Cellular Internalization and Inhibition Capacity of New Anti-Glioma Peptide Conjugates: Physicochemical Characterization and Evaluation on Various Monolayer- and 3D-Spheroid-Based in Vitro Platforms

Self-assembled IR dye/mitoxantrone loaded Porphysomes nanosystem for enhanced combinatorial chemo-photothermal cancer therapy

Chemo-photothermal therapy (PTT) is an emerging non-invasive cancer treatment modality. Light-responsive porphysomes (DPP IR Mtx @Lipo NPs) nanosystems ablate breast cancer cells upon oxidative stress and hyperthermia. The unique self-assembled porphysomes were formed spherical shape in the size range of 150 ± 30 nm formed by the co-assembly of porphyrins along with IR 775 and chemotherapeutic drug, Mitoxantrone (Mtx), forming a camouflaged nanosystem (DPP IR Mtx @Lipo NPs, porphysomes). The advent of the prepared porphysomes aids in proper tuning of NIR absorbance improving singlet oxygen species generation among other anticancer drugs. The eminent release of DPP and adjuvant chemo-drug, Mitoxantrone from the self-assembled porphysomes is triggered by IR 775, a NIR photosensitizer upon laser irradiation. These multifunctional DPP IR Mtx @Lipo NPs have an efficient photothermal conversion efficiency of 65.8% as well as bioimaging properties. In-vitro studies in 2D and 3D models showed a significant cell death of 4T1 cells via the apoptotic pathway when irradiated with NIR laser, causing minimal damage to nearby healthy cells. DPP IR Mtx @Lipo NPs exhibited commingled PDT/PTT interdependent via NIR laser exposure, leading to mitochondrial disruption. Interestingly, the transient transfection using p53-GFP in cancer cells followed by DPP IR Mtx @Lipo NPs treatment causes rapid cell death. The activation of p53-dependent apoptosis pathways was vividly expressed, evidenced by the upregulation of Bax and increased pattern of Caspase-3 cleavage. This effect was pronounced upon transfection and induction with DPP IR Mtx @Lipo NPs, particularly in comparison to non-transfected malignant breast cancer 4T1 cells.

Tumor-Homing Peptides as Crucial Component of Magnetic-Based Delivery Systems: Recent Developments and Pharmacoeconomical Perspective

According to data from the World Health Organization (WHO), cancer is considered to be one of the leading causes of death worldwide, and new therapeutic approaches, especially improved novel cancer treatment regimens, are in high demand. Considering that many chemotherapeutic drugs tend to have poor pharmacokinetic profiles, including rapid clearance and limited on-site accumulation, a combined approach with tumor-homing peptide (THP)-functionalized magnetic nanoparticles could lead to remarkable improvements. This is confirmed by an increasing number of papers in this field, showing that the on-target peptide functionalization of magnetic nanoparticles improves their penetration properties and ensures tumor-specific binding, which results in an increased clinical response. This review aims to highlight the potential applications of THPs in combination with magnetic carriers across various fields, including a pharmacoeconomic perspective.

Peptide-based non-viral gene delivery: A comprehensive review of the advances and challenges

Gene therapy is the most effective treatment option for diseases, but its effectiveness is affected by the choice and design of gene carriers. The genes themselves have to pass through multiple barriers in order to enter the cell and therefore require additional vectors to carry them inside the cell. In gene therapy, peptides have unique properties and potential as gene carriers, which can effectively deliver genes into specific cells or tissues, protect genes from degradation, improve gene transfection efficiency, and enhance gene targeting and biological responsiveness. This paper reviews the research progress of peptides and their derivatives in the field of gene delivery recently, describes the obstacles encountered by foreign materials to enter the interior of the cell, and introduces the following classes of functional peptides that can carry materials into the interior of the cell, and assist in transmembrane translocation of carriers, thus breaking through endosomal traps to enable successful entry of genetic materials into the nucleus of the cell. The paper also discusses the combined application of peptide vectors with other vectors to enhance its transfection ability, explores current challenges encountered by peptide vectors, and looks forward to future developments in the field.

