Blasts Express Phospho-Akt in the Majority of Adult Patients with Acute Lymphocytic Leukemia (ALL).

Background: Akt, a serine/threonine protein kinase, is a critical regulator of cellular apoptosis, proliferation, and differentiation. Constitutive activation (phosphorylation) of Akt is frequently observed in various types of cancer, and may represent a therapeutic target. Akt inhibitors, such as perifosine, are in clinical development. We evaluated the expression of phosphorylated Akt (pAkt) in patients with newly diagnosed ALL.

Methods: Between 1998 and 2005, patients with newly diagnosed ALL and an available diagnostic bone marrow biopsy performed at the Cleveland Clinic Foundation were evaluated. B5-fixed bone marrow core biopsies were reviewed for areas with the highest concentration of blasts. A tissue microarray was constructed using 1 mm tissue cores. The cores were arrayed in duplicate in the majority of samples, with a few samples having only 1 core. Immunohistochemistry was performed for pAkt with a monoclonal antibody to pAkt (Rockland Immunochemicals), using automated stainers and heat induced epitope retrieval. pAkt staining of blasts was estimated in 10% increments. The pattern of staining for pAkt was classified as positive (activated) if nuclear or cytoplasmic staining occurred in more than 10% of the blasts.

Results: Eighty-eight patients with newly diagnosed ALL were treated at our institution during this time. Forty-five patients were evaluable. Thirty-three cases were not evaluable for the following reasons: bone marrow cores not available (9), bone marrow aspirate performed at an outside hospital (20), bone marrow aspirate sample not sufficient (1), and diagnostic bone marrow aspirate not performed (3). The median age was 37 [range 18–81]. Sixteen patients (35%) had poor risk cytogenetics, 12 (27%) normal karyotype, 9(20%) miscellaneous abnormalities, and 8 (18%) unknown cytogenetics as defined by CALGB criteria. Forty-one patients (91%) had precursor B-cell ALL, and 4 patients (9%) precursor T cell ALL. The median white count was 6.6 × 10⁹/L [range 0.93–278], and median LDH 772 U/L [range 155–4608]. The expression of pAkt was characterized predominately by cytoplasmic staining with 8 cases exhibiting nuclear staining. Akt was activated (phosphorylated) in 32 out of 45 patients (71%) with newly diagnosed ALL. The median percentage of blasts with pAkt in the cytoplasm was 30%, with 19 patients (42%) having ≥50% blasts with cytoplasmic pAkt. There was a trend towards more patients with Philadelphia chromosome (Ph) positive ALL having ≥50% blasts with pAkt in the cytoplasm (7/10 patients) versus patients with other cytogenetic abnormalities (12/33) (p=0.079).

Conclusions: Akt was activated in the majority of patients with newly diagnosed ALL. Akt may be a therapeutic target in ALL, and especially for patients with Ph+ ALL. Larger studies will be needed to define the prognostic significance of Akt activation in ALL.