Trojan peptides: the penetratin system for intracellular delivery

Cell-penetrating peptides and peptide nucleic acid-coupled MRI contrast agents: evaluation of cellular delivery and target binding

Molecular imaging of cells and cellular processes can be achieved by tagging intracellular targets such as receptors, enzymes, or mRNA. Seeking to visualize the presence of specific mRNAs by magnetic resonance (MR) imaging, we coupled peptide nucleic acids (PNA) with gadolinium-based MR contrast agents using cell-penetrating peptides for intracellular delivery. Antisense to mRNA of DsRed2 protein was used as proof of principle. The conjugates were produced by continuous solid-phase synthesis followed by chelation with gadolinium. Their cellular uptake was confirmed by fluorescence microscopy and spectroscopy as well as by MR imaging of labeled cells. The cell-penetrating peptide D-Tat(57-49) was selected over two other derivatives of HIV-1 Tat peptide, based on its superior intracellular delivery of the gadolinium-based contrast agents. Further improved delivery of conjugates was achieved upon coupling peptide nucleic acids (antisense to mRNA of DsRed2 protein and nonsense with no natural counterpart). Significant enhancement in MR contrast was obtained in cells labeled with concentrations as low as 2.5 μM of these agents. Specific binding of the targeting PNA containing conjugate to its complementary oligonucleotide sequence was proven by in vitro cell-free assay. In contrast, a lack of specific enrichment was observed in transgenic cells containing the target due to nonspecific vesicular entrapment of contrast agents. Preliminary biodistribution studies showed conjugate-related fluorescence in several organs, especially the liver and bladder, indicating high mobility of the agent in spite of its high molecular weight. No conjugate related toxicity was observed. These results are encouraging, as they warrant further molecular optimization and consecutive specificity studies in vivo of this new generation of contrast agents.

Cell-penetrating HIV1 TAT peptides float on model lipid bilayers

Cell-penetrating peptides like the cationic HIV1 TAT peptide are able to translocate across cell membranes and to carry molecular cargoes into the cellular interior. For most of these peptides, the biophysical mechanism of the membrane translocation is still quite unknown. We analyzed HIV1 TAT peptide binding and mobility within biological model membranes. To this end, we generated neutral and anionic giant unilamellar vesicles (GUVs) containing DPPC, DOPC, and cholesterol and containing DPPC, DOPC, cholesterol, and DPPS (DOPS), respectively. First, we characterized the mobility of fluorescently labeled lipids (TR-DHPE) within liquid-ordered and liquid-disordered lipid phases by single-molecule tracking, yielding a D(LO) of 0.6 +/- 0.05 microm(2)/s and a D(LD) of 2.5 +/- 0.05 microm(2)/s, respectively, as a reference. Fluorescently labeled TAT peptides accumulated on neutral GUVs but bound very efficiently to anionic GUVs. Single-molecule tracking revealed that HIV1 TAT peptides move on neutral and anionic GUV surfaces with a D(N,TAT) of 5.3 +/- 0.2 microm(2)/s and a D(A,TAT) of 3.3 +/- 0.2 mum(2)/s, respectively. TAT peptide diffusion was faster than fluorescent lipid diffusion, and also independent of the phase state of the membrane. We concluded that TAT peptides are not incorporated into but rather floating on lipid bilayers, but they immerged deeper into the headgroup domain of anionic lipids. The diffusion constants were not dependent on the TAT concentration ranging from 150 pM to 2 microM, indicating that the peptides were not aggregated on the membrane and not forming any "carpet".

Antisense applications for biological control

Although Nature's antisense approaches are clearly impressive, this Perspectives article focuses on the experimental uses of antisense reagents (ASRs) for control of biological processes. ASRs comprise antisense oligonucleotides (ASOs), and their catalytically active counterparts ribozymes and DNAzymes, as well as small interfering RNAs (siRNAs). ASOs and ribozymes/DNAzymes target RNA molecules on the basis of Watson-Crick base pairing in sequence-specific manner. ASOs generally result in destruction of the target RNA by RNase-H mediated mechanisms, although they may also sterically block translation, also resulting in loss of protein production. Ribozymes and DNAzymes cleave target RNAs after base pairing via their antisense flanking arms. siRNAs, which contain both sense and antisense regions from a target RNA, can mediate target RNA destruction via RNAi and the RISC, although they can also function at the transcriptional level. A considerable number of ASRs (mostly ASOs) have progressed into clinical trials, although most have relatively long histories in Phase I/II settings. Clinical trial results are surprisingly difficult to find, although few ASRs appear to have yet established efficacy in Phase III levels. Evolution of ASRs has included: (a) Modifications to ASOs to render them nuclease resistant, with analogous modifications to siRNAs being developed; and (b) Development of strategies to select optimal sites for targeting. Perhaps the biggest barrier to effective therapies with ASRs is the "Delivery Problem." Various liposomal vehicles have been used for systemic delivery with some success, and recent modifications appear to enhance systemic delivery, at least to liver. Various nanoparticle formulations are now being developed which may also enhance delivery. Going forward, topical applications of ASRs would seem to have the best chances for success. In summary, modifications to ASRs to enhance stability, improve targeting, and incremental improvements in delivery vehicles continue to make ASRs attractive as molecular therapeutics, but their advance toward the bedside has been agonizingly slow.

Lipophilic lysine-spermine conjugates are potent polyamine transport inhibitors for use in combination with a polyamine biosynthesis inhibitor

Cancer cells can overcome the ability of polyamine biosynthesis inhibitors to completely deplete their internal polyamines by the importation of polyamines from external sources. This paper discusses the development of a group of lipophilic polyamine analogues that potently inhibit the cellular polyamine uptake system and greatly increase the effectiveness of polyamine depletion when used in combination with DFMO, a well-studied polyamine biosynthesis inhibitor. The attachment of a length-optimized C(16) lipophilic substituent to the epsilon-nitrogen atom of an earlier lead compound, D-Lys-Spm (5), has produced an analogue, D-Lys(C(16)acyl)-Spm (11) with several orders of magnitude more potent cell growth inhibition on a variety of cultured cancer cell types including breast (MDA-MB-231), prostate (PC-3), melanoma (A375), and ovarian (SK-OV-3), among others. These results are discussed in the context of a possible membrane-catalyzed interaction with the extracellular polyamine transport apparatus. The resulting novel two-drug combination therapy targeting cellular polyamine metabolism has shown exceptional efficacy against cutaneous squamous cell carcinomas (SCC) in a transgenic ornithine decarboxylase (ODC) mouse model of skin cancer. A majority (88%) of large, aggressive SCCs exhibited complete or nearly complete remission to this combination therapy, whereas responses to each agent alone were poor. The availability of a potent polyamine transport inhibitor allows, for the first time, for a real test of the hypothesis that starving cells of polyamines will lead to objective clinical response.

