Anti-neoplastic effects of topoisomerase inhibitors in canine mammary carcinoma, melanoma, and osteosarcoma cell lines.

Numerous topoisomerase inhibitors with proven efficacy have been used extensively to treat various human neoplasms. However, among these, only doxorubicin has been used and studied extensively in veterinary oncology. The current study was performed to evaluate the responsiveness of canine osteosarcoma (cOSA), mammary gland tumour (cMGT), and malignant melanoma (cMM) cell lines to several topoisomerase inhibitors. In addition, the correlation between the sensitivity to treatment and multi-drug resistant (MDR) factors was investigated. cOSA cell lines exhibited higher sensitivity than cMGT and cMM cell lines to all the topoisomerase inhibitors tested in vitro; this was associated with the levels of multi-drug resistance protein 1 (MDR1) gene expression in the cOSA cell lines. Treatment of cOSA (HMPOS) and cMGT cell line (CHMp) xenograft mouse models with etoposide markedly delayed tumour progression in HMPOS xenografts, but failed to elicit lasting anti-tumour effects on CHMp xenograft mice. The present findings suggest that MDR1 represents a molecular signature for prediction of treatment efficacy of topoisomerase inhibitors, especially that of etoposide, which may be a clinically useful anti-tumour agent for cOSA; however, further study is necessary to refine the treatment protocol.