A Multitargeted Approach: Organorhodium Anticancer Agent Based on Vorinostat as a Potent Histone Deacetylase Inhibitor

Diversity in the Interaction of Amino Acid- and Peptide-Based Hydroxamic Acids with Some Platinum Group Metals in Solution

Complexes that incorporate both ligand(s) and metal(s) exhibiting cytotoxic activity can especially be interesting to develop multifunctional drug molecules with desired activities. In this review, the limited number of solution results collected in our laboratory on the complexes of Pd(II) and two other platinum group metals—the half-sandwich type, [(η⁶-p-cym)Ru(H₂O)₃]²⁺, and [(η⁵-Cp*)Rh(H₂O)₃]²⁺—with hydroxamic acid derivatives of three amino acids, two imidazole analogues, and four small peptides are summarized and evaluated. Unlike the limited number of coordination sites of these metal ions (four and three for Pd(II) and the organometallic cations, respectively), the ligands discussed here offer a relatively high number of donor atoms as well as variation in their position within the ligands, resulting in a large versatility of the likely coordination modes. The review, besides presenting the solution equilibrium results, also discusses the main factors, such as (N,N) versus (O,O) chelate; size of chelate; amino-N versus imidazole-N; primary versus secondary hydroxamic function; differences between hydrolytic ability of the metal ions studied; and hydrolysis of the coordinated peptide hydroxamic acids in their Pd(II) complexes, which all determine the coordination modes present in the complexes formed in measurable concentrations in these systems. The options for the quantitative evaluation of metal binding effectivity and selectivity of the various ligands and the comparison with each other by using solution equilibrium data are also discussed.

Anti-Proliferative, Anti-Angiogenic and Safety Profiles of Novel HDAC Inhibitors for the Treatment of Metastatic Castration-Resistant Prostate Cancer

Metastatic castration-resistant prostate cancer (CRPC) has a five-year survival rate of 28%. As histone deacetylases (HDACs) are overexpressed in CRPC, the HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) was trialled in CRPC patients but found to be toxic and inefficacious. Previously, we showed that novel HDAC inhibitors (Jazz90 (N1-hydroxy-N⁸-(4-(pyridine-2-carbothioamido)phenyl)octanediamide) and Jazz167 ([chlorido(η⁵-pentamethylcyclopentadieny[1–4](N1-hydroxy-N⁸-(4-(pyridine-2-carbothioamido-κ²N,S)phenyl)octanediamide)rhodium(III)] chloride) had a higher cancer-to-normal-cell selectivity and superior anti-angiogenic effects in CRPC (PC3) cells than SAHA. Thus, this study aimed to further investigate the efficacy and toxicity of these compounds. HUVEC tube formation assays revealed that Jazz90 and Jazz167 significantly reduced meshes and segment lengths in the range of 55–88 and 43–64%, respectively. However, Jazz90 and Jazz167 did not affect the expression of epithelial-to-mesenchymal transitioning markers E-cadherin and vimentin. Jazz90 and Jazz167 significantly inhibited the growth of PC3 and DU145 spheroids and reduced PC3 spheroid branching. Jazz90 and Jazz167 (25, 50 and 75 mg/kg/day orally for 21 days) were non-toxic in male BALB/c mice. The efficacy and safety of these compounds demonstrate their potential for further in vivo studies in CRPC models.

Heptadentate, Octadentate, Or Even Nonadentate? Denticity in the Unexpected Formation of an All-Carbon Donor-Atom Ligand in RhIII(Cp*)(Anthracenyl-NHC) Complexes

Investigations on incorporating an N-flanking anthracenyl moiety to [Rh(Cp*)(NHC)Cl₂] complexes surprisingly led to the formation of an intramolecular C-C bond between the Cp* and anthracenyl moieties, with additional auxiliary interactions between the metal and the anthracenyl ring system. In silico modeling supports a reaction mechanism whereby Rh(η⁴-tetramethylfulvene) intermediates undergo metallocycloaddition and the abstraction of a chlorido ligand, affording unique cationic complexes that feature Rh centers coordinated by a nonadentate ligand with exclusively carbon donor atoms. Some Rh-C interactions were extremely weak but nevertheless exhibited covalent bonding character. These weak Rh-C interactions were readily displaced by stronger electron donors, and the nonadentate ligand reverted to the heptadentate coordination mode observed in the intermediate. As far as we are aware, this study provides the first conclusive evidence of complexes bearing a single nonadentate κ⁹-coordinating ligand that features only carbon donors bound to a metal center.