New Salicylanilide Derivatives and Their Peptide Conjugates as Anticancer Compounds: Synthesis, Characterization, and In Vitro Effect on Glioblastoma

Pharmacologically active salicylanilides (2-hydroxy-N-phenylbenzamides) have been a promising area of interest in medicinal chemistry-related research for quite some time. This group of compounds has shown a wide spectrum of biological activities, including but not limited to anticancer effects. In this study, substituted salicylanilides were chosen to evaluate the in vitro activity on U87 human glioblastoma (GBM) cells. The parent salicylanilide, salicylanilide 5-chloropyrazinoates, a 4-aminosalicylic acid derivative, and the new salicylanilide 4-formylbenzoates were chemically and in vitro characterized. To enhance the internalization of the compounds, they were conjugated to delivery peptides with the formation of oxime bonds. Oligotuftsins ([TKPKG]n, n = 1-4), the ligands of neuropilin receptors, were used as GBM-targeting carrier peptides. The in vitro cellular uptake, intracellular localization, and penetration ability on tissue-mimicking models of the fluorescent peptide derivatives were determined. The compounds and their peptide conjugates significantly decreased the viability of U87 glioma cells. Salicylanilide compound-induced GBM cell death was associated with activation of autophagy, as characterized by immunodetection of autophagy-related processing of light chain 3 protein.

Characterisation of the cell and molecular biological effect of peptide-based daunorubicin conjugates developed for targeting pancreatic adenocarcinoma (PANC-1) cell line

Pancreatic adenocarcinoma is one of the tumours with the worst prognosis, with a 5-year survival rate of 5-10%. Our aim was to find and optimise peptide-based drug conjugates with daunorubicin (Dau) as the cytotoxic antitumour agent. When conjugated with targeting peptides, the side effect profile and pharmacokinetics of Dau can be improved. The targeting peptide sequences (e.g. GSSEQLYL) we studied were originally selected by phage display. By Ala-scan technique, we identified that position 6 in the parental sequence (Dau=Aoa-LRRY-GSSEQLYL-NH2, ConjA) could be modified without the loss of antitumour activity (Dau=Aoa-LRRY-GSSEQAYL-NH2, Conj03: 14. 9% viability). Our results showed that the incorporation of p-chloro-phenylalanine (Dau=Aoa-LRRY-GSSEQF(pCl)YL-NH2, Conj16) further increased the antitumour potency (10-5 M: 9.7% viability) on pancreatic adenocarcinoma cells (PANC-1). We found that conjugates containing modified GSSEQLYL sequences could be internalised to PANC-1 cells and induce cellular senescence in the short term and subsequent apoptotic cell death. Furthermore, the cardiotoxic effect of Dau was markedly reduced in the form of peptide conjugates. In conclusion, Conj16 had the most effective antitumor activity on PANC-1 cells, which makes this conjugate promising for developing new targeted therapies without cardiotoxic effects.

Oxime-Linked Peptide-Daunomycin Conjugates as Good Tools for Selection of Suitable Homing Devices in Targeted Tumor Therapy: An Overview

Chemotherapy is still one of the main therapeutic approaches in cancer therapy. Nevertheless, its poor selectivity causes severe toxic side effects that, together with the development of drug resistance in tumor cells, results in a limitation for its application. Tumor-targeted drug delivery is a possible choice to overcome these drawbacks. As well as monoclonal antibodies, peptides are promising targeting moieties for drug delivery. However, the development of peptide-drug conjugates (PDCs) is still a big challenge. The main reason is that the conjugates have to be stable in circulation, but the drug or its active metabolite should be released efficiently in the tumor cells. For this purpose, suitable linker systems are needed that connect the drug molecule with the homing peptide. The applied linker systems are commonly categorized as cleavable and non-cleavable linkers. Both the groups possess advantages and disadvantages that are summarized briefly in this manuscript. Moreover, in this review paper, we highlight the benefit of oxime-linked anthracycline-peptide conjugates in the development of PDCs. For instance, straightforward synthesis as well as a conjugation reaction proceed in excellent yields, and the autofluorescence of anthracyclines provides a good tool to select the appropriate homing peptides. Furthermore, we demonstrate that these conjugates can be used properly in in vivo studies. The results indicate that the oxime-linked PDCs are potential candidates for targeted tumor therapy.

