A Self-Assembled 3D Model Demonstrates How Stiffness Educates Tumor Cell Phenotypes and Therapy Resistance in Pancreatic Cancer.

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a dense and stiff extracellular matrix (ECM) associated with tumor progression and therapy resistance. To further the understanding of how stiffening of the tumor microenvironment (TME) contributes to aggressiveness, a three-dimensional (3D) self-assembling hydrogel disease model is developed based on peptide amphiphiles (PAs, PA-E3Y) designed to tailor stiffness. The model displays nanofibrous architectures reminiscent of native TME and enables the study of the invasive behavior of PDAC cells. Enhanced tuneability of stiffness is demonstrated by interacting thermally annealed aqueous solutions of PA-E3Y (PA-E3Yh) with divalent cations to create hydrogels with mechanical properties and ultrastructure similar to native tumor ECM. It is shown that stiffening of PA-E3Yh hydrogels to levels found in PDAC induces ECM deposition, promotes epithelial-to-mesenchymal transition (EMT), enriches CD133+/CXCR4+ cancer stem cells (CSCs), and subsequently enhances drug resistance. The findings reveal how a stiff 3D environment renders PDAC cells more aggressive and therefore more faithfully recapitulates in vivo tumors.

Macrophages direct cancer cells through a LOXL2-mediated metastatic cascade in pancreatic ductal adenocarcinoma.

OBJECTIVE: The lysyl oxidase-like protein 2 (LOXL2) contributes to tumour progression and metastasis in different tumour entities, but its role in pancreatic ductal adenocarcinoma (PDAC) has not been evaluated in immunocompetent in vivo PDAC models. DESIGN: Towards this end, we used PDAC patient data sets, patient-derived xenograft in vivo and in vitro models, and four conditional genetically-engineered mouse models (GEMMS) to dissect the role of LOXL2 in PDAC. For GEMM-based studies, K-Ras +/LSL-G12D;Trp53 LSL-R172H;Pdx1-Cre mice (KPC) and the K-Ras +/LSL-G12D;Pdx1-Cre mice (KC) were crossed with Loxl2 allele floxed mice (Loxl2Exon2 fl/fl) or conditional Loxl2 overexpressing mice (R26Loxl2 KI/KI) to generate KPCL2KO or KCL2KO and KPCL2KI or KCL2KI mice, which were used to study overall survival; tumour incidence, burden and differentiation; metastases; epithelial to mesenchymal transition (EMT); stemness and extracellular collagen matrix (ECM) organisation. RESULTS: Using these PDAC mouse models, we show that while Loxl2 ablation had little effect on primary tumour development and growth, its loss significantly decreased metastasis and increased overall survival. We attribute this effect to non-cell autonomous factors, primarily ECM remodelling. Loxl2 overexpression, on the other hand, promoted primary and metastatic tumour growth and decreased overall survival, which could be linked to increased EMT and stemness. We also identified tumour-associated macrophage-secreted oncostatin M (OSM) as an inducer of LOXL2 expression, and show that targeting macrophages in vivo affects Osm and Loxl2 expression and collagen fibre alignment. CONCLUSION: Taken together, our findings establish novel pathophysiological roles and functions for LOXL2 in PDAC, which could be potentially exploited to treat metastatic disease.

Bioengineered 3D models of human pancreatic cancer recapitulate in vivo tumour biology.

Patient-derived in vivo models of human cancer have become a reality, yet their turnaround time is inadequate for clinical applications. Therefore, tailored ex vivo models that faithfully recapitulate in vivo tumour biology are urgently needed. These may especially benefit the management of pancreatic ductal adenocarcinoma (PDAC), where therapy failure has been ascribed to its high cancer stem cell (CSC) content and high density of stromal cells and extracellular matrix (ECM). To date, these features are only partially reproduced ex vivo using organoid and sphere cultures. We have now developed a more comprehensive and highly tuneable ex vivo model of PDAC based on the 3D co-assembly of peptide amphiphiles (PAs) with custom ECM components (PA-ECM). These cultures maintain patient-specific transcriptional profiles and exhibit CSC functionality, including strong in vivo tumourigenicity. User-defined modification of the system enables control over niche-dependent phenotypes such as epithelial-to-mesenchymal transition and matrix deposition. Indeed, proteomic analysis of these cultures reveals improved matrisome recapitulation compared to organoids. Most importantly, patient-specific in vivo drug responses are better reproduced in self-assembled cultures than in other models. These findings support the use of tuneable self-assembling platforms in cancer research and pave the way for future precision medicine approaches.

