Nonlinear regression curves of LeTx (PrAg/LF) (square) and PrAg/FP59 (triangle) on human AML cell lines. HL60 (A) and TF1-vRaf (B) cell lines are sensitive to both LeTx and PrAg/FP59. Mono-Mac-1 (C) and U937 (D) are only sensitive to PrAg/FP59 but not to PrAg/LF, indicating resistance to the LF-mediated inhibition of the MAPK pathway. (E) Compilation of LeTx nonlinear regression curves on all AML cell lines tested. (F) Nonlinear regression curves of the specific MEK1/2 inhibitor U0126 on TF1-vRaf (square), HL60 (triangle), Mono-Mac-1 (inverted triangle), and U937 (diamond) cell lines. The LeTx-sensitive cell lines TF1-vRaf and HL60 are sensitive to U0126, whereas the LeTx-resistant cell lines Mono-Mac-1 and U937 are resistant to U0126.