Targeting the Melanocortin 1 Receptor in Melanoma: Biological Activity of α-MSH-Peptide Conjugates

Malignant melanoma is one of the most aggressive and resistant tumor types, with high metastatic properties. Because of the lack of suitable chemotherapeutic agents for treatment, the 5-year survival rate of melanoma patients with regional and distant metastases is lower than 10%. Targeted tumor therapy that provides several promising results might be a good option for the treatment of malignant melanomas. Our goal was to develop novel melanoma-specific peptide-drug conjugates for targeted tumor therapy. Melanocortin-1-receptor (MC1R) is a cell surface receptor responsible for melanogenesis and it is overexpressed on the surface of melanoma cells, providing a good target. Its native ligand, α-MSH (α-melanocyte-stimulating hormone) peptide, or its derivatives, might be potential homing devices for this purpose. Therefore, we prepared three α-MSH derivative-daunomycin (Dau) conjugates and their in vitro and in vivo antitumor activities were compared. Dau has an autofluorescence property; therefore, it is suitable for preparing conjugates for in vitro (e.g., cellular uptake) and in vivo experiments. Dau was attached to the peptides via a non-cleavable oxime linkage that was applied efficiently in our previous experiments, resulting in conjugates with high tumor growth inhibition activity. The results indicated that the most promising conjugate was the compound in which Dau was connected to the side chain of Lys (Ac-SYSNleEHFRWGK(Dau=Aoa)PV-NH2). The highest cellular uptake by melanoma cells was demonstrated using the compound, with the highest tumor growth inhibition detected both on mouse (38.6% on B16) and human uveal melanoma (55% on OMC-1) cells. The effect of the compound was more pronounced than that of the free drug.

Quantitative Analysis of a Pilot Transwell Barrier Model with Automated Sampling and Mathematical Modeling

In the preclinical phase of drug development, it is necessary to determine how the active compound can pass through the biological barriers surrounding the target tissue. In vitro barrier models provide a reliable, low-cost, high-throughput solution for screening substances early in the drug candidate development process, thus reducing more complex and costly animal studies. In this pilot study, the transport properties of TB501, an antimycobacterial drug candidate, were characterized using an in vitro barrier model of VERO E6 kidney cells. The compound was delivered into the apical chamber of the transwell insert, and its concentration passing through the barrier layer was measured through the automated sampling of the basolateral compartment, where media were replaced every 30 min for 6 h, and the collected samples were stored for further spectroscopic analysis. The kinetics of TB501 concentration obtained from VERO E6 transwell cultures and transwell membranes saturated with serum proteins reveal the extent to which the cell layer functions as a diffusion barrier. The large number of samples collected allows us to fit a detailed mathematical model of the passive diffusive currents to the measured concentration profiles. This approach enables the determination of the diffusive permeability, the diffusivity of the compound in the cell layer, the affinity of the compound binding to the cell membrane as well as the rate by which the cells metabolize the compound. The proposed approach goes beyond the determination of the permeability coefficient and offers a more detailed pharmacokinetic characterization of the transwell barrier model. We expect the presented method to be fruitful in evaluating other compounds with different chemical features on simple in vitro barrier models. The proposed mathematical model can also be extended to include various forms of active transport.

Evaluation of the Chemical Stability, Membrane Permeability and Antiproliferative Activity of Cyclic Diarylheptanoids from European Hornbeam (Carpinus betulus L.)

