The recurrent global exposure to highly challenging viral epidemics, and the still limited spectrum of effective pharmacological options step on the accelerator towards the development of new antiviral medicines. In this work we explored the anti-SARS-CoV-2 potential of a recently launched chiral ring system based on the uracil scaffold fused to carbocycle rings. The asymmetric synthesis of two generations of chiral uracil-based compounds (overall 31 different products), and their in vitro cytotoxicity and antiviral screening against wild-type SARS-CoV-2 in U87.ACE cells allowed us to identify seven non-cytotoxic enantioenriched derivatives exhibiting in vitro EC50 in the 6-37 μM range. Among these compounds, bicyclic uracil 10 showed the best antiviral potency against SARS-CoV-2 (EC50 20A.EU2 = 7.41 μM and EC50 Omicron = 19.4 μM), combined with a favourable selectivity index. Additionally, it exhibited single-digit micromolar inhibition of the isolated SARS-CoV-2 RNA-dependent RNA polymerase (IC50 = 2.1 μM). Starting from a reported cryo-EM structure of RdRp, docking and molecular dynamics simulations were performed to rationalize possible binding modes of the active compounds. Interestingly, no inhibition of viral replication in cells was observed against a wide spectrum of human viruses, while some derivatives, and especially hit compound 10, exhibited specific low micromolar antiviral effect against β-coronavirus OC43. Collectively, these data indicate that this novel uracil-based ring system represents a valid starting point for further development of a new class of RdRp inhibitors to treat SARS-CoV-2 and, potentially, other β-coronavirus infections.

Peptide-drug conjugates (PDCs) have recently emerged as interesting hybrid constructs not only for targeted therapy, but also for the early diagnosis of different pathologies. In most cases, the crucial step in the PDC synthesis is the final conjugation step, where a specific drug is bound to a particular peptide-/peptidomimetic-targeting unit. Thus, this concept paper aims to give a short guide to determining the finest conjugation reaction, by considering in particular the reaction conditions, the stability of the linker and the major pros and cons of each reaction. Based on the recent PDCs reported in literature, the most common and efficient conjugation methods will be systematically presented and compared, generating a short guide to consult while planning the synthesis of a novel peptide-drug conjugate.

Though the bulk of the COVID-19 pandemic is behind, the search for effective and safe anti-SARS-CoV-2 drugs continues to be relevant. A highly pursued approach for antiviral drug development involves targeting the viral spike (S) protein of SARS-CoV-2 to prevent its attachment to the cellular receptor ACE2. Here, we exploited the core structure of polymyxin B, a naturally occurring antibiotic, to design and synthesize unprecedented peptidomimetics (PMs), intended to target contemporarily two defined, non-overlapping regions of the S receptor-binding domain (RBD). Monomers 1, 2, and 8, and heterodimers 7 and 10 bound to the S-RBD with micromolar affinity in cell-free surface plasmon resonance assays (KD ranging from 2.31 μM to 2.78 μM for dimers and 8.56 μM to 10.12 μM for monomers). Although the PMs were not able to fully protect cell cultures from infection with authentic live SARS-CoV-2, dimer 10 exerted a minimal but detectable inhibition of SARS-CoV-2 entry in U87.ACE2+ and A549.ACE2.TMPRSS2+ cells. These results validated a previous modeling study and provided the first proof-of-feasibility of using medium-sized heterodimeric PMs for targeting the S-RBD. Thus, heterodimers 7 and 10 may serve as a lead for the development of optimized compounds, which are structurally related to polymyxin, with improved S-RBD affinity and anti-SARS-CoV-2 potential.

Growth factors and cytokines released in the lung cancer microenvironment promote an epithelial-to-mesenchymal transition (EMT) that sustains the progression of neoplastic diseases. TGFβ is one of the most powerful inducers of this transition, as it induces overexpression of the fibronectin receptor, αvβ6 integrin, in cancer cells which, in turn, is strongly associated with EMT. Thus, αvβ6 integrin receptors may be exploited as a target for the selective delivery of anti-tumor agents. We introduce three novel synthesized conjugates, in which a selective αvβ6 receptor ligand is linked to nintedanib, a potent kinase inhibitor used to treat advanced adenocarcinoma lung cancer in clinics. The αvβ6 integrin ligand directs nintedanib activity to the target cells of the tumor microenvironment, avoiding the onset of negative side effects in normal cells. We found that the three conjugates inhibit the adhesion of cancer cells to fibronectin in a concentration-dependent manner and that αvβ6-expressing cells internalized the conjugated compounds, thus permitting nintedanib to inhibit 2D and 3D cancer cell growth and suppress the clonogenic ability of the EMT phenotype as well as intervening in other aspects associated with the EMT transition. These results highlight αvβ6 receptors as privileged access points for dual-targeting molecular conjugates engaged in an efficient and precise strategy against non-small cell lung cancer.

Organocatalytic asymmetric transformation of common aromatic heterocycles via in situ formation of highly reactive dearomatized ortho-quinodimethane diene species and subsequent [4+2] cycloaddition with suitable dienophiles has become a powerful tool to enter cyclohexane-fused heterocycles. Most of these reactions were previously applied to benzo-fused heterocycles or poorly aromatic rings. Herein, we disclose how previously intractable aromatic imidazole rings, equipped with removable methylidene malononitrile activating handle, could be involved as competent cycloaddends with β-aryl enals in efficient eliminative [4+2] cycloadditions under mild organocatalytic conditions. This method allowed the efficient and direct preparation of scantly represented 6,7-dihydrobenzo[d]imidazoles with optimal enantio- and regioselectivities. Post-cycloaddition chemical editing provided imidazole-based ring systems with diverse oxidation state and functional groups.

