4 research outputs found
Sequence-Specific Base Pair Mimics Are Efficient Topoisomerase IB Inhibitors
Topoisomerase IB controls DNA topology by cleaving DNA
transiently. This property is used by inhibitors, such as camptothecin,
that stabilize, by inhibiting the religation step, the cleavage complex,
in which the enzyme is covalently attached to the 3ā²-phosphate
of the cleaved DNA strand. These drugs are used in clinics as antitumor
agents. Because three-dimensional structural studies have shown that
camptothecin derivatives act as base pair mimics and intercalate between
two base pairs in the ternary DNAātopoisomeraseāinhibitor
complex, we hypothesized that base pairs mimics could act like campthotecin
and inhibit the religation reaction after the formation of the topoisomerase
IāDNA cleavage complex. We show here that three base pair mimics,
nucleobases analogues of the aminophenyl-thiazole family, once targeted
specifically to a DNA sequence were potent topoisomerase IB inhibitors.
The targeting was achieved through covalent linkage to a sequence-specific
DNA ligand, a triplex-forming oligonucleotide, and was necessary to
position and keep the nucleobase analogue in the cleavage complex.
In the absence of triplex formation, only a weak binding to the DNA
and topoisomerase I-mediated DNA cleavage was observed. The three
compounds were equally active once conjugated, implying that the intercalation
of the nucleobase upon triplex formation is the essential feature
for the inhibition activity
Identification of Novel Inhibitors of DNA Methylation by Screening of a Chemical Library
In order to discover new inhibitors of the DNA methyltransferase
3A/3L complex, we used a medium-throughput nonradioactive screen on
a random collection of 1120 small organic compounds. After a primary
hit detection against DNA methylation activity of the murine Dnmt3A/3L
catalytic complex, we further evaluated the EC<sub>50</sub> of the
12 most potent hits as well as their cytotoxicity on DU145 prostate
cancer cultured cells. Interestingly, most of the inhibitors showed
low micromolar activities and little cytotoxicity. Dichlone, a small
halogenated naphthoquinone, classically used as pesticide and fungicide,
showed the lowest EC<sub>50</sub> at 460 nM. We briefly assessed the
selectivity of a subset of our new inhibitors against hDNMT1 and bacterial
Dnmts, including M. SssI and EcoDam, and the protein lysine methyltransferase
PKMT G9a and the mode of inhibition. Globally, the tested molecules
showed a clear preference for the DNA methyltransferases, but poor
selectivity among them. Two molecules including Dichlone efficiently
reactivated YFP gene expression in a stable HEK293 cell line by promoter
demethylation. Their efficacy was comparable to the DNMT inhibitor
of reference 5-azacytidine
Synthesis and Evaluation of Analogues of <i>N</i>āPhthaloylālātryptophan (RG108) as Inhibitors of DNA Methyltransferase 1
DNA
methyltransferases (DNMT) are promising drug targets in cancer provided
that new, more specific, and chemically stable inhibitors are discovered.
Among the non-nucleoside DNMT inhibitors, <i>N</i>-phthaloyl-l-tryptophan <b>1</b> (RG108) was first identified as
inhibitor of DNMT1. Here, <b>1</b> analogues were synthesized
to understand its interaction with DNMT. The indole, carboxylate,
and phthalimide moieties were modified. Homologated and conformationally
constrained analogues were prepared. The latter were synthesized from
prolinoĀhomotryptophan derivatives through a methodology based
aminoāzincāeneāenolate cyclization. All compounds
were tested for their ability to inhibit DNMT1 in vitro. Among them,
constrained compounds <b>16</b>ā<b>18</b> and NPys
derivatives <b>10</b>ā<b>11</b> were found to be
at least 10-fold more potent
than the reference compound. The cytotoxicity on the tumor DU145 cell
line of the most potent inhibitors was correlated to their inhibitory
potency. Finally, docking studies were conducted in order to understand
their binding mode. This study provides insights for the design of
the next-generation of DNMT inhibitors
Rational Design of Bisubstrate-Type Analogues as Inhibitors of DNA Methyltransferases in Cancer Cells
Aberrant DNA hypermethylation
of promoter of tumor suppressor genes
is commonly observed in cancer, and its inhibition by small molecules
is promising for their reactivation. Here we designed bisubstrate
analogues-based inhibitors, by mimicking each substrate, the <i>S</i>-adenosyl-l-methionine and the deoxycytidine,
and linking them together. This approach resulted in quinazolineāquinoline
derivatives as potent inhibitors of DNMT3A and DNMT1, some showing
certain isoform selectivity. We highlighted the importance of (i)
the nature and rigidity of the linker between the two moieties for
inhibition, as (ii) the presence of the nitrogen on the quinoline
group, and (iii) of a hydrophobic group on the quinazoline. The most
potent inhibitors induced demethylation of <i>CDKN2A</i> promoter in colon carcinoma HCT116 cells and its reactivation after
7 days of treatment. Furthermore, in a leukemia cell model system,
we found a correlation between demethylation of the promoter induced
by the treatment, chromatin opening at the promoter, and the reactivation
of a reporter gene