Aptamer-targeted delivery of Bcl-xL shRNA using alkyl modified PAMAM dendrimers into lung cancer cells

PAMAM Dendrimers as a Delivery System for Small Interfering RNA

Polyamidoamine dendrimers (PAMAM) form positively charged nanoparticles that function as nonviral delivery vectors for gene therapy. They protect nucleic acids from enzymatic degradation and facilitate endocytosis and endosomal escape. In this chapter, we describe the preparation and in vitro evaluation of small interfering RNA (siRNA)-PAMAM dendrimers. The physicochemical properties of the designed formulations were evaluated by size and zeta potential assessment and atomic force microscopy (AFM). The binding and release of the siRNA molecules from the PAMAM dendrimers were also assessed. Visualization and quantitative analysis of the siRNA-PAMAM dendrimers in live cells were analyzed by fluorescence microscopy and flow cytometry, respectively. Improving siRNA delivery to human cells through PAMAM dendrimers should accelerate the clinical applications of RNA interference.

Cholesterol-conjugated PEGylated PAMAM as an efficient nanocarrier for plasmid encoding interleukin-12 immunogene delivery toward colon cancer cells

IL-12 is a pleiotropic cytokine, which shows an ideal applicant for tumor immunotherapy, because of its features of creating an interconnection between innate (NK cells) and adaptive (cytotoxic T lymphocyte) immunity. IL-12 gene therapy is a useful technique to deliver an immune-modulatory gene directly into tumor site thereby limiting the adverse effects of systemic administration of IL-12 proteins. One of the most largely investigated non-viral gene carriers is polyamidoamine (PAMAM). In the current research, 5 and 3% of PAMAM primary amines were substituted to transmit the plasmid encoding IL-12 gene to cells by cholesteryl chloroformate and alkyl-PEG, respectively. The features of modified PAMAMs containing size and surface charge density, cytotoxicity, and transfection efficiency were investigated in colon cancer cells. in vitro experiment showed that this modified carrier with average size of about 160 nm and zeta potential of 30 mV was able to increase the level of IL-12 production up to two folds as compared to that of the unmodified PAMAM. Improvement of the polymer hydrophobic balance along with of the modulation of the surface positive charge could provide an efficient and safe non-viral IL-12 gene for colon cancer immunogene therapy.

Aptamers Chemistry: Chemical Modifications and Conjugation Strategies

Soon after they were first described in 1990, aptamers were largely recognized as a new class of biological ligands that can rival antibodies in various analytical, diagnostic, and therapeutic applications. Aptamers are short single-stranded RNA or DNA oligonucleotides capable of folding into complex 3D structures, enabling them to bind to a large variety of targets ranging from small ions to an entire organism. Their high binding specificity and affinity make them comparable to antibodies, but they are superior regarding a longer shelf life, simple production and chemical modification, in addition to low toxicity and immunogenicity. In the past three decades, aptamers have been used in a plethora of therapeutics and drug delivery systems that involve innovative delivery mechanisms and carrying various types of drug cargos. However, the successful translation of aptamer research from bench to bedside has been challenged by several limitations that slow down the realization of promising aptamer applications as therapeutics at the clinical level. The main limitations include the susceptibility to degradation by nucleases, fast renal clearance, low thermal stability, and the limited functional group diversity. The solution to overcome such limitations lies in the chemistry of aptamers. The current review will focus on the recent arts of aptamer chemistry that have been evolved to refine the pharmacological properties of aptamers. Moreover, this review will analyze the advantages and disadvantages of such chemical modifications and how they impact the pharmacological properties of aptamers. Finally, this review will summarize the conjugation strategies of aptamers to nanocarriers for developing targeted drug delivery systems.

Aptamers as Delivery Agents of siRNA and Chimeric Formulations for the Treatment of Cancer

Both aptamers and siRNA technologies have now reached maturity, and both have been validated with a product in the market. However, although pegaptanib reached the market some time ago, there has been a slow process for new aptamers to follow. Today, some 40 aptamers are in the market, but many in combination with siRNAs, in the form of specific delivery agents. This combination offers the potential to explore the high affinity and specificity of aptamers, the silencing power of siRNA, and, at times, the cytotoxicity of chemotherapy molecules in powerful combinations that promise to delivery new and potent therapies. In this review, we report new developments in the field, following up from our previous work, more specifically on the use of aptamers as delivery agents of siRNA in nanoparticle formulations, alone or in combination with chemotherapy, for the treatment of cancer.

