Abstract: Background and purpose: With the application of novel agents and immune therapeutic strategies, treatment outcomes of multiple myeloma (MM) patients have dramatically improved including not only rates and depth of response, but also progression-free survival. However, a considerable number of patients become relapsed/refractory cases. Studies revealed that the treatment with cyclic adenosine monophosphate (cAMP) or arsenic trioxide (As₂O₃) might be a promising strategy for MM therapy. The present study aimed to explore the possible effects of cAMP analogue 8-(4-chlorophenylthio) adenosine 3’, 5’-cyclic monophosphate (8-CPT-cAMP) combined with As₂O₃ on MM cells and its potential mechanisms. Methods: The MM cell line U266 cells were treated with different concentrations of As₂O₃ and 8-CPT-cAMP. The proliferation of U266 cells was evaluated through cell counting kit-8 (CCK-8) assay. The synergistic manner of the two agents was determined by calculation of combination index (CI). Meanwhile, flow cytometry was used to analyze the changes of cell cycle distribution and apoptotic rate. Furthermore, Western blot assay was applied to detect expression levels of apoptosis modulator caspase-3 and Bcl-2. Results: After treatment with As₂O₃ and/or 8-CPT-cAMP for 72 and 120 h, the growth inhibition rates of U266 cells in combination groups reached (18.01±0.13)% and (28.01±0.14)%, which were significantly higher than those in As₂O₃ or 8-CPT-cAMP alone group ［As₂O₃ group: (11.35±0.01)% and (16.01±0.14)%; 8-CPT-cAMP group: (12.26±0.30)% and (15.43±0.23)%; P<0.05］. The CI value of As₂O₃ combined with 8-CPT-cAMP was higher than one in U266 cells. The apoptotic rates of U266 cells in combination groups were (22.26±0.13)% and (31.03±0.14)%, which were significantly higher than those in As₂O₃ or 8-CPT-cAMP alone group ［As₂O₃ group: (10.06±0.01)% and (12.35±0.14)%; 8-CPT-cAMP group: (13.26±0.30) % and (18.76±0.23)%; P<0.05］. It was also shown that As₂O₃ combined with 8-CPT-cAMP induced degradation of caspase-3 and down-regulated expression of Bcl-2 in U266 cells. Conclusion: The effect of As₂O₃ combined with 8-CPT-cAMP on induction of apoptosis in MM cells was stronger than that of single drug, but there was no synergistic effect.

Key words: Arsenic trioxide, Cyclic adenosine monophosphate, Multiple myeloma, Apoptosis