I am growing LN-18 glioblastoma cells following ATCC's reccommendations (5% FBS, 1% p/s). I seeded 500.000 cells in a T75 flask, and cells seemed to grow without any problem. However after several days of culture, I started to see less cells, and a lot of floating cellular debris. It seems that cells are dying, but I do not see any contamination and the conditions are the same I have been using for previous experiments. Has anyone know how could I rescue these cells, or give me any recommendation for future expansions?