Canine
hemangiosarcoma (HSA) is an aggressive malignant endothelial
tumor in dogs and characterized by poor prognosis because of its high invasiveness, high metastatic potential, and poor responsiveness to anti-
cancer drugs. Although
doxorubicin-based
chemotherapy is regularly conducted after surgical treatment, its effects on survival rates are limited. Acquisition of drug resistance is one of the causes of this problem, but the underlying mechanisms remain unclear. In the present study, we aimed to identify the drug-resistance mechanism in canine HSA by establishing
doxorubicin-resistant (DR) HSA cell lines. HSA cell lines were exposed to
doxorubicin at gradually increasing concentrations. When the cells were able to grow in the presence of a 16-fold higher
doxorubicin concentration compared with the initial culture, they were designated DR-HSA cell lines. Characterization of these DR-HSA cell lines revealed higher
drug efflux pump capacity compared with the parental cell lines. Furthermore, the DR-HSA cell lines did not show activation of the DNA damage response despite carrying high DNA damage burdens, meaning that apoptosis was not strongly induced. In conclusion, canine HSA cell lines acquired
doxorubicin resistance by increasing their
drug efflux pump capacity and decreasing the DNA damage response. This study provides useful findings to promote further research on the drug-resistance mechanisms in canine HSA.