Interactions between the L1 cell adhesion molecule and ezrin support traction-force generation and can be regulated by tyrosine phosphorylation

An Ig superfamily cell-adhesion molecule, L1, forms an adhesion complex at the cell membrane containing both signaling molecules and cytoskeletal proteins. This complex mediates the transduction of extracellular signals and generates actin-mediated traction forces, both of which support axon outgrowth. The L1 cytoplasmic region binds ezrin, an adapter protein that interacts with the actin cytoskeleton. In this study, we analyzed L1-ezrin interactions in detail, assessed their role in generating traction forces by L1, and identified potential regulatory mechanisms controlling ezrin-L1 interactions. The FERM domain of ezrin binds to the juxtamembrane region of L1, demonstrated by yeast two-hybrid interaction traps and protein binding analyses in vitro. A lysine-to-leucine substitution in this domain of L1 (K1147L) shows reduced binding to the ezrin FERM domain. Additionally, in ND7 cells, the K1147L mutation inhibits retrograde movement of L1 on the cell surface that has been linked to the generation of the traction forces necessary for axon growth. A membrane-permeable peptide consisting of the juxtamembrane region of L1 that can disrupt endogenous L1-ezrin interactions inhibits neurite extension of cerebellar cells on L1 substrates. Moreover, the L1-ezrin interactions can be modulated by tyrosine phosphorylation of the L1 cytoplasmic region, namely, Y1151, possibly through Src-family kinases. Replacement of this tyrosine together with Y1176 with either aspartate or phenylalanine changes ezrin binding and alters colocalization with ezrin in ND7 cells. Collectively, these data suggest that L1-ezrin interactions mediated by the L1 juxtamembrane region are involved in traction-force generation and can be regulated by the phosphorylation of L1.

Sox11 transcription factor modulates peripheral nerve regeneration in adult mice

The ability of adult peripheral sensory neurons to undergo functional and anatomical recovery following nerve injury is due in part to successful activation of transcriptional regulatory pathways. Previous in vitro evidence had suggested that the transcription factor Sox11, a HMG-domain containing protein that is highly expressed in developing sensory neurons, is an important component of this regenerative transcriptional control program. To further test the role of Sox11 in an in vivo system, we developed a new approach to specifically target small interfering RNAs (siRNAs) conjugated to the membrane permeable molecule Penetratin to injured sensory afferents. Injection of Sox11 siRNAs into the mouse saphenous nerve caused a transient knockdown of Sox11 mRNA that transiently inhibited in vivo regeneration. Electron microscopic level analysis of Sox11 RNAi-injected nerves showed that regeneration of myelinated and unmyelinated axons was inhibited. Nearly all neurons in ganglia of crushed nerves that were Sox11 immunopositive showed colabeling for the stress and injury-associated activating transcription factor 3 (ATF3). In addition, treatment with Sox11 siRNAs in vitro and in vivo caused a transcriptional and translational level reduction in ATF3 expression. These anatomical and expression data support an intrinsic role for Sox11 in events that underlie successful regeneration following peripheral nerve injury.

Gene therapy using TRAIL-secreting human umbilical cord blood-derived mesenchymal stem cells against intracranial glioma

Adenovirus-mediated gene therapies against brain tumors have been limited by the difficulty in tracking glioma cells infiltrating the brain parenchyma. Human umbilical cord blood-derived mesenchymal stem cells (UCB-MSC) are particularly attractive cells for clinical use in cell-based therapies. In the present study, we evaluated the tumor targeting properties and antitumor effects of UCB-MSCs as gene delivery vehicles for glioma therapy. We efficiently engineered UCB-MSCs to deliver a secretable trimeric form of tumor necrosis factor-related apoptosis-inducing ligand (stTRAIL) via adenoviral transduction mediated by cell-permeable peptides. We then confirmed the migratory capacity of engineered UCB-MSCs toward tumor cells by an in vitro migration assay and by in vivo injection of UCB-MSCs into the tumor mass or the opposite hemisphere of established human glioma in nude mice. Moreover, in vitro coculture, experiments on Transwell plates, and in vivo survival experiments showed that MSC-based stTRAIL gene delivery has more therapeutic efficacy compared with direct injection of adenovirus encoding the stTRAIL gene into a tumor mass. In vivo efficacy experiments showed that intratumoral injection of engineered UCB-MSCs (MSCs-stTRAIL) significantly inhibited tumor growth and prolonged the survival of glioma-bearing mice compared with controls. These results suggest that human UCB-MSCs have potential use as effective delivery vehicles for therapeutic genes in the treatment of intracranial glioma.

Maurocalcine as a non toxic drug carrier overcomes doxorubicin resistance in the cancer cell line MDA-MB 231

PURPOSE

The aim of this study is to overcome tumour cell resistance that generally develops after administration of commonly used anti-cancer drugs, such as doxorubicin.

METHODS

Recently, cell penetrating peptides have been used for their ability to deliver non-permeant compounds into cells. One such cell penetrating peptide, maurocalcine, has been isolated from the venom of a Tunisian scorpion. Herein, we report the effects of doxorubicin covalently coupled to an analogue of maurocalcine on drug-sensitive or drug-resistant cell lines MCF7 and MDA-MB 231.

RESULTS

We demonstrated the in vitro anti-tumoral efficacy of the doxorubicin maurocalcine conjugate. On a doxorubicin-sensitive cancer cell line, the maurocalcine-conjugated form appears slightly less efficient than doxorubicin itself. On the contrary, on a doxorubicin-resistant cancer cell line, doxorubicin coupling allows to overcome the drug resistance. This strategy can be generalized to other cell penetrating peptides since Tat and penetratin show similar effects.

CONCLUSION

We conclude that coupling anti-tumoral drugs to cell penetrating peptides represent a valuable strategy to overcome drug resistance.