Roles of cell fusion, hybridization and polyploid cell formation in cancer metastasis.

Cell-cell fusion is a normal biological process playing essential roles in organ formation and tissue differentiation, repair and regeneration. Through cell fusion somatic cells undergo rapid nuclear reprogramming and epigenetic modifications to form hybrid cells with new genetic and phenotypic properties at a rate exceeding that achievable by random mutations. Factors that stimulate cell fusion are inflammation and hypoxia. Fusion of cancer cells with non-neoplastic cells facilitates several malignancy-related cell phenotypes, e.g., reprogramming of somatic cell into induced pluripotent stem cells and epithelial to mesenchymal transition. There is now considerable in vitro, in vivo and clinical evidence that fusion of cancer cells with motile leucocytes such as macrophages plays a major role in cancer metastasis. Of the many changes in cancer cells after hybridizing with leucocytes, it is notable that hybrids acquire resistance to chemo- and radiation therapy. One phenomenon that has been largely overlooked yet plays a role in these processes is polyploidization. Regardless of the mechanism of polyploid cell formation, it happens in response to genotoxic stresses and enhances a cancer cell's ability to survive. Here we summarize the recent progress in research of cell fusion and with a focus on an important role for polyploid cells in cancer metastasis. In addition, we discuss the clinical evidence and the importance of cell fusion and polyploidization in solid tumors.

Integrin αvß6-specific therapy for pancreatic cancer developed from foot-and-mouth-disease virus.

Goals of investigation: The 5-year survival rate for pancreatic ductal adenocarcinoma (PDAC) has remained at <5% for decades because no effective therapies have been identified. Integrin αvß6 is overexpressed in most PDAC and represents a promising therapeutic target. Thus, we attempted to develop an αvß6-specific peptide-drug conjugate (PDC) for therapy of PDAC. Methodology: We conjugated the DNA-binding pyrrolobenzodiazepine (PBD)-based payload SG3249 (tesirine) to an αvß6-specific 20mer peptide from the VP1 coat protein of foot-and-mouth-disease virus (FMDV) (forming conjugate SG3299) or to a non-targeting peptide (forming conjugate SG3511). PDCs were tested for specificity and toxicity on αvß6-negative versus-positive PDAC cells, patient-derived cell lines from tumor xenografts, and on two different in vivo models of PDAC. Immunohistochemical analyses were performed to establish therapeutic mechanism. Results: The αvß6-targeted PDC SG3299 was significantly more toxic (up to 78-fold) for αvß6-expressing versus αvß6-negative PDAC cell lines in vitro, and achieved significantly higher toxicity at equal dose than the non-targeted PDC SG3511 (up to 15-fold better). Moreover, SG3299 eliminated established (100mm3) Capan-1 PDAC human xenografts, extending the lifespan of mice significantly (P=0.005). Immunohistochemistry revealed SG3299 induced DNA damage and apoptosis (increased γH2AX and cleaved caspase 3, respectively) associated with significant reductions in proliferation (Ki67), ß6 expression and PDAC tumour growth. Conclusions: The FMDV-peptide drug conjugate SG3299 showed αvß6-selectivity in vitro and in vivo and can specifically eliminate αvß6-positive cancers, providing a promising new molecular- specific therapy for pancreatic cancer.

Author Correction: TGF-ß induces miR-100 and miR-125b but blocks let-7a through LIN28B controlling PDAC progression.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

TGF-ß induces miR-100 and miR-125b but blocks let-7a through LIN28B controlling PDAC progression.

