MORAb-003 inhibits FRα-dependent cell growth. (A) FACS analyses of CHO-FR cells stained with MORAb-003 or isotype control IgG confirming high expression of the receptor on the cell surface. (B) CHO-FR and parental CHO cells were cultured for 72 hours in low folate (<20 nM) medium and then fed increasing concentrations of 5-MTF. After 96 hours, EC50 was calculated as an average of three experiments. (C) CHO-FR and parental CHO cells were grown in the presence of 10 nM or 1 µM of 5-MTF. Growth at 10 nM 5-MTF is presented as a percentage of growth measured at 1 µM 5-MTF. (D) CHO-FR and parental CHO cells were cultured as in (B) and EC50 were measured in the presence of increasing concentrations of MORAb-003. MORAb-003 treatment (blue line) did not significantly change 5-MTF EC50 in parental CHO cells, while it increased 5-MTF EC50 in a dose-dependent fashion in CHO cells expressing human FRα (red line).