene regulation of complexes.

A gene-delivery system specific for hepatoma cells and an intracellular kinase signal based on human liver-specific bionanocapsules and signal-responsive artificial polymer

Recently, our group has proposed a novel gene-regulation system responding to cAMP-dependent protein kinase (PKA) that has been applied to living cells. In this study, human liver-specific bionanocapsules (BNCs) are used as a gene-delivery system to increase transfection efficiency and to target specific cell types. BNCs can efficiently deliver a target gene to human hepatocytes and hepatoma cells in vitro or in vivo. The combination of a signal-responsive gene-delivery system with BNCs led to an increase in the transfection efficiency and selectivity for hepatoma cells. Expression from the delivered gene was identified from PKA-activated hepatoma cells (HepG2), but not from colon tumor cells (WiDr). These results show that the combination of a gene-regulation system responding to an intracellular signal with BNC can be used for the selective treatment of human hepatoma cells.

Bio and nanotechnological strategies for tumor-targeted gene therapy

Gene therapy is a new medical approach for the treatment of tumors. For safe and efficient gene therapy, therapeutic genes need to be delivered efficiently into the target tumor cells. Development of gene delivery systems to specifically recognize and target tumor cells and to distinguish them from normal cells, especially in the same tissue or organ, is one of the most important issues regarding the present gene delivery methodologies. The enhanced permeability and retention (EPR) effect using the characteristics of angiogenic tumor blood vessels, as well as gene delivery systems recognizing hyperactivated receptors or intracellular signals, is broadly applied to tumor-targeted gene therapy. In addition, bacterial vectors can be a useful means for targeting hypoxic or anoxic regions of a tumor.

Specific transgene expression in HIV-infected cells using protease-cleavable transcription regulator

Gene therapy is a promising strategy for the treatment of HIV infection, but cell specificity remains an issue. Recently we have developed a new concept for a drug or gene delivery system responding to cellular signals (D-RECS) to achieve cell-specific transgene expression using a non-viral polymer-based vehicle. According to this concept, intracellular signaling enzymes, which are activated specifically in target cells, are used to trigger transgene expression. We previously applied this concept to HIV-1 protease and showed that the recombinant protease could act as a suitable signal. Here we further developed this system to achieve highly specific transgene expression in HIV-infected cells. We prepared a polymeric gene regulator grafted with a cationic peptide containing the HIV-Tat peptide via a specific substrate for HIV-1 protease. The regulator formed a stable polyplex with the transgene, suppressing its transcription. HIV-1 protease cleaved the peptide and released the transgene, which was consequently expressed specifically in activated HIV-infected cells, but remained unreleased and inactive in uninfected cells. The validity of this approach was further confirmed by applying it to the CVB1 2A protease of coxsackievirus (Picornaviridae family). This strategy should be widely applicable for specific expression of a variety of therapeutic genes in virus-infected cells.

Protein kinase Calpha-responsive polymeric carrier: its application for gene delivery into human cancers

For cancer-targeting gene delivery, we applied a protein kinase C (PKC)alpha-responsive polymeric carrier to human cancers (U-87 MG [human glioblastoma-astrocytoma, epithelial-like cell line] and A549 [human lung adenocarcinoma epithelial cell line]). Two polymers, one a PKCalpha-responsive polymer (PPC[S]) containing the phosphorylation site serine, and the other a negative control polymer (PPC[A]), in which the serine was substituted with alanine, were synthesized. No cytotoxicity of the polymer was identified. When the complexes were transfected into cancer cells or tissues in which PKCalpha was hyper-activated, the luciferase expression from the PPC(S)/plasmid (pDNA) complex was higher than that from the PPC(A)/pDNA complex. These results show that the phosphorylation of complex by PKCalpha in cancer cells leads to high gene expression and that our system can be used as a human cancer cell-targeting gene delivery system.

