DNA topoisomerase II inhibitors are a major class of cancer chemotherapeutics, which are thought to eliminate cancer cells by inducing DNA double-strand breaks. Here we identify a novel activity for the anthracycline class of DNA topoisomerase II inhibitors: histone eviction from open chromosomal areas. We show that anthracyclines promote histone eviction irrespective of their ability to induce DNA double-strand breaks. The histone variant H2AX, which is a key component of the DNA damage response, is also evicted by anthracyclines, and H2AX eviction is associated with attenuated DNA repair. Histone eviction deregulates the transcriptome in cancer cells and organs such as the heart, and can drive apoptosis of topoisomerase-negative acute myeloid leukaemia blasts in patients. We define a novel mechanism of action of anthracycline anticancer drugs doxorubicin and daunorubicin on chromatin biology, with important consequences for DNA damage responses, epigenetics, transcription, side effects and cancer therapy.

/pdf/drug-induced-histone-eviction-from-open-chromatin-4q5dorbtbz.pdf

Drug-induced histone eviction from open chromatin contributes to the chemotherapeutic effects of doxorubicin

http://www.u.arizona.edu/~raghunan/Reprints/Raghunand_A12.pdf

Tumor acidity, ion trapping and chemotherapeutics: I. Acid pH affects the distribution of chemotherapeutic agents in vitro

Tumor acidity, ion trapping and chemotherapeutics. II. pH-dependent partition coefficients predict importance of ion trapping on pharmacokinetics of weakly basic chemotherapeutic agents

Summary The phylogenetic antiquity of DNA topoisomerases indicates their vital function. Structure and maintenance of genomic DNA depend on the activity of these enzymes, and without them DNA replication and cell division are impossible. Topoisomerase IIα has therefore become the main target of many antitumour therapy regimens, even though the exact mechanism of cell killing remains elusive. The success of this approach is limited by the development of spontaneous resistance, and drug-induced DNA damage can increase malignancy. Nevertheless, the combined use of topoisomerase-inhibiting drugs with different mechanisms of action promises to improve particular treatment designs. The degree of topoisomerase II expression in tumours may predict the clinical course and responsiveness to therapy.

https://www.thelancet.com/pdfs/journals/lanonc/PIIS1470-2045(02)00715-5.pdf

Culprit and victim -- DNA topoisomerase II.

Different types of antineoplastic drugs, such as the alkylating agents busulfan, N-methyl-N'-nitro-N-nitrosoguanidine, N-methyl-N-nitrosourea, procarbazine and temozolomide, the antimetabolites, mercaptopurine and 6-thioguanine, the platinum compounds carboplatin and cisplatin, the anthracycline doxorubicin and the epipodophyllotoxine etoposide act by damaging DNA directly or indirectly Increasing evidence has shown that tumours could acquire resistance to these drugs by loss of DNA-mismatch repair (MMR) activity This phenomenon is caused by a decreased MMR-dependent stimulation of signal-transduction pathways causing programmed cell death Simultaneously, the mutation rate in MMR-deficient tumours is increasing, which could lead to additional secondary drug/resistance phenotypes to other antineoplastic agents In addition to this, an enhanced mutation rate may contribute to increased phenotypic variation and therefore the clinical aggressiveness of primary tumours and their metastases

Involvement of the DNA mismatch repair system in antineoplastic drug resistance.

We have developed a method to quantify topoisomerase (topo) II activities in partially purified nuclear extracts from human leukemia cells. By virtue of their different pH optima in the reaction buffer, two different topo II activities were found with activity optima at pH 7.9 and at pH 8.9 under high stringency conditions. The activities could be identified as topo II beta activity (pH 7.9) and topo II alpha activity (pH 8.9) by their different sensitivities to topo II alpha inhibitors, dephosphorylation experiments and immunoprecipitation with polyclonal antibodies. Seventy-two bone marrow or blood samples from patients with acute myeloid leukemias have been examined and their in vitro sensitivities to anthracyclines and epipodophyllotoxines correlated to the activities of topo II alpha and topo II beta. Although the topo II alpha activity could be directly inhibited by incubation of the cells with the mentioned drugs, no correlation between the topo II alpha activity and the sensitivity of the cells could be found. In contrast, the topo II beta activity which was not substantially inhibited by the drugs inversely correlated with the sensitivity of the cells. These findings were statistically significant for idarubicin (P= 0.017) and daunorubicin (P = 0.006). Vice versa, resistant cells (IC50 > median) had a higher topo II beta activity. Clinical relevance might be indicated by the finding that cells from patients that relapsed after initial treatment with anthracyclin-containing regiments had a significantly higher topo II alpha/beta activity ratio (P=0.0276). Obviously, the sensitivity of AML cells is substantially influenced by the activity of the resistant topo II (topo II beta) which gives evidence that the remaining topo II activity after treatment helps the cell to survive the DNA repair phase.

Topoisomerase II activities in AML blasts and their correlation with cellular sensitivity to anthracyclines and epipodophyllotoxines.

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Topoisomerase II activities in AML blasts and their correlation with cellular sensitivity to anthracyclines and epipodophyllotoxines.