Crosstalk between let-7a-5p and BCL-xL in the Initiation of Toxic Autophagy in Lung Cancer

Autophagy is essential for cellular metabolism and plays pivotal roles in carcinogenesis, while excessive autophagy induces toxicity and cell death. Our previous studies have suggested that let-7a-5p/BCL-xL might regulate autophagy in lung cancer, but the regulatory mechanism is unclear. The central goal of the study was to figure out the role of let-7a-5p/BCL-xL in the initiation of autophagy and its effect on the migration, invasion, and proliferation of A549 cells as well as its therapeutic potential in lung cancer. Based on the genome-wide expression profiles of lung cancer, BCL-xL and let-7a-5p were found to be dysregulated and negatively correlated in lung adenocarcinoma, which was associated with the survival of lung cancer. The crosstalk between BCL-xL and let-7a-5p was then investigated using dual-luciferase reporter assay, and it was found to suppress the migration and invasion of A549 cells. Further, we found that the crosstalk between BCL-xL and let-7a-5p could lead to toxic autophagy and cell death through activating the PI3K-signaling pathway, which was independent of apoptosis or pyroptosis. These findings indicate that let-7a-5p is a sensitive initiator for toxic autophagy in A549 lung cancer cells and is an appealing target for lung cancer therapy.

Long Non-coding RNAs as Communicators and Mediators Between the Tumor Microenvironment and Cancer Cells

Long non-coding RNAs (lncRNAs) are a class of more than 200 nucleotides RNA transcripts which have limited protein coding capacity. They regulate numerous biological processes in cancers through diverse molecular mechanisms. Aberrant expression of lncRNAs has been frequently associated with human cancer. Furthermore, the tumor microenvironment (TME) is composed of different cells such as cancer-associated fibroblasts (CAFs), endothelial cells and infiltrated immune cells, and all of which participate in communication with tumor cells affecting the progression of tumor. LncRNAs are directly and indirectly involved in the crosstalk between stromal cells and tumor cells and dysregulated lncRNAs expression in these cells could drive tumorigenesis. In this review, we explore the influence of aberrantly expressed lncRNAs in tumor progression, clarify the critical roles of lncRNAs in the TME, summarize findings on crosstalk between infiltrated immune cells, CAFs, endothelial cells, and tumor cells via lncRNAs, and discuss the promise of lncRNAs as tumor diagnostic markers and therapeutic targets.

Recent advances in aerosol gene delivery systems using non-viral vectors for lung cancer therapy

INTRODUCTION

Lung cancer commonly occurs at a high incidence worldwide. Application of aerosol gene delivery systems using various kinds of vectors can improve the patient's quality of life by prolonging the survival rate.

AREAS COVERED

This review provides a recent update on aerosol gene delivery strategies using various kinds of vectors and gene-modification technologies. Peptide-mediated gene therapy achieves specific targeting of cells and highly improves efficacy. Promoter-operating expression and the CRISPR/Cas9 system are novel gene therapy strategies for effective lung cancer treatment. Furthermore, hybrid systems with a combination of vectors or drugs have been recently applied as new trends in gene therapy.

EXPERT OPINION

Although aerosol gene delivery has many advantages, physiological barriers in the lungs pose formidable challenges. Targeted gene delivery and gene-editing technology are promising strategies for lung cancer therapy. These strategies may allow the development of safety and high efficiency for clinical application. Recently, hybrid gene therapy combining novel and specific vectors has been developed as an advanced strategy. Although gene therapy for lung cancer is being actively researched, aerosol gene therapy strategies are currently lacking, and further studies on aerosol gene therapy are needed to treat lung cancer.

The recent progresses in shRNA-nanoparticle conjugate as a therapeutic approach

The recent trend of gene therapy is using short hairpin RNA conjugated with different types of nanoparticles. shRNAs have a significant role in gene silencing and have a promising role in treating several genetic and infectious diseases. There are several drawbacks of delivering bare shRNA in the blood as they are fragile in nature and readily degradable. To overcome this problem shRNAs can be conjugated with nanoparticles for a safe deliver. In this article several nanoparticles are mentioned which play significant role in delivery of this payload. On one hand they protect the shRNA from degradation on the other they help to penetrate this large molecule in to the cell. Some of these nanoconjugates are in clinical trials and have a promising role in treatment of diseases.