Membrane transducing activity of recombinant Hoxc8 protein and its possible application as a gene delivery vector

In order to examine whether the Hoxc8 protein can deliver nucleic acid into mammalian cells, we designed several Hoxc8-derived recombinant proteins to be synthesized as glutathione S-transferase (GST) fused forms in E. coli (GST-Hoxc8(1-242), containing a full length of Hoxc8; GST-Hoxc8(152-242), possessing a deletion of the acidic N-terminus of Hoxc8; GST-Hoxc8(149-208), which contained the homeodomain only). After labeling these proteins with Oregon 488, we examined their membrane transduction ability under the fluorescence microscope and verified that all three proteins showed similar transduction efficiency. The ability of the proteins to form in vitro protein-DNA complexes was analyzed on agarose gel; both GST-Hoxc8(1-242) and GST-Hoxc8(149-208) formed complexes. In contrast, the GST-Hoxc8(152-242) protein did not form a complex. The GST-Hoxc8(149-208) protein formed a complex with DNA at a mass ratio of 1ú1 (DNAúprotein), and GST-Hoxc8(1-242) formed a complex at a mass ratio of 1ú5. When the DNA (pDsRed1-C1) and protein complexes were added to culture media containing mammalian cells, the cells uptook the complexes, which was indicated by red fluorescence expression under the fluorescent microscope. These results indicate that recombinant Hoxc8 derivatives that harbor a homeodomain are able to traverse the mammalian cellular membrane. DNA that is bound to the recombinant derivatives can be carried across the membrane as well. This process could be applied in the development of a useful delivery vector for gene therapy in the future.

Arginine-rich cell penetrating peptides: design, structure-activity, and applications to alter pre-mRNA splicing by steric-block oligonucleotides

Rerouting the splicing machinery with steric-block oligonucleotides (ON) might lead to new therapeutic strategies in the treatment of diseases such as beta-thalassemia, Duchenne muscular dystrophy, or cancers. Interfering with splicing requires the sequence-specific and stable hybridization of RNase H-incompetent ON as peptide nucleic acids (PNA) or phosphorodiamidate morpholino oligomers (PMO). Unfortunately, these uncharged DNA mimics are poorly taken up by most cell types and conventional delivery strategies that rely on electrostatic interaction do not apply. Likewise, conjugation to cell penetrating peptides (CPPs) as Tat, Arg9, Lys8, or Pen leads to poor splicing correction efficiency at low concentration essentially because PNA- and PMO-CPP conjugates remain entrapped within endocytotic vesicles. Recently, we have designed an arginine-rich peptide (R-Ahx-R)4 (with Ahx for aminohexanoic acid) and an arginine-tailed Penetratin derivative which allow sequence-specific and efficient splicing correction at low concentration in the absence of endosomolytic agents. Both CPPs are undergoing structure-activity relationship studies for further optimization as steric-block ON delivery vectors.

New approaches to in-cell detection of protein activity: genetically encoded chemiluminescence probes pave the way to robust HTS assays

New genetically encoded biosensors utilizing the modified firefly luciferase promise a great improvement in the signal-to-noise ratio and the dynamic range of response in living cells. These biosensors are particularly suitable for high-throughput screening assays that use large-well-capacity formats because of their excellent response characteristics. The biosensor design strategies are highly generalizable and will be extremely valuable for expanding the repertoire of screenable targets in living cell systems.

Regulation of survival in adult hippocampal and glioblastoma stem cell lineages by the homeodomain-only protein HOP

Background

Homeodomain proteins play critical roles in shaping the development of the embryonic central nervous system in mammals. After birth, neurogenic activities are relegated to stem cell niches, which include the subgranular layer of the dentate gyrus of the hippocampus. Here, we have analyzed the function of HOP (Homeodomain only protein) in this stem cell niche and in human glioblastomas.

Results

We find that HOP is strongly expressed by radial astrocytes of the dentate gyrus in mice, which are stem cells that give rise to hippocampal granular neurons throughout adulthood. Deletion or down-regulation of HOP results in a decrease of apoptosis of these stem cells without changes in proliferation, and in an increase in the number of newly formed granule neurons. We also find that human glioblastomas largely lack HOP expression and that reintroduction of HOP function in glioma cells cultured as gliomaspheres leads to enhanced apoptosis in a subset of cases. In these cells, HOP function decreases clonogenicity.

Conclusion

These data suggest that HOP participates in the regulation of the adult mouse hippocampal stem cell niche by negatively affecting cell survival. In addition, HOP may work as a tumor suppressor in a subset of glioblastomas. HOP function thus appears to be critical in the adult brain in a region of continued plasticity, and its deregulation may contribute to disease.

Protein transduction: generation of full-length transducible proteins using the TAT system

This unit describes the technology that allows an investigator to transduce full-length proteins by utilizing a minimal, eleven-amino acid, HIV-TAT transduction domain that can be fused to a protein of choice using the pTAT or pTAT-HA protein expression plasmids. Bacterial expression, followed by solubilization of protein aggregates with a denaturing agent, affords high yields of transducible fusion protein. The fusion protein, once added to the culture medium, can cross the cell membrane and then be degraded or refolded by the cellular machinery. Correct targeting and function of the fusion protein can be easily examined by fluorescent microscopy or immunohistochemistry. This strategy was established and improved to its current state by the purification and transduction of a multitude of fusion proteins. Because the pool of fusion proteins spans many different functions, the protocols cover a wide variety of commonly used protein isolation and characterization methods.

Effective penetration of cell-permeable peptide mimic of tyrosine residue 654 domain of beta-catenin into human renal tubular epithelial cells

Phosphorylation of beta-catenin tyrosine residue 654 plays an important role in the epithelial to myofibroblast transition (EMT). Introducing mimic peptide of tyrosine residue 654 domain of beta-catenin into cells may influence phosphorylation of beta-catenin tyrosine residue 654. To deliver this mimic peptide into renal epithelial cells, we used penetratin as a vector, which is a novel cell permeable peptide, to deliver hydrophilic molecules into cells. A tyrosine 654 residue domain mimic peptide of beta-catenin (PM) with fused penetratin was constructed, purified and then detected for the penetration of the mimic peptide into human renal tubular epithelial cells (HK-2). The results showed that purified fusion mimic peptide could efficiently and rapidly translocate into human renal tubular epithelial cells. It is concluded that a cell-permeable peptides mimic of tyrosine residue 654 domain of beta-catenin was successfully obtained, which may provide a useful reagent for interfering the human renal tubular epithelial-mesenchymal transition.

