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

Gene Therapy, A Potential Therapeutic Tool for Neurological and Neuropsychiatric Disorders: Applications, Challenges and Future Perspective

Neurological and neuropsychiatric disorders are the main risks for the health care system, exhibiting a huge socioeconomic load. The available range of pharmacotherapeutics mostly provides palliative consequences and fails to treat such conditions. The molecular etiology of various neurological and neuropsychiatric disorders is mostly associated with a change in genetic background, which can be inherited/triggered by other environmental factors. To address such conditions, gene therapy is considered a potential approach claiming a permanent cure of the disease primarily by deletion, silencing, or edition of faulty genes and by insertion of healthier genes. In gene therapy, vectors (viral/nonvial) play an important role in delivering the desired gene to a specific region of the brain. Targeted gene therapy has unraveled opportunities for the treatment of many neurological and neuropsychiatric disorders. For improved gene delivery, the current techniques mainly focus on designing a precise viral vector, plasmid transfection, nanotechnology, microRNA, and in vivo clustered regulatory interspaced short palindromic repeats (CRISPR)-based therapy. These latest techniques have great benefits in treating predominant neurological and neurodevelopmental disorders, including Parkinson's disease, Alzheimer's disease, and autism spectrum disorder, as well as rarer diseases. Nevertheless, all these delivery methods have their limitations, including immunogenic reactions, off-target effects, and a deficiency of effective biomarkers to appreciate the effectiveness of therapy. In this review, we present a summary of the current methods in targeted gene delivery, followed by the limitations and future direction of gene therapy for the cure of neurological and neuropsychiatric disorders.

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.

Effect of peptide content on the regulation of transgene expression by protein kinase Cα-responsive linear polyethylenimine-peptide conjugates

We examined a series of linear polyethylenimine (LPEI)-based nanocarriers that activate transgene expression in response to cancer-specific protein kinase Cα (PKCα). Eight types of LPEI-peptide conjugate differing in peptide content and number were synthesized using click chemistry. The conjugates could form polyplexes with pDNA through electrostatic interaction, but the degree of pDNA condensation, sizes, and surface charges of the resulting polyplexes depended on the pendant-peptide content and number. None of the polyplexes showed significant cytotoxicity toward human hepatoma cells (HepG2). Furthermore, pendant peptide content and number markedly affected transgene activation in response to PKCα. To achieve an all-or-none response to PKCα, we determined the optimum peptide content and number in LPEI-peptide conjugates as ≈6 mol% and ≈40 peptides/conjugate.

Development of nanoparticles incorporating a novel liposomal membrane destabilization peptide for efficient release of cargos into cancer cells

In anti-cancer therapy mediated by a nanoparticle-based drug delivery system (DDS), overall efficacy depends on the release efficiency of cargos from the nanoparticles in the cancer cells as well as the specificity of delivery to tumor tissue. However, conventional liposome-based DDS have no mechanism for specifically releasing the encapsulated cargos inside the cancer cells. To overcome this barrier, we developed nanoparticles containing a novel liposomal membrane destabilization peptide (LMDP) that can destabilize membranes by cleavage with intramembranous proteases on/in cancer cells. Calcein encapsulated in liposomes modified with LMDP (LMDP-lipo) was effectively released in the presence of a membrane fraction containing an LMDP-cleavable protease. The release was inhibited by a protease inhibitor, suggesting that LMDP-lipo could effectively release its cargo into cells in response to a cancer-specific protease. Moreover, when LMDP-lipo contained fusogenic lipids, the release of cargo was accelerated, suggesting that the fusion of LMDP-lipo with cellular membranes was the initial step in the intracellular delivery. Time-lapse microscopic observations showed that the release of cargo from LMDP-lipo occurred immediately after association of LMDP-lipo with target cells. Consequently, LMDP-lipo could be a useful nanoparticle capable of effective release of cargos specifically into targeted cancer cells.

