Metallodrug Profiling against SARS-CoV-2 Target Proteins Identifies Highly Potent Inhibitors of the S/ACE2 interaction and the Papain-like Protease PLpro.

The global spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has called for an urgent need for dedicated antiviral therapeutics. Metal complexes are commonly underrepresented in compound libraries that are used for screening in drug discovery campaigns, however, there is growing evidence for their role in medicinal chemistry. Based on previous results, we have selected more than 100 structurally diverse metal complexes for profiling as inhibitors of two relevant SARS-CoV-2 replication mechanisms, namely the interaction of the spike (S) protein with the ACE2 receptor and the papain-like protease PLpro . In addition to many well-established types of mononuclear experimental metallodrugs, the pool of compounds tested was extended to approved metal-based therapeutics such as silver sulfadiazine and thiomersal, as well as polyoxometalates (POMs). Among the mononuclear metal complexes, only a small number of active inhibitors of the S/ACE2 interaction was identified, with titanocene dichloride as the only strong inhibitor. However, among the gold and silver containing complexes many turned out to be very potent inhibitors of PLpro activity. Highly promising activity against both targets was noted for many POMs. Selected complexes were evaluated in antiviral SARS-CoV-2 assays confirming activity for gold complexes with N-heterocyclic carbene (NHC) or dithiocarbamato ligands, a silver NHC complex, titanocene dichloride as well as a POM compound. These studies might provide starting points for the design of metal-based SARS-CoV-2 antiviral agents.

Chimeric siRNA-DNA Surfactants for the Enhanced Delivery and Sustained Cytotoxicity of a Gold(III) Metallodrug.

Using a recently developed nucleic acid delivery platform, we demonstrate the effective delivery of metallodrug [AuIIIBr2(SSC-Inp-OEt)] (AP228; Inp = isonipecotic moiety), a hydrophobic, low solubility gold complex cytotoxic to cancer cells. It is shown that AP228 is delivered more effectively into HeLa cells using micellular surfactant assemblies compared to that of a more polar derivative [AuIIIBr2(SSC-Inp-GlcN1)] (AP209; GlcN1 = (α,ß)-d-glucosamino moiety). When AP228 is codelivered with siRNA targeting Bcl-2, a key regulator of apoptosis, the overall cytotoxic therapeutic effects of the drug are maximized. The optimized delivery and distribution of the compound is monitored by both fluorescence microscopy and inductively coupled plasma mass spectrometry. We show that codelivery of the AP228 and Bcl-2 targeting siRNA results in a substantial increase in drug efficacy, wherein the cytotoxic therapeutic effects of the drug are maximized, reducing the IC50 from 760 nM to 11 nM. This hybrid small molecule drug and therapeutic nucleic acid delivery vehicle is shown to enable both the improved solubility and uptake of the gold(III) metallodrugs and the delivery of chemically unmodified siRNA, resulting in enhanced cytotoxic effects.

Ruthenium(II/III)-based compounds with encouraging antiproliferative activity against non-small-cell lung cancer.

Hereby we present the synthesis of several ruthenium(II) and ruthenium(III) dithiocarbamato complexes. Proceeding from the Na[trans-Ru(III)(dmso)(2)Cl(4)] (2) and cis-[Ru(II)(dmso)(4)Cl(2)] (3) precursors, the diamagnetic, mixed-ligand [Ru(II)L(2)(dmso)(2)] complexes 4 and 5, the paramagnetic, neutral [Ru(III)L(3)] monomers 6 and 7, the antiferromagnetically coupled ionic α-[Ru(III)(2)L(5)]Cl complexes 8 and 9 as well as the ß-[Ru(III)(2)L(5)]Cl dinuclear species 10 and 11 (L = dimethyl- (DMDT) and pyrrolidinedithiocarbamate (PDT)) were obtained. All the compounds were fully characterised by elemental analysis as well as (1)H NMR and FTIR spectroscopy. Moreover, for the first time the crystal structures of the dinuclear ß-[Ru(III)(2)(dmdt)(5)]BF(4)⋅CHCl(3)⋅CH(3)CN and of the novel [Ru(II)L(2)(dmso)(2)] complexes were also determined and discussed. For both the mono- and dinuclear Ru(II) and Ru(III) complexes the central metal atoms assume a distorted octahedral geometry. Furthermore, in vitro cytotoxicity of the complexes has been evaluated on non-small-cell lung cancer (NSCLC) NCI-H1975 cells. All the mono- and dinuclear Ru(III) dithiocarbamato compounds (i.e., complexes 6-10) show interesting cytotoxic activity, up to one order of magnitude higher with respect to cisplatin. Otherwise, no significant antiproliferative effect for either the precursors 2 and 3 or the Ru(II) complexes 4 and 5 has been observed.

