A novel stealth liposomal topotecan with amlodipine: apoptotic effect is associated with deletion of intracellular Ca2+ by amlodipine thus leading to an enhanced antitumor activity in leukemia.

The objectives of the present study were to define whether amlodipine induces apoptosis and what mechanism is involved in the process in human resistant and non-resistant leukemia cells following co-administration of stealth liposomal topotecan with amlodipine, a novel antiresistant liposomes developed by our institution. In three leukemias, K562, HL-60, and multidrug resistant (MDR) HL-60, cytotoxicity of topotecan was potentiated by amlodipine, while topotecan alone was resistant to MDR HL-60 cells. In two selected K562 or MDR HL-60 cells, the apoptotic effects were increased by addition of amlodipine, showing a dose-dependent manner. The activities of caspase 3 and 7 (marked as caspase 3/7), and caspase 8 were significantly activated by topotecan with amlodipine co-treated as the stealth liposomes. The deletions of intracellular Ca2+ stores induced by amlodipine correlated with the activated activities of caspase 3/7, or 8, respectively. In xenograft model with MDR HL-60 in nude mice, antitumor activity of stealth liposomal topotecan with amlodipine was significantly enhanced as compared to that of stealth liposomal topotecan or topotecan alone. In conclusion, apoptotic effect is associated with deletion of intracellular Ca2+ by amlodipine through activation of caspase 8 and then 3/7 activities. The enhanced antitumor activities by stealth liposomal topotecan with amlodipine are mainly due to the potentiating apoptotic effect and reversing the resistance by amlodipine. Stealth liposomal encapsulation of anticancer agent with a modulator may provide a novel strategy for improving the chemotherapeutic effects.