Anti-gene padlocks eliminate Escherichia coli based on their genotype

OBJECTIVES

Several therapeutic strategies that target nucleic acids exist; however, most approaches target messenger RNA, rather than genomic DNA. We describe a novel oligonucleotide-based strategy, called anti-gene padlocks (AGPs), which eliminate Escherichia coli based on their genotype.

METHODS

The strategy employs an oligonucleotide with a double hairpin structure where both strands of the AGP are complementary to both strands of a target gene. We tested AGPs for in vitro binding and inhibition of DNA polymerization. AGPs were electroporated into bacterial cells with and without gene targets along with an ampicillin resistance plasmid, and cell survival was measured.

RESULTS

In vitro, AGPs bound the DNA target in a sequence-dependent fashion and inhibited DNA synthesis. When transformed into bacterial cells containing 10, 20 or 30 bp lacZ or 20 bp proA DNA targets in their genomes, AGPs selectively killed or otherwise inhibited growth of these cells, while those lacking the target demonstrated little, if any, toxicity. A single transformation resulted in approximately 30% to 40% loss of target-bearing cells. Structure-function experiments were performed to define essential AGP requirements.

CONCLUSIONS

These results suggest that AGPs may be a useful tool to eliminate specific cell populations.

HIV-Tat protein transduction domain specifically attenuates growth of polyamine deprived tumor cells

Polyamines are essential for tumor cell growth, and the polyamine pathway represents an attractive target for cancer treatment. Several polyamine transport proteins have been cloned and characterized in bacteria and yeast cells; however, the mechanism of polyamine entry into mammalian cells remains poorly defined, although a role for proteoglycans has been suggested. Here, we show that the HIV-Tat transduction peptide, which is known to enter cells via a proteoglycan-dependent pathway, efficiently inhibits polyamine uptake. Polyamine uptake-deficient mutant cells with intact proteoglycan biosynthesis (CHO MGBG) displayed unperturbed HIV-Tat uptake activity compared with wild-type cells, supporting the notion that HIV-Tat peptide interferes with polyamine uptake via competition for proteoglycan binding sites rather than a putative downstream transporter. HIV-Tat specifically inhibited growth of human carcinoma cells made dependent on extracellular polyamines by treatment with the polyamine biosynthesis inhibitor alpha-difluoromethylornithine; accordingly, the Tat peptide prevented intracellular accumulation of exogenous polyamines. Moreover, combined treatment with alpha-difluoromethylornithine and HIV-Tat efficiently blocked tumor growth in an experimental mouse model. We conclude that HIV-Tat transduction domain and polyamines enter cells through a common pathway, which can be used to target polyamine-dependent tumor growth in the treatment of cancer.

Correlation of in vitro and in vivo models for the oral absorption of peptide drugs

The aim of this study was to evaluate two in vitro models, Caco-2 monolayer and rat intestinal mucosa, regarding their linear correlation with in vivo bioavailability data of therapeutic peptide drugs after oral administration in rat and human. Furthermore the impact of molecular mass (Mm) of the according peptides on their permeability was evaluated. Transport experiments with commercially available water soluble peptide drugs were conducted using Caco-2 cell monolayer grown on transwell filter membranes and with freshly excised rat intestinal mucosa mounted in Using type chambers. Apparent permeability coefficients (P (app)) were calculated and compared with in vivo data derived from the literature. It was shown that, besides a few exceptions, the Mm of peptides linearly correlates with permeability across rat intestinal mucosa (R (2) = 0.86; y = -196.22x + 1354.24), with rat oral bioavailability (R (2) = 0.64; y = -401.90x + 1268.86) as well as with human oral bioavailability (R (2) = 0.91; y = -359.43x + 1103.83). Furthermore it was shown that P (app) values of investigated hydrophilic peptides across Caco-2 monolayer displayed lower permeability than across rat intestinal mucosa. A correlation between P (app) values across rat intestinal mucosa and in vivo oral bioavailability in human (R (2) = 0.98; y = 2.11x + 0.34) attests the rat in vitro model to be a very useful prediction model for human oral bioavailability of hydrophilic peptide drugs. Presented correlations encourage the use of the rat in vitro model for the prediction of human oral bioavailabilities of hydrophilic peptide drugs.

Modulation of muscle contraction by a cell-permeable peptide

In contrast to immortal cell lines, primary cells are hardly susceptible to intracellular delivery methods such as transfection. In this study, we evaluated the direct delivery of several cell-permeable peptides under noninvasive conditions into living primary adult rat cardiomyocytes. We specifically monitored the functional effects of a cell-permeable peptide containing the 15 amino acid N-terminal peptide from human ventricular light chain-1 (VLC-1) on contraction and intracellular Ca2+ signals after electrical stimulation in primary adult cardiomyocytes. The transducible VLC-1 variant was taken up by cardiomyocytes within 5 min with more than 95% efficiency and localized to sarcomeric structures. Analysis of the functional effects of the cell-permeable VLC-1 revealed an enhancement of the intrinsic contractility of cardiomyocytes without affecting the intracellular Ca2+. Therefore, peptide transduction mediated by cell-penetrating peptides represents not only a unique strategy to enhance heart muscle function with no secondary effect on intracellular Ca2+ but also an invaluable tool for the modulation and manipulation of protein interactions in general and in primary cells.

Activation of targeted necrosis by a p53 peptide: a novel death pathway that circumvents apoptotic resistance

Cancer cells escape apoptosis by intrinsic or acquired mechanisms of drug resistance. An alternative strategy to circumvent resistance to apoptosis could be through redirection into other death pathways, such as necrosis. However, necrosis is a nonspecific, nontargeted process resulting in cell lysis and inflammation of both cancer and normal cells and is therefore not a viable alternative. Here, we report that a C-terminal peptide of p53, called p53p-Ant, induced targeted necrosis only in multiple mutant p53 human prostate cancer lines and not normal cells, because the mechanism of cytotoxicity by p53p-Ant is dependent on the presence of high levels of mutant p53. Topotecan- and paclitaxel-resistant prostate cancer lines were as sensitive to p53p-Ant-induced targeted necrosis as parental lines. A massive loss of ATP pools and intracellular generation of reactive oxygen species was involved in the mechanism of targeted necrosis, which was inhibited by O(2)(.) scavengers. We hypothesize that targeted necrosis by p53p-Ant is dependent on mutant p53, is mediated by O(2)(.) loss and ATP, and can circumvent chemotherapy resistance to apoptosis. Targeted necrosis, as an alternative pathway for selective killing of cancer cells, may overcome the problems of nonspecificity in utilizing the necrotic pathway.

