Cyclic nucleotide phosphodiesterase profiling reveals increased expression of phosphodiesterase 7B in chronic lymphocytic leukemia.

Cyclic nucleotide phosphodiesterase (POE) isoforms can influence disease pathogenesis and be novel therapeutic targets. Because lower cAMP levels may contribute to the decreased apoptosis that occurs in chronic lymphocytic leukemia (CLL), we assessed the expression levels of POE isoforms in peripheral blood mononuclear cells (PBMC) of healthy adults and patients with CLL. We found a unique POE mRNA signature in CLI: higher levels than in normal PBMC of PDE7B (increased ≈23-fold) and lower levels of PDE3B, 4D, 5A, and 9A mRNA (each decreased ≈30-fold). Increased POE7B mRNA in CLL correlates with a 10-fold-higher expression of PDE7B protein and results in an increased contribution of PDE7 to total PDE activity. Consistent with the higherlevel of PDE7B expression, inhibitors of PDE7 (BRL-50481, IR-202) and a dual PDE4/PDE7 inhibitor (IR-284) selectively increase apoptosis in CLI cells compared with normal PBMC or B cells. Apoptosis of CLI cells promoted by inhibitors of PDE7 and PDE4I7 is attenuated by PKA inhibition, occurs via a mitochondrial-dependent process, and is associated with increased cAMP accumulation and down-regulation of the antiapoptotic protein survivin and of PDE7B. The increase in PDE7B expression and PDE7 inhibitor-promoted apoptosis implicates PDE7B as a drug target in CLI. Our findings identify a unique PDE signature in CLL and illustrate the utility of broad analyses of POE isoform expression in human disease. [ABSTRACT FROM AUTHOR]