DNA-dependent DNA and RNA polymerases are important modulators of biological functions such as replication, transcription, recombination, or repair. In this work performed in cell-free media, we studied the ability of selected DNA polymerases to overcome a monofunctional adduct of the cytotoxic/antitumor platinum-acridinylthiourea conjugate [PtCl(en)(L)](NO3)2 (en = ethane-1,2-diamine, L = 1-[2-(acridin-9-ylamino)ethyl]-1,3-dimethylthiourea) (ACR) in its favored 5'-CG sequence. We focused on how a single site-specific ACR adduct with intercalation potency affects the processivity and fidelity of DNA-dependent DNA polymerases involved in translesion synthesis (TLS) and repair. The ability of the G(N7) hybrid ACR adduct formed in the 5'-TCGT sequence of a 24-mer DNA template to inhibit the synthesis of a complementary DNA strand by the exonuclease-deficient Klenow fragment of DNA polymerase I (KFexo-) and human polymerases eta, kappa, and iota was supplemented by thermodynamic analysis of the polymerization process. Thermodynamic parameters of a simulated translesion synthesis across the ACR adduct were obtained by using microscale thermophoresis (MST). Our results show a strong inhibitory effect of an ACR adduct on enzymatic TLS: there was only small synthesis of a full-length product (less than 10%) except polymerase eta (~20%). Polymerase eta was able to most efficiently bypass the ACR hybrid adduct. Incorporation of a correct dCMP opposite the modified G residue is preferred by all the four polymerases tested. On the other hand, the frequency of misinsertions increased. The relative efficiency of misinsertions is higher than that of matched cytidine monophosphate but still lower than for the nonmodified control duplex. Thermodynamic inspection of the simulated TLS revealed a significant stabilization of successively extended primer/template duplexes containing an ACR adduct. Moreover, no significant decrease of dissociation enthalpy change behind the position of the modification can contribute to the enzymatic TLS observed with the DNA-dependent, repair-involved polymerases. This TLS could lead to a higher tolerance of cancer cells to the ACR conjugate compared to its enhanced analog, where thiourea is replaced by an amidine group: [PtCl(en)(L)](NO3)2 (complex AMD, en = ethane-1,2-diamine, L = N-[2-(acridin-9-ylamino)ethyl]-N-methylpropionamidine).

• Keywords
• DNA polymerases, antitumor, cytotoxic, drug resistance, lesion bypass, metal–intercalator, microscale thermophoresis, platinum–acridine, thermodynamic, translesion synthesis,
• MeSH
• DNA Adducts chemistry   MeSH
• DNA-Directed DNA Polymerase metabolism   MeSH
• Intercalating Agents chemistry   MeSH
• Humans MeSH
• Urea analogs & derivatives   chemistry   MeSH
• DNA Repair * MeSH
• Organoplatinum Compounds chemistry   MeSH
• DNA Damage * MeSH
• DNA Replication MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• 1-(2-(acridin-9-ylamino)ethyl)-1,3-dimethylthiourea MeSH Browser
• DNA Adducts MeSH
• DNA-Directed DNA Polymerase MeSH
• Intercalating Agents MeSH
• Urea MeSH
• Organoplatinum Compounds MeSH

Translesion synthesis (TLS) through DNA adducts of antitumor platinum complexes has been an interesting aspect of DNA synthesis in cells treated with these metal-based drugs because of its correlation to drug sensitivity. We utilized model systems employing a DNA lesion derived from a site-specific monofunctional adduct formed by antitumor [PtCl(en)(L)](NO3)2 (complex AMD, en = ethane-1,2-diamine, L = N-[2-(acridin-9-ylamino)ethyl]-N-methylpropionamidine) at a unique G residue. The catalytic efficiency of TLS DNA polymerases, which differ in their processivity and fidelity for the insertion of correct dCTP, with respect to the other incorrect nucleotides, opposite the adduct of AMD, was investigated. For a deeper understanding of the factors that control the bypass of the site-specific adducts of AMD catalyzed by DNA polymerases, we also used microscale thermophoresis (MST) to measure the thermodynamic changes associated with TLS across a single, site-specific adduct formed in DNA by AMD. The relative catalytic efficiency of the investigated DNA polymerases for the insertion of correct dCTP, with respect to the other incorrect nucleotides, opposite the AMD adduct, was reduced. Nevertheless, incorporation of the correct C opposite the G modified by AMD of the template strand was promoted by an increasing thermodynamic stability of the resulting duplex. The reduced relative efficiency of the investigated DNA polymerases may be a consequence of the DNA intercalation of the acridine moiety of AMD and the size of the adduct. The products of the bypass of this monofunctional lesion produced by AMD and DNA polymerases also resulted from the misincorporation of dNTPs opposite the platinated G residues. The MST analysis suggested that thermodynamic factors may contribute to the forces that governed enhanced incorporation of the incorrect dNTPs by DNA polymerases.

