[Influence of the Poly(ADP-Ribose) Polymerase 1 Level on the Status of Base Excision Repair in Human Cells]

Base excision repair (BER) is aimed at repair of damaged bases, which are the largest group of DNA lesions. The main steps of BER are recognition and removal of the aberrant base, cutting of the DNA sugar-phosphate backbone, gap processing (including dNMP insertion), and DNA ligation. The precise function of BER depends on the regulation of each step by regulatory/accessory proteins, the most important of which is poly(ADP-ribose) (PAR) polymerase 1 (PARP1). PARP1 plays an important role in DNA repair, maintenance of genome integrity, and regulation of mRNA stability and decay. PARP1 can therefore affect BER both at the level of BER proteins and at the level of their mRNAs. There is no systematic data on how the PARP1 content affects the activities of key BER proteins and the levels of their mRNAs in human cells. Whole-cell extracts and RNA preparations obtained from the parental HEK293T cell line and its derivative HEK293T/P1-KD cell line with reduced PARP1 expression (shPARP1-expressing cells, a PARP1 knockdown) were used to assess the levels of mRNAs coding for BER proteins: PARP1, PARP2, uracil DNA glycosylase (UNG2), AP endonuclease 1 (APE1), DNA polymerase β (POLβ), DNA ligase III (LIG3), and XRCC1. Catalytic activities of the enzymes were evaluated in parallel. No significant effect of the PARP1 content was observed for the mRNA levels of UNG2, APE1, POLβ, LIG3, and XRCC1. The amount of the PARP2 mRNA proved to be reduced two times in HEK293T/P1-KD cells. Activities of these enzymes in whole-cell extracts did not differ significantly between HEK293T and HEK293T/P1-KD cells. No significant change was observed in the efficiencies of the reactions catalyzed by UNG2, APE1, POLβ, and LIG3 in conditions of PAR synthesis. A DNA PARylation pattern did not dramatically change in a HEK293T/P1-KD cell extract with a reduced PARP1 content as compared with an extract of the parental HEK293T cell line.

[Effect of Usnic Acid-Derived Tyrosyl-DNA Phosphodiesterase 1 Inhibitor Used as Monotherapy or in Combination with Olaparib on Transplanted Tumors In Vivo]

Tyrosyl-DNA phosphodiesterase 1 (Tdp1) is a DNA repair enzyme that removes various adducts from the 3' end of DNA. Such adducts are formed by enzymes that introduce single-strand breaks in DNA during catalysis (for example, topoisomerase 1) and a number of anticancer drugs with different mechanisms of action. Poly(ADP-ribose) polymerase 1 (PARP1) is an enzyme that catalyzes posttranslational modification (PARylation) of various targets and thus controls many cell processes, including DNA repair. Tdp1 is a PARP1 target, and its PARylation attracts Tdp1 to the site of DNA damage. Olaparib is a PARP1 inhibitor used in clinical practice to treat homologous recombination-deficient tumors. Olaparib inhibits PARylation and, therefore, DNA repair. The Tdp1 inhibitor OL7-43 was used in combination with olaparib to increase the antitumor effect of the latter. Olaparib cytotoxicity was found to increase in the presence of OL7-43 in vitro. OL7-43 did not exert a sensitizing effect, but showed its own antitumor and antimetastatic effects in Lewis and Krebs-2 carcinoma models.

Influence of Tyrosyl-DNA Phosphodiesterase 1 Inhibitor on the Proapoptotic and Genotoxic Effects of Anticancer Agent Topotecan

To date, various strategies have been proposed to increase the efficiency of cancer therapy. It is known that the action of DNA repair system can determine the resistance of cancer cells to DNA-damaging chemotherapy and radiotherapy, and one of these ways to increase therapeutic efficiency is the search for inhibitors of enzymes of the DNA repair system. Inhibition of the DNA repair enzyme tyrosyl-DNA phosphodiesterase1 (Tdp1) leads to an increase in the effectiveness of the topoisomerase 1 (Top1) inhibitor, the anticancer drug topotecan. Covalent complexes Top1-DNA, which are normally short-lived and are not a threat to the cell, are stabilized under the influence of topotecan and lead to cell death. Tdp1 eliminates such stabilized complexes and thus weaken the effect of topotecan therapy. We have previously shown that the use of the usnic acid hydrazonothiazole derivative OL9-119 in combination with topotecan increased the antitumor and antimetastatic efficacy of the latter in a mouse model of Lewis lung carcinoma. In this work, it was shown that the combined use of topotecan and Tdp1 inhibitor, the hydrazonothiazole derivative of usnic acid OL9-119, leads to an increase in the DNA-damaging effect of topotecan which is used in the clinic for the treatment of cancer. The study of the proapoptotic effect of the compound OL9-119 showed that the compound itself does not induce apoptosis, but increases the proapoptotic effect of topotecan. The results of the study could be used to improve the effectiveness of anticancer therapy and/or to reduce the therapeutic dose of topotecan and, therefore, the severity of side effects.

