Protein degradation with photoactivated enediyne-amino acid conjugates

2-Naphthol Moiety of Neocarzinostatin Chromophore as a Novel Protein-Photodegrading Agent and Its Application as a H2 O2 -Activatable Photosensitizer

A 2-naphthol derivative 2 corresponding to the aromatic ring moiety of neocarzinostatin chromophore was found to degrade proteins under photo-irradiation with long-wavelength UV light without any additives under neutral conditions. Structure-activity relationship studies of the derivative revealed that methylation of the hydroxyl group at the C2 position of 2 significantly suppressed its photodegradation ability. Furthermore, a purpose-designed synthetic tumor-related biomarker, a H₂ O₂ -activatable photosensitizer 8 possessing a H₂ O₂ -responsive arylboronic ester moiety conjugated to the hydroxyl group at the C2 position of 2, showed significantly lower photodegradation ability compared to 2. However, release of the 2 from 8 by reaction with H₂ O₂ regenerated the photodegradation ability. Compound 8 exhibited selective photo-cytotoxicity against high H₂ O₂ -expressing cancer cells upon irradiation with long-wavelength UV light.

Target-protein-selective inactivation and labelling using an oxidative catalyst

Reactive oxygen species (ROS) and radical species generated by oxidative single-electron transfer (SET) catalysts induce local environmental oxidative reactions, resulting in protein inactivation and labelling in proximity to the catalysts.

Enediyne-based protein capture agents: demonstration of an enediyne moiety acting as a photoaffinity label

Two enediyne based protein-capture compounds 1 and 2 were synthesized.

Opening Enediyne Scissors Wider: pH-Dependent DNA Photocleavage by meta-Diyne Lysine Conjugates

Photochemical activation of meta-diynes incapable of Bergman and C1-C5 cyclizations still leads to efficient double-strand DNA cleavage. Spatial proximity of the two arylethynyl groups is not required for efficient DNA photocleavage by the enediyne-lysine conjugates. Efficiency of the cleavage is a function of the external pH and DNA damage is strongly enhanced at pH < 7. The pH-dependence of the DNA photocleavage activity stems from the protonation states of lysine amino groups, the internal electron donors responsible for intramolecular PET quenching and deactivation of the photoreactive excited states. DNA-binding analysis suggests intercalative DNA binding for phenyl substituted conjugate and groove binding for TFP-substituted conjugate. Additional insights in the possible mechanism for DNA damage from the ROS (Reactive Oxygen Species) scavenger experiments found that generation of singlet oxygen is partially involved in the DNA damage.

Target-selective degradation of proteins and oligosaccharides by light-activated hybrid molecules for molecular-targeted photodynamic therapy

Proteins and oligosaccharides are key players in many biological events. The development of novel methods for the selective degradation of targeted proteins and oligosaccharides has attracted much attention in the fields of chemistry, biology and medicine. Target-selective degradations of proteins, such as estrogen receptor-α androgen receptor and HIV-1 protease, by light-activated 2-phenylquinoline-steroid hormone hybrids, porphyrin derivatives and fullerene-sugar hybrids, and target-selective degradation of oligosaccharides, such as a T-antigen disaccharide, by a light-activated anthraquinone-lectin hybrid have been achieved. This novel class of light-activated and molecular-targeted molecules, namely molecular-targeted photosensitizers, promise bright prospects for finding not only molecular-targeted bioprobes for future application in the life sciences but also molecular-targeted drugs for future photodynamic therapy.

C-lysine conjugates: pH-controlled light-activated reagents for efficient double-stranded DNA cleavage with implications for cancer therapy

Double-stranded DNA cleavage of light-activated lysine conjugates is strongly enhanced at the slightly acidic pH (<7) suitable for selective targeting of cancer cells. This enhancement stems from the presence of two amino groups of different basicities. The first amino group plays an auxiliary role by enhancing solubility and affinity to DNA, whereas the second amino group, which is positioned next to the light-activated DNA cleaver, undergoes protonation at the desired pH threshold. This protonation results in two synergetic effects which account for the increased DNA-cleaving ability at the lower pH. First, lysine conjugates show tighter binding to DNA at the lower pH, which is consistent with the anticipated higher degree of interaction between two positively charged ammonium groups with the negatively charged phosphate backbone of DNA. Second, the unproductive pathway which quenches the excited state of the photocleaver through intramolecular electron transfer is eliminated once the donor amino group next to the chromophore is protonated. Experiments in the presence of traps for diffusing radicals show that reactive oxygen species do not contribute significantly to the mechanism of DNA cleavage at the lower pH, which is indicative of tighter binding to DNA under these conditions. This feature is valuable not only because many solid tumors are hypoxic but also because cleavage which does not depend on diffusing species is more localized and efficient. Sequence-selectivity experiments suggest combination of PET and base alkylation as the chemical basis for the observed DNA damage. The utility of these molecules for phototherapy of cancer is confirmed by the drastic increase in toxicity of five conjugates against cancer cell lines upon photoactivation.

