H2O2 (30% wt/wt) (CAS number 7722-84-1), phenol red (catalog number P-2417), and horseradish peroxidase (HRP) (catalog number P2088-10KU) were from Sigma-Aldrich Co. (St. Louis, MO). Hanks’ Balanced Salt Solution (HBSS) was from Hyclone (Logan, UT). Sodium hydroxide was from EMD (Gibbstown, NJ). Dimethyl sulfoxide (DMSO) (99.9% high-performance liquid chromatography grade under argon) was from Alfa Aesar (Ward Hill, MA). All other materials were reagent grade. The quinolinedione DA3003-1 [NSC 663284 or 6-chloro-7-(2-morpholin-4-yl-ethylamino)-quinoline-5,8-dione] was synthesized and obtained as described previously.7 (link),15 (link)