Effect of the tumor microenvironment on vincristine response in triple-negative and triple-positive primary canine mammary tumor cells: A 2D and 3D culture study

Abstract

Canine mammary tumors (CMTs) are among the most common neoplasms in female dogs, with over half exhibiting malignant and aggressive behavior. Although vincristine is routinely used in veterinary oncology, its cytotoxic potential in relation to hormone receptor and HER2 status remains unclear. This study evaluated vincristine responsiveness in triple-positive (ER⁺/PR⁺/HER2⁺) and triple-negative (ER⁻/PR⁻/HER2⁻) primary cultured CMT cells grown under two-dimensional (2D) and three-dimensional (3D) culture systems, the latter better mimicking the tumor microenvironment. Tumor tissues excised from clinical cases were histopathologically confirmed as malignant, and receptor status was determined by RT-PCR. Primary CMT cells (CMT1-CMT5) and normal mammary epithelial cells were treated with graded concentrations of vincristine (0-100 µM), and IC₅₀ values were calculated. Vincristine induced dose-dependent cytotoxicity in all CMT lines, with CMT2 and CMT3 showing the highest sensitivity, whereas CMT5 exhibited partial resistance. Normal mammary cells displayed significantly lower mortality (p