Recent advances in peptides for enhancing transdermal macromolecular drug delivery

Application of biomacromolecule-based passive penetration enhancement technique in superficial tumor therapy: A review

Transdermal drug delivery (TDD) has shown great promise in superficial tumor therapy due to its noninvasive and avoidance of the first-pass effect. Especially, passive penetration enhancement technique (PPET) provides the technical basis for TDD by temporarily altering the skin surface structure without requiring external energy. Biomacromolecules and their derived nanocarriers offer a wide range of options for PPET development, with outstanding biocompatibility and biodegradability. Furthermore, the abundant functional groups on biomacromolecule surfaces can be modified to yield functional materials capable of targeting specific sites and responding to stimuli. This enables precise drug delivery to the tumor site and controlled drug release, with the potential to replace traditional drug delivery methods and make PPET-related personalized medicine a reality. This review focuses on the mechanism of biomacromolecules and nanocarriers with skin, and the impact of nanocarriers' surface properties of nanocarriers on PPET efficiency. The applications of biomacromolecule-based PPET in superficial tumor therapy are also summarized. In addition, the advantages and limitations are discussed, and their future trends are projected based on the existing work of biomacromolecule-based PPET.

Inhibition of nicotinic acetylcholine receptors by oligoarginine peptides and polyamine-related compounds

Oligoarginine peptides, known mostly for their cell-penetrating properties, are also inhibitors of the nicotinic acetylcholine receptors (nAChRs). Since octa-arginine (R8) inhibits α9α10 nAChR and suppresses neuropathic pain, we checked if other polycationic compounds containing amino and/or guanidino groups could be effective and tested the activity of the disulfide-fixed "cyclo"R8, a series of biogenic polyamines (putrescine, spermidine, and spermine), C-methylated spermine analogs, agmatine and its analogs, as well as acylpolyamine argiotoxin-636 from spider venom. Their inhibitory potency on muscle-type, α7 and α9α10 nAChRs was determined using radioligand analysis, electrophysiology, and calcium imaging. "Cyclo"R8 showed similar activity to that of R8 against α9α10 nAChR (IC50 ≈ 60 nM). Biogenic polyamines as well as agmatine and its analogs displayed low activity on muscle-type Torpedo californica, as well as α7 and α9α10 nAChRs, which increased with chain length, the most active being spermine and its C-methylated derivatives having IC50 of about 30 μM against muscle-type T. californica nAChR. Argiotoxin-636, which contains a polyamine backbone and terminal guanidino group, also weakly inhibited T. californica nAChR (IC50 ≈ 15 μM), but it revealed high potency against rat α9α10 nAChR (IC50 ≈ 200 nM). We conclude that oligoarginines and similar polycationic compounds effectively inhibiting α9α10 nAChR may serve as a basis for the development of analgesics to reduce neuropathic pain.

Research progress of physical transdermal enhancement techniques in tumor therapy

The advancement and popularity of transdermal drug delivery (TDD) based on the physical transdermal enhancement technique (PTET) has opened a new paradigm for local tumor treatment. The drug can be directly delivered to the tumor site through the skin, thus avoiding the toxic side effects caused by the first-pass effect and achieving high patient compliance. Further development of PTETs has provided many options for antitumor drugs and laid the foundation for future applications of wearable closed-loop targeting drug delivery systems. In this highlight, the different types of PTETs and related mechanisms, and applications of PTET-related tumor detection and therapy are highlighted. According to their type and characteristics, PTETs are categorized as follows: (1) iontophoresis, (2) electroporation, (3) ultrasound, (4) thermal ablation, and (5) microneedles. PTET-related applications in the local treatment of tumors are categorized as follows: (1) melanoma, (2) breast tumor, (3) squamous cell carcinoma, (4) cervical tumor, and (5) others. The challenges and future prospects of existing PTETs are also discussed. This highlight will provide guidance for the design of PTET-based wearable closed-loop targeting drug delivery systems and personalized therapy for tumors.

