Cyclic AMP induces apoptosis in multiple myeloma cells and inhibits tumor development in a mouse myeloma model

As a model system, we primarily used the murine multiple myeloma cell line MOPC315 which can be grown both in vivo and in vitro. Human multiple myeloma cell lines U266, INA-6 and the B-cell precursor acute lymphoblastic leukemia cell line Reh were used only for in vitro studies. Cell death was assessed by flow cytometry and western blot analysis after treatment with cAMP elevating agents (forskolin, prostaglandin E2 and rolipram) and cAMP analogs. We followed tumor growth in vivo after forskolin treatment by imaging DsRed-labelled MOPC315 cells transplanted subcutaneously in BALB/c nude mice.In contrast to the effect on Reh cells, 50 μM forskolin more than tripled the death of MOPC315 cells after 24 h in vitro. Forskolin induced cell death to a similar extent in the human myeloma cell lines U266 and INA-6. cAMP-mediated cell death had all the typical hallmarks of apoptosis, including changes in the mitochondrial membrane potential and cleavage of caspase 3, caspase 9 and PARP. Forskolin also inhibited the growth of multiple myeloma cells in a mouse model in vivo.Elevation of intracellular levels of cAMP kills multiple myeloma cells in vitro and inhibits development of multiple myeloma in vivo. This strongly suggests that compounds activating the cAMP signaling pathway may be useful in the field of multiple myeloma.Multiple myeloma (MM) is a B-cell malignancy characterized by accumulation of plasma cells in the bone marrow, osteolytic bone lesions, and immunodeficiency [1]. It accounts for ~10% of hematological malignancies [2] with a median survival of 4 years [3]. Despite the progress made the last decades in the development of new therapies, multiple myeloma remains an incurable disease for which a constant search for new treatment strategies must continue.Cyclic adenosine monophosphate (cAMP) is an intracellular messenger formed in response to diverse extracellular stimuli including hormones or neurotransmitters. It is generated from ATP by adenylyl cyclases, and