8-Amino-adenosine and induction of apoptosis in multiple myeloma: Effect of novel purine analog on cellular signaling pathways

Multiple myeloma (MM) is a slowly proliferating B-cell malignancy, which accounts for 10% of all hematologic cancers. MM responds poorly to traditional chemotherapeutics, and remains incurable despite aggressive, high-dose therapy and advances in autologous stem cell transplants. Therefore, new therapeutic approaches that prolong survival and quality of life of MM patients are severely needed. 8-Amino-adenosine (8-NH2-Ado) is a purine nucleoside analog shown to have a potent, apoptotic affect in pre-clinical studies in myeloma cell lines both sensitive and resistant to conventional chemotherapies. This apoptotic effect requires phosphorylation of 8-NH2-Ado to its tri-phosphate form, and accumulation of 8-NH2-ATP results in a concomitant loss of endogenous ATP levels.; A novel effect of 8-NH2-Ado on the phosphorylation status of key cellular signaling molecules is described in this dissertation. MM cells treated with 8-NH2-Ado exhibit a rapid and dramatic loss of phosphorylation of several important signaling proteins, including p38 MAPK, ERK1/2, and Akt kinase. However, cells depleted of ATP by antimycin A or 2-deoxyglucose treatment to mimic 8-NH2-Ado-induced ATP depletion do not exhibit the same decrease in phosphorylation of vital cellular proteins. Therefore, the significant shifts in endogenous ATP pools caused by 8-NH 2-Ado treatment are not sufficient to induce the changes in phosphorylation levels. Instead, 8-NH2-Ado appears to be partially affecting the activity of protein phosphatases involved in the negative regulation of these signaling molecules. Based on studies using the phosphatase inhibitor okadaic acid, it appears that PP2A may play a role in the 8-NH2-Ado-induced decrease in phosphorylation of p38. The distinctive effect of 8-NH2-Ado on the phosphorylation status of cellular proteins is a novel phenomenon for a nucleoside analog drug and is unique to 8-NH2-Ado among this class of drugs.; The kinetics of 8-NH2-Ado-mediated changes in phosphorylation levels of critical pro-survival and apoptosis-regulating proteins suggest that the modulation of these proteins at early time-points may be an important mechanistic step in 8-NH2-Ado induced apoptosis. Given its potent in vitro anti-tumor activity and its ability to specifically target signaling pathways involved in myeloma cell growth and proliferation, 8-NH2-Ado shows remarkable promise as a novel therapeutic agent in the treatment of MM.