• Keywords
• DNA polymerases, antitumor, microscale thermophoresis, platinum-acridine, translesion DNA synthesis,
• MeSH
• DNA Adducts chemistry   genetics   metabolism   MeSH
• Acridines chemistry   pharmacology   MeSH
• Biocatalysis MeSH
• DNA-Directed DNA Polymerase metabolism   MeSH
• DNA biosynthesis   MeSH
• Guanine metabolism   MeSH
• Catalysis MeSH
• Nucleotides genetics   metabolism   MeSH
• DNA Repair MeSH
• DNA Replication MeSH
• Platinum Compounds chemistry   pharmacology   MeSH
• Thermal Diffusion MeSH
• Thermodynamics MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• DNA Adducts MeSH
• Acridines MeSH
• DNA-Directed DNA Polymerase MeSH
• DNA MeSH
• Guanine MeSH
• Nucleotides MeSH
• Platinum Compounds MeSH

Oxidative stress in cells can lead to the accumulation of reactive oxygen species and oxidation of DNA precursors. Oxidized nucleotides such as 2'-deoxyribo-5-hydroxyuridin (HdU) and 2'-deoxyribo-5-hydroxymethyluridin (HMdU) can be inserted into DNA during replication and repair. HdU and HMdU have attracted particular interest because they have different effects on damaged-DNA processing enzymes that control the downstream effects of the lesions. Herein, we studied the chemically simulated translesion DNA synthesis (TLS) across the lesions formed by HdU or HMdU using microscale thermophoresis (MST). The thermodynamic changes associated with replication across HdU or HMdU show that the HdU paired with the mismatched deoxyribonucleoside triphosphates disturbs DNA duplexes considerably less than thymidine (dT) or HMdU. Moreover, we also demonstrate that TLS by DNA polymerases across the lesion derived from HdU was markedly less extensive and potentially more mutagenic than that across the lesion formed by HMdU. Thus, DNA polymerization by DNA polymerase η (polη), the exonuclease-deficient Klenow fragment of DNA polymerase I (KF-), and reverse transcriptase from human immunodeficiency virus type 1 (HIV-1 RT) across these pyrimidine lesions correlated with the different stabilization effects of the HdU and HMdU in DNA duplexes revealed by MST. The equilibrium thermodynamic data obtained by MST can explain the influence of the thermodynamic alterations on the ability of DNA polymerases to bypass lesions induced by oxidative products of pyrimidines. The results also highlighted the usefulness of MST in evaluating the impact of oxidative products of pyrimidines on the processing of these lesions by damaged DNA processing enzymes.

• Keywords
• 2’-deoxyribo-5-hydroxymethyl- uridin, 2’-deoxyribo-5-hydroxyuridin, DNA polymerases, microscale thermophoresis, oxidized nucleotides, translesion DNA synthesis,
• MeSH
• DNA-Directed DNA Polymerase metabolism   MeSH
• DNA biosynthesis   drug effects   MeSH
• HIV-1 MeSH
• Humans MeSH
• Mutagens chemistry   metabolism   pharmacology   MeSH
• DNA Repair MeSH
• Oxidation-Reduction MeSH
• Oxidative Stress * MeSH
• Pentoxyl analogs & derivatives   chemistry   metabolism   pharmacology   MeSH
• DNA Damage MeSH
• Pyrimidines chemistry   metabolism   pharmacology   MeSH
• DNA Replication drug effects   MeSH
• Thermodynamics MeSH
• Uracil analogs & derivatives   chemistry   metabolism   pharmacology   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• 5-hydroxymethyluracil MeSH Browser
• 5-hydroxyuracil MeSH Browser
• DNA-Directed DNA Polymerase MeSH
• DNA MeSH
• Mutagens MeSH
• Pentoxyl MeSH
• Pyrimidines MeSH
• Rad30 protein MeSH Browser
• Uracil MeSH