Histidinylated poly-L-lysine-based vectors for cancer-specific gene expression via enhancing the endosomal escape

In this work, we synthesized a series of poly-L-lysine (PLL)-based polymers for gene delivery, by modifying the PLL with both cationic peptide and histidine. The peptide moieties serve as cationic centers for polyplex formation, and also as substrates for protein kinase Cα (PKCα), which is specifically activated in many types of cancer cells, to achieve cancer-specific gene expression. The histidine groups serve as buffering moieties to increase the ability of the plasmid DNA (pDNA)-polymer complex (polyplex) to escape the endosome and thus to promote expression of the pDNA in the transfected cells. The facile synthesis of the polymers proceeded by modifying the PLL with side-group-protected peptide and protected histidine, followed by deprotection of the functional groups. The synthesized polymers showed significant buffering capacity over the neutral to acidic pH range and showed less cytotoxicity in vitro compared with histidine-unmodified polymers. The polyplexes successfully showed PKCα-responsive gene expression immediately after their introduction into cancer cells and the gene expression continued for at least 24 h. These PLL-based carriers thus show promise for cancer-targeted gene therapy.

Branched polyethylenimine-based PKCα-responsive gene carriers

We examined in vitro performance of the branched polyethylenimine (bPEI)-based gene carriers which respond to cancer-specific activation of protein kinase Cα (PKCα) to express plasmid DNA. The carriers were synthesized straightforward by using amide bond formation between a peptide terminal carboxyl and a primary amine group of bPEI. To examine the effect of the peptide contents in the carrier, we prepared several carriers with various peptide contents. The obtained polymers form polyplexes with tighter condensation of plasmid DNA than our previous gene carriers. After internalization of the polyplexes via endocytosis, the polyplexes effectively escaped from the endosome into cytosol. Then, the polyplexes showed a clear-cut response to PKCα to release plasmid DNA for gene expression. We determined the optimum contents of the peptides in carriers as 5 mol% to achieve the clear-cut response to PKCα.

Gene carrier showing all-or-none response to cancer cell signaling

In this work we designed a novel nano carrier, a linear polyethylenimine (LPEI)-peptide conjugate, for cancer-specific expression of transgenes. The conjugate was easily synthesized by using a click chemistry scheme orthogonal to the reactive side groups of the peptide, which is the substrate of protein kinase Cα (PKCα). Polyplexes of the conjugates with plasmid DNA (pDNA) were intact and stably dispersed even in the presence of cell lysate. Despite this stability, the polyplexes readily dissociated upon phosphorylation of the grafted peptides by PKCα. Because of its endosomal escape ability and adequate susceptibility to PKCα, the polyplexes showed an all-or-none type response to PKCα activity in transgene expression in vitro. The polyplexes achieved cancer tissue-specific transgene expression even for a tumor with a relatively low PKCα activity. Thus the LPEI-peptide conjugate has high potential as a nanocarrier for cancer-targeted gene therapy.

Liver cell specific targeting by the preS1 domain of hepatitis B virus surface antigen displayed on protein nanocages

Protein nanocages are self-organized complexes of oligomers whose three-dimensional architecture can been determined in detail. These structures possess nanoscale inner cavities into which a variety of molecules, including therapeutic or diagnostic agents, can be encapsulated. These properties yield these particles suitable for a new class of drug delivery carrier, or as a bioimaging reagent that might respond to biochemical signals in many different cellular processes. We report here the design, synthesis, and biological characterization of a hepatocyte-specific nanocage carrying small heat-shock protein. These nanoscale protein cages, with a targeting peptide composed of a preS1 derivative from the hepatitis B virus on their surfaces, were prepared by genetic engineering techniques. PreS1-carrying nanocages showed lower cytotoxicity and significantly higher specificity for human hepatocyte cell lines than other cell lines in vitro. These results suggested that small heat-shock protein-based nanocages present great potential for the development of effective targeted delivery of various agents to specific cells.

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 hydrophilic polymer grafted with a histone tail peptide as an artificial gene regulator

In chromatin, gene transcription is regulated through posttranslational modifications on the histone N-terminal tail sequences, typically an acetyl group modification on lysine residues. To realize a simple model of the gene regulation of chromatin, we designed a hydrophilic polymer grafted with histone H3 tail peptides. The polyplex formed from the polymer and DNA suppressed the gene expression effectively although the polyplex was weaker than the polyplex of poly-L-lysine and DNA. This weaker polyplex afforded the acetylation of the lysine residue of the grafted peptides by histone acetyltransferase. Subsequently, the gene expression was activated due to the relaxation of the polyplex which was brought by a cationic charge decrease in the grafted peptides. This molecular system is the first functional model of the gene regulation of the chromatin.

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.