ABSTRACT
Biochemical recognition processes mediated through pi-stacking interactions are a potential target for rational drug synthesis. A combination of electrostatic, hydrophobic, solvation, charge-transfer, induction, and dispersion interactions has been used to account for the three-dimensional arrangements observed in such motifs. A principal example involves the interaction of purine and pyrimidine rings of nucleic acids with aromatic amino-acid residues such as tryptophan, phenylalanine, and tyrosine. Protonation, alkylation, or coordination of a metal ion such as Pd(II) or Pt(II) to a nucleobase strengthens this interaction by lowering the energy of the lowest unoccupied molecular orbital (LUMO) of the modified nucleobase and improving overlap with the highest occupied molecular orbital (HOMO) in N-acetyl tryptophan. The relative energy difference between the frontier orbitals of isolated molecules, obtained using Density Functional Theory (DFT), is explored as a predictive tool for the strength of the pi-stacking interaction of the nucleobase/tryptophan pair. From the optimized structures of these species, evaluation of the donor-acceptor HOMO-LUMO gap (Deltaepsilon d-->a) suggests that this parameter is a promising predictor of pi-stacking strength for the donor-acceptor pairs presented in this study. The analysis correlates well with experimental association constants, measured by fluorescence spectroscopy, of metallated and alkylated nucleobases with tryptophan in comparison to free nucleobases.
Subject(s)
Cytosine/analogs & derivatives , Guanine/analogs & derivatives , Models, Chemical , Tryptophan/chemistry , Cytosine/chemistry , Guanine/chemistry , Models, Molecular , Organometallic Compounds , Organoplatinum Compounds/chemistry , Palladium/chemistry , Platinum/chemistry , Static Electricity , Thermodynamics , Tryptophan/analogs & derivativesABSTRACT
Noncovalent interactions are ubiquitous in ternary systems involving metal ions, DNA/RNA, and proteins and represent a structural motif for design of selective inhibitors of biological function. This contribution shows that small molecules containing platinated purine nucleobases mimic the natural DNA(RNA)-tryptophan recognition interaction of zinc finger peptides, specifically the C-terminal finger of HIV NCp7 protein. Interaction with platinum results in Zn ejection from the peptide accompanied by loss of tertiary structure. Targeting the NCp7-DNA interaction for drug design represents a conceptual advance over electrophiles designed for chemical attack on the zinc finger alone. These results demonstrate examples of a new platinum structural class targeting specific biological processes, distinct from the bifunctional DNA-DNA binding of cytotoxic agents like cisplatin. The results confirm the validity of a chemical biological approach for metallodrug design for selective ternary DNA(RNA)-protein interactions.
Subject(s)
DNA/metabolism , Zinc Fingers , Amino Acid Sequence , Capsid Proteins/metabolism , Drug Design , Gene Products, gag/metabolism , Nuclear Magnetic Resonance, Biomolecular , Platinum/metabolism , Protein Binding , Spectrometry, Fluorescence , Spectrometry, Mass, Electrospray Ionization , Viral Proteins/metabolism , gag Gene Products, Human Immunodeficiency VirusABSTRACT
BACKGROUND AND OBJECTIVE: The hypoxia PET tracer, 1-[18F]fluoro-3-(2-nitro-1Himidazol- 1-yl)-propan-2-ol ([18F]FMISO) is the first radiotracer developed for hypoxia PET imaging and has shown promising for cancer diagnosis and prognosis. However, access to [18F]FMISO radiotracer is limited due to the needed cyclotron and radiochemistry expertise. The study aimed to develop the automated production method on the [18F]FMISO radiotracer with the novel fully automated platform of the BG75 system and validate its usage on animal tumor models. METHOD: [18F]FMISO was produced with the dose synthesis cartridge automatically on the BG75 system. Validation of [18F]FMISO hypoxia imaging functionality was conducted on two tumor mouse models (FaDu/U87 tumor). The distribution of [18F]FMISO within tumor was further validated by the standard hypoxia marker EF5. RESULTS: The average radiochemical purity was (99±1) % and the average pH was 5.5±0.2 with other quality attributes passing standard criteria (n=12). Overall biodistribution for [18F]FMISO in both tumor models was consistent with reported studies where bladder and large intestines presented highest activity at 90 min post injection. High spatial correlation was found between [18F]FMISO autoradiography and EF5 hypoxia staining, indicating high hypoxia specificity of [18MF]FMISO. CONCLUSION: This study shows that qualified [18F]FMISO can be efficiently produced on the BG75 system in an automated "dose-on-demand" mode using single dose disposable cards. The possibilities of having a low-cost, automated system manufacturing ([18F]Fluoride production + synthesis + QC) different radiotracers will greatly enhance the potential for PET technology to reach new geographical areas and underserved patient populations.
Subject(s)
Carcinoma, Squamous Cell/diagnostic imaging , Glioblastoma/diagnostic imaging , Misonidazole/analogs & derivatives , Positron Emission Tomography Computed Tomography , Radiopharmaceuticals/chemical synthesis , Radiopharmaceuticals/pharmacology , Animals , Autoradiography , Cell Hypoxia , Cell Line, Tumor , Chromatography, High Pressure Liquid , Humans , Mice , Misonidazole/chemical synthesis , Misonidazole/pharmacology , Radiographic Image Interpretation, Computer-Assisted , Tissue DistributionABSTRACT
The interaction of the complexes [Pd(dien)(1-MeCyt)]2+ (2) and [Pd(dien)(9-EtGH)]2+ (3) with the amino acids L-tryptophan (Trp) and N-acetyltryptophan (N-AcTrp) was studied and compared with the previously studied platinum analogues [Pt(dien)(1-MeCyt)]2+ (4) and [Pt(dien)(9-EtGH)]2+ (5). Solid-state structures for 2 and 4 are reported. For the palladium complexes, the interaction is pH sensitive. Below pH 5, the noncovalent interaction with stacking between the aromatic amino acid residue and the metalated nucleobase was observed. Fluorescence quenching experiments indicated similar association constants for platinum and palladium derivatives 2-5. Unusual substitution of the model nucleobases 1-methylcytosine (1-MeCyt) and 9-ethylguanine (9-EtGH) by tryptophan was observed in the range of pH 5-11. The resulting species [Pd(dien)(Trp)]+ (6) and [Pd(dien)(N-AcTrp)]+ (7) were characterized using 1H NMR, 13C NMR, and ESI-MS spectroscopy with coordination indicated through the amino and deprotonated amido nitrogens, respectively. Complexes 6 and 7 were also obtained from a solution of [Pd(dien)Cl]+ (1) incubated with either Trp or N-AcTrp, respectively.
Subject(s)
Cytosine/chemistry , Palladium/chemistry , Tryptophan/chemistry , Crystallography, X-Ray , Models, Molecular , Nuclear Magnetic Resonance, Biomolecular , Spectrometry, FluorescenceABSTRACT
Fluorescence quenching experiments show that the stacking interaction between nucleic acid bases and l-tryptophan is enhanced significantly upon base coordination to a metal center such as Pt(II), and the biological implications of such enhancement are discussed.