Abstract 1243: A novel series of celecoxib derivatives lacking COX-2 inhibitory activity more potently inhibits cancer cell growth by inhibiting PDE5
Authors: Sigler Sara C. , Ramirez Veronica , Abadi Ashraf , Piazza Gary 
Published: May 2015

Abstract
Background: The chemopreventive use of the COX-2 selective inhibitor celecoxib is not recommended because of potentially fatal cardiovascular toxicity. However, there is evidence that celecoxib inhibits tumor growth via a COX-2 independent mechanism. We synthesized a novel series of celecoxib derivatives designed to have reduced COX-2 inhibitory activity and determined if tumor cell growth inhibitory activity is related to inhibition of phosphodiesterase 5 (PDE5).
Methods: COX-2 inhibitory activity was measured using colorimetric assay of Ovine COX-2. The IMAP fluorescence polarization PDE assay was used to measure PDE5 activity. Cell growth in colon (HT-29, HCT-115, SW-480) and breast (MDA-MB-231) tumor cell lines was determined using the luminescent Cell Titer Glo Assay. Intracellular cGMP levels in live cells were measured using a cGMP biosensor constructed from the human PDE5A GAF-A domain fused to a modified firefly luciferase. Protein kinase G activity was measured indirectly by western blotting using a phosphospecific antibody to VASP. β-catenin and survivin levels were determined by western blotting. The Caspase 3/7 Glo Assay was used to detect apoptosis.
Results: A novel series of celecoxib derivatives were synthesized and found to have reduced COX-2 inhibitory activity and improved PDE5 inhibitory activity. The majority of derivatives were appreciably more potent than celecoxib to inhibit the growth of colon and breast tumor cell lines. Celecoxib inhibited growth and PDE5 activity with an IC50 of 23-35 µM and 37 µM, respectively, while a derivative, NAS28 inhibited growth and PDE5 activity with IC50 values of 3-7 µM and 0.03 µM, respectively. Celecoxib had an IC50 of 0.058 µM for COX-2 inhibition while NAS28 lacked inhibitory activity at 50 µM. NAS28 increased cGMP in a dose dependent manner, increased PKG activity at concentrations that inhibited growth, increased apoptosis, and decreased β-catenin protein levels as well as survivin, which is regulated by B-catenin-dependent TCF transcriptional activity.
Conclusions: A novel series of celecoxib derivatives were identified which lack COX-2 inhibitory activity but have improved potency to inhibit tumor cell growth. PDE5 inhibition appears to be an important activity of this class of compounds. These findings may lead to the development of novel drugs with improved chemopreventive efficacy, PDE5 inhibiton and reduced risk of cardiovascular toxicity. This project is supported by NIH grant 1R01CA155638.
Citation Format: Sara C. Sigler, Veronica Ramirez, Ashraf Abadi, Gary Piazza. A novel series of celecoxib derivatives lacking COX-2 inhibitory activity more potently inhibits cancer cell growth by inhibiting PDE5. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1243. doi:10.1158/1538-7445.AM2014-1243