Abstract 155: Mining for novel JAK3 mutations in pediatric patients with acute lymphoblastic leukemia

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Background: Acute lymphoblastic leukemia (ALL) is the most common cancer occurring in children. Treatment strategies have been based on risk stratification comprising clinical and biologic features. Despite success in treating ALL, children continue to relapse, and recurrent ALL is difficult to cure with contemporary chemotherapy, suggesting a drug-resistant phenotype and an urgent need of a better understanding of the biology of ALL that will ultimately lead to the development of an alternative therapeutic approach targeting specific molecules associated with the pathogenesis of ALL. JAK3 is preferentially expressed in hematopoietic cells and mediates signals through a common gamma chain shared by receptors for various cytokines. Consistent with JAK3 function in the hematopoietic development, activating mutant alleles of JAK3 have recently been identified in several different types of blood cancer, and functional analyses of a subset of these alleles showed that the mutations can cause lethal hematopoietic malignancies in animal models. Given the central role of JAK3 in the regulation of hematopoiesis, it is likely that additional genetic alterations that activate JAK3 will be identified in other blood malignancies. Objective: We proposed that somatic mutations in JAK3 occur in a subset of pediatric patients with ALL, and that these mutations represent an important therapeutic target which can be leveraged to improve outcomes for ALL patients with JAK3 mutant. Results: A large set of DNA samples extracted from fresh bone marrows of ALL patients for mutations in JAK3 were analyzed. In 91 clinical specimens, a substitution of Val for Ile at amino acid position 722 was identified in 12, and an identical silent mutation was identified in 4. We found a significant increase in the phosphorylation levels of JAK3, Stat5, Erk1/2 and Akt in Ba/F3-JAK3V722I cells, compared with those in Ba/F3-JAK3WT cells. Furthermore, we found the expression of JAK3V722I transforms Ba/F3 cells to factor-independent growth, whereas JAK3WT-transduced cells retain the dependence on IL-3 for proliferation. Importantly, the transforming ability of JAK3V722I in the cells was abolished by treatment with the known JAK3 inhibitor CP-690550. Conclusion and Future Directions: These results suggest that IL-3-independent growth of Ba/F3-JAK3V722I cells resulted from persistent JAK3 activation and JAK3V722I-mediated transformation can be blocked by JAK3 inhibitors. In order to model the effects of JAK3V722I in vivo, we are employing a murine bone marrow transplantation assay to express MIG-JAK3WT and MIG-JAK3V722I constructs. Our preliminary studies reveal engraftment (>10% GFP positive) of both MIG-JAK3WT and MIG-JAK3V722I transduced cells 2 weeks after transplantation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 155. doi:1538-7445.AM2012-155