Dual Targeting of Apoptotic and Signaling Pathways in T-Lineage Acute Lymphoblastic Leukemia

Purpose: Relapsed T-acute lymphoblastic leukemia (T-ALL) has limited treatment options. We investigated mechanisms of resistance to BH3 mimetics in T-ALL to develop rational combination strategies. We also looked at the preclinical efficacy of NWP-0476, a novel Bcl-2/Bcl-xL Inhibitor, as single agent and combination therapy in T-ALL.

Experimental design: We used BH3 profiling as a predictive tool for BH3 mimetic response in T-ALL. Using isogenic control, venetoclax-resistant (ven-R) and NWP-0476-resistant (NWP-R) cells, phosphokinase array was performed to identify differentially regulated signaling pathways.

Results: Typical T-ALL cells had increased dependence on Bcl-xL, whereas early T-precursor (ETP)-ALL cells had higher Bcl-2 dependence for survival. Bcl-2/Bcl-xL dual inhibitors were effective against both subtypes of T-lineage ALL. A 71-protein human phosphokinase array showed increased Lck activity in ven-R cells, and increased Ack1 activity in ven-R and NWP-R cells. We hypothesized that pre-TCR and Ack1 signaling pathways are drivers of resistance to Bcl-2 and Bcl-xL inhibition, respectively. First, we silenced Lck gene in T-ALL cell lines, which resulted in increased sensitivity to Bcl-2 inhibition. Mechanistically, Lck activated NF-κB pathway and the expression of Bcl-xL. Silencing Ack1 gene resulted in increased sensitivity to both Bcl-2 and Bcl-xL inhibitors. Ack1 signaling upregulated Akt pathway, which inhibited the pro-apoptotic function of BAD. In a T-ALL patient-derived xenograft model, combination of NWP-0476 and dasatinib demonstrated synergy without major organ toxicity.

Conclusions: Lck and Ack1 signaling pathways are critical regulators of BH3 mimetic resistance in T-ALL. Combination of BH3 mimetics with tyrosine kinase inhibitors might be effective against relapsed T-ALL.