Delivering Combination Chemotherapies and Targeting Oncogenic Pathways via Polymeric Drug Delivery Systems

The side-effects associated with chemotherapy necessitates better delivery of chemotherapeutics to the tumor. Nanoparticles can load higher amounts of drug and improve delivery to tumors, increasing the efficacy of treatment. Polymeric nanoparticles, in particular, have been used extensively for chemotherapeutic delivery. This review describes the efforts made to deliver combination chemotherapies and inhibit oncogenic pathways using polymeric drug delivery systems. Combinations of chemotherapeutics with other drugs or small interfering RNA (siRNA) combinations have been summarized. Special attention is given to the delivery of drug combinations that involve either paclitaxel or doxorubicin, two popular chemotherapeutics in clinic. Attempts to inhibit specific pathways for oncotherapy have also been described. These include inhibition of oncogenic pathways (including those involving HER2, EGFR, MAPK, PI3K/Akt, STAT3, and HIF-1α), augmentation of apoptosis by inhibiting anti-apoptosis proteins (Bcl-2, Bcl-xL, and survivin), and targeting dysregulated pathways such as Wnt/β-catenin and Hedgehog.

Design, Synthesis, and In Vitro Evaluation of Low Molecular Weight Protamine (LMWP)-Based Amphiphilic Conjugates as Gene Delivery Carriers

Development of efficient non-viral carriers is one of the major challenges of gene delivery. In the current study, we designed, synthesized, and evaluated the in vitro gene delivery efficiency of novel amphiphilic constructs composed of cholesterol and low molecular weight protamine (LMWP: VSRRRRRRGGRRRR) peptide. Vectors having both hydrophobic and hydrophilic moieties were evaluated in terms of particle size and charge, DNA condensation ability, cytotoxicity, and gene transfection efficiency. The prepared vectors spontaneity self-assembled into the liposome-like particles with a high local positive density. The nano-vehicle A (H5-LMWP-Cholestrol) and nano-vehicle B (LMWP-Cholesterol) could form micelles at concentrations above 50 μg/mL and 65 μg/mL, respectively. The gel retardation assay showed that nano-vehicles A and B could condense pDNA more efficiently than the corresponding unconjugated peptides. The mean of size and zeta potential of complexed nano-vehicle A at N/P ratios of 5, 15, and 30 were 151 nm and 23 mv, and those of nano-vehicle B were 224 nm and 19 mv, respectively. In terms of transfection efficiency, the designed nano-vehicles showed almost two-fold higher gene expression level compared to PEI 25 kDa at optimal N/P ratios, and also exhibited negligible cytotoxicity on a model cancer cell, Neuro 2a. The findings of the present study revealed that these cationic micelles can be promising candidates as non-viral gene delivery vehicles.

Long noncoding RNAs in cancer cells

Long noncoding RNA (lncRNA) has recently been investigated as key modulators that regulate many biological processes in human cancers via diverse mechanisms. LncRNAs can interact with macromolecules such as DNA, RNA, or protein to exert cellular effects and to act as either tumor promoters or tumor suppressors in various malignancies. Moreover, the aberrant expression of lncRNAs may be detected in multiple cancer phenotypes by employing the rapidly developing modern gene chip technology and bioinformatics analysis. Herein, we highlight the mechanisms of action of lncRNAs, their functional cellular roles and their involvement in cancer progression. Finally, we provide an overview of recent progress in the lncRNA field and future potential for lncRNAs as cancer diagnostic markers and therapeutics.

