Clinical significance of CD95, Bcl-2 and Bax expression and CD95 function in adult de novo acute myeloid leukemia in context of P-glycoprotein function, maturation stage, and cytogenetics

Resistance to chemotherapy-induced apoptosis and a multidrug-resistance (MD R) phenotype, mainly mediated by P-glycoprotein (P-gp), contribute to chemo therapy failure in hematologic malignancies. To study apoptosis-regulating factors in acute myeloid leukemia (AML), we investigated cell samples of ad ults with de novo AML by flow cytometry for constitutive expression levels of the apoptosis-related molecules CD95(n = 135), Bcl-2 (n = 131), and Bar (n = 66), as well as spontaneous apoptosis in vitro (n = 104) and susceptib ility to anti-CD95-induced apoptosis (CD95 sensitivity) (n = 93). We correl ated these findings with P-gp function as detected by the rhodamine123-effl ux test (n = 121), immunophenotype, FAB morphology, cytogenetics, and clini cal data of the examined patients. Immature FAB M0/1 AML cells expressed si gnificantly more Bcl-2 (P < 0.0002) and less CD95 (P < 0.0003) compared wit h AML cells of the more mature FAB M2-5 subtypes, No maturation-dependent d ifference in Bar expression was observed. FAB M2-5 AML cells were more susc eptible to anti-CD95-induced apoptosis (P < 0.008) and showed a lower P-gp function (P < 0.002) than FAB M0/1 AML cells. Leukemic cells of AML patient s who achieved a complete remission (CR) after induction chemotherapy expre ssed less Bcl-21 than nonresponder (NR) (69 CR, 23 NR; P = 0.05). CR was as sociated with a higher extent of spontaneous apoptosis in vitro (58 CR, 17 NR; P=0.05) and a tendency towards a higher CD95 expression (73 CR, 23 NR; P = 0.08) compared to NR. CR also correlated with a low P-gp function (70 C R, 21 NR; P = 0.008) and a tendency towards CD34 negativity (73 CR, 23 NR; P = 0.08). No correlation between Bar expression and response to induction chemotherapy (49 CR, 12 NR) was observed. In stepwise logistic regression a nalyses, P-gp function and the extent of spontaneous apoptosis in vitro as well as CD95 sensitivity but not Bcl-2, CD95, Bar, and CD34 expression leve ls emerged as significant markers for response to induction chemotherapy. W e conclude that the constitutive expression of CD95 and Bcl-2, as well as C D95 sensitivity and P-gp function but not constitutive Bar expression depen d on the maturation stage of leukemic cells in adult de novo AML. P-gp func tion, the extent of spontaneous apoptosis in vitro and CD95 sensitivity are more predictive for response to induction chemotherapy in adult de novo AM L than the constitutive expression levels of the apoptosis-related molecule s CD95, Bcl-2 and Bar.