Toward Angiogenesis Inhibitors Based on the Conjugation of Organometallic Platinum(II) Complexes to RGD Peptides

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.

RGD peptide in cancer targeting: Benefits, challenges, solutions, and possible integrin-RGD interactions

RGD peptide can be found in cell adhesion and signaling proteins, such as fibronectin, vitronectin, and fibrinogen. RGD peptides' principal function is to facilitate cell adhesion by interacting with integrin receptors on the cell surface. They have been intensively researched for use in biotechnology and medicine, including incorporation into biomaterials, conjugation to medicinal molecules or nanoparticles, and labeling with imaging agents. RGD peptides can be utilized to specifically target cancer cells and the tumor vasculature by engaging with these integrins, improving drug delivery efficiency and minimizing adverse effects on healthy tissues. RGD-functionalized drug carriers are a viable option for cancer therapy as this focused approach has demonstrated promise in the future. Writing a review on the RGD peptide can significantly influence how drugs are developed in the future by improving our understanding of the peptide, finding knowledge gaps, fostering innovation, and making drug design easier.

Transition metals in angiogenesis - A narrative review

The aim of this paper is to offer a narrative review of the literature regarding the influence of transition metals on angiogenesis, excluding lanthanides and actinides. To our knowledge there are not any reviews up to date offering such a summary, which inclined us to write this paper. Angiogenesis describes the process of blood vessel formation, which is an essential requirement for human growth and development. When the complex interplay between pro- and antiangiogenic mediators falls out of balance, angiogenesis can quickly become harmful. As it is so fundamental, both its inhibition and enhancement take part in various diseases, making it a target for therapeutic treatments. Current methods come with limitations, therefore, novel agents are constantly being researched, with metal agents offering promising results. Various transition metals have already been investigated in-depth, with studies indicating both pro- and antiangiogenic properties, respectively. The transition metals are being applied in various formulations, such as nanoparticles, complexes, or scaffold materials. Albeit the increasing attention this field is receiving, there remain many unanswered questions, mostly regarding the molecular mechanisms behind the observed effects. Notably, approximately half of all the transition metals have not yet been investigated regarding potential angiogenic effects. Considering the promising results which have already been established, it should be of great interest to begin investigating the remaining elements whilst also further analyzing the established effects.

Encapsulation of Ru(II) Polypyridine Complexes for Tumor-Targeted Anticancer Therapy

Ru(II) polypyridine complexes have attracted much attention as anticancer agents because of their unique photophysical, photochemical, and biological properties. Despite their promising therapeutic profile, the vast majority of compounds are associated with poor water solubility and poor cancer selectivity. Among the different strategies employed to overcome these pharmacological limitations, many research efforts have been devoted to the physical or covalent encapsulation of the Ru(II) polypyridine complexes into nanoparticles. This article highlights recent developments in the design, preparation, and physicochemical properties of Ru(II) polypyridine complex-loaded nanoparticles for their potential application in anticancer therapy.

BODIPY-Ruthenium(II) Bis-Terpyridine Complexes for Cellular Imaging and Type-I/-II Photodynamic Therapy

A series of multichromophoric ruthenium(II) complexes with the formulation [Ru(tpy-BODIPY)(tpy-R)]Cl₂ (1-4), having a heteroleptic Ru(II)-bis-tpy (tpy = 4'-phenyl-2,2':6',2″-terpyridine) moiety covalently linked to a boron-dipyrromethene (BODIPY) pendant, have been prepared and characterized and their application as a phototherapeutic and photodetection agent in cancer therapy has been explored. Ligand L¹ with a terpyridine-BODIPY moiety and complex 1 as its PF₆ salt (1a) have been structurally characterized by a single-crystal X-ray diffraction study. Complex 1a has a distorted-octahedral RuN₆ core with a Ru(II)-bis-terpyridine unit that is covalently linked to one photoactive BODIPY unit. The complexes exhibit strong absorbance near 502 nm (ε ≈ (3.7-7.8) × 10⁴ M^-1 cm^-1) and high singlet oxygen sensitization ability, giving singlet oxygen quantum yield (Φ_Δ) values ranging from 0.57 to 0.75 in DMSO. An emission-based study using complex 4 and Singlet Oxygen Sensor Green (SOSG) displays the formation of singlet oxygen inside the cells and also in the buffer medium upon light irradiation. DNA (pUC19) photocleavage experiments using ROS scavengers/stabilizers reveal photoinduced generation of singlet oxygen by a type-II process and of the superoxide anion radical by a type-I process. Complex 4 having a pendant biotin moiety as a cancer cell targeting group shows high photocytotoxicity with a remarkable phototherapeutic index (PI) value of >1400 in HeLa cancer cells with a low light dose activation (400-700 nm, 2.2 J cm^-2). The complexes display reduced activity in noncancerous HPL1D cells. The emission property of the complexes is used for cellular imaging, thus making them suitable as next-generation theranostic PDT agents.

