Tyrosyl-DNA phosphodiesterase 1 (TDP1) is a human DNA repair protein. It is a member of the phospholipase D family based on the structure similarity. TDP1 is a key enzyme involved in repairing stalled topoisomerase 1 (TOP1)-DNA complexes. Previously we obtained with the CRISPR/Cas9 method HEK293A cells with the homozygous knockout of the Tdp1 gene and used knockout cells as a cellular model for studying the mechanisms of anticancer therapy. In this work we studied for the first time by transcriptomic analysis the effect of Tdp1 gene knockout on genes expression changes in human HEK293A cell line. We received original data that may indicate a role of TDP1 in other process besides repair of DNA-TOP1 complex. The differentially expressed genes (DEGs) analysis revealed that TDP1 could be involved in different processes such as cell adhesion and communication, spermatogenesis, mitochondrial function, neurodegeneration, cytokine response, and MAPK pathway signaling.

Tdp1 and Tdp2 are DNA repair enzymes that repair DNA damages caused by various agents, including anticancer drugs. Thus, these enzymes resist anticancer therapy and could be the reasons of resistance to such widely used drugs as topotecan and etoposide. In the present work, we found compounds capable of inhibiting both enzymes among derivatives of (-)-usnic acid. Both (+)- and (-)-enantiomers of compounds act equally effectively against Tdp1, and only (-)-enantiomers inhibited Tdp2. Surprisingly, the compounds protect HEK293FT wild type cells from the cytotoxic effect of etoposide but potentiate it against Tdp2 knockout cells. We assume that the sensitizing effect of the compounds in the absence of Tdp2 is associated with effective inhibition of Tdp1, which could take over the functions of Tdp2.

Tyrosyl-DNA phosphodiesterase 1 (Tdp1) is an important DNA repair enzyme and one of the causes of tumor resistance to topoisomerase 1 inhibitors such as topotecan. Inhibitors of this Tdp1 in combination with topotecan may improve the effectiveness of therapy. In this work, we synthesized usnic acid derivatives, which are hybrids of its known derivatives - tumor sensitizers to topotecan. New compounds inhibit Tdp1 in the micromolar and submicromolar concentration range; some of them enhance the effect of topotecan on the metabolic activity of cells of various lines according to the MTT test. One of the new compounds (compound 7) not only sensitizes Krebs-2 and Lewis carcinomas of mice to the action of topotecan, but also normalizes the state of the peripheral blood of mice, which is disturbed in the presence of a tumor. Thus, the synthesized substances may be the prototype of a new class of additional therapy for cancer.