Copper ions are novel therapeutic agents for uterine leiomyosarcoma.

Multidrug resistance is a major concern in uterine leiomyosarcoma treatment. Development of effective chemotherapies and management of drug resistance in patients is necessary. The copper efflux transporter adenosine triphosphatase copper transporting beta is a member of the P-type adenosine triphosphatase family and is also known as a strong platinum efflux transporter. Various reports have shown the association between adenosine triphosphatase copper transporting beta and platinum resistance; however, suitable inhibitors or methods for inhibiting platinum efflux via adenosine triphosphatase copper transporting beta are not developed. Our study focused on platinum resistance in uterine leiomyosarcoma. The role of adenosine triphosphatase copper transporting beta in uterine leiomyosarcoma resistance to platinum drugs was investigated both in vitro and in vivo. Adenosine triphosphatase copper transporting beta expression was investigated by Western blotting and the efficacy of copper sulfate pretreatment and cisplatin administration in adenosine triphosphatase copper transporting beta-expressing cells was investigated both in vitro and in vivo. Western blot analysis of SK-LMS-1 cells (uterine leiomyosarcoma cell line) revealed strong adenosine triphosphatase copper transporting beta expression. A permanent SK-LMS-ATPase copper transporting beta-suppressed cell line (SK-LMS-7B cells) was generated, and cisplatin exhibited a significant antitumor effect in SK-LMS-7B cells, both in vitro (SK-LMS-1 cells, half-maximal inhibitory concentration, 17.2 μM; SK-LMS-7B cells, half-maximal inhibitory concentration, 4.2 μM, P < .01) and in xenografts compared with that in SK-LMS-1 cells (5.8% vs 62.8%, P < .01). Copper sulfate was identified as a preferential inhibitor of platinum efflux via adenosine triphosphatase copper transporting beta. In SK-LMS-1 cells pretreated with 15 μM copper sulfate for 3 hours, the cisplatin half-maximal inhibitory concentration decreased significantly compared with that in untreated cells and resulted in significantly increased intracellular platinum accumulation (1.9 pg/cell vs 8.6 pg/cell, P < .01). The combination of copper sulfate pretreatment with cisplatin administration was also effective in vivo and caused cisplatin to exhibit significantly increased antitumor effects in mice with SK-LMS-1 xenografts (3.1% vs 62.7%, P < .01). Our study demonstrates that adenosine triphosphatase copper transporting beta is overexpressed in uterine leiomyosarcoma cells and that copper sulfate, which acts as an inhibitor of platinum efflux via adenosine triphosphatase copper transporting beta, may be a therapeutic agent in the treatment of uterine leiomyosarcoma.