Effect of DNA Repair Deficiencies on the Cytotoxicity of Drugs Used in Cancer Therapy - A Review
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Tumor cells often have defects in DNA repair pathways that make them vulnerable to specific DNA-damaging anticancer agents. The identification of DNA repair defects in tumor cells and the evaluation of their influence on the cytotoxicity of anticancer drugs are active areas of scientific investigation that may help rationalize and improve cancer chemotherapy. This article reviews the available data on the influence of defects in proteins involved in the major DNA repair pathways (i.e., homologous recombination, non-homologous end joining, base excision repair, nucleotide excision repair, mismatch repair, Fanconi anemia repair, translesion synthesis and direct reversal repair) on the cytotoxicity of the FDAapproved anticancer drugs. It is shown that specific deficiencies in these DNA repair pathways alter the cytotoxicity of 60 anticancer drugs, including classical DNA-targeting drugs (e.g., alkylating agents, cytotoxic antibiotics, DNA topoisomerase inhibitors and antimetabolites) and other drugs whose primary pharmacological target is not the DNA (e.g., antimitotic agents, hormonal and targeted therapies). This information may help predict response to anticancer drugs in patients with tumors having specific DNA repair defects. Keywords: Anticancer, chemotherapy, DNA damage, DNA damage response.Cleavage (geology)
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Topoisomerase IV
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Fanconi anemia caused by mutations of the FANCA gene. FANCA gene mutations are the most common cause of Fanconi anemia. This gene provides instructions for making a protein that is involved in the Fanconi anemia (FA) pathway.
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The discovery of new topoisomerase I inhibitors is necessary since most of the antitumor drugs are targeted against type II and only a very few can specifically affect type I. Topoisomerase poisons generate toxic DNA damage by stabilization of the covalent DNA-topoisomerase cleavage complex and some have therapeutic efficacy in human cancer. Two iridoids, aucubin and geniposide, have shown antitumoral activities, but their activity against topoisomerase enzymes has not been tested. Here it was found that both compounds are able to stabilize covalent attachments of the topoisomerase I subunits to DNA at sites of DNA strand breaks, generating cleavage complexes intermediates so being active as poisons of topoisomerase I, but not topoisomerase II. This result points to DNA damage induced by topoisomerase I poisoning as one of the possible mechanisms by which these two iridoids have shown antitumoral activity, increasing interest in their possible use in cancer chemoprevention and therapy.
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MSH2
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Topoisomerase inhibitor
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Abstract Topoisomerases are nuclear enzymes that play essential roles in DNA replication, transcription, chromosome segregation, and recombination. All cells have two major forms of topoisomerases: the type I enzymes, which make single‐stranded cuts in DNA, and the type II enzymes, which cut and pass double‐stranded DNA. In this unit, an in vitro assay for topoisomerase I activity based on relaxation of supercoiled DNA by that enzyme is described. This is followed by an assay for topoisomerase II based on the decatenation of double‐stranded DNA. In conjunction with these assays, the preparation of mammalian cell extracts for assaying topoisomerase activity is described. Procedures are also detailed for the assay of topoisomerase covalent complexes in vivo and for measuring DNA cleavage caused by topoisomerase I and topoisomerase II in vitro. A related electrophoretic method for mapping topoisomerase II cleavage sites is finally included.
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There is significant evidence to suggest that protein kinase C and DNA topoisomerases are functionally linked in signal transduction pathways. Much of this is based on the observation that phosphorylation of topoisomerase II by protein kinase C may lead to its activation in vitro and that inhibitors of topoisomerase II block phorbol diester-induced differentiation in HL-60 cells. In the present study, the activities of the DNA topoisomerases I and II have been quantitated to examine their regulation in phorbol diester-treated HL-60 cells undergoing differentiation. The activity of topoisomerase I increased rapidly after treatment with phorbol myristate acetate (PMA); it increased maximally (150% of control activity) at 3 hr post-treatment and remained elevated for at least 24 hr. Conversely, from the onset of exposure to PMA through 12 hr, there was no measurable alteration in topoisomerase II activity in PMA-treated cells. Moreover, there was a measurable decrease in topoisomerase II activity at the later time points, a result that occurred concomitantly with the loss of proliferative potential in differentiating HL-60 cells. Similar results were obtained when the activities of both enzymes were measured in nuclear extracts. The apparent increase in topoisomerase I activity was not due to an increase in the mass of the enzyme after PMA treatment, as measured by both western blotting and by the formation of camptothecin-dependent, topoisomerase I-DNA complexes. Taken together, these data suggest that the activities of the topoisomerases I and II may have been regulated independently in PMA-treated HL-60 cells, that the activity of topoisomerase II was not increased under conditions in which protein kinase C was activated in vivo, and that an increase in the activity of topoisomerase I may have had a role in the mechanism through which HL-60 cells underwent monocytic maturation in response to phorbol diesters.
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