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.
Polyketide synthase (PKS) derived natural products are biosynthesized by head-to-tail addition of acetate and malonate extender units resulting in linear extended-polyketide chains. Despite the well-documented structural diversity associated with PKS-derived natural products, C-C chain branching deviating from the usual linear pattern is relatively rare. Herein, type-II PKS angucyclic natural products containing a hemiaminal functionality were identified and proposed as the parent of a series of C-C-branched analogues. These C-C linked acetate or pyruvate branching units were located at the α-positions on the extended polyketide chains of jadomycins incorporating 3- and 4-aminomethylbenzoic acids. Labeling studies utilizing [1-C]-d-glucose provided mechanistic evidence that the C-C bond formation occurred as a result of a previously unidentified post-PKS processing, additional to the enzymes encoded within the biosynthetic gene cluster. Selected compounds were evaluated in cytotoxic or antimicrobial assays.
Despite numerous therapeutic options, multidrug resistance (MDR) remains an obstacle to successful breast cancer therapy. Jadomycin B, a natural product derived from Streptomyces venezuelae ISP5230, maintains cytotoxicity in MDR human breast cancer cells. Our objectives were to evaluate the pharmacokinetics, toxicity, anti-tumoral and anti-metastatic effects of jadomycin B in zebrafish larvae and mice. In a zebrafish larval xenograft model, jadomycin B significantly reduced the proliferation of human MDA-MB-231 cells at or below its maximum tolerated dose (40 μM). In female Balb/C mice, a single intraperitoneal dose (6 mg/kg) was rapidly absorbed with a maximum serum concentration of 3.4 ± 0.27 μM. Jadomycin B concentrations declined biphasically with an elimination half-life of 1.7 ± 0.058 h. In the 4T1 mouse mammary carcinoma model, jadomycin B (12 mg/kg every 12h from day 6-15 after tumor cell injection) decreased primary tumor volume compared to vehicle control. Jadomycin B treated mice did not exhibit weight loss, nor significant increases in biomarkers of impaired hepatic (alanine aminotransferase) and renal (creatinine) function. In conclusion, jadomycin B demonstrated a good safety profile and provided partial anti-tumoral effects, warranting further dose-escalation safety and efficacy studies in MDR breast cancer models.
IntroductionBreast cancer is the second leading cause of death due to cancer in women, and often becomes multidrug resistant (MDR) to adjuvant drug therapies due to the overexpression of ATP‐binding cassette (ABC) drug efflux transporters or through the decreased expression of drug uptake transporters, which can lead to treatment failure. MDR breast cancer cells can have complex drug translocation processes due to attempts to reduce intracellular anti‐cancer drug concentrations. It is critical to investigate possible drug targets for MDR cancers that can lead to increased drug accumulation. Solute carrier organic anion (SLCO) transporters are a family of transmembrane proteins that can uptake amphiphilic organic compounds into cells. Preliminary evidence suggests that SLCO transporters may be responsible for the targeted uptake of an emerging class of anticancer molecules called jadomycins, topoisomerase II and aurora B kinase‐targeting compounds which retain their cytotoxic potency in ABC‐transporter overexpressing MDR breast cancer cells.ObjectiveThe objective of this study is to evaluate the gene expression of SLCO transporters in a panel of breast cancer cell subtypes.MethodsThe mRNA expression 11 SLCO transporters was quantified using quantitative polymerase chain reaction (qPCR) in drug sensitive MCF7 (MCF7‐CON) and taxol (MCF7‐TXL), etoposide (MCF7‐ETP), and mitoxantrone (MCF7‐MITX) resistant MCF7 breast cancer cell lines which overexpress ABCB1, ABCC1, and ABCG2 drug efflux transporters, respectively. Comparisons were also made between BT474, SKBR3, and MDA‐MB‐231 breast cancer cell lines with different hormone receptor profiles as well as non‐cancerous MCF‐10A breast epithelial cells.ResultsGenerally, SLCO4A1 and 3A1 are significantly higher than the remaining transporters in drug resistant MCF7 cells, whereas this is not seen in the drug sensitive MCF7‐CON cells. There was significantly higher expression of: SLCO3A1 and 4A1 compared to the remaining transporters in MCF7‐MITX cells; SLCO3A1, 4A1, 4C1 compared to the remaining transporters in MCF7‐TXL cells; SLCO4A1 compared to the remaining transporters in MCF7‐ETP and SKBR3 cells; and SLCO3A1 and 4C1 versus all other transporters in MCF7‐ETP cells. There was significantly higher expression of SLCO1C1 versus SLCO3A1, 5A1, 1B3, 2B1, 1B1, 2A1, and 6A1 in MCF7‐CON cells.When differentiating between cancerous cells and non‐transformed MCF‐10A cells there were no significant differences between SLCO3A1 and any transporters found in breast epithelial MCF‐10A cells, however there was significantly higher expression of SLCO4A1 versus SLCO5A1, 1B3, 2B1, 1B1, and 4C1. Furthermore, there were no significant differences when comparing the transporters in BT474 and MDA‐MB‐231 cell lines.ConclusionSLCOs are differently expressed in breast cancer cell lines. SLCO4A1 and 3A1 were the most commonly expressed at significantly higher levels versus the other transporter genes in the cell lines used. They also were most highly expressed in the MDR MCF7 breast cancer cell lines and could serve as a conserved transport mechanism for intracellular delivery of anti‐cancer drugs, thereby suggesting they may be responsible for the cellular uptake of jadomycins. To explore this hypothesis, our future work will evaluate the jadomycin accumulation and cytotoxicity in SLCO3A1 and 4A1 knockdown cell lines.Support or Funding InformationLeah Bennett is a trainee in the Cancer Research Training Program of the Beatrice Hunter Cancer Research Institute, with funds provided by a CIBC Graduate Scholarship in Medical Research and the QEll Foundation.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.
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