The Optimized Delivery of Triterpenes by Liposomal Nanoformulations: Overcoming the Challenges

The last decade has witnessed a sustained increase in the research development of modern-day chemo-therapeutics, especially for those used for high mortality rate pathologies. However, the therapeutic landscape is continuously changing as a result of the currently existing toxic side effects induced by a substantial range of drug classes. One growing research direction driven to mitigate such inconveniences has converged towards the study of natural molecules for their promising therapeutic potential. Triterpenes are one such class of compounds, intensively investigated for their therapeutic versatility. Although the pharmacological effects reported for several representatives of this class has come as a well-deserved encouragement, the pharmacokinetic profile of these molecules has turned out to be an unwelcomed disappointment. Nevertheless, the light at the end of the tunnel arrived with the development of nanotechnology, more specifically, the use of liposomes as drug delivery systems. Liposomes are easily synthesizable phospholipid-based vesicles, with highly tunable surfaces, that have the ability to transport both hydrophilic and lipophilic structures ensuring superior drug bioavailability at the action site as well as an increased selectivity. This study aims to report the results related to the development of different types of liposomes, used as targeted vectors for the delivery of various triterpenes of high pharmacological interest.

Transdermal Drug delivery: A step towards treatment of cancer

BACKGROUND

Transdermal drug delivery is an emerging and tempting system over oral and hypodermic drug delivery system. With the new developments in skin penetration techniques, anticancer drugs ranging from hydrophilic macromolecules to lipophilic drugs can be administered via transdermal route to treat cancer.

OBJECTIVE

In the present review, various approaches to enhance the transdermal delivery of drugs is discussed including the micro and nanotechnology based transdermal formulations like chemotherapy, gene therapy, immunotherapy, phototherapy, vaccines and medical devices. Limitations and advantages of various transdermal technologies is also elaborated.

METHOD

In this review, patent applications and recent literature of transdermal drug delivery systems employed to cure mainly cancer are covered.

RESULTS

Transdermal drug delivery systems have proved their potential to cure cancer. They increase the bioavailability of drug by site specific drug delivery and can reduce the side effects/toxicity associated with anticancer drugs.

CONCLUSION

The potential of transdermal drug delivery systems to carry the drug may unclutter novel ways for therapeutic intercessions in various tumors.

Molecular perspective of efficiency and safety problems of chemical enhancers: bottlenecks and recent advances

Chemical penetration enhancer (CPE) is a preferred approach to improve drug permeability through the skin, due to its unique advantages of simple use and high compatibility. However, CPEs efficiency and safety problems frequently arise, which greatly restrains the further application in transdermal drug delivery systems (TDDS). To get access to the root of problems, the efficiency and safety of CPEs are reviewed especially from molecular perspectives, which include (1) the possible factors of CPEs low efficiency; (2) the possible contribution of CPEs in the evolution of safety problems such as skin irritation and allergic reaction; (3) the interactive relationship between CPEs efficiency and safety, as well as the bottlenecks of achieving their balance. More importantly, based on these, recent advances are summarized in improving efficiency or safety of CPEs, which offers a guidance of rationally selecting CPEs in future research.

Current Status of Amino Acid-Based Permeation Enhancers in Transdermal Drug Delivery

Transdermal drug delivery (TDD) presents many advantages compared to other conventional routes of drug administration, yet its full potential has not been achieved. The administration of drugs through the skin is hampered by the natural barrier properties of the skin, which results in poor permeation of most drugs. Several methods have been developed to overcome this limitation. One of the approaches to increase drug permeation and thus to enable TDD for a wider range of drugs consists in the use of chemical permeation enhancers (CPEs), compounds that interact with skin to ultimately increase drug flux. Amino acid derivatives show great potential as permeation enhancers, as they exhibit high biodegradability and low toxicity. Here we present an overview of amino acid derivatives investigated so far as CPEs for the delivery of hydrophilic and lipophilic drugs across the skin, focusing on the structural features which promote their enhancement capacity.

Development and evaluation of a heparin gel for transdermal delivery via laser-generated micropores

Aim: Our study investigated the feasibility of transdermal delivery of heparin, an anticoagulant used against venous thromboembolism, as an alternative to intravenous administration. Materials & methods: Skin was pretreated using ablative laser (Precise Laser Epidermal System [P.L.E.A.S.E.^®] technology) for enhanced delivery of heparin. In vitro permeation studies using static Franz diffusion cells provided a comparison between delivery from 0.3% w/v heparin-loaded poloxamer gel and solution across untreated and laser-treated dermatomed porcine ear skin. Results: No passive delivery of heparin was observed. Laser-assisted delivery from solution (26.07 ± 1.82 μg/cm²) was higher (p < 0.05) than delivery from heparin gel (11.28 ± 5.32 μg/cm²). However, gel is likely to sustain the delivery over prolonged periods like a maintenance dose via continuous intravenous infusion. Conclusion: Thus, ablative laser pretreatment successfully delivered heparin, establishing the feasibility of delivering hydrophilic macromolecules using the transdermal route.