TGF-ß/Activin induces epithelial-to-mesenchymal transition and stemness in pancreatic ductal adenocarcinoma (PDAC). However, the microRNAs (miRNAs) regulated during this response have remained yet undetermined. Here, we show that TGF-ß transcriptionally induces MIR100HG lncRNA, containing miR-100, miR-125b and let-7a in its intron, via SMAD2/3. Interestingly, we find that although the pro-tumourigenic miR-100 and miR-125b accordingly increase, the amount of anti-tumourigenic let-7a is unchanged, as TGF-ß also induces LIN28B inhibiting its maturation. Notably, we demonstrate that inactivation of miR-125b or miR-100 affects the TGF-ß-mediated response indicating that these miRNAs are important TGF-ß effectors. We integrate AGO2-RIP-seq with RNA-seq to identify the global regulation exerted by these miRNAs in PDAC cells. Transcripts targeted by miR-125b and miR-100 significantly overlap and mainly inhibit p53 and cell-cell junctions' pathways. Together, we uncover that TGF-ß induces an lncRNA, whose encoded miRNAs, miR-100, let-7a and miR-125b play opposing roles in controlling PDAC tumourigenesis.

The miR-25-93-106b cluster regulates tumor metastasis and immune evasion via modulation of CXCL12 and PD-L1.

The stromal microenvironment controls response to injury and inflammation, and is also an important determinant of cancer cell behavior. However, our understanding of its modulation by miRNA (miR) and their respective targets is still sparse. Here, we identified the miR-25-93-106b cluster and two new target genes as critical drivers for metastasis and immune evasion of cancer cells. Using miR-25-93-106b knockout mice or antagomiRs, we demonstrated regulation of the production of the chemoattractant CXCL12 controlling bone marrow metastasis. Moreover, we identified the immune checkpoint PD-L1 (CD274) as a novel miR-93/106b target playing a central role in diminishing tumor immunity. Eventually, upregulation of miR-93 and miR-106b via miR-mimics or treatment with an epigenetic reader domain (BET) inhibitor resulted in diminished expression of CXCL12 and PD-L1. These data suggest a potential new therapeutic rationale for use of BET inhibitors for dual targeting of cancers with strong immunosuppressive and metastatic phenotypes.

Multifunctionalized iron oxide nanoparticles for selective targeting of pancreatic cancer cells.

Nanomedicine nowadays offers novel solutions in cancer therapy by introducing multimodal treatments in one single formulation. In addition, nanoparticles act as nanocarriers changing the solubility, biodistribution and efficiency of the therapeutic molecules, thus generating more efficient treatments and reducing their side effects. To apply these novel therapeutic approaches, efforts are focused on the multi-functionalization of the nanoparticles and will open up new avenues to advanced combinational therapies. Pancreatic ductal adenocarcinoma (PDAC) is a cancer with unmet medical needs. Abundant expression of the anti-phagocytosis signal CD47 has also been observed on pancreatic cancer cells, in particular a subset of cancer stem cells (CSCs) responsible for resistance to standard therapy and metastatic potential. CD47 receptor is found on pancreatic cancer and highly expressed on CSCs, but not on normal pancreas. Inhibiting CD47 using monoclonal antibodies has been shown as an effective strategy to treat PDAC in vivo. However, CD47 inhibition effectively slowed tumor growth only in combination with Gemcitabine or Abraxane. In this work, we present the generation of multifunctionalized iron oxide magnetic nanoparticles (MNPs) that include the anti-CD47 antibody and the chemotherapeutic drug Gemcitabine in a single formulation. We demonstrate the in vitro efficacy of the formulation against CD47-positive pancreatic cancer cells. This article is part of a Special Issue entitled "Recent Advances in Bionanomaterials" Guest Editor: Dr. Marie-Louise Saboungi and Dr. Samuel D. Bader.

MiR-93 Controls Adiposity via Inhibition of Sirt7 and Tbx3.

