Pharmacological Inhibition of Lck is Able to Revert Glucocorticoid Resistance in Pediatric T-ALL
Authors: Serafin Valentina , Capuzzo Giorgia , Milani Gloria , Bresolin Silvia , Pinazza Marica , Minuzzo Sonia , Indraccolo Stefano , Bortolozzi Roberta , Basso Giuseppe , Accordi Benedetta 
Published: October 2019

Abstract
The AIEOP-BFM group has traditionally used the peripheral blood blast cells count after a 7-day glucocorticoids (GC) prephase to classify patients as Prednisone Good Responders (PGR) or Prednisone Poor Responders (PPR). As described by Schrappe M. in 2011, PPR patients tend to have a worse prognosis, despite the fact that all of them are assigned to the High Risk protocol. Little is known about the molecular mechanisms that lead to GC resistance, guiding our research to the identification of new specific molecular targets in order to develop new approaches to improve therapy efficacy in these patients.
To this end, we performed a Reverse Phase Protein Analysis (RPPA) of 54 PGR and 33 PPR pediatric T-ALL patients at diagnosis, and studied the activation or expression of 87 proteins involved in key cellular signaling pathways. Interestingly, we found a higher expression of LCK phosphorylated at Y505 (inhibited form) in PGR patients (p=0.001), together with a higher phosphorylation of SRC Y416 (active form) in PPR patients (p=0.01). Total LCK and LCK RNA expression were not differentially expressed in the two subgroups of patients, suggesting an increased activation of LCK in PPR patients. Indeed, in agreement with these results, also LCK downstream target PLCɣ, phosphorylated at Y783, resulted hyperactivated in PPR compared to PGR patients (p=0.05), confirmed also by a positive correlation between PLCɣ Y783 and SRC Y416 (r=0.51, p=0.01). Taken together, these results indicate a hyperactivation of the LCK pathway in PPR patients compared to PGR ones. LCK is part of the TCR multiprotein complex together with the GC receptor. In normal T lymphocytes, after GC treatment the complex is disrupted, LCK activation is decreased and downstream prosurvival signaling inhibited, thus leading to cell death. In this light, in GC resistant patients hyperactivated LCK might sustain cell survival regardless of GC activity.
We then tested if FDA-approved or recently developed LCK inhibitors would revert GC resistance in T-ALL cells. GC resistant cell lines ALL-SIL, T-ALL1 and CEM were treated with Dasatinib, Bosutinib, Nintedanib and WH-4-023 alone or in combination with Dexamethasone (Dex). All four inhibitors alone are able to decrease cell survival, and all of them strongly synergize with Dex, bringing to the sensitization of these cells to GC treatment. We also tested these compounds alone or in combination with Dex in 4 PPR T-ALL patients cells derived from xenograft mice. Also in these cases we observed an enhanced sensitization of cells to GC treatment. Finally, corroborating the crucial role of LCK in GC resistance, we observed a strong decrease in cell viability after specific LCK gene silencing and Dex treatment in ALL-SIL cells, together with an increased GC resistance following LCK hyperactivation in P12-ICHIKAWA GC sensitive cells.
Thus, our results strongly suggest that the inhibition of LCK using clinically approved drugs could represent a promising new additional therapeutic strategy to revert drug resistance in high-risk pediatric T-ALL patients.

Disclosures
Indraccolo: OncoMed Pharmaceuticals, Inc.: Research Funding.