Anti HIV-1 virucidal activity of polyamide nucleic acid-membrane transducing peptide conjugates targeted to primer binding site of HIV-1 genome

We have shown that polyamide nucleic acids (PNAs) targeted to the PBS (PNA(PBS)) and A-loop (PNA(A-loop)) sequences, when transfected into cells, inhibit HIV-1 replication by blocking the initiation of reverse transcription via destabilizing tRNA(3)(Lys) primer from the viral genome. Here we demonstrate that both PNA(PBS) and PNA(A-loop) conjugated with the membrane-transducing peptide (MTD) vectors penetratin and Tat are rapidly taken up by cells and inhibit HIV-1 replication. Moreover, MTD peptide conjugates of PNA(PBS) and PNA(A-loop) displayed potent virucidal activity against HIV-1. Brief exposure of HIV-1 virions to these conjugates rendered them noninfectious. The IC(50) values for virucidal activity were in the range of approximately 50 nM; IC(50) values for inhibition of HIV-1 replication/infection were 0.5 microM-0.7 microM. The virucidal property of these conjugates suggests that a cocktail of anti-HIV-1 PNA-MTD peptide conjugates targeting critical regions of the HIV-1 genome could serve as a prophylactic agent for inactivating HIV-1 virions after exposure to HIV-1.

Crotamine mediates gene delivery into cells through the binding to heparan sulfate proteoglycans

Recently we have shown that crotamine, a toxin from the South American rattlesnake Crotalus durissus terrificus venom, belongs to the family of cell-penetrating peptides. Moreover, crotamine was demonstrated to be a marker of centrioles, of cell cycle, and of actively proliferating cells. Herein we show that this toxin at non-toxic concentrations is also capable of binding electrostatically to plasmid DNA forming DNA-peptide complexes whose stabilities overcome the need for chemical conjugation for carrying nucleic acids into cells. Interestingly, crotamine demonstrates cell specificity and targeted delivery of plasmid DNA into actively proliferating cells both in vitro and in vivo, which distinguishes crotamine from other known natural cell-penetrating peptides. The mechanism of crotamine penetration and cargo delivery into cells was also investigated, showing the involvement of heparan sulfate proteoglycans in the uptake phase, which is followed by endocytosis and peptide accumulation within the acidic endosomal vesicles. Finally, the permeabilization of endosomal membranes induced by crotamine results in the leakage of the vesicles contents to the cell cytosol.

Involvement of transportin 2-mediated HuR import in muscle cell differentiation

Muscle fiber formation requires the sequential expression of myogenic regulatory factors (MRFs) such as MyoD and myogenin. The messenger RNAs encoding these two proteins are regulated posttranscriptionally through their ability to associate with the RNA-binding protein HuR. HuR localizes first to the nucleus and then to the cytoplasm during muscle differentiation. Therefore, we examined the link between this localization and the promyogenic function of HuR. We show that early in muscle differentiation, HuR is localized to the nucleus of myoblasts by active Transportin 2 (TRN2)-mediated import. In differentiated muscle fibers, however, the TRN2-HuR complex is disrupted, leading to the cytoplasmic localization of HuR, as well as to the stabilization of MyoD and myogenin mRNAs. Interrupting the TRN2-HuR complex using RNA interference against TRN2, or the cell-permeable peptides (AP) fused to the HuR nucleocytoplasmic shuttling domain (HNS), enhanced the efficiency of myofiber formation. Together, our data suggest that HuR import is disrupted in differentiated muscle fibers and this event constitutes an important regulatory step during myogenesis.

Differential membrane perturbation caused by the cell penetrating peptide Tp10 depending on attached cargo

The membrane leakage caused by the cell penetrating peptide Tp10, a variant of transportan, was studied in large unilamellar vesicles with the entrapped fluorophore calcein. The vesicles were composed of zwitterionic 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine. A significant decrease in membrane leakage was found when the 55kDa streptavidin protein was attached to Tp10. When a 5.4kDa peptide nucleic acid molecule was attached, the membrane leakage was comparable to that caused by Tp10 alone. The results suggest that direct membrane effects may cause membrane translocation of Tp10 alone and of smaller complexes, whereas these effects do not contribute for larger cargoes.

A Simple Fluorescence-Spectroscopic Membrane Translocation Assay

We have established a combination of fluorescence-spectroscopic uptake, release, and dilution experiments as a powerful tool for studying the translocation of fluorescent compounds across lipid membranes, demonstrating this through intrinsic tryptophan fluorescence for the interaction of the cell-penetrating peptide penetratin with phospholipid membranes, for which conflicting results have been reported. We found that penetratin is not membrane-permeant under the conditions used here. To confirm this finding and to validate the approach, we also employed an established titration-calorimetric method, the results of which were in excellent agreement with a thermodynamic analysis of the fluorescence-spectroscopic experiments. Further support was provided by a comparison with published data obtained under similar conditions by using a variety of techniques. Unlike these methods, however, the new approach allows consistent and simultaneous assessment of membrane binding and transbilayer movement without depending on extrinsic labels attached to the molecule of interest or on reporter moieties inserted into the lipid membrane.

A Fluorescence Spectroscopy Study on the Interactions of the TAT-PTD Peptide with Model Lipid Membranes

Protein-transduction domains (PTDs) have been shown to translocate into and through the living cells in a rapid manner by an as yet unknown mechanism. Regardless of the mechanism of translocation, the first necessary step must be binding of the PTD peptide to the surface of the lipid membrane. We used fluorescence spectroscopy to study the interaction between PTD of the HIV-1 Tat protein (TAT-PTD; residues 47-60 of Tat, fluorescently labeled with tryptophan) and the lipid bilayer labeled with various fluorescence membrane probes. The TAT-PTD tryptophan exhibited a decrease in fluorescence intensity and an increase in anisotropy upon interaction with lipid bilayers. The fluorescence changes were linearly proportional to the density of negative charge in the membrane. Kinetic analysis of the interaction showed two apparent dissociation constants. The value of one dissociation constant (Kd1 = 2.6 +/- 0.6 microM), which accounted for 24% of the interaction, was found to be independent of the negative charge density, suggesting its nonelectrostatic nature. The value of the second dissociation constant (Kd2), which accounted for 76% of the interaction, decreased linearly from 610 +/- 150 to 130 +/- 30 microM with an increase in negative charge density from 0 to 25 mol %, suggesting this interaction is electrostatic in nature. Even though the binding was predominantly electrostatic, it could not be reversed by high salt, indicating the presence of a second, irreversible, step in the interaction with lipid. When TAT-PTD was bound to lipid vesicles labeled with 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH), fluorescence resonance energy transfer between the tryptophan and the probe occurred at a distance of 3.4 nm. No change in fluorescence anisotropy of either TMA-DPH or DPH was observed upon the interaction with TAT-PTD, indicating no significant disruption or perturbation of the lipid bilayer by the peptide. TAT-PTD did not cause dissipation of membrane potential (165 mV, negative inside). Inclusion of 3% pyrene-labeled phosphatidylglycerol (pyrene-PG) in the membrane revealed that TAT-PTD preferentially bound to the membrane in the liquid state. We conclude that membrane fluidity is an important physicochemical parameter, which may regulate binding of TAT-PTD to the membrane.