Conquering obesity has become a major socioeconomic challenge. Here, we show that reduced expression of the miR-25-93-106b cluster, or miR-93 alone, increases fat mass and, subsequently, insulin resistance. Mechanistically, we discovered an intricate interplay between enhanced adipocyte precursor turnover and increased adipogenesis. First, miR-93 controls Tbx3, thereby limiting self-renewal in early adipocyte precursors. Second, miR-93 inhibits the metabolic target Sirt7, which we identified as a major driver of in vivo adipogenesis via induction of differentiation and maturation of early adipocyte precursors. Using mouse parabiosis, obesity in mir-25-93-106b(-/-) mice could be rescued by restoring levels of circulating miRNA and subsequent inhibition of Tbx3 and Sirt7. Downregulation of miR-93 also occurred in obese ob/ob mice, and this phenocopy of mir-25-93-106b(-/-) was partially reversible with injection of miR-93 mimics. Our data establish miR-93 as a negative regulator of adipogenesis and a potential therapeutic option for obesity and the metabolic syndrome.

The miR-17-92 cluster counteracts quiescence and chemoresistance in a distinct subpopulation of pancreatic cancer stem cells.

OBJECTIVE: Cancer stem cells (CSCs) represent the root of many solid cancers including pancreatic ductal adenocarcinoma, are highly chemoresistant and represent the cellular source for disease relapse. However the mechanisms involved in these processes still need to be fully elucidated. Understanding the mechanisms implicated in chemoresistance and metastasis of pancreatic cancer is critical to improving patient outcomes. DESIGN: Micro-RNA (miRNA) expression analyses were performed to identify functionally defining epigenetic signatures in pancreatic CSC-enriched sphere-derived cells and gemcitabine-resistant pancreatic CSCs. RESULTS: We found the miR-17-92 cluster to be downregulated in chemoresistant CSCs versus non-CSCs and demonstrate its crucial relevance for CSC biology. In particular, overexpression of miR-17-92 reduced CSC self-renewal capacity, in vivo tumourigenicity and chemoresistance by targeting multiple NODAL/ACTIVIN/TGF-ß1 signalling cascade members as well as directly inhibiting the downstream targets p21, p57 and TBX3. Overexpression of miR-17-92 translated into increased CSC proliferation and their eventual exhaustion via downregulation of p21 and p57. Finally, the translational impact of our findings could be confirmed in preclinical models for pancreatic cancer. CONCLUSIONS: Our findings therefore identify the miR-17-92 cluster as a functionally determining family of miRNAs in CSCs, and highlight the putative potential of developing modulators of this cluster to overcome drug resistance in pancreatic CSCs.

Inhibition of CD47 Effectively Targets Pancreatic Cancer Stem Cells via Dual Mechanisms.

PURPOSE: Pancreatic ductal adenocarcinoma (PDAC) is a cancer of the exocrine pancreas with unmet medical need and is strongly promoted by tumor-associated macrophages (TAM). The presence of TAMs is associated with poor clinical outcome, and their overall role, therefore, appears to be protumorigenic. The "don't eat me" signal CD47 on cancer cells communicates to the signal regulatory protein-α on macrophages and prevents their phagocytosis. Thus, inhibition of CD47 may offer a new opportunity to turn TAMs against PDAC cells, including cancer stem cells (CSC), as the exclusively tumorigenic population. EXPERIMENTAL DESIGN: We studied in vitro and in vivo the effects of CD47 inhibition on CSCs using a large set of primary pancreatic cancer (stem) cells as well as xenografts of primary human PDAC tissue. RESULTS: CD47 was highly expressed on CSCs, but not on other nonmalignant cells in the pancreas. Targeting CD47 efficiently enhanced phagocytosis of a representative set of primary human pancreatic cancer (stem) cells and, even more intriguingly, also directly induced their apoptosis in the absence of macrophages during long-term inhibition of CD47. In patient-derived xenograft models, CD47 targeting alone did not result in relevant slowing of tumor growth, but the addition of gemcitabine or Abraxane resulted in sustained tumor regression and prevention of disease relapse long after discontinuation of treatment. CONCLUSIONS: These data are consistent with efficient in vivo targeting of CSCs, and strongly suggest that CD47 inhibition could be a novel adjuvant treatment strategy for PDAC independent of underlying and highly variable driver mutations.

