Linker Hydrophilicity Modulates the Anticancer Activity of RGD-Cryptophycin Conjugates

Natural compounds-based nanomedicines for cancer treatment: Future directions and challenges

Several efforts have been extensively accomplished for the amelioration of the cancer treatments using different types of new drugs and less invasives therapies in comparison with the traditional therapeutic modalities, which are widely associated with numerous drawbacks, such as drug resistance, non-selectivity and high costs, restraining their clinical response. The application of natural compounds for the prevention and treatment of different cancer cells has attracted significant attention from the pharmaceuticals and scientific communities over the past decades. Although the use of nanotechnology in cancer therapy is still in the preliminary stages, the application of nanotherapeutics has demonstrated to decrease the various limitations related to the use of natural compounds, such as physical/chemical instability, poor aqueous solubility, and low bioavailability. Despite the nanotechnology has emerged as a promise to improve the bioavailability of the natural compounds, there are still limited clinical trials performed for their application with various challenges required for the pre-clinical and clinical trials, such as production at an industrial level, assurance of nanotherapeutics long-term stability, physiological barriers and safety and regulatory issues. This review highlights the most recent advances in the nanocarriers for natural compounds secreted from plants, bacteria, fungi, and marine organisms, as well as their role on cell signaling pathways for anticancer treatments. Additionally, the clinical status and the main challenges regarding the natural compounds loaded in nanocarriers for clinical applications were also discussed.

Peptide direct growth on poly(acrylic acid)/poly(vinyl alcohol) electrospun fibers coated with branched poly(ethylenimine): A solid-phase approach for scaffolds biofunctionalization

Due to their resemblance to the fibrillar structure of the extracellular matrix, electrospun nanofibrous meshes are currently used as porous and mechanically stable scaffolds for cell culture. In this study, we propose an innovative methodology for growing peptide sequences directly onto the surface of electrospun nanofibers. To achieve this, electrospun fibers were produced from a poly(acrylic acid)/poly(vinyl alcohol) blend that was thermally crosslinked and subjected to a covalent coating of branched poly(ethylenimine). The exposed amino functionalities on the fiber surface were then used for the direct solid-phase synthesis of the RGD peptide sequence. In contrast to established strategies, mainly involving the grafting of pre-synthesized peptides onto the polymer chains before electrospinning or onto the nanofibers surface, this method allows for the concurrent synthesis and anchoring of peptides to the substrate, with potential applications in combinatorial chemistry. The incorporation of this integrin-binding motive significantly enhanced the nanofibers' ability to capture human cervical carcinoma (HeLa) cells, selected as a proof of concept to assess the functionalities of the developed material.

Small molecule- and peptide-drug conjugates addressing integrins: A story of targeted cancer treatment

Targeted cancer treatment should avoid side effects and damage to healthy cells commonly encountered during traditional chemotherapy. By combining small molecule or peptidic ligands as homing devices with cytotoxic drugs connected by a cleavable or non-cleavable linker in peptide-drug conjugates (PDCs) or small molecule-drug conjugates (SMDCs), cancer cells and tumours can be selectively targeted. The development of highly affine, selective peptides and small molecules in recent years has allowed PDCs and SMDCs to increasingly compete with antibody-drug conjugates (ADCs). Integrins represent an excellent target for conjugates because they are overexpressed by most cancer cells and because of the broad knowledge about native binding partners as well as the multitude of small-molecule and peptidic ligands that have been developed over the last 30 years. In particular, integrin αVβ3 has been addressed using a variety of different PDCs and SMDCs over the last two decades, following various strategies. This review summarises and describes integrin-addressing PDCs and SMDCs while highlighting points of great interest.

Harmful and beneficial properties of cyanotoxins: Two sides of the same coin

Cyanotoxins are by definition "harmful agents" produced by cyanobacteria. Their toxicity has been extensively studied and reviewed over the years. Cyanotoxins have been commonly classified, based on their poisonous effects on mammals, into three main classes, neurotoxins, hepatotoxins and dermatotoxins, and, considering their chemical features, mainly identified as peptides, alkaloids and lipopolysaccharides. Here we propose a broader subdivision of cyanotoxins into eight distinct classes, taking into account their molecular structures, biosynthesis and modes of action: alkaloids, non-ribosomal peptides, polyketides, non-protein amino acids, indole alkaloids, organophosphates, lipopeptides and lipoglycans. For each class, the structures and primary mechanisms of toxicity of the main representative cyanotoxins are reported. Despite their powerful biological activities, only recently scientists have considered the biotechnological potential of cyanotoxins, and their applications both in medical and in industrial settings, even if only a few of these have reached the biotech market. In this perspective, we discuss the potential uses of cyanotoxins as anticancer, antimicrobial, and biocidal agents, as common applications for cytotoxic compounds. Furthermore, taking into account their mechanisms of action, we describe peculiar potential bioactivities for several cyanotoxin classes, such as local anaesthetics, antithrombotics, neuroplasticity promoters, immunomodulating and antifouling agents. In this review, we aim to stimulate research on the potential beneficial roles of cyanotoxins, which require interdisciplinary cooperation to facilitate the discovery of innovative biotechnologies.

