The blood-brain barrier (BBB) is a natural protective semipermeable membrane that shields the central nervous system (CNS) from harmful substances in the bloodstream. While this barrier is essential for protecting the brain, it also presents significant challenges for therapy in treating brain tumor such as glioblastoma multiforme (GBM). This limitation is particularly relevant for most chemical drugs and biopharmaceuticals. They struggle to penetrate the BBB, making efficient delivery to the brain highly sought after. Inadequate drug delivery to the brain can reduce therapeutic effectiveness and lead to increased side effects due to accumulation in other organs and tissues, especially after systemic administration. Overcoming the challenges related to drug delivery would open new treatment options for GBM and other CNS diseases. Nanoparticle-based approaches are highly promising, potentially offering a safer and less invasive alternative to current treatment options. This review provides a summary of the structure of the BBB and the main cell types that contribute to its function, with a specific focus on the barrier’s relevance in GBM. It also examines strategies for crossing the BBB, current treatment options, and prospects for GBM therapies. It emphasizes the significance of efficient delivery across the BBB and the potential of nanoparticles in advancing improved GBM treatments. Additionally, it introduces versatile nanoparticle-based drug delivery systems, including organic, inorganic, and biologics-derived approaches.

In this chapter, we present the current situation in the area of cancer vaccines. While cancer vaccines evidently show great potential and hope for many cancer patients worldwide, today only few cancer vaccines were approved by the US Food and Drug Administration (FDA). They are divided into preventive and therapeutic cancer vaccines. The approved cancer vaccines are discussed in more details in the text. Beside approved vaccines, a huge number of vaccines are currently in clinical trials, and representative, well-documented trials are shown in the text and appear in Table 1. Finally, some auxiliary adjuvants and approaches to intensify cancer vaccine efficiency are also shown.

Following up on the first PBPK model for an oral vaccine built for alpha-tocopherol, three peptides are explored in this article to verify if they could support an oral vaccine formulation as adjuvants using the same PBPK modeling approach. A literature review was conducted to verify what peptides have been used as adjuvants in the last decades, and it was noticed that MDP derivatives have been used, with one of them even being commercially approved and used as an adjuvant when administered intravenously in oncology. The aim of this study was to build optimized models for three MDP peptides (MDP itself, MTP-PE, and murabutide) and to verify if they could act as adjuvants for an oral vaccine. Challenges faced by peptides in an oral delivery system are taken into consideration, and improvements to the formulations to achieve better results are described in a step-wise approach to reach the most-optimized model. Once simulations are performed, results are compared to determine what would be the best peptide to support as an oral adjuvant. According to our results, MTP-PE, the currently approved and commercialized peptide, could have potential to be incorporated into an oral formulation. It would be interesting to proceed with further in vivo experiments to determine the behavior of this peptide when administered orally with a proper formulation to overcome the challenges of oral delivery systems.

A summary of the results obtained in the collaboration between the laboratory of Prof. Viktor Mutt at Karolinska Institutet and our laboratory at Stockholm University, headed by Prof. Tamas Bartfai, is given. It is demonstrated that the contribution of Viktor Mutt to the discovery and study of bioactive peptides has led to several further developments, which extend far beyond the original goals of his study and allow us to discuss their importance today and in the future. This perspective has made the contribution of Viktor Mutt to bioactive peptide research excellent and extraordinary.

Currently, one of the most significant and rapidly growing unmet medical challenges is the treatment of neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). This challenge encompasses the imperative development of efficacious therapeutic agents and overcoming the intricacies of the blood-brain barrier for successful drug delivery. Here we focus on the delivery aspect with particular emphasis on cell-penetrating peptides (CPPs), widely used in basic and translational research as they enhance drug delivery to challenging targets such as tissue and cellular compartments and thus increase therapeutic efficacy. The combination of CPPs with nanomaterials such as nanoparticles (NPs) improves the performance, accuracy, and stability of drug delivery and enables higher drug loads. Our review presents and discusses research that utilizes CPPs, either alone or in conjugation with NPs, to mitigate the pathogenic effects of neurodegenerative diseases with particular reference to AD and PD.

