I am facing slow growth rates for u251 and u87. For U251 I am using low glucose DMEM and for U87 high glucose DMEM. I always work with the two cell lines at different times so media has not interchanged. U251 cells in a T75 flask looked close to confluent but had just 1.5 million cells! Does anyone who has worked with these cell lines have any tips to improve the growth rates?