Chloroquine targets pancreatic cancer stem cells via inhibition of CXCR4 and hedgehog signaling.

Pancreatic ductal adenocarcinoma is one of the deadliest carcinomas and is characterized by highly tumorigenic and metastatic cancer stem cells (CSC). CSCs evade available therapies, which preferentially target highly proliferative and more differentiated progenies, leaving behind CSCs as a putative source for disease relapse. Thus, to identify potentially more effective treatment regimens, we screened established and new compounds for their ability to eliminate CSCs in primary pancreatic cancer (stem) cells in vitro and corresponding patient-derived pancreatic cancer tissue xenografts in vivo. Intriguingly, we found that in vitro treatment with the antimalarial agent chloroquine significantly decreased CSCs, translating into diminished in vivo tumorigenicity and invasiveness in a large panel of pancreatic cancers. In vivo treatment in combination with gemcitabine was capable of more effectively eliminating established tumors and improved overall survival. The inhibitory effect of chloroquine was not related to inhibition of autophagy, but was due to inhibition of CXCL12/CXCR4 signaling, resulting in reduced phosphorylation of ERK and STAT3. Furthermore, chloroquine showed potent inhibition of hedgehog signaling by decreasing the production of Smoothened, translating into a significant reduction in sonic hedgehog-induced chemotaxis and downregulation of downstream targets in CSCs and the surrounding stroma. Our study demonstrates that via to date unreported effects, chloroquine is an effective adjuvant therapy to chemotherapy, offering more efficient tumor elimination and improved cure rates. Chloroquine should be further explored in the clinical setting as its success may help to more rapidly improve the poor prognosis of patients with pancreatic cancer.

Metformin targets the metabolic achilles heel of human pancreatic cancer stem cells.

Pancreatic ductal adenocarcinomas contain a subset of exclusively tumorigenic cancer stem cells (CSCs), which are capable of repopulating the entire heterogeneous cancer cell populations and are highly resistant to standard chemotherapy. Here we demonstrate that metformin selectively ablated pancreatic CSCs as evidenced by diminished expression of pluripotency-associated genes and CSC-associated surface markers. Subsequently, the ability of metformin-treated CSCs to clonally expand in vitro was irreversibly abrogated by inducing apoptosis. In contrast, non-CSCs preferentially responded by cell cycle arrest, but were not eliminated by metformin treatment. Mechanistically, metformin increased reactive oxygen species production in CSC and reduced their mitochondrial transmembrane potential. The subsequent induction of lethal energy crisis in CSCs was independent of AMPK/mTOR. Finally, in primary cancer tissue xenograft models metformin effectively reduced tumor burden and prevented disease progression; if combined with a stroma-targeting smoothened inhibitor for enhanced tissue penetration, while gemcitabine actually appeared dispensable.

Multimodal Treatment Eliminates Cancer Stem Cells and Leads to Long-Term Survival in Primary Human Pancreatic Cancer Tissue Xenografts.

PURPOSE: In spite of intense research efforts, pancreatic ductal adenocarcinoma remains one of the most deadly malignancies in the world. We and others have previously identified a subpopulation of pancreatic cancer stem cells within the tumor as a critical therapeutic target and additionally shown that the tumor stroma represents not only a restrictive barrier for successful drug delivery, but also serves as a paracrine niche for cancer stem cells. Therefore, we embarked on a large-scale investigation on the effects of combining chemotherapy, hedgehog pathway inhibition, and mTOR inhibition in a preclinical mouse model of pancreatic cancer. EXPERIMENTAL DESIGN: Prospective and randomized testing in a set of almost 200 subcutaneous and orthotopic implanted whole-tissue primary human tumor xenografts. RESULTS: The combined targeting of highly chemoresistant cancer stem cells as well as their more differentiated progenies, together with abrogation of the tumor microenvironment by targeting the stroma and enhancing tissue penetration of the chemotherapeutic agent translated into significantly prolonged survival in preclinical models of human pancreatic cancer. Most pronounced therapeutic effects were observed in gemcitabine-resistant patient-derived tumors. Intriguingly, the proposed triple therapy approach could be further enhanced by using a PEGylated formulation of gemcitabine, which significantly increased its bioavailability and tissue penetration, resulting in a further improved overall outcome. CONCLUSIONS: This multimodal therapeutic strategy should be further explored in the clinical setting as its success may eventually improve the poor prognosis of patients with pancreatic ductal adenocarcinoma.

