Development of ZMYM2‐FGFR1 driven AML in human CD34+ cells in immunocompromised mice

Abstract

Acute myelogenous leukemia (AML) has an overall poor survival rate and shows considerable molecular heterogeneity in its etiology. In the WHO classification there are >50 cytogenetic subgroups of AML, many showing highly specific chromosome translocations that lead to constitutive activation of individual kinases. In a rare stem cell leukemia/lymphoma syndrome, translocations involving 8p11 lead to constitutive activation of the fibroblast growth factor receptor 1 (FGFR1) kinase. This disorder shows myeloproliferative disease with almost invariably progresses to AML, and conventional therapeutic strategies are largely unsuccessful. Because of the rare nature of this syndrome, models that faithfully recapitulate the human disease are needed to evaluate therapeutic strategies. The t(8;13)(p11;q12) chromosome translocation is most common rearrangement seen in this syndrome and creates a ZMYM2-FGFR1 chimeric kinase. To understand more about the molecular etiology of AML induced by this particular rearrangement, we have created a model human CD34+ cells transplanted into immunocompromized mice which develop myeloproliferative disease that progresses to AML with a long (> 12 months) latency period. As in humans, these mice show hepatospenomegaly, hypercellular bone marrow and a CD45+CD34+CD13+ immunophenotype. Molecular studies demonstrate upregulation of genes such as KLF4 and FLT3 that promote stemness, and overexpression of MYC, which is associated with suppression of myeloid cell differentiation. This murine model, therefore, provides an opportunity to develop therapeutic strategies against the most common subtype within these FGFR1 driven neoplasms and opportunities for a more in depth study the molecular etiology of this disease.

Mutation in the FGFR1 tyrosine kinase domain or inactivation of PTEN is associated with acquired resistance to FGFR inhibitors in FGFR1‐driven leukemia/lymphomas

“…Despite minor differences, such as the presence of eosinophilia in some cases, or a preference for the development of T‐lymphoma or B‐lymphoma between the subsets of common rearrangements, the BCR‐FGFR1 gene stands out in that this is typically a more aggressive disease. We have also seen this in our model systems where disease onset is disproportionately early amongst the mouse syngeneic models as well as in human xenograft models using transformed CD34+ stem cells . The BCR‐FGFR1 rearrangement is also distinct amongst the SCLL rearrangements in that the BCR component of the chimeric gene encodes for a serine‐threonine kinase which may modify and enhance the phenotypes generated as a result of its expression.…”

“…Although we have defined two mechanisms of resistance to FGFR1 inhibitors, it is possible that other mechanisms may arise that will need alternative strategies to treat these resistant clones. Extensive molecular analyses of SCLL models in vivo and in vitro have suggested some potential targets, [13][14][15]25,30,41 such as FLT3, MYC and NOTCH1. Although AML is the primary consequence of constitutive activation of FGFR1 in SCLL, B-and T-cell lymphomas also develop.…”

“…Recently, a patient with BCR‐FGFR1 driven SCLL treated with ponatinib showed partial morphological remission after 12 weeks treatment and markedly reduced disease burden following bone marrow transplantation, demonstrating the importance of FGFR1 kinase activity in a clinical setting . As a result of our development of mouse models of SCLL several cell lines expressing different chimeric kinases have been developed and have proved useful in evaluating the effectiveness of various anti‐FGFR1 drug regimens …”

FGFR1 fusion kinase regulation of MYC expression drives development of stem cell leukemia/lymphoma syndrome

“…Because human leukemia/lymphomas associated with FGFR1 rearrangement is rare, we have developed several humanized mouse models engrafted with the FGFR1 fusion kinase-transduced human CD34+ progenitor cells in immunocompromised mice as described previously. 4 , 7 , 8 CD34+ progenitor cells transduced with either ZMYM2-FGFR1, 7 CNTRL-FGFR1, 4 or BCR-FGFR1, 8 developed acute myeloid leukemia (AML) with a human CD45+CD13+CD34+/CD38+ immunophenotype. Quantitative RT-PCR analysis showed that MYC is highly transcribed in cells from mouse spleens from all three models compared with either control pMIG3 transduced mouse splenocytes or healthy human PBMC ( Figure 2 ).…”

Concise Review: Regulation of Self-Renewal in Normal and Malignant Hematopoietic Stem Cells by Krüppel-Like Factor 4

“…In addition to CpG methylation, downregulation of KLF4 is associated with deregulation of microRNAs such as miR‐10a and miR‐10b, and the transcriptional repression of KLF4 by CDX2 in AML is associated with inhibition of PPARγ signaling . Conversely, when human CD34 + cells are transduced with ZMYM2‐FGFR, the fusion protein product of the t(8;13)(p11;q12) chromosomal translocation found in myeloproliferative neoplasm, and transplanted into NSG mice, the mice display elevated KLF4, suggesting a potential oncogenic function . In contrast, AML patients with a low level of HDAC1, which is negatively correlated with KLF4 level, exhibit better prognosis .…”