Abstract
Chronic Myelogenous Leukemia (CML) is one of myeloproliferative disorders characterized by the chromosome translocation (9; 22), which causes the generation of the Bcr-Abl fusion protein. Latter activates a number of signal transducers and transcription factors, thus leading to multi-resistance to chemotherapeutic agents. Introduction of imatinib mesylate (Gleevec) significantly increased CML patients’ response but still some of patients got disease progression. Therefore, it still remains a high priority to develop new approaches to treat Bcr-Abl+ leukemia. Aim: We aim to investigate the synergy of bortezomib and arsenic trioxide on inducing the apoptosis on Bcr-Abl+ K562-s as well as K562-r cells, which was sensitive or resistant to imatinib treatment respectively. Material and methods: Bcr-Abl+ K562-s and K562-r cells were chosen to evaluate the drugs’ effect. We observed the inhibition of cell growth and cell viability after bortezomib and/or arsenic treatment. Flow cytometric evaluation and western blot analysis were performed to detect the development of apoptosis, the changeable expression of Bcr-Abl protein and the apoptosis-related proteins. Results: K562-s and K562-r cells had different response to imatinib treatment. As expected, 0.25μM of imatinib can inhibit half of K562-s cell growth whereas 10–15 more times of concentration of imatinib were necessary to reach the same inhibitory effect in K562-r cells. Combined bortezomib at 12nM with 1μM of ATO, the concentration inducing 50% of K562-s growth arrest, synergistically induced apoptosis in K562-s cells after 48hrs of cotreatment, confirmed by notable elevation of Annexin V+ cells through flow cytometric analysis, when compared to those in the control or single treatment (p<0.01), and immunoblotting detection of caspase-3 cleavage, degradation of poly-adenosine diphosphate-ribose polymerase (PARP), and decreased expression of Bcr-Abl protein. More surprisingly, 24nM concentration of bortezomib and 2μM of ATO, 2 times of concentration needed for 50% of K562-s cell growth inhibition respectively, inhibited 50% of K562-r cells growth, far less than the increased proportion needed during imatinib treatment. And more of important, although single treatment of bortezomib or ATO had no or little effect on inducing apoptosis, combined treatment significantly induced the apoptosis in K562-r cells (p<0.05), associated with activation of apoptosis-relevant proteins and obvious degradation of Bcr-Abl protein.
Conclusion: Taken together, these findings indicate that bortezomib combined with ATO could be developed into a novel therapeutic strategy for CML. More study will be needed to further explore its potent mechanism involved during cotreatment.
Autophagic degradation of the BCR-ABL oncoprotein and generation of antileukemic responses by arsenic trioxide
