JADOMYCIN B AFFECTS CYCLOOXYGENASE-2 RELATED SIGNALLING AND ACTS SYNERGISTICALLY WITH CELECOXIB TO KILL HUMAN BREAST CANCER CELLS

Abstract

Breast cancer affects 1 in 8 Canadian women and 10-20% of advanced breast cancers are triple negative. Triple negative breast cancers (TNBC) lack receptors required for hormone and targeted therapy and, thus, require cytotoxic therapy as first line treatment. Development of multi-drug resistance (MDR) is expected with long term chemotherapy, leading to eventual treatment failure. One mechanism of MDR involves removal of the cytotoxic substance by efflux transporters, namely P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2). Jadomycin B remains effective in killing many different types of breast cancer cells, including MDR and TNBC. While increased expression of ABCB1 or ABCG2 transporters do not result in resistance to jadomycin B, it is important to identify possible pathways for the development of jadomycin B resistance as this will aid our understanding of how jadomycin B exerts a cytotoxic effect. Jadomycin B is a compound produced by the soil bacterium Streptomyces venezuelae and has previously been shown to exert a cytotoxic effect through induction of reactive oxygen species (ROS) and to interact with topoisomerase 2 (TOP2). While each of these pathways are supported, neither fully explains the observed cytotoxic effect of jadomycin B in vitro. The goal of this project was, therefore, to elucidate and describe further pharmacological mechanism(s) through which jadomycin B may exert anticancer activity. By selecting for jadomycin B resistance in the MDA-MB-231 human TNBC cell line, increased cyclooxygenase 2 (COX2) expression was observed suggesting jadomycin B may affect COX2 signalling. COX2 is found in many solid tumours where its expression is associated with increased inflammation, proliferation, metastasis, apoptosis avoidance, and poor patient outcome. These effects are mediated by prostaglandin E2 (PGE2) which is synthesized by COX2 from arachidonic acid (AA). Additional studies showed that jadomycin B exposure in control breast cancer cells increased cellular AA levels and decreased media levels of PGE2. Jadomycin B alone did not inhibit COX2 but acted synergistically with the known COX2 inhibitor celecoxib. COX2 inhibitors were subsequently used to determine that a synergistic cytotoxic effect with jadomycin B occurred in vitro. This synergistic interaction was observed in control MDA-MB-231, jadomycin B-resistant cells, and MCF-7 breast cancer cells. Finally, jadomycin B was shown to decrease the formation of MCF-7 cell spheroids, indicating an inhibitory effect toward cancer stem cells. This work has identified a novel interaction between jadomycin B and the known chemotherapy target COX2 in cellular models of breast cancer. By better understanding this anticancer effect, jadomycin B continues to show promise as a potential therapy for MDR breast cancer.