Four cyclic diarylheptanoids-carpinontriols A (1) and B (2), giffonin X (3) and 3,12,17-trihydroxytricyclo [12.3.1.12,6]nonadeca-1(18),2(19),3,5,14,16-hexaene-8,11-dione (4)-were isolated from Carpinus betulus (Betulaceae). Chemical stability of the isolated diarylheptanoids was evaluated as a function of storage temperature (-15, 5, 22 °C) and time (12 and 23 weeks). The effect of the solvent and the pH (1.2, 6.8, 7.4) on the stability of these diarylheptanoids was also investigated. Compounds 2 and 4 showed good stability both in aqueous and methanolic solutions at all investigated temperatures. Only 2 was stable at all three studied biorelevant pH values. Degradation products of 1 and 3 were formed by the elimination of a water molecule from the parent compounds, as confirmed by ultrahigh-performance liquid chromatography-high-resolution tandem mass spectrometry (UHPLC-HR-MS). The permeability of the compounds across biological membranes was evaluated by the parallel artificial membrane permeability assay (PAMPA). Compound 3 possesses a logPe value of -5.92 ± 0.04 in the blood-brain barrier-specific PAMPA-BBB study, indicating that it may be able to cross the blood-brain barrier via passive diffusion. The in vitro antiproliferative activity of the compounds was investigated against five human cancer cell lines, confirming that 1 inhibits cell proliferation in A2058 human metastatic melanoma cells.

Biomaterial-based in vitro 3D modeling of glioblastoma multiforme

Adult-onset brain cancers, such as glioblastomas, are particularly lethal. People with glioblastoma multiforme (GBM) do not anticipate living for more than 15 months if there is no cure. The results of conventional treatments over the past 20 years have been underwhelming. Tumor aggressiveness, location, and lack of systemic therapies that can penetrate the blood-brain barrier are all contributing factors. For GBM treatments that appear promising in preclinical studies, there is a considerable rate of failure in phase I and II clinical trials. Unfortunately, access becomes impossible due to the intricate architecture of tumors. In vitro, bioengineered cancer models are currently being used by researchers to study disease development, test novel therapies, and advance specialized medications. Many different techniques for creating in vitro systems have arisen over the past few decades due to developments in cellular and tissue engineering. Later-stage research may yield better results if in vitro models that resemble brain tissue and the blood-brain barrier are used. With the use of 3D preclinical models made available by biomaterials, researchers have discovered that it is possible to overcome these limitations. Innovative in vitro models for the treatment of GBM are possible using biomaterials and novel drug carriers. This review discusses the benefits and drawbacks of 3D in vitro glioblastoma modeling systems.

Interactions of Nanoscale Self-Assembled Peptide-Based Assemblies with Glioblastoma Cell Models and Spheroids

Peptide nanoassemblies have garnered remarkable importance in the development of novel nanoscale biomaterials for drug delivery into tumor cells. Taking advantage of receptor mediated recognition of two known peptides, angiopep-2 (TFFYGGSRGKRNNFKTEEY) and A-COOP-K (ACGLSGLC10 VAK) that bind to the over-expressed receptors low density lipoprotein (LRP-1) and fatty acid binding protein (FABP3) respectively, we have developed new peptide conjugates by combining the anti-inflammatory, antitumor compound azelaic acid with angiopep-2, which efficiently self-assembled into nanofibers. Those nanofibers were then functionalized with the A-COOP-K sequence and formed supramolecular hierarchical structures that were found to entrap the chemotherapeutic drug doxorubicin efficaciously. Furthermore, the nanoassemblies were found to release the drug in a dose-dependent manner and showed a stepwise increase over a period of 2 weeks under acidic conditions. Two cell lines (U-87-MG and U-138-MG) were utilized as models for glioblastoma cells grown in the presence of serum and under serum-free conditions to mimic the growth conditions of natural tumors. The drug entrapped assemblies were found to inhibit the cell proliferation of both U-87 and U-138MG glioblastoma cells. Three dimensional spheroids of different sizes were grown to mimic the tumors and evaluate the efficacy of drug release and internalization. Our results indicated that the nanoassemblies were found to have higher internalization of DOX and were well-spread throughout the spheroids grown, particularly under serum-free conditions. The nanoassemblies also displayed blood-brain barrier penetration when tested with a multicellular in vitro model. Such self-assembled nanostructures with targeting ability may provide a suitable platform for the development of new peptide-based biomaterials that can provide more insights about the mechanistic approach for drug delivery for not only 2D cell cultures but also 3D tumoroids that mimic the tumor microenvironments.