Design, physico-chemical characterization and in vitro biological activity of organogold(III) glycoconjugates.

To develop new metal-based glycoconjugates as potential anticancer agents, four organometallic gold(iii)-dithiocarbamato glycoconjugates of the type [AuIII(2-Bnpy)(SSC-Inp-GlcN)](PF6) (2-Bnpy: 2-benzylpyridine; Inp: isonipecotic moiety; GlcN: amino-glucose scaffold; Au3-Au6) and the corresponding model non-glycosylated counterparts [AuIII(2-Bnpy)(SSC-Inp-R)](PF6) (R: OEt (Au1), NH2 (Au2)) have been generated and characterized by means of several analytical techniques (elemental analysis, FT-IR, 1H-/13C-NMR, ESI-MS, UV-Vis, X-ray crystallography). Their stability under physiologically-relevant conditions (PBS solution) and n-octanol/PBS distribution coefficient (D7.4) have also been evaluated. Gold(iii) glycoconjugates showed an antiproliferative effect against ovarian carcinoma A2780 cells, with GI50 values in the low micromolar range. Remarkably, their cell growth inhibitory effect increases upon the addition of a glucose transporter 1 (GLUT1) inhibitor, thus ruling out the involvement of GLUT1 in their transport inside the cell. Additional mechanistic studies have been carried out in A2780 cells, supporting the hypothesis of a facilitated diffusion mechanism (possibly mediated by glucose transporters other than GLUT1), and revealing their capability to act as topoisomerase I and II inhibitors and to disrupt mitochondrial membrane integrity, leading to the generation of ROS, thus resulting in the promotion of oxidative stress and, eventually, cell death.

An innovative and efficient route to the synthesis of metal-based glycoconjugates: proof-of-concept and potential applications.

With a view to developing more efficient strategies to the functionalization of metallodrugs with carbohydrates, we here report on an innovative and efficient synthetic route to generate gold(iii) glycoconjugates in high yields and purity. The method is based on the initial synthesis of the zinc(ii)-dithiocarbamato intermediate [ZnII(SSC-Inp-GlcN)2] (Inp = isonipecotic moiety; GlcN = amino-glucose) followed by the transfer of the glucoseisonipecoticdithiocarbamato ligand to the gold(iii) center via transmetallation reaction between the zinc(ii) intermediate and K[AuIIIBr4] in 1 : 2 stoichiometric ratio, yielding the corresponding glucose-functionalized gold(iii)-dithiocarbamato derivative [AuIIIBr2(SSC-Inp-GlcN)]. No protection/deprotection of the amino-glucose scaffold and no chromatographic purification were needed. The synthetic protocol was optimized for glucose precursors bearing the amino function at either the C2 or the C6 position, and works in the case of both α and ß anomers. The application of the synthetic strategy was also successfully extended to other metal ions of biomedical interest, such as gold(i) and platinum(ii), to obtain [AuI(SSC-Inp-GlcN)(PPh3)] and [PtII(SSC-Inp-GlcN)2], respectively. All compounds were fully characterized by elemental analysis, mid- and far-IR, mono- and multidimensional NMR spectroscopy, and, where possible, X-ray crystallography. Results and potential applications are here discussed.