YOSHIAKI KUBO

Canine prostate cancer (cPCa) is a malignant neoplasm with no effective therapy. The BRAF V595E mutation, corresponding to the human BRAF V600E mutation, is found frequently in cPCa. Activating BRAF mutations are recognized as oncogenic drivers, and blockade of MAPK/ERK phosphorylation may be an effective therapeutic target against BRAF-mutated tumors. The aim of this study was to establish a novel cPCa cell line and to clarify the antitumor effects of MEK inhibitors on cPCa in vitro and in vivo. We established the novel CHP-2 cPCa cell line that was derived from the prostatic tissue of a cPCa patient. Sequencing of the canine BRAF gene in two cPCa cell lines revealed the presence of the BRAF V595E mutation. MEK inhibitors (trametinib, cobimetinib, and mirdametinib) strongly suppressed cell proliferation in vitro, and trametinib showed the highest efficacy against cPCa cells with minimal cytotoxicity to non-cancer COPK cells. Furthermore, we orally administered 0.3 or 1.0 mg/kg trametinib to CHP-2 xenografted mice and examined its antitumor effects in vivo. Trametinib reduced tumor volume, decreased phosphorylated ERK levels, and lowered Ki-67 expression in xenografts in a dose-dependent manner. Although no clear adverse events were observed with administration, trametinib-treated xenografts showed osteogenesis that was independent of dosage. Our results indicate that trametinib induces cell cycle arrest by inhibiting ERK activation, resulting in cPCa tumor regression in a dose-dependent manner. MEK inhibitors, in addition to BRAF inhibitors, may be a targeted agent option for cPCa with the BRAF V595E mutation. This article is protected by copyright. All rights reserved.

Case series summary Two Japanese domestic cats with GM2 gangliosidosis variant 0, diagnosed at different times, are included in this case series. Both cats were diagnosed by genetic analysis and had the HEXB:c.667C>T pathogenic genetic variant, which have been previously reported in Japanese domestic cats with GM2 gangliosidosis variant 0. Clinical signs and the identification of vacuolation in circulating lymphocytes were consistent with those in previous reports of feline GM2 gangliosidosis variant 0. Radiography showed that both cases had similar skeletal radiographic manifestations, which has not been previously reported in Japanese domestic cats with GM2 gangliosidosis variant 0. Radiographic findings included abnormally shaped vertebral bodies, obscure or irregular endplates (both of which were seen especially in the cervical and thoracic vertebrae), generalised osteopenia and new bone proliferation around articular facets.Relevance and novel information To the best of our knowledge, this is the first report to present the skeletal radiographic abnormalities of Japanese domestic cats with GM2 gangliosidosis variant 0 caused by the HEXB:c.667C>T pathogenic genetic variant. Furthermore, together with a report published in 2015 on the radiographic findings of feline GM2 gangliosidosis variant 0 caused by another pathogenic genetic variant, this report suggests that these findings may be indicators of feline GM2 gangliosidosis variant 0. The easily obtained radiographic findings described in this report may be useful as a finding suggestive of feline GM2 gangliosidosis variant 0, in addition to the cytological finding of the vacuolated cells. The report emphasises the utility of radiography for diagnosis of cases with suspected progressive neurodegenerative diseases.