Photochemical generation and reversible cycloaromatization of a nine-membered ring cyclic enediyne

Irradiation of the nine-membered ring enediyne precursor, which has one of its triple bonds masked as cyclopropenone, efficiently (Phi = 0.34) generates the reactive 4,5-benzocyclonona-2,6-diynol. The latter rapidly equilibrates with the corresponding 1,4-didehydronaphthalene diradical and then undergoes rate-limiting hydrogen abstraction to produce the ultimate product of the Bergman cyclization, benz[f]indanol.

Triggering of the Bergman cyclization by photochemical ring contraction. Facile cycloaromatization of benzannulated cyclodeca-3,7-diene-1,5-diynes

Eleven-membered ring enediyne 1 , which incorporates α-diazo-β-diketone moiety, undergoes efficient light-induced ring contraction to produce two isomeric ten-membered ring enediyne compounds. The latter undergo spontaneous facile Bergman cyclization at or below room temperature. In the photochemical or thermal Wolff rearrangement of 1 the alkyl substituent migrates ca. 2 times faster than the alkynyl group.

Two-photon photochemical generation of reactive enediyne

p-Quinoid cyclopropenone-containing enediyne precursor (1) has been synthesized by monocyclopropanation of one of the triple bonds in p-dimethoxy-substituted 3,4-benzocyclodeca-1,5-diyne followed by oxidative demethylation. Cyclopropenone 1 is stable up to 90 degrees C but readily produces reactive enediyne 2 upon single-photon (Phi(300)(nm) = 0.46) or two-photon (sigma(800 nm) = 0.5 GM) photolysis. The photoproduct 2 undergoes Bergman cyclization at 40 degrees C with the lifetime of 88 h.

Synthesis and Protein Degradation Capacity of Photoactivated Enediynes

[structure: see text] The viability of proteins as targets of thermally and photoactivated enediynes has been confirmed at the molecular level. Model studies using a labeled substrate confirmed the efficacy of atom transfer from diyl radicals produced from enediynes to form captodatively stabilized carbon centered aminoacyl radicals, which then undergo either fragmentation or dimerization. To exploit this finding, a family of enediynes was developed using an intramolecular coupling strategy. Derivatives were prepared and used to target specific proteins, showing good correlation between affinity and photoinduced protein degrading activity. The findings have potential applications in the design of artificial chemical proteases and add to our understanding of the mechanism of action of the clinically important enediyne antitumor antibiotics.

The synthesis and evaluation of 10- and 12-membered ring benzofused enediyne amino acids

The enediyne moiety is a versatile functional group found in natural anticancer and anti-infective agents, undergoing the Bergman cyclization reaction to afford a diradical which cleaves double-stranded DNA. We have incorporated the enediyne group into 10- (4-10) and 12-membered ring (11) cyclic amino acids and dipeptides, respectively, and explored their relative reactivity toward cyclization, varying N-substitution in the case of the 10-membered ring substrate, which gave the expected cyclization products in good yields when using either thermal conditions in the presence or absence of microwave irradiation. The N-tosyl substituted derivative (4) was shown to nick double-stranded supercoiled DNA. N-Arylsulfonyl substitution on the ring promoted the cyclization, when compared to N-mesyl or acyl substitution, possibly because of a pi-pi stacking effect as an endo-relationship of the aryl group with the enediyne was demonstrated in both the solid state and in solution. The 12-membered ring enediyne dipeptide (11) was inert to the Bergman cyclization under a variety of conditions. When this substrate was irradiated with ultraviolet light, regio- and stereospecific reduction was observed in which one of the alkynes was reduced to a Z-olefin (47).

Anthraquinone derivatives as a new family of protein photocleavers

Certain anthraquinones, which are present in many biologically important natural products, effectively and randomly cleaved proteins (BSA or Lyso) during photoirradiation using a long wavelength UV light without any further additives. It was also found that this ability could be improved by the attachment of a suitable substituent into the anthraquinone core skeleton.

Resistance to enediyne antitumor antibiotics by CalC self-sacrifice

Antibiotic self-resistance mechanisms, which include drug elimination, drug modification, target modification, and drug sequestration, contribute substantially to the growing problem of antibiotic resistance among pathogenic bacteria. Enediynes are among the most potent naturally occurring antibiotics, yet the mechanism of resistance to these toxins has remained a mystery. We characterize an enediyne self-resistance protein that reveals a self-sacrificing paradigm for resistance to highly reactive antibiotics, and thus another opportunity for nonpathogenic or pathogenic bacteria to evade extremely potent small molecules.