Ru–TAP complexes and DNA: from photo-induced electron transfer to gene photo-silencing in living cells

Abstract

In this review, examples of applications of the photoinduced electron transfer (PET) process between photo-oxidizing Ru-TAP (TAP = 1,4,5,8-tetraazaphenanthrene) complexes and DNA or oligodeoxynucleotides (ODNs) are discussed. Applications using a free Ru-TAP complex (not chemically anchored to an ODN) are first considered. In this case, the PET gives rise to the production of an irreversible adduct of the Ru complex on a guanine (G) base, with formation of a covalent bond. After absorption of a second photon, this adduct can generate a bi-adduct, whereby the same complex binds to a second G moiety. These bi-adduct formations are responsible for photo-cross-linking between two strands of a duplex, each containing a G base, or between two G moieties of a single strand such as a telomeric sequence, as demonstrated by polyacrylamide gel electrophoresis analyses or mass spectrometry. Scanning force microscopy also allows the detection of such photobridgings with plasmid DNA. Other applications, for example with Ru-

Specificity of Light‐Induced Covalent Adduct Formation between RuII Oligonucleotide Conjugates and Target Sequences for Gene Silencing Applications

“…70 %), the yields of the interstrand adducts are diminished in the DS topology (40 and 13 %) relative to those of the three previous cases, as anticipated (Table 2, Entries 4–5 and Figure 5). With Ru‐5G6C, the yield of the interstrand adduct is especially low because the G position in the complementary strand corresponds to the longest distance or limit distance reachable by the linker 17,18. Interestingly, even with this lower yield of interstrand adduct, no intrastrand adduct is formed in the DS topology.…”

“…The photoreactivity of the first three Ru–ODNs (Table 1, Entries 1–3) was first tested. The common characteristic of these three sequences is the presence of three G bases at the 3‐, 4‐, and 6‐positions of the complementary target strand; the other G bases at the 8‐, 9‐, 12‐, 13‐, and 14‐positions of the target strand cannot be reached by the tethered complex in the double strand (DS) topology owing to the restricted length of the linker 17,18. The three probe sequences differ by their number of G bases; they have either no G bases (Ru‐0G) or one G base.…”

“…Among the photosensitized DNA reactions of the Ru II complexes, DNA oxidation by different mechanisms, either with the participation of oxygen (or oxidizing intermediate species)12,13 or by electron transfer, usually from DNA guanine (G) bases, has been widely studied 14,15. In this area, we have focused our interest on Ru II complex photosensitizers containing at least two π‐deficient ligands such as 1,4,5,8‐tetraazaphenanthrene (TAP) in the presence of DNA 16–18. It has been thoroughly demonstrated that these compounds can photoreact with DNA G bases through an electron transfer (ET) process from the G unit to the excited Ru II complex16 to produce two radical species, one centred on the complex and the other on the G base.…”

“…These two intermediates react together to form a covalent adduct of one TAP ligand with the G base after different reaction steps (Figure 1; the adenine unit remains unaffected because its reducing power is too low) 16,17,19. Under irradiation, Ru–ASOs (ASO = antisense oligonucleotide) or Ru–ODNs (ODN = oligonucleotide) containing such Ru–TAP complexes tethered to the probe sequences (Figure 2) can give rise to irreversible covalent cross‐linking between the two strands,16–18 which inhibits the enzymatic activity of polymerase and exonuclease with 100 % efficiency 16,17…”

An overview of photosubstitution reactions of Ru(II) imine complexes and their application in photobiology and photodynamic therapy

“…87,88 Other important PCT schemes, such as light-induced oxidation of DNA, photocrosslinking, and H-abstraction, are discussed elsewhere. 89–92 Additionally, photoinduced ligand exchange has been employed in the controlled release of neurotransmitters to study neuron activity. 93–98 …”