Effects of trastuzumab emtansine on canine urothelial carcinoma cells in vitro and in vivo.

Urothelial carcinoma (UC) is the most common malignancy of the urinary tract in dogs and has aggressive behaviour. Although human epidermal growth factor receptor 2 (HER2) is a known therapeutic target with evidence in canine UC, the efficacy of anti-HER2 antibody drugs remains unknown. This study aimed to investigate the effects of anti-HER2 antibody drugs including trastuzumab and trastuzumab emtansine (T-DM1) on canine UC cell lines in vitro and in vivo. Four canine UC cell lines (Nene, TCCUB, Love, and Sora) were used. In western blotting, HER2 protein expression was observed in all the cell lines. Although both trastuzumab and T-DM1 showed dose-dependent growth inhibitory activity in the cell lines, T-DM1 showed much stronger activity than that of trastuzumab. In flow cytometry analyses with the canine UC cell line (Sora), T-DM1 but not trastuzumab significantly increased the percentages of early and late apoptotic cells in annexin V apoptotic assays and the sub-G1 phase fraction in cell cycle analyses. For the in vivo experiment, the canine UC cells (Sora) were subcutaneously injected into nude mice. Four days after inoculation, trastuzumab, T-DM1, or vehicle was administered intraperitoneally once a week for three times. Tumour volumes were significantly smaller in the T-DM1 group compared to the trastuzumab and vehicle control groups. These findings indicate that T-DM1 exerts a stronger antitumour effect than that of trastuzumab on canine UC cells in vitro and in vivo, possibly by inducing apoptosis due to DM1.

Podoplanin promotes cell proliferation, survival, and migration of canine non-tonsillar squamous cell carcinoma.

Podoplanin (PDPN) is a prognostic factor and is involved in several mechanisms of tumor progression in human squamous cell carcinoma (SCC). Canine non-tonsillar SCC (NTSCC) is a common oral tumor in dogs and has a highly invasive characteristic. In this study, we investigated the function of PDPN in canine NTSCC. In canine NTSCC clinical samples, PDPN overexpression was observed in 80% of dogs with NTSCC, and PDPN expression was related to ki67 expression. In PDPN knocked-out canine NTSCC cells, cell proliferation, cancer stemness, and migration were suppressed. As the mechanism of PDPN-mediated cell proliferation, PDPN knocked-out induced apoptosis and G2/M cell cycle arrest in canine NTSCC cells. These findings suggest that PDPN promotes tumor malignancies and may be a novel biomarker and therapeutic target for canine NTSCC.

Podoplanin Drives Amoeboid Invasion in Canine and Human Mucosal Melanoma.

Mucosal melanoma metastasizes at an early stage of the disease in human and dog. We revealed that overexpression of podoplanin in tumor invasion fronts (IF) was related to poor prognosis of dogs with mucosal melanoma. Moreover, podoplanin expressed in canine mucosal melanoma cells promotes proliferation and aggressive amoeboid invasion by activating Rho-associated kinase (ROCK)-myosin light chain 2 (MLC2) signaling. PDPN-ROCK-MLC2 signaling plays a role in cell-cycle arrest and cellular senescence escape as a mechanism for regulating proliferation. Podoplanin induces amoeboid invasion in the IFs of mouse xenografted tumor tissues, similar to canine mucosal melanoma clinical samples. We further identified that podoplanin expression was related to poor prognosis of human patients with mucosal melanoma, and human mucosal melanoma with podoplanin-high expression enriched gene signatures related to amoeboid invasion, similar to canine mucosal melanoma. Overall, we propose that podoplanin promotes canine and human mucosal melanoma metastasis by inducing aggressive amoeboid invasion and naturally occurring canine mucosal melanoma can be a novel research model for podoplanin expressing human mucosal melanoma. IMPLICATIONS: Podoplanin could be a new therapeutic target to restrict the metastatic dissemination of canine and human mucosal melanoma.