[Mechanism of BIM-induced ibrutinib resistance in chronic lymphocytic leukemia]

Objective: To investigate the relationship between the BCL2 family protein BIM and ibrutinib resistance in chronic lymphocytic leukemia (CLL) and to analyze its regulatory mechanisms on apoptosis and autophagy. Methods: RNA sequencing (RNA-seq) was used to examine changes in the expression of BCL2 family proteins in samples from patients with CLL, MEC1 cell lines, and ibrutinib-resistant cell lines (MR). Western blot was used to analyze changes in BIM protein expression during apoptosis in MR. shRNA knockdown was used to assess the effects of BIM on cell proliferation and apoptosis. RNA-seq and the autophagy inhibitor chloroquine treatment were used to study autophagy-related changes in MR. Results: BIM expression was significantly downregulated before and after drug resistance in CLL primary cells and MEC1 cell lines (P<0.0001). Knockdown of BIM in CLL cells inhibited ibrutinib-induced apoptosis and promoted cell proliferation (P<0.05 for both). In addition, protective autophagy was increased in MR and apoptosis was increased after administration of chloroquine and small interfering RNA. The increased expression of LC3-Ⅱ protein in BIM-knockdown cell lines (P<0.01) suggested that reduction of BIM may mediate autophagy activation. Conclusion: Downregulation of BIM may be a key factor in promoting ibrutinib resistance in CLL by activating protective autophagy. These findings provided a potential target for improving CLL treatment.