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 (231-TXL) from drug-sensitive MDA-MB-231 cells (231-CON). Using MTT 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 γH2AX western blotting. Co-incubation with the antioxidant N-acetyl cysteine (NAC) 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 which 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 qPCR, 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 IIβ. 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 induction of DNA damage and apoptosis.
- The American Society for Pharmacology and Experimental Therapeutics