A 2-(benzothiazol-2-yl)-phenolato platinum(II) complex as potential photosensitizer for combating bacterial infections in lung cancer chemotherapy†

Cancer and antibiotic resistance are two global health threats that usually hamper clinical chemotherapeutic efficacy. Particularly for lung cancer, bacterial infections frequently arise thereby complicating the course of cancer treatment. In this sense, three new neutral luminescent cycloplatinated(II) photosensitizers of the type [Pt(dmba)(L)] (dmba = N,N-dimethylbenzylamine-κN,κC; L = 2-(benzo[d]oxazol-2-yl)-phenolato-κN,κO1, 2-(benzo[d]thiazol-2-yl)-phenolato-κN,κO2, and 2-(1-methyl-1H-benzo[d]imidazole-2-yl)phenolato-κN,κO3) have been characterized and developed to potentially eliminate both resistant bacteria and lung cancer cells. The phototherapeutic effects of complex 2 have been evaluated using low doses of blue light irradiation. Complex 2 exerted promising photoactivity against pathogenic Gram-positive bacteria strains of clinical interest, displaying a phototoxic index (PI) of 15 for methicillin-resistant Staphylococcus aureus, one of the major microorganisms predominating lung infections. Likewise, the anticancer activity of 2 was also increased upon light irradiation in human lung A549 cancer cells (PI = 36). Further in vitro experiments with this platinum(II) complex suggest that ROS-generating photodynamic reactions were involved upon light irradiation, thus providing a reasonable mechanism for its dual anticancer and antibacterial activities.

Building up PtII -Thiosemicarbazone-Lysine-sC18 Conjugates

Three chiral tridentate N^N^S coordinating pyridine-carbaldehyde (S)-N4-(α-methylbenzyl)thiosemicarbazones (HTSCmB) were synthesised along with lysine-modified derivatives. One of them was selected and covalently conjugated to the cell-penetrating peptide sC18 by solid-phase peptide synthesis. The HTSCmB model ligands, the HTSCLp derivatives and the peptide conjugate rapidly and quantitatively form very stable PtII chlorido complexes [Pt(TSC)Cl] when treated with K2 PtCl4 in solution. The Pt(CN) derivatives were obtained from one TSCmB model complex and the peptide conjugate complex through Cl- →CN- exchange. Ligands and complexes were characterised by NMR, IR spectroscopy, HR-ESI-MS and single-crystal XRD. Intriguingly, no decrease in cell viability was observed when testing the biological activity of the lysine-tagged HdpyTSCLp, its sC18 conjugate HdpyTSCL-sC18 or the PtCl and Pt(CN) conjugate complexes in three different cell lines. Thus, given the facile and effective preparation of such Pt-TSC-peptide conjugates, these systems might pave the way for future use in late-stage labelling with Pt radionuclides and application in nuclear medicine.

Monofunctional Platinum(II) Anticancer Agents

Platinum-based anticancer drugs represented by cisplatin play important roles in the treatment of various solid tumors. However, their applications are largely compromised by drug resistance and side effects. Much effort has been made to circumvent the drug resistance and general toxicity of these drugs. Among multifarious designs, monofunctional platinum(II) complexes with a general formula of [Pt(3A)Cl]⁺ (A: Ammonia or amine) stand out as a class of "non-traditional" anticancer agents hopeful to overcome the defects of current platinum drugs. This review aims to summarize the development of monofunctional platinum(II) complexes in recent years. They are classified into four categories: fluorescent complexes, photoactive complexes, targeted complexes, and miscellaneous complexes. The intention behind the designs is either to visualize the cellular distribution, or to reduce the side effects, or to improve the tumor selectivity, or inhibit the cancer cells through non-DNA targets. The information provided by this review may inspire researchers to conceive more innovative complexes with potent efficacy to shake off the drawbacks of platinum anticancer drugs.

Polymeric Encapsulation of a Ruthenium Polypyridine Complex for Tumor Targeted One- and Two-Photon Photodynamic Therapy

Photodynamic therapy is a medical technique, which is gaining increasing attention to treat various types of cancer. Among the investigated classes of photosensitizers (PSs), the use of Ru(II) polypyridine complexes is gaining momentum. However, the currently investigated compounds generally show poor cancer cell selectivity. As a consequence, high drug doses are needed, which can cause side effects. To overcome this limitation, there is a need for the development of a suitable drug delivery system to increase the amount of PS delivered to the tumor. Herein, we report the encapsulation of a promising Ru(II) polypyridyl complex into polymeric nanoparticles with terminal biotin groups. Thanks to this design, the particles showed much higher selectivity for cancer cells in comparison to noncancerous cells in a 2D monolayer and 3D multicellular tumor spheroid model. As a highlight, upon intravenous injection of an identical amount of the Ru(II) polypyridine complex of the nanoparticle formulation, an improved accumulation inside an adenocarcinomic human alveolar basal epithelial tumor of a mouse up to a factor of 8.7 compared to the Ru complex itself was determined. The nanoparticles were found to have a high phototoxic effect upon one-photon (500 nm) or two-photon (800 nm) excitation with eradication of adenocarcinomic human alveolar basal epithelial tumor inside a mouse model. Overall, this work describes, to the best of our knowledge, the first in vivo study demonstrating the cancer cell selectivity of a very promising Ru(II)-based PDT photosensitizer encapsulated into polymeric nanoparticles with terminal biotin groups.