An Available Strategy for Nasal Brain Transport of Nanocomposite Based on PAMAM Dendrimers via In Situ Gel

Polyamidoamine (PAMAM) dendrimers are efficient drug carriers. The presence of a physiological pathway for nasal brain transport provides a potential path for direct brain-targeted delivery of dendrimer nanocomposites. In this study, we synthesized PAMAM dendrimer composites with a nanoscale size; the particle size of PAE (Paeonol)/mPEG (the heterofunctional PEG polymer with a methoxy)-PAMAM G5.NHAc and mPEG-PAMAM G5.NH₂-FITC were 72.41 ± 11.58 nm and 96.51 ± 7.77 nm, and the zeta potential of PAE/mPEG-PAMAM G5.NHAc and mPEG-PAMAM G5.NH₂-FITC were + 0.57 ± 0.11 mv and + 9.60 ± 0.41 mv, respectively. The EE% and DL% of PAE in PAE/mPEG-PAMAM G5.NHAc were 53.77% and 13.92%, respectively. PAE/mPEG-PAMAM G5.NHAc/DGG ionic-sensitive in situ gel was prepared, the viscosity of solution and gel state were 112 ± 3.2 mPa and 1403 ± 38.5 mPa, respectively. The in vitro goat mucoadhesive strength of the gel was 4763.36 ± 85.39 dyne/cm². In situ gel system was proven to be a non-Newtonian pseudo-plastic fluid with shear thinning, thixotropy and yield stress. The optimal model of PAE released from PAE/mPEG-PAMAM G5.NHAc and PAE/mPEG-PAMAM G5.NHAc/DGG were the Higuchi equation and the Korsmeyer-Peppas equation, respectively. The cytotoxicity of the nanocomposites showed a concentration-dependence, and the cell viabilities of PAE/mPEG-PAMAM G5.NHAc were both higher than 95% between 0.0001 μM and 10 μM. mPEG-PAMAM G5.NH₂-FITC was efficiently taken up by cells and exhibited strong fluorescence in the cytoplasm and nucleus. Significant accumulation of nanocomposites was observed in the brain after administration of the in situ gel group, and maximum accumulation was reached at 12 h. A small amount of accumulation was observed in the nanocomposite solution group only at 2 h. Therefore, the direct nasal brain transport efficiency of PAMAM dendrimer nanocomposites can be significantly improved after combining with in situ gel. PAMAM dendrimer nanocomposite/DGG is a potential drug delivery system for nasal brain transport.

Dendrimers for pulmonary delivery: current perspectives and future challenges

Dendrimers and dendrimer-based delivery systems are potential biomedicines in the rapidly growing field of nanomedicine.

Aptamer-iRNAs as Therapeutics for Cancer Treatment

Aptamers are single-stranded oligonucleotides (ssDNA or ssRNA) that bind and recognize their targets with high affinity and specificity due to their complex tertiary structure. Aptamers are selected by a method called SELEX (Systematic Evolution of Ligands by EXponential enrichment). This method has allowed the selection of aptamers to different types of molecules. Since then, many aptamers have been described for the potential treatment of several diseases including cancer. It has been described over the last few years that aptamers represent a very useful tool as therapeutics, especially for cancer therapy. Aptamers, thanks to their intrinsic oligonucleotide nature, present inherent advantages over other molecules, such as cell-based products. Owing to their higher tissue penetrability, safer profile, and targeting capacity, aptamers are likely to become a novel platform for the delivery of many different types of therapeutic cargos. Here we focus the review on interfering RNAs (iRNAs) as aptamer-based targeting delivered agents. We have gathered the most reliable information on aptamers as targeting and carrier agents for the specific delivery of siRNAs, shRNA, microRNAs, and antisense oligonucleotides (ASOs) published in the last few years in the context of cancer therapy.

A positron emission tomography image-guidable unimolecular micelle nanoplatform for cancer theranostic applications

