Chloroquine Enhances BIIB021-induced Apoptosis in Chronic Myeloid Leukemia Cells Bearing T315I Mutation

Abstract

To explore the combined pro-apoptosis effect of HSP90 inhibitor BIIB021 and chloroquine (CQ) in chronic myeloid leukemia (CML) cells bearing T315I mutation and its mechanism. The p210-T315I cells were divided into 4 groups by different treatment: control, BIIB021, CQ, and BIIB021 + CQ. After treated with BIIB021 or/and CQ for 24 hours, Annexin V/PI binding assay was used to detect apoptosis rates of CML cells. DAPI staining was used to observe nuclear fragmentation, and Western blot was used to detect the expression of caspase 3, PARP (apoptosis related proteins) and p62, LC3-I/II (autophagy related proteins). P210-T315I cells were inoculated subcutaneously into mice and CML mouse models were established. The mice in treatment groups were injected with BIIB021 and/or CQ while mice in control group were treated with PBS and normal saline. The tumor volume of mice was measured every 4 days, and protein level of cleaved-caspase 3 and LC3-II in tumor tissue were detected by immunohistochemistry. The results showed that BIIB021 induced apoptosis of CML cells in a dose-dependent manner ( r=0.91). CQ could enhance the apoptosis-inducing effect of BIIB021. Flow cytometry analysis results showed that the apoptosis rate of p210-T315I cells in combination group was higher than that in BIIB021 or CQ only group (P<0.05). DAPI staining showed nuclear fragmentation in combination group could be observed more obviously. Western blot analysis showed that BIIB021 could induce LC3-I to convert to LC3-II and decrease p62 protein levels (P<0.05). Moreover, the combination group had higher expression of LC3-II, p62 (P<0.05), activated PARP and activated caspase 3 than BIIB021 only group (P<0.05). Besides, experiment in vivo showed the mean tumor volume in co-treatment group was lower than that in single drug group (P<0.01). Immunohistochemistry of tumor tissue also showed the protein level of cleaved-caspase 3 and LC3-II in combined group was higher than that in BIIB021 only group. HSP90 inhibitor BIIB021 induced significant apoptosis of CML cells bearing T315I both in vivo and in vitro. CQ can enhance this effect probably by autophagy inhibition.