αVβ6 Integrin plays a fundamental role in the activation of transforming growth factor-β (TGF-β), the major profibrotic mediator; for this reason, αVβ6 ligands have recently been forwarded to clinical phases for the therapy of fibrotic diseases. Herein, we report the synthesis and in vitro biological evaluation as antifibrotic agents of three new covalent conjugates, constituted by c(AmpLRGDL), an αVβ6 integrin-recognizing small cyclopeptide, and nintedanib, a tyrosine kinase inhibitor approved for idiopathic pulmonary fibrosis (IPF) treatment. One of these conjugates recapitulates optimal in vitro antifibrotic properties of the two active units. The integrin ligand portion within the conjugate plays a role in inhibiting profibrotic stimuli, potentiating the nintedanib effect and favoring the selective uptake of the conjugate in cells overexpressing αVβ6 integrin. These results may open a new perspective on the development of dual conjugates in the targeted therapy of IPF.

Melanoma is the deadliest form of skin cancer, and more than 150,000 cases are diagnosed every year in Europe. New strategies in treatment approved over the past decade, such as immunotherapy and targeted therapy, have prolonged life expectation even in stage IV melanoma patients. However, due to the increasing incidence of this cancer, the development of new therapeutic strategies remains urgent. Recent studies revealed the combination of nintedanib, a tyrosine kinase inhibitor approved as an antifibrotic drug, and immuno- and/or targeted therapy drugs to be promising. Here we present three new dual covalent conjugates, in which a nintedanib unit is permanently linked to a cyclopeptidomimetic ligand for the alpha(V)beta(3) integrin, a transmembrane receptor involved in cell survival, proliferation and migration, which is overexpressed by tumour cells, and therefore recognized as marker for tumour targeting. In vitro assays on human melanoma tumour cells confirmed the high binding affinity of these conjugates for alpha(V)beta(3) integrin-positive melanoma cells, as well as their integrin-mediated cell internalization. Two of these conjugates were efficient in inhibiting the mitogen activated protein kinase (MAPK) signalling pathway, common to both integrin- and growth factor- biological targets. Such targeted conjugates could therefore be of special interest in melanoma treatment alone or in combination with other anticancer drugs.

Integrin α4β1 belongs to the leukocyte integrin family and represents a therapeutic target of relevant interest given its primary role in mediating inflammation, autoimmune pathologies and cancer-related diseases. The focus of the present work is the design, synthesis and characterization of new peptidomimetic compounds that are potentially able to recognize α4β1 integrin and interfere with its function. To this aim, a collection of seven new cyclic peptidomimetics possessing both a 4-aminoproline (Amp) core scaffold grafted onto key α4β1-recognizing sequences and the (2-methylphenyl)ureido-phenylacetyl (MPUPA) appendage, was designed, with the support of molecular modeling studies. The new compounds were synthesized through SPPS procedures followed by in-solution cyclization maneuvers. The biological evaluation of the new cyclic ligands in cell adhesion assays on Jurkat cells revealed promising submicromolar agonist activity in one compound, namely, the c[Amp(MPUPA)Val-Asp-Leu] cyclopeptide. Further investigations will be necessary to complete the characterization of this class of compounds.

The outbreak of SARS‐CoV‐2 has been an extraordinary event that constituted a global health emergency. As the novel coronavirus is continuing to spread over the world, the need for therapeutic agents to control this pandemic is increasing. α V β 6 Integrin may be an intriguing target not only for the inhibition of SARS‐CoV‐2 entry, but also for the diagnosis/treatment of COVID‐19 related fibrosis, an emerging type of fibrotic disease which will probably affect a significant part of the recovered patients. In this short article, the possible role of this integrin for fighting COVID‐19 is discussed on the basis of recently published evidence, showing how its underestimated involvement may be interesting for the development of novel pharmacological tools.

In recent years, targeted therapies have raised increasing interest as effective strategies to improve therapeutic efficiency, reduce the impact of adverse side effects, and overcome drug resistance, particularly in the field of cancer chemotherapeutics. Many examples of RGD (Arg-Gly-Asp) peptide-drug conjugates (PDCs) have been proposed as targeted drug delivery systems. These molecular hybrids embody high affinity ligands targeting disease signatures (overexpressed integrin receptors or specific integrin-related pathways within diseased cells/tissues) connected to recognized therapeutic units by means of carefully designed linker-spacer combinations, to ultimately control stability, physico-chemical properties, timing, and localization of drug release. This account has collected and critically surveyed relevant contributions from the period of 2015 to the present day, wishing to provide a window open on new synthesis strategies facing the challenging issues of site-selective drug delivery and dual drug targeting.

In recognition of the key role played by integrins in several life-threatening dysfunctions, the search for novel small-molecule probes that selectively recognize these surface receptors is still open and widely pursued. Inspired by previously established aminoproline (Amp)-RGD based cyclopeptidomimetics with attracting alpha(V)beta(3)integrin affinity and selectivity, the design and straightforward synthesis of 18 new AmpRGD chemotypes bearing additional structural variants were herein implemented, to shift toward peptide-like alpha(V)beta(6)integrin targeted binders. The ligand competence of the synthesized products toward alpha(V)beta(6)was evaluated in competitive binding assays on isolated receptors, and alpha(V)beta(6)/alpha(V)beta(3)selectivity was determined for a subgroup of compounds, resulting in the identification of four very promising candidates. SAR considerations and docking simulations allowed us to appreciate the key structural features responsible for the observed activity.