Efficient siRNA Delivery by Lipid Nanoparticles Modified with a Nonstandard Macrocyclic Peptide for EpCAM-Targeting

More than a delivery system: the evolving role of lipid-based nanoparticles

Lipid-based nanoparticles, including liposomes and lipid nanoparticles (LNPs), make up an important class of drug delivery systems. Their modularity enables encapsulation of a wide range of therapeutic cargoes, their ease of functionalization allows for incorporation of targeting motifs and anti-fouling coatings, and their scalability facilitates rapid translation to the clinic. While the discovery and early understanding of lipid-based nanoparticles is heavily rooted in biology, formulation development has largely focused on materials properties, such as how liposome and lipid nanoparticle composition can be altered to maximize drug loading, stability and circulation. To achieve targeted delivery and enable improved accumulation of therapeutics at target tissues or disease sites, emphasis is typically placed on the use of external modifications, such as peptide, protein, and polymer motifs. However, these approaches can increase the complexity of the nanocarrier and complicate scale up. In this review, we focus on how our understanding of lipid structure and function in biological contexts can be used to design intrinsically functional and targeted nanocarriers. We highlight formulation-based strategies, such as the incorporation of bioactive lipids, that have been used to modulate liposome and lipid nanoparticle properties and improve their functionality while retaining simple nanocarrier designs. We also highlight classes of naturally occurring lipids, their functions, and how they have been incorporated into lipid-based nanoparticles. We will additionally position these approaches into the historical context of both liposome and LNP development.

Lipid Nanoparticle (LNP) -A Vector Suitable for Evolving Therapies for Advanced Hepatocellular Carcinoma (HCC)

Hepatocellular carcinoma (HCC) stands as the predominant form of primary liver cancer, characterized by a dismal prognosis. Therapeutic options for advanced HCC remain sparse, with efficacy significantly hampered by the emergence of drug resistance. In parallel with research into novel pharmacological agents, advances in drug delivery systems represent a promising avenue for overcoming resistance. Lipid nanoparticles (LNPs) have demonstrated considerable efficacy in the delivery of nucleic acid-based therapeutics and hold potential for broader applications in drug delivery. This review describes the development of LNPs tailored for HCC treatment and consolidates recent investigations using LNPs to target HCC.

Acid-degradable lipid nanoparticles enhance the delivery of mRNA

Lipid nanoparticle (LNP)-mRNA complexes are transforming medicine. However, the medical applications of LNPs are limited by their low endosomal disruption rates, high toxicity and long tissue persistence times. LNPs that rapidly hydrolyse in endosomes (RD-LNPs) could solve the problems limiting LNP-based therapeutics and dramatically expand their applications but have been challenging to synthesize. Here we present an acid-degradable linker termed 'azido-acetal' that hydrolyses in endosomes within minutes and enables the production of RD-LNPs. Acid-degradable lipids composed of polyethylene glycol lipids, anionic lipids and cationic lipids were synthesized with the azido-acetal linker and used to generate RD-LNPs, which significantly improved the performance of LNP-mRNA complexes in vitro and in vivo. Collectively, RD-LNPs delivered mRNA more efficiently to the liver, lung, spleen and brains of mice and to haematopoietic stem and progenitor cells in vitro than conventional LNPs. These experiments demonstrate that engineering LNP hydrolysis rates in vivo has great potential for expanding the medical applications of LNPs.

The future of genetic medicines delivered via targeted lipid nanoparticles to leukocytes

Genetic medicines hold vast therapeutic potential, offering the ability to silence or induce gene expression, knock out genes, and even edit DNA fragments. Applying these therapeutic modalities to leukocytes offers a promising path for treating various conditions yet overcoming the obstacles of specific and efficient delivery to leukocytes remains a major bottleneck in their clinical translation. Lipid nanoparticles (LNPs) have emerged as the leading delivery system for nucleic acids due to their remarkable versatility and ability to improve their in vivo stability, pharmacokinetics, and therapeutic benefits. Equipping LNPs with targeting moieties can promote their specific cellular uptake and internalization to leukocytes, making targeted LNPs (tLNPs) an inseparable part of developing leukocyte-targeted gene therapy. However, despite the significant advancements in research, genetic medicines for leukocytes using targeted delivery approaches have not been translated into the clinic yet. Herein, we discuss the important aspects of designing tLNPs and highlight the considerations for choosing an appropriate bioconjugation strategy and targeting moiety. Furthermore, we provide our insights on limiting challenges and identify key areas for further research to advance these exciting therapies for patient care.