Protein kinase C alpha-specific peptide substrate graft-type copolymer for cancer cell-specific gene regulation systems

We recently proposed a novel gene regulation system responding to specifically and abnormally activated intracellular enzymes in diseased cells. In the present study, we focused on protein kinase C (PKC)alpha, which is hyper-activated in most tumor cells, as a trigger for transgene regulation. We prepared cationic copolymers comprising hydrophilic and neutral polymers in main chains and cationic peptide substrates with different contents in side chains. Our copolymer with high peptide content (>3 mol%) condensed with pDNA more weakly than with poly(L-lysine) (pLL) having a similar molecular weight, but gene suppression was nearly identical to that of pLL, probably due to the steric hindrance of the main chains in our copolymer. Steric hindrance of the main chains barely affected the phosphorylation reaction of the pendant peptide. In cell and mouse experiments, higher gene expression was observed in complexes of pDNA with copolymers pended PKC alpha-specific substrate peptide than that in complexes with negative copolymers pended peptide substituted phosphorylation site of serine residues with alanine. These results indicate that our system can recognize intracellular PKC alpha as a trigger to regulate transgene expression, and may be useful for tumor gene therapy.

Molecular mechanism of caspase-3-induced gene expression of polyplexes formed from polycations grafted with cationic substrate peptides

We previously reported a novel disease-site-specific gene targeting system that can release plasmid DNA (pDNA) from polymeric carriers responding to abnormally activated signal proteins in disease cells. In this study, the molecular mechanism of the gene targeting system responding to Caspase-3 activity was studied in detail. The polymeric carrier used was composed of a neutral main chain polymer and a grafted oligocationic peptide which contains the substrate sequence of Caspase-3. The polyplex formed from the polymeric carrier and pDNA was stable in physiological saline solution and protected from access of RNA polymerase and the transcriptional factors. These results indicate that the polyplex adopts a core-shell-like structure with a polyion complex core surrounded by neutral main chain polymers. In spite of the inert character of the polyplex to transcription, the polyplex afforded the access of Caspase-3 to the substrate peptide because the electrostatic interaction between each peptide and DNA is essentially weak. After the Caspase-3 reaction, the polyplex was weakened and then became available as a template for transcription.

Engineered polymers for advanced drug delivery

Engineered polymers have been utilized for developing advanced drug delivery systems. The development of such polymers has caused advances in polymer chemistry, which, in turn, has resulted in smart polymers that can respond to changes in environmental condition such as temperature, pH, and biomolecules. The responses vary widely from swelling/deswelling to degradation. Drug-polymer conjugates and drug-containing nano/micro-particles have been used for drug targeting. Engineered polymers and polymeric systems have also been used in new areas, such as molecular imaging as well as in nanotechnology. This review examines the engineered polymers that have been used as traditional drug delivery systems and as more recent applications in nanotechnology.

Regulation of Transgene Expression in Tumor Cells by Exploiting Endogenous Intracellular Signals

Recently, we have proposed a novel strategy for a cell-specific gene therapy system based on responses to intracellular signals. In this system, an intracellular signal that is specifically and abnormally activated in the diseased cells is used for the activation of transgene expression. In this study, we used protein kinase C (PKC)alpha as a trigger to activate transgene expression. We prepared a PKCalpha-responsive polymer conjugate [PPC(S)] and a negative control conjugate [PPC(A)], in which the phosphorylation site serine (Ser) was replaced with alanine (Ala). The phosphorylation for polymer/DNA complexes was determined with a radiolabel assay using [gamma-(32)P]ATP. PPC(S)/DNA complexes were phosphorylated by the addition of PKCalpha, but no phosphorylation of the PPC(A)/DNA complex was observed. Moreover, after microinjection of polymer/GFP-encoding DNA complexes into HepG2 cells at cation/anion (C/A) ratios of 0.5 to 2.0, significant expression of GFP was observed in all cases using PPC(S)/DNA complexes, but no GFP expression was observed in the negative control PPC(A)/DNA complex-microinjected cells at C/A ratios of 1.0 and 2.0. On the other hand, GFP expression from PPC(S)/DNA complexes was completely suppressed in cells pretreated with PKCalpha inhibitor (Ro31-7549). These results suggest that our gene regulation system can be used for tumor cell-specific expression of a transgene in response to PKCalpha activity.

