Combination therapy with CpG oligodeoxynucleotide and imatinib can reverse the drug resistance when applied alone through promoting BAX activation and overcoming BCR-ABL1-independent PI3K/AKT activation.

Abstract

e18502 Background: Philadelphia chromosome is an independent prognostic factor in B-cell acute lymphoblastic leukemia (B-ALL). Due to the emergence of TKIs resistance such as imatinib, new methods are yet to be explored. Toll-like receptor 9 (TLR9) agonists have been used in many cancers as immune adjuvants, due to the immune effects as well as direct effects. However, the effect of TLR9 agonists on Ph(+) B-ALLs remain unknown. Methods: Expression levels in primary B-ALL cells from 41 patients in our hospital were determined by real-time quantitative PCR and correlated to clinicopathological factors. WST-1 cell viability assay and flow cytometry were used to confirm the biological behaviors of proliferation, cell cycle arrested, apoptosis, and surface molecules expression in Ph(+) B-ALL cell line. GST pull-down, western blot, and relevant inhibitors were used to detect the mechanism of the monotherapy and combination therapy. All data were analyzed using SPSS 24.0 software. Results: Expression of TLR9 in 19 patients with Ph chromosome was higher than that in 22 patients with the normal chromosome (Median: 0.10 vs. 0.03, P= 0.047). Sup-B15, one of imatinib resistance Ph(+) B-ALL cell line, showed no proliferation suppression, no cell cycle arrested and no apoptosis after CpG 685 stimulation. However, the combination use of CpG 685 and imatinib significantly increased apoptotic cells and upregulated the expression of CD40, MHC class Ⅰ and PD-L1. By comparing the downstream signaling pathway of TLR9 in B-ALL cell lines, Sup-B15 also promoted apoptosis through P38/P53/BAX signaling pathway as other B-ALLs. After imatinib pre-treatment, the inhibition of BAX activation by BCR-ABL kinase as well as C-MYC was exposed, and the resistance of CpG 685 was reversed. In addition, CpG 685 downregulated miR-21, further upregulated PTEN, and ultimately reversed the drug resistance of imatinib which caused by BCR-ABL1-independent AKT phosphorylation in Ph(+) B-ALL. Conclusions: The combinational use of imatinib and CpG 685 to treat B-ALL cells can reverse the drug resistance when applied alone. This method can not only kill Ph(+) B-ALL directly, but also increase the immunogenicity and enhance the recognition by CD8+ T cells. Besides, due to the increasing of PD-L1, adding PD-L1 antibody with imatinib and CpG ODNs in Ph(+) B-ALL warrants more data before moving into clinical practice.