Cell penetrating peptides (CPPs) have emerged as promising materials for the fabrication of synthetic nanovectors endowed with potential for improving the future landscape of gene therapy. A group of well-studied CPPs includes the transportan family, comprised of chimeric molecules combining segments derived from the antimicrobial wasp-venom mastoporan and the neuropeptide galanin. The success of these CPPs is supported by their effective use as the base for commercial peptide-based transfection reagents. Herein, we present a comprehensive study of the structure of peptiplexes formed between DNA fragments and transportan 10, a prototype example of amphipathic CPP. We conducted a thorough analysis of the self-aggregation of TP10, its secondary structure, and revealed details of its interaction with DNA. We employed atomic force microscopy-based nanospectroscopy to obtain single-particle data that revealed details of the conformations assumed by the peptide and DNA in the inner structure of nanoassemblies with different morphologies. Our structural results showed that TP10 exhibits self-aggregation capabilities and a strong propensity to assume α-helical conformations upon association with DNA strands. This behavior contrasts with that of prototype CPPs such as TAT-HIV and penetratin, potentially explaining why peptiplexes based on transportans demonstrate increased uptake compared to their cationic counterparts. Also, single-particle spectroscopy indicated that the secondary structure in peptiplexes is strongly dependent on the size and shape, reinforcing that controlled self-assembly is crucial for optimizing CPP-based nanotherapeutics. The peptiplexes were also evaluated for cell uptake efficiency and kinetics, revealing a logistic time–response increase in permeability, suggestive of cooperativeness. We anticipate that the findings presented here might contribute to refining structure–activity relationships of peptiplexes based on amphipathic CPPs, assisting the optimization of products based on this relevant class of CPPs with potential applications in therapeutic delivery systems.

The low bioavailability and high toxicity of plasmid DNA (pDNA)-based therapeutics pose challenges for their in vivo application. Extracellular vesicles (EVs) have great potential to overcome these limitations, as they are biocompatible native cargo carriers. Various methods for loading pDNA into EVs, including electroporation, sonication, and co-incubation, have been previously investigated, but their success has been questionable. In this study, we report a unique method for loading EVs with pDNA through transient transfection using cell-penetrating peptides (CPPs). With this method, we found a 104-fold increase in the expression levels of the luciferase reporter protein in recipient cells compared to the untreated cells. These data point to the high transfection efficacy and bioavailability of the delivered encapsulated nucleic acid. Furthermore, the in vivo experimental data indicate that the use of pDNA-loaded EVs as native delivery vehicles reduces the toxic effects associated with traditional nucleic acid (NA) delivery and treatment.

Alzheimer’s disease (AD) is the most common neurodegenerative disease (ND) and the leading cause of dementia. It is characterized by non-linear, genetic-driven pathophysiological dynamics with high heterogeneity in the biological alterations and the causes of the disease. One of the hallmarks of the AD is the progression of plaques of aggregated amyloid-β (Aβ) or neurofibrillary tangles of Tau. Currently there is no efficient treatment for the AD. Nevertheless, several breakthroughs in revealing the mechanisms behind progression of the AD have led to the discovery of possible therapeutic targets. Some of these include the reduction in inflammation in the brain, and, although highly debated, limiting of the aggregation of the Aβ. In this work we show that similarly to the Neural cell adhesion molecule 1 (NCAM1) signal sequence, other Aβ interacting protein sequences, especially derived from Transthyretin, can be used successfully to reduce or target the amyloid aggregation/aggregates in vitro. The modified signal peptides with cell-penetrating properties reduce the Aβ aggregation and are predicted to have anti-inflammatory properties. Furthermore, we show that by expressing the Aβ-EGFP fusion protein, we can efficiently assess the potential for reduction in aggregation, and the CPP properties of peptides in mammalian cells.

In this book, a summary and update of the most important areas of cell-penetrating peptides (CPP) research are presented, while raising relevant questions for further development. The CPP sequences are presented and discussed throughout the book. The methods for testing CPP mechanisms are discussed in detail. Various approaches for the testing of endocytotic pathways of CPP uptake are also described. Different CPP uptake experiments are compared since it is becoming clear that it is often best to apply several methods in a complementary manner in order to most comprehensively evaluate CPP uptake mechanisms due to the complexity of these processes. A brief summary of functionality issues of CPPs, both in vitro and in vivo, is discussed. Therapeutic potential of CPPs and commercial developments are discussed. The present, second edition of this book is the updated and expanded version of the first edition, published in 2019. The development of the field of cell-penetrating peptides in these five years has been obvious and exciting. This second edition of the book has been partly reorganized and comprehensively expanded with the exciting research in 2019-2023. Around 2500 novel scientific articles have become available, most of them are reviewed in the second edition. Additional rapidly growing areas of high impact presented in this second edition are therapeutic developments (Chapter 16) and delivery of oligonucleotides and proteins/peptides (Chapters 5 and 6) including novel reports on genome editing with CPP assistance. Also, several additional examples are available now on clinical trials using CPPs (Chapter 15). The book is written for researchers and students in the field.