Comparative evaluation of antitumor effects of methionine-γ-lyase in <i>in vitro</i> 2D and 3D human tumor models

BACKGROUND: Promising antitumor drug screening results obtained from monolayer cultures are often poorly reproduced in the in vivo models. Using clinically relevant 3D in vitro human tumor models, such as spheroids, provides a more reliable framework for evaluating antitumor activity. This is particularly important when the drug’s mechanism of action targets cellular metabolism. AIM: To conduct a comparative study of the antitumor activity of methionine-γ-lyase (MGL) in 2D and 3D human tumor models. MATERIALS AND METHODS: Human fibroblast cell culture and tumor cell lines, e.g. MCF7 human breast cancer, HCT-116 colorectal cancer, PANC-1 human pancreatic cancer, Huh7 liver cancer, and LNCaP human prostate cancer were used to evaluate MGL cytotoxicity. Cultural plates with low-adhesive coating were used to produce the spheroids. Cell survival was assessed using the resazurin test. RESULTS: The spheroid model showed higher cell survival after 72-hour MGL exposure compared with the monolayer culture model in all tested cultures. Fibroblasts demonstrated the lowest sensitivity to MGL exposure in both 2D and 3D culture models, with IC50=2.2 and 9.1 IU/mL, respectively. The rapidly proliferating PANC-1 and HCT-116 cells showed the highest sensitivity to MGL in 2D and 3D models: IC50=0.23 and 1.5 IU/mL; IC50=0.83 and 1.43 IU/mL, respectively. CONCLUSION: The effect of MGL on cell survival in the spheroid systems is less pronounced than in monolayers. The viability of cells exposed to survival MGL in the spheroid culture system is independent of spheroid size or growth rate. Despite the maximum cytotoxic effect being observed in the fast-growing spheroid model of colon cancer HCT-116, and the lowest in the model of slowly dividing fibroblasts, this dependence was not so obvious for other cell types. Overall, the spheroid model has proven useful for testing the specific activity of enzyme-based antitumor drugs, as far as it overcomes the excessive intrinsic sensitivity observed in monolayer cancer models.