A Comparative Study on the In Vitro Effects of the DNA Methyltransferase Inhibitor 5-Azacytidine (5-AzaC) in Breast/Mammary Cancer of Different Mammalian Species.

Murine models are indispensible for the study of human breast cancer, but they have limitations: tumors arising spontaneously in humans must be induced in mice, and long-term follow up is limited by the short life span of rodents. In contrast, dogs and cats develop mammary tumors spontaneously and are relatively long-lived. This study examines the effects of the DNA methyltransferase (DNMT) inhibitor 5-Azacytidine (5-AzaC) on normal and tumoral mammary cell lines derived from dogs, cats and humans, as proof of concept that small companion animals are useful models of human breast cancer. Our findings show that treatment with 5-AzaC reduces in vitro tumorigenicity in all three species based on growth and invasion assays, mitochondrial activity and susceptibility to apoptosis. Interestingly, we found that the effects of 5-AzaC on gene expression varied not only between the different species but also between different tumoral cell lines within the same species, and confirmed the correlation between loss of methylation in a specific gene promotor region and increased expression of the associated gene using bisulfite sequencing. In addition, treatment with a high dose of 5-AzaC was toxic to tumoral, but not healthy, mammary cell lines from all species, indicating this drug has therapeutic potential. Importantly, we confirmed these results in primary malignant cells isolated from canine and feline adenocarcinomas. The similarities observed between the three species suggest dogs and cats can be useful models for the study of human breast cancer and the pre-clinical evaluation of novel therapeutics.

Studies on the inhibition of feline EGFR in squamous cell carcinoma: enhancement of radiosensitivity and rescue of resistance to small molecule inhibitors.

This study investigated different methods of EGFR (Epithelial Growth Factor Receptor) targeting in feline squamous cell carcinoma with the ultimate aim of establishing a large animal model of human head and neck cancer. Both small molecule receptor tyrosine kinase inhibitor (TKI) and RNA interference (RNAi) techniques were employed to target the feline EGFR. We demonstrated that the human drug gefitinib caused a reduction in cell proliferation and migration in a feline cell line. However, we also document the development of resistance that was not associated with mutation in the kinase domain. RNAi caused a potent reduction in EGFR activity and was able to overcome acquired gefitinib resistance. In addition, RNAi targeting of EGFR, but not gefitinib, caused an additive effect on cell killing when combined with radiation. These results support the use of feline SCC as a model of head and neck cancer in man in the search for novel and effective treatments for both tumors.