Haijia Yu

Chiral metallo-supramolecular complexes selectively recognize human telomeric G-quadruplex DNA

Here, we report the first example that one enantiomer of a supramolecular cylinder can selectively stabilize human telomeric G-quadruplex DNA. The P-enantiomer of this cylinder has a strong preference for G-quadruplex over duplex DNA and, in the presence of sodium, can convert G-quadruplexes from an antiparallel to a hybrid structure. The compounds chiral selectivity and its ability to discriminate quadruplex DNA have been studied by DNA melting, circular dichroism, gel electrophoresis, fluorescence spectroscopy and S1 nuclease cleavage. The chiral supramolecular complex has both small molecular chemical features and the large size of a zinc-finger-like DNA-binding motif. The complex is also convenient to synthesize and separate enantiomers. These results provide new insights into the development of chiral anticancer agents for targeting G-quadruplex DNA.

DNA Loop Sequence as the Determinant for Chiral Supramolecular Compound G-Quadruplex Selectivity

It is important to develop G-quadruplex binding agents that can discriminate between different quadruplexes. Recently we reported the first example that a chiral supramolecular complex can selectively stabilize human telomeric G-quadruplex among different G-quadruplex and duplex DNA, and the two enantiomers show different inhibition effect on telomerase activity. Here, we report that DNA loop sequence can be determinant for this chiral complex G-quadruplex selectivity. Adenine in the diagonal loop plays an important role in G-quadruplex hybrid structural transition, thus, it strongly influences the chiral complex induced DNA structural transition. The complexs preference for human telomeric DNA and its chiral selectivity prompted us to investigate whether the two enantiomers, M and P, can show different effects on cancer cells. The P enantiomers chiral selectivity has been demonstrated in cancer cells by telomere shortening, beta-galactosidase activity, and up-regulation of cyclin-dependent kinase inhibitors p16 and p21.

Metallosupramolecular complex targeting an α/β discordant stretch of amyloid β peptide

The accumulation of amyloid β-peptide (Aβ) is one of the pathological hallmarks of Alzheimers disease (AD). Developing Aβ amyloid inhibitors has received much attention. Most reported Aβ inhibitors are small organic molecules or peptides. Here we use a cell-based novel Aβ–enhanced cyan fluorescent protein (ECFP) fluorescent fusion inhibitor screen system, biochemical and biophysical approaches and in vivo studies to identify two zinc-finger-like triple-helical metallo-supramolecular cylinders, [Ni2L3]4+ and [Fe2L3]4+, that can strongly inhibit Alzheimers disease β-amyloid aggregation. Further studies indicate that the two metallo-supramolecular cylinders are specifically targeting the α/β-discordant stretch and reducing Aβ cytotoxicity. In vivo studies demonstrate that these complexes can ameliorate spatial memory deficits in a transgenic mouse model and decrease the insoluble Aβ level. This is the first demonstration that zinc-finger-like metallo-supramolecular cylinders can be Aβ aggregation inhibitors that specifically target an α/β-discordant stretch. Our work will prompt design and screening of metallo-supramolecular complexes as potential therapeutic agents for AD.

Different Hydration Changes Accompanying Copper and Zinc Binding to Amyloid β-Peptide: Water Contribution to Metal Binding

The pathological hallmark of Alzheimer’s disease (AD) is the ACHTUNGTRENNUNGaccumulation of extracellular amyloid plaques. The primary component of the plaques, amyloid b-peptide (Ab) is a metalloprotein. Both copper and zinc can bind to Ab and the levels of copper and zinc in the amyloid plaques are heavily increased and considered related to Ab toxicity. 4] Recent NMR and EPR studies on the fulllength Ab have suggested that copper and zinc binding to Ab cause deprotonation. Theoretical calculations also show that copper binding results in release of water. Therefore, it is important for deciphering the role of metal ions in AD to uncover the hydration changes upon metal binding to Ab. However, to our knowledge, there is no report to show how hydration changes occur upon copper and zinc binding to Ab. Herein we report that both copper and zinc binding to Ab cause dehydration and their hydration changes were different as studied by the osmotic stress method. Zinc binding causes water molecules to be released more than twice as much as copper binding and leads to even more destabilised and aggregation prone Ab than following copper binding. The osmotic stress method has been widely used as a direct in vitro probe to quantify hydration changes accompanying drug binding to DNA, Ca binding to protein, and DNA–protein interactions. We and others have shown that hydration changes are related to drug properties. In the present study, we choose three commonly used osmolytes— sucrose, betaine, and triethylene glycol—whose size and physicochemical properties differ. Fluorescence titrations were used to calculate the binding constants according to a 1:1 model. The sample was excited at 278 nm and the fluorescence emission spectrum was recorded. Typical data for Cu and Zn binding to Ab in the absence or presence of an osmolyte (betaine) are shown in Figure 1A and B. From the preliminary data, the apparent binding constants can be esti-

Hydration of drug-DNA complexes: greater water uptake for adriamycin compared to daunomycin.

Water is an integral part of DNA, and the conserved water molecules at the binding sites can modulate drug binding to DNA or protein. We report here that anthracycline antitumor antibiotics, adriamycin (AM) and daunomycin (DM), binding to DNA is accompanied by different hydration changes, with AM binding resulting in the uptake of about twice as many water molecules as DM. These results indicate that water is playing an important role in drug binding to DNA.

PolydA and polyrA self-structured by a europium and amino acid complex.

Different DNA selectivity was found for the newly synthesized europium–l‐valine complex. Unexpected DNA and RNA selection results showed that europium–l‐valine complex can cause single‐stranded polydA and polyrA to self‐structure. The sigmoidal melting curve profiles indicate the transition is cooperative, similar to the cooperative melting of a duplex DNA. This is different from another europium amino acid complex, europium–l‐aspartic acid complex which can induce B‐Z transition under the low salt condition. To our knowledge, there is no report to show that a metal–amino acid complex can cause the self‐structuring of single‐stranded DNA and RNA.