Surface modification of lipid nanoparticles for gene therapy

Gene therapies have the potential to target and effectively treat a variety of diseases including cancer as well as genetic, neurological, and autoimmune disorders. Although we have made significant advances in identifying non-viral strategies to deliver genetic cargo, certain limitations remain. In general, gene delivery is challenging for several reasons including the instabilities of nucleic acids to enzymatic and chemical degradation and the presence of restrictive biological barriers such as cell, endosomal and nuclear membranes. The emergence of lipid nanoparticles (LNPs) helped overcome many of these challenges. Despite its success, further optimization is required for LNPs to yield efficient gene delivery to extrahepatic tissues, as LNPs favor accumulation in the liver after systemic administration. In this mini-review, we provide an overview of current preclinical approaches in that LNP surface modification was leveraged for cell and tissue targeting by conjugating aptamers, antibodies, and peptides among others. In addition to their cell uptake and efficiency-enhancing effects, we outline the (dis-)advantages of the different targeting moieties and commonly used conjugation strategies.

Nano-scale delivery systems for siRNA delivery in cancer therapy: New era of gene therapy empowered by nanotechnology

RNA interference (RNAi) is a unique treatment approach used to decrease a disease's excessive gene expression, including cancer. SiRNAs may find and destroy homologous mRNA sequences within the cell thanks to RNAi processes. However, difficulties such poor cellular uptake, off-target effects, and susceptibility to destruction by serum nucleases in the bloodstream restrict the therapeutic potential of siRNAs. Since some years ago, siRNA-based therapies have been in the process of being translated into the clinic. Therefore, the primary emphasis of this work is on sophisticated nanocarriers that aid in the transport of siRNA payloads, their administration in combination with anticancer medications, and their use in the treatment of cancer. The research looks into molecular manifestations, difficulties with siRNA transport, the design and development of siRNA-based delivery methods, and the benefits and drawbacks of various nanocarriers. The trapping of siRNA in endosomes is a challenge for the majority of delivery methods, which affects the therapeutic effectiveness. Numerous techniques for siRNA release, including as pH-responsive release, membrane fusion, the proton sponge effect, and photochemical disruption, have been studied to overcome this problem. The present state of siRNA treatments in clinical trials is also looked at in order to give a thorough and systematic evaluation of siRNA-based medicines for efficient cancer therapy.

Surface engineering of lipid nanoparticles: targeted nucleic acid delivery and beyond

Harnessing surface engineering strategies to functionalize nucleic acid-lipid nanoparticles (LNPs) for improved performance has been a hot research topic since the approval of the first siRNA drug, patisiran, and two mRNA-based COVID-19 vaccines, BNT162b2 and mRNA-1273. Currently, efforts have been mainly made to construct targeted LNPs for organ- or cell-type-specific delivery of nucleic acid drugs by conjugation with various types of ligands. In this review, we describe the surface engineering strategies for nucleic acid-LNPs, considering ligand types, conjugation chemistries, and incorporation methods. We then outline the general purification and characterization techniques that are frequently used following the engineering step and emphasize the specific techniques for certain types of ligands. Next, we comprehensively summarize the currently accessible organs and cell types, as well as the other applications of the engineered LNPs. Finally, we provide considerations for formulating targeted LNPs and discuss the challenges of successfully translating the "proof of concept" from the laboratory into the clinic. We believe that addressing these challenges could accelerate the development of surface-engineered LNPs for targeted nucleic acid delivery and beyond.

