The Role of Inhibitor of Apoptosis Proteins Family Expression In Acute Myeloid Leukemia Patients

IAPs (Inhibitor of Apoptosis Proteins) family acts as an inhibitor of both external and internal apoptosis pathways by binding to specific caspases. These proteins also participate in intracellular signal transduction. Seven human IAPs have been identified: XIAP, cIAP-1, cIAP-2, survivin, livin, NAIP and BRUCE/Apollon. IAPs family can be inhibited by Smac/DIABLO (second mitochondrial derived activator of caspase/direct IAP binding protein with low pI) protein. The role, pathway of action and prognostic significance of IAPs family is not clearly determined in acute myeloid leukemia (AML) patients.

The main objective of this study was to verify whether expressions of selected IAPs as XIAP, cIAP-1, cIAP-2 and survivin proteins have a prognostic impact on response to induction chemotherapy of adult AML patients. Additionally, to analyse the correlation between members of IAPs family and their inhibitor, Smac/DIABLO protein in leukemic blasts.

Intracellular expression of XIAP, cIAP-1, cIAP-2, survivin and Smac/DIABLO proteins were examined in leukemic blasts isolated from bone marrow or peripheral blood of 56 de novo AML patients with median age 57 (range 21–82). All measurements were carried out using multi-colour flow cytometry. In parallel, the isotype controls were performed for all measurements. Protein expression was assessed by percentage of XIAP, cIAP-1, cIAP-2, survivin and Smac/DIABLO positive cells. Expression above 20% of cells was recognized as positive.

The median of intracellular expression of XIAP, cIAP-1, cIAP-2, survivin and Smac/DIABLO proteins were 1% (ranged 0,1–16,7%), 3,2% (ranged 0,1–67,0%), 1,7% (ranged 0–41%), 29,9% (ranged 0,3–71,1%) and 65,9% (ranged 3,8–99,9%); respectively.

Correlation of cIAP-1 with cIAP-2 and XIAP was observed (p<0.001, p<0.01; respectively). Trend of correlation between cIAP-1 and survivin was also noticed (p=0.07). Similarly to cIAP-1, cIAP-2 was strongly correlated with XIAP (p<0.01). Neither cIAP-2 nor XIAP showed correlation with survivin. Additionally, all of investigated IAPs family members except survivin showed reverse correlation with Smac/DIABLO protein (p<0.01).

Thirty three out of 56 AML patients received standard induction chemotherapy with daunorubicine and cytarabine (Ara-C) (3+7), 23/56 received non-intensive chemotherapy. Twenty (60.7%) of intensively treated patients achieved complete remission (CR). We examined influence of presence of cIAPs family members in leukemic blast on response to chemotherapy in intensively treated patients. It was found that probability of CR with absence of cIAP-1, cIAP-2 and survivin was 83%. CR rate with presence of one of IAPs member was 68%. Patients with expressions of three IAPs members did not respond to the induction therapy.

Strong correlations between members of IAPs family may bear the evidence for cooperation between these proteins in leukemic blasts. Additionally, reverse correlation between members of IAPs family and their antagonist Smac/DIABLO protein confirm intracellular interaction between them. These data also demonstrate that lack of IAPs family members expressions is associated with higher sensitivity to standard chemotherapy.

However, further investigations evaluating the relationship between all known IAPs family members and their inhibitors should be undertaken to better demonstrate its pathways of action as well as prognostic and potentially therapeutic value.

Robak:Johnson & Johnson: Research Funding.