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Type 4 cyclic adenosine monophosphate phosphodiesterase as a therapeutic target in chronic lymphocytic leukemia
1Department of Medicine, Section of Hematology and Oncology, Boston Medical Center, Boston, MA 02118, USA.
Abstract:
Theophylline, a drug known to inhibit several classes of adenosine 3'5' cyclic monophosphate (cAMP) phosphodiesterases (PDEs), induces apoptosis in chronic lymphocytic leukemia (CLL) cells. Because the PDE target for theophylline in CLL remains unknown, we examined the ability of isoform-specific PDE inhibitors to increase cAMP levels and induce apoptosis in primary CLL cells. Reverse transcriptase-polymerase chain reaction of purified CLL cDNA amplified transcripts for PDE1B, 4A and 4B. The type 4 PDE inhibitor rolipram but not the type 1 inhibitor vinpocetine increased CLL cAMP levels. Rolipram-inhibitable (type 4) but not calcium-calmodulin augmented (type 1) PDE enzyme activity was detected in CLL samples. In samples from 13 of 14 CLL patients, rolipram induced apoptosis in a dose-dependent fashion over a 48-hour period. Interleukin-2 (IL-2)-cultured whole mononuclear cells (WMC) and anti-Ig stimulated CD19(+) B cells were resistant to the induction of apoptosis by rolipram while unstimulated CD19(+) B cells, which had a high basal apoptotic rate, were more sensitive. Rolipram stimulated elevations in cAMP levels in all four of these cell populations, suggesting that they differed in sensitivity to cAMP-induced apoptosis. Consistent with this hypothesis, incubation with the cell permeable cAMP analog dibutyryl-cAMP induced apoptosis in CLL cells and unstimulated B cells but not in IL-2-cultured WMC or anti-Ig stimulated B cells. These data identify PDE4 as a family of enzymes whose inhibition induces apoptosis in CLL cells.
Insights
Theophylline induces apoptosis in chronic lymphocytic leukemia (CLL) cells by inhibiting phosphodiesterase 4 (PDE4) enzymes. This inhibition increases cyclic adenosine monophosphate (cAMP) levels, triggering programmed cell death in CLL cells.
Area of Science:
- Molecular Biology
- Cell Biology
- Pharmacology
Background:
- Theophylline is known to inhibit phosphodiesterases (PDEs) and induce apoptosis in chronic lymphocytic leukemia (CLL) cells.
- The specific PDE targeted by theophylline in CLL remains unidentified.
Purpose of the Study:
- To investigate the role of specific PDE isoforms in mediating the apoptotic effects of theophylline in CLL.
- To determine if PDE inhibitors can induce apoptosis in primary CLL cells by modulating cyclic adenosine monophosphate (cAMP) levels.
Main Methods:
- Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to identify PDE transcripts in CLL cells.
- Isoform-specific PDE inhibitors (rolipram for PDE4, vinpocetine for PDE1) were used to assess their effects on cAMP levels and apoptosis.
- Enzyme activity assays were performed to detect PDE1 and PDE4 activity in CLL samples.
- Apoptosis was measured in CLL cells and various B cell populations after treatment with rolipram and a cAMP analog (dibutyryl-cAMP).
Main Results:
- CLL cells express PDE1B, PDE4A, and PDE4B.
- The PDE4 inhibitor rolipram, but not the PDE1 inhibitor vinpocetine, increased cAMP levels in CLL cells.
- Rolipram-inhibitable PDE4 enzyme activity was detected in CLL samples.
- Rolipram induced dose-dependent apoptosis in primary CLL cells from 13 out of 14 patients.
- While rolipram increased cAMP in all tested cell populations, only CLL cells and unstimulated B cells underwent apoptosis, indicating differential sensitivity to cAMP-induced apoptosis.
Conclusions:
- PDE4 represents a family of enzymes that, when inhibited, can induce apoptosis in chronic lymphocytic leukemia cells.
- Targeting PDE4 with specific inhibitors is a potential therapeutic strategy for CLL.
- The sensitivity to cAMP-induced apoptosis varies among different B cell populations in CLL.