Lipid nanoparticle mRNA systems containing high levels of sphingomyelin engender higher protein expression in hepatic and extra-hepatic tissues

Lipid nanoparticles (LNPs) for delivery of mRNA usually contain ionizable lipid/helper lipid/cholesterol/PEG-lipid in molar ratios of 50:10:38.5:1.5, respectively. These LNPs are rapidly cleared from the circulation following intravenous (i.v.) administration, limiting uptake into other tissues. Here, we investigate the properties of LNP mRNA systems prepared with high levels of "helper" lipids such as 1,2-distearoyl-sn-glycero-3-phosphorylcholine (DSPC) or N-(hexadecanoyl)-sphing-4-enine-1-phosphocholine (egg sphingomyelin [ESM]). We show that LNP mRNAs containing 40 mol % DSPC or ESM have a unique morphology with a small interior "solid" core situated in an aqueous compartment that is bounded by a lipid bilayer. The encapsulated mRNA exhibits enhanced stability in the presence of serum. LNP mRNA systems containing 40 mol % DSPC or ESM exhibit significantly improved transfection properties in vitro compared with systems containing 10 mol % DSPC or ESM. When injected i.v., LNP mRNAs containing 40 mol % ESM exhibit extended circulation lifetimes compared with LNP mRNA systems containing 10 mol % DSPC, resulting in improved accumulation in extrahepatic tissues. Systems containing 40 mol % ESM result in significantly improved gene expression in spleen and bone marrow as well as liver post i.v. injection compared with 10 mol % DSPC LNP mRNAs. We conclude that LNP mRNAs containing high levels of helper lipid provide a new approach for transfecting hepatic and extrahepatic tissues.

Current state of RNA delivery using lipid nanoparticles to extrahepatic tissues: A review towards clinical translation

Genetic medicine, including ribonucleic acid (RNA) therapy, has delivered numerous progresses to the treatment of diseases thanks to the development of lipid nanoparticles (LNPs) as a delivery vehicle. However, RNA therapeutics are still limited by the lack of safe, precise, and efficient delivery outside of the liver. Thus, to fully realize the potential of genetic medicine, strategies to arm LNPs with extrahepatic targeting capabilities are urgently needed. This review explores the current state of next-generation LNPs that can bring RNA biomolecules to their targeted organ. The main approaches commonly used are described, including the modulation of internal lipid chemistries, the use of conjugated targeting moieties, and the designs of clinical administration. This work will demonstrate the advances in each approach and the remaining challenges in the field, focusing on clinical translation.

Effect of PEG Anchor and Serum on Lipid Nanoparticles: Development of a Nanoparticles Tracking Method

Polyethylene glycol (PEG) is used in Lipid Nanoparticles (LNPs) formulations to confer stealth properties and is traditionally anchored in membranes by a lipid moiety whose length significantly impacts the LNPs fate in vivo. C18 acyl chains are efficiently anchored in the membrane, while shorter C14 lipids are quickly desorbed and replaced by a protein corona responsible for the completely different fate of LNPs. In this context, a method to predict the biological behavior of LNPs depending on the lipid-PEG dissociation was developed using the Nanoparticle Tracking Analysis (NTA) method in serum. Two formulations of siRNA-containing LNPs were prepared including CSL3 or SM-102 lipids and were grafted with different lipids-PEG (C18, C14 lipids-PEG, and Ceramide-PEG). The impact of the lipid-PEG on the interactions between LNPs and serum components was demonstrated by monitoring the mean particle size and the concentration over time. In vitro, these formulations demonstrated low toxicity and efficient gene knockdown on tumor MDA-MB-231 cells, but serum was found to significantly impact the efficiency of C18-PEG-based LNPs, while it did not impact the efficiency of C14-PEG-based LNPs. The NTA method demonstrated the ability to discriminate between the behaviors of LNPs according to serum proteins' interactions. CSL3 lipid and Cer-PEG were confirmed to have promise for LNP formulation.

Innovative System for Delivering Nucleic Acids/Genes Based on Controlled Intracellular Trafficking as Well as Controlled Biodistribution for Nanomedicines

This review paper summarizes progress that has been made in the new field of "Controlled Intracellular Trafficking." This involves the development of new systems for delivering plasmid DNA (pDNA), small interfering RNA (siRNA), mRNA, proteins, their escape from endosomes, the mechanism for how they enter the nucleus, how they enter mithochondria and how materials subsequently function within a cell. In addition, strategies for delivering these materials to a selective tissue after intravenous administration was also intensively investigated not only to the liver but also to tumors, lungs, adipose tissue and the spleen. In 2020, a new mRNA vaccine was developed against coronavirus disease 2019 (COVID-19), where ionizable cationic lipids were used as a delivery system. Our strategy to identify an efficient ionizable cationic lipids (iCL) based on a lipid library as well as their applications concerning the delivery of siRNA/mRNA/pDNA is also described.

