Ex Vivo Mitochondrial Respiration Parallels Biochemical Response to Ibrutinib in CLL Cells

SIMPLE SUMMARY: Chronic lymphocytic leukemia (CLL) is a cancer that is characterized by dysfunctional mitochondria. This results in a deranged mitochondrial metabolism. Many drugs are tested using simple live or dead cell assays and as such the impact on the altered mitochondrial function is not evaluated. One such drug is ibrutinib. The use of ibrutinib at full doses can lead to significant side effects resulting in dose reduction or even discontinuation of the drug in clinical practice. In this study, we reviewed the effect of the dose of ibrutinib on mitochondrial function of the CLL cells from patients treated with ibrutinib and did not observe any difference in the mitochondrial respiration. We also evaluated the effect of progression of CLL cells from patients on ibrutinib treatment and the impact on mitochondrial respiration. We believe our findings are novel and suggest that evaluation of mitochondrial function of CLL cells is of importance to help design safe treatments in the preclinical setting. ABSTRACT: Mitochondrial respiration is becoming more commonly used as a preclinical tool and potential biomarker for chronic lymphocytic leukemia (CLL) and activated B-cell receptor (BCR) signaling. However, respiration parameters have not been evaluated with respect to dose of ibrutinib given in clinical practice or the effect of progression on ibrutinib treatment on respiration of CLL cells. We evaluated the impact of low and standard dose ibrutinib on CLL cells from patients treated in vivo on mitochondrial respiration using Oroboros oxygraph. Cytokines CCL3 and CCL4 were evaluated using the Mesoscale. Western blot analysis was used to evaluate the BCR and apoptotic pathways. We observed no difference in the mitochondrial respiration rates or levels of plasma chemokine (C-C motif) ligands 3 and 4 (CCL3/CCL4), β-2 microglobulin (β-2 M) and lactate dehydrogenase (LDH) between low and standard doses of ibrutinib. This may confirm why clinical observations of the safety and efficacy of low dose ibrutinib are observed in practice. Of interest, we also observed that the mitochondrial respiration of CLL cells paralleled the increase in β-2 M and LDH at progression. Our study further supports mitochondrial respiration as a biomarker for response and progression on ibrutinib in CLL cells and a valuable pre-clinical tool.