Comparison of the efficiency of complexes based on S4(13)-PV cell-penetrating peptides in plasmid DNA and siRNA delivery.

The successful application of gene therapy approaches is highly dependent on the efficient delivery of nucleic acids into target cells. In the present study, new peptide-based nonviral systems were developed to enhance plasmid DNA and siRNA delivery, aiming at generating appropriate gene delivery and gene silencing tools for preclinical and clinical application. For this purpose, a new cell-penetrating peptide derived from the wild-type S4(13)-PV peptide was synthesized through the addition of a five-histidine tail to its N-terminus (H5-S4(13)-PV), and its ability to mediate gene expression and gene silencing was evaluated and compared to that of the wild-type peptide. The histidine-enriched peptide, H5-S4(13)-PV, proved to be generally more efficient and less toxic than the wild-type peptide in the delivery of plasmid DNA. In addition, complexes of H5-S4(13)-PV with siRNAs, but not of S4(13)-PV, were efficiently internalized by cells and presented high knockdown activity (63%). Interestingly, systems containing the S4(13)-PV or the H5-S4(13)-PV peptide exhibited superior biological activity when compared to those containing the reverse NLS or scrambled peptides, suggesting that both the cell-penetrating sequence and the NLS of the S4(13)-PV peptide influence the competence of binary and ternary complexes to accomplish nucleic acid delivery. In order to unravel the cancer therapeutic potential of formulations with the histidine-enriched peptide, their efficiency to mediate silencing of the oncogenic protein survivin was evaluated. As opposed to complexes with the wild-type peptide, H5-S4(13)-PV complexes showed the ability to promote a high survivin knockdown at the level of both protein (44%) and mRNA (73%), in HT1080 cells.

Cell-penetrating peptides as nucleic acid delivery systems: from biophysics to biological applications.

The increasing knowledge on the genetic basis of disease has allowed the development of promising gene-targeted therapies that can be applied to numerous diseases. Such genetic-based approaches involve the use of nucleic acids as therapeutic agents, either for the insertion or repair and regulation of specific genes. However, the clinical application of these large and charged molecules remains highly dependent on the development of delivery systems capable of mediating efficient cellular uptake. Since the first observations, two decades ago, that some protein-derived domains can translocate across biological membranes, a wide group of peptides called cell-penetrating peptides (CPPs) have been considered one of the most promising tools to improve non-invasive cellular delivery of therapeutic molecules. The mechanistic basis of CPP and CPP conjugate cellular uptake remains controversial. However, biophysical studies on the interactions of CPPs with membrane models have contributed to unravel the mechanisms underlying CPP membrane translocation as well as to propose relationships between those mechanisms and CPP efficiency in mediating cargo delivery. In this review, representative examples of CPPs were gathered from the most recent literature in order to emphasize the contributions of chemists, biophysicists and cell biologists towards the rational design of increasingly more efficient delivery systems. In this context, the present review aims at giving an overview of some of the most significant CPP families and their biological applications as nucleic acid delivery systems.

Cell-penetrating peptide-based systems for nucleic acid delivery: a biological and biophysical approach.