Efficacy of epi-1 modified epirubicin and curcumin encapsulated liposomes targeting-EpCAM in the inhibition of epithelial ovarian cancer cells

Treatment of epithelial ovarian cancer (EOC) is a challenge because it still leads to unsatisfactory clinical prognosis. This is due to the toxicity and poor targeting of chemotherapeutic agents, as well as metastasis of the tumor. In this study, we designed a targeted liposome with nanostructures to overcome these problems. In the liposomes, epirubicin and curcumin were encapsulated to achieve their synergistic antitumor efficacy, while Epi-1 was modified on the liposomal surface to target epithelial cell adhesion molecule (EpCAM). Epi-1, a macrocyclic peptide, exhibits active targeting for enhanced cellular uptake and potent cytotoxicity against tumor cells. The encapsulation of epirubicin and curcumin synergistically inhibited the formation of neovascularization and vasculogenic mimicry (VM) channels, thereby suppressing tumor metastasis on SKOV3 cells. The dual drug loaded Epi-1-liposomes also induced apoptosis and downregulated metastasis-related proteins for effective antitumor in vitro. In vivo studies showed that dual drug loaded Epi-1-liposomes prolonged circulation time in the blood and increased the selective accumulation of drug at the tumor site. H&E staining and immunohistochemistry with Ki-67 also showed that targeted liposomes elevated antitumor activity. Also, targeted liposomes downregulated angiogenesis-related proteins to inhibit angiogenesis and thus tumor metastasis. In conclusion, the production of dual drug loaded Epi-1-liposomes is an effective strategy for the treatment of EOC.

siRNA Functionalized Lipid Nanoparticles (LNPs) in Management of Diseases

RNAi (RNA interference)-based technology is emerging as a versatile tool which has been widely utilized in the treatment of various diseases. siRNA can alter gene expression by binding to the target mRNA and thereby inhibiting its translation. This remarkable potential of siRNA makes it a useful candidate, and it has been successively used in the treatment of diseases, including cancer. However, certain properties of siRNA such as its large size and susceptibility to degradation by RNases are major drawbacks of using this technology at the broader scale. To overcome these challenges, there is a requirement for versatile tools for safe and efficient delivery of siRNA to its target site. Lipid nanoparticles (LNPs) have been extensively explored to this end, and this paper reviews different types of LNPs, namely liposomes, solid lipid NPs, nanostructured lipid carriers, and nanoemulsions, to highlight this delivery mode. The materials and methods of preparation of the LNPs have been described here, and pertinent physicochemical properties such as particle size, surface charge, surface modifications, and PEGylation in enhancing the delivery performance (stability and specificity) have been summarized. We have discussed in detail various challenges facing LNPs and various strategies to overcome biological barriers to undertake the safe delivery of siRNA to a target site. We additionally highlighted representative therapeutic applications of LNP formulations with siRNA that may offer unique therapeutic benefits in such wide areas as acute myeloid leukaemia, breast cancer, liver disease, hepatitis B and COVID-19 as recent examples.

Emerging Nanotherapeutic Approaches to Overcome Drug Resistance in Cancers with Update on Clinical Trials

A key issue with modern cancer treatments is the emergence of resistance to conventional chemotherapy and molecularly targeted medicines. Cancer nanotherapeutics were created in order to overcome the inherent limitations of traditional chemotherapeutics. Over the last few decades, cancer nanotherapeutics provided unparalleled opportunities to understand and overcome drug resistance through clinical assessment of rationally designed nanoparticulate delivery systems. In this context, various design strategies such as passive targeting, active targeting, nano-drug, and multimodal nano-drug combination therapy provided effective cancer treatment. Even though cancer nanotherapy has made great technological progress, tumor biology complexity and heterogeneity and a lack of comprehensive knowledge of nano-bio interactions remain important roadblocks to future clinical translation and commercialization. The current developments and advancements in cancer nanotherapeutics employing a wide variety of nanomaterial-based platforms to overcome cancer treatment resistance are discussed in this article. There is also a review of various nanotherapeutics-based approaches to cancer therapy, including targeting strategies for the tumor microenvironment and its components, advanced delivery systems for specific targeting of cancer stem cells (CSC), as well as exosomes for delivery strategies, and an update on clinical trials. Finally, challenges and the future perspective of the cancer nanotherapeutics to reverse cancer drug resistance are discussed.