Parallel evaluation of antimicrobial peptides derived from the synthetic PAF26 and the human LL37

The antimicrobial hexapeptide PAF26 was de novo designed towards phytopathogenic fungi of agricultural importance. To analyze its clinical potential, the activity of PAF26 has been determined against several microorganisms of clinical relevance including Staphylococcus, Candida, and several dermatophytes. For comparison purposes, the peptides KR20 and KI26 derived from the human cathelicidin LL37 were selected and fungal pathogens of agronomic relevance were included. PAF26 has similar antimicrobial activity in vitro compared to KR20 despite their different lengths and amino acid compositions. Moreover, neither peptide is lytic to human erythrocytes or keratinocytes. The hybrid peptide PAF26:KR20 showed better antimicrobial properties than the original peptides against most of the pathogens tested. The structural properties of PAF26:KR20 compared to related 26-amino acid peptides support the idea that the increment in toxicity correlates with positive charge and hydrophobicity. However, the degree of peptide helicity was not a predictor of antimicrobial activity.

Non-metabolic membrane tubulation and permeability induced by bioactive peptides

Background

Basic cell-penetrating peptides are potential vectors for therapeutic molecules and display antimicrobial activity. The peptide-membrane contact is the first step of the sequential processes leading to peptide internalization and cell activity. However, the molecular mechanisms involved in peptide-membrane interaction are not well understood and are frequently controversial. Herein, we compared the membrane activities of six basic peptides with different size, charge density and amphipaticity: Two cell-penetrating peptides (penetratin and R9), three amphipathic peptides and the neuromodulator substance P.

Methodology/Principal Findings

Experiments of X ray diffraction, video-microscopy of giant vesicles, fluorescence spectroscopy, turbidimetry and calcein leakage from large vesicles are reported. Permeability and toxicity experiments were performed on cultured cells. The peptides showed differences in bilayer thickness perturbations, vesicles aggregation and local bending properties which form lipidic tubular structures. These structures invade the vesicle lumen in the absence of exogenous energy.

Conclusions/Significance

We showed that the degree of membrane permeabilization with amphipathic peptides is dependent on both peptide size and hydrophobic nature of the residues. We propose a model for peptide-induced membrane perturbations that explains the differences in peptide membrane activities and suggests the existence of a facilitated “physical endocytosis,” which represents a new pathway for peptide cellular internalization.

Tracking a new cell-penetrating (W/R) nonapeptide, through an enzyme-stable mass spectrometry reporter tag

We have designed a mass stable reporter (msr) tag with m/z over 500, trifluoroacetyl(alpha,alpha-diethyl)Gly-Lys(Nepsilonbiotin)-(D)Lys-Cys, for the quantification of the uptake and study of the degradation processes of cell-penetrating peptides (CPP), by matrix assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. This tag was found stable in cell lysis conditions. Using a quantitative MALDI-TOF mass spectrometry analysis based method, an accurate tracking of a new CPP and of its degradation products could be done. (1) The new msr(W/R) nonapeptide (H-RRWWRRWRR-NH2) enters chinese hamster ovary (CHO) K1 cells with a kinetic reaching a steady state after 30-60 min of incubation. This plateau was stable for 4 h and decreased slowly afterward. (2) The peptide msr(W/R) nonapeptide was not cytotoxic over 48 h incubation with CHO cells. (3) After 1 h incubation, the msr(W/R) nonapeptide accumulated with a 3-fold higher concentration than the extracellularly added concentration (7.5 microM). (4) The intracellular quantification was accurate with less than 3% of the quantified peptide being potentially membrane-bound. (5) There was no leakage of the full-length CPP outside the cells. And, finally, (6) analysis of the degradation process of this new CPP suggests that the peptide did not traffick to lysosomes.

Amyloid precursor protein cytoplasmic domain antagonizes reelin neurite outgrowth inhibition of hippocampal neurons

The function of the amyloid precursor protein (APP), a key molecule in Alzheimer's disease (AD) remains unknown. Among the proteins that interact with the APP cytoplasmic domain in vitro and in heterologous systems is Disabled-1, a signaling molecule of the reelin pathway. The physiological consequence of this interaction is unknown. Here we used an in vitro model of hippocampal neurons grown on a reelin substrate that inhibits neurite outgrowth. Our results show that an excess of APP cytoplasmic domain internalized by a cell permeable peptide, is able to antagonize the neurite outgrowth inhibition of reelin. The APP cytoplasmic domain binds Disabled-1 and retains it in the cytoplasm, preventing it from reaching the plasma membrane and sequesters tyrosine phosphorylated Disabled-1, both of which disrupt reelin signaling. In the context of AD, increased formation of APP cytoplasmic domain in the cytosol released after cleavage of the A beta peptide, could then inhibit reelin signaling pathway in the hippocampus and thus influence synaptic plasticity.

