Abstract 3524: Functional characterization of KIT and FcεR1 receptor mutations in Mast Cell Leukemia using Single Cell Network Profiling (SCNP).
Authors: Westfall Matt , Spector Mona S. , Gulrajani Michael , Marimpietri Carol , Kritharis Athena , Fields Scott Z. , Allen Steven L. , Hawtin Rachael 
Published: August 2014

Abstract
Background: A recent report described an imatinib/dasatinib (Imat/Dasat) resistant MCL patient (pt) with mutations in KIT (V654A) and FcεR1 (L188F) receptors [Spector et al, Leukemia 2011]. The pt did not respond to cytarabine-based induction therapy combined with Dasat or to post-induction Imat. The functional consequence of the receptor mutations on downstream signaling networks, and sensitivity to alternative therapeutics, was unknown. SCNP is a flow cytometry-based assay that quantitatively and simultaneously measures, in single cells, extracellular surface markers and activation of intracellular signaling proteins in response to modulation. SCNP was applied to interrogate downstream signaling networks and network sensitivity to targeted therapeutics by examining:
1) Basal and modulated signaling using stem cell factor (SCF) or α-IgE
2) Effect on basal and modulated signaling of:
a) KIT inhibitors Imat, Dasat, and Nilotinib
b) PI3K inhibitor GDC-0941
c) SYK inhibitor fostamatinib R406
Methods: Cryopreserved MCL BMMCs and healthy donor BMMCs were processed alongside fresh healthy donor basophils (FHDB) as controls. BMMCs were modulated with SCF for 5 and 15 min +/-KIT or PI3K inhib. MCL BMMCs and FHDB were modulated with α-IgE for 5min +/- fostamatinib. Signaling in the KIT and FcεR1 pathways was quantified through measurement of p-AKT/ p-ERK/ p-S6 and p-ERK/ p-PLCγ2 / p-SYK levels, respectively, in the MCL population: CD45+, CD34+, CD33+, and CD117+.
Results: As previous reported, the V654A KIT mutation did not result in constitutive activation of the PI3K or MAPK pathways in MCL blasts, but was associated with dysfunctional SCF modulated signaling. Specifically, SCNP identified SCF induced p-AKT levels at 5min, higher (2X) compared to CD34+/CD117+ FHDB, and sustained to 15min with no simultaneous induction of p-ERK or p-S6. Consistent with the clinically observed Imat/Dasat resistance of the MCL case, in vitro AKT induction was unaffected by the presence of KIT inhibitors but sensitive to the PI3K inhib GDC-0941. KIT inhibitors and GDC-0941 blocked SCF induced signaling in the healthy BMMC control. Despite robust p-ERK induction in the FHDB control after α-IgE modulation of the FcεR1 receptor and inhibition by fostamatinib treatment, no basal or α-IgE modulated FcεR1 receptor signaling was detected in MCL BMMC cells.
Conclusions: SCNP functionally characterizes signaling and drug resistance profiles in MCL BMMCs and can potentially inform on therapeutic selection. Despite robust p-ERK induction in the FHDB control after α-IgE modulation of the FcεR1 receptor and inhibition by fostamatinib treatment, no basal or α-IgE modulated FcεR1 receptor signaling was detected in the cryopreserved MCL BMMCs. Further studies will elucidate whether the lack of detected signal could be related to the freeze/thaw process and/or to cell-type specific differences.
Citation Format: Matt Westfall, Mona S. Spector, Michael Gulrajani, Carol Marimpietri, Athena Kritharis, Scott Z. Fields, Steven L. Allen, Rachael Hawtin. Functional characterization of KIT and FcεR1 receptor mutations in Mast Cell Leukemia using Single Cell Network Profiling (SCNP). [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3524. doi:10.1158/1538-7445.AM2013-3524