Carboplatin, an analogue of "classical" cis-diamminedichloridoplatinum(II) (cisplatin), is a widely used second-generation platinum anticancer drug. Cytotoxicity of cisplatin and carboplatin is mediated by platinum-DNA adducts. Markedly higher concentrations of carboplatin are required, and the rate of adduct formation is considerably slower. The reduced toxic effects in tumor cells and a more acceptable side-effect profile are attributable to the lower reactivity of carboplatin with nucleophiles, since the cyclobutanedicarboxylate ligand is a poorer leaving group than the chlorides in cisplatin. Recently, platinum complexes were shown to be particularly attractive as potential photochemotherapeutic anticancer agents. Selective photoactivation of platinum complexes by irradiation of cancer cells may avoid enhancement of toxic side-effects, but may increase toxicity selectively in cancer cells and extend the application of photoactivatable platinum complexes to resistant cells and to a wider range of cancer types. Therefore, it was of interest to examine whether carboplatin can be affected by irradiation with light to the extent that its DNA binding and cytotoxic properties are altered. We have found that carboplatin is converted to species capable of enhanced DNA binding by UVA irradiation and consequently its toxicity in cancer cells is markedly enhanced. Recent advances in laser and fiber-optic technologies make it possible to irradiate also internal organs with light of highly defined intensity and wavelength. Thus, carboplatin is a candidate for use in photoactivated cancer chemotherapy.

• MeSH
• DNA chemistry   drug effects   MeSH
• Photochemical Processes radiation effects   MeSH
• Carboplatin chemistry   pharmacology   radiation effects   toxicity   MeSH
• Kinetics MeSH
• Humans MeSH
• Tumor Cells, Cultured MeSH
• Plasmids MeSH
• DNA Damage drug effects   MeSH
• Cell Proliferation drug effects   MeSH
• Antineoplastic Agents chemistry   pharmacology   radiation effects   toxicity   MeSH
• Drug Screening Assays, Antitumor MeSH
• Cattle MeSH
• Ultraviolet Rays MeSH
• Binding Sites drug effects   MeSH
• Cell Survival drug effects   MeSH
• Dose-Response Relationship, Drug MeSH
• Structure-Activity Relationship MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Cattle MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA MeSH
• Carboplatin MeSH
• Antineoplastic Agents MeSH

The trinuclear BBR3464 ([{trans-PtCl(NH(3))(2)}(2)µ-(trans-Pt(NH(3))(2)(H(2)N(CH(2))(6)NH(2))(2))](4+)) belongs to the polynuclear class of platinum-based anticancer agents. DNA adducts of this complex differ significantly in structure and type from those of clinically used mononuclear platinum complexes, especially, long-range (Pt, Pt) intrastrand and interstrand cross-links are formed in both 5'-5' and 3'-3' orientations. We show employing short oligonucleotide duplexes containing single, site-specific cross-links of BBR3464 and gel electrophoresis that in contrast to major DNA adducts of clinically used platinum complexes, under physiological conditions the coordination bonds between platinum and N7 of G residues involved in the cross-links of BBR3464 can be cleaved. This cleavage may lead to the linkage isomerization reactions between this metallodrug and double-helical DNA. Differential scanning calorimetry of duplexes containing single, site-specific cross-links of BBR3464 reveals that one of the driving forces that leads to the lability of DNA cross-links of this metallodrug is a difference between the thermodynamic destabilization induced by the cross-link and by the adduct into which it could isomerize. The rearrangements may proceed in the way that cross-links originally formed in one strand of DNA can spontaneously translocate from one DNA strand to its complementary counterpart, which may evoke walking of the platinum complex on DNA molecule.

• MeSH
• DNA Adducts chemistry   MeSH
• Calorimetry, Differential Scanning MeSH
• DNA chemistry   MeSH
• Organoplatinum Compounds chemistry   MeSH
• Antineoplastic Agents chemistry   MeSH
• Cross-Linking Reagents chemistry   MeSH
• Thermodynamics MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA Adducts MeSH
• BBR 3464 MeSH Browser
• DNA MeSH
• Organoplatinum Compounds MeSH
• Antineoplastic Agents MeSH
• Cross-Linking Reagents MeSH