Bioflavonoids promote stable translocations between MLL‐AF9 breakpoint cluster regions independent of normal chromosomal context: Model system to screen environmental risks

Abstract

Infant acute leukemias are aggressive and characterized by rapid onset after birth. The majority harbor translocations involving the MLL gene with AF9 as one of its most common fusion partners. MLL and AF9 loci contain breakpoint cluster regions (bcrs) with sequences hypothesized to be targets of topoisomerase II inhibitors that promote translocation formation. Overlap of MLL bcr sequences associated with both infant acute leukemia and therapy‐related leukemia following exposure to the topoisomerase II inhibitor etoposide led to the hypothesis that exposure during pregnancy to biochemically similar compounds may promote infant acute leukemia. We established a reporter system to systematically quantitate and stratify the potential for such compounds to promote chromosomal translocations between the MLL and AF9 bcrs analogous to those in infant leukemia. We show bioflavonoids genistein and quercetin most biochemically similar to etoposide have a strong association with MLL‐AF9 bcr translocations, while kaempferol, fisetin, flavone, and myricetin have a weak but consistent association, and other compounds have a minimal association in both embryonic stem (ES) and hematopoietic stem cell (HSC) populations. The frequency of translocations induced by bioflavonoids at later stages of myelopoiesis is significantly reduced by more than one log. The MLL and AF9 bcrs are sensitive to these agents and recombinogenic independent of their native context suggesting bcr sequences themselves are drivers of illegitimate DNA repair reactions and translocations, not generation of functional oncogenic fusions. This system provides for rapid systematic screening of relative risk, dose dependence, and combinatorial impact of multitudes of dietary and environmental exposures on MLL‐AF9 translocations. Environ. Mol. Mutagen. 60: 154–167, 2019. © 2018 Wiley Periodicals, Inc.

DNA Damage and Repair Mechanisms Triggered by Exposure to Bioflavonoids and Natural Compounds

“…DNA reporter assays suggest that quercetin interferes with DNA repair mechanisms such as HR and C-NHEJ by inhibition of PI3K/Akt signaling. In support of these studies, exposure to multiple bioflavonoids promotes the generation of chromosomal translocations in a dose-dependent manner [29,87].…”

“…For example, among the flavonols, structure predicts that myricetin has high activity, quercetin has intermediate activity, and kaempferol has weak activity, if at all, as a covalent Top2 poison (Figure 4). Cell free studies support this and show that myricetin as well as epigallocatechin-gallate (ECGC) act as strong coalvent poisons, quercetin acts as a weak traditional poison, but kaempferol does not have this activity [29,87].…”

“…Due to their antioxidant capacity, bioflavonoids are included in dietary supplements for their presumed health benefits in protecting against inflammation, cardiovascular diseases, and cancer [87]. These beneficial health properties are due to the number of pleiotropic effects bioflavonoids have on cells by impacting signal transduction pathways, DSB repair and the cellular epigenetic landscape, which can lead to protein level changes, cell cycle stalling, and apoptosis [16,69].…”

An extra chromosome 9 derived from either a normal chromosome�9 or a derivative chromosome 9 in a patient with acute myeloid leukemia positive for t(9;11)(p21.3;q23.3): A case report

“…t(9;11) positive AML can occur primarily as a de novo neoplasm or as a result of previous therapy, for example t-AML, typically caused by topoisomerase II inhibitors (15–17). It has been suggested that the topoisomerase II cleavage site and the DNase I hypersensitive site can colocalize in the break cluster regions of MLLT3 and KMT2A (16,18,19). Furthermore, an in vivo experiment reported the cleavage site of VP-16 (a topoisomerase II-like inhibitor) localized in the break cluster regions of KMT2A in a patient with AML (20).…”

Broken by the Cut: A Journey into the Role of Topoisomerase II in DNA Fragility

“…Importantly, bioflavonoids can induce DNA cleavage at the same location in MLL and a partner gene as classic TOP2 poisons, and they can inhibit in vitro TOP2 activity to a similar extent as etoposide and doxorubicin [12]. Recent work demonstrated that quercetin and genistein can promote the formation of MLL / AF9 translocations in hematopoietic stem cells [143]. Overall, there is strong support for the role of TOP2 inhibition, from occupational exposure and/or maternal diet, in promoting DNA cleavage of oncogenic loci, as well as the subsequent translocations that drive adult and pediatric AML.…”