Jadomycins Inhibit Type II Topoisomerases and Promote DNA Damage and Apoptosis in Multidrug-Resistant Triple-Negative Breast Cancer Cells

Abstract

Jadomycins are natural products that kill drug-sensitive and multidrug-resistant (MDR) breast cancer cells. To date, the cytotoxic activity of jadomycins has never been tested in MDR breast cancer cells that are also triple negative. Additionally, there is only a rudimentary understanding of how jadomycins cause cancer cell death, which includes the induction of intracellular reactive oxygen species (ROS). We first created a paclitaxel-resistant, triple-negative breast cancer cell line [paclitaxel-resistant MDA-MB-231 breast cancer cells (231-TXL)] from drug-sensitive control MDA-MB-231 cells (231-CON). Using thiazolyl blue methyltetrazolium bromide cell viability-measuring assays, jadomycins B, S, and F were found to be equipotent in drug-sensitive 231-CON and MDR 231-TXL cells; and using ROS-detecting assays, these jadomycins were determined to increase ROS activity in both cell lines by up to 7.3-fold. Jadomycins caused DNA double-strand breaks in 231-CON and 231-TXL cells as measured by H2AX Western blotting. Coincubation with the antioxidant-acetyl cysteine or pro-oxidant auranofin did not affect jadomycin-mediated DNA damage. Jadomycins induced apoptosis in 231-CON and 231-TXL cells as measured by annexin V affinity assays, a process that was retained when ROS were inhibited. This indicated that jadomycins are capable of inducing MDA-MB-231 apoptotic cell death independently of ROS activity. Using quantitative polymerase chain reaction, Western blotting, and direct topoisomerase inhibition assays, it was determined that jadomycins inhibit type II topoisomerases and that jadomycins B and F selectively poison topoisomerase II We therefore propose novel mechanisms through which jadomycins induce breast cancer cell death independently of ROS activity, through inhibition or poisoning of type II topoisomerases and the induction of DNA damage and apoptosis.

Double Strand Break DNA Repair occurs via Non-Homologous End-Joining in Mouse MII Oocytes

“…These attributes include its capacity to act as a nucleophile (and therefore antioxidant), modulate DNA repair, alter cellular metabolism, influence anti-inflammatory and finally anti-angiogenic activity 42 . Despite these myriad of beneficial actions, supplementation of NAC (2.5 mM 43 ) in our culture system failed to significantly improve the response of ETP treated MII oocytes. Thus, γH2A.X related fluorescence remained equivalent in both ETP/NAC exposed oocytes and those exposed to the ETP insult alone (Fig.…”

The expansive library of jadomycins

“…At the time of publication, over forty-five of the described jadomycins have been evaluated for biological activity, including various cancer cytotoxicity assays [7][8][9][10]13,15,[17][18][19][20]25,[32][33][34][35] and antimicrobial panels. 6,20,33,34 Jadomycins have been implicated in the inhibition of aurora kinase B 10,54 and topoisomerases.…”

“…6,20,33,34 Jadomycins have been implicated in the inhibition of aurora kinase B 10,54 and topoisomerases. 8,55 Other studies have demonstrated DNA-cleavage by jadomycin through a generation of reactive oxygen species in the presence of Cu(II), 9,17,18,25,56 although further studies have concluded that ROS-dependant mechanisms are not the primary contributor to bioactivity. 8 In triple negative breast cancer cell lines, jadomycins have shown resistance of drug efflux mechanisms.…”

“…8,55 Other studies have demonstrated DNA-cleavage by jadomycin through a generation of reactive oxygen species in the presence of Cu(II), 9,17,18,25,56 although further studies have concluded that ROS-dependant mechanisms are not the primary contributor to bioactivity. 8 In triple negative breast cancer cell lines, jadomycins have shown resistance of drug efflux mechanisms. 10,33 While an extended evaluation of the structure-activity relationships was beyond the scope of this review, given the various techniques employed in the evaluations rendering direct comparisons challenging, there was ample evidence in the above studies to suggest that the incorporated amino acid effected the observed bioactivity.…”

“…2,3 The jadomycins are distinct from the other natural product angucyclines by their inclusion of a nitrogenous heterocycle, 1 which is the result of a non-enzymatic incorporation of an amino acid into the polyaromatic core. 4,5 This non-enzymatic process has permitted the generation of a large library of jadomycins, enabling the determination of structureactivity relationships with respect to the antibiotic 6 and cytotoxic [7][8][9][10] activity of the jadomycins. Jadomycin nomenclature often includes the incorporated amino acid, for instance, jadomycin S (Jd S) refers to the natural product isolated through incorporation of L-serine into the jadomycin.…”