Analysis Of EphA3 Expression In Hematologic Malignancies By Quantitative PCR

EphA3 is a receptor tyrosine kinase that plays an important role in cell positioning and tissue organization during fetal development, but is not thought to play a significant role in healthy adults. However, aberrant EphA3 expression has been reported in a variety of hematologic and solid tumors. KaloBios is conducting a clinical study (KB004-01) of the anti-EphA3 monoclonal antibody KB004 in patients with hematologic malignancies. To gain further insight into the expression of EphA3 in human cancer, we are analyzing EphA3 mRNA expression in a broad range of hematologic diseases using quantitative PCR analysis. The goal of this research is to determine EphA3 expression in hematologic diseases, to identify cytogenetic and/or molecular mutations associated with aberrant EphA3 expression, and to identify EphA3 positive patient populations for inclusion in the ongoing KB004-01 clinical trial. To date, a total of 45 bone marrow aspirate samples have been analyzed from a cohort of patients with AML, MDS, multiple myeloma (PCM), PMF, CML, ALL, or CLL and the study is ongoing. Relative quantification of EphA3 mRNA was determined by normalization to GAPDH and B2M control genes, and expression calculated relative to the level of EphA3 found in normal bone marrow. Patients were designated EphA3+ if the relative EphA3 expression was >2-fold above normal bone marrow. In AML, 8 out of 14 (57.1%) were EphA3+ with expression levels ranging from 2 - 203 fold. The two AML samples with the highest EphA3 expression (43 and 203 fold) were from refractory AMLs. In MDS, 7 out of 15 (46.7%) were EphA3+ with expression ranging from 2 - 33 fold. In PCM, 2 out of 3 (66.6%) were EphA3+ with expression ranging from 10 - 55 fold. The sample with high EphA3 expression of 55 fold had involvement of both PCM and PMF disease. In PMF, 2 out of 3 (66.6%) were EphA3+ with expression levels ranging from 8 - 977 fold. The PMF sample with 977 fold EphA3 expression is the highest level of EphA3 measured in the study to date. The remaining samples analyzed consisted of 1 unspecified MPN, 3 CML, 2 ALL, and 4 CLL all of which had EphA3 mRNA levels equal to or lower than normal bone marrow. In summary, elevated levels of EphA3 mRNA were detected in a number of bone marrow aspirates from AML, MDS, PCM, and PMF patients suggesting these diseases as possible candidates for anti-EphA3 targeted therapy.