Recent Advances in Cyanotoxin Synthesis and Applications: A Comprehensive Review

Over the past few decades, nearly 300 known cyanotoxins and more than 2000 cyanobacterial secondary metabolites have been reported from the environment. Traditional studies have focused on the toxic cyanotoxins produced by harmful cyanobacteria, which pose a risk to both human beings and wildlife, causing acute and chronic poisoning, resulting in diarrhea, nerve paralysis, and proliferation of cancer cells. Actually, the biotechnological potential of cyanotoxins is underestimated, as increasing studies have demonstrated their roles as valuable products, including allelopathic agents, insecticides and biomedicines. To promote a comprehensive understanding of cyanotoxins, a critical review is in demand. This review aims to discuss the classifications; biosynthetic pathways, especially heterogenous production; and potential applications of cyanotoxins. In detail, we first discuss the representative cyanotoxins and their toxic effects, followed by an exploration of three representative biosynthetic pathways (non-ribosomal peptide synthetases, polyketide synthetases, and their combinations). In particular, advances toward the heterologous biosynthesis of cyanotoxins in vitro and in vivo are summarized and compared. Finally, we indicate the potential applications and solutions to bottlenecks for cyanotoxins. We believe that this review will promote a comprehensive understanding, synthetic biology studies, and potential applications of cyanotoxins in the future.

Recent Trends and Opportunities for the Targeted Immuno-Nanomaterials for Cancer Theranostics Applications

The targeted delivery of cancer immunotherapies has increased noticeably in recent years. Recent advancements in immunotherapy, particularly in blocking the immune checkpoints (ICs) axis, have shown favorable treatment outcomes for multiple types of cancer including melanoma and non-small-cell lung cancer (NSLC). Engineered micromachines, including microparticles, and nanoplatforms (organic and inorganic), functionalized with immune agonists can effectively deliver immune-targeting molecules to solid tumors. This review focuses on the nanomaterial-based strategies that have shown promise in identifying and targeting various immunological markers in the tumor microenvironment (TME) for cancer diagnosis and therapy. Nanomaterials-based cancer immunotherapy has improved treatment outcomes by triggering an immune response in the TME. Evaluating the expression levels of ICs in the TME also could potentially aid in diagnosing patients who would respond to IC blockade therapy. Detecting immunological checkpoints in the TME using noninvasive imaging systems via tailored nanosensors improves the identification of patient outcomes in immuno-oncology (IO). To enhance patient-specific analysis, lab-on-chip (LOC) technology is a rapid, cost-effective, and accurate way of recapitulating the TME. Such novel nanomaterial-based technologies have been of great interest for testing immunotherapies and assessing biomarkers. Finally, we provide a perspective on the developments in artificial intelligence tools to facilitate ICs-based nano theranostics toward cancer immunotherapy.

Synthesis and Evaluation of a Non-Peptide Small-Molecule Drug Conjugate Targeting Integrin αVβ3

An integrin α_Vβ₃-targeting linear RGD mimetic containing a small-molecule drug conjugate (SMDC) was synthesized by combining the antimitotic agent monomethyl auristatin E (MMAE), an enzymatically cleavable Val-Ala-PABC linker with a linear conjugable RGD mimetic. The structure proposal for the conjugable RGD mimetic was suggested upon the DAD mapping analysis of a previously synthesized small-molecule RGD mimetic array based on a tyrosine scaffold. Therefore, a diversifying strategy was developed as well as a novel method for the partial hydrogenation of pyrimidines in the presence of the hydrogenolytically cleavable Cbz group. The small-molecule RGD mimetics were evaluated in an ELISA-like assay, and the structural relationships were analyzed by DAD mapping revealing activity differences induced by structural changes as visualized in dependence on special structural motifs. This provided a lead structure for generation of an SMDC containing the antimitotic drug MMAE. The resulting SMDC containing a linear RGD mimetic was tested in a cell adhesion and an in vitro cell viability assay in comparison to reference SMDCs containing cRGDfK or cRADfK as the homing device. The linear RGD SMDC and the cRGDfK SMDC inhibited adhesion of α_Vβ₃-positive WM115 cells to vitronectin with IC₅₀ values in the low µM range, while no effect was observed for the α_Vβ₃-negative M21-L cell line. The cRADfK SMDC used as a negative control was about 30-fold less active in the cell adhesion assay than the cRGDfK SMDC. Conversely, both the linear RGD SMDC and the cRGDfK SMDC are about 55-fold less cytotoxic than MMAE against the α_Vβ₃-positive WM115 cell line with IC50 values in the nM range, while the cRADfK SMDC is 150-fold less cytotoxic than MMAE. Hence, integrin binding also influences the antiproliferative activity giving a targeting index of 2.8.

Design of α/β-Hybrid Peptide Ligands of α4β1 Integrin Equipped with a Linkable Side Chain for Chemoselective Biofunctionalization of Microstructured Materials

Arg-Gly-Asp (RGD)-binding integrins, e.g., αvβ3, αvβ1, αvβ5 integrins, are currently regarded as privileged targets for the delivery of diagnostic and theranostic agents, especially in cancer treatment. In contrast, scarce attention has been paid so far to the diagnostic opportunities promised by integrins that recognize other peptide motifs. In particular, α4β1 integrin is involved in inflammatory, allergic, and autoimmune diseases, therefore, it represents an interesting therapeutic target. Aiming at obtaining simple, highly stable ligands of α4β1 integrin, we designed hybrid α/β peptidomimetics carrying linkable side chains for the expedient functionalization of biomaterials, nano- and microparticles. We identified the prototypic ligands MPUPA-(R)-isoAsp(NHPr)-Gly-OH (12) and MPUPA-Dap(Ac)-Gly-OH (13) (MPUPA, methylphenylureaphenylacetic acid; Dap, 2,3-diamino propionic acid). Modification of 12 and 13 by introduction of flexible linkers at isoAsp or Dap gave 49 and 50, respectively, which allowed for coating with monolayers (ML) of flat zeolite crystals. The resulting peptide–zeolite MLs were able to capture selectively α4β1 integrin-expressing cells. In perspective, the α4β1 integrin ligands identified in this study can find applications for preparing biofunctionalized surfaces and diagnostic devices to control the progression of α4β1 integrin-correlated diseases.