Two novel fan-shaped trinuclear Pt(ii) complexes act as G-quadruplex binders and telomerase inhibitors.

Two new trinuclear Pt(ii) complexes {[Pt(dien)]3(tib)}(NO3)6 (1) and {[Pt(dpa)]3(tib)}(NO3)6 (2) (dien: diethylenetriamine, dpa: bis-(2-pyridylmethyl)amine, tib: 1,3,5-tris(1H-imidazol-1-yl)benzene) have been designed, synthesized, characterized and applied to a series of biochemical studies. We found that both of the Pt(ii) complexes exhibited much better selectivity for human telomeric G-quadruplex sequence than promoter G-quadruplexes (c-kit, c-myc, and bcl2) or duplex DNA. Both complexes displayed comparative stability and affinity towards human telomeric G-quadruplex by the studies from surface plasmon resonance, fluorescence resonance energy transfer and polymerase chain reaction stop assays. The circular dichroism indicated that both complexes could induce and stabilize anti-parallel G-quadruplex structures. Molecule docking presented that Pt(ii) complex intercalated into the large groove of human telomeric G-quadruplex (PDB ID: 143D). Furthermore, telomeric repeat amplification protocol assays quantitatively evaluated the inhibition of telomerase activity caused by the Pt(ii) complexes. The obtained IC50 values of 6.41 ± 0.042 µM and 2.67 ± 0.035 µM for 1 and 2, respectively, exhibited strong telomerase inhibitions. All results suggest that such fan-shaped trinuclear Pt(ii) complexes are effective and selective G-quadruplex binders, as well as strong telomerase inhibitors. This study provides insight into the development of human telomeric G-quadruplex targeted anticancer drugs based on the metal complex.

Mitochondria-targeted phosphorescent cyclometalated iridium(III) complexes: synthesis, characterization, and anticancer properties.

Cyclometalated iridium(III) complexes represent a promising approach to developing new anticancer metallodrugs. In this work, three phosphorescent cyclometalated iridium(III) complexes Ir1-Ir3 have been explored as mitochondria-targeted anticancer agents. All three complexes display higher antiproliferative activity than cisplatin against the cancer cells screened, and with the IC50 values ranging from 0.23 to 5.6 µM. Colocalization studies showed that these complexes are mainly localized in the mitochondria. Mechanism studies show that these complexes exert their anticancer efficacy through initiating a series of events related to mitochondrial dysfunction, including depolarization of mitochondrial membrane potential (MMP), elevation of intracellular reactive oxygen species (ROS) levels, and induction of apoptosis. Mitochondria-targted cyclometalated iridium complexes induce apoptosis through depolarized mitochondria, elevation of intracellular ROS and activated caspase.

A Nitroxide-Tagged Platinum(II) Complex Enables the Identification of DNA G-Quadruplex Binding Mode.

We reported a novel strategy for investigating small molecule binding to G-quadruplexes (GQs). A newly synthesized dinuclear platinum(II) complex (Pt2L) containing a nitroxide radical was shown to selectively bind a GQ-forming sequence derived from human telomere (hTel). Using the nitroxide moiety as a spin label, electron paramagnetic resonance (EPR) spectroscopy was carried out to investigate binding between Pt2L and hTel GQ. Measurements indicated that two molecules of Pt2L bind with one molecule of hTel GQ. The inter-spin distance measured between the two bound Pt2L, together with molecular docking analyses, revealed that Pt2L predominately binds to the neighboring narrow and wide grooves of the G-tetrads as hTel adopts the antiparallel conformation. The design and synthesis of nitroxide tagged GQ binders, and the use of spin-labeling/EPR to investigate their interactions with GQs, will aid the development of small molecules for manipulating GQs involved in crucial biological processes.

Conformations of Human Telomeric G-Quadruplex Studied Using a Nucleotide-Independent Nitroxide Label.

Guanine-rich oligonucleotides can form a unique G-quadruplex (GQ) structure with stacking units of four guanine bases organized in a plane through Hoogsteen bonding. GQ structures have been detected in vivo and shown to exert their roles in maintaining genome integrity and regulating gene expression. Understanding GQ conformation is important for understanding its inherent biological role and for devising strategies to control and manipulate functions based on targeting GQ. Although a number of biophysical methods have been used to investigate structure and dynamics of GQs, our understanding is far from complete. As such, this work explores the use of the site-directed spin labeling technique, complemented by molecular dynamics simulations, for investigating GQ conformations. A nucleotide-independent nitroxide label (R5), which has been previously applied for probing conformations of noncoding RNA and DNA duplexes, is attached to multiple sites in a 22-nucleotide DNA strand derived from the human telomeric sequence (hTel-22) that is known to form GQ. The R5 labels are shown to minimally impact GQ folding, and inter-R5 distances measured using double electron-electron resonance spectroscopy are shown to adequately distinguish the different topological conformations of hTel-22 and report variations in their occupancies in response to changes of the environment variables such as salt, crowding agent, and small molecule ligand. The work demonstrates that the R5 label is able to probe GQ conformation and establishes the base for using R5 to study more complex sequences, such as those that may potentially form multimeric GQs in long telomeric repeats.