Design of polymeric carriers for cancer-specific gene targeting: utilization of abnormal protein kinase Calpha activation in cancer cells

We succeeded in cancer cell specific gene expression by using a polyplex responsive to protein kinase Calpha, which is activated in various types of cancer cells.

Effect of the addition of diammonium citrate to alpha-cyano-4-hydroxycinnamic acid (CHCA) matrix for the detection of phosphorylated peptide in phosphorylation reactions using cell and tissue lysates

The ionization of phosphorylated peptides is usually suppressed by non-phosphorylated peptides when alpha-cyano-4-hydroxycinnamic acid (CHCA) is used as a matrix for matrix-assisted laser desorption/ionization-time-of-Flight (MALDI-TOF) mass spectrometry analysis. In the present study, we examined the effect of diammonium citrate addition to the CHCA matrix on the detection of phosphorylated peptides. Substrates for protein kinase C (PKC) and c-Src were synthesized and phosphorylated by reaction with cell and tissue lysate samples. The addition of diammonium citrate to the CHCA matrix increased the sensitivity for distinguishing phosphorylated peptides from background noise. However, the effect depended on substrate concentration.

Overall interaction of cytosolic proteins with the PEI/DNA complex

Little is known on mechanisms involved in transport of complex of DNA and gene carrier molecules from the cytosol to the nucleus. We aimed to identify cytosolic proteins interacting with the polyethylenimine (PEI)/DNA complex, using 2-D gel electrophoresis and peptide mass fingerprinting. Fifteen proteins including actin, beta-tubulin, and other metabolic proteins were identified. They demonstrated various molecular weights and isoelectric points, and were categorized into 3 groups: early binding, late binding, and transient binding proteins. Protein binding caused DNA release from the PEI/DNA complex with a cation/anion (C/A) ratio of 2, where complex formation was weak. Knowledge on interactions between cytosolic proteins and DNA/carrier complexes will help understand intracellular gene delivery mechanisms.

Mass-tag technology responding to intracellular signals as a novel assay system for the diagnosis of tumor

A novel mass spectrometry-based assay system for determining protein kinase activity employing mass-tagged substrate peptide probes was used for the diagnosis of tumors. Two peptide probes (H-type and D-type) were synthesized containing the same substrate peptide sequence for protein kinase C (PKC). The molecular weights of the two probes differ because of the incorporation of deuterium into the acetyl groups of the D-type probe. The lysates of the normal and tumor tissue were prepared and reacted with the H- and D-type peptide probes, respectively. The PKC activities of the normal and tumor tissues can be compared simply and directly by calculating the phosphorylated ratio to each peptide probe, obtained from the peak intensity of the mass spectrum after mixing of the two reaction solutions. The phosphorylation ratio for the reaction of the H-type peptide probe with the tumor tissue lysate (B16 melanoma) was more than three times higher than that of the D type peptide probe with the normal skin tissue lysate. These results show that the novel assay system for detecting protein kinase activity using mass-tag technology can be a simple and useful means to profile protein kinase activity for cell or tissue lysate samples, and can be applied to the diagnosis of tumors.

A protein kinase signal-responsive gene carrier modified RGD peptide

We have previously reported artificial gene-regulation systems responding to cyclic AMP-dependent protein kinase (PKA) using a cationic polymer. However, this polymer alone cannot deliver any gene into living cells. In the present work, we modified the signal-responsive polymer to the RGD peptide for the introduction of a polymer/DNA complex into living cells and succeeded in regulating the gene expression responding to intracellular PKA activation.