Combating Drug Resistance by Exploiting miRNA-200c-Controlled Phase II Detoxification

Abstract

Acquired drug resistance constitutes a serious obstacle to the successful therapy of cancer. In the process of therapy resistance, microRNAs can play important roles. In order to combat resistance formation and to improve the efficacy of chemotherapeutics, the mechanisms of the multifaceted hsa-miR−200c on drug resistance were elucidated. Upon knockout of hsa-miR−200c in breast carcinoma cells, a proteomic approach identified altered expression of glutathione S-transferases (GSTs) when cells were treated with the chemotherapeutic drug doxorubicin. In different hsa-miR−200c expression systems, such as knockout, inducible sponge and inducible overexpression, the differential expression of all members of the GST family was evaluated. Expression of hsa-miR−200c in cancer cells led to the repression of a multitude of these GSTs and as consequence, enhanced drug-induced tumor cell death which was evaluated for two chemotherapeutic drugs. Additionally, the influence of hsa-miR−200c on the glutathione pathway, which is part of the phase II detoxification mechanism, was investigated. Finally, the long-term effects of hsa-miR−200c on drug efficacy were studied in vitro and in vivo. Upon doxycycline induction of hsa-miR−200c, MDA-MB 231 xenograft mouse models revealed a strongly reduced tumor growth and an enhanced treatment response to doxorubicin. A combined treatment of these tumors with hsa-miR−200c and doxorubicin resulted in complete regression of the tumor in 60% of the animals. These results identify hsa-miR−200c as an important player regulating the cellular phase II detoxification, thus sensitizing cancer cells not expressing this microRNA to chemotherapeutics and reversing drug resistance through suppression of GSTs.

Unravelling the metastasis-preventing effect of miR-200cin vitroandin vivo

“…Song et al analyzed the distant metastasis in 134 breast cancer patients and revealed that it was more likely to find patients with distant metastases in the group of patients with low levels of miR-200c (49). Moreover, our lab correlated a decreased overall survival of breast cancer patients, which especially in mammary tumors is connected with metastases, with low miR-200c expression (21). Taken together we strongly propose miR-200c as a metastasis suppressor in vivo .…”

“…In previous studies, we and others extensively studied the role of the tumor suppressor microRNA 200c (miR-200c), which is involved in many processes of tumorigenesis, e.g. apoptosis, proliferation, chemotherapy resistance, motility, epithelial-mesenchymal transition (EMT), and metastasis (21)(22)(23)(24)(25)(26). MiR-200c belongs to the microRNA-200 family.…”

“…Many of its targets like ZEB1, ZEB2, USP25, MSN and FN1 alter migration directly or re-organize the actin cytoskeleton (FHOD1, FLNA and PPM1F) and thus can indirectly affect migration and invasion (28). In vivo studies of miR-200c overexpression showed a reduced tumor growth and prolonged survival (21, 30, 31), whereas metastases formation was investigated by overexpressing the miR-200c/141 cluster (32) or only focused on the analysis of lung metastases in claudin-low breast cancer (33).…”