Tyrosyl-DNA Phosphodiesterase I a critical survival factor for neuronal development and homeostasis

Transcriptomic analysis of HEK293A cells with a CRISPR/Cas9-mediated TDP1 knockout

Tyrosyl-DNA phosphodiesterase 1 (TDP1) is a human DNA repair protein. It is a member of the phospholipase D family based on structural similarity. TDP1 is a key enzyme of the repair of stalled topoisomerase 1 (TOP1)-DNA complexes. Previously, with the CRISPR/Cas9 method, we obtained HEK293A cells with a homozygous knockout of the TDP1 gene and used the TDP1 knockout cells as a cellular model for studying mechanisms of action of an anticancer therapy. In the present work, we hypothesized that the TDP1 knockout would alter the expression of DNA repair-related genes. By transcriptomic analysis, we investigated for the first time the effect of the TDP1 gene knockout on genes' expression changes in the human HEK293A cell line. We obtained original data implying a role of TDP1 in other processes besides the repair of the DNA-TOP1 complex. Differentially expressed gene analysis revealed that TDP1 may participate in cell adhesion and communication, spermatogenesis, mitochondrial function, neurodegeneration, a cytokine response, and the MAPK signaling pathway.

Human Tyrosyl-DNA Phosphodiesterase 1 Possesses Transphosphooligonucleotidation Activity With Primary Alcohols

Human tyrosyl-DNA phosphodiesterase 1 (TDP1) belongs to the phospholipase D superfamily, whose members contain paired catalytic histidine and lysine residues within two conserved motifs and hydrolyze phosphodiester bonds. TDP1 is a DNA repair enzyme that processes 3′ DNA end blocking lesions and a wide range of synthetic DNA adducts as a substrate. TDP1 hydrolyzes DNA-adducts via two coordinated S_N2 nucleophilic attacks mediated by the action of two histidine residues and leads to the formation of the covalent intermediate. Hydrolysis of this intermediate is proposed to be carried out by a water molecule that is activated by the His493 residue acting as a general base. It was known that phospholipase D enzymes are able to catalyze not only hydrolysis but also a transphosphatidylation reaction in the presence of primary alcohols in which they transfer the substrate to the alcohol instead of water. Here, we first demonstrated that TDP1 is able to undergo a “transphosphooligonucleotidation” reaction, transferring the substrate residue to the alcohol, thus inducing the formation of covalent DNA adducts with different primary alcohol residues. Such adducts can be accumulated in the conditions of high concentration of alcohol. We demonstrated that glycerol residue was efficiently cleaved from the 3′-end by TDP1 but not by its mutant form associated with the disease spinocerebellar ataxia with axonal neuropathy. Therefore, the second reaction step can be carried out not only by a water molecule but also by the other small nucleophilic molecules, e.g., glycerol and ethanol. Thus, in some cases, TDP1 can be regarded not only as a repair enzyme but also as a source of DNA damage especially in the case of mutation. Such damages can make a negative contribution to the stability of cell vitality.

Design and Synthesis of Chlorinated and Fluorinated 7-Azaindenoisoquinolines as Potent Cytotoxic Anticancer Agents That Inhibit Topoisomerase I

The 7-azaindenoisoquinolines are cytotoxic topoisomerase I (Top1) inhibitors. Previously reported representatives bear a 3-nitro group. The present report documents the replacement of the potentially genotoxic 3-nitro group by 3-chloro and 3-fluoro substituents, resulting in compounds with high Top1 inhibitory activities and potent cytotoxicities in human cancer cell cultures and reduced lethality in an animal model. Some of the new Top1 inhibitors also possess moderate inhibitory activities against tyrosyl-DNA phosphodiesterase 1 (TDP1) and tyrosyl-DNA phosphodiesterase 2 (TDP2), two enzymes that are involved in DNA damage repair resulting from Top1 inhibitors, and they produce significantly more DNA damage in cancer cells than in normal cells. Eighteen of the new compounds had cytotoxicity mean-graph midpoint (MGM) GI50 values in the submicromolar (0.033-0.630 μM) range. Compounds 16b and 17b are the most potent in human cancer cell cultures with MGM GI50 values of 0.063 and 0.033 μM, respectively. Possible binding modes to Top1 and TDP1were investigated by molecular modeling.