PTEN loss confers resistance to inhibition of MEK but not PI3K or Akt. IC₅₀s and mean growth curves of T-ALL cell lines with and without PTEN expression in varying doses of (A) the PI3K inhibitor GDC-0941, (B) the Akt inhibitor MK2206, and (C) the MEK inhibitor PD0325901. (D) PD0325901 induces apoptosis in PTEN-positive, but not PTEN-negative, cell lines. Curves indicate mean growth of 4 PTEN-positive cell lines (E1, E2, E3, and Y4) and 6 PTEN-negative cell lines (E4, Y1, Y2, Y3, Y5, and Y6) ± SEM. ***P < .001, *P < .05.