Cofilin plays a critical role in IL-8-dependent chemotaxis of neutrophilic HL-60 cells through changes in phosphorylation

Cofilin is a ubiquitous, actin-binding protein. Only unphosphorylated cofilin binds actin and severs or depolymerizes filamentous actin (F-actin), and the inactive form of cofilin is phosphorylated at Ser 3. We reported recently that cofilin plays a regulatory role in superoxide production and phagocytosis by leukocytes, and in the present study, we investigated the role of cofilin in the chemotaxis of neutrophilic HL-60 cells. IL-8 is a potent, physiological chemokine, and it triggers a rapid, transient increase in F-actin beneath the plasma membrane and rapid dephosphorylation and subsequent rephosphorylation of cofilin. In this study, cofilin phosphorylation was found to be inhibited by S3-R peptide, which consists of a peptide corresponding to part of the phosphorylation site of cofilin and a membrane-permeable arginine polymer. When S3-R peptide was introduced into the neutrophilic cells, their chemotactic activity was enhanced, whereas a control peptide that contained an inverted sequence of the phosphorylation site of cofilin had no enhancing effect. Cofilin small interfering RNA (siRNA) decreased cofilin expression by about half and inhibited chemotaxis. In IL-8-stimulated cells, unphosphorylated cofilin accumulated around F-actin, and colocalization of F-actin and phosphorylated cofilin was observed, but these changes in cofilin localization were less prominent in cofilin siRNA-treated cells. The inhibitors of PI-3K wortmannin and LY294002 inhibited the chemotaxis and suppressed IL-8-evoked dephosphorylation and rephosphorylation of cofilin. These results suggested that unphosphorylated cofilin plays a critical role in leukocyte chemotaxis and that PI-3K is involved in the control of the phosphorylation/dephosphorylation cycle of cofilin.

New recombinant vaccines based on the use of prokaryotic antigen-display systems

A major challenge in vaccine design has been to identify antigen presentation systems that elicit strong T- and B-cell responses. In the authors' laboratory, two new delivery vehicles derived from nonpathogenic prokaryotic organisms were recently designed and investigated. Conserved antigenic determinants were inserted into the N-terminal region of the major pVIII coat protein of bacteriophage fd virions or on the surface of an icosahedral scaffold formed by the acyltransferase component (E2 protein) of the pyruvate dehydrogenase complex of Bacillus stearothermophilus. The data indicate that the antigenic determinant displayed by either fd virions or on the surface of the E2 lattice are accessible to the immune system, and are able to trigger a humoral response as well as a potent helper and cytolytic response in vitro and in vivo. These systems offer the potential for safe and inexpensive vaccines to elicit full-spectrum immune responses.

A multivalent peptide library approach identifies a novel Shiga toxin inhibitor that induces aberrant cellular transport of the toxin

Infection with Shiga toxin (Stx)-producing Escherichia coli O157:H7 causes bloody diarrhea and hemorrhagic colitis in humans, sometimes resulting in fatal systemic complications. Among the known Stx family members, Stx2 is responsible for the most severe forms of disease. Stx2 binds to target cells via multivalent interactions between its B-subunit pentamer and globotriaosyl ceramide. After binding, it is first retrogradely transported to the Golgi and then to the endoplasmic reticulum (ER). Using a multivalent peptide library approach, we identified a tetravalent peptide that exhibits a high affinity for the Stx2 B-subunit pentamer (KD = 0.13 microM) and markedly inhibits Stx2 cytotoxicity. The tetravalent peptide exerted its inhibitory effects by inducing aberrant cellular transport of Stx2. Although the tetravalent peptide/Stx2 complex was incorporated into cells and translocated to the Golgi, this process was followed by the effective degradation of Stx2 in an acidic compartment rather than by its transfer to the ER. This peptide thoroughly protected mice from a fatal dose of E. coli O157:H7 even when administered after an established infection. Thus, the multivalent peptide library approach enabled the identification of a peptide-based Stx2 inhibitor that has remarkable therapeutic potency and appears to function by inducing aberrant cellular transport and degradation of Stx2.

Bcl-XL antisense oligonucleotides coupled with antennapedia enhances radiation-induced apoptosis in pancreatic cancer

BACKGROUND

Pancreatic cancer is highly resistant to radiation and chemotherapy, and its resistance reflects the enhancement of apoptosis inhibitory genes, including Bcl-2 family. Antennapedia (pAnt) is capable of almost 100% internalization into cells through the lipid bilayer without any cytotoxic effect. The aim of this study was to examine the effects of the Bcl-XL antisense oligonucleotide for radiosensitivity of in vitro and in vivo pancreatic cancer using oligonucleotide conjugated with antennapedia.

METHODS

In in vitro experiments, expression of Bcl-XL protein was examined in 5 pancreatic cancer cell lines. In AsPC-1 cells, internalization of the oligonucleotide was confirmed, and the effects of antennapedia-antisense (pAnt-AS) or antennapedia-scramble (pAnt-Scr) on Bcl-XL protein expression were examined. Cells were treated with pAnt-AS, pAnt-Scr or phosphorothioate antisense (S-AS) for 3 days, then the effects of irradiation on the cell survival, caspase-3 activity, and apoptotic index were evaluated. In AsPC-1 xenograft mice, pAnt-AS, pAnt-Scr, or S-AS was injected, and 5 or 10 Gy irradiation was added. Bcl-Xl protein expression was measured before irradiation. Apoptosis was evaluated at 48 hours after irradiation. On the 14th day after 10-Gy irradiation, tumor wet weight was measured, and tumor growth was estimated over 5 weeks.

RESULTS

In in vitro experiments, all pancreatic cancer cell lines expressed Bcl-XL protein. pAnt-AS was internalized into AsPC-1 cells within 2 hours. pAnt-AS at 10 mumol/L reduced more than 90% of the Bcl-XL protein in AsPC-1 cells, whereas pAnt-Scr or S-AS treatment at the same concentration reduced as much as 10% of the Bcl-XL protein. Treatment with pAnt-AS followed by irradiation significantly reduced cell viability when compared with that of pAnt-Scr or S-AS. Caspase-3 activity was significantly upregulated in the pAnt-AS-treated group (P = .033). The rate of nuclear fragmentation was significantly higher in the pAnt-AS group (P = .013). In in vivo experiments, Bcl-XL protein was reduced about 40% in the pAnt-AS-treated mice. Tumor doubling time of the pAnt-AS-treated mice was elongated by 10-Gy irradiation. The tumor wet weight of mice treated with pAnt-AS and 10-Gy irradiation was significantly reduced when compared with mice treated with pAnt-Scr and 10-Gy irradiation (P = .046). The apoptosis index at 48 hours after irradiation was significantly increased in pAnt-AS-treated mice (P < .01).

CONCLUSIONS

The results suggest that, when coupled with antennapedia, the antisense oligonucleotide against Bcl-XL could be a good therapeutic tool for radiosensitization of pancreatic cancer.