The RaPID Platform for the Discovery of Pseudo-Natural Macrocyclic Peptides

Although macrocyclic peptides bearing exotic building blocks have proven their utility as pharmaceuticals, the sources of macrocyclic peptide drugs have been largely limited to mimetics of native peptides or natural product peptides. However, the recent emergence of technologies for discovering de novo bioactive peptides has led to their reconceptualization as a promising therapeutic modality. For the construction and screening of libraries of such macrocyclic peptides, our group has devised a platform to conduct affinity-based selection of massive libraries (>10¹² unique sequences) of in vitro expressed macrocyclic peptides, which is referred to as the random nonstandard peptides integrated discovery (RaPID) system. The RaPID system integrates genetic code reprogramming using the FIT (flexible in vitro translation) system, which is largely facilitated by flexizymes (flexible tRNA-aminoacylating ribozymes), with mRNA display technology.We have demonstrated that the RaPID system enables rapid discovery of various de novo pseudo-natural peptide ligands for protein targets of interest. Many examples discussed in this Account prove that thioether-closed macrocyclic peptides (teMPs) obtained by the RaPID system generally exhibit remarkably high affinity and specificity, thereby potently inhibiting or activating a specific function(s) of the target. Moreover, such teMPs are used for a wide range of biochemical applications, for example, as crystallization chaperones for intractable transmembrane proteins and for in vivo recognition of specific cell types. Furthermore, recent studies demonstrate that some teMPs exhibit pharmacological activities in animal models and that even intracellular proteins can be inhibited by teMPs, illustrating the potential of this class of peptides as drug leads.Besides the ring-closing thioether linkage in the teMPs, genetic code reprogramming by the FIT system allows for incorporation of a variety of other exotic building blocks. For instance, diverse nonproteinogenic amino acids, hydroxy acids (ester linkage), amino carbothioic acid (thioamide linkage), and abiotic foldamer units have been successfully incorporated into ribosomally synthesized peptides. Despite such enormous successes in the conventional FIT system, multiple or consecutive incorporation of highly exotic amino acids, such as d- and β-amino acids, is yet challenging, and particularly the synthesis of peptides bearing non-carbonyl backbone structures remains a demanding task. To upgrade the RaPID system to the next generation, we have engaged in intensive manipulation of the FIT system to expand the structural diversity of peptides accessible by our in vitro biosynthesis strategy. Semilogical engineering of tRNA body sequences led to a new suppressor tRNA (tRNA^Pro1E2) capable of effectively recruiting translation factors, particularly EF-Tu and EF-P. The use of tRNA^Pro1E2 in the FIT system allows for not only single but also consecutive and multiple elongation of exotic amino acids, such as d-, β-, and γ-amino acids as well as aminobenzoic acids. Moreover, the integration of the FIT system with various chemical or enzymatic posttranslational modifications enables us to expand the range of accessible backbone structures to non-carbonyl moieties prominent in natural products and peptidomimetics. In such systems, FIT-expressed peptides undergo multistep backbone conversions in a one-pot manner to yield designer peptides composed of modified backbones such as azolines, azoles, and ring-closing pyridines. Our current research endeavors focus on applying such in vitro biosynthesis systems for the discovery of bioactive de novo pseudo-natural products.

