Discovery of New H₂S Releasing Phosphordithioates and 2,3-Dihydro-2-phenyl-2-sulfanylenebenzo[<i>d</i>][1,3,2]oxazaphospholes with Improved Antiproliferative Activity

Abstract

Hydrogen sulfide (H₂S) is now recognized as a physiologically important gasotransmitter. Compounds which release H₂S <i>slowly</i> are sought after for their potential in therapy. Herein the synthesis of a series of phosphordithioates based on <b>1</b> (GYY4137) are described. Their H₂S release profiles are characterized using 2,6-dansyl azide (<b>2</b>), an H₂S specific fluorescent probe. Most compounds have anticancer activity in several solid tumor cell lines and are less toxic in a normal human lung fibroblast, WI38. A preferred compound, <b>14</b>, with 10-fold greater anticancer activity than <b>1</b>, was shown to release H₂S in MCF7 cells using a cell active probe, <b>21</b>. Both permeability and intracellular pH (pHi) were found to be significantly improved for <b>14</b> compared to <b>1</b>. Furthermore, <b>14</b> was also negative in the AMES test for genotoxicity. Cyclization of these initial structures gave a series of 2,3-dihydro-2-phenyl-2-sulfanylenebenzo­[<i>d</i>]­[1,3,2]­oxazaphospholes, of which the simplest member, compound <b>22</b> (FW1256), was significantly more potent in cells. The improved therapeutic window of <b>22</b> in WI38 cells was compared with three other cell types. Potency of <b>22</b> was superior to <b>1</b> in MCF7 tumor spheroids and the mechanism of cell death was shown to be via apoptosis with an increase in cleaved PARP and activated caspase-7. Evidence of H₂S release in cells is also presented. This work provides a “toolbox” of slow-release H₂S donors useful for studies of H₂S in biology and as potential therapeutics in cancer, inflammation, and cardiovascular disease