Activating mutations of the interleukin-7 receptor (IL7R) occur in approximately 10% of patients with T-cell acute lymphoblastic leukemia. Most mutations generate a cysteine at the transmembrane domain leading to receptor homodimerization through disulfide bond formation and ligand-independent activation of STAT5. We hypothesized that the reducing agent N-acetylcysteine (NAC), a well-tolerated drug used widely in clinical practice to treat acetaminophen overdose, would disrupt disulfide bond formation, and inhibit mutant IL7R-mediated oncogenic signaling.
To first identify a suitable cell model to study mutant IL7R signaling, we sequenced exon 6 of IL7R in 21 T-ALL cell lines. We identified a 4-amino-acid insertion (p.L242_L243insLSRC) in DND-41 cells which is predicted to form IL7R homodimers through disulfide bond formation with the unpaired cysteine of neighboring mutant IL7Rs. We found that treatment with NAC at clinically achievable concentrations disrupted IL7R homodimerization in IL7R-mutant DND-41 cells in vitro (IC50 approximately 150 micromolar) and led to STAT5 dephosphorylation and cell apoptosis. These effects could be rescued in part by a constitutively active allele of STAT5, indicating the mechanism of NAC is mediated predominantly through disruption of IL7R-STAT5 signaling in these cells. In a murine xenograft model of T-ALL, intraperitoneal NAC treatment led to significant inhibition of tumor progression, indicating NAC has activity in vivo. Previous studies of NAC pharmacokinetics in humans have shown steady state plasma levels range from 200 to 900 micromolar when given on standard treatment regimens for acetaminophen overdose, well within the therapeutic range required to kill DND-41 cells in vitro. Targeting leukemogenic IL7R homodimerization with NAC offers a potentially effective, cheap and feasible therapeutic strategy that warrants testing in clinical trials.
Rodig:Daiichi-Sankyo/Arqule Inc., Ventana/Roche Inc., Shape Pharmaceuticals Inc.: Consultancy; Ventana/Roche Inc.: Research Funding.
Asterisk with author names denotes non-ASH members.