Effect of Chemical Permeation Enhancers on Skin Permeability: In silico screening using Molecular Dynamics simulations

Breaching of the skin barrier is essential for delivering active pharmaceutical ingredients (APIs) for pharmaceutical, dermatological and aesthetic applications. Chemical permeation enhancers (CPEs) are molecules that interact with the constituents of skin’s outermost and rate limiting layer stratum corneum (SC), and increase its permeability. Designing and testing of new CPEs is a resource intensive task, thus limiting the rate of discovery of new CPEs. In-silico screening of CPEs in a rigorous skin model could speed up the design of CPEs. In this study, we performed coarse grained (CG) molecule dynamics (MD) simulations of a multilayer skin lipid matrix in the presence of CPEs. The CPEs are chosen from different chemical functionalities including fatty acids, esters, and alcohols. A multi-layer in-silico skin model was developed. The CG parameters of permeation enhancers were also developed. Interactions of CPEs with SC lipids was studied in silico at three different CPE concentrations namely, 1% w/v, 3% w/v and 5% w/v. The partitioning and diffusion coefficients of CPEs in the SC lipids were found to be highly size- and structure-dependent and these dependencies are explained in terms of structural properties such as radial distribution function, area per lipid and order parameter. Finally, experimentally reported effects of CPEs on skin from the literature are compared with the simulation results. The trends obtained using simulations are in good agreement with the experimental measurements. The studies presented here validate the utility of in-silico models for designing, screening and testing of novel and effective CPEs.

Transdermal delivery of human growth hormone via laser-generated micropores

The epidermal skin barrier plays an important role in protecting underlying structures. It allows the passage of low molecular weight lipophilic molecules, but restricts the passage of hydrophilic molecules and macromolecules. The objective of this study was to investigate the feasibility of transdermal delivery of human growth hormone (hGH) through laser-microporated dermatomed porcine ear skin. The permeation of hGH was evaluated at different laser fluences and micropore densities. In vitro permeation studies were performed on vertical Franz diffusion cells using dermatomed porcine ear skin treated with ablative laser (2940 nm; P.L.E.A.S.E®, Pantec Biosolutions AG). The effect of different fluences (34.1, 45.4, and 68.1 J/cm²) at 10% pore density as well as different densities of micropores (5, 10, and 15%) at fluence of 34.1 J/cm², on the permeation of hGH was evaluated. After 48 h, 77.12 ± 10.77 μg/cm² hGH was delivered into the receptor with the application of fluence of 45.4 J/cm², which was significantly higher than that observed from 34.1 J/cm² group (53.13 ± 1.75 μg/cm², p < 0.05). Application of fluence of 68.1 J/cm² showed permeation of 90.94 ± 3.93 μg/cm² that was significantly higher than that from 34.1 J/cm² group (p < 0.05), but not as compared to the 45.4 J/cm² group (p > 0.05). With the increase in density of micropores from 5 to 15%, permeation of hGH increased significantly from 7.1 ± 2.63 μg/cm² to 95.89 ± 13.43 μg/cm² after 48 h (p < 0.05). Thus, overall, the variations in the fluence as well as micropore density of the laser were observed to influence hGH permeation, through laser-microporated dermatomed porcine skin.

Peptide-Induced Self-Assembly of Therapeutics into a Well-Defined Nanoshell with Tumor-Triggered Shape and Charge Switch

Peptide-tuned self-assembly of macromolecular agents (>500 Da) such as therapeutic peptides offers a strategy to improve the properties and biofunctions of degradable nanomaterials, but the tough requirement of macromolecular therapeutics delivery and a lack of understanding of peptide-based self-assembly design present high barriers for their applications. Herein, we developed a new strategy for nanoengineering macromolecular drugs by an elaborate peptide, termed PSP (VVVVVHHRGDC), capable of directly conjugating with cargo to be a PSP-cargo monomer as building block tending to self-assemble into a well-defined nanoshell with tumor-triggered shape and charge switch. As a proof of concept, conjugation PSP to a D-peptide activator of tumor suppressor p53 termed DPMI (1492.5 Da) generated hollow spheres ~80 nm in diameter named PSP-DPMI that disintegrated only in the acidic microenvironment of tumor tissues, followed by integrin-mediated cellular uptake of PSP-DPMI monomers. Importantly, PSP-based self-assembly successfully endowed the DPMI with long circulation time and high cancer-cell-specific intracellular accumulation. PSP-DPMI nanoshells potently inhibited tumor growth in vitro and in vivo by the p53 restoration, while maintaining a highly favorable in vivo safety profile. Out of conventional encapsulation and conjugation, our study showcases a clinically viable novel method to nanoengineer macromolecular agents such as peptide for anticancer therapy and provides a hazard-free alternative strategy for the theranostics delivery.

