Proof-of-concept study of the caninized anti-canine programmed death 1 antibody in dogs with advanced non-oral malignant melanoma solid tumors

Abstract

Background: The anti-programmed death 1 (PD-1) antibody has led to durable clinical responses in a wide variety of human tumors. We have previously developed the caninized anti-canine PD-1 antibody (ca-4F12-E6) and evaluated its therapeutic properties in dogs with advance-staged oral malignant melanoma (OMM), however, their therapeutic effects on other types of canine tumors remain unclear.

Objective: The present clinical study was carried out to evaluate the safety profile and clinical efficacy of ca-4F12-E6 in dogs with advanced solid tumors except for OMM.

Methods: Thirty-eight dogs with non-OMM solid tumors were enrolled prospectively and treated with ca-4F12-E6 at 3 mg/kg every 2 weeks of each 10-week treatment cycle. Adverse events (AEs) and treatment efficacy were graded based on the criteria established by the Veterinary Cooperative Oncology Group.

Results: One dog was withdrawn, and thirty-seven dogs were evaluated for the safety and efficacy of ca-4F12-E6. Treatment-related AEs of any grade occurred in 13 out of 37 cases (35.1%). Two dogs with sterile nodular panniculitis and one with myasthenia gravis and hypothyroidism were suspected of immune-related AEs. In 30 out of 37 dogs that had target tumor lesions, the overall response and clinical benefit rates were 6.9% and 27.6%, respectively. The median progression-free survival and overall survival time were 70 days and 215 days, respectively.

Conclusions: The present study demonstrated that ca-4F12-E6 was well-tolerated in non-OMM dogs, with a small number of cases showing objective responses. This provides evidence supporting large-scale clinical trials of anti-PD-1 antibody therapy in dogs.

Keywords: Dog; immune checkpoint inhibitor; immunotherapy; monoclonal antibody; tumor.

Fig. 1. The flow chart of the enrollment of eligible dogs in the clinical study.

CR, complete response; PR, partial response; SD, stable disease; PD, progressive disease; NE, not evaluation.

Fig. 2. Tumor response of ca-4F12-E6 in dogs with target tumor lesions (n = 19). (A) Percent changes of individual tumor volume of target lesions over time from baseline. The shaded lesion indicates the endpoint of the first treatment cycle. Dashed lines correspond to a 30% decrease and a 20% increase in tumor volume. The end of the line indicates the termination of this trial. (B) Percentage changes in the size of the target lesion from baseline at the endpoint of the first treatment cycle are indicated by a waterfall plot.

Asterisks indicate new lesions.

Fig. 3. The clinical course of two dogs with metastatic undifferentiated sarcoma and primary lung epithelial tumor. (A) Case 14: Representative CT scan images of lung metastasis of an undifferentiated sarcoma dog treated with ca-4F12-E6 for the first cycle. The red arrow indicates the target lesion. (B) Case 24: Measurement of the longest diameter of each lung tumor, including one target lesion and two non-target lesions. Case 24 received three cycles of ca-4F12-E6.

Fig. 4. Tumor response and immunohistochemistry for tumor-infiltrating lymphocytes in a case with nasal squamous cell carcinoma. (A) Case 6 received a total of four ca-4F12-E6 cycles. The pictures show the target lesion at the indicated time point. (B) Tumor-biopsy specimens with immunohistochemistry using anti-CD8 antibody or anti-Foxp3 antibody for lymphocytic markers reveal that cytotoxic T cells (indicated as CD8-positive cells) were accumulated in post-treatment tumor tissues. The peroxidase and DAB staining method was used to visualize the immunolabelling. Scale bars: 20 μm.