Unimolecular micelles based on hyperbranched polyamidoamine (PAMAM) dendrimer were synthesized as both a cargo delivery vector and an imaging agent for triple-negative breast tumors, and the chemical synthesis procedures are detailed in this study. With the chemical conjugation of a peptide (F3, against cellular nucleolin) to increase its cellular internalization, these micelles can accumulate potently and specifically in breast cancer cells (e.g., MDA-MB-231). The size and morphology of these PAMAM-based micelles have been measured by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The hydrazone bond (responsive to pH alteration) between the loaded doxorubicin (DOX, as a model drug here) and PAMAM micelles enables cargo release following pH changes. Flow cytometry and confocal fluorescence microscopy revealed that PAMAM micelles with F3 attachment (PAMAM-DOX-F3) had stronger internalization into MDA-MB-231 cells (nucleolin-positive) than PAMAM micelles without F3 conjugation (PAMAM-DOX), whereas both of them have minimal interactions with L929 fibroblasts (nucleolin-negative). The positron-emitting isotope ⁶⁴Cu was added into PAMAM micelles by chelation to track their pharmacokinetic behavior (organ distribution profile) in vivo by positron emission tomography (PET) imaging. Serial PET imaging demonstrated that the accumulation of ⁶⁴Cu-PAMAM-DOX-F3 in MDA-MB-231 tumors was fast, potent, and persistent (tumor uptake: 6.1 ± 1.2% injection dose per gram [%ID/g] at 24 h p.i.), significantly higher than that of ⁶⁴Cu-PAMAM-DOX (2.5 ± 0.4%ID/g at the same time). Their distribution profiles in other organs/tissues were quite similar, with a relatively short circulation time. In addition, ex vivo fluorescence imaging confirmed that DOX can be delivered efficiently by these PAMAM micelles to MDA-MB-231 tumors. Deducing from these data, we believe that PAMAM-based micelles can be useful for selective combinational treatment of cancer.

STATEMENT OF SIGNIFICANCE

Micelles are a very useful biomaterial for theranostic purposes, and one of the major hurdles for micelles (particularly those from self-assembling) is their relatively low stability, especially when administered in vivo. In this study, we have attempted to overcome this limitation by designing unimolecular micelles (based on the concept of "one micelle is composed of one macromolecule") from polyamidoamine (PAMAM) dendrimers, in which the drug cargos (e.g., doxorubicin) are chemically attached to PAMAM through a hydrazone bond; hence, they can be used as a tumor-selective diagnostic/therapeutic platform. These unimolecular micelles possess superior stability compared to conventional micelles and can undertake stimulus (pH)-responsive cargo release for more "targeted" cancer therapy. With the incorporation of a tumor-targeting peptide sequence (F3) and a positron-emitting isotope (copper-64), the pharmacokinetic behavior of these micelles can be readily monitored by positron emission tomography imaging technique to confirm their specificity against cancer tissues. With further optimization, this micellar platform can have a broad clinical applicability owing to its biocompatibility, selectivity, and stability.

RNAi-based therapeutics for lung cancer: biomarkers, microRNAs, and nanocarriers

INTRODUCTION

Despite the current advances in the discovery of the lung cancer biomarkers and, consequently, in the diagnosis, this pathology continues to be the primary cause of cancer-related death worldwide. In most cases, the illness is diagnosed in an advanced stage, which limits the current treatment options available and reduces the survival rate. Therefore, RNAi-based therapy arises as a promising option to treat lung cancer.

AREAS COVERED

This review provides an overview on the exploitation of lung cancer biology to develop RNAi-based therapeutics to be applied in the treatment of lung cancer. Furthermore, the review analyzes the main nanocarriers designed to deliver RNAi molecules and induce antitumoral effects in lung cancer, and provides updated information about current RNAi-based therapeutics for lung cancer in clinical trials.

EXPERT OPINION

RNAi-based therapy uses nanocarriers to perform a targeted and efficient delivery of therapeutic genes into lung cancer cells, by taking advantage of the known biomarkers in lung cancer. These therapeutic genes are key regulatory molecules of crucial cellular pathways involved in cell proliferation, migration, and apoptosis. Thereby, the characteristics and functionalization of the nanocarrier and the knowledge of lung cancer biology have direct influence in improving the therapeutic effect of this therapy.

Aptamer-guided nanomedicines for anticancer drug delivery

Aptamers are versatile nucleic acid-based macromolecules characterized by their high affinity and specificity to a specific target. Taking advantage of such binding properties, several aptamers have been selected to bind tumor biomarkers and have been used as targeting ligands for the functionalization of nanomedicines. Different functionalization methods have been used to link aptamers to the surface drug nanocarriers. The pre-clinical data of such nanomedicines overall show an enhanced and selective delivery of therapeutic payloads to cancer cells, thereby accelerating steps towards more effective therapeutic systems. This review describes the current advances in the use of aptamers as targeting moieties for the delivery of therapeutic and imaging agents to tumors by conjugation to organic and inorganic nanocarriers.