Peptides as Pharmacological Carriers to the Brain: Promises, Shortcomings and Challenges

Central nervous system (CNS) diseases are among the most difficult to treat, mainly because the vast majority of the drugs fail to cross the blood-brain barrier (BBB) or to reach the brain at concentrations adequate to exert a pharmacological activity. The obstacle posed by the BBB has led to the in-depth study of strategies allowing the brain delivery of CNS-active drugs. Among the most promising strategies is the use of peptides addressed to the BBB. Peptides are versatile molecules that can be used to decorate nanoparticles or can be conjugated to drugs, with either a stable link or as pro-drugs. They have been used to deliver to the brain both small molecules and proteins, with applications in diverse therapeutic areas such as brain cancers, neurodegenerative diseases and imaging. Peptides can be generally classified as receptor-targeted, recognizing membrane proteins expressed by the BBB microvessels (e.g., Angiopep2, CDX, and iRGD), "cell-penetrating peptides" (CPPs; e.g. TAT_47-57, SynB1/3, and Penetratin), undergoing transcytosis through unspecific mechanisms, or those exploiting a mixed approach. The advantages of peptides have been extensively pointed out, but so far few studies have focused on the potential negative aspects. Indeed, despite having a generally good safety profile, some peptide conjugates may display toxicological characteristics distinct from those of the peptide itself, causing for instance antigenicity, cardiovascular alterations or hemolysis. Other shortcomings are the often brief lifetime in vivo, caused by the presence of peptidases, the vulnerability to endosomal/lysosomal degradation, and the frequently still insufficient attainable increase of brain drug levels, which remain below the therapeutically useful concentrations. The aim of this review is to analyze not only the successful and promising aspects of the use of peptides in brain targeting but also the problems posed by this strategy for drug delivery.

Obstacles to Glioblastoma Treatment Two Decades after Temozolomide

Simple Summary

Glioblastomas are the most common and aggressive brain tumors in adults, with a median survival of 15 months. Treatment is surgical removal, followed by chemotherapy and/or radiotherapy. Current chemotherapeutics do not kill all the tumor cells and some cells survive, leading to the appearance of a new tumor resistant to the treatment. These treatment-resistant cells are called tumor stem cells. In addition, glioblastoma cells have a high capacity for migration, forming new tumors in areas distant from the original tumor. Studies are now focused on understanding the molecular mechanisms of chemoresistance and controlling drug entry into the brain to improve drug performance. Another promising therapeutic approach is the use of viruses that specifically destroy glioblastoma cells, preserving the neural tissue around the tumor. In this review, we summarize the main biological features of glioblastoma and the therapeutic targets that are currently under study for new clinical trials.

Abstract

Glioblastomas are considered the most common and aggressive primary brain tumor in adults, with an average of 15 months’ survival rate. The treatment is surgery resection, followed by chemotherapy with temozolomide, and/or radiotherapy. Glioblastoma must have wild-type IDH gene and some characteristics, such as TERT promoter mutation, EGFR gene amplification, microvascular proliferation, among others. Glioblastomas have great heterogeneity at cellular and molecular levels, presenting distinct phenotypes and diversified molecular signatures in each tumor mass, making it difficult to define a specific therapeutic target. It is believed that the main responsibility for the emerge of these distinct patterns lies in subcellular populations of tumor stem cells, capable of tumor initiation and asymmetric division. Studies are now focused on understanding molecular mechanisms of chemoresistance, the tumor microenvironment, due to hypoxic and necrotic areas, cytoskeleton and extracellular matrix remodeling, and in controlling blood brain barrier permeabilization to improve drug delivery. Another promising therapeutic approach is the use of oncolytic viruses that are able to destroy specifically glioblastoma cells, preserving the neural tissue around the tumor. In this review, we summarize the main biological characteristics of glioblastoma and the cutting-edge therapeutic targets that are currently under study for promising new clinical trials.

