A Novel Approach Combining Type II JAK Inhibitor Chz-868 with Nutrient Restriction to Augment Cell Death in Philadelphia like Acute Lymphoblastic Leukemia

Background: There is an urgent clinical need to improve therapeutic outcomes in Philadelphia chromosome–like acute lymphoblastic leukemia (Ph-like ALL). Approximately 60% of Ph-like cases harbor rearrangements in the CRLF2 locus, often with accompanying mutations in JAK kinases. Current clinical trials are assessing whether ruxolitinib, a type I JAK inhibitor, can enhance responses to chemotherapy in CRLF2-r acute leukemias. Notably, preclinical studies have shown that type II JAK inhibitors provide greater anti-leukemic effects than ruxolitinib. Other work has demonstrated promising ability of nutrient limitation to enhance the efficacy of tyrosine kinase inhibitors (TKIs) in solid tumors and chemotherapy in hematologic malignancies. Indeed, there is growing excitement for short-term application of fasting-mimicking diet (FMD), since clinical studies have shown promising therapeutic efficacy with higher compliance rates than other dietary interventions. The objectives of this study were to compare the cytotoxicity of type I and II JAK inhibitors in CRLF2-r Ph-like ALL, and to determine whether nutrient restriction via FMD enhances JAK inhibitor efficacy.

Methods: We conducted both in vitro and in vivo experiments. For in vitro experiments, we used the human B-precursor ALL cell lines MUTZ5 and MHH-CALL-4 as well as patient derived Ph-like ALL cells that carry CRLF2 translocation. We used flow cytometry techniques to measure cell viability. Western blotting analysis was used to quantify pro-survival and pro-apoptotic proteins in the treated cell lines. For in vivo experiments, we used mouse patient-derived xenograft (PDX) model in which NSG mice were injected with patient derived Ph-like ALL cells.

Results: In vitro experiments confirmed that the type II JAK inhibitor CHZ-868 had more potent cytotoxic effects than ruxolitinib in CRLF2-r cell lines and cells derived from PDX models. Short-term starvation with low glucose and low serum strongly sensitized CRLF2-r cell lines to CHZ-868 cytotoxicity. Mechanistically, the combination of CHZ-868 and starvation was associated with decreased expression of the pro-survival protein MCL-1 and increased expression of the pro-apoptotic protein BIM. In vivo experiments using a CRLF2-r PDX model showed that FMD reduced leukemic burden and enhanced the efficacy of CHZ-868.

Conclusion: Efficacy of the type II JAK inhibitor CHZ-868 in CRLF2-r cells is enhanced by nutrient restriction. These results provide proof-of-concept for testing FMD as a diet-based approach to enhance TKI efficacy in Ph-like B-ALL patients.