Preventing chemotherapy-induced myelosuppression by repurposing the FLT3 inhibitor quizartinib.

We describe an approach to inhibit chemotherapy-induced myelosuppression. We found that short-term exposure of mice to the FLT3 inhibitor quizartinib induced the transient quiescence of multipotent progenitors (MPPs). This property of quizartinib conferred marked protection to MPPs in mice receiving fluorouracil or gemcitabine.

Dasatinib promotes the activation of quiescent hematopoietic stem cells in mice.

Dasatinib is an orally available broad-spectrum tyrosine kinase inhibitor that is widely used to treat chronic myeloid leukemia. It is also in clinical trials for the treatment of other malignancies, including solid tumors. Despite its wide use, little is known of its effects on normal hematopoietic stem and progenitor cells.

The targeting of human and mouse B lymphocytes by dasatinib.

Dasatinib inhibits B-cell receptor-Abelson murine leukemia viral oncogene homologue 1, Src, and other tyrosine kinases. Few studies have addressed the impact of dasatinib on normal blood cells, especially in vivo. Here we show that dasatinib leads to a reduced number of human CD19+ peripheral B cells owing to a strong induction of apoptosis.

Loss of c-Cbl E3 ubiquitin ligase activity enhances the development of myeloid leukemia in FLT3-ITD mutant mice.

Mutations in the Fms-like tyrosine kinase 3 (FLT3) receptor tyrosine kinase (RTK) occur frequently in acute myeloid leukemia (AML), with the most common involving internal tandem duplication (ITD) within the juxtamembrane domain. Fms-like tyrosine kinase 3-ITD mutations result in a mislocalized and constitutively activated receptor, which aberrantly phosphorylates signal transducer and activator of transcription 5 (STAT5) and upregulates the expression of its target genes. c-Cbl is an E3 ubiquitin ligase that negatively regulates RTKs, including FLT3, but whether it can downregulate mislocalized FLT3-ITD remains to be resolved.

Dasatinib targets B-lineage cells but does not provide an effective therapy for myeloproliferative disease in c-Cbl RING finger mutant mice.

This study aimed to determine whether the multi-kinase inhibitor dasatinib would provide an effective therapy for myeloproliferative diseases (MPDs) involving c-Cbl mutations. These mutations, which occur in the RING finger and linker domains, abolish the ability of c-Cbl to function as an E3 ubiquitin ligase and downregulate activated protein tyrosine kinases. Here we analyzed the effects of dasatinib in a c-Cbl RING finger mutant mouse that develops an MPD with a phenotype similar to the human MPDs.

Flt3 inhibitor AC220 is a potent therapy in a mouse model of myeloproliferative disease driven by enhanced wild-type Flt3 signaling.

High levels of expression of wild-type Flt3 characterize many hematopoietic proliferative diseases and neoplasms, providing a potential therapeutic target. Using the c-Cbl RING finger mutant mouse as a model of a myeloproliferative disease (MPD) driven by wild-type Flt3, in the present study, we show that treatment with the Flt3 kinase inhibitor AC220 blocks MPD development by targeting Flt3(+) multipotent progenitors (MPPs). We found that daily administration of AC220 caused a marked reduction in Flt3 expression, induction of quiescence, and a significant loss of MPPs within 4 days.

c-Cbl promotes T cell receptor-induced thymocyte apoptosis by activating the phosphatidylinositol 3-kinase/Akt pathway.

The ability of thymocytes to assess T cell receptor (TCR) signaling strength and initiate the appropriate downstream response is crucial for determining their fate. We have previously shown that a c-Cbl RING finger mutant knock-in mouse, in which the E3 ubiquitin ligase activity of c-Cbl is inactivated, is highly sensitive to TCR-induced death signals that cause thymic deletion. This high intensity signal involves the enhanced tyrosine phosphorylation of the mutant c-Cbl protein promoting a marked increase in the activation of Akt.

Unaltered negative selection and Treg development of self-reactive thymocytes in TCR transgenic Fyn-deficient mice.

The tyrosine kinase Fyn has been implicated as playing an important role in the generation of both stimulatory and inhibitory signaling events induced by TCR engagement. To assess the role of Fyn for antigen-driven negative selection and Treg development, which are both dependent on the strength and nature of TCR signaling, we generated mice that co-express the transgenes for OVA and the OT-II TCR, which recognizes a peptide from OVA. In mice expressing both transgenes, negative selection, Treg development in the thymus, and the number of Treg in the periphery were each unaffected by ablation of Fyn.

The Cbl-b RING finger domain has a limited role in regulating inflammatory cytokine production by IgE-activated mast cells.

The RING finger type E3 ubiquitin ligase, Cbl-b, is abundantly expressed in bone marrow-derived mast cells (BMMCs) and functions as a potent negative regulator of signalling responses from the high-affinity IgE receptor (FcvarepsilonRI). To determine the contribution of Cbl-b E3 ligase activity we generated knockin mice with a loss-of-function mutation in the RING finger domain. We find the mice to be healthy and, unlike equivalent c-Cbl RING finger mutant mice, produce homozygous offspring at the expected frequency.