Redesigning of Cell-Penetrating Peptides to Improve Their Efficacy as a Drug Delivery System

Cell-penetrating peptides (CPP) are promising tools for the transport of a broad range of compounds into cells. Since the discovery of the first members of this peptide family, many other peptides have been identified; nowadays, dozens of these peptides are known. These peptides sometimes have very different chemical–physical properties, but they have similar drawbacks; e.g., non-specific internalization, fast elimination from the body, intracellular/vesicular entrapment. Although our knowledge regarding the mechanism and structure–activity relationship of internalization is growing, the prediction and design of the cell-penetrating properties are challenging. In this review, we focus on the different modifications of well-known CPPs to avoid their drawbacks, as well as how these modifications may increase their internalization and/or change the mechanism of penetration.

Novel Assay Platform to Evaluate Intracellular Killing of Mycobacterium tuberculosis: In Vitro and In Vivo Validation

One of the main hallmarks of tuberculosis (TB) is the ability of the causative agent to transform into a stage of dormancy and the capability of long persistence in the host phagocytes. It is believed that approximately one-third of the population of the world is latently infected with Mycobacterium tuberculosis (Mtb), and 5%-10% of these individuals can develop clinical manifestations of active TB even decades after the initial infection. In this latent, intracellular form, the bacillus is shielded by an extremely robust cell wall and becomes phenotypically resistant to most antituberculars. Therefore, there is a clear rationale to develop novel compounds or carrier-conjugated constructs of existing drugs that are effective against the intracellular form of the bacilli. In this paper, we describe an experimental road map to define optimal candidates against intracellular Mtb and potential compounds effective in the therapy of latent TB. To validate our approach, isoniazid, a first-line antitubercular drug was employed, which is active against extracellular Mtb in the submicromolar range, but ineffective against the intracellular form of the bacteria. Cationic peptide conjugates of isoniazid were synthesized and employed to study the host-directed drug delivery. To measure the intracellular killing activity of the compounds, Mtb-infected MonoMac-6 human monocytic cells were utilized. We have assessed the antitubercular activity, cytotoxicity, membrane interactions in combination with internalization efficacy, localization, and penetration ability on interface and tissue-mimicking 3D models. Based on these in vitro data, most active compounds were further evaluated in vivo in a murine model of TB. Intraperitoneal infectious route was employed to induce a course of slowly progressive and systemic disease. The well-being of the animals, monitored by the body weight, allows a prolonged experimental setup and provides a great opportunity to test the long-term activity of the drug candidates. Having shown the great potency of this simple and suitable experimental design for antimicrobial research, the proposed novel assay platform could be used in the future to develop further innovative and highly effective antituberculars.

Dithiolane quartets: thiol-mediated uptake enables cytosolic delivery in deep tissue

The cytosolic delivery of various substrates in 3D multicellular spheroids by thiol-mediated uptake is reported. This is important because most orthodox systems, including polycationic cell-penetrating peptides, fail to deliver efficiently into deep tissue. The grand principles of supramolecular chemistry, that is the pH dependence of dynamic covalent disulfide exchange with known thiols on the transferrin receptor, are proposed to account for transcytosis into deep tissue, while the known but elusive exchange cascades along the same or other partners assure cytosolic delivery in kinetic competition. For quantitative detection in the cytosol, the 2D chloroalkane penetration assay (CAPA) is translated to 3D deep tissue. The targeted delivery of quantum dots, otherwise already troublesome in 2D culture, and the controlled release of mechanophores are realized to exemplify the power of thiol-mediated uptake into spheroids. As transporters, dithiolane quartets on streptavidin templates are introduced as modular motifs. Built from two amino acids only, the varied stereochemistry and peptide sequence are shown to cover maximal functional space with minimal structural change, i.e., constitutional isomers. Reviving a classic in peptide chemistry, this templated assembly of β quartets promises to expand streptavidin biotechnology in new directions, while the discovery of general cytosolic delivery in deep tissue as an intrinsic advantage further enhances the significance and usefulness of thiol-mediated uptake.