Modified PAMAM vehicles for effective TRAIL gene delivery to colon adenocarcinoma: in vitro and in vivo evaluation

TRAIL (tumour necrosis factor-related apoptosis-inducing ligand) gene therapy is considered as one of the promising approaches for cancer treatment. Polyamidoamine (PAMAM) is one of the most extensively applied polymeric vector in gene delivery. In the current study, PAMAM (G4 and G5) dendrimers were modified with alkyl-carboxylate chain, PEG and cholesteryl chloroformate in order to enhance transfection efficiency through overcoming extracellular and intracellular barriers while reducing PAMAM cytotoxicity. Gene delivery efficiency of synthetized vectors was evaluated by both GFP (green fluorescent protein) reporter gene and TRAIL plasmid in colon cancer cells, in vitro and in vivo. The obtained results demonstrated that PAMAM G4-alkyl-PEG (3%)-Chol (5%)-TRAIL complexes at C/P ratio 4 could significantly increase cell death (29.45%) in comparison with unmodified PAMAM vector (15.5%). Moreover, in vivo study in C26 tumor-bearing BALB/c mice suggested that the prepared non-toxic safe vector could inhibit the tumor growth. This study represented the potent vehicle based on cholesterol-grafted PAMAM dendrimers with alkyl-PEG modification for efficient gene delivery in vitro and in vivo.

Chloroquine in combination with aptamer-modified nanocomplexes for tumor vessel normalization and efficient erlotinib/Survivin shRNA co-delivery to overcome drug resistance in EGFR-mutated non-small cell lung cancer

Although novel molecular targeted drugs have been recognized as an effective therapy for non-small cell lung cancer (NSCLC) harboring epidermal growth factor receptor (EGFR) activating mutations, their efficacy fails to meet the expectation due to the acquired resistance in tumors. Up-regulation of the anti-apoptotic protein Survivin was shown to contribute to the resistance to EGFR tyrosine kinase inhibitors (TKI) in EGFR mutation-positive NSCLC. However, the unorganized tumor blood vessels impeded drug penetration into tumor tissue. The resulting insufficient intracellular drug/gene delivery in drug-resistant cancer cells remarkably weakened the drug efficacy in NSCLC. In this work, a multi-functional drug delivery system AP/ES was developed by using anti-EGFR aptamer (Apt)-modified polyamidoamine to co-deliver erlotinib and Survivin-shRNA. Chloroquine (CQ) was used in combination with AP/ES to normalize tumor vessels for sufficient drug/gene delivery to overcome drug resistance in NSCLC cells. The obtained AP/ES possessed desired physicochemical properties, good biostability, controlled drug release profiles, and strong selectivity to EGFR-mutated NSCLC mediated by Apt. CQ not only enhanced endosomal escape ability of AP/ES for efficient gene transfection to inhibit Survivin, but also showed strong vessel-normalization ability to improve tumor microcirculation, which further promoted drug delivery and enhanced drug efficacy in erlotinib-resistant NSCLC cells. Our innovative gene/drug co-delivery system in combination with CQ showed a promising outcome in fighting against erlotinib resistance both in vitro and in vivo. This work indicates that normalization of tumor vessels could help intracellular erlotinib/Survivin-shRNA delivery and the down-regulation of Survivin could act synergistically with erlotinib for reversal of erlotinib resistance in EGFR mutation-positive NSCLC.

STATEMENT OF SIGNIFICANCE

NSCLC patients who benefited from EGFR-TKIs inevitably developed acquired resistance. Previous research focused on synthesis of new generation of molecular targeted drugs that could irreversibly inhibit EGFR with a particular gene mutation to overcome drug resistance. However, they failed to inhibit EGFR with other gene mutations. Activation of bypass signaling pathway and the changes of tumor microenvironment are identified as two of the mechanisms of acquired resistance to EGFR-TKIs. We therefore constructed multifunctional gene/drug co-delivery nanocomplexes AP/ES co-formulated with chloroquine that could target the both two mechanisms. We found that chloroquine not only enhanced endosomal escape ability of AP/ES for efficient gene transfection to inhibit Survivin, but also showed strong vessel-normalization ability to improve tumor microcirculation, which further promoted drug delivery into tumor tissue and enhanced drug efficacy in erlotinib-resistant NSCLC.