Abstract
Approximately one third of patients suffering from acute myeloid leukemia (AML) harbor an internal
tandem duplication in the FLT3 gene (FLT3-ITD), which is clinically associated with an increased rate of
relapse in response to standard therapies. As a result, targeted small molecules such as quizartinib, a
type 2 FLT3 inhibitor that induces differentiation of AML cells, have garnered attention as a means by
which relapsed FLT3-ITD+ AML can be effectively treated. Unfortunately, the median duration response
of these patients to quizartinib was found to be 12.1 weeks due to the acquisition of secondary mutations
at the D835 locus in the FLT3 gene. A second type 1 inhibitor of FLT3-ITD, midostaurin, was developed
by Novartis, which, as a single agent failed to induce complete remission (CR) and when bone marrow
was analyzed, there was no significant difference seen between the midostaurin-treated and placebo
groups. However, in combination with chemotherapy, the CR rate was 59% compared to 54% CR
induced by chemotherapy alone. Midostaurin, in combination with daunorubicin and cytarabine,
decreased the risk of AML-related death by 22% compared with placebo and was approved by the FDA
for the treatment of AML. To explain the lack of efficacy of midostaurin as a single agent, it has been
proposed that AML cells often overexpress SRC family kinases and their elevated expression may
provide a survival advantage. This theory was further supported by studies which showed that
combination of midostaurin and dasatinib (a SRC inhibitor) were more effective in killing FLT3-ITD+
cell lines (in vitro) than single agent therapy. These observations suggest that there is a need to develop
additional FLT3 inhibitors which can induce complete remission in AML patients harboring mutant
FLT3. To address this medical need, we developed a compound that inhibits both FLT3 and SRC family
kinases (150030). 150030 is a Type I inhibitor that inhibits the FLT3-ITD as well as the D835 mutant forms.
Cell viability assays showed that 150030 induced apoptosis of FLT3-mutant AML cells while sparing
AMLs with WT-FLT3. 150030 is orally bioavailable, exhibited excellent pharmacological profile and
induced complete regression of tumors in nude mouse xenograft assays. The studies proposed are aimed
at further evaluating the mechanism of action and therapeutic potential of 150030 in an effort to advance
this compound to clinical trials. The aims are: (1) To compare the effects of midostaurin and 150030 on
the growth and differentiation of murine myeloid cell line, 32Dcl3, co-expressing FLT3-ITD and SRC
family kinases and determine the effects of these two compounds on leukemia progression in syngeneic
animal models; (2) To compare the efficacy of 150030 and midostaurin in clinically relevant PDX models
of AML to develop protocols for a single agent and combination therapy; and (3) To determine the
resistance mechanisms associated with 150030.