The increasing knowledge on the genetic basis of disease provides a platform for the development of promising gene-targeted therapies that can be applied to numerous pathological conditions, including cancer. Such genetic-based approaches involve the use of nucleic acids as therapeutic agents, either for the insertion or for the repair and regulation of specific genes. However, despite the huge pharmacological potential of these molecules, their application remains highly dependent on the development of delivery systems capable of mediating efficient cellular uptake. The discovery of a class of small peptides, the so-called cell-penetrating peptides (CPPs), which are able to very efficiently cross cell membranes through a mechanism that is independent of membrane receptors or transporters and avoids lysosomal enzymatic degradation, has been enthusiastically considered of key interest to improve noninvasive cellular delivery of therapeutic molecules. A large number of CPPs have been applied successfully to mediate the intracellular delivery of nucleic acids, including the S4(13)PV peptide for which interactions with membranes and resulting biological effects are illustrated in this chapter. Here, we provide a description of the experimental procedures for the preparation of CPP-based nucleic acid complexes and assessment of their formation, the selection of those protocols leading to the most efficient complexes, the biophysical characterization of CPP membrane interactions, and the evaluation of the biological and cytotoxic activity of the complexes.

S4(13)-PV cell-penetrating peptide induces physical and morphological changes in membrane-mimetic lipid systems and cell membranes: implications for cell internalization.

The present work aims to gain insights into the role of peptide-lipid interactions in the mechanisms of cellular internalization and endosomal escape of the S4(13)-PV cell-penetrating peptide, which has been successfully used in our laboratory as a nucleic acid delivery system. A S4(13)-PV analogue, S4(13)-PVscr, displaying a scrambled amino acid sequence, deficient cell internalization and drug delivery inability, was used in this study for comparative purposes. Differential scanning calorimetry, fluorescence polarization and X-ray diffraction at small and wide angles techniques showed that both peptides interacted with anionic membranes composed of phosphatidylglycerol or a mixture of this lipid with phosphatidylethanolamine, increasing the lipid order, shifting the phase transition to higher temperatures and raising the correlation length between the bilayers. However, S4(13)-PVscr, in contrast to the wild-type peptide, did not promote lipid domain segregation and induced the formation of an inverted hexagonal lipid phase instead of a cubic phase in the lipid systems assayed. Electron microscopy showed that, as opposed to S4(13)-PVscr, the wild-type peptide induced the formation of a non-lamellar organization in membranes of HeLa cells. We concluded that lateral phase separation and destabilization of membrane lamellar structure without compromising membrane integrity are on the basis of the lipid-driven and receptor-independent mechanism of cell entry of S4(13)-PV peptide. Overall, our results can contribute to a better understanding of the role of peptide-lipid interactions in the mechanisms of cell-penetrating peptide membrane translocation, helping in the future design of more efficient cell-penetrating peptide-based drug delivery systems.

A non-covalent strategy combining cationic lipids and CPPs to enhance the delivery of splice correcting oligonucleotides.

Modulation of pre-mRNA splicing by steric-block oligonucleotides constitutes a promising strategy for the treatment of many diseases, but requires efficient delivery to cell nuclei. In the present study, we evaluated the efficacy of a non-covalent strategy that combines a cell penetrating peptide with a lipoplex-based formulation to mediate the delivery of splice-switching oligonucleotides. The splice correcting ability of these new formulations was assessed using splice-switching oligonucleotides targeted towards the mutated splicing site of human beta-globin pre-mRNA in the HeLa pLuc/705 splice correction model. Importantly, the optimal splice correcting activity was exhibited by the formulation containing both lipid and peptide components, the order of component addition in these formulations being crucial for their efficacy. Our results demonstrate that the inclusion of cationic liposomes in the formulation provides the ability to improve release from endocytic vesicles, a barrier that severely limits the efficiency of oligonucleotide delivery by cell penetrating peptides. On the other hand, cell penetrating peptides potentiate the cellular uptake and delivery of the oligonucleotides by the lipoplexes. Moreover, when combining cell penetrating peptides with the lipoplex formulations, a significant reduction in the amount of required cationic lipid could be achieved, while maintaining or even enhancing biological activity.