The heterogeneous nature of human breast cancer (HBC) can still lead to therapy inefficacy and high le-thality and new therapeutics are needed as well as new spontaneous animal models to benefit translational HBC research. Dogs are primarily investigated since they spontaneously develop tumors which share many features with human cancers. In recent years, different natural phytochemicals including berberine, a plant alkaloid, have been reported to have antiproliferative activity in vitro in human cancers and in rodent animal models. In this study, we report the antiproliferative activity and mechanism of action of berberine, of its active metabolite berberrubine, and of eight analogues, on a canine mammary carcinoma cell line and in transgenic zebrafish models. We demonstrate both in vitro and in vivo the significant effects of specific analogues on cell viability, via induction of apoptosis, also identifying their role in inhibiting the Wnt/β-catenin pathway and activating the Hippo signals with a downstream reduction of CTGF expres-sion. Particularly the berberine analogues NAX035 and NAX057 show the highest therapeutic efficacy, de-serving further analyses to elucidate their mechanism of action more in detail, and in vivo studies on spon-taneous neoplastic diseases aiming at improving veterinary treatments of cancer as well as translational cancer research.