New minor groove covering DNA binding mode of dinuclear Pt(II) complexes with various pyridine-linked bridging ligands and dual anticancer-antiangiogenic activities

New anticancer platinum(II) compounds simultaneously targeting tumor cells and tumor-derived neoangiogenesis, with new DNA interacting mode and large therapeutic window are appealing alternative to improve efficacy of clinical platinum chemotherapeutics. Herein, we describe three novel dinuclear [{Pt(en)Cl}₂(μ-L)]²⁺ complexes with different pyridine-like bridging ligands (L), 4,4'-bipyridine (Pt1), 1,2-bis(4-pyridyl)ethane (Pt2) and 1,2-bis(4-pyridyl)ethene (Pt3), which highly, positively charged aqua derivatives, [{Pt(en)(H₂O)}₂(μ-L)]⁴⁺, interact with the phosphate backbone forming DNA-Pt adducts with an unique and previously undescribed binding mode, called a minor groove covering. The results of this study suggested that the new binding mode of the aqua-Pt(II) complexes with DNA could be attributed to the higher anticancer activities of their chloride analogues. All three compounds, particularly complex [{Pt(en)Cl}₂(μ-4,4'-bipy)]Cl₂·2H₂O (4,4'-bipy is 4,4'-bipyridine) (Pt1), overcame cisplatin resistance in vivo in the zebrafish-mouse melanoma xenograft model, showed much higher therapeutic potential than antiangiogenic drug sunitinib malate, while effectively blocking tumor neovascularization and melanoma cell metastasis. Overall therapeutic profile showed new dinuclear Pt(II) complexes could be novel, effective and safe anticancer agents. Finally, the correlation with the structural characteristics of these complexes can serve as a useful tool for developing new and more effective anticancer drugs.

Synthesis and Characterization of an Epidermal Growth Factor Receptor-Selective RuII Polypyridyl-Nanobody Conjugate as a Photosensitizer for Photodynamic Therapy

There is a current surge of interest in the development of novel photosensitizers (PSs) for photodynamic therapy (PDT), as those currently approved are not completely ideal. Among the tested compounds, we have previously investigated the use of RuII polypyridyl complexes with a [Ru(bipy)2 (dppz)]2+ and [Ru(phen)2 (dppz)]2+ scaffold (bipy=2,2'-bipyridine; dppz=dipyrido[3,2-a:2',3'-c]phenazine; phen=1,10-phenanthroline). These complexes selectively target DNA. However, because DNA is ubiquitous, it would be of great interest to increase the selectivity of our PDT PSs by linking them to a targeting vector in view of targeted PDT. Herein, we present the synthesis, characterization, and in-depth photophysical evaluation of a nanobody-containing RuII polypyridyl conjugate selective for the epidermal growth factor receptor (EGFR) in view of targeted PDT. Using ICP-MS and confocal microscopy, we could demonstrate that our conjugate has high selectivity for the EGFR receptor, which is a crucial oncological target because it is overexpressed and/or deregulated in a variety of solid tumors. However, in contrast to expectations, this conjugate was found to not produce reactive oxygen species (ROS) in cancer cells and is therefore not phototoxic.

Synthesis and Cytotoxic Study of a Platinum(IV) Anticancer Prodrug with Selectivity toward Luteinizing Hormone-Releasing Hormone (LHRH) Receptor-Positive Cancer Cells

Platinum drugs including cisplatin are widely used in clinics to treat various types of cancer. However, the lack of cancer-cell selectivity is one of the major problems that lead to side effects in normal tissues. Luteinizing hormone-releasing hormone (LHRH) receptors are overexpressed in many types of cancer cells but rarely presented in normal cells, making LHRH receptor a good candidate for cancer targeting. In this study, we report the synthesis and cytotoxic study of a novel platinum(IV) anticancer prodrug functionalized with LHRH peptide. This LHRH-platinum(IV) conjugate is highly soluble in water and quite stable in a PBS buffer. Cytotoxic study reveals that the prodrug selectively targets LHRH receptor-positive cancer cell lines with the cytotoxicities 5-8 times higher than those in LHRH receptor-negative cell lines. In addition, the introduction of LHRH peptide enhances the cellular accumulation in a manner of receptor-mediated endocytosis. Moreover, the LHRH-platinum(IV) prodrug is proved to kill cancer cells by binding to the genomic DNA, inducing apoptosis, and arresting the cell cycle at the G₂/M phase. In summary, we report a novel LHRH-platinum(IV) anticancer prodrug having largely improved selectivity toward LHRH receptor-positive cancer cells, relative to cisplatin.