In-silico design of nanoparticles for transdermal drug delivery application

Nanoparticles are used in the medical field for various applications like cell imaging, drug delivery, gene and si-RNA delivery, to name a few. Designing nanoparticles for a given application, purely based on the trial and error experimentation, requires a lot of time and effort. In this study we show that computer simulations could help in designing nanoparticles for drug delivery thus reducing the time and cost associated with their design, development and deployment. The permeation of nanoparticles, having various surface chemistries and patterns, through the skin lipid bilayer was studied using constrained and unconstrained molecular dynamics simulations. Interestingly, the permeation mechanism of nanoparticles having the same surface chemistry but different patterns was found to be completely different. Nanoparticles (NPs) were screened based on the free energy of permeation through the skin lipid bilayer. The behavior of the screened NPs was further validated with unconstrained simulations using the skin lipid bilayer. Nanoparticles thus screened through both of the techniques were further used for the co-delivery of a model protein into the skin lipid bilayer. It was observed that the nanoparticles having a 2 : 1 homogeneous ratio of hydrophobic to hydrophilic regions were the most promising in transdermal delivery of proteins. The obtained results are in line with the results of recent permeation experiments on cell and plasma membrane. Our study could help in in-silico design of nanoparticles for delivery of actives through skin. These in-silico experiments thus could help speed up the development process by guiding formulation chemists.

Transdermal cellular membrane penetration of proteins with gold nanoparticles: a molecular dynamics study

Transdermal delivery, where the skin acts as the route for local or systemic distribution, presents a lot of advantages over conventional routes such as oral and intravenous and intramuscular injections. However, the delivery of large biomolecules like proteins through the skin is challenging due to their size and structural properties. A molecular level understanding of their transport across the skin barrier is desirable to design successful formulations. We have employed constrained and unconstrained coarse grained molecular dynamics simulation techniques to obtain the molecular mechanism of penetration of the horseradish peroxidase (HRP) protein into the skin, in the presence and absence of gold nanoparticles (AuNPs). Unconstrained simulations show that HRP, when considered individually, was not able to breach the skin barrier, while in the presence of AuNPs, it first binds to the AuNPs and then breaches the barrier. The constrained simulations revealed that there was a free energy barrier for HRP to permeate inside the skin lipid layer when taken alone, while in the presence of gold nanoparticles, no barrier was found. Our study opens up the field of computational modeling based design of nanoparticle carriers for a given protein's transdermal delivery.

Getting Drugs Across Biological Barriers

The delivery of drugs to a target site frequently involves crossing biological barriers. The degree and nature of the impediment to flux, as well as the potential approaches to overcoming it, depend on the tissue, the drug, and numerous other factors. Here an overview of approaches that have been taken to crossing biological barriers is presented, with special attention to transdermal drug delivery. Technology and knowledge pertaining to addressing these issues in a variety of organs could have a significant clinical impact.

Transdermal Vascular Endothelial Growth Factor Delivery with Surface Engineered Gold Nanoparticles

Skin injuries caused by burns or radiation remain a serious concern in terms of clinical therapy. Because of the damage to the epidermis or dermis, angiogenesis is needed to repair the skin. Vascular endothelial growth factor (VEGF) is one of the most effective factors for promoting angiogenesis and preventing injury progression, but the delivery of VEGF to lesion sites is limited by the skin barrier. Recently, gold nanoparticle (AuNP)-mediated drug delivery into or through the epidermis and dermis has attracted much attention. However, the efficacy of the AuNP-mediated transdermal drug delivery remains unknown. In this study, gold nanoparticles were conjugated with VEGF and generated a surface by carrying negative charges, showing an ideal transdermal delivery efficacy for VEGF in wound repair. Our findings may provide new avenues for the treatment of cutaneous injuries.

Patent highlights: February-March 2016

A snapshot of noteworthy recent developments in the patent literature of relevance to pharmaceutical and medical research and development.