Immunostimulatory Response of RWFV Peptide-Targeted Lipid Nanoparticles on Bladder Tumor Associated Cells

Bladder carcinoma is the most expensive tumor type to treat on a cost-per-patient basis from diagnosis to death. Treatment with Bacillus Calmette Guerin (BCG) instillation is the only approved immunotherapy in the clinic for the remission of superficial bladder carcinoma. Unfortunately, frequent relapses, high local morbidity, risk of systemic mycobacterial infection, and occasional supply chain interruptions limit the utility of BCG for bladder cancer treatment. It is well known that BCG utilizes an adhesin protein known as fibronectin attachment protein that possesses a crucial RWFV peptide sequence for binding to the bladder tumor microenvironment prior to the initiation of the immunotherapeutic response. We report a RWFV-targeted, pH-responsive stabilized lipid nucleic acid nanoparticle (LNP) vehicle for the effective delivery of an immunotherapeutic oligonucleotide, CpG, that is assembled using a glass microfluidic Chemtrix 3221 reactor. Our small-angle X-ray scattering studies revealed a layer-by-layer assembly of the oligonucleotides with a repeat distance of 6.04 nm within the LNP. Using flow cytometry to evaluate the different cell types found in the bladder tumor microenvironment, RWFV-targeted LNPs were found to attach specifically to fibronectin-secreting cells in culture during a 2 h incubation period. The trafficking and cellular fate of these targeted LNPs were revealed by confocal microscopy of RAW264.7 macrophages to enter the endocytotic pathway within 4 h post treatment. Importantly, control studies reveal that only the pH-sensitive LNP formulation is capable of efficiently releasing the payload within 12 h. As a result, the targeted pH-sensitive LNP resulted in higher expression levels of costimulatory molecules CD83, CD 86, and MHC II, while also inducing higher levels of TNF-α secretion from macrophages. These results demonstrate that RWFV-targeted, pH-sensitive LNP formulations are capable of maximum immunotherapeutic response, potentially making them a highly efficient, lower risk, and readily manufactured alternative to BCG immunotherapy.

Recent advances in siRNA delivery mediated by lipid-based nanoparticles

Small interfering RNA (siRNA) has been expected to be a unique pharmaceutic for the treatment of broad-spectrum intractable diseases. However, its unfavorable properties such as easy degradation in the blood and negative-charge density are still a formidable barrier for clinical use. For disruption of this barrier, siRNA delivery technology has been significantly advanced in the past two decades. The approval of Patisiran (ONPATTRO™) for the treatment of transthyretin-mediated amyloidosis, the first approved siRNA drug, is a most important milestone. Since lipid-based nanoparticles (LNPs) are used in Patisiran, LNP-based siRNA delivery is now of significant interest for the development of the next siRNA formulation. In this review, we describe the design of LNPs for the improvement of siRNA properties, bioavailability, and pharmacokinetics. Recently, a number of siRNA-encapsulated LNPs were reported for the treatment of intractable diseases such as cancer, viral infection, inflammatory neurological disorder, and genetic diseases. We believe that these contributions address and will promote the development of an effective LNP-based siRNA delivery system and siRNA formulation.

Encoded Library Technologies as Integrated Lead Finding Platforms for Drug Discovery

The scope of targets investigated in pharmaceutical research is continuously moving into uncharted territory. Consequently, finding suitable chemical matter with current compound collections is proving increasingly difficult. Encoded library technologies enable the rapid exploration of large chemical space for the identification of ligands for such targets. These binders facilitate drug discovery projects both as tools for target validation, structural elucidation and assay development as well as starting points for medicinal chemistry. Novartis internalized two complementing encoded library platforms to accelerate the initiation of its drug discovery programs. For the identification of low-molecular weight ligands, we apply DNA-encoded libraries. In addition, encoded peptide libraries are employed to identify cyclic peptides. This review discusses how we apply these two platforms in our research and why we consider it beneficial to run both pipelines in-house.

Optimizing Advances in Nanoparticle Delivery for Cancer Immunotherapy

Cancer immunotherapy is one of the fastest growing and most promising fields in clinical oncology. T-cell checkpoint inhibitors are revolutionizing the management of advanced cancers including non-small cell lung cancer and melanoma. Unfortunately, many common cancers are not responsive to these drugs and resistance remains problematic. A growing number of novel cancer immunotherapies have been discovered but their clinical translation has been limited by shortcomings of conventional drug delivery. Immune signaling is tightly-regulated and often requires simultaneous or near-simultaneous activation of multiple signals in specific subpopulations of immune cells. Nucleic acid therapies, which require intact intracellular delivery, are among the most promising approaches to modulate the tumor microenvironment to a pro-immunogenic phenotype. Advanced nanomedicines can be precisely engineered to overcome many of these limitations and appear well-poised to enable the clinical translation of promising cancer immunotherapies.