Ethanol sensitizes NF-kappaB activation in pancreatic acinar cells through effects on protein kinase C-epsilon

Although ethanol abuse is the most common cause of pancreatitis, the mechanism of alcohol's effect on the pancreas is not well understood. Previously, we demonstrated that in vitro ethanol treatment of pancreatic acinar cells augmented the CCK-8-induced activation of NF-kappaB, a key signaling system involved in the inflammatory response of pancreatitis. In the present study, we determine the role for individual PKC isoforms in the sensitizing effect of ethanol on NF-kappaB activation. Dispersed rat pancreatic acini were treated with and without ethanol and then stimulated with CCK-8; 100 nM CCK-8 caused both NF-kappaB and PKC-delta, -epsilon, and -zeta activation, whereas 0.1 nM CCK-8 did not increase PKC-epsilon, PKC-zeta, or NF-kappaB activity. CCK-8 (0.1 nM) did activate PKC-delta. PKC-epsilon activator alone did not cause NF-kappaB activation; however, together with 0.1 nM CCK-8, it caused NF-kappaB activation. Ethanol activated PKC-epsilon without affecting other PKC isoforms or NF-kappaB activity. Of note, stimulation of acini with ethanol and 0.1 nM CCK-8 resulted in the activation of PKC-delta, PKC-epsilon, and NF-kappaB. The NF-kappaB activation to 0.1 nM CCK-8 in ethanol-pretreated acini was inhibited by both PKC-delta inhibitor and PKC-epsilon inhibitor. Taken together, these results demonstrate the different modes of activation of PKC isoforms and NF-kappaB in acini stimulated with ethanol, high-dose CCK-8, and low-dose CCK-8, and furthermore suggest that activation of both PKC-epsilon and -delta is required for NF-kappaB activation. These results suggest that ethanol enhances the CCK-8-induced NF-kappaB activation at least in part through its effects on PKC-epsilon.

Tryptophan- and arginine-rich antimicrobial peptides: Structures and mechanisms of action

Antimicrobial peptides encompass a number of different classes, including those that are rich in a particular amino acid. An important subset are peptides rich in Arg and Trp residues, such as indolicidin and tritrpticin, that have broad and potent antimicrobial activity. The importance of these two amino acids for antimicrobial activity was highlighted through the screening of a complete combinatorial library of hexapeptides. These residues possess some crucial chemical properties that make them suitable components of antimicrobial peptides. Trp has a distinct preference for the interfacial region of lipid bilayers, while Arg residues endow the peptides with cationic charges and hydrogen bonding properties necessary for interaction with the abundant anionic components of bacterial membranes. In combination, these two residues are capable of participating in cation-pi interactions, thereby facilitating enhanced peptide-membrane interactions. Trp sidechains are also implicated in peptide and protein folding in aqueous solution, where they contribute by maintaining native and nonnative hydrophobic contacts. This has been observed for the antimicrobial peptide from human lactoferrin, possibly restraining the peptide structure in a suitable conformation to interact with the bacterial membrane. These unique properties make the Arg- and Trp-rich antimicrobial peptides highly active even at very short peptide lengths. Moreover, they lead to structures for membrane-mimetic bound peptides that go far beyond regular alpha-helices and beta-sheet structures. In this review, the structures of a number of different Trp- and Arg-rich antimicrobial peptides are examined and some of the major mechanistic studies are presented.

Glucagon-like Peptide 1 Activates Protein Kinase C through Ca2+-dependent Activation of Phospholipase C in Insulin-secreting Cells

Although the stimulatory effect of glucagon-like peptide 1 (GLP-1), a cAMP-generating agonist, on Ca(2+) signal and insulin secretion is well established, the underlying mechanisms remain to be fully elucidated. We recently discovered that Ca(2+) influx alone can activate conventional protein kinase C (PKC) as well as novel PKC in insulin-secreting (INS-1) cells. Building on this earlier finding, here we examined whether GLP-1-evoked Ca(2+) signaling can activate PKCalpha and PKCepsilon at a substimulatory concentration of glucose (3 mm) in INS-1 cells. We first showed that GLP-1 translocated endogenous PKCalpha and PKCepsilon from the cytosol to the plasma membrane. Next, we assessed the phosphorylation state of the PKC substrate, myristoylated alanine-rich C kinase substrate (MARCKS), by using MARCKS-GFP. GLP-1 translocated MARCKS-GFP to the cytosol in a Ca(2+)-dependent manner, and the GLP-1-evoked translocation of MARCKS-GFP was blocked by PKC inhibitors, either a broad PKC inhibitor, bisindolylmaleimide I, or a PKCepsilon inhibitor peptide, antennapedia peptide-fused pseudosubstrate PKCepsilon-(149-164) (antp-PKCepsilon) and a conventional PKC inhibitor, Gö-6976. Furthermore, forskolin-induced translocation of MARCKS-GFP was almost completely inhibited by U73122, a putative inhibitor of phospholipase C. These observations were verified in two different ways by demonstrating 1) forskolin-induced translocation of the GFP-tagged C1 domain of PKCgamma and 2) translocation of PKCalpha-DsRed and PKCepsilon-GFP. In addition, PKC inhibitors reduced forskolin-induced insulin secretion in both INS-1 cells and rat islets. Thus, GLP-1 can activate PKCalpha and PKCepsilon, and these GLP-1-activated PKCs may contribute considerably to insulin secretion at a substimulatory concentration of glucose.

Cholesteryl Oligoarginine Delivering Vascular Endothelial Growth Factor siRNA Effectively Inhibits Tumor Growth in Colon Adenocarcinoma

Vascular endothelial growth factor (VEGF) is a multifunctional angiogenic growth factor that is a primary stimulant of the development and maintenance of a vascular network in the vascularization of solid tumors. It has been reported that a blockade of VEGF-mediated angiogenesis is a powerful method for tumor regression. RNA interference represents a naturally occurring biological strategy for inhibition of gene expression. In mammalian systems, however, the in vivo application of small interfering RNA (siRNA) is severely limited by the instability and poor bioavailability of unmodified siRNA molecules. In this study, we tested the hypothesis that a hydrophobically modified protein transduction domain, cholesteryl oligo-d-arginine (Chol-R9), may stabilize and enhance tumor regression efficacy of the VEGF-targeting siRNA. The noncovalent complexation of a synthetic siRNA with Chol-R9 efficiently delivered siRNA into cells in vitro. Moreover, in a mouse model bearing a subcutaneous tumor, the local administration of complexed VEGF-targeting siRNA, but not of scrambled siRNA, led to the regression of the tumor. Hence, we propose a novel and simple system for the local in vivo application of siRNA through Chol-R9 for cancer therapy.