[Study on accumulation of polysaccharides and alcohol-soluble extracts contents of Dendrobium officinale leaves].

This paper revealed the accumulation regularity of polysaccharides and alcohol-soluble extracts contents of Dendrobium officinale leaves, which have provided basis for the development and utilization of the leaves. The polysaccharides and alcohol-soluble extracts contents of three D. officinale strains leaves collected in different growing periods were determined by phenol-sulfric acid method and hot-dip method respectively. The results showed that the content of polysaccharides in leaves was 4.45% -12.17%, and was about a quarter in stems. The alcohol-soluble extracts content in leaves was 7.45% - 29.34%, and was 1.5 times that of stems. The quality variation of polysaccharides in leaves was closely related to the phenophase. The leaves with lower level of metabolism in three stages: winter, early germination stage and deciduous period, which led to lower content of polysaccharides. The leaves at the vigorous growth stage with higher content of polysaccharides. The alcohol-soluble extracts were closely associated to the formation and germination of buds. The content of alcohol-soluble extracts peaked before sprout, and promoted the growth of new shoots.

Stabilization of human telomeric G-quadruplex and inhibition of telomerase activity by propeller-shaped trinuclear Pt(II) complexes.

Two novel propeller-shaped, trigeminal-ligand-containing, flexible trinuclear Pt(II) complexes, {[Pt(dien)]3(ptp)}(NO3)6 (1) and {[Pt(dpa)]3(ptp)}(NO3)6 (2) (dien: diethylenetriamine; dpa: bis-(2-pyridylmethyl)amine; ptp: 6'-(pyridin-3-yl)-3,2':4',3''-terpyridine), have been designed and synthesized, and their interactions with G-quadruplex (G4) sequences are characterized. A combination of biophysical and biochemical assays reveals that both Pt(II) complexes exhibit higher affinity for human telomeric (hTel) and c-myc promoter G4 sequences than duplex DNA. Complex 1 binds and stabilizes hTel G4 sequence more effectively than complex 2. Both complexes are found to induce and stabilize either antiparallel or parallel conformation of G4 structures. Molecular docking studies indicate that complex 1 binds into the large groove of the antiparallel hTel G4 structure (PDB ID: 143D) and complex 2 stacks onto the exposed G-quartet of the parallel hTel G4 structure (PDB ID: 1KF1). Telomeric repeat amplification protocol assays demonstrate that both complexes are good telomerase inhibitors, with IC50 values of (16.0±0.4) µM and (4.20±0.25) µM for 1 and 2, respectively. Collectively, the results suggest that these propeller-shaped flexible trinuclear Pt(II) complexes are effective and selective G4 binders and good telomerase inhibitors. This work provides valuable information for the interaction between multinuclear metal complexes with G4 DNA.

Cyclometalated iridium(III)-ß-carboline complexes as potent autophagy-inducing agents.

Two cyclometalated Ir(III)-ß-carboline complexes were identified as potent inducers of autophagic cell death. Autophagy induced by these complexes is ROS-mediated and caspase-independent.

V-shaped dinuclear Pt(II) complexes: selective interaction with human telomeric G-quadruplex and significant inhibition towards telomerase.

A quaternized trigeminal ligand, 4-[4,6-di(4-pyridyl)-1,3,5-(2-triazinyl)]-1-methylpyridine-1-ium hexafluorophosphate (dptmp·PF6), and two derivative V-shaped dinuclear Pt(II) complexes, {[Pt(dien)]2(dptmp)}(PF6)5 (1) and {[Pt(dpa)]2(dptmp)}(PF6)5 (2), were synthesized, characterized and applied to a series of biochemical studies. FRET and SPR analyses showed these compounds, especially Pt(II) complexes, bound more strongly to human telomeric (hTel) G-quadruplex than to promoters (such as c-myc and bcl2) or to the duplex DNA. PCR-stop assays revealed that the Pt(II) complexes could bind to and stabilize G-quadruplex far more effectively than corresponding ligand. CD analyses further indicated the three compounds likely stabilized the formation of mixed-type parallel/antiparallel G-quadruplex structures. Their efficacy as telomerase inhibitors and potential anticancer drugs was explored via TRAP. The IC50 value was determined to be 0.113 ± 0.019 µM for 1, indicating that it is one of the strongest known telomerase inhibitors. These results confirm that both V-shaped dinuclear Pt(II) complexes act as selective G-quadruplex binders and significant telomerase inhibitors.