Recognition Sites for Cancer-targeting Drug Delivery Systems

BACKGROUND

Target-homing drug delivery systems are now gaining significant attention for use as novel therapeutic approaches in antitumor targeting for cancer therapy. Numerous targeted drug delivery systems have been designed to improve the targeting effects because these systems can display a range of favorable properties, thus, providing suitable characteristics for clinical applicability of anticancer drugs, such as increasing the solubility, and improving the drug distribution at target sites. The majority of these targeting systems are designed with respect to differences between cancerous and normal tissues, for instance, the low pH of tumor tissues or overexpressed receptors on tumor cell membranes. Due to the growing number of targeting possibilities, it is important to know the tumor-specific recognition strategies for designing novel, targeted, drug delivery systems. Herein, we identify and summarize literature pertaining to various recognition sites for optimizing the design of targeted drug delivery systems to augment current chemotherapeutic approaches.

OBJECTIVE

This review focuses on the identification of the recognition sites for developing targeted drug delivery systems for use in cancer therapeutics.

METHODS

We have reviewed and compiled cancer-specific recognition sites and their abnormal characteristics within tumor tissues (low pH, high glutathione, targetable receptors, etc.), tumor cells (receptor overexpression or tumor cell membrane changes) and tumor cell organelles (nuclear and endoplasmic reticular dysregulation) utilizing existing scientific literature. Moreover, we have highlighted the design of some targeted drug delivery systems that can be used as homing tools for these recognition sites.

RESULTS AND CONCLUSION

Targeted drug delivery systems are a promising therapeutic approach for tumor chemotherapy. Additional research focused on finding novel recognition sites, and subsequent development of targeting moieties for use with drug delivery systems will aid in the evaluation and clinical application of new and improved chemotherapeutics.

A pH-sensitive polymer based precise tumor targeting strategy with reduced uptake of nanoparticles by non-cancerous cells

A T₂-weighted MRI contrast agent (SPION-AN-FA@mPEG) can precisely target cancer cells with folate receptor α (FRα) diminishing non-specific uptake by normal healthy cells.

Pharmacokinetic evaluation of liposomal nanoparticle-encapsulated nucleic acid drug: A combined study of dynamic PET imaging and LC/MS/MS analysis

In vivo biodistribution analyses, especially in tumors, of nucleic acids delivered with nanoparticles are important to develop drug delivery technologies for medical use. We previously developed wrapsome® (WS), an ~100 nm liposomal nanoparticle that can encapsulate siRNA, and reported that WS accumulates in tumors in vivo and inhibits their growth by an enhanced permeability and retention effect. In the present study, we evaluated the pharmacokinetics of nucleic acid-containing nanoparticles by combining dynamic positron emission tomography (PET) imaging and liquid chromatography-tandem mass spectrometry (LC/MS/MS) analysis. An 18-mer phosphorothioate oligodeoxynucleotide (ODN), trabedersen, was used as a model drug and was encapsulated in WS. Dynamic PET imaging and time-activity curve analysis of WS-encapsulated ⁶⁴Cu-labeled ODNs administered to mice with MIA PaCa-2 subcutaneous xenograft tumors showed tumor accumulation (~3% injected dose per gram (%ID/g)) and liver accumulation (~30 %ID/g) at 24 h. Under these conditions, LC/MS/MS analysis showed that the level of intact ODNs was 1.62 %ID/g in the tumor and 1.70 %ID/g in the liver. From these pharmacokinetic data, the intact/accumulated ODN ratios were calculated using the following equation: intact/accumulated ODN ratio (%) = %ID/g _{LC/MS/MS, tissue, mean}/%ID/g _{PET, tissue, mean} × 100. Interestingly, the ratios for the tumor and kidney were maintained at 20-50% over 48 h after administration of the WS-encapsulated form. In contrast, the ratio for the liver rapidly decreased at 24 h, showing the same pattern as that for naked ODN. These different patterns indicate that WS effectively protected the ODN in the tumor and kidney, but protected it less efficiently in the liver. A combined approach of dynamic PET imaging and LC/MS/MS analysis will assist the development of nanoparticle-encapsulated nucleic acid drugs, such as those using WSs, to determine their detailed pharmacokinetics.

RNA Display Methods for the Discovery of Bioactive Macrocycles

The past two decades have witnessed the emergence of macrocycles, including macrocyclic peptides, as a promising yet underexploited class of de novo drug candidates. Both rational/computational design and in vitro display systems have contributed tremendously to the development of cyclic peptide binders of either traditional targets such as cell-surface receptors and enzymes or challenging targets such as protein-protein interaction surfaces. mRNA display, a key platform technology for the discovery of cyclic peptide ligands, has become one of the leading strategies that can generate natural-product-like macrocyclic peptide binders with antibody-like affinities. On the basis of the original cell-free transcription/translation system, mRNA display is highly evolvable to realize its full potential by applying genetic reprogramming and chemical/enzymatic modifications. In addition, mRNA display also allows the follow-up hit-to-lead development using high-throughput focused affinity maturation. Finally, mRNA-displayed peptides can be readily engineered to create chemical conjugates based on known small molecules or biologics. This review covers the birth and growth of mRNA display and discusses the above features of mRNA display with success stories and future perspectives and is up to date as of August 2018.

Lipidation of polyethylenimine-based polyplex increases serum stability of bioengineered RNAi agents and offers more consistent tumoral gene knockdown in vivo

Recently we have established a novel approach to produce bioengineered noncoding RNA agents (BERAs) in living cells that carry target RNAi molecules (e.g., siRNA and miRNA) and thus act as "prodrugs". Using GFP-siRNA-loaded BERA (BERA/GFP-siRNA) as a model molecule, this study was to define the in vitro and in vivo knockdown efficiency of BERAs delivered by liposome-polyethylenimine nanocomplex (lipopolyplex or LPP). Compared to in vivo-jetPEI® (IVJ-PEI) and polyplex formulations, LPP offered greater protection of BERA/GFP-siRNA against degradation by serum RNases. Particle sizes and zeta potentials of LPP nanocomplex remained stable over 28 days when stored at 4 °C. Furthermore, comparable levels of BERA/GFP-siRNA were delivered by LPP and IVJ-PEI to luciferase/GFP-expressing human SK-Hep1-Luc-GFP or A549-Luc-GFP cells, which were selectively processed into target GFP-siRNA and subsequently knocked down GFP mRNA and protein levels. In addition, LPP-carried BERA/GFP-siRNA was successfully delivered into xenograft tumors and offered more consistent knockdown of tumoral GFP mRNA level in an orthotopic hepatocellular carcinoma (HCC) SK-Hep1-Luc-GFP xenograft mouse model, while IVJ-PEI formulation showed larger variation. These findings demonstrated that lipidation of polyplexes improved serum stability of biologic RNAi molecules, which was efficiently delivered to orthotopic HCC tissues to knock down target gene expression.

EpCAM Immunotherapy versus Specific Targeted Delivery of Drugs

The epithelial cell adhesion molecule (EpCAM), or CD326, was one of the first cancer associated biomarkers to be discovered. In the last forty years, this biomarker has been investigated for use in personalized cancer therapy, with the first monoclonal antibody, edrecolomab, being trialled in humans more than thirty years ago. Since then, several other monoclonal antibodies have been raised to EpCAM and tested in clinical trials. However, while monoclonal antibody therapy has been investigated against EpCAM for almost 40 years as primary or adjuvant therapy, it has not shown as much promise as initially heralded. In this review, we look at the reasons why and consider alternative targeting options, such as aptamers, to turn this almost ubiquitously expressed epithelial cancer biomarker into a viable target for future personalized therapy.

Max-Bergmann award lecture:A RaPID way to discover bioactive nonstandard peptides assisted by the flexizyme and FIT systems

Although general review articles should cover various people's achievements related to the subject, this review is privileged to describe the technology developed by Suga (and colleagues) as a recipient of the Max-Bergmann Medal in 2016. The technology consists of 3 unique and essential tools, flexizymes, FIT, and RaPID systems. This review describes the history of the development of each tool and discusses the recent applications of the RaPID system to discover potent nonstandard peptides for therapeutic and diagnostic uses.