Abstract 997: Targeting the Jak/Stat signaling pathway is highly effective in xenograft models of early T cell precursor (ETP) acute lymphoblastic leukemia (ALL)
Authors: Maude Shannon L. , Dolai Sibasish , Delagdo-Martin Cristina , Vincent Tiffaney , Robbins Alissa , Selvanathan Arthavan , Ryan Theresa , Hunger Stephen P. , Loh Mignon L. , Mullighan Charles G. , Wood Brent L. , Hermiston Michelle L. , Grupp Stephan A. , Lock Richard B. , Teachey David T. 
Published: May 2015

ETP ALL is a recently described subtype of T-ALL with poor prognosis and is defined by a unique immunophenotype, expressing T-lineage and myeloid/early progenitor markers. ETP ALL blasts have a diverse array of genetic alterations without a unifying mutated gene or pathway. A fraction have mutations in genes involved in Jak/Stat signaling, and we hypothesized targeting Jak/Stat may be effective for some ETP ALL patients.

We evaluated Jak/Stat signaling by phosphoflow cytometry and immunoblotting of blasts collected from patients with ETP ALL with and without Jak/Stat pathway mutations and compared them to non-ETP T-ALL blasts. We xenografted blasts from 6 different ETP ALL patient samples with heterogeneous mutations (Table) into immunodeficient NSG mice and tested the in vivo efficacy of the Jak1/2 inhibitor ruxolitinib (rux). Mice were randomized to rux or vehicle after they developed &gt;1% peripheral blood (pb) blasts (cytoCD3+/CD45+) by flow cytometry (FACS). Disease burden was assessed by FACS enumeration of pb blasts weekly and splenic blasts at sacrifice.

We found that the Jak/Stat signaling pathway was dysregulated in ETP ALL samples, including in samples without identifiable mutations in Jak/Stat. ETP ALL blasts had marked increased expression of pSTAT1 (p = 0.01), pSTAT3 (p = 0.01) and pSTAT5 (p = 0.02) when compared to non ETP T-ALL by immunoblot, results confirmed by phosphoflow. All 6 ETP samples had a profound in vivo response to rux; circulating and splenic blasts were markedly reduced in all treated animals compared to controls (Table). The degree of response was comparable to that seen with TKIs in BCR-ABL ALL, using the same xenograft model. These results strongly suggest that ETP ALL blasts may be addicted to Jak/Stat signaling, irrespective of the presence of identifiable Jak/Stat mutations and that clinical trials testing Jak/Stat inhibitors are needed.

Ruxolitinib is active in ETP ALLGenetic alterationAvg splenic blasts in millions. Control vs Rux Treated (p value by 2-tailed t-test)DNM2 m, JAK3 m157 vs 5 (p &lt;0.01)PTPN11 SV124 vs 31 (p &lt;0.01)GATA3 del, JAK1m, SH2B3 SV192 vs 18 (p &lt;0.01)EZH2 m, RUNX1 m, NOTCH1 m, IKZF1m, SUZ12 m, SH2B3 SV452 vs 25 (p &lt;0.01)EED m256 vs 1 (p &lt;0.01)GATA3 m, JAK1 m, PTEN del, RB1 del, CDKN2A/B del332 vs 4 (p &lt;0.01)m = mutation; del = deletion; SV = structural variationPK obtained from mice demonstrated serum levels that correlate with humans treated with drug and that would be expected to target JAK1 and JAK2 but not JAK3.

Citation Format: Shannon L. Maude, Sibasish Dolai, Cristina Delagdo-Martin, Tiffaney Vincent, Alissa Robbins, Arthavan Selvanathan, Theresa Ryan, Stephen P. Hunger, Mignon L. Loh, Charles G. Mullighan, Brent L. Wood, Michelle L. Hermiston, Stephan A. Grupp, Richard B. Lock, David T. Teachey. Targeting the Jak/Stat signaling pathway is highly effective in xenograft models of early T cell precursor (ETP) acute lymphoblastic leukemia (ALL). [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 997. doi:10.1158/1538-7445.AM2014-997