Suppression of cyclic GMP-specific phosphodiesterase 5 promotes apoptosis and inhibits growth in HT29 cells

Abstract

Phosphodiesterase 5 (PDE5) is a major isoform of cGMP phosphodiesterase in a variety of human tumor cell lines and plays a key role in regulating intracellular cGMP concentrations ([cGMP]i). Here, we demonstrate that suppression of PDE5 gene expression by antisense pZeoSV2/ASP5 plasmid transfection results in a sustained increase in [cGMP]i, growth inhibition, and apoptosis in human colon tumor HT29 cells. With stable transfection, antisense transcripts exhibited a specific suppression in PDE5 activity, mRNA levels, and a 93 kDa hPDE5A1 protein. In cloned antisense cells, prolongation of the cell growth doubling times correlate positively with suppressed PDE5 activity and increased [cGMP]i. The growth inhibition in PDE5 antisense clones is due to an increased apoptotic rate and delayed cell-cycle progression. These results corroborate previous findings with the PDE5 inhibitor exisulind and its derivatives showing that sustained [cGMP]i induces apoptosis and growth inhibition in tumor cells. Furthermore, an inducible mitotic inhibitor p21WAF1/CIP1 has been found to account for the delay of cell-cycle progression in PDE5 antisense clones at G2/M phase. A proteolytic cleavage of p21WAF1/CIP1 in the antisense clones is also increased at the later stage of serum stimulation. The protein kinase G (PKG) inhibitor, KT5823, can prevent the cleavage of p21(WAF1/CIP). These data substantiate a pivotal role for PDE5 as a modulator of apoptosis and cell-cycle progression for human carcinoma via a mechanism involving the activation of [cGMP]i/PKG signaling pathways.

The Role of PDE-5 Inhibitors in Prostate Cancer

“…These studies suggest a functional role of an up-regulated PDE-5 in controlling tumor cell growth and death. PDE-5 selective inhibitors, sildenafil and vardenafil induced caspase dependent apoptosis and antiproliferation in B-cell chronic lymphatic leukemia (Sarfati et al, 2003;Zhu et al, 2005). Vardenafil when given in combination with DOX significantly improved the survival and reduced the tumor size in the brain-tumor-bearing rats (Black et al, 2008).…”

“…PDE-5 was also detected as a predominant isoform of cGMP-PDEs in many carcinoma cells lines in culture, including colonic adenocarcinoma (SW480, HCT116, HT29, T84), breast cancer (HTB-26, MCF-7), lung cancer, bladder and prostate cancer (LNCAP, PC-3), and leukemia (Thompson et al, 2000;Whitehead et al, 2003;Zhu et al, 2005). These studies suggest a functional role of an up-regulated PDE-5 in controlling tumor cell growth and death.…”

Chemosensitizing multiple drug resistance of human carcinoma by bicyclol involves attenuated P-glycoprotein, GST-P and Bcl-2

“…To compare Mdr-1 and Bcl-2 mRNA levels before and after Bicyclol treatments versus an internal control 18S RNA (332 bp), relative quantitative (RQ) RT-PCR was performed according to QuantumRNA 18S Internal Standards Competimers techniques (Ambion, Austin, TX). 21 Primers for human Mdr-1 were: forward 5'-GTG-GTGTCACAGGAAGAGAT-3', and reverse 5'-CCTTCTCTGGCTTTGT-CCAG-3' according to reported exonE23 primer, 22 to produce a 257 bp product. Primers for human Bcl-2 were: forward 5'-TAAGCTGTCGCA-GAGGGGCT-3', and reverse 5'-GGTGCCGGTTCAGGTACTC-3' according to reported primer, 23 to produce a 491 bp product.…”

A dose-ranging study of the pharmacokinetics and pharmacodynamics of the selective apoptotic antineoplastic drug (SAAND), OSI-461, in patients with advanced cancer, in the fasted and fed state

“…Prior studies show that cancer cells in the bladder, colon, breast, and lung share increased amounts and activity of PDE5 [24,25,31,40], and that suppression of PDE5 promotes apoptosis and inhibits growth in human colonic HT29 cancer cells [45]. Selective inhibitors of PDE5 appear to maintain a persistent increase in cGMP as opposed to a transient increase when PDE5 activity is present.…”