[5'-Deoxyribose Phosphate Lyase Activity of Apurinic/Apyrimidinic Endonuclease 1]

One of the most common DNA lesions is the appearance of apurinic/apyrimidinic (AP-) sites. The main repair pathway for AP sites is initiated by apurinic/apyrimidinic endonuclease 1 (APE1). Upon hydrolysis of the phosphodiester bond by this enzyme, a one nucleotide gap flanked by 3'-hydroxyl and 5'-deoxyribose phosphate groups on the 5'-side of the AP site is formed. After hydrolysis of the AP site, APE1 remains associated with the product for some time. In the present work, the ability of APE1 to form a product of covalent attachment of APE1 to DNA containing a gap with a 5'-deoxyribose phosphate residue was demonstrated. In addition, it was found that while in a complex with the product of hydrolysis of the AP site, APE1 exhibits 5'-deoxyribose phosphate lyase activity, cleaving off the 5'-deoxyribose phosphate residue. The presence of lyase activity in APE1 may be important for the repair of AP sites if there is a deficiency of, or mutations in DNA polymerase β, the main enzyme that removes the 5'-deoxyribose phosphate group.

[Initiation of pharmacotherapy as a risk factor for older patients.]

The article presents the literature and original data on the problems of falls in elderly patients. The connection of the fact of falling with initiation of therapy by a number of drugs known to have a negative impact on the risk of falling is considered. The article presents data on the frequency and structure of falls on the example of patients with cardiovascular diseases older than 75 years, treated in a multidisciplinary hospital. The analysis of the data showed a tendency of prevalence of the fact of falling in 1/3 patients (33,8%) in the first 5 days of hospital stay, which may be associated with high drug burden and the appointment of «new» drugs for the patient. The study noted that it was on the first day that the selection of therapy took place and additional drugs were often prescribed, leading to a state of polypragmasia. Analysis of individual groups of drugs was able to reliably confirm the relationship between the appointment of drugs that increase.

Interaction of poly(ADP-ribose) polymerase 1 with apurinic/apyrimidinic sites within clustered DNA damage

To study the interaction of poly(ADP-ribose) polymerase 1 (PARP1) with apurinic/apyrimidinic sites (AP sites) within clustered damages, DNA duplexes were created that contained an AP site in one strand and one of its analogs situated opposite the AP site in the complementary strand. Residues of 3-hydroxy-2-hydroxymethyltetrahydrofuran (THF), diethylene glycol (DEG), and decane-1,10-diol (DD) were used. It is shown for the first time that apurinic/apyrimidinic endonuclease 1 (APE1) cleaves the DNA strands at the positions of DEG and DD residues, and this suggests these groups as AP site analogs. Insertion of DEG and DD residues opposite an AP site decreased the rate of AP site hydrolysis by APE1 similarly to the effect of the THF residue, which is a well-known analog of the AP site, and this allowed us to use such AP DNAs to imitate DNA with particular types of clustered damages. PARP1, isolated and in cell extracts, efficiently interacted with AP DNA with analogs of AP sites producing a Schiff base. PARP1 competes with APE1 upon interaction with AP DNAs, decreasing the level of its cross-linking with AP DNA, and inhibits hydrolysis of AP sites within AP DNAs containing DEG and THF residues. Using glutaraldehyde as a linking agent, APE1 is shown to considerably decrease the amount of AP DNA-bound PARP1 dimer, which is the catalytically active form of this enzyme. Autopoly(ADP-ribosyl)ation of PARP1 decreased its inhibitory effect. The possible involvement of PARP1 and its automodification in the regulation of AP site processing within particular clustered damages is discussed.