We report the synthesis, DNA-binding properties and antitumor activity of ThiaNetGA, a hybrid molecule in which are conjugated a thiazole-lexitropsin and an intercalating anilinoacridine chromophore. This combilexin molecule binds to DNA via a bimodal process involving minor groove binding of the lexitropsin moiety and intercalation of the acridine moiety. The uptake and distribution of the hybrid in L1210 leukemia cells were investigated by ESR spectroscopy using a spin-labeled derivative. The nitroxide-containing conjugate accumulates preferentially in the cell nuclei and rapidly saturates the nuclear receptor sites. Both in vitro and in vivo assays indicate that the drug is practically nontoxic but exhibits moderate antitumor activity against P388 leukemia cells in mice.

Acridines↗

PubMedDate not supplied

Synthesis, DNA binding, and cleaving properties of an ellipticine-salen.copper conjugate.

The synthesis of a DNA-cutting agent that conjugates an ellipticine chromophore and a copper complex of bis(salicylidene)ethylenediamine, referred to as a salen, is reported. The presence of the salen.Cu complex allows cleavage of DNA via oxygen-based radicals, and the ellipticine moiety serves as a DNA anchor. Spectroscopic measurements indicate that the intercalation geometry of the ellipticine chromophore is preserved with the hybrid. The cleavage is much more efficient with the conjugate than with the Schiff base copper complex alone.

Chelating Agents↗

PubMedDate not supplied

Sequence-recognition and cleavage of DNA by a netropsin-phenazine-di-N-oxide conjugate.

We report the synthesis, DNA-binding and cleaving properties, and cytotoxic activities of R-128, a hybrid molecule in which a bis-pyrrolecarboxamide-amidine element related to the antibiotic netropsin is covalently tethered to a phenazine-di-N-oxide chromophore. The affinity and mode of interaction of the conjugate with DNA were investigated by a combination of absorption spectroscopy, circular dichroism, and electric linear dichroism. This hybrid molecule binds to AT-rich sequences of DNA via a bimodal process involving minor groove binding of the netropsin moiety and intercalation of the phenazine moiety. The bidentate mode of binding was evidenced by linear dichroism using calf thymus DNA and poly(dA-dT).(dA-dT). In contrast, the drug fails to bind to poly(dG-dC).poly(dG-dC), because of the obstructive effect of the guanine 2-amino group exposed in the minor groove of this polynucleotide. DNase I footprinting studies indicated that the conjugate interacts preferentially with AT-rich sequences, but the cleavage of DNA in the presence of a reducing agent can occur at different sequences not restricted to the AT sites. The main cleavage sites were detected with a periodicity of about 10 base pairs corresponding to approximately one turn of the double helix. This suggests that the cleavage may be dictated by the structure of the double helix rather than the primary nucleotide sequence. The conjugate which is moderately toxic to cancer cells complements the tool box of reagents which can be utilized to produce DNA strand scission. The DNA cleaving properties of R-128 entreat further exploration into the use of phenazine-di-N-oxides as tools for investigating DNA structure.

Animals↗

PubMedDate not supplied

The plant alkaloid usambarensine intercalates into DNA and induces apoptosis in human HL60 leukemia cells.

Usambarensine is a plant alkaloid isolated from the roots of Strychnos usambarensis collected in Central Africa. This bis-indole compound displays potent antiamoebic activities and shows antigardial, antimalarial and cytotoxic effects. Usambarensine is highly toxic to B16 melanoma cells and inhibits the growth of leukemia and carcinoma cells. To date, the molecular basis for its diverse biological effects remains totally unknown. However, its capacity to inhibit nucleic acids synthesis in melanoma cells, on the one hand, and its structural analogy with DNA-binding pyridoindole plant alkaloids recently studied (cryptolepine and matadine), on the other hand, suggested that usambarensine could also bind to DNA. Consequently, we studied the strength and mode of binding to DNA of usambarensine by means of absorption, circular and linear dichroism. The results of the optical measurements indicate that the alkaloid effectively binds to DNA and behaves as a typical intercalating agent. Biochemical experiments indicated that, in contrast to cryptolepine and matadine, usambarensine does not interfere with the catalytic activity of topoisomerase II. Human HL60 leukemia cells were used to assess the cytotoxicity of the alkaloid and its effect on the cell cycle. Usambarensine treatment is associated with a loss of cells in the G1 phase accompanied with a large increase in the sub-G1 region which is characteristic of apoptotic cells. The DNA of usambarensine-treated cells was severely fragmented and the proteolytic activity of DEVD-caspases is enhanced. Usambarensine is thus characterized as DNA intercalator inducing apoptosis in leukemia cells.

Alkaloids↗

PubMedDate not supplied

DNA but not topoisomerases is a target for a cytotoxic benzo[5,6]cyclohepta[b]indol-6-one derivative.

The interaction of a newly designed benzocycloheptaindol-6-one derivative with DNA has been investigated by complementary spectroscopic techniques including absorption, circular and linear dichroism. Footprinting measurements were performed to delineate the sequence-selectivity of the drug-DNA interaction and a plasmid relaxation assay was used to study the effects of the drug on human DNA topoisomerases I and II. The results clearly indicated that the test compound behaves as a typical DNA intercalating agent but does not stimulate DNA cleavage by topoisomerases. At the cellular level, the cytometry measurements showed that the drug provoked a marked accumulation of HL60 human leukemia cells in the G2/M phase of the cell cycle. DNA is thus identified as a valid target for this new series of drugs particularly toxic to human (HL60) and murine (P388) leukemia cells.

Animals↗

PubMedDate not supplied

[HMG1 domains: the victims of circumstance].

The method of circular dichroism (CD) was used to compare DNA behavior during its interaction with linker histone H1 and with non-histone chromosomal protein HMG1 at different ionic strength and at different protein content in the system. The role of negatively charged C-terminal fragment of HMG1 was analyzed using recombinant protein HMG1-(A + B), which lacks the C terminal amino acid sequence. The psi-type CD spectra were common for DNA interaction with histone H1, but no spectra of this type were observed in HMG1-DNA systems even at high ionic strength. The CD spectrum of the truncated recombinant protein at high salt concentration somewhat resembled the psi-type spectrum. Two very intense positive bands were located near 215 nm and near 273 nm, and the whole CD spectrum was positive. The role of C-terminal tail of HMG1 in formation of the ordered DNA-protein complexes is discussed.

Amino Acid Sequence↗