Although immune checkpoint inhibitors (ICIs), such as the anti-programmed death-ligand 1 (PD-L1) antibody, have been developed for the treatment of canine malignant melanoma, desirable clinical efficacies have not been achieved. Recent studies in humans have suggested that radiation therapy (RT) combined with ICIs induces robust systemic antitumour immunity in patients with cancer. This study retrospectively examined the therapeutic efficacy of combination therapy (hypofractionated RT and anti-PD-L1 antibody [c4G12]) in dogs with pulmonary metastatic oral malignant melanoma. The intrathoracic clinical benefit rate (CBR)/median overall survival (OS) in the no RT (n = 20, free from the effect of RT), previous RT (n = 9, received RT ≤8 weeks prior to the first c4G12 dose), and concurrent RT (n = 10, c4G12 therapy within ±1 week of the first RT fraction) groups were 10%/185 days, 55.6%/283.5 days (p < 0.05 vs. no RT group), and 20%/129 days (p > 0.05 vs. no RT group), respectively. The adverse events were considered to be tolerable in the combination therapy. Thus, hypofractionated RT before the initiation of c4G12 therapy can be an effective approach for enhancing the therapeutic efficacy of immunotherapy, with acceptable safety profiles. Further prospective clinical studies are required to confirm the findings of this study.

The transcription factor hypoxia-inducible factor 1α (HIF-1α) drives metabolic reprogramming in gliomas (GLs) under hypoxic conditions, promoting glycolysis for tumor development. Evofosfamide (EVO) releases a DNA-alkylating agent within hypoxic regions, indicating that it may serve as a hypoxia-targeted therapy. The aim of this study was to investigate the glycolytic metabolism and antitumor effects of EVO in a canine GL model. Our clinical data showed that overall survival was significantly decreased in GL dog patients with higher HIF-1α expression compared to that of those with lower HIF-1α expression, and there was a positive correlation between HIF-1α and pyruvate dehydrogenase kinase 1 (PDK1) expression, suggesting that glycolytic activity under hypoxia conditions may contribute to poor outcomes in canine GL. Our glycolysis assay tests showed that the glycolytic ATP level was higher than the mitochondrial ATP level in three types of canine GL cell lines by activating the HIF-1 signal pathway under hypoxia conditions, resulting in an overall increase in total cellular ATP production. However, treatment with EVO inhibited the glycolytic ATP level in the GL cell lines under hypoxia conditions by targeting HIF-1α-positive cells, leading to decrease in total cellular ATP production. Our in vivo tests showed that EVO significantly reduced tumor development compared to controls and temozolomide in murine GL models. A metabolic analysis demonstrated that EVO effectively suppressed glycolytic metabolism by eliminating HIF-1α-positive cells, suggesting that it may restore metabolism in canine GLs. The evidence presented here supports the favorable preclinical evaluation of EVO as a potential improvement in cancer metabolism.

Oral malignant melanoma (OMM) is a highly aggressive malignancy in dogs. The development of effective systemic therapies is urgently required to improve the treatment of canine OMM. Immunotherapy using immune checkpoint inhibitors (ICIs) has been investigated in canines following their dramatic success in human cancer treatment; however, there is still a need for extensive veterinary clinical studies to clarify and optimize their clinical benefits. Among the ICIs under development for canine cancer immunotherapy, c4G12 (HFC-L1), a canine chimeric anti-PD-L1 antibody, has shown promising efficacy in dogs with pulmonary metastatic OMM in previous clinical studies. However, the optimal dose of HFC-L1/c4G12 has not yet been determined. To explore the dose–response relationship of HFC-L1, a multicenter, randomized clinical study was conducted using three different doses (2, 5, or 10 mg/kg via intravenous infusion every 2 weeks) to treat dogs with pulmonary metastatic OMM (n = 8–9 per group). The safety profiles were similar among the dose groups, and numerically longer median overall survival was achieved in the higher dose groups (5 and 10 mg/kg) than in the 2 mg/kg group. Although the study was exploratory in nature with a small sample size, 5–10 mg/kg should be considered the preferred dose in future clinical studies using HFC-L1.