N-Cadherin Immunoexpression in Patients with Acute Myeloid Leukemia

Introduction:

N-cadherin (NCAD) is a member of the cadherin family which is involved in calcium ion dependent adhesion between cells by interaction with catenin on neighboring cells. In our previous work, we have shown differential patterns of N-cadherin expression in acute myeloid leukemia (AML) cell lines when cultured in traditional 2-dimensional (2-D) culture conditions (over monolayer of stromal cells) compared to 3-D culture conditions. In addition, we observed that AML cell lines which were more resistant to chemotherapy in vitro had higher expression of N-cadherin. In order to further examine the role of NCAD in AML, we studied patterns of NCAD immuno-expression in bone marrow samples taken from AML patients prior to induction therapy and compared them to control bone marrow samples. We then compared patterns of NCAD immuno-expression among different AML cytogenetic risk groups as well as by their response to treatment.

Methods:

Bone marrow aspirate/biopsy sections of leukemia patients and controls comprising of lymphoma patients were stained for NCAD by immunohistochemistry. The percentage of NCAD positive cells and the intensity of nuclear and cytoplasmic NCAD staining were determined using Automated Cellular Imaging system. A four-tier grading system from grade 0 (negative) to grade 3(highest) was used. Control bone marrow biopsies were chosen from lymphoma patients with negative staging bone marrow.

Results:

A total of 33 AML bone marrow samples were examined and compared with 16 controls. The percentage of nuclear NCAD expression was significantly higher in AML compared to controls (58.36% vs 39.75%, p=0.000636). Though grade 1 and grade 2 NCAD expression was statistically significantly higher in AML samples compared to controls (grade 1: 38.10% vs 27.13%, p=0.000044; grade 2: 17.40% vs 10.38%, p=0.034), there was no statistically significant difference in grade 3 expression between AML cases and controls (2.91% vs 2.25%, p=0.607). Similarly, cytoplasmic NCAD staining was quantified. The percentage of cytoplasmic NCAD expression was significantly higher in AML samples compared to controls (84.30% vs 65%, p=<0.00001). In the case of cytoplasmic NCAD expression, grade 2 and grade 3 immuno-expression was significantly higher in AML cases compared to controls (grade 2: 24.70% vs 7.38%, p=0.000142; grade 3: 2.79% vs 0.81%, p=0.023), while grade 1 NCAD cytoplasmic immuno-expression was not significantly different between AML cases and controls (56.67% vs 56.81%, p=0.9692). NCAD expression between different cytogenetic risk categories (favorable vs intermediate, intermediate vs poor, favorable vs poor) was compared; no significant difference in NCAD expression between different cytogenetic risk groups was detected. Similarly when we compared NCAD expression between AML cases and the response to chemotherapy, there was no significant difference in NCAD expression between AML cases that achieved complete remission with chemotherapy and AML cases that did not achieve complete remission.

Conclusion.

Based on these results, we conclude that nuclear and cytoplasmic N-cadherin expression is significantly higher in AML patients than control bone marrow samples. We did not see a difference in level of NCAD expression among different AML cytogenetic risk groups or by response to chemotherapy. These results should